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LECTURES
ON THE
elements of  e&emtettiy
DELIVERED
 IN  THE UNIVERSITY OF EDINBURGH*? *


               J3Y TI}E LATE

         JOSEPHS BtiftCK, %M. I>.

  Professor* of chemistry in that university ;
PHYSICIAN TO HIS MATESTY FOB SCOTLAND; MEMBERiOF THE BOYAi
  SOCIETY OT EDINBURGH, OF'THE ROYAL ACADEMY OF SCIENCES
       AT PARIS, AND THE IMPERIAL ACADEMY OF
         ,  SCIENCES AT ST. PETERSBURG.
PUBLISHED FROM HIS MANUSCRIPTS
       JOHN ROBISON, LL.D.

PXOTESSOR OF NATURAL PHILOSOPHY IN THE UNIVERSITY
            OF EDINBURGH.
/A/fSr AMERICAN EDITION FROM THE LAS* LONDON EDITION-,
VOL. III.
              \t*. f ■  :■■
         PHILADELPHIA:

IRINTED FOR MATHEW CAREY, NO. 122r M*.RKET.STaEET,
  - BY B. GRAYES, NO. 40, KORTB FOURTH-STREET.

              1806,            '*' 
Ol--
101



**-^y<&^^ 
1^L«
        XECTURES


   CHEMISTRY.  y$%?

                       rMou
CLASS .III.—CONTINUED.
     CHARCOAL is the fourth kind of inflammable matter
 Which I enumerated,  and which deserves a f separate consid-
 eration.
   What is commonlyjcalled  charcoal,  is not produced by na-
 ture ; tKough there are native Inflammable substances which ap-
 proach to  it nearly by their qualities and constituent parts.
 But they are known by other names.  What is commonly meant
 by this term is artificial, and produced"from wood, by burning
 it, or rather scorching it "with a smothered fire, until it be red
 hot, and then stopping the further progress of combustion, by
 covering it so-closely as to  exclude completely the further ac-
 tion of the air.*
   This process is practised, as I  said,  with wood only, when
 we wish"to prepare what is commonly called charcoal, which is
.employed in refining iron, preparing-steel,  &c.   But a  similar
 product may be obtained, by similar treatment,  from all vege-
table and animal substances, and from  the bitumens; all of
 which, if heated gradually until all their  volatile matter is ex-
pelled, and with proper precaution to prevent inflammation, will
 afford charcoals.  Such is the charcoal from pit-coal, called
Coaks.  Small pieces of charcoal may be  finely prepared for
             * Vide Les Arts ct Metiers, Charbon. 
MANUFACTURE OF CHARCOAL.
experiments, by plunging a piece  of hard wood into red hot
lead, and keeping it there till all ebullition or eruption of vapours
of any kind is over; or by putting it into a crucible with good
sand, and luting on a  cover,  to prevent  all action of the air,
and then keeping this for an hour or more in a red heat.  Dr.
Priestley observes', that charcoal,  which is made with extreme
slowness, retains much inflammable  matter', which  a hasty ope-
ration dissipates in vapour'; anfl\hat, after it has so retained it,
no heat can afterwards dissipate it in close vessels.
  .All these substances from which  charcoal  can be prepared,
contain a considerable proportion of inflammable matter.  Their
other constituent parts are&rsmall portion of earth and  salts,
and a large quantity, of water.  By the action of the smothered
heat^ the water is dissipated, partly alone, in watery steams,
partly combined with other matters, in oily  or sooty vapours,
which are still  very inflammable.  But a particular kind of the
inflirnin tbi _■ matter rejnains united with the earth and the more
fixed salts; and  with  these constitutes the  charcoal that is at
present to occupy our  attention.
   Charcoal is always black and opaque ; and, if produced from
a solid  substance, such, as wood,  bone, or the like,  generally
retains the external form,  and some appearance of the organic
structure of the mass  from which it was produced.
   Charcoal thus formed is distinguished among the  inflamma-
bles by several remarkable and peculiar qualities :
   1st, When we expose it to  the action of heat alone, and take
 care that all access of fresh air to it be effectually prevented, it
 appears to be perfectly fixed and unalterable by heat.  The ut-
 most violence  of  heat applied in this manner has no  power ei-
 ther to melt it or to volatilize  it.   Dr. Priestley, it  is true,
 thought that he had converted charcoal totally into a species of
 inflammable air by the action of heat alone.   He made the ex-
 periment by placing the charcoal  in the vacuum of an air-pump,
  and directing  the focus of. a  burning  glass on it.   But there is
  great reason to suspect that this effect was not produced by the
  action of heat alone,  but by that  of heat and waterv vapour ap-
  plied at the same time to charcoal.  That watery vapour, as-
  sisted with a red heat,  very.quickly  consumes and  volatilize? 
         CHARCOAL....HYDRO-CARBONAT.       5

-charcoal, is now very  certain,  from the experiments of Mr.
 Lavoisier, Dr. Priestley, and others; viz. those already men-
 tioned, which were made by pushing the steam of  the water
 through a red hot tube, in which  different substances were ex-
 posed to its action.   When the experiment was made with char-
 coal, it was attended by the production of hydrogen gas  and
 carbonic acid.  This hydrogen gas from  charcoal contains some
 charcoal dissolved in it; and being thereby heavier than pure
 hydrogen gas, it is named by some  authors heavy  infitmmable
 air, by others, carbonated hydrogen.            . %
   Mr. Lavoisier is of opinion  that the charcoal is  only  dis-
 solved on  this  occasion, but not, properly  speaking, de-
 compounded.    He  thinks  that  it is the  fratery  vapour
 which  is decompounded, and supplies the hydrogen gas, the
 charcoal joining with the oxygenous  principle,  or basis  of
 vital air, which the water contains, and being thereby dis-
 solved aid converted into  carbonic acid.    We have not,
 therefore, as yet,  any proof that charcoal can be volatilized
 by the action of heat  alone, unless we reckon on some light
 black powder obtained in distillations of sulphuric  acid from
 inflammable substances.
    As charcoal suffers no change frojtn »the  most violent  ac-
 tion-of heat alone: so  it does equally resist the powers of
 the air and humidity when these are not aided by  heat.   It
 is  a common practice  to scorch the ends of  stakes  which are
 to  be driven into the ground,  that they may be less liable to
 rot and decay:  and this  is done with  considerable success.
 They become  thereby a  great  deal  more durable*.   But
 when wood is perfectly charred, we have no experience  of
 any end to its  duration.   It  is totally exempted  from anv
 change  or  decay to which so manj^ other substances are  lia-
 ble by the long continued action of the elements on them.

  *  About forty years ago,  a number  of pointed oak stakes were discovered
 in the bed of the Thames,"in the very spot where Tacitus says that the Bri-
 tons fixed a vast number of such stakes, to prevent Julius Caesar from passing
 his  army over by that ford.  They were all charred to'a considerable depth,
 and retained their form completely ; and were so  firm at the heart, that a vast
 number of knife-handles v ere manufactured from them, and sold as antiques,
 at  a high price....editor. 
*>     CHARCOAL VERY INDESTRUCTIBLE.
    The knowledge of this incorruptibility of charcoal has
  given  occasion  to  a most useful  contrivance, which has
  been lately thought  of, for preserving water uncorrupted at
  *ea.   Water at sea corrupts, in consequence of its drawing a
  tincture,  or dissolved matter,  from  the  wood of  the cask,
  which dissolv-ed matter is a very corruptible substance. But it
  has been lately contrived to burn or sear, the internal surface
  of the cask with flame or hot irons, until that internal surface
  is changed into charcoal, after  which it no longer yields any-
 corruptible matter to  the water.
    Charcoal equally resists  the most powerful and destructive
 solvents. Those which tear into atoms the metals themselves
 have not the least effect on it so long as the charcoal  remains
 cold.   It is only by being heated that it becomes liable  to the
 action of various bodies.   In its hot state,  all those sub-
 stances which are disposed to act remarkably on the inflam-
 mable bodies in general shew that they have the same power
 on charcoal.   Such are the sulphuric acid, the nitric acid
 nitre, the phosphoric  acid, calces of metals, and the vdpour
 ot water.   Hepar sulphuris has also the power  to dissolve
 charcoal.
   When a  pound of sulphuric  acid  was distilled with half
 an ounce of charcoal, the charcoal was totally dissolved, and
 it changed a part  of  th^  acid into sulphurous  acid.   The
 liqpior became of a sea-green colour, which disappeared  when
the liquor was cooled, and returned when it was again heated.
 A greater portion of  charcoal produces sulphur, by distilla-
 tion,   The operation is extremely troublesome,....the  pro-
duction of sulphur very partial:  and a  great part of the
charcoal is volatilized, in the form of an.impalpable  powder,
 which collects in the neck of the retort, and often chokes it
 up.   The distillation  may be repeated again and again  with
the volatilized  acid and charcoal, and always produces the
most  intolerable suffocating  fumes : but the colour at length
disappears.   It  also deserves remark, that both the  sulphur
and the volatilized charcoal appear before any considerable
quantity of  the  acid has come over.
   Nitric acid also acts remarkably on dry charcoal, when
very strong.  When  the  mixture  takes  place properly, it
bursts out into a flame. In all cases, the charcoal decompo'ses ' 
CHARCOAL.                    V
much of the acid, by depriving it of oxygen, and we obtain-
nitrous gas and carbonic acid.
   We have already seen the effect 61 the  acid of phospho-
rus on charcoal.  It is  decompounded by the charcoal, and
we obtain phosphorus and carbonic acid;^ which last must be
allowed to escape.
   It dissolves in hepar sulphuris  both  in the  humid'and
dry way, rendering it  of a much deeper  colour.   In the dry
way, charcoal combined in a very great proportion, produces
very  singular effects.   To produce this combination, howr
ever, in the best manner, the sulphur must be taken red hot,
in its nascent state, as in the process for producing sulphur
de novo, by treating charcoal in a red heat with a vitriolic
salt.   In this compound, the United attractions of  both  the
sulphur and the charcoal for oxygen produces such a rapid
combination and heat, that the mixture  takes fire when ex*
posed to the air.  Such mixtures are therefore called pyro~
phori.   I shall conclude this article with  a particular account
of them.
   As heat disposes  charcoal to be attacked and decom-
pounded  by these substances,  so  does it also prepare and
dispose it to be acted on by the air.  You all know that the
consequence of heating it red hot in-the  open air, is an im-
mediate beginning of its  inflammation,  during which it is
gradually consumed,  and a great deal of heat is produced*.
The apparent quantity of  the unhrflamraable  matter into
which the charcoal is changed, or which remains in its place
when  the inflammatiqn is completed, is very small indeed,
when compared with  the quantity  of the charcoal  before it
was inflamed.   It is only one-ninth of its weight.   But this
appearance  is a deceitful  one.  There  is  a much greater
quantity of uninflammable matter produced ; but itrHissumes
a« elasctic aerial form, and is diffused in the atmosphere im-
perceptible to the sight. It is fixed air, or the carbonic acid gas,
ihe total weight of which far. exceeds the weight of the char-
coal that  has been consumed.   We can collect and condense
this gas, so as to reduce it to a more perceptible form,  by
the attraction of caustic alkalis or quicklime. And there are
other ways by which we can render it perceptible, and esti-
mate the quantity of it.  When this is done with exactness,
the weight of it  is always found equal to  the joint weights of 
tf
CHARCOAL.
 the consumed charcoal and that of the oxygen gas expended
 in consuming it,  and changed along with it into carbonic acid
 gas.   Mr. Lavoisier, by a very careful measurement, found
 that 100 parts, by weight, of carbonic acid, contain nearly 72
 parts of oxygen, and 28 of charry matter.
   We have an example of this in the deflagration of char-
 coal with nitre.   You remember what a blowing noise, and
 succession  of explosions,  accompanies  that deflagration.
 Curiosity to learn what happens on this occasion, and  what
 was the cause of the astonishing  force of gunpowder, sug-
 gested a contrivance to fire some,  of it, or a mixture  of char-
 coal and nitre, in a  strong pistol barrel,  the end of which
 was soldered close, and  the  touch-hole screwed up.   And
 the quantity of materials fired-at once being  but very small,
 there was no report or explosion ; the strength of the machine
 being sufficient to confine the flame and elastic matter.  The
 only external sign of the firing of the powder or composition
 was, that the barrel became  hot.  It was  allowed to cool,
 and then opened under water, by unscrewing the touch-hole.
 A quantity of elastic aerial matter came out,  which was sur-
 prisingtygreat when compared with the quantity of charcoal
 and nitre which had been fired. This experiment was made
 by Mr.  Robins,  Engineer to the Honourable East-India
 Company.
   But others having repeated it since the nature of the aerial
 fluids became a subject  of inquiry, they found that the elas-
 tic aerial matter produced by charcoal and nitre is a mixture
 of carbonic acid gas and of azotic gas.
   Knowing, as we now  do, that nitrous acid is composed of
 seven parts of oxygen, and three parts  of azote nearly,  we
 are enabled to explain very clearly the production of azotic
 gas during the deflagration of charcoal with nitre.  And the
 other  experiments which have been described to you  explain
 the production of carbonic acid at the same time.  It appears
 that the charcoal when heated, acts by a powerful attraction
for the oxygen, which abounds in the nitric acid. By uniting
 they form the carbonic  acid.   The  other  principle  of the
nitric  acid, the azotic gas, is thus 3et at liberty,  and being
added to the fixed  air,  makes up  that great quantity of
 elastic aerial matter which is  disengaged from charcoal and
nitre. 
   CHARCOAL  DEFLAGRATED  WITH  NITRE-  9

   There is another production sometimes obtained from this
 deflagration, viz.  a very small quantity of volatile alkali.
 This is explained  by another late  discovery which I already
 mentioned, concerning  the component  principles of  the
 volatile alkali, which is  now supposed  to be a compound of
 hydrogen and azote.  This being admitted, we can account
 for the formation  of a small quantity of it from- some of the
 mixtures of  charcoal and nitre.   Some part of the water or
 humidity inherent in charcoal, and in nitre crystals, is decom-
 pounded during the heat of deflagration, by the attraction of
 the charcoal for the oxygen of the water.   Thus the other"
 principle of the water, the hydrogen, is let loose, and, joining
 with  a part of the azote,  forms the volatile alkali.   This,
 however,  is in this case an accidental production, in small
 quantity only,  and not  always perceptible.   A  chemist in
'Birmingham, whose name I do not recollect at present, forms
 volatile alkali in abundance, by passing common air over a
 mixture of charcoal and vitriolic salts with an earthy basis
 (such as alum, or  Epsom salt)  made red hot.
   After this explication of the  deflagration  of nitre with
 charcoal, I may so far take notice of the deflagration of the
 same salt with  sulphur, as to remark th5t the products of that
 deflagration are accounted for  by  the same principles.    The
 products of the deflagration  of nitre acid sulphur, are sulphuric
 acid, formed by the union of the sulphur with the oxygen of
 the nitric acid, and azotic gas, formed of the azote of the
 nitric acid  and latent heat.  The sulphuric acid, the moment
 it is formed, joins itself to the alkali of the nitre, so that very
 little of it is volatilized.
   By the same inestimable discovery of Mr. Cavendish, by
 which we  first learned the  constitution of nitrous acid, we
 can also account for. what happens in the operation by which
 the largest possible quantity of vital air  may-be extracted
 from nitre.  In that operation, the nitre  is exposed to the
 action of heat in  a small retort of earthen ware,  or of glass
 well  coated with clay and sand, and which has a long neck.
 Sometimes an iron retort or gun-barrel is used ; but it is not
 so proper.   The  retort  is exposed to jche immediate contact
 or action  of the burning fuel, but heated gradually in the
 beginning.   As soon as the  mort and nitre  begin, to be
     VOL. IT I.                 P, 
to          CHARCOAL, A POWERFUL
 ignited, the vital air begins to come forth.   At the first it is
 very pure, provided  the  nitre be  quite free from dust or
 admixture of  vegetable or animal  matter.   If such matter
 be present in it, though in exceedingly small quantity,  some
 carbonic acid gas is  formed at first, and comes  out mixed
 with the first portions of  vital  air  and some azote.   After
 this, or from the beginning, if the nitre was quite pure, we
 obtain  a great quantity of good vital air, which, it not  quite
 pure, contains a small admixture of  azotic  gas.  But towards
 the end of the operation, when the heat must be increased to
•a higher degree, the vital  air comes over mixed with a  more
 considerable portion of azotic gas.   The reason of this dif-
 ference in  the  purity of the vital air is, that in the beginning,
 the  nitric  acid gives out only a part of the oxygen which it
 contains,  (nearly T7^) and it is changed  into nitrous  acid,
 retaining perhaps -ffo, and in this state continues adhering to
 the alkalis.  In the nitrous acid, therefore, there is a deficient
 proportion of oxygen, and a superfluous  quantity of azote.
 When the  process is continued,  and the heat increased to
 produce a more complete decomposition of the acid, the azote
 must nedtssarily  make its appearance in  a ^proportion con-
 tinually increasing.
   All these facts, and many more, to be  mentioned  as we
 proceed, and which are so well explained.by Mr. Cavendish's
 discovery, confirm the solidity  of that discovery, making it
 one of  the most important which the mbdern chemistry has
 produced.
   One  of  the  most remarkable  properties of charcoal,  when
 recently taken from  the  fire, is  an attraction for a certain
 quantity of humidity, and for various odorous and colouring
 matters of different fluids,  containing animal  or vegetable
 substances, subject to fermentation  or corruption, as also for
 the acetous acid.
   We  have proofs of its attraction  for humidity  in  many
 curious experiments  of  Dr.  Scheele  and  Dr.  Priestley.
 Although  indestructible  by heat in close  vessels without
 addition,  yet, if moistened, it will yield carbonic acid and
 hvdrogenous gas.  This  may be  repeated by another moist-
 ening;  and so  on, till it is all expended in these productions.
 This is evidently owin^  to its  strong  attraction for oxygen, 
        CORRECTOR OF PUTRESCENCE.        11

in which it exceeds all substances yet examined.   It decom-
poses  the water,....combining with  the  oxygen, and thus
forming carbonic  acid, and thus also leaving the hydrogen
at liberty.
  Its action on  odorous effluvia  is no less  remarkable.  If
laid  (fresh made) on silk or  linen  gummed  or oiled for
umbrellas, a preparation which continues to exhale a heavy
sickening smell for  many years, it will remove it in a few
hours.   It sweetens bilge water, and all  kind of corruption
that is accompanied  with Amission  of hepatic ammonia.  It
clears saline  solutions of their  colouring  matter and rank
smells, causing them to crystallize  in snow-white purity ;
and  is much used for this purpose in pharmacy ;  as in the
preparation of the terra foliata tartari, which was formerly a
tedious process, and considered as a test of pharmaceutical
dexterity.  It removes in  an instant the  heavy flavour of
corn spirits hastily distilled.   It clears foul camphor in the
sublimation from all fuliginous taints.   It sweetens water
which has grown putrid by long keeping.    It even sweetens
meat which  has. already putrified  to a very great  degree.
Mr. Cappe  at E-ille has published  valuable experiments on
this subject,....as has also  Mr. Lowitz an  eminent chemist
at Petersburg!* in Russia.  Charcoal is therefore an excellent
dentrifice, as very well adapted to  the ^mechanical operation
of  cleansing the teeth, and still more as the most powerful
corrector of all putrescence,  which is the  chief cause of all
disorders of the teeth and gums.
   The acting principle  in these effects is  not yet distinctly
understood.   As they are generally accompanied by an im-
mediate and great increase of the offensive smells, we are led
to ascribe its efficacy to its attraction for oxygen, by which
most of those gases  are set at liberty.
   Powdered  charcoal clears water impregnated with carbonic
acid so completely that it no more renders lime-water milky.
   Charcoal is found to act powerfully in relieving from the
pain of heartburn.
   In consequence of its strong  attraction  for  pure acetous
acid,  it becomes a powerful  agent  for  concentrating it by
distillation.   Wc are  indebted for  this, as well as for the
full confirmation of the lust mentioned chemical property of 
12
CHARCOAL.
 charcoal,  to  Mr.  Lowitz.   After having concentrated this
 acid as much as possible by freezing, he mixed it with a great
 proportion of charcoal  fresh made, and distilled it  till the
 charcoal was seemingly dry ; then, changing his receiver, he
 obtained from this charcoal acetous acid, in the utmost state
 of concentration and purity, and which crystallized in a cold
 little below that of freezing water.   This is somewhat of an
 anomalous fact j  because charcoal exhibits no  remarkable
 attraction  for acetous acid in  a less concentrated state.
   I have  already  observed, that- charcoal attracts oxygen
 more powerfully than any other substance  does that  we are
 acquainted with.  We cannot decompose  carbonic acid by
 any single elective   attraction.   Charcoal is  employed for
 separating it from all other bodies.   And, in consequence of
 this power, charcoal is the great instrument in all metallurgic
 operations ; and in- all operations by which we restore to
 bodies their quality of inflammability.  For inflammability
 is destroyed only by attracting oxygen  from the atmosphere,
 and becoming saturated with  it.   I have already mentioned
 the  ingenious process by which   Mr.  Tenant effected the
 decomposition of the^rbonic acid, by means of phosphorus
 and an alkajjne substiuTCe.
   From  all that has  been said of charcoal, you  perceive that
 there is  a  principle common to every combustible substance
 procured by  charring  combustible bodies ;  and that  this
 principle is exceedingly subtile, since it is  found to compose
 so pure a fluid as carbonic acid, or fixed air.   You now see
 that although  the black substance obtained  by the smothered
 burning of many bodies be solely  the production of art, yet
 the common principle, the carbon,  so  called to  distinguish it
 from the grosser body in which it is found, is one of the most
 copious and uniform productions of nature.  The calcareous
 and other absorbent earths, must now be added to the numerous
 classes of  bodies that contain it.   And we must, in short
 consider every  thing as an ore  or matrix  of carbon,  which
 contains  fixed air, or which produces fixed air by union with
oxygen.
  It is remarkable that a principle so abundant in nature  should
never be  seen in  its native form,  pure and unmixed.  But this
arises from its activity and  disposition to combine with  almost 
DIAMOND  IS PJJRE CARBON.         13
every substance in nature.  The wonderful changes of external
appearance which may be  induced by such combinations, are
now so familiar  to you,  that although you may be surprised,
you  will not be disposed to doubt,  when I venture to say that
ki all probability  the native, unmixed, form of carbon,  is what
is known to the world under the name  of the Diamond ! Surely
nothing can be more  unlike than the most brilliant, the most
transparent of all bodies, to a substance  essentially black, and
completely impervious to light.  You will be eager to know the
evidence on which I venture such an unlooked-for opinion.
   When considering the siliceous earths, I observed that quartz,
crystal, and others abounding In them, were distinguished from
the rest by several peculiarities.  A remarkable smell when they
are rubbed together; the light which their friction produces v
several appearances of elastic matter issuing from them in then
union  with fixed alkalis; and  their refusal to unite with othei
siliceous earths, were considered by many chemists, and pai t i
cularly by the Chevalier Dolomieu, as indications ofinflam • .
ble matter  in them.
   The diamond, besides these qualitigfc is farther distinguish..
ed by being tottftly dissipated by a violent heat; but this only
when exposed to  the joint action of heat and air.  Till the ne-
cessity of  this combination was discovered,  the dissipation of
diamond was considered as analogous to the decrepitation of
salt, and of many fossils,  which may be dispersed by heat in
small fragments,  which in  some cases are  even  a fine  powder.
But  these  fragments could always be collected ;  whereas the
diamond disappears altogether.  It has long been suspected,
therefore, to be inflammable.
   Accordingly, several chemists have lately examined it with
the express view  of ascertaining this  point.  Crucibles of fine
porcelain, having ground stoppers of the  same substance, were
employed j and it was found  that  only a part of the diamond
could be evaporated in this way; so much the more, as the ves-
sels contained more air.  When covered with  the powder of
charcoal in the crucible, no change whatever was produced by
the most intense heats.  When so heated in free air, it gradu-
ally consumed, and was all the while of a dazzling brightness, 
14
CHARCOAL.
much more brilliant than the capsule on which it wj»s lying.  Al-
though there may be  some impropriety in saying that diamond
is inflammable, like oils, yet it appears to  be combustible like
charcoal.  Count Sternberge, a gentleman in Bohemia, burnt a
diamond in oxygen  gas, by fixing to the point of it a bit of iron
wire, which he made  red hot, and then plunged the whole into
a vessel containing vital air.  The wire burned with great splen-
dour and production of heat:  and this being communicated to
the diamond, it took fire and burned in the same manner.  The
experiment  was repeated in a  glass vessel, whose inside was
moistened with lime-water.  It very soon became dim, and was
totally obscured, so that  the progress of the  combustion could
not be observed.  But this  gave  strong indication of the pre-
sence of carbon in the diamond.
  Mr. Smithson Tenant mixed 2-* grains of diamond dust with
one-fourth ounce of nitre cleared of the water of crystallization,
and exposed the  mixture in a tube or retort of gold.   A good
deal  6f  nitric acid was disengaged before the nitre began to act
on the diamond.  By this circumstance, the carbonic gas, pro.
dueed by the action of the oxygen in the instant of decomposi-
tion,  was absorbed by the fixed alkali, for which it has a strong
attraction, and it was all retained.  This was obtained by dis-
solving in water, and adding muriat of lime,  which formed a
digestive salt,  and  precipitated a crude calcareous earth, and
thus gave Mr.  Tenant hold of the carbonic acid. He found this
calcareous earth to contain 9| grains of carbonic acid.   By Mr.
Lavoisier's repeated examination of the proportion of ingredi-
ents in this acid, he found that it held 2-* grains of carbon, which
is precisely the weight of the diamond employed.
   By this ingenious experiment,  which has been  repeated both
in London and Paris, we seem entitled to conclude that diamond
is carbon in a crystalline form.
   Another experiment leading to the  same conclusion, has late-
ly been made by Mr. Guyton de Morveau.   He exposed to an
hour's intense  heat, a diamond inclosed in a tube of iron,  put
into a crucible, and surrounded with a mixture of siliceous and
argillaceous matter, which  had been burnt in a burnt clay cru-
cible.  This crucible  was inclosed in another, which was  coat- 
           DIAMOND IS  PURE CARBON.         15

ed with a similar composition.  The diamond vanished entirely,
though the tube had no aperture :  and the inside of the tube was
converted into perfect steel.  You will afterwards learn that this
change is produced by the union  of iron and carbon.  You see
the propriety of Mr. Morveau's precaution to cut off all commu-
nication from the fuel to the tube.
  The diamond burns at a much lower heat when mixed with
nitre, than by any other  treatment.  When  merely heated in
contact with atmospheric  air,  a  very strong red heat is  neces-
sary  to induce that bright shining, which is  the indication of its
uniting with oxygen, or of burning.  When this is done in pure
oxygen, the combustion begins a little sooner,....but when mix-
ed with nitre, the  combination begins with  the lowest red heat.
Mr.  Tenant found that common  charcoal may by rendered ex-
tremely hard, so as  to scratch and work upon tempered steel,
by long continued ignition in  close  vessels ; and that by  this
treatment its tendency to combustion is so much  repressed, that
it does not begin to burn till red  hot.  There are some very re-
markable examples of this kind  which have lately come to my
knowledge.   In the dreadful  eruption of lava in Iceland, trees
growing in crevices of the rocks have been Duried under the melt-
ed lava, and there charred and covered with melted matter, which
has not ceased to be red hot  for  more than two  years.  Frag-
ments of these are sometimes brought into  view  by the convul-
sions and shatterings of subsequent eruptions,  and are called
sva'c'rt  souierbrant.  Some pieces of them in my possession re-
quire a full red heat for their  combustion,  and they are totally
consumed.  I have observed the same thing in a native coak,
lately discovered" near Newcastle,  which has been produced by
the protrusion of a mass of melted  whinstone, which now forms
a dyke in the strata,  and  it  has  charred above two fathoms of
the seams on each side.

                   Appendix.....Pyrophori.

   I conclude this article with the account of a very curious class
of chemical preparations, which derive their distinguishing pro-
perties from charcoal. The are called Pyrophori, because they 
16          <»        PYROPHORI.
are always in a disposition to take fire and burn whenever they
are exposed to the free air.  They are as commonly, but  with
less propriety, known by the name of phosphori,....light bearers,
because they have this resemblance to  Brandt's  phosphorus of
urine.   They are distinguished, however, by the name of Horn-
berg's phosphorus, or phosphorus of alum.
  This is generally a blackish or dark coloured powder, like
charcoal, or the half burnt ashes  of combustible  bodies.   It is
kept in bottles well corked. And if a quantity be poured out in-
to the air, especially if the air be a little damp and warm, it
grows  hot,  smokes, and presently takes fire, burning like as
much charcoal, with a disagreeable smell.
  This phosphorus  of Homberg is prepared by  first roasting a
quantity  of meal  or flour of any kind, till it is almost  charred,
taking care that it be not completely so.   This charry powder is
mix<d with  a quantity of alum, deprived of its water of crystal-
lization ; and the mixture is put into a phial,  so  as nearly to fill
it.  The phial is set among sand in a crucible.  The sand  must
surround the phial as far up as it is filled with the powder.  The
whole is kept in a moderately hot  fire, till all fumes have  ceas-
ed, and a very faint flame,  like that of sulphur, has continued
for some time.   It is now removed, and the mouth of the  phial
stopped with a cork as soon as it is cool enough to allow it.
  When a little of this powder is  shaken out of the phial, and
formed into a heap, it grows hot, smokes, smelling strongly of
hepar sulphuris, and then takes fire^ if well prepared.   If much
over or under calcined, it is apt to fail ; .and it is generally in
its best state when it has something of a dirty green colour mix-
ed with it, as if it contained powder of sulphur.
  Subsequent experiments and observations have  shewn that
any salt which contains the sulphuric  acid will  do  as well as
alum for the preparation of this pyrophorus.  Scheele obtain-
ed the finest from vitriolated tartar, or sulphat of potash.   Nay,
the natural productions, gypsum, fluor, and others, formed by
the  same acid  will  answer.  We know that all  such  com-
pounds,  when treated with combustible bodies in a strong heat
produce  sulphur Or  hepar  sulphuris.   These pyrophori may
•hercfore be called  sulphureous  pyrophori,  or perhaps hepatic) 
      PHOSPHORI PROPERLY SO  CALLED.      17

pyrophori.  Dr.  Scheele  has  observed that the steams  of
hepar  sulphuris generate  much heat when they  absorb vital
 air. It is  very probable that the copious absorption in the pre-
sent case (for it is very copious) may  produce enough to kin-
dle the mixture of nascent sulphur and charcoal.
   This substance has not yet been examined with the attention^
which it deserves ; and we  are  not yet well assured of the
procedure of nature  in  its inflammation.   Mr. Lavoisier has
bestowed particular  attention on  compounds nearly allied to
it,  in  his first essays, published  in 1777,  and also in  his sub-
sequent papers.
   There are many other substances which take  fire of them-
selves, by the heat produced in  the mutual action of their  in-
gredients.   Of this we have already seen  an example  in the
mixture of nitric acid with essential oils j  also with phospho-
 rus.   We know that the same  thing happens in  many  cases,
where vegetable or animal substances  are  heaped together in
a moist state.  They ferment, grow hot,  and frequently burn,
or  at least are reduced to ashes." We shall  have occasion to
take notice of some  remarkable examples  of  this kind,  as  we
proceed in our examination of inflammable bodies.
   At present, I propose to bestow a little  attention on another
class   of  bodies  known by the name  of  Phosphori, and to
Which that name does more peculiarly belong.  These bodies
do not take fire, that is, do not suffer a decomposition of their
parts, accompanied with the production of heat and light.  The
bodies I now mean to consider  only  shine in the dark, but
without any sensible  heat.   And they acquire this faculty, not
immediately by exposing them to the action of the air,  b^it to
that of a strong light.
   Of these there is a class very nearly allied to the substance
I have last described,  by its composition and  chemical proper-
ties.   The most remarkable of them, and the first observed, is
that called the  Bolognan phosphorus,....the. Bolognan stone, be-
cause first found in the neighbourhood  of  Bologna, about the
year 1630, by one Cascarioli (a shoemaker I believe) who ob-
served, that  when taken from the light into  a dark place, it
    Vol. hi.              c 
1* BOLOGNAN, AND CANTON'S PHOSPHORUS,
continued to shine  for some time.   As soon as this was pub-
lickly known, several philosophers of that time examined the
appearances with more care.  It was found that two or  three
seconds exposition  to the light was sufficient to make it shine,
and that longer exposure did not increase its luminousness.   It
shone for four or five minutes, and  some fine pieces shone for
a quarter of an hour.  The light of  the sun was the most ef-
fectual.   After this the clear light of day.  Nay, the light of a,
torch made  it shine.   Moon light  had no effect.   The light
emitted was enough to make the smallest print legible,  when
held very  near.
  These facts attracted  much  attention,  and  were very  inter-
esting to the philosophers  of last  century, who were at that
time much  divided in their opinions concerning the nature of
light.   Some  imagined, with the  vulgar, and with  the  fol-
lowers of Newton, that light was a material emanation from
the  luminous  body ;  while  others, with  Des Cartes at their
head, imagined that light, or vision, was the effect of a tremulous
motion  of an elastic fluid, as sound, or hearing, is the effect of the
tremulous motion of elastic air. The first class drew strong argu-
 ments in support of their opinion from  the phenomena of this
stone, for it seems to imbibe the light to which it is exposed,
and afterwards to give it out again.
   It is  somewhat  singular  that so curious a phenomenon did
not engage the chemists of that age in a very minute examina-
 tion of the constitution or ingredients of  the Bolognan  stone,
 and cause them to speculate about the way in which it produced
 those effects.   This inquiry was more strongly suggested  to
 them by the methods which must be taken to make the stone a
 powerful phosphorus.   It must be  beaten to fine  powder, and
 then made into a  paste with water and oil, and then calcined.
 But it lay a half century neglected;  till, in 1675, Baldwin, a Ger-
 man chemist, observed that the residuum from the distillation
 of the  nitrat  of lime  imbibed the light and emitted it in the
 same manner ; and  in 169o,  Homberg discovered the same
 thing in the Muriat of lime ; and  in 1730, Dusay found that
 many other substances, when  calcined  in the same way, had
 the same property-  A series  of carious observations  of this
 kind by Beccaria  (Giacomo Bartholorueo) greatly augmented 
       CONJECTURES AS TO THEIR NATURE.   19

 this list.  But although  these discoveries naturally occasioned
 some chemical examination of the Bolognan stone and calcin-
 ed phosphori, no addition of knowledge was obtained, till Mr.
 Margraaf examined  them with his accustomed skill, in 1749.
 He found that the Bolognan stone Tajas a sort of gypsum,  or a
 heavy spar,  containing the  sulphuric acid united to calcareous
 earth.   Subsequent observations,  however, prove it to be a
 barytes  united to that acid.   He found that all heavy spars
 could be made phosphorescent by proper calcination., Leibnitz
 made the same observation in the first vol. of the Bfiscell. Berol.
 with respect to fluor.   Margraaf gives  the manner of prepar-
 ing those substances in the best manner, viz.  by pulverizing,
 and then making the powder into small cakes with a little gum
 water, then drying them slowly, and calcining them amidst the
 coals in  a reverberatory furnace.   So prepared they shine like
 glowing embers.  He obtained phosphori from all earths which
 contained the sulphuric acid.; and the  earth of alum was the
 best, and some calcareous ones scarcely  inferior.   Some time
 after this, .Mr. Canton of London produced a shining prepara-
 tion of the same kind,  by calcining oyster shells half an hour,
 and then reducing them to powder,  and mixing them with one-
 third of sulphur.   The mixture was rammed into a small cruci-
 ble, and calcined for an hour in a clear fire.  The mass, when
 broken,  was found unequally luminous.   The best parts were
 therefore selected, and were very brilliant. It is to be remarked,
 that different parts emitted light differing considerably in colour.
 Figures  may be drawn on paper with white of egg, which  will
 take hold of the powder  and  exhibit  the figure in the dark.
 Canton's phosphorus equals any of the natural stones in bright-
 ness, and in the quickness in which it is saturated with light, so
 as  to  attain  its greatest  possible  brilliancy.  Indeed,  in this
 respect,  it may be thought superior j for Mr.  Margraaf says,
that two  or three minutes exposure is necessary for his prepara-
 tions.  When this light emitted by these  phosphori  has  ex-
pended itself, or is no  more sensible, heating the body renews
 it  for a little time;  and when  this has ceased,  a  greater heat
causes'another emission.  But,  in all these cases, a greater heat
.sooner exhausts the power of shining.  In short, in this experi- 
20           CONJECTURES AS  TO THE

ment, heat operates in the same way as in expelling dampness,
or any other volatile matter.   Also a great heat applied to the
phosphorus, while it is exposed to the light, hinders it from ac-
quiring the luminous  faculty.  All these  circumstances concur
in strengthening the opinion, that this composition imbibes, and
then emits something material, which is light, or the cause of
light.  Beccaria said  that the  Bolognan phosphorus most cer-
tainly did so, because, .when illuminated by coloured lights, it
emitted only the colour which had illuminated it.  This would
indeed be almost a demonstration of the doctrine of imbibition,
and of the materiality of light; but the  experiments of Mr.
Wilson with Canton's phosphorus,  render this doubtful.   Cer-
tain parts emitted a particular colour, whatever had been the
colour of the illuminating light.
  When we reflect on the composition of this curious substance,
we cannot but ascribe it's-shining to the same cause which pro-
duces the inflammation of the pyrophorus of Homberg.  They
consist of the same ingredients, united  by the same process,
and they continue to emit the same  hepatic odour, though long
kept, if kept from damp air.   Accordingly, Mr. Macquer con-
siders  the shining of  these phosphori as  instances of a low and
imperfect combustion, similar to what we observe in the phos-
phorus of urine, which begins  to shine  when exposed to the air,
and by this  shining, is slowly converted into  phosphoric  acid,
still  mixed however  with a very great proportion of unburnt
phosphorus in a volatile state.   It is well known too, that sul-
phur, fat oils, suet, and many other  substances, nay, even gun-
powder when heated to a degree far below ignition, emit a faint
lambent  flame  and suffocating fumes, which slowly consume
them to a certain  degree, and that this happens, without  their
becoming of themselves sources  of  heat sufficient for the con-
tinuation even  of this low degree of inflammation.  If an iron
bar be heated red hot at  one end, and allowed to become very
hot also at the other end, and if we then make a line along it with
a bit of tallow, or white bees  wax,  or sulphur, or rather make a
set of detached  spots, we shall see them shine with various
brightness according  to their  distance  from the hottest part  ot
the bar, and  the brightest are  soonest exhausted of this faculty. 
             NATURE OF PHOSPHORI.            21

Macquer, therefore, ascribed these and all other phosphores-
cences to the same cause, and supposed that they were cases of
slow and imperfect combustion.  This opinion is very plausible,
and is well supported by the emission of the hepatic smell, and
some other appearances.  Many kinds of spar are very lihninous
when thus heated. The Derbyshire fluor is remarkably so. Cor-
rosive sublimate shines the brightest of all.  Next to this is
pure chalk, crude magnesia, earth of alum, vitriolated tartar,
French chalk, &c.  Mr. Wilson of London  observed similar
appearances in many other bodies,....indeed in most bodies of a
white colour.  Even paper had this property.           -  A
  But there are circumstances attending the phosphorescence at
present under consideration, which will by no  means agree yith
this explanation.  All the emissions of light just now spoken of
require the application of heat, and the contact of vital air,  and
consume this air in the same  manner as common combustion
does.  But the Bolognan stone, and the phosphori, of this class,
require nothing but exposition to the light, and do not require
the renewal of the air.   Mr. Canton put some of his phosphorus
into small glass balls, and sealed them hermetically, and found
them as good as ever after  twelve  months subjection to  every
trial.   He found this to be the best way  of keeping his pow-
dered phosphorus.  After twelve months, two seconds exposi-
tion to the sun made it shine, so as to make  the figures on his
watch dial perfectly visible.   An electrical flash, or even  the
light of a single candle, sufficed for causing it to shine.   Long
exposure to dry air impairs it, and damp air does this immedi-
ately.  In short,  these  phosphori only emit the light they have
received, or they are rendered luminous by the action of light
alone.  The first appears the most probable,  because a greater
heat occasions a brighter light and a more rapid exhaustion of
all that will  be dissipated by that  heat.  This  is very like the
expulsion of ^semething received.   Another circumstance con-
firms this.   No length of keeping in the  dark will hinder the
emission of the light which had been imbibed, and would have
been expelled by that heat.  A ball kept fifteen months in the
dark,  after  having  been illuminated by the moon  only,  and
which did not shine immediately after, on account of the  weak- 
22
PHOSPHORI.
 ness of the light, was distinctly seen by plunging it into boiling
 hot water.
   Mr. Canton  found that humidity inclosed  with the phos-
 phorus, that it might stick to the glass, impaired it much, and
 destroyed it.   Alcohol did  not nurt it so much, and aether not
 at all.   ./Ether, 'therefore, with a minute portion of resin or gum,
 would make the powder adhere as Mr. Canton wished.  The
 phosphorus might be attached in this way to a plate of glass, and
 another plate laid on it, and the edges secured with varnish and
 paper pasted round.
  These circumstances  evidently distinguish this phenomenon
 from ordinary combustion.   But it were worth while to exam-
 ine by  some proper train of experiments, whether the shining is
 effected by the absorption of vital air, and  a subsequent decom-
position by the action of fresh light.   As humidity spoils the
phosphorus,  perhaps a permanent compound is now formed
which fresh light cannot decompound again.  We might perhaps
learn this by examining  the change produced after a long time
on  the air which was shut up with the phosphorus in a damp
state.  It would be proper to try  this with  two balls, one of
them to be exposed day  and night,  and the other kept in the
dark.
  Mr. Wilson thinks that this  phenomenon is not merely an
 imbibition and subsequent emission of light, but rather that light
acts on some matter in the body,*in such a way as to cause it to
emit light.   Thus only, he thinks,  can we  account for white
light being emitted by a part  which was illuminated only by a
 red or  blue light.
  The foregoing observations on  the phosphori, properly so
 called, are, in  my opinion, as interesting to  the chemist as to
 the optician, and they are very interesting tp both. To us, they
 are important,  being nearly connected with the whole doctrine
of combustion,....a doctrine still full of difficulties Notwithstand-
 ing the very great discoveries which have beeir made.  The
separability of light and  heat by a plate of  glass, in the valuable
 observation of Scheele,  and their seeming separability in  the
 present instances,  are undoubtedly  facts  of great moment in
 philosophical chemistry, especially when considered  along with 
PHOSPHORI.                   23
 Herschel's observations.  The observation also of Mr. Goett-
 ling, that phosphorus shines bright |in azote and in volatile al-
 kali, and the shining of vegetable and animal substances,  (par-
 ticularly sea fish), in a certain stage of putrescence, and  their
 shining  in vacuo and other situations incompatible with combus-
 tion, merit a much more careful attention  than has yet  been
 given.
   The four inflammable bodies which have now been consider-
 ed appear to us in the character of simple substances.  I do not
 mean that they are elements, but only that we are not authorised,
 by any observation or experiment, to say that they are  com-
 pounded of other •more simple substances known to  us in a se-
 parate state.  We have never decompounded them, nor formed
 them by the union of known substances.  We have only been
 able to extricate them from more complex bodies, and to shew
 that they are ingredients m their composition.
   This simidkity,  and  the  manifold^relations of hydrogen,
 phosphoru§(sulphur, and  charcoal,  have been of great service
 to us, by giving us a conception of theremarkable phenomenon
 of combustion, which  is incomparabfj^ore agreeable to our
 general knowledge of chemical facts than the ingenious doctrine
 of Dr. Stahl, and is really supparted by proofs which 6eem in-
 controvertible.  Even though imperfect, this new doctrine fur-
 nishes us with a fact, formerly unnoticed, which accompanies all
 combustion, namely, the  combination of the body called com-
 bustible with vital air.  We shall find that this fact, when traced
, through all other cases of inflammation, will give us almost all
 the  knowledge of chemical changes that we possess,  and enable
 us to explain a vast number of the most complicated operations
 of nature, inasmuch as all explanation of phenomena consists in
 shewing that they are particular cases of  general laws er facts
 already known.
   We proceed now to consider inflammable substances of a more
 complex nature.   In doing this,  I shall still endeavour to  intro-
 duce them to your acquaintance in the order of their simplicity,
 as far as I can perceive any gradation or order in this respect.
 With these views, I begin with spirit of wine. 
24
                V.....ARDENT SPIRITS.

   Vinous Spirit is produced from some vegetable substances
by fermentation, and  subsequent distillation.  And the vege-
table materials which by these processes yield  the most of it are.
   1st.  The sweet juices  of vegetables, in  their naturally dilut-
ed state.
   2d, The sugar,  or  sweet matter extracted from vegetables,
when properly diluted with water.
   3d, Grain, or other farinaceous parts  of vegetables, malted
and diluted in water.                         *             •
  4th,  Grain, or other farinacea, dissolved or dilated in water,
without being malted.
   All these are  capable of the vinous fermentation, by which
the vinous spirit is formed; but not all with  equal facility and
perfection.  They ferment the more  easily and perfectly, and
yield the more spirit, nearly in the order  in whichBUiave  now
enumerated them.                                ^^*^t*
   The nature of ferm^Prnon  shall be considered when we treat
of the vegatable substances in general.   It is sufficient at  pre-
sent to  know  that the  vegetable matter  which undergoes fer-
mentation, or a part of that matter, is changed by it into vinous
spirit.
   This spirit is  at first diluted and combined in the fermented
liquor with a large quantity of  water, a portion of vegetable acid,
some mucilaginous and colouring matter, and a small  quantity
of a subtile and volatile oil.
  "The spirit is separated more or less perfectly from these sub-
stances by distillation, it being more volatile than most of them,
especially the  acid, mucilaginous and colouring matter.   The
water is but imperfectly separated at first, on account of the
small difference of volatility between it and the spirit.
   To  reduce the spirit to a state of purity, we must  perform
several other  operations;  such  as distilling  it again  once or
tv\;ice, with a gentle heat, which is called rectifying.  By this
we separate the  greater part of the water which had come over
in the first distillation." 
SPIRIT OF WINE.
25
   But, even after these rectifications, it still retains a considera-
 ble portion of water, and along with it another ingredient which,
 being very volatile, always arises  with the  spirit, though dis-
 tilled ever so often.  This is the volatile oil, which I mentioned
 as being intimately blended with the  spirit at first.  The quan-
 tity of it and the flavour are different,  according to the m c ire
 of  the particular vinous liquor which we have chosen, and also
 according  to the manner in which the fermentation has been
 conducted.  It is this oily  ingredient in vinous  spirits which
 produces a diversity among them in point of flavour.  When it
 is separated from them as much as possible, they are all alike, or
 are distinguished with difficulty.  It is this oil which makes the
 spirit obtained from all sorts of grain in particular so nauseous
 at first, when compared with some others.  This becomes most
 obvious is them  when  they  are hastily diluted  with  water,
 being then more perceptible by its disagreeable  smell and  fla-
 vour, and  often by some degree of  milkiness, which  appears
 when the spirit and water are mixing together and for some
 time after.
   In order to free the spirit from this oily principle, and from a
 portion of the water which it retains too strongly to admit of its
 being'separated by distillation alone, we must have recourse to an
 elective attraction.  And the  usual  method is  to employ the
 common vegetable fixed  alkali in  its ordinary state, or  in the
 state  of pearl  ashes.   About one pound weight  is added to
 every gallon of the spirit, and allowed to remain with it 24hours.
 It is  dissolved by the  watery part of  the  fluid,  and forms  a
 liquor which remains at the bottom,  and cannot be mixed with
 the spirit above it.  The spirit may therefore  be poured off
 from  it into  another vessel,  in which we may add to it  half a
 pound more of the same  fixed alkali perfectly dry.  This may
not perhapsbecome perfectly liquid ; but it may attract as much
humidity as will make it soft,  and will half  dissolve it.  After
 waiting 24 hours more, the spirit may be poured from this also
 into a  clean  vessel, and we may make a  third addition to it of
 the dry salt.   By these repeated operations, we bring it to that
 state of strength in which it no longer  imparts any watery  hu-
 midity to the dry alkali.
    VOL. III.                    D 
26
VINOUS SPIRITS....ALCOHOL,
  Thus we at last separate the whole of the water  which the
alkali can attract from it.   But, at the same time, the spirit re-
ceives a disagreeable taste, and a yellowish colour.  This hap-
pens  in consequence  of its dissolving a small  portion  of the
alkali, which,  acting on the volatile oily matter,  produces the
yellow colour.  The quantity of alkali thus dissolved,  is, how-
ever, but small, though it  is sufficient to give the bad taste and
flavour.   But in order to separate this also,  as well as the oily
matter with which it is  combined,  another  operation  must be
performed; which is, to distil the spirit with a gentle heat, until
a small quantity of it  only remains in the still.   The alkali and
oily matter will be found remaining with this small  quantity in
the still:  and the  spirit that has passed over in the distillation
will thus be brought to the highest degree of  purity and per-
fection to which it can be reduced by these operations.
 • The artists named rectifiers and compounders, who employ
themselves  in  purifying   coarse  spirits,  and  changing their
flavour, use also, in some of their distillations, a small quantity of
the sulphuric acid, and sometimes the nitric.   These act on the
small portion of water, and of the oil which  may still  remain ;
and they diminish the volatility of both these ingredients: and
by their  action on the spirit itself, they  communicate more or
less of an agreeable flavour.
   When spirit of wine is thus  highly purified,  it is lighter than
water, in the  proportion of 82, 83, or 84, to  10O:  and in this
state it is called Alcohol.  But  I have sometimes brought it
up to an higher degree of strength ; so that,  in the  heat of 60*
of Fahrenheit, 80 parts of it  by  weight were  exactly equal in
measure  to 100  by  weight of water.   It was  brought to  this
strength by distilling it with the addition of dry muriat of lime
which has a very strong attraction for water, and retains it pow-
erfully in the distilling vessel.  This intermedium for rectifying
 spirits has also the great advantage of not acting sensibly on the
 vinous spirit; and therefore imparts nothing of that disagreea-
 ble soapy taste and flavour which are often produced by the fixed
 alkalis.
   Vinous spirits make an article of commerce that  is very  ex-
 tensive.  As they derive all their value  from the alcohol which
 they contain, a method for accurately determining how much al- 
         ITS DISTINGUISHING QUALITIES.     27

 cohol, and  how iriuch water, there is in any spirit, is a very
 valuable  acquisition.     This is  best discovered  by the
 specific gravity.   A cubic foot of water, of the temperature
 55°, weighs 1000 ounces precisely.   The like measure of the
 purest alcohol that I have been able to prepare, weighs 800;
 and ardent spirits approach to this levity, in proportion as
 they contain alcohol.   A  mixture of equal measures of wa-
 ter, and of an alcohol which weighs 820 ounces, forms what is
 called Proof Spirits.   Its specific gravity is 0,925: or the
 weight  of a cubic foot is  nearly 925 ounces*.
    When  a  vinous spirit is by  such operations brought to an
 high degree of purity, it is an exceedingly fluid, penetrating,
 fragrant, and  highly inflammable  liquor, named by the che
 mists Alcohol ; a word introduced into chemical language
 by the Arabians, and which means, I believe, something very
 subtile and  elaborately prepared.
    It is an inflammable substance, distinguished from the rest
 by its singular qualities.
    la the first place,  it has  an extraordinary disposition to re-
 tain the form of fluid.   The most  intense cold that has yet
 been observed in nature, or  produced by art, is not suffici-
 ent to congeal it.
   Another remarkable property of alcohol is, a disposition
 to be much  expanded by heat and contracted by cold.   It is
 therefore  often used in the construction of  thermometers.
   But thermometers  made  of it can only be employed  in
 measuring  intense colds, and  the  heats of the atmosphere
 and of animal bodies.   In a heat equal to  174° of Fahren-
 heit, which  is far  below the boiling point of water,  alcohol
 begins to be changed into  elastic vapour, which, if allowed
 t6 increase in quantity, would burst the thermometer.'   Its
 expansion  is not in proportion  to  its increase  of  tempera-
 ture.,

  * There is considerable uncertainty in this.  Proof spirits is that strength by
■which the liquor pays, the excise duty. " The statute by which this is imposed,
 declares that an  English wine gallon, which is 231 cubic-inches, or _yi  of a
 cubic foot, shall weigh seven pounds and 12 ounces, avoirdupois weight. This
gives 927 6_ ounces for the weight of a cubic foot.  The  hydrometers used by
the officers suppose it still weaker.  (See  Encycl.  Rritannica,  Spirits.)
  ...editor
"V 
28           VINOUS SPIRITS CONSIST

   We may therefore reckon  as a third of the remarkable
qualities of alcohol, its volatility.   In the vacuum of an air-
pump it  would boil  and produce elastic vapour in l°wfr
heats than the ordinary heats of the atmosphere.   And in
an open vessel, even  under  the  pressure of  the  atmos-
phere, it evaporates spontaneously much  faster than water.
If a person dip one finger  into alcohol, and  another into
water of the same temperature, and then expose them to a
dry air, the finger which was dipped into the spirit will imme-
diately feel vastly  colder than the  other, owing to the more
quick evaporation, and the rapid absorption of heat. Its latent
heat is scarcely inferior to that of water, if it does not ex-
ceed it.
   A fourth well known quality of it is an high  degree of
inflammability.  The vapour of it, in whatever manner pro-
duced, is eminently inflammable.  Whenever it is  touched
or approached by  flame it immediately takes fire,  and burns
with a blue  transparent flame, which has not the  smallest
appearance of smoke ; and the whole  of the  alcohol is gra-
dually consumed in this manner, with as little appearance of
its leaving  any earthy or other  fixed incombustible  mat-
ter behind.   This, as I  formerly observed,  induced  Dr.
Boerhaave to consider alcohol as the pure pabulum of fire,
or as a matter which was totally spent and consumed in pro-
ducing heat and light.   And he insinuates a suspicion that
the other iufhrnmable bodies  may have their  inflammability
from alcohol present in their composition.
   But this notion  of its being totally spent and consumed by
inflammation, and converted into heat and light, was a great
mistake. The  fact is, that it is converted into a great quan-
tity of water.
   Newman observes, that if we burn the purest alcohol in a
deep vessel, such  as a large brass  mortar, and keep the sides
of  it cool  by surrounding it with  cold  water, a  quantity
of. water will remain  equal  to  one-third  of  the spirit;
and if we suspend another  mortar inverted over the first  a
quantity will remain equal to one-half ;  and that by  other
contrivances, which still more effectually condensed the wa-
tery vapour, he could obtain a much greater quantitv.
   I have long  been of opinion that a quantity of water might
be collected from burning alcohol equal in weight  to the aU 
     CHIEFLY OF HYDROGEN AND CARBON.  29

cohol itself, or even exceeding it.   And this has been found
to be  fact by  some experiments ingeniously contrived  and
carefully executed by Mr.  Lavoisier, in which he employed
very effectual means for condensing the watery vapour which
arises from its  flame.   He caused  it  to burn very  slowly,
under a tall chimney of thin plate surrounded by cold water.
By a medium of repeated trials, he obtained nine ounces of
water from eight ounces of alcohol burnt in dry*air,  yet the
air unavoidably carried off with it a very sensible portion of
moisture. (See his Essays).
   Some part of this water was undoubtedly present in the
alcohol before it was inflamed;  for it is extremely difficult,
and perhaps impracticable, to separate from it completely the
whole of  the water in which it is originally diluted.   But as
we get more of the water than there v/as of the alcohol, it is
evident that the  whole of this water could  not be contained
in it.  Mr.  Lavoisier, therefore, has accounted for the origin
of  it in another  way, by supposing that alcohol contains a
great quantity of hydrogen in its composition, and that the
atmospheric oxygen combines with this by inflammation, and
thus produces water.   This supposition is founded on very
satisfactory experiments,  the first of which were made by
Dr. Priestley, who published an account of  them without
attempting to build  any theory upon them.    And  Mr. La-
voisier immediately afterwards repeated them with the great-
est accuracy.
   They were made by forcing the  vapour of alcohol to pass
through a red hot tube of metal  or earthen ware.    The
greatest part of  the alcohol was  thus changed into hydrogen
gas, or inflammable air, the bulk of which, on account of.the
rarity of that sort of gas, was astonishingly great, when com-
pared with the bulk  of the alcohol: for in the alcohol, it is
not in the form of hydrogen gas,which is a compound  of hy-
drogen and latent heat.   It is in the dense form of hydrogen,
destitute of that latent heat;  and this, together with a small
portion of carbon, makes  up almost the whole of the alco-
hol; for it appears to contain, besides these two, a very small
quantity only of  some other principles;  such as a very little
oxygen and perhaps of  azote. The presence of the carbon ir>
taown by a small quantity of. very light charcoal which it 
30
VINOUS  SPIRITS
leaves in the red hot tube, and a part of which is dissolved
in the hydrogen ga9.  And the presence of the oxygen is
proved by a small  quantity  of carbonic acid  gas, which is
found mixed with the inflammable air.
   Mr. Lavoisier, therefore, is of  opinion that the greater
part of the water which arises in vapour from burning alco-
hol is formed by the union of the hydrogen with the oxygen
of  the atmosphere, which contributes to its inflammation.
This opinion appears  to be very well founded.
   Besides these ultimate  principles  which have been found
in the composition of alcohol, we can extract from it,  by
some less destructive processes, a small quantity of vegetable
acid, similar to vinegar or the acetous acid :  and  we can
even convert a  great part  of  it into that acid, by diluting it
largely with water, and making it undergo'a particular fer-
mentation, to be described hereafter.  But this is not sur-
prising ;  as  the acetous, acid itself  is now known to be com-
posed of oxygen, combined in a particular and loose  manner
with carbon, and with a  small portion of hydrogen.   The
small quantity of acetous  acid, which is often  concealed in
alcohol, is lost however when the alcohol is consumed by in-
flammation.    In passing through  the outside of the flame
where the heat ianroduced, it is burnt and destroyed, together
with the carbon^ajjd is changed by the oxygen of the atmos-
pherical air  into carbonic acid gas, and a  small quantity of
water.   (See Note 46. at the end of the Volume.)
   This may suffice for a general  account of the  nature of
alcohol, and of the  manner in which  it is affected by  heat.
We must next consider its properties ia  mixture with other
bodies....
   One of these properties, which  appears remarkable when
we consider this fluid as an inflammable  body, is its mixing
so  readily  and completely  with water in any proportion
which no other inflammable substance will do. It even shews
a considerable attraction for water.  When I have prepared
alcohol of an extraordinary strength,  1 found it was  difficult
to  preserve it  in that state.    It  attracted  humidity even
through the corks of the bottles.   This shews a very strong
attraction between this fluid and water.   And this attraction
further appears by the readiness with wnich these two fluids 
TREATED  WITH  ALKALIS.
will deposit other substances that they may unite together.
Most of  the  compound  salts  may be precipitated more or
less from water by the admixture of alcohol.   And alcohol,
which can-dissolve a variety of oils and resinous substances
not soluble in water, deserts or deposits these, to unite with
water.
   The union of alcohol with  water,  in equal weights, pro-
duces eight or ten degrees increas*e of temperature : and the
bulk  of the mixture is less than that  of the ingredients by
one part  in thirty-four.
    It is this attraction which  renders it so difficult to make
alcohol very strong by distillation alone, although the alcohol
in  its  separate state is much more volatile than water.
    Among  the saline substances,  there are a number that act
one way  or other upon alcohol.   We  have already noticed
one property of the common vegetable fixed alkali with respect
to this fluid, that of attracting the water from it when weak,
and therefore assisting us to make it strong. And I observed,
 that if much alkali  be employed  in this way, a small part is
 dissolved,  and gives the alcohol a yellow  colour and  dis-
 agreeable taste, which can only be removed by  distilling it
 slowly, until a small quantity only remains in the still.   I
 must now add, that alcohol, thus tinctured with fixed alkali,
 has been esteemed a more powerful solvent;2r some subjects
 than a purer alcohol  would be.   And  hence  the chemists
 some time, ago took much pains  to learn the best manner *o(
 preparing it, or the way to have  it as strong of the alkali as
 possible : and they  called it tartarized spirit of wine.   You
 will find that  Dr.  Boerhaave gave  much attention to the
 combination of spirit of wine with alkali ; and considered the
 preparing of a good tartarized spirit of wine as a nice"and
difficult operation.   He  recommends or enjoins  attention to
 two particulars : 1st, To use the strongest or purest alcohol:
 2dly,  To use alkali of tartar well calcined, and put into the
 alcohol perfectly dry  and hot.  If there be the least moisture
, in  the salt, or water in the alcohol, it  will be  impossible to
 dissolve  the proper  quantity of alkali.   But I must add, that
 Dr. Boerhaave met with sO much difficulty, in consequence
 of his using the alkali combined  with carbonic  acid, or in its
ordinary state,  as we  find it in pearl-ashes or alkali of tartar; 
 32               VINOUS  SPIRITS

 that  state of alkaline salts being supposed at that  time to
 be their purest state, which  it is not in reality,  the caustic
 state of alkalis being the purest.  If we take an alkali that is
 perfectly caustic, or totally deprived of its carbonic acid,
 we can dissolve as much of it as we please in  spirit  of wine,
 weak or strong,  or though the  alkali itself be  not very dryj
 This property I  discovered in  the caustic alkali ;  and it is
 a  consequence of its being more soluble,  and its  having a
 greater attraction for other bodies than mild alkali has.   It
 unites with alcohol, as  we have seen  it  unite  with other
 inflammable substances.
   Thus  we  have an easy method for  making a tartarized
 spirit of wine, as it was  called, as strong of the alkali as  we
 please, which Dr. Boerhaave thought  to be such a difficult
 business.
   As the  effects produced with alcohol by a fixed alkali,
 perfectly  pure,  are different  from  those produced by  the
 same  alkali in its ordinary state, so, on the other hand, are
 they very  different;, if we take the same alkali perfectly
saturated with carbonic acid.  If alcohol be suddenly poured
 upon  a  spirit of  sal ammoniac,  formed  by  dissolving  as
 much as  possible of the crystallized volatile alkali in water,
the alcohol separates  the  salt  from the water,  forming a
thick, and sometimes firm coagulum,  called  the ojfa  Hel-
montii alba.  It is a crystalline sponge, containing ardent
 spirits.
   We shall now turn our attention to the mixing of this fluid
 with the  different acids,  taking them in their usual order :
the sulphuric therefore in the  first place.....
   This  acid is known to act powerfully on the inflammable
 bodies in general;  and  it  accordingly  unites  with  alcohol
 rapidly and violently.  It will be proper to pour in the acid.
 at one side of the retort, by little at a time, that it may slide
 down under the alcohol; and. after each addition, to agitate
 the mixture with  a circular motion.  Thus we temper the
 very great heat produced  by  the mixture.   Equal weights
 may be thus mixed by cautious agitation with interruptions •
 but in whatever  way we  proceed, a violent commotion  is
 excited, and a heat which the  hand could not bear.   A thin
 glass  must therefore be used ; for if we were to  proceed so 
     WITH THE  VITRIOLIC ACID....j£THER.   33

slowly that the heat should never be considerable, we should
lose much of the valuable product of the operation.   Each of
the first additions of spirits produces a puff of ebullition :
but this becomes moderate by the time that two-thirds of the
spirit  have been mixed ;  and the  mixture now requires
somewhat greater heat to make it boil.
   This mixture has  not a little engaged the attention of the
chemists, on account of some remarkable  productions whicft
are obtained from it when it is  distilled.   A  condensing
apparatus must be fitted  to the retort:  and this must  be
immediately set upon  hot sand for distillation.   This mav
be carried on at first with a pretty brisk heat.  But this must
be quickly diminished, when a certain sign (to be mentioned
presently)  appears,  or  when the  liquor  in the  receiver 19
reduced to nearly one-half of the alcohol.
   The distillation produces as follows :
  • l?no, There  is condensed a clear liquor,  of a penetrating-
diffusive aromatic odour,  the quantity of which is equal  to
half the spirit of wine employed.
   2do, Sulphurous acid and oleum vini duke then coirie over.
But to have these without danger, the heat must be gentle, and
long continued:  if otherwise, the matter boils over, and the
hot froth cracks the  top of the retort.
   3tio,  A thick bituminous  matter or coal is left in the
retort.
   But the fragrant fluid which  comes first,  called ALtkert
is the  desirable product of this distillation,  and the one  on
account  of which it is  commonly performed.  It owes  its
fragrancy to a subtile and volatile oily fluid, which makes
up  the greater  part of it,  and which  was formerly called
the vitriolic aether, but now  the  sulphuric.   As it is the
principal product of  the operation, I shall point out  the best
method of managing the process to obtain it in quantity, and
perfect.
   First, of the different proportions in which the acid'and
alcohol may be mixed  together.   The proportion of equal
weights is the best for producing the greatest yield of aether
from the same  quantity of the materials.   If more alcohol
be taken, a great part of it rises  unchanged.   If a larger
    vol. in.                 • r 
J4
VINOUS  SPIRITS.
 proportion of acid is used, the- mixture soon becomes black
 and thick, and forms sulphurous acid.
   The chemists  are indebted  to  Mr.  Beaume for having
 investigated the best manner of conducting this  operation.
 He tried many different proportions ; and found that the one
 we have taken was the best.   You may see an account of his
 experiments in his little volume on aethers.
 '  In the conduct of  the  distillation,  it was  formerly the
 practice to  apply a gentle  heat, and  distil  slowly from the
 beginning to the end.  It  is,  however, quite unnecessary to
 be so cautious at first; we may distil briskly in the beginning,
 and until the aether has distilled over.   But then, indeed, it
 is  absolutely necessary  to  diminish the heat  greatly ;  and
 the best way to do this is  by  removing  the retort from the
 hot sand,  and thus putting a sudden stop to the distillation.
 If we neglect  to do this,   the sulphurous acid begins to be
produced  so suddenly and abundantly, that it  makes the
matter in the retort boil over in the form of a black foam ;
blows up the vessels ; and poisons the whole air of the house
with an insupportable and suffocating stench.
  The signs by which we may know when it is time to stop,
that we may avoid this accident, are these.....
  It is  time to stop when'a quantity has distilled equal to
one-half of the alcohol, or a little more.   This critical period
of the operation may be also perceived by the appearance of
a whitish vapour, like a mist, appearing in the retort.   And
the bubbles  formed in the retort by the boiling of the liquor
are more  numerous,  and remain  longer before they burst.
 The odour of the vapours perceived at the luting is also less
fragrant than at the beginning.
   Another reason for stopping is, that after having perform-
 ed one distillation, we may perform a second with the same
 acid,  by adding to  the retort a quantity of fresh  alcohol,
 equal in measure to the fluid that was distilled off, and then,
 proceeding as before, we obtain a second product, which is
 exactly similar to that of the first distillation.  And in the
 same manner,  by another fresh dose of alcohol, and a third
 distillation, we  obtain a third product  as good as  the  two
 first; and this  repeatedly   a number of times.   But after a
 certain number,  suppose six or eight, the acid becomes too 
        PROCESS FOR SULPHVRIC ACID.      35

weak, and has much less effect on the alcohol.  In practising
these distillations, a little  of the acid always passes over
along with the last of the aether, and  is intimately blended
with it: and as a small quantity of spirit of wine comes over
in the beginning unchanged,  it is always necessary to rectify
the aether, or re-distil it, to have it quite pure.
   This second distillation is very simple, requiring only a
very gentle heat, the vessels to be well luted, and the opera-
tion performed with day-light. A small quantity of caustic ley
is put into the liquor in the  retort, to absorb the volatilized
acid : and we  must stop when two-thirds have  come over,
reserving the rest, which still contains aether, to be mixed
with the  materials  for another process.  Some  prefer the
cucurbit for this operation :  but the retort answers perfectly
well.  (See'Note 47. at the end of the Volume.)
   It is time now to examine this aether,  and attend to the
properties of it which have attracted notice.
   First, it is called  an oily liquor, being a liquor which does
not mix  with  water, except in small proportion.  It was
once represented as not mixable at all with water : but Mons.
Lauragais  has shewn  that  this  was  a mistake; and  that
water will dissolve one-tenth part of its bulk of aether, but no
more.  I knew this, and had been long in the use of mixing
it with water, to  give as a medicine.
   Along  with this oily nature, it is the lightest of all  fluids,
and of great volatility.  Its specific gravity is about  0,735.
A little of it poured  out very quickly, evaporates, and spreads
its flavour generally through the whole house in which the
bottle is  opened.   A few drops from the height of the arm
will seldom reach the floor.  As it evaporates very fast in the
spontaneous way, so  also  ft  very soon arrives at a boiling
heat.  It boils at  about 100° of Fahrenheit,  even  under the
pressure of the air.   And when we examine its proper boil-
ing point, by.removing the pressure of the air, we find  it as
much lower than  those of other fluids in the same circum-
stances, and far below the freezing point of water.  (See Note
48. at the end of the Volume.)
   Cold is  produced also by the spontaneous evaporation of
aether.   Beaume made Reaumur's thermometer descend be-
low frost with  cloths wet with aether, and  wrapped round the
 phial. 
S6          VINOUS SPIRITS.....JETHER.

   Another quality for which aether is eminent, is inflamma-
bility.   It is very liable to catch fire by the mere approach of
a candle while we pour it from  one  vessel  into another....
Therefore, as it cannot always be fully condensed, the ope-
ration for aether ought always to be performed  in day light.
   It is an usual experiment by itinerant showmen to throw a
iump of sugar, soaked in  aether, into a glass of warm water.
When  a  candle is  applied  to  the surface of the water, it
catches fire, and burns in a very amusing fluttering manner.
The heat of the water expels the aether in a stream of bubbles,
which take fire at the top of the water.   The  glass must be
deep and narrow, that the succession of bubbles may escape
near enough to set each other on fire.
  yEther burns  with a remarkably bright flame,  frequently
emitting sparks more brilliant than the rest, and produces a
sensible soot.
  Ihe remaining properties of this fluid are chiefly those of
a solvent of many  substances.   It dissolves  a  number  of
resins, gums, &c. as we shall  learn afterwards  more particu-
larly.
  The medical qualities  of this singular substance are also
eminent, and deserve our notice.   Internally taken in water,
in the quantity  of 10, 20, 30, or 40 drops,  it is a powerful
antispasmodic.   But its effects as an external application are
the most remarkable.   Applied to the  forehead  in the palm
of the" hand,  it performs all the wonders  of Dr. Ward's
•volatile essence, in resolving spasms and removing nervous
pains in a  moment,  as it were  by charm.   Toothache and
headache commonly yield to it.   I am  inclined to think that
it acts in such cases  by a sort of revulsion.   It brings on, in
a moment,  heat and inflammation upon the skin, which,  to
some, become  insupportable.  But it goes off immediately
when the hand is removed.   It brings on this  superficial in-
-flammation more quickly than any blisterf'sinapism, or such
application ; and it is much  more under  command ; for as
soon as the hand is  removed  from the part, the heat and un-
easiness abate, and soon go off entirely.  1 :in,  therefore per-
suaded that it is very proper in many  cases in which it has
not been thought of, as in pleuritic stiu.hes, rheumatic pains,
an-d other  such  esses. In <vhich  blistering and cupping are oC 
          ALCOHOL AND  NITRIC ACID.       at

service.   There are many such cases,  in which it is expe-
dient to apply remedies of quick operation.  Rectified aether
should be used.
   Of the  effects of mixing alcohol with the nitric acid, che-
mistry furnishes many examples, which are remarkable, both
for the appearances which they exhibit,  and the information
that we derive from  them.                          •
   This acid, when obtained from nitre  by the  process for-
merly described, and which has the name of Glauber's smok-
ing spirit of nitre, and was thought the strongest and  purest,
is in fact the weakest as an acid, and impure.  It is a mixture
of two acids, now distinguished by the name of Nitric and
Nitrous.   The Latin names express their distinction more
precisely, nitrosum denoting an abundance of that which dis-
tinguishes it as nitrous, viz. th»e fiery colour, the copious deep
blood-coloured fumes, and offensive suffocating smell.  The
nitric, on  the other hand,  is colourless* and emits no sensible
fumes.   Yet, in all the distinguishing properties of an acid,
it exceeds the~other, having a much stronger attraction for
water, alkali,  and every  thing that is dissolved by it ; nay,
even for that which seemed to characterise the excellency of
the other,....I mean for inflammable substances.   It  acts on
all substances much more  violently than the nitrous ; dissolves
more alkali, earth, or  metal, or even inflammable substance ;
and its virtues are permanent :  whereas the red fumes of the
nitrous acid waste by exposure, and the  acid becomes unable
to dissolve the same quantity of alkali as before.  It was long
suspected, therefore, that  Glauber's spirit of nitre was  a com-
pound ; and that it contained inflammable  matter combined
with it, arising from impurities in the nitre employed in the
process for obtaining it.   This suspicion was confirmed by
observing that small additions of the more  inflammable sub-
stances to the colourless acid immediately produced that fiery
colour,  and those red fumes, for  which Glauber's spirit of
nitre is remarkable.
   I was the first,  I  believe,  who entertained a notion some-
what distinct on this subject.   Finding that Glauber's spirit
of nitre,  when distilled to about two-thirds of its bulk," had
lost entirely its  fuming quality, and  that the liquor  which
came over possessed it more eminently, while the first was 
38     VINOUS SPIRITS WITH NITRIC ACID.
 stronger as an acid, I was led to consider the original liquor as
 a mixture of two separable substances,  of which that was the
 compound which exhibited the weakest action on the substances
 which are dissolved by both.   This I conceived to be confor-
 mable to the general facts in chemistry.
   I was therefore disposed to consider Glauber's spirit of nitre
 as a compound of the acid of nitre and  inflammable matter,  or
 perhaps of the principle of inflammability.   With this view  of
 the subject, I tried to form anew this  fuming  spirit of  nitre,
 by  adding  to the pale spirit of nitre a small quantity of alco-
 hol, which I considered! as an inflammable substance sufficient-
 ly simple not to contaminate the new compound  with unsuitable
 ingredients.  And I succeeded quite to my wish.  A very mi-
 nute portion of alcohol being added to a quantity of the pale and
 very strong acid of nitre, from which I had separated the  high-
 ly fuming acid by  distillation, immediately imparted to  it the
 fiery colour and blood red fumes, and made it in all respects si-
 milar to Glauber's fuming  spirit of nitre, having all  its  proper-
ties.  This was,  I think, in the year 1760.
  This experiment being very instructive,  it will not be amiss
that I tell you the method of making  it in the  neatest and most
 perspicuous manner.  Take a glass tube, about  one-tenth of an
 inch in  diameter, and draw one end of it more slender.   Hav-
 ing put the acid  into a solution glass, dip  the small end of the
 tube five or six inches into spirit of wine ; and then,  closing the
 top of it with the finger,  take up the spirit with it, and dip it to
 the bottom  of the nitrous acid.   Then, taking off the finger, let
 some (about half an inch)  of the spirit run out of the pipe into
 the acid, and then stop the pipe again.  You will see the union
 take place immediately, and small bubbles form on the mixture
 few of which will reach the top.  The  whole will acquire an
 orange colour. Pursuing this method, you will see the progres-
 sive alteration very distinctly.  One of my students, at Glasgow,
 asked me,  after lecture,  whether inflammable air would answer
 the same purpose, seeing that  some imagined it  to be the  prin-
 ciple of inflammabiiin-.   The thought pleased me : and I tried
 it with perfect success.   It produced the same effects;  but re
 quired an immense quantity; which did not surprise me, by rea-
 son of its preat rarity. 
VINOUS SPIRITS.
39
    But this mixture of nitric acid and alcohol merits further at-
 tention.   I found that, by gradually adding more alcohol, the
 volatility of the acid, or a disposition to emit red fumes, increas-
 ed, and the attraction for water, and its acidity, diminished ;
 and that,  by proceeding in this manner, the acid may be totally
 dissipated in those offensive fumes,  leaving only acidulated wa-
 ter, having no inflammability, nor the smell of nitrous acid, but
 rather that of vinegar, which it also  resembles in taste and in its
 mixture with other substances.
    This process is  accompanied with great heats, notwithstand-
 ing the copious eruption of these^umes:  and it is very hazard-
 ous, because every addition  produces a great and  sudden in-
 crease of heat, which contributes to  increase the explosive pow-
 er of the mixture,  and will throw it about the room, while the
 vessels run the risk of splitting by-  the sudden changes of tem-
 perature.  To succeed to  the degree I have mentioned requires
 a very longtime, mixing very small  portions of alcohol  at once,
 and keeping both ingredients in vessels surrounded with.ice and
 water.  It will often be observed, that, after alcohol, amount-
 ing to one-fourth of the weight of the acid, has been added, the
 explosions are  colourless and  transparent,  and are  accom-
 panied with a fragrant smell, resembling that of vitriolic aether.
 This indicated the production of something different from the
 nauseous blood  red fumes, and gave the chemists hopes of ob-
 taining an  aetherous fluid, different from the vitriolic.-
   They were better conducted to this by another mixture,  well
 known in pharmacy,....the preparation for obtaining what is call-
 ed Dulcified Spirit of Nitre. This isfprepared by cautious-
 ly mixing with rectified spirit of wine,  one-fifth or one-fourth of
 its weight  of strong nitric acid, and  distilling  the mixture.   It
 produces a liquor with no remarkable acidity, having a fragrant
 smell,  much resembling that of apples.  This  encouraged to
 extend  the addition of acid to the alcohol.   Their mutual ac-
 tion was incomparably  more quiet and manageable.  For, as
 it already appears that a very small quantity of alcohol gives  this
ungovernable  volatility to  a great deal of the acid,  it is plain,
that, since a small quantity of acid is not converted at once into
incoercible steams by mixing with a great proportion of alcohol, 
40       PROCESSES  FOR  NITRIC jETHER.
 repeated  additions of such small quantities, after the heat and
 ebullition produced by the preceding addition have ceased, must
 in all probability be quiet and safe.   So the case turns out;  but
 still,  although the successive  mixtures go  on without much
 trouble,  it is  found that when something more than one third
 of acid (by weight) has been added, the mixture begins to ex-v
 plode and become troublesome ; and, if one-half be added, it
 is, almost unmanageable.  Mr. Navier, a French physician,
 was the first, I believe, who published a practicable and success-
 ful process,  founded, I presume, on similar observations.   He
 prescribes the  cautious and grarlual  mixture of one-half of acid
 with the  alcohol, in a very strong glass vessel, which he  imme-
diately corks  up, and secures the cork with leather,  tied hard
over it, and secured by packthread; and the bottle is kept in
cold water.  Thus are the elastic steams prevented from form-
ing, by the great pressure,produced by those already generated.
The fluids gradually act on each other ; and an aether is produc-
ed,  which, like the vitriolic,  floats a-top.  As all this goes on
under a very great pressure,  it is plain that if we pull out the
cork,  or  even  untie the packthread, the elastic explosion  will
take place in an instant, through the whole liquor, and it will be
thrown  out.   Mr. Navier, therefore,  directs  the  cork  to be
pierced with a  pin, and the vapour allowed to escape.  After this,
the aether may be separated by a funnel.   It amounts to one-
third, or one-half of the  alcohol.
  This process was still hazardous ; for the bottle often burst.
 Mr. Beaume,  of the French  Academy of Sciences,  improved
this process, by  carefully investigating the best proportion  and
 manipulation.  ' He found riiat two parts of acid to three of spi-
 rits gave the greatest produce of aether  from the same alcohol,
 and directed both ingredients to be used in the coldest state, by
 keeping each in melting ice, or water and ice, and by setting the
 corked-up bottle in the same  situation.   This proportion of in-
 gredients secures us against the chance of explosions wholly un-
 governable : and the low temperature greatly moderates the ac-
 tion that is unavoidable.  He also directs us to  give  the liquor
 in the bottle a brisk  whirling motion immediately before pour-
 ing in any more acid. This prevents any accumulation in a par
 ticular spot. 
VINOUS SPIRITS.
4%
  By this process we obtain, in three or four hours, a consider-
able  quantity of aether, which is observed to form in little drops
all over the liquor, and  rise gently  to the top.   But allowing
the bottle to remain undisturbed for eight or ten days,  we ob-
tain about half the weight of the alcohol, after which no more is
produced in these  circumstances.
  I am by no means certain that this process will give the great-
est product.  I suspect that  the external pressure  really prevents
the chemical union, in the  same manner as it certainly prevents
it in the boiling of water.  That it is prevented  in this,instance
is evident, because heat  is not absorbed unless the pressure* be
removed.   Therefore the heat is not combined when vapour is
not produced.  The like may happen here.  I  am justified in
this,  from observing that more nitric aether is obtained by other
artificial processes, in which this pressure does  not take place.
I shall mention one, which I practised before I  heard of those
of Navier and Beaume, and which is extremely simple  and
easy.
   Into a strong phial, having a ground stopper, I first pour four
ounces of strong pale nitric acid.   I then add three ounces of
water, pouring it in so gently that  it  swims on the surface of the
acid.  I then pour in, after the  same manner, six ounces of al-
cohol.  I put in the stopper slightly : and I set the  phial in a tub
of water and ice.  The acid mixes slowly with the water ; and,
in a diluted state, comes in contact  with the alcohol, on which
it immediately acts, and aether is produced slowly and quietly.
The liquor gets a dim appearance, because imperceptible bubbles
are formed,  which rise to  the top :  and having collected to a
certain degree,  they lift the  stopper and escape.   After eight
or ten days, I find upwards of three ounces of  nitric  aether,
though I am certain,  by the smell, that much escapes with  the
vapour.   This is, however, a certain, easy, and  safe process,
though it  is slow and imperfect.
   More artificial processes have been followed by several emin-
ent chemists.
   1.  Mr. Woulfe's, in his general manner of managing all dis-
tillations where  fumes of difficult condensations are produced.
He uses a succession of receivers,  which are tubulated.  A tube
       vol.  in.               T 
42
PROCESSES FOR NITRIC  jETHER.
goes from the top of the first into the  second,  down to the bot-
tom, and another from the top of the second into the third, and
so en.   By this contrivance, what is not condensed in the first
receiver, is condensed in the liquor of the second, &c.  A  mix-
ture of equal parts of strong acid  and alcohol is thus distilled
with a very moderate heat;  and a good produce of  aether is ob-
tained.
  2. Nitric or nitrous acid is made to act, in the very  instant
of its formation, on alcohol.  Nitre is put into a tubulated re-
tort, to which is fitted a receiver.   Vitriolic acid is  poured
on this, and  immediately after, spirits of  wine.  The nitrous
acid is disengaged,  which rises through the vitriolic,  aud acts
on the alchol : and aether is produced, whose steams are con-
densed in the receiver.
  3. Instead of putting the alcohol upon the vitriolic acid and
nitre, it is put into  a glass vessel,  which communicates,  by
means of a bent tube, with  a Jarge receiver luted to the retort,
containing the nitre and vitriolic  acid..  Heat being applied to
the retort,  the nitrous acid is disengaged, and part of  it is con-
densed  in the receiver ; and part  passes on to  the bottle contain-
ing the  alcohol, on  which  the vapours act : and aether  is pro-
duced without any troublesome explosions.
   Mr.  Chaptal, who prepares a  great deal in the way of  com-
 merce, uses  two receivers  in succession, the first  being set in
water, and the  second covered with wet cloths : and it has a
tube proceeding from the  top, which is bent downward, and
immersed  in a bottle of water. He says that the process is easy
and sure, affording very pure aether, and in good quantity.
   But all the processes, and indeed every treatment of nitric
acid with alchol, requires much caution,  that we  may  escape
accidents.
   The residue of the distillation is acid,  much changed  in  its
 properties, appearing more like vinegar, or even more resemb-
 ling the acid of sorrel, or of sugar.  It burns to a coal, and pro-
 duces, by a great heat in close vessels,  carbonic acid, and em-
 pvreumatic oils, like all other vegetable substances.
   The  aether of all the processes here described requires  recti-
 ficaiior., to clear it of acid and alcohol, which come over with 
VINOUS SPIRITS.                  43
 it in the distillations, or mix with it in the processes by diges-
 tion.  This rectification is performed by distilling it from caus-
 tic alkali.   This reduces its quantity ; for  we must not distil
 more than two-thirds or one-half of the first aether. To bring this
 to still greater purity, some direct it to be mixed with one-fifth
 nitrous acid, and distilled again,....taking two-thirds of the pro-
 duct set apart, and rectified from caustic alkali.  The rest of
 what comes over is a less perfect aether,...the mineral anodyne
 liquor of Hoffmann ;  and the remainder in the retort is nxlidci-  -.
jied spirit of nitre.
   Pure nitrous aether greatly resembles the vitriolic in lightness,
 inflammability, and flavour.   This last quality, indeed, is infe-
 rior to the  vitriolic,  being stronger, and somewhat pungent.
 The taste is also more acrid ;  the colour inclines considerably
 to yellow.   It burns  with a brighter flame than the vitriolic,.
 produces more smoke, and leaves a stain in the  dish.  When
 kept, it is apt from time to time toublow out the cork.  This is
 attributed to aether not yet perfectly formed; and is said never
 to happen, if the produce be carefully rectified from caustic al-
 kali, and if we do not take too much of what comes over.
   The muriatic acid, in  its ordinary state, exhibits no disposi-
 tion to act on alcohol, or any other inflammable substance.  But
 the chemists, curious after a knowledge of this new discovered
 fluid,  the aether, were eager to compose one by this  acid also,
 although their then received theories gave them  little encour-
 agement to  expect it.  Many attempts, however, were made,
 but long without success.
   The simple mixture and distillation of the muriatic acid and
 alcohol has no effect.   The mixture is indeed called  the dulci-
fied muriatic acid ; but there seems no combination or change
 of properties.   Nor has better success followed the attempts
 to combine  them in the instant of the  production of the acid,
or by uniting their vapours.  At last, methods were discovered,
in which, by employing the acid in  a compound and peculiar
state, a combination took  place, and muriatic aether  was pro-
duced.   Of some of thosi. methods I shall give you a short ac-
count. "                                               .
   I. The Marquis de Courtanvaux-mixed alcohol with a liquor 
 44     PROCESSES FOR  MURIATIC iETHER.

 called the smoking liquor of Libavius.   This as you will learn
 afterwards, consists of muriatic acid surcharged  with oxygen,
 and united with tin.  Alcohol, being mixed with twice its weight
 of this liquor in a retort, produced  heat  and white suffocating
 vapours, but accompanied with an agreeable smell.  When dis-
 tilled, we  first  obtain a stronger alcohol  : and then the aether
 appears, indicated by the smell, and by trickling down the sides
 of the receiver.  After some time, the  smell becomes suffocat-
 ing.  The receiver must now be removed, otherwise the aether
 will be tainted with many products, such as acid, oil, a substance
 like butter, &c.  which you will understand afterwards.
   The aether thus obtained must be rectified from caustic alkali:
 and only half of what comes over must be  taken.
   II. Similar to this is the process of the Baron de Born.   He
 uses a compound of muriatic acid and the flowers of zinc. (Mem.
des Szavans Etrgngers, mi.)  The acid obtained from twelve
 pounds of sea salt,  being  saturated with the flowers  of  zinc
 completely dissolved, the solution  is evaporated till of the con.
 sistence  of grease.   This  is mixed very gradually  with six
 pdunds of alcohol : and after digesting  the mixture eight days,
 and filtrating  it, the  dear liquor  is  distilled beginning with
a very gentle heat.   We obtain,
   1.  Water, amounting to almost half of the spirits.
   2.  An aromatic spirit of  wine.   The matter  in the retort
 now  grows thick like melted wax.
   3.  jEther.  When this has all passed, the matter in the retort
 is dry and the heat must be increased.
   4.  A sweet oil  like essence of lemon.  This  will  swim on
 the aether,  and  is the last volatile product.
   Great care must be taken that the heat be not too great before
 the matter in the retort becomes dry :  for it is apt to burst up
 in sudden clammy oubbles,  which, touching.the.colder parts of
 the retort,,  will split it.
   The aether must be rectified from the aromatic spirit, bv the
 gentlest heat of a lamp furnace ; ana the spirit which remains
 may be poured  back  on  the residuum  in the first retort,  and
 more ssther, &c. obtained, in the manner  practised for vitriolic
 ssther, without  end. 
VINOUS SPIRITS.                 45
  The author obtained by this process two pounds of aether, and
four ounces of the sweet oil, both.of which  were remarkably
fragrant.
  III. Mr. Woulfe made muriatic aether by causing the vapour
of boiling' alcohol  to meet  with the muriatic acid gas, as it was
disengaged from sea'salt, in a glass vessel, from which a syphon
tube proceeded into another  glass  containing alcohol.   The
tube reached  almost  to the bottom of the alcohol:  and the va-
pours which did not  condense here escaped,  and went by an-
other glass tube  into a second vessel containing alcohol:  and
what was  not condensed there went into  a  third, and so on.
By this management the union was effected, and aether obtained
in  each of those  vessels,  swimming on the  alcohol.   These
portions were mixed  and rectified by distillation  with a gentle
heat, from caustic alkali, being  much  contaminated with acid
vapours.  The whole process was extremely  tedious and trou-
blesome, requiring several cohobations, or returning the liquors
 back again upon  the residuum, before a tolerable quantity of
 xther was obtained.  The vessels of alcohol  were heated to a
 great degree by  condensing the  vapours,  and soon gave over
 condensing.  (See Phil. Trans. 1767.)
   IV.  A Mr. Schroeter of Berlin prepared a  muriatic aether by
 distilling from a mixture of eight parts of sea salt, four of sul-
 phuric acid, four of  black manganese, (a substance containing
 much oxygen) and three of alcohol.  In this  process, the muri-
 atic acid was disengaged from the sea salt by the sulphuric, and,
 in its nascent state,  acted on the  alcohol, being assisted by the
 manganese (without which^|know that it will not succeed) in
 such a way as to produce M Kance of aether.  Mr. Pelletier of
 Paris,  by a similar proces^ootained four ounces of aether from
 eight of alcohol.   The manganese evidently  appears to favour
 the production of aether exceedingly.  If the ordinary muriatic
 acid be distilled  from manganese, its properties  are remarkably
 changed: and  if employed in this state in Woulfe's manner, it
 produces aether with great facility.  There is, therefore, some-
 thing which it possesses, in this state, and in those of the muriats
 of tin and of zinc, that is similar, and  which fits it for this pre-
 paration.  This  change on the muriatic acid will be minutely
 considered in due time. 
46     PROCESSES  FOR  MURIATIC jETHER.
    The aether obtained by any of these processes, when pure, is
 like the other two, immiscible with water except in a small de-
 gree, extremely light, highly odorous and penetrating, but much
 more offensive to the lungs than they  are.  It is highly inflam-
 mable ;  and in burning  has  much smoke, and emits a smell as
 penetrating as sulphuric acid.   It is less agreeable to the taste,
 having the styptic taste of alum.
   Thus we see that the three principal acids have in one respect
 a similarity in their action upon vinous spirits.   Even  the mu-
 riatic, which, in its ordinary state, shews no action on inflamma-
 ble substances in general, or on this one in particular, can be put
 into such a state, competent to it as an acid, which  enables it to
 contract an union with alcohol, or produce a change on it, simi-
 lar even to that produced  by the njtric, which  acts the most
 violently of all on them.  This must be considered as a common
 property of the acids, which it behoves the chemical philosopher
 to investigate in his own way.   A chemist is disposed to ascribe
 it to some ingredient common to the acids.   And we  are in-
 terested to discover what this may be.
  This may be considered as giving a theory of aethers, or an
 explanation how they are produced.   They were discovered at
 a time when  chemical science had made considerable progress,
 and its cultivators were  eager to give a rational account of  the
 many surprising effects or changes which it presents  to our view.
 Therefore attempts were soon made to explain all these appear-
 ances.
  One of the first who attempted this was Mr. Macquer.  He
 imagined that the production o^^aese light oily  fluids  was
nothing but an abstraction of watHBm the ardent spirits ;  and
that this was  effected by the stroriP^traction for water   which
 is a distinguishing property of all the acids.  By this abstraction
of water, he  conceived the  alcohol to be reduced to its state of
purity.   And this he thought was a compound of a subtile oily
principle  and water strongly combined, and which,  by the pre-
sence and  quantity of the  water in its composition, becomes
miscible  with water in  any proportion.   The acids, by their
strong attraction of water, rob the spirit of a part of its elementary
 constitution,  rendering it more  inflammable  and oily,  and no 
VINOUS SPIRITS.
47
longer so miscible with water, but more volatile and inflamma-
ble,
   But this theory is insufficient for explaining the phenomena.
It is incongruous  with the general train of chemical facts, that
depriving ardent spirit of water will diminish its attraction for
it.  And it is not  fact that the acids which have the strongest
attraction for water are the most effectual for changing alcohol
into aether. Acetous acid, which has a weak attraction for water,
produces more aether  from a quantity of alcohol than the fossil
acids  do.  And the muriatic acid, which  attracts wafer  with
great  force, produces aether with great difficulty, especially when
employed in that state in which it  attracts water most strongly.
It should also  be a  consequence of Mr.  Macquer's theory,
that all aethers should be alike, which is very far from being ttie
case.
   Mr. Berthollet, a chemist of the first eminence, thinks that
all the aethers are formed  merely by the addition of more oxygen
to the composition of  the alcohol.  This opinion seems chiefly
founded on  the necessity of employing acids, which abound in
oxygen,  and on  the phenomena and consequences of some of
those processes, which shew the acid to  be very  much deoxy-
genated.
   But I  confess that I view the formation of the aether in a dif>
ferent light.   When the processes are  conducted in the  best
manner,  we have no appearance of deoxygenating the acid during
the formation of the aether.   The sulphurous acid does not ap-
pear  till all the aether has passed  over.   And we obtain the '
greatest  quantity of nitrous aether, when we succeed best in
preventing  the  explosion  and the deoxygenation of the acid.
When we neglect the precautions for preventing this,  such as
the keeping the mixture very cold, and making the additions
very gradually, we have red fumes, indicating the deoxygenation
of the acid, and we obtain less aether.
   I am persuaded that the aethers are compounds of the alcohol,
with a greater or less portion of the acid employed.  The acids
which are most abundant  in oxygen are the fittest,  for  this
reason, that they have the strongest action on alcohol and other
inflammable substances.   I believe that the acid is combined 
 4S                 VINOUS  SPIRITS.

 with the alcohol, so as to be neutralized by it, while the attrac-
 tion of the alcohol for water is diminished, for the same reason,
 and in the same manner, as the attraction of both acids and alkalis
 for  water and other substances is diminished when they are
 combined in forming  a neutral salt.   The  alcohol, therefore,
 assumes that immiscible and oily nature which is observed in
 it.   That an oily appearance and consistency may be produced
 and increased in this way,  is evident from the example of the
 oleum vitrioli duke,  which has  more the  appearance of an oil
 than the aether itself.  Yet it is  only aether super-saturated with
 acid.  The aether is  totally convertible into this oil by repeated
 distillation with the  acid; so is also the nitrous aether.   The
presence of an  acid in the most perfect aethers has been proved
by Crell and Scheele.  Both of these chemists have substituted
one  acid for another in the same ae her, so as to change one
aether into another, in a certain order.   Were pure oxygen all
that is united with the alcohol in forming aether, all acids would
be indifferent, and all aethers alike.*
  Mr. Lavoisier has  been the most successful in explaining
 many phenomena in  the action of the acids on alcohol and simi-
 lar  substances, and  has made  many judicious, accurate,  and
 instructive experiments with this view.   His explanations are
 founded on a careful analysis of the ultimate constituent princi-
 ples of alcohol, and of the vegetable substances.from which it ia
 produced.
  Mr. Lavoisier's opinion was, that the vegetable substances in
 general, and those susceptible of fermentation,  such as sugar,
 mucilage,  farina, and the~Jike, are composed of carbon, hydro-
 gen, and some oxygen, loosely  joined, and in various propor-
 tions.   By receiving more of the oxygen from the nitric acid^X
 when it acts on them, or from the air, in the  acetous fermenta-
 tion, they are changed into vinegar, or some other acid.  When
 the nitric acid is made to act violently, it produces effervescence
 and elastic matter: 1. By the changes which the nitric acid
 undergoes into acidum nitrosum, or into nitrous air, according
 * Do not the more brilliant flame, and the smoke and soot, indicate a
dundancy in the carbon rather than in the oxygen '....editor. 
                 THEORY OF  OTHERS.             49

 to the degree of deoxygenation; 2. By the change of part of
 the  carbon into carbonic acid gas,  in consequence of its  close
 union with part of the oxygen of the nitric acid.
   Alcohol is composed of the  same  principles  which comprise
 these vegetable fermentable  substances.  But the principles are
 combined in  the alcohol in different proportions from those
 which constitute sugar, and the rest of them.   In alcohol there
 is a less  proportion of oxygen  to  the  others,  especially to the
 hydrogen.  In consequence  of this it is more inflammable and
 volatile than diose other vegetable productions.
   The carbonaceous  matter in alcohol is clearly exhibited in}^
 the experiment ofT?riestley  and Lavoisier formerly mentioned,
 where the vapour of alcohol was made to pass through a red hot
 tube.  It also presents itself in the  process for sulphuric aether,
 by imparting a black colour to the acid in the retort, in propor-
 tion as the aether forms, and oxygen is abstracted from part  of
 the acid.   Its place  is supplied  by the carbon expelled from the
 alcohol by this elective attraction.   At last, the matter in the
 retort becomes coaly ; and a considerable quantity of very fine
 charcoal is elevated.   It is probably thus partly retained and se-
 parated from the  other  elements of the alcohol, by the strong
 attraction of the sulphuric acid, which^ when the distillation is
 too  long  continued, is imperfectly decompounded by it, and
 changed into sulphurous acid :  and the vapours of this volatile
 sulphurous acid,  in conjunction with the carbonic acid gas, into
 which a part of the carbon is changed on this occasion, explain
 the violent and sudden ebullition of the matter in the retort, and
 bursting of the vessels, when the distillation  is  pushed far with
 too great  a heat.   And during  the formation of nitrous  aether,
 there is always a little effervescence or  a production of gas,
 formed from a part of the carbon changed into carbonic acid by
 some of the oxygen of the nitric acid, which, being thus partly
 changed into azotic gas,  contributes to make up the quantity  of
the elastic gas.  And along with these gases, vapours of the ni-
trous aether, formed in consequence of its great volatility, also
escape. The  matter of these different gases, however, can be
confined and made to remain combined with the nitrous aether
for some time ; of which  we have an example in Mr. Navier's
     vol.  in.                     o 
50           VINOUS SPIRITS....SUGAR.
and in Mr. Beaume's processes for nitrous aether ; the strong
pressure to which the materials are subjected in the corked bot-
tles repressing their volatility. But whenever the bottle is open-
ed they are sure to escape.
  All the aethers, therefore,  as I said before, appear to be com-
pounds of the alcohol, and of a small portion of the acids made
use of.   A part only, and that very little, of the acid is decom-
pounded, less or more, by the loss of some oxygen during the
process : and a part only of the carbon is taken  from the alcohol.
iEthers, therefore,  contain a less  proportion  of this principle,
and a larger one of the hydrogen than alcohol does.   This idea
appears probable, from the lightness and volatility of aether, and
from the  black colour and other appearances of the acid which
remains in the retort in the distillation to obtain sulphuric aether.
  The experiments  you have now seen with  mixtures of alco-
hol and nitric acid confirm the character of this  acid, which is
eminent b\- a disposition to act violently and powerfully on the
inflammable substances,  and others allied to them, which pow-
erful action  of it plainly depends  on the great quantityof sepa-
rable and active oxygen  which it contains.
  Of this we have another eminent example in the action of su-
gar and nitric acid on one another.
   Some of the  qualities of sugar  are sufficiently known to you,
such  as its solubility in water, arid the crystals called sugar-can-
dy which it forms, when the solution of it, or  syrup, is proper-
ly crystallized.   Loaf sugar is only a mass of very small crys-.
tals cohering together, and therefore more readily soluble.
   Sugar is entirely a vegetable  production, and is found in the
juices of many  vegetables.  It is commonly obtained  from the
juice of one plant,  which abounds with it  the  most of any viz.
 the sugar-cane.  But many other vegetables, or parts  of vege-
 tables, contain some sugar.  It is often crystallized or  concret-
 ed in fruits that are dried.
    As  sugar is always a  vegetable production, not being found in
 any other part  of nature,  we may expect to  find in it the same
 elementary principles of which  vegetables are  composed   or
 some  of those principles.  Accordingly,  when  it is  subjected
 to the most destructive kind of analysis by fire, it vields a larp-e 
           SUGAR AND NITRIC ACID.          51

quantity of hydrogen gas, mixed with carbonic acid, and hold-
ing dissolved  a small portion of the carbon not combined with
oxygen.  But a considerable portion of carbon remains behind
in the apparatus, in the form of charcoal.  From the result of
this analysis,  it is plain that sugar is composed of carbon, com-
bined  with  hydrogen and with some  oxygen at the same
time. These  two last ingredients are in their dense unelastic
state.   And  all the three are combined with  that weak at-
traction with which the elements of vegetables are known to
cohere.
   You can easily imagine that such a compound as sugar
may be made to receive a larger quantity of oxygen than that
which it naturally contains.  And this  is found  to be true,
when we apply to it the  nitric acid.  But no one can imagine,
till he has seen it,  the  violence with which the action goes
on.   When a bit of  loaf  sugar is put into nitric acid, it is
some time (about three  or four minutes) before the combin-
ation becomes  observable.  Small  bubbles begin to  detach
themselves, and immediately on their reaching the surface,
acquire a deep blood red colour. The liquor becomes warm:
and the emission of bubbles becomes more and more copious,
till the whole is in violent ebullition, and the upper part of
the vessel is  filled with the blood red vapour, which becomes
transparent;  and  the production of those red vapours goes
on till the sugar is dissolved  or consumed, and the  liquor
acquires the greenish colour of fresh made aquafortis.
   If this mixture be made by employing common aquafortis,
a gentle heat is required:  and then the phenomena are nearly
the same in kind, though in a much more moderate degree.
What  I  chiefly mean to  consider just now is the vapours
which are produced.   They are found to consist of oxygen
and azote, the  same which I  have given as the constituent
parts of  the  nitrous acid.   But they are in a very different
proportion, being nearly as 68 to 32 ; and require a great
addition of  oxygen to make them equivalent to nitric acid,
or  even  to  nitrous  acid.   When pure, they  are  not only
transparent, but as colourless as common air, and are perfectly
incondensible by pure water,  or ordinary cold.   The deep
red  colour acquired by the fumes,  arises entirely from the
mixture  with  the  vital air of  the atmosphere.   The  gas 
52          VINOUS  SPIRITS....SUGAR.
combines with  oxygen, and  the  two collapse into  nitrous
acid.   If  a glass  jar, filled  with vital  air or  oxygen, be
inverted on water,  and some of the gas obtained from sugar,
in the way now described, be letup into it through the water,
we have an  instantaneous deep red  cloud, and the water
rises to the top of the glass, in consequence of the collapsing
of the two gases.   It contracts  no such union with azote or
carbonic acid gas.   From this account you see that it is the
fluid called hitrous  air, or nitrous gas fas the French  call it)
which was  first discovered by  Dr. Priestley, but produced by
him by other processes than this.   And by making a great
number of experiments with it, he made many useful, interest-
ing, an ! 'ns'nictivr discoveries.   I shall shew the principal
experiments  with  it soon,....when we shall have an  ODpor-
tunity for preparing it in  a more perfect and pure state  than
this. I shai1  only remark  on it at present, that it is the nitric
acid  hanged to a  much greater degree from its  common
state !:ian it  is  in the acidum nitrosum,  and this  in conse-
q m >ce of having lost a greater proportion of  its oxygenous
principle.  And therefore it has no perceptible acidity, and
but little attraction  for water.    It retains, however, the dis-
position to unite again readily with oxygen :  and in uniting
with it, forms first the acidum  nitrosum, and afterwards, with
a larger quantity, the most perfect nitric  acid.
   These are  the changes produced in the nitric acid while
it and sugar act on one another.
   The sugar too, as might be  expected, undergoes a great
change.  It  totally loses its sweetness ; and is converted into
a perfect acid by its union with the oxygen of  the nitric
acid.
   Mr. Bergmann,  by distilling  aquafortis from one-sixth of
its weight of sugar, obtained a prodigious quantity  of  the gas
just now described,  and  reduced the sugar to a  pure acid
salt, called the Acid of sugar.   It crystallizes in four-sided
spiculae, terminated by a ridge.
   The acid of sugar, exposed  to a heat gradually increased to
a red heat,  first  effloresces, losing its water of crystallization
and then becomes  brown,  and  emits  compounded vapours
which, by careful treatment, condense into the same products
that are obtained  from all vegetable  substances, or  remain 
    SACCHARINE  ACID,....ITS  AFFINITIES.   53

in the form of elastic gases ; that is, empyreumatic acid and
oil, soot, and a great quantity of carbonic acid and inflamma-
ble air. Part of the salt, however, sublimes, no way differing
from its original form.
   WJien examined in the way of mixture with the substances
which we  have already considered,  it exhibits  several re-
markable properties.
   With the mineral alkali, it forms a salt of difficult solution,
having an excess of alkali  in its crystals.
   With the vegetable alkali,  it forms a deliquescent  salt,
when perfectly  neutral, but which crystallizes when either
ingredient exceeds in  a certain proportion.
   With volatile alkali,  it  forms a salt which crystallizes in
four-sided  prisms.    This  salt is decomposed in  a very
singular manner by  heat, namely,  by the destruction of its
acid :  and we obtain very mild volatile alkali, formed by the
carbonic acid which arises from the destruction  of the acid.
It is worthy of particular remark, that no deflagration  appears
in treating the acid of sugar, or its compounds, by great heats,
nor is any azote obtained.   This shews that it does not owe
its acidity to its  containing nitrous  acid,  as was  supposed
when it was first discovered.
   With lime, it forms a salt insoluble in water (if that name
be competent to such a substance).   It is very remarkable
that the attraction of  this acid for lime exceeds that of the
three mineral acids.  Lime also decomposes the three salts
already mentioned.  Acid of sugar,  therefore, will detect
lime  in mineral waters,  by  taking  it  from  every other
solvent.
   It  forms a white powdery  salt with magnesia,  and with
barytes ; which last  earth decomposes the magnesian  salt.
   Acid of sugar dissolves in sulphuric acid, giving it a brown
colour.
   Nitric acid acts on it, and decomposes part of it:  and we
obtain, by distillation, vinegar and  carbonic acid.
   If fresh nitric acid be distilled from what remains, we have
the same products.
   When this  action of nitric acid and sugar on one another
was first discovered by Professor Bergmann, it was supposed
that the acid we obtain was a principle or production peculiar 
  54 SACCHARINE ACID, OR  ACID OF SORREL.

  to sugar.  It was therefore called the acid of sugar.   But by
'  similar experiments, which have  since been made  on  a
  variety of vegetable and animal substances, subjected to the
  action of the nitric acid,  we have learned that the acid acts
  on them all in a similar manner ; that is to say, with similar
  effervescence and the  production of similar elastic fluids ;
  and that many  of those substances  are thus changed also, at
 least  in part, into  an  acid exactly similar to that  obtained
 from  sugar, although they are not at all sweet, nor appear to
  contain any  sugar.   This  happens with the vegetable mu-
 cilages and glues, gum  arabic,  tragacanth, and others ; also
 with starch, and the mucilaginous part of lemon juice.   Its
 presence in this  last was discovered by  Scheele :  and he
 evinced its being the mucilaginous part of lemon juice which
 contained  the  saccharine  acid,  by crystallizing the acid of
 lemons, and then  examining this for the saccharine acid.  It
 contained none.  Note, That the citric or lemon  acid is very
 easily crystallizable, by first combining it  with lime, and
 separating  them  by means of  the sulphuric acid.   Even
  alcohol yields  a little  of this acid, when the action  of the
 nitric acid on it is violent and long continued. Many animal
  substances yield it  also, as Mr. Berthollet discovered : and
  some of them  yield it in much greater quantity than  sugar
  does.  Sugar  yields one-third of  its weight.   Wool more
  than  one-half.
    There*is, therefore, no  good reason now for calling it the
  acid of sugar, especially since it has been found ready formed
  in some other  vegetable substances, as in sorrel. Since this
  acid  has been  well examined and  characterised, the salt of
  sorrel has  been found  to contain it,«ud to derive its acidity
  from it;  the  salt  of  sorrel itself  being  an alkali  super-
  saturated with  this acid.   Vide Bergmann on Elective Attrac-
  tions.
    We may here  further remark, that all the vegetable acids
  are more or less similar in their composition to the acid  of
  sugar,  being  composed of hydrogen, carbon,  and oxygen,  ,
  in different proportions.   All  these salts are convertible into  "
  one  another in a certain order, by the action of the nitric   ^
  acid  on them.   The acid of tartar is changed into the  oxalic
  -   saccharine ; the oxalic, into the  acetous ;  and this into the 
SIMILARITY OF THE ACIDS OF PLANTS 55
carbonic.   But this  department of chemical analysis  is yet
in its infancy :  and it will probably be a long while before any
perspicuous knowledge of  it will be acquired.  We run a
great risk of being led into important mistakes,  by too con-
fident application of imperfect and perhaps erroneous theory.
We will correct with reluctance mistakes which  result from
ingenious conceptions and laborious investigation.   The pre-
sent subject in particular seems to encourage our researches
by great appearances of success.   But  the convertibility of
acids, which  at first exhibited  such uniform distinctions,
should  make us extremely  cautious in forming general con-
clusions.   I have not room to enter into a discussion of so
many particulars.   Nicholson gives  the current  opinions on
the present subject with great candour and distinctness.
   Thus we  have  considered the  consequences of mixing
spirit of wine  with  alkalis and acids in different ways.
   Of the compound salts,  there are a few which can be dis-
solved  in  this spirit; though the greater number cannot.
The soluble are, the muriats of lime and magnesia,  acetite
of potash, the acetite and nitrat of ammonia.  The rest, in
general, are not soluble ; but, on the contrary,  are  precipi-
tated by  it from water.   Hence it  is  that the fixed alkali
which is dissolved in vinous spirits,  in the process for rec-
tification,  is of  the utmost purity.   Mr. Woulfe employs
this method for examining their purity.
   Vitriolated tartar,  after long digestion with vinous spirits,
exhibits some remarkable  appearances.   We obtain aether*
sulphurous acid, and volatile alkali.
   None of the earthy substances have any remarkable actio**
on vinous spirits.
   Phosphorus unites with  it imperfectly, but without any
phenomenon  very interesting to the chemist.  Mr. Boyle
may be consulted on the subject.
   Sulphur does not unite,  even by long digestion.   Count
Lauraguais combined them perfectly, when in the form  of
vapour, issuing from two retorts.   They form a fcetid liquor.
   Charcoal speedM clears spirits of wine from all distinc-
g trom
leedpT
r,ind i
tions of davourjmd makes all alike, and quite colourless.
6 
                            so


                       VI.....OILS.

   Under this division I comprehend, along with what are
 commonly called Oils, the  solid fats of animals,  and resins
 of vegetables, as being distinguished  only by a slight differ-
 ence in fusjbility from the fluid inflammable substances of ve-
 getables and animals, to  which the term oil is in common
 language confined.
   The bodies which belong to this division are far inferior to
alcohol  in simplicity and inflammability.  Yet, when  their
inflammation is properly  excited, they give more heat and
light than alcohol does.  They are, therefore,  stronger fuels,
or may be considered as  more inflammable substances than
alcohol  is.  And yet they are not  (many of  them at least)
quite so easily set on fire, or brought  into a state of inflam-
mation.   Most of them require to be heated more :  and their
inflammation in ordinary circumstances is not so  complete.
Their flame commonly throws out from  the top of it a quantity
of sooty matter, called  lamp  black, the inflammability of
which  is not exhausted.   I  call it sooty matter;  but it is  a
matter considerably different from common soot, which is an
article of  the materia medica.   This consists partly of lamp
black,  or the half burnt oily matters of vegetables,  and partly
of many other substances, not inflammable, which are vola-
tilized and expelled by the heat, along with the inflammable
vapours.  Soot generally contains an ammoniacal salt, formed
of the volatile alkali, existing or  generated by  the heat,
 in the  vegetable, and an  empyreumatic acid of the acetous
 kind.   Lamp black is a less complex substance,  being the
 scorched  or half burnt oily vapour ;  and is always produced
 when the flame, is of such a large size, or of such a form,
 that the air has not a sufficiently extensive contact with it to
 act with full power on the  whole of the  vapour that composes
 it.   But when the flame is of a small size, or when a stream
 of air is  made to rise up through the middle of it,  as in Ar-
 gand's lamps, or when a small stream of air is forced through
 it with the blow-pipe, the formation of soft is effectually pre-
 vented.   I observe,  however, that  even a very  small and
 clear flame from oil, without the  least appearance of  soot, 
OILS.               *       57
 carries up a minute portion of whitish earth,  which, during
 a long continued process with a lamp furnace, attaches itself
 to the bottom of the vessel that is heated by the flame.  This
 is  certainly  part  of the  ashes,  not volatilized,  but merely
 blown out by the stream of vapour.
   The component parts of oils are best discovered when we
 gradually convert them into vapours, and cause those vapours
 to pass immediately through a red hot tube, without mixing
 with air,  into a proper apparatus for collecting gases.   The
 result of this operation  is the  production of an immense
 quantity of hydrogen gas,  mixed with some carbonic acid gas,
 and a small quantity  of  watery vapour.   And in the  tube
 and distilling vessel, when they are allowed to cool, we find.
 a portion of charcoal, which,  when burned in the open  air,
 yields, a small quantity of ashes, and a still  smaller of sa-
 line matter, commonly fixed alkali.
   This analysis, therefore,  shews that the constituent prin-
 ciples of oils  are hydrogen and carbon, with a small propor-
 tion of oxygen, and a still smaller of earthy and of saline
 matter.   The presence of the oxygen is  evident  by the ap-
 pearance of the carbonic acid, which is formed by the tin ion
 of  that principle with a part of the carbon, and  also by our
 procuring a small quantity of watery vapour,  which  it forms
 by  uniting with some of the hydrogen.   The hydrogen gas
 obtained by this operation is necessarily of that  kind which
 contains a small quantity of carbon dissolved in it, and which,
 on  account  of its being rendered denser by this admixture
 than a pure hydrogen gas, is therefore named heavy inflam-
 mable air.
  When the oils are subjected to  the treatment  which was
 named  Chemical Analysis,  by  the  elder chemists, in
 which they  were merely  distilled  in retorts  and receivers,
 and the vapours  of them thus condensed  as fast  as  they
 were  formed, and  without  being  ever made red hot,  the
 products obtained are considerably different;  for this reason,
that the principles  of the  oil are not so completely separated,
 from one another.   The greater part of the vapours are con-
 densed into an oil,  or oily fluid,  which has very  different
 properties from those of  the  original oil.  We procure also
     vol. III.                h 
53                 SEBACIC ACID.

some acid water,  and some carbonic acid gas.  And a small
portion of charcoal remains in the retort.
  Repetitions of the same process, with the same oil,  di-
minish the quantity of the oil every time,  rendering it more
attenuated and volatile, and produce a little more water  and
a little more charcoal.  And  Mr. Lavoisier discovered  that
more water was produced every time from the same quantity
of oil, when the distilling  vessels were of a large  size than
when they were small.  He therefore concludes  that all  this
water did not pre-exist  in the oil, but  was formed in the
distilling vessels  from the hydrogen,  which, uniting with
the  oxygen of the air contained in the vessels,  formed the
water, or a  great part of it.   And the  acid found  in  this
water, and which is of a peculiar kind, is undoubtedly  formed
of a part of the oxygen, loosely combined with a part of the
hydrogen  and of the carbon,  as it is  in the vegetable acids.
Dr. Crell of Helmstadt made a very satisfactory set of expe-
riments to investigate its peculiar properties.  They are  pub-
lished in the 70th volume of  the Philosophical Transactions.
This acid is now named the sebacic acids :  and the compounds
it forms with alkaline substances are named sebats.
   The consequences are different when we apply heat to the
oils in the open air, so as to-inflame  them in the  most per-
 fect  manner.  The  whole of the hydrogen and the carbon
 unite with the oxygen of the atmosphere,  and form water,  or
 vapour  of water, and carbonic acid in an elastic-state.
    I have long bagn of opinion, that a great quantity of wa-
 ter arises from burning oils.   A plate of very cold  glass or
 metal being held for a  moment  above a  very  small and
 clear flame, will  immediately be  covered with dew;  and a
 bell glass held over the flame and kept cold by  snow will
 joon have  drops of water hanging at its  brim.  But Mr.
 Lavoisier has collected this water more accurately and  com-
 pletely, by means of a well contrived apparatus : and  he  finds
 that it  exceeds the weight of the  oil.  Something, therefore
 supplied by the atmosphere must contribute to form  it.
    The  only question is, whether this water has been exist-
 ing previously in the air,  or has been formed in the manner
 as  igned by Lavoisier? The last is more probable;  because 
         OILS....AROMATIC....UNCTUOUS.      5%

we cannot see how the heat produced by inflammation can
make the  air deposit water which it  suspended when col-
der*.
   If the  inflammation be improperly  managed, the change
and destruction of the oil is not so complete.  The soot which
is produced from all oils,  when  we attempt to burn them
with too  large a flame,  is formed principally from the  car-
bon.
   To  treat of the oils more particularly, they must be dis-
tinguished into two  principal kinds, the Aromatic and the
Unctuous ; to which it is usual to subjoin a third section,
named Empyreumatic
   The aromatic oils are all formed  by  nature, and chiefly in
vegetables.  In  these  they are  secreted juices, lodged in
particular parts or repositories in the structure of  the plant.
All the  aromatic oils make  a strong impression on  the
organs of taste and smell, exciting on the tongue the feeling
of heat and acrimony.  And they have not that smoothness
and slipperiness, when felt between the fingers, which is na-
med  unctuosity.  They are also all capable of rising in va-
pour, in the heat of boiling  water, or at least along with the
vapour of water.   And they are very inflammable.   The
wicks  of  candles are often prepared for being quickly lighted
up, by putting a small quantity of some of these oils on the
extremity of  them.
   The unctuous oils  are also natural productions ; and are
found in  vegetables and animals, in both 6*f which they are
also secreted  juices, or are formed and lodged in particular
parts or repositories.
   When not  corrupted, they have not any pungent taste, or
remarkable odour,  but  have unctuosity in  a great degree ;
and for that reason are much employed  to diminish friction in
machines of all kinds.    The  heat of boiling water is not
sufficient  to convert them  into vapour'  j and they are not so
readily and quickly inflamed as the aromatic oils.

  * It is perhaps owing to this actual formation of dampness, or water.that Dr.
Franklin found that all electrical experiments are almost stopped, while a burn-
ing candle is connected with the insulated part of the apparatus.  We  have
the means of deciding this question....editor. 
60            EMPYREUMATIC  OILS.

   The empyreumatic oils resemble the aromatic so much by
many of their chemical qualities,  that  they are not distin-
guishable from  them by any general difference, except the
circumstance of their origin.   None  of  thtm  are natural
productions.   They are all produced  by art; and are either
oils, changed from their natural state by the action of violent
heats,  or are entirely  produced by heat from vegetable or
animal substances  which do not contain a formed oil before
the heat is applied to them.   We may also add, as an article
in the character  of the empyreumactic oils, that the odour of
them is in general offensive.
                    AROMATIC OILS.

   Let us now take a nearer view of the first of these sections,
 tne aromatic oils.
 - We find almost the whole of  them in  vegetables.  There
 are a few examples of similar oils  got  from some  animal
 substances: but they are very few.  It is by examining vege-
 tables that we find a great number  and variety of these oils.
 All the vegetable substances which  affect our organs with any
 remarkable odour, or hot pungent taste,  produce these effects
 by the action of  an oil, or oily principle of the aromatic
 kind  which they contain.
   And, as in a great number of such vegetables,  these oils
 are the most remarkable, and the most useful  and active mat-
 ter which they  contain, they are for this  reason  named the
 Essential Oils, or Essences of  such  vegetables.
   The variety of them found in the different vegetables, or
 vegetable substances, is very great.   But the greater  num-
 ber of  them have  not yet been found applicable to any useful
 purpose.   And many others are contained in the vegetables
 in such very small quantity, that we cannot extract them ex-
 cept at a very  great expence,  far  exceeding  any value that
■' can be set on them.   Such, for example, is oil of roses which
 lias the fragrancy of that favourite  flower in the highest per-
 fection.   Roses contain more of it in the warmer climates
 and yet even in these, so little, that it is valued at an extra-
 vagant price.    Some of this oil is  collected in India, partly
 from rose-watex. 
        AROMATIC OR  ESSENTIAL OILS.     m

   The odour of these oils, which is in most of them strong
and fragrant, is one of the most remarkable of their obvious
qualities.   And this  odour is different and specific in each
particular oil.   But they are diversified by other properties
besides the variety of odours.
   Some of them are extremely fluid, light, subtile, and vola-
tile.  Others are more heavy and thick.  And some are fro-
zen in ordinary heats of the air.  Many taste extremely hot,
pungent, and acrid, when applied to the tongue.  Some have a
much milder taste.   And  it  is difficult  to  give any gene-
ral rule with regard to these qualities.  It is very generally
said, that the  essential  oils produced in colder latitudes are
lighter than water; while those of the hot are so heavy as to
.sink  in it.  But this cannot be admitted  as a  general fact.
 The oil from parsley seeds sinks in water.   There are too
 many exceptions to it, and the same oil does not always ap-
 pear of the same density.  Oil of cinnamon  will float  or
 sink, according as it has been drawn off  by a  gentler or a
 stronger  heat.   And I  am inclined to believe that  this in-
 ference, with respect to the weight of the aromatic oils  of
 warmer latitudes, has been  drawn chiefly from experiments
 made on the oils procured from the dry spices brought from
 the East and West Indies, in which the oil has grown thicker
 and heavier by age and evaporation, and by combination with
 oxygen, than it was in the  recent and green vegetable.
   All authors have observed, with regard to these oils, that
 it is difficult to  preserve them long in perfection.  The only
 way is to keep them in phials, with glass stoppers carefully
 ground to the phials, so as to shut them perfectly close. And
 further, it is proper to set them in a cool place.  If these pre-
 cautions be neglected, they  are sure, after some time, to be-
 come less fragrant, less fluid, and generally to suffer a change
 of their colour.  These changes happen to them  more quickly
 when they are exposed to the air ;  and, in this case, a part of
 them commonly evaporates at the same time.   These parti-
 culars, therefore, shew that the depravation they suffer, if
 kept with too little care, proceeds,  in part at least, from ex-
 halation  of their more subtile and volatile  part, upon the
 presence of which their odour and tenuity chiefly depend.
 This is confirmed by the nature of the operation which has
 been found most  proper for restoring again to a state of per- 
'62  DEPRAVATION AND RECOVERY  OF OILS.
fection some part  at least  of the oils which  have suffered
this depravation.   This operation is to subject them to dis-
tillation, along with some water, so that a part of the water
and oil may distil over with gentle heat.   These oils, when
recent and in perfection, are,  in general, very volatile.   Oil
of sassafras, for example,  if dropped  on  a bit of paper, and
held over a candle, at a great distance,  wiH quickly disappear,
leaving no stain.   They evaporate slowly if exposed to air.
And when the heat of boiling water is applied to them, they
emit visible steams, and evaporate copio#usly. This volatility
they shew most  remarkably when freshest and  in greatest
perfection.   When old and ill kept, we do not find them so
volatile ; at least it is not so easy to evaporate them entirely.
But if such depraved oils be put into a retort with water, and
part be distilled off, the part distilled is found to be much im-
proved, and  what remains in  the retort to be grown worse ;
that is thicker, heavier, darker, and  less odorous.  If the
distillation be not too long continued,  the portion distilled is
equal in goodness  to  the  oil in its recent state.   By  this
operation, therefore, we recover, in a state of perfection, one
part of bur  depraved oil.  And  if it be repeated  several
times, we increase the tenuity  and volatility of it, even be-
yond  the natural or more ordinary state ; but, at the same
time,  we still'diminish its quantity so  much the more.'
   Mere loss of some  of the more  fragrant  part,  is  not,
however, all  the -change which the aromatic oils sustain by
exposition to the air.   They actually  combine with the oxy-
genous  portion  of  atmospherical air.   This  was observed
very early by Dr. Scheele and Dr. Priestley. The thickening of
oils and resins was one of the most effectual means of phlo-
gisticating the air in Priestley's numerous and  important ex-
periments, and indeed one of the most specious arguments
for his opinions.  The oil exhaled  its fragrant ingredient,
which was  thought replete with phlogiston.   The air was
rendered unfit for the support of flame.   Scheele, however
drew a  more warrantable conclusion.    He  saw that  the
air was diminished in the same way as by the absorption of
hepar sulphuris.   Therefore,  he inferred that the  fire-air
was absorbed, and that the mephitic  portion of atmospheri-
cal air alone remained.   He ascribed  the  change on the oil 
AROMATIC  OILS.
to this  combination.  This has at length  been evinced by
clear experiments in some few cases, in which the weight of
the inspissated oil was found  greater  than that of the fresh
oil.   When exposed in vital air,  the  change  is much more
rapid and remarkable.  The fact  is no longer doubted.
   When we try how these oils are affected by mixture with
other bodies, we find, in the first place, that they can be
combined in small quantity with water, by churning and ma-
ceration.   By this operation, the water acquires a good deal
of the flavour, and  still more  of  the  acrid pungency of the
oil.   But it does not contain any  sensible portion of it, nor
does the oil lose any weight   The mixture can scarcely be
called a chemical combination ; for the water is soon cover-
ed with a shining film, which thickens by exposure to the air
(probably by absorbing oxygen) ;  and the water  in a short
time loses the  greatest part  of the pungent taste it had ac-
quired.   If a small quantity of this water, while fresh made,
and quite limpid, be agitated in a large vessel filled with
vital air,  it becomes milky immediately, and much air is ab-
sorbed.  It would seem that it is this portion, so miscible
with water, that acts  the  most powerfully on oxygen,  and
combines with it.
   Of the salts,  the  alkalis have a disposition to unite with
these oils.  A composition of this kind has long been des-
cribed  by chemical authors under the  title of Starkey's soap^
formed of oil of turpentine, or of juniper, and the alkali of
tartar.   But they speak of much.difficulty attending the pro-
cess.   This difficulty, however, proceeded from their taking
the  alkali of tartar in its  ordinary state.  Dr. Crell found
that caustic fixed  alkali readily unites with the oil.   This
combination has not been much studied,  except for medical
uses : and it does not seem to be of much importance in this   *
respect.
   Combinations or mixtures of the volatile alkali also with
these oils are formed for the purposes  of  medicine,  on
account of their having  some  medicinal powers  similar to,-
those of volatile alkali, viz. cordial, stimulating, and  antis-
pasmodic.  We have examples of such combinations in Spi-
r tus Volatilis Oleosus, and Spiritus Volatilis  Foe-
tidus, and Eau de Lucf. 
£4
AROMATIC OILS.
      When  the nitric acid, in a  concentrated  state, that is,
   having as little water as possible combined  with it, is  sud-
   denly  mixed with  any  inflammable body, its  oxygen is so
   looselv oombined, and retains so much of its latent heat,  that
   it is immediately acted  on, and its  heat is extricated by com-
   bining with that body.   If the substance be fluid, so as to
   allow an extensive surface of action, and not so volatile as to
   be dissipated in vapour at the  first warming,  the heat  pro-
   duced  may increase to ignition.  This is remarkably the case
   with the  aromatic  oils.   Besides  this, they shew a  re-
   markable disposition to  unite with  oxygen.   They are thick-
   ened by exposition to the  atmosphere, as has been already
   observed,  and this  is attended by an absorption of vital air.
   They have also a low temperature  of inflammation.
     For all these reasons, when nitric acid is poured into an
   aromatic oil, such  as oil of cloves, or oil of turpentine,  the
   mixture generates  heat,  boils up with great  violence,  and
   bursts  out into flame.   When this phenomenon was first ob-
   served, it tvas seen that a strong acid was necessary, and as
  ^the  process for the  spiritus nitri  fumans Glauberi is particu-
   larly directed to every circumstance that can ensure its con-
   centration, this smoking acid was always employed : and it
   will always succeed, if the concentration be  as perfect as we
   suppose.   But you have seen that a very fuming spirit may
   be had that contains much water, merely by dissipating some
   of the  active ingredient by a little vinous  spirits, sugar, or
   such like.** ^Strong, pale, or  nitric acid  will much more
   surely  rapduce. the  required effect.  The manipulation pre-
   scribed by Dr. Slare is also very proper, viz. to pour in about
   half of what we ultimately intend, and in four or five seconds
   after, to add the rest at once.  When the heat produced by
.  the first is at the height, and  has expended  part  of  the
   strength of the acid, we then add a parcel  in  its full force.
   Nor is the mixture of a little very strong sulphuric acid  im-
   proper.   This quickly generates a most inflammable  vapour
   ^(sulphurous) which catches fire the more readily, as it meets
   with so much  loosely combined oxygen in the nitrous acid.
   Nay,  the sulphuric acid alone, if  clear and strong, will in-
   flame the heavy aromatic oils, such as the oil  of cloves ....and
   frequently too, in favourable circumstances,  even oil  of tur- 
           DEFLAGRATE  WITH  ACIDS.         6£

pentine.  The mixture,  when it does  not kindle, acquires*
by long digestion qualities which greatly resemble the bitu-
minous oils  and solid  bitumens.   If the acid has  been
diluted, the mixture  has  a soapy appearance, mixing pretty
intimately with water.
   Even the muriatic acid may be combined with oxygen (by
a process which  will soon be explained to you) in so abun-
dant and  loose a manner that it will fire the aromatic oils
with great readiness.
  The neutral salts have no action on essential oils in mixture
without such heat as  to burn  them.   Nor have any of the
earths except quicklime.   By  long trituration it renders
them  miscible in some measure with water ; and is thought
to dispose them to a more ready yielding their most odorous
part by distillation.
   Essential oils  unite with sulphur very readily, and  corn-
pose balsams of sulphur,  drugs of a very disagreeable smell
and  taste, which have remarkable effects on  the  nervous
system.   The vapours are highly inflammable.   They also
dissolve phosphorus: and the  compound becomes luminous
by coming into contactSvith the air, and takes fire in very low
temperatures.  The  warmth of the  hand is in many cases
sufficient.
   They are dissolved by alcohol;  but are  separable  by
water, and in some measure  also by distillation.  When we
distil the alcohol, however, from an aromatic oil or vegeta-
ble, the more subtile and fragrant part  of  the'jbir generally
rises with the spirit, if a very gentle heat be employed.  On
this account, the  odorous spirits  distilled from them may be
so prepared  as  to have a more  subtile  and delicate  flavour
than the odorous waters derived from the same oils ; because
the heat of boiling water considerably exceeds that of  boiling   <f
alcohol.   Thus  are  formed,  from  some aromatic oils  or
aromatic vegetables, the compound spirits and cordials of the
apothecaries.   Brandy is  the spirit commonly used.  Some
of the finest perfumes are  also  prepared in this manner.
(See BeaumK)
  Such is  the general nature of the aromatic oils.  There  are a
few,  however, which differ so  far from the rest as  to  require
some notice of their particular qualities. These are distinguish-.
    Vol. iji.               i 
 (>6                     CAMPHORS.

 ed by the appellation of Camphors.  But there is only one spe-
 cies commonly known,  and which  is always suggested by that
 term ; the others not being in use.   The species I mean is that
 commonly used in medicine.  It is procured from a tree of the
 laurel kind, and has these qualities:
   First, it is,  like the other aromatic oils, highly inflammable,
 burning with a most brilliant flame, but producing a good deal
 of soot.   It leaves no ashes whatever.  It will burn on the sur-
 face of cold water.  It is dissolved in small quantity  by hot wa-
 ter, and imparts to it its taste and odour.   It is readily soluble
 in alcohol, and separated by water.  In all which respects it re-
 sembles the rest of the essential oils.  It is particular by being
always solid.   When dissolved in alcohol in great quantity, it
crystallizes by evaporation of the alcohol, as also when it is slow-
ly separated by water, when the spiritous solution is set  in a cold
clamp place.   When  heated,  it does not melt, but  evaporates,
and sublimes in beautiful;crystals.  And this it does more readi-
ly and completely than the other aromatic oils, never leaving,
when pure,  the smallest matter behind.   It  is therefore one of
those bodies which  are more volatile than fusible under the
pressure of the atmosphere.  But by confining it much, it may
 be melted *.
   The relation of camphor to  acids is more remarkable.  It is
 dissolved by the sulphuric and nitric acids, but without violence;
 and with the last it forms a fluid which appears like  oil.   Heat
 applied to this oil occasions the acid and camphor to act on one
 another.  And the acid is imperfectly decompounded, and gives
 out red vapours.   By repetition of this process, the  camphor
 itself is changed into an  acid which has peculiar properties  re-
 sembling those of the  acid of sorrel.  Its properties have not
 been much examined, the preparation of it being very expen-

     * In the  process for refining camphor, It is set in a sand heat, in very
 low flat matrasses, shaped like a flat turnip, and having a short neck about
 an inch and  a half  in diameter.   This  is shut by a bit of paper looselv
 twtsted. In this situation I saw it boiling like water. The cake of subl'
 mate formed very vast; and though the vessel may  be said to  be open and
 more jhan a hundred were on the furnace, there was only a very moderate
 smell of camphor in tlie laboratory....EDiTOR. 
             AROMATIC OILS....CAMPHOR.         67

  sive, and requiring eight distillations with fresh nitric acid. But
  »t quickly loses this appearance by the application or contact of
  pure water to it, which immediately attracts the acid from  the
  camphor again.
    This habit of camphor in relation to the acids, especially the
  nitric, is  its most distinguishing quality.   This acid acts with
  such violence on all inflammable substances, and particularly on
  the aromatic oils, and camphor being so eminently inflammable,
  we should expect very  different phenomena.   The  nitric acid
  suffers none, or almost none of the changes which result from a
  separation of oxygen.   There is, therefore, something very pe-
  culiar in the constitution of camphor :.... but it is of difficult in-
 vestigation.   For, when a strong  heat is applied to  it, it flies
 off unchanged,  and crystallizes in the first cooler place it comes
 to.   Many  chemists think that camphor is the principle of
 aromatic oils and of resins; but on what grounds I know not.
   There is only one species of camphor used in medicine,  or
 found in the shops.  But there are several kinds, which may be
 obtained from different vegetables,  and even from some aroma-
 tic oils already  separated from the plant, all of which have the
 properties  I have now described, and differ from one another
 only by odour.   Newmann gives experiments and examination
 of a camphor which crystallized from the oil of common thyme.
 And he enumerates the  roots of the cinnamon tree,  zedoary,
 schoenanthus, cardamomus,  oriental mint, abrotanum, milfoil,
 daisy, juniper, rosemary, salvia camphorata, lavender, hyssop
 clary, maudlin,  marjoram,  &c. I am informed that it has been
 obtained lately from the leaves of the pimento, or Jamaica pep-
per tree.  If so, we may  soon expect it in great abundance,  that
being a very common tree, with exuberant  foliage.   Camphor
is obtained from all these matrices much in the  same way as
from the laurus camphora, namely, by maceration in water,  and
then boiling the  materials in an alembic, having the head  occu-
pied by loose straw.   A  good deal of the camphor sublimes, at-
taching itself to the straws :  and the rest goes over with the va-
pours into the receiver.*
    •"From some trials, I  am disposed to thii.k that both the wood and the
leaves of the pimento, or Jnninica pepper, will yield a  very (rood camphor 
68 AROMATIC  OILS METHOD OF OBTAINING.
   As camphor is different from the rest of the aromatic oils by
these chemical properties, it is remarkably distinguished  from
them also by its medicinal qualities, being much less heating and
stimulating than the essential oils ; though at the same time it «
has great powers as an antispasmodic,  an antiseptic, and a dia-
phoretic.  By its being free of the heating quality,  it is safe and
useful in a great number  of diseases in which the other aroma-
tic oils are improper,.  But we must not give it in such large
doses  as are  said  by Mr. Fourcroy  to be given in England
Two scruples  at once are not safe,  except perhaps  in mania.
(Vide Dr. Alexander's Experiments.)   Applied externally, in
ointments or,  other forms, it is very powerful in discussing or
displacing  rheumatic pains.   But there may be cases in which
this use of it may be improper, as in external rheumatic pains
of the thorax, unless other remedies are employed at the same
time.
   I may add, that  when burning, its light seems to be the same,
or to consist of the  same proportion of coloured rays,  with that
of the sun.   All delicate  colours, which appear different in can-
dle  light,  appear  of the proper colour when illuminated by
camphor.
   And now I have said enough of the aromatic oils. The man-
ner of extracting them from the vegetables which contain them,
is so fully described in every book on chemistry and pharmacy,
and it is so commbruy known and  frequently practised by the
apothecaries,  that  I need not take up much of your time  with
it here.
   The most common operation by which they are extracted is
distillation of the vegetable with water.   A quantity of the aro-'
im^tic vegetable is  put into a common still, with' as much  wafer
as floats it or covers it;  and  the distillation is begun  immedia-
tely, or after a day or two.  The hot water penetrates the ve-
getable matter ; softens  it;  and dissolves more or less its aro-
matic parts, so as  to disengage tlve oil in some  measure.   And
v/hile the distillation goes on, the oil is  changed into vapour
%\. is even deserving of serious trial,  because camphor would be very ex-
tensively used in several manufactures if cheaper. The pimento is so abun-
^aot.zK the West Indies, .that it would COst nothing'....editor, 
BALSAMS AND  RESINS.          69
along with a part of the water ;  which vapour of the oit"is car-
tied over with the vapour of the water into the refrigeratory.
Thus  the oil is  distilled over faster than it could be with the
same heat by itself; while, at the same time, the water prevents
the vegetable, or the oil, from ever becoming hotter than 212°
Fahrenheit, which it would certainly, do, were it exposed to
heat by itself.   And experience has shewn, that these oils are
. the more fragrant in proportion as they are obtained with less
heat.
   The oily substances called Balsams and Resins belong to
the same division with the aromatic oils, and resemble them ve-
ry much by their principal qualities.   They  are  found in a
number of vegetables, and, like the aromatic oils, are secreted
juices, deposited in particular spots, or particular vessels of the
plants.  They are in general more or less odorous substances,
 and also produce the sensation of taste, with mere or less pun-
 gency and heat. They are all very inflammable, and burn with
 the same phenomena as aromatic oils, only they give more soo;,
 and more fixed carbonaceous matter.  Infused in water, mot.
 of them impart to it some taste and odour.  They  are affect  :•
 by acids as aromatic oils  are.   They dissolve with ease  in :
 rit of wine, and are separable from it again by water.  S
 you may imagine I am describing^he aromatic oils.
    The chief distinction is the degree of fluidity and volati uy.
 Balsams in general are  not so fluid %t volatile as aromatic
 oils;  and as there is great diversity among tliem in the degree
 of these qualities, there are many that are commonly solid,
 and even considerably hard.   The terms of balsam and resin
 refer only to differences of this kind.   The  greatest part of
 what are called balsams have a  sensible degree  of fluidity,
 and  some are  almost as fluid as some  of the thicker oils.
 Resins are solid and  brittle in the ordinary temperature of
 the air.   But  if heat be applied to them,  they melt into  a
 viscid oily fluid, which, so long as it is melted by a gentle
 heat,  is not distinguishable  from what is called a balsam.
 But the balsams themselves vary  greatly in  consistence by-
 age.   By the  evaporation of their more volatile and odorous
 k-arts  they always become more solid, and even hard. 
 70         PREPARATION OF  BALSAMS.

   These substances  in general  are  more  disposed  than
 aromatic oils to unite with alkaline salts.   And it  appears
 that soap-boilers have found it their interest, for some time
 past, to employ a proportion of common resin in the compO-
 sition of hard soap, by which they render it much  more
 detersive.
   Besides these differences of balsams and resins from the
 aromatic oils, I just now said that they are  less volatile.
 This is true, however, with respect  only to the greater part
 of their  substance.   When balsams and resinous substances
 are exposed to the heat of boiling water, or rather, are boiled
 with the water, they are always in part converted into vapour,
 and disperse  their odour  around.   Of  many, a very  con-
 siderable part rises along with the vapour  of the water.
 This volatile part, when condensed in distillation, is a perfect
 aromatic oil.   And the  part which remains in the distilling
vessel is a resin, which becomes solid and brittle when  cold,
and is far less odorous and volatile than  before.  We  have
an example  of all this in turpentine.   If it be submitted to
distillation without addition of water, we first obtain from it
a quantity of an aromatic oil,  similar to that which arises
when it is distilled with water. But  before  it has all arisen,
the resinous matter becomes too hot ;  for it is capable of
being heated to a much higne.r degree than that of  boiling
water.   The  heat,  therefore,  accumulates  in it, and  soon
begins to decompound and destroy  it ;  in consequence of
which it is changed  into a species of empyreumatic oil, and
a small  portion of water, and of vegetable  acid.   And a
charcoal remains in  the retort, in greater quantity than that
which  is produced  from the  aromatic oils  when  they are
treated in a  similar manner.
  It is worthy of remark, that when  we  distil turpentine
with water,  the produce of the  distillation, together with the
resin in the retort, weigh considerably more than the original
turpentine.    The  resin  and  the  oil are  immiscible  with
water.   Water has, therefore, been so combined as now to
form part (nearly one-sixth)  of the oil. Observe also, that the
oil is vastly more odorous than  the turpentine. This in some
measure explains how effete aromatic oils  are improved bv
distillation with water. 
OFFICINAL  BALSAMS.            71
  There is a considerable number of vegetables which con-
tain balsams, or resins, all distinct and diversified from one
another.  And some have been found  useful in medicine, and
in the arts. Their powers in medicine are, in general, similar
to those of the aromatic oils:  but they are not so heating.  In
the arts, they are employed in  varnishes, paints, and perfumes,
and other such compositions ; also  in natural  history,  for
preserving insects.
  Those  ordered by the colleges of  London  and  Edinburgh
to be kept in the shops are,

TEREBINTHINA Chia, sive Cypria.   Lond.
.....---------Veneta, (Ed.) From the larch of the Alps
          and Pyrenees.  A kind from New  England  ge-
          nerally supplies its place in the shops.
----  '         ----Argentoratensis, (Lond.) Strasburg tur-
          pentine,  prepared  in different parts of Germany,
          from the firs  which are native and most common
          in England and Scotland.
BALSAMUM Canadense, (E.) Another fir in America, the
          Virginian, or  Canada fir-tree,  yields  a turpentine
          much superior, brought over  under  the name of
          Balsamum Canadense.
BALSAMUM  Commune,  (L.)  The coarsest, &c. from  the
          pinus syhestris,  common in different parts of Eu-
          rope-          jp.
---------------— Copaiba, (L. and E.) From the Spanish
          West-Indies.
OPOBALSAMUM....BalmofGilead. The best kind exudes
          from the plant in  Arabia ; but  is never seen in
          Europe.  The inferior is separated from the leaves
          and branches by light boiling in water ;  but is also
          extremely scarce, so as to  be hardly procurable.
BALSAMUM  Peruvi'anum,  (L. E.) From  an odoriferous
          shrub in  Peru, and the warmer parts of America,
          and extracted by coction.   It does not unite with
          water, milk,  unctuous oils,  or  wax.   There is
          another balsam of Peru,  of a white colour, and
          more fragrant, said to  be procured by incision.
---»,  .  ■   ■ ■ .  ■    Tolutanum, (L.  E.)  From a tree of the 
72              OFFICINAL  BALSAMS.

          pine kind  in Tolu,  Spanish West  Indies,  and
          brought in little gourd shells.
BENZOINUM, (L. E.) The juice of a large tree, in both
          Indies, and bearing our winters.   But the benzoin
          is brought from the East Indies  only.   It is used
          chiefly  as a perfume.  Water extracts very near
          as much of the flores by coction as is obtainable by
          heat.
GUMMI Guaiacum,  (E. L.) Procured by incision from a
          tree  in  the warmer parts  of the  Spanish West
          Indies.
-------Animi.   A resin, procured by incision from a large
          American tree.  It dissolves  totally, though not
          easily,  in spirit of wine, and has a transparent
          amber colour.
■i    ----Elemi, (L.)  A resin,  brought from  the  Spanish
          West Indies, and sometimes from the East Indies.
          It distils with water, gives a fragrant oil, and de-
          serves more notice.
——----Hederoe, From ivy.
GUMMI Juniperi, Exudes  from the  juniper,  in warm cli-
          mates.
SANGUIS Draconis,  Brought from the East-Indies.
SAGAPENUM, (L. E.) i9|oncrete juice  from Alexandria.
LAUDANUM, (L.) Exudes  upon  the  leaves of a small
          sbjrub.in  Candia,  and other  islands of the Aichi-
          peljfigt and is brushed  off with a sort of rake,
          withlrathern thongs for  teeth.   It sticks to the
          thongs, and is afterwards scraped off. It is mixed
          with much  sand,  and  does not bear separation by
          extraction,  without diminution of its  fragrancy.

   I observed before, that the balsams and resins are secreted
juices in the plants which afford  them.    Many are collected
by bleeding or extravasation, at  natural or  artificial wounds,
as turpentine.  Others are  an exudation or excretion from
the surface of the leaves or other parts  of the plant, as  in the
moss rose,  and labdanum.   Others are obtained by boiling
gently with water.   And  some resins are extracted from
dried vegetable substances by the application of alcohol, and 
COPAL....BENZOIN.
7$
separated from the alcohol afterwards by gentle distillation,
or by the addition of water.
   And now I have given a description of the balsamic and
resinous substances, which  is  general, and applies to all of
them except a few species.   In all parts of nature, we find
her productions so greatly diversified, that it is impossible to
give general characters and descriptions that  will suit every
particular.  There are always  some species,  which must be
considered as exceptions from  the general nature of the rest.
In this light must v/e view three or four resinous or balsamic
substances,  which  I shall now mention.   These are copal,
benzoin or benzoe, and ambergrise.
   1. Copal is very transparent, and considerably hard, and
is not dissolved, but only softened by alcohol.  This distin-
guishes it from gum anime,  which resembles it perfectly in
external appearance.  But it Gan be dissolved by some of
the aromatic oils ;  and thus forms the most beautiful and
durable varnish employed in the arts.  It was  invented in
France, and long known  by the name of vernis Martin.  In
England it is called copal varnish, and is highly prized for its
horny toughness.    The art of  preparihg it is not commonly
known.
   When copal  is  treated with oil of turpentine in a close
vessel, from which  the vapoucaapre not allowed to escape,
they exert a great pressure,  which prevents the boiling ; and
the mixture acquires a highertemperature. A vewAonsiderable
portion of copal is dissolved : and with the addJBon of a little
poppy-oil, it forms an excellent  elastic varnish^ inferior to the
vernis  Martin only  in a tint  of brownness, scarcely per*
ceptible.
   Another good elastic varnish is made of copal, by keeping
it melted till an  acid or sour-smelling aromatic  vapour has
ceased, or become scarcely sensible.   It must then be mixed
with an equal quantity of lintseedoil, which has been deprived
of all  colour by  long exposure to  the sun's light.   The
varnished ware must also be dried in  the sun.
   2. Benzoin is  obtained  from a tree  in  India, and is  a
balsamic substance of the  more solid kind.  It differs re,
markably from most other balsams by the nature of its volatile
•^T..  ITT. 
<4          BENZOIN.... AMBERGR1SE.
   part.   It is not  an aromatic oil, but a substance  of a very
   peculiar kind.
     Benzoin is commonly  in  the  form  of  tears, like other
   resinous exudations.   It is very fragrant when hard rubbed,
   on when touched by a hot iron, or if sprinkled on a hot plate ;
   and is  much used on the Continent for incensing a room.
     When merely heated, it swells  up  and becomes  very
   fragrant:  but when thrown on  hot coals, it burns violently,
)  and the odour is too  piercing.  If slowly heated in a low
   pipkin, on  which a cone of paper is fitted, a vapour arises
   from it, which collects on the inside of this rone in fine white
   spicular crystals.    These are equally fragrant, but provoke
   coughing.  They  are very acid, with some pungent bitterness.
   This \s forcers of benzoin, or the benzoic acid.
     The  same crystalline  acid matter  may  be  obtained by
   boiling  powdered benzoin in a great  deal of  lime-water,
   evaporating to a  small quantity, and then detaching the  lime
   by muriatic acid.   The benzoic acid then  crystallizes.
     This is  a  singular substance,  holding a sort of middle
   rank between the aromatic oils and the salts. For it is highly
   fragrant, and inflammable, yet truly acid, uniting with all
   alkaline  substances,  and  with  the  metals.   It  seems to
   maintain its character more firmly than any other  vegetable
   acid.   For it dissolves  in the  vitriolic and the nitric  acid
   quietly, and without inducing that change which they suffer
   from  the loss of a part of their oxygen.  The nitric  acid
   emits some faint  ruddy fumes indeed,  but without efferves-
   cence or commotion.  A v^ry small quantity of water added
   makes the compound of nitric and benzoic* acids  float  on the
   top like an  oil :  but  a little more separates the latter in
   filaments, and unchanged in its properties.
     Benzoin, like  other resins,  dissolves in alcohol,  and is
  ■separated by water.
   •  3. Ambergrise differs from the other balsamic or resinous
   substances.chiefly by its origin.   The  greater part of what
   is brought to the  market is found floating on the sea  some-
   limes in the.northern parts of the Atlantic Ocean,  but more
  frequently  in the  Indian Ocean, where it is sometimes found
'   adhering to the rocks on the coast.   For a long time  verv
   different opinions-were formed of Its oriirin.. It was supposed 
AMBERGRISE.                   7S
by many to be a fossil substance, which had been washed out of
its original place by the waves.  More lately, it was  alleged to
be  the production of a tree in  America, from  which the am-
bergrise issued  as the  balsams do from  other plants, and that
it was carried into the sea by rivers.  Had  this been true, we
should  have heard  of this tree long before now,  and got the
ambergrise from it.   The latest opinion is,  that it is formed in
the body of an animal.  There are many reasons for  believ-
ing that  ambergrise  is  really  formed  in  that species  of
whale  called the physeter  macrocephalus, or bottlenose:  1st,
Masses of it have been  found in the bowels  of the  animal:
and  though  it  has   been  alleged that  the  animal,   which
is very voracious,  had in this  case found it in  the sea,» and
had swallowed  it, this is  a mere  supposition.   2dly, There
are often found mixed with it, little bones of fish,  and beaks,
and feet of the  sepia,  or cuttlefish,  which is known to be eaten
by that whale.  3dly, The substance of the ambergrise is of a
brown colour,  and has a consistence like that of bees wax, but
 contains numerous* white grains  which are calcareous.  This
does not occur in  any vegetable production.  4thly, A small
mass of ambergrise, which I saw in Apothecaries Hall  at Lon-
don, was like a gall-stone.   It had  evidently a sort of nucleus,
 surrounded with thick concentric layers. I am therefore inclin-
 ed to suspect thai it is a morbid  concretion,  formed in some
 part of the alimentary canal of that animal, or in some  cavities
 which  communicate  with  it,  in  the same manner as the gall-
 stones are formed in other animals.
    We may  further add  here,  that substances remarkable by  a
 strong, odour, are produced in a  similar manner in several ani-
 mals.   Such are musk, civet, and castor.   And there is in dogs
 a similar matter,  which  has an insupportable heavy smell; and
 in insects, of different kinds,  as bugs, &c*.
    That  ambergrise,  though  an animal  production,  must be
 considered as a balsamic or resinous substance, appears from its

   * There is a kind of whinstone roclc^n the coasts of Scotland, and ajso on
 the jiorth shore of the Frith of  Forth, which has jnany small cavities, about
 the size of small pease, or pin-heads,  many of which are filled with a substance
 having- the colour, consistence, odour, and chemical qualities of ambergrise
  ....Editor 
76   MUSK....CIVET....CASTOR....GUM-RESINS.

properties.   It has an aromatic odour,  and it is volatile by heat,
though not so volatile as aromatic oils.  It is also soluble in al-
cohol.   Its general appearances, however, more resemble those^
of the bitumens.
   Musk, Civet, and Castor, cannot properly be called either
oils, balsams, or  resinous substances.  They are animal  con-
creted juices, prepared by secretion ;  but they contain an aro-
matic oily principle, which gives them their odour, and which
rises in distillation with water.  The quantity of it, however, is
small, or the nature of it such that it cannot be collected by itself
in form of an oil, but remains combined with the distilled water.
   Before we dismiss  the consideration of balsams and.resins^
I must  observe, that the term gum is often, and  very impro.
perly, applied to many of them in pharmacy; as to copal, gum-
hederse, guaiac,  juniper, anime, elemi,  benzoin.  When the
term gum is used with propriety, it is applied to substances to-
tally different in quality from resin.  A gum  is indeed a juice
which exudes from plants, but it dissolves in water, and not in
spirit of wine.   On  the contrary, it is separated from water by
spirit of wine.   And it  has no more inflammability than any
other vegetable substance.   Gum-arabic is an example.
   There is  still another set of products of vegetables to which
the term gum is improperly applied.  They are likewise inspis-
sated juices.   Experiments  shew  them  to be composed  of a
mixture of gum  with resinous, balsamic, or oily substances.
Such mixtures  are gum-ammoniacum, galbanum,  sagapenum,
asafcetida, opium, and several others.   The proper name for
these is Gum Resins*« By applying alcohol, we dissolve the re-
sinous or oily part, and leave the gum.   Water, on the other
hand, acts chiefly on the gum, and but very imperfectly on the
resinous or  oily part.   I say no more at present on this subject.
We are to treat more of these things when expressly considering
■vegetable substances  ; as gum is a  merely vegetable substance,
which does not properly belong to any of the five classes  of the
objects of chemistry.
  As among the resins,  so  among these gum resins,  there are
some distinguished by their peculiar naUire or useful qualities.
Such, for example, is the substance called Lac, or Gum-lac.
It isproduced from the extravasaud juice of some trees in India. 
              LACCA....CAHOUTCHOUC.            77

 when they are punctured by a small insect in their tender new
 branches or shoots.   The insect is a coccus.   The lac itself has
 all the chemical qualities of a resin.  It is of a deep red colour,
 ....and makes* the*basis of  the finer kinds of sealing wax, and
 of many varnishes.   The natural  history of this substance, and
 of the insect which occasions its production, is curious.   (See
 Phil. Trans. 1781.)
   The American concreted juice, called by the natives cahouU
 chouc, is also a singular substance, which  I  think  belongs to
 the gum resins.   It is the milk of a tree.   It shews that it con-
 tains a  gummy  or mucilaginous  matter by  the effect of warm
 water upon it, which softens it, and makes  it swell.   And the
 resinous or oily principle in it appears by the action of the sul-
 phuric aether, and by its inflammability.   It  is used for rubbing
 out pencil lines,....for injection bottles....to form boots, port-
 manteaus, flexible perforated bougies, &c.   But the manufac-
 ture of it is as yet extremely imperfect*.  We  get it in the form
 of little bottles.   These are formed by receiving the milk  of the
 tree on  clay  moulds, by repeatedly smearing them over with
 the exudation, and drying each coat by a wood fire, the smoke
 of which gives it the dirty brown colour.   When all is dry, the
 moulds are crushed and washed out.
   This  substance melts, but without forming a  perfect fluid.
 When cold again, its texture is quite changed, and its tenacity and
 elasticity are gone.   It burns with violence and much smoke,
 and leaves much coal.-
   No solvent has yet been found from which it can be separated
 in an elastic and uniform state.  Nitrous aether dissolves it, and
 may be evaporated from it,  but leaves it filamentous like paper
 or washed leather, permeable to water.  Vitriolic aether, satu-
 rated with water, is said to soften it so that it  can be  easily
joined in any way.   The inspissated juice of the fruit of the
 briony, has a considerable resemblance to cahoutchouc; as also
 the juices of some plants which grow in the East Indies, such as
 the feus Indica,  and a plant described in the Asiatic Researches
 under the name oi'urceola elastica.

  # An ingenious chemist of Glasgow has discovered a method of expanding
 it to any size and thinness, as glass is blown.....editor. 
78
                    UNCTUOUS OILS.

     These are very commonly called Expressed Oils, from
the operation by which the greatest number are extracted from
the vegetable or animal substances which contain them.
   Under this title I comprehend the solid fats of animals, which
are but little different  by their  chemical qualities from  the
unctuous oils of vegetables : and there are vegetables which con-
tain unctuous oils as solid as the animal  fats.
   These oils are distinguished from the aromatic by being mild,
free of taste and smell, and feeling unctuous or greasy between
the fingers: and besides, they require a much stronger heat
than that of boiling water  to  convert  them  into vapour;  and
they do not take fire so readily as the aromatic.
   They resemble one another upon the whole, more than the
aromatic do.  They are more nearly of the same gravity, being
all lighter than water.   And the greatest number of those which
are commonly fluid, are sluggish and thick, compared with many
of the aromatic.
   As the unctuous oils, in their  perfect state, have no sensible
odour, and are far  less volatile than the aromatic, they do not
soon suffer any  remarkaWe loss or  evaporation by exposure to
the air, nor undergo the same change with the aromatic.  But,
in certain circumstances, they are liable to another sort of de-
pravation, called rancidity.   This appears when they have been
 too long kept, especially in a warm place, or  in warm weather.
 They acquire a thicker consistency and offensive smell, and a
 great  degree of acrimony, or at least  a power to  irritate die
 nerves of delicate stomachs with  very great violence.  The
 beginning of this sort of corruption is generally attended with a
 diminution of the colour of the oil.   Thus, the fine oil of olives,
 when fresh imported, and perfectly sound,  is of a strong and
 bright yellow colour. When it begins to grow rancid, it becomes
 colourless, like water:  and  this is the case  with  many others.
 The nature of  this corruption has not yet been examined or ex-
 plained.   But I believe it depends upon an incipient resolution
 and separation of the principles of  the  oil from one another.  I 
             THEIR RELATIONS TO HEAT.        79

 know that oils, in a high state of rancidity, generate slowly in-
 flammable vapours.  Bellows of an iron finery were often burst
 by the firing of an inflammable air produced within them from
 the oil with which the leather was anointed.  This  rancescence
 seems chiefly owing to an extractive mucilage which unctuous
 oils contain ; for one way of preventing or greatly retarding it,
 is to churn the oil with a great deal of warm water, repeating
 this operation till it comes off perfectly clear from the oil.   This
 change in the mucilage seems a fermentation, occasioned by ab-
 sorption of oxygen ; for Scheele observed, that oils becoming
 rancid absorb and spoil air:  and it has been since found that
 these oils become much  sooner  rancid in vital air.  Oils and
 butter have been kept in water for fifty years perfectly sound.
   We find a'great difference  between these  oils and the  aro-
 matic, in their  disposition to be affected by  heat.  I observed
 before that they are not near so inflammable ; nor have they the
 least degree of volatility in boiling  water, nor even in degrees
 considerably above it.   Most of them contain a little humidity
 and mucilaginous matter, which, when the  heat rises above that
 of boiling water, produces a little crackling and boiling.   But
 this is soon over, and then the oil is capable of being heated to
 400 or 500 degrees.   But, as the heat increases, they begin to
 emit vapour and smoke, acrid and oifensive to  the throat and
 eyes.  The remainder becomes thicker, and darker coloured,
 and capable of receiving more heat: and the vapour and smoke
 become thicker, until at last  they  break  out into flame.   But
 before this,  the oil is so hot, that tin and lead very easily melt in
 it; and it is nearly as hot as mercury boiling.
   In many employments of the fat oils in the arts, it is necessary
 not only to clear  them of the water  they contain, but also to
 give them a boiling heat, which acts on some of their principles,
 so as to produce  changes which fit them  for  particular  pur-
 poses. As this heat is near to that in which they  catch fire, the
 operation is frequently performed out of doors.   If,  iri this con-
 dition, a shower of rain falls,  there is  great danger of  the oil
 being dashed out of the vessel.  If it falls from a height, it pene-
trates to some depth, where it  is blown up into bubbles of elastic
vapour, audit explodes, dashing the oil about on all sides.   But 
 80            UNCTUOUS OILS....SOAr.

beside this, it is discovered that water is decomposed by oils n>
this temperature, and a vast quantity of inflammable air is gene-
rated.  One drop  of water  will produce above  an  English
pint.   This is the chief cause of the explosion, and increases the
danger by its inflammability.   Great heat is necessary for this
action.
   When we simply distil these oils in a retort without addition,
the greatest part distils over, in the form of an oil, quite changed
from  its natural state.  It has acquired a brown or black colour,
and a penetrating offensive smell, mixed  however  with some
fragrance,  and an acrid taste.  It is  now become  one of the
empyreumatic oils, which are soon to be described.  The quan-
tity of it is somewhat less than that of the oil before this opera-
tion:  but the deficiency is  made up by a portion of water ob-
tained at the same time, and into  which a part of the, oil is
changed, as I formerly observed.* In this watery fluid is found
the sebacic acid of Crell.
   By trying to mix the unctuous oils with other substances, we
learn, in the first place, that they do not communicate any taste
or other sensible quality to water, as the  aromatic do ; nor can
they be dissolved in alcohol.   But they can be combined readily
and intimately with  the  alkalis, and form  with them perfect
Soaps, which can be dissolved, either in water, or in a mixture
of  water and alcohol.  To produce a good soap, we must take
the alkali in its pure or caustic state.   Common alkali will not
do.   The  usefulness of soap, and its  importance as a manufac-
ture, are very well known.   It derives its solubility in water,
with  its detergent and penetrating qualities,  from  the caustic
alkaii which it contains.   Nothing is so  detergent  and pene-
trating as  the caustic alkali by itself.   But the oil is necessary
in  the composition, in order to moderate the sharpness and  ac-
tivity of the alkali, and to give a slipperiness  to the clothes to
which the  soap is  applied.   Were  the alkali used  alone,  the
 clothes could neither be handled with safety  in washing them,
nor bear the hard  rubbing and other mechanical violence  ne-
 cessary to extricate the matter which renders them  foul.
   The general process for the preparation of soap is to boil the
 ♦♦ils  or animal  fats with a ley made of  pure or caustic fixed 
MANUFACTURE OF SOAP.          81
alkali.  The boiling is continued till  almost the whole of the
water  is dissipated.  The  vegetable alkali produces a  softer
aoap, and the fossil a hard one.  Soft soap can be changed into
hard by boiling it with a solution of common salt.   A double
exchange takes place: and  we  have a muriat of potash  and a
hard soap.   The process is a little delicate.
  If we decompound the soap, and separate the oil from the
alkali, we find that the oil will now dissolve in alcohol by itself.
It has undergone  some change  in this respect which  we  do
not understand.  We have an easy way of thus separating the
oil of  soap  for  such  experiments, by  adding  an  acid  to  it.
The cohesion of the  oil and alkali in soap is easily overcome
by acids, which, uniting with the alkali, immediately detach the
oil.
  From this effect of acids upon soap has been deduced the
cause of what is called hardness in waters.   Waters are called
hard, when they decompose a little of the soap, and the oil comes
to the top in a curdy form.   We are told that such waters as do
not dissolve soap are found to contain an acid, combined with
some substance, which does not adhere to it so strongly as to
hinder it from acting upon the alkali of the soap.  Neutral salts
do not render water hard.   Macquer was led into  the m'stake
that they did, by finding sea water generally in this  state.   But
this is owing to Epsom salt contained in it.  This sal;, gypsum,
alum, or metallic salts, always produce this effect. The addition
of an alkali cures  hardness  in waters.  This is too expensive
when water is to be used in large quantity,  as in bleaching, and
other manufactures.'  In such cases, the choice of a good water
is of immense consequence.   Many  chemical trials and tests
are delivered bv authors: but soap itself is the best of all.
  The  same hard  waters  are  unfit for some operations in
cookery, such  as boiling vegetables soft.  A little alkali may
be of use here,  and would improve  the colour of  the vegeta-
bles.
  The effects of the mixture of acids with unctuous oils, are not
so violent in general as with the aromatic oils.  When the ex-
periment is made  with the sulphuric  and nitric acids, a part of
the acids is deoxygenated to a certain degree: but another part
     vol.. in.                  T' 
82
UNCTUOUS AND DRYING OILS.
 unites with the oil, and forms a compound which has soma solu-
 bility  in water, and is named an acid soap'.  Strong nitric acid,
 however, mixes with the fat oils with violence and the extrica-
 tion of great heat.  Some of them, which are called drying oils,
 and are found to have a superior attraction for oxygen, are even
 set on fire, -when  the operation  is judiciously  managed, by
 pouring the second quantity of acid on the part that appears dry
 and charred.
   Of the earths, the pure calcareous earth, or lime in its active
 state,  shews a considerable disposition to unite with these oils.
 We have an useful example of this in mixing any of them with
 lime-water, which will mix with olive oil very intimate!.-'  oy a
 little agitation in a  phial, and the compound  is found  .o be a
 most excellent extemporaneous remedy for scalds and burns.
   Of the  other inflammable substances, sulphur is  sometimes
 combined with some of these oils,  for the purposes of medicine, ..jt:
 forming the Balsamum Sulphuris Crassum.  It has a heavy
 hepatic smell.  When the oil is very much saturated with sul-
 phur, by means of a considerable heat, if  the  mixture be made
to cool with extreme slowness, it deposits a great part of the sul-
phur in very beautiful transparent crystals of a dark ruddy brown
 colour.  Sometimes the  experiment appears  not  to have suc-
ceeded : and if we give the vessel  a shake, it  crystallizes in an
instant, and so milch heat  is  extricated  that  the  mixture has
 sometimes taken fire.
   So far as we Have proceeded,  the account I have given is ap-
 plicable to the whole of these oils.   But, in order to give more
 full information upon this subject,  it is necessary to point out a*
 few species,  distinguished from the rest  by peculiar qualities.
 These shew a little affinity with the  aromatic, by containing a
 volatile principle, the presence  of which in them is necessary
 to their fluidity, and which preserves them fluid in violent colds.
 It does not, however, give* them an acrid and stimulating.qua-
 liiy ; for when they are quite  fresh and uncorrupted, they are
 very mild : but it gives  to  some of them a perceptible odour.
 And, while it evaporates, in consequence of their being expos'
 ed to the air and to light, the oil becomes thick, and at last so.
 lid; for which reason, such oils'are'employed with paints, or 
                SPERMACETI....BEES  WAX.          *d

  as varnishes.   This change is found to be  accompanied with ft
  copious absorption of oxygen from the atmosphere.
    The oils that come under this description, are those of lint-
  seed, hemp-seed,  poppy-seed,  and walnut-oil.  On account of
  their drying up, and thus leaving a varnish on the surface of
  wood or other things to which they are applied, they are called
  Drying Oils. Other unctuous  oils never dry, but remain
  greasy, until they evaporate by decomposition, or are absorbed
  by di st, or other impurities.  The drying oils  also unite with
  ac t's a little more v vently, and more like the aromatic oils
  than the other unctuous oils do.
    Spermaceti and  bees wax also  belong to  the section of unctu-
  ous oils, but differ in  some particulars from the general des-
  cription.
    Spermaceti is an  animal fat, obtained  from a particular
  species of whale, and differs from  other fats,  chiefly  by having
  much more solidity and dry consistency in ordinary heats of the
  air.   Hence it does not stain cloths,  but rubs off; and in con-
 gealing, after being melted, it always  displays a foliated tex
 ture.  Dr. Crell made a very perfect soap  with it.  It  burns
 with a brighter  flame than the greater p§rt  of animal  fats.
   Bees wax also differs from the unctuous  oils, chiefly by hav-
 inga greater degree of solidity in the  ordinary heats  of the air
 than most of them; by becoming ductile anoVplastic with a gen.
 tie heat before it melts ; by giving a brighter flame ; and by its
 origin.  It is well  known to be formed and used by  the  corn* •
 mon  honey bee in constructing its combs ; and has  generally
 been supposed to be formed by the insect from  the staminal dust
 of plants,  which they are known to gather  and carry to  their
 hives.   But Mr. John Hunter lately found reason to assign a
 different origin to it.  He thinks that it is a sebaceous  excretion
 from  their  bodies,  and comes out from  under the scaly rings
 which  cover their hinder parts ; and that by  the motion of those
 rings on one another, it is formed-into the very thin plates  with
 which they  make up their cells,  and incrust  the inside of their
 hive,  and any extraneous body in it which might give  them of.
 fence,  as a snail, &c
   Among the effects which these oils shew in mixtures, we must
not omit to mention  some consequences which attend mixing 
84      SPONTANEOUS INFLAMMATION.
them with one another ; as some of them in such mixtures pro-
duce effects which demand the greatest attention.  There are
some of them which, soon after they are mixed begin to act che-
mically on one another.The mass becomes first warm,then hot,and
at last takes fire ;  and, in some examples which happened in Rus-
sia,  has set fire to ships of war, or to magazines of naval stores.
  Four pounds of suet,  rather greasy than firm, and half that
quantity of lintseed, hempseed, or other drying oil, being mix-
ed together, after a few hours become warm : and if this gene-
rated heat be prevented from escaping, by wrapping up the mix-
ture in flannels, it increases to inflammation.   The same effects
follow when these oils are worked up' into paints, with ochre
and  other colours : and when cloths, fresh smeared with them,
are loosely  rolled up in bundles, they grow  hot, and  scorch,
and  are thus consumed to ashes: and they frequently burst in-
to flame.
  This propensity to take fire seems owing to a stronger attrac-
tion  of the ingredients for oxygen when in their compounded
state.  Of this we have many instances, such as sulphur, phos-
phorus, and mixtures of metals.  The black wad, from  Derby.
shire, was sold for a bjack pigment,  till it was found that cloths
pair.ted with it, ground with oil, could scarcely  be laid up in
the nagazines without the risk of taking  fire  spontaneously.
  The origin and u*es of these oils deserve our attention, as they
are subjects of  a» extensive commerce.  Though the aromatic
pils  are more plecious, these are incomparably more valuable
and  useful: but they are afforded by nature in far greater quan-
tity, and therefore not so highly prized.
  In many of the warm climates, the olive affords an excellent
and very perfect unctuous oil in great quantity.  In Africa, the
negroes extract from the kernel of a palm  an  oil of this descrip-
tion,....the  oleum palmar.   An excellent oil, which keeps very
well, may be obtained from the arachis hypogaios Americanus of
Ray. . The pistil and germen of this" plant  point downwards,
and penetrate the ground, under which the germen ripens to a
sort or nit, or husky seed,  called ground pease.   It is much
used f- r fattening fowls and swine.   A bushel of this seed coste
about eighteen pence, and will yield a gallon of oil of delicate 
UNCTUOUS OILS.                 6S
taste,  and which keeps  very well.   (Phil. Trans, vol. 59.J*
Through the whole extent of Europe,, and in many other parts
of the world, the subjects from which we get these oils  are the
animals which are slaughtered for our food,  and the seeds of
some plants,  rape-seed,  lint-seed, hemp-seed, beech-mast, and
walnuts,....and also milk, the butter of which contains an oil of
this kind  as its principal ingredient.  But besides, expensive
voyages are made to the polar regions, to  kill whales of differ-
ent kinds, for a plentiful supply of theMipil they afford.  The in-
habitants of  countries nearer  the pole obtain their oil entirely
from different marine animals.
   The uses,  to which these  oils  are applied, are numerous and
important.
   lmo, They make up a part of the  food of mankind in every
part of the world in which they can be procured.
   2do, They serve by their inflammation to give us light. And
the Laplanders and Esquimaux use  their fish oil, not  only  as
their best cordial and most luxurious food, but depend on it for
both light and heat in their subterraneous dwellings during their
long winter nights.
   Stio, Soaps, which are among the  m«st useful productions of
the chemical arts, cannot be made without these oils.
   Ato, They are  also highly useful and much employed  in all
 machinery,  to diminish friction.
   5to, And lastly, some.of them are useful as paints or varnishes.

    • The  oil expressed from the seeds of hemp, which  has been carefully
 reared for tills purpose,  and cleared  from  all bad stalks, is, when fresh,
 almost equal to the finest butterin sweetness.  The ofFensive odour of hemp oil
 is partly owing to the husk, and partly to. a natural  change which this oil and
 some others undergo.  The  Russians, who  are very nice,  choose for this
 purpose the seeds before they are  grown hard and dry,  and do  not allow
 cither  the plant or the seed to lie in a heap.  The oil, when expressed, is
 not perfectly fluid and transparent,  but rather like  honey beginning to grain.
 They put it into small bladders,  and keep it hanging in  running water.  I
 have eaten it three, months old, and thought it preferable to their best but-
 ter.-..,EDijo*.
* 
•6           EMPYREUMATIC OILS.
                  EMPYREUMiiTIC OILS.

     As Newman,  Lewis, and others, have treated of these oils
  separately from the others, I have thought proper to follow the
  example.  This term is applied to all oils which have been forc-
  ed to rise in vapour, and pass over in common distillation, with
  a heat greater than that of boiling water, or which are produced
  by such a  heat from  substances which  were not oily before.
  When oily substances, cfpable of bearing a heat higher than that
  of boiling water,  are  exposed  to  it, and made to assume the
  form of vapour, and distilled,  they  always  undergo a change
  From their natural state.   Oils,  which naturally are quite bland,
  insipid,  and destitute of odour, become  acrid and stimulating
  and strongly foetid, and disagreeable.
   ' Empyreumatic oils may be distinguished into four kinds :
     1. Those produced from balsams or  resins.           ''■*'£*■
    2. Those produced from unctuous oils.
>    3. Those produced from vegetable substances that are aot
  of an oily nature.              '
    4. Those produced by heat from animal  substances not of
  an oily nature.      *n*
    The  first kind have^.with  the  empyreumatic  fcetor, an
  odour of the aromatic cAl, which  the  balsam or resin  con-
  tained.   The second  have the smell of  the smoke of a candle
  or lamp when blown out*.  The third smell of wood burning.
  The fourth of burning feathers, horn, hair, bones, and other
  such animal substances.
    When these oils are first distilled, they are  dark coloured,
  and even  dirty, by reason  of charry matter which comes
  over with the oil.  But  this oil being  put  into  the  retort,
t will rise with a less heat, and  come over more volatile and
  attenuated, leaving a carbonaceous residuum.   TRis oper-
  ation, repeated  several  times, brings  the oil to a  greater
  degree of purity, and, which  is important,  ofCiniformity or
  sameness,  in so much that it is highly  probable  that by re-
.  peated dis'llations all distinctions  will be removed.   Bees
  wax yields an oil which approaches the most  rapidly to  this
  state : and indeed, after  two distillations, it tfan  scarcely be
 ■distinguished from an empyreumatical oil of olives that has
  been eight times distilled. 
EMPYREUMATIC OILS.
87
   It may appear surprising to those to whom it is new, that
such  hard and  dry  substances  as  the  hardest and driest
wood, and the bones, horns, and other parts of animals, that
have  not the least of an oily nature, should afford empyreu-
mauc oils by distillation with a proper heat.  The fact, how-
ever, is easily explained by the discoveries and new principles
of tiie modern chemistry.
   i lately  remarked, that all oils, in general, are principally
compc-c 1 of hydrogen and carbon, with a small quantity of
oxygen, and perhaps of azote,  together with a very small
nation of earth.
   Now these principles, which  have thus been discovered to
constitute the oils in general, are contained in all the animal
and vegetable  substances, as will be explained to you more
fully  hereafter, not excepting the dryest and hardest of these.
When such substances, therefore, are exposed to the mode-
rate action of destructive heat in close vessels, a part of the
hydrogen, which is  always a volatile substance, is volatilized,
without being combined with that large quantity of caloric,
which is necessary for converting it into inflammable air. It
carries up with it a part of the carbon : and being condensed
by cold in tiie receiver, it must necessarily be condensed  into
an oil, which is black, in consequence of the carbon it con-
tains, perhaps imperfectly combined with  it: and has a pene-
trating disagreeable smell, in consequence of the imperfect
union of the  hydrogen with the carbon and other principles
which it contains/   If there bo'azote in  the composition of
the matter, which is the case with all the  animal substances,
and even some  of  the vegetable,  this  principle, combining
with some of the hydrogen, forms some volatile alkali: and if  'i--
there be  much of the oxygen,  which  is the case with all the
vegetable substances, it contributes*o form a quantity of car-
bonic acid gas, and very often  an acid now called pyro-lignic
 (pyro-xy/ic),  which is nearest by its nature to the acetous
 acid.
   The same view of the nature of o?!s  in general will alsft
 enable you to  understand why dark-coloured, acrid,  and
 foetid, empyreumatic oils are produced by subjecting to heat
 for distillation the mildest and most bland of the natural oils.
 The mildness  and  sweetness arid unctuosity of these depend 
88
TAR....PITCH.
 on the  proper union and  cohesion  and proportion of their
 principles ;  all of which conditions are altered by the action
 of heat.
   The  empyreumatic oils agree with the aromatic in several
 particulars.   A small  quantity  of them  can be  combined
 with water, or dissolved by  it.  They are  dissolvable by al-
 cohol :  and they have not the lubricating quality of the unc-
 tuous oils.
   All  of them contain a very fluid  and volatile oil,  mixed
 with a grosser one.  And the tenuity, volatility, and inflam-
 mability of  the more volatile part of them, is in some cases
very remarkable.   Oil of wax is one of these.
   One  is valued in medicine,  but not much used....Oleum
 Animale,   or Oleum   Cornu  Cervi   Rectificatum.
 (ih. rm. Edin.)  Another,  called the oil of bricks, because
it  is distilled  from  a red hot brick which  has been thrown
into olive oil and impregnated with it, is used by the seal-
cutters  and lapidaries, for moistening the diamond powder
with which  they work, that it may adhere  to their tools.
   The  principal example we have of the application of oils
of this  division to useful purposes,  is in the  use of  tar and
pitch.   Tar is the first production.  It is  procured from all
 the trees of the pine kind, by a rude kind of distillation.  In
 Germany, Norway, and  Sweden, where this  timber is very
abundant, it is piled up in billets, in a sort of oven, which is
 covered with another oven, at a very  small distance.  The
 fuel is put  into the interval between them.   Thus the  inner
 oven becomes a sort of retort, and the oily vapours having
 no other outlet, run from a  gutter made in the floor of the
 oven.   This exudation contains much soot intimately mixed?
 which makes the tar quite*bjack.  Pitch is made  of tar, by
 separating the more volatile and fluid parts by evaporation
 or distillation.   The tar is an empyreumatic oil extracted by
 heat, and contains a portion of the essential oil of turpentine,
 which is in all firs, and a quantity of the acid called  now pyro*-
 lignic.   Hence tar-water, while it has that irritating acrimony
 common to all the empyreumatic oils, is manifestly acid, and
 affects the vegetables purples.. 
89
                  VII....BITUMENS.

   The seventh section of the inflammable substances con-
tains Bitumens.  Under this title I comprehend all the fossil
inflammables, except sulphur, already described.
   Some of these are fluid, and some are solid.   The  most
subtile of them is certainly that  species of inflammable air
which often occurs  in coal-mines and other subterraneous
places, and which I had an opportunity to mention formerly,
as liable  to take, fire  from the flame of a  candle,  and to
make dangerous  explosions.   It must be considered as an
inflammable substance of  such great volatility, that under no
greater pressure than that of the atmosphere, the ordinary
temperature  of heat is much more than sufficient to   pre-
serve it constantly in  the form of vapour.   The  hydrogen
gas is surely its most abundant ingredient.   I do not know
that any person has made experiments with this kind of air,
to investigate the nature of it very particularly.   But I have
no doubt  that it is heavy inflammable air, or that variety
which contains carbon dissolved in it*.
   Next  to this vapour, we may reckon the fos§il oil called
Naphtha, and the varieties of it, called Petrolea.   The
naphtha is described as a  fluid of a Very light yellow colour,
or sometimes colourless ; and which has a degree of fluidity
and tenuity equal in appearance to  that of alcohol or sether:
but it is oily, and floats on water like sether.   It is also very
volatile, and highly inflammable, catching fire at the approach
of flame rather more readily than alcohol.   The flame of it,
when not very  small,  is attended with some smoke or  soot,
as that of all other oils.   The  odour of it is strong  and op-
pressive to most persons.  Such a fluid is said to be gathered
from the surface of the water of certain wells in Persia, and
in the dutchy of Modena  in Italy.   But it is a rare produc-
tion of  nature.

  * What escapes from the crevices of the Whitehaven coal-mines gives no
indication"uf any carbon.  The  air  in  which it burns for a yery long while
^oe.v-not. affect limovater.. .  editor.
       VOX .Til-              1JE 
'jo       BITUMEN....PISSASPHALIUM,  &c

   The fossil oils, called petrolea, are not so rare ;  but are in-
ferior to naphtha in  fluidity-and volatility, though some are still
very  fluid and volatile.  The different varieties have different
shades of a yellow or brown  colour, and a heavy,  oppressive,
penetrating odour; and are highly inflammable. Such are found
in several places in Italy,  Sicily, Bavaria, and France,  issuing
from the crevices of rocks, or floating on the waters of springs
or wells ; and readily take fire by the contact of flame, and burn
on the surface of cold water.
   The fossil  inflammable  substances which are next inferior to
these in fluidity,  are those to which the  name  of bitumen has
been most particularly applied.   Such are a number of species
which have a consistency resembling that of tar or pitch, or that
of the vegetable balsams.  They are distinguished, according
to their different degrees of fluidity or consistency, 1>, the names
of pissoleum,pixjudaica, and pis:.asphaltum. Some are littledark-,
er in their colour, or thicker in their consistency than the coarser
petrolea ;  while the thickest,  or most gross,  the  pissasphaltum,
 is actually solid when cold, and requires heat to give it fluidity,
 in the same  manner as pitch.  When cutting a level to a coal
 mine on th^bank of the Severn, near the iron bridge, a source
 of this kind was discovered in a stratum of free-stone.  It yield-
 ed this tar in considerable abundance at  first; but this gradual-
 ly abated,....and after two years seemed to be exhausted. It had
 accumulated in the pores  of the sand-stone through  a length of
• time, and had now drained  off.  A similar case  occurred in
 Renfrewshire a few years ago.  St. Catharine's well  at Liber-
 ton has yielded this substance for more than a century, and does
 not seem to abate.  But the quantity is not great.
    The very fluid bitumens are  in general such rare  productions
 of nature, especially the more subtile and volatile kinds of them,
 that they have been but little examined by the chemists.  They
 have much of the  appearance  and properties of the empyreu-
 matic oils.
    The solid bitumens are Amber  and Coal.  The  common
 appearance  of amber is  too well known, to  need description.
  There are also  varieties  of it.   The most valued pieces are of *
  a light yellow colour, and  either transparent, or agreeably clouded 
               BITUMEN....AMBER, &c              91

with white.  But it is much more frequently found of a deeper
yellow or brown, or  even almost  black and opaque.   Amber is
distinguished by an aromatic odour, which it emits when  rub-
bed.  This, and some other particulars, give it a  great resem-
blance to some vegetable resins.  But it differs from all that are
known in some of its properties.
   If  it be  heajed gradually, and the vapours condensed in close
vessels, it gives first  a small quantity of water. This is followed
by a salt, part of which, is dissolved in the water,  and part con-
densed into a solid form.  Along with this salt, and  after it passes
over a large quantity of empyreumatic oil, and some inflamma-
ble gas.  Little charcoal remains.  This salt is an  acid, strongly
tainted with the empyreumatic oil, more resembling the vege-
table acids than any other.  The  oil has an • exact resemblance
to some petrolea;  and,  if  repeatedly distilled, becomes  so
like naphtha in every property,  that  they  cannot   be distin-
guished.
   The natural history of amber,  as found on the  coasts of the
Baltic, is  given by  Hoffmann  and Newman;  to which  may
now be added, that  it has been found of late years  abounding
in Royal Prussia, near the shores of the Baltic, by digging pits
of considerable depth,  till they reach a stratum of forest trees,
bedded in sand, or at least under a stratum of sand..   The trees
are all charred, and perfectly black. The amber is found among
them  in nests, and the working of these mines is found very pro-.
fitable.  The floating amber is, in all probability,  torn up from
the bottom, where  the  sea  has  penetrated to  this stratum.
(CreWs Annals of Chem.)  It is  found in general in small bits.
Pieces that are four, or five,  or six inches in diameter, are ex-
ceedingly rare; and if they happen at the same time to have
beauty, aue very highly valued.   It has, therefore, been a desi-
deratum among the chemists to unite  small bits of  amber into
larger masses ;  and some  have  been reputed to possess such a
secret.  But it  does not appear that it  has ever been practised,
or that it is possible.
   Pit-coal, the other solid-bitumen,  is of much greater value
to the countries which possess it,  in which it is well known to
' onstitute thick, numerous, and extensive strata.  And though 
92
PIT-COAL.
inattentive observers consider it all as the same,we find remarka-
ble varieties of it in the different strata which it forms.   I shall
here mention the most distinguished varieties only.  There are
many others intermediate between these ;  but we need not attend
to them all.
   1. Cannel coal, or candle coal; or,  as it is named  by  our
colliers, parrot coal.
   2. Common Scotchcoal, in which our colliers distinguish some
varieties; but we need not enumerate them.
   3. Fat, or caking, or blacksmith's coal,....smithy coal.
   4. Kilkenny coal; or, as our miners call it, blind coal.
   These different kinds of coal are distinguished by their man-
ner of burning, and by the products they afford, or phenomena
they exhibit,  when  they  are subjected to the  operation called
chemical  anal) sis.
   The first kind, or candle  coal, kindles easily, and  gives in
burning an extraordinary blaze of bright white flame.
   The second, which is the most common  in this country, also
gives in  burning a good  deal of white flame,  though not so
much  as the first;  and  the  cinder or  charcoal  that remains,
when it ceases to flame, is a better fuel, or contains more of the
carbonaceous principle than the cinder or charcoal of the candle
coal.
   The third kind, the fat, or blacksmith's coal, gives less flame
 jn burning than either of the two former: but in beginning to
burn, or*  before it begins, it is in some measure melted by the
heat;  at least a bituminous* matter that is softened and melted
 by the heat,  oozes  out of it, and occasions those bits that are in
 contact to cohere together.   So that,  when a quantity of  it  in
 small fragments, or perhaps partly in dust, is laid on a fire, and
 wetted with a little  water, to  make the fragments and^dust enter
 into closer contact, it very soon coheres together into one mass,
 which being  afterwards broken or divided a little, to let the air
 pass through it, burns strongly and a long while, giving a  great
 deal of heat before it be totally consumed.  The cinder or char-
 coal of this kind of coal is very rich in the quantity of,its car-
 bonaceous principle.                                 . 
              BITUMEN....PIT-COAL, &c.            93

  This kind of coal is but rare in this country [Scotland] ; but
in some of the principal coal  counties of England, Newcastle
and Whitehaven,  it is the most abundant. It is  the most valuable
of any, on account of its not suffering waste by being broken down
small;  for in the  smallest fragments, it  is equally  good  for
household  purposes as the large pieces;  whereas the greater
part of the  Scotch coal, when broken down to dust and small
fragments, becomes  quite unfit  for household purposes.   By
running  like sand into all the  interstices through  which the air
should pass, it extinguishes a fire instead of mending it.  In
this state, therefore,vit is not called coal, but culm; and is only
employed for burning brick and  lime, and for  making salt from
Sea-water.  The English fat coal, though ever  so small, is never
called culm ; for this reason, that by its caking quality, it makes
excellent household fires,  and gives  a great  quantity of heat
before  it be totally consumed.  It is also the most thrifty; as
it does not burn much when the fire is left at rest.
  This kind of caking coal, when it is free from any admixture
of sulphur or pyrites, is also highly valued by the blacksmiths,
and is  even necessary in some measure to their operations.   It
enables them to make what they call a hollowfirifo  When they
have occasion to heat a mass of iron, or a thick bar, they put it
into their fire, and cover it with a large round  heap of this sort
of coal, wetted on the outside,  and then by working their bellows
for some time, and other management, the coals that were in
immediate contact with the iron are consumed, and a  nollow is
formed around it  like an arch or little cavern, the sides of which
are all composed of coal caked  together.  While the wind of
the bellows is  driven into this  cavity, and circulates in it, a vio-
lent heat is produced all around the mass of the iron ; and every
part of its surface receives the necessary  degree of it, which
could not easily be obtained by using other coal that is unfit for
forming the hollow fire.   Such are the properties of  the third
kind of coal, the fat or caking  coal, or smith's coal.
  The fourth and last kind of coal I mentioned,  the Kilkenny
coal, or, as it is  called by our colliers, the blind coal, differs
greatly iirom the  others by its manner of burning.  It is more
difficultly kindled ;  and  when perfect of its kind, gives no flame 
 94      BITUME*JS....PIT-COAL DISTILLED.

 whatever, but burns exactly like charcoal, and gives a great deal
 of heat before it is consumed.   As  it neither  gives flame  nor
 smoke, it is burnt in malt-kilns for drying the malt, the air which
 comes from it in burning being quite bee from luligmous va-
 pours.   It appears probable, therefore, that the volatile parts of
 this kind of coal have been separated or expelled from itby some
 operation of nature.
   Such are the differences of these four kinds of  coal in their
 manner of burning.   They differ also, as I said, by the products
 they afford when they are subjected to distillation performed
 without addition, in retorts and receivers.
   I shall  first describe the effects of  this operation  when per-
 formed with the most common coal of this country, the common
 Siou.h coal.
   If the receiver be  closely luted to the retort, and kept very
c6ol, and provided with an air-pipe,  we obtain, first, a small
 quantity of  water, little different from pure water.
   Second///,  While the distillation advances, and the heat is in-
creased, more water comes over, attended  with a brown oil.
   Thirdly,  The heat still  increasing, less of the water  comes
over, but much* more of the oil;  and at last scarce any thing but
black oil is seen to condense in the receiver.
   The  oil that comes  at  first is thin  or very fluid, and of a
 Drown  colour.   That which comes afterwards is thicker and
darker Miloured: and at last it condenses quite black, and as thick
 as tar.   It continues to come in the form of a thick smoke, to
 :he end of the operation, that is, until the  retort is heated to a
 degree of ignition,  by which the  remaining matter is changed
 into charcoal, and no more volatile matters can  be expelled from
 it by an increase of heat.                                •    «
   Fourthly, During all the time, when the oil is distilling, espe-
 cially after  the first  of it  has been condensed  an  immense
 quantity of  elastic airial matter passes out through  the air-pipe,
 and may be collected in inverted vessels.   A part of it  is car-
 bonic acid gas, which precipitates lime from lime-water. But
 the greater part is hydrogen gas, or inflammable air, not  of the
 purest and lightest kind, but containing a quantity of the carbon
 or carbonaceous principle, intimately  combined with it.   And 
                             THE PRODUCTS, rf-^ 95

therefore, when a mixture of it and oxygen gas or vital air are
fired together, the consequence  is not the production of water
alone, but of water and of a quantity of carbonic acid.
   The whole of the oil is of the empyreumatic kind, not unlike
to tar in colour and consistence, only more  fluid: and  it has a
very offensive smell, similar to  that of the smoke of coal fires
when they are beginning to  burn.  Like other empyreumatic
oils, it is partly composed of  a very volatile anc* fluid part,  and
a grosser one.  They can be separated  by distillation with a
gentle heat, by which we obtain apportion of the oil very fluid,
and  volatile, and transparent, and of aj yellow colour, very much
resembling some of the petrolea. What remains* in the distilling
vessel becomes more like tar or pU^AMn its consistence and pro-
perties ; and is now manufactured, in order to  be employed as
tar,....the more volatile oil being at the same time prepared for
making a sort of varnish.
   Along with these oils, I said that a quantity of water is always
extracted from the coal by the same operation.  And this water
contains some volatile alkali, which at first  is intimately com-
bined with some of the  oil, but is separated from it by rectifica-
tion, Sec. and afterwards can be employed in the manufacture of
 al ammoniac.
   These are the products which we obtain by distillation from
the common Scotch coal.   But there is some variation when we
perform the same operation with the other kinds of coal I enu-
merated.                                             r
   The candle coal yields much more of empyreumatic  oil and
other volatile products than the other kinds.        ,
   The common Scotch  coal is the  next to it with respect to the
quantity of empyreumatic oil, or  volatile inflammable matter,
which it affords.
   The fat or caking coal affords still less oil, but a very rich char-
coal.
   And the Kilkenny,  or blind  coal, affords none at all, and
scarcely any volatile matter whatever.  It may be considered as
a naturaj charcoal.
   Such  are the principal varieties of bituminous  inflammable
substances found in the earth.  And when we «tudv their natu-
 
96    IS PIT-COAL  of vegetable; origin?

ral history, and some other particulars relating to them, we find
great reason  to be persuaded that all have derived their origin
from vegetable matter.
  In  pit-coal many appearances occur which lead  us to such a
conclusion with regard to this sort of bitumen.   It is common
to observe impressions  of  leaves and other parts of  vegetables
in the strata, which lie  above or below the coal.  And very fre-
quently in the coal itself we find a black matter, which has so
much of the  structure of wood, and so exactly resembles bits of
wood which have been scorched or burnt to a sort of charcoal,
that there is  no room to doubt of its origin.  This matter fre-
quently occurs in the coal which we burn here, and always forms
a sort of thin strata intermft&fd with those coals, and composing
part of it, and  occasioning it to split  easily, in the direction
parallel to the two surfaces of the stratum.
  Sometimes little masses of the  coal are entirely  made up of
this sort of  matter.  I have been informed that some of the
coals of England contain  a remarkable quantity of it, and are
distinguished by the name of clod-coal,  and valued as the best
for melting iron from its ore.  And the same matter appears in
a bit  of coal which was brought me from the coast of Green-
land.*
   From these and other facts and appearances, it has been con-
cluded that pit-coal has been formed of vegetable matter, carried
into the .sea by rivers;  and which having sunk to the bottom in
consequence of its being thoroughly soaked, has there undergone
a degree of decomposition,  and has been  strongly compressed
by other materials- deposited over it,  and in  some cases has

  * In 1759, coals were brought on board the Royal William, in Louisburg
harbour, which had been bought for the captain's firing.   When his steward
saw them, he refused to take them, saying that they were only charred wood.
The vegetable structure was very distinguishable in the greatest part of them.
 One piece in particular had unquestionably been a large root of the common
marsh  iris.  Its joints, and the commencement of the air vessels at the big
 end, could  not be mistaken.  Same  pieces  being first made red hot under
 sand in a pipkin, so as to dissipate a  heavy stinking smoke, burnt afterwards
 with a smell perfectly resembling that of wood charcoal.  This coal had been
 brought in the boat fro/n the mouth of the mine,  in the face of a cliff, from
 which they had been let down by a pulley into the boat., .editor. 
         REASONS  FOR  THIS  OPINION.         97

been penetrated with mineral vapours and subterranean heat,
so as to give it the various qualities and appearances we see in
coal.
   The  other facts,  besides  the  appearances already men-
tioned, which have suggested such an opinion are these :
   1st, Great rivers, in different parts of the globe, are well
known to carry annually vegetable matter into the sea,  espe-
cially those which have a long course through immense uncul-
tivated tracks of the earth's surface that are overgrown with
wood, as some of the  great rivers  of North  and South
America, Africa, India, and the Russian territories.  Great
rivers necessarily have a  great part of their course-through
level  countries,  through  which they  make many serpentine
turns.   And they are constantly undermining their  banks in
some of those turns, and occasioning wood, leaves, moss, and
other vegetable matters, to fall into their stream.   Some of
this matter floats for a long time, until it be so thoroughly
soaked as to sink to the  bottom.  But while it floats, it is
carried down to the sea,  and perhaps afterwards to a very
great distance,  by tides and  currents.  Sometimes it runs
aground in the shallows that are at the mouths of such rivers,
and gradually forms islands in those shallows, as*at the mouth
of the Mississippi.  But the greater par* is carrWd out to sea.
Great quantities of timber are found floating in the  northern
seas,  on the  coast of Iceland and Greenland, and the  north
coast  of Russia.  All this, after floating some time, must
sink to the bottom.  In Iceland there is a large bay^hich is
always  full of  floating wood, and  supplies the  innabitants
with fuel.
   2dly, The very circumstance of coals being formed into
strata is strong  in favour of  this opinion; as  we  have.the
greatest reason to be satisfied that all strata have been  form-
ed of matter carried  into the sea.   But,  besides, we find
these  strata  of coal  always intermixed  with  other strata,
which have been manifestly formed in the sea,  as sandstone,
limestone, and clays of various kinds.
   3dly, In some parts of the world,  among  strata of  the
same kind with  those which commonly  accompany coal, are
found strata manifestly composed of wood, even trees com-
     VOT. HI.                N 
98
BITUMENS
pressed and compacted together, so as to form  strata, bear-
ing some  resemblance to  those of coal,  but in which the
wood retains so much of its original structure and shape that
it cannot be mistaken.   There is an example in Devonshire,
called Boveycoal; and a stratum of  fossil wood in the north
of Ireland.
   All these reasons, therefore, leave little room to doubt of
the origin  of pit-coal in general, although in many varieties
of this bitumen, the first contexture of the materials has been
so much abolished by  immense compression, and the pene-
trating and dissolving powers  of water and heat, and other
causes, that we  hardly find any remains  of it.   It is proba-
ble,  too, that many strata of coal have been  formed of other
vegetable matter, as moss  or peat,....carried into the sea du-
ring a long course of time, by rivers which have their course
through extensive tracks of the earth's surface,  abounding
with bogs and moors.
   When we study the  varieties of  the other solid bitumen,
....amber, we can clearly trace  its origin also from vegetable
matter.  It is not at all uncommon to find in amber, insects
of various kinds, either such as creep on the trunks of trees,
as ants, spiders, caterpillars, or flying insects that frequently
alight upon trees, or live upon them: such are a variety of flies
and moths.  In the BritishMjjseum there is a lizard in amber;
a reptile which is w.ell known to creep on the trunks of trees,
or to dwell  about their roots.   Further, these things are im-
mersed* in  the  amber, and every way  surrounded with it;
and, from other appearances about them, it is plain that the
amber must have been soft and viscid, 'like the  vegetable
balsams, when they adhered to it, and when it involved them.
  This, and the chemical qualities  of amber, by which it re-
sembles  greatly the vegetable, balsamic,  and resinous sub-
stances, gives sufficient proof that it was once one of these.
It is well known that many forest trees, in different parts of
the world,  at certain times of the year, shed from ruptured
parts of their bark, large quantities of balsams or turpentines
a part of which  must fall into rivers; or,  if deposited in the
soil, must be washed out  by them afterwards some time or
other, while they gradually change their channel by undermin- 
       PROBABLY  OF VEGETABLE  ORIGIN.   99

 ing their banks.   This matter must be rolled along by the
 river until it reaches the sea, or is left behind, in some part
 of the  bottom  where the water  has  little motion, and  by
 length of time,  and the action of  mineral  vapours, assumes
 the qualities which we find in amber.
   Such,  therefore, appears  to be the  origin of the  solid
 bitumens, coal  and amber.   That of  the fluid may perhaps
 be thought more  difficult to trace.  But  I  think  we  have
 clear lights  for this part of our subject also.   We must,  in
 the first place,  consider that the fluid bitumens bear a sur-
 prising resemblance to the empyreumatic oils which may  be
 extracted or produced by fire from the solid.   Some speci-
 mens of the  petroleum resemble  exactly the  empyreumatic
 oil of amber.   Others resemble the oils which may be ex-
 tracted by fire from different  kinds of pit-coal or fossil-wood.
 And  all the fluid bitumens resemble these oils more or less.
 We must also  reflect on the evident signs of subterranean
 fires which are frequent in different parts of the globe, parti-
 cularly the  hot  springs ;  many of which pour forth amazing
 quantities of hot water,  and  thereby  shew that the fires  by
 which their heat is maintained have great power and perma-
 nency.   This is further proved by the eruptions^ and steams
 of volcanoes, which are very numerous over the face of the
 globe; the fires of which must be at an  immense depth be-
 low the surface, and  must have very extensive communica-
 tions, as  is plain  from the extensive effects of earthquakes,
 which manifestly depend on these  subterranean fires."'  If  to
 this we add what we observed in some kinds of pit-coal, which
 shew by their properties that the volatile parts have been ex-
pelled, it will be easy to gather from all this some highly pro-
bable conjectures concerning the origin of the fluid bitumens.
We can hardly avoid  being  persuaded that they have been
 produced by the long-continued  action of subterranean  heat
on the materials of the solid bitumens, the volatizable parts
of which are gradually separated from the  rest by a sort of
natural  distillation or  chemical analysis, and are driven up-
wards through the crevices or pores of the  earth, until they
come near to the surface, where they escape from the further
action of  the  subterranean heat,  and  are within our reach. 
 100                 BITUMENS.

 In confirmation of this supposition, it may further be remark-
 ed, that some of the countries in which those oils are found
 the most frequent, are well known to be undermined by sub-
 terranean fires, especially Italy.  »
  And not only the fluid bitumens, to which this  name is
 commonly applied,  but that  more subtile substance, the in-
 flammable air, or fire-damp, which occurs in mines, or breaks
 out at the surface of the  earth in some places,  may be ima-
 gined to have the same origin.   When we expose the solid
 bitumens to  the action of heat in close vessels,  besides the
 empyreumatic oils which  we  obtain, and which resemble the
 fluid  bitumens; we obtain also great quantities of inflamma-
 ble  air, or inflammable gas,  which must necessarily be pro-
 duced from solid  bitumens or fossil wood, on many occasions
 by subterranean  fires!
  Thus, therefore, the whole of the subterranean inflamma-
ble  matter, that belongs to the title of bitumens, maybe im-
agined to derive  its origin from vegetables.  From whence
the  vegetables agam  derive theirs, will perhaps appear when
we come to consider the matter of vegetables,  and  its pro-
duction, as a  particular subject of chemical inquiry.  (See
Note 49. at the end of the Volume.)
                 '   f ■
                    \ 
CLASS  IV.
          METALLIC SUBSTANCES.


  THE metallic substances are now to be considered as the
Fourth Class of the objects of Chemistry.
  They probably  attracted the attention of mankind at first
by their shining surface.   But when their nature and pro-
perties became better known, they were valued as materials
with which we can easily execute many purposes in arts which
cannot be attained without them.
  The qualities which render them useful and valuable are,
  lmo,  Their fusibility and malleability,  by which we are
enabled to melt different masses of them into one, or easily
to divide large ones into small ones, ani to jnould or hammer,
or otherwise  work them into the forms which our purposes
require.                           ;
  Sdo, The strong cohesion of their parts, in  consequence of
which  they are the proper materials for  all parts of  ma-
chinery,  or  other  works in which great  strength  or long
duration is required.
  3tio, The  different  degrees  of hardness and elasticity
which some  of them can  be made to assume, render them
highly useful to us on innumerable occasions, for the fabri-
cation of tools, springs, and many other implements necessary
in the arts.
  4to, The density of their substance, which is impenetrable
to water,  and most other kinds of matter, is one more of
their useful qualities.   And,
  5to,  and lastly,  Their bearing sudden alterations of heat,
without being broken, is another. 
 102          M-ETALLIC SUBSTANCES,

   These several qualities render  them  useful  for many
 different purposes.   And further, by their lustre and bright-
 ness, and the facility with which they are polished and wrought  ^
 into ornamental forms, they are fit subjects for many of the
 elegant arts.
   The metallic substances are, for these and other reasons,
 much more  the objects of attention and study than the other
 classes  of natural bodies.
   And yet we  have  gained  less advantage  from  the re-
 searches of  many of the chemists on this subject, than what
 might have  been expected,  from  the great labour which has
 been  bestowed on  it.   The reason  is plain.   The greatest
 number  of  experiments formerly made upon metals were
 prompted by the  visionary projects and notions of the alche-
 mists.   Instead  of directing  their  investigations  to  the
 discovery of new productions that  might be useful in life, their
 sole aim was to convert cheaper metals into gold and silver.
 And it happened at the same time, that the greatest number
 of those who were employed in this pursuit, were persons of
 so little education, and so ignorant, not  only of other sciences,
but even of  any rational principles of chemistry itself, or of
 the nature of  the materials  which they employed, that they
were for the most part incapable  of making experiments in
 a judicious manner, or'of understanding them properly when
 they had made them, tTheir extraordinary labours must no
 doubt have led them to the knowledge of many curious facts.
 But every experiment v/hich deserved attention, was coucealed
 by them with.the greatest  care :  or if they mentioned,  or
 pretended to describe  any  discovery,  they did  it in such
 mysterious and ambiguous language, as must render the study
 of  it insupportable  to  those that  ever  read  any thing else ;
 besides that they every where  abound with  absolute  false-
 hoods.
   I shall not, therefore, attempt the disagreeable and fruitless
 toil of inquiring into the meaning of their opinions and pro-
 cesses ; but confine myself to such an  account of the  metals
 as may be deduced from clear and simple experiments.
   Upon this  plan, I shall  first mention, the  more  general
 qualities of the metals, and afterwards describe  the nature of
 each in a more particular manner. 
         THEIR GENERAL PROPERTIES.       103

   1st, The  most obvious general quality of the metals is
their great weight or density, in which they exceed all other
known matter.   The heaviest stones are not more than four
times as heavy as water, or scarcely so much.  The lightest
of the metals is  seven times heavier.
   2dly,  They are remarkable  also  for a  great degree of
opacity,  and a power of reflecting the light strongly from
their  surface ; in consequence of which all mirrors are made
of metallic  substances, or are made to reflect light by their
means.  The thinnest leaves  or  films  of metal have  this
power to a  surprising  degree :  but  we can  in some cases
reduce them to  films of such exceeding thinness, that they
transmit a  very  small part of the  light which falls upon
them.   ,
   3dly, Metals are distinguished from all other solid bodies
by some qualities with regard to electricity, which give them
the first rank among conductors of electricity, and which  sub-
ject them on all occasions to be more  affected by lightning
than any other sort  of  matter which comes in its way.   By
conductors  electricians mean bodies which are disposed to
receive readily and  quickly the  electrical fluid, and  to trans-
mit  it  in  a moment  through their whole  substance  and
surface ; so  that when we communicate a charge of electricity
to any one part  of them, it is communicated to every other
part of them at the  same instant of ti|ne ; or if we abstract
electrical matter from any one part of them, every part of them
will be found to be equally affected by the abstraction. Non-
conductors  are the opposite to this. They receive difficultly,
and transmit very slowly. For this reason they are employed
in electrical experiments for insulating bodies,....and also for
collecting the electrical fluid when we desire to accumulate
it or make it act on different bodies.  The  electrical fluid is
collected in general  by  rubbing a smooth polished surface of
these non-conducting bodies.
   All other kinds of solid matter,  provided they are made
perfectly dry, have  more or less  of the nonconducting  and
insulating power.  But the metals  have none of it.   The
electrical fluid,  when accumulated in any other bodies,  has
always a disposition to  pass from  these to the metals, and to
be diffused from one  part of them to another, with  such 
104          METALLIC SUBSTANCES,
 astonishing velocity, that it can be conveyed by a wire to the
 greatest distance without requiring any perceptible time for
 its passage. Mr. Cavendish found by experiments, that iron
 conducts the electrical fluid 400,000,000 times better  than
 water ;  that  is, a current of this fluid  will pass as readily
 through 400,000,000 inches of iron wire  as through one  inch
 of a cylinder of water equal in diameter to the wire.
    Athly, Another quality of the metals in general is observed
 in their manner of assuming a fluid form bv heat.  They retain
 their opacity in their melted state, and form a fluid which has
 a bright and reflecting surface, and which is repelled by most
 other kinds of matter, or which does not adhere to them, and
 spread itself  on them, as  water and many other fluids do.
 Small drops of melted  metal, therefore, form themselves into
 little spheres, in consequence  of the  stronger attraction  of
 their  particles for one  another than for  the surrounding
 matter.   This happens not only when  the small drops  of
 melted metals lie on the surface of various solid bodies, but
 also when they  are immersed in fluids, as water, oils, melted
 salts,  and  melted earths,  none of which will mix with the
 metals,  so  long as- these retain  their metallic form.
    These several qualities of the metals,....their excessive
 weight,,...the opacity and reflecting brightness of their  sur-
 face,....their being'such perfect conductors of electricity,....
 and their, mercurial manner of fusion, as it is called, form the
 distinction  between them and other bodies, and  are the  only
 qualities^which are found in them all without exception.
    But-we  may also take notice  here of malleability, lamina-
 bility, an4  ductility, as among the general qualities  of the
 metals ; for,  though these qualities are not found in all of
 them, the greater number have them, and metals are the  only
 bodies in nature in which they are found in an equal degree.
 These qualities are distinct from one another,  and  do not
 always  go  together.    Some metals  have all the three  in  a
 high degree, e. g. copper, silver, gold, and platina, when pure.
 Others have two only, as tin and lead, which are malleable
 and laminable,  but not ductile.'  Others, on the  contrary, as
, iron, are ductile, but not malleable and laminable.  Others,
 as zinc, are laminable,  but not at all ductile,  and scarcely
 malleable. 
            THEIR GENERAL PROPERTIES.     105

     The most malleable metals, however, are liable to become
  rigid and hard by hammering, in consequence of the expulsion
  of latent heat: and they must be softened again by annealing,
  before we can proceed to  hammer them further.   I had occa-
• sion formerly to explain annealing, and how it is performed.
  Tin and lead are annealed in some degree by the heat of
  boiling water, and, by a somewhat stronger heat, are perfectly
  softened.   Iron, copper,  silver, and gold,  must be made red
  hot.  Platina is with great difficulty annealed.
     Such, therefore, are the more obvious general qualities of
  the metals.
     To take, in the next place,  a more chemical view of them,
'  let us attend to the effects of heat on the metals in general.
     1st, Each of the metals is well known to require a particular
  degree of heat for its fusion  ; and some require very violent
  degrees.  Dr. Boerhaave's opinion or suspicion, concerning
  the heat of some metals in their  melted state, is perfectly
  groundless.
     2dly, After a metal is  melted, if we increase its heat to a
  much higher  degree, most of them may thus be changed into
  vapour.   And in  close vessels,  some of them can actually
  be distilled or sublimed; though in general the free access of
  air to such metals, when violently heated, makes them eva-
  porate much  more readily than they will do in close vessels.
     But, in order to understand fully the action of the air on
  the metallic substances, when they are strongly heated, it is
  necessary to know that they greatly resemble ttie inflammable
  bodies, by having a remarkable disposition to Attract oxygen,
  and to  combine  with it.  And this combination in some
  cases, is attended with the same phenomena of heat and light
  as in the case of bodies commonly called inflammable.   For
  example,  filings of zinc, or of iron, when thrown into a clear
  coal fire,  burn with a distinct flame.   This inflammability
  appears from many  other facts and  experiments ;  among
  others, from  the effects of nitre, when it is applied very hot
  to  the metals : there is a deflagration,  as it is called, in tha
  same  manner as when that salt is made to act on the inflam-
  mable substances ; with  this difference  only, that in the
  experiments  with  metals, it  is necessary to apply a  much
  stronger heat to bring on the action of the nitre and  metal
      Vox. tii. v                o 
106          METALLIC SUBSTANCES.

on one another.  Filings of zinc, when thrown into meltetf
nitre, burn  with a  flame  so brilliant and dazzling,  that the
eye  cannot  bear it.   If the nitre be red hot, filings of iron
will  exhibit the same appearance ;  but  it  is not  near  so
brilliant.   Filings of a mixture of lead and tin come next to
these two in inflammability and brilliancy.   The metals are
thus  suddenly changed into an earthy-like matter,  which is
mixed with  the remainder of the nitre.   I call it an earihy.
like  matter,  this being its general appearance.   It is still,
however, very different, according as  the experiment is made
with the different metals.   But in none of them does it retain
the appearance  of any of the  general  qualities of metals
which have  been already described.
   A further proof of the  affinity of the metals to the inflam-
mable substances,  is, that they are liable to suffer a change
by the joint action of heat and air, similar to that which the
inflammable substances   undergo,  a  change  analogous  to
inflammation.  This change,  in  the case of the  metals, was
called Calcination.  A higher degree of heat is necessary
to bring  on this change in most of  the metallic substances
than that which is  sufficient for the commencement  and con-
tinuation of  the inflammation  in the bodies usually called
combustible.  And  there  is a c.ertain latitude,  or  range of
the scale  of heat, which  is best adapted to  the calcination
of the metals.  In the lower degrees of  this range, metals
are calcined slowly and with difficulty. Near to the middle of
it, the metals, in general, are the most quickly  or  perfectly
calcined.  In the higher degrees, the calcination does not go
on so well.   And when we increase heat to an  intensity
much above the range I now speak of, some of the metals
exposed to such violent heats will retain their metallic form,
though they may easily be calcined in inferior heats.  The
reason apparently is, that in very violent heats the  air acquires
too much elasticity, and is too much  rarefied, to  act on them
with sufficient power: and the action of the air is fully as
necessary to their calcination as the action  of heat.   If you
would wish  to know in. what part  of the general scale of heat
this  range fit for calcination is contained, I cannot be precise
in pointing out its limits,  as they are by no means  distinct.
I  can only  say that it appears to be  comprehended within 
CALCINATION...RESEMBLES COMBUSTION.  107

what are called the red heats, which, however, have many  dif-
ferences of intensity.  Below these red heats,  and also in heats
that are far above them, or what  are called the  white heats,
calcination does  not go on so  well,  at least with most of the
metals.
   The matter,  into which the metals are changed by calcination,
is also an earthy-like matter, similar  to the matter  into which
they are changed by the action of nitre.  The  colour and other
properties of it are different, according to the metal from which
it is obtained, and partly too, according to the  manner in which
the calcination has been performed. This matter has  been a long
time called the Calx of the metal;  and from it the operation
by which it is obtained was called calcination.   The term  cal*
was chosen on account of a supposed analogy between the calci-
nation of the metals and the burning of lime ;  though it is now
well known that these two  operations are of a totally different
nature:  and  accordingly, the French chemists propose to set
aside these terms of cabt and calcination, as very improper,  and
to substitute others which I shall soon explain to  you.   In  the
mean  time, we shall proceed  to make a few more  remarks on
the calcination of metals in general.
   In the first place,  I wish  you to understand,  that metals, thus
calcined, or changed into calces, are not always calcined to the
utmost degree of which they are capable.  By a certain mode-
rate action of heat  and air,  they can be changed into calces,
which may be further changed by a continued or more effectual
action of the same powers.  This gives occasion to a great di-
versity in the calces  of some of  the metals  which ar.e capable of
these different degrees  of calcination.  A general account of
which diversity may be given in this proposition,  That the  far-
ther the calcination is pushed, the more does the calx resemble
an earthy substance, or it is whiter, and the less disposed to fu-
sion by  itself; and  on the  contrary, the less they are calcined,
they have the more colour, or they are less white, and retain
more of their fusibility.  Of this there are many examples, as
in the  calces of antimony,  tin, and some others.
   But the nature of the calx produced, and the phenomena and
quickness of calcination, are very different in the different cases,
partly in proportion as the  heat is more or less strong, and more 
108           metallic Substances.

 especially, as  the operation  is performed with  the different
 metals.   You  will easily perceive that there  must be great va-
 riety in the calcination of the different metals, if  you attend to
 these particulars :
   1st. The different metals are more or less calculable one than
 another.   Some with great difficulty,  and they are  but  imper-
 fectly calcinable.  Others are more calcinable,  but still are cal-
 cined slowly,  and with some difficulty.  Others,  again, are
 nrtich more  disposed for  calcination, and,' in  proper circum-
 stances,  are calcined easily and quickly.   While there are others
 which can be  calcined to a certain degree only, but after this,
 resist the action of heat and air, without suffering much further
 change.
   2d, If you also  reflect on the  great  difference of the metallic
 substances in their fusibility and volatility ; some being easily
 melted with a very  moderate heat,  while others require the
 most violent;  and that some can  also be easily converted into
 vapour,  while  others endure an intense heat a long time, with-
 out  being volatilized by it;....you wilr*perceive that the  heats
 proper for their calcination must bear different relations to the
 heats necessary for their  fusion, or  conversion  into vapour.
 Some, which require  strong heats to melt them, are best calcin-
 ed in degrees of heat inferior to those necessary to their fusion.
 Others,  much  more  fusible, must be  melted and heated much
 above their melting point, before they can be  calcined.  And
 of the volatile  metals, some do not calcine fast, without apply-
 ing to them so m»»th  heat as converts  them into vapour.
   Further, the calcination,  in some cases, goes  on so  slowly
 or to such a  moderate degree only, that it is not attended with
 emission of perceptible heat and light.  But in other cases, there
 is a plain appearance of inflammation,  the calcining metal being
 seen to glow like a burning coal;  and in others, a bright flame
 is produced, like that of some volatile inflammable bodies.
   What I have now said will give you some general knowledge
of the phenomena which attend the calcination of  metals indif-
ferent cases and varieties of this operation.  But you may form
 a more distinct notion of this variety  by attending to some ex-
amples which I shall now relate : 
  CALCINATION...VARIO*US DEGREES OF IT. 109

   1.  Copper requires  a strong heat to  melt it; and therefore
calcines best in a heat inferior to its melting heat.  It is not ca-
pable of being calcined fast,  or to a great degree: and no light
or  heat is observed to be produced by its calcination.
   2.  Tin is very fusible ; and therefore melts before it calcines.
But when  a proper heat is  applied to it, it calcines fast, and
more  perfectly than copper,  and with appearances of combus-
tion.   The calx, when well calcfned, is very refractory, or hard
to melt.
   3.  Lead, like tin, is very fusible, and therefore melts before
it calcines.   When the calcination is  performed with a  strong
heat, the metal smokes all the while,  or emits vapours ; and it
appears inflamed,  or emits more  heat and light than the  sur-
rounding matter,....and its calx, being a very fusible one, flows
around it in a melted state.
  4.  Antimony is very volatile ;  and therefore  emits vapours
plentifully in a calcining heat, which vapours are at the same time
calcined, and the calcining metal emits light and heat.
   5.  Zinc is similar to the former, only more  volatile, and in.
calcining,  gives a dazzling light.
   6.  Lead and  tin mixed.   Mixing metals together increases
their  disposition to calcine.   It increases  their fusibility  also;
and therefore diminishes their cohesive attraction ; which dimi-
nution of the cohesive attraction  is probably il consequence of
the chemical attraction of the two metals for one another;  as
chemical and  cohesive attractions are generally antagonists to
each  other.  But  by the diminution of cofftsion the chemical
attraction of the metals for oxygen will be increased*.
   As the matter, into which some of  the inflammable substan-
ces are changed by inflammation, can be restored again to its
former state;  so the calces  of metals can also  be restored to
their former state, and made to resume the metallic form. The

  '  I would just observe here, thatDr Black, in his earliest lectures, ascribed
much of the increase of weight which is observed in the calcination of metals,
to the absorption of ah', and  its combination with the metallic substance.  He
observed that this increase is always small when the operation is performed in
close vessels ; and asserted that there would be none in vessels exhausted of
air.  I have before me  notes taken at his lectures in Glasgow, in 1762, contain-
^ng all th^se remarks.....bditor. 
 HO REDUCTION OF MTTALS....HOW EFFECTED.

operation by which this is effected is called Reduction, and is
commonly  performed by heating  the  metallic calx strongly, in
contact with charcoal, or mixed  with it.  Thus die charcoal,
or a part of it, is consumed, while the metallic matter recovers
the  metallic form.   And to reduce a metallic calx in this man-
ner, we can employ the charcoal  of any inflammable substance
 from which a charcoal can be obtained,  whether it be vegetable,
 animal, or fossil.   There are  even examples of metallic calces
being reduced, by inflammable  substances, under other forms|than
that of charcoal. Oils, and even alcohol,  may be used. And no-
thing reduces the greater number of calcined metals better than
hydrogen gas, when it is properly applied. This was first taught
us  by seme of  Dr.  Priestley's  experiments.  He  placed  dif-
ferent metallic calces under glass receivers, or jars, filled  with
inflammable air, confined by  water or mercury ;  and then ap-
plied to them the rays of the sun,  collected into a focus  by a
burning-glass.   The consequence  was, the  quick reduction of
 the metallic calx,  while a quantity of the inflammable air dis-
• appeared.
   Although any charcoal may be used in the reduction of a me-
 tallic calx, the most proper and convenient are charcoals of ve-
 getable substances : and the  charcoal of tartar , is reckoned the
 best of all.  It  is, however, too costly for comfcion occasions ;
 and is used only when the quantity of calx is small, and we de-
 sire to perform the operation  neatly,  and without loss,  as in as-
 saying of ores,  qr in experiments with small quantities of me-
 tals :....and the  op^ation is performed in a crucible.  The reason
 why charcoal of tartar is thf  best, is,  that it contains  an alkali
 in such quantity as renders it fusible.  It therefore applies itself
 more closely to the metallic matter,  and also dissolves or melts
 any earthy matter which may happen  to be present; in conse-
 quence of which fusion the particles of reduced metal more easi-
 ly  sink to the  bottom of the  mixture,  and unite  there  to form
 one mass, called in this case  a Regulus.  The charcoal of the
 tartar prepared for this purpose is called Black Flux.
    But in  the large way of working, when tons of metallic calces
 are to be reduced,  they are simply heated in contact with the
 fuel, and intermixed with it.   In the great iron  furnace, the
 •re, broken into small pieces, and mixed with substances which 
METALLIC  SUBSTANCES.           lit
 promote the fusion, is thrown into the furnace ; and baskets of
 charcoal,  or coaks,  in  due  proportion,  are  thrown in along
 with it.   A part of the bottom of the furnace (which is also the
 narrowest)  is filled  with fuel  only.  This being kindled,  the
 blast of the  great  bellows is  directed on it, and soon raises the
 whole  to a most intense heat.  This melts the ore immediately
 above  it: and the reduced metal drops down through the fuel,
 and collects at the very bottdm.....The rest sinks down, to fill
 up  the void  left by the consumed fuel and metal. Thus it comes
 in the  way of the bellows ; and here it is raised to the same in.
 tensity of heat, and melts, and is reduced,  in its turn.   More
 ore and fuel are supplied above : and the operation goes on, till
 the melted  metal  at  the  bottom, increasing in quantity,  rises
 almost to the aperture for the blast.   It is now let out, by pierc-
 ing a hole in another side of the furnace, close to  the bottom.
   There is an opinion among the chemists, founded, as  they
 say, upon experience, that the less calcined calces are most easi-
 ly reduced ; and that the calces of some metals,  if exposed to
 the action of heat and air for along time, can hardly be reduced
 at all, or not without  a considerable loss.   Hence the notion of
 a  mercurial,principle, &fc.  in metals, which they imagined to be
 partly expelled.and lost by violent calcination.  I suspect, how-
 ever, there is another more simple reason for the loss or dimi-
 nution  of the>metal, which is, that all the metallic substances,
 whether calcined or not, have more or less of volatility, and art
 liable to suffer a  loss by evaporation, when they are long expos-
 ed to the action of heat and air.           jp
   After thus describing the calcination of the metals in general,
 and the reduction of them again to the metallic state, I have
 been accustomed to mention the opinions which have been form-'
 ed of the nature of these  operations, and  the arguments  and
 proofs on which these opinions are founded.
   The  most distinct  and plausible opinion, which  prevailed
 among the chemists for a considerable period,  was that of Dr.
 Stahl, similar to that which he  entertained concerning the  na-
ture of the inflammable substances  and of inflammation, viz.
that  the metals are compounded substances, consisting of that
matter which was called the calx-,  and of the phlogiston ; and 
112  STAHL'S THEORY  OF CALCINATION, &c.

that they ha'd their metallic qualities from the principle of inflam-
mability ; and that during calcination,  this principle  was sepa-
rated from them ; and therefore the  basis or calx of the metal
appeared in its separated state, deprived.of the metallic quali-
ties ;  but that in the operation of reduction,  the calx recovered
again from the charcoal,  or or'ier inflammable matter, the phlo-
giston which  it had lost, and by  this  recovery, was restored
again to the metallic state.
  This appeared so far a plain intelligible account of the  mat-
ter.   But there was one material fact,  which was a very great
difficulty in the way of this theory.   The  fact  I mean is, that
the quantity of calx is greater than that of the metal,....one hun-
dred  pounds of lead, for example, produces 110, or 112 pounds
of calx.
  Different attempts were made to get over this perplexing dif-
ficulty ; some of them very extraordinary, and almost incom-
prehensible, e. g. that the  principle  of inflammability  was not
only destitute of weight,  but that it had the power of diminish-
ing the weight of bodies  to which it was added, &c *
   All these difficulties proceeded from their not having yet stu--
died the part which air performs during calcination.  This was
not sufficiently done until of late, when  the nature and powers of
the different airs, or elastic fluids,  became so much the subject
of inquiry. .       ,
   Among the experiments which this inquiry has occasioned, it
was soon discovered  by  Dr.  Priestley, Scheele, and Beccaria,
hut especially by M.  Lavoisier,  and other French chemists,
that when a metal is calcined, it always absorbs and fixes a part
of the air which contributes to its calcination and is necessary to
it ; and that  the increase of weight in  the calx  is always equal
to the quantity of the air absorbed.

    * Nur could any valid objection have been made to  this  explanation,
however unlike  our more familiar notions, had not Sir Isaac Newton made
experiments on p,-.KluI?inis of all different kinds of matter, metals-,- and the
cakes of metals, and found that all vibrated alike, if of equal length*. Che-
mists acquiesced,  l.oweu ;•,  in this explanation by Stahl; because  few, if
 any of them, were mathematical philosophers, and as few of the mathema-
 tician were evo'-.itneed chemists....foitgk. 
               METALLIC SUBSTANCES.          113

   Dr. Mayhow of Oxford observed this in the cases of antimony
 and lead, and suspected that it was so in all,....1674.
   It has further appeared from such  experiments, that it is al-
 ways oxygen  gas which the metals  attract in  this manner. They
 are  calcined most easily and  quickly in pure oxygen gas; and
 cannot be calcined in any other,  except when it contains a mix-
 ture of the oxygen,  as atmospheric air does. When calcined in
 a limited quantity of atmospherical air, therefore, they extract
 the  vital part from it, after which the rest of  the air has no more
 power to calcine them. *
   It has also  been proved in  the clearest manner, that oxygen
 gas  can be extracted from the calces of metals; from  some by
 heat alone,....the calx at the  same time recovering its metallic
 form.   This happens to mercury, silver, gold, platinum.  From
 others, the  oxygen  gas may be extracted by an  elective attrac-
 tion ; as happens in lead, the calx of which, viz.  minium, af-
 fords oxygen  gas by the action of sulphuric acid assisted with a
 moderate heat-   On the other hand, in the  reduction of metal-
 lic calces by the action of charcoal, a  great quantity of elastic
 atrial matter is  extricated from the materials, which is carbonic
 acid, that is a  compound of oxygen  and charcoal.  AH these
 particulars  are now completely proved by many experiments :
 and  upon these M. Lavoisier  and his friends founded their new
 system concerning calcination and reduction, totally opposite to
 that of the older chemists.  The  new opinion is, that the metal
 is not a compound, but  a simple  body ; that the calx is com-
 pounded of the metal and oxygen extracted  from the vital air ;
 and  that the heat and light are no proof of a principle of inflam-
 mability.  They are extricated  chiefly from the oxygen gas^
 which  is supposed  to have an extraordinary capacity for heat,
 and  which,  as being an elastic fluid, contains a great deal be-
 sides in a latent state.
  In reduction again, the new doctrine is thatjthe oxygen is se^
parated from the metal, and nothing else happens or is necessa-
ry to the  recovery  of the metallic  state ; and therefore, in the

   * A similar  doctrine was maintained  by Mr. Bayen,  a French apothe-
cary.  Journ. de  Phys. III. 120,....IV. 487.....VII. 390.
     VOL. HI.                    p 
114      LAVOISIER*S THEORY....OXYD, &c.
reduction of mercury, silver, gold,  and platinum,  which  have
but a moderate attraction for oxvgen,. heat alone is sufficient to
separate  it.   Other metals-cannot be reduced by heat alone, on
account of their having a strong attraction for the  oxygen, and
retaining it too strongly to admit of its being forced off by heat:
but such are commonly reduced by the action of charcoal, aided
by heat ;  and then the carbon attracts the oxygen from the me-
tal, and forms carbonic acid with it.  The production of carbo-
nic acid gas in this manner has been ascertained by numerous
and incontestable experiments.   And when inflammable air is
employed, the basis of this air, the hydrogen, acts like the char-
coal, by  its strong attraction for the oxygen that is in the calx.
They unite together, and form water.  This  also has been as-
certained by many experiments.
   A change  of 3ome names has been proposed in consequence
of this  theory, viz. calx and cakination are  to be set aside, and
calcined  metals or calces are to be  named Oxyds ; des oxydes,
in French ;  oxydum, oxyda, in  Latin.  But this term of oxyd
is applied by the French chemists to every compound, whether
metallic or not, that contains oxygen in less quantity than that
which  gives acidity.
   On the whole,  this system is much more  directly and plainly
supported by fact* and experiments than the ancient system of
the chemists.
   The onJy$f«ct which the French theory has not yet explained
is, the effect'of light in reducing the oxyds of medals.  There
are several ejuimples-of it, in consequence of which it is suppos-
ed, by the danders of the old doctrine, that the light unites it-
self to the metallic matter, and thereby  restores it to the metal-
lic form. But it must be acknowledged that when metallic oxyds
are reduced by light, oxygen gas is always detached; and the
French chemists  say,  that the light affects  the reduction, not
by attachmg  itself to the metallic oxyd, but  by  some power
which it has to occasion the separation  of the oxygen, perhaps
by joining with it, and thus forming with it oxygen gas
   One fact more  which has been discovered by the experiments
lately  made on the metallic oxyds, must not be omitted  viz.
  Ilmt many of them, when once formed, are capable of attract 
PROPERTIES  OF METALS.
115
ing carbonic acid, and of uniting with it,  and even of being
dissolved by it in water, like the alkaline earths.

   I now proceed to consider the properties of metals  res-
pecting their mixture with other bodies.
   The first class of  the objects of chemistry,...the salts, and
of these  the  acids,  are  found to have the greatest activity
with regard to metallic substances, and to produce the great-
est variety of effects.
   To give a general idea of those  effects, I may begin by
saying that there is  a chemical attraction between metals and
acids ; that metals are  capable of uniting with acids, much
in the  same  manner as alkalis and  the alkaline earths  are ;
that they, are disposed  to form with them saline compounds,
many of which readily crystallize ; and in most, the natural
activity or corrosiveness of the acjd is very sensibly  abated
by its adhesion to the metal, though, in general, not near so
much as in the salts composed of alkalis or earths.
   The chemical combinations of metals with acids are com-
monly named solutions or dissolutions of the metals, on account
of their  being commonly produced  by putting the metal me-
chanically divided,  or with  an  increased  surface, into the
liquid acid, which acts on it as a solvent.   The action of the
acid is promoted by gentle  heat, and als«  by annealing or
softening the metal  before it  is put  into the aci<j»- This last
practice is useful, probably, by diminishing in  the metal that
species  of cohesive attraction called  hardnes&g which is  an
antagonist to the power by which the dissolution is perform-
ed.  At any  rate,  the fact  is certain.  If wiijtake a few of
the small cast iron  tacks, (made of the white metal) which
have not been annealed, and as many of the same tacks long
annealed, and put each parcel in equal quantities of acid, the
last will be found much more diminished in weight than the
other in the  same time.  Moreover, the  unannealed  nails
seem to resist most at the surface ;  and when half dissolved,
preserve their form  completely.   In this particular metal,
indeed, a spongy nail remains coherent to the last.
    In performing^these dissolutions of the metals, we find
also that in  many cases there is a mutual saturation, as with
 the acids and alkaline  substances ;  a certain quantity of acid 
116          METALLIC  SUBSTANCES,
 being capable of dissolving,  and converting  into  a saline
 compound, a certain quantity only of the metal; and the metal
 on the other  hand,  neutralizing or  mitigating a  certain
 Quantity only of the acid.   This does not happen, however,
 in  all the  compounds of metals  with  acids.    In many of
 them there  is no fixed point of saturation, the same quantity
 of  metal being capable of combining with different propor-
 tions of  acid,  and forming  compounds which differ  in ap-
 pearance and other qualities, according to the  proportion of
 acid which  they contain.   Even in this case, however, it is
 not so properly said that there is no fixed point of saturation.
 The fact would be better expressed by saying, that the satu-
 ration is  not confined to one proportion.  For, in these cases,
 we find that when a certain proportion is attained, the addi-
 tion of more  acid, for example, dissolves  the  salt,  without
 changing its properties,  till we reach  another proportion,
 when a manifest change of chemical and other properties en-
 sues.  Sometimes we shall have a third proportion, in which
 a kind of saturation obtains.  This resembles  the combina-
 tion of water and salt, in the states of crystal and solution,
 and  in the combinations of heat,  inducing solidity, fluidity,
 or vapour.  When the proportion  of acid is large, the acid is
 less  mitigated,  and the compound is more soluble in water,
 and  in some cases deliquescent.   When the quantity  of acid
 is very small, it is much mitigated,  and the compound has
little or  no solubility, the metal  being only divided  by the
acid into a powder, and not dissolved.   In this  case, that is,
•when the acid divide's  the metal into a powder,  but does not
 dissolve it,'or render it soluble in  water, it is said to corrode
 it ; and the metal is said to be corroded.
   It must  be understood further, that every  metal  is not
 equally disposed to unite with each of the acids.  Some of
 them can be combined with  all the acids,  or any of them;
 but others with a certain number of them only.   And there
 are  some which are  not acted upon in the least, except by
 one  or two, or  by  certain mixtures of the acids with one
 another.
   Those metals  which are capable of uniting with a number
 of the acids generally have the strongest attraction  for the
 muriatic, and next to the muriatic, for the  sulphuric.   The 
           THEIR SOLUTION 4Nt ACIDS.        117

acid of sugar, or the oxalic, and the taifarnpvM acid,  and the
phosphoric, are also strongly attracted by tfl^Baetals  m gene-
ral.   The nitric acid, although it dissolveWJ^$£at  number
of the metals readily and easily, is  not so* sfri£n^ry:$!ttr|fcteil
and  retained by them.  It is  more easily separated frs^V
them by heat or Otherwise.   The muriatic, when combined
with them, is so strongly retained^ that it is not separable by
heat, but renders the metallic matter volatile along with itself.
   Among several metals which can be dissolved by the same
acid, great differences are found  in their attractions for it;
and  some  of them can be employed to precipitate others in
a certain  order.   Zinc or iron, for example, can be  employ-
ed to precipitate silver, or  quicksilver, or copper,  or lead,
from the nitric acid.   Lead precipitates copper, quicksilver,
or silver.   Copper precipitates these two last; and quicksilver
precipitates silver.   Zinc is therefore  supposed to have the
strongest attraction for the acid ; next to  zinc, iron ;  next
lead, copper, mercury, and silver.
   There  is a remarkable circumstance which distinguishes
the solution of metals in the  acids from the solutions of alka-'
line  and other  substances.   While  metals are dissolving in
acids there is,  in  many cases,  a  violent  effervescence,...an
effervescence sometimes as strong as that which attends the
action of acids on common alkalis or calcareous earths.   It
is, however,  quite different in its nature from the efferves-
cence of alkalis or alkaline  earths.   It is  not  produced by
the separation  of fixed air or carbonic acid.   The metals in
their metallic state do not contain any.  These effervescences
are explained in a very satisfactory manner by a great num-
ber  of the modern experiments,  which shew that  either a
part of the acid or a part of  the water is decomposed by the
dissolving metal, which attracts to itself a part of  tlieir oxy-
gen, and is thereby changed into an oxyd, (formerly called
a calx); which oxyd, as a peculiar substance, is dissolved by
the remaining acid, or is united to it.  When the  oxygen is
taken up by the metal from a part of the water, hydrogen gas
is produced  in the effervescence, as you saw lately when iron
was  dissolved  in diluted sulphuric acid.   When the oxygen
is taken up from a part of the acid,  the acid is partly decom-
posed ; and  a  different elastic fluid, or other matter is pro- . 
  118          METALLIC SUBSTANCES,
                    •
  duced, peculiar to tiiat acid.    All this will be more fully
  explained as t^^ases occur.  (See Note 50. at the end of the
  Volume.) •"' j(F
  ^#e  find reason to  be  satisfied that this  theory is well
flflmded, when we examine the state to which the  metals are
  reduced by being dissolved.   A metal, while dissolving,  is
  always calcined, or oxydated, more or less ; in many cases, it
  is true, to a very small degree only : but in every case, some
  degree of this change does happen to it; for, if we  precipitate
  the metal by the action of a pure alkali, we always get it in
  form of a calx : and  we get it in nearly the same  state if we
  expel the acid from it by the action of heat alone.  And when,
  on  the other hand, we  change the metal into an oxyd by the
  action of heat and  air, before we apply the acid to it, there
  never is an  effervescence;  the  metallic  matter generally dis-
  solves quietly, in some cases more easily than the metal itself,
  when put into the same acid.   But this happens  only when
  the  metal  is  calcined  in the  slightest degree possible.   If
  much calcined,  it dissolves more slowly and difficultly,  and
i-  requires a greater quantity of  acid to its dissolution than the
  metal  itself would  have required.
    We may further remark here, that the different acids act
  on  the  metals with different degrees  of quickness and  vio-
  lence.   The action of tne nitric is generally the most quick
  and violent, and  most  effectual  in oxydating the metals:
  next to this the sulphuric.   The muriatic acid generally acts
  in a more  slow and  languid manner on the metals' in their
  metallic state.   This  appears plainly  to proceed  from its
  having less of the  oxygen to impart to the metal; for if the
  metal  be first slightly oxydated, no  acid whatever unites with
  it so readily and strongly as the muriatic acid.   We have  a
  proof of, this, when we  add muriatic acid to a metal already
  oxydated by another acid, as the nitric, or  even the sulphu-
  ric acid.   There  are also particular states  or conditions of
  the muriatic acid, in which it acts more  readily and power-
  fully on the metals than it does in its ordinary watery state'.
  We apply it, for example, in some  cases, in the form of dry
  and hot vapour, as in cementation, described in my general
  account of chemical  operations.   And there are  other pro-
  cesses  soon to be described, by  which we add oxygen to the 
          THEIR SOLUTION  IN  ACIDS.       119

muriatic acid.   By this its power to penetrate and dissolve
the metals is greatly increased.
   The  compounds, or the solutions of metals with acids, are
of different colours, when made with different metals, or with
the same metals in different states of oxydation.          ,
   Fourcroy  (Annales de Chymie. torn. x. on Mercurial Preci-
pitates) mentions an opinion of the French chemists, that the
colour of the solution or compound is similar to that of the
oxyd contained in it;  and that when, from such solutions or
compounds,  a precipitate  is produced of a different colour,
this proceeds from a  change the oxyd has undergone  in  its
degree  of oxydation,  while  it was precipitated, or immedi-
ately after.   Yet  he  says,  (page 309, et alibi) that Turbeth
mineral, or sulphat of mercury, with excess of oxyd  or calx,
is soluble in 2000 waters,  and  forms a colourless solution.
Caustic alkalis precipitate  from this solution a grey oxyd.
This colour  indicates some degree of deoxygenation.  Four-
croy imputes this change to the caustic alkalis :  but this is
no explanation.
   The  compounds of metals  with acids may be decom-
pounded in  general without difficulty.  The acid and oxyd
are  united together in the  greater  number of cases, by an
attraction that is  not very strong,  which  is plain  from its
being overcome by many other  attractions ; by alkalis, the
alkaline earths, and even by some of  the inflammable sub-
stances,  which are disposed to  unite with acids.   If fresh
calcined litharge (which is an oxyd of lead) be ground to fine
powder, and be put into a solution of lime in muriatic acid,
we find the Time precipitated in a caustic state: and the liquid
now contains a compound of lead and the acid.  Or if sea
 salt be digested with litharge, we procure a caustic mineral
alkali.   (Scheele on Fire, 174. J  This explains the corrosion
of the  lead  pipes which convey water.   It very commonly.
 holds both of these muriats in solution.
   Heat alone is sufficient,  in many  cases, to  separate acids
 from metals.   All this proves  that the attraction between
them is not strong,  in the  greater  number of  cases.  It is
probably in  consequence of this moderate attraction,  that
in some of  the  compounds of  metals with acids,  the acid
 is very little mitigated, the compound being  nearly as cor- 
  12©          METALLIC SUBSTANCES,

  rosive, when applied to animal substances, as the pure acids
  themselves.   In this way we have obtained some of the most
  useful potential caustics  and  escharotics employed  by the
  surgeons.
    This being a very general property of the metallic salts,
  and  being a property purely chemical,  because it is equally
  effective on the dead and on the living subject, has attracted  « ,
 the attention of the chemists,  and they have  attempted to
 discover some general principle on which it  depends.   Mr,
 Berthollet, unquestionably one of the most eminent, published
 a dissertation  on this subject in the fournal de Medicine in
 1779.  He ascribes it to the action of  the acids on  the
 phlogiston  contained in  animal and  vegetable  substances  ;
 and supports this by a very judicious series  of experiments.
 The  doctrine of phlogiston being exploded, this explanation,
 as far as it was valid before, is  easily accommodated  to the
 new doctrines: and we must ascribe  the corrosive power of
 the metallic salts  to the  action of the oxygen which they
 contain.  It is very true, that the action of oxygen produces
 very  remarkable effects on animal and vegetable substances.
 But I do not think that they have a  great analogy with the
 action  of the highly corrosive  metalline salts, such as that
 formed of mercury with the sulphuric,  nitric, and muriatic
 acids, or that formed by silver and the nitric acid.   Some of
 those salts are  most highly corrosive  when they contain the
 smallest quantity1 of oxygen? a quantity so small that they-are
 scarcely saline, and very strongly united.   Others ar& more
 corrosive when they are truly saline,  and contain  not only
 oxygen, but also the distinguishing ingredient of the  acid. v
 And others are so  far from being corrosive  in  either  state,
 that they promote the healing of wounds and sores, seeming
 friendly to the  functions of organised  substances.   Perhaps
 the corrosiveness is sufficiently accounted for, when we ascribe
 it to the acid itself.  Nor is it incongruous with the general
 course of chemical facts to say,  that in some of these  com-
pounds, new properties are induced, differing from those of
either ingredient.
   The other order of simple salts,  the alkalis,  have not so
much dissolving power with  regard  to metals as the acids.* '* 1
They are more  commonly employed^to precipitate rattaU 
       THEIR  RELATION  TO THE  SALTS.    12%

from acids,  which they  do by their  great superiority of
attraction.
  The separation of a metal from solution in an acid, presents
such a variety of phenomena, that I can scarcely bring them
under general rules, and shall therefore notice them as they
occur in treating the several metals.   I observe, however, in
this  place, that in most cases, a smaller quantity of alkali  is
sufficient for separating a metal from a given quantity of acidy
than suffices for saturating this quantity of pure acid.   The
precipitate is in the form of an oxyd, and in these cases, has
decomposed part of the acid.   It is only the remainder that
employs the alkali to  separate  it from the  metalline oxyd*
How this is  effected, even in those cases where water is de-
composed,  and  inflammable air is produced, must be con-
sidered as a difficulty still  remaining in the  new doctrines of
the French chemists.
   The alkalis themselves may also, in  some cases, be made
to act as solvents, and will dissolve most metallic substances
very perfectly.   They act most powerfully in  their caustic
state, especially  if applied with a melting heat.   In the state
of watery solutions, they  act but weakly in  general,  though
there are some of the metals which they dissolve  very per-
fectly  even  in this way.  And  if  the  metal be previously
oxydated, especially by acids, there are few of them that will
not yield to the action  of alkalis.
   Thus it happens, in many cases, that whffiji we precipitate
a metal from the solution  in an acid, by a caustic alkali, if we
put in too much alkali,  we redissolve the metallic oxyd. The
volatile alkali does this in  most cases.  A certain preparation
of alkali, which will be described  in clue time,  ensures the
alkaline solution.
   In a dry melting heat the alkalis are powerful solvents  of
the metalline calces, and form with them a variety of coloured
glasses.
   Among the compound salts,  borax is found useful in the
melting of gold  aud silver,  and in soldering these  and other
metals.   Its usefulness is remarkable, especially when filings
or small pieces are to be united by fusion.    It helps to make
them melt more readily,  and to join all together the more
completely, and  with the least losjs.  The borax promotes the
     vol. in.                 <l 
122    METALLIC SUBSTANCES TREATED

union of the melted particles or globules  of  the  metals, by
making their surfaces clean and bright, and preserving them
in that state. The necessity of this is plain in mercury, which
the smallest foulness hinders from uniting.   Its globules are
then rather disposed to separate into  smaller globules when
we attempt to bring them together.   And the  borax effects
this,> by covering and defending  the metal from air, and
thereby preventing  the formation of  any calcined crust or
pellicle, and likewise by dissolving any matter of thiskind
which is "already  formed ;  borax  having much power  to
dissolve and melt the earthy substances and  metallic oxyds.
By spreading itself also ovej the surface  of  the  crucible, it
gives a smooth  glazing, whifh allows the petal to be poured
out.                       <f
   The other neutral salts are* not much disposed to acton
metallic substances, except, when assisted by a strong heat;
but,  with  its assistance, tlic.se which contain the acids that
have the greatest power over the metals are disposed to act
upon them,  and dissolve or corrode them, more or less, the
acids being loosened by'the heat.   Glauber's salt, vitriolated
tartar, common salt, and digestive salt, produce this  effect.
 The effects of nitre and ammoniacal salts are more remark-
 able.  Many of the metals, when they are thrown into melted
nitre, are  inflamed or burnt, as has been already seen ; and
 the  metal is reduced to the state of an oxyd.  This oxydation
concurs with the effects which you formerly saw in the mix-
 tures  of nitrous  acid with alcohol,  to  shew how easily the
 nitric acid is decomposed.  No part of it is to be found in the
 crucible, if enough of metal have been employed.   We find
 only a caustic fixed alkali, sometimes, indeed, tainted  by the
 metallic oxyd which it has dissolved.   Hence  we must con-
 clude that the metal is  oxydated by attracting the oxygen of
 the nitric acid,  and thereby allowing the nitrous air or the
 azote to escape.   This  escape must be  considered as the
 cause of the deflagration.
    The  effect  of  common sal  ammoniac  upon the  metal
 is easily understood.   The  attraction of the  acid for the
 volatile alkali is scarcely greater than for some of the  metals
 or their oxyds.   Therefore,  when  one  of them,  in fine
 particles,^ is mixed  intimately with  sal  ammoniac,  and 
      WITH EARTHS AND INFLAMMABLES.  123

distilled, we  obtain the volatile alkali in a caustic form ; a
proof, by the way, that metals do not yield fixed air in their
effervescence with acids.   In this decomposition of the am-
moniacal salt, the effect is brought about by the heat, which
volatilizes the alkali.   The vitriolic ammoniac exhibits the
same appearances.
   The oxyds of some metals, when put into a watery solution
of sal ammoniac, act with great variety of appearances, which
Will be explained afterwards.
   With respect to the second class of the objects of chemistry,
the  earths, the  relations of these to metals  in general has
been, in some measure, pointed out already, and amounts to
a very few propositions only.  I have already observed, that
some of the  alkaline earths have a stronger attraction for
acids than  most metals.   I also had  occasion to  notice
that melted earths and  melted  metals cannot  be   mixed,
at least so long  as the metals  retain their  metallic  form.
But  when  they  are  in the  form of  oxyds  or calces,
they  can easily  be  mixed  with melted earths  or  glasses;
and some  of them have even great power in*this  state to
promote the fusion of some of the earths,  or to dissolve
them in a melting heat.    They are,  therefore, added to
some of the compositions,  for making glass  in  some cases,
in  order to make it  more perfect  and  transparent,  and in
others,  to give it colours, in the imitations of the   natural
gems.  When metallic oxyds happen to be mixed and  com-
bined in considerable quantity with vitrified earths, they can
be separated from them by fusion with charcoal or black flux.
Thus, a piece of fine English flint glass, or  the false  dia-
monds called Paris pastes,  being reduced to powder,  and
urged with a  strong heat, in contact with charcoal or black
flux, will be decompounded, and we shall find  a button of
lead at the bottom of  the crucible.
   Among  the substances  of the third class,  the inflamma-
ble,  some  serve for the  reduction of metallic oxyds.   But,
excepting this use t>f them, none  but sulphur, phosphorus,
and charcoal in some cases, are remarkable for a disposition
to unite with  any of  the metals.
   Sulphur shews a strong attraction fpr most metallic sub-
stances; and may be united with most of them, readily and 
124 METALLIC SUBSTANCES...THEIR UNION

intimately, in the way of fusion.  And though the  heat be
not sufficient to melt the metal, but only  the sulphur, if  the
metal be only divided into small pieces, the sulphur penetrates
it, and entirely changes its appearance, examples of which
shall be given hereafter.
   In making many of these compounds of sulphur and me-
tal, a great quantity of heat is extricated from  the materials,
which  make them become  ignited, and glow as if they were
inflamed.   This was mistaken at first for a real inflamma-
tion.    The most remarkable of these  experiments  were
made by Van Troostwick and Dieman.  They mixed sulphur
with different metals, in  a closed phial,  or in an exhausted
tube hermetically sealed, or in a tube filled with hydrogenous
or azotic gas, or carbonic acid.   With an external  heat, by
no  means very great, the  sulphur melted,  and,  after  some
time, the combination with the'metal  took place.   In that
moment, the whole broke  out into a bright  glow,  in some
cases brilliant, and almost  like a real  deflagration.   Three
parts   of copper to one of sulphur  produced the  brightest
light.   Lead also, and tin, and especially zinc,  produced a
bright flame.   (See Note 51. at the end of the Volume.)
   In  the new  language of  chemistry  these compounds  are
called   sulphureta, for the  Latin word, or, in the singular,
sulphuretum.   And our  chemists,  who  have adopted this
language, call them sulphurets.
   Sulphur, in such experiments, not only  shews an attraction
for most metals,  but like other bodies which have  a power
of this kind, it is  found to attract different metals with  dif-
ferent  forces.   And some metals can  be employed in many
cases  to separate sulphur from  others,  in a certain order.
When this separation is performed in the way of fusion,  in a
crucible, the sulphur, uniting with the  added metal, which it
attracts most,  forms a matter which flows uppermost;  the
other  metal separates  and falls  to the bottom, or  forms a
 Regulus.   but this method of separating  sulphur from
metals is not  the necessary or  only method in  all cases.
 There are many, in  which rhe  sulphur can be separated by
heat alone : and it is more usual to expel it in that way.
    Gold, platinum, and zinc,  are exceptions to the general
 account I  have given  of the relation  of sulphur to metals, 
      WITH SULPHUR AND PHOSPHORUS.   125

Sulphur  cannot be made to penetrate  these three, or unite
with them,  if it be applied pure, and these metals are in
their metallic state.   But when sulphur is combined with
an alkali, this compound acts much more powerfully as a sol-
vent, in the way of  fusion, upon metallic substances in gen-
eral; and even the three I  just now mentioned are readily
dissolved by it.   The different metals, when dissolved by
this compound,  unite with it with different degrees of force,
in the same order as sulphur does.   Thus, we have it in our
power to separate the metals  from  it also by one another.
The best proportion  for dissolving metals  is equal parts of
sulphur and alkali.
  The management of phosphorus, in combining it with me-
tals  melted or made red hot, requires much caution.  The
best way is to cut it into bits of four or five grains weight,
-and keep them under  water ;  and  when they are  used, to
take out one at a time,  wipe it dry with bibulous paper care-
fully, and  introduce it into the crucible with a long pair of
pincers, plunging it to the bottom.   The greater part of it
is always dissipated;  but some combines each  time.  Per-
haps a composition,  which will produce phosphorus, hard
pressed into the bottom of a crucible, would answer better.
The crucible being made hastily red hot,  the melted metal
may be poured into it, and the heat  continued.    The phos-
phorus would thus be presented to the metal in its nascent
state, which is found to be  favourable in most cases of diffi-
cult  combination.   The fusibility of the metal is improved
by this addition.
   By Pelletier's experiments (Mem. de VAcad, des  Sciences')
100 grains of platinum are changed into  an  easily fusible
phosphoret, by the addition of eighteen grains of phosphorus:
and 100 grains of gold require only four gains of phosphorus
to change them into phosphoret.  These compounds, if ex-
posed a long time to the action of heat, burn at their surface
until all the phosphorus is consumed ;  and  the above  metals
remain  in their ordinary state.
   In the experiments which have been made by mixing me-
tals with one another, it appears that metals unite in general
with one another, and this in  every  proportion.   But there
are  some exceptions, as iron  and lead,  iron and mercury,
;lead and cobalt, nickel and cobalt, cobalt and bismuth.  The 
126          METALLIC SUBSTANCES,
mixtures are of  different specific gravity from what corres-
ponds with the ratio of the composition. * In general, the spe-
cific gravity and density are greatly increased, so that in many
cases the compound is denser than the densest of the ingredi-
ents.    Thus the density of tin is 7363, and that of brass is
8006.  But the density of a mixture of two parts of brass and
one part of tin is 8916.   The proportion of the composition
should have given 7793 *  They are also more fusible: hence
they are employed as solders,....for gold, we employ a mix-
ture of  gold and silver,....for silver, silver and mercury,....
for copper, brass,....and for brass another  still more com-
pounded,....for either lead or tin, a mixture of both.
   Mixtures of metals,  in general, can also-be calcined more
quickly than the same metals in their separate state;  of which
you have an  example in  the mixture of lead and tin, which
burns like a  bit  of turf.   If you would wish to know the
cause, I shall hazard a conjecture.    I am inclined to think
that  this effect is produced by the chemical attraction of the
metals for one another,  which counteracts  the  cohesive at-
traction of each of them, and diminishes its  force, and there-
by gives advantage to another  chemical  attraction,....their
attraction for  oxygen.    That  their  cohesive  attraction  is
diminished by their  union  with one another is evident, the
mixture being  always more fusible than the separate metalsf.
   The method of separating metals from one another again,
is very various in the different cases, and depends upon cer-
tain particular properties and differences of the metals which
are to be separated.   Thus in some cases, difference of fusi-
bility is made the means of separation: thus lead is separa-
ted from copper.   In others, difference of volatility: Thus
mercury is separated from antimony.   In many others, dif-
ference of solubility: Thus gold and silver are  separated by
aquafortis, or aqua regia, or sometimes by sulphur ; or gold
and iron by sulphur and  lead.

  * It is also an almost universl fact that the cohesion of tiie compound  is
greater than in the  proportion of the composition.  In the ductile metals,
whose cohesions are  not extremely different, the cohesion of the compound
  \ceeds"that of the firmest of the ingredients.   Thus the mixture of twelve
parts of lead with one part of zinc is twice as coherent as the zinc....editor.
   f Yet the mixtures are generally more densf and much morecoherenf than
-he ingredients separately., .editoe. 
           HOW SEPARATED WHEN  MIXED.     127

     Other separating-operations, which are frequently performed,
   depend on different degrees of their attraction for oxygen, and
   more or less disposition to unite with it;  that is, on a difference
   in their  tendency  to calcination.   Thus lead, and most other
   metals along with  it,  are separated from silver and from gold:
   and thus copper also  is refined from admixture of the  coarser
   metals.   In most cases of separation performed in this manner,
   the process is called Scoripication.
     The mixture is exposed to a violent heat and to a current of
   fresh air, which causes the surface to tarnish, and then to gather
   a film or scale of the more  calcinable  metal.  This is  usually
   blown to one side of the melted  mass, as it forms, by the bel-
   lows.  It is succeeded by more ;  and this continues, till the less
   calcinable metal be as much purified as is possible by this opera-
   tion.  What is thus blown or raked off, is called Scorie, Slag,
   Dross.   It is  not always a slag or filth,....but a portion of the
   metal, of the same purity, but  no longer perfectly metallic,
   but a compound  of the metal and the oxygen of the atmos-
   phere.
     The rusting of iron and ojher metals is a change  of  pre-
   cisely the same kind, and is produced by the same cause.  It
   is very remarkable in iron, because this metal also decomposes
   water very fast, and therefore rusts very fast in damp and warm
   air.
     You are now informed of the general character and qualities
   of the metals.  We must now attend  to their natural history,
   or the different states in which they are found in nature.  .
     The first remark we have to make on this subject is, that few
   of them are produced by nature in a state of purity.  They are
*  most commonly found in  the form of what are called Ores,
   which are compound minerals, in which the metal is intimately
   mixed with other  substances, so as  to have neither the mallea-
   bility, nor the other qualities of the metals, except sometimes a
   degree of the shining metallic appearance.
     Frequently the ore is an oxyd of  tne metal, and only requires
 ,  the operation of reduction to be performed in  order to  give it
  the metallic properties. 
123       METALLIC SUBSTANCES....ORES.

   The ores of metals are commonly fund' in the veins of Che
hardest mountains, and hardest stony strata.  They are gene-
rally separated from the rock, being intermixed in the vein with
a  quantity of spar or quartz, or  sometimes a  softer matter.
When a spar involves the ore, it is in some cases a calcareous
spar,....in others a fluor; but more  frequently a  sulphat of
naiytes.   When the ore is involved in  quartz, it is sometimes a
pure quartz,  but oftener an intermixture of quartz with some
or several of the spars ; and often also we find intermixtures of
the spars without any quartz.  These matters,  thus accompa-
nying the ore in the vein,  are called in general the Matrix of
the ore, and  by the English miners, the  Rider.  The manner
in which the  ore and matrix are interspersed through the vein is
altogether  irregular.   In some parts  of the vein,  the whole
wideness of  it  is filled with ore;  in other parts, with  matrix
alone; in others the ore and matrix are found together, in all
the variety of proportions and modes of intermixture  that can
be imagined.  Such mixtures are called brangled ores.
   The ore being separated and picked out from the matrix to be
examined by itself, is commonly found to contain, not  only the
metal on account of which it is valued, but, aiong with it some
of the other  metals, and a considerable proportion of  sulphur or
arsenic, or both of these, and sometimes a small proportion of
earthy matter.
   These rhgredients are intimately united in the ore, that is, they
are chemically combined with the metal; and the operations by
which the  metal is extracted  are processes for separating these
matters from it.
   But before we can well understand  these processes,  it is ne-
cessary to have some knowledge of arsenic.  It will be found
to be a metal;  and it will he very convenient to make it the first
subject of our study. 
129
                       METALS.


               GENUS  I.....ARSENIC.

     Arsenic is a matter which resembles the salino substances
 so much by some of its properties, and the metallic by others,
 that the chemists were  long in doubt to which class it should be
 referred.   Dr. Boerhaave describes it among the  sulphureous
 minerals, probably on account of its being  often found in its
 natural state combined with sulphur.  But when the  arsenic is
 found pure, or is purified by art, it is widely different from sul-
 phur.
   The nature of arsenic was very little understood till  Mr.
 Macquer published some papers in the Memoirs of the Royal
 Academy, containing a number of experiments he had made on
 this mineral.  And more lately, Dr. Scheele, of Sweden, com-
 municated his instructive experiments on  it to the Academy at
 Upsal.
   The ordinary  appearance of arsenic is that of a compact
 heavy matter, of  a white or yellowish colour,  and having the
 glassy fracture, sometimes  transparent, oftener of an opaque
 white.- Exposed  to heat,  under the ordinary  pressure of the
 atmosphere, it becomes soft, or approaches to fusion, when very
 near the lowest degree of ignition.   But in the same heat also,
 it begins  to evaporate  in white fumes, of  a  sickening heavy-
 smell, thought to resemble garlic;  and is thus totally converted
 into vapour by degrees, without becoming perfectly fluid. The
 fumes, if  confined and condensed by cold, form a white powder,
 or chalky-like matter,  which  afterwards,  if the vessel be of a
 proper shape, is softened  and compacted by the  heat  into a
•whitish glassy-like substance.  It is always by  sublimation that
 it is brought to this form.
   The qualities,  by which arsenic  resembles the metals,  are,
 1st, Its weight.   2dly, A capability to  be  metallized, or to
 assume some  of the  metallic qualities,  such as  the metallic
     VOT,. III.                     R 
130
ARSENIC.
 opacity and bright reflecting surface, and a density  or specific
 gravity similar to that of the  metals.   It  also becomes  a  con-
 ductor of electricity, and fit for mixing intimately with the other
 metals, which it will not do in its ordinary state.
   It  may  be so far  metallized  by several  processes.   Mr.
 Macquer describes one in which this effect is produced by means
. of oil and sublimation.   I have succeeded equally well by sub-
 liming the arsenic repeatedly  with charcoal dust.
   But one of the best is Scheele's  process, described by Berg-
 mann.  White arsenic is put into a  crucible, with thrice its
 weight of black flux;  and an inverted, crucible  is luted to it.
 The lower crucible is set on the fire, and slowly raised to a red
 heat.   But the upper crucible must be defended from it, by
 means of an iron plate, having a hole exactly filled by the rim of
 the  lower crucible.   In this manner, the upper crucible will be
 covered  within  with a crust of regulus perfectly clean,  and in
 a crystallized form.   And  it  may be detached from it at once
 by a dexterous knock.
   Arsenic, when thus made to assume the metallic appearance,
 is quite brittle like several other metals, and its surface is liable
 to tarnish ; so that it loses its lustre very soon, if  exposed to the
 air.    Or if we evaporate it in  the open air, the vapour may be
 at once condensed into white arsenic;  also if sublimed with
 fixed  alkali.   By these processes,  therefore,  it returns imme-
 diately to its former appearance.
   These  several particulars give us reason to consider arsenic
 as a substance of a metallic nature  ; and to view it, when in its
 common  form, as in  a calcined state, or as an  oxyd of arsenic.
 But it differs from the oxyds of the  other metals,  by having
 qualities decidedly saline.  We have a clear example of this, in
 its solubility  in water, and in  its action upon the alkaline salts,
 and upon nitre.   The solubility of white arsenic in water  ap-
 pears, if  we beat it to powder, and boil it  in the water.   We
 thus learn, that it may be completely dissolved in fifteen  time9
its weight,  and from this  solution the arsenic  may be obtained
in the form of crystal:-.  Arsenic unites also with watery solu-
tions of alkalis, especially caustic alkalis, and  with lime-water;
 and  its volatility is somewhat  repressed by the union. 
                   ARSENICAL ACID.               131

   Its action upon nitre was thought the most remarkable, as it
 shews that arsenic may be employed to decompose nitre by ex-
 pelling its acid.   Equal parts of nitre and arsenic being mixed
 in fine powder, and exposed to heat in a retort, the  acid of the
 nitre arises very volatile and elastic, and of a deep red colour;
 and does not condense unless there be water in the receiver.  It
 tinges water a fine blue.   When the  whole acid is expelled,
 there remains melted a  white mass in the retort, composed of
 arsenic and fixed alkali,  which  dissolves  in water, and  easily
 crystallizes into very regular crystals.   It  melts  in a crucible,
 and forms a transparent fluid, and is very fixed, emitting no ar-
 senical fumes ; the arsenic appearing to be very strongly combi-
 ned with the alkali.   Again, the qualities of this compound are
 quite different from those of a compound formed  by combining
 white arsenic, with a pure alkali. It requires for its production not
 only the acid of arsenic, but so much of it as to make it acidu-
 lous and crystallizable. The other  compound is called by Mac-
 quer Liver of Arsenic  It might as well be called Arsenic a-
 ted Alkali. It has a particular weak but heavy  smell. If heated
 in a crucible,  it is not fixed like the other, but emits arsenical
 fumes in  abundance.  When dissolved in water,  it will not
 crystallize ; but, when evaporated, becomes pasty or gelatinous.
 Mr. Macquer was at a loss to explain how this happens,  parti-
 cularly why the crystallizable salt, formed by expelling the nitric
 acid by arsenic, should be different from  common arsenicated
 alkali ;  and why  arsenic  does not decompose common  salt,
 though it decomposes nitre.
  But the whole of this subject has been cleared up by  the ex-
 periments of Scheele, who made much more progress in disco-
 vering the nature  of arsenic,  and  has given  us principles by
 which all the phenomena are explained.  He learned,  by a series
 of instructive experiments, that one reason why  the crystalli-
 zable arsenical salt, and the common arsenicated alkali,  have
not the same property, is, that the arsenic,  in the crystallizable
arsenical salt, has undergone a change from the state of com-
mon white arsenic ; the acid of the nitre having acted upon it
as it does upon sugar and some other substances, so as to change
it into an acid.  Of this he gave the most satisfactory demon-
stration, by applying the nitric* acid to white arsenic by other 
 132    FORMATION OF ARSENICAL ACID.

 different ways, by which he changed it into an acid, which he
 obtained separate from any other matter: and  afterwards, com.
 bining  this acid with the vegetable  alkali in sufficient quantity,
 he formed a perfectly crystallizable arsenical salt.
   He contrived two processes bv which he changed white arse.
 nic into an  active acid.   The first of these is  entirely an imita-
 tion of  the process by which sugar is changed into an acid,  with
 this  difference only,  that some muriatic acid  is first employed
 to dissolve the arsenic, that the nitric acid may act on it  with
 more advantage.
   Scheele's process is as follows : Into a tubulated retort,  fitted
 with a receiver,  put two parts of powdered white arsenic, and
 seven of muriatic acid ;  and dissolve by a gentle boiling  heat.
 When all is dissolved, pour back what is in the receiver, and
 add three and one half parts aquafortis, and distil.   The nitric
 acid rises in red fumes, and after some time they cease.   Now
 add one part arsenic,  and one and a-half  aquafortis.   Red va-
 pours arise again.  Distil to dryness, and make the retort red hot.
   In the retort you have the arsenical acid,  fixed in the  fire, and
 deliquescent in the air, and soluble in twice its weight of water.
   Mr. Pelletier,  however,  says that we succeed equally well by
 using the nitric acid alone,  in the proportion of six parts of the
 acid to  one of the white arsenic.  The acid  comes off in red
 fumes of nitrous  gas, and the white arsenic assumes the  true
 characters of the  arsenical  acid (so it is now called.)   It  must
 be kept a good while in a strong heat, to expel  all the redundant
 nitrous acid.  (Fourcroy II. 507. Ed.  1786.J
   This is an exact enough account of the phenomena,  and per-
 fectly instructive  in the  nature of the operation.  But having
 practised both methods, I agree with Dr. Scheele,  that his pre-
 vious solution in muriatic acid enables the nitric acid to act on
 a much  greater quantity of the arsenical oxyd.
   The manner,  in which this process produces its effect  is suf-
 ficiently evident.  White arsenic must be considered as a  me-
 tallic oxyd, containing a very moderate quantity of oxygen,
 and capable of a higher degree of oxydation.   I always viewed
 it in this light ; and  on this principle, I explained Mr. Mac-
 quer's experiments, and the effects which it produces with ni-
tre ; a part of which is the change of the nitric acid into nitrous 
              ARSENIC....ARSENIXTS.             133

acid, in  consequence of the abstraction from it of a part of its
oxygen,  attracted by  the  arsenic.  In Scheele's process, the
nitric acid alone supplies oxygen to  the arsenic, and thus oxy-
dates it to the greatest degree of which it is capable ; in which
high state of oxydation,  the abundance of oxygen which it con-
tains, gives it the qualities of an acid, and deprives it of attrac-
tion for other acids, but disposes it to unite strongly with alka-
lis.  This is the  proper explication of the process according to
the  principles of the new theory ; and there is an experiment
described by  Scheele, which gives great support  to the French
explication  of the  phenomena,  and establishes  it  without a
doubt.   This experiment is made with the acid of arsenic.  If
some of this acid be put into a retort by itself, and exposed to
the  action of heat alone,  it endures a low red  heat  without
change,  or is only melted-   But if the heat be increased, and
continued, the greater part of the acid arises gradually into the
neck of the retort, in the form of a common white arsenic: and
while this happens, a very considerable quantity of oxygen gas
is produced or extricated from  it.  This is certainly a clear
proof, that a redundance of oxygen  is contained in the acid of
arsenic,  considered merely as an oxyd, since we see that when
a part of it is separated by the  action of heat, the acid of ar-
senic returns to the state  of white arsenic.
   I may add here, the mention of one process more for obtain-
ing arsenic in the state of an acid. It was discovered and com-
municated by Mr. Pelletier.   He performed Macquer's  process
but used the nitrat of ammonia in place of common nitre.  He
thus expelled the nitrous acid, which passed over in distillation
and  an arseniat  of ammonia remained in the retort.  But  by
changing the receiver,  and  increasing the heat, he was able to
make the ammonia or volatile alkali arise in a caustic state from
the arsenical acid, which remained in the retort.
   This acid is now called the Arsenical Acid:  and the com-
pounds  it forms with  other substances are Arseniats, in the
new language of chemistry.  Dr.  Scheele made a great number of
experiments with this acid,  by combining it with  other bodies,
and investigating  its properties.   He informs us that it has not
a strong  taste ; that it dissolves slowly  in water, but may be
dissolved in twice its  weight of that fluid ;  that in this fluid 
 134    VARIOUS RELATIONS OF ARSENIC.

 state it neutralizes the alkalis and alkaline earths,  and dissolves
 many of the metals, or unites with them, with particular phe-
 nomena, which he describes.  You may see all this in his Essays,
 and an  abstract of  the whole in Bergmann's  Treatise on Elec-
 tric Attractions ; and in Nicholson's Chemistry, article Arsenic,
   Scheele found, in attemping to dissolve some of the metals
 in the watery solution of this acid, that it oxydated them, and
 was itself restored to the state of  white arsenic ;  a proof that it
 does not retain the oxygen so strongly as to prevent its commu-
 nicating some of it to other  bodies that have a stronger attrac-
 tion for it.  We  have a more striking proof of  this in the result
 of several  of the experiments Scheele made  by causing the dry
 acid  to -jet upon  metals and  other bodies.  This acid is easily
 reduird *■> a dry  siate andean be  melted into a  transparent mat-
 ter,  like glass.   If some of  this dry acid is  beaten to powder,
 and  then mixed v/ith dry charcoal in powder, or with filings of
 different metals, and  these  mixtures are heated, there  is,  in
 many cases, a strong deflagration, su.h as is  produced by nitre
with the same substances : and the acid is in a moment changed,
partly into white  arsenic,  and  partly  into  pure or metallic
 arsenic, both  of  which are sublimed.
  Dr. Scheele  discovered that Mr.  Macquer's-  crystallizable
arsenical salt, prepared with nitre, is a compound not exactly
neutral, but is a little  acidulated by a small surplus of the acid
of arsenic : and when it is made exactly neutral,  it will crystal-
lize,  but is deliquescent. And he explains how it is,formed in
the process with nitre.
  When arsenic is in  its ordinary state of white  arsenic, it is
 soluble, in small quantity, in a variety of fluids.  Boiling water, I
 observed before, dissolves one-fifteenth or one-twentieth. Spirit
 of wine also dissolves a little  of it, and even oils. Aquafortis, or
 diluted  nitric acid, also dissolves it with difficulty, but changes it.
 more or less into acid  of arsenic.   The readiest solvent is mu-
 riatic acid,, which dissolves  oxyds of metals in general better
 than other acids do.   It forms a compound,  which can be dis- *
 tilled or sublimed ;  and sometimes condenses like oil.   Four-
 croy says,  that calx of arsenic,  that is, white arsenic  will not
 afford thisoil; but that it is easily  obtained from one part of me-
 tal' 'Z;d arsenic and two parts  of sublimate  of mercury.....th'j
 mercury being revived. 
                 ORIGIN OF  ARSENIC.                 "

   Arsenic has a disposition to mix in small quantity with earthy
 bodies in a vitrified state, or to act on them ; and this  is on * of
 its useful qualities, a good deal of it being employed by the m:
 nufacturers of glass.  White enamel is made with it, with which
 Delft ware is glazed; and  also all t; e pretty ornaments, which
 were formerly twisted in very beautiful scrolls^ in  the  stalks of
 wine glasses,  &c.
   Sulphur also can be combined with arsenic, as with the me-
 tals ; and  the compound is more fusible than arsenic alone.  The
 fusibility is increased by increasing the quantity of the  sulphur;
 and the colour is yellow, orange, or deep red.  It is called yel-
 low arsenic, and orpimcnt,  the {sandarac of the ancients) and
 realgar.   The dangerous powers of the arsenic are considerably
 abated in these compounds.  Hence it is that the Chinese, and
 other Orientals, form realgar into medical cups ; and employ as
 a purgative, lemon*juice whicji has stood some hours  in them.
 The sulphur can be separated again by  sublimating the  com-
 pound  with potash,  and by other processes.
   A,rsenic can easily be united with the metals in their metallic
 form,  but only when it is itself metallized.  The common way
 is to mix it with materials that will metallize it, and apply this
 mixture to the metal, with a proper heat,  in the form of vapour.
 It whitens them, and makes  them brittle.  One of the distin-
 guishing qualities of arsenic is that of uniting, when heated in
 any  inflammable mixture, with some of those substances, and
 flying off with  it.  Hence it is reckoned a purger or purifier of
 glass;  and is a powerful calciner, or scorifier of the metals.
 But it is no less hurtful, on the other hand, in metallurgy, by
 carrying the metals off with it; to prevent which is one of the
 great operations upon the ores in metallurgy.

            Origin, or  Natural State of Arsenic.

  Arsenic  is sometimes found pure, or in the form of solid me-
tallic arsenic,  but oftener more loosely concreted, like a grey or
black friable  matter.  But  pure arsenic  in any shape  is rare ;
though, in  the state of combination, there is plenty of it in ma-
ny of the ores of metals, especially those of cobalt,  copper,  sil- 
 136      NATURAL STATE  OF ARSENIC.

 ver, and iron.  In the white pyrites,  it is known by the garlic
 smell when struck.  It is most plentiful in this mineral, and in
 the ore of cobalt.  Existing in so many compounds, from which
 it may be expelled by heat, it abounds in volcanic countries. In
 Solfatara,  it contaminates every, volatile subterraneous produc-
 tion,  and is found in many of those forms into which we bring
 it in the operations of our laboratories.
   There are also natural compounds of arsenic and sulphur, cal-
 led orpiment and zarnic ; but the  greatest part of the orpiment
 in the shops  is artificial.  Arsenic for the use of the arts is pre.
 pared chiefly from cobalt ores and white pyrites,  in Saxony, as
 a  secondary  business  only,  in the  manufacture of zaffre  and
 smalt.   The arsenical  fumes are collected in chambers, which
 act as subliming vessels, as we shall see presently.  It is useful
 in the manufacture of glass,  and in dying.  Such,  therefore, is
 the history of arsenic, considered* as an object of chemistry.

   The knowledge of this  mineral is necessary to the physician,
 both on account of its great efficacy in the cure of some diseases,
 when it is properly used, and also on account of its noxious pow-
 ers, in consequence  of  which, it is sometimes given  with  the
 most criminal intentions.   In such cases,  the  physician is cal.
 led in to assist in forming a  judgment whether arsenic has ac
 tually been given or  not.
   It has long been one of the secret remedies employed by some
 empirical practitioners,....externally, for the cure of cancers,  and
 other obstinate ulcers ;  and internally, for the cure of intermit-
 tent and other fevers.   And the ancient physicians, in some of
 their prescriptions, employed some of the natural compounds of
 arsenic and sulphur.   In later times, the first example of its be-
 ing publicly recommended as a remedy  for the cure of fevers,
 is in the Memoirs of the Academy at Mentz,  for the year 1757,
 by a Dr. Jacobi.   But we are most indebted to Dr. Fowler for
 his late accurate trials of it.  They were conducted in the most
judicious manner, to secure exactness in the dose, and to ascer-
 tain the efficacy; of the medicine; and they are related  so fully
 and circumstantially, that  they  give complete  information  and
 satisfaction, with respect to every particular that is most inter- 
       ARSENIC....ITS POISONOUS  EFFECTS.   137

esting in the use of this powerful remedy. A better plan cannot
be contrived for ascertaining the powers and uses of the medi-
cines we employ.
  Physicians and surgeons are sometimes called upon, in cases
of supposed murder by arsenic, to give their opinion : and the
questions commonly put to them are these:
  1. Whether  the appearances or symptoms  observed in the
dying and dead person give reason to conclude that they were
killed with arsenic ?
  2. WJiether certain drugs or powders which were given to the
dead person, or mixed with his food,  and a part of which are
committed to the physician to be examined, be arsenic, or con-
tain arsenic ?
  It is necessary to be cautious in giving our answer to the first
question, which seldom admits of a perfectly decisive answer,
if the presumption of poison rests on the symptoms alone ; the
symptoms  produced  by arsenic being not unlike those which
appear in some  diseases, such as the cholera.  But these symp-
toms may add to the proof which may arise from other evidence.
  The symptoms produced by a dangerous  dose of arsenic be-
gin to appear in a quarter of an hour, or not much longer,  after
it is taken.  First, sickness, and great distress at the  stomach,
soon followed by thirst, and burning heat in the bowels.  Then
come on violent vomiting, and severe colic pains, and  excessive
and painful purging. This brings on faintings, with cold sweats,
and other signs  of great debility. To this succeed painful cramps,
and contractions of the legs and thighs, and extreme weakness,
and death.
  After.death,  the intestines are found inflamed and corroded.
And sometimes inflammations  and erosions  of the anus happen
before  death.
  In examining the dead body, we must take  care that we be
not deceived by the dissolution of the stomach by the gastric li-
quor, and account it an indication of arsenic.
  If we actually find arsenic in the stomach  or intestines, or in
the drugs or other suspected matters which were given to  the
dead person, we can give a decisive answer to these two ques-
     -nr..  tit.                 s 
138
MEANS OF DETECTION.
tions.  But we must make ourselves sure that what we judge to
be arsenic be really so.
   We must, therefore, take care- to be well acquainted with the
qualities of arsenic, bv which it is distinguishable from all other
substances.  And its distinctive properties are these :
   Imo, It is a heavy substance, which may therefore be separat-
ed by  skilful elutriation  from animal or vegetable matter, with
which it may happen to be mixed in the bowels or in the drugs.
Elutriation is commonly performed with water ;  but if  the
arsenic is mixed with oily or resinous drugs, it may be performed
with alcohoL  In examining the dead  body, therefore, it  may
be proper  to wash out the whole contents  of the stomach  and
bowels into a bason of water,  and then, by careful elutriation,
to try  if any arsenic can be found  in them.  And in examining
the drugs, if they be a mixture of different ingredients, we must
dilute  or dissolve them, by grinding them a little with water
or spirits,  and then elutriate.
   2do, Arsenic,  besides being a  heavy  substance,  is volatile.
When heated on a red hot iron, it evaporates totally  before it be  <i
red hot, and goes off in white smoke.
   3tio, It is easily metallized by mixing it with three times its
weight of  the black flux, and heating the mixture in a tube.
   4to, In this metallized state, it easily penetf ates copper, when
 assisted by heat, and. gives to the  copper a whitish col.Gfjar like
 that of lead or tin.   It  must be made of a dull red heat/  This
 will completely dissipate corrosive sublimate,  or other things
 which can whiten copper.
   5to, In its metallized state, if it be suddenly heated to a suf-
 ficient degree on a red  hot iron, it takes fire, and burns with a
 flame, from which arises a smoke, which is white arsenic.   Or
 if the iron be not sufficiently hot to make it take fire, it simply
 evaporates, and gives vapours which have an odour  like that of
. garlic.  The same odour is perceived, if we mix white arsenical
 with  an equal weight of charcoal dust, and throw a little of the  '
 mixture on a burning coal,  or on iron  strongly heated  so  as to
 set the  charcoal dust  on fire.   This experiment has been  often
 misunderstood. 
           POISON BY  ARSENIC-REMEDIES.     139

     Having had occasion some time ago to exercise  myself in
   these experiments, and  to try with how  small a  quantity of
   arsenic they might be made,  I found I was able, by  means of
   a small tube, to get metallized arsenic from one grain  weight of
   white arsenic :  and with this metallized arsenic I made the other
   experiments.

      Remedies to save, if possibk, the life of a person who has
                          taken Arsenic.

     The  first symptoms which the arsenic produces shew  plainly
   that for some time after it is taken, it acts on the stomach and in-
   testines,  as an highly irritating, inflammatory, corrosive sub-
   stance.   But if the patient survive the first violent effects, the
   poison being evacuated out of the bowels,  the symptoms which
   appear  afterwards are those of excessive debility, and  a great
   irritability  of  the  intestinal canal, and of the  whole system.
   The degree of debility is particularly remarkable.   It is evident
   not only from the languor,-distress, and feebleness of the patient,
   but also from the state of the  pulse.  I never felt a more feeble
   pulse than that of a person in  this situation.  All this  is attend-
   ed with a sort of paralytic affection of the limbs, and a degree of
   marasmus.
     The methods commonly recommended to save the life of the
   person*in the first of these states is, to give plenty of milk and
   oil, as obtunding remedies, and which help to  wash and carry
   off the  arsenic out of the intestines, while vomiting and purging
   continue.
     A better practice, however, might be  substituted for this.
   Arsenic being  a heavy substance, is not easily washed  out by
   milk:  and  it may  probably coagulate the  milk by its acidity.
:,  Oil will not mix with it  after it is wet.   I should prefer muci-
■-«,: lage, taken in large quantities: and if it do not pass off quickly,
   I would promote its passage by means of a purgative, such as
   Glauber's salt, or sal catharticus amarus. A friend of mine once
   gave whites of eggs with success.
     In the second stage of the disorders produced  by arsenic,
   which is commonly  of long  duration, a  mild  diet of milk 
140   METALLURGY....DRESSING THE  ORE.

is proper.   The frequent use of  opiates, to relieve from
constant distress, and after some time electricity,  are very
serviceable.   De Haen  found electricity one  of  the  best
remedies for the cure  of  the disorders occasioned by lead.
Mineral waters have been recommended, especially the sul-
phurous waters : and to imitate  these,  hepar sulphuris dis-
solved  in  water may be  employed.   But this practice  is
founded upon project and speculation, not upon experience.,


                     METALLURGY.

   The nature of arsenic being now explained, you are pre-
pared to  understand  the  operations by which metals are
extracted from their ores.
   The first of these operations is to separate the ore as much
as possible from the spar, or other stony matter that  accom-
panies it.
   When the ore is found in the  vein in large masses, or fills
ftp the  whole, or a considerable part of it,  many feet wide,
which is often the case, it may be  cut out tolerably clean, or
free from the adhering matrix: or, after it is taken out of the
vein, any part of the matrix that adheres to it, may be struck
off.  But,  in many  mineral veins, the  ore  is  interspersed
through the matrix in very small masses, and so entangled in
it, that they cannot  be separated in this way.
   The expedient to which the metallurgists have recourse in
 this  case,  is, to take advantage of  the great difference of
 specific gravity  between  the  ore and  the  stony or earthy
 matter in which it is involved.   They break  or bruise  the
 whole into small fragments,  like.gravel  or  sand,  and then
 expose  it,  upon a board or shallow trough,  to  the action of
 a small stream of  water running over  it with moderate  ve-
 locity, while the broken ore is gently stirred at the  same
 time.   The moving  water carries along,  and washes  away
 the earthy and stony particles before it can move the  heavier
 particles of the ore.  This is  called washing, or dressing  the
 ore :  in Latin,  elutriatio.  There are  many ingenious  and
  simple  ways of  performing this process, of  which you  will
  find a distinct account in Agriccla De re metallica.   This pro- 
CRUDE  SMELTING.             141
cess is easy,  when the ore is found in sand or earth, which
is often the case with regard to some  metals.   But others
are, in general, found in a solid matrix, not divisible by water
alone, or diffusible in it..  It must therefore be divided, or
broken down mechanically.   This is done, in some cases, by
flat iron  mallets,  or  by means of  stamping mills.    It often
happens,  too, that the matrix is much harder than the ore,
and then mechanical pulverization  alone will not  answer.
This difficulty can often be obviated, by burning or calcining
the mineral with a brisk fire of short continuance, and throw-
ing water on it  while red hot.  The effect of this upon the
stone or matrix is great, if it be calcareous or sparry, but less,
yet very considerable, even upon  quartz.  Thus, therefore,
this sort  of  ore, in  a reduced  state, can be pulverized and
dressed  with success.  But, although  the skill and address
with which this art is practised enables the miners, in many
cases, to separate the ore from very great quantities of the
stony  matter, some  ores  cannot be powdered and washed
without loss of some of the metal: and, where circumstances
are unfavourable, a great quantity is lost, in  consequence of
its being broken so small  that the water carries  it away.
Therefore, in  such  cases,  it is found  more expedient  to
procure  the  separation by  bringing the whole into  fusion.
This is  much practised in Germany, in the management of
some  ores, but very little, if at all, in this country.   They
perform the fusion in the ordinary furnace, and mix the ore
and stones of  different  kinds.  When the whole  is thus
hastily melted,  the ore, as it consists of metallic substances
and sulphur or arsenic in an uncalcined 6tate separates  from
the melted earthy matter, and is collected at the bottom.  It
also undergoes  some change by this hasty fusion.   Some of
the sulphur and  arsenic is dissipated ; and some of the more
calcinable metals are calcined and mixed with the  scoriae.
But it still retains so much of its impurities, that  it may  be
considered only as a sort of ore.   This operation is called
crude melting, or crude fusion.  It is not for all sorts of ore,
but only for those which are entangled with the matrix, so as
not to be  conveniently separable by washing, but capable of
perfect fusion by proper additions. 
148  METALLURGY....ROASTING....REDUCTION.

   When the ore is freed from all the earthy matter, which
can by this or the former operation be separated from it, the
next set of operations which it undergoes, are intended for
separating ihe sulphur, or arsenic, or both, if it contain them.
It is necessary to separate these with milder heat,  and the
action of air, before it be melted, on account of their strong
adhesion, and their occasioning  much loss of the metal, by
carrying some of it off in vapours, and also occasioning more
to calcine and mix with the scoriae.  The ore is, therefore,
first exposed to the action of a gentler redheat,long continued,
which is called roasting of it (ustulatio), most commonly in
heaps, with fuel intermixed, in the same manner as bricks are
burned.   Sometimes this is done in a furnace of a particular
structure, contrived with great ingenuity, for collecting and
preserving the  arsenic, and even some volatile and" very
calcinable metals, contained in  the  ores of that metal  for
which the whole process is chiefly carried on.
   Some ores require several repetitions of this process of
ustulation  before they  are sufficiently  freed from  volatile
matters.
   When these  operations are finished,  the metal  remains
more or less  calcined,  and therefore requires,  in the next
place, that the operation of reduction be performed.  This is
done in particular furnaces, of different structures, according
to the degree of heat necessary,  and the mode in different
places.   A considerable variety  are  described by Agricola,
from which those at present in use do not differ essentially,
except in the very large size, to which some are now  carried.
In these,  the ore is melted in contact with the fuel,  that the
whole of the oxygen and sulphur, still  combined with  the
me.tal, may be absorbed by the burning  fuel, and carried off
in the form of  carbonic acid and sulphurous  acid.  Proper
fluxes are also added for any earthy matters that  still  remain:
and also earths,  and even metals, are sometimes added, which\<i
still  more completely absorb the sulphur.  The desired metal^dj
thus freed from extraneous matters,  collects at the  bottom,
and  the earthy and sulphurated matter floats above as a scum
or slag.  This is let off, in some cases, by a tap-hole, at some
distance from the bottom.  In other cases, it is drawn off with
rakes, or driven off by the bellows. The melted metal is then 
METALLURGY....ASSAYING.
   let out by a lower tap-hole, in the great furnaces, or lifted out
   of the  small furnaces with ladles. The slag is, in many cases,
   rich in some  other  metal,  which has been  scorified in this
   process for the principal metal, and is worked off for  it in
   other furnaces.
     The next operation generally is refining the metals.
     Many ores either do not require,  or do not admit of all
   these operations, but agree  best with the  omission of  some,
   and variation of others, as I shall observe more particularly
   hereafter.
     In treating this  subject, it  is usual to mention the art
   of Assaying ores and metals,  which is  an assistant to the
   art  of separating metals  from  their  ores,  and  of refining
   them.   The art of  assaying is  the art of performing all the
   operations I have been describing, upon  small quantities of
   the subjects,  and in a very short time, in order to judge of
   the nature of an ore, the metal  it contains, the best manner
   of working it, and the profits it will yield.  It is also necessary
   to the  art of coining, and to the regulation of the  fineness of
   plate.
     The practice of this art  requires  the  greatest degree of
   attention and  accuracy in  the artist,  to  avoid the smallest
   loss  of any  part of the subject he  is  working upon, by
   any  mismanagement; as  a small loss of this kind  would
   occasion very great  errors  in the calculations of  the profit-
   ableness of working the ore, or of the value of the subject of
   the  assay.
     To describe the art of assaying would require much more
   time than can  be spared in an elementary course of chemis-
   try.   I must, therefore, refer you to those authors who treat
   it in the most judicious manner.  I need scarcely name ano-
   ther, after mentioning Cramer's Ars Docimastica.   He was a
   most excellent chemist: and his work is complete with res-
v';' pect to the docimasia via sicca.   Of late,  however, another
  .'-method of assaying,  via humid&, has  been much cultivated.
   The best writers on  this assay are Bergmann, Fordyce, and
   Woulfe.  Mr. Fordyce was, I believe, the first who'thought
   of this as a complete mode  of assay.   It certainly gives a
   more complete analysis than the dry way; but is too  tedi-
   ous  for the necessary dispatch of business. 
144         ASSAY  BY  THE BLOWPIPE.

   The dexterous use of the blowpipe is of unspeakable ser-
vice in the examination of ores and minerals.  By a proper
application of the flame, we can either burn off all  inflamma-
ble matter, or we can assist the substance on which it is di-
rected to unite with, or act on the  inflammable matter of the
charcoal on which it lies. When we envelope the body in the
blue point of the interior flame, the exterior flame keeps off
the air, and allows the combination with the charcoal to take
place,  and to continue.   But by directing the very point of
the flame on the body,  we consume all  inflammable matter
by the application of unsaturated air to it.  Therefore, when
we operate on metallic  ores, we can, in an instant, either cal-
cine or reduce the metallic part.
   The operations  of  metallurgy, in the  great way for com-
merce, are too various, and too complicated, to be described
and explained in an elementary course of chemistry, and at
any rate, cannot  be introduced at present; because, since the
propriety of  them depends on the nature of the various me-
tals contained in the ores, which is yet unknown to'you, you
could not understand the most perfect account of them.  On
this subject,  which comprehends  almost the whole of  our
science, you  must consult the Ars Metallica of Agricola, and
the Metallurgy of Schlutter.   From this last work, which is
a very excellent performance, Macquer has given  very good
extracts in the articles of his chemical dictionary.

   The very short account which I have now given  you of the
art of metallurgy was a necessary preamble  to the philoso-
phical study of the different metals, considered as the sub-
jects  of chemical  science.   It was, I confess,  somewhat
irregular to  include  arsenic,  one of their number, in this
preamble;  but so many of the metallurgies processes are per-
formed in order to get  rid of this troublesome ingredient,
which is not sought for on its  own account, nor  was  even •
thought metallic,  till of late, that we could not proceed $*
intelligibly  without  a  certain  knowledge   of  its  peculiar
qualities.
   I-shall  now enter professedly on the investigation of the
peculiar properties of the different metals, following, in each,
the method of treatment already familiar to you: and I shall 
                      MAGNESIUM.                 145

  conclude each article with  a  short account of its natural
  state, and the metallurgic processes for obtaining it in its
  purest metallic form;...processes which, although somewhat
  alike  in  all,  must yet be modified, in compliance with the
  peculiarities in the chemical properties of each.
    In  prosecuting this important part of the course, which,
  with pharmacy, constituted almost  the whole of ancient che-
  mistry, I shall take the metals in that order in which I think
  their properties  most easily explained.  This is almost the
  same with that of their disposition to be calcined or burnedi
  which are equivalent changes of  their appearance and pro-
  perties.   Of all the metals,  gold,  or platinum, is the most
  tenacious of the metallic form: and, on the other hand, the
  most calcinable or combustible of  them all, is the mineral
  called manganese, now found to be a metal, having singular
  properties, which are most curious  in themselves,  and are of
  great assistance to us in explaining and establishing some of
  the leading doctrines of chemistry.
     For these  reasons, manganese shall take the lead : and I
  shall consider the metals in the following order : magnesium,
  iron, mercury,  antimony, zine, bismuth,  cobalt,  niccolum,
  lead,  tin, copper, silver, gold, and platinum.  Having al-
  ready considered arsenic, I  now proceed to


              GENUS  II....MAGNESIUM.

    This is by no  means a rare production : and it has been
  long in our hands, and much employed,  although  its nature
  is but lately  understood.    It  often occurs  in our mines:
  few are  altogether without it;  and some contain very great
  quantities.    Its common appearance is a hard substance, of
  a grey colour, and  frequently of a chocolate colour, which
-may almost be called black.   It is easily known by  its soiling
:■•■' the hands excessively, like  a dark  brown greasy pigment.
  The Germans, for this reason, call it braun  stein.   It may be
  seen at every potter's kiln,  where it is  used for giving the
  black, or dark  purple glazing to the very coarsest of our
  earthen ware.   It  is  very  abundant in  Derbyshire,  in  a
  fossil called  black wad;  and  was, for awhile,  sold for a
        VOL. Til.              T 
146                 MAGNESIUM

coarse  pigment, till the  knowledge of  some of its  re-
markable  properties put  a stop to its employment in this
way.   For  its other varieties,  I  refer you to  Kirwan's  or
Cronstedt's Mineralogy.   It is  employed for tinging glass
purple, and to compose the  enamels that are used in deco-
rating the glazing of some earthen ware,  such as the tiles
with which our chamber fire-places were formerly lined,....
and indeed for the figures on much of the common kinds of
Delft ware.   It is also used for a purpose which seems the
opposite to these,  namely, for clearing glass  of all  colour,
especially  that  green colour  with  which it  is  generally
tainted.
   The chemists knew nothing  farther  about manganese.
They  supposed it to be an ore of iron,  but of a bad quality,
because little or no iron is obtained  from it.   Some, how-
ever,  have  long suspected that it was  a metallic c,alx, of a
peculiar kind, and by such curious naturalists,  it has been a
good  deal  tortured.  It has been described under various
names,....black wad in England ; braun stein among the Ger-  §
man miners ; in Latin it has been called manganesium, mag-  "'
nesium, magnesia nigra, &c.  Chemists  have now agreed to
call it Magnesium ; and under this name I shall speak of it.
    It is needless to mention the many vague and random ex-
periments which were made on it during the  nonage of che-
 mical science.  We never had any clear notion  of its proper-
 ties,  till Dr. Scheele took it in charge :  and he has given an
 account of his examination in an admirable paper, read to the
 Royal Academy at Upsal, and printed in the Transactions,
 in the Swedish language, from which it was  soon translated
 into  German, and thence into French, and here into English.
 Whatever  is the subject of  Scheele's examination, he shews
 in his investigation such an uncommon degree of industry, of
 ingenuity,  and of chemical  skill,  that you cannot  have a bet-
 terpattern for the proper conduct of chemical researches. I
 have  often quoted  this excellent  author, and shall yet often'^
 refer you to his ingenious dissertations.   To him, as I have
 said, we owe our first clear knowledge of this mineral.  But
 it was Dr. Gahn, another chemist of the same academy, who
 first demonstrated magnesium to be a metal, by reducing it
 completely to  the  state of a hard  and brilliant metal,  by
 
    IS USUALLY COMBINED WITH OXYGEN.  147

 treating it properly with charcoal  in a most violent and long
 continued heat.
   Magnesium has no volatility in its natural state.  But,  if ex-
 posed for a long time to a red heat, it suffers a considerable loss
 of weight.  If this be done in a proper apparatus, we obtain from
 it a prodigious quantity of atrial matter.   This,  when examin-
 ed,  is found to be vital air, of the purest kind,....when the mag-
 nesium itself is pure, which, however, is rarely the case.  It is
 frequently tainted with iron, and with  arsenic, and with earthy
 matters.   Carbonic acid, therefore, often taints the aerial pro-
 duct.   Many chemists  affirm also, that the purest manganese
 always emits azotic gas in the beginning of the experiment;  and
 that a stronger heat is necessary for  detaching  the vital air.
 This, however, is its most abundant product: and it is at pre-
 sent the substance from which it is obtained for most of our ex-
 periments, and also for most important purposes in the  arts.
   This effect of heat on magnesium induces us to consider it as
 a metallic oxyd, similar to many others very familiar to the che-
 mist ;  but it  differs from them in a remarkable circumstance.
 When this great quantity of vital air has been obtained from it,
 the remainder is of a much brighter colour than before : and in
 some, cases, *$n which we  have expelled the greatest quantity
 possible, it becomes perfectly white.   The oxyds  of other  me-
 tals are always of the deepest colour when the greatest quantity
 of oxygen has been taken from, them.       V
   When magnesium has been thus deprived of some oxygen, it
 speedily  recovers  it again, merely by exposing it to the com-
 mon air.  The rapidity with which it attracts the oxygen of the
 atmosphere, is indeed very remarkable. A few hours will some-
 times  suffice for restoring it to its former state of repletion with
 .oxygen :  and in thus recovering its natural share,  it also recov-
ers its natural colour, and becomes black as before.
   When oxygen, already in a gaseous form, is made to com-
 bine with  other matter,  there is always an extrication of heat
 and light.  The present case  is  no exception, when  circum-
 stances are favourable.  Wheri a considerable quantity of mag-
 nesium, which has been deprived of  its abundant oxygen, is
- exposed  to the air  in an extensive surface,  it recovers it with 
148
MAGNESIUM,
  heat, and  even incandescence.   It cannot flame,  because it is
  not  volatile.
    This  surprising  property  of magnesium occurred to Dr.
  Scheele  in the course  of his  examination.  Having exposed a
  quantity of black magnesium  to a red heat for  a quarter of an
  hour in a phial, the mouth of  which was stopped with a piece of
  chalk, he turned it out, still white  on a piece of paper.   It soon
  deflagrated,  and  became black.  If it was kept shut up till quite
  cold, and then turned out on a hot plate, it immediately became
  red hot.   It  does so in an  instant,  if loosely poured into ajar
  containing vital air ; and may be seen white, as it enters this air,
  and black before  it reach the bottom, when the jar is tall.
    These and other analogous  phenomena made Dr. Scheele sup-
  pose that black manganese  was a substance which had attracted
  phlogiston.  And this  opinion, natural to a chemical  philoso-
  pher of that  day, was confirmed by a series  of the most curious
  experiments, made by treating magnesium with the more active
  chemical substances. Of these the acids afford the most instruc-
»  tive phenomena,  which I  shall take pretty much in  the  order in
  which they occurred to Dr. Scheele, led by  the train of his spe-
  culations and conjectures, presuming that the procedure of such
  a mind will not be unpleasantto you.
    Magnesium, in its natural  black state,  dissolves in the acids
  but slowly, and with difficulty : and in some it does not dissolve
  at all.  I lately had occasion  to remark, that the metals,  when
  very much calcined, that  is, when combined with a great quan-
  tity of oxygen, have their attraction for acids greatly diminish*
  ed : and there are several  examples of their being thereby ren-
  dered altogether insoluble.  Manganese  in its  natural state is
  similar to those oxyds.   But  if some vital air be expelled from
  it by heat, or if it be taken  in  its white state, it will be dissolved•}
  in such as did not act on it in  its black state.                  •":'*
    The sulphuric acid is altogether inactive  on it in its natural
  state.   But if it be treated  with charcoal,  and made by heat to
  give out a prodigious quantity of carbonic  acid,....and if it be
  then put into  sulphuric acid, it dissolves very readily.   It is
  pretty much the same with  respect to the other acids. If strong
  sulphuric acid  be boiled  for fjome  time on black manganese, a 
    DISSOLVED BY  THE SULPHUROUS ACID.  149

 small portion is dissolved, the acid having expelled some oxygen
 by the  assistance of the great heat.
   If precipitated by a caustic alkali  from any of those solutions,
 it is always  white, or  at least,  is  far from its ordinary dark
 colour  .....and in this state it dissolves readily in all the acids.
   These facts  make  it clear that the solubility of magnesium
 in the  perfect mineral acids  depends greatly  on its  degree of
 oxydation.  It  is insoluble when the oxygen  is abundant, but
 soluble when this is diminished to a certain degree.  What pro-
 portion of the  abundant  oxygen must be abstracted, has not
 yet been ascertained with precision.  It appears also, that char-
 coal has a greater attraction  than magnesium for oxygen,....at
 least when its  attraction  is aided  by  the volatility of oxygen
 augmented by heat.   But there are some other circumstances
 in the  relation of magnesium to the acids, which are  not a little
 mysterious and puzzling.  Although the  sulphuric  acid does
 not dissolve manganese, the sulphurous acid dissolves a part of
 it very readily :....yet the salt is not  of the kind we expect from
 such ingredients ;....it is a permanent sulphat of magnesium :...»
 and if we precipitate the magnesium by an alkali, it is in its de-
 oxydated state.  Therefore the acid in it is not the sulphurous
 but the sulphuric, having its full share of oxygen.
   Perhaps this phenomenon explains the solubility.   The black
 manganese may be supposed to have a portion  of its oxygen re-
 dundant, while  the sulphurous acid is deficient  in oxygen.   The
 attractions may be supposed nearly equal;  so that when the acid
 has taken as much of the redundant oxygen as completes it to the
 state of sulphuric acid, this acid dissolves what part of the man-
 ganese has been  so much deoxydated  as to  become  soluble.
 This explanation is rendered very probable by the subsequent
 experiments of Dr. Scheele.
v' An ounce of aquafortis and twenty grains of  manganese being
 mixed, no solution follows.   But upon adding about a drachm
 of vinous spirits, and making the mixture lukewarm,  there is
 an effervescence and eruption of nitrous gas ;....and the manga-
 nese now dissolves completely: and after  this, four  additions,
 of twenty grains each, will be dissolved.  The mixture grows
 very hot.   I  imagine that the effervescence is  chiefly produced 
 150    MAGNESIUM....EFFECT OF  LIGHT.

 by the carbon of the alcohol, and partly perhaps by the oxygen
 gas or vital air.
   Dr. Sheele effected  the solution of manganese  in nitric acid
 in different ways,...by means of sugar, or essential oil, &c.  But
 a much more curious means occurred to  him.  He, and indeed-
 other chemists before him, had noticed the remarkable effect af
 the sun's light,  in blackening the vitriolic acid, and in  causing
 the pale nitric acid to become ruddy and fuming:  and they at-
 tributed this to the introduction of phlogiston, because  sulphur
 was produced, and because sugar produced the ruddy fum^s.
 Observing that sugar enabled the nitric acid to dissolve manga.
nes<, he tried whether the same effect might not be also produced
by  ihe  sun's light.  Pouring half  an ounce of nitric acid on
twenty grains of  manganese, and agitating the mixture, it  con-
tinued quite inactive.   He  then set the  matrass in the strong
light of the s in, on midsummer day: and in an hour's time,
he had a perfect solution.   He added twenty grains  more,
which were also dissolved,....and continued adding till no more
was taken up.   He precipitated the manganese  by means  of a
diluted solution of potash :  it was perfectly white.  He consi-
dered  it as manganese united with phlogiston  and  fixed air.
 He mixed it with one-fourth part of nitre, and gave it a red
 heat in a retort, and obtained a quantity of nitrous gas.   The
 nitre in the retort was alkalized.
   Reflecting on  these experiments, shewing the  solubility of
 manganese in pale nitric  acid  by means  of inflammable bodies
 or light, we  have reason to  conclude,  that these bodies act
 first on the nitric acid, producing their  usual effects, viz. ab-
 stracting or expelling a part of its oxygen,  and changing it into
 a  more volatile acid.  It then becomes  a solvent  for the man-
 ganese.
   But in whatever way we dissolve it, we always find it in a dtrM
 oxygenated or white state, when we precipitate it with an alkalies
 and in this state it will dissolve without difficulty, if done soon,....
 but if  allowed to remain some days, it becomes black and in.
 soluble.
   I  have called a portion of the oxygen combined with man-
 ganese rrdundanf.  It is  unquestiohably provided with it, to the. 
           MAGNESIUM KINDLES SOME OILS.     151

    very point of saturation ; and what has been last accumulated
    seems to be weakly united :  for it is easily abstracted from it by
    other  bodies,....particularly by some inflammable  substances.
    Of this we have a remarkable example, by mixing a quantity
    of black wad in powder, with as  much boiled lintseed oil as
    will just make  it stick together in clots.  If this  mixture be
    made  up into a heap, and set in a warm place, as on the  hearth,
    before a glowing fire, so as to become lukewarm, it will take fire
    in about half an hour; and it  deserves remark,  that this com-
    bustion is accompanied by a smell by no means offensive, though
    very strong.  It is somewhat aromatic,  and altogether  unlike
    the  smell  of lintseed  oil burning with a smothered heat.  I
    imagine that the redundant oxygen is combined with the oil,
    which we know to have a considerable  attraction for it, and to
    absorb a g*eat deal from the atmosphere.  This combination is
    accompanied by the extrication of heat in the same manner as
    in the  mixture of nitric acid with such oils.   Only, the oxygen
    of the magnesium is probably neither so copious nor so loose
    as in the nitric acid.  During this combustion, the  carbon and
    hydrogen of the oil fly off  with the oxygen of the  manganese,
    forming carbonic acid and water.  And the manganese soon
    recovers its abundant share of oxygen again, by exposition to the
    atmosphere.
      The mixtures of manganese with muriatic acid exhibits phe-
    nomena still more remarkable, and indeed  is  one of the most
    curious facts in  chemistry. ' When the common muriatic acid
    is applied to black manganese, it dissolves it, slowly  indeed, but
    easily, and in considerable quantity, and needs no  addition of
    inflammable matter..  But it adheres so feebly, that  even  water
    suffices for precipitating the greatest part of it, in its  ordinary
 >. form.   This easy solution made Dr. Scheele suspect that muri-
»- >"atic  acid, in its ordinary state, contained some phlogiston, natu-
^ orally combined with it, which reducec* the manganese to a less
    calcined state, and thus disposed it to dissolve so easily  in the
    acid.  This conjecture was confirmed by the phenomena which
    the mixture presented when  a gentle heat was applied to it.   He
    learned that a part of the  acid is greatly  changed from  its or-
    dinary state, and is  gradually converted into a penetrating va- 
  152    MAGNESIUM AND MURIATIC  ACID.

  pour, of a yellow colour,  and most  insupportable suffocating
  -.mell.
    This gas is one of the remarkable objects in  chemistry.  It
  is with difficulty obtained  in any other form than that of an
  elastic  a "rial matter,  having scarcely  any attraction for water.
  The  ordinary muriatic acid  gas has a strong attraction for water,
  and is, by this means, obtained in the ordinary form of a watery
  acid : but when distilled from black manganese,  it will scarcely
  unite with water, and unites only in very small quantity, and is
  easily separated again,  or  rather  is with great difficulty pre-
•• served  in a combined state.   A freezing cold, indeed, will con-
  dense it into a sort of soft  or solid matter,  but  when  the cold
  abates,  it  immediately reassumes- the gaseous form.   It may,
  however, be condensed, in consequence of its attraction for other
  substances, such as the alkaline salts, and especially the inflam-
  mable substances, such  as oils, animal and vegetable substances,
  some bitumens,  and  metals in their metallic state.  It acts so
  strongly on many of those substances as to inflame them.  Thus
  phosphorus, plunged  into this gas, takes fire immediately   Sul-
  phur  also, if hot enough to begin to melt, instantly takes fire.
  Even charcoal, if in exceeding fine powder(such as may be obtain-
  ed by washing the nitre out of gunpowdcr)when made warm, and
  thrown  looselv into this gas,  instantly kindles. I have met with
  some assertions that the  vapour of  alcohol also takes fire in it:
 but I  have not found  it so,  either with the vapours of  alcohol,
 or that of the vitriolic aether.  Nor have I found that it kindles
 some of those compound hydrogenous gases which are so ready
 to take  fire.  The abominably foetid gas, containing phosphorus
 and hydrogen, fires pretty readily in this muriatic gas,  but re-
 quires particular management,  and  a particular state of the in-
 gredients, which you will understand as we proceed.
   Most of these curious facts occurred to Dr. Scheele, although i
 in a more complex manner,  because he was not thoroughly in-*^
 structed in the  nature of this vapour.   But  he saw enough to
 make him conclude that the muriatic aeid,  in the state of a
 yellow vapour, is deprived of a part at least of the phlogiston
 which he supposed it  to contain when in its ordinary state. He
 also found reason to conclude that it lias  a strong disposition to 
SCHEELE'S  THEORY.            153
   reunite  itself to that principle ;  and in consequence of this at-
   traction, it acts on bodies which contain it,....and this with great
   vivacity, when they hold it in abundance, and but loosely com-
   bined.  He accounts in the same way for its action on the metals,
   by which it is eminently distinguished from the  common mu-
   riatic acid, which, as I  have told you, acts on them in a languid
   manner, if  in their metallic  form, though  it  dissolves  their
   calces very readily,....more readily indeed than the other acids.
     Induced by all these  facts, Dr. Scheele called  this vapour or
   gas the dephlogisticated muriatic acid.   We need not  wonder
   that he employed this language, and viewed the phenomena in
   this light; for, when he made and  published his  examination
   of manganese, the phlogiston was  every where admitted as a
   principle in  chemistry :  and Dr. Scheele was the very first that
   expressed any dissatisfaction with the simple form in which this
   doctrine  was  delivered  by Dr. Stahl.   I have already had oc-
   casion to  mention  the  ingenious and fanciful modifications of
   the original  doctrine of Stahl, which this excellent chemist at-
  tempted to establish,  but which he would have been the first to
  abandon, had  he pushed some of his own experiments one step
  farther.  I hold it,  therefore, to be unpardonable arrogance  in
  the French chemists to  say that no man can entertain the belief
  of the  existence of phlogiston who has  a grain  of common
  sense.  Scheele's dissertations, of every  kind, will ever stand in
  the first very rank of chemical writings.  By the natural progress
  of all knowledge that  is  founded on experiment, we have come
  to interpret  the many discoveries of Dr. Scheele in a different
  way.  But the discoveries remain the same ; and they are his,
  and resulted from deep and ingenious  meditation.  He con-
  sidered all the phenomena which  we derive from the privation
  or absence of  oxygen as proceeding from the addition or pre-
 sence  of  phlogiston:  and  he ascribed to the  abstraction of
 • phlogiston what we know to be owing to the acquisition of oxy-
:\gen.
    Since the time of  Dr. Scheele, all these phenomena of the
  muriatic acid  arid  manganese have been maturely considered,
  carefully investigated, and clearly explained, principally  by the
 chemists of  France.   We now  hold that  the change of  ap-
      yor..  in.                  u 
   154   MAGNESIUM....OXV-MURIATIC  ACID,

   pearance and properties which the muriatic acid suffers, depends
   on the addition to it of a  great  quantity of oxygen,  which it
   acquires from the  manganese.  For this reason, the muriatic  •
   vapour, which I am now considering, has acquired the name of
   Oxygenated Muriatic Acid.   Mr.  Knwan calls  it the
   Oxy-muriatic Acid.    You certainly recollect, that I have
   several times had occasion to mention a particular state of this aciq\
   in which it was surcharged with oxygen ;  and in consequence of
   this redundancy, had some singular properties. It was thus that I
   explained the process for preparing muriatic aether by  means of
   the smoking liquor of Libavius,  and several  experiments of    j
   Berthollet, establishing the constitution of volatile alkali, with
   other things of similar nature.   It was this preparation  which
   I then had in my thoughts.
     We have proof that the acid, in Dr.  Scheele's experiment of
   distilling it from  manganese, has abstracted  oxygen from that
   mineral.  Filtrate  what remains in the retort,  and add a very
   pure fixed alkali,....the manganese'is precipitated in the form of
   a white powder or mud ;  a sure  sign of its having lost some of
   its oxygen.  If the precipitate be hastily washed and dried, and
   then urged by a strong heat, in a  proper apparatus,  we  may per-
   haps still obtain some oxygen, by the extreme foiee of heat;
   but the quantity will be exceedingly small.
     I shall now  repeat, in a more comprehensible and instructive
   manner, what I formerly mentioned when I gave you an example
   of the manner in which the French chemists extended the doc-
   trine of Lavoisier to almost every chemical phenomenon in this
   world ;  namely, their account of the constitution and formation
   of the volatile alkali. When the pure or caustic alkaline gas
   is made to mix with the oxy-muriatic gas, there is an'immediate
   decomposition  of both.   The redundant  oxygen  of the latter
   seizes on the hydrogen of the volatile alkali,  and forms water ;,y
   the azotic  gas is set at  liberty; and the oxy-muriatic  gas i»;/'s£
   changed into  common muriatic  acid, by the  departure of the'' ?
»   redundant oxygen.   If we have  made use of a watery solution
   of the caustic volatile alkali, and make the oxy-muriatic gas pass
   through it, we have an effervescence, occasioned by the extri-    I
   cation of the azotic gas. All this was discovered by Dr. Scheele.
   and is related in his Essays. 
       ITS  VERY  SINGULAR  PROPERTIES.   155

   Some of  the French chemists,  and particularly  Mr. Ber.
 thollet, the most eminent of them, have followed Dr. Scheele
 in the investigation of the properties of this remarkable gas;
 and have made some very curious and important discoveries
 relating to it.
   I shall briefly mention some of its leading properties, re-
 ferring you for farther information to Mr. Berthollet's most
 excellent dissertation,  Observations sur quelques combinaisons
 de VAcide Marin dephlogistique,  on  de Pacide tnuriatique
 oxygene.   It is one  of the best pieces  of experimental phi-
 losophy that has appeared in any language.
   1. The oxy-muriatic gas retains its  affinity for alkalis; but
 wonderfully diminished, and modified by very particular cir-
 cumstances.   It unites, he  says,  with mild alkalis without
 effervescence.  I have not yet examined this with sufficient
 care, but am disposed  to doubt it.   It is scarcely possible to
 procure an alkali perfectly saturated with carbonic acid.   I
 never saw potash that  was so but once.  This gas contains
 so little saline matter, and its attraction is so  weak,  that it
 must of necessity attach itself in preference to such of the
 alkali as  is in a caustic state;  and I  apprehend that this may
 have been enough to absorb  the whole.   The  vast quantity
 of water also,  that is necessary for condensing the  gas, may
 absorb a great part of the carbonic acid that is really detached
 from the alkali : and  the fact  is, that  heat applied to this mix-
 ture will  detach much  carbonic acid from it.
   2. When  the oxy-muriatic gas  was condensed by a very-
 diluted solution of caustic potash, the alkali became  turbid,
 and deposited some  earth, and some saline  crystals.  The
 mixture being evaporated by a most gentle sand heat, afforded
 two salts,....namely, the ordinary salt of Sylvius, and another,
 easily separable from  that salt, because it  dissolves much
 more copiously in hot  than in cold water. When the process
 is well performed, we obtain about four parts of  salt  of Syl-
'vius and one of this  new salt.
   3. This salt has  many singular properties.   Its crystals
 are hexaedral prisms,  or more frequently confused laminae.
 It has an unpleasant  maukish taste  ; and raises a feeling of
 coolness on  the tongue, as nitre does.   It contains the acid
 in its highly oxygenated state.  An hundred grains of  the dry 
156       MAGNESIUM....OXY-MURIATS.

salt  yield 75 cubic inches of vital air by means of heat, and
yield it  more  easily than nitre does.   Mr.  Berthollet, ob-
serving the vital air so copious in it, and so loosely  combined,
mixed it with  charcoal, and tried whether this would detach
it by the assistance of heat.   It deflagrated  with  prodigious
violence :  and the acid was  not destroyed, but only reduced
to its ordinary form ;  for the residuum was the ordinary salt
of  Sylvius.    Therefore no oxygen had  operated  in  this
detonation, except the  portion obtained from the manganese.
Mr. Lavoisier found that 100 grains of the salt contains 37
of oxygen, which requires  14 of carbon to separate it, and
produces 51  cubic inches of carbonic acid.
   4. Mr.  Berthollet,  from  these and  other analogous ex-
periments,  infers  that all the oxygen which produced that
change in the  marine acid is  concentrated in this salt; and
that it Contains no other, nor any acid  in its ordinary state.
He therefore calls it the Oxygenated Muriat of potash or
of soda.   One part of this salt contains all the  redundant
oxygen that is furnished by six of oxy-muriatic  acid.  I may
remark that the nitrose acid, in its union with alkali, exhibits
phenomena pretty similar.    We obtain a true nitre, and a
nitrous gas.
   The union of the ingredients of this oxy-muriat  seems very
slight.   Exposition to the air seems to decompose the  acid:
for in a few  days,  or  even hours,  the salt  changes to the
ordinary salt of Sylvius.   This decomposition happens more
speedily in  a  watery solution of the salt :  and  we see  a
continual simmerirg on its surface,  by  the escape of minute
bubbles of elastic matter.   This  is increased by exposure to
the rays of the sun, so  as to be like an effervescence.   This
is vital air. of the purest kind.  It would seem that  the caustic
alkali acts too powerfully on the  ha si:;  of  the ordinary mu-
riatic acid, and thus dimi-Ti^hes its attraction for theoxygen; «,
or the oxygen exists in it, perhaps, in a semi-elastic state. Mr.?;'
Berthollet also thinks that the vast abundance of water neces» '
sary for absorbing  this p,as  prevents a closer union of the
acid and alkali.   lie found  that the combination  could not
be effected unless the  solution  of the alkaline salt be ex-
tremely diluted.    If this liquor be  evaporated,  preserving it
at the same time from the action  of light, or the naked fire 
         PROPERTIES  OF  THESE  SALTS.         157

   it undergoes,  at a  particular period  of the  evaporation,  a
   sudden  change, by which the above salt is formed;  and after
   this, neither the liquor, nor any of the salts which it affords
   by evaporation, are  possessed of the peculiar powers of the
   oxy-muriats.
      Dr. Scheele discovered in this oxygenated  acid another
   most remarkable property, namely,  a power to  destroy all
   vegetable and  animal colours, and even those which are most
   permanent, prepared for the purposes of dyeing.  It whitened
   or bleached vegetable  substances in  a  surprising manner.
   Mr. Berthollet first thought  of applying  it to this use ; and
   found that bees wax, brown linen yarn, and cloth, are bleached
   by it in a few hours or minutes, as effectually, and with as
   much safety to the staple of the goods, as if they had been
   exposed to the sun and air, with that intention, for as many
   weeks.
      In consequence of  this great  discovery, trials have been
   made, with a view to the employing it in the art of bleaching
   fine  linen, or cotton cloths, threads, and  light manufactured
   goods.   Mr. Berthollet has  published the process, as it has
   been practised in some manufactories in  France;  and  his
   account of it is translated into  our language*.
      The  first trial of it in the great way, however, was (ac-
   cording to  the best of  my information) made  in  Scotland,
   with the assistance, and under the direction of Mr. Watt, who

     * Therefore I need only mention here, that Mr. Berthollet produces the
   oxygenated vapour of muriatic acid, or oxygenates the acid, during its forma-
   tion.  He mixes,  in dry powder,  six ounces of black manganese with 16 of
   common salt.  A tubulated distilling vessel is prepared, whose pipe is inserted
   into a receiver with two necks ; and into the opposite neck is inserted the pipe
   which conveys the  gas into the vessel containing the liquor which is to absorb
   it, or the matters which are to be bleached by it.  This powder is put into the
   retort; and  then there is poured on it 12 ounces of strong sulphuric acid,
"•; diluted with nearly as much water; and the stopper is put in.  Gas is imme-
-':'.■ diately produced in vast abundance, and passes into the rest of the apparatus.
   The  two-necked receiver condenses the  ordinary muriatic acid; but the
   oxygenated gas passes on to the absorbing vessel.  No heat is  applied till the
   emission of vapour becomes very gentle.  The heat is cautiously and slowly
   raised to boiling, and continued till the two-necked receiver grows hot.  This
   finishes the distillation.  The absorption is promoted by churning vanes, which
   are worked  by some machinery.   Thus the absorbing  liquor  is more
   speedily and thoroughly  impregnated.  C'Annates de Cbvvn'e, t.  ii.) 
 158 .       NEW BLEACHING PROCESS.,

 had been at Paris, and had conversed with Mr. Berthollet,
 and immediately  formed the  design to try if the powers of
 this acid could be employed in practice ; for Mr. Berthollet
 had only considered it as a project in speculation.  Mr. Watt
 had an opportunity soon  after to make his experiments in
 the bleachfield of  a friend at Glasgow : and since that time,
 the process has been applied  to  this purpose in many other
 bleachfields.  It is best adapted, however, to the bleaching
 of thin goods, such as lawns, and fine muslins, and fine thread,
 and stockings.  These require less of the acid than coarser
 goods,  the thick and harsh  threads and fibres  of which  are
 penetrated with difficulty, and  also contain much colouring
 matter, which soon exhausts the strength of the gas. Attempts
 have also been made to bleach rags  for paper.   The  methods
 employed are frequently to wet the  matter to be bleached, by
 dipping it into water, while  it is at  the same time exposed to
 the \apour of the acid ; or  water which  has been  made
to absorb some of  the vapour is, applied to it; or it is steeped
 in a solution of  fixed alkali, or in lime-water, which has
 absorbed  some of  the vapour.   Such  solutions are  found to
 have the bleaching power, although the acid be saturated with
 alkali.
   Different methods are employed by different manufacturers,
 according to their notions of  their respective efficacy : and
 each manufacturer has his nostrum, which is a secret.   At
 present, none  of them, I believe, use the simple oxygenated
 acid, which was formerly prepared for  them, as a steep. The
 smelt which it occasions is abominable, and cannot be cleared
 from the hands for  many days.   The workmen therefore
 will- not submit to it.  They either use the vapour procured
 by Berthollet's process, with alternate dippings into water,....
 the whole of which operation is performed in a close  chamber
 by the  intervention of machinery ; or, more commonly, they
 employ solutions of alkali impregnated with the vapour.  A
 chemist in Glasgow has made  a great, improvement upon the
 whole  process by employing lime instead of alkali.  He
 thereby prepares the drug in a very concentrated, and even a
 solid state.
   Mr.  Berthollet's trials to  combine this volatile acid with
 fixed alkali have  also produced  some  other surprising dis- 
   DETONATION OF  THE OXY-MURIATS.   159

coveries. Observing how much the oxyd itself was disposed
to give out its oxygen to inflammable substances, and how
loosely it is combined in the  acid  over-charged with  it,
while this acid still  retains its relation  to  alkalis, he  tried
the effect of  the  neutral salts  produced by it.   When the
oxygenated  muriat  of potash is ground  in a  mortar  with
sulphur, small explosions happen under  the pestle, which
affect  the hand  of the  operator  like  an  electric shock.
And if hastily ground, with strong pressure, the whole will
explode.   Nay,  if  the salt alone be thrown  into sulphurous
acid, it will explode.
   Mr. Berthollet also examined, in the same way, the super-
ox^ genated muriat  of soda.  This deliquescent neutral salt
gives out its abundant oxygen by mere exposition to the air,
and changes  to common sea-salt.   When  treated in close
vessels, 100 grains yielded 75 cubic inches of vital air, of the
greatest purity, with much less  heat than nitre yields it.   It
was now a common muriat of soda.
   He  composed  a  gunpowder  with the muriat of potash:
and it was said to  be vastly stronger than the nitrous  gun-
powder.   Trials  were made  of it  at Woolwich ; and it was
found  that it was  really stronger in small charges.  But there
was no sensible  difference in great quantities  ; so that it
was not  thought worth while  to prosecute the discovery
further.*
   Such gunpowder  has qualities which make it inferior to
the common.  The very loose  combination of this oxygen
must cause the powder to become effete.   The residuum
of the detonation will be digestive salt, instead of the hepar
sulphuris left by the ordinary powder.  This will be  more
hurtful to the fire  arms  than fixed alkali.  It would  also
appear, from the accident which  happened in the prepara-
tion, that it is more disposed to explode in the operation  of
grinding.

   From  the  whole  of what I   have said  on this subject,
it appears that the  nature  of   the  muriatic acid is very

  • The oxy-muriat* of lime, barytes, and strontite-s, deserve a trial for a ful-
minating composition.....bbit«r. 
 160 MAGNESIUxM  COMBINED  WITH  ALKALI.

 singular,  when we  compare it  with the  other two  fossil
 acids.....These, when they  have  not the sufficient quantity
 of  oxygen, are more volatile than  ordinary.  And  their
 attraction  for  water  is  diminished.    The muriatic  acid,
 on  the contrary,  has its  volatility increased,  and its  at-
 traction  for water diminished, by receiving enough of oxy-
 gen.
   Dr. Scheele's experiments and reasonings have also shewn
 that there is a singularity in  manganese, when we consider it
 as  a metallic calx.   It is most  coloured, or darkest,  when
 most calcined ; and becomes white by abstraction of oxygen,
 contrary to other metallic calces.    And it gives colour  to its
 solutions, and to glass, when it is highly oxydated ; but  when
 this high degree of oxydation is abated, the colour disappears.
 The oxyds of other metals in general give most colour  when
they are least oxydated.   This  singularity in  manganese is
 finely seen by treating a small portion of it with the blowpipe.
 A small bit of  the sal  microcosmicus being melted on  char-
 coal by the blowpipe, if  a minute  portion of the black  man-
 ganese be added, the globule acquires a red colour, so  much
 the fuller, as we have added more  of this  oxyd.  If we keep
 this globule in  the middle or blue  part of the flame, where it
 is defended from the action of the air, the red colour vanishes,
 by the reduction of the calx by  the charcoal.  If we now
 direct the point or exterior part of the flame to the under side
 of the globule,  the effect of the charcoal is prevented, and the
 reduction already operated  is destroyed,  and  the  globule
 becomes red.   We may thus change the  colour as often as
 we please.  The smallest particle of nitre  being put to the
 colourless globule makes it red in an instant, by calcining the
 manganese.
   A globule of manganese and borax preserves its dark red
 or black colour under  this treatment, probably by keeping it
 from touching the charcoal.
   We have an example of the colour it gives in its highly
 oxydated state, in a watery solution of a compound of manga-
 nese and  fixed alkali,  analogous  to a liquor silicum.   This
 combination is  best  formed by mixing the manganese with
 nitre, and giving the mixture a mild melting heat. The  nitric
 acid is expelled by the heat, leaving the manganese well 
                CHAMELION MINERALE.           161

   stored with oxygen.   The alkali remains combined with the
   manganese; and forms with it a dark green or blackish mass,
   which is soluble in watef,.* and gives it a green colour.  We
   should perhaps account it a blue ;  because in a  day or two a
   yellow powder falls down,  and the solution is  blue.   The
   combination is but loose.  Water separates  it, first of a yiolet
   colour,....then red, which grows  brown,....and lastly  black.
   If sulphuric awd be added, to  separate the alkali, the solution
  becomes colourless,  the acid  dissolving  the deoxygenated
  manganese.   Such a variety of colours have procured to this
  solution of nitre alkalized by manganese the name oichamelion
  minerale.
     If we add a few drops of  a  solution of hepar sulphuris to
  the solution  of  manganese in  the fixed alkali,  it no longer
  exhibits the changes of colour.   It produces this effect  by its
  strong attraction for oxygen,  by which it deprives the manga-
  nese of that precise quantity which enabled it to  impart those
  colours.
    It would appear that manganese clears glasses of the yellow
  and green colours which  tinge  them, by yielding a quantity
  of oxygen sufficient for calcining the colouring matters. When
  too much  manganese  is employed,  after having discharged
  the  colours  produced by other metallic  contaminations,  it
  communicates its own colour,....a purple.*
   Liquid phosphoric acid, as produced by the spontaneous
  decomposition of  phosphorus without  heat,  dissolves  man-
 ganese, giving a fluid of a rich  red  colour.   If this be kept
 m a phial closely shut up, it loses its colour,...but resumes  it
 by exposing the whole to the air in  the  process of filtration.
 This may be  repeated as often as we please, and no matter is

   * This property seems tome to have been longer known than is commonly
 supposed.  Pliny says,  " Mox, ut est astuta et ingeniosa solertia,  non fuit
 " enntenta nitrum miscuisse.  Co:ptus addi et magnes lapis.-  quoniam in se
 " liquorem vitri quoque ut ferrum trahere creditus."  I think it probable that
 magnes lapis is manganese.  The sentence has no  truth,  if the loadstone be
 meant; for thhr destroys all beauty in glass.  Fossils were then little known :
 and Pliny was not a skilful foss'iWsl,....liquorem may be a corruption for colorem
or livarevi. He is speaking of the perfection to which the manufacture had
been brought; and says that the most valued was what was clear and colour-
less as crystal; and then he relates the above practice.
     Vot.'vMTI.                  X 
162  MAGNESIUM...ITS ACTION  EXPLAINED.

separated by the filtration.   This  is undoubtedly produced
by abstraction of oxygen from manganese, and restoration of
it by the atmosphere.           •
   Acetous acid dissolves the black oxyd ;  and,' in this state,
very readily produces aether, when treated with alcohol.   It
also gives most beautiful crystals, when employed to dissolve
copper.
   Mr. Milner of  Oxford  published a paper in the 79th vo-
lume of the Philosophical Transactions, giving the general re-
suit of a number of experiments  he  had made with manga-
nese, by makingit red hot, in tubes  of iron, or of earthen ware,
and forcing  the  steam  of  water and of other things to pass
over it, or through it: and  among these, he tried the vapours t
of  the pure  or caustic volatile alkali.   It always happened,
that when the vapour of this  alkali passed through the red
hot manganese, it was  partly converted into vapour of ni-
trous acid.  This effect was constant.  But he did not attempt
to examine and ascertain how  much of the nitrous acid might
be  produced from  a limited and known quantity of the vola-
tile alkali.
   This remarkable and interesting experiment is easily ex-
plained by Mr. Cavendish's discoveries, and the new theories
in chemistry to which  they have given rise.   He discovered
that watt-r is produced from  inflammable air and vital air;
and that nitrous acid can be produced from azotic gas (phlo-
gisticated air) and vital air.   Therefore, to understand Mr.
Milner's experiments, since we know that the volatile  alkali
is a compound of hydrogen and azote, we need only suppose
that part of it  is totally decomposed and destroyed by the
action of the oxygen  contained in the manganese.   Part of
it, uniting with the hydrogen,  forms water or watery vapour;
and part, uniting  with the azote, forms vapours of nitrous
acid.
   He observed also that the steam of water,  passing through
red hot manganese, promoted  very much  the  extrication of'
those  gases  which it affords by heat.'*

  * There is a rumour tiiat the Fi encli manufactured saltpetre during the late
v:u-, by obtaining nitrous acid from the vapours of volatile alkali, farced to
pass thrung!i red hot iriup-aiu- e. 
     MAGNESIUM IN ITS METALLIC STATE.  163

   Having mentioned the most important properties of this
 remarkable substance, we shouro next consider the methods
 of reducing it to its metallic state.  This has been but little
 studied ;  and its  metallic properties  are  very  imperfectly
 known.   The reduction of manganese to a regulus is a very
 difficult process.  This was first accomplished by Mr. Gahn
 of Sweden.
   A crucible must be lined with wetted charcoal, (rendered
 very dense, and  compacted by beating), leaving a small hol-
 low in the centre, to receive  a ball of the oxyd, made up with
 oil into a compact paste.   Charcoal is put in above it,  and
 well  compacted by beating: and another crucible is luted on,
 also  filled  with charcoal.   The most  violent heat must be
 given for an hour and a half.    A button is thus procured, of
 a dull iron colour, commonly rough on the surface.   This
 arises from minute  globules  of  manganese  less perfectly re-
 duced.  It requires even more heat than iron for its fusion :
 and no chemist  has been  able to join*pieces in this  way. All
 saline fluxes are found hurtful to the  operation.
   The metal quickly calcines by exposure to the air, and is
 soon resolved into a black oxyd.   To preserve specimens in
 a metallic state, it is necessary to varnish them; for even the
 air of a phial suffices for rusting it in  a few hours.  I have
 some suspicion that it absorbs azote  as well as oxygen, for I
 observe that it leaves a smaller portion of that gas unabsorbed
 than  any other process I have tried.   200 grains of regulus
 increased in weight 76 grains  in the open air.  Another 200,
 from the same mass, exposed  in vital air, increased only 65.*
 The specific gravity of magnesium is about 6,35.  It is quite
 brittle; and usually contains iron, which is not separated with-
 out extreme trouble.

  * This conjecture of Dr. Black's is corroborated by the observation cf Mr
Seguin, that black manganese yields azotic gas in low heats....editor. 
16-t
                 GENUS til.....IRON.

   After manganese, we are now  to consider iron.
   I choose to describe iron next, and among the first of the
metals, for many reasons.    It is the most abundantly pro-
duced by nature.   It  is also by far the most useful among
the metars and of the  greatest importance, by having a com-
bination of  properties, which make it an excellent subject for
the  ingenuity and industry of man to work on.  These pro-
perties are, a strong cohesion of its parts, by which it excels
all the other metals: and which,  in some states of the iron,  is
attended with great toughness and ductility ; in others, with
excessive hardness ;  and in others,  with great elasticity.*
In these different states, or intermediate ones,  it is excel-
lently adapted to different  uses.   We can also soften it by
heat, and thus work it easily, under  the  hammer, or by the
compression  of rolbrs,  into different forms:    and  when
strongly heated, different pieces of it can be joined firmly
together.   We can also have it  in a fusible state, and cast it
in moulds.
   Iron is singular among the metals, and  indeed all  other
bodies in nature, by being the only one affected by the mag-
net.    And as the  magnet can be made to communicate to
iron its own polarity, and other magneetic qualities, this me-
tal becomes thereby still the more useful.  Artificial magnets
can be made of it, far exceeding the natural ones in strength.
A very small magnet, turning freely on a  point, .is the needle)
of the  mariner's compass, and  pilots our ships through the
trackless ocean.
    While iron is cold,  though it be tough and flexible,  it is
too hard and  strong  to  be brought  under the  hammer,  as
 some metals are;  and, besides, it soon loses its toughness    J
when we hammer it strongly, its latent heat being thus  easily  jfl
 driven out  of  it.   It  retains its  latent heat and toughness  ;t|
 much better white it is drawn  into wire; and it can there-    1
 fore be drawn into very fine  wire.   Its  cohesion is greatly

   * An iron wire, of one-tenth of an inch in diameter, will carry 450 pounds.
 A copper wire not quite 300.                            A v liiop
% 
         IRON....IS VERY INFLAMMABLE.     165

increased by this operation.   When it is red hot, it is very
malleable, and almost plastic  like clay;  and can be beaten
by hammers, or compressed by rollers  into very thin plates.
   It  is  one  of the most refractory metals,  when  in  its
purest state.   The most intense fires can hardly melt it when
it is exposed simply to  the action of heat in close crucibles.
In its unrefined state, it can be melted easily, and perfectly,
by a violent heat, in  the temperature 17,977° Fahrenheit, or
130°  Wedge wood:  and the contact of the fuel increases its
fusibility.  Mr'. Lewis  says that gypsum has the sanre..effect.
   When pure or tough iron is heated to a white heat, 90°
of* Wedgewood, different  pieces of it can be made to cohere
and unite perfectly into one piece by hammering them into
close  contact.  This is a common operation of the blacksmiths.
They call it welding.  Some  sand, or  pounded  sand stone,
is thrown into the  fire  in  performing this operation.  The
sand  melts on the surface  of the heated iron, by uniting with
a little of the metal that is calcined ;  and forms a liquid
glazing,  which defends the metal from  farther  calcination,
and keeps the surface of the different pieces in  a condition
for uniting together, when they, are properly applied to one
another.   Sand is  of the same use here as borax  is in sold-
dering.   This liquid glazing readily flies away from between
the pieces, when they aTe  hammered into contact.
   The  only defects of this  metal are those of  being  too
easily calcinable, and too liable to  the  action of different
solvents.  It  is capable of being calcined so suddenly and
violently, as to give all the appearances of inflammation: As,
   1st, When heated to a white and dazzling heat, and sud-
denly exposed a to stream  or blast of air, brilliant  sparks are
darted from  it,  which the metallurgists call brandishing.
These are signs of  the iron being inflamed,  and calcining
rapidly.
  2dly, The fiery sparks produced by  the collision  of flint and
steel  are  another example of it.  They are small parts or rags
of the steel, torn off by the  flint.   By the violence with  which
they are  separated from the mass, and the extrication of latent
heat,  they are heated red hot; and in falling through the air,
are blown up into an inflamed state.  That it is not a simple ig- 
166           CALCINATION OF  IRON.
nition or incandescence, occasioned by the great heat generated
by friction, is evident from this, that if the same experiment be
made in fixed air, they are then seen just like so many ignited
particles of sand, and the light is seen only  in the very spot
where the  collision is  made : whereas the same sparks,  in free
air, are brightest when they have got to some  distance, and
seem to brighten by  degrees  as they recede  from the stroke.
Sometimes a brilliant  spark is not seen at all, till at a considera-
ble distance : and it branches and splits into two or three sparks.
Also,  when the two sets of particles are examined with a mi-
croscope,  those that were driven  off into fixed air are plainly
thin rags of metal, which have  been scraped off by the flint, and
rolled up into a sort of spiral ; whereas those, struck off into good
air are scorified and  blistered, and can be crushed to powder
between the fingers.   Nay, if a fine steel wire be twisted round
a thick one, and if the  whole be thrust red hot into a vessel con-
taining vital air,  the fine wrire  will take fire, and burn away like
a squib, crackling and brandishing with great brilliancy.
   3d/y, Similar sparks are produced by throwing  fine iron  fil-
ings through the flame of a candle.
   4thly, Larger masses of iron are easily made to Jburn  in the
same  manner, by heating them in vital air, or introoucing them
red hot into it.   It is  this violent inflammation that  makes the
spark of iron struck off by flint  kindle gunpowder with such ab-
solute certainty.  Were  it merely red hot when struck  off,  it
would be so much cooled  in its passage,  that it would produce
no such effect.   Other metals,  equally or perhaps more inflam-
mable,  will not do,  being too soft for producing the first heat
by the stroke.
   Iron, exposed to a mild heat gradually increased, is calcined
at the surface,  without producing any heat or light.   The first
phenomenon of this calcination  of a bit of polished  iron,  is the
appearance of rainbow colours on its  surface,  before the iron  is
red hot, but just approaching to that heat.   The succession of
colours is faint yellow, golden colour, purple,  violet,  and deep
blue, weakened insensibly to a  water colour, which is the last
shade distinguishable before it is red hot.   After this, a dusky
crust and friable scales appear.  When long calcined,  the colour 
         IRON....ITS CALCINATION....PvUST.      167

is deep red.    All the calces  of'iron, if much calcined,  are
either  dusky yellow, red, or purplish.   Hence  they are call-
ed croci.
  This succession of colours admits of a very satisfactory expla-
nation, by the  discoveries of Sir Isaac Newton concerning the
colours produced by transparent thin plates.  The colours suc-
ceed each other in that order in which they should follow, were
they produced  by a transparent plate, gradually increasing in
thickness.   Now we know that this succession of colours termi-
nates <in the production of a scale of calcined or  oxydated iron.
We  also know that the calces of metals are frequently transpa-
rent coloured glasses ; and,  in all cases,  compose  such glasses
by admixture with earths.
  When iron is thus calcined, the power of the  magnet over it
diminishes ;  and when the  calcination  is  carried to a certain
length, becomes imperceptible.  The scales are still  attracted,
but much more weakly than iron :  and if further calcined, there
is no more sensible attraction.   Nor is the rust, formed by long
exposition to the air,  or any of the natural calces or ochres of a
yellowish or  reddish colour, attracted sensibly, in the common
way of making the experiment.  They are easily brought back
again,  however, to a less calcined, or less oxydated state, so as
to recover the  black or dusky colour of the scales: and then
they are attracted by the magnet.   We need only  to mix them
with a little  charcoal dust,  or any animal or vegetable matter,
and make them red hot.
  Iron is not  only  dissolved by  several acids, but it is acted
upon by all the saline substances without exception. They either
corrode the metal, or dissolve the rust or  calx.   Water alone,
or moist air, has  considerable effect; and  is perhaps the chief
agent in all these corrosions.  It has, therefore, long been a de-
sideratum to preserve the  surface of polished iron from corro-
sion  by the air  and weather,  i. c from rusting.   The only me-
thod is to cut off the communication by some varnish.  Oily or
greasy  matters  are the fittest,  especially  such as harden  in the
air.  Pure lintseed oil, or hempseed oil,  is  therefore preferable,
when spread over the iron,  by rubbing it with  a  clean flannel
cloth dipped  in the oil,  and rubbed on so as to leave no sensible 
168        IRON AND SULPHURIC  ACID.
quantity.   The  very operation of polishing has a considerable
effect; for it is always by the means of cutting powders, rubbed
on with grease of some kind or other.  The blue colour produc-
ed by heating the iron is  also thought to defend it.
  All the acids act on iron, and dissolve it.  Even the carbonic
acid, especially if assisted by water, dissolves it.   For this rea-
son, it is usual, in the manufactories of polished goods, to throw
them into lime-water, or water having lime in it,  to preserve
them from rusting during the time that they are  in the hands of
the workmen.  The sulphuric acid dissolves the iron the most
re.idi'y and completely. But it must not be applied in its strong-
est  state.   It is necessary that a good deal of water be added at
the same time.  I had an opportunity not long ago to shew you
how the iron is dissolved by sulphuric acid thus diluted, and the
great quantity of inflammable air which is^produced during the
dissolution.  Thep roduction of this inflammable air is undoubt-
edly best explained by the  new theory of  the French chemists.
It proceeds from the water, which the iron decomposes.
  The proofs of this are,  1st, When we  force the  strong sul-
phuric acid to act on iron filings,  without  adding water,  but
simply by heat, we do not get inflammable air,....we obtain sul-
phurous acid.  And  the acid, deprived of part of its oxygen,
becomes sulphurous acid,  whicli does not act readily on iron.
This action requires a very great heat: and when the mixture
is distilled to dryness, we obtain a sublimate of sulphur, depriv-
ed of all the oxygen with which it formed the acid.L The solu-
tion of the iron, therefore, required more oxygen than was sup-
plied by that part of the acid which really dissolved it, and com-
bined with it.  Even this ruddy compound of acid and iron is
not  completely neutralized,  it being a very deliquescent salt;
whereas the green-coloured salt,  produced from a diluted acid,
even falls to powder by evaporation.
  2dly, Water alone can be made to acton iron, so as to pro-
duce inflammable air in great abundance.   Even in the ordinary
heat of the atmosphere, it produces  sdme inflammable air,  and
changes the  iron into a  rust or calx.  Iron filings,  digested in
pure water, are  converted into calx ;  and a quantity of inflam-
mable air  is produced.   To  plunge red  hot iron  into water, 
              IRON....DECOMPOSES WATER.        169

  causes a thick black scale to form instantly on the iron, and much
  inflammable air  is disengaged.   This scale  is  similar to  that
  which forms on iron simply heated in the air.   This, I believe,
  suggested to Dr. Priestley a mucn more  effectual way of apply-
  ing the water,  namely, in the form of steam, when the iron it-
  self was red hot.  It was sent through a porcelain or copper tube,
  in which iron wire is coiled up, and it converted the whole  into
  the same calx; and  inflammable air was disengaged.   Water
  consists of oxygen and hydrogen, the basis of inflammable air.
  It appears, therefore,  that the calx is produced by the decom-
  position of the water, which oxydates the iron, while the inflam-
  mable air escapes.
    When the diluted acid acts on iron, as the solution goes  on,
  a double operation seems to be going forward.   There is a co-
  pious formation of a black mud, which is of the' same nature (at
  least a great part of it) with the oxyd formed by iron and water.
  This  seems to be a different process from the saturation of the
  acid : for, if the 'acid has been but little diluted, the  solution
  stops, but is  renewed  by adding  more  water.   The water of
 the acid is  employed in forming the martial salt; and now the
 acid has not enough to continue this formation, till fresh water
 be added.  But the mud is an oxyd deriving its oxygen from
 the water only.
   When the sulphuric acid is saturated with iron, and the effer-
 vescence ceases, the solution is muddy  for some time, but at
 last becomes clear, and of a light green  colour.  The matter
 which made  it muddy is observed partly at the bottom, and
 partly at the top.   It is of a blackish colour, and resembles  the
 dust of what is called black lead, or plumbago.   Professor Berg-
 mann  analysed this blackish  sediment,  and found that it has
 really the qualities of plumbago, which had been analysed be-
 fore by  Dr. Scheele.   It is composed of carbon, united to a
 small quantity of iron.  If we take either black lead  of the
 finest kind,  or the black matter now spoken of,  and expose  it
 to the most intense heat in close vessels,  it suffers little or  no
 change.  But in open  air, it is all  consumed,  except an ochry
 calx, variable  in quantity.  But much of  it escapes, by being
volatilized without change.  It detonates with nitre,  requiring
    vol. in.              y 
Ko    VITRIOL....COPPERAS....COLCOTHAR.

 i very great proportion of nitre to finish the detonation entirely.
 We obtain carbonic acid by  this process : and the nitre, besides
 being alkalized, contains some ochre, and is greatly diminished
 in quantity.  It would seem that these things happen, because
 this combination of carbon requires a heat for its combustion
 so  much greater than charcoal does, that the nitre must be raised
 to so high a temperature that much of it is dissipated in vapour.
 Plumbago may therefore be considered as a species of  charcoal,
 which has  a small quantity of iron for its basis, instead of the
 small portion of earth and salt contained in common charcoal.
   To free  the solution  of  iron from this black matter, it must
 be filtrated, and then evaporated.  It gives green crystals, called
 green vitriol, or sal martis.  Great  quantities of it  are used in
 some of the  arts  by the name of copperas; but it is made by a
 much cheaper process.  These  crystals contain much water.
 They undergo the watery fusion and spontaneous  calcination.
 The matter which remains, after the  water is  evaporated from
 them, is called calcinedvitriol: and, according to the  degree of
 hea^ employed, vitriol  is calcined to whiteness,....to light  red,
 ....to redness,....and lastly, we  have colcothar of vitriol.   The
 heat applied enables the iron to act powerfully on the  acid,  and
 to attract  from it a part of its  oxygen.  Hence the  metal be-
 comes highly oxydated : and  in that highly oxydated state it has
 a deep red colour.   From this compound the vitriolic acid was
 formerly  obtained; whence  its  name.   And it is still used  in
 some processes,  in which  the action of the vitriolic acid is ne-
 cessary, as in the old process for aquafortis.
    I presume that you now see the propriety of considering vi-
 triol, and  other metallic salts, formed by an union with acids,
  as salts of a secondary order of composition ; one of their in-
  gredients, namely,  the acid, being avowedly a compound of
  oxygen and another base.   Hence arises the difference of the
  salts formed of the same metal and different acids.  We  must
  therefore  consider vitriol and colcothar as very different  frem
  the black ccthiops martialis3 from which the carbonic acid has
  been expelled.   This is a compound  of iron,  and oxygen: but
  colcothar  is a compound of iron, and oxygen, and sulphur*.
    • There is here some difference of opinion among the  chemists, or at least
  in the way of conctiving this circumstance.  By proper treatment, all the acid 
                IRON....IN  NITRIC  ACID, &c.        171

   The nitric acid, the next in order,  is seldom applied to the
 metals in its strongest state.   In that state,  it contains too little
 water to dissolve'the compounds which it forms with the metals.
 In dissolving metals with it, we commonly employ  it diluted
 with an equal quantity of water:  and in this diluted state it is
 called aquafortis.
   If we attempt to  dissolve iron  filings in aquafortis, in  the
 same manner as  when we dissolve  them in diluted sulphuric or
 muriatic acid, the action of the materials is rapid ; the mixture
 becomes hot in a moment; and there is an outrageous efferves-
 cence,  or a sort of explosion.  The acid is changed into elastic
 red vapours and "mcondensible gases.  The  iron  attracts  the
 oxvgen  of the acid  with too much violence,  and  in  too great
 quantity.   It decomposes too much  of the acid ;  and is  itself
 oxydated to so  high a degree,  that  it requires a very  large
 quantity of the acid  for its dissolution.   The acid employed is,
 therefore,  not  sufficient  for dissolving it, and the  iron  is only
 corroded.
   To dissolve iron well in this acid, we must moderate the ac-
 tion of the metal and acid on one another,  by  preserving them
 cool, and adding the iron very gradually, and with much  less
 surface for the acid to act on.   In this way, an ounce  of aqua-
 fortis dissolves only  26 grains, somewhat less than one-eight-
 teenth.
   There never is any inflammable air produced during this dis-
 solution of the iron in the acid of  nitre,  nor in dissolving any
 other metal in that acid. The reason is plain.   The iron, while

 may be expelled from the green vitriol by heat: and the iron is left combined
 with about one-half its weight of pure oxygen.   The name of colcothar^s given
 also to this oxyd by several eminent chemists ; while others consider colcothar
 as this very oxyd, with this dose of oxygen, but farther combined with a Small
 portion of sulphuric acid.  They consider green vitriol as another oxyd, hav-
 ing a much smaller dose of oxygen (about -?i) combined with  a much larger
 dose of sulphuric acid.  They think that iron has only these two states of  ox-
 ydation, and that the apparently different states in which we see it,  are only
 mixtures of these oxyds.  This doctrine or view of the matter is to be found
very distinctly expressed In" a dissertation of Mr. Proust on Prussian blue.
This variety of opinions is very embarrassing, when we read the explanations
given of other phenomena : and a theorist may often shift his ground in de-
scribing the internal procedure.....editor. 
 172          IRON....VOLATILE ALKALI,

 dissolving, is disposed to attract a quamiy of oxygen : but it
 easily obtains it from the acid.   The nitric acid abounds with
 this principle ; and contains it in a more loos^,  and separable,
 and active state, than the sulphuric or muriatic acids do in their
 ordinary form.   The iron, therefore, gets it readily from the
 arid: and no part of  the water seems to be decomposed, nor is
 any inflammable air produced.
   When the  iron is dissolved in this manner it first tinges the
 aquafortis of a fine green colour, and some thin red vapours of
 the nitrous acid make  their appearance.   And by afterwards
 gradually adding a little more iron, the acid becomes saturated,
 and will not dissolve  any more.   Then the red  vapours gradu.
 ally  disappear by  living away ;  and  the colour  of the solution
 changes to a  pale brownish yellow.
   The green colour,  which appears at first,  is therefore produ-
 ced by the presence of the nitrose acid in the solution ; since
 the  colour disappears  as soon as this acid has time to evaporate
 entirely.   You  no, doubt,_ remember,  that the nitrous  aciu
 afwavs gives  a green or blue tincture to  water with  which it is
 diluted ;  and that when this volatile  acid  is allowed to evapo-
 rate, the colour  disappears.
   You will now better understand  the reason of the  violent
 outrageous effervescence  which happens, when, in  place of
 taking this method, we throw a quantity of fine iron filings into
 the aquafortis.   The  acid is allowed, in this case, to act on a
 very extensive surface  of the iron, and'to come into contact
 with a great quantity of it at the same time.   It  therefore dis-
 solves a small part of  the metal,  and corrodes the rest with the
 greatest rapidity, or in a moment of time.   But  this rapid dis-
 solution and  corrosion  is attended  with two accidents: \mo,
 Thetsudden change of the nitric acid into  the nitrous acid, by
 abstraction of its oxygen ; and 2do,   With the extrication of a
 great quantity of latent  heat from the iron.  The mixture be-
 comes so hot in a  moment,  that the glass is too hot to be touched.
 This heat gives  great elasticity,  and a deep red colour, to the
nitrous acid vapour; and thus is produced that sort, of explosion.
  We cannot  obtain crystals from this solution by evaporating
it with that intention :  but I  have got remarkable crystals from
it by accident, of an amethystine colour. 
        THEORY OF  ITS  APPEARANCE.         173

    Chemists have often  observed a smell of  volatile  alkali
 in the decompounding metallic salts by fixed alkalis and by
 lime.  It passed unheeded, being attributed to impurities in
 the alkali or lime, which are known to be  generally con-
 taminated by a minute portion of volatile alkali.
    But, in the decomposition of a fresh-made  nitrat of  iron,
 this smell is very remarkable, if  the arbitrary circumstances
 of the experiment chance to be favourable.    Thus,  take
 two drachms of aquafortis, and dilute it with four of water,
 so that the action on the metal may be very moderate.  Dis-
 solve two drachms of clean iron  filings in  this diluted  acid,
 keeping all as cold as possible : and when the solution seems
 ended, add three drachms of slaked lime.   There will be
 little  effervescence during solution ;  and the lime will im-
 mediately occasion a very strong smell  of volatile alkali.
 The formation of this  gas is so copious that we can  even
 make its escape visible.   Moisten the inside  of  a  tall  glass
 (like a beer glass, or small cylinder) with oxygenated  mu-
 riatic  acid,  and  hold  this over  the mouth of the  solution
 glass :  and it will instantly be filled with a white cloud, and
 the sal ammoniac will fall down like snow.
    This is one of the most interesting experiments  in chem-
 istry,....and  eminently instructive.  There was not an atom
 of volatile alkali  in the  materials.  It must, therefore, be
 produced by a separation, and a new combination of simpler
 substances contained  in them.    We  can  now guess at the
 hidden process, by what we know of those materials.   The
 filings of iron decompose water,  by attracting its  oxyen, and
 set  the hydrogen at liberty.   We know also, that, by the
 same strong attraction for o>ygen, it decomposes the nitric
 acid, and sets  its azote at liberty;  or,  at least, in a state of
 redundance,  as an ingredient of  nitrous gas.   We da not
 know of any other substances being disengaged v/rom their
 former combinations  in  this  experiment.   It would   not,
 therefore, be unreasonable, though perhaps a little hasty, to
 conclude that these two substances have united, and  by their
 union,  compose volatile alkali.   Dr. Priestley, by passing
 the electric spark through volatile alkali a great many times,
 either extricated or produced  a vast quantity of hydrogenous
gas.   It is very true that Dr. Austin (Phil.  Trans. 1788) 
174       IRON....AND  MURIATIC  ACID.

could not combine those gases by heat, nor by the electric
spark, so as to produce ammonia.  But he could not expect
it, since the electric spark separated them.   Scheele found
that  when  metallic oxyds are reduced by ammoniacal gas, a
great quantity of azotic gas is extricated. His former experi-
ments did not permit him to say that it was produced; because
they had convinced  him that it is  a primitive substance.
Bergmann, therefore, was disposed to think*that volatile al-
kali consisted of the two substances, azote and hydrogen.
   Dr.  Austin could not combine the gases by heat. This is
not an objection.   Heat combines oxygen and azote in the
same manner as it  promotes all combustions.   But here is
no combustion.   There are many other examples where the
bases of the elastic gases combine, although the gases them-
selves  will not, being hindered by  their  combination with
caloric." I take this to be one.   The  two substances meet
in the very instant of  their extrication  from their  former
combination.   Dr. Austin succeeded, however, when only
one of the substances was in  the  gaseous state.  Iron filings,
moistened with  water, were put into a small  quantity of
azotic  gas,  confined by mercury.   The volatile alkali  was
produced.
   The  operation of the quicklime in the  experiment which
led me into this discussion is very evident.  It prevents the
instant union  of the volatile alkali with some of the acid;
or it decomposes the nitrous ammonia as fast  as  it is  for-
med.   The want  of this prevents  the  appearance of the
volatile alkali in every solution  of iron in nitric acid.
   On the whole, I  consider this as  a very distinct fact in
confirmation of Bergmann's  sagacious conjecture, and a cor-
roboration of  the proofs which  Mr.   Berthollet has given of
the s^amc opinion.    I have already mentioned several of
them, in my account of hydrogen,  drawn from a variety of
sources.   I believe  I forgot to  mention a very distinct  one,
which, I think, admits of no other explanation.   When the
vapour of oxygenated  muriatic acid is passed  through  the
pure vapour of volatile alkali, both disappear, and we get a
watery solution of common  muriatic acid, and a quantity of
 azetic gas ; and heat is produced.   The  redundant oxygen
of the muriatic acid attracts the hydrogen of volatile alkali, 
          IRON....AND  MURIATIC  ACID.      175

and forms water, setting the  azote of the alkali  at liberty.
There was nothing  else in the materials that could  yield
azote, nor any other way in which it could be detached.
   The muriatic acid dissolves iron with effervescence, occa-
sioned by the  production of  inflammable  air,  which is the
same in quantity and quality,  or very  nearly the same, with
that produced by the  sulphuric  acid  and  iron.   When the
iron is dissolved, and the acid is saturated, we have a solution
which has a green colour, like the solution in sulphuric acid,
and in which there is also  some plumbago,  which makes it
muddy, and must be separated by filtration.   To  have these
phenomena in the best manner, use the following proportions:
Iron,  one ounce; muriatic acid, six ounces (equal in bulk
to  5\ of water); and  add  2\ ounces of water.   Thus  we
have  it of a clear green.   It readily  affords crystals of  the
same  colour.
   These crystals are not affected by heat in the same manner
as the vitriol or sulphat of iron.  We can gradually expel the
sulphuric acid from iron, by the force of heat: and the iron
remains in the state of an oxyd. But when we attempt to expel
the muriatic acid in the same manner, a great part of the iron
is volatilized by it.   Thus, if we expose a compound of iron
and mutriatic acid to heat- in a retort, and gradually increase    ,
the heat to the greatest degree wbich  the retort can bear, no
part  of the  acid arises pure : but what rises first, however,
is less charged with iron, and condenses into a  yellow liquor.
What follows  this is combined   with  more iron,  and con-
denses into shining deep  yellow or black scaly crystals,  in   k
the neck of the retort.   In the bottom of the retort remains
a  mass,  concreted  into scaly crystals.*   It  consists of  a
greater part of the iron,  retaining a portion of the  acid,
but not enough to give  it volatility.    All  this agrees with
other  phenomena, in shewing that metals have  a  stronger
attraction for  the muriatic acid  than for either of the other
two fossil acids.

  * This sublimate is deliquescent.  When mixed with thrice its weight of
sulphuric aether, and digested, the aether takes all the colour to  itself.  Seven
parts of alcohol added to this, forms Bestuscheff's drops, a medicine of high
character on the'Continent.  It becomes colourless by a fevr minutes exposure
to ttie sun's light....iditor. 
  176  IRON....ACIDS DISSOLVE  ITS OfcYDS.

    The  muriatic  acid dissolves iron readily also,  when this
 acid is  combined with  water in its oxygenated state:  but
 then there is no effervescence of inflammable air.  The only
 effects produced are, that the  iron is calcined and dissolved,
 and the  acid returns to the state of common muriatic acid.
 The solution is, therefore, not  different from one produced
 by dissolving iron in common  muriatic acid, excepting that
 no inflammable air is produced.   The reason  is  evident.
 The oxygenated muriatic acid  contains plenty of oxygen to
 satisfy the  attraction of the iron  for this principle.   No
 part  of  the water therefore is decomposed, nor any inflam-
 mable air produced from it.  In this respect, the  oxygenated
 muriatic acid  is similar  to  the  nitric acid,....in the action of
 which upon metals inflammable air is never produced.
   Thus, I have described the action of the three fossil acids
 on iron, when applied  to this  metal in its  ordinary metallic
 state.   If the iron be previously calcined before  these acids
 are applied  to it,  it can  be dissolved by them  in  this state
 also, but with  more difficulty,  and in less quantity; much
 more acid being required to dissolve an  ounce of  calx than
 an  ounce of iron.   And  such  dissolutions  are performed
 without  effervescence,  except when the  calx happens to be
 combined with carbonic acid.
   The muriatic acid dissolves the calcined iron  better than
 other acids.   But even  of  this acid a much greater quantity
 is required to dissolve  calcined iron than  metallic iron, and
 always a greater quantity in proportion as the iron is more
 calcined.  The  colour of the solution also is different from
that of the solution of metallic iron.   Instead of being green,
it is yellow.   There is no inflammable air produced «pn this
occasion; nor is it to be  expected :  for the iron being used in
the state of a calx, or already combined with oxygen,  has no
power to attract oxygen from the water, or to decompose any
part of it.
   This yellow colour, which is very like that of the solution
of gold,  has often misled visionary and  ignorant^ chemists,
and made them  imagine they had discovered gold in earths
and stones, and  other minerals,  of which  there are a great
number containing iron  in the  state of a calx, and therefore
disposed to dissolve in muriatic acid, and to tinge it of the
 same yellow colour. 
  ITS OXYDAT. CONTINUALLY INCREASES. 177

   The vegetable acids act also on iron, and by uniting with
it, give it a solubte saline form.   But they dissolve it much
more slowly than the fossil acids, and reqtiire to be assisted
by digestion.   They produce solutions  of a green colour  at
first,  but changing,  by time and the action of the air, to a
russet, or rusty colour.   This, or some similar  change of
colour, happens to all the solutions of  iron, when they are
kept for some time, and especially if they are exposed to the
air.    And if they were saturated with the iron at first, they
are sure to  deposit a part of it, in the form of ochre,  or of a
rusty  coloured  calx.   Fourcroy  says that the calx of iron,
dissolved in the acetous acid,  gives us a solution of a fine
red colour.   The separation of part of the iron in this man-
ner is much promoted by boiling  such solutions in an open
vessel, or by evaporating and diluting them repeatedly.  By
adding more acid,  we  can in most cases redissolve the iron
or calx, which is  separated, and make the  solution clear
again.
   I  have been long accustomed to explain this separation  of
part of the iron from  its solutions and  change  of colour
which these undergo, by  shewing that it proceeds from a
farther oxydation which happens to this metal after it is dis-
solved.   During the  effervescence which appears while the
iron is dissolving in the sulphuric  or muriatic or  acetous
acids, this  metal  is  oxydated to a  very moderate  degree
only ;  but after  it is dissolved, it undergoes a farther oxy-
dation.  The dissolved iron continues to act still,  though
much  more slowly than at first, upon the water, and to attract
oxygen from a small  part of it, or perhaps from the air con-
tained in  the water.   And the iron, by becoming more oxy-
dated, has its attraction for acids diminished.   It requires a
greater quantity of the acid to  keep it dissolved.  Hdftce
the quantity of acid which was sufficient at  first,  is  insuffi-
cient  afterwards : and some of the most oxydated  part of
the iron separates in form  of oehre or calx.
   That this is a just  account of the phenomena, is  proved
by several facts.   1st, Recent solutions of metallic iron emit
an odour of inflammable air, and continue to emit it, though
not so strongly, for a long time after they are made.  2dly,
Changes of colour, which happen in them by keeping, are
    vol.  III.                 z 
178     IRON....OCHRE....IRON-MOULD, &c.

always such as to end in the colour produced by dissolving
a calx in the same acid.   3dly, An old solution, which has
suffered  this  change  of colour,  will  resume  its  primi'ive
colour, if sore fresh iron be dissolved in  it by means or a
little  additional  acid.    1 he  fresh iron,  while  dissolving,
reduces the other to a less calcined state,  by taking iiom it
a part of  its oxygen.   4thly,  The calces of iron,  otherwise
produced, are well known to be less dissoluble  than iron.
They require a greater quantity of acid to dissolve them,  in
proportion as they are more calcined.  And they have much
less attraction for acids than iron has which is less calcined.
   From  this change which happens to the solutions of iron,
you will easily understand  the origin of the great quantity of
Ochre,' or yellow calx  of iron, which  mineral springs,  con-
tafning vitriol of iron, deposit in their course.   In the same
manner is produced the durable yellow stain which all the
solutions of iron leave upon white cloths, on account of which
some are used in painting linens.   The metal is introduced
in a dissolved state into the very substance of the fibres : and
there, bv the action of air, which calcines it to a great de-
gree, it is deposited in the form of  ochre, which never can
come out until  it is again dissolved.   This also points out
 the proper method of removing those stains, viz. by apply-
 ing  such acids  as  can safely  be used  to redissolve the iron.
 The muriatic acid is the most  powerful dissolver of the calces
 of iron:  and  when  applied weak, effectually takes  out the
 stain, without injuring :he cloth in the least.  Some vegeta-
 ble acids also, such as the acid of tartar, are very effectual.
  A.nd even the sulphuric  acid may be used for this purpose,
 if applied  with  caution, and in a  proper state  of  dilution.
 The nitric acid has  little action Upon  the calces of iron.
  It*»s rather disposed to render them  more difficult  of solu-
 tion; and  is actually employed for this purpose in some pro-
 cesses.
    You will also understand  the propriety  of the process
  given in the last edition of the Edinburgh Pharmacopoeia for
  r'mc.iura Martis.*
    Alkalis, in their ordinary state, shew little power to act
  upon iron.   We commonly  evaporate watery  solutions of
                     .  • Vide Dispensatory. 
         ACTION OF  ALKALIS  ON  IRON.      179

the alkalis in iron vessels, when we wish to have the alkalis
in a dry state:  and they neither corrode the iron,  nor are
sensibly tainted by it. If we add alkalis to solutions of iron in
acids, they precipitate the iron.  If the sulphat of iron be re-
cently  made, the precipitate is bluish green.   It is in that
state of very moderate oxydation to which the  iron was re-
duced during-its dissolution.   But if it stand a while exposed
to the air, or when the water in which the precipitation is
performed contains plenty of good or respirable air,  the pre-
cipitated metal attracts more oxygen, and changes its colour,
ami  becomes ochry or  rusty coloured.  Scheele foucd that
the rapid exhibition of this colour was the surest test of the
pr-stnce of vital air in water.   (On Fire, &c. No. 94.)   It
is evident  that the yellow colour which the oxyd assumes, is
in consequence  of its becoming  more oxydated, or absorb-
ing more vital air.   It is  also very much disposed to absorb
carbonic acid, when in this  state.
   In some cases of the precipitation of iron by an alkali, the
precipitate can be re-dissolved by adding more  alkali.   The
most noted example of this is in the precipitation and redis-
solution  of the nitrat of iron.  The blood red solution thus
obtained is called the tinctura martis alkalina of Dr. Stahl.
   But  among  the most remarkable  effects  produced  by
alkalis on the solutions of  iron, are those of the Prussian
 Alkali, or Lixivium.Sanguinis.

                    Lixivium Sanguinis.

   This is  a preparation of alkali discovered by a Prussian
 chemist named  Diesbach.  He evaporated blood to dryness,
 and mixed it with half its weight of fixed alkali  : and roasted
 or charred the mixture with a strong heat, till little  Or no
 more fumes arose from it.   He dissolved this charry mat-
 ter  in Vater ; and filtrated the solution, which had  a deep
 brown colour, and a strong disagreeable smell.  When the
 lixivium is thus cleared  of impurities, and brought to  a pro-
 per degree  of  concentration  by boiling, it is then- called
 Lixivium  Sanguinis, Prepared Alkali,  and Prussian
 Alkali. 
180           IRON....EXAMINATION
  If this lixivium be dropped into a fresh made solution of
iron in sulphuric acid, to which a few drops of muriatic acid
have been previously added,  we shall see  each  drop of the
lixivium produce  a f^cula of  the  most rich and  beautiful
blue, which  will slowly descend  to the bottom, and there
collect.  It  may be separated by decantation,  and repeated
washings with water.    Without  the muriatic acid,  it is
gentrdly tainted with a brown or yellow ochry matter.  I his
ijct^a is manufactured for a pigment, by the name of Prus-
S1AN i l  E.
   The unost minute quantity of iron in a  mixture becomes
discernible by this addition, which is therefore a trial of the
presence of iron in mineral waters.
   The colour of this precipitate  is  not liable to fade in the
air ; neither is  it altered by diluted acids.   It manifestly
depends on  a matter which is joined to the iron, and preci-
pitates with it ;  the  iron having received it from the alkali by
a double elective  attraction ;  the  alkali  combining  at the
same time with the acid which had dissolved the iron.  These
are the manifest facts.
   This is further proved by an experiment described by Mr.
Lewis, in his Materia Medica, and also by Macquer.   In this
experiment' this blue precipitate is decompounded by digest-
ing it.with  a dissolved alkali.  The iron is suddenly deprived
of its  colour : and the alkali shews that it has attracted a part
of the tinging matter, for  it will now precipitate iron blue.
This shews that a particular  matter is combined with the
iron in the blue precipitate, which matter  can be taken from
it and restored  again.
   A careful  examination of the phenomena in this  experi-
ment  shews that, on the one hand, the alkali poured on the
Prwpian blue n#t  only  abstracts the colouring  matter, but
also dissolves some of the oxyd of iron ;  for an acid added
to it will make  it deposit some Prussian blue.   This seems
to  happen, because the added acid first dissolves this oxyd,
and the solution is immediately acted on by  the Prussian
alkali, and thereby precipitated blue.
   On the other hand,  there is the same  evidence that the
ochry matter left by the  alkali is not an ordinary  calx ;  for
when an acid is poured on it,  we  have  a blue  precipitate. 
           OF  THE PRUSSIAN ALKALI.       '181

Mr. Berthollet says, that after repeatedly  washing the calx
left by the alkali, with*water, which comes  off clear, we still
at last obtain a blue precipitate.   How this is produced will
be explained afterwards  :  but in the  mean  time, we see that
some of the tinging mattey remains combined with the iron.
   Therefore the alternate treatment with  acids and alkalis,
and  the concomitant production and  removal of the blue
precipitate, must have a period.  We shall  see presently that
the colouring matter is ultimately decomposed by this treat-
ment.
   But we have also learned by experiments, that there is not
enough of this matter in the lixivium sanguinis, as it is usually
prepared, to convert the whole of the precipitated iron into
blue precipitate ; and that a good deal is in the state of an
ordinary oxyd.   Hence  we perceive the  use of the muriatic
acid in preparing the blue precipitate.   It is  necessary for
re-dissolving that part of the iron which  is precipitated in
the  form of  ordinary  calx,  and which spoils the  colour.
There is no danger that the  acid will dissolve any part of the
blue precipitate.  It  resists the action of acids in their diluted
state.
   The nature of this matter, which is joined to the iron in
the blue precipitate,  is singular and  surprising.   It appears
to be a  sort of  ammoniacal  compound.    It  contains  a
volatile alkali,  intimately  combined with a very  peculiar
volatile matter, which is inflammable  ; the vapour of it readily
taking fire; while at the same time, it partakes also of an acid
nature, or has an attraction for alkalis, alkaline earths, and
metals.
   But when this acid sort of matter  is combined with alkalis
alone, it adheres to  them with a force which is very weak.
It diminishes very little their alkaline qualities ; and is-ejfeily
separated from them by the  weakest  acids,  even by fixed air.
There is only one way by which it  can be made to  adhere-
strongly to the alkaline salts; that is, by  adding to the com-
pound some of the metallic substances, particularly iron very
slightly oxydated.   A small quantity of the iron is dissolved
by the compound of  alkali and tinging matter ; and thus is
formed a compound of three ingredients,  all of which cohere
together much more strongly than the volatile tinging matter 
182          IRON....MANUFACTURE

and the alkali did before by themselves.   Mr. Macquer first
gave us somewhat of a distinct notion of it, by demonstrating
the double exchange which happens in the formation of the
blue  precipitate.    Dr. Scheele  discovered  the  particular
substance in  which the  colouring power resides, and investi-
gated several of its chemical  relations.  His experiments are   ,
to be seen in his chemical essays, translated by Dr. Beddoes,
1786.   Mr.  Berthollet prosecuted the  discovery of Scheele,
and has greatly added to  our knowledge of this remarkable
substance.
   The triple compound I just  now mentioned is  formed at
once, either  by adding a  calx  of iron to the lixivium san-
guinis, or by mixing a  solution  of pure fixed alkali with the
blue precipitate, as in  that experiment I lately mentioned ;   '
and thus  the alkali can be completely  saturated and neutra-
lized.   7"he  solution of it in  water has a ) ellow colour, from
the iron which it contains.    It  can be  separated from water
by evaporation, and in  some measure  crystallized  into flakes
or scaly crystals ;  or it may  be made  to separate from the
water, and to crystallize suddenly by means of alcohol.  If
into a saturated solution of Prussian alkali, somewhat inspis-
sated and filtrated, we pour an equal measure of alcohol, the
mixture becomes immediately thick by  shaking, and  the pre-
cipitated  matter appears  a soft  granulated substance, like
soaked rice.    By long  keeping, some  spirit separates to the
top, and the granulated matter becomes scaly.
   I said  just  now that the  common  process for  preparing
the  Prussian  alkali  is to^ mix the alkali with  dried ox-
blood,  and burn  the mixture to a charcoal, from  which the
alkali'is extracted with water.   But  several  other ways to
prepare this  alkali have been  discovered.
   Ml the minimal  substances, from which a volatile alkali can
be formed or extricated by heat, will  serve as well  as dried
blood to be mixed and charred with the alkali. Horn shavings,
hair, wool,  pounded bones,  &.c. are  extremely fit  for this
purpose.  And Dr.  Scheele  prepared  a very  good Prussian
alkali, by makjing  fixed alkali and charcoal dust red  hot, and
then thrusting down a little mass of  sal ammoniac  to the
bot-om of the crucible, and continuing the mixture  for a short  ; 
                OF PRUSSIAN BLUE.             183

while in alow red heat.  This shews thfeit a volatile alkali is
necessary 10 the production of this tinging matter.*
   This effect of the lixivium sanguinis on solutions of iron, is
the  foundation of the art of preparing the  colour  called
Prussian  blue, for painters, and other artists.   The che*mist
who first  discovered  it, lived at Berlin, and kept it secret for
some time, that he might sell the blue at an high price: and
hence it is called  Berlin, or Prussian blue.  Many chemists
have made experiments on it, and endeavoured to investigate
the nature of  it,  and  to  improve  the  art of  preparing  it,
of which you may  see  many examples in  the Memoirs
of the  Academy  of  Sciences.  But the greatest progress
has been made  by Mr. Macquer, by Scheele,  and by Mr. *
Berthollet.  (See Dictionary  of Chemistry, Scheele's Essays*
and  the  Annales de  Chymie, also Note 52. at  the end of the
 Volume.)
    I must not, however, omit informing you that the Prussian
blue of the shops has' other ingredients  besides  the vitriol
and Prussian alkali.    This would produce a pigment almost
black, so intense is its colour.   A great quantity of alum  is
used in the preparation.   Its acid adheres very loosely, and
saturates the alkali which is not already combined with the
 Prussic acid.   Of this there is always a great portion, even
 after the  most careful preparation.   The alum being thus
 decompounded, its earth, which is a snowy white, dilutes the
 intense blue,  without discolouring it.   It is  better liked  in
 this  state.  But surely the painters  will find it much less
 powerful in mixture with other colours.
    Mr. Macquer contrived a  very ingenious method of de-
 positing  this most beautiful colour on cloth, paper, &c.   The
 stuffs are first  soaked in a solution of vitriol and alum. \yTien
 thoroughly impregnated,  they are dipped in the lixivium  of
 Prussian alkali.   Any ochry matter in the precipitate maybe
 removed by dipping into a vitriolic  or muriatic acid, greatly
 diluted.

   * A mixture of chalk with the sal ammoniac greatly improves the process,
 and is the most certain and expeditious method for obtaining Prussian alkali....
 *ditor. 
 184. IRON....E1FECT  OF VEGETABLE ASTRING. ■

   Such are the differl-nt ways of precipitating iron from acids
 by alkaline salts.   We ma\  next subjoin to these precipitations
 an account of the effect  of astringent vegetables upon  the solu-
 tions of iron.
   By astringent vegetables are meant those  whose juices have
 the power to contract animal  fibres, and which, when  tasted,
 occasion a sensation in the mouth as if they produced that effect
 there.  The}- seem to draw  the mouth together.   More or less
 of this quality is found in  a  great number of vegetables.  It is
 remarkable  in sloes, and many ®ther unripe  fruits, and in all
 parts of the oak,....the leaves, the bark, the juices, and the galls,
 which are a tumour produced by extravasation of juices. Galls
 are the most powerful astringents.
   If a decoction of any  of those vegetables be thrown into any
solution  of  iron in an acid,  the mixture immediately  becomes
 a dark blue, or black ; and its transparency is greatly diminish-
 ed.   This may be called a precipitation ; although a great por-
 tion of the black faecula will remain  suspended for any length of
 time in close vessels ;  for the greatest part of it may  be separat-
 ed by filtration.
   I introduced the mention  of this  effect of astringents  among
 die precipitations of iron, because, although it is not commonly
 a precipitation, but generally a mere change of colour, especial.
 ly at first, there are  however some astringents, logwood,  for
 example, that actually separate  the iron from the  black sedi-
 ment, especially  when  much diluted.   Besides,  a little acid
 destroys the colour, and a  little alkali restores it: indicating, I
 think, that the astringent matter was imperfectly separated from
 the acid,....seeing that more  acid destroys the colour, by bring-
 ing tile iron into more perfect solution.   The added alkali res-
 tore#*things to  their former state,  merely  by saturating the
 acid.
   These experiments shew  some sort of power in astringents
 to loosen the cohesion of iron with acids.  There are other ex-
periments which shew that they have a disposition to unite with
 the iron themselves, and to dissolve a small quantity  of it.  Se-
 veral chemists,  therefore,  have chosen  to consider  the  matter
 which thus affects  the iron  as an acid : and thev have named it 
               IRON....INK  FOR  WRITING.          185

 the Gallic Acid, because  most abundant in nut galls ; and
 they think that the iron has a stronger  affinity with* this  than
 with the sulphuric acid, and precipitates with it from vitriol.
   A surprisingly small quantity of dissolved  iron, and  astrin-
 gent vegetable matter, have a perceptible effect on one another in
 this manner.  If a little infusion of green tea,  for example, be
 spilled on a knife, it soon becomes tinctured with an inky black-
 ness.   The astringent matter of the tea acts on the knife, and
 dissolves a minute portion of the iron,  with which it produces
 that appearance : or if a knife,  or any  thing  made of iron, be
 laid on a wet table,  the  table,  especially  if oaken, is  stained
 black where it is touched by the iron.  Hence this experiment
 too,  as well as that with the Prussian alkali, is used as a test of
 the presence of iron in mineral waters.
   The black colour also given to silk, wool, leather, &c. by the '
 dyer, depends on this effect of astringents and iron.  The prin-
 cipal materials employed  in those arts are  always some  of the
 compounds of iron with acids, (generally vitriol  or sulphat of
 iron) and some of the astringent vegetable substances.  s Com.
 mon tanned leather requires only vitriol, because it is already
 impregnated with the juice of oak bark,  one of the most power*
 ful astringents.
   We  also derive from these discoveries the art of making the
 ink now used for writing, which is an object  well worthy the
 attention of the chemist;  as upon the perfection and durability
 of it may often depend the preservation of important records,
 or valuable manuscripts.   The art of making good ink has ac-
 cordingly been studied by several chemists.   (See Caperarius
 de Atramentis) and by none  so thoroughly as by Mr. Lewis,
 who published his experiments in his Philosophical Commerce of
 Arts, to which I refer you upon this  article.  He  found^hat
 galls, when found, are the best of all the astringent vegefirole
 substances,  especially  for  durability.  Logwood  concentrated
 the colour, by combining more  iron in the composition, by nearly
 one-fifth.   One part of recently made vitriol to  three of galls
 seemed the  best  proportion.   More  vitriol made the writing
blacker at  first, but greatly impaired its power to resist the
action of air  and light.   Gum-arabic both hinders  the ink from
    vol. in.              a  a 
186         IRON....AFFECTED BY  NITRE
spreading, and proves a varnish, which defends the composition
from the air.   The ancients  wrote  with levigated charcoal, the
most indestructible substance we know.  And accordingly, the    J
writings found in Herculaneum  are still* a perfect  black.  Ihey
were  pigments.   Their defect isv that being superficial,  they
may easily be erased,  whereas the  ink of modern times pene-    '
trates into the paper.   Dr. Lewis combined the two inks  very
satisfactorily, by mixing some fine lamp black with his ink, in    i
such  quantity only as to  make it very  sensibly  blacker at  first.   J
This  ink withstood all action of the weather.  It  ran from  the   I
pen with abundant ease.   I recommend this paper of Dr. Lewis  m
as being also a good   example of the chemical investigation of
any complicated subject, and  for many judicious and useful in-  9
cidental observations  through the whole.    I shall only add to   <
what  he recommends,  the use of a small quantity of cloves, and
to keep the ink  in a cool and dark place,  and not too long.   The
reason  of  this last caution is the corruption of the vegetable
 astringent.  The effect of the cloves is to retard this, and to pre-
 vent the formation of mould upon the surface.*
   * As vinegar has not the power to dissolve and discolour  this black com-
pound, Dr. Lewis recommends vinegar or wine as the best solvent of the ma-
terials.  It undoubtedly becomes more  durable:  but it is found to soften the
nib of  the pen so much that it is quickly worn away by the  paper.  The  great
art in ink-making is to have a superabundance of-astringent matter, to counter-
act the disposition of the  iron to a farther calcination, which renders the ink
brown.   It wfhild be a great improvement in the manufacture of writing paper,
if some astringent matter could be introduced.  A little ardent spirits effectu-
ally prevents the spoiling  of in): by keeping, but makes it sink and spread.
Corrosive sublimate prevents inouldiness completely.
              A. GOOD PROPORTION. TOR WRITING INK,
       Rasped logwood    .  .  ' .  . ■- .  ,  .  ...   .  .   .  1 ounce.
       #Best gall nuts in coarse powder     ....   .  .   3 ounces.
       Gum-arabic in powder..........2 ounces.
       Green vitriol.............1 ounce.
    I   Rainwater.....,.........2 quarts.
   ,    Cloves  in coarse powder.........    1 drachm.
   Boil the water with the logwood and gum to one half; strain the hot decoc-
tion into a glazed vessel; add the galls and cloves; mix and cover it up.  When
nearly  cold, add t;,e green vitriol, and  stir it repeatedly.  After some days,
decant or strain the ink into a bottle, to be kept close corked, in a dark place.
   A ruddy fryable gum resin, not unlike gum-kino,  from  New Zealand, was
given me by a friend.  Finding its taste remarkably astringent,  and the whole 
                  AND SAL  AMMONIAC.            187

   Of the compound salts, I observed formerly that none are so
 remarkable  for their effects on the metals as nitre and sal am-
 moniac.
   Nitre deflagrates violently with iron  in a strong heat, and is
 alkalized,  or its acid is decompounded and dissipated, as in the
 other cases of deflagration with this salt.   The alkali remains
 mixed  with the calx of  the metal, and is caustic ; in conse-
 quence of  which it acts on the calx, and unites with a part of it,
 ....rendering  it soluble  in water to a certain degree  along with
 itself.  But this solution is not permanent.
   Sal ammoniac and this metal act remarkably on one another.
 I pointed out the reason of this in treating of metals in general,
 namely, the volatilizing power of the muriatic acid.   Common
 sal ammoniac contains the acid which has the strongest attrac-
 tion for the metals ; and this acid is combined with the weakest
 of the  alkaline salts,....the alkali which has the weakest attrac-
 tion for acids,  in general.  Accordingly, if we mix together
 equal weights of sal ammoniac and iron filings, and grind these
 materials well in a  mortar, they  soon after begin to act ;....the
 matters grow warm,....the more readily, if a little humidity be
 added.  The sal ammoniac begins to be decompounded ;  the
 acid joins itself to the iron;  and the volatile alkali is detached,
 and shews  itself in  a separated state  by its pungent  odour.
 There  is also separated at the same time a quantity of inflam-
 mable air,  the  odour of  which mixes  itself  witk that of the
 volatile alkali.   This inflammable air is produced by the decom-
 position of  some of the water.  The action of these materials,
 and the decomposition of the sal ammoniac, are not complete,
 however, until  we  apply heat to the mixture in glass  vessels. *-
 Then the sal ammoniac is totally  decompounded, and a caustic ^
 volatile alkali rises,  which it  is almost  impossible to condense
 completely, on  account of its being accompanied with inflam-
 mable air.   The whole  of the acid remains combined with the
 iron in the retort.
very mucilaginouu,  I mixed some of it with ink-powders, and found that it im-
 proved the ink in a very remarkable manner, both deepening the colour, and
 giving it body.  Writings with it, and with ink made by Dr. Lewis's receipt,
on a card, being exposed to the weather on a  south wall, this  addition was
found to have encreased its durability surprisingly.....editor. 
188
IRON....FLORES  MARTIALES.
        All these effects are also  produced on sal ammoniac by the
     calces of iron,  with this difference only, that it requires a larger
     quantity of the calx to decompound the whole of the sal ammo-
     niac, and  that, during the action of the materials, there is no
     heat or inflammable air produced.
        But when sal ammoniac and iron are made to act on one ano-
     ther, it is not usual to take such a large proportion of iron, or of
     calx of iron, as will  decompound the whole of the sal  ammo.
     niac.  There is a preparation obtained from sal ammoniac and
     iron, ordered in both the London and Edinburgh Pharmaco-
     poeias, under the title  of Flores Martiales.  This is produc
     ed by  mixing with the sal ammoniac such  a quantity of iron
     filings,  or of a calx of iron, as is sufficient for decompounding
     only the half of the sal ammoniac : and this mixture is exposed
     to  heat in  proper vessels.  First,  we obtain a caustic volatile
     alkali, detached from that part of the sal ammoniac which  is de-
     compounded.   After this has come over, the heat is increased,
     to make the entire part of the sal ammoniac arise, which re-
     quires a much stronger heat. The vapours of it condense into a
     solid matter, or what is called Flowers.   But while it arises in
     this manner, it carries with it a part of the compound of acid
     and iron that was formed in the beginning of the operation.  This
     compound is in some degree volatile, when there is enough of
     acid combined  with  the  iron.   A part of  it, therefore,  rises,
     and is condensed with the  sal ammoniac;  and forms the red-
     dish and yellow flowers to  which we give the name of fores
     martiales.
        It is  found that an oxyd, instead of the metal in its purest
 ^.  state, "ensures  the desirable appearance of this preparation,....
     the red and yellow  colour of the  flowers.  Therefore,  when
     filing of  iron are employed, it is of considerable use to expose
     them for some time to the damp air of a cellar.   An oxyd still
     more replete with vital air,  such as colcothar is, more certainly
     produces red flowers.   (See note 53.  at the end of the volume.)
 »  •    Iron  in its calcined state can  be mixed in fusion with vitrified
s •'  earths ; and the glass compound is tinged of various colours,
     according to the quantity of the iron, and the degree to which
  *  it is calcined.  The colour  which this metal most readily com-
     ;:mnicat'-.  is a ;re r. like that of its solutions in acids.v  Such 
        IRON  COMBINED  WITH SULPHUR.     189

a green is seen in the common glass of which bottles are made,
and in crown or window glass :  and the green phials of the apo-
thecaries are tinged with iron.  But when the  calx of  iron is
veiy  highly calcined, it  will sometimes give a dull yellow co-*
lour,  and a red.  And in all cases,  when much of the  iron is
added to the glass, the colour is increased or darkened, so much
as sometimes to produce almost a blackness.
   It is owing to the presence  of this calx, in some degree or
other, in almost every fossil body, that our clays are in  general
so much disposed to vitrify,  when  urged  by great heats.  A
very  minute portion of  it gives an incipient vitrification to the
best of them ;  and produces the compactness that js so  desira-
ble in all,  with very moderate heats.  It  is this  which gives
the red colour to our common brick and tile.
   Such bricks  are unfit  for the construction of furnaces ; be-
cause a moderate heat makes them run into  slag.   The greenish
yellow  colour of the small Dutch bricks is not owing to a want
of iron, for they contain a great deal, but to the presence of
magnesia.   The grey stock bricks of London have supplanted
the red bricks, which are now to be seen only in the old  houses,
but are inferior to them in their power to resist the weather.
   Experiments made with the different earths have shewn that
the flinty is the most disposed  of any to unite with calx  of iron
in the fire,  and be melted by it.  Hence the use of  it in welding
iron.
   The effects of  sulphur and iron on one  another deserve parti-
cular notice.
   Sulphur unites very easily with this metal in the dry way, or.
by  fusion, as with  most others.  And it penetrates iron more  it
quickly than most other metals, shewing thereby a stronger at-
traction for it.   A bar of iron, thrust-red hot into meltflg sul-
phur will presently melt and drop off like  wax held in hot water,
with a bright dazzling glow.
  Also, if  one  part of flowers of sulphur be ground with five
parts  (by weight) of fine iron filings, and  the  mixture  be put  4
into  a thin glass vessel,  such as a matrass, or cucurbit, and if "" "'
this be held over, clear burning coals, we shall observe the sul-
phur begin to shew softness very soon, sticking to the side of the
glass, long before the heat has  arrived at that degree that would 
190
IRON,
    otherwise produce this effect on sulphur unmixed.   It does not
    rise much in its temperature for a good while,  l hen, it sud-
    denly  becomes  fluid all over,  and the filings almost undistin-
    guishable :  and presently, the heat rises rapidly, the mass fixes
    and becomes red hot.  This is one of the best examples of the
    emission of latent heat.   It takes place when the chemical com-
    bination is  accomplished:  and this required previous fluidity.
    But the temperature is too low for the compound being fluid :  it
    therefore congeals,  and latent heat emerges.  If there be too
    much  sulphur, this takes fire.   This compound of iron and sul.
    phur is a hard brittle substance, of a metallic appearance.
      In consequence of this disposition to unite with sulphur, iron
  i  is often employed to separate sulphur from other metals, in the
    way of fusion.   The iron,  uniting with the sulphur,  fo.ms a
    very fusible compound, which flows uppermost: the other metal
  * subsides to  the bottom.
  *    But besides the way by fusion,  there is another way of apply.
    ing sulphur and iron to one another,  so as  to make them act.
    It may be called the humid way.   The iron is taken in filings,
,-.> and the sulphur in powder: and they are mixed  together with
    as much water as makes the mixture into a paste.
      If this mixture be shut up closely, to prevent its communica-
    tion with the atmosphere, the ingrediev.ts begin, after some
    hours, to act upon one another.  The iron is corroded into a
    bl?ck  mud  or paste, in which  the sulphur and  it  are somehow
    combined ;  for the yellow colour of the sulphur entirely disap.
    pears.   This paste has a surprisingly strong attraction for vital
    air ; and may be employed  to absorb it when we wish, to know
  .  what quantity of  vital air is contained in atmospherical air, or
*'  other  such  mixtures of different airs.   Dr. Scheele used it as a
    eudiapieter, in a set  of  experiments  which he continued for a
    whole \ ear, to learn what proportion of vital air was contained
    in  the atmosphere of  Stockholm in all the different seasons and
    months of  the year.
      A  drachm of flores sulphuris, mixed  with two  drachms of
t _»  filings of iron, and as much water as will make it a thick gruel,
» '   must  be put into a  little dish, connected with a piece of  cork,
* #  ho as  to flonf on water.   If we invert upon this ajar capable of 
          MIXED WITH SULPHUR TAKES FIRE.    191

   holding 66 ounces of water, (nearly two. quarts), all the oxygen
   contained in the atmospheric air, which fills  this jar, will be
   absorbed by the mixture of iron and sulphur,....the water of the
   tub rising up into the jar, and occupying its place.  When the
   filings are extremely fine and clean, and are mixed with the dry-
   sulphur by  grinding, and  then  a moderate quantity of  water
   quickly mixed with these materials by kneading briskly, and this
   preparation put into  a hot floating dish, it will absorb the vital
   air so rapidly that it will take fire.  This may be ensured, by
   smearing  with this magma some small twigs.   This exposes a
   great surface, and soon heats.
     If some pounds of this  mixture be exposed  to  the atmos-
   pherical air, they will attract the vital air so fast  from it,  as to
   grow hot and to take fire.  They grow hot also, although thev
   be not exposed to the open air,  if the  quantity of them be so
   great as 50 pounds or more; for, in this case,  there is so much
   air.entangled in the paste in making it up, that the absorption of
   this  air is enough to produce a considerable heat, and even to
   fire it.
     After this absorption  and  heat are over, if* we examine the
   remaining matter,, we find the sulphur changed  more or less into
   sulphuric acid, which remains cojnbined with the iron, and forms
   with it a vitriolic compound, more or less perfect. It is evident,
   that  the  vitriolic compound  is formed  in  consequence of the
"  strong attraction, both of the  sulphur and of  the iron for the
   oxygenous ".principle,  which they draw partly  from the  water,
   but  principally  from the air.  By this principle the  iron is
   slightly;calcined, and the sulphur  is chrnged, at  least in part,
   into sulphuric acid.   The decompounded water,  when there is
   enough of it, gives inflammable air:  and the air from  which
   the oxygenous principle is attracted, gives out a great part a£ its
   latent heat or caloric, in the form of sensible heat, which heats
   the materials sometimes to  such a degree as to make them  take
   fire.   When the  materials are in large quantity, and covered up,
   or buried, so as to have little communication with the air, there
   is more water.decompounded, and more inflammable  air pro-
   duced.  When, on the contrary, the quantity of them is  small,
   and they are confined with a quantity of air, they draw the oxy- 
 192   IRON....MARTIAL PYRITES....VITRIOL.

 genous principle  chiefly from that  air, and  decompound the
 whole air which the vessel contains.*'
   A  similar change of sulphur happens in some kinds of pyrites,
 which are  natural  compounds of iron and  sulphur.   And the
 discovery of this has given origin to the art by which common
 vitriol, or the sulphat  of iron, is prepared in  large quantities,
 and at a cheap rate.   I formerly observed,  that the manner of
 preparing it, by dissolving iron in sulphuric acid, is only prac.
 tised  as a process in pharmacy, and the vitriol, or sal martis, so
 prepared, applied  only  to  purposes of  medicine;  but  that a
 much cheaper way of obtaining this  compound has  long been
 practised, to supply the consumption made of  it in several arts.
 By this cheaper method, it is prepared  chiefly from some par-
 ticular  kinds of pyrites, which, when exposed to the action of
 the air, and of humidity at the same time,  undergo a change,
 by  which the  sulphur becomes sulphuric  acid, and we  get a
 vitriol, or sulphat of iron, in place of the pyrites, or compound
 of iron and sulphur.   Humidity alone  is not  sufficient.   The
 pyrites has not the power of decompounding  water.  Cramer
 says,  he observed  immense quantities of pyrites  all along the
 English shores, especially about Harwich, which naturally  lie in
 a bed at the depth of some feet below the surface  of the  sand.
 As long as  they lie there, though they  are  constantly wet with
 sea water, they continue entire and  quite  insipid: but  when
 thrown up to the air by the waves, they are crumbled down, and
 converted almost  entirely into a heap  of  little  crystals,  in a
 fortnight.  This is indeed the case every where, for the pyrites
 is always exposed to abundance of humidity in the bowels of  the
 earth, but nevertheless retains its form until it is dug up and ex-
 posed.
  TJhis change, which the pyrites of iron is liable to undergo, is
 called vitriolization :....it is said to vitriolize.
  It is proper to remark, however, that 6nly particular kinds of
 pyrites  are liable to it, not every kind.  Some kinds, such as
the cubical pyrites,  common in slate, and some others, withstand
  *  Consult on this subject Mr. Lavoisier's Essays, published in 1777,  where
the whole procedure is analysed with great precision and distinctness.  Le
 Sage E!em. de Chymie, i. 42.....Werner on the Origin of Volcanoes.....Hopfner'i
 Magazine of Natural History.....Lemery, Mem. Acad. Paris 1700. 
       MANUFACTURE OF  GREEN  VITRIOL.   193

  he action of air and humidity a  long time without suffering a
 change :  or if they are changed, it  is very slowly, and only into a
 i ard rust at their surface, but without affording vitriol.
   The cause of this  difference  among the varieties of pyrites
 has not  been discovered.   I  suspect that it depends upon  the
 proportion  of the sulphur to the  iron;  and that those which
 contain most sulphur, are most liable to vitriolization.

             Process for Vitriol from Iron  Pyrites.

   The account which I have given you of the chemical proce.
 dure will naturally direct you  to the proper methods of accele-
 rating the operation.  I have only to remark,  that some kinds
 of pyrites require a preparation, by roasting in a heap  with a
 small quantity of fuel.   This is found  to dispose the harder
 pyrites to  a more  rapid decomposition;  probably  opening
 their texture  by the expulsion of some of  their volatile  ingre-
 dients.
   The pyrites being thus in a proper state for vitriolization, the
 rest of the process is the same for all kinds.  A piece of ground
 is chosen, having a very gentle declivity, just enough to make
 the water run in one direction. This is laid out in narrow quar-
 ters, like a kitchen  garden,....the furrows which separate them
 having the/direction of the slope.   The  ground'between is co-
 vered with firm clay, well beaten,  so as to be quite impervious
 to water.  The surface of each quarter has a slope on each side
 toward the  furrows.  Another furrow is led across the lower
 extremities of those  which separate the ridges : and this furrow
 terminates in  a great cistern*
   The pyrites, broken into small pieces, are spread on the quar-
 ters  or ridges, and  made  up into  beds Tabout two feet tlftck.
 They effloresce :  and the rains wash off the saline crystals.  The
 solution trickles off into the gutters, which conduct it down the
 slope into the  cross drain,  and by it into the cistern.   In very
dry weather, it may even be necessary to sprinkle the pyrites on
the ridges.  As  the solution is very weak, especially in the
rainy seasons, it  is frequently thrown again on the vitriol beds
    vor.  nr.                  b  b 
194     IRON....ORIGIN OF VOLCANOES, &c.

by a forcing pump: and it comes off them still more impregnat-
ed with the salt, till at length it is fit for boiling.
  For this purpose, it is  pumped up into  the  boiling housie,
which is built over the cistern, and is reduced to  a strength pro-
per for crystallization,  by boiling off the  superfluous water.
From the boilers the liquor goes into the vats or cisterns, where
it is allowed to cool and to  crystallize.
  There are some pyrites which are so much disposed to vitri-
olize, that heaps of them are liable to grow hot and take fire:
and this has happened on different occasions to  some kinds of
pit-coal abounding with pyrites, and  which had been collected
together in large quantity.   At Ayr, for example, an immense
body of coal,  built up for exportation, took fire : and in Dublin
it happened to a large qaantity of English coal, which had been
provided by the corporation to prevent scarcity ; and this hap.
pened in both cases after a heavy shower.  Vessels loaded with
such  coal have unfortunately been set on fire sometimes in that
way.
  In  many coal pits, the pyritical rubbish, which is mixed with
the coal, and  would spoil its sale, is picked out,  and left below.
When these pyrites have been accidentally in too large heaps, they
have  frequently  taken fire,  and  have set fire to the coal works,
George Agricola, who wrote in the 15th century, speaks of the
fire in the  coalwork at Dysart in Scotland as a  very old thing.
It is not yet extinguished.   At Kilkerran, in Ayrshire, a very
extensive coal-work has been burning now for  fifty years.  At
Johnstown, near Paisley, a stratum near seventy feet thick was
set on fire  by  the rubbish, and  continued burning with incredi.
ble fury, having a great current of fresh air.  In  one place there
was a face of coal red hot for near 100 yards, and the flame as-
cended through one of the pits to the height of above 100 feet.
It was at last extinguished by  drowning it.  But whenever the *
air is admitted,  it takes, fire in a few davs.
   From such examples, some  have endeavoured to account for
hot springs,  subterraneous fires,  volcanoes, and earthquakes.
They have even attempted  to imitate some of these convulsions
of the earth.   Lemery was, I believe, the first  who attempted
this imitation.  (See Mem. Acad. Par. 1700.)  It has often been
done since.  The general process has been, to  mix as large a 
RELATION  OF IRON TO METALS.    195
quantity as can be conveniently had of clean iron filings, with
somewhat more of sulphur, and as much water as will make a
firm paste, and to bury this in the earth,  (first wrapping it up
in a cloth) and ram the earth firmly above it.   In a  few hours
it grows warm,  and swells so as to raise the ground.  Sulphu-
rous steams  make their way through the crevices,  and  some-
times flames appear.  Rarely is there any explosion: but when
this happens, the fire is vivid and brandishing,....and the heat
and fire continue for sometime, if the quantity of materials has
been great.
   We cannot expect more,....we see the production  of internal
heat, sufficient for  more violent operations: but other circum-
stances must concur.   If water get in by a crevice into a cavern
containing red hot materials, there seems no bound to the  effects
which it may produce.
   The phosphorus of urine can also be combined in small quan-
tity with  iron,  by melting the  phosphoric acid with iron and
charcoal dust.   The compound is more fusible than iron, and
is not decompounded but with great difficulty,  which  we should
not expect of a substance so volatile and inflammable. It makes
iron cold-short,  that is,  it will not bear hammering out when
cold,  but cracks all over.

             Relation of Iron to other Metals*'

   Iron can be  mixed with all the other metals, excepting lead
and mercury.   It shews a disposition to unite  the most readily
and strongly  with arsenic, and with the regulus of antimony,
and with gold.   None of the mixtures of it with metals have
been found useful,  except perhaps manganese, which is sup-
posed to improve iron:  but  its effect is not sufficiently ascer-
tained by experiments.
   Iron is, in  general,  much  impaired in  its most valuable
qualities, cohesion, malleability, and toughness, by any metal-
lic  mixture.  Arsenic  in particular  unites  most  readily, and
adheres most obstinately ; and  makes it red short,  that is,
apt to  crack  under the hammer while forging,  and even to
fall in  pieces. 
196                IRON....ITS ORES.
                       Ores  of Iron.

  Iron is seldom found pure and metallic ;  but examples of this
however have occurred.  A mass  of 1600 pounds weight was
found in Siberia.  Its  interstices were  all filled up with glass,
of a beautiful bright green, and so friable as not to cut the fing-
ers. This circumstance shews that it has been the effect of fire,
and that the glass has been quenched in water while yet red hot.
Another mass, much larger, has been found in Paraguay.  Such
masses  are said to be not uncommon in Senegal.  (See  Note 54.
at the end of the Volume.)  Mr. Margraaf has found malleable
iron in strings  at  Eibenstock in Saxony.  These are  the only
known instances ;  but the ores of this useful metal are  plentiful
in all parts of the world.  And  besides, iron is  found mixed
with many of the other productions of nature, such as the ores
of other metals, coloured clays, and  boles.  Indeed few earths
are free from it.  The garnet, the emerald, the  ruby, topaz,
sapphire,  and amethyst,  appear to derive  their colours from it.
It is found even in the ashes of vegetable and animal substances,
....in the blood, milk, flesh,  and hair.  It has been  found in
plants which have  been  raised from a  seed in distilled water.
Some fossils containing  iron  are of great use, although not as
ores of iron ;  such as emery for the lapidary ; haematites for the
burnishers ;  the red, yellow,  and blue ochres for the painters;
and the loadstone for the navigators.
   As the  ores  of  iron  are very common,  only the richest or
most pr  fitable are  wrought.  In this country,  the  minerals
melted to extract iron from them  are distinguished into  three
 kinds.
    1st,  Iron ores found in veins.
    2d', Iron-stones, interspersed through strata, or forming thin
 strata  among  others.
    3d,  Bog ores, jntimately blended  with clay, and with the re-
 mains  of animal and vegetable substances;  not mixed  but in
 many cases chemically combined.
    All  these are in general oxyds of iron, in different states of
 oxydation:  and some are combined with  fixed  air  and with
  mall  nuantities of some of the earths.   When thev  are much 
            SMELTING OF IRON ORES.        197

oxydated, and nearly pure, qr with very little of the earthy
substances combined with them, they  have a dull and deep-
red colour, which is the natural colour of the oxyd of iron
highly oxydated.  Or if some fixed air be united with them
at the same time,  they are yellowish : these are the spathose
ores of  iron,  .or  carbonats  of iron.   If, on  the  contrary,
they contain the iron but little oxydated,  they are grey or
black, or approach by their colour to iron  itself.   They are
also variously  crystallized;  of these  the  bloodstone, or
haematites, is the most beautiful.   Their  appearance is also
very much affected by the mode of their concretion, and by
the admixture of earthy matter.  White ores and micaceous
ores often contain manganese,  and are thought to yield ex-
cellent iron.
   The hard pyrites,  though it contains much  i|on,  is not
treated  as such: It is considered only as  an dre of  sul-
phur.                                            *
   To  extract the iron, the minerals are first roasted.  This
operation appears to  be necessary or useful, in  exiracting
iron from many of  the  minerals from which it is obtained.
It is probably useful by expelling sulphur or sulphuric acid.
   The next operation is to reduce the roasted ore to  a me-
tallic state,  or metallize it completely.
   This  is done in a high furnace, shaped internally some-
what  like two round crucibles joined by their mouths, the
uppermost without a bottom.  The bottom of the furnace is
hollow, having on one side a hole through which the blast of
a bellows can be directed a few inches above the bottom. On
the other *ide  is a  larger hole,  through which the melted
metal  can run entirely off.   A^heap of brushwood is thrown
into the furnace.    It is kindled,'and immediately covered
with   charcoal  or  coak:   and then  baskets  of  ore.  and
fuel are added till the furnace is filled,....the bellows being
worked all the while. The tap-hole of the furnace is shut up
with clay.   Every thing being loose and open, the flame is
forced by the blast of the bellows through the whole furnace
and a  -violent heat is  raised all over it.   As the  fuel con.
sumes, the matters  subside; and baskets of ore and fuel are
repeatedly thrown in to fill  up the furnace.    The  earthy
matters and ore are  melted by the intense heat into a  glass.
And since the burning fuel is every where in contact with the 
198       IRON....SMELTING  OF  ITS  ORES.

ore, and the coal has  a much greater attraction for the oxy.
gen than the iron has, the metal is reduced, and sinks to the
bottom of the  furnace under the melted glass produced by
the fluxing of the earths.   The metal is now defended from
the action of the bellows.    When the workman thinks that
there  is enough collected,  he makes a hole in the clay with
the tap-iron : and the  metal runs  out, and is followed by the
glass or slag.
   A  considerable  quantity of limestone is mixed with the
ore in this operation ;  seldom less than one-sixth of the ore.
Its use is partly to promote the fusion of the earthy matters
mixed with the metalline oxyd, and partly to  combine with
the sulphuric  and sulphurous  acid ;   by which means it is
carried off  in   a  vaporous  form,  but takes  with  it  some
iron.    It is  thought that a better  quality of iron is ob-
tained by th'e large use of lime, even when not required as a
mere  flux.
   It is  also found, in all cases,  of great advantage to the
quality of the iron to use a verv great quantity of fuel. This,
unquestionably,  produces a  more complete  absorption of the
oxygen and reduction  of the metal.   A great allowance of
fuel brings more  metal  from the same ore,  and  makes it
more fusible after repeated meltings.   It is very grey, shew-
ing shining  black facets, and talky-Iike matter, and is softer
and easier cut  than white  cast-iron which has been made
with less fuel.   But  the room occupied by the fuel causes
the furnace to produce less iron per day; while the blast or
quantity of air consumed remains the same. Therefore, this
iron is much more costly.   In the Scotch furnaces, the iron-
stone  requires  between three and four times its weight of
soft pit-coal:  and each  ton of iron produced  requires the
consumption of  672,000 cubic feet of  common air.   Some
fuels, particularly blind-coal,  require  much  less.    Much
move  is required in summer than in winter.
   The quality of the iron is  affected also by the nature of the.
fuel.  Wood charcoal is best for producing iron to be refined
and made into bars.   Charred pit-coal is best  for iron to ba
employed in cast work.
   When first melted down from the ore in the great furnaces,
the metal is  in the state called pig-iron, or  pot  metal;  and is 
VARIETIES OF  CAST-IRON.        199
fit for cast work ;  in which state it is perfectly fusible, but is
either quite inflexible and brittle, or has very little flexibility
and toughness.  It is useful, however,  for  many purposes.
In consequence of its fusibility, it can be cast in moulds, to
form large massy pieces, and instruments of a very great size,
which  are thus formed at a far less expence  than  if it  were
necessary to forge them ;  besides that some, on  account of
their large size, could  not be forged.   But fusible iron  is
unfit for anchors, and other such instruments, which must be
exceedingly strong and tough.
   I should observe, in this place, that the cast iron obtained
by this process appears in three states,  which are very dis-
tinguishable, both in appearance and qualities,  according to
the manner  in^yhich it  has been manufactured.
   1st, White Cast-Iron, extremely hard  and brittle.   It
cannot be filed, or bored, or repaired in any way, nor bend.
It cannot bear very suddenchanges of temperature,  without
cracking.  Its structure is crystallize5,i with very small bril-
liant facets.         ••  •*          ^ b
  2d,  Grey Cast-iron, of a granulatecl texture, and often
plated, but of an unequal dull colour.  It is much more cohe-
sive than the former;  and  is therefore employed for artil-
lery.   It is also softer, and may be cut and bored, and even
turned in a lathe.
   3d,  Black Cast-iron, the most  unequal in its  texture
the most fusible, and therefore often mixed with the  white to
make it  stand a repeated melting.   It is less tenacious than
either of the former.
   The  first seems to  contain  much unreduced  oxyd,  and
even some earthy  matters, which vitrify along with it. These
are entangled among the truly metallic parts ; and thus defend
them from the action of the air.   The second kind has little
unreduced oxyd, or earthy matter, having been prepared with
more fuel and greater heat:  but there is more of the inflam-
mable matter of the fuel combined with it.   The last also
contains  much of  this,  and derives other varieties from the
nature of the ores.  It makes the best refined  or malleable
iron.
   Iron  is changed  from  this fusible and rigid  state into
tough  and malleable  iron,  in the fotge,  or finery  as  it is 
 200  IRON....MANUFACTURE OF  BAR IRON.

 c- lied,  and by an operation which is considered as  a refine-
 ment of it.
   Until lately, the only manner of performing this operation
 was by heating two or three hundred weights of it at once,
 in a hollow forge,  in which the iron was covered with a fire
 of charcoal, and lay in  a bed of charcoal dust and ashes untij
 it just melted, with no more heat than what was barely suffi-
 cient ;  and it was kept in this heat for some time,...the wind
 of the bellows being directed through the charcoal,  so as to
 have some effect on the surface of the metal; and being stir-
Ted now and  then, it  was taken out a toughish cavernous
 mass, and  was compacted by hammering.
   But  within these few years, another process was contrived
 by a Mr. Cort, which admits of an immediate Jnspection and
 examination of all the phenomena;  the metal not  being
♦ covered with the fuel, but  exposed  to the view of the opera-
 tor and observer.
   Here the, iron is meTred in a  reverberatory furnace : and
 a strong flame is kept  Wowing oyer»'ijtf\so as to k'eep  it in a
 most intense  heat,. ""It is  all the while stfrred about with a
 rake, so as to bring every  part of it to the surface in succes-
 sion.   By this treatment certain impurities of the  iron are
 dissipated in a way that we do  not yet  understand.   The
 fact is, that it gets into a particular state, which is  indicated
 without any danger of mistake,  by the iron becoming thick
 like  gruel, swelling up a little,  and the  surface of it all at
 once becoming of a  dazzling brightness,  by a low flame
 which  gleams upon it.  It is  now   said to be  brought into
 nature.
    When the  iron  is thus brought into nature, that is, has lost
 its fusibility, and  is become  malleable, it is collected into
 two masses in the laboratorium of the furnace, by raking it
 together,  and compacting  it with the strokes of an  iron club
 or mace.   The x  masses  are called loops.  They are very
 porous and spongy, and  contain a  great deal of scoriae, or
 semi-vitrified matter, mixed  with  the iron.   The heat to
 which  they are exposed is  hen  increased for a short time
 until these scoriae  are completely melted, at which time the
 loop is taken out,  and  immediately  exposed to the strokes of
 a large and heavy hammer,  wrought  by a  water  wheel or 
       CORT'S PROCESS....FINERY CINDER.   201

steam engine.   This compresses the mass ; unites the partsy-,
of it more closely ; and forces out the greater part  of the
vitrified  matter,  or finery cinder, as it is  called,  out of its
pores.   The mass is turned under the hammer, until  it is
formed  into a short and  thick prism or cylinder called  a
bloom, the parts of which are not yet so closely united as they
ought.    But by heating it  again, and subjecting it again to
the great hammer, or passing it between rollers contrived
for this purpose, the parts  of it are made to enter into close
eohesion, the liquid  dross completely squeezed  out of its
pores,  while it is at the same time forged into bars of diffe-
rent kinds.
   The iron made by this process,  from very  ordinary iron,
such as  was known to yield bad bar iron, proved equal to
the best Swedish iron.  Very severe trials were made by
Government, as  it was  recommended for the use of  the
navy, for anchors, bolts,  straps of blocks, and other uses,
where  toughness was an indispensable  requisite.   But,  to
make bad iron so eminently good, required much labour and
expence.   Cast  iron,  which yielded better bar iron  by the
usual processes,  was amenable to the same degree  of  fine-
ness with much less trouble.   I mention this  circumstance,
to shew  that the  process  is general, and  depends on prin-
ciple.                                                        »
   By this  process, the expence of wood charcoal, which is
a very dear fuel  in this country, is saved ; the whole opera-
tion being performed by the flame and heat of pit-coal.
   By whatever process fusible iron is refined to the state of
tough iron,  a considerable part of it (one-third commonly)
is scorified or calcined, forming a fusible calx or oxyd, called
Finery Cinder.  It is  exactly similar in its appearance to
the fusible oxyd formed from iron when it is burnt  in vital
air.  The production of this finery cinder is absolutely ne-
cessary.   And  the  skilful workmen say,  that  for the  right
performance of  this process,  it is necessary that the refining
iron be well soaked,  and mixed to a certain degree with this
 finery cinder ; for which reason, although they let  some  of
this cinder run out at a  tap-hole of the furnace or forge,
when it accumulates too much, they never let it all run out,
     Vol. hi.               c c 
 202  IRON....MANUFACTURE OF  BAR IRON.

 Jmt retain a proper  quantity in the furnace or forge all the
  time they are working.
    But it is also certain that the iron loses a quantity of in.
  flammable matter, which is contained in it while in its hard
  and brittle and  fusible state.
    When we try to dissolve f\v ble irr- "n acids, we  find  it
  more  difficult to dissolve it,  and  *iiere  is an incomparably
  greater  quantity of  plumbago  left nom  it than from tough
  iron.   You  know that plumbago is principally composed of
  carbon,  or carbonaceous matter; but there is, besides, often
  some sulphur or some phosphorus.   The  change of fusible
  into malleable iron appears, therefore,  to  depend chiefly on
  the destruction of the plumbago, or of the greatei part of it.
  And it is easy to shew in  what manner this happens in the re-
  finement of iron.   Dr. Beddoes  has endeavoured to explain
  how it happens in Mr. Cort's  process: and he has explained .
  it in some measure, bat assumes  a principle which  I cannot
  admit.
    The  principle assumed bv Dr.  Beddoes and the French
  chemists,  is, that the unrefined fusible  iron, besides  contain-
  ing a  quantity of carbon, also  contains  iron  in the state of
  an oxyd; and that the oxygen of this ill-reduced iron acts on
•  the carbon, and produces the increase of heat, and the intumes-
  cence, or fermentation, and the  eruption of elastic fluid and of
  flame.
   But it always appears to me inconceivable, that there should
 be present in fusible  iron, at the same  time while it flows
 white hot from the great furnace, both an abundance of carbon
 and an oxyd of iron, without acting on one another originally, /
 especially in the grey iron, which most abounds in carbon.
    There is no  occasion  for having recourse to  so unwar-
 rantable a supposition. It is evident that the effect of a great
 part  of Mr. Cort's process is to calcine a part  of the iron in
 the first  place..  While the workman is busily employed in
 stirring it over from one side of its bed to the other, separating
 it into sm;dl parts, and mixing the whole carefully together, a
 quantity of the iron (to which the air is admitted all the while)
 must be calcined or oxydated.   He then increases the heat a
 little, to make  the oxygen  of this calcined iron act on  the car-
 bon of the uncalcined. This increases the heat in the iron,  and 
              SOFTENING  OF CAST IRON.      203

 produces the fermentation, or formation of carbonic acid gas,
 which, while it rises, carries some oarbon with it,....and hence
 the blue  flame.   The nicety of this  operation depends on
■knowing how far to carry the  calcination  of part of the iron,
 that there may be enough of oxygen to consume'the whole of
 the carbon.   If  more iron than enough be calcined, it is so
 much lost.
   Such a persuasion suggested to Mr. Reaumur a project
 to soften or give  toughness to cast iron by cementation.   He
 conceived iron to differ from other metals  by combining with
 much'more  inflammable substances than was necessary for
 its  ductile form,  and expected to absorb or consume this by
 proper substances.   He  therefore cemented cast  iron with
 earthy powders  ;  and after the cementation  is  carried a
 certain leng'h, the iron vields to the file, if slowly cooled, out
 if tempered, is quite hard.   It has some malleability when
 red hot, but none when cold. If it be strongly heated, it flies
 to pieces under the hammer. Thus it plainly resembles steel.
 Continuing the •. e mentation longer, it becomes now so soft
 as to  be easily cut, ..i_d, bent, or forged, and doe? not become
 much harder by temper.   In proportion as it becomes s »>  it
 loses its fusibility; and the internal parts can  be melted out;
 so that in every respect it is similar to  forged iron, only it is
 not so compact or solid.   All these changes seem accountable
 by a gradual exhalation of the carburet  included in  the crude
 iron.   This may be assisted in Reaumur's processes by the
 cementing matters, either by their absorbing this matter as it
 exhales or comes to the surface, "or perhaps diminishing the
 attraction, by presenting  to the iron  or  the carbon some
 vapour for which they have  some attraction.  But we do not
 know  any matters  that are much preferable to others  which
 are not obviously improper.  Though Mr. Reaumur did not
 succeed in. establishing such  an art in France, it is now prac-
 tised  in Britain.
   The very best  kinds of refined, or bar iron, are very strong
 and tough when  cold;  and bear to be  bent  backwards  and
 forwards very much  before  they break:  and they are also
 very malleable when hot. Sweden is remarkable for producing
 iron,  from some of its ores, of this very  best quality. But the
 greater number of iron  ores do not produce iron  so  good,
 though it be good enough for common uses. 
204 IRON....RED-SHORT....COLD-SHORT  IRON.

   The blacksmiths distinguish  the  common  kinds of iron
into two varieties, of which however there are many degrees.
To these  two varieties thev give the names  of red-short iron
and cold-short iron.  The red-short is tough and flexible
when cold, and works very well when strongly heated: but if
under-heated, it is brittle under the hammer.  And as there
are many varieties, the  smiths make trials at first to learn
how  the  iron is  best wrought.   The  cold-short iron,  if
cooled slowly after being heated, proves quite brittle while
cold,  especially  thick bars of it ;  and acquires flexibility
by being plunged red hot into cold water,  but is  always
deficient  in it.  In its brittle  state it breaks  so  as to shew
facets or plates  remarkably large in  the   surfaces  of the
fracture.
   Professor Bergmann made  a great number of experiments
to learn the causes of these different qualities  of  iron ; and
thought he had discovered the cause of cold-shortness, as-
cribing it to the presence of a metal which he called siderum:
but this has been  found to be a mistake.  Mayer shewed that
it is a  phosphat  of iron.  Mr. Cort's  process removes or
prevents this  bad quality.
   When  a piece  of tough hammered iron is broken by bend-
ing, it is  found to be fibrous.   But if the same piece be kept
red hot for some  time, and again broken, the fibrous appear-
ance is almost gone.  It would seem that it acquires it by the
action of the hammer ;  and that iron consists of malleable
infusible stuff, mixed with a remainder of fusible  iron. Such
a mass, when heated red hot, must work under the hammer,
like a paste in kneading,'4ne fluid part being squeezed along
between the ductile parts like so much grease. Perhaps this
is the source of that shining or glowing skin which it acquires
in a welding  heat, which enables two  pieces to be struck
together by the force of blows.
   I have now described the progress of iron from the ore to
that state  of  this metal  which appears to be the  purest and
most perfect state of it,  and in which it is called  tough iron,
or bar iron.  I must, in the next place, give some account of
Steel, which is iron in a  different  state,  and possessed of
properties by which it is much better adapted to  serve some
of our purposes than tough iron  is. 
          STEEL....ITS MANUFACTURE.       205

  Steel is refined iron,  intimately combined with a small
quantity of pure carbonaceous matter,  or the carbon of the
French chemists.
  Slender bars of iron are put into a crucible,  and covered
with charcoal dust rammed close round them.  The crucible
is luted, and set in a furnace, where it  is exposed to a strong
red heat for some hours.  When the  iron is taken out,  its
surface  is frequently found  rough and blistered.   This I
believe is owing to the pushing the operation a little too far.
It is now  converted into  steel, and considerably increased in
weight.
   At Newcastle, and other places in England,  they have
furnaces for this purpose, in which large quantities  arc made.
These have the form of a large oven or arch, terminating in
a vent at  the top.  The  floor of this  oven is flat  and level.
Immediately under the middle of this floor there is a long
arched fire-place with grates, which runs quite across from the
one side to the other, so as to have  two doors for  putting
in fuel from the outside  of the building. A number of vents
or flues pass from the fire place to different parts of the floor
of the oven, and  throw up their flame into it,  so as  to heat all
parts of  it equally.   In the oven itself there are  two large
and long  cases, or boxes, built of a  good  fire-stone : and
in these boxes  the bars of iron are regularly stratified with
charcoal dust,  ten or twelve  tons of iron at once,  ?nd all is
covered   with  bed-sand.   The heat  is continued five or
six days  and nights  without intermission.   And it requires
as long  a time for  the  furna£<2j .to eool again, before the
steel can  be taken out, and thef^xes filled with fresh bars of
iron.
   This  process  is  a  cementation,  and the carbonaceous
matter must be introduced into the iron in the form of heavy
inflammable air.   You must recollect the experiment of Mr.
Morveau, in which he exposed a diamond to  intense heat,
shut  up in a small cavity in tough  iron.  The  diamond
vanished, and  the iron  around it was converted into steel.
These facts shew very plainly what happens.   The charcoal,
or carbon in substance, combines with  the metal.
   Accordingly, a chemical analysis of steel shews  this com-
pletely, by giving us the  carbon again in some other combin- 
 206 IRON....PECULIAR  NATURE OF  STEEL..,.

 ation,  as will appear in a variety of ways.   It appears by the '
 results of  its exposure to great heats.   It is gradually de-
 prived of its qualities of steel  by long continued red heat:
 and it emits carbonaceous matter, if  not carbonic acid.   A
 fine steel wire burns with amazing brilliancy in vital air, and
 produces both fixed air and inflammable air.   This carbona-
 ceous matter is discoverable in steel by the action of acids,
 particularly aquafortis.  When steel is  dissolved in an  acid,
 we obtain much more plumbago from it than from the worst
i kinds of tough iron, although not so much as from the grey
 cast iron. If this experiment be performed with  sulphuric or
 muriatic acids, the difference is not so  remarkable, but not
 less real.   In these acids, the solution  proceeds chiefly,  or
 primarily, from the decomposition of the water, and inflam-
 mable  or pure hydrogenous gas is produced.  This combines
 with part of the carbon in its nascent state; and composes the
*heavv  inflammable air, which is really obtained in the  solu-
 tion of steel in  sulphuric acid; whereas pure tough iron gives
 us hydrogenous gas.
    With aquafortis, the produce of  plumbago is much more
 considerable, when the process is carefully managed.   The
 nature  of it is also more distinctly seen.  And I am persuaded
 that iron constitutes an ingredient of it; and that the French
 chemists are right when they call it a carburet of iron; though
 others  say that the iron exists in it only accidentally.  In the
 trials I have made, its quantity or proportion is too constant
 to be accidental.
    Steel, therefore, appears to be  pure iron combined  with
 inflammable matter.   By pure iron, I mean the metal  com-
 pletely reduced,  that  is,  cleared  of all  oxygen, and of all
 eivthy and combustible matter ;  in  which  respect  it differs
 from /cast  iron,  which undoubtedly contains much  earthy
 matter, united with an oxyd  of iron  in  the  form of glass,
.which  is entangled in  the pores, and cannot be squeezed out
 without a vast deal of hammering and labour.  The cast iron
 resembles the steel in this, that,  like it, it  contains much
 inflammable  matter,  which  it acquired  from the fuel, and
 which  remains defended from the action of the air by the very
 fluidity which it  occasions, and which  is expelled  only bv
 stirring, and presenting a p/cat surface for a long time to the
" action of the air. 
           IRON....TEMPERING  OF STEEL.       207

   This notion  is confirmed  by the fact, that a slender rod of
iron, plunged into white or grey cast iron in fusion, is converted
into steel.*
   The qualities of steel, by which it differs from iron, are,
   1. It is more fusible.  Tough iron cannot be melted in the
most violent fires of common furnaces.  It only becomes very
soft, but  never  fluid.   But steel can  be  melted  perfectly in
crucibles, if exposed to the most violent heats of common fur-
naces.
   2. In its solid state, steel is more rigid and  hard than  iron;
nor can it be so much softened by heat, without losing its tenacity
and flying in pieces under the hammer.   It  requires  therefore
more care and attention to forge it well than to forge iron.
   3. Steel  is much more readily broken  by  bending it  than
tough  iron.  It does not bear to be so much  bent backwards
and forwards.   When a bar of it is broken,  the surface of the
fracture is quite different from that of iron.  A bar of tough iron
shews  by its fracture that it is composed of fibres,  the surface
of  the fracture being very rough, with the ragged ends of them.
But steel, when  broken, shews that it is  composed of very small
grains, of  a plated structure; and presents a whitish grey sur-
face, much more plain than that of the broken iron.
   The most useful qualities by which steel excels iron, are the
strong cohesion of its parts,f and the, extraordinary hardness it
acquires when made red hot, and very suddenly cooled.  It is thus
made so hard as not only to cut iron with ease, but steel itself in
its softer state.                    ;
   This excessive hardness is attended with perfect rigidity and
inflexibility,  which makes such  hard steel  in  some  measure
brittle.   Fibs, which are hardened to this degree, can be broken
by a fall.   But the artists temper this hardness more or less, to
fit the steel for different purposes.

  * Should not finery cinder, and all pure oxyds of iron, when reduced by
charcoal and proper fluxes, in the nice experiments of the laboratory, be steel,
and not iron >, Are  they always so?  I think not.....editor.
  f A steel  wire of one-tenth of an inch in diameter, will just bre"ak when
loaded with 900 pounds, if properly tempered, and more  than 700, if soft....
EDITOR. 
208
CASE-HARDENING.
  This is done by heating the hard stet 1  again.   If >ts surface
be made clean by grinding or polisning, then, when it is heated
again, it will  acquire a straw colour, which  will gradually  pro-
ceed to a full gold colour,  with ruddy  purple  streaks, which
afterwards  become  full purple, violet, and deep blue.   These
colours direct the artist in what state he shall arrest the temper,
by dipping the steel into water or grease.  The first appearance
of yellow fits it for  the edges of chizels and punches, which are
to be employed upon iron itself.  The full gold colour, or the
beginning of purple, fits it for chizels which are to be employed
on the  softer metals.  A little  more of the purple fits it for
common edge tools.   And  the  violet or blue fits it for watch
springs.  When  clouds of a dingy yellow appear  among this
blue, it is becoming too soft.
  It would be a very desirable  thing to combine this extreme
hardness of steel with the toughness and tenacity of iron.   The
only way we can do this  is by welding  them together.  It  is
thus that our edge tools are made.  A bit of steel is welded  to
the iron, on that  side of  the plate or bar which is to be worked
into an edge.
  There is another way,  which is peculiarly serviceable on par-
ticular occasions.   We can  convert the surface of any piece  of
iron into steel by cementation, which we can stop before it pene-
trate so far as to make the whole become steel, and brittle. This
is called Case-hardening.  The piece of work, when  very
nearly finished,  is  covered  with a  paste made of charcoal  or
other combustible matters.   Long experience has produced  an
universal preference of animal  charcoals, or rather the crude
substances.   Horn  or hoofs, chopped hair, bone shavings, and
some other fanciful ingredients are made into a paste.   The iron
is covered  with it, and the whole wrapped up in  clay.   This is
first dried and hardened  before the  fire, and then put into the
forge, and  kept of  a  low red heat for an hour or two.  When
taken out, it is superficially  steeled.   In this manner are almost
all the parts of gun locks  treated.  Besides the superficial hard-
ness acquired by it, it is well known that they have incomparably
less friction than when only iron: and they are much less liable to
rusting. 
       IRON....STEEL  ORES....CAST  STEEL.    209

  The extreme hardness appears to me to depend on the extri-
cation of latent heat.   And the abatement of this hardness by
the  temper seems to be produced by the restoration of a part of
that heat.
  With respect to the qualities of steel in mixture, they are
precisely the same as those of iron, except the small differences
proceeding from the excess of inflammable matter which steel
contains.   It is  more  fusible, more inflammable, not  quite so
readily rusted  or  dissolved:  and  it can be reduced  to iron
again, by abstracting,  or otherwise separating this inflammable
matter.
  Besides  the steel produced from bar iron by cementation, we
sometimes have it directly from the  ore.   The  spathose ores
in Corinthia afford it at the first.   The cast metal from .them is
melted in  a pot.   By throwing a little water on it, a plate is
congealed  on the surface, and lifted off:  and this  is repeated till
all  is expended.   These plates are then  melted again, and kept
in a melting heat  for  a long time, which  requires ,a continual
increase of heat; and they are found to be  steel.   An ore  in
the island  of Elba, and  some ores in Barbary, have the  same
qualities with the  German ores now mentioned.  We do not
well know the various processes, many of which seem very fan-
ciful.
   The finest and best "kind of steel is called cast steel:  and  the
process for preparing it was  invented in England.   All fine in-
struments  and razors are now made of it.  (See Note 55.  at the
end of the Volume.)
   I conclude this  article by referring you to Fourcroy, who has
treated this important subject with the greatest distinctness, and
a very fair and copious narration of facts ; so that I think a
judicious  chemist will find himself quite independent of-all his
theories, which seem but ill supported.

                   Medicinal Virtues  of Iron.

    This  metal has always been esteemed as a valuable'article of
 the materia medica;  and furnishes, in its preparations,  medi-
 cines of  great efficacy.  There  seems to be no  foundation,
        vol. hi.              o d 
%   210       MEDICINAL VIRTUES OF IRON.

    however, for the opinion which chemists entertained with regard
    to it,  that, according as it is differently  prepared, it acquires
    powers over the body of a different, and almost opposite nature.
      Iron itself, and most of its preparations, taken into the body,
    has often a very manifest  constringing effect, which is still more
    remarkable  in several of  its preparations,  when applied exter-
    nally, in cases of hemorrhage from wounds, &c   They act with
    some  degree of acrimony and  pain,  in contracting the vessels
    from which the  hemorrhage  proceeds.  They have often had
    this effect, when given in  cases where it was not practicable, or
    not eligible, to apply a remedy directly to the part  itself from
    which the hemorrhage proceeded; as in dysentery, hem(  ^hoids,
    too profuse flow of the menses, lochia?, &c.   These observa-
    tions first established the character of iron as an astringent medi-
    cine.  But its effects  upon other occasions seemed to be of a
    different kind.   Both the  metal itself in substance, and  all its
    preparations, were long noted  as some of the  most powerful
    remedies by which the menstrual evacuation  may  be restored,
    after it is suppressed; and for  promoting the motion of  fluids
    through the whole body.   The saline preparations of iron, if
    exhibited along with  a considerable quantity of water, increase
    very sensibly the evacuations in the form of urine, and of pers-
    piration ; and, if given in  a greater dose, have a quick effect in
    exciting discharge from the guts.  On account of these effects,
    the metal  was also supposed to be  endued with an aperient or
    deobstruent virtue,  attributed to one of the ingredients in its
    composition, viz. the phlogiston; while the astringent  virtue
    was referred to another,....the earth.  And the chemists endea-
    voured, by a variety of processes, to separate  them, or obtain
    some  medicines possessed only of the aperient quality, and
    others only  astringent.  And some  even  imagined that they
    performed this in a certain degree ; so that we still find, in  some
    dispensatories, preparations distinguished by the titles of aperient
    or astringent.  It h, indeed, certain that some of the prepara-
    tions contain a larger proportion of the inflammable metal than
    others.  But it appears from the consent of practical physicians
    on the subject, that this only renders-the medicine more or less
    efficacious,....those containing the greatest quantity of this subtile 
         IRON....ITS MEDICINAL POWERS, &c.    211

  principle producing their effects more sensibly and  certainly,
  bui not differing in the manner of their operation from others.
    The powers by which iron produces its effects are, in the first
  place,  its  astringerlcy; or constricting virtue, a power of bra-
  cing the fibres  over the whole body, diminishing in some de-
  gree the cavities of  the vessels, and increasing the force where-
  with they  compress the fluids.  Secondly, a powerful stimulus,
  friendly to life.  By this it excites or promotes circulation, and
  all those motions in the body by  which the alimentary parts are
  converted into good fluids, and the fluids preserved in a sound
  healthy state;  and  by which all  secretions, both of resremen-
  titious and useful fluids, and all absorptions, are performed in
  different parts of the body.   By this last property,  iron differs
  from lead, which,  together with astringency, shews  a power
  rather of diminishing and deadening motion; and therefore is
  a much more  powerful, though dangerous  astringent.   The
  astringent quality of the preparations  of iron shews  itself, by
v the taste of acerbity, which draws the  mouth together, and by
  Dr.  Hale's experiments with Chalybeate water.   Their stimu-
  lating  effects become  sensible, if a large quantity of them be
  taken: they prove purgative, or even emetic, with a good deal
  of heat and disturbance.  These effects shew, that when applied
  in considerable quantity to the nerves of the  stomach and guts,
  they not only stimulate these,  so as to produce a considerable
  increase of the secretions performed in those parts, but also ex-
  cite  a motion by which they are expelled.   Their stimulating
  effects are likewise extremely evident over the whole system,
  when used in smaller quantity,  so as not to produce disturbance
  in the stomach and guts.  This stimulus is shewn by the warmth
  it diffuses over the  whole body of the person who uses it, by
  giving a fresher colour to the skin, by the vigour and alacrity
  with which it inspires,  in consequence  of exciting a more brisk
  circulation.   Physicians have  doubted whether this action of
  iron proceeded from  its entering the lacteals, and being mixed
  with the blood; because they observed that persons put under
  a course of such medicines  very evidently  void a considerable
  quantity of ochre,  or calx,  in the faeces.  And, indeed,  it is
  certain that the stimulus and constriction with which it affects
  the stomach must have immediate effect on the  whole system, 
212   MEDICINAL PREPARATIONS OF IRON.

on account of the remarkable sympathy daily observed between
the nerves of the stomach and those of every other part almost
of the body.   But it is very probable, too, that some part enters
the blood ; because, although salts obtained from  iron readily
deposit a considerable quantity of ochre, it is not found that they
can be entirely resolved in this manner.   But in whatever way
it acts, it is certain that a very quick change  is wrought in the
blood and circulation.  The belly is, indeed,  often bound in
some measure : and  the costiveness  is produced, probably  by
quick absorption of the thinner parts of the food ; but it is easily
obviated by a small dose of rhubarb.
  Upon  account of these  two qualities, iron and  its prepara-
tions are among the most powerful remedies in weakness and
laxity of the solids, and in watery disposition and poverty  of
the fluids, together with all diseases depending upon such a state
of the body,....such as disposition to dropsy, and anasarca, or
watery sw< lling, fluor albus, gleet,  hysterical and hypocondri-
cal  diseases, indigestion, diabetes,  diarrhoea, and  the too co-
pious flow of the menstrual flux, when these  proceed  simply
from a weakness and relaxation of the solids.  In the chlorosis,
it not only removes the languor, but restores the proper flow of
the menses, by the stoppage of which this disease is either pro-
duced, or very much increased.
  In autumnal intermittent fevers,  when obstinate, and  the bo-
dy much wasted, it prepares for bark.
  The preparations from  iron are  not  adviseable, if the hu-
mours are considerably acrid, or when there are appearances of
a putrid  tendency.  In such cases the nervous system is gene-
rally too irritable.
  When the vessels are very full, iron medicines are hazardous,
for the same reasons ; and indeed it is always a proper precau-
tion to take off some blood before a course  of them.
   In persons of strong and rigid  fibres, and  those subject to
violent cramps, these medicines  have often left sensible effects,
in a disposition to these convolaints.               .. .
   In ulcerated  lungs,  and  old  and obstinate  obstructions
of  the  viscera, they  are  serviceable :  and  it is  always pro-
per to give them in small doses,  and continue them some time, 
MERCURY.
213
  The most certain preparations are, limatura ferri,....ferrum
saccharatum,....crocus martis aperiens,....crocus martis astrin-
gens,....tincturae martis,....sal martis,....flores martiales.

              GENUS IV.....MERCURY.

     Mercury is distinguished by being always fluid, and be-
ing  by far the most volatile of all metallic  substances.   And
these two qualities have laid some chemists under difficulties and
doubts with respect to its proper rank among the metals. They
made  it a question whether it ought to be called a metal or semi-
metal : and many have thought it could not properly come un-
der  either one or other denomination.   But there is no  reason
to doubt that it is a metal.   All the metals are fusible, or capa-
ble  of fluidity,  and  volatile too, as well as it:  and it  differs
from them, only in being more fusible, and volatile than any of
them.  We know  now that it becomes solid, and proves  very
malleable,  when cooled to a sufficient degree, viz.....40° of Fah-
renheit's thermometer.
   Chemists have given much of their attention  to  mercury,
partly with alchemical views, and partly with a view to medi-
cine.  The alchemists probably expected success in their at-
tempts upon it,  on account of its great weight, by which it ap-
proaches more nearly to gold then the other metals then known,
...its specific gravity being 13,568*.  And it became very much
the  object of pharmaceutical chemistry, soon after it was dis-
 covered to be a specific for the venereal disease,  and before the
 best manner of applying it in the cure of that distemper was
 well understood.   Its action on the human body,  as it was em-
 ployed at first, was attended with great inconveniences, and per-
 manent injury,  and even fatal consequences.  It was thrown in
 hastily,  and in  great quantities,  until it brought on a plentiful
 salivation,  which was so violent, that it kept the  patient in mi-
 sery so long as it lasted.   And moreover, the  mercury, when
 employed  in this manner, is  liable to stimulate some other se-
 cretory  organs beside the salivary glands, with a degree of vio-
 lence that is not without danger.
   The chemists imagined that these troublesome effects depen-
 ded upon  somfe noxious  corrosive principle in the composition
   • A cubic foot weighs l.":,568 ounces avoirdupois, or 848pounds. 
214- MEDICINAL VIRTUES  OF  MERCURY.

of mercury ;  and therefore tried innumerable  processes with it,
and  changed it into a thousand forms,  to separate,  if possible,
the noxious  corrosive parts of it, and increase the medicinal
powers of the rest.  But the opinion upon which they proceed-
ed appears to have been  erroneous : and  their labour has been
in a  great measure lost.  Many of their preparations,  it is true,
are useful, and applicable to particular purposes for which crude
mercury is not adapted; and in several,  they reduced it  to the
most efficacious forms:  but in none of them have  they  taken
away its power to produce noxious  effects.   These are only to
be avoided by  attention and  skill  in  the  management  of it.
When employed in the  venereal disease,  it never should  be
thrown in so hastily as to produce a great salivation, by  which
it will run out of the body  again as fast as it is thrown in. We
generally give it in such  quantities as to  bring on a slight spit-
ting  and affection of the  gums; for unless this sign of its  action
can be perceived,  we cannot be sure that its powers are employ-
ed :  but  it never should be  made to act with greater violence.
And we  must be- careful  that it do not excite other evacuations,
and run off by them.  We must  be also  careful to remove or
obviate any disposition to inflammation, which may appear by
inflammation  actually present, or by a fulness and hardness of
the pulse. The first impression of the mercury always increases
the  inflammatory disposition :  and  unfortunate  consequences
often follow.  The fortunate use  and effects of mercury,  there-
fore, depend more on the judicious management of it, than on
its having been  prepared by elaborate  processes.   At  least, if
we consult experienced practitioners, who know more of diseas-
es than of chemistry, the most will give it as their opinion, that
the plain pill or ointment are equal,  for the cure of the venereal
disease,  to  all other preparations.  It is necessary, however,
to make it undergo at least the process of trituration, and that
with  the greatest care,  and in the most perfect manner, that
the parts of it may be divided and attenuated,  and that verv sub-
tilely, to make it  act certainly upon the  human body.   When
thrown in undivided, it runs through the intestines, and produces
no  effect,  or  very little,  and  very uncertain.   It  was the
fashion,  abour fifty years ago, to take mercury in this manner, 
     MERCURY....MEDICALLY CONSIDERED.  215

from an opinion that it had extraordinary good effects, by virtue.
of a spirit, or effluvium, that was supposed to be extracted from
it  by the  intestines, though no part of the mercury itself,  or
none of its grosser parts, entered the blood.  It happened, how-
ever, in some cases, that even the crude mercury,  thus given,
brought on a salivation.  But from its having produced this ef-
fect in  a few cases only,  there is reason to believe that it had
lodged in the intestines, and was divided by their motion.
   When we desire  to  give it with certainty of its producing an
effect, and of the effect  being proportional to the quantity thrown
in, we must take care that it be  prepared  at least by the most
careful division or separation of its particles from one  another.
One way of doing this  is, by rubbing it long and patiently with
viscid and other substances, which,  by  interposing themselves
between the divided parts, hinder them from readily  joining
again.   The substances suitable to  this intention, are axunge,
turpentine, and other balsams ; mucilages,  that is, mixtures of
gummy substances with water : viscid sweete, as  honey ; even
earthy  powders sometimes, and  water.  Boerhaave first pro-
duced  a black powder from mercury by agitating it in water ;
and Dr. Priestley has made many experiments upon this black
powder and  its production, and has discovered a number of cu-
rious particulars relating to it.  You  will see them described in
the volumes  which he has published,  to which I refer you.
   In whatever way mercury is thus divided, it acquires a small
degree of solubility in the animal humours, and affects the tongue
with a sensation of a particular  nauseous  taste,  which shews
that some of it is dissolved by the saliva.   This power in our
fluids to dissolve mercury probably depends upon the ammonia-
cal salt they contain ;  for common  sal ammoniac .plainly acts
upon mercury when rubbed with it.
   But it is also believed by many, that water,  unassisted with
any other  matter, has  some power to dissolve it,  or to receive
from it some medicinal efficacy.  Gaubius, the French physi-
cians, and many others,  aver, that when it is boiled in water,"
it gives to the water the power of killing worms  in  the intestines
of animals.  Such water has been recommended by many as an
effectual and safe  anthelmintic.  And this power it can only 
 216  MERCURY....ITS BOILING TEMPERATURE.

 derive from some small part of the mercury  dissolved in it;
 though, if there be any, it must be exceeding small, as the mer-
 cury does not suffer a perceptible loss.  The water certainly ac-
 quires what is called the metallic taste, not sensible at first, but
 sufficiently so in a few hours, and for a long while after.
   When mercury is exposed to  the action of heat,  it soon be-
 gins  to evaporate and boil like water.  This happens when the
 mercury is heated t^ about 600° of Fahrenheit's thermometer.*
   The vapour of it, when mixed with air, does not immediate-
 ly  calcine, as the vapour of some of the other volatile  metals
 does.   If immediately condensed,  it returns again to the form
 of mercury.  And this metal may be distilled in a retort, with-
 out suffering any material change.   We  can therefore purify it
 by  this process from admixture with other metals, most of which
 it is capable of dissolving or mixing with.  And  it happens to
 be  mixed with them sometimes, either by accident or by design,
 in  different  operations in which it is  employed.  When thus
 mixed, it is called foul or impure mercury.  The signs  of this
 foulness are,
   1st, A flat surface in the phial, not convex  like that of pure
 quicksilver,  the  convexity of which shews that it has more co-
 hesive attraction than the impure.
  2dly, The formation of a pellicle on its surface, in consequence
 of which a sort of wrinkles are formed on it in moving it  gently.
 This pellicle, adhering to the surface of the vessel, leaves a train
 behind the mercury, when it  is made to run from one part of the
 glass to another.
  3dly, The formation of a black powder upon the surface of
 mercury, when  it is shaken in a phial with good or respirable
 air, and still more quickly with vital air.

    *  It evaporates  in  temperatures far below this, when the pressure of
the  atmosphere is  removed.  If a  well  filled barometer be kept near a win-
dow in a warm room, the  part of the tube above  the column of mercury be-
comes dim  within,  on the side next the window.  When thi$ is  viewed
through a magnifying glass, it will be seen owing to small spherical drops
of morcury, which the coolness  of this side of the tube has condensed.  If
the  barometer  be inclined,  so as to make the mercury reach the top of the
tube, it will lick them all  up, and the -tube becomes quite clear....editor. 
   MERCURY...PURIFIED BY DISTILLATION.  21*7

   It sometimes  has the appearance of a pellicle on  its sur-
 face from dust or  greasiness, or dampness adhering  to  it.
 In this case, straining it through thick linen or leather,  or
 passing it through a paper cone, will make it clean. But if it
 become foul again, there  is  reason to conclude, that other
 metals are the cause of its foulness ; and  it must be made
 clean.  There are various methods of doing this.  Simple
 agitation, in contact with atmospheric air, will produce this
 effect. It is  a general fact, that all mixtures of metals attract
 oxygen more strongly  than the metals when separate.   This
 is remarkably  the  case with mercury.    Agitation with air
 quickly produces a black powder, which, when separated by
 filtration and expression,  is found to be  chiefly  a calx of
 the other metals:  and we can obtain the mercury perfectly
 pure by this process.   But some of the mercury is entang-
 led in the powder5, and some is really oxydated.   It is not,
 therefore, the best process for purifying mercury:  and it  is
 but a lately discovered one.   The usual process has been by
 distillation.  Iron  filings are added, and with good effect.
 Their usefulness is commonly  imputed to their attraction
 for the  metallic impurities.   But lead is the most common
 impurity ;  and iron has no attraction for it.  Others suppose
 that they serve only to prevent  any drops of the  boiling
 mercury from starting  over into the neck of the retort.  But
 though sand answers this purpose,  it has  not the  effect of
 iron, which gives the mercury a remarkable degree of bright-
 ness and mobility.
   Iron calcines most easily and rapidly; and must therefore
 be a powerful opponent to the calcination or oxydation of the
 mercury,  quickly absorbing any vital air that maybe in the
 apparatus.   The greasy matter too, which is in  all filings
 of iron, contributes in the same manner to prevent the  oxv-
 dation of the mercury.  I have very frequently perceived a
 strong smell of volatile alkali in the vessels in which mer-
 cury has been  distilled with iron filings..  I apprehend that
this is formed by the union of atmospherical azote with hy-
drogen disengaged by  the  iron from moisture contained in
the vessel and materials.
vol. m.
f. e 
218  MERCURY...CALCINED BY HEAT AND AIR.

   Though  this  metal  does not  calcine  very perceptibly,
when only changed  into vapour to be immediately condens-
ed again, it is not incapable of being calcined.
   There is a process described in chemical books, by which
it is changed into calx or  oxyd by the action of air and hrat.
The  heat applied must be  such as  will keep the  mercury
constantly circulating ;  and it must be applied without in.
terruption for several months, to produce a moderate quan-
tity  of calx.   This is performed  in a matrass of  a low flat
shape, with along neck, and a capillary opening at  the ex-
tremity.  Some chemists also recommend a small opening be.
low.  The mercury is kept continually, thougn gently ' <.i,..,g:
and  after a long time, a red  calx or oxyd appears on its sur-
face, which  continues to increase.   It is called  mercurius
calcinatus,vclprecipitatus, per se. The combination with vital
air in the formation of  this  precipitate, may be very plain-
ly seen by  tying an  inflated  bladder  to the top of the ma-
trass.   It will gradually  collapse, and in a short time be
quite flaccid.  Chaptal, a great practical chemist, says that
it absorbs nearly eight per cent.   It is said that a small por-
tion of gold greatly expedites the calcination of the mercu^y.',,
   The  calx is  much  less  volatile than mercury  in its me-
tallic form ;  and even endures the first beginning of ignition,
and melts into a  beautiful  glass. But if  the heat be increased^
above this degree, the calx is gradually converted  into vaJ
pour, and  at the same time returns again to the form of
quicksilver;  for  these  vapours, when  condensed,  afford
quicksilver instead  of calx.   While  this  reduction of it is
performing, a great quantity of  very  pure vital air is ob-
tained from it, each ounce  of oxyd yielding about fiftv cubic
inches.    This method of producing pure vital air was first
discovered  by Dr. Priestley and Dr. Scheele.  But it is to
Mr. Lavoisier that we  are chiefly indebted for the distinct
account of  this process, and for the ingenious and most im-
portant inferences which may be made from  it.   I may ven-
ture  to state  this  as the most  interesting fact in modera
chemistry.   Mr. Lavoisier saw it in all its importance; and
made a  multitude of  experiments on it, which  are  models
of judicious procedure, and  evince the soundest judgment,
as well  as the greatest ingenuity. 
       MERCURY  AND  SULPHURIC ACID.    219

   According to him, this calx consists of mercury and oxy-
 gen, in the proportion of twenty-eight to one nearly.   This
 oxygen was imbibed from the air in the vessel.   It appears
 from Dr. Priestley's experiments with mercury, agitated in a
 phial, that the production of the black powder (which is also a
 less perfect calx) is always accompanied by the absorption of
 the vital  air of the atmosphere.   For  Dr. Priestley found
 that the air of the phial  was phlogisticated, that is,  by what
 we know now of the matter, the azote was left alone.   And
 when we afterwards agitated the mercury with vital air, he
 found it not phlogisticated, but consumed or absorbed.   La-
 voisier observes that this absorption goes on during the tedious
 process just now described for  the calcination of mercury ;
 for the  calcination soon  stops if the  capillary tube  be shut
 up.   In this case, if we push the heat a little farther, part of
 the calx is reduced again.  And if we go too far, we burst
 the vessel.  When these facts are  compared with the extri-
cation of vital air in the  reduction of the mercurius calcinatus
 per se,  the inevitable conclusion seems to be, that the union
 between mercury and oxygen is so slight, that a very low tem-
 perature is sufficient for separating  them.  Mr. Lavoisier
 varied this experiment in many ways that lead to the same
 conclusion.
   No substance has been so much tortured by  the chemists
 as  this metal.  It has  been united or mixed  with almost
 every substance in nature: and it appears to form some com-
 bination with them all; for by simple trituration with any sub-
 stance whatever, even dry sand, the mercury loses its metallic
 lustre and its fluidity, and becomes black; at the same time it
 becomes  very sensibly sapid, and affects  the nerves of the
 stomach and the secretory organs.   But this is owing to its
 divisibility, and its disposition to oxydate when presented to
 the air  in such an extended surface..
   All the more powerful chemical agents combine with it
 very readily ; and the combination affords a great many re-
 markable and instructive appearances.   I shall first  consider
 its  relation to the acids.....
   1st, The vitriolic acid has no action in the cold, not even
 though  in its  strongest  state.   If  we dilute  it with  water,
 it cannot act on m.-rcu*y,  **.ven though  assisted by  heat. 
220     MERCURY....TURBITH MINERAL.

In order to combine the acid with this metal, we must take
the acid in its strongest state, and employ the assistance of
heat to make it act.  It will then dissolve half or two thirds of
its weight.
   When the acid becomes near boiling hot, it begins to dis-
solve the mercury with effervescence.  This effervescenee is
occasioned by the change of a part of the acid into sulphurous
acid, which change always happens to a part of this acid, when
made to act on metals in its strong state, without addition of
water.   The dissolving metal, not having water to act upon,
and to  supply it with oxygen, attracts a part of the oxygen of
the acid.  This, in consequence, is decomposed, and returns
more nearly to the state of sulphur from which it was origin-
ally produced.   And there are even many examples of the
change of a part of this acid into perfect inflammable sulphur,
when  it is made  to  act in  its  strong state on some of the
metals.   On  account of the change which  a part of the acid
undergoes in this manner, we must use more of it than what
actually remains afterwards combined with the oxyd of the
mercury. In  proportion as  the oxydated metal and acid unite,
they form a saline compound of  difficult solubility, which is
accumulated around the mercury in form of a white matter.
And if we have used a proper quantity of sulphuric acid, the
whole js converted into a white saline mass,  whose regular
crystals are four-sided columns,  terminated at  each end by
pointed pyramids.   Seldom,  however,  does  it attain this
complete form.
   This is a singular salt, and presents an appearance of much
importance to be  attended to in the metallic salts.'  It seems
to  be  a mixture  of  two very different  substances.   For if
boiling water be applied, we separate  from this mass a portion
having a yellow  colour, and  almost perfectly insoluble  in
water,  and not containing a particle of sulphuric acid.  Its
colour occasioned its being called turpethum minerale: and
it was  conceived to  be a perfect calx of  the mercury, like
that obtained by  the action  of heat and air.   It is indeed
found  to  be  a perfect  oxyd, united only  with  the oxygen
which was  separated from that part of  the acid which es-
caped  in the form of sulphurous acid, that is,  deficient in
oxygen.   This turbith.  when urged by strong heat, is de- 
    EXAMINATION  OF THIS  COMPOUND.  221

 compounded, affording mercury in its metallic form, and vital
 air.
   The other portion, separated by the boiling water, consists
 of  the oxyd now described, combined with  the acid ; and is
 a real sulphat of mercury. It crystallizes  in  slender deliques-
 cent  needles.   Still  this sulphat  exhibits  nearly the same
 properties with the mass  from which it was separated.  For
 long  boiling separates the acid from part of it, and leaves it
 in  the form of  a turbith.   And I believe the same effect will
 be produced on what has now been separated, and  that the
 whole  may in this way be changed into turbith.   When the
 turbith, and water  first  poured  on it for washing it,  have
 boiled  together for some time, aneffervescence takes place;
 and some  elastic matter escapes, which I have not examined.
 In these processes,  it is plain to observation that the first
 boiling water separates the greatest part of  the acid.  But if
 the mixture be allowed to  cool, the calx resumes a con-
 siderable portion of it:  and the paleness  of colour shews that
 the turbith  is  not nearly perfect.   The water containing
 the acidulous  sulphat should therefore be poured off imme-
 diately.
   With respect to the other part of the saline mass, which
 has been cleared of the mercurial oxyd, and is a  true sulphat
 of mercury, I must  observe, that it is a very acrid mercurial
 compound, and speedily  destroys  all organized substances'*.
 It  is  much less volatile than quicksilver: and when urged by
 a strong heat, it sublimes without decomposition.  The truth
 is, that the ingredients differ so  little in volatility that  they
 should rise together, and we  should not expect  any decom-
 position.   But if the vapours  come  in  contact  with the
 atmosphere, they seem to be completely  decompounded, and

  * The various appearances which this salt exhibits arise from a different
proportion of sulphuric acid which it may contain.  In its yellow state, it con-
 tains least of all;  when white,  it contains more.  Washing the white mass
with boiling  water makes it yellow, the water taking off the more soluble part.
When this is evaporated and ready to crystallize, or would crystallize by
cooling, the addition of a very minute quantity of acid prevents the precipita-
tion till farther evaporated,....shewing plainly that the greater  solubility
arises from an excess of acid.   Consult Fourcroy for a very distinct account
of sdl these states.....editor. 
222     MERCURY....WITH  NITRIC ACID.

this in a variety of ways, yielding mercury, cinnabar, sulphur,
and sulphurous acid, according to circumstances.
   The  sulphat  of  mercury is  decompounded by alkalis.
Fixed alkali precipitates  the mercury of an  orange brown
colour, when mild, but more approaching to yellow, when
caustic.  Volatile alkali,  in its  caustic state, will scarcely
decompose the sulphat: but by the help of a double elective
attraction,  it decomposes it very readily, when united with
excess  either to carbonic or muriatic acid.   Lime-water
also precipitates the mercury, of a brown  or  yellow colour,
according as little or much lime-water has been employed.
   I observe that some chemists assert, that by repeated dis-
tillation of sulphuric acid  from mercury, in this process, the
mass becomes more and more fixed,  and melts into  a blood
red fluid before it evaporates. (See Cornette Mem. Acad. 1799.)
I have not observed this; nor has Mr. Bayen, who has made
a great many very judicious and interesting experiments on
this subject.
   The nitric acid dissolves mercury more quickly and readily
than any other acid does.   The  most convenient strength of
the acid is when diluted with about an equal weight of water;
in which diluted state it is called aquafortis.   It is properly
diluted when an ounce of it can dissolve an ounce of mercury.
   This solution  exhibits  no remarkable appearance  at first.
Generally the metal  lies quiet for  some little time at the
bottom: and all that we  observe is  a green  colour in  that
part only of the solution, where it is in contact  with the mer-
cury.   This colour gradually spreads farther  up:  and small
bubbles appear rising from the mercury, but are absorbed as
they ascend,  till the green colour produced by them at last
reaches the surface.  They then fly off in the usual form of
red fumes.  If water be carefully added to the mixture, before
the green colour  reach the  surface,  the bubbles will rise a
little way in  the  water before they are absorbed:  and they
tinge it green, and promote the mixture of the acid liquor with
the water above it. By very careful management of the process
in this way,  Bergmann has  sometimes obtained a complete
solution, without any escape of red fumes.  This, however is
a very rare case: and the solution has rare pronerties. Hori ™* 
          PHENOMENA...NITROUS GAS.       223
                       •
 the water been added, and had the  fumes broken out, and a
 complete solution  been obtained, the addition of so much
 water to the solution would have caused a great portion of
 the mercurial nitrate to fall down.  But the solution obtained
 without  effervescence will bear any dilution with water.
   The more common phenomenon of the process is a speedy
 formation of the  ruddy effervescence.  The rise of the  bub-
 bles from the mercury is  accompanied by a considerable ex-
 trication or formation of heat.  And  when the solution is
 carefully observed, the bubbles are plainly  seen to  form in
 all parts of the green liquor.   In short, the acid is changing
 from nitric to nitrous:  and an elastic matter breaks out that
 is deficient in oxygen.  The solution grows very warm : and
 the fumes become  very copious, and blood red.   Hence we
 must conclude, in conformity to the numerous facts  already
 mentioned on different occasions, that the metal is now acting
 on the acid,  and decompounding either the whole, or only a
 part of it, by abstracting from it a portion of its oxygen.
   When those fumes, instead of being allowed to escape into
 the atmosphere, and mix  intimately with  it, are made to  pass
 through a narrow glass vessel, the ruddy colour  soon disap-
 pears  in the  tube .  and  the expelled gas becomes quite
 transparent there, and almost colourless.  It may  be collected
 in the same way that we have  employed for other gases, by
 making  it pass  ipto inverted jars  filled with  water,  and
 standing in a cistern of that fluid.   Taking this  method, we
 find that all the^^cid qualities are gone. The gas has scarcely
 any taste.  -It ha3 very little attraction for water.  Distilled
 water dissolves about one-eighth of  its bulk ;  but retains it
 so weakly that a short exposure to the air dissipates  it com-
 pletely.
   This colourless, elastic,  aerial matter, was first described
 by Dr. Priestley, who called it nitrous air. The  French call
 it nitrous gas.   The most  common name of it in  England,
 however, is  still nitrous  air.   It is now well known to  be a
 portion of the acid of nitre, disguised or changed by the  loss
 of a great quantity of its oxygen, which the dissolving quick-
 silver has abstracted from it.   One proof of this is, that if
 we separate the quicksilver from the acid, either by precipi-
tating it  with a  pure alkali, or by the actipn of  heat alone, 
 Z24 MERCURY...TEST  OF WHOLESOME AIR.

 we obtain, by either way, an oxyd of the mercury, which is
 not unlike to the oxyd obtained by the action of air and heat.
 And like that oxyd,  it yields a large quantity of pure vital
 air, when heated red hot in  a retort, the mercury at the same
 t:me resuming its metallic form.  We have another  proof,
 by  mixing this elastic fluid with atmospherical air,  or vital
 air, which has much,  more effect.  Either of them, by sup.
 plying oxygen,  changes the nitrous  air into nitrous  acid,
 which shews itself in red vapours, and is immediately attract-
 ed  and absorbed by the water.   Much less  of the vital than
 of the atmospherical air is sufficient to produce  this change
 on  the nitrous air: and  it  is  evident, from  other experi-
 ments, that the  atmospherical  air produces its effect only by
 virtue of the vital air which it  contains.
  When these red  vapours are> formed, a considerable heat
 is produced in  the glass.   This heat is  supposed  by the
F'rench chemists to be a part of the heat, or matter of  heat,
or  calorique, which was contained  in  a latent  state in the
 composition of the two elastic fluids.   (See note 56.  at the
 end of the Volume.)
   By means of this nitrous "air, Dr.  Priestley very ingeni-
ously contrived  to  distinguish wholesome  or  respirable air
 from the different kinds  of tainted or noxious air ;  and en-
 deavoured to measure the different degrees of wholesomeness
 or purity in common atmospheric air.  His method of doing
 this is described in the volumes he  has published; and hia.
 apparatus was such as enabled  him to subject  a  small  quan-
 tity of air to this sort of trial or test, as he calls it.   The
 principle of the  method  is  briefly this.  Nitrous air is the
vapour of nitric  acid, deprived of part of its oxyge*n.  If,
therefore, a cubic inch of it  be mixed with as much vital air
 as will make up the deficiency, they will unite and form  nitric
 or nitrous acid,  miscible with water.   If,  therefore, a cubic
 inch of this gas be thrown up into a jar inverted  over water,
 and containing  an  air consisting of  as  much vital air as is
 required by this nitrous air,  and three cubic inches of any
 other gas immiscible with water,  whatever may  be the bulk
 of this compound air,  it will be'reduced to the bulk of three
 inches.   If, therefore, nitrous air be  very uniform  in its
 composition, a single experiment will inform us what bulk of 
       Audiometer...of priestley, &c.     225

 vital air it will unite, and disappear  with,  by absorption  in
 the water.   Therefore, throwing up nitrous air,  till there
 ceases to be a diminution, will inform us how much vital air
 is in the mixture.   Nay, as this requires time, and certain
 complicated precautions, a series of  proper experiments will
 teach us the proportion of vital air, by means o' the contrac-
 tion occasioned  by mixing a given  measure of nitrous air
 with any quantity of compound air : and we may proceed on
 this principle, that 100 parts of nitrous air  absorb 48 of pure
 vital air, so that both disappear.
   Dr. Priestley's apparatus  consists of a tube, in which the
 bulk of  the mixed airs is measured.   It is about three feet
 long; and one-third of an inch wide.   In examining atmos-
 pherical air, or air like it, he mixes two  ounce measures of
 such air with one of nitrous  air  in  a small jar;  and soon
 after throws  up the mixture  into  the long tube, the cavitv of
 which is divided inti  ounce  measures,  and each of these
 into a hundred parts  by a scale :  and  he expresses the result
 of the trial,  by telling the number of these  parts which  the
 mixtue  fills  after the absorption is over.   The  best  air,
 therefore, gives the smallest number.
   In trying  air better than  atmospherical,  he adds to one
 measure of  such air two measures  of nitrous  air, which
 quantity  of the nitrous air is  enough  for  the  purest vital
 air.
   .Other authors have endeavoured to make improvements
 in the manner of employing nitrous air for this purpose. The
 Abbe Fontana has studied this point with  particular care ;
 and  has described his apparatus, or the eudiometer,  as it was
 first called by Landriani, in which there are many neat contri-
 vances.  Mr. Cavendish  also has given some accurate and
 skilful remarks in  the  73d  volume  of  the  Philosophical
 Transactions.  And  Dr.  Ingenhousz has  made some im-
 provements  in the  manner  of using the  apparatus.   But
 the contrivance which appears  to  me the most  simple and
 convenient, as well as the  most exact, is that of. Mr. Saus-
 sure.
   He uses a phial, which he calls the  receiver, containing
about five and a half ounces of  water.   Its diameter and
 height are nearly equal : and it  has  a ground stopper well
     VCL. III.              F f 
226   MERCURY...SAUSSURE'S EUDIOMETER.

fitted.  He has another small phial, called the measure, which
contains somewhat less than one-third of the former.   He
has also a small funnel, and a small exact balance.  (Sous-
sure Voyage dans les Alpes, p. 514.)
   Having prepared the requisite quantity of  nitrous air on
the  spot, he  proceeds  as follows:  1st,  Having filled the
recipient with water, and holding  it  under water in  the
bucket, he  introduces into it two measures of  atmospheric
air,  and one  measure  of  nitrous air.   He  then shuts  the
recipient with its stopper, and shakes it under water, opening
it now and then, to  let in  the water.   This shaking and
opening is performed just three times in every experiment,
in order that  all  may  be perfectly  similar.   2d, The reci-
pient is now stopped close, and its  outside  is wiped quite
dry.   It is then weighed, and its weight compared with what
it would be if three measures of common air had been ad-
mitted.  The difference in his apparatus amounted commonly
to one ounce six drachms and forty  grains.  N.  B.  His
measure contained one ounce six drachms twelve grains of
water.   Supposing, therefore, that  two parts of nitrous air
combine with,  or are decompounded by one of  oxygenous
gas, the quantity of this gas in common air is, by the  above
result,  just one-fifth  of the  whole  common air, or 340 in
1704 :  more exactly, it is 22 per cent.   By such  experiments
he learned that the air of the valleys among the Alps,  and at
 Geneva, is better  than that on the tops  of high mountains by
 about nine grain measures of oxygenous ga&^n the above two,'
 measures*   This is  probably owing to  the action of  plants  '
 during sun-shine.                                jl
   I am persuaded that this apparatus is more useful than the
 expensive and  fragile  eudiometers  consisting of tubes and
 stop-cocks.   But when I reflect on the unavoidable  differ-
 ences in the proportions of the  ingredients  of nitrous  air
 extemporaneously prepared, and on  the different propensities
 of ordinary water to absorb or emit elastic fluids,  I cannot
 think that  these  eucliometrical  experiments are  a proper
 foundation for  any accurate judgment of the salubrity or un-
 wholesomeness of airs.   And I  should be sorry to see much
 dependance placed on them.  I have always considered them
 as too  delicate for the hand of any person but a judicious 
       EUDIOMETRY....IS VERY UNCERTAIN.  227

  chemist, perfectly at leisure.  The odds of 10 or 20 grains in
  1740, is an error from which it would be difficult to secure our-
  selves.   Yet even this is a very great part of the greatest dif-
  ferences that have been observed.  It is also very inaccurate to
  consider this experiment as a test of  the wholesomeness of air,
  and to call the instrument a eudiometer.  Chemically speaking,
  it only measures the quantity of oxygenous gas contained  in
  every air. We know very well, that the commixture of some ex-
  halations, particularly of flowers of the lily kind, in a quantity too
  small to be perceived by such a test, gives the air a power  of
  affecting some of our organs in a way, which, though not im-
  mediately deadly, is yet extremely prejudicial to good health.
    Accordingly, the experiments made to examine the goodness
  of air by employing nitrous air, do not always agree exactly
  together, even though made with the same  airs and materials,
  and the same apparatus.   And when we wish to be exact, it is
  necessary to repeat them  several times, and to take a medium  of
  the results.   And when  we choose to compare two portions  or
  specimens of atmospheric air with one another, the experiments
  for this purpose should always be made at the same time, and
  in the  same  place, and with the same nitrous air recently pre-
  pared ;  experience having shewn that nitrous air is sensibly dif-
  ferent in its quality, "as it is prepared at different times, and  in
  different places.  This is now understood to proceed  from the
  more or less violent change which the acid suffers when we are
  preparing the nitrous air.   A part of the acid always undergoes
'  the changes you have seen: but a small  portion of it  is com-
  pletely flkompounded, the whole oxygen being taken from it:
  and then what remains of  this portion  is  azotic gas, which
  cannot  be brought back  to the  state of nitric acid by simple
  mixture with respirable or vital air.   Ther^e is only one waysby
  which we can bring it back to the state of nitric acid, or convert
  it into  that acid;  that  is,  by mixing three  measures of  it
  with seven measures of vital air, and then  promoting the union
  of the two airs, or their action on one another, by a strong heat,
  or by repeated flashes of electrical fire, in the manner practised
  by Mr. Cavendish, in the course of those curious and important
  experiments which I have  frequendy referred to,  as the great 
228   PECULIAR STATE  OF NITROUS  GAS.

support of the new chemical doctrines and discoveries.   Now,
when metals are dissolved in nitric acid, some  small portion of
the acid is, as I said just now, so totally deprived of  oxygen,
that it is changed into azotic gas:  and  this happens more or
less according to  the violence, rapidity, and heat,  with which
the  dissolution is performed ;  and  therefore the  nitrous air
which we obtain,  turns out different on different occasions, by-
its containing different quantities of azotic gas, and being more
or less fit for the examination of the wholesoinemss of respirable
air.
   By this trial air is judged to be wholesome, or  fit for respi-
ration,  in propoiion to the qu,inutv of  nitrous air which  it can
de.ompc und :   and  this  is known by the  diminution  of  bulk
whit h.happens  in the mixture of the two  airs as  confined by
watt r.   I* there be no diminution of the two airs, the one which
was m  v^d with the nitrous air is totally unfit for the support of
am rial life,  even  for a moment; and if there be but little dim-   j
inution, an animal will die in it in a very short time.
   When common respirable air is examined  in this  manner, by
mixing  it with  an equal measure of nitrous air, the diminution   ':■
of the  mixture, when shaken  with water, has been observed to
be 90 or 100, or 110, ©r even  120 parts in 200 of the mixture,*
with frequent variation however of the result,  though  the trial
be made with the very same materials,  and in  the same place.
   For all these reasons, I think, that it may be worth while to
try whether  Dr. Scheele's way of examining  the goodness of
atmospherical air, or the quantity of  vital air it contains at difV
ferent times, and in different places, may or may notbe prefer. 3
able to this.  Scheele's  way  was,  as you may remember,  by   \
absorbing the vital part by humid sulphuretof iron filings.
   JTo finish  these remarks on  the changes which a portion of the
nitric acid undergoes while it  dissolves the metals,  we  may no-
tice here, that part of it,  on some occasions, is reduced  to  an
intermediate state,  between the state of nitrous air and that of

   * In some of Dolomieu's experiments, the loss was from 118 to 85;  but the
heat of t> e air was very different when so gTeat a difference', was observed.
In the first case, the wind was north-v est, and the thermometer $51.   In the
second it was a sirocco, or siu*h-east wind, and the thermometer 82. 
DEPHLOGISTICATED NITROUS AIR.    229
 pure or perfect  azotic gas.   In this intermediate  state,  it is a
 colourless elastic fluid or gas, like nitrous air; but has different
 properties.
   1 mo,  It is much more absorbable by water,  and  can be sepa-
 rated again from the water by heat, unchanged.
   2do, It is not  converted into nitrous acid by the  admixture of
 vital, or of atmospherical,  or of nitrous air; or,  to express it
 more accurately, it does not unite with the oxygenous gas in
 these airs by simple mixture.
   3tio, Though it is  totally unfit for supporting animal life by
 respiration,  it brightens and enlarges  the flame of  a candle im-
 mersed in it.  And inflammable air mixed with  it  and fired,
 explodes much in the same manner as when it is mixed and fired
 with atmospherical air, but with a green flame.  But it has very
 little power to maintain the combustion of charcoal, or of some
 other combustible substances.
   4to,  It may be produced or obtained from nitrous air, by ex-
 posing such nitrous air to the action of substances or mixtures
 which have a strong attraction for oxygen, such as the sulphu-
 ret of potash, the  humid sulphuret of iron, the muriat of tin,
 &c. From several phenomena which have occurredto me inexpe-
 riments,  I apprehend that the most expeditious way  of obtaining
 it pure, would be to employ the neutral salts formed by the alkalis
 and the sulphurous acid.   I  imagine that it is by such inteime-
 dium that even the sulphurets effect its production.   Such mat-
ters first change  the nitrous  air into this intermediate kind, in
►two or three day*;  and afterwards, by a continuance of their
 action, change it completely into azotic gas, the bulk of it be-
 ing at the same time very greatly diminished.  (See Note 57. at
 the end of the Volume.}
   It may be also produced,  and in a purer state, by some%ar-
 ticular modes of  managing the action of nitric acid upon the me-
 tals,  which we shall notice soon.
   It was first discovered by Dr. Priestley, who gave it the name
 of dephlogisticated nitrous air, on account of its promoting the
 burning of a candle and having the power to brighten and en-
 large the^ flame  of  it.   He  discovered several* different  ways
 of producing it,  and made many experiments with  it.   But its
 nature has been best illustrated and explained by the society of 
230         VARIOUS OXYDS OF AZOTE.

philosophical chemists at Amsterdam, in consequence of an in.
genious inquiry, and a great number of experiments they ,made
with this view.   (See a very good account of these experiments
in the Analytical Review, vol. 17. p. 356.)
   They  are  of opinion, that, like nitrous air, or nitrous ga?,
it is a compound of azote and oxygen, combined by  chemical
attraction : but that it  contains less  oxygen  than nitrous air
does, though a greater quantity than that contained in atmos-
pherical air.  But in the air of the atmosphere, the oxygen is
closely combined with the latent heat only,  or is in the form of
a gas, simply mixed with azotic  gas; whereas, in the sort of
air which we are at present describing, the oxygen is combined,
as I said just now, with the azote, by chemical attraction.
  The chief reason for thinking the union of azote and oxygen
different  in these two compounds is,  that the  peculiar  qualities
of this last take place at a pretty  precise proportion of the in.
gredients, somewhat like other chemical combinations, when a
mutual saturation takes place.   I  cannot say that this is a  very  V
strong argument, although it is not without some weight.   Bat
it is more difficult to account for its increasing the flame  of a
burning body, while nitrous air, which contains more oxygen
similarly combined, so far from having such effect, extinguishes
flame in an instant.
  The proportions of oxygen in these different gases, or  airs,
are thus stated by these gentlemen,^ from some accurate expe*
riments:                                 v3j               £4
   lmo, The atmospherical air is 'known to contaU^ 27 or 28 rfjk
parts of oxygen gas, or vital air, in 100 parts of the air*"       r ia
  2do, The air or gas we are now describing,  contains 37 or 38'" ^
parts of oxygen in the 100.
   Stio, And nitrous air contains 68 parts.
  These gentlemen have given a new name to the gas we have
j ust now described.  They name  it gaseous oxyd of azote.  But
this name is just as proper for nitrous  gas, which is,  like the
other,  azote, in the state of an oxyd,  or combined with oxygen,
but with  less of it than what is necessary to form an acid.  It
would have been better,  therefore, to have named the gas we 
MERCURY.
231
  have  been considering, the less oxidated nitrous gas,  or, the
  less oxydated oxyd of azote*.                ^
     They have also made an ingenious attempt to explain its pe-
  culiar properties, especially the power it has to promote the
  burning of a  candle, and to brighten and enlarge its flame,
  although breathing animals cannot live in it a moment.  These
  apparently inconsistent  qualities y^bjuripute  to the peculiar
  mode of combination of the elemfllHrtjriis gas, which are so
  strongly united, that the oxygen, though it has power to act on
  hydrogen with the assistance of heat, n"as  very little power to
  act on carbon ; and accordingly, the gas has very little power to
  promote or sustain the inflammation of charcoal.  But in the re-
  spiration of animals, it  is necessary that a carbonaceous princi-
  ple be discharged from the blood,  wlBj^arbonaceous principle
  is dissolved and carried taway from tne^nngs,  by respirable air
  in the f rm of carbonic acid gas ; whereas the  gas we have now
  d( st tied cannot serve this purpose.  But it can serve for sus-
        g the flame  of a candle, for this reason, that tallow, and
      fher oils,  contain a much larger proportion of the hydroge-
  i)  us  principle than of any other in their composition.  And the.
  oxvgen of this gas is in that state  which disposes  it to  unite
  readily with hydrogen,  while the  hydrogen is separating  itself
  from  other matter, and before it has time to attract latent  heat,
  and to expand with it into a gas.  This state of  hydrogen was
  named by Dr. Priestley the nascent state of inflammable air.
.^We have alread&had several examples of a greater facility of
Rninion in th^s^artlcmar condition of thingsf.
BSJ The quicksilver, while it produces these changes in a portion
 "' bf,the acid,  is  itself changed into an oxyd, by  its union  with
  the'oxygen which  it has  attracted; and this oxyd of the quick-

  * Surely the name nitrous oxyd, given it by Chaptal and others, is more
 agreeable to the  general plan of the French nomenclature.  This compound
 seems to he in the smallest possible degree of oxydation...'..editor.

  f Perhaps jL.his explanation may not be thought to agree very well with the
 proportion of oxygen that appears, by the experiments of Lavoisier, La Place,
 and Monge, to be required for the inflammation of equal weights of hydroge-
 nous gas and -charcoal; the last requiring so much less than the •former. Nor
 does it agree with the superiority that i9 assigned to carbon, in affinity for ox-
ygen....editor. 
'232 PROPERTIES OF MERCURIAL NITRATE.

 silver is then combined with the remaining acid, or is absorbed
 by it*.
   The compound, or mercurial nitrate, being sufficiently solu-
 ble, part of it will, in a day or two,  crystallize at the bottom of
 the solution.   The rest continues dissolved by the water of the
 acid,  and forms  a heavy, transparent,  and nearly  colourless
 fluid, very acrid and  coigJfl^e with respect to animal and vege-
 table substances.   A drlW^it makes an indelible black mark
 on the skin.   The salt which it contains is sometimes more,
 sometimes less soluble* in water,  according to the quantity of
 acid with which the metal is combined, and in proportion as it
 is new, or has been long kept ; for the same thing happens to it
 in  some degree as to the solutions of iron.   The metal which,
 while it is dissolved,  is^jftlently oxydated to a  certain degree,
 by decompounding a pirr^f  the acid, becomes somewhat more
 oxydated afterwards in the solution : it therefore becomes less
 soluble, or requires a greater quantity of acid to keep it dissolved;
 and with that acid it forms a compound not quite so soluble in
 water as the similar compounds  which contain the mercury in
 a less oxydated state.                                             i
   I may farther observe, that the solubility of the nitrate of mer-    1
 cury  varies  exceedingly  with the  temperature of the water.
 Water boiling hot takes up a great  deal more, which is depo-
 sited  or cooling,  in  crystals.  Nay, for the same reason, the
 acid will dissolve more of  the  mercury,  by the assistance of
 heat,  and this is speedily let go in cooling, and is of a different^  ^
 kind, as we have seen already, from what is^obtain^ from the
 metal when it is  dissolved in a cold temperature, being more ■•  ;
 oxydated.   Also, if  we add a great quantity of distilled water
 to  a strong fluid solution, we have  a precipitation of an oxyd,  ,
 velldwish,  if hot,  and white, if  cold.  A small redundancy of
  * This experiment, the solution of 'uicksilver in the nitrous acid, is, per-
 haps, the most perspicuous and instructive example of the general nature ol
 metalline salts ; and for this reason has met with particular attention from Mr.
 Lavoisier and his coadjutors.  The character of the compounds, in their dif-
 ferent states of oxygenation, are more distinct than in any other example.
 There seems to be several degrees of this : and eacii has a uniform effect, even
 on the structure of the crystals. They are  also very distinguishable, by the
 differences in their affinity for water, being so singularly and uniformly affected
 by its being hot or cold.....editor.                                     " 
                                                            4
              MERCURY....RED PRECIPITATE.       233

    acid prevents this precipitation; so various are the appearances
    of this Proteus metallorum.  But these  differences are similar,
    as I have said, to what we see in iron :  and they  are produced
    in the same way, or by the same causes, only more diversified.
      The nitrate salt  of mercury  has attracted much notice.   It
    was tortured by the  alchemists into a thousand forms, being the
    produce of their favourite mercury, on which they professed to
    build their greatest hopes, and  of Ihe  wonderful acid, which
    manifested the most remarkable and important properties. This
    precipitate is white or yellow in its first  preparation, in the cir-
    cumstances I have considered.  But,  if long continued in a low
    heat, it  becomes of a full red, perfectly similar in appearance,
    and also similar in many of its  properties,  to the mercurius pre-
    cipitatus per se.   It  is called Red Precipitate.
      This compound is much used in medicine and surgery, as an
    escharotic, or  cautery, for destroying  fungous flesh, &c.   It
    has also become of great value  to the philosophical chemist, as
    affording the readiest method for obtaining oxygenous gas in its
    purest state.  It is,  therefore, of importance to. prepare it in die
    most perfect manner, and particularly, to prepare it.so as to be
    uniform in the proportion of oxygen it contains.
      When the mercurial nitrate is simply evaporated to dryness,
    especially when the* precipitation has been partly effected by cold
    water, it is white, or  yellowish ; for  which reason it has been
    called Nitrous  Turbith.  If it be exposed to a very Jbw  red
    heat in this state, a considerable portion  of acid  is driven from
    ft, and becomes &f the fine full red colour,  fit for the marker.
    When this is done in a sand bath, it frequently happens that be-
$:•  fore the central parts and surface-have acquired the proper co-
•  ' lour, the part at the bottom has been deprived of its oxygen, and
    the mercury  revived.   Dr. Higgins,  therefore, performs this
    process in a deep porcelain dish,  under a  muffle,  applying |the
    heat all around, and covering  the  dish with a glass plate.'   A
   small portion of mercurial muriat usually  exhales in this process.
    It arises  from impurity in almost all the  nitric acid that we can
   procure: even a little of the  nitrate itself sometimes toes  off.
   Chaptal, to have it in perfection, with a rich colour, pours fresh
   nitric acid on it,  and distils it to dryness, three times.,
       vol. III.                G  g 
134      VARIOUS  STATES  OF NITRA 1 i

 . I .said that, in the state of a nitrate, this compound exhibited
certain uniform differences in the form and structure of its crys-
tals.   If the solution has been made without  the assistance of
heat, and  the mixture kept close during the  process, and if it
be  allowed to evaporate spontaneously, the  crystals are thin
square pla'tes, whose  four sides are formed into an edge, like
that of a stone-cutter's chizel, and having the four angles cut
off; that is, the crystals are formed of two tetrahedral pyramids,
joined at their base, and having the angles cut off.   (See Rome
del"Isle, No. 38. VI. L.)
   But if  the evaporation  has  been promoted  by considerable
heat,  the crystals are flat-pointed spiculse, having the  flat side
elegantly striated in an oblique direction, like a sword blade which
has been ground by holding it very obliquely  on a rough stone.
 If the  solution has  been effected by heat, the crystals are also
 flat spiculae, like lancets :  but the strise  are now parallel to their
 lengths.  This pointed form of all the  crystals has been much
 insisted on  by the mechanical chemists, in their attempts to ac-
 count for the corroding powers  of the mercurial nitrate, but, un-
 luckily, the most corrosive are the crystals in  flat plates.
   Mr. Fourcroy has treated this subject with the same distinct.
 ness and perspicuity as the solution in sulphuric acid.   And his
 analysis of the different  states of the nitrate seems to me very
 judicious  and instructive.
    The muriaitic acid, in its ordinary state,  has little power to
  act on mercury in its metallic form.  This is^a consequence of;
  the weak  power, or rather want of power, in this acid to oxydatc*
  the metals : and they must be oxydated in some degree, in or
  der to form compounds with acids.  But the muriatic acid, ox-'tfj
  ygenated by  manganese, readily unites with metals in general,~.+■■
  and |brms a saline compound, the oxygen being in this case sup-
  plied to the metal by the acid.   We can therefore easily obtairf
  a compound of mercury and  the  muriatic acid, by employing
  this acid  in its oxygenated state.   Or,  if the quicksilver be first
  oxydated  by air and heat,  or by  other acids than the muriatic,
  tr;at acid will then readily unite  with it, and even separate the
  other acids from it.   *                   • 
            MERCURY....WITH  MARINER ACID.       235

       Whether it has in  this manner separated the mercury from
    another acid,  or dissolved the mercury calcined by the action of
    hea^ and air, no difference can be perceived in  the muriat.  If,
    for example, mercurius calcinatus, and red precipitate (accurate-
    ly  prepared)  be dissolved in separate quantities of  muriatic
    acid, no difference whatever can be perceived.  This must be
    received as an abundant proof,  that red precipitate contains no
    nitric acid, or anv thing that it may not acquire by simple expo-
    sition to heat and air.
       The compound of the muriatic acid and mercury is soluble in
    water ;  but not so easily soluble as the  compound with the nitric
    acid.
       The usual method, therefore, for combining quicksilver with
    the muriatic acid, is, first to oxydate or dissolve the metal with
    another acid,  the  nitric for example, and then apply  to it the
    muriatic, which can be applied  effectually by  several different
•   ways.   We can apply it pure, or combined with an alkali, as in
    common salt.
       When applied pure to the mercurial nitrate in solution, a co-
    pious precipitate,  or  rather coagulum, is immediately formed.
    This is usually  called the white precipitate of mercury.   If we
    apply common salt, or any earthy muriat, we have similar pre-
    cipitate of mercury, and a neutral or earthy salt in solution.
       If, however, we use the oxygenated  muriatic acid, we do not
  .^obtain the same precipitate ; because the mercurial muriat in
   - this case is verjjsoluble in water; whereas the common muriat
W is far les^kso, indeed scarcely soluble, requiring almost 2000
$k times % weight of water, according to Beaume and  Lemery.
f^tXhe muriat, and the oxy muriat (as the French call it) of mer-
£$£ cury, differ also in many other important properties.
^P*    But when th« muriat of mercury is formed by these methods,
    the separation of it afterwards  from the  other acids,  or salts,
    which are in the  mixture,  is very difficult.   These methods,
    therefore, are not convenient for practice : and a different one
    is commonly followed, by which this muriat is formed,  and at
    the same time separated by sublimation  from the other materials
   employed in the  process ;  this muriat being totally volatile in a
   moderate heat. 
236   METHODS FOR  COMBINING ACIDS.

   The proper materials for this purpose are,
   1st, The quicksilver, reduced  e;ther to an  oxyd, or to
a saline compound,  by the action of the nitric  or sulphuric
acii.
   2dly,  Materials which, when heated,  will supply to the
quicksilver a proper quantity of muriatic acid in the form of
dry vapour.  You will find in Newman's Chemistry a copious
list of all these mixtures for procuring a combination of mer-
cury with tht  muri.itic acid.
   The  process which was formerly most generally  recom-
mended in chemical books, was to mix a dry nitrate of mer-
curv  in powder, with an equal quantity of common salt, and
as muth exsiccated sulphat of iron, and tp sublime this mix-
ture. This is a sure  process for obtaining a perfect corrosive
muriat of mercury.
   Ntuman says, and I believe he says truly, that those pro-
ceases in which the nitrous acid has  acud, produce  a more
comphte union of mercury with the  acid.  The mercury is
more completely oxydated by this previous treatment ; and
will therefore unite with a greater quantity of the  acid, and
 make a more active or corrosive compound.   T he truth  is,
that the metal attaches to itself a greater quantity of unmixed
 oxygen  than it  can obtain  in any other way, and  it is  on
 the abundance of oxygen that the corrosive nature of the
 muriat entirely depends.   But the process now practised is
 more simple.
    The quicksilver is first combined with th^e sulphuric acid^
 and the sulphat mixed with dry common salt in fif$e powdery?
 and this mixture is  sublimed.   This is Neuman'sjfseventh
 process.  The  sulphuric acid quits  the quicksilver to join■'$
 itself to the alkali of the common salt, forming with it Glau-  *
 ber's salt, or sulphat of soda; while  at the same time, the
 muriatic acid unites with the oxyd of quicksilver, and they
 sublime together in the form  of a corrosive muriat of quick-
 silver.  The sulphat of soda not being volatile, remains at the
 bottom of the subliming vessel.
    This compound, when well made,dissolves totallyin water;
 but requires about nineteen time-,  its  weight of water.
    When it is less  soluble than usual, we find  that it will
 effervesce with nitric acid, being in a state which resembles in ; 
         MERCURY....CORROSIVE SUBLIMATE.  237

    some degree another preparation, to be mentioned presently,
    in which the mercury is redundant, corroded, but not perfectly
    oxydated:  and therefore it decomposes the nitric acid.   It
    dissolves more easily, if some muriatic acid be  added, or sal
    ammoniac, or common salt; the muriatic acid  in these salts
    acting in some degree, in consequence of the force with which
    it attracts the quicksilver. It is extraordinary that two volatile
    substances,  often  sublime together,  should  become more
    fixed.  Yet  this  happens with  mercurial sublimate, and sal
    ammoniac.
       It must be considered as  a triple salt.   It  is an ancient
    preparation,  and was called sal alembroth, i.  e. salt of the wise,
    or of the artists,  by the alchemists.   It crystallizes readily,
    by cooling the solution made in hot water.
       This preparation was called the corrosive sublimate of mer-
    cury, both on account of its being in fact very acrid and cor-
    rosive, in consequence  of  the quantity of muriatic  acid it
    contains, and also to distinguish it from  another sublimate,
    of mercury which resembles it a little in external appearance,
    but is quite free from any corrosive quality. It is now called
    the hydrargyrus muriatus.   This mild sublimate,....mercurius
    sublimatus dukis, or calomelas,  or  hydrargyrus muriatus, as it
    is now called, is produced by a process whjch was contrived
    at random, in order to correct the corrosiveness of the former
    preparation.
       Corrosive sublimate  is  carefully mixed,  by trituration,
i:V< with an  equal quantity of mercury, or with as much as can
*v  be grounjd with  it, so as completely to disappear: and this
£   mixtt^e is  then  sublimed.   It rises very imperfectly sub-
''.?  limed in the  first sublimation, and therefore of a dirty colour.
(.   Repeating the whole process makes it whiter, and by a third
. *'  sublimation, we have it in its  best state,....a white striated
    mass. The process is exceedingly hazardous to the workman
    who mixes  the materials; for  the  dry  powder is apt to  be
    received into the  lungs; and  a very small quantity may  be
    fatal.  This is remedied in a great measure by adding a little
    water.
       The compound  is a corroded mercury,  quite  insoluble and
    insipid,  having no more taste  than  the mildest preparations. 
  238  MERCURIUS  DULCIS....PREPARATION.

  In it the  mercuiy is  much less oxydated  than  in corrosive
  sublimate.
    I tailed this a random process; because at the time of the
  first preparation of this drug, the chemists had no knowledge
  of any properties of mercury which could lead them to expect
  an intimate combination.  Nay, to this hour it is not tasy to
  say what is the exact nature of it.  The mercury is here not
  merely  oxydated, but  combined  with the acid, in  a state in-
  termediate between that of an oxyd and a muriat.   Beaume,
  a very judicious and experienced pharmaceutist, affirms, that
  by reason of the great difference in the volatility of corrosive
  sublimate  and sweet mercury, the two cannot be  uniformly
  mixed by any number  of sublimations; and recommends, as
  the only way of  freeing the drug from corrosive quality, to
  boil it with water, and a little sal ammoniac, by which all the
  corrosive part is  dissolved.
    This  compound is not very different from  what  may be
, obtained by dissolving mercury in the nitric acid; for  it may
 be saturated with metallic mercury without allowing the for-
 mation of nitrous gas:  and then pouring muriatic acid on the
 solution, a  salt immediately falls down, scarcely distinguish-
 able from mercurius  dulcis.
    The extremely  corrosive nature of the mercurius sublima-
 tus is very  evidently owing to the action on the inflammable
 matter in the substances  corroded by  it.  Mr. Berthollet,,
 while  he  held the Stahlean doctrine, attributed the  corrosiv§&
 quality of all metallic salts to their action on the  phlogiston!',.'^.
 His chief-arguments were drawn from his "experiments with
 this compound.   When digested with vinous spirits^ con-
 siderable portion  became  sweet  mercury, and  some was
 revived. When distilled along with oils, the mercury sublimed
 in  a-metalline form,  and the oil was rapidly destroyed, and
 left a prodigious quantity of charcoal.   He now explains the
 same phenomenon  by the powerful action of the oxygen. No
 doubt there is a rapid combination of oxygen with the inflam-
 mable matters. But we  do not  see how the combination of it
 with the metal tends  to promote ity combination  with other
 substances: and I am by no means certain that the cprrosive
 salts are more so than the acids themselves. It were, perhaps,
 .>■ just to say, that thr- natural  corrosiveness of the acids is 
VARIOUS  COMBINATIONS,  &c.     239
   less mitigated by a combination with metals than with alkaline
   substances.   IS or is Mr. Berthollet's opii.ion consistent with
   the inoffensive, nay sanative quality of the martial and satur-
   nine compounds.
      It is found that there is no intermediate state of oxydation
   between  this of  corrosive sublimate and that of mercurius
   dulcis. When too little mercury has been triturated with  the
   corrosive sublimate, the  mild sublimate is still formed per-
   fectly mild:  but,  under it, next to the vessel, we find  the
   unoecompounded corrosive sublimate.
     ■Thus  we have seen how mercury may be  combined with
   each of  the three fossil acids, and  with some in different
   proportions, and  in different states.
      Mr. Margraaf discovered that  it may also  be  combined
   with the vegetable acids  and with  the fixed alkalis.  And
   Others since, by following his method,  have found that  it  can
   be joined with a  number of other acids.
      Mr. Margraaf's method is to precipitate the mercury from
   a nitrate of mercury, by a pure fixed alkali.  The precipitate
   dissolves with  effervescence in acetous acid, in vinegar, in
   the acid of lemons and of sorrel, and even in Rhenish  wine.
   It requires digestion, but has no difficulty, and a great deal
   is dissolved. See also Fourcroy, IV. 277. also the publication
   of the  Dijon academy. The acetate  of mercury is the basis
   of Keyser's pill.
      With  respect to the order in which the acids attract mer-
   cury, I shall only observe, that of the fossil  acids, the sul-
   phuric anrj the Muiriatic  attract the  metalline oxyd  more
   strongly  tlfen the nitric,  as appears by  the  process of  the
  ' corrosffe sublimate.   The  sulphuric  acid finding the mer-
   cury properly oxydated, unites  with it very readily, without
^: \ the assistance of  heat.  These two acids can also be combin-
  ' ed with the mercury, by double elective attraction, or double
   exchange,  when  neutral salts which contain them are added
   to the  solution of mercury  in  nitric acid, e. g. vitriolated
   tartar, or Glauber's  salt, or vitriolic ammoniac ;....and in  the
   same manner, any of the compound salts which contain  the
   muriatic acid.
     Mr. Chaptal gives another process  extremely simple ; and
   recommends it as producing a very perfect mercurius dulcis. 
240      VARIOUS  DECOMPOSITIONS, &c.

Decompose mercurial water (solution of nitrate of mercury)
by a solution of common  salt.    This throws down a white
precipitate, which gives by sublimation a mercurius dulcis.
Scheele practised the same process.
   And by a similar double exchange, this metal may be easily
combined  with  the acid of tartar, or  with that of salt of
sorrel, with which acids it forms a pearly precipitate, that is
probably the preparation of mercury used in Chini.
   It can also  be combined in the same manner with the acid
of phosphorus.
   Let us next consider how it may be separated again from
the fossil acids....I said already, that neither the sulphat nor
the muriat of  quicksilver can be decompounded by heat;....
the acid and  metal in these compounds rise  in vapour toge-
ther.
   It is not so with the nitrat.   The quicksilver remains in
the form of a red oxyd, which if the acid be expelled from it
as completely as possible, by the continued action of heat,
becomes very  similar to the calx or oxyd of quicksilver pre-
pared by the action of air and heat.   By the deep colour of
the vapours of the nitrous acid thus expelled from the quick-
silver, as well as the appearances during its  dissolution, it is
evident that the  metal retains a great quantity of the oxygen
of the  acid.   This oxyd is much less volatile than mercury:
but if  made red hot,  it is totally converted into vapours or
elastic fluids.
   In collecting  these vapours,  we obtain by a proper appa-
ratus,                                    s<
   lmo, A quantity of nitrous acid in red fumes, bvtf; too small
to be condensed.                                  V        -d
  2do, A small portion of the quicksilver, which is combined. .-H
with a part of the  acid vapour, and forms  with it a-yellow
subjimate in very small quantity.
   Stio, The greater part of the quicksilver gradually distils
over, restored completely to its fluid metallic form,....and
  4to,  Along with this a large quantity of vital air is obtained.
This vital air is  much purer than that  which  is obtained
from nitre.  Still,  however,  it is not perfectly pure.   It is
always tainted  with a minute  quantity of  azote ;   and, I
/ 
 DISCOVERY  OF OXYGEN BY PRIESTLEY.  241
                    r
believe, with a small portion of the nitrous acid, and  even of
the quicksilver itself.
  This manner of preparing vital air was first discovered by
Dr. Priestley.
   He obtained it from mercurius calcinatus,  by means of a
burning glass,  on the 1st of August 17 74 :  and soon after,
from red lead.moistened with  nitrous acid, by distillation in
close vessels.   Next month he went to Paris ; and communi-
cated his discovery of this wonderful fluid to Mr. Lavoisier,
and other members of the Academy of Sciences, then assem-
bled at his house, who were surprised and delighted with the
discovery.'  Returning to Britain, he engaged in so many re-
searches that this had but a share of his thoughts.   Mr. La-
voisier, with perhaps as much curiosity, had more of  a philo-
sophical and scientific mind, and  was a much better reasoner
than Dr. Priestley. He took a juster view of ihis expeiiment;
and  saw at  once  its  vast importance in philosophical  chemis-
try ; and he repeated Dr. Priestley's experiment with an at-
tention and exactness in all  his measures, that was altogether
his own.   He was the first who  made it certain that mercury
and  other metals have the power to decompound the acid of
nitre;  and that we are thus enabled to obtain from it  two dif-
ferent substances in their separate state,  namely nitrous air
 and vital air.    We obtain by  itself nitrous air or nitrous
 gas, while  the mercury is  dissolving.    And we obtain the
 vital air afterwards, when we expose the dissolved or cor-
' roded mercury toja strong heat.  And if we' mix these two
 elastic flujcls  together, they immediately unite, or their fun-
 dament^,  matters  or  bases unite, and  form  again nitrous
 acid.
   It is plain that I  here speak of pure azote and  pure oxy-
 gen.   But it is  very difficult  to obtain these  in  a  gaseous
 form, and  at the same time perfectly pure.  The processes
 for  obtaining them always leave  a taint of the substances
 from which they are obtained.  It  is not difficult to procure
 the  a^ote very pure.  Lime will free it  from carbonic,acid :
 and hepar  sulphuris will free  it from oxygen.   It  is  more
 difficult „to procure vital air perfectly purey  and, especially,
 free from  azote.   The  red  nitrate of  mercury affords  the
 best process I know for it.   But  I have generally  found it
     vol.  in.                  n h 
 242  MERCURY....VARIOUS  PRECIPITATES.

 tainted with nitrous  air, and with azote.  I call your atten-
 tion  to this circumstance ;  because many of Dr. Priestley's
 experiments, by which he conceived that the theory of Stahl
 was supported, had  results which were certainly owing to
 such impurities.  I  have particularly in my eye at present
 those which he published in 1792.
    1 hus, therefore,  we can by heat alone recover mercury,
 which has been combined with the nitric  acid.
    We  cannot in  the  same manner  separate the  other two
 fossil acids from mercury alone.  I observed  already,  that
 they adhered to it too strongly; but we can separate them by
 other substances which have a stronger attraction for them
 than mercury has,and some of these bodies still more readily
 separate the nitric acid.
  ,  The  substances, which may be thus employed to atrract
 these acids more or less perfectly from the quicksilver, are
 very numerous.
    1st,  Water applied in large quantity, and especially if
 heated,  will  in  some  cases  produce  a partial  separation.
 This is remarkable  with respect to the sulphat of quick*
 silver.
    In washing the mercurius vitriolatus to make turbith,  it is
 plain that the  first boiling water takes  from the mercurial
 calx the greater part of  the acid.  If, indeed the  mixture be
 allowed to cool, the  calx resumes a great part of the acid
 again, and  becomes  soluble.    I have examined  again  and.
 again the quantity of acid it contains in these different states^
 wuh  care: and the differences are very sensible.  -It is diffi- f
 cult to say whether the heat increases or diminishes.chemkal
 action in this  experiment.  It is owing, in all probability, to
 the different proportions that are necessary, in different tern-.-
 peratures, for  saturation,  when we mix the  compound of
 ox\d and acid with the  compound of water and acid.  If
 this proportion  vary  very much with  respect to  the  last of
 these compounds, and very little with respect to the first, the
 phenomena will be what we observe.   The nitrate is not so
 liable to be  decompounded by water: but if largely diluted,
 it suffers also  a ftttle decomposition.   The muriatU«ann©t be
decomposed by pure water alone.                 '*-<*$ 
EXPLANATION OF  THEIR VARIETIES. 243
    2do, The precipitates by the fixed alkalis are of a reddish
  brown colour, approaching thereby to that of a pure oxyd of
  mercury.  The reason is, that they are  nearly pure oxyds, but
  not  perfectly pure.   They retain a small portion of the acid.
  The fixed  alkali has  taken from them nearly the whole,
  but  left a minute quantity,  which adheres  strongly to  the
  oxyd.
    But the precipitates by the volatile alkali are remarkably
  different from these, and from one another; the nitrate giving
  a grey,  and  the muriat a  white  precipitate.   The cause of
  this difference is,  that the  volatile  alkali has much  more
  power to separate nitric acid from quicksilver, than to sepa-
  rate muriatic acid from it.  The volatile alkali has a stronger
  attraction for the nitric acid than for the muriatic acid :  and,
  in addition to this, the mercurial oxyd does not retain nitric
  acid so  strongly, by far, as it retains  the. muriatic acid.   In
  the white, or muriatic precipitate,  therefore, the  mercury
  retains  a considerable part of the acid, but not enough to
  render it soluble in water.   In the dark-grey precipitate from
  the nitric acid,  not only the acid is almost totally separated,
  but a great part of the oxvgen and the  quicksilver is restored,
  in part, to its metallic state, by the superfluous volatile  alkali
  employed in forming the precipitation.  1 he volatile  alkali
  contains hydrogen to attract the oxygen.  There is, however,
  combined with the mercury, a very small remainder of the
  .acid, and some  of the volatile alkali.   And it also retains a
^ small portion of ^e oxygen.
     There  arose great varieties and uncertainties on the  sepa-
$ ration oV mercury from  corrosive sublimate, by  means of
  volatile alkali,  depending  much on the  management.   The
  reason is,  that the acid seems to attract the  mercurial oxyd
  'more powerfully than it does the volatile alkali: for if mer-
  cury be dissolved with sal ammoniac, we instantly disengage
  the alkali in a caustic state.   When  this alkali is applied to
  corrosive sublimate, it takes up such acid only as is not neces-
  sary for saturating the mercury ;  and with this forms sal am-
  moniac, leaving the rest  in the form of mercurius dulcis.
. Lemery observed this, by collecting and subliming the pre-
  cipitator 
244  MERC....SEPARATION FY OTHER METALS.

  3tio, Quicklime, too, has power to  attract the acid from
quicksilver, and to precipitate it even from those acids with
which it is most strongl\ combined.  The  change of colour,
when much lime-water is added,  seems  to proceed  from
some  action  of  the  lime on  the  mercury which has  not
been  examined.   Half a  drachm of corrosive sublimate,
thrown into a pound of lime-w..ter, forms  a yellow precipi-
tate.   This water  is  used, before subsidence, for cleaning
the skin  from pimples, tetters, &lc.  by the name of Aojja
Phagedenic a.'
   Mr.  Bayen  discovered  that the precipitate  of mercury
from the  acids  by means of alkalis,  particularly the mild
volatile  alkali, or by lime-water, when ground with a small
portion  of  sulphur, forms  an exploding compound, similar
to pulvis fulminans.  If  exposed to heat, slowly .increased, till
it melt, it explodes with great violence, leaving a residue,
which  sublimation shews to contain meicury  and  sulphur, by
forming a good cinnabar.    Something approaching to this
had been observed by  Brugnatelli, and others, and also very
remarkable detonations by  concussion.   (See Note 58. at the
end of the Volume.)
   4to, Precipitation of mercury with milk may be .mentioned
here.    A  saturated solution of mercury with  nitric acid,
mixed with hot milk,  gives a rose-coloured precipitate of
mercury:  but when the milk is but just  warm, it is of a
purple  colour.    The  intenseness of  the colour, and  the-
firmness  of the  coagulum,  depended on the   heat of the ...
milk.  They are soluble in all the acids, and are mild tasted, yj
Other metallic solutions  form  a  coloured  coagulum  with;*
milk,  in the same manner.                                 il
    Many of the other  metals have a stronger attraction for  y
acids than  mercury: but these, in general, precipitate it'in
its metallic form.
   If a piece of clean  copper be moistened with the nitrate
of mercury in solution, and, after remaining a few minutes,-
be dipped in water, the surface will be  found whitened :  and
if  it be  then rubbed hard with a clean  and soft linen (loth, it
will be as bright  and white as silver.   Putting this in. a low
heat, approaching to incandescence,  the  whitening film eva. 
  REVIFICATION...MERCURYAND SULPHUR.  245

  porates, leaving  the surface  corroded by the nitrous acid.
  Had the copper been allowed  to remain long  enough in the
  soLution,  it would have been  dissolved entirely ;  and  run-
  ning mercury would have  been found at the  bottom of the
  vessel.   (See Note 59. at the end of  the Volume.)
     Such is the variety of appearances this metal can be made
  to  assume  by the  action  of salts,....red, yellow, white,
  black powders, white transparent soluble salts.   In some of
  these states it is much more fixed than before.
     But however it is thus changed, it can be  easily  restored
   again to its natural  form.    It returns  readily to its usual
   form,  when exposed to heat, along with substances which
   can attract the acid from it, provided they separate the whole
   acid, or nearly  the  whole, and reduce the  mercury to the
   state of a pure oxyd.   This  oxyd, as  I observed before,
   when heated to a certain  degree  in close vessels, recovers
   its metallic state.   The substances added are iron filmg^, or
   fixed alkali, or quicklime, &c.    The  restoration of the
   mercury  is not called reduction,....but  Revival:  and the
   mercury  is said to be revived.    This  refers to its name
   Argentum  Vivum.
     When  an  oxyd of quicksilver is  revived  by the simple
   action  of heat,  and without any addition, it often happens
   that besides the vital air, which it affords in  great quantity,
   there is mixed  with this  a small quantity of carbonic  acid.
   This is supposed to have been attracted from the atmosphere
   when the oxyd was too much exposed to  it.

     Neitfier mercury nor its oxyds can be made to combine
;  with earthy substances, being too volatile.
      Of  the inflammables, sulphur  alone  is disposed to unite
 '. jiiith mercury.  Other inflammables are only employed to
   divide  it.  Sulphur may be combined with mercury, either
   by long and patient triture, or, more readily, by the assistance
   of heat,  viz.   by melting the sulphur, and  pouring in the
   mercury warm, and stirring well.   The compound  in either
   case is of aq intensely black colour;....hence, probably, called
   «th'i9p\.\   When prepared by triture alone,  the mercury is
   grad^Jly divided and  disappears;  the mixture becoming
   £rey and/, blackish.   But although the mercury appears to 
246      MANUFACTURE  OF VERMILLON.

be perfectly incorporated with the sulphur, it does not acquire
the full black colour until it has been kept for some time, especi.
ally if kept warm.  Indeed, I find that the union by trituration
is rendered at least three times more expeditious, and  the com.
bination more perfect, by a heat just enough to make the sulphur
emit a sensible smell.   Perhaps a little more heat would still
improve  the process.   But still, after the longest keeping, the
mercury and sulphur  are more easily separated than  when
mixed by fusion.  When the mixture is made by heat, they are
more perfectly combined.  But if they  be  made too  hot, heat
and flame are produced,  seemingly by a sudden extrication of
heat in  the  very act  of union.  This  again arises from two
causes: 1st,  The compound  may have  a less capacity for heat
than the sum of the ingredients.  2dly, In the act  of  combina-
tion the mixture becomes stiff, and sometimes hard.  The heat,
therefore, which makes an ingredient  in their fluid forms, as
latent heat, now emerges in sufficient quantity to kindle the sul-
phur.  One  part of sulphur is capable of forming a  perfectly
uniform avhiops with five, or six,  or even  seven parts of mer.
cury.  They are united together in this  proportion for  obtaining
another preparation of mercury, viz. Cinnabar,  or  Vermil-
lion, by a brisk sublimation, in oval or oblong vessels  of coated
glass, or of earth.
   This preparation forms  a very  considerable  manufacture,
chiefly  carried on in  Holland, to  supply the market  with the
great quantity used in painting, and for medicinal  preparations.
And  the  descriptions  given  by authors of  approved  processes
are numerous, and  have considerable  varieties.   The  most
valuable property of the compound is the richness  of its colour.
When this is very deep or full, a moderate quantity of this ex-
pensive article  bears dilution  with a great deal of  other colour.
The fulness of colour corresponding also to its purity, becomes
a general test of its goodness.   The attention of  the  artists is
therefore, chiefly  directed to this circumstance.  It is  found
best  to use an  aethiops prepared by fusion.   That obtained by
trituration and  digestion is apt to separate, in part, in  the' subli-
mation.   Stahl's process, or that in the London Pharmacopoeia
1788, seems to me the easiest and best. 
VARIETIES IN THE PROCESS.      247
   The mercury is made hot, and  poured into the melted sul-
phur, and the mixture carefully stirred.  The flame should be
extinguished by covering the mouth of the pot.  The compound
is then powdered and sifted,  and rammed into an oval shaped
vessel, so as to fill one-third of it.  This is set in sand up to the
neck ; and has  its mouth open, in order to allow the escape of a
fuliginous vapour of irbeombined materials.
   When these fumes are condensed, they form a mass as black
as pitch.   It is composed of the superfluous sulphur: and this
is blackened by a small quantity of the metal loosely combined
with it.  The sublimation is carried on with a brisk heat: and
it produces a very good cinnabar. Beaume says that two or three
sebsequent sublimations greatly improve its colour.
   The sublimate is  a solid cake, of a blood  red  colour, which
grinds to a red, so much the brighter as it is more levigated.
It may be made so fine as to become too pale.  Chemists have
wondered at this red colour, imputing it to some kind of oxyda-
tion:  and indeed  an experiment of Lemery's seems to confirm
this.  Vitriolic acid renders it white, and fit to afford turbith:
and the operation is accompanied with effervescence.   Now we
know that the acid does not attack it till it be oxydated.
   Hoffmann mentions a process by which he  produced cinnabar
without sublimation.  He  mixed  running mercury  with the
volatile tincture of sulphur, that is, the  compound of sulphur
and volatile  alkali.   The mixture' was  long  agitated violently.
It soon became btack, and at length grew a beautiful red, and a
perfect cinnabar.  Beaume describes the  same phenomenon as
a discovery of his own.
   Mercury is also said to be  affected by  the fat  oils.  In par-
ticular, it is said to acquire some ductility, if poured boiling hot
into lintseed oil.  I  have not observed any thing of  this sort;
nor can I indeed have any notion of the ductility it can acquire.
A solid that  is brittle or friable  may become ductile: a fluid
cannot.   It may be  rendered  sluggish, clammy, and perhaps
viscid -or tough, like melted glass, or sealing wax.  But I have
never 'observed this change produced on mercury by the treaty
mentaow mentioned. 
248    MERCURY....W1TH OTHER METALS.
                                                    *
   All  these combinations of mercury with sulphur are decom.
posed, and the mercury revived again, by distillation with quick-
lime, fixed alkali, iron filings,....all of which retain the sulphur.
The mercury obtained  from  cinnabar,  is  thought to be  the
purest that can be had:  and  that obtained by means of iron
filings is thought to excel the rest.   I am sensible of its having
a  more  perfect colourless brilliancy.   Its density is  also  the
greatest.

                   Relation to other Metals.

   Mercuiy unites with all the metals except iron, arsenic,  and
platina.   With  the  regulus of  antimony,  indeed,   it unites
very imperfectly, as we shall  shortly see.   And  its more inti-
mate union with the other metals will also be considered in their
places.
   Although arsenic does not unite with mercury, it affects the
mercurial compounds, and is itself affected in a particular man- ,
ner.   If reguline arsenic be heated with twice its weight of the
mercurial  muriat (corrosive  sublimate) in  the way of distilla-
tion, the vapours condense into an  oil-like liquor;  part of which
grows gelatinous,  and almost like very soft butter which  has
been melted, being grumous or a little granulated, which I take
to be an incipient crystallization.  When this has finished, the
vapours condense into metalline quicksilver.
   This is a curious process.   Neither the mercurial muriat, nor
the regulus of arsenic, are so volatile  as this compound:  and
the regulus is not so Volatile alone as mercury is.  The fluid and
gelatinous matter are a compound of arsenic and muriatic acid.
Water decomposes it in the same  way as it does other metalline
salts; that  is, it separates it into two parts," one of which  is
nearly in the state of an oxyd, and the  other contains this oxyd
dissolved  in the acid.  This  oxyd is an  intermediate  state be-
tween that of the arsenical acid  and an  arsenical,oxyd.
   I mav remark on this  occasion, that  mercury clears the acid
of arsenic (white arsenic) from sulphur and other inflaVnmable
matters which  frequently make it foul.  With the  sulphur it
forms an sethiops, whuh yields cinnabar in the usual way.   I do 
AMALGAMA....NATURE  OF.        249
not see so well how mercury can separate the other impurities:
and it is the more remarkable, because  all other  metals  (silver
and gold excepted) render arsenic foul.
   I may also remark, that all the metals, when they decompose
the muriat of mercury, form the same kind of butter-like com-
pound: and  it is most violently corrosive,  destroying  all  or-
ganized bodies in a minute.  Leaks in the distilling apparatus
are, therefore, productive of the most fatal consequences to  the
operators.
   Mercury is susceptible of mixture, in some manner, with all
the other metals.  And  such mixtures, called  amalgamate,  are
of different consistency, according to the proportion of the  in-
gredients.   If there be little of the other metal, they are fluid;
if more, they are soft, like  paste  or butter.   If there be less
mercury than an equal weight,  they form a sort of solid, more
or less brittle  and friable, in proportion as  there is more or less
mercury.   The colour of these mixtures is always white.  In
amalgamas that are very soft or  fluid, the mercury is in two dif-
ferent states.  Part of it is fluid, and nearly pure.  The  other
part is united  to the metal in a  solid form, in the same manner
as water is united to salt in crystals of salts.   This solid matter,
composed of the metal and part  of the inercury,is felt like gritty
grains in the amalgam : or  sometimes it actually forms oblong
crystallizations in it.   Thus, if we dissolve gold in boiling
mercury, so as to form a soft amalgam, and then allow it to cool,
the gold crystallizes or concretes with part of the mercury into
sp*icular concretions, which are  felt  by the  fingers.   Hence
amalgams, if fluid, may  have part of the mercury imperfectly
separated by  expression  through leather; but  long triture, or
long digestion, seems to produce more intimate union.   It can
be separated, however, by distillation.
   Upon the  discovery of these preparations of  mercury,  in
mixture with the  different metals, have been founded the arts of
separating  gold  and  silver, but  especially  gold,  from  their
matrices,  (of  which hereafter) ; also  the  art of foiling  glass
for mirrors ;  and that of gilding silver, copper, or brass.
   The process for foiling glass mirrors*is performed, in the fol-
lowing  manner.  The glass is  laid flat on a very smooth and
       vol. in.                T  i 
350 MERCURY....FOILING  MIRRORS....GILDING.
firm table.  A small border is made all round the. edges, to hold
in the mercury.   The  glass is then wiped  very clean ;  and
sometimes rubbed over with a piece of soft leather, on which a
little amalgam of mercury  and  tin has been spread.   It is then
covered all over with tinfoil; and mercury is poured  on  it, till
the border is full.  The mercury  penetrates the tinfoil, and makes
it lie close to the glass, like a wet cloth.   Indeed mercury pene-
trates the tinfoil  just as water  penetrates and  softens a cloth.
When this has remained some  time, the  mirror is slowly raised
on  one edge, that the superfluous  mercury may run off;  and it
is allowed to stand  in that position  some days.  Thus  all the
mercury not combined with  the tin  gradually  subsides  to the
lower edge, leaving only what  is necessary for keeping the tin-
foil adhering to the glass plate.
  Glass globes are coated on the inside, by warming them very
much, and pouring  in some  fluid amalgam, which adheres to
the glass  like water.  By  turning the globe round and round,
the whole inside may be thus smeared with the amalgam, so as
to look like a metal globe highly polished.   But when held be-
tween the eye  and the  window, we discover that it is covered
only as with a cobweb of the metal.
   Silver and brass are gilded by smearing them  with an amal-
gam of mercury and gold.   This  makes them as covered with
silver.  The piece is then put  into an oven : and the heat eva-
porates the mercury, leaving the gold  adhering to the piece, in
the form  of a dirty brown powder.  This is now  gone over
with  a fine burnisher,  made of steel or of haematites,  highly
polished.  This flattens down all the particles of the gold, spreads
them out, and causes them to adhere, while it also polishes them.
Copper and brass  acquire a skin that is undistinguishable from
gold.  But this gilding on  silver has always a brown colour, very
distinguishable.   Moistening  the surface of  the  piece with
aquafortis causes the gilding to be more  uniform and adhesive:
for whenever the mercury touches the wet surface, the metalline
nitrate adhering to it is  decomposed by  the copper:  and some
mercury is left on  it  in a metalline state.  The buttery amalgam
unites with this very readily-: and when the mercury is.expelled
by  heat,  the gold remains.   Without this precaution, parts of 
ORES  OF MERCURY....ARE RARE.     251
the surface refuse to let the amalgam attach itself to them.   In
consequence of the  same properties, it may also be applied to
some useful purposes in medicine and surgery; to dissolve a
lead ball,' a piece of  leaden tube, or probe, in the bladder * also
to take off a ring from a swelled finger.
  All the metals exhibit a peculiar appearance, when employed
to decompose the muriat  of mercury.   They unite with  the
acid  in a soft buttery form.   Another general circumstance in
this decomposition is, that this butter is more volatile than the
muriat, and even than the mercury, although the metal employed
may be much more fixed.   These  compounds will be mentioned
in course: but I thought it proper to make you notice these ge-
neral characters.

                      Ores, or Origin.

  Mercury is scarcer than gold.   The only mines are at Alma-
den, in Spain ;  Idria, in  Hungary ;  in  the Dutchy of Deux
Ponts ; in  Friuli, in  Italy ; in the East, and in the Spanish
West Indies.  Small quantities are sometimes found in France
and  Britain.  Virgin, or  fluid mercury, is often interspersed
through other minerals. But 'the  most common ore  is cinnabar.
The fluid mercury is oftenest found where cinnabar is most
abundant.  I think that the  rarity  of this metal, and  even of
small portions of it  mixed with other ores, is an abundant proof
that there is no such thing as a mercurial principle, the basis of
metallization.   Were  it so, we should find  imperfect  metals
very frequent,  and  in different stages of the  progress, to the
state of perfect metal.
  The account  given of the chemical  properties of mercury
makes it easy to perceive how we shall obtain it from its ores.
All the processes, performed at all the mines,- are distillations,
managed with more or less art, and Varied according to the na-
ture of the ores.  Even where found in ? fluid form, it is gene-
rally in globules, too small to be  separated by the hand, or  by
pounding and washing. It is  much easier to do it by distilla-
tion.   The cinnabar ores are generally mixed with so much cal-
careous matter,  that no addition is necessary for separating the
sulphur.   When this is not the case, (as at Deux Ponts,) slaked 
252    MERCURY....WORKING OF  ITS ORES.

li.ne is mixed with the ore in the retorts.  These are placed in
a row, in a long furnace like a gallery.   Their  necks project
through  holes in the sides.  To these are fitted receivers con-
taining water,  into which the  mercury  falls.   At Almaden in
Spain, a long row of earthen aludels go from each retort, down
a gently sloping terrace, and  then  up  a  similar terrace ;  and
terminate in a chamber,  having a concave floor, and a tall chim-
ney.   The  distillation is forced by  considerable  heat: and the
vapours condense in the aludels, both in the descent and subse-
quent ascent   What are not  condensed  there, are condensed
in the chamber.   The sloping1 position of  the aludels causes the
mercury to run out of the higher into the lower,  on both sides
of the valley formed by the two terraces: and.all of it collects
in the aludel at the bottom.  This one has a short pipe,  or neck,
in its under side, which is plunged  into a hole cut in the stone
which forms the gutter between the two terraces.  The gutter
is filled with water.  From this construction, it is plain the
aludels  have no communication  with  the  air, except by the
chamber.   The  distilled  mercury,  therefore,  runs out of the
lower aludel of each row ; fills the hole in the gutter ;  and then
runs over,  with water above  it, into  the gutter.  This has a
very small declivity towards one end.  The mercury, therefore,
runs along this gutter into a gutter at one end of it.   Thus the
distillation  is carried on with rapidity :  and there is no risk of
bursting the vessels, or of the vapour escaping by any leaks.

              Medicinal Preparations of Mercury.

   The very great activity of mercury on the human body, and
 its effects when  exhibited as a medicine,  are so  remarkable in
 the  treatment  of many diseases,  that physicians have  turned it
 into almost every possible shape :  and the mercurial preparations
 are   almost innumerable.  In this respect  it has but one rival in
 the  fossil kingdom, viz. antimony, the preparations of which
 are  no less various.   To  pass them by  would be highly impro.
 per.  But to describe them all would require a winter's session;
 and  would  be no less improper.   I must content myself with
 considering them in txvo points of view.  I shall describe such
 of them as indicate any singular chemical property of "mercurv 
ANTIMONY.                  253
and antimony, by which your chemical science is improved.   I
shall also take particular notice of any connection or dependence
that I can discover between the medicinal effects of the prepa-
rations, and the general chemical resemblances that may obtain
among the  methods of preparing them.  This  will direct the
medical chemist to such treatment of the metals as are the most
likely to produce the  desired medicinal effect.   Thus will the
philosopher be instructed, and  the artist directed.   (See note
26. at the end of the Volume.)


              GENUS  V.....ANTIMONY.

     After  mercury, I shall next consider the brittle and vo-
latile metals,  which on account of their wanting ductility, are
 called imperfect, or semi-metals; and antimony (stibiumolem)
being one of these, we shall take it first.  It is the one to which
the chemists  and physicians have  paid the greatest attention,
torturing it into an endless variety of forms.
   Antimony is  a dull  silver-coloured metal,  of the specific
 gravity 6,7.   Its surface exhibits facets, and a star-iik>>  ngure.
 This appearance proceeds from  a  crystallization, or arrange-
 ment of its parts  in  cooling.   It is totally destitute  of mallea-
 bility, and can easily be beaten to powder.  It is possessed  of
 fusibility and volatility.   The  vapours of  it calcine to a white
 smoke, and condense on the surface of any cold body exposed
 to them.   Or if they are collected, and somewhat confined,  in
 the cavity of a vessel applied to receive them,-they condense
 into a  matter composed of minute spicular crystals, very like
 snow, or flores benzoini, called  nix antimonii,....snow of anti-
 mony ; or by some chemists,sil very flowers,....fleurs argentines.
 You may see all these phenomena by heating a  little  bit  of an-
 timony with the blow-pipe on charcoal.  There is here an evi-
 dent inflammation.   The white smqke is partly composed of an
oxyd, formed by the action of the air, and it  adheres to any
cold body in form of a white powder.   It  is pretty highly oxy-
dated.   But when the heat of the mass abates, and the vapours
arise more slowly, and are less calcined, a part of them conden-
ses oh- the surface of the metal itself, appearing like a covering
of snow.  . 
 254          ANTIMONY WITH ACIDS.

   We can also calcine this metal with an inferior heat, so as not'to
 convert it into vapour.  It must be beaten to powder, and spread
 out  in a broad and shallow vessel, and exposed to a very gra.
 dual heat.  The surface of the metallic particles soon becomes
 tarnished and dusty : and they are by degrees converted into a
 dust, or earthy-like powder ; first"dark grey, or ash-coloured,
 but  by continuance of the calcination, yellowish, and  at last
 white.
   These calces, or oxyds, are remarkable by proving all volatile,
 if exposed to the action of heat and air at the same time : and
 when the yapour of them is condensed by cold and a proper ap-
 paratus, they form  the silvery flowers.
   Some  chemists have  thought that there  was a resemblance
 between  antimony and  arsenic.   And they certainly resemble
 one another in this respect, that the calces of both, when in a
 state of moderate calcination,  can be converted into vapour very
 easily.  But the calx of antimony  differs from white arsenic in
 this  point, that whereas white arsen»c will evaporate in  closed
 vessels, or by the action of heat alone,  without requiring the
 assistance of fresh air, the calces  of antimony will not evapo-
 rate, except  when  exposed to the  action of both heat and air.
 If the access of fresh air is excluded, they endure a very violent
heat.   And the effect of the heat in this case is to melt them into
 a glass.  They melt the more easily, the less they have been cal-
 cined.   And the glass thus produced  has always a deep  ruddy
brown yellow colour, which is so much the deeper and darker,
 in proportion as the  calx was less calcined.
   All  such calces or glasses are reducible to  a metallic state;
the less calcined, however, the more easily and  completely. The
 reduction  is performed by fusion with charcoal dust, or black
 finx, or fixed alkali  and  soap.  So  far of the effects of heat.
   The greater number of the acids can be made to act on anti-
 mony in one way or another.   Some attack it.readily in its me-
 tallic state;  others better when it is slightly or moderately cal-
 cined.   But  when it is greatly calcined, few  of them are  dis-
 posed  to unite with it.   Dr. Pearson, in his dissertation on
 James's powder, (Phil.  Trans. 1791.) gives an account of a
 series  of experiments made with  the view of comparing their
 different solubility.   And it appears that  the degree of calcina- 
ANTIMONY  WITH  ACIDS.          255
tion has a very steady  connection with  the  solubility of the
calces.
   The action of the sulphuric acid on antimony very  much re-
sembles its action on mercury. It must be strong  and  hot. The
action is attended with effervescence and the eruption of fumes
x>f  sulphurous  acid;,  and towards  the end of the  process,
actual sulphur.   The effervescence being frothy, it is very trou-
blesome, rising in the vessel  and running over.   After some
time, this ceases,  and the liquor may be said to boil rather than
to effervesce....it  is still  however the  same elastic gas which  it
emits.  At length, the metal  is completely taken  up,  or chang-
ed : and we have a white precipitate, and a solution of a sulphat
of antimony.   The precipitate-is nearly a perfect oxyd.  The
solution will  not crystallize by evaporation :  but  when reduced
to a dry mass,  it imjnediately deliqui^ftes again.* The solution
may be decompounded by alkalis; andjrives anoxyd extremely
difficult of reduction.
   Nitric acid can  scarcely be called a solvent  of antimony ; for
its form never disappears.  After remaining some days in the
acid, the metal is only found divided, swelled up, and covered
with bumps like colli-flowers, just as in its calcination.   The la«
minae are separated, and  the interstices filled with a white oxyd.
All this is accompanied  by  a great change  in the  acid....red
fumes are emitted in abundance: and the liquor acquires a green
colour.   In short the acid is decomposed.  When the materials
are examined,  we find the metal completely changed.  There is
a matter lying at the bottom, which, on examination, is an oxyd
of  the metal, with some excess of oxygen.  The liquor con-
tains a nitrate of antimony.   Water causes some precipitation:
and the  remainder is the solution of a  very  deliquescent Halt,
which can be decompounded by an alkali.  This precipitates an
oxyd of antimony, which it is very difficult to reduce to the me.
tallic state.
   Muriatic acid acts very slowly and languidly  on antimony;
but it acts on it, and dissolves it with a  slight effervescence. If,
however, it be  digested On antimony, it dissolves  it, and retains
il,  when nitric acid, either strong or weak, is added  to the so-
lution ; thus, making it evident that it attracts the metal. With 
 256    ANTIMONY  WITH MURIATIC  ACID.

 care, the muriat may be made to crystallize in  spiculae:  but it
 is extremely deliquescent.
   The action of the marine acid on antimony is much promot-
 ed by adding to it p  small  quantity of nitric acid.   When this
 mixture is poured on the metal, we have at once a brisk solu-
 tion, and the copious eruption of nitrous fumes, even although
 the quantity of nitric  acid should not amount to one-tenth of the
 muriatic.  It is better however to add  one-fifth.   This mix-
 ture dissolves a considerable quantity :  and the muriat yields a
 very deliquescent  salt, which is also very fusible and volatile,....
 and is parted by water, like the nitrate, yielding  an oxyd, and
 retaining the true muriat:  and this may be decompounded by
 an alkali.
   These phenomena, exhibited by anUmony  in  the nitric and
 muriatic acicls*are easrfy%inderstood.*  The nitric acid contains
 oxygen^vejy^jv^^y'unj^.  ^Pajjt.  of it unites  with  the antimo-
 ny, and the oxyd,  being very little soluble in water, lies at the
 bottom of the liquid.   The fumes are nitrous gas. .  The muria-
 tic acid  has its ingredients united too firmly ;  and does not
 therefore act on  the  metal  without  long digestion, and  even
 then acts feebly. But  a little nitric acid supplies it v. ith as much
 oxygen as  suffices for the oxydation of the  metal: and the
 fumes which break out are nitrous. Indeed the simple addition
of colourless nitric acid to the muriatic immediately emits the
fumes.  When we have got the metal into the  state  of an pxyd,
the solution goes on apace.  In confirmation qf this explanation,
 I must observe, that the oxygenated muriatic acid dissolves the
antimony with great facility, and produces the very  same com.
pound with that just now described.              '*
  This, however,  is  not the usual or most complete way of ef-
fecting a combination  of antimony with the muriatic acid.  The
processes in common  use are different, but  they depend on the
same principles.
  In  one of these processes  we mi v sixteen parts of corrosive
muriat of quicksilver  with six parts of the  metal of antimony,
both in  powder, and apply to this mixture  a subliming heat in
a retort and receiver.   The metal is in this case both oxydated,
 and at the same  ar.ie  combined with the dry and strong  muria- 
ANTIMONY....BUTTER OF PULV. ALGAROTH. 257

tic acid of the corrosive muriat of merctiry.   The oxydation is
effected by the mercury, which being itself in a highly oxydated
state, or combined with a good store of oxygen as well as with
acid, transfers both the oxygen and acid at the same time to the
antimony,  which has a stronger attraction for them both than
the quicksilver has.   The antimony therefore is both oxydated
sufficiently, and combined with the  acid,....the quicksilver re-
suming its metallic form.  In this, as well as in the similar pro-
cess with arsenic and mercurial muriat, the mercury requires a
greater heat to raise it in vapour than the antimonial muriat;
and  this last is even more volatile than the mercurial, Though •
antimony is more fixed than  mercury.       J
  The new compound differs from the corrcj^e muriat of mer-
cury by being more easily melted than yj^ftilized,  whereas the
corrosive mercury is more volatile thflffiiusible.   The antimo-
nial caustic or corrosive, therefore, rises in vapours, which con-
dense first  into a fluid matter, on some of the cool parts of the
retort: but when they reach parts still colder, the fluid matter
quickly congeals  into a solid icy-like substance, which  can be
easily melted again,  and congealed at pleasure,  melting  with a
gentle  heat, almost  like tallow  or  butter.  Hence  the ancient
chemists gave it the  name of butter of antimony.   Its colour is
dark at first: but, by rectification, it becomes white or colour-
less like  ice'; a little superfluous metallic matter and some im-
purities being thus separated  from it.
  When we malNf further experiments with this compound, we
learn that  it has a strong  attraction  for water.  A very small
quantity  of watfer dissolves the greater part of it, or reduces it
to a liquid form;  and it readily attracts so much water from the
air, if it  be exposed  in open vessels.   As  it is more convenient
to keep and use it in a liquid form, it is commonly sold liquid,
by the name of antimonial caustic.  In the last editions  of the
London and Edinburgh Pharmacopoeias, this compound is call-
ed antimonium muriatum.   It is  very  acrid or corrosive with re-
spect to animal and vegetable substances.  A little of it applied
to the skin  very soon burns or destroys the part.   Whence anti-
monial caustic  is  employed  to  destroy fungous excrescences
from ulcers or other parts.
     '-ni. m.                 k  k 
258  VARIOUS AFFINITIES OF ANTIMONY.

  Water, added in large quantity  to this compound, affects it
in the  same manner  as it does the sulphat of mercury.  The
water attracts and dissolves the acid, leaving the  metal in the
form of a white oxyd, which,  although washed with repeated
additions of hot water, retains still a small part of  the acid.  It
is called powder of Algarotti, from the name of an Italian physi-
cian, the inventor ; also  mercurius vita:, though it contains no
mercury.   Nor does it contain  any acid, if prepared with pro-
per care.  It should be a pure oxyd, pretty copiously oxydated.
   Antimony unites  also with the  vegetable acids.   The
acetous and tartarous acids, and  the acid of vinous liquors,
dissolve  it,  and become violent emetics.    But these acids
dissolve it much better when it is slightly oxydated.   They
are medicines  of great  activity;  and should therefore be
very accurately prepared.   Unfortunately, it  is very diffi-
cult, if possible, to  reduce them  to the same strength when
prepared by different processes.   And the physician prescri-
bing his  dose by the  effects of  a preparation to which he has
been accustomed, may produce very unexpected effects, when
the same dose is given of the  medicine otherwise prepared.
I think that the precipitate from the aniimonial muriat has a
greater probability of being  uniformly the  same  than any
other oxyd of metal.  It is, therefore, a good basis for these
vegetable additions.
   Of  the  neutral salts,  only  nitre  and sal  ammoniac act
upon antimony.   The first deflagrates: and the  heat of de-
flagration volatilizes some of  the metal.   We  thus get an
oxyd whiter and less fusible in proportion to the quantity of
nitre.   Nitre two parts, to antimony one part, gives an oxyd
very white and unfusible.   The alkali of the nitre, mixed
with this oxyd, is called reguline caustic.
   Sal  ammoniac presents nothing particular, or different from
its action on metals in general.
   Of  the inflammable substances,  sulphur  readily unites
with this semi-metal  in the fire, and forms a fusible  com-
pound, which bears  a great resemblance  to the semi-metal
by itself.   But the  sulphuric compound has less brightness,
and a  darker colour, and more slender crystallizations.
   The sulphur can  be separated, and the metal  recovered in
itspurf  state  by different processes;  as, 
             ANTIMONY AND SULPHUR.       259

   1st,  By roasting the sulphurated antimony, so as to eva-
 porate the sulphur, we get the metallic matter in the form of
 an oxyd, which retains very little of the sulphur, and may
 be reduced to the metallic state by melting it with black flux.
 The first part of this process requires patience and attention,
 on account  of the volatility of the metallic  matter.   I shall
 take further notice of it hereafter.
   2dly, Another method,  which is shorter, is  to melt the
 sulphurated antimony  with an equal, or half its weight of
 black flux.   The alkali joins the sulphur:  and a part of the
 metal in its pure state separates to the bottom of the vessel.
 But by this method we obtain only a part of the metal.   A
 considerable partis dissolved by  the alkaline sulphuret,  and
 if a pure alkali is used in place of black flux, it dissolves the
 whole.
   3dly, We  can separate the sulphur by other metals, many
 of which have a stronger attraction for it than this semi-me-
 tal has.   Iron is commonly used, either in filings, or small
 nails, or the  scraps from the tinplate-workers.-   A strong
 heat is necessary.  Thus the antimony settles to the bottom:
 the sulphurated iron  flows uppermost;  and  is separated
 more easily, if some  saline matter has been added  to pro-
 mote the fusion.
   When this  metal happens to be combined with sulphuret
 of alkali, 'it can hardly be  separated again,  except in  this
 manner, by melting the  compound with other metals which
 have a  stronger attraction for  the sulphuret.  Other metals
 thus employed to  separate the  antimony  from sulphur,  or
 alkaline sulphuret, are liable  however  to mingle with  it a
 little, and  to  make it impure.   For it  is disposed to mix
 with all other metals,  if properly  applied to them with a mel-
 ting heat.    Iron  appears to  have the strongest attraction
 for it.    With all the  tough metals, it produces compounds
 more or less  brittle.    And besides this effect on iron,
 it deprives  the iron of its magnetic qualities and disposi-
 tions to be attracted  by the magnet.    No  other metallic
substance affects iron in this manner.*

  * I find that less than three parts of antimony to one of iron will not des-
troy the magnetism of the iron....editor 
n
260            CRUDE ANTIMONY, &c.

   The method of separating it from the different metals is
various, according to the nature of the metal with which it is
joined.
   From gold or platinum it is separated by evaporation, or
the action of heat and air.   From other metallic substances
it is best separated  by the  addition of sulphur, or, in some
cases,  by scorificalion, as from  lead.
   Such is the chemical nature of this semi-metal.   It is one
of those which are produced by nature  in large quantity in
some  places;  and the ore of it is  every  where nearly of  the
same kind.   Sometimes, though rarely, it has occurred in a
state of purity.   But such specimens are very rare, and  the
quantity trifling.  The  most common  state in which it is
found  is combined with  sulphur: and I believe there is some
variety in the proportion of the sulphur to the metal  in  the
different ores.  Most of them  contain a little arsenic.   Its
presence is  easily known by the white and silvery appearance
of the ore,  and by the orpiment which it yields  by sublima-
tion.   The appearance  of these ores  is very like that of the
artificial compound of the metal and sulphur.   And the only
operation which the metallurgists perform  with these ores,
before they send them to the market, is to separate from them
the  earthy and stony matters or matrix,  which happens to be
combined with them.
   This is done by the process named in metallurgy Eliqua*
tion.   The crude antimony is put into earthen pots,  pierc-
ed in  the bottom.   These are set upon  other pots buried in
the  ground.  The fuel  is thrown in around the pots ;  and
the  fire kept in a uniform state, by the judicious structure of
 the  furnace.  When the ore is fused, it runs  into the lower
pots,  and the earthy matters remain in the upper ones.   It
 is frequently  moulded in truncated  conical loaves.   As this
 is the only operation performed  on this mineral to fit it for
 sale,  it comes into  the hands of  the chemists and druggists
 in this state, in which the metal  is still combined with sul-
 phur,  and  may be considered as  yet in the  state of an ore.
 They were accustomed to call it  crude antimony, or, simply,
 antimony.   And the pure metallic part, when separated from
 the sulphur, has been commonly  named regulus of antimony.
 But the later chemists give the name of  antimony to the pure 
ANTIMONY....MEDICINAL PREPARATIONS. 261

metallic part; and to this compound, that of sulphurated anti-
mony, or sulphuret of  antimony.
   It is therefore by working on this sulphurated antimony,
or crude antimony, as it is called, that most of the prepara-
tions of antimony are produced, in the art of pharmacy.  By
what you know already of the nature of its two constituent
parts, I mean sulphur, and the metallic substance which  I
have already described, you will now easily understand the
changes it undergoes by the action of heat and air, or of dif-
ferent solvents, and other active substances.


                Preparations of Antimony.

   Before I begin to describe the different preparations of this
mineral, I beg leave to make a remark upon the whole of the
subject, which will assist you to understand how these pre-
parations  differ  from one  another, in point of efficacy as
medicines:  for the general purpose  of preparing  crude anti-
mony is to give it more or less medicinal efficacy, to make  it
either a strong and powerful remedy for some purposes,  or
one that shall be mild and safe for others.
   In the first place, there is good reason,  from experience,
to  believe that  antimony  never acts as a medicine, except
when dissolved or combined with an acid, either before it is
taken into the stomach,  or in consequence of its finding an
acid there with which it unites.   But in crude antimony, the
metal neither is already united with an acid, nor is it much
disposed to join with the weak acid  which alone it  can meet
with in the stomach.   The sulphur  with which it is joined,
and the uncalcined state  of the metal, are unfavourable to its
being easily dissolved by a weak acid.   In order  to make
it easily soluble  in the acid of the stomach, we must separate
more or less of the sulphur, and calcine or oxydate the metal
to a moderate degree.   I say a moderate  degree:  for if we
oxydate it very much, we again diminish its disposition to be
dissolved.  By  taking away, therefore, more or less of  the
sulphur, and  moderately oxydating  the metal, we produce
preparations which are capable of acting very powerfully. But i
their action is not  always the  same, or in proportion to the 
 262       ANTIMONIUM PRAEPARATUM.
»
 dose. It depends on their meeting with acidity in the stomach,,
 which is not always present there in sufficient quantity to give
 them all their efficacy.
    The surest way to reduce antimony to a form in which it
 will act equally and strongly (at least so far equally as the
 different constitutions of different patients will permit), is to
 separate the sulphur, and combine the metal with an acid, so
 as to give  it a saline  soluble form before  it is thrown into the
 stomach.
    And  now,  having premised these remarks, we shall pro.
 ceed to describe the different  preparations, in the order in
 which they are arranged in the table of  them which I have
 put into your hands.  (See Note 61. at the end of the Volume.)
   The first is the antimonium praeparatum, in both our phar-
 macopoeias.   It is crude antimony, reduced  to a very fine
 powder,  simply by  triture and elutriation  with water.  I
 remarked  already, that crude antimony has but little efficacy
 as a medicine, or is an exceedingly mild one.   This is a con-
 sequence of the state of the metal in it, which is neither
 already united with an acid, nor much disposed to unite with
 the acid of the stomach, not being prepared by any degree
 of calcination, and  having also the sulphur adhering to it.
 The antimonium praeparatum is, therefore, never given when
 we propose to vomit or purge.   It is only used to promote
 perspiration, or to excite the other evacuations so gently that
 its effect is hardly perceived, and  that the use of it may be
 continued  constantly  for some time:  and  to make it act everi
 thus, the greatest levigation is necessary.  The  antimonium
 praeparatum  is, therefore,  crude antimony,  reduced to this
 state of a very fine powder ready for use.  Kunkel, an eminent
 German chemist, is said to have  cured himself of a rheuma-
 tism with  it.   I once had an opportunity of perceiving that
 it sometimes excites nausea, and expels worms: a proof that
 it is not quite inactive.   In preparing it, we must be careful
 to avoid  the base or broader end of the conical loaf into
 which it is moulded for sale. If any impurities, or admixture
 of other metals be in the mass, they  are in this  upper part.
 They scorify with part of the sulphur ; and being thus lighter
 than the rest, float above it. 
 ANTIMONY....AS AFFECTED BY HEAT,  &c. 263

  The next  preparations are those produced by the action
of heat and air.
  When crude antimony is exposed  to  heat suddenly,  the
most of it evaporates, especially if air be admitted.  This
is to be expected ;  as both the metal and sulphur are vola-
tile  substances.   Its evaporation is attended with some in-
flammation, visible  in the dark.   By careful procedure, the
sulphur may  be completely dissipated by roasting the pow-
dered antimony.  No  suffocating smell  will be  perceived.
A sudden increase of heat  would mar the operation, by
melting the antimony, and thus diminishing its  extensive
surface.   As the operation advances, we  may increase the
heat without danger of melting.   This may be continued
till all the sulphur  is expelled.   The metal now begins  to
attract oxygen, and grows grey,  and at  last white ;  and in
this state  is a pure oxyd.   Thus you  see that by terminating
the process at different periods, we shall procure the metal
in very different states. It is therefore a matter of importance
that it be conducted in a very uniform manner.
  There  is the same, or perhaps a greater variety, when the
heat is so great as to  cause the sulphur to attract oxygen.  In
this case we have suffocating fumes, &c.
   The only preparations which  have been  produced by the
action of heat and air are, the fores antimonii sine addito, the
calx antimonii, the vitrum antimonii, and  the vitrum ceratum,
 (Pharm.  Edin.) prepared  from the vitrum.
   To prepare the flores antimonii sine addito, the sulphuret
is put into a crucible, or unglazed earthen vessel.   A set of
aludels are set on it:  and a  pipe is inserted by a proper open-
ing in the side  or lip of the crucible.  The fire being kindled,
and having grown  pretty strong, the fumes begin  to arise:
and then  a pair of  bellows are  applied  to  the pipe; and a
gentle stream of air  is made to play on the surface of the
 materials, but in the most  gentle manner possible.  The
metallic and sulphurous  fumes now rise;  and are condensed
in the different aludels.  The sulphur of the flores, being the
most volatile of  the fumes, rises highest, and  the oxydated
flowers are contaminated by it so much the more as they rise
higher, or rather they rise  so much the  higher as they con- 
264             VITRUM ANTIMONII.
       tain more sulphur.  The artificial stream of  air cannot be
       managed with such delicacy as to  preserve that regular
       gradation  which  may  be  obtained  in a  small  quantity
       sublimed without the blast.   This  preparation, therefore,
       is unequal and uncertain ; and is  now disused.
          Vitrum.........In making the glas of antimony, we begin by
       separating the sulphur, or the greater part of it, by the action
       of heat and air, and at the same time oxydate the metal to a
       moderate degree.
          Both these objects are attained by performing the  opera-
       tion practised with ores of metals to free them from sulphur.
       It  is named ustulation.   The operation of ustulating sulphu-
       rated antimony is difficult on account of the fusibility of this
       mineral, and of the volatility of its metallic part.
          To  diminish  fluidity,  some  add charcoal dust.   Others
       add common salt,  which is easily separated afterwards by
       water.
          But the  common way  is to  ustulate it without addi-
       tion.
          It necessarily happens  in this operation, that the metallic
       part is oxydated,  while  most of the sulphur is evaporated.
       And, if the operation be properly managed, we have an oxyd
       of the metal of a  grey or ash colour, moderately oxydated,
       and with very little of the sulphur remaining in it, and there-
       fore  in a condition to be  easily melted  into  glass :   for we
       have learned by experience that the presence  of a little of the
       sulphur greatly promotes its melting into glass.
          It is therefore by simply melting an  oxyd of  antimony,
       prepared in. this manner, that the glass of antimony is  ob-
i       tained.
          Vitrum ceratum is prepared (in order to mitigate the ac-
       tion  of the vitrum  antimonii) by kneading the  pulverised
       glass  of  antimony with  bees wax,  and then burning away
       the wax.
          The next preparations  of antimony in the table are those
       prepared with alkaline salts.
          The  fixed  alkalis act readily on  crude  antimony, on
       account of the sulphur which it contains, and with which they
       have a strong  disposition  to join. 
CRUDE ANTIMONY....TREATED WITH ALK. 265
  Of this we have examples, when we apply these salts to the
crude antimony,  either in the dry  way  by  fusion, or in the
humid way in the form of  watery solution.   They act most
readily and  powerfully when applied in  the way of  fusion.
The alkali joins itself to the sulphur, and forms a sulphuret
of potash,.. ..a compound which has  great power to act on the
metals in fusion,  and to dissolve even those with which sul-
phur alone cannot be combined.   The  metallic part of the
antimony, therefore, does not separate, or very seldom, and
in small quantity only.  Commonly the whole mixture melts
into one  uniform vithfied-like  mass.  If one  part of fixed
alkali and five  of crude antimony are melted together,  and
some common  salt added, which promotes their fusion, we
obtain a  dark  coloured vitriform mass, once  known under
the  improper  name of regulus antimonii medicinalis.  It  is
easily ground to powder;  and gives a powder of  a reddish
brown, or a sort of chocolate colour, which is insipid on the
tongue, and not soluble in water.   It is a very mild prepa-
ration;  but has a  little more efficacy than  the antimonium
praeparatum.                  £
   Larger proportions of alkali form masses which prove more
or less soluble in water.   Those which contain one of alkali
to two of crude antimony are  soluble in hot  water, not in
cold.  With large proportions of alkali, they are soluble in
cold water  as  well as in  hot.   With two  of  alkali  to  one
of  crude  antimony, they are  even deliquescent,  or attract
humidity.
   The most proper name for all these compounds is alkaline sul-
phurets of antimony.
   When we apply water to them, to  dissolve thdse that are so-
luble, none of them are dissolved completely.  There is always
a separation of  a reddish or brownish sediment,  which  is more
plentiful in proportion as there is less alkali in the composition
 of the mass.  This sediment is formed by a part of the  antimo-
ny: and it is some of the more  metallic part which thus sepa-
rates.  The rest,  which in consequence  of  this separation  is
more' sulphurous,«md has more alkali combined with it, remains
 dissolved.
                           l1
VOL. HI- 
266  ALKALINE  SULPHURETS OF ANTIMONY.

   Beside the way by fusion,  I observed before, that we can
 form compounds of this kind in the way of watery solution, or,
 according to the language of the chemists, in the humid way.
    Though the alkali,  in whatever manner applied, acts by its
 attraction for the sulphur chiefly, it dissolves in this way also the
 greater part of the metal.   It continues adherent; to the sulphur,
 and is dissolved along with it.  The solution, therefore, which
 we thus obtain, is a solution of an alkaline sulphuret of antimo-
 ny, which is rather  more  easily  decompounded, and  requires
 more water to keep  it dissolved,  than a plain sulphuret of pot-
 ash: and  the cause of this is, that the  metal,  by its attraction
 for the sulphur, diminishes a little the cohesion of this last with
 the alkali.
    We quickly decompound this sort of sulphuret, when we add
 an acid to the solution.   This immediately neutralizes the al-
 kali, and occasions the sulphur and  metal to separate  from it.
 While they separate from  the alkali,  they remain combined to-
 gether, and  form a powder or precipitate  of a deep orange or
 red colour, called formerly sulphur antimonii auratum, now sul.
 phur antimonii prxcipitatum.
    In this preparation, the antimony, although it retains  much
 the same  principles as in its crude state, is much  more active,
 however, as a medicine.  The dissolution  it underwent has di-
 vided the particles far more subtilely than  can  be done by any
 mechanical division or triture.  And the close  union of the sul-
 phur and metal was diminished during the  combination, in con-
 sequence of the action of the alkali on the sulphur.  The metal
 is therefore more disposed for being dissolved by the acids of
 the stomach, than it is in  crude antimony.
    But, in order to make the product of this process always  equal,
 it is necessary to add the requisite quantityof acid for saturating
  the  alkali, and precipitating  the antimony all at  once.   If we
 add only  a part, and collect the  first precipitate before we add
 the  rest of the acid, the first and second precipitates will be un-
  equal. The first will contain more  of the metal, and less of
  the  sulphur, than the second  precipitate;  trie  attraction  of the
  alkali being chiefly for the sulphur of crude antimony. It there-
•  fore quits it more slowly  than it quits the metallic part. 
        PROCESSES FOR KERMES MINERALIS.   267

   When we take the potash  in its common state of an imperfect
 carbonat,  and dissolve the antimony by it in the same humid
 way, it acts much more  slowly and with less power. And when
 the boiled solution is allowed to cool, it deposits again the great-
 est  part of the crude antimony which it had dissolved, shewing
 thereby that the presence and assistance of l:eat is necessary to
 enable  such an alkali to  hold the crude antimony dissolved.
   We  have an  example of this in the process for kermes mi-
 neralis.                                           ' --.
   This kermes mineralis is reckoned in France one of the t*$}-
 tal preparations of antimony.  It  first  attracted notice while it "\  (9
 was a secret remedy in the hands  of a Carthusian monk,  who
 performed several surprising cures with it in the pneumonia, and
 other violent fluxions or congestions in the lungs.  Upon in-
 quiry it appeared that the monk  had got it from  one Ligerie,
 who was possessed  of the secret, and who had learned it from
 Glauber, or from a  scholar of Glauber's.   The Duke of Orle-
 ans, then  regent, was advised by the king's, physician, to pur-
 chase the  discovery of it at the king's expence, and make it pub-
 lic*   But the younger Lemery, in a memoir, inserted in the
 Mem. del'Acad,  for  the  year 1720, proves that this medicine
 was contrived, or at least the process for it published by his fa-
 ther, in his treatise  on antimony; and that his father's process
 is rather better than  La Ligerie's.  The elder Lemery called it
 a sulphur auratum antimonii, and not improperly ;  for the ker-
 mes mineral,  in whatever manner it be prepared, is very much,
 and almost precisely, ©f the same  nature with the antimonium,
 or sulphur antimonii precipitatum,  which was formerly named
 sulphur auratum. jf

    * Ligerie's Process.....Crude antimony broken small, four  ounces ;  deli-
 qnium of nitrate of lime, one ounce ; and water eight ounces.  Boil the mix-
 ture  two hours.   Decant and nitre it while  hot.  While it cools, the ker-
 mes is precipitated.  Add to the remaining antimony six drachms of the
 nitrate of lime, and eight ounces of water; repeat the  boiling and filtrate.
 ...... .Repeat the last part of the process ; collect the three precipitates ; and
 edulcorate with water.
   f The elder  Lemery's original process  is  this.....Put into an iron pot"
fire or six pounds of a solution of pure fixed  alkali, with three or four times 
268    ANTIMONY....KERMES  MINERALIS.

   Lemerv 's process, however, and the product of it, had been
neglected, until it attracted notice  as a secret remedy,  and was
purchased for the use of the public ; and then it  became so much
an object of attention, that the most celebrated  French chemists
have txer: ised their ingenuity in throwing light on the  process,
'and improving it.
   A great inconvenience  in  La Ligerie's  process is,  that the
quantity of kctmes produced by  each boiling of the materials is
very smau.
   Cjeoffroy,  who made many experiments to investigate the na-
 ture of this preparation,  proposed  a process by which it may be
 obtained  in  far  greater  quantity,  and with incomparably less
 trouble.*
    The precipitated matter, when  well washed and  dried, is a
 soft and  tender powdery  matter, of a  deep brownish red, or
 rather a coffee colour.
    The liquor from which it has been  deposited, retains  the
 greatest part of the  alkali, together with a small quantity of the
 antimony adhering to it; but retains so much of the uncombined
 alkali, that,  if boiled with more antimony,  it dissolves it again,
 and by cooling,  deposits a fresh quantity of kermes ;  and this
 after many repeated operations of the same kind.
    This preparation is much the  same with  the sulphur precipi.
 tatum.   It has a moderate degree of power as an antimonial.
    Meuder,  a pharmaceutical chemist of reputation, says that all
 depositions  by cooling1,  from the warm washings of the hepatic

 as much water.  When the  liquor boils, throw  into it  four or five ounces of
 finely po'.vdered crude antimony.  Boil the mixture  a short time, stirring it
 with an iron spatula, and then filtrate it boiling hot through paper.  It will
 deposit the kermes, which must be well washed, dried, and ground to a fine
 powder,....a grey powder remains, which is regulus which the hepar could
 not dissolve.  The same alkaline liquor  may be used several times.
    *  Geoffroy's process.....Two parts of antimony,  and one of alkali, are melt-
  ed together and pounded.   This makes an alkaline sulphuret, soluble only
  in hot water.   It is boiled with water,  and filtered into a large quantity of
  hot water; and upon cooling, yields of  kermes, three-fourths of the weight
  of the antimony.
    In young Lumen's  process,  fine powder of antimony is boiled with the
  pure deliquium of nitrate of lime :  and thus the whole  antimony is dissolved. 
 ANTIMONY....DEFLAGRATED WITH NITRE. 269

preparations of antimony, may be distinguished from a kermes
mineralis by  the following marks :
  1. The kermes  is red ; and the others are brown.
  2. Kermes act much more gently as a medicine.   I may ob-
serve, that if the kermes be prepared by employing a caustic al-
kali, we have the sulphur fixum Stabelii.
  And  now, having enumerated the preparations of antimony
obtained by the use of alkalis, as well as those produced by the
action of heat and air, we shall next take those produced by de-
flagration with nitre, which are in some respects similar to those
already described.
  When crude antimony is mixed with nitre, and this mixture
is set on fire,  or  thrown  by degrees into  a hot crucible or iron
pot, there is more or less deflagration, according to the propor-
tion of  the nitre in the  mixture.   In  this  deflagration, the acid
of  the nitre, by its abundant oxygen,  acts most violently on the
 sulphur, which it changes into sulphuric acid : and  the greater
 part of  this acid combines with the alkali of the nitre.   But the
 acid of the nitre acts also more or less on the metallic part  of
 the crude antimony, and oxydates it either moderately,  or to a
 high degree, according to the quantity of the nitre employed.
 A number of preparations made in this way have been contrived,
 and highly recommended,  at different times.  I shall describe
 a few of them.
   First, what Mr. Lewis calls  crocus medicinalis.   A mixture
 of one part  of nitre and eight of antimony in fine powder, is
 projected into a red hot crucible'.  So small  a portion of nitre
 can produce no sensible deflagration.  It seems only to assist
 the fusion  and solubility of the  mixture.   It  breaks  with  a
 glassy fracture, is opaque,  and has a surface like polished steel.
 It  produces  a mass of  a deep purple colour, like that obtained
 from antimony acted on by  a small  quantity of alkaline salts.
 This preparation is also very similar  in its degree of efficacy to
 the alkaline sulphuret,  which was called regulus antimonii medi-
 cinalis  : and  indeed the same  name of regulis medicinalis has
 been given sometimes to this preparation also.   It is insoluble
 in  wa'er, and insipid. 
                       §
  270 ANTIMONY....DEFLAGRATED WITH NITRE.

    In the other preparations of this kind with nitre,  larger pro-
 portions of nitre are used, and produce more active effects : but
 the chief of them is the crocus antimonii, formerly named (often
 very improperly) crocus metallorum.   (Pharm. Lond.)  In this
 preparation, since  the proportion of nitre (equal parts) is very
 considerable, the deflagration is very brisk, or rather violent:
 and the fusion does not require the crucible to be red hot in the
 beginning: the first projection may be kindled by a bit of lighted
 paper.   And by properly timing the subsequent projections, the
 heat rises to a great pitch, and makes the whole melt very com.
 pletely.  The saline part is  separated  and thrown away : the
 vitrified metallic matter only  being the useful part.   It assumes
 a yellow colour when ground to powder, whence it has got the
 name of crocus.  The nitre is partly  converted into  vitriolated
 tartar,  and partly  alkalized.   If the operation be  managed so
 that all  shall be fluid at once, the  greatest part of the salt col-
 lects uppermost by itself.  The metallic matter goes to the bot-
 tom semi-vitrified ; but the glassy matter at the bottom is  not
 perfectly free from salt.  It  contains,  united with  the vitrified
 matter, a small quantity  of alkaline salt,  produced  from that
 part of  the nitre which deflagrated with the metallic part of the
 antimony.   And,  besides this alkaline salt,  there is even a very
 small portion of sulphur remaining united with the alkali  and
 metallic oxyd.   It was, therefore, some time ago, a practice to
 separate as much  as  possible this saline matter from the  cro-
cus, by  reducing the crocus  to a fine powder, and  boiling it in
water, which (after subsidence) being  poured  off, the crocus
 was dried, and was named crocus lotus.  I find the most suc-
 cessful way of proceeding is,  to deflagrate in a  hot  iron mortar
 set  on the fire,  projecting very small quantities, but  in quick
succession.   Thus  you will have a good fusion  and separation,
 and a fine  crocus without further trouble.   Crocus,  or crocus
Rolandi, according to Meuder, is the deflagrated stuff edulco-
rated without previous fusion.
  You will find great confusion in the names of these produc-
tions of antimony.   It  was formerly called, with the greatest
impropriety, crocus  metallorum.  And you will find  that the
French  writers, Lemery  and  Macquer, choose to  call it liver 
ANTIMONY....DEFLAGRATED WITH  NITRE.  271

 of antimony,....foie d"*antimoine; and  with as little  propriety,
 gave it the name of crocus metallorum after it was washed.
   The nature of this preparation, as a medicine,  is similar to
 that of the glass, but rather inferior in violence.
   When the  dose of nitre is much farther increased, besides
 the  complete  destruction of the  sulphur, the  metallic part is
 more calcined: and this may be to such a degree,  that its  ope-
 ration as a medicine is  thereby diminished, as it becomes less
 disposed to unite with the acids found in the stomach.  Such is
 the  antimonii emeticum  mitius of  Boerhaave,  viz. antimony,
 one part; nitre, two parts : such  also is the antimonium calcina-
 tum,  (Lond.)  viz. antimony, one  part;  nitre,  three parts.
 The matter at first taken out of the crucible contains sulphat of
 potash, and a little unsaturated alkali.  These salts are separat-
 ed by hot water: and then we have  the pure white oxyd.  Four
 ounces of antimony yield five and a half ounces of the antimo-
 nium diaphoreticvfm lotum Meuderi,  which  is accordingly called
 antimonium calcinatum; as also antimonium diaphoreticum.*
    The antimonium. ustum cum nitro of the Edinburgh Pharma-
 copoeia may be considered as similar to these preparations,  only-
 more active than the antimonium calcinatum.  The crude an-
 timony is first  roasted to a calx;  then mixed with an  equal
 quantity of nitre, and  melted, or made red hot one hour; and
 then edulcorated with water.   It was meant to be an imitation
 of James's powder; the process being copied from the specifica-
 tion of his  patent.   But either Dr. James changed  his process
 afterwards,  or gave a  false or disguised description of it: for
 lately it has been clearly proved to be very different, by Dr.
 Pearson's experiments, read to the Royal Society of London,
 in 1791, and published in the Philosophical Transactions.   It
 now appears to be a combination of  antimony with the acid  of
 phosphorus, or  rather with a phosphat of lime.  Nitrous acid

   * Geoffroy observed a singular phenomenon in his operations on this medicine.
  Having ground an ounce of it with  two ounces of black soap, he roasted the
 mixture to a coal; and then ground it coarsely with another ounce, and  expos-
 ed it to violent heat, in a covered crucible.  Five hours after all was cold, he
 took off the cover.   The mixture instantly took fire : and being very spongy,
 so that the air had easy access to the interior parts, it took fire all over, an^
 ^dissipated with a terrible explosion 
272.     ANTIMONY....JAMES'S  POWDER.
dissolves the phosphat; and the phosphoric acid remaining in
the solution is easily discovered,  by means of a solution of mer.
curial nitrate, or by a nitrate of lead.   The antimonial oxyd is
discovered by  means of muriatic acid, and precipitation from
it by water.
   Dr. Pearson's judicious examination led  him to attempt the
preparation,  on the principles arising from this analysis.  And
his imitation is so undistinguishable from Dr. James's powder,
that it is adopted by the London and Edinburgh Dispensatories,
under the name of pulvis antimonialis,  or antimonium calcareo.
phosphoratum.   Equal weights of antimony and horn shavings
are calcined till of a very fair grey colour, and then kept  red
hot in a coated crucible, for two hours; and when cold, reduced
to a fine powder, which when well prepared, is of a pure white,
or has a slight cast of yellow, but not inclining to brown.

                  Preparations with Acids.

   In  general, the acids do not act so well on crude antimony as
they do on the regulus, or pure metallic part  of  it.  The sul-
phur, in some  measure,  protects the metallic mattei*  but  not
to such a degree as to prevent entirely the action of  the  fossil
acids, nor even some  weak  action of the vegetable  acids.  I
shall now describe the preparations made with acids  applied to
antimony in different states.  And first, with the
   Sulphuric acid.....There are no preparations wiwkthis acid in
either of our pharmacopoeias.  A Dr? Klaunig ofKBreslaw, in
a book entitled  Nosocomium Charitatis^xecommenap the follow-
ing :  Distil vitriolic acid from antimony several  times.   By
doing this the metallic part is oxydated by the acid, and combin-
ed with a part of it: and the sulphur is, at  the same  time,  se-
parated by sublimation.  'After which, the sulphat of antimony
is taken out of  the retort, ground to powder, and some alcohol
burned  on it.   It is a  medicine,  of which two grains  work
gently,  by stool, and vomit, and sweat. And he recommends it
strongly for quartans.  Wertholfs (in his Obs. deFebribus) testi-
fies that it is emetic,  and purgative, and diaphoretic.  Wilson's
antimonium catharticum is probably of the same nature.  Wilson
calls  it  an infallible purge;  and says that  he knew  three  io- 
ANTIMONIAL  CAUSTIC
273
 stances of the venereal disorder cured  by it.   They were pro-
 bably some cutaneous diseases which he mistook for venereal.
    There are no preparations obtained by the action of nitric acid
 upon crude  antimony; unless we choose to  consider  the be-
 zoardicum miner ale as such, in some measure : but it is different,
 as I shall mention presently.
    The  muriatic  acid, assisted  with a little nitric acid, or in
 form of aqua regia, dissolves the metal, and leaves the sulphur.
 It therefore  thus forms a solution^of the metal,  which is quite
 the same a$ if the pure metal had been useck  And the* corro-
. iixe ,n£i<u-iat of quicksilver, on  account of the  abundance  of
 muriatic aci'd and oxygen it contains*, caiv*also be^nae^to act on
 the metal in sulphuret of antimony, as well as upon the metal
 in its separate state.  The muriat of quicksilver and  the sul-
 phuret of antimony  being mixed together in powder, and dis-
 tilled in a retort, a  corrosive muriat of antimony arises: and
 the quicksilver unites with the sulphur, and remains in the retort,
 in the form of a black sulphuret  of quicksilver, which, if the
 heat be very much increased, sublimes into the neck of  the re-
 tort, in the form of  cinnabar.    To this cinnabar the chemists
 give the name of cinnabar of antimony.  This was the process
 most commonly practised for preparing the antimonialcaustic, or
 corrosive muriat qf antimony.
    But the  London  college of physicians, learning  probably
 diat the chejaflrsts  had another method, much cheaper, and which
 is as goodjEve adopted it in the last edition of their pharma-
 copoeia.   &ks is, to for^m the muriat of antimony directly,  in
 the same, ol^nearly the same way, as was practised for corrosive
 sublimate.  Equal  quantities of vitriolic acid and  antimonial
' crocus arc mixed witrTa quantity of common salt equal to their
 sum, and treated  in the distilling apparatus.  I  refer you to Mr.
 Russel's own account of the process, given in the  first volume of
 the Transactions of  the Ro\ al Society of this place.
    It may also be effected by the oxygenated acid,  as it is formed
 by distilling the ordinary  muriatic acid from the black oxyd of
 manganese. But  Mr. Russel's process is much better.  Scheele's
 process is not very different.
      yor..  in.                m  m 
274,      ANTIMONY....PULV. ALGEROTHI.

  I observed before, that this antimonial caustic, or muriat of
antimony, is extremely corrosive.  On account of its extreme
acrimony, chemists studied how t» render it milder.   The most
simple way is,  by adding to it plenty of water.   The greater
part of the acid is thus immediately separated.   A small por-
tion  remains adhering to  the metallic calx;  and precipitates
with it, in the form of a white powder, called  pulvis Algerothi,
from  Victor Algeroth, or  Algarotti, formerly a physician at
Verona, who called it pulvis Angelicus.   It is an  oxyd  very
moderately oxydated, and  which still retains,  as I already ob-
served, a very  small portion of the acid combined with it;  and
on both  these-accounts, is  very soluble in more acid,, and also
very  fusible.   It  melts  most easily into a  transparent yellow
glass.   Mr. Macquer, and others, will have it to be  a pure calx,
totally free  from  acid: but in this I am  persuaded they are
mistaken.   Its fusibility is a  proof.   It dissolves readily in
vegetables acids,  and  in  solution  of  sal  ammoniac.    It is
recommended  by  Dr. Saunders in this form as a good applica.
tion to  ill-conditioned ulcers;   and also as a milder internal
medicine.
  Bezoardicum minerale may also be considered as a  mitigated
mumt of antimony.  The preparation of this drug  seems to
me a process which has been  undertaken very touch at random,
just to see what would result from it.
   To four  ounces of butter  of  antimony twelve or sixteen of
nitrous acid are added, by two ounces at a time.  Violent fumes
and  ebullition, or  effervescence,  are immediately produced,
which must be carefully avoided, they being extremely acrid or
corrosive.  The effervescence is less at  each  subsequent addi-
tion.  When all is quiet, the whole is distilled to dryness: and
the residuum in the retort is the bezoardicum minerale.
   The  first effervescences are chiefly an oxygenated muriatic
acid:  and the  nitrous  acid does not rise till  some time after.
This  is not the usual opinion : and it ;s  even thought that this
preparation is  nearly the same with diaphoretic antimony, or a
pet feet white oxyd.  It may not be impossible to bring it to this
state.   But in  my own experiments, as well as in the examina- 
         BEZOARDICUM  MINERALE, &c.       275

tion of such specimens as, I was well assured, had been prepared
from butter of antimony, I found it to be still a muriat of anti-
mony.   I believe indeed that the antimonium diaphoreticum  is
often sold for it, being a much cheaper preparation ; and, when
made with impure nitre, it may be  intrinsically the same.   But
I have  not  found that any number of abstractions  of pure
nitrous acid will free butter of antimony completely from muri-
atic acid.   The mistake, if any,  is of  little consequence  in
medicine.   But it is perhaps a more difficult  matter to  explain
or account for the deoxygenation of the muriatic acid by means
of the nitric, which we know to be  the speediest means to oxy-
genate it.  We  must consider it, not as a deoxygenation of what
part of  the acid remains combined with the antimony,  but as a
super-oxygenation of what is expelled from it.  The  efferves-
cence is violent, and the fumes are  uncommonly corrosive.  We
know that the acid combined in the antimonial muriat is in  its
oxygenated  state.  The  metal, already saturated w'uh oxygen
cannot decompose the nitric acid, and thereby occasion the fumes
of aqua regia. •  It is decomposed by the nascent muriatic acid;
and this comes  off in a super-oxygenated state. There are two
or three other processes in which this rare acid is  formed in the
same manner.
  The only remtining saline preparations are those produced with
the vegetable acids.  The antimonium tartarisatum; (E^in.and
Lond.) The vinum antimonii tartarisatum; (Edin. and Lond.)
and the vinum antimonii.  (Lond.)
   The  vegetable acids do not act sensibly upon crude antimony,
and but weakly on the pure antimony.  To facilitate their action
we must take the metal,  not only  separated  from the sulphur
but moderately oxydated, or reduced to its most soluble state.
Accordingly, the  compounds  of  it  with  the vegetable acids
were formerly ordered in  our despensatories to be  prepared
either with  the washed crocus, or the vitrum antimonii.   But
 the crocus was formerly  in most  general use for this  purpose,
 (and it is still used at London), until complaints prevailed every
 where of the weakness, inefficacy, and inequality of the emetic
 tartar.  This  was occasioned by frauds in preparing the crocus 
276            EMETIC  TARTAR, &c.
used much  for horses, &c.  The great demand  for  it encou-
raged  the druggists to attempt cheaper preparations: and in-
stead of employing the crocus antimonii  lotus, as was directed
by  the pharmacopoeia, which  is  made  by  deflagrating equal
quantities of nitre and crude antimony, they used only half, or
three  parts, and even less,  of the  nitre, the most expensive
article.  And to succeed the better in bringing the mixture into
thin fusion,  so as  to make an  uniform glass, they employed a
little alkali.    The result of all this  is a preparation nearly the
same with the regulus medicinalis ;  a drug almost inactive, and
insoluble.   If the weakness of  this preparation were all its
imperfection, it could easily be remedied  by increasing the dose.
But, by thus stinting the nitre, it is almost impossible to make an
uniform mass; and  different  portions of the same lump  will
often be in different states.   This spurious crocus may be easily
distinguished from the true by its colour.   In  the  mass the
spurious is  opaque, and almost black :  and when reduced to fine
powder,  it  is of  a dirty purple colour.  The genuine is liver.
coloured in the mass,  and a  deep yellow when finely powdered.
   Now the  state  of the crocus is of most consequence for the
preparation of emetic tartar; for a large  quantity of the nitre
is  necessary for destroying the sulphur,  and then bringing the
metal into that state of moderate oxydation that renders it most
soluble in the weak acids.   Less nitre will leave some sulphur,
which sheathes the metal;  and the pure  regulus has little solu-
bility in the vegetable acids, and requires a little previous  oxy-
 dation.       •
    In  consequence of  these frauds in preparing the crocus, the
 emetic tartars and wines, as prepared by different apothecaries,
 were  widely different in strength, and often totally disappointed
 the practitioner.
    Different chemists have exerted themselves to remedy this
 inconvenience in a medicine of so much activity  and Impor-
 tance,....indeed the most valuable of the antimonial medicines;
 and in consequence of their experiments, and of what has been
 published  on this subject, the tartrite of antimony,  or antimo-
 nium tartarisatum,  is now always made.  I believe, sufficiently
 strong. 
       ANTIMONIUM  TARTARIZITUM.       277

  One of the best processes they recommended, and which
was lately the process of the Edinburg Pharmacopoeia,  was
to use the vitrum antimonii, which is preferable to crocus,
because we have no experience yet af any mistakes or frauds
committed with  regard to it, and we can  always know if it
be  .good.    We are there directed  to  beat it to very  fine
powder,  and mix it with an equal weight of the  crystals of
tartar, also powdered'.   In the next place, for every ounce
of  the mixture, or half ounce of tartar,  take one pound of
pure  water, (distilled water is the  best,) and set it in a fur-
nace  to  boil.  As soon  as  it boils,  throw  in  the mixture of
tartar and vitrum  by degrees, until all is  in ;  and continue
to  boil  gently for several  hours.   The  number of hours
necessary cannot be  specified with precision.   It depends
upon the degree of pulverization of the vitrum.  If it  be a
very  fine and almost impalpable powder, about four hours, or
 sven less; if not  so fine,  twelve hours.    It is more neces-
 sary  to  attend to this, when the vitrum  is employed,  than
 when we employ the crocus.    The first, being powdered
 mechanically, can never be so impalpably levigated as the
 crocus,  which falls a soft powder, completely divided by the
 separation of the saline matter.   Beaume, in examining the
 preparations of  eminent apothecaries,  found differences  in
 the quantity of  metal obtainable from  an  ounce of the tar-
 tarized  antimony, which were surprisingly great.   In some
 he  found 150, and in  others scarcely 40 grains.   Vinum
 emeticum may also differ in consequence  of a difference in
 the acidity of the wine.
    I  need scarcely insist on the necessity of much water and
 a boiling heat.   We knowr that water dissolves  only  one-
 twenty-fourth of its weight of  tartar with a boiling heat; and
 that  it lets  go a  great portion of this by a moderate diminu-
 tion  of  its heat.
    Mr.  Macquer  would prescribe the mercurius  vitse  in
 preference  to the crocus  or glass, as more to be depended
 on for perfect uniformity,  But  I. do not see  reason to doubt
 of the goodness of  these  preparations;  and prescribing so
 costly a thing as mercurius vitae would only occasion  more
 substitutions or  adulterations. 
278      ANTIMONY....EMETIC  TARTAR.

   Beaume  has further  given a caution  with regard to the
vessel in which  the mixture is  boiled.   He  says it must
neither be iron nor copper.   He finds  that these vessels de-
compound the emetic  tartar in some measure.   The vessel
must be glass,  or silver,  or earthen ware not glazed with
lead.   But  M. de la Caille assures  us that  iron may be
used.
   When the operation is conducted in this manner, the tar-
tar is saturated with  the antimonial calx, part of which re-
mains undissolved.   And the liquor  being filtrated affords,
by evaporation,  fair  crystals, pyramids of three  sides,...,.
transparent while wet, but becoming white and opaque in  the
air.   And these crystals are the saturated tartrite; and  are
powerfully emetic.  The  dose is from one grain, or one-half,
to two, or three at the  utmost, for an emetic. This may seem
an inconvenience: but it is  easily remedied  by mixing  ten
grains, for instance, with three or four times as  much sugar ;
and  thus  we  will  have a powder which it will be easy to
weigh out in moderate doses:  or a more common way is to
dilute it  in water,....three or four grains,  for example, in
six ounces;  and a spoonful is taken every half  hour until it
operate.
   But beside the vitrum amimonii, any other preparation in
which the metal is freed from the sulphur, afid very  mode-
rately oxydated, may be employed to  saturate the tartar, and
produce a medicine equally powerfuland certain.
   To complete this article, Dr. Saunders added a simple and
useful method of examining emetic tartar, so as to judge if
it be properly prepared, and as strong as possible, or what  de-
gree of strength it possesses.   On examining the solubility
of different tartars, he found, by experiments, that they^are
more soluble in  proportion as they are more completely satu-
rated with antimony :  and that the difference  among tartars,
in this respect, is so  considerable, that it  is easy to  distin-
guish them.   Thus, one ounce of water, at a middling tem-
perature, dissolved,
             Of the saturated tartar   52 grains.
             Apothecaries'hall        38
             A London  chemist's     32
             Edinburgh  shops       less, 
                 EMETIC TARTAR.              279

  I only wish he had specified the degree of heat more par-
ticularly.
  The next set of preparations we have  to mention are the
reguli, and preparations from them.
  The process by which antimony is obtained in the largest
quantity and purest,  is similar  to that followed in extracting
other metals  from sulphurous ores, viz.  evaporation of the
sulphur by ustulation,  and reduction of the calx.   But other
processes have been commonly followed.   These have  in
general been two : the  process for simple  regulus of anti-
mony, and that for martial regulus of antimony.
   For the simple metal, or what is called simply regulus  of
antimony, the  crude antimony is melted  with  about half its
weight of black flux, or rather the ingredients for producing
black flux, viz. nitre and tartar, which occasions part of the
regulus to separate : the hepar sulphuris formed  by the alkali
 and sulphur, having rather more attraction for  the charcoal
 of the black flux than for the metal.   But this superiority of
 attraction is not so great as to occasion a complete separation
 of the antimony.   Part only separates.  The rest remains
 dissolved in the saline sulphurous scoria, and forms with it
 a hepar antimonii,  and is employed as such  in the London
 Pharmacopoeia.
   The other process  which I said is also often  followed, is
 that  for  regulus antimonii martialis.   Crude antimony and
 iron filings,  or small nails, in equal parts,  are mixed and
 melted with a violent heat, and commonly with  the addition
 of a  small quantity  of nitre or fixed alkali.   In this opera-
 tion, the sulphur shews a stronger attraction for  the iron than
 for the antimony ; and forms with the iron a hard sulphurous
 compound.   The antimony sinks separately in large quantity,
 but not so pure as by the former process.  It dissolves some
 of the ire-..   It is purified by crude antimony, and two or
 three meltings with a little nitre.   The  sulphur of the crude
 antimony forms a scoria with  the iron, and floats above : and
 thus the regulus is freed from the iron.  Melting again with
 nitre destroys the sulphur brought in by the crude antimony,
 and not carried up  by the  iron.  Thus it may be made as
 pure as the other.   Many other  metals may also be used 
280   REGULUS AND CERUSSA  ANTIMONII.
all, except  gold, zinc, and platinum,  having a stronger at-
traction for sulphur than antimony has.*
   In whatever manner the antimony is separated from sul-
phur, if it be made very pure, and cast  into a conical vessel,
it exhibits a star.   Regulus antimonii stellatus,...regulus stella-
tus.   Many mysteries have been supposed to be indicated by
the figure which the  surface  of this metal assumes  in  cool-
ing ;  it having generally a stellated or radiated figure.  This
is owing  to  its  mode of crystallization,  combined with the
progress  of cooling,  which  proceeds from the  sides of the
vessel to  the centre.    It is needless to take up your time with
proving the  folly of these fancies.
   Preparations from  the Regulus.....Cerussa  antimonii; sto-
machicum Potcrii ; cardiacum Poterii ; fantihecticum  Poterii;
tinctures of antimony.
   Uses of Antimony....It affords, in many of its preparations,
medicines of great efficacy to remove many  diseases of the
human  body, as well as of other animals.
   In the arts, it is used  for refining gold :  and the regulus
is mixed  with tin and lead to harden them, for the composi-
tion of pewter.   But I apprehend that the greatest quanti-
ties are employed to  mix with these metals for letter found-
ing.   In  this  composition,  great hardness,  and great fusi-
bility, are important  properties.   It is  also peculiarly fortu-
nate, that the latent  heat necessary for the  fluidity of this
composition is very moderate; so that a man can work with-
out  intermission,  when  the letters are small.   The mould
loses so  much heat  while  opening  to  shake out the letter,
and  shutting again, that the  next letter makes no accumula-
tion of heat.   Were it otherwise, the mould must be cooled
after a  few letters, and the  expedition of  the work greatly
diminished.                      '
  * Lehman relates a very singular experiment made with antimony and
arsenic, which being- dis'illed together, with a violent heat, yield a sulphurous
s'blimate, which  does not deflagrate with nitre :  and he says that a regului
of antimony remained in the retort.  I found this residuum not distinguisliahle
from a regal us by its chemical properties, but very distinguishable  from it by
a beautiful  chani^eidjlc colour upon  the facets of the metal when brolfcn.  I
attributed this to a iilru <f  arsenic, w. !(•■:, being transparent, should exhibit
such odours.  But no trial that I  colju i'■■ :t to supported my conjecture.
The h vl.liinate did r.ol deflagrate, but burnt slowly v.'.ha dull heat....editor- 
281
         GENUS VI.....ZINC, OR SPELTER.

    Another brittle metal, orsemimetal, bears some resemblance
  to the last. Like it, it shews a plated texture when broken. But
  it is easily distinguished.   1st. It is not so brittle ; but can  be
  compressed by the strokes of a hammer;  and even bears some
  degree of extension under the hammer.   It bears extension  by
  rollers very well ;  and can thus be drawn into very thin plates, if
  carefully annealed  between the operations.  It also bears draw-
  ing in the wire.plate.  Itf has therefore more  cohesion, and is
  broken  to pieces with more difficulty.  The plates are not so
  broad :  and its colour inclines to bluish,  when compared with
  the other twc   It is the  most expansible of all  the metals  by
  heat. It melts  before it begins to grow red hot; and flows quite
  thin at 680.  When melted and poured into a vessel, it may  be
  reduced to a pretty fine powder by simple agitation.  Its speci-
  fic gravity is nearly 7,2.  It has some-singular properties relative
 to its solid form.   This imperfect ductility is accompani-d by a
  singular kind of toughness, which  makes  it extremely  difficult
 to work it in  the ordinary way, by filing  it.   It  sticks  in the
 files; and soon renders thtm useless.  Lead, though  a much
 softer metal, has not  this  quality.   Pure copper has a little  of
 it.  It sticks in like manner to the edges  of the cutting tools,
 with which it is scraped or turned in the lathe ; and, what is still
 more singular,  when  mixed with copper which has the same
 quality,  it fornis a metal which the workmen find to work more
 pleasantly than  any  other metal.  Moreover, although annealing
 it, after every passage  through the flatting mill, enables it to ex-
 tend much more than it would otherwise do, yet if it be ham-
 mered in its  hot state, it crumbles to .pieces  with  the greatest
 ease.
   If the heat be further increased to a  vivid red or white heat,
 in close vessels  of proper form, such as an earthen  retort or re.
 ceiver, the whole arises in vapour, which,  in close  vessels, may
be condensed again  without further change.  But when the same
     vol. in*                  Kn 
282            CALCINATION OF ZINC.

heat is applied in the open air, it suddenly takes fire like an in-
flammable body, and burns rapidly, with a bright and dazzling
flame :  and the metal is quickly changed into a calx.  This is
very white, and soft, and rarefied, in comparison with other me.
tallic calces. The greater  part of this  calx is accumulated in the
vessel, just over the burning zinc, and soon impedes the further
action of the air on the remaining zinc.  But some part of it
rises up into the air, and floats or flies about  in it like cobwebs.
In this state it was called pompholix, and philosophic wool, also
nihil album.  This, therefore, is the  most expeditious method
of calcining zinc.  The  process described  in  the Edinburgh
Pharmacopoeia is this: " Place a large or deep crucible, or other
44 deep earthen vessel, in a melting furnace, inclined  a little to-
44 wards  the door.   When heated to the proper degree, let the
44 zinc be thrown into it in small pieces, waiting till the first is
44 entirely burnt, before the second is thrown in.  Thus the oxyd
44 of the  zinc is  accumulated in the  crucible; and being  light
44 and bulky, it must be stirred now and then with an iron rod,
"that the air may be admitted to the burning metal.  And when
"a quantity of it is accumulated,  it must be taken out with an
41  iron spoon before any more of the zinc is thrown in."
   The  late  Professor Gaubius of Leyden, who recommended
this oxyd to physicians as an useful remedy for convulsive dis-
orders,  described  a different way of preparing it, but not so
good.
   From these phenomena, it is evident that this metal is one of
the most calcinable of any, when it is exposed to a violent heat.
And it is reasonable to conclude, from the great brilliancy  of its
flame, and the great heat  which its inflammation produces, that
in its calcination it attaches to itself a very great quantityof oxy-
gen.  But it has not a disposition to attract oxygen easily  from
the  atmosphere, and  to calcine by means of humidity, without
the  assistance  of heat, in  which it differs from iron  and  most
 other metals.*

     * It  is not altogether inactive in this respect.  Its polish is very easily
 tgrnished by exposing it to very damp air: and if wetted, and kept in that
 state an hour or two, its  polish  is cntiiely  taken away, and it becomes of
 a dull leaden colour.   When viewed in this state with a microscope,  we see 
        ZINC....ITS  RELATION  TO ACIDS.       283

  The oxyd of zinc is so unfusible,  because it is probably more
highly calcined than the fusible oxyds of some other metals.  It
is, however,  in some degree fusible in a very violent heat,  and
forms a fine yellow glass.
  The reduction  of this oxyd was long a difficult problem.   It
was found so difficult,  that many supposed it impossible.   But
this proceeded from the improper manner of attempting it. They
tried  it in the manner usually  practised with other metals, by
mixing the oxyd  in a crucible with black flux, or with charcoal
and salts.   In this way the heat which was necessary for the re-
duction, was sufficient for totally evaporating the metal as soon
as it was formed.   It was therefore  all lost.
  Mr. Margraaf, attending to this, first contrived to accomplish
the  reduction. He mixed the oxyd with one-eighth of its weight
of powdered charcoal,  or lamp black; introduced the mixture
into a small earthen retort luted to a receiver ; and urged it with
an intense white heat.   He thus got  zinc again in the form of a
metallic sublimate, or  mass,  attached to the neck of the retort:
and he found it rather more malleable than ordinary  zinc.
  The same expedient  occurred to Neuman : but he tried too
small a quantity, (two drachms)  so that the air inclosed  was
sufficient to burn  the zinc again.   And he got nothing hut half
burnt flowers in the neck of the retort,  which shewed, unques-
tionably, that thtey had been once reduced, otherwise the  calx
would never have been sublimed.
  Zinc is easily dissolved by  all the acids ; and is united with
them by a very strong attraction.   The acids are therefore more
neutralized by it than by most other  metals: and the compounds
do not easily  suffer any  separation of the acid  from the metal by
large dilution with water.
  The  sulphuric  acid even requires to be diluted considerably
with water,  to make it dissolve  the zinc  well, just as in  dis-
it evidently corroded. But I have not observed this to increase by length
of time.  This is surely an oxydation, or rust.  It seems completely to cover
the surface, rendering it neutral or saturated; and this defends the interior
parts.  But if the metal be made nearly red hot, and water be sprinkled
oh it with a brush,  it then acts powerfully on the water,  decompounds it,
and  produces much  hydrogenous gas.  Zinc is oxydated in this way, jugt
as jron is.....iditor 
284
ZINC,
solving iron.  And  further, the zinc,  while dissolved by this
acid, decompounds a part of the water, as iron does:  and a great
quantity of inflammable air is, in consequence, produced during
the brisk  effervescence with which this dissolution is perform-
e,d.  One ounce of zinc produces 356 ounce measures with one
ounce  of sulphuric acid.  One ounce of iron gives 412 of air,
with 2 ounces of the acid.   The metal is therefore oxydated as
well as dissolved,  but receives  all the oxygen from the water.
The compound of oxvdated zinc and sulphuric acid thus formed
is easily crystallized; and gives crystals that are not deliques-
ce! t.   Thev are an  article  of the  materia medica; and were
named '"orm rly white vitriol; in the new language of chemistry,
sulphat of zinc.
   The nitric acid, in the diluted state of aquafortis, dissolves
this metal with the greatest- violence and rapidity ; and becomes
excessively  hot.   In the violent  effervescence  which attends
this dissolution, the acid suffers a great and violent  abstraction
of its oxygen, and all the changes which are necessary concomi-
tants of such abstraction.  Part of it  is therefore changed into
red vapours; a great part  in'o nitrous gas; another part into
the less oxydated nitrous gas,  which I lately described; and
lastly a part into pure azote.
   By some variations in the manner of dissolving the metal, we
can modify these  changes  of the  acid.   If, for example,  the
aquafortis be largely diluted with water before it be applied to
the metal,  the gas produced is  almost totally the less oxydated
nitrous gas, or dephlogisticated  nitrous gas of Dr. Priestley.
   The muriatic acid,  in its common state,  also dissolves zinc
easily, with effervescence and production of a great quantity of
inflammable air.  But when applied in its oxygenated state,
there is no  inflammable air produced.  The reason is  obvious.
The zinc is supplied with oxygen, which was very loosely com.
bined with  the acid. This  muriat of zinc does not give crystals
easily.  It  is a deliquescent compound.  The  solution of it,
mixed with glue,  or employed to dissolve  it, forms a compound
which does not become dry in the air, but has  the inviscating
quality of birdlime.  This  birdlime would probably be >be best
 for catching birds and  insects  for the natural  historian; as it 
             ITS RELATION TO  ACIDS.          28!>

could easily be washed off from the feathers of birds, or limbs
of insects, by water.
   The vegetable  acids  act also on zinc without difficulty and
some inflammable air is  produced during  their action.  The
oxyd of zinc  also dissolves in all the acids, but without effer-
vescence.   A saturated solution in the acetous acid is a liquor
very like olive oil.
   The alkalis act on zinc  as upon some  other metals.  Applied
to it in its metallic state, they corrode it in some measure.
Applied to it in the state of oxyd  precipitated from acids, they
in some cases dissolve, it.  Volatile alkali  is thought to act on
it in a peculiar  mannfer.  When powdered zinc is put into a
solution of the caustic volatile alkali, it yields, after a longtime,
inflammable air.   This, however, seems rather to come from
the water  than from the alkali.  Did it come from the alkali, we
should also obtain azotic gas,  which I  have never been able to
discover by this treatment.
   Such of the compound salts as act on other metals, act more
readily upon  zinc,  which, in  consequence of its inflammable
nature, produces remarkable effects on them, similar to those
produced  by the inflammable bodies.   Thus, melted with sul-
phat of potash or of soda, it changes them into alkaline sulphu-
ret,  and is changed  itself into  an  oxyd: and with the saltof
urine, or phosphoric acid, it yields phosphorus.  It also decom-
poses sal  ammoniac,' by grinding them together, as appears by
Margraaf's experiments, which I mentioned when delivering
the theory of lime.   This is  unquestionably owing to its very
strong attraction for acids, which is such, that alkalis decom.
pound the nitrate of zinc with difficulty.   To the same cause we
may ascribe the decomposition of alum by boiling it with  zinc.
If the sal ammoniac  and zinc be treated in  the  way of distilla-
tion, we obtain first an incondensible suffocating alkali,...then a
volatile muriatic acid,  in  thick white fumes,...in an open firej
white flowers succeed ; and at length,  a  reddish and  a black
butter.
   Nitre deflagrates violently with  zinc.   But it must be heated
so hot that it is not easy to distinguish its deflagration with the
nitre from the inflammation to which it is so much disposed of 
 286 ZINC, WITH NITRE....SULPHUR....METALS.

 itself.  Its  flowers  do not  sensibly  deflagrate ;  yet  they
 alkalize double their weight  of nitre.   The fixed  alkali and
 calx form together a mass externally greenish, internally pur-
 ple. Infused in water, the alkali dissolves, and with  it a part
 of the calx, tinging the water purple.*
    Zinc does not unite with sulphur, nor hepar sulphuris, nor
 with crude antimony ; and is  therefore purified by  the action
 of sulphur from admixtures of lead, which it frequently con-
 tains.   Alkaline and calcareous sulphurets, however readily
 unite with  the calx,  and dissolve it, forming a  substance
 resembling its  ores.
    None of  the  earths have  been observed to have  any re-
 markable effect on zinc or  its  calx.    *
   It unites with all the metals except bismuth and nickel.  It
 is indeed difficult to combine  it with iron ;  because the great
 heat that is necessary dissipates the volatile metal, and it car-
 ries off some iron with  it.   It has somewhat of this effect on
 all the more  calcinable metals.  Most of these mixtures boil
 and deflagrate more than zinc  alone, and globules of the metal
 are  frequently scattered about.    Hence  it is  called  metallic
 nitre.   Copper is but little affected this way:  and the cadmia
fornacum of the brass-founderies rarely contains any copper.
 When they are melted separately, and  then mixed, there is
 frequently a violent  detonation, and much of the  metal is
 thrown about.   When lead is added to  melted zinc, the mix-
 ture takes fire, and the zinc burns  away.  They mix quickly,
 when the  zinc  is added to melted lead.   Arsenic makes it
 black and fiiablc.
   United  with mercury in the  form of  amalgam, it is the
 most powerful exciter of  an   electric globe.   The  best pro-
 portion is four parts of mercury to  one of  zinc.
   Mixed with tin, in a small  portion, it greatly increases its
 hardness, and improves its colour, making it like silver. But
 this mixture is more apt to be corroded by acids. It is used,
 however, in the manufacture of pewter.

  * With respect to the other neutral salts,  the only remarkable effect that I
 know, is the formation of a hutyraceons sublimate of zinc,  like the muriat of
 antimony, by distilling common solt and the sulphat of zinc, or by subliming the
 solution of zinc in the oxygenated muriatic acid...  editor. 
         ZINC....WITH COPPER....BRASS.      287

  Mixed with lead in the proportion of one to  twelve,  or
even less, it improves its  tenacity in a most surprising man-
ner, making it four or five times stronger.   It would there-
fore be a great improvement on water pipes.
  The most useful mixtures of zinc are those with copper, in
various proportions.   It communicates a yellow colour, not-
withstanding  its  own  whiteness : and  it removes the dis-
agreeable toughness which makes copper so difficult to work
with the file and in the lathe, while it very little impairs  its
tenacity and  ductility.   In a very large proportion  to  the
copper, it makes the hard, or spelter-solder, used  for copper,
brass,  and iron.  In  a smaller proportion, it makes brass :
and in other proportions it makes more  or less perfect imi-
tations of gold. Such are pinchbeck,., princes metal,....similor,
....Bath metal,....tutenag,  &c.   Homberg, Geoffroy,  Hellot,
and Lewis, have made many experiments and useful observa-
tions on these  mixtures: and to their writings I refer you for
farther information on this head.  Observing, in general, that
all these  mixtures lose  some of the zinc by evaporation in
great heats: and that long continuance of it will expel  the
whole.   This  is owing  both to the volatility  and to the in-
flammability of the  zinc.  You will always observe an uncom-
mon brightness on the surface of the melted  metal, greater
than that of the surrounding fuel.   This isjustalow flame,
not one-tenth  of an inch high.
  It remains  only to mention the operations by which it is
extracted from its ores.
  For a  long time, all the zinc  used in  Europe was im-
ported from   China,  except a  small quantity  which was
obtained  in the Hartz forest in Germany, from an ore which
yielded lead, and copper, and silver, and a little gold at the
same time.   We have not been informed how the Chinese
zinc is obtained. The process by which the German was pro-
cured was a little uncommon.
  In  the side of the  furnace, (which is  a reverberatory)
opposite  to the bellows, the wall is double, consisting of two
thin fire stones, with a hollow between.  On a level with the
usual surface  of the melted metal,  there is a chink opening
into this  cavity.  The zinc evaporates as fast as it is formed:
and the vapour is driven into this  hollow through the chink 
288       ZINC....CALAMINE.. ..BLENDE.
  by the blast of the bellows.  The side of the cavity, which is
  in contact with the air of the hut, is cool in comparison with
  the rest, the stone being thin and  being often sprinkled with
  water.   Here, therefore, the  sublimed metal attaches itself,
  while the flowers, which are unavoidably formed by the cal-
  cination of part of this metallic vapour, rise farther up, and
  get into the long funnel, where they collect, and are got out
  from time to time by the name of cadmia fornacum,  Tutia,
  diaphryges.
    This very singular process  was the contrivance of a com-
  mon smelter, who had observed this strange  metal collecting
  in the retired corners of the furnace, at Rammelsberg.   It is
  certainly ingenious,  and shews a  sagacious and intelligent
  mind.   Such have been most of the processes in metallurgy:
  and it is by a collection of these casual arts that our science
  has arisen.  The quantity thus procured was but very small:
  and no other method was known or attempted in Europe for
.  producing tn{s metal, although its  ores, which are very plen-
  tiful, appear to"iaave been sufficiently known as such from their
  effect in making\^rass.
    In the greater part of these ores, the  zinc is in the state
  of a calx; in consequence of which, they appear  more like
  stones than metallic  minerals ;  and were  actually considered
  by many as a particular species of stone or earthy matter, and
  called lapis calaminaris.   The  original name, however, by
  which it was known to the ancients, and mentioned by Pliny,
  was that of cadmia.
    Sometimes it  is in a less calcined state,  which gives it
  more or less  metallic opacity and  lustre: and in some cases
  there is sulphur in its composition, which produces the same
  effect.   It is then called black Jack, by the English miners;
  by the Germans,  blende; and  by natural historians, pseudo-
  galxna,....i. e. mock-lead ore.
    This  ore is somewhat curious.    It is transparent  when,
  pure; and in a very strong light, although seemingly opaque,
  it transmits a very deep brown light.   It  breaks also with a
  glassy  fracture.   Notwithstanding these  marks  of  being
  homogeneous, a bit of it, slowly  dissolved in weak aquafortis,
  leaves a spongy mass, which retains the original shape com- 
                PROCESS  FOR BRASS.            289

pletely: and this weighs about one-fifth or one-sixth of the
blende.   It is pure sulphur,  not chemically combined.
 • These several varieties of it have been long employed for
making of brass. The process consists first of roasting;* then
cementation with charcoal and copper.   The copper  fixes
the  zinc, and acquires the yellow colour.
  This was the  only use made of the ores of zinc in Europe :
and the manner  in which they produced their effect was not
thoroughly understood, until Mr. Margraaf extracted zinc
from them, without the assistance of any other metal.  But
now, in consequence of his discovery, manufactories of zinc
have been established in England,  and elsewhere.
  The English  process is" ,>j£at the chemists call destillatio
per descensum.   The ore,  rq^ed  with charcoal, is put into
conical pots, having in the bottom an  iron pipe, which passes
through a hole in the hearth of the furnace,  and  reaches to
the mouth  of a rude  receiver containing water.   Fuel being
kindled around the pots,  (whose  mouths  are stopped with
clay) and care being taken that it shall not be so hot as to melt
their contents, the metallic vapours are expelled downwards,
and condensed in the receivers.
  But lapis calaminaris is still much more used for making
brass, the process for which is the  cheapest way of extracting
the zinc, while by the same fire it  is also mixed with the cop-
per.   The ore  being  cleared  from  sulphur, and other im-
purities, by roasting, is ground and mixed with charcoal. The
mixture  is  put into pots, and stratified with plates of copper.
A  proper  heat  being  given, the  ore is  metallized, and the
metallic  vapour is immediately seized on by the copper,....
renders it  more fusible, and melts down with it, and lodges
in the  bottom of the pot, where it is defended from the air
by  the vitrified flag floating above  it.  When the proportion is
properly observed, the copper gains an addition of one-third
of its weight, in becoming brass.             \
   Although copper fixes zinc to a certain degree, it does not
entirely  prevent its evaporation  and calcination  in  strong
heats.   Hence  when brass is melted, if it be exposed to air,
it is liable  to lose part of the zinc, and by repeated fusions,
the whole.   Hence cadmia fornacum,,...pompholix,,..tdiaphry •
ges,....nihil album,,...tutia, &c. which are different names for
     vor.  ut.                o o 
290             PROCESS FOR  BRASS.

the condensed vapours which escape from the furnaces  in
these processes for brass.
   Uses of Zinc.....It is chiefly useful for metallic compounds,
....brass,....pinchbeck,....pewter,.... for   tinning,....and   for
solders: and it is  an useful article of the materia medica.
   Until lately, zinc was hardly ever used internally:  except
sometimes the white  vitriol was used as a vomit of quick
operation.  It was chiefly confined  to external use.   It  pos-
sesses useful powers as  an astringent  and repellent;  and is
used particularly in inflammations of the eyes.  Its prepara.
tions are,....Lapis calaminaris praparatus ; Edin.  ai 1  Lend.
....Tutiapraparata; Ed. and Lond.....Calx zinci, vulgo,fores
zinci ;  &d.....Zinawi  calcinatum; Lond.....Vitriolum  album;
Ed. made of zinc and  sulphuric acid.....Zincum vitriolatum
purificatum; Lond.....Aqua vitriolaca ; Ed.....Ceratum e lapide
calaminari;   Ed.....Ungucntum e tilth;  Ed.  and Lond....
Unguentum  ?■ cake zinci; Ed.
   But  certainly,  it might be easy to substitute preparations
of this metal, instead of some of these, which could be much
more  depended  on.   For lapis calaminaris is extreme!)'
different, (Vide Essays on different kinds of it, by Margraaf)
and may  accidentally  contain arsenic and other minerals.
   With respect to tutia, see  the experiments of Neuman,
which shew it plainly  to be artificial.   And it is seldom suf-
ficiently levigated for ointments.
   Both of these might be  excellently  superseded by  a pure
calx of zinc, or pompholix, which is extremely fine ; and the
vitriolum album by an  artificial sulphat of zinc.
   When  the chemical state of the preparations is once such
as may be depended on, they are medicines of very uniform
operation,1 and of considerable powers.    The sulphat in the
dose, a drachm or a  drachm and a half, is a quick emetic,
with  little distress or  sickness.   The calx in much smaller
dcses,  not  exceeding five, grains,  produces sickness afra
vomiting.  We are but  little informed  hitherto as  to.the
internal use of the preparations  of zinc.   But  it has been
long known as a powerful astringent, emollient, and cooling
application, when we  desire to  remove  the  remains of a
tedious inflammation,  and  restore  strength to the'vessels. 
                       BISMUTH.                   291

The sulphat and nitrate, in the quantity of two grains to an
ounce of water, answer very well in such cases.
   GENUS VII.....BISMUTH, OR TINGLASS.


   Bismuth has a near resemblance to antimony in external
appearance.  It is  nearly as brittle,  and exhibits  the same
texture when broken.  But it is  much heavier; its specific
gravity being 9,823:  and the colour of it inclines a little to
red.   It is also more fusible, and less volatile than antimony.
It melts sooner than lead;  and flows the thinnest of all the
metals.   It also expands  in congealing, and therefore takes
the finest impressions of its mould.
   1 his metallic substance  is easily calcined to a moderate
degree, forming in its oxydated state a very thin yellowish
glass, one-eighth heavier than the metal. But it is difficult to
calcine it further; at least the oxyd of it is always fusible in
a  moderate red heat;  by which  quality,  and some others,
it  resembles the oxyds of lead.  It may be procured, either
by keeping the  bismuth  melted,  and stirring it constantly,
to expose the different parts of it to the air, or more quickly,
by way of scorification in a more violent heat, wich may cal-i
cine it faster, and melt the calx as  fast as it is formed; so that
it  may constantly  run off from the surface of the melted
metal, and leave it exposed.   1 he metal smokes constantly,
while any of it  remains uncalcined:  and a faint blue flame
may be observed on its surface.
   It  is easily reduced again, by melting it with addition of
charcoal, or of  the black flux.
   When we try it in mixture with salts, we find that the sul-
phuric acid acts only when  applied strong, and assisted with
neat.   The metal is then corroded and oxydated, by attract-
ing oxygen from the acid :  but we do not get a soluble com-
pound.
   A soluble compound of this  metal  is best and most easily
obtained by the  action of the nitric acid, which dissolves it
witji a strong effervescence, and the production of great heat, 
 292 BISMUTH WITH ACIDS....PEARL  WHITE.

 red vapours, and nitrous gas, in consequence of the abstrac-
 tion of t xygen from a part of the acid by the  dissolving
 metal.   The solution, when completed, is almost colourless :
 and the  compound it contains is liable to suffer an imperfect
 separation of the acid from the metal, when we dilute it
 largely with water.
   This  precipitate has been supposed by some authors to be
 the pea^ wrftte, said to be employed as a cosmetic : and it is
 said also that the transpiration by the skin blackens the oxyd,
 as if by an imperfect reduction, and thus destroys the skin.
 But I believe  that this is a  mistake, having examined many
 specimens of pearl white, which  I found to be precipitates
 from a nitrate by  a solution of common salt, or of tartar.
 Water alone makes but a very imperfect separation, and leaves
 so much acid adhering to the  metal, as unfits it for any such
 purpose.        #
   In consequence of this  mutability of  colour by the steams
 of inflammable substances,  the  solutions of  bismuth, like
 those of some other metals, form what are called sympathetic
.inks; that  is,  inks  which are  invisible, till something has
 been done to the paper.  When we write  with the solution of
 the nitrate of bismuth, the exhalation from hepar  sulphuris,
 or putrescent animal substances, soon make the writing legi-
 ble.  All bad smells have this effect.
   You will  find in Neuman ( p.  107,  108.)  a number  of
 experiments upon the  precipitation of bismuth from aqua-
 fortis, by a variety of different  additions,  which you may
 consult, if you have occasion to attend, to this particular sub-    j
ject.                                  .                      \
   The  same author also describes a process for combining
 bismuth  with the muriatic acid, by means of muriat of mer-
 cury, and the consequences .of dissolving it with  vegetable
 acids and alkalis, and of unking it with sulphur, with which,
 it forms a mass very like crude antimony. To him, thereforey*. A
 I refer you for these particulars, which are  not so  important
 as to require our time.   Mr.  Pott of Berlin  also  may^fte
 consulted, who wrote a dissertation upon this metal.
   The compounds of bismuth are remarkably fusible, so that
h may be employed in the composition of solders for lead or
tin.   The fusible metal, called Newton's  metal,  has bismuth 
               BISMUTH....ITS USES,  &c.          293

  for its principal  ingredient.   The  best proportions for the
  fusible  metal are,  eight  parts of bismuth, five of lead, and
  three of tin.  When thus  mixed, it  will  become fluid  in a
  temperature something below that of boiling water.   It is
  from the same cause, probably, that when  dissolved in mer-
  cury, it disposes the mercury to form more fluid amalgams
  with  other  metals,  particularly  with lead, than ordinary. '
  And  hence it has been proposed to be added'to mercury, the
  more readily to  dissolve lead  balls  lodged  deep  in a wound.
  Mr. Lewis says  (Notes  on Neuman,  p.  93.) that  mercury
  united into a fluid amalgam with one-fourth, one-eighth, or
  one-twelfth of its weigtit of bismuth, dissolves masses of lead
  in  a  gentle warmth,  without the  necessity of agitation.
  Whether this would answer the purpose,  I  cannot positively
  say;  because the  bismuth, or part of it,  separates in  the
  form of powder  while the lead dissolves, which might possi-
  bly prove inconvenient.   An abuse of this quality of bismuth
  has been  practised in adulterating mercury.
    The  principal uses  of bismuth are, to  mix with tin  for
  proper  hardness  in the composition of pewter for  solders
  for lead and tin.   It is sometimes used also in the composi-
  tion of  metal for printers' types ; and when used, seems  to
  be  intended  for greater tenuity of fusion, and sharp impres-
  sion.   The  proper degree of hardness is  always procured
  by the cheaper regulus of antimony..   With lead one part,
  tin one, bismuth  two, and mercury ten parts, it composes a
  kind of fluid amalgam,  which being moved backwards  and
  forwards  in  a clean  glass  vessel, leaves a train behind it,
  adheres to the glass,  and foils  or silvers it.   It is therefore
  used for  foiling  the inside  of  glass globes.   (Vide  Boyle's
  Treatise on the Usefulness of Exper. Phil.; and for other uses,
  vide Neuman, p.  112.J  But  it has never  been  introduced
  iflto the materia medica, nor is there any reason yet  for  in-
ftroducing it.
   Its ore is  most  plentiful in Saxony,  near Schneeberg.
  There is some too in Bohemia, and  in Duaphine,  and some
  in England.  Sometimes the bismuth is found pure ;  seldom
 or never a vein of it pure, but intermixed with other orgs
 especially arsenical, and particularly the ore called  cobalt.
 The bismuth is easily separated from the ore by eliquation. 
294             COBALT....ZAFFRE.
It separates in its metallic form ;  and runs along the4nclined
hearth into a channel, by which it is conveyed to a receptacle,
where it is defended from the further action of  heat.   Mr.
Macquer gives along account of a very curious  tincture, or
solution, obtained from ores of this kind.   But as the bis-
muth has no part in its production,  I shall consider it after.
wards in its proper place.


              GENUS VIII.....COBALT.

     This name has been  long appropriated to certain mine-
rals or ores, which when duly prepared, and melted with glass
or enamels, give them a deep and rich blue colour.   In their
natural  state,  these ores have commonly the metallic opacity
and lustre, and a colour resembling that of iron, although it
is  various, in  consequence of their being  more or less com-/
pounded with other minerals.
   Those parts of them which  are long exposed to the air
are liable to decay, and contract a sort of  rust   which has a
pale purplish red or  pink colour, like that of peach blossoms.
It  is named cobalt bloom.
   All the  varieties  of  cobalt generally contain a large quan-
tity of arsenic, the greater part of which  is easily separated
from  them by ustulation : after which, the  remaining me-
tallic  matter is an oxyd of a dark colour, like soot, or  some-
times it has a violet hue.  It still retains  arsenic, which ap-
pears to have been changed  by the ustulating process into its  i
acid state,  and in that state  remains  strongly combined with 4
the oxyd of cobalt.                                          *
   The  dark coloured oxyd,  obtained by ustulating the ores
of cobalt,  is na.mtd'zaffre ;  * and, when  added  to glass, or
the materials for making  glass, gives  it  the  blue, or deej^
violet colour,  in proportion to the quantity used.  But it witts.'J
employed for  this purpose a long  time before we knew.thai-
it could be redtfced to a metallic state.   Dr.  Brandt,  of.trje
Swedish academy, first shewed that it may be procured by

 * This  zaffre, however, which we  procure in the shops, contains btfi'a fourth   .
* fifth part of this oxyd; and the rest is powdered -flint. 
             HELLOT'S  SYMPATHETIC INK.       295

    the help of the common inflammable fluxes :  and he called it
    regulus of cobalt.   From the experiments he made upon it, as
    well as the properties of its calx which  were known before,
    there is no doubt but that it is a metallic substance,....a semi-
    metal of  a peculiar kind.   The following are its  most re-
    markable qualities.
       Its  colour approaches to  that of iron or antimony.    It
    breaks  with  a granulated surface,  like  steel.    Its specific
    gravity is 7,7.   It requires a  pretty strong red heat to its
    fusion, and*can  be calcined without difficulty.   But its  cal-
    cination goes on slowly, like that of  copper, and  withput the
    appearances  of inflammation.   The calx produced from  it is
    always  of a  blackish colour, and is not easily melted by it-
    self.  But if it be added to glass, it melts with it, and colours
    it to different shades of blue,....from  the lightest to  a deep
    blue, which appears black.
       Of the acids aquafortis dissolves  it the most readily,  and
    with effervescence.  The sulphuric acid will not  act upon
    it, except when applied strong, and with the  assistance of
    heat.   A very diluted acid, however, will readily dissolve
    the oxyd obtained by precipitation from  any acid, by  alkali
    or  lime.    The  muriatic  acid  acts best Upon the calx,  or
    when it is assisted with a little of the nitric acid.  The so-
    lution  has a faint rose  colour,  which  becomes green  when
    heated.
       All the saline compounds  thus  produced are soluble in
    water, and capable of being largely  diluted without separa-
.    tion of the acid :  and the solutions are all of a rose colour,
I   or reddish.
       The muriatic solution, as also the saline compound which
    it contains, is remarkable for changing its colour when gently
    heated, and resuming its former colour when the heat leaves
   , it.   Air  deprived of  its natural humidity by quicklime, or
a  . .by  sulphuric  acid, produces the same effect;  and breathing
   . jclymp on/it effaces the green, though  hot.
   '•*;.'  This solution is the sympathetic ink of Mr. Hellot;  and is
    the most curious of all the preparations which  go  by that
    name.   The process for it is described by Macquer.   Hellot
    described  it  as produced from ore of bismuth :  but this
    was a mistake, as  I mentioned when describing the properties 
296
COBALT.....SMALT.
of that  metal.   The calx, or  zaffre,  is dissolved iri  aqua
regia, (which keeps it much better suspended than aquafor-
tis) and the solution,  when cold, has a pale  rose colour, and
becomes green when hot.    Writings with this solution are
invisible (when recently  done) in the cold.   But  when held
before a fire,  they  acquire  a beautiful leek  green  colour.
This disappears again  when cold, and may  be renewed by
heat.   And this may be repeated as often as  we please,
taking care that we do not  make the paper too hot.   This
will render the colour permanent.   Frequent  repetition has
somewhat of  this,  effect: and in this respect, a solntion of
the calx in muriatic acid is preferable to that in aqua regia.
If a drawing of a  plant of  abundant foliage be  washed
with a full straw colour, which is not very unlike the wither-
ed lt-af  of  some  plants,  the solution  of  cobalt  being laid
over it,  raises it to  a very  beautiful lively green:  and is a
pretty fancy for a fire-screen.   There is another preparation
of a similar kind, made by boiling oxyd of cobalt in sixteen
times it weight of  distilled vinegar, till the  liquor is redu-
ced to  one-fourth.    It  is filtered,  and again reduced by
evaporation to one-half.   Muriat of soda is now added to
it,....and the muriatic acid takes the oxyd  from the acetous,
This solution is invisible, like  the other, when  cold; but
when heated,  shews a fine  blue, which disappears on cool-
ing.*
   In trying  to mix cobalt with  other  metals, it has  been
found incapable of uniting with  mercury and  lead, except in
small quantity, or  with silver,  according to  Bergman.  It
mingles with  all the rest;  and makes the  moAt malleable  ]
metals quite brittle.   But it was thought  rather  to increase
the  toughness of iron.
   It is precipitated from acids by zinc, but not by iron.
                                                 •          *
   * The action of the neutral salts has not been much attended  to. It is some-
what remarkable that it scarcely detonates  with nitre, ...less  than even <aWM*
per  Yet in its oxydation, it seems to combine with more oxygen than anyt^httf
metal.  The oxyd produced from 100 grains weighs 140   '(Fourcr >v.) Nitre
calcines or oxydates it.  What becomes of the caloric of the oxygen ? The diffi-
culty to reconcile this with the general doctrine is great, but not peculiar to this
metal: for the deflagration of the metals with nitre is  by no mearis ift'the prfl.
portion that we should expect from their increase of weight by calcination..
 SDITOR. 
I     NICKEL.
297
   When borax, which has been tinged with cobalt, is boiled
 in water,  the water dissolves the  borax, and leaves a firm
 gelatinous matter,  which becomes friable by drying, and of
 a transparent rose colour, like cobalt bloom.
   The only use  that I know to be made of cobalt,  is  to
 tinge glass and enamels.   The calx or zaffre, being mixed
 with a certain  proportion  of flint or glass, is melted, and
 forms a glass of  a rich purplish blue.   This is ground to a
 coarse  powder, and sold by the name of smalt,...An which
 state  it is used by the  sign-painters.   Smalt is ground  in
 mills to a very fine powder, which is sorted, by its precipita-
 tion in water, into parcels of different fineness, and sold  by
 the name  of powder blue.   The same compound, ground to
 the utmost degree of fineness,  is used  in painting all the
 blue that we see on  porcelain,  Delft  ware, and  all other
 imitations of porcelain.    Some of it  has  a richness  of
 colour  surpassing all  other works  of the pencil.   This is
 particularly remarkable in the Saxd!fporcelain. The painters
 in enamel complain that it is so fusible, that the heat neces-
 sary  for raising  their other colours makes the blue spread
 just as  ink does on bibulous paper.


              GENU^I^....NICCOLUxM.

   The name now given to this metal is derived  from the
 name which was first given to the ore of it by the German
 miners, at Freyherg in Saxony,  where it  is  most  abun-
 dant.       ^.
  As  the colcuir of this ore resembles in some degree the co-
 lour of copper, they expected at first to obtain copper from it.
 But  not succeeding in their attempts to obtain copper from
 i*by any process,  they gave it the name of  cupfer nickel,....
the^ literal translation of  which  into  English is NiccoPs
copper.
  V*A laborious investigation of the component parts of this
ore by several of  the modern chemists, especially Cronstedt
and Bergmann, has shewn that it contains a peculiar metal,
to which the name  niccolum is now appropriated, but which
is intimately and  strongly combined in the ore -with several
    Vol.  hi.               p p 
298                     NICKEL.

others, and with sulphur.   Cronstedt was the first who made
the  discovery.   The other  metals  present in this ore are
iron, arsenic, and generally some cobalt.   And all these in-
gredients cohere so strongly  together,  that an  attempt to
separate them, or to obtain the niccolum pure, is a task of the
greatest difficulty and labour.   Of this you will be satisfied,
when you look into Bergmann's dissertation or essay on nic-
colum,  in the second volume of his  Chemical Essays.  He
was  at astonishing pains with it; and after all, was not satis.
fied  that he had completely succeeded.   The  most highly
r fined  niccolum that he was  able  to obtain  by his great
labour and skill was still attracted by the  magnet, and had a
very considerable degree of toughness or malleability.  And
he remained doubtful whether these qualities proceeded from
iron still adhering to it,  or were  qualities belonging to this
metal as well as  to iron.
   Nickel resembles bismuth in its colour,....it being white,
with a  eastc\)f reddishneW;  and its specific gravity is about
8,60.
   When it is exposed to the action of the air  and heat for
calcination, it is slowly calcined or oxydated in the same man-
ner  as copper:*  but the  oxyds  procured from  it  are  of a
green  or greeuish colour, whereas  the  oxyd  of copper is
sooty black.                   "  | $
   It can be dissolved by most of the acids : and its solutions
are  all  of  a pleasant green colour.  In  these  the  metals is
strongly combined with the acid : and no other metal has the
power  to precipitate it.
   It can only be  precipitated  by the fixed alkalis, and the
alkaline earths, and  by  some of the compound salts or saline
 compounds which  contain some  of the acids, for which this
 metal has a strong  attraction, and which form with it inso-
 luble compounds.    The metal is combined with such acid uv.
 this case, in consequence of a double elective attraction, aio
 precipitates with  it.                                  ^.,.\i
    When it is precipitated by alkalis, it  is necessarily in1 an
 oxydated state; and in this state can be redissolved by ad-
 ding more of the  alkali.   The volatile alkali especially dis-
   * Cronstedt says that, v-'aza strongly heated, it emits sparks, or brandishes
 like iron.
i 
                             LEAD.                       299

  solves it with  facility ; and can even act on  the pure metal in
  its metallic form, and always forms with it a blue solution.
     In trying to  mix the oxyd of  nickel with vitrified -earthy sub-
  stances, we find that it can be employed to give a colour to glass:
  and the colour  it gives is a reddish yellow.   No other property
  of it relative to the earthy substances has yet been discovered.
     Of the inflammables, sulphur readily unites with it,  and ad-
  heres to it very strongly.   It also disposes the nickel and arsenic
  to be more easily separated by ustulation.  And a part of Berg-
  mann's experiments for refining niccolum was founded  on  thin
  fact.
     Phosphorus  also  combines with  nickel:  and they  adhere
  strongly,  so as to bear a melting heat.  Long exposure to  this
  heat, and the  action of air,  dissipates the phosphorus,  the
  metal all  the while having a sensible  fluttering glow.   When it
  cools, so  as to  freeze, the phosphorus flames out very briskly.
  This is probably owing to the emersion of latent heat.
     Nickel  can be mixed with most of the other metals,  except-
  ing quicksilver,  and a few others to be mentioned afterwards.
  And it is  said that the Chinese packfong, which is a white me-
  tal, or metallic mixture  very like silver, is compounded of
  copper combined with nickel and zinc.  We shall take  farther
  notice of  this when treating  of  copper.

                    GENUS  X....LEAD.

j*;     Lead is   the softest of the metals; and has scarcely any
|* elasticity or sound.   It is the least ductile; and cannot be beat
  into thin leaf.   Its cohesion  is weak.   A wire  one tenth of an
  inch in thickness breaks with 29± pounds.  But what is very
 r*emarkable, a  rod of cast lead becomes almost four times as
 ,'strong by  wire-drawing.
  .V*Jts specific gravity is 11,35.
  *  The fusibility of lead is familiarly known to you all.   When
  passing from a fluid to a solid state, it has a singular interme-
  diate state, in which  it can be easily divided into very small
  parts or grains.*  When  poured then into a  hot iron mortar,
   • This obtains, in a greater or less degree, in all bodies, while they congeal.
  It does not surprise us in the brittle metals, nor in thejroaching of alum,  and 
300 LEAD....MANUFACTURE OF SMALL SHOT.

set so as to cool very slowly, if it be continually stirred with a
stick, it comes  to a state in which the parts cohere  somewhat
like  wet or greasy  sand: and by  stirring it now briskly, the
greatest part can be reduced to the size of a coarse sand.  This
is called the granulation of  a metal.  An apparatus is made on
purpose for  this operation ;....a sort of  oval wooden box, the in.
side of which has partial partitions, and is rubbed all over with
chalk.   The melted lead is poured into this box,  the lid fixed
on, and the box is violently shaken for some time.  This dashes
the lead against the sides and partitions, and soon breaks a great
deal into grains.   But the other method will convert more of it
into grains,  because it does not cool so fast.
   There is anot.^r and more curious  manufacture of lead, in
which  it is also divided,  when fluid, into verys small parts.
This is the manufacture of  small shot.   A little orpiment or
arsenic is added to the lead, which disposes it to run into sphe-
rical drops, much  more  rapidly than  it would do  when pure.
The melted lead is poured  into a cylinder whose circumference
is pierced with holes..  The lead, streaming through the holes,
soon divides into drops, which fall into water,  where they con-
geal.   They are far from  being all spherical,  however, many
being shaped like pears ;  and  must be picked.   This is done by
a very ingenious contrivance.   The whole is sifted on the upper
end of a long smooth inclined plane,  and the grains roll down
to the lower end.   But  the pear-like  shape of the bad grains
makes them roll down irregularly, and they waddle,  as it were,
to a side ; while the round  ones  run straight down.  They are
received into a sort of funnel which extends from the one  side
of the inclined plane to the  other, and is divided by several par-'
titions, so that it is really the common mouth of several funnels,
which lead  to different boxes.  Those in the middle receive the
round  grains.   On each  side  are grains'of a worse  shape, but
good enough for low priced shot.   The grains which havegpne
far aside are melted  again.   The good  ones  are  sorted into
sizes by sieves. (See Note  62. at the end of the Volume.)

many other cases, where the solid is brittle, and the fluidity thin : tiut in vis-
cid fluids, or  even in metals with a clammy or oily appearance ' it Attract'
mois attention, audit is even thought peculiar to them.....editor. 
                 CALCINATION OF  LEAD.           301

     Lead is cast into sheets, by letting it run out of a box through
   a long horizontal slit at the bottom,  while the box is drawn
   along the table,  leaving the melted lead behind it  to  congeal.
   The Chinese  cast it extremely thin  in this way on cloth, for
   lining their chests of tea.
     Lead is very calcinable.  It calcines  slowly in  a heat a little
   above  its melting one.   Its surface is  quickly covered with a
   dirty wrinkled pellicle, which is renewed  as  fast as  it can be
   raked off.  This calcination goes on most quickly at a heat ra-
   ther below redness.   If allowed to become too hot, the surface
   of the pellicle calcines in  a moment to  a much greater degree,
   forming a fluid film, which protects the rest from the action of
   the air.
     Lead  calcines much more quickly and  perfectly by way of
   scorification.  Great quantities  are changed into  calx by this
   method in the process for  separating  it from silver,  which is
   generally found  in lead ores.  This is  done in a reverberatory
   furnace,  the  bottom  of which,  called  the hearth,  is made of
   materials which can withstand the  dissolving power of this
   calx.  The lead is pretty strongly heated : and the fluid  calx
   immediately forms on its  surface.  Two pairs of bellows blow
   slantingly on the middle of  the melted lead ; and thus blow this
   scum over to the other  side of the  hearth,  where there is a
   channel by which it may  run off.   It collects in  a mass of an
   unequal flaking texture, just as  we should expect from the way
   by which it is forced to accumulate.    By  thus blowing off the
^  scum, the air is continually applied to metallic lead, which is in
h.  a fit condition for absorbing its oxygen.  But  it is very imper-
ii  fectly calcined ;  because,  by running  off the hearth, the air no
   longer acts on it.  It is  of a greenish yellowish colour, with
   here and there some ruddy streaks,' where  it has been more ox-
grj,; ydated.   The calx, in this  state of oxydation, has some vola-
   tility : and very noxious vapours rise  from it during this opera-
   tion, which  produce  terrible effects on the  human  body,....
   bringing on, sometimes in a moment,  an universal paralysis and
   rigidity, so that the arm  that was lifted up cannot be let down
   again.:.
     The calx thus formed,  when  allowed to cool, congeals,  as I
   just now observed, into a mass which is not transparent,  but of 
 302       LEAD....LITHARGE....MINIUM.

 a yellow colour, and plated texture, and is called litharge. The
 litharge  in the apothecaries' shops is the same matter,  broken
 into a coarse powder.
   The lead gains about one-tenth of its weight by oxydation.
 This was the phenomenon  which induced the French chemist
 Rey, in the 17th century, to ascribe the calcination  of  metals
 to the combination of them with air; a truth which no body at.
 tended to for more than a century.  This observation was much
 more  distinct than Dr. Mayhow's, to the same effect, on dia-
 phoretic antimony.
   This is not, however, the most highly calcined calx of lead.
 Litharge can be calcined more perfectly,  by beating it to pow.
 der, and exposing it two or three days to a heat hardly sufficient
 for producing the  most obscure  degree  of ignition.  This is
 done also in a low reverberatory furnace :  and the flame of wood
 rushing along it is beat down by the form of the arch, so as to
 play continually on the surface of the litharge.  The colour of
 it is thus gradually changed  from  the yellow to an orange, and
 from that to a bright red,  when it is called red lead, or minium.
   We have here a striking example of the superior power of a
 moderate heat to that of a stronger one for enabling a metal to
 attract plenty of oxygen, and become thereby highly calcined :
 for this very minium,  if exposed to a full red heat, gives out a
 quantity of vital air,  returning at the same time to a less cal-
 cined state, and becoming a yellow powder, which, if the heat
 be increased,  melts into litharge.
   A quantity of vital air can be expelled from minium also, by ,
 the elective attraction of the sulphuric acid, assisted by a gen- i
 tie heat.   By this easily separable portion of vital air which mi-
 nium contains, it has the power to oxygenate to a  certain de-
 gree the muriatic acid, as Scheele has observed.             ?
   All the calces of lead are easily  fusible, forming a thin fluid^
 without viscidity; and when pure, concrete like litharge.  Atfe^
 these oxyds, by melting them with one-eighth of charcoal, are*?
 easily reduced,  Common  red wafers burn and yield  drops of
lead.  Red lead, on a bit of  charcoal, is converted into lead in
 a moment  by the blow-pipe.  Dr.  Priestley  reduced it -in am-
monical gas : and water was  produced at the same time.   He
also reduced it in hydrogen gas,  and also had water.  By giving 
           REDUCTION OF  THESE OXYDS.     803

  its oxygen so readily to other substances, this oxyd greatly
  promotes the calcination of other metals.  Red lead, melted
  with iron filings, will be reduced, and  the iron  oxydated or
  corroded.
     In the  manufactures of lead work, they prevent the cal-
  cination  by throwing grease or pitch upon the surface,....the
  operation of which is  easily  understood.   When a private
  person has occasion to employ a plumber,  he may observe
  that he  never throws grease upon the melting pot, because
  the  dross,  as  they call it, is considered as useless by the
  employer,  and  becomes the property of the workman.   He
  rather encourages its formation;  and  contents himself with
  clearing the surface with a piece of deal before he casts the
  lead.* .
     The older chemical writers speak of a golden and a silver
  litharge.   These names are given to litharge', as it is more of
  an orange or'of  a grey colour.  The  first is  most abundant
  when the flame of  wood is employed ;  and the second,  when
  other fuels are used.  .These distinctions are now neglected,
  there  being but  one calx, which, when it cools greatly, is of
   a glassy  structure,  with traces of oblong crystallizations.
     Such  is the  nature of lead with regard to heat.  In trying
  it with the different acids, we find that this metal is affected
  by them nearly  in the same  manner as several of those  we
  have already described.
     The sulphuric'acid will hardly act upon it, except the lead
   be in thin plates, and the acid  applied, strong, and with the
■;.  assistance of heat.  During its action, part of the acid be-
?■'  comes volatile and sulphurous, its oxygen being taken by the
«*-"  lead.   And when  the operation is managed in a particular
   manner, part is changed into perfect sulphur.  The oxydated
  lead forms, with the rest of the  acid, an insoluble sulphat
\jK*of lead.  Leaden vessels are useful in preparing vitriol and
  .^jjdum, and even sulphuric acid itself,  in consequence of the
  ^insolubility  of the  sulphat of lead.
  '.*'::-The nitric acid, properly diluted, dissolves lead the most
   easily, producing some nitrous air.   It forms a soluble com-

     *  This  observation is by Dr. Hooke, who said, in a meeting of the Royal
   Society, that the  plumber can make it alt dross, and much more, by the air
   with which it combines, (Bircbe's Hist.),, .eh'tor. 
 304 LEAD....ITS RELATIONS TO  THE  ACIDS.

 pound, which bears to be largely diluted with water without
 being decompounded ; and it gives crystals which decrepitate
 with great noise, but do not deflagrate.
   The crystals of this salt are of a singular shape, namely
 triangular prisms, like those used in optical experiments.  I
 know no  other crystals of this  form.  They have not a fine
 edge,  but a narrow facet  scarcely  visible.  These are  fre-
 quently so grouped as to form hexagonal prisms, whose sides
 are striped or fluted, by the want of every second triangular
 prism, which is the primitive molecula,  or nucleus, of  this
 crystallization.
   This nitrate has  its ingredients but  weakly  united.  A
 moderate heat long continued will expel the acid from it,....
 leaving a  fusible oxyd in the retort.
   The muriatic  acid,  in  its ordinary state,  acts  but  very
 slowly and imperfectly on this metal.  Woulfe says that some'
 inflammable  air is produced during  the  solution.  I have
 never found this.   It acts much more powerfully  in the form
 of the corrosive  muriat of  quicksilver,....the lead being then
 supplied by the quicksilver,  with both  oxygen and acid at
 the same time.  Or if the lead has been previously oxydated
 in any  other way, the muriatic acid very readily joins with it:
 nay, it will  sometimes be oxygenated by a  calx of lead.  .1
 Such a calx  may then be  considered as  super-oxygenated.
 When, for example, we add  muriatic acid to  the nitrate of
 lead, we immediately form a muriat of lead, which is always
 less soluble than the nitrate.
   The same thing happens if we add to the nitrate of lead  j
 any neutral salt which contains the muriatic acid.   A double  )
 exchange  takes place.
   The qualities of the muriat of lead are, difficult solubility
 in water,  and  volatility.  .It is  remarkably fusible, melting
before  it is red hot.   When  cold,  it congeals into a semi-'*i
transparent uniform mass, called plumbum corneum, on account,"
of its resemblance to a muriat of silver, which has long beety*
called  luna cornea, from its colour, flexibility,  and a degi^fe
of softness, which allows it to be cut with a knife like horn.
 Plumbum  corneum is the rnnsf powerful  astringent that I
know. 
          MANUFACTURE  OF WHITE  LEAD.    305

    It is also considerably volatile, like all the metallic muriats;
  but  has little of the butyraceous appearance which most of
  them have.
    The acetous acid can also be combined with this metal, so
  as to reduce it to a saline and soluble form.   But it unites
  much more readily with some  of  its  oxyds  than with  the
  metal in its perfect state.
    The oxyd which dissolves the most readily,  is a carbonat
  of this metal, well known by the name of white lead, or cerussa,
  formed by a process contrived on purpose.
    Vinegar is put into a stone-ware pot:  and at the distance
  of two inches from its surface, there is a cross of wooden
  bars, on which is set a roll of sheet lead, of six feet long, six
  inches broad, and about one-tenth thick.  It is rolled up loose,
  with the distance of about one-fourth of an  inch between
  each turn.   The pot is set in  a bed of tan, dr horse dung,
  and covered with a plate of lead.   In  about three weeks,
  the  whole surface  of the sheet is covered with a saline crust,
  which is detached by unrolling  the lead, and scrubbing with a
  wire brush.  The sheet is then rolled up again, and under-
  goes the same process till the whole is dissolved.*
    Here the acid is found to have greater effect when  applied
  in the  form of  vapour.   A certain quantity unites with the
  lead,  in  the form of  a white  powder, which is  afterwards
  much  more easily dissolved.   This substance, dissolved in
  distilled vinegar, affords salt of lead, called saccharum saturnit
  from the sweetish taste with which  it affects the tongue, re-
,  sembling  that  of  sugar.   It crystallizes, or  rather  grains,
 , very readily.   If the salt be again dissolved in more vinegar,
H- it combines  with a greater proportion of it, becomes  more
  soluble, and affords fine crystals.

  . •.'•  .This process merits the attention of the philosophical chemist.  Dr.
 "'Black calls white lead,  not a simple osyd of lead,  but a carbonat:  and in
  fact,"white lead contains a very great quantity of carbonic acid, and this acid
  sterns to he combined with the lead. The insolubility in water does not prove
  that white lead is not  a combination of the metal with an acid; for we know
  others, such as the sulphat of this metal, not more soluble.  How does the
  lead acquire this acid,  and what is the nature of the vapour, after it has fur-
  nished this ingredient'... editor.
       vol.. lir.                o q   ' 
306      LEAD....SACCHARUM SATURNI.

  With the tartarous acid, lead forms a compound very inso-
luble.  It may be produced bv boiling a solution of tartar, and
adding any pure oxyd of lead.   The superfluous acid of the
tartar joins with the lead, as with chalk, and forms an insolu-
ble sediment: and  the tartar is- thus neutralized, being de-
prived of the acidulating part of its acid.
   Or if, instead of an oxyd  of  lead, we take a compound of
this metal with nitric or acetous acidr and add this compound
to a solution of tartar, or  any liquor  which contains tartar
dissolved in it, the  tartar is then completely decompounded
by a double elective attraction ;  the whole of its acid uniting
with the lead, to form a white insoluble precipitate.
   Lead also forms an insoluble compound, in the same man-
ner, with the acid of phosphorus, which can therefore be
precipitated from urine by a solution of  lead.
   When we, in the next  place, compare the  forces  of at-
traction between  lead and these different acids, we find the
strongest is that  of the sulphuric acid.  Other metals in
general unite most  strongly with muriatic acid.   But in the
case of lead, it is the sulphuric acid that is most strongly at-
tracted :  and when Combined with the lead,  it always forms
an  insoluble compound.  It therefore precipitates lead from
other  acids,  by joining  itself  to  this  metal in their place.
This happens, not only with pure sulphuric acid, but with any
salt or saline compound which contains the sulphuric acid.
In however small quantity the sulphuric acid be thus applied
to the dissolved lead, we have  a double exchange, and a pro.
portional part of the lead precipitates with it.
   The solutions of lead, especially the acetite, are therefore,
when  properly used, an exceeding nice trial  of the  presence
of the sulphuric acid, pure or compounded, in mineral waters,
or  other mixtures, by occasioning turbidness.
   After the sulphuric acid,  the muriatic is  next  in force.of
attraction for lead.   As I already remarked, it separates *h* •
nitric  acLd, and joins itself to the lead in its place, formingthb
plumbum corneum, or muriat of lead.                  (..;«
   The muriat of soda, and the muriat of lime or magnesia
are decomposed by the oxyd of lead : hence the corrosion of
leaden pipes.   A process has been followed for procuring the
fossil alfcali by employing litharge.  Accordingly#he decom. 
        ELECTIVE  ATTRACTIONS OF  LEAD.   307

  position of the sea salt is accomplished; and soda is produced.
  But the expence would be far too great, were it not that the
  muriat  of lead  is manufactured into a  fine yellow pigment,
  of  considerable demand.   The  manufacture  is chiefly car-
  ried on for the  pigment: and the soda  is a very  secondary
  object.
     Lead  has  also  a  strong  attraction for   the   tartarous
  .acid, and the  phosphoric acid-; and will quit other acids to
  unite with  them: and they  always  form with it,insoluble
  compounds.  They therefore precipitate the  lead from  its
  solutions in the nitric or acetous acid, and the lead ^precipi-
  tates them.   I  made a number of experiments on such pre-
  cipitations of lead some years ago; in consequence of which I
  found it easy  to distinguish different kinds of vinegar from
  one another.
     These compounds of the different acids with lead are all
  decompounded by common mild fixed alkalis, or carbonats of
  alkalis, and by  calcareous earth.* Some of the other metals
  also attract acids more strongly, as  zinc, which separates it
  in  fine  metallic crystals.   There are also two of them that
  can be decompounded by heat alone, viz. the nitrate and the
  acetite  of  lead; the  first, just in  the  same manner as the
  nitrate  of quicksilver, with this difference, however, that the
  oxyd of lead is not reduced.  The second may be decom-
  pounded  with a heat inferior to red ; and  is sometimes
  decompounded  by such a heat, in order to extract the vinegar
  from it in a very strong state. During this operation the lead
  calx is  reduced: and a  small quantity of inflammable fluid,
*'.  resembling alcohol, is produced, and found mixed with the
  vinegar.
     From  Lemery's  account of this  distillation, it does not
 ♦appear  that much pure or strong acid is obtained. He rectifies
Jt.„4^e  distilled liquor afterwards by itself, to separate the more
 -Vdlatile half of  it, which is inflammable, like spirit of wine.
  The other half,  he says, is called oil of Saturn; and is used as
  a detergent for  the eyes of horses.

    ♦ tyxritu.'.....Is the precipitate of lead, produced by a mild alkali, the same
  aith white lead"' It is surely a carbonat: and white lead is not a pure oxyd....,
   KOITOn  . ,71to i 
308    LEAD....WITH  ACETOUS  ACID, &c.

   But by means  of the sulphuric acid, an exceeding strong
vinegar can be procured from saccharum saturni. The saccha-
rum being first distilled by itself, with a moderate heat, gives
an ardent  spirit; after which,  sulphuric acid  being  added,
extricates a strong vinegar.
   Sulphat and muriat of lead  cannot be  decompounded by
heat.  The first melts in the fire, without separation of the
acid, unless inflammable matter be made to touch  it, which
volatilizes the acid. The muriat not only melts, and that very
easily, but also proves  volatile ; and will wholly evaporate
without being decompounded, and cannot be reduced by in-
flammable matter alone.
   Alkalis, in their liquid form, especially if caustic, corrode
lead.
   Nitre calcines  it, when applied with  a  proper degree of
heat; and converts it  into a yellow powdery substance, pre-
cisely similar to litharge in all its properties.
   Common salt is decomposed by calx of lead.
   Sal ammoniac, distilled with granulated lead,  is partly
decompounded by the lead,  but much  more  easily by the
calces of  lead:  and this is the readiest way  for  plumbum
corneum.   The volatile alkali is caustic, or nearly so.
   The muriat of lead made with sal ammoniac, when heated
with a covered patella under  the muffle, becomes pasty, and
in some degree fluid, diminishing much in bulk. When it is
just red hot, it begins to fume: and, upon increasing the heat
still  more, it becomes perfectly fluid, contracting .still more
in its bulk.   It now emits elastic fumes.   When allowed to
cool, it is of a greenish grey colour, with a little transparency,
andLis quite  brittle.   When  viewed  with a microscope,
its^reyness appears owing  to very small globules of re-
duced lead.
   With respect  to the earths,  when they are exposed to.
melting heats with the calces  of lead, we have an opportunity
here to observe one of the most remarkable and useful quali-
ties of the metal.   This  is a power which its calces have,
to dissolve and  melt in the fire the earthy substances, very
few of which can resist this power: and they form with them
glassy compounds.  This property is so eminent in the calces
of lead,  that no  ear hen vessels can be contrived to  contain 
                 LEAD....FLINT GLASS, &c.        309

   them melting for any length of time.   Some chemists have
   said that they are  possessed of such  a secret, but do not
   choose to discover  it. Pott of Berlin has made a vast number
   of experiments, in order to discover a composition of earthen
   vessels which can resist the action of the glass of lead.  The
   result of his research is, that pure clay, which is free from
   iron, is  the best.   And as it  must be  kneaded with some
   dividing matter like  sand, to prevent its cracking by sudden
   changes of temperature, the best addition is pure flay, which
   has already been burnt in the most intense fire.  This, beaten
   to powder, and sorted into a sand somewhat coarse, makes a
   compound which will resist fusion by the calx of lead much
   longer than any other:  but it also will imbibe  it,  and then
   will melt, as salt dissolves in water.
      Inconsequence of  this property, lead is employed in many
   processes, in which it is necessary to bring earthy substances
   into fusion, as in working the ores of  the  precious metals.
   Also, on account of  its being transparent, it is  employed in
   making the finest kinds  of glass, called fint-glass and pastes.
   This name is given to the artificial glasses  for imitating the
   gems. The calx of lead  is eminently fitted for this purpose ;
   because it communicates to the composition  a greater refract-
   ing  and dispersing  power  than  any  substance except the
   diamond:  and to this it approaches very nearly.   Unfortu-
   nately, these pastes are so  very soft, that they soon lose their
   brilliancy,  being scratched by almost every thing. This great
   dispersive power has enabled  us to remove the defect of
   optical  instruments  by  refraction, which had been  long
   despaired of.   Mr. Dollond, and Mr. Hall, a country gen-
   tleman, at the same time,  and unknown to  each other, dis-
   covered  a  method  of constructing achromatic telescopes, by
 *  joining lenses of crown and  of  flint glass.  There remains,
, ,„. however, a great   obstacle to their perfection,  which the
 " superior skill  of the chemist only can  remove.   Flint glass
   is never  uniform in its composition.  The  great weight  of
   the calx of lead seems to make it fall down  towards the bot-
   tom  of  the pot: and  when  the workman  takes  it up, and
   collects it into a mass at the end of his pipe, by turning  it
   round and round, it is collected  in strata of different density
   and refracting power,  which greatly disturbs  the formation of 
       J10 ENAMELS AND GLAZINGS FOR POTTERY.

       a fine image in the optical instrument.  A premium of seve-
       ral thousand pounds is offered for the removal of this defect.
       It is remarkable that the calces of lead not only increase the
       refractive and  dispersive powers of the  glasses of which
       they are ingredients, but that they  produce the same effect
       in  their  watery solutions.   Sir Isaac Newton first observed
       that a solution of sugar of lead had a much greater refracting
       power than pure water.   Mr. Zeiher, an ingenious chemist
       of Berling by increasing the dose of minium,  composed a
       paste which scarcely  yielded to the diamond  in  brilliancy
       and refracting power, and exceeded it in  the dispersive qual-
       ity, by which the  different colours  of light  are  separated
       from each other.*   Minium, with a very small proportion of
       diaphoretic antimony,   when mixed with  flint, produces a
       paste scarcely distinguishable from the finest topaz.
          Calx of lead, or glass containing lead, is  necessary for ma-
       lting all white opaque compositions calied enamels.   Arsenic
       and tin alone will not do.
          Flint-glass and pastes often have veins, or eels, as they are
       called, which differ in their refracting and dispersing power
       from the rest, like a mixture  of syrup and  water ; and on
       account  of this, are  not used  for  mirrors.   If the calx of
       lead be very redundant in  such glass,  and especially if it be
       not much  calcined, it  is of a yellow colour.  It forms the
       glazing of common  earthen ware :  but it is very  liable to
.       corrosion  by  acids, which  renders  it very unfit for many
       culinary purposes.   The solution also is very  hurtful to the
       constitution.   The common soft glaz'mg on earthen ware is
       quickly corroded by vinegar : and such ware cannot be  used
       for holding pickles.  .  There are no vessels fit for this pur-
       posiSfRut those of  the porcelain kind,  or what  we call stone-
       ware.   Till within  these 30 years,  it  was made in great *
       abundance in this  country :  and it had no glaze,  but a slight-*.
                                                                  '-f
         * As the difference of dispersive power  in different substances is very
       considerable, and as it  is much more remarkable with regard to some colours
       of ii^ht than others, it has all the appearance of being owing  to electiv^at-
        tractions for the rays of light.  It is not improbable, therefore, that there may
|        be found  a substance that attracts them all alike.   Such a substance  would
       be a most precious discovery to the  optician.  In the mean time, it afford*
        aiv-'her string argument for the materiality of light....editor. 
    LEAD WITH INFLAMMABLE SUBSTANCES. 311

    superficial vitrification of the  ware itself,  by the vapour of
    soda thrown into the fire-place  while the whole  kiln was in
    a white heat.   The  present ware for the table, which  has
    supplanted the stone ware, is  a bibulous clay, glazed with
    lead:  and pots  for pickles  and sweet-meats are  made of it.
    But they should  be rejected entirely for such uses, and we
    should only use the stone-ware.   It is still to be had, but of
    a brown, or dirty colour.
      Lead is easily recovered from glass which contains it. Such
    glass is liable to be smoked or  blackened with the flame of
    the  blow-pipe.    This is  nothing but the  reduction of  the
    lead.
      Of the inflammable substances, several act upon lead.
      Many of the oils can dissolve lead or its calces: and it is
    remarkable that they are dissolved most readily, and in
    greater quantity, by the mildest, or the unctuous oils.  The
    solution of  the  calces  of lead  in these requires the heat of
    boiling water to assist it: and  when they have  dissolved a
    proper quantity, and are then allowed to cool, they form 3
    m iss which  is firm and hard when cold, but which becomes
    soft, and  tough, and adhesive, by being warmed  a little.  On
    account  of  these qualities, and  its oily nature  in conse-
    quence of which it cannot be dissolved or changed by humi-
    dity, it is very valuable.
      The emplastrum lythargyri,  or commune, of the shops, is
    made in this manner;  and forms the basis of several others.
    A small quantity  of the calx of lead is also dissolved,  by
    boiling in the lintseed oil, which is used as paint.   It makes
    the oil dry sooner, and leave a thicker varnish on the surface
    of bodies to which it is applied*   Oil-paints in  which the co-
    loured calces of lead are  employed, are, for this reasofr, the
 *  most durable pigments.  White lead and  lintseed-oil con-
.,«.-  tracts  a skin  on its surface which is almost impenetrable by
'■•*<!  any action of the air and weather.   Its only defect is that sul-
    phurous and putrid steams soon blacken it.  Hence it is that
    this  brilliant white cannot be used in water colours in minia-
    ture painting.
      Lead,  either metallic, or in  the state of calx, has also a
   strong attraction for sulphur.    Sulphur is added to melted
   lead; and when  mixed with it,  readily unites, and forms a 
312    LEAD  WITH HYDRO-SULPHURETS.

compound less fusible than lead, and which in cooling pro-
duces a mass internally crystallized into glittering particles,
and greatly resembling one of its ores. It is decompound>ed
with difficulty by ustulation; more readily and perfectly by
iron.
   Sulphur acts  also upon the oxyds  of lead, and upon the
compounds of these with acids, when it is applied in the form
of a liquid alkaline sulphuret.   The  sulphur unites with the
oxydated ^ead, and blackens it, or gives it  a dark-brown, or
blackish colour.
   This effect  is also  produced by the  inflammable air, or
sulphurous hydrogen, that is contained in liquid alkaline sul-
phurets, and which separates from them  in the  form of a
foetid gas, when acids are added to them, or when they are
largely diluted with water.  The hydrogen gas having, when
pure, very little attraction for water, has a tendency to eva-
porate from such a diluted mixture : and it carries away a
small portion of the sulphur, which,  if it meet with any oxvd
of lead, will  certainly be attracted  by it,  and  blacken it.
This is the  origin of what is called  sympathetic ink, or ink
that appears by sympathy.   In  the course of the numberless
experiments of the alchemist on lead, in  the fond  hope of
converting it into silver,  it appears that none  engaged their
fancy so much as those that were disgusting.   Human urine,
human  ordure, rotten eggs, and such things, were favourite
objects of research, or means of farther  inquiry.  When the
abominable  smell of hepar sulphuris was observed, hepar sul-
phuris was  tortured by  every alchemist in Europe, and its
mysterious  properties were innumerable.  Basil Valentine
discovered  that rags  moistened with acetite of lead became
black" in a few minutes if near hepar sulphuris : and he made
a magical trick by it.  If you write with a solution of sac- 9-
charum saturni, and lay the paper between the first pages of „.
a thick book, and put between the last pages a leaf of paper.'$'.
that is  moistened with a solution of an arsenical preparation
containing hepar sulphuris, the writing will become legible in
a few minutes, which  was ascribed to a certain inexpliiiaDle
sympathy between lead  and arsenic.   Lemery  discovered   ■
that the arsenical preparation was  effectual, only because  it
contained hepar  sulphuris.  The  hydrogen gas itself, inde- 
     LEAD....ADULTERATION OF  WINES,  8cc. 313

  pendently of the  sulphur which is combined with it, has some
  share in producing this eff<»ct: and it is not improbable that
  the sulphur alone would not produce it.   The hydrogen gas
  acts by reducing the lead to its metallic state, and thus dis-
  posing it  to unite the more readily with the sulphur.   Of the
  power of this gas to restore dissolved mi tals to their metallic
  state, we have many examples in  some ingenious experiments
  made by  Mrs. Hulsham.   A wet mark  made  with liquid
  acetite  of lead,  when exposed  to the hydrogen gas as it
  arises from iron  filings and sulphuric acid, blackens immedi-
  ately.
    Mrs. Hulsham discovered that water must be present with
  the metal and acid, otherwise the reduction will not succeed.
  The effect of  the water probably depends on its attraction
  for the acid,  by which  it  promotes the  separation of the
  metal, while the  hydrogen attracts the oxygen from it.  But
  the presence of water is not necessary to the action of sulphur-
  ated hydrogen gas.   The  metal  is then separated from  the
  acid by the power of two  attractions acting at once ;  the at-
  traction of the hydrogen for the oxygen  of the metal, and
  that of the sulphur for the metal itself.
    The same effects are also produced on the oxyds and solu-
  tions of bismuth, and rather more strongly than on those of
  lead.   Pearl white, precipitated  from the nitrate of bismuth,
  by the solution of cream of  tartar, being rubbed on paper,
  and exposed  to  the hydrogen gas, is much more blackened
  than the similar preparations of  lead.   And these "effects
  enables us to discover the presence of  lead in various liquids
  in which it may  happen to  be concealed,  as  in wines espe-
 ' cially,  in cyder,  and in oils  and other fluids.   The anxiety
  of the JFYench chemists about this matter  may be seen in the
^works of Macquer and others.
    Cyder made  in Devonshire was  formerly  liable to  this
^adulteration: but I believe that care is now taken to avoid it
  in future.  It was produced by  putty and other preparations
  of white lead,  which were used  for filling  the  seams, and
  stopping leaks in  the press-floors and vats.    A better con-
  struction of them has  made this unnecessary.
      VOL. III.               r r 
U4 LEAD WITH  METALS....SCORIFICATION.


              Relation of Lead to other Metals.

   It will not mix with iron or cobalt, but unites easily with
all the rest;  and  is  employed  sometimes to  promote  the
calcination of some which are otherwise calcinable  indeed,
but which  calcine more quickly with the lead.  Of this I
shah point out particular examples hereafter.
   The useful  compounds of this metal with others, are,  1st,
Typefounders  metal, in which it is the principal ingredient,
but mixed with antimony.   2d, Organ-pipe metal,  in which
it is mixed with tin.  3d, Pewter, in which tin is the princi-
pal metal:  but there is commonly some lead as an alloy to the.
tin;  commonly too much.   Nails made of a composition of
three parts  of tin, two of lead, and one of antimony,  are
hard enough to be driven into oak without  being blunted;
and are not rusted by salt water.
   Another great use of lead is  in  working of the ores  and
metallic mixtures containing the precious metals, silver and
gold.   In working the ores of those metals,  it produces a
thinner fusion  of all  earthy  and vitrifiable matters than any  i
other substance.  In such a thin liquid, the smallest globule m
of the precious metal makes its way to the bottom, which it  *|
could not do through a more  clammy glass.
   Iron, tin, and all other metals, except copper and platinum,
are separated  from the gold and silver by means of lead, by
actually destroying them as metals, and reducing them to a
thin vitreous slag or scoria, which is blown off the surface of
the melted mass, in the same  way as  litharge is, or is absorbed
by the porous vessel  or test in which this scorifieation is per-
formed.  The gold or silver is left in the vessel, because it
completely resists the action of heat and air,  and the scori-*
fviiig power of the lead.  The scoriae which are driven off,
or imbibed by the test, are reduced to metal by pounding and)..
melting it along with inflammable matters.
   With regard to  the ores  of this metal, there is no great
variety.  There is only one  species found in abundance, the
galama saturni, which varies a little in its appearance.   The
richest is  commonly  that which breaks with broad andbright
surfaces, and  into cubical masses.   Some of the varieties of 
LEAD....ITS ORES, &c.
31$
 it break  with less broad and more  irregular  surfaces,  and
 some with such small  ones,  that  the  fracture looks more
 or  less  like  that of  steel.    But  though galaena is  the
 principal, and  only  abundant ore  of lead, small quantities
 of this metal are found in other states in the mines which
 abound with galaena: for example, 1st, Lead almost pure
 and metallic.   2d, Calx variously crystallized and combined
 with  fixed air; 3d,  And sometimes combined  with some
 acids, as in green  ore, &c.  Some  colourless crystals of this
 kind contain  arsenical acid, and  others the sulphuric.

       Treatment of the Ores  of Lead to extract the Metal.

    If pyrites  be mixed with it, the galaena must  be roasted.  If
 it be free from pyrites, it may be melted out without roast-
 ing, or roasted and  melted at the same time.  This is done
 in Scotland in  very lpw furnaces, or  a sort of  open hearths.
 In England it is done in reverberatories.
    As an article of the materia medica, this metal is reckoned
 powerful.   As an internal medicine, it has an  established
 character as  a most powerful  astringent.  It is  therefore
 used sometimes,  after all other  remedies have failed,  in
 profuse  hemorrhages from the uterus, the  lungs, or the
 stomach.  But it is not employed,  except in cases which
 appear otherwise  desperate ;  as  it  is certainly in  itself a
 dangerous remedy.  It  is well known that  the  workmen
 employed in many of  the  manufactories  of lead lose their
 health by it, and become objects of compassion ;....such  as
 those who melt  it  from its  ores, and those  who  prepare
 colours  from lead,  or  grind  them for  the painters. JSflich
 persons   are  seized with  obstinate constipation,  dre"feful
fegriping pains,  contractions, and paralytic  affections  of the
 legs and arms : and as  all comes on very slowly, they are not
\ alarmed ;  and the profits of their  employment  make them
 continue at it till their case becomes distressing, and generally
 incurable.
  , "Mr. Clutterbuck, of the college of surgeons  in  London,
  gives an account of  a new and successful method of treating
 those affections.   His  method  is to  give mercury, which  he
 considers as a powerful stimulant  and exciting remedy, and
 therefore opposite to lead, which is powerfully sedative, and 
316 LEAD....ITS  QUALITIES  AS  A  .MEDICINE.

often hurtful, and even mortal, by its sedative, and weakening
benumbing power.  A number of cases are related,  in every
one of which a cure was completed in six weeks at  farthest.
To obviate the costiveness produced by lead, he used calomel.
A grain or two every night operated more certainly and easily
than  any other laxative.   He also removed the palsy of the
hands, by continuing the morcu-y until the mouth was a little
affected.
   As external  applications,  however,  the  preparations of
lead  are not only safe, but in the highest degree useful and
salutary.    The character it bears in this view,  is that of a
cooling  sedative  anodyne,   and dUcutient medicine.   A
French aurhor, Goulard, wrote  two hooks upon it,  in which
he shews plainly that he is an enthusiast in his  opinion of its
value ; but relates,  in  a very simple and  distinct  manner,
cases which  are  very  striking ptoois.  He recommends it
highly in most external  inflammations, when.- there  is  great
pain  or   heat,  and  especially  in   paranychia, phymosis,
and paraphymosis, buboes,erysipelas, when tending to mor-
tification.;  the painful inflammation before  mortification;
gun-shot  wounds  that  are long  in healing,  and all  ill-
conditioned ulcers ;  the  hard  painful  swellings,  and  the
ulcerations of women's breasts ;  all sort of fiery eruptions
of the skin ;  and itch.   In  these  ill-conditioned ulcers, and
painful influramations, its effects  are often very remarkable
 in relieving the patient from pain, abating the inflammation,
 and  all its symptoms ;  inducing sleep, and changing the state
 of ulcers for the better in every respect, and  facilitating the
 separation or  extraction of  extraneous bodies  from them.
 In some, however,  it does not do  service :  and  such  are
 more relieved by relaxing emollient applications.   I was in-
 former!  bv a navy 'surpeon,  that it seldom did service in the '
 cases of sailors.   A weak  solution of saccharum saturni is
 at present lound the best  dressing for scrophulous sores or"
 tumours.
    Mr.  Goulard's  preparation is made by boiling litharge
 two  or dine hours in vinegar.   But as this must be of very
 uncertain  strength, according to the different vinegars  em-
 ployed, we find it more  advisable to use saccharum saturni,
 d'ssolving a scruple, or ha'.f a drachm, in a bottle of water.
 This givss a determinate  strength, if the water  be pure. 
                TIN....VERY FUSIBLE.             317

But  it  generally  becomes  milky, in consequence of some
muriat or vitriolic salt contained in it.   This diminishes the
strength a little.


          GENUS XI.....TIN....STANNUM.

   This is the lightest of all the  metals,  its specific gravity
 not exceeding 7,3.  The finest English tin when melted does
.not exceed 7,29.   Hammering will bring it to 7,3.   There-
 fore lightness must be considered as a test of  its  purity.   It
 is remarkable  that when mixed  in due proportion with all
 other metals, except regulus of antimony, the  specific gravity
 of the  mixture  is much greater than what should result from
 the weights of the ingredients. Nay, mixed with some much
 heavier than itself, the mixture has a greater specific gravity
 than the  heaviest metal.   The  tin must receive the other
 metal into its pores, in  such a manner as not to increase the
 bulk.
    The colour  of this metal is very like  that of fine silver:
 and  it retains its colour and brightness in the air better than
 many others.  It has a considerable  degree of malleability,
 and  can  be hammered into very  thin  leaves: but it has not
 enough of that kind of  tenacity that fits it for being drawn
 into wire.   When thick pieces of it are bended,  it gives a
 grating sound,  which appears to proceed from some deficiency
 of  tenacity, or  some imperfect union and  cohesion of its
 parts.
    It is the most fusible of the metals ; and is easily melted
  with a heat considerably less than the boiling heat of quick-
  silver.   And  when large quantities of  it are meltecrj and
  then allowed  to cool and congeal without disturbance,  its
  parts  concrete into oblong angular masses or prisms.    This
  is seen most distinctly  when a large mass or block of pure
  tin  is broken  in pieces  with  the strokes  of  a large hammer,
 'immediately  after it has  concreted from a melted state, or
  rather before the concretion of it is quite completed.   It then
  appears in the  form of what is called grain tin.  We can also
  reduce it to a powder, or to small grains like sand, by melting
  it in an iron mortar, and stirring the melted tin briskly and 
318        TIN....WITH SULPHURIC ACID.

incessantly until it be congealed.   Thus we get the pulvis stanni
of the dispensatories.
   Tin has a strong attraction for oxygen,  calcining with a very
moderate heat.   And from the whiteness and infusibility of the
oxyds which it affords, it appears to undergo, in proper circum-
stances, an high degree of oxydation, which can  even be carried
so far by the action of the nitric acid as to convert it  into a sort
of acid.
   The oxyds of tin cannot be melted or vitrified by themselves,
and are even difficultly melted in mixture with  other vitrifiable
bodies.  For this reason an oxyd of tin,  mixed with the ingre-
dients of glass,  forms one of the best of the white enamels.*
   When we dissolve tin in some of the acids, we find that while
dissolving, it has some degree of power to decompound water.
   It can,  for example, be dissolved by digestion with sulphuric
acid, a little diluted,  in which  it dissolves slowly:  and while
dissolving, it decompounds a little of the water, and produces
some inflammable air,  but far less  than  iron or zinc.   The tin  jj
is thus slightly  oxydated as well  as dissolved ; or it is combined
with a small quantity of oxygen taken  from the water.  But
when it has attracted this small quantity of oxygen, its attraction
for more is diminished to such a degree that it has not power to
decompound any more of the water, although it is capable of
attracting a far greater quantity of oxygen when this is applied
to it in a more simple state;  in the form, for example, of oxygen
gas,  either pure, or as contained in atmospherical air. f

    * This, however, cannot be made in perfection  without a little lead.
 A glass  containing lead may be whitened with  tin or arsenic, or diapho-
 retic antimony.  But if the calx of tin be added to a glass that was free of
 lead, it is dissolved, and becomes transparent.                         -.
     f Is this conformable to the general train  of chemical phenomena, or  .
 even to the particular phenomena in the oxydation of metals ? It seems to be  «\?'
 a doctrinal point; that when once  a metal has combined with  pure oxygen,
 Jt is then, and not till then, disposed  to combine wiih more oxygen clogged
 with another substance in the  form of an add.  Is the oxygen  in oxygefc
 ous gas more simple than in water ? It requires, in most cases, a very high
 temperature to begin the combination of combustible bodies with the- oxygen
 in the gaseous form....editor.                             : 
              TIN....WITH NITRIC ACID.          319

   The sulphuric acid, not diluted, and applied hot, can corrode
and  dissolve half its weight of tin ;  and is at the  same time
changed in part into sulphurous acid,  the dissolving tin attract-
ing in this case from the acid itself a part of its oxygen.  If the
action of the acid be made less rapid,  by diluting it with a very
small proportion of water before it be applied to the tin, a por-
tion of it can be changed into perfect sulphur,  as is the case also
with  lead.  ["But,  largely diluted,  it will not act upon tin."
Fourcroy.] *
   The nitric acid and tin act on one another in the  same man-
ner as the same acid and the metal of antimony.  The tin is not
dissolved,  but oxydated to an high degree, by attracting to  it-
self the  oxygen of the acid.   But this action, which is slow when
we make the experiment with the metal of antimony, is sudden
and violent in the case of tin.  The acid is violently changed
and decompounded.   Part is changed  into nitrous acid; part
into nitrous air; and a considerable part even into azotic gas.
   The oxydation of tin by the nitric acid affords another distinct
example of the formation of volatile alkali.  Tin, as well as iron,
decomposes water,....and we see that it decomposes  this acid in
a more remarkable manner, since it extricates pure  azotic gas.
That the hydrogen of the decompounded water unites with the
azote of the acid,  appears  (in the same manner as in the case of
iron) by adding a caustic alkali or lime.  This immediately de-
taches the volatile, alkali: and we perceive it by the smell, or by
the cloud which  it forms with the vapour of the muriatic acid.
We may use, of aquafortis three parts, water five, tin leaf three,
and  slaked  lime three.  Dr. Austin was the contriver  of this
experiment, having first made it in another form,  namely,  by
moistening tin leaf with the acid,  and  rolling it up loosehjtill it
was  corroded.  He then wetted it  with a  solution of potash,
which instantly detached the volatile alkali.

  ;.*  Is  the theory quite perfect here, and in some other1 similar instances I
T)H_disengages hydrogen by reason of its strong attraction for oxygen.  Yet
if Water be added to the sulphuric acid, and thus afford a more copious and
easier  supply of oxygen, the  sulphuric acid is, in this case, more deprived
f its oxygen than yiken the water supplied it less liberally.....editor. 
 '-20 TIN...WITH NITRIC  AND MURIATIC ACIDS

  This experiment, therefore,  coincides admirably with the
others from which we have acquired the knowledge of the com-
pounded nature of the volatile alkali.   And it is the more satis-
factory, on account of its succeeding equally well  when made
with other metals which have a powerful attraction for oxygen,
of which iron is an example.*
  The muriatic  acid,  in  its ordinary state, dissolves tin very
well,  and in great quantity,  especially when assisted with a di.
ges-tive heat.   It will dissolve one-third of its weight.   During
the dissolution, some inflammable air is produced  by the de-
composition of a small part of the water, from which the dis-
solving tin attracts the oxygen.  And if there  be the smallest
quantity of arsenic in the tin, which is often the case, it remains
undissolved in the form of a black matter, which is metallized
arsenic.
  The solvent, however,  which has been commonly employed
for  dissolving this metal is the nitro-muriatic, or aqua regia.  It
has hitherto been employed by the dyers for producing the solu-
tion of tin  necessary for fixing the scarlet dye in the  cloth dyed
with  cochineal:  and it was  universally believed, both  by the
dyers and the philosophical chemists who wrote on the art of
dying, that no other solution of tin was fit for this purpose; and
that it was necessary for giving the bright red or flame colour to
the dye of the  cochineal, which when used alone, gives only a
purplish red.
  But Dr. Bancroft, who has benefited the world with  a most
                                             y *
valuable treatise on the art of dying,  has sheS*ntfhat these were
very great mistakes.  He has shewn that the'-Mght and florid
colour of the scarlet dye is not produced by the  solution of tin
alone, or principally, But by it and a quantity of tartar, which

  *  Dr. Black has omitted taking notice of what has been called the acid
of tin, or stdnnic  acid, by some late chemists.  It is a singular combination
of tin  with oxygen, first observed by Mr. Hermstaedt.  A solution of tin
in muriatic acid, being boiled with nitric rcid, which has been distilled from
manganese, till the red fumes have ceased, is then distilled to dryness. The
remaining mass is soluble in water, saturating thrice its weight.   This is call-
ed acid of tin.  It melts by a red heat,  and is deprived of its solubility and
acid taste,... but long exposure to the air restores these properties.....editor. 
     TIN EMPLOYED IN DYING OF  SCARLET. 321

is absolutely necessary in the process,  and chiefly by the acid
of the tartar.   The solution of tin and the tartar mutually de-
compound one another, by a  double elective  attraction :  and a
tartrite of tin is produced,  which is  necessary for the effect de-
sired.   And the doctor has shewn that a cheaper solution of tin
than that produced by the nitro-muriatic solvent is fitter for this
purpose.   It is made by dissolving about fourteen ounces of tin,
in a mixture of two pounds of the strong sulphuric acid and three
pounds of the muriatic acid.   This  mixture may be called the
muriatico-sulphuric solvent.   It is a far cheaper solvent than the
nitro-muriatic employed  by  dyers:  and  it dissolves a  much
greater proportion of tin.
   The nitro-muriatic solution of tin  is also employed for pre-
paring from the solution of gold a fine purple or red colour, em-
ployed in enamels.  For this purpose it is  necessary that the tin
in this solution,  should be as little oxydated is possible.   1 his
 condition is obtained by dissolving it slowly,  a little at  a time,
 in an aqua regia composed of four parts of aquafortis, and one
 of muriatic acid, diluted with an equal quantity of vinous a* " i -;.
 We must keep all very cold.  When enough of tin has been dis-
 solved,  the  liquor has a light yellow colour.    This solutie.r;
 must be preserved from communication with the air, both while
 the tin is dissolving, and afterwards ; for the tin, when dissolv-
 ed in anv acid, especially  in the muriatic, has  a powerful attrac-
 tion for more oxygen,  and attracts it very  fast from the vital air
 of the atmosphere, and from other bodies. This appears from
 many facts, and.esjpfecially from a remarkable one discovered by
 Mr. Woulfe.   i|cTound that white arsenic in powder, put into
 a recent solution of tin in muriatic acid, was metallized.
   We have another remarkable muriat of tin,  viz.  the  liquor
' fumans  Libavii.   The  French  call  it the oxygenated, or su-
per-oxygenated  muriat of tin.  It has  several remarkable pro-
 perties, which we have not time to consider,....and.I must refer
 you to Mr. Fourcroy.
   To make this preparation, amalgamate  the tin with one fifth
 of mercury,  and  triturate with  an equal weight  of corrosive
 sublimate.   This  mixture,  distilled  with a gentle heat,  gives
 out,  first an  insipid liquor,  and then suddenly  produces abun-
    VOL. Ill*               S S 
•322
OXV-MURIAT OF TIN.
dance oi white vapours,  which condense  into a transparent li.
quor, which emits similar vapours by mere exposure to the air.
I take  this to be the muriat of tin overcharged with  oxygen:
for we have in the retort, besides an amalgam of tin and mer-
cury, the common muriat of tin in a solid form, and needing
only a greater heat to volatilize it completely.
  Some  experiments  made by Mr.  Adet give  us more infor.
mation concerning the nature of this singular muriat; and justify
my calling it a super-oxygenated muriat of tin.   A  certain pro.
portion of water, nearly one-third, added to it,  causes it to be.
come concrete.  In their combination, a considerable  quantity
of common air is disengaged from the water, if it has not been
carefully cleared of it before.   Heat melts this mass : and it is
then able to dissolve more tin, and  in  this solution no inflam-
mable air is disengaged.  Thus saturated with tin, the compound
will bear a red heat without sublimation: but vapours  arise,
which  are a muriat of  tin.   What remains after a strong heat,
is a white calx.
   From these facts it  would seem,  that  the compound,  satu-
rated with the metal, is an ordinary  muriat of tin ; and the
smoking liquor of Libavius is an oxygenated muriat,  differing
from the other as corrosive sublimate differs from calomel. Mr.
Adet's notions about the consolidating effect of  water are inge-
nious, but are not explanatory: and  I think the inferences are
not justly drawn.
   I do not know any remarkable effect of other  compound salts
on tin.  Nitre deflagrates with it as with other metals.  The
vitriolic salts are decomposed by it: and its avidity for oxygen
decomposes  the  acid;  and we have sulphur.   It acts in the
same manner in decomposing sal ammoniac : and we obtain in-
flammable air by the decomposition of  some of the water.
   None of the earths  exhibit any interesting phenomena in conr
junction with tki.                                          ?
   Sulphur combines with it in a remarkable manner.   An ounce
 of flowers of sulphur being  added to  five ounces  of tin in
fusion, they form a black compound, much less fusible than the
metal.   The  mixture therefore fixes as soon  as the chemical
union takes place.  The latent heat of both ingredients emerges,
and there is a bright  incandescence, and  the  mass  suddenly 
                TIN....AURUM  MUSIVUM.           323

 catches fire.  When the sulphur is in a much larger proportion,
 the tin seems to deflagrate.
   This combination of tin with sulphur is the basis of another
 remarkable preparation, which long  amused  the fancy of the
 alchemists.....I mean aurum musivum.
   Aurum musivum,  or mosaicum, is made by various processes.
 The one most certain of success is the old one of Woulfe.
 (Phil.  Trans. 1771.)  Melt  twelve ounces of  tin,  and add
 three ounces of mercury.   Triturate the mixture with seven
 ounces of sulphur, and three of sal ammoniac.   Put  the pow-
 der  into a matrass,  and set this  in  the sand-pot of a furnace
 deeper than the surface of the contents.   Employ first a gentle
 heat for several hours,  and then raise it considerably for several
 hours  more.   In the  bottom  of the vessel will be  found the
 golden  scaly  mass,  of a slippery texture, like  black  lead.  If
 the heat has been too great, or too long continued, it acquires
 a dark colour a ad striated texture.   Farther up from the heat,
 we have cinnabar, and a compound or muriat of tin ;....a vola-
 tile hepar escapes.   The aurum musivum contains seven parts
 of tin  and  five of sulphur ; and  considerably exceeds half of
 the materials.  The cinnabar is much overcharged with sulphur.
 The volatile hepar is but  trifling.   There is no mercury in the
 aurum  musivum.   This  muriatic sublimate  greatly  excels all
 solutions of tin for giving a scarlet dye.   The mercury and sal
 ammoniac are not essential, but improve the colour remarkably.
 And aurum  musivum, prepared  without mercury, does  not
 make a good amalgam for increasing the power of an  electrical
 machine, for which the other preparation is  very remarkable.
 Chaptal, however, says, that this pigment, as generally  pre-
 pared, contains almost one-sixth of  mercury.*
    Tin produces some useful mixtures with other metals.f First,
; it  is useful for tinning iron, and  copper, and  brass vessels.

            * Process for preparing a beautiful Aurum Musivum.
   Precipitate nitrate of tin by a liquid sulphat of potash.  Wash and dry the
 precipitate and mix it with one-fourth of sal ammoniac, and one-half of sul-
 phur. Put this mixture into a retort, and give it a subliming heat.
   t  A mixture of tin and lead calcines faster than any metallic mixture that
 we know, burning like a dull peat: and the compound calx is more oxydated
 'han either of the metals can be singly  Hence the advantage in the admixture
 of a small quantity of lead with the tin for making white enamel. 
£24       TIN....ENAMELS....ORES OF TIN.

 Tinned plate iron, or white iron, is a most  usefu  production of
art, as it is so easily wrought. The tin not only adheres to die iron,
but penetrates it to a considerable depth; and renders it extremely
soft  and  ductile,  so that it can be forced up into any shape by
the hammer,  without cracking, or losing much of its pliancy.
   Fine pewter is a mixture of tin with a small proportion of cop-
per,  or zinc,  and  bismuth.    The copper  gives  hardness:  the
other two improve the colour.
   A  metallic mixture,  which  has the beautiful  whiteness of
fine silver, is made of tin and bismuth.   It is probable that cop-
per or iron  may  be easily  tinned with it.  I suppose some of
the iron work of chariots is whitened with it.
   Tin is  also added to copper in different proportions, to serve
different purposes, which I  shall mention when I speak of copper.
   I have  already observed, that the calx of tin is employed  for
the composition of white enamels,  i is a mistake in the writers
on this subject to say that tne pure calx of tin is »he proper basis
of this composition.   It n.ust contain a minute portion of lead;
or the flux used with it must contain lead, otherwise it will make
only  a  semi-transparent white.   Montamy,  who has  written
the most accurately, and indeed excellently, on enamel painting,
gives minute directions for the preparation of this article;  he-
cause it is used with almost every colour, in order to give to
each its proper intensity.  It is a most tedious process, so that
the article must bear  a  very high price.   He prescribes pure
tin.   But then his fondant,  or Jlux, with which it is diluted, is
crystal d'Angleterre, which is our flint-glass, containing lead.
The  common white glazing used  for the  cover of  Delft ware
is a much cheaper composition, being merely the  calx of pewter
carefully  made,   and often having  an  admixture  of arsenic.
Tassie's medallions are  made of this, with a little magnesia,....
with dipt, and minium,  or  flint-glass, for a flux.
   Tin is  very rarely produced by nature  in its  pure and me-
tallic state :  and  there  is no great variety of its ores.   Only
one kind  is found in plenty.   And no part of  the world abounds
with it so much as Cornwall.  There  is an exact register kept
there of the  produce of the tin-mines:  and it appears that  the
average of 20 years has been about 3000 tons weight annually.
   The component parts  of the ore are,  calx of tin, and some
iron,  and sometimes  a  little arsenic.   Beino- thn« rr»mnosed 
MEDICINAL PREPARATIONS.      325
entirely of  metallic  matter,  it is remarkably  heavy:  and
being at the same time very hard, it is the ore  which, of all
others, bears pounding and washing best, and which remains
the longest time  in  the gravel  and sands, and  soil,  of the
mountainous countries in which the veins of it are found. In
such  countries great quantities of this  ore are  procured by
washing the sands and gravel of the brooks, or the soil that is
near them.
   After being well  dressed, that is, washed clean from the
matrix or sand, it is roasted, and then melted in air-furnaces,
or reverberatories, with addition  of some small coal to pro-
mote its reduction  to the metallic state.   It is afterwards
assayed, to  ascertain its fineness or purity: and a stamp is
put upon it according to the  result of the assay.
   Grain tin may always be accounted pretty pure;  because  a
very  small portion of lead, which is the cheapest adulteration,
and  most frequently practised,  destroys the tendency of the
melted tin to assume that particular form. Antimony changes
the form, destroying the greasy look of the fracture. Bismuth
changes  the crystallization still more; and is never mixed for
gain.
   I find nothing so effectual for clearing tin for medicinal use
from the minute portion of arsenic, which it sometimes re-
ceives from the matrix, as distillation with sal ammoniac.
Mercury also  separates it  very well.   But a very long and
careful trituration with water is necessary for causing the
amalgam to throw out  all that it contains.
   Tin  is used, in the  practice  of medicine, as a remedy to
kill worms in the intestines: for this purpose it is reduced
by granulation to a powder like  sand,  called powder of tin.
This powder, however, has been often prepared, not from pure
tin, but from pewter. And in the directions given for preparing
it, by Dr. Alston, who  first recommended it, in the Edinburg
Medical Essays, we are  expressly desired to take pewter metal.
But common pewter contains a  good quantity of lead:  and I
think I once observed  colic pains, that appeared to  proceed
from the use of tin powders. I believe this seldom happens at
present, the tin powder being now commonly prepared with
pure  tin.       Q 
326                     COPPER,
   It may be proposed as a question, whether the efficacy of
the original powders, in killing or expelling worms, depended
on the tin or the lead?  The lead,  however  never was sus-
pected. But different opinions have been formed on this sub-
ject.   The most general  one has been,  that the  powder
operates mechanically.  If this be just, sand might serve the
purpose better, being less heavy, and more easily moved by
the intestines:  and I  have been told that sand is sometimes
given to horses.   Mr. Lewis hinted a suspicion that the tin
might act by the powers of a small quantity of arsenic con-
tained in it. But late  experiments do not support this notion.
They go  against it: and shew that commonly tin does not
contain arsenic,  or so very little that it cannot  produce its
effect.  And the truth is, that so  very little, if any, of the
tin is dissolved  or corroded in the  intestines,  that it is im-
possible the very small quantity of arsenic which it has been
found to contain should act in  any  perceptible manner : the
opinion therefore of its acting mechanically appears the most
probable: or if it be supposed to  act in consequence of  its
being  corroded or dissolved, some other preparation  of it
would be preferable.


               GENUS  XII.....COPPER.

   The obvious qualities of this metal are well known.
   Of all the metals,  copper is the  most susceptible  of con-
densation by hammering, or wire-drawing.   For this reason,
it is  very difficult to say what is  its  specific  gravity.  In
Muschenbroeck's voluminous table of specific gravities,  we
have it from 7,243 to 9000.  Brisson  says that copper melted
is 7,788 ;  and when drawn into wire is 8,878.  1 his is  much
owing to the manner of casting.  Unless  poured out in  a
very liquid state, that is, of very great heat, it will not cast
either solid or tenacious,  but is cavernulous  and weak.  Injts
best state,  it seems porous.   It is considerably softer when
just red  hot, and bears  the hammer.  In this  state it was
employed in the hasty coinage of the Romans; frequently in
ramp, with the general's die.               o 
      ABSORBS MUCH  HEAT IN MELTING.- 327

   It is far more ductile  and malleable than any of the metals
 yet described; and therefore is considered as a more perfect
 metal.   Its tenacity is also very great when  wire-drawn,
 exceeding that of all other metals except iron.   It resists the
 injuries  of the weather much better than iron ; and acquires
 by time an obscure glossy  skin, which  helps to defend  it,
 like a varnish. There is a way to give it this sort of superficial
 colour by  art. It is done by first polishing  it, and then daub-
 ing over  its polished  surface  the  deep  red  oxyd  of iron
 called colcothar, or Spanish brown, diluted with water; after
 which, the copper is heated to a certain degree, and the Col-
 cothar again rubbed off.
   Copper, though not much inferior to iron in hardness, will
 not strike fire when violently driven or rubbed on  flint,  or
 other hard bodies.   This is owing to its being so much less
 calcinable, that is,  inflammable; so that,  although, when a
 rag of copper is torn  off  by the  stroke, it is  perhaps red
 hot,  yet it does not kindle,   and become a source of heat  to
 kindle other  bodies.  Copper is therefore employed in the
 powder  mills for every  purpose that iron is required for in
 other works.  The hoops of powder casks, the chizels, mauls.
 hammers,  and even nails, are  all  made of copper.
   It  requires a degree of white heat for its fusion ;  and  in
 its fluid state has a bluish green colour.    Melting it simply,
 without  any addition, renders it less  malleable.  But when
 melted with a little charcoal on its surface,  its  malleability is
 preserved.  When copper  is urged by very great   heat,  it
 smokes; and the smoke is found to be metallic copper, (Mem.
 Acad, des Sciences, 1769, Jan.)
   It  has a great capacity for heat; and  requires besides, a
 great quantity of latent heat to render it fluid. A consequence
 of which  is,  that when  melted copper comes into  contact
 with a small quantityof water, or watery humidity, the melted
 metal commanicates  heat to it  so rapidly,  and  in such im-
 mense quantity, that dreadful explosions are often thus pro-
 duced,  by the instantaneous change  of  the humidity into
 highly elastic vapour.    The most anxious care  is therefore
 employed,  in  foundaries of  copper, to have the moulds per-
 fectly dry.   They are even made red hot for some hours be-
fore they venture to cast any  large piece of work. 
  328     COPPER....NOT EASILY  CALCINED.

     When we choose to calcine copper by the action of air and
  heat alone, this is best done by exposing it to a red heat far
  inferior to that by which it is melted. The surface of it is then
  gradually  changed  into a  blackish crust, which  is brittle
  and pulverable,  and gives a powder of a deep  red colour.
  This is an  oxyd of the metal,  which is but little oxydated;
  and is  very easily reduced again to pure metallic copper, by
  the usual means.
     All  the  saline substances act with great facility on  this
  metal.   The  more simple  and active  dissolve  it perfectly.
  The more  compounded  or milder salts corrode  it into
  rust.
     The sulphuric acid requires the assistance of heat to make
  it act upon copper.    Except when made very hot, it has not
  power to dissolve this metal:  and it must also be applied in
  its strong state.   During its action, part of it is changed into
  sulphurous acid, by the loss of a portion of its oxygen, which
  is attracted by the copper.  And the metal, being thus oxy-
  dated,  and then combined with the rest of the acid, assumes
  the form of a whitish mass, which  can afterwards be easily ■ ^
  dissolved in water, and gives a liquor  of a fine blue colour,
  which  admits of large dilution  in water,  without  separation
  of the  acid.  From this liquor again we can obtain, by due
  evaporation,  deep  blue  crystals,   commonly named  blue
  vitriol.
     This is, therefore,  the third of the compounds which were
  commonly called vitriols, which have been already mentioned
  in this  course. The first was the sulphat of iron, commonly
  named  green vitriol.   The second was the sulphat of zinc,
  commonly called white  vitriol.   And  this third  one,  as I
  said just now, is commonly known by the name of blue vitriol.
  There  is also  mentioned, in Mr. Boyle's works, and thcwof
  other ancient chemists, a vitriol by the name of Roman vitrWol.
  This was a mixed one,  accidentally  formed of ^he  sulphat of
  iron and sulphat of copper, crystallized  together, but contain-
  ing more copper than iron.
     The nitric acid,  in the  diluted state of aquafortis,  dis-
  solves  copper the most readily and  quickly.   The acid be-
  comes  very warm, and  there is  a strong  effervescence, and
  production of a great quantity of nitrous air,  into which a
i 
SINGULAR  PROPERTY OF  ITS  NITRATE.   329

part of the acid is changed, in consequence of the abstraction
of oxygen  from it by the dissolving copper.   This nitrous
air, is so pure, or nearly pure, that Dr.  Priestley commoly
used  it  in  his experiments  for trying  and comparing the
wholesomeness of different airs.   It is  not,  however, quite
so pure  as that  produced by dissolving quicksilver :  but
copper produces it more  conveniently.*    The compound
formed by  the  oxydated  copper  and the remainder of the
nitric acid  is very soluble, and  tinges the solution of a" fine
sky blue.   It bears large dilution in distilled water, without
separation  of the acid and metal.    By due evaporation,  it
yields  crystals  of a very  deep and rich blue  colour,  very
soluble, and even  deliquescent.
   If the crystals of the nitrate* of  copper be  bruised, and
slightly  moistened,  and then be hastily wrapped up  in tin-
foil,  touching  it in  as much  surface as  possible,  nitrous
fumes immediately  come  out; the  mass becomes hot;  and
presently catches  fire, brandishing  and throwing out desul-
tory darts  of flame and  melted tin.  "It is not at all clear
whence does arise the  great  heat  in this experiment.   The
only  chemical change that  we observe is a nitrate of tin in
the place of a nitrate of copper, and the eruption of nitrous
fumes.   Some more oxygen seems, therefore,  to be neces-
sary  for the  new  compound:   and  we should  rather have
looked for  a diminution than an increase of heat;  unless we
admit the  heat to be  produced in the same way as when
alcohol or sugar is. added to nitric  acid.
   Paper, moistened with  a  solution of this nitrate,  when
held  before the fire, catches fire at a very low temperature,...
not sufficient to melt  tin.
    <•
  *^haptal says that when the copper is put into this acid in small pieces, so
as TO present an extensive surface, the action is excedingly violent; the acid
is rapidly decomposed; and, after the eruption of much gas, there is a sudden
re-absorption,  and ammonia is produced.   This is a curious, and a somewhat
embarrassing fact.   Whence conies the hydrogen ?  for we know that a tube
of pura copper, red hot, does not decompose watery vapour.   If, indeed, wa-
ter be decomposed, and hydrogen disengaged, the re-absorption might be at-
tributed to its  combination with the azote disengaged from the nitrous acid,
had we net learned from Dr. Austin's experiments, that although gaseous
azote will combine with nascent hydrogen, gaseous hydrogen will not combine
with nascent azore ...suitor.
       VOL. III.                 T t 
 130 COPPER...IN NITRIC,...IN MURIATIC ACID.

   These crystals are very fusible ;  but it is a sort of watery
fusion they  undergo ; for they are very  retentive of water.
And if we  inc/ease the heat a little too  high,  the acid be-
gins to evaporate, and carries away a  small  portion of the
copper.
   The muriatic acid dissolves this metal slowly.   The co-
lour of the solution is at first dark brown, but becomes green
by keeping.  Sympathetic, or rather changeable  ink, of Mr.
Macquer, is prepared from this solution.
   The solution,  when duly  diluted, has  a light blue colour;
and when spread on paper, exhibits the same hue as long as
any moisture  adheres to it.   But when  slowly  dried before
the fire, and allowed to attract the moisture again, it returns
to  its former  state  of  an almost imperceptible blue.   In
order to insure the disappearance when cold, dip a pencil in
the solution (very weak) of muriat of lime.   Pass this over
the copper solution : it will not decompose it, but, by attract-
ing moisture, will  cause the colour to vanish almost entire-
ly.   Care must betaken with this, and indeed with all those
sympathetic inks, not to let the paper become too hot.  This
scorches  that part on  which  the solution is  spread,  and
makes it a permanent brown.
   The scales  of  copper,  formed by calcination,  exhibit
nearly  the  same appearances in  solution  in this  acid.   A
recent  and brown  solution of the  scales, if largely diluted
with  water, deposits part of the copper  in  the form of a
white precipitate, super-saturated with copper.   This white
precipitate, if  immediately dissolved  in fresh acid,  gives a
brown solution, which, like  the brown solution  of copper, or
of the scales,  becomes green, if exposed to the  air; absorb-
ing oxygen from the atmosphere, becoming more  calcined,
 and more  soluble.
   Hence we may conclude, 1st,  that the scales are very mode-
 rately calcined ; and that metallic copper  undergoes nearly the
 same  degree of calcination, when forming a brown solution in
 the muriatic acid.   -Id, That copper cannot be  more calcinedby
 mere heat and air,  its surface being already neutralized.  But
 if the copper be divided by solution, and e-posed simply  to
 the air, it  absorbs more oxygen :  and the solution becomes
 green. 
  SINGULARITIES....IN  VEGETABLE ACIDS. 331

  The vegetable acids do not dissolve copper readily in its me-
tallic st?te.  The confectioners  have observed that acids, syrups,
and pickles, made with  vegetable  acids, do not acquire  a bad
taste from copper vessels, if onl\ boiled quickly, and not allow-
ed to cool in them, or to remain after cooling.  It  is only  when
we apply such acids to copper in the state of an oxyd, that they
have power to dissolve it.   But an  ox\ d is very soon formed, if
these acids  or any saiine  substance  whatever, is applied to this
metal, while air is allowed at  the  same time  to act on it.   A
green or blue rust is  soon formed,  which is mostlv ar. oxvd of
this metal,  in an highly oxydated state, and very soluble in ve-
getable acids.   And  the reason why these may be hastily boiled
in clean  copper vessels  without being tainted, is,  that there is
not time nor sufficient action of the air for the formation of an
oxyd.*
   Verdigrise is an acidulous oxvd  or rust of copper, produced
by art, prepared much in the same manner as the saccharum sa-
turni.   It is also prepared in a coarser way, by taking what re-
mains in the winepress, after the must has been entirely squeez-
ed from the grapes,  adding some  soured wine, and stratifying
this mixture with plates of copper.   As the husks grow sour,
the copper is corroded :  and after some weeks of this treatment,
the saline crust is beaten off by the hammer.  This coarse pre-
paration is then dissolved in weak vinegar,  with the addition of
some more copper;  and lastly  the  crystals  are purifyed in  the
usual manner.
   This  substance dissolves readily  in distilled vinegar  ; and
gives a liquor of a deep green,  which being evaporated, affords
crystals of the same  colour: but the powder of them  is bright
and elegant, like that of all semi-transparent bodies.   Hence it

  * This co-operation of the air, in  the slow solutions, or rather oxydations
of copper, is unquestionable ; and is the source of some .very curious ap-
pearances, which have long puzzled  the chemists, but are  now prettj  well
understood.   It is not peculiar to copper  : but its effects in  the case of cop-
per are more remarkable  But it is surely  a difficulty in the theory.  It is
unlike the whole train of chemical phenomena, that a  partial combination
with any particular substance should increase the disposition  to combine with
more.   There still lurks >;onie yet undiscovered agent. ...editor. 
 J32 COPPER....DECOMPOSITION WITH ACIDS, &c.

 is used  by painters, though they find it corrosive.   The name
 they give it is very improper.....distilled verdigrise.
   All these  compounds of  copper with  acids, when  they are
 thrown  into the fire, or mixed with  flaming fuel,  give a green
 or blue colour to the flame,  and noxious  fumes.
   If we desire to decompound these  compounds of copper with
 acids, we can effect the decomposition of some of them by heat
 alone.   Others can scarcely be decompounded without the aid
 of an elective attraction.
   The one which is the most easily decompounded by heat alone,
 is the  acetite of copper.  This must be done  by distillation of
 the dry materials, that we may obtain  the acid as  concentrated
 as possible.  As a dry powder cannot communicate the heat so
 quickly and perfectly to the interior  parts,  as  a fluid body can
 do, this distillation always  destroys  some of the  acetous acid.
 The first part of the produce is tainted with a small por.ion of
 copper,  which gives it a green colour : and before the produc-
 tion of acid vapours is much  abated, there is  a very sensible em-
 pyreurrra.  We therefore do not obtain nearly the whole of the
 acid in  a  state which can  be purified.   The taint of copper is
 easily removed by a rectification.   But the empyreumatic smtll
 cannot be taken from a considerable portion, obtained about the
 end of the  distillation,  when the bottom of the retort is even red
 hot.  If this be left  out, we obtain the. acid in a very concen-
 trated  state,  having a very pungent,  but agreeable odour; in-
 feriorhowe'ver to  that which may  be  obtained,  by a careful dc
 phlegmation  of vinegar concentrated  by freezing.
   From sixteen ounces of crystallized verdigrise we may obtain
three ounces of water,  and six and a half of acid, of which five
 and a half are (after rectification)  free from copper and from
 empvreuma.  There  is  a residuum of five ounces and three quar-
 ters, and a loss of nearly an ounce.  This loss is sustained before
the strong acid comes over.
   Mr. Berthollet has shewn that it is  a more  powerful acid, and
has a stronger attraction for alkalis than common vinegar; and
that this  is  in consequence of its receiving oxygen from the oxvd
of copper,  which is reduced  nearly to its  metallic state  enuring
the distillation, and  is  generally a pyrophorus.  (See note 63.
at the end of the Volume.) 
                COPPER....WITH ALKALIS.           333

   Of the other acids, only the nitric acid can easily and perfect-
 ly be  separated by heat ;*  the  sulphuric acid difficultly.   The
 muriatic acid is not separable by heat alone ;  but rather renders
 the  copper volatile along with itself.
   But alkaline salts, and alkaline earths, precipitate the copper:
 and some of the precipitations deserve notice.
   1st.  Lime-water is sometimes employed to precipitate copper
 from some of its solutions ;' and gives a precipitate, which is an
 oxyd of the metal, combined with a small quantity of the lime,
 of a pleasant light blue colour, and is called verditer.   It is em-
 ployed by the  painters.   The French call it cendres blues,....blue
 ashes.   The copper is  first precipitated  exactly by  quicklime:
 and then from seven to ten per cent, of quicklime is ground with
 the calx and a little water.
   2dly, Dr. Scheele has taught us another way of precipitating
 the  copper, by which  we obtain another  colour useful for pain-
 ters. *f"
   When alkalis in their ordinary  state are used, the  copper is
 precipitated in form of a very pale or whitish-green oxyd, which
 can  be dissolved again by adding more  of the alkali than what

  * If the acid so obtained be condensed in a receiver containing a solution
 of caustic  fossil alkali, it forms a nitrate  of soda, differing exceedingly from
 that  formed by dissolving soda in nitric acid.  I could  not bring it into a
 good state of crystallization^ nor would  it form cubical crystals at any rate,
 but coalesced in  flakes, which felt slippery and soft.
  t Mr. Scheele's process is nearly as follows.....Dissolve two pounds.of the
 blue  vitriol in a copper kettle, over the fire, in about six quarts of pure wa-
 ter.  Dissolve in another vessel two pounds of dry potash, and eleven ounces
 of pulverized arsenic, (N. B. what is sold  ready pulverized is generally adul-
 terated with gypsum) in  two quarts of water, also over the fire.   When
 all is dissolved, strain the solution through linen.           -  . '
  Pour this arsenical solution into  the solution  of blue vitriol,  stirring the
 mixture  all the while with  a wooden  spatula.  Let the mixture stand quiet
 some hours, that the green  colour may settle.  Then  pour off the clear li-
 quid, and edulcorate the sediment with repeated hot  waters.  At last the
 green pigment  is  obtained by draining it through a  linen  cloth,  hanging
 loosely between four sticks;  and  then it is dried on  blotting p'aper,  or a
 chalk stone.  By this process we obtain one pound six ounces of the powder.
  The most carefid 'edulcoration is necessary ; for if it retain any of the al-
 kali,  it  will  not  work with oil as a  paint.   It  makes a very elegant and
lively green.....EDiron. 
 334    COPPER  WITH VOLATILE  ALKALI.

 is necessary to saturate the acid; the superfluous alkali acting
 on the metal as a solvent.    This is most remarkable when
 we use the volatile alkali.
   The volatile alkali has this power of a solvent with respect
 to a 1 the purer oxyds or rusts of  copper,  and acts, though
 more slowly, even on the metal in its metallic state.  And the
 deepness or richness of the colour is surh, that it enables us
 to  detect a very small quantity of. copper in  any  mixture.
 One-hundredth of  a  grain will sensibly tinge a  pound of
 water.
   The action of ammonia on copper, or its oxyds, presents a
 very  remarkable phenomenon. If a solution of caustic volatile
 alkali be  poured on copper filings, we have  in a short time a
 solution of a beautiful blue.   If a bottle be filled  quitt full
 of the solution of alkali,  and we  put in some filings,  and
 immediately put in the stopple, we  shall not have any sensible
 blue colour till after a  very long while.   When ammonia is
 in a vessel not quite full,  and has acquired this blue colour,
 it loses it by long keeping when the vessel  is  all the while
 close.  But if we open it, the  blue colour begins to appear at
 the surface; and in time it penetrates to the  bottom. Closing
 the vessel causes it to  lose the colour completely after some
 time  : and it will again return when the vessel is left open.
 And  this may be repeated several times  before it  becomes
 permanently blue.   Chemists attempt to explain these ap.
 pearances,  by observing, 1st, That when the alkali  has
 become saturated with copper,  the  solution is permanently
 blue;  2d,  The solubility in  alkali increases,  as  the  metal
 is more oxydated, to a certain degree ; 3d, The action of the
 air contributes greatly to the oxydation, when there  is some-
 thing at hand ready to take up the oxyd.   Therefore the first
 solution  is that of a very minute portion of copper at the sur-
 face;  all below has such an excess of alkali that it is colourless.
 When the vessel is now closed,  the copper, which is more
 abundantly  dissolved at the surface, diffuses,  and  is again
 combined with  an  excess of alkali, and  grows colourless.
 Now  open  the  vessel,....the  superficial  parts become more
 oxydated : a  greater quantity  is dissolved :  and the colour
re-appears, and will reach the bottom, if  the vessel be kept
 open ; if  not, the  copper  again  diffuses  till the solution is 
      COPPER....MELTED  WITH SULPHUR.   335

again equable,  with excess of alkali,  and colourless.  This
may go on till all the alkali is saturated when the colour be-
comes permanent.
   Alkalis, therefore, have the power  to dissolve copper, as
well as to precipitate it from  acids.    They shew this power
also when  applied to it in the way of fusion ; but act  more
easily on the oxyds  than on the pure metal.  And not only
the alkalis  alone, but any glass that contains them, acts upon
those oxyds, and dissolves a certain quantityof them.  The
glass is thus coloured by the copper combined with it: and the
colours it assumes are either transparent blues or greens, more
or less similar, to the colours of the  solutions of copper :  or,
when a great quantity of this  metal is combined with the
glass, the  colour of the mixture  is  an  opaque red.  The
beautiful greens that  are  seen in the figures and foliage
on the glazings of pottery are generally done with copper.
   Another precipitation of .copper  from its solutions, which
des< rves notice, is the precipitation by iron.   The copper is
precipitated in its metallic form, as in many other cases of
the precipitation of  one metal by another; the iron attracting
both the acid and oxygen at the same time. This manner of
precipitating the copper is practised in some places with the
waters of mineral springs, which flow through veins or mines
of copper  ore,  and which contain  a  small quantity of blue
vitriol dissolved in them.  This is in some places so abundant,
that they are treated for the copper they  contain, by putting
old  iron into the gutters  in  which they run,....the cupreous
mud which settles on it is collected and reduced to metal in
the  usual manner,  by a very small  quantity of inflammable
matter and flux.       *.-
   Sulphur unites readily and strongly  with copper, when they
are  properly mixed, and made to act on one another with the
assistanee  of heat:  and while they are  uniting, a quantity
of heat is extricated from them,  which suddenly produces
in  the  mixture a remarkable and  bright degree of  igni-
tion.
   Some very  remarkable  experiments were  made by the
Dutch   chemists,  Van Troostwyck5   Deiman,  and others,
which occasioned considerable surprise, and led some to call
in question the theory of  combustion published by Mr. La- 
336      EMERSION OF LATENT  HEAT.

voisier.  It appeared  that bodies could  burn  without  the
absorption of oxygen.   For the heat and incandescence pro-
duced in these  experiments  were so  remarkable as  to be
mistaken for a real inflammation in  close vessels.   When
three parts of copper are mixed with one of sulphur, and are
rammed into a  small narrow-mouthed phial, and exposed to
a heat  gradually raised to redness, the mixture swells, and
then  almost in a moment, becomes luminous all over, and
bursts out into  a violent flame.    Zinc and sulphur require a
stronger  heat,  and  give a brighter flame : so  do iron and
sulphur.  This experiment succeeds equally well in vacuo, in
carbonic acid, in azotic, or in hydrogenous gas.   (See Exper.
Phys. et Chym. par V.  Troostxvyck,  Deiman, cjfe. Amsterd.
torn, iii.)   But  since these facts  have been  more carefully
examined,  it appears that it is not an inflammation or com-
bustion, but merely an incandescence, arising from a copious
emergence  of  latent heat,....the  compounds are  totally dif-  |
ferent from those  formed by real combustion.   They have
not, however, been sufficiently examined, though very inter-
esting.*
   The compound, when the parts of it are completely united,
is a dark leaden-coloured mass, which is quite brittle, not in
the  least malleable; and  I suspect that a great part of that
heat  which was extricated from it Was the latent heat, which
gave toughness and  malleability to the metal in its separate
state.   The sulphur is not easily burnt out of this compound.
There is less difficulty in freeing iron  from sulphur, although
iron  is supposed to have, and  has in reality, a stronger at-
traction for sulphur than  copper has.    The  reason why the
sulphur is not so easily evaporated from copper is, that this
metal is not so  calcinable by heat as iron, and can be calcined

  * I think that it  may be inferred from  this,  and many similar facts which
have'already come in our way, that the oxygenous gas is  not the sole source
of the heat and light which emerge in the combustion of bodies.  In the union
of sulphur with dry filings of iron, copper, zinc, lead, tin, silver, and with run-
ning mercury, there is no oxygenous gas,  nor gas of any kind in action, and
yet a very great deal of heat and light escape from the bodies. Not to call
this combustion is,  at best, philosophical affectation and fastidiousness.  It is
not oxydation,....nor is the union of azotic-gas with oxygen combustion. So
to misname the one is ignorance, and so to misname the other is pedantry...
EDITOR. 
 COPPER....WITH INFLAMMABLE  METALS. 337

only to a very moderate degree.  In this moderately calcined
state, it retains the sulphur strongly, and parts with it slowly;
whereas iron, when joined with sulphur, forms a compound,
in which the iron is  very easily calcinable, and to a high de-
gree.   It has a strong attraction for oxygen or vital air ; and
when the  iron is highly calcined, its attraction for sulphur or
the sulphuric acid,  is greatly  diminished,....the  calces -of
metals which are highly calcined, having in  general but little  >
attraction for sulphur or acids.   But although we  cannot so
easily  and quickly burn and evaporate sulphur from  couper,
it  may be burnt out and  evaporated from it by a slow and
skilful ustulation or calcining process, continued for some
time.   The first  effect of  it is to  change the sulphur into
acid,  which remains adhering to the copper,  and makes it
soluble in water into  a blue liquor, from which blue vitriol
may be  obtained  by  crystallization ; or if, instead of dis-
solving the calcined  matter in water, we roast it further with
a stronger heat, we can evaporate the sulphuric acid, and have
at last an oxyd of  copper, nearly in a pure state.
   Some of the other inflammable substances also shew an
attraction for copper or its oxyds.   Several of the aromatic
oils can dissolve so  much as to receive a deep green  tincture
from it. Some of the unctuous oils alsOjespecially when rancid,
easily dissolve so much copper, or rust of copper,  as is suffi-
cient  to tinge them  blue or green.*-  In the tallow of com-
mon  candles, a small quantity of verdigrise is added to im-
prove the colour.
   The usual compounds of copper with other metals  are, 1st,
paak fong,  or paak tong, the  white copper of the Chinese,
which is  supposed to be copper alloyed with nickel.   And
when zinc is added to the compound, it resembles silver by
its colour.   An imitation of silver is also  attempted with
copper and arsenic.  2dly, The metallic compounds, of which
brass guns are cast, and bells, and the mirrors of reflecting
telescopes, are copper or brass, mixed with  different propor-
tions of tin.   A small proportion of the tin gives the copper
a  yellowish colour,  and makes it  very hard and  inflexible,
although  it has still sufficient toughness, and great strength.
This composition i,s therefore employed in casting what are
 •  Hence the terrible effects produced by copper vessels employed in cookery.
     Voj.. IT.T.               t- U 
368 VARIOUS COMPOUNDS..CURIOUSTROCESS.

called brass guns.  A larger proportion makes it very elastic,
though less tough  and  strong.   This is used for  bells.   A
still larger proportion of the tin  forms a dense white com-
pound, which receives a very perfect  polish, but is quite in-
flexible  and brittle as glass.   This is used for mirrors of
telescopes.  The best composition for the mirrors of teles-
copes was  discovered by the industry of Mr. Edwards, and
published in the Nautical Almanac for the year 1787.   You
will find  an account of  it in Nicholson's Chemistry', where  he
mentions the combinations of copper with other metals. The
ancients made  use of tin very much, as  an alloy of copper,
and in the  composition of their brass,  for their arms and cut-
ting instruments, which required  great hardness.  It  is defi-
cient in  toughness :  but this  is considerably improved, as I
am informed, by passing it between the rollers of a flatting
mill.
   There is something curious in the process  for whitening
pins.  It  is commonly believed that this  is done by mer-
cury.   But it is a coating with tin, incomparably more du-
rable.
   Copper, dissolved in any acid whatever, is precipitated
completely by tin.   Yet in this process the tin is precipitated
by the copper.   The effect depends on the attraction of pure
or metallic copper for pure or metallic tin.  The tin is first
dissolved  by a mixed solvent, which  contains some  tartar;
during  which dissolution, the tin is slightly oxydated : and
this solution alone does not whiten copper in the least. But
if fresh  tin, or a small quantity of iron, be added  while it is
boiled with the copper, the fresh tin, or iron, by their attrac-
tion for  oxygen, deoxydate the dissolved tin, or deoxydate a
part of the water, the hydrogen of  which deoxydates  the
dissolved tin, which, before it has time to form coherent par-
ticles by itself, is attracted by the surface of the copper, and
adheres  to it.   Mr. Gadolin tinned  gold in  this manner,
although the solvent  he used  could not act in the least upon
gold.
   Of solvents for such a purpose, when a bright and shining
surface is required, rather than an high degree  of whiteness,
the solution of tartar is to be preferred.   The  solution of
alum gives merely an exquisite whiteness ; but it is a dead 
      COPPER....PINCHBECK....SIMILOR,  &c.  339

white.  If tartar and common salt  are added to the  alum>
they take off the deadness of the white, and give some polish
and brightness.  One part of white tartar, two of alum, and
two of common salt, form  the  best solvent.  The solvent
should not dissolve any of the copper.  If  any  part of the
copper should be dissolved,  it would frustrate the  process.
(Nicholson's Diet. p. 947.)
   This metal is also alloyed with zinc, to form pinchbeck,
brass,  and similor.   Copper, mixed with zinc,  in the pro-
portion of  two parts of copper to one of  zinc, forms brass,
which has  a light  greenish  yellow colour, and when made
red hot, becomes quite brittle.  I have  already described the
process for making this compound  by cementation.   But
with equal parts of zinc, the copper forms  a Bath  metal, or
similor, which is malleable when heated, like iron.  And if a
little iron,  or  cast steel be added to this compound, the mix-
ture proves as malleable  when heated as iron, and  as strong
and difficult to bend and break when cold.    They are,  there-
fore,  making  trial of  it  now for  bolts in  building ships of
war.  Copper, in the proportion of three or four parts  to one
of zinc, makes pinchbeck.   Similor has a rich yellow colour,
and in consequence of its softness and malleability when hot,
is formed into all sorts of goods at Birmingham, by stamping
or coining.
   Copper  is also the most fit metal to be used as »n alloy to
silver and  gold, to give  these metals stiffness and hardness,
without diminishing their toughness too much.
   The relation of  lead to copper is somewhat particular.
Copper does not mix with lead,  unless the.lead be  heated to
the boiling or scorifying  degree.  The copper then sinks in,
and is dissolved very quickly ; but if allowed to cool, sepa-
rates  in some measure,  so that the mass becomes like sand
and  water.  When  copper  and lead are  mixed,  they are
therefore  easily separable  ; first by  eliquation,  then by
skimming the lead, which will make it sufficiently pure from
the copper; and as the copper still retains  a little lead, this
is worked off  by scorification.   Copper  is separated  from
other coarser  metals in  general  by scorification, especially
with lead. 
340            ORES, &c. OF COPPER. '


               Natural  History of  Copper.

   Copper is frequently found in its metallic state, and nearly
pure, in the form of plates or  fibres,  or branched masses,
or irregular lumps, intangled  in  the matrix of  the  vein.
In the inland parts of  North America, there are rich veins
containing  copper in  this form.    It abounds in the same
state  in some  of  the islands  that are to the west  of  Noith
America ; and is found more  or less in many other parts of
the world.
   Professor Robinson  told me that  an  old  officer in  the
Russian  service  who was v/ith Captain  Bering in the first
voyage from Kamtschatka to America,  informed him that
on the beach in Bering's Island ihere lav an immense  quan-
tity of metal,  rounded like pebbles by the  washing of the sea,
which  were all  malleable copper.   He  thought that  many
ships might be loaded with it.   This has probably been a
volcanic production ; for Kamtschatka, and the whole cluster
of  islands  between  it and  America, seem  to have been
raised  byx  the  same   cause.   I  'also suspect that  it was
rather an ore, or  an  oxyd, than  the native  metal  which
was seen at Bering's  island.    The  western district of  the
Siberian mines contains  many horizontal strata of copper
gravel, in  which are  found  plants and trunks  of  trees (all
exotic) completely penetrated by the  copper.
   But it occurs much more  frequently in the  form of ores,
of which there  is a  considerable variety  and abundance.
Anglesea contains the richest  bed of copper perhaps in the
world; and of late years, yields about twenty-five thousand
tons  of metal annually.   The  vein  is  about  seventy feet
thick.
   In  taking a cursory, but comprehensive view of the ofes,
they may be distinguished into three  principal kinds:
        1st, The natural oxyds of copper.
        2d, The grey  ores of this metal.
        3d, The yellow ores.
   The most remarkable natural oxyds are of four varieties ;
   1.  The deep red oxyd of  copper.....minera vitrea rubra.
   2,  The  blue oxvd.....minora lazurea. 
                COPPER....ITS  ORES.            341
   •
  3. The green oxyd....minera viridis.
  4. The fibrous green oxyd, named malachites.
  The second general section of the ores, the grey ores,
comprehends those in which the copper  is combined  with
sulphur, arsenic, and other metals, but  is itself the most
abundant  ingredient in the compound.    Iron is generally
contained in  these ores,  and often some silver.  If the sil-
ver is in such quantity that the extraction of it is a profita-
ble business, they are often named silver ores.
  The third general section comprehends  the yellow ores,
or copper pyrites.    In  these, the copper is not the most
abundant  metal, iron being present  in greater quantity, toge-
ther with much sulphur, and often arsenic; but the copper is
in such quantity, that it  is the most  valuable  ingredient,
and is the only one which gives value to  these ores.    They
have a yellow colour and metallic lustre, like that of brass,
or a little resembling that of the  common pyrites, which
contains iron and sulphur only, but  are easily distinguishable
from the common pyrites by obvious differences.   The  com-
mon  pyrites is so hard that a knife or file makes no im-
pression  on it;  and  it scratches glass, and strikes fire  with
steel.    The  copper pyrites, is so  soft  that a  knife easily
makes impression on it, and scrapes or scratches the surface
of it.   They are also remarkably different in colour.  The
yellow of the common pyrites is pale ;   that of the copper
pyrites is deeper and richer, often similar to that  of gold,
and it  is  liable to a sort of tarnish, which produces the  pris-
matic colours on its surface, as they are produced on the
surface of several metals by the action of heat.
   We can be satisfied by an easy  experiment,  whether or
not a pyrite contains copper.   We  need only to beat a small
quantity  of it to powder,  and ustulate or roast this powder
with a low degree of red heat, by which we shall burn out the
sulphur, or the greater part of it.   If we then apply liquid
ammonia to the remaining matter,  this will immediately
produce  a deep  blue  solution, if there is copper contained
in it.
   As the grey and yellow ores of copper are most abundant,
and are found to contain, although in various proportions, the
preatest  quantity of sulphur, arsenic, and iron,  I shall first 
342        WORKING  OF COPPER ORES.
describe the process by which  the copper is extracted from
these.    To effect this separation,  both labour and time are
required, on account of the strong adhesion of some of these
substances to the copper.
   The  first operations which  the  richer ores of this kind
undergo, are repeated roastings with a  moderate heat, and
subsequent fusions with  a stronger  one.   Thus the greater
part of  the sulphur and arsenic are gradually dissipated, and
the iron is calcined and scorified, or vitrified with the earthy
and stony matter that is intermixed with the ore, especially
if this stony mater is quartz.  This siliceous stone, when it
happens to be mixed with the  ore in  moderate  quantity,
greatly promotes and facilitates the extraction of the copper,
by its having a remarkable disposition to unite with calcined
iron, and to be vitrified  with  it, or converted into scoria or
slag.   And when a rich  copper ore is brangled with quartz,
so much that it cannot be pounded and washed clean without
considerable loss, it is usual to melt the whole, with addition
of common pyrites; the iron of which being very calcinable,
soon vitrifies along with the quartz, or brings it into fusion,
while the sulphur,  or a part of it, joining itself to the cop-
per ore, increases its fusibility,  and makes it more readily
subside  from the scoriae.   This manner of melting the poor
or stony copper ores, is called  crude melting, or crude fusion;
and  the product of the operation is afterwards  treated as a
rich ore of copper, by repeated roastings and melting proces-
ses.   In England,  the first roasting of the copper pyrites is
performed in such a manner, that a  great part of the sulphur
is saved, by a contrivance which  I described not long since,
when I  gave you the  natural history of  sulphur.   The sub-
sequent roastings and meltings are  performed in low rever-
beratories, -or  ovens of  considerable  length, heated with
flame.  This is kept playing on the surface of the metal; and
there are transverse ribs in the arch of the oven,  which ob-
struct the direct passage of the flame, to the chimney, and
beat it down on the melting matter.   The flame carries with
it abundance   of unconsumed vapour  and  smoke, which
robs the ore of its oxygen,  and leaves it in  a metallic state.
It  is  stirred  from time  to time, through a hole at  the
far end of the oven, immediately below the upright chim- 
           REFINEMENT....ROSE  COPPER.       343

ney;  thus  no cold air gets to the metal, to calcine  it or cool
the furnace.   A  tap hole is opened at the side, at the lowest
part of the bed; the metal flows out, with the scoriae floating
above it, and then falls into a mould, which gives it the form of
a triangular prism.  When this  mould  is full, the metal runs
over into another, which it seldom fills, but has slag above it;
and the rest of the slag runs over into a receptacle large enough
to hold it all.   I  must content myself with this short descrip-
tion :  for it would employ a  session  to describe these things
minutely.
   On the continent, a variety of  furnaces are employed, which
you may see described  and represented in  copperplates,  in
Schlutter's work  on metallurgy, which  was translated  into
French by M. Hellot.
   When the  copper is, by these operations, freed from its im-
purities to  a  certain degree,  but  still  retains a small quantity of
them, it is  called black copper, and is very deficient in  mallea-
bility ;  and often has not at all the colour of copper.  If it con-
tain silver, some lead is  added  to  it  in this state, and is then
separated from it again by eliquation.   In this process, all the
lead melts  and sweats out of the copper, and runs off, except a
small portion, which remains inherent  in the spongy  mass of
the copper.  The silver  is taken out by the lead, which has a
strong attraction for it.   The copper then undergoes the last
operation, which is the refinement of it; and the small portion
of lead which it retains,  facilitates this process,  and makes it
more perfect.
   The hearth or furnace for refining copper contains two tons,
or two tons and a half, of copper, which is refined at once.  The
diameter of the melted metal is about three feet, the depth about
two feet.  A little  water is  sprinkled upon  it from a broom.
This  is dissipated in vapour in an instant, and the surface of the
copper is frozen.   The skin is lifted off immediately with a pair
of ton;js, and thrown into a tub of cold water.  Its under sur-
face is of a bright rose  colour, and somewhat rougn and glitter-
ing by a sort of crystallization.  It is  called rose copper.   This
operation is continued till the whole of the copper is thus lifted
off in  skins. 
344   COPPER....MEDICINAL PREPARATIONS.

  The refined copper requires water  to be poured  on about
forty times before the last of it is consolidated.   This is a clear
evidence of the great quantity of latent heat which melted cop.
per contains,  for the first water must  cool the metal to its con.
gealing point, otherwise no part of it would be congealed.  All
the subsequent additions of water,  therefore, are necessary to
extract the latent heat only, the perceptible heat continuing the
same.
  We have only now to add further, that in some of the states
or conditions in which  copper is  found, it  does not need all
these operations to fit it for use.   Such of it as  is found in its
metallic state, and nearly pure, requires only the operation of
refinement.  And the ores in which it is in the state of an oxyd,
need only to be first reduced to the metallic state, and then
refined.
   The very poor yellow ores also, which sometimes contain no
more than three, or four,  or five pound of  copper in the hun-
dred weight,  are often treated in a particular manner.  They
are first ustulated with a very low red heat,  during which ope-
ration the metallic matter is oxydated,  and  the  sulphur burnt,
and changed into sulphuric acid, and part of it evaporated ; but
a part remains adherent to the oxyd of copper ; and water being
afterwards applied to the ustulated matter, a solution of blue
vitriol is formed,  which is either evaporated  afterwards and
crystallized, to be sold in that state, or instead of evaporating
the liquor,  pieces of old iron are put into it, and allowed  to
remain until the copper  is precipitated  on them, which is then
 collected and melted into a mass.
   The preparations of copper for medicinal use, are,
        Cuprum ammoniatum;....Ed\n.
        Pilulce cxrulea:;....Edm.
    For external use,
        Aerugo ;....Kd\n.
        Ungmentum ex cerugine ;...Ed\n.      *"*
        Vitriolum carideum ,-...Edin.
        Aqua styptica /...Edin.
       " Aqua vitriolicacarulea ;...Lond.
        Aqua sapphirina ;...Edin. and Lond.
        Ens veneris, formerly in* the Edin. Pharm, 
345
                 SILVER  AND GOLD.

  We have now considered  all the metals which have been
commonly known and used, except silver and gold.
  These two have been long distinguished by the chemists from
the rest of the metals, by the title  of the more noble or perfect
metals, on account of their having the metallic properties, mal-
leability, ductility, and durability, or iftcorruptibility, in a much
more eminent degree than the other metals.
  I  shall first consider  the qualities by which  they thus excel
other metals, and afterwards those which distinguish these two.
  First, therefore, their  amazing ductility and malleability are
qualities in which they far surpass all other metals.  By expe-
riments made upon silver,  it appears that a single  grain,  which
hardly exceeds  in  bulk the head of  an ordinary  pin, may be
drawn out  into  a wire near nine feet long.  And  further, this
wire, or any part of it, can be beaten out by hammering,  into a
thin  plate or leaf one inch  broad.   It can therefore be made to
cover 108 square inches.
  Of the ductility and extensibility of gold, we have examples
in the different branches of the art of gilding, or the art of cover-
ing the  surface of other substances with gold.   One way  is with
what is called gold leaf.  And the art of beating out the gold
into  leaf, is very well and  accurately described  by Mr. Lewis»
The degree of extension and thinness to which gold is brought
in common gold leaf is astonishing.   It  is plain from the most
evident and satisfactory  calculations,  that the thickness of gold
leaf  is not the ^^ro^rse tn °*"an "ncn#  But S°^ IS much more ex-
tended  in manufacturing gold lace.   What is called gold lace
is not woven of  gold wire, but of silver; the  surface of  which
only is covered with a film of gold.  To make the wire, a thick
cylinder of silver,  weighing forty-eight ounces, has its surface
covered with one ounce of gold, and is then drawn  out into wire
so fine that six feet weigh only one grain.   It is then flatted and
twisted round silk thread, &c.  While the silver is  thus extend-
ing,  the gold is extended along with it, so as to cover the whole
surface of the silver.  The wire, if examined  with a micros-
     vol.. m;                v x 
346  EXTENSIBILITY OF  SILVER AND GOLD.

cope, does not shew the smallest atom of  the silver uncovered
at its surface, although the gold is only one-forty-ninth part of
its weight, and less than the- one-eightieth  of  its bulk.   (I find
it to be the one-eighty-sixth of its bulk.)   But this proportion
of gold to the silver is much greater than  what is barely neces-
sary for covering or coating the wire.  It is sufficient for giving
it such a coat of  gold  as will bear some wearing before the sil-
ver appears.   Mr.  Reaumur had the curiosity to get some wire
drawn with such  a  thin coat of gold, that there was in his wire
only one part of gold  to 36Q of silver.  It was drawn to the
fineness of six feet to each grain, and then was flattened between
polished steel rollers,  which gave it  a breadth of one-forty-
eighth of an inch, and  extended it in length one-fourth.
  When our calculations end in such numbers as these, we lose
all distinct comprehension  of our subject.  In order to under-
stand the thinness of the gold on  such gilt wires a little more
clearly, I thought it worth while to compare it with the thick-
ness of paper,  in this manner :....It would take 14,000,000 of
films of gold, like that on some gilt wire, to make up the thick.
ness of one inch,  i^wcrr/tar...What thickness would^l4,000,000
leaves of common printing paper make up?  Anszver..,. 1262J
yards, or near three-fourths of a mile.  The thickness of the
gold on Mr. Reaumur's gilt wire, therefore, bore the same pro-
portion to one inch, that the thickness of a single leaf of print.
ing paper  does to  three-fourths of a  mile nearly,  or wanting
fifty-eight yards.
   Another eminent quality of these metals, I said, is their dura-
bility, or the power they have to  retain their metallic form, and
remain unchanged, though  exposed  in circumstances, and to
the action of bodies,  which produce great  changes in  other
metals.  One example of this we  have in the difficulty of cal-
cining them.  They cannot be calcined by the ordinary action
of heat and air, by  which other metals are  calcined, nor by that
of nitre, nor with the assistance of lead. In a  violent heat, they
remain perfectly  metallic and unchanged.  Mr. Boyle exposed
some silver and gold in  separate vessels  to the fire of  a glass-
house furnace one month.   The  gold  was neither changed  nor
diminished in weight.  The silver was unchanged, but dimi- 
          NOT  CALCINABLE  BY HEAT, &c.       347

 nished by one-twelfth.  Kunkel, making the same experiment,
 found the silver diminished only one-sixtieth ;  and when he re-
 peated it with the same bit of silver, there was no  diminution;
 from which he concludes, that the  diminution  in the first expe-
 riment was occasioned by  impurity.   Cramer also attests the
 truth of these facts from his own experience.  It is said, how-
 ever, by  Fourcroy, that  Mr. Macquer, by exposing the same
 silver in  a porcelain  crucible  twenty  times  to  the  fires  in
 which porcelain was baked, found it changed at last into an olive-
 coloured vitrified matter,  which is supposed to  have been  a cal-
 cined and vitrified silver,   f do not however  find this fact in
 Mr. Macquer's own writings, though  he relates some experi-
 ments which he  and other members  of the Academy of Sciences
 made, by exposing silver and gold to intense heats, produced by
 means of  the best burning glasses in France.   In these experi-
 ments, these metals were  in part volatilized,  or emitted visible
 vapours.   These vapours were formed by the  metal in an un-
 calcined state, as appeared plain from their condensation  on
 the surface of silver or gold.  After a long continuation of these
 experiments, a very small  quantity of vitrified matter was form-
 ed ; but Mr. Macquer justly doubts  whether it was simply a part
 of the metal calcined.  It is possible, however, that by  mixing
 these metals with others,  and exposing such  mixtures to  mihl
 calcining heats,  continued for a long time, some degree of cal-
 cination might be effected.  But if they should undergo a slight
 degree of calcination by such a process, a stronger heat alone
 makes them immediately reraime their pure and metallic form.*
   When nitre  is applied to silver or gold in a strong fire, pro-
 vided these metals are pure, there  is no deflagration or calci-
 nation of the metal.  The nitre evaporates without producing
 any effect.
   Neither can they be calcined with  the assistance of lead.
 Lead is often employed to promote  the calcination or scofrffica-
 tion of other metals, or metallic substances ;  and its power de-

  * The allusion, therefore, in the Bible, to this quality of the precious
 metal, to illustrate the triumph of a good heart over misfortune, is peculiarly
 beautiful; and, as this is to be seen in the book of Job, the  discovery must bjc
erv ancient.....editor. 
     348       PURIFICATION OF  SILVER,  &c.

     pends on two particulars :   1st,  The disposition which mixtures
     of metals have to calcine  more easily and quickly than the me.
     tals in their separate state.  2dly, 1 he great fusibility and dis-
     solving power of the calx of lead.   For when another  metal,
     which produces an  unfusible calx, is calcined by itself, its s\ir-
•   face is soon covered over  with a crust of its calx, which defends
 '   it more or less from the further action of Jthe air, and occasions
     the calcination  to  go on  afterwards slowly and with difficulty.
     But,  if to such metal we add a certain proportion of lead, the
   i mass  is disposed to calcine faster, in consequence of its being a
     mixture of metals.  Antl trte calx of  the^tad dissolves and li.
     quefies the other calx, a*d occasions  it to*$ow  off  continually
     from  the surface of the m&ked metallic mass towards the sides,
     so as  to leave this surface exposed to the constant action of the
     air;  and  thus the  calcination,  or scorification, as it  is rather
    • called in this case,  gosj.i on much faster.
        But when we make this' experiment  with silver or gold, there
     is  no  calcination or  scorification of  either of those metals.
     They mix easily with lead in the fire ;  and  when thus mixture
     is  exposed to a  proper heat and  the  action of the air, the lead
     alone is  calcined, or scorified, and is gradually thrown out of
     the melted metal;  for a calx and a metal cannot mix together.
     But  all this time, the silver  and gold remain unchanged, and
     will be found pure and undiminished in  quantity, after all the
     lead  is separated from them by the  scorifying process. The
     eighth part of an ounce,  or even a smaller quantity of either of
     these metals, contained in one hundred weight of lead,  maybe
     separated from  it by this  process.
        In consequence of their powct to remain uncalcined  in such
     processes, silver and gold are often refined or purified from the  —
     admixture of other metals by nitre or by had.                 ■
        These metals are purified with nitre, by simply mixing it  '
     with them, and melting.   It consumes the base metal, bringing  ?
     it to the top in a scoria,  which is easily  worked off with a little  ;
     lead.   If they are  much  contaminated, it is usual to melt them
     with lead, which takes to itself the greatest part of  all the otherjr
     metals.   The  mixture is separated from the gold and silver hv  I
     .liquation ; and they are then treated with the vaii*. 
                      CUPELLATION.                 943

  The purification by lead is usually called cupellation, from the
sort of vessel in which  it is performed.   The cupel is a very
flat cup,  but of great thickness, made of bone ashes burnt to a
perfect whiteness.   These vessels are formed by filling a strong
brass mould with the ashes, previously damped a little.   The
depth of the mould  is  considerably- greater than the intended
thickness of the cupel,  because it  is necessary that all the ma-
terials be put in at once, and afterwards compressed by a piece
of steel like a pestle,  with strong blows of a hammer.  If there
has  not  been enough, any addition would  form a layer which
would afterwards separate in the heat.   The face of the pestle
must have nearly the convexity of a watch glass, and must be
well polished.
   The gold or silver is mixed with lead that is known to con-
tain none of either of  these metals.  They are then subjected
to a strong heat under a muffle, and to the action of a free cur-
rent of fresh air.  This calcines the lead, and along with it the
baser metals,  converting them into a thin glass,  which is ab-
sorbed by the cupel as  it  forms.   The operation is known to be
finished, when the last  film of lead quits the surface of the but-
ton  of gold or silver, which in an instant  grows resplendent.
This is called its fulguration or coruscation.   The practice with
large quantities of metal differs from the  above only in this, that
the  glass of lead,  instead  of being absorbed  by the cupel, is
blown  off by bellows.  The lead  is got from the cupels again
 (which  are expensive) by beating them to coarse powder,  and
 reducing the lead with  flux and charcoal dust.
   In considering these  properties of silver and  gold, we might
 perhaps be inclined t© conclude that they must be quite different
 in their nature from the other metals, since we  do not perceive
 in them  that affinity with the inflammable substances, which is
 so obvious and remarkable  in the other metals.*  But when we

   *  Is not this affinity, and their perfect inflammability, distinctly seen in
 their dissipation by the electrical flash?  They exhibit all the appearances of
 heat and light, and they are dissipated in smoke, which  has a very peculiar
 and disagreeable smell,  different in each metal.
   This smoke should be examined.   The dissipation shouli* be made in water
 which would enable us to collect it, or form some judgment by the changes
 which it produces in tint fluid.   When  the combustion  (for I must give it
 this name) is effected between two plates of glass, (even the purest and free«t- 
 350     SILVER  AND  GOLD IN GENERAL.

 study their other qualities,....those which  they shew in mixture
 with acids,....we plainly perceive that they have  a close affinity
 and similarity tp  the other metals, and  are at  bottom of the
 same nature : for  we can calcine or oxydate them by means of
 some of the  acids,....and they produce the same changes on
 these acids that are  produced on  them by other metals.  Both
 silver and gold, for  example, can be oxydated by the nitric acid,
 and they convert a part of  it into nitrous air.  And silver can
 also be oxydated  by the  sulphuric acid, and converts a part of
 it into sulphurous  acid, or sulphur.
  It therefore appears that they are of the same nature with the
 other metals, and differ  from them chiefly by being more dif-
 ficultly oxydated,  having less attraction  for  oxygen, and resist-
 ing completely some of the agents, by which  this change is eftsilv
 produced on the other metals.  And when we  do bring  them
 into a calcined state by particular  processes, they are capable of
 resuming their  metallic form by  the simple action of  heat on
 them, which expels the oxygen  in the form of  vital air,  with-
 out their requiring the assistance  of  any inflammable matter to
 attract it from them, as it is attracted by  charcoal and some
 other inflammable substances in the reduction of most other me-
 tallic oxyds.
  These are the qualities by which silver and gold differ from
 the other metals already described.   We  shall now take a view
 of the qualities peculiar to each of these two metals.


                GENUS  XIII....SILVER.

  The  appearance  of this metal is ioi well known  to need
 any de.ti iption.  Its specific gravity is nearly 10,5 or 10,47.
  It is never liable to have rust formed on it,  but it becomes tar-
 nished if it be  not  frequently cleaned ;  that is,  the surface of
 it becomes dark-coloured, as if it had been smoked, and some-

 from metallic admixture) some of the gold or silver is incorporated with it.
 We know that metal  and glass will not unite, though their oxyds unite  per-
fectly. These farts have not been sufficiently attended to.   If it be thus ex-
ploded when surrounded by az jtic gas, whence comes  the light and heat ?
                                                     editor. 
            SILVER....ITS CONGELATION.        351

 times almost  black.  This happens the most certainly, and ir.
 the shortest time, when the silver is exposed to the  vapours of
 sulphur, or sulphurous gas.   And putrid vapours from rotter
 animal  or vegetable substances (eggs especially) produce also
 the same effect on it.  Late  observations,  indeed, have shewn
 that such putrid vapours frequently contain sulphur dissolved in
 them.  Inflammable air alone is said also to tarnish silver, and
 to give to the surface of it a purple hue.   This sometimes ac-
 cumulates on  the surface of silver to such a degree as to form a
 sofcle, which may be detached, and is found to be a compounc
 of stiver and sulphur.
   Plate, when thus tarnished, may be cleaned by soap and wa-
 ter,  but more perfectly by soot and vinegar.  A solution in wa-
 ter of the camaeleon minerale, or nitre alkalized by manganese,
 does it  in the  completest manner.
   The  metal is melted by a bright red heat, and when in fusion,
 has exactly the appearance that pure  quicksilver has, reflecting
 with an equally bright surface the objects around it.
  While it is congealing from a melted state, it is liable to forn
 suddenly protuberances from its  surface,  which are  sometimes
 branched, and are named the vegetations of fine silver.  Theii
 formation is accompanied with a remarkable  incandescence, oi
 sudden  increase of ignition in the congealing silver, which  in-
 candescence is named coruscation, and happens  in the congeal.
 ing of very small quantities of melted  silver, although no vege.
 tations  are formed  on  its surface.  But these vegetations are
 scarcely ever formed when the quantity of the congealing silvei
 is very  small.   The cause of their formation appears to  be 3
 power which silver has, as well as many other bodies, to retain
 the latent heat which gives it fluidity,  although it be cooled to a
 degree  considerably lower than  its  proper  congealing point.
 And this happens chiefly when it is cooling slowly, and without
 being disturbed.  At last, however,  the  latent heat suddenly
 breaks out, or emerges from  a part of the fluid silver,  and as-
 sumes the form of sensible heat, which produces the incandes-
 cence ;  and that part of  the metal from which it is extricated,
being at the surface, suddenly congeals.   Thus a thin  crust of
silver is instantly  formed on the surface of the mass.   But this
sudden  formation of the solid crust being attended with the in- 
 352     SILVER....IN  SULPHURIC  ACIDS,  &c.

 :rease of sensible  heat, the fluid  silver within the  crust is ex-
 panded, and bursts through the crust in one or two places, start-
 ing up  in one or more protuberances, which suddenly congeal
 while they are rising, and in congealing frequently throw out
 lateral protuberances.   And  thus  are formed the  branched
figures, fike cauliflowers, which  are sometimes produced,  and
are preserved by the curious.
   Most of the active  salts may be combined  with silver in one
 .vay  or another.  Sulphuric acid acts only when  stfong,  and
 )oiling  hot.  Sulphurous acid and sulphur are produced.  The
salt formed is of little solubility, except it contain abundance of
the acid.
   Diluted  nitric acid is the best solvent of silver.   It dissolves
it  with moderate effervescence, during which the metal is  ox-
ydated, by attracting oxygen from a  part of the acid -, and that
part of the  acid is changed into Very  pure nitrous air ; the rest
mites with the oxydated silver, to form nitrate of silver.  The
 (olution of pure silver is greenish at first, a common phenome-
 ion in the  solutions by this acid, which decompose  the acid in
 jart; but in a  little  while it is colourless.   If it remain green,
:he silver has  been tainted  with copper.   This solution bears
dilution in  pure  water, and stains hair, bones, and many woods
i deep and lasting black ; or if weak,  a brown.  It gives a per-
 nanent stain even to stones; as marbles, agates, and jaspers.
 This stain  does not appear  unless the bodies be exposed some
:ime to the light of day.  The  way to see this effect  of the sun's
light in producing the stain, is to dip a  bit of chalk or maiblc
 nto the solution of silver.   If  we then, keep it in darkness, it
will remain white ; hut if any part of it be exposed to the light
of the  sun, that part becomes black in a short  time.*  Those
bodies to which the solution is thus applied, attract the acid from
the calcined silver, while at the same timogdris metal is restored
to  its metallic state,  or made to approach to that state by the
action of the light, which expels from  the calx a quantity of vital
air.  This effect of light,  in  this and some other  similar ex-

  * And, which is remarkable,  it ;s much  more stained by  the blue and
violet light than by the rcl and yellow, which are much more luminous and
Heating.....e d-it o r . 
      EFFECT OF LIGHT ON  THE NITRATE.  353

amples, is well known  by experience; but we do  not clearly
understand how it is produced.  We can imagine that the light
joins itself to the metal, and expels the air from it. Others think
that it joins itself  to the air,  or oxygenous principle, and res-
tores to it the a; real form, or  gives it elasticity  to fly off  from
the metal.   In consequence of this quality of the.nitrate of sil-
ver, it is  employed for staining hair brown, and for stamping
cambrics,  and lawns, and staining marbles, jaspers,  &c.
•  By evaporation, the  nitrate of silver is reduced to crystals,
which are  very corrosive.  They melt like nitre, and they may
he  moulded into small  cylindrical pieces, call«d lunar  caustic^
used by surgeons  as an escharotic, and to corrode fungous ex-
crescences.
   This nitrate  is perhaps the  most powerful antiseptic  known.
Meat impregnated with it so as to acquire a sensible taste, though
never so slight,  will not putrefy even in a warm place. In 12000
times its weight of water, it  will preserve it from putrefaction
for ever ;  and it will separate in a few minutes by throwing in a
pinch of common salt.
   The muriatic acid is the most strongly attracted by  silver, and
will separate it from every other acid; but it has  very  little
power to act while the silver  is  in its  pure and metallic state.
The silver must be somehow oxydated to prepare it for joining
with this acid.   The usual way is, to take the solution of silver
in aquafortis, in which the silver has received oxygen from the
acid.   If  we add  muriatic acid to this solution, the silver in-
stantly quits  the nitric acid to  join with the muriatic, and with
this last forms a compound nearly insoluble in water.  It there-
fore subsides like  a curd or coagulum; and this effect is pro-
duced, "not only  by the pure muriatic acid, but by any saline
compound whatever which contains it;  such as muriat of soda,
muriat of ammonia, and all other muriatic compounds, a double
exchange taking place.   This  compound, when washed,  to free
it from the saline liquid, and dried,  is 'j. operly called muriat of
silver by the French chemists.   It contains ^ of acid, and has
some remarkable properties ;  as,
   1st, It is insoluble in  water  to  that degree, that the most mi-
nute quantity of muriatic acid, or of common salt, or any other
     vor..  in.               y y 
   354 SILVER....MURIAT OF AFFECTED BY LIGHT.

   saline compound whatever that contains muriatic acid, can be
   discovered in water by adding the nitrate of silver.
      2dly, In tl^e  same manner as the nitrate of silver,  it is chang.
   ed in its colour, and some other properties,  by the  light of the
   sun, or the light of day. We have an opportunity of seeing this,
   if we take two  portions of it new made, and keep one of  them
   in a dark place, while  the  other is exposed to the light.  The
   one kept in the dark will continue while and unchanged ; the
   other will aesume a bluish, or  dove  colour, and in it some of
i   the silver will be restored to its pure and metallic state.   This
   has often occasioned great embarrassment in the examination of
   mineral waters.  After having  indicated the presence, of muria-
   tic acid, by growing milky  all over when set by, they have be-
   come brown, and the chemist was made to suspect the existence
   of some other taint in the water, and led into a long and  fruit-
   less investigation to find out what  it was.   It was the change
   produced  by light in the lunar salt floating  all over the  fluid.
   The test of this is, that if a portion of the milky solution be set
   by in the dark, its  colour will  not change.   Nor will this salt,
   perfectly dry and white, change its colour in air that is alsb per-
   fectly drv, although accessible to light.   In an experiment  made
   by Mr.  Scheele, some of it being exposed to the light, with a
   large quantity of water covering it, or mixed with it, the  silver
   was restored to its pure metallic state, and the muriatic acid
«  which was before combined with it, was  found in the  water
   which had attracted it.   The evidence for this was unquestiona-
   ble.  Nitric acid, being poured on the edulcorated black muriat,
   took up all the  black part of it, leaving  the  rest white.  When
   some of the  liquor which had been decanted from the black mu-
   riat, was dropped into this solution, as also into another solution'
   of silver in nitric acid,  a muriat was immediately formed.
      Mr. Berthollet says that this salt, exposed and coloured  in
   the  sun, emits oxygenous gas very copiously, and that this also
   happens when  the  nitrate of silver blackens by the action  of
   light under  water.   But Scheele also  remarks, that if  nitric
    acid be  poured on the  muriat,  it does not blacken.   The  cause
   of all these changes is not very clearly understood. The action of-
   the  sun's light seems to expel  oxygen  from  the solution.   If
   this be taken from the acid, it  leaves it in the state of common 
          EXPLANATION....LUNA CORNEA, &c    355

   muriatic acid, unable to dissolve metallic silver; but the pre-
   sence of a little nitrous acid supplies this, (itself becoming
   fuming) and thus prevents the deoxygenation of the muriatic,
   and the reappearance of metallic silver.
     3dly,  It  is fusible and volatile, and after fusion assumes a
   horny flexible appearance, which has occasioned it to be called
   luna cornea.
     Mr. Beaume, however, denies that luna cornea has any flexi--
   bility.   Indeed it has but little, being commonly shivery, and
   full of transverse cracks, arising from its  shrinking faster in
   cooling than the substance to which it adheres.  Kunkel, how-
   ever,  imagined that this is the substance of which a cup was
   made which an artist presented to one of  the Roman emperors.
   He threw it  on the ground, and the fine transparent glass cup
   did not break, but was  dimpled by the fall.  The artist took it
   up, and putting it again to rights,  returned it to the emperor.
   It was therefore, says Kunkel,  a malleable glass; and he pro-
   poses the manufacture as a chemical problem, declaring that he
   was in possession of the secret.   The whole is in all probability
   a fiction, too easily credited by  Pliny or Solinus, who were but
   indifferent chemists. At any rate, luna cornea would make but a
   poor figure as a glass.
     . This  substance contains the silver in a very pure state.   The
   muriatic acid precipitates no metals from its acid solutions, but
   silver, mercury, and lead.   Copper,  which may have  resisted
   the cupellation  with lead,  is thus retained in the acid.  This
   method, therefore,  is frequently employed for purifying silver.
   It requires some art, however,  to separate it without loss from
   the muriatic  acid.   They are not separated by a low red heat;
fr for the  compound partly escapes in  fumes united with the acid,
   and partly runs through tiie vessel.   It must be ground with an
   equal weight of fixed alkali, and bedded and covered with  the
   same in the crucible.   It  is then obtained in  a  metallic form,
   and of  the highest  purity.*
      Sulphuric acid also,  added to the nitrate of silver, separates
   the nitric acid,  and is joined to the silver in its place, forming
  'a sulphat  of silver.  If the  quantity of the  sulphuric  acid is
     • I observe it said, though I do not recollect by whom, that this muriat,
   4ried and triturated with calx of tin, catches lire....editoh. 
35©    SILVER  PRECIPITATED  BY COPPER.

 small, or moderate, a great part of the sulphat of silver is pre-
 cipitated, or separates from the fluid by a hasty crystallization ;
 the  sulphat of silver,  when  not super-saturated with  acid,
 being much  less soluble in water  than  the  nitrate.  But  if
 abundance  of sulphuric  acid  be  added, the silver  is super-
 saturated with acid,  and forms a  much more soluble com.
 pound, which does not  precipitate.  It has been  usual how.
 ever,  to attempt  to purify  aquafortis by adding to it a small
 quantity of nitrate of silver ; for if  there be a little of muriatic
 acid in  the aquafortis,  it is sure to form a muriat  of silver,
 which precipitates.   And if a  little  of  the sulphuric  acid were
 present, it was supposed that this also would form an insoluble
 compound with a part of the  silver, and also fall down.  But
 this is a mistake ; and the only way to have aquafortis perfectly
 pure  is to add a little of  the nitrate of silver to  it, and distil it.
 Thus the small quantity of both the  muriat and sulphat of silver
 which had been formed, remain in the retort, along with some of
 the  nitrate of silver, when itis  more than sufficient for separating J
 the  two acids.                                              *
   In these different ways  can silver be combined  with  the
 greater number of the simpler salts: even with the vegetable
 acids of wine, of sorrel, and  of tartar.   This  was first done
 by Margraaf, in  the same way that I mentioned as followed
 by him with mercury, namely, by applying the acid to an oxyd
 of silver.
   I shall now inform  you how it may be recovered in its
 pure  metallic state.   It is  from  its  solution in aquafortis
 that  we have most frequent occasion to  recover  silver;
 this metal  being  often dissolved  in aquafortis to separate it
 from  gold.                .                                ,j
   The recovery of the silver  from aquafortis may be effectedQSl
 oy different means;  but there is but one method that is com- t\
 monly practised, on account of its being convenient,  effectual,
 and quick.    This method is to precipitate the  silver by cop-  i
 per.  The copper attracts from the silver both the  acid and ,f
 the  oxygen.   The silver concretes in its metallic state on the .1
 surface  of  the copper,  and crystallizes .into  a thick downy  '
 covering, which,  when viewed with a magnifying  glass,  or *
 with young eyes, is seen to resemble in form  a thick foliage 
             SILVER....ARBOR  DIANiE.         557
of vegetables, or the down of feathers.  The way to see this
crystallization the most distinctly,  is to drop  some of this
solution on a plate of  glass a little concave, and then to put
a bit  of  copper  in the midst of  it.  We shall see a silver
fringe form all around it in a minute; and this will continue
to increase by ramifications  in all  directions  till the whole
silver is precipitated.                                 »
   This forms one of the most agreeable objects for micros-
copic observation.  A single drop  of diluted  solution being
placed before the microscope, and a particle of copper made
to touch its margin, we  shall observe a  stem arise  imme-
diately, protruding its  branches by starts; and in five minutes,
the little bush occupies the whole  field of the instrument.
(See  Note 30, at the end of the Volume.)
   Clock dials are silver-washed in  this way.  The dissolved
nitrate of silver is applied to them, along with a mixture of
the same with a  quantity of common salt  and  tartar.   They
are then dried, and rubbed with  a  soft linen cloth, and im-
mediately varnished.
   While silver is thus precipitated by copper, a small portion
of the copper is said to unite with the precipitated silver: but
it is a very small one indeed, and such as produces no incon-
venience  in  business.  If edulcorated and redissolved in
nitric acid,  the solution becomes  perfectly  colourless;  a
sufficient proof  of the purity and  fitness for the most nice
experiments.
   Quicksilver has also been used  sometimes for precipitating
the silver; but the difference of their attraction for the acid
is so little, that the  precipitation  is slow and indistinct,....
they  rather mix  in a thick solution.  The separation of the
silver by quicksilver,  when managed in a particular way, is
attended with some amusing appearances.
   Into a nitrate, formed  by one ounce of silver and  pure
nitric acid, not greatly diluted,  but afterwards diluted with
twenty ounces of water, put two  ounces of mercury.   The
silver crystall'iEes  as  it  separates  from  the  acid, forming
beautiful  ramifications resembling  broom.  It is called the
tree of Diana.  It requires thirty or forty days, and the most
undisturbed repose.   Much more expeditious processes, but
inferior in beauty, have been published by Homberg, Beaume, 
  358   DECOMPOSITION OF LUNAR  SALTS, &c.

  and others*.  The success depends upon the proportion of
  the mercury to the silver,  and the strength and state of  the
  solution.                            «
    I said that silver happens most frequently to be combined
  with the nitric  acid.   Sometimes too it is combined with
  the muriatic acid, by adding common  salt to  the  solution of
  the silver in nitric acid. A  muriat of silver is instantly formed
  by a double exchange, and when this muriat of silver is pro-
  perly washed, and the silver recovered from it, we have it in
  the  purest possible state.....It is recovered from this  com-
  pound, as I have already observed, by grinding it with fixed
  fossil alkali, and exposing  it to a melting heat, bedded in this
  alkali, and  covered with it.   It is of  great consequence  to
  employ the alkali in  a caustic state.   I find  that much less
  heat suffices for the  fusion, which is a great  advantage,
  because a  very small  excess  of heat  volatilizes the  lunar
  muriat;  whereas, by this precaution, I have always recovered,
  the silver without any perceptible loss.
    Silver Is easily separated from vegetable  acids,  or from
  alkalis,  when it happens  to be combined  with  those  salts,
  which is never except in the way of experiment.  Heat alone
  is sufficient to destroy the vegetable  acid, and  to dissipate
• the  volatile alkali.   And the  fixed  alkalis  are separated
  merely by being melted.
    The sulphuric acid is separated, and the silver recovered
  from it, by fusion with pure fixed alkali.  The caustic  alkali
  is the fittest.
    The combination of silvertwith the-volatile alkali has some
  very surprising properties, first observed, I believe^ by Mr.
  Berthollet, who prescribed the following process.........Let
  silver He precipitated from a solution  in  pale nitric acftl by  ^m
  quicklime.   The calx is then to be separated  by decantation,
  and carefully dried for two or three days, by exposure  to the
  light and air.   When this is stirred and mixed with volatile
  alkali, it separates in form of a black  powder.    Decant the    ,
  liquor, and allow the powder to dry in the air. This powder,

    ' Beaume's process is to mix two saturated solutions of r/dver and mercury, S*%|Sh
  to dilute the mixture with distilled water, and to add a bit of amalgam.   If a  *■
  a skeleton of  a bush be made of glass, and set up in the mixmre, and smeared   '
  over with as  much amalgam as can be made to  stick to it, the ramifications
  will soon cover it, and make the toy very pretty.....editor. 
   SILVER....ITS  FULMINATION  EXPLAINED.  S59

   if touched in the smallest degree, so as to press it against the,
   vessel, and often, if merely parted so as to break a  grain,
   explodes with astonishing violence,  dashing  the vessel to
   pieces.   It far exceeds gunpowder, or aurum fulminans, and
   requires no heat, the most trifling agitation or friction b^ing
   sufficient,....even  though produced by a drop of water  falling
    into it.   We dare not  attempt to inclose it in a bottle, and it
    must  remain in the dish  in which it was  prepared.   We
    should never attempt to explode  more than a  grain at once.
      The  volatile alkali  employed  in preparing this powder,
    being exposed to  ebullition in a small matrass, crystallized on
    cooling.  When  one of the crystals was touched under the
    liquid, in order to separate it from the glass,  the whole ex-
    ploded  and beat every thing to pieces.
      Mr.  Berthollet considers this as a loose compound of  oxy-
    gen, silver, hydrogen and azote, having their double affinities
    30 nearly balanced, that the slighest alteration of temperature,
    or even of that position of  ingredients  which produces the
    equilibrium  of affinities,  is enough to disturb this tottering
    equilibrium, in such a manner, that the superiority shall  incline
    to that  side  which  produces the  union  of  the  oxygen and
    hydrogen. The azote of the volatile alkali is disengaged, and
    the silver is reduced, and water is formed.  The explosion is
    produced therefore by the azote,  and from the  vapour into
    whith the water is  changed in the very  instant of its forma-
    tion*.               .       *-
       This metalcan also be joined with earthy bodies in  vitrifi.
    cations; and die  colour which it gives,to glass is a beautiful
    yellow. v^It  is accordingly  used  to produce that colour  in

      * The explanation is ingenious.  But even in this easy case, we are not yet
 ■   sufficiently acquainted with the forces which tend to continue the old assem-
 •   blage, and those which tend to the production of the new, to be able to give an
    explanation on  which the mind can rest with confidence.  Were we certain
    that these are really the only forces in action, we could say, from the fact, that
    these are the prevalent forces which unite the oxygen and hydrogen.  But this
    is all post factum, and we are ignorant of the source from which the heat is to
    be drawn. The new  doctrines constantly hold  forth the oxygen gas as the
«£' "great source of all the heat which appears in combustion.  Now in the present
PP* case, the oxygen is in  the liquid or solid form already, and has npne to bestow.
    Nor do we know any thing of the capacity of the azote for the heat.    Besides,
    this is not a case; of double affinity.  The silver and azote are not united. The
    phenomenon is by no means explained on established principles.....editor. 
360 SILVER  WITH EARTHS....AND SULPHUR.

enamels, and the  art of staining glass.   And when more of
the silver is used, the colour is deepened to  a blood red,
especially with luna cornea,  which  has been exposed to the
light.   But the colours  thus given  to  glasses by silver are
liable to change by over-heat. Leaf silver applied to common
glass  or plates, and made red hot with  them, penetrates into
them, or is  dissolved, tinging them of a deep yellow colour.
The lowest  red heat is sufficient, and the most proper is such
as wi'l  not  spoil in the least any impression which the glass
may have received before.  A stronger heat produces a dull
dirty  colour, and a degree of opacity.  All  degrees of it may
be perceived in the dissipation of a stripe  of silver leaf in
a strong electrical shock.  The best process for this elegant
enamel  is as follows : Take glass of  litharge three parts, flint
in gross powder one  part.   Pour on this a solution of  one-
twentieth of its weight of silver.   Stir the mixture till very
uniform) and  then dry it, carefully  avoiding all dust of an
inflammable or combustible nature.   Melt  it and pour it out.
Grind it into  a very fine  powder.   This  is applied to  the
porcelain previously  heated,  and the  ignition is continued
under a muffle  till it melts, which is observed by its glisten-
ing.  The piece  is taken out,  and while continued red hot,
it is exposed to the smoky flame of burning  vegetables, which
brings out  the  beautiful  colour.  (Lewis'1 notes  on Neuman,
p. 51.)
   Sulphur  may easily be combined with this metal in  the
usual manner, and produces a compound of a colour like lead,
but duller,  and somewhat soft and  malleable,   it is  more
fusible than silver. This composition so much resembles the
minera argenti  capillaris, that it is frequently imposed on col-
lectors of ores  as natural, by forming it on fragments of spar,
and other usual matrices of such ores,  and  by conducting the '
refrigeration in a particular manner, which causes it in the
moment of  congelation to dart up slender capillary filaments,
which congeal  like a crush on its surface.   The sulphur is
separable by ustulation.   Many other metals also attract the
sulphur, as  lead, iron, and others.                        ^
   From experiments made by mixing it with  other metals, it"
appears that all the other metals will readily mix with  silver.
Mercury amalgamates most readily, even in the palm of the
hand; and their union produces a very sensible beat.  Nickel 
  SILVER....WITH METALS....SEPARATION. 361

will not unite with it, and is, I think, the only metal which
it rejects.   Lead has a strong attraction for it, and will absorb
the silver from  iron  or  copper.  All of them diminish its
malleability greatly,  except  gold  and copper.   Tin   does
it most.   A  moderate quantity of copper does  not change
its colour  much,  but increases  its  hardness a little,  in
which quality it is rather deficient when quite pure.  Hence
copper is  commonly  added,  and  the quantity regulated by-
law to  form the alloy, is about one-twelfth or one-thirteenth.
Silver mixed with this proportion of copper is called sterling
or standard silver.   Nicholson  says (on what authorm  I
know not) that our standard admits but one-sixteenth of cop-
per,  that is, one part of  copper  to fifteen of  silver.
   When silver is  mixed or  alloyed  with other metals, and
we wish to separate them, this is done by  different processes.
The  art of doing it completely  has been  studied  with  great
attention,  on  account of the value of this metal, which often
happens to be mixed with other metals in their ores, and on
other occasions.   The process is  different, according to the
nature  of the metal  combined  with  the  silver.   Thus  it is
separated.
   1.   From  quicksilver; 1*;,  by expression, and 2dly, by
heat.
   2.  From all>  except gold  or platina, by scorification and
cupellation with lead, or by nitre.   It is separated at  Bir-
mingham from plated copper, by boiling the plates in strong
sulphuric  acid,  to which has been  added one-tenth of its
weight of nitre.   The acid  acts mare readily only upon the;
silver than the copper, and the plates are  taken out when this
is thought to  be effected.   The  silver is obtained in the form
of a white precipitate, and the  copper with  which it is 3till
tainted is  easily separated by cupellation.                 <
  3.  From gold by aquafortis, or aqua regia.   This process
is  called  the, departing.   Mr.  Tillet, *6f the Academy of
Sciences,  considered this process by order of Government,
with great care, and has  published very valuable memoirs on
the subject;  and to him I must refer you, because a proper
account of the process, shewing the propriety of its different
parts, would take up a great deal of our time, without much
addition to chemical science.  Aquafortis, or aqua regia, is
     vol.  in.                  z  z 
362        SEPARATION  FROM GOLD.
employed according as the silver or  gold exceeds in quan-
tity.
   These are the methods followed in practice to separate it
from the metals and from gold ; and they bring it to as great
a degree of purity as  is ever needed for common use.  But
these methods do not render it perfectly pure.  Scorification
with lead, or calcination by nitre, leaves a little copper in it.
And in separating it from gold by aquafortis, some of the
copper employed for precipitating it from the acid, joins itself
to  the precipitated silver.   Or if we separate it from gold
by aqua regia, some gold is left in it.
   But the process by which it is reduced to the most perfect
purity,  is  by first purging  it of all  the coarser  metals by
cupellation with lead, or by  melting it with nitre,  and then
making it into muriat of silver, and reducing it.    Thus any
gold which might have been in it, or any minute quantity of
copper which the lead might have left, is separated from it.
(Vide  Cramer.)

                      Natural History.

   Silver is found more or less in all  parts of the world that
are remarkable  for metallic veins ;  most plentifully, however,
in South America, particularly Peru  and Potosi.
   It is found either,
    lmo, In its metallic state,  and pure, or nearly pure.
   2do, In the form of ores, in which  it is the most abundant
metal, and which are called proper  ores of silver:  Or,
    3tio, As an ingredient, contained in small quantity, in the
ores  of other  metals,  which  are often, on account of the
value  of the silver, called silver ores; but distinguished by  *jjj
 the title of improper ores of silver.
    When  it is  in its  metallic state, it is found  formed into
 fibres,  or plates, or branched masses,*often crystallized into
 regular figures in the cavities of the vein, or intermixed with
 the solid matrix.   Not unfrequently  ijt adheres to an ore of
 silver.   The  fineness  of  the fibres  is  often  surprising.   ,
 They  affect  a singular arrangement,  nearly  rectangular,
 forming chequers that are interrupted like a fret-work orna-
 ment  in architecture,  each being a sort of  quadrangular
 spiral.  The geologists ascribe this  formation  to a  gradual 
        SILVER....NATURAL  STATES OF.      &6S

shrinking of the matrix from without, like what is more dis-
tinctly observed in the round balls of iron pyrites.
   Of the ores of silver, the proper are chiefly three or four
in number:
        1. Miner a argenti vitrea.... glassy ore.
        2. Minera cornea....horny  ore.
        3. Minera rubra....the  red ore.
        4.  Minera alba....the white ore.
   The first is very improperly called vitrea. t It has neither
transparency nor any other  quality by which it resembles
glass.   It is silver combined,with  sulphur, and is exactly
similar to an artificial compound of silver and sulphur, being
soft and malleable, almost like lead, and  of the  same colour
with  metallic lead, and  very  fusible.    The  clean pieces
of it contain more than three-fourths  of their weight of
silver.
   The horny ore has been analysed with great  accuracy by
Mr. Woulfe.  (Phil. Trans,  anno 1776.)  He found it to
be silver combined partly with  muriatic, partly with sulphuric
acid, and there is often pure  metallic silver, or sulphurated
silver, intermixed with it, which darkens its colour.  It is a
rare sort of  ore,  but when  specimens of it are found pure
and unmixed, it bears a great  resemblance in appearance and
properties to muriat of silver.  It then  contains about two-
thirds of its weight of silver.
    The red silver ore is of  a  deep red colour, and more or
less transparent, often crystallized, brittle, and very fusible.
 Professor Bergmann found that 100 parts of it contain 60 of
silver, 27 of arsenic, and 13  of sulphur.  But the propor-
 tions are a little  different in different specimens; and some
 kinds of it are said to contain  antimony instead of  ars«nic.
    The white silver ore,.....minera alba, has  the metallic
 opacity and reflecting surface when broken, and a white or
 whitish colour,  often inclining to  yellow or gray.  It con-
 tains the silver combined with arsenic and with other metals,
 as iron, copper, &c.  ,-  and the proportion of the silver in it
 is very various;  some kinds of this ore  being very rich, and
 others but  poor.   And  it is subdivided by mineralogists
 into a variety of species. These anxl the improper  or poorer
 ores of silver are accurately  enumerated and  described  in 
364        WORKING OF  SILVER ORES.

Mr. Kirwan's Mineralogy, and other works, to which I refer
you ; and  I proceed  to give a short account of the  pro*
cesses by which silver is extracted from its ores.
  When the silver is found in its metallic state,  almost
pure, and only entangled in the state of filaments,  or  thin
plates, or grains, or branched forms, in a stony matrix, there
is only one way of extracting it ;  and that is, by reducing
the whole  to powder, or small grains, by stamping mills, or
by other machinery, and macerating and working this pow-
der in tubs with water and quicksilver,  so as to  give it the
consistency of mortar for building.   It is kept in this state
for some time,...and is the better of  being kept in  a warm
place ; after which, it is diluted  with plenty of water in
large wooden vessels : and a  circular motion is given to this
water by machinery, while more water  is supplied by a small
pipe.  Thus the water runs out slowly, over the brims of the
vessels, and carries away with it the earthy and stony part of
the powder.   The silver and quicksilver united together,
and forming a  very heavy compound  or amalgama, remain
at the bottom of the vessels, and  are at last completely freed  '
from the earthy and stony matter.   The amalgama, which is
in some  measure fluid, is then taken out and dried; and,
being tied  up  in pieces of leather, is  strongly compressed,
that the  fluid parts of the quicksilver  may pass through  the
pores of the  leather.  These fluid parts of the quicksilver
contain a little only of the silver dissolved in them,  and  are
employed again with fresh ore.   The rest of the quicksilver
remains in the leather bags,  combined with so much silver
that it has  the consistency of  a stiff paste, or is almost solid. .
This  rich amalgam is afterwards exposed to a proper heat to wfj
make the quicksilver evaporate, and leave the silver in a pure  ^
state  ; this operation being so conducted that the  vapours of
the quicksilver are condensed by themselves  in another part   '
of the apparatus.
   It  often  happens that the  metallic silver is intermixed in
the matrix with some  of the proper ores of silver, and  also
with ores of other metals which  contain a small quantity,  **l
more or less, of mineralized  silver.  When this is the case,
the whole, after it is reduced to powder, must be subjected   ]
to a process of ustulation, by  which the sulphur and arsenic 
              CUPELLATION...OR TESTING.        365

   are evaporated from those parts of the silver which are in the
   state  of ore:  and the other coarser metals are oxydated, and
    therefore separated from the silver, which cannot be oxydated
   or calcined by a roasting process, but retains its metallic form,
   and is ready to unite with the quicksilver, in the process of amal-
   gamation.  To facilitate this,  some common salt is generally
   added.  It helps to clean the surface of the particles of silver,
   and thereby promotes the union of this metal with the quick-
   silver.
      All this is detailed by different authors, who have given trea-
   tises  on this particular subject, or  who have described the rich
   mines of South America,  in which the silver is almost univer-
   sally  found in its metallic  state.   The  most  noted of these
    authors are Alonzo Barba,  Don George Juan de Ulloa;  but
    above all Baron Born, who never visited America, but who, in
    consequence of an office he held, was induced to study the pro-
    cess of amalgamation, as practised in Hungary,  for  extracting
    silver and gold from their matrices.  He published a book on
    this subject, in which he has  proposed some important improve-
    ments, and described the whole of his apparatus, and illustrated
    his descriptions with accurate  figures.  It is translated into our
    language by the late Mr. Raspe.
      When silver is found in the state of rich'ores, in which it is
    combined with sulphur or arsenic, and with  other metals, the
    extraction of it is commonly effected by the action of lead, and
    on a large cupel.   This cupel is made of bone ashes, or often of
   \- wood  ashes, from  which all  the salts have been carefully ex-
 >>;  tracted.  It is two and a half feet or three feet in diameter, and
f   is  formed and fixed in  an iron hoop of proper depth, which
    limits  and supports the sides of it, while some cross bars sup-
    port  the bottom.   This large  cupel in its iron frame is placed
    in a  reverberatory furnace fitted to it, to be heated with flaming
    fuel; and the iron hoop is defended from the destructive action
    of the heat by covering  it well with plenty of bone ashes, made
    to cohere with a little water.  The flame and heat are applied
    to the cavity of the cupel only; the under surface is defended
    from the heat.  A  good quantity of lead is then melted, and
    made red hot on this cupel; and the silver ore is added to the 
366         CUPELLATION....OR TESTING.
lead.  A part of the lead immediately unites with  the sulphur
and arsenic, or other matters with which the silver was cornbin.
ed.  And these  matters  occasion or promote the scorification
of a part of the lead, which is also promoted by the wind of one
or two bellows which  play on the surface of the metal.  The
scorified lead is a powerful flux or dissolvent for the earthy and
stony substances, or other metals in which  the silver was in-
volved ;  and  the whole becomes fluid scorified matter, flowing
uppermost, or around the melted  and red  hot metallic lead.
This last powerfully absorbs  the silver that has been extricated
from the ore.   The scoriae thus produced are soon after drawn
off by  making  a little  gutter in the edge of the cupel,  on the
opposite side, from the blast of the bellows.   And the lead, if
sufficiently enriched, is further  scorified by heat and air, until it
be totally changed into litharge, the silver remaining at last on
the cupel.  In scorifying lead,  to extract silver from it  in the
large way of working, the scorified lead is not allowed  to sink
into the cupel,  or to be  absorbed by it, as is done in refining
small quantities of silver, or in assays.   This at least is avoided
as much as possible.   The melted  litharge is made to  run out
of the cupel by the little gutter I mentioned:  and it drops intp
a cavity below, where  it immediately congeals.   The reason of
this is, that when the litharge is pure,  it is very easily reduced
again into lead.   But when it is absorbed into the bone ashes, it
is difficult to reduce it; and it cannot be reduced without con-
siderable loss.
   These  processes are sometimes  varied in other ways, the
reasons of which you will easily understand from what has been
already explained to you.  If an ore,  for example, containing
some silver, is very much brangled or dispersed through a large
quantity of stony matter, the whole is  melted among  the  char-
coal ; some other kind  of sparry or stony matter being added to
promote the fusion of that which involves the ore : and they add
also some litharge or scorified  lead, which has  been produced
in other processes, such as the cupellation lastdescribed. 
367
                   GENUS  XIV.....GOLD.

      This metal has been distinguished  by the chemists with the
    tides of sol and  rex metallorum, on account of its excelling all
    the rest by the perfection of its metallic qualities ;  but chiefly,
    I imagine, because it is the most highly prized in society.
      When pure, it is  soft and flexible not elastic or sonorous.   I
    already noticed its great ductility and malleability.   Mr. Lewis
    considers its specific gravity with  great accuracy.  It is about
    nineteen times as heavy as water : and a cubic inch of it weighs
    4902 grains,  or 10 ounces and  102 grains.  It requires for its
    fusion  a very strong red  heat, or almost a white heat, a heat
    stronger than that of melting silver: and when infusion, it emits
    or reflects a bluish green light from its surface.
      Its surface always remains bright in the  fire  : and if foul or
    tarnished before, it is always cleaned and  brightened by a red
    heat.
      When we try it in mixture  with salts, we find that none of
    the acids, applied in their ordinary state, produce any effect on
    it.  The sulphuric acid,  or the nitric, or the common muriatic,
    if applied separately, either in their watery form, or in the much
    more active state of dry and burning hot vapour in cementation,
    make no impression on it, or shew any power to dissolve it in
    its pure and metallic state.  Upon this is  founded a trick for
    defrauding  the  purchasers  of  gold.    The bars  or  ingots of
    impure gold are cemented  for a  while with proper materials,
v .,.  which  refine it to a  depth proportioned to the continuance of the
    cementation.  Trinkets treated in this manner bear to be burn-
    ished and polished ; and when tried  by the touchstone appear
    perfectly fine.    When  trinket gold  appears  of this extreme
    fineness by the touchstone, it is always to be suspected as being
    only a crust covering base gold.   An ingot, so treated, appears
  / fine, even when cut through with a chizel, because this carries
    a film  along with it from the surface,  which covers  the rest.  It
    is proper,  therefore, to  cut it  only half through, and then to
    break  it. 
368    GOLD PURIFIED BY  CEMENTATION.

  The saline solvents which act on metallic gold, are only the
oxygenated muriatic acid, and the nitro-muriatic solvent, which
is therefore called aqua regia.   The oxygenated muriatic acid
is  effectual in consequence of its power to  oxydate the gold,
which the common muriatic acid cannot do ;  and the nitro-mu-
riatic acid has the same power.
  This mixed acid  may be prepared and  applied by different
ways, so as to be effectual in dissolving gold ; as
  1st,  By mixing the pure nitric and muriatic acids together.
  2dly, By adding common salt, or sal ammoniac, in moderate
quantity,  to the nitric acid, and distilling this mixture.
  3dly, The mixture  I just now mentioned  can be  employed
very well  without distilling it.
  4thly, Alum, nitre, and common salt boiled with water, form
a solvent of gold, though not a strong one.
  Scheele, the first discoverer of the oxygenated muriatic acid,
was of opinion, that the nitric acid dephlogisticated, or, in other
words,  oxygenated the muriatic, and thus enabled it to dissolve
the gold.
  But  Dr. Priestley found that  nitrose acid,  and especially the
most red and volatile vapour of it, which he calls nitrons vapour,
when added to the muriatic acid, occasions a more rapid disso-
lution of the gold than the more perfect nitric acid does, which
cannot easily be explained upon Scheele's principle.
  Another fact, analogous to this observation of Dr. Priestley's,
is, that when the solution in aqua regia  is going on,  in a slow
and languid manner, the addition of a small quantity of aether, or
of alcohol, makes  the solvent very active.   The solution goes
on briskly, and is  accompanied by much effervescence.  This
also seems very unlikely to produce  an oxygenation of the mu-
riatic acid.  It  seems more fitted for depriving it of oxygen:
and it is not clear how the  vapours of nitrose acid should supply
oxygen more readily  than nitric acid, which contains more of
it.  Yet, from what experience I have in the  dissolving of gold,
and  by attending to  the odour of the acid  when it is acting
properly ^ I am persuaded that  Scheele  was  right.  While the
acid is  acting on the  gold, it always gives the  distinguishing
pungent disagreeable  odour of the oxygenated muriatic acid. 
         NITROSE ACID DISSOLVES GOLD.      369

When it is saturated, the nitrose fumes are plainly distinguish-
able : and then the addition of a little muriatic acid immediately
renews the action, and yields the smell of the oxygenated mu-
riatic acid.   The addition of a little nitric acid, when the solu-
tion flags, does not produce the same effect.  From this I think
the inference is  plain.   The  muriatic acid  is the basis of the
solvent, but requires more oxygen, and the saturated solution
is a solution in oxygenated acid.  Therefore more nitric acid
can do  nothing.    More muriatic acid can, because there is
enough  of nitric in the mixture to oxygenate it.
   But there is also reason to be of opinion that the acid of nitre
itself, when  it has lost a part of its oxygen, becomes in some
measure a solvent of gold, or assists in dissolving it, and that
in the nitro-muriatic solvent, both acids act.
   It has been found by experiment, particularly by Dr. Brandt,
that a strong nitrose acid, although employed  alone, will dis-
solve a  small proportion of gold, when boiled with it some time.
But, in truth, it  is  only a very small quantity that is thus dis-
solved ;  and even this small quantity is liable to separate again
from the acid spontaneously.   Moreover, when gold is dissolv-
ed in the usual manner in aqua regia, the muriatic acid adheres
the most strongly to the gold, and is the principal solvent.   Ni-
trous vapours arise from the salt while evaporating to dryness.
Mr. Lewis remarks, in  his Notes  on Neuman,  that when the
solution of gold  is distilled, the nitrous acid easily passes over
into the  receiver,  leaving  the  muriatic alone  in  possession
of the metal.  And when gold is obtained in the state of an oxyd,
by precipitation from its solution, or any other process, the mu-
riatic acid alone, and even a weak one, can easily dissolve it, and
forms a solution which has all the properties of the common so-
lution of gold.
   It is a sufficient answer to any doubts  about  the real solvent
of gold, that the compound resulting from  the  solution in the
oxygenated  muriatic acid is perfectly the same in all respects
with the salt formed by any of the compounded solvents.   The
nitric, or even nitrous acid may perhaps  oxydate the gold,  but
it does not combine with it in a saline form.
     vor..  nr.               3  a 
370  GOLD PRECIPITATES....FULMINATING.
  The solution of gold is always of a rich yellow colour: But
when applied to animal or vegetable substances, it produces an
indelible stain, of a reddish purple.   By evaporation, it can be
made tcf form yellow crystals.  In  these  the  muriatic acid ad-
heres so strongly to the gold, that it cannot be completely sepa-
rated by heat.   When they are exposed to heat in a retort, part
of the gold rises with the acid, and is condensed into a red or
deep yellow fluid, or into crystals  or flowers of the same rich
hue, in the neck of the retort called, by the alchemists the red
lion:
  We can easily, however, precipitate the metal from its solvent
by  various additions, such  as alkaline salts and other metals.
  Fixed alkalis and  lime precipitate gold of a ruddy yellow:
and the oxyd is soluble in all the acids.
  Nut galls,  or the gallic acid, also precipitate gold  of a purple
colour: and it was discovered by Mr. Monnet, that this  preci-
pitate dissolves most readily in nkric acid, giving it a fine blue
colour.
  The volatile alkali  is one of the best precipitants of the gold,
and produces the remarkable precipitate named aurum fulminans^m
k is an oxyd of the gold,  which has a dull yellow colour; and
is thus  named on  account of its disposition to  explode with
astonishing violence, when  exposed to a very moderate degree
of heat.                                         .
  To see this explosion  properly in its fuH  energy, we must
wash away the saline matter from the precipitate carefully with
pure water,  and then dry it well in a cool'place.  After this pre-
paration, if we expose it to a gradual heat, it first becomes dark
coloured : and soon after, if the  heat be increased,  it explodes
with an obscure and momentary flash, visible in darkness. And
when the experiment is made with a view to know what becomes
of the gold, by covering it, for example, with a glass bell, it is
found dispersed in small particles, and all of it  restored to its
metallic form.
  The  explosion of this  preparation of gold  is so exceedingly
violent,  that gre^t caution is required to prepare it with safety,
or to make experiments with it;  terrible  consequences having
in some cases  proceeded from the want of care or skill in  hand- 
     FULMINATION  OF GOLD EXPLAINED. 371

ling it.  Its force is such, that when so small a quantity as ten
grains are exploded on a thin metallic plate, it makes an impres-
sion like that of the stroke of a hammer, or sometimes breaks^
hole through it.   And after it is rightly prepared,  it is danger-
ous to treat it in any manner by which it may be heated,  or ex-
posed to friction or compression.   Grinding it in a mortar, nay
even the  friction of the glass-stopper on a grain left in the neck
of the phial in which  it is kept, has been known to occasion its
explosion.
   It is remarkable that the heat produced in this explosion is
very small.  It  will not singe paper.  If a little be rubbed into
a bit of soft spongy  paper, and held over a candle, or before
a hot fire, it will turn dark coloured,  and then go  off in a suc-
cession of cracks, with scarcely any light, and without chang-
ing the colour of the paper.   I imagine that even the light arises
from  an  electrical concussion of the air.   (See Note 65. at
the end of the Volume.)
   The nature  of this surprising preparation of gold,  and the
cause of its explosion, has been but lately even guessed at with
any probability-;  for I cannot say that it has  been discovered:
and the sagacious conjecture was made by Dr. Scheele.   For-
merly it was supposed to contain nitrous salts, combined with
the gold, and that these gave  it this fulminating quality.  And
it  is in fact a little heavier (almost one-fourth) than the gold
from which it is pfepared.  But neither can any nitrous salts be
found in  it,  nor is the heat at which it explodes sufficient for the
explosion of nitrous compositions.
   When I was engaged in making my experiments on magnesia
and other alkaline substances, I had an idea that the explosion
of aurum fulminans depended on carbonic acid communicated
to the gold by the  precipitating alkali-   And this conjecture was
founded on my observing that gunpowder and pulvis fulminans
contained, or produced in the explosion, a  great quantity  of
this gas.   But the important discoveries which have been made
since that time,  shew  clearly  that it proceeds from a very dif-
ferent cause.
   Professor Bergmann, in a dissertation on aurum fulminans,
proves that  it  cannot be made without volatile alkali.   If the
gold be dissolved in a solvent composed of the pure  nitric and 
 372            GOLD....FULMINATING.

 muriatic acids, and we then precipitate it with a fixed alkali,
 we get an oxyd totally destitute of the exploding power.  But
 if we digest  this oxvd with liquid volatile alkali, we then give
 it that property.  And  further, the pure  or caustic volatile
 alkali serves  rather better for  making  good  aurum  fulminans
 than the carbonat of ammonia.  All this, and many other facts
 to the same purpose, were ascertained by Professor Bergmann.
   And afterwards Scheele in Sweden, and Berthollet in France,
 gave us more complete knowledge on this subject, by  demon-
 strating the presence of  volatile  alkali adhering to  the  gold
 in this  preparation,  and  shewing  by  experiments, that this
 volatile  alkali  is decompounded when  the explosion  takes
 place.  Mr.  fierthollet,  equally judicious  in   his choice  of
 decisive experiments,  and ingenious in his  conclusions from
 them, made  two experiments on these  compounds, which
 leave  little  doubt  as  to their  chemical  constitution.  He
 exposed aurum fulminans in a copper tube to a very gentle heat,   4
 gradually increased, and  obtained from  it great abundance  of
 alkaline gas, by which its weight was diminished considerably,   J
 and its exploding power entirely taken away.   He exploded dry  , .
 aurum fulminans in a proper apparatus,  and obtained water and
 azotic gas,....and  the gold was reduced to the metallic state.    .,,.,
   The volatile alkali is now known to be a compound of hydro-.  -  ;
 gen and azote.  The precipitate of gold also contains the oxy-
 gen which the metal received  from the nitric acid.  The attrac-
 tion,  however, of the oxygen for the metal, and  of the hydro-.
 gen for the azote, prevents them from acting on each other until
 heat be  applied.  But when heat is applied, the oxygen and
 hydrogen unite with a rapid or  momentary  combustion, and-.j^jy
 form  vapour of water with an explosion : and  the azote also as-  *
 suming the elastic aereal form,the explosion is thereby increased.*
   Another discovery which has been lately  made, and which
 is connected with the subject, is, that silver can  also  be prepa-   \
red so as to have the properties of fulminating gold, and that in
a  far  higher degree  than  the  gold  itself.   This  discovery  was -jm
 also made by Mr. Berthollet,  and has been considered already.
  * I observe that some French and  Italian chemists consider this phenome-
non as the combustion of azote ;  but this is inconsistent with the experiments
 of Mr-Berthollet...,-sditoh. 
FURTHER OBSERVATIONS.         373
   As  to  the formation of  this curious  compound, I  must
observe, that when the gold is precipitated in  this manner
from the aqua regia by alkaline salts, it may be redissolved,
like the precipitates of some other metals, by adding to the
mixture a superfluous quantity of the alkali. The fixed alkalis
dissolve it better than the volatile alkali; and, according to
Margraaf, the phlogisticated alkali is better for this purpose
than the common or pure fixed alkali.   These solutions are
not permanent, the gold being deposited from them, especially
from the volatile alkali.
   If we choose to  deprive  the precipitate of its exploding
power, and bring back the gold to its metallic state,  we can
effect this by several different methods ; as,
   1st, By  calcining long, with a very gentle heat, inferior to
that which makes it explode.  Thus it slowly assumes a dark
purple colour; and the volatile alkali is thus evaporated from
it.   This  method requires great caution to  avoid friction or
concussion.
   2dly, By heating  it in a strong  and close vessel.*
   3dly,  If the particles of  it be separated from one another
by the interposition of any powdery substance mixed with it
on purpose, as sulphur, or any of  the neutral salts,  or earthy
powders,  it may be  heated securely, until  it is deprived of the
power of  exploding, and can afterwards be melted  into a
mass.
   4thly, If some strong sulphuric  acid be boiled with it, and
evaporated from it, the gold remains bereft of its exploding
power.
   5thly, The vitriolic asther, by digestion, simply reduces
a  part, and dissolves a  part, which is also afterwards re-
duced.
   Gthly, Muriatic acid, digested with it, dissolves it: and
then,  by precipitating with  the  fixed alkali, we obtain it no
longer fulminating.
  * A small quantity of aurum fulminans was shut up in an iron ball, of which
it completely filled the cavity. This was  exposed  to a great heat, but did
not explode.  (See Fourcroy, Vol.  iii. p. 369. Edin. 1788).  Can this have
happened because external pressure prevented the chemical combination, as
we see it prevent the absorption of.caloric by water, so as to make it boil ?....
ED1TOP, 
374   GOLD....HOW AFFECTED  BY jETHER.

   You  will find it  alleged in books,  that  washing  aurum
fulminans  with much water, or boiling it  in water,  takes
away its exploding power. But this is a mistake.  The more
perfectly it  is washed,  it explodes  the better.  And  if we
neglect to wash it,  and thus leave in  it any quantity of
the  salts  formed  in precipitating  it,  it will  not explode
well.
   Such are the effects of alkaline  salts on  the solution of
gold.
   This metal can also be precipitated in some measure from
its solution, by some inflammable fluids,  as some aromatic
oils, and spirit of wine.   These  liquors act by attraction for
the acid.
   The  effects of the vitriolic aether have been thought more
remarkable.   It seizes on the gold immediately,  and often
reduces it to the metallic state, in fine films, which are ren-
dered buoyant, even in the aether,  by the  adhesion of im-
perceptible  bubbles  of vital  air.    By adding  sether to a
solution of gold in aqua regia, the whole of the  metal may
be brought to the surface, forming a stratum above the sether;
and  neither of the fluids below (the sether nor the aqua regia)
contain  a particle  of  it.    Generally,  however, the gold
remains for some time dissolved in the aether (but completely
abstracted from the acid), tinging it of a rich yellow.
   This effect  of the aether has  been the more admired, on
account of its being the lightest fluid of any we know, and
therefore was thought the  less  qualified to  suspend such a
ponderous metal.  But the power of chemical attraction per-
forms greater wonders than this; for gold can even be ren-
dered volatile by  some of the salts  which have the strongest
attraction  for it.   And in  this case of the  dissolution and
suspension by sether, the sether acts  more by its attraction for
the  acid with which the gold is  united, than for the calcined
gold.  But it appears also to have some attraction for  the
oxydated gold itself.  Mr. Lewis and  others say that aurum
fulminans  can be dissolved by it  at least in part.   Still, how-
ever, I am inclined  to suppose that the  sether acts, even in
this case, by its attraction for the oxygenous principle, and
the  small quantity of saline matter combined with the gold;
for it is certain that when we apply it to pure gold in its me- 
              PRECIPITATES  OF GOLD.           375

 tallic state, it has not the least power to act on it,  or to dis-
 solve it.   And when  it dissolves the  aurum  fulminans,  it
 does not hold it  long suspended,  but deposits it in  its pure
 and metallic form.*
    Other metals also can be employed to precipitate the gold:
 and there are several  that precipitate it,  although they are
 themselves combined  with an acid.  They produce this effect
 in consequence of the strong  elective attraction which they
 have for the muriatic acid, and for the oxygen, both of which
 they separate from the gold.
    The metallic solutions which have been applied to this pur-
 pose, are,
    The solution of sulphat of iron;
    The solution of nitrate of quicksilver;....and
    The solution of tin in the nitro-muriatic solvent.
    It is easy to understand how the  two first produce  their
 effect.   And I shall only observe, that the  precipitate by the
 mercurial nitrate is very readily dissolved by mercury.  It is
 useful in this way for gilding upon glass or porcelain.    But
 the precipitate by martial vitriol is far preferable, affording a
 much  richer colour,  seemingly owing to a small quantity of
 copper contained in the vitriol.
    The effect of the solution of tin depends on this  particular
 circumstance, that though the tin be already combined with a
 quantity  of the muriatic acid  in the nitro-muriatic solvent,

   * Since we see the aether separate the gold from its solvent in the metallic
 state, we can scarcely expect any action of aether on metallic gold.  Experiments
 on this  metal being so expensive, they have not been made on large enough
'" quantities for observing with accuracy what changes are induced on the aether,
 in this experiment.  The phenomena accompanying the separation of  gold by
 aromatic oils, give considerable information, and very conformable  to Dr.
 Black's opinion.  These oils are inspissated in the same manner as by the
 contact of vital air.  We should expect a similar change on the aether to what
 pure vital  air produces on  it, forasmuch as it deoxydates the gold :  and we
 should expect some combination of the aether with the acid.  If we observe
 the aether changed as it would be by so much aqua regia, we should ascribe
 the separation of ths gold entirely to the attraction of the aether  for the acid.
 If the change be different, we should ascribe it, at least in part,  to  its attraction
 for pure oxygen.  The phenomena give indications of both. The  xther mixes
 with the acid only to a certain degree : and the acid, thus combined with aether,
 has no further action  on metallic gold... .editor. 
376       GOLD....PURPLE OF CASSIUS.

and also with a quantity of oxygen, it is not saturated with
either of them.  It has still an attraction for more, and there-
fore takes them from the gold.
   The precipitate of gold, thus obtained, is the most remark-
able of any by its fine and rich colour.  The colour is so deep,
that this experiment is a way to discover the smallest quantity
of gold in a solution.   And a red or purple appears to be the
colour natural to gold, when very subtilely divided,....by
electrical fire, for example, or other means. The purple stain
given by the solution of gold  to animal and vegetable sub-
stances, is another example.
   This precipitate is valued, and very much used, as a fine
purple for enamel colours.   It has the advantage of enduring
the fire without undergoing any change of its colour, to which
many other enamel colours are liable.
   I  have  already described the process  for  preparing the
solution of  tin that is  employed  in the  preparation of this
purple precipitate of gold, known by the name of  the purple
of Cassius.   It  was  described as  a solution  of tin in aqua
regia, and with every precaution to have the metal as slightly
calcined  as  possible,  and the acid completely  saturated with  JL
tin.   I shall  now take notice of  the  circumstances which Jn
must be attended to, in order have the solution of gold in
the most  proper state.   It is  found often to  fail,  when the
gold is dissolved in  a mixture of  the  two acids;  seldom,
when the aqua regia is made by adding common salt,  very
pure, to nitric acid ;  and scarcely ever, if sal ammoniac be
employed.  The greatest nicety lies in the degree of dilutiotr^vjjj
of the solution of tin.   As this  depends  on  the  oxydation '10
of the tin, it is best to determine it  by trial. Having diluted   i
the tin solution with  eighty  times its bulk  of water, put   J
three or  four portions of it into glasses, and  dilute each of   B
them  differently ;  then,  dipping a glass  rod to  a certain ■JM
depth in the solution of gold, rinse it  in one of the glasses; ^1
do the same to  another;  to a third,  &c.   Then notice in   $
which  glass the precipitate has the richest and  most beautiful
tint of purple, and dilute the whole according"to that standard.  :^
The precipitate both forms and falls down  very slowly, being
in some  degree  gelatinous.   By  lone; rest, however,  it all 
OBSERVATIONS  ON  ITS PREPARATION. 377
falls down :   and then  the clear liquor  may  be decanted
off, and the precipitate cleared by edulcoration and a filtre.
   Orschall, one of the celebrated older chemists, says, that
he obtained a very fine precipitate by means of the  fuming
.liquor of Libavius ;  also by means of a solution of tin with
corrosive sublimate made by deliquescence ;  and a still more
beautiful precipitate than what tin can produce, by means of
mercury dissolved in aqua regia.
   But Orschall  knew only the  preparation of the  enamel
colour, which has great body, as the painters call it, but little
transparency.  The transparent red and purple  is of great
value for staining glass.   It is made by diluting the  purple
of Cassius with pure crystal or glass.   This is a preparation
still more  capricious and uncertain.   Frequently the glass
has no colour whatever.   But if a rod of  such glass be made
red hot, and held in  a  smoky flame of  wood,  it becomes
purple in an instant.   But this is merely superficial:  and
if the glass is  to be  formed  into  any  other  shape,  the
colour vanishes  in  the working,  and  it again  requires  the
assistance of the oily flame.  This is called Jew's glass.
   Neuman says, and Dr. Lewis confirms it  in his notes, that
the preparation of the purple precipitate never  fails, if made
by simply  putting pure tin  into the solution of  gold  greatly
diluted.
  ^jffargraaf has published, in the Mem. Acad.  Berlin, 1779,
a series  of most judicious experiments for  determining the
best process for this valuable precipitate ; and  I refer you to
him for farther information*-  I must observe, however, that
our artists call the purple of Cassius a tender colour;  because
 a considerable heat makes it transparent,  and therefore of a
different tint, according to its thickness on the ware.   It does
 not suit enamel, therefore, so well as  staining of  glass ;
 because the  other colours by copper, cobalt, &c.  require much
 higher heats in order to bring them to their full colour ;  and
 are therefore melted several times in crucibles before they
 ure ground to powder for the painting in enamel.  Even then,
 they require  more heat than the  purple of Cassius bears
 without ri:]c of  losing its body.
yoi.. 11 j. 
378      GOLD....WITH INFLAMMABLES.
             Inflammable Substances with Gold.

   Sulphur, which unites  so readily with most of the other
metals, cannot be combined  with gold.   But if we first join
the sulphur with a fixed alkali, equal in quantity to  the sul-
phur, the sulphuret thus  fbrmed, if applied to gold in thin
plates or leaves, and in the way of fusion, very readily com-
bines with it, or dissolves it.  And if the compound be im-
mediately poured out of the crucible, and soon after dissolved
in water, a part of the  gold  will be dissolved along with the
sulphuret, while the rest remains in the state of a very subtile
powder.   Dr. Stahl had a notion that this process, which is
certainly an ancient one,  was known to Moses, and was prac-
tised by him when he made  the children of Israel drink the
golden  calf.  It is indeed true that this potion is  extremely
nauseous,  having a pungent bitterness not  to be  felt in the
similar preparations of  other metals.
   The  effects of  alcohol, sether, and aromatic oils, on the
solution of gold, have been mentioned already.
   The only other inflammable substance remarkable for its ef-
ffects on gold, is phosphorus, the powers of which, with respect
to metals in general, have been ably investigated by M. Pelle-
tier.  When thrown into melted gold, a certain quantity unites
with the metal, forming a phosphoret  of gold, which is more
fusible  than the  gold  by itself.   But  if  the   compound
remain in  the fire, and  air be admitted,  the phosphoruses
gradually burnt, and changed intcvacid, which separates from
the gold.                        *£

               Relation of Gold to other Metals.
                                   y
   Gold may be mixed with any of the other metals;  and it is
by the admixture of some of these that it is made to appear of
those different  colours  which are seen in  the inlaid  gold  of
trinkets and toys.   Copper inclines the colour of gold to red;
silver makes it-pale ; and if the silver be one to four of the gold,
a greenish hue is produced.  Pure gold is a full yellow.  The
Venetian chi quin  has  the sichest  colour  of any   gold; and
the art  of giving  it this  high c. lour  is  kept a secret in the
mint of Venice.  I made  a piece of fine gold acquire the  same 
                    GILDING  OF METALS.            379

     colour, (but it was only superficial) by keeping it long  red hot
     under charcoal du*t.
       In its pure state, it is thought too soft and flexible for making
     toys and utensils, or coin.  And the general practice is to add
     some  of the  other  metals, which give it more  stiffness and
     hardness.   This addition is named the alloy of  the gold.   It is
     commonly  silver  and copper, of which one  part is added  to
     eleven of the  pure  gold,  for the  standard of Great Britain.
     One  pound avoirdupois  of.  standard gold,  is worth 5&\\\l-
     Sterling.....1000/. Sterling weighs  (avoirdup.) 7 pound 9 TV/is
     ounces.
       In  speaking  of the quantity of alloy in gold, the term carat
     has been used.  A carat is the twenty-fourth part of a mass of
     gold,  great or small: And each carat is subdivided into twenty-
     four  parte, denominated grains.  Our coin then  is of  twenty-
     two carats.
       The relation  of gold to quicksilver, and the art of gilding
     metals founded on it, has been noticed already in  treating  of
I    quicksilver.
1      Other methods are practised for gilding, in  which mercury
     has no share.  As almost all the metals precipitate gold from its
Br   solution, and precipitate it in the metallic state,  any of these
|    metals, put into a solution of gold, will be immediately cover-
*    ed with the deposited gold.   This covering will rarely be made
i.    to adhere ; because the surface of metal which we would gild is
 Ky$xydated.   But,  by methods resembling  what I  described for
 MT whitening or tinning pins,%ie pure  metals may  be applied  to
m-  each other; and then the burnisher makes them adhere, spread-
K.   ing,  at the same time, the gold over the parts where none was
W   deposited.  The best of these processes are kept secret by the
|    possessors.  There is a family at Nuremberg, which has pre-
I    served one a secret for upwards of two centuries ; and their
^    gilding, even on  the most common work, has a solidity and
     richness of colour that  is  not equalled by any other artists  in

       There is a still more simple way of slight gilding.   Linen
     rags,  soaked in the solution  of gold, are burned  t® ashes.  A
     smooth cork, superficially  charred, is wetted and dipped among
     the«e ashe*: and then  rubbed carefully over the piece to be 
380   TRIALS OF GOLD. ..CEMENTATION.

gilded.  The reduced gold among the ashes is thus pressed on
the work so  as to adhere ; and by going over it several  times,
it is completely covered ; and bears to be rubbed very hard with
a fine linen  rag, strained  on a bit  of cork.   This gives the
work  a fine polish,  and great brilliancy :  and is pretty durable
on the inside of cups, and other situations which do not require
often  scouring.
  You must have often  heard the terms  of  tried gold,  and of
the trials of gold.  These are trials, or processes, by which wc
can assure ourselves whether a metal  which  resembles gold be
gold or not;  and if it be gold, whether it-is pure or alloyed: and
if alloyed, what proportions of pure gcJd and of alloy it contains.
The operations which have been long  n common  use for these
purposes are five in number :
  1.  The use of  the touchstone,  (lapis lydius.)
  2.  Cementation.
  3.  Refinement with antimony.
  4.  Cupellation with lead.
  5.  Parting, or the depart.
  1st, The touchstone shews whether a metal be gold or not;  -
and if gold, of what fineness nearly, by needles.   The piece of  1
gold  is rubbed on  a  black stone of the jasper kind,  having a
fine  siliceous grain and argillaceous cement.  Some  of the
hardest of the antique,  or  of Wedgewood's  black pottery, an-
swers the same purpose. The metal leaves a trace  on the  stone.
A set of touch needles are made, ^consisting  of gold,  with va,
rious  proportions of alloy.   The tryer makes a stroke with one
of the needles close by the one made by the metal under trial;   \
and changes the needle,  till he has got a stroke exactly like it.
Thus  he  judges of  the  proportion.  To be more  exact, he
draws over both strokes a pencil dipped in aqua regia.   This
dissolves all the gold, and leaves the silver.   The  proportion of  •
alloy  in thus more clearly seen.                                A
  This method will not detect adulteration, when the piece has
been  cemented in the manufacturing.  This  makes it fine su-
perficially, though internally base. If the stroke shew very fine
gold, we may be almost certain that the piece has been cemented.  (
  . 2d, Cementation is seldom used, as requiring repetitions.
Although a small quantity  of base metal,, conceakd in a large 
CUPELLATION....PARTING.        381
quantity  of gold,  is thereby shielded from the acids acting  in
the hunHd way, they cannot resist their action in dry burning
vapours.  Therefore adulterated gold, being first laminated, is
stratified with a mixture of calcined martial vitriol and nitre,  or
common salt,  (not both,) and a quantity of powdered brick, and
exposed  to  a cementing heat for  some hours.   The piece is
taken out, melted, and again laminated, and again  cemented,....
" seven times tried in the  furnace."   By each operation, part
of the base metal is destroyed.
   3d,  Crude  antimony  is  more frequently used.  It is better
than  pure  sulphur ; because pure sulphur is too  volatile, and
metallic antimony washes down the gold.   But the crude anti-
mony absorbs and scorifies all the baser metals.
   4th, Cupellation is still more  frequent as a means of purging
the gold of copper, and all baser metals: and an addition of
silver facilitates this operation,  and makes it more perfect.  If
there be no silver in the mixed  metal, the  gold retains,  in the
end of the cupellation,  a small portion of  copper, which it de-
fends from the action of the lead and heat.
   5th, But after thus cupelling  the gold with this admixture of
silver, we must have recourse to  the operation of parting, to
have the gold pure.  This parting  is the separation of the gold
from the silver, performed by aquafortis, or aqua regia.  Aqua-
fortis is commonly employed: and the use of it is quite simple
and easy.   I shewed you an example when I dissolved silver in
aquafortis.  The small portion  of gold which the silver con-
tained, remains undissolve, and retains its shape: and it needs
only  to be boiled with a little fresh aquafortis to make it quite
pure ; for if this be not done,  it retains some of the silver.  In
 order to enable the aquafortis  to  act properly on this metallic
 mixture, there must be at least twice as much of the silver as
 of the gold, and the aquafortis  must be sufficiently strong.  It
 is also usual to reduce the metallic mass into small grains  and
 fragments, by melting it, and pouring it into cold water.  This
 is done to increase the surface of contact between it and the
 aquafortis.  Or if we have but a small quantity of it, as in  as-
 saying,  it is rolled out into a thin plate,  between two small stee,
 rollers: and this plate \* twisted into a spiral. 
382      GOLD....DIFFERENT PROCESSES.

  When the mixture contains more gold than silver, in the pro.
portion of two to one at least, we may use aqua regia til separate
these two metals.  It will dissolve the gold,  and leave the silver
at the bottom, in the form  of muriatic silver.  The solution of
gold being then carefully separated  from the silver, the gold is
commonly precipitated withs6lution of quicksilver in aquafortis.
This occasions the gold to  fall in the form  of a dark-coloured
powder, which, after it  is  well washed, is  easily melted into a
mass with a little borax.
  There is another method of refining gold, which is now com-
monly practised, when the gold contains a small quantity of al.
loy only,  and that of such  a nature  as to deprive it of toughness
and malleability, such as  iron, tin, brass,  or any ot the semi-
metals.  The method I mean is, to melt it, and add to it re-
peatedly, while in fusion,  small doses of the corrosive muriat
of quicksilver,  until  it  is fine or  tough.  This corrodes  the
alloy, and soon  brings  it  to the surface  as a scoria,  where it
works off.
   When a small proportion only of gold is contained in a metal-
lic  mixture, the processes for extracting it are often different
from those already described.   In general  it is separated from
all other metals, except copper,  in the same manner as silver
is extracted from them.  But when the gold is contained in cop-
per,  it cannot be extracted by the  same operation which serves
for extracting silver from  copper;  which is the  addition of lead
 and the eliquation of the lead.   The gold is not brought out by
this process.   It has  a stronger attraction  for  copper than for
 lead.  A successful method was, however, discovered in Ger-
 many, which was very profitable to those who practised it first:
 and it still continues to be  the best method  for extracting a little
 gold from metallic copper.  It is  done by melting the copper
 with sulphur and  lead  at the same time.   The copper,unites
 with the sulphur, and is thereby disposed to quit the gold to the
 lead.  The  process  is described in Lewis's Commercium,  and
 Cramer's book on Assaying.
    A somewhat similar process, by which gold was extricated
 from silver that contained but a small quantity of it, had long
 been practised before the chemists thought of employing it in the 
         GOLD....ITS  NATURAL HISTORY.      383

ease of copper.  Cramer describes this process with  silver very
particularly.

                    Natural History of Gold.


   It must be aknowledged, that gold, though it be not the most
useful of  the  metals, has  some admirable qualities.   Its rich
colour and lustre,  which are never obscured with tarnish or rust,
and its astonishing extensibility, which enables us to employ it
in the embellishment of the works of art at a very moderate ex-
pence,  are one foundation for the value that is set on it.   The
principal cause, however, of the high price of gold,  is the diffi-
culty of procuring it.  And yet there is more of it produced by
nature than is commonly imagined.   But it is generally dispers-
ed through such immense quantities of other matter,  that it can-
not be collected without great labour and expense.
   The  Spanish and Portuguese parts of Arryerica, and some
parts of India and Africa, afford the largest quantities of gokL
Amazing reports  have been published of the abundance of this
metal in some of the Spanish possessions in America; but these
reports  are published in late accounts of some newly  discovered
places where gold has been found, and the accounts of such new
discoveries are  commonly amplified.*

   * Some  parts of the  new kingdom of Grenada (which is a high inland
country east of the  Andes, and in the north end of South America)  are
rich in  gold, which  is all washrgold.  On a rising ground near Pamplona,
single labourers have colIected*s"m a day what was equal in value to  1000
pesos, or to 2251.  Sterling =  57 ounces 4 drachms 42 grains% A late go-
vernor of Santa Fe brought with him to Spain a lump of virgin  gold esti-
mated to he worth 70401. Sterling. (The weight of it must have been about
189 ounces, or 23 merks- and 5 ounces, even supposing it gold equal in pu-
rity to English standard.)
   At  Cineguilla, in  the province of Sonora,  the Spaniards  found a plain
fourteen  leagues in extent,  in which they found wash-gold at the depth of
only sixteen inches, the grains of such a size that some of them- weighed
nine merks, and in  such  quantities,  that in  a short time, with  a few  la-
bourers,  they collected 1000 merks  of gold in grains,  (equal in value to
31,2191. 10s. Sterling) even without taking time to wash the earth that had
been dug, which appeared to be so rich, Ah at persons of skill computed that
it might  yield gold to the value of a' million of pesos ,- which is equal to
225,0001. Sterling.  In one place, called the Mine Tccorata, in  Cinalod, they 
384        GOLD....PERFECTLY  METALLIC.

  Wherever gold occurs,   it is  found much  more  commonly
in its metallic state, and nearly pure, than in the state of an ore.
This is probably a consequence  of its having no attraction for
sulphur, and very little for arsenic, and of its resisting the action
of the mineral acids.  I believe all the gold collected in America
and  Africa is  found metallic, and uncombined with the com-
mon mineralizing substances.  But  in Europe there are some
mines which yield ores,  containing  a  small quantity of it.
These ores are not, properly speaking, ores of gold.   They are
ores of other metals; but the small quantity of gold  which they
contain along with the other  metals, occasions their being con-
sidered as ores of gold.  In Hungary, a considerable quantity
is extracted from some ores of quicksilver,  and from a pyrites
of iron and sulphur.  In the Hartz forest in Germany,  there is
an ore  which affords zinc,  and  lead, and silver, and  a small
quantity of gold.  And both there and in other  parts of  Europe,
there is found in some places a  black sand,  like small grained
gunpowder, which is an ore of iron,  and contains some gold.
  In some of  those ores,  it  is either  intimately combined and
mineralized with the materials  of which the  ore is principally
composed ; or, if it be in its metallic and pure state, it is in such    j
minute atoms, that it is not discoverable by vision until it be   • ]
collected  together by itself.   There  is reason,  however, to be-    j
lieve that it is always in this state.  When the Hungarian pyrites
is dissolved with aquafortis, it is  said that the gold is left by
that acid in the form of minute atoms, and fine films, which are
in a metallic state.  And as this pyrites varies much in the quan-
tity  of gold it  contains, and  some of it does not contain any,    (
there is reason to believe that all the  gold in  it, is metallic and    ;
pure, and only dispersed through it in very minute films not mi-
neralized.  However that be, by far  the greater part of the gold
which is  collected indifferent quarters of the v/orld,  is found    jj
free from mineralizing substances,  and nearly pure;  or con-   "M
tains only some silver,  and sometimes a little iron or copper,    i
And this virgin  gold, as it is, called,  is found in two states or****

found a grain of gold 22 carats fine,  which weighed 16 merks 4 ounces 4
ochavas.  It is now deposited in the  royal cabinet at Madrid.  This grain
is worth 498y^!. Sterling. 
GOLD....WASH  GOLD.             385
   conditions ; that is, either in the solid veins of the mountains,
   in which it seems to have been originally formed, or deposited
   by nature like other metals, and from which it is in this case cut
   out by mining in the usual manner,....or mixed  with the  loose
   soil and  rubbish, on the surface of such mountains, or in the
   plains that are below them, or near  them.
      In the first of these states (I mean in the original veins) it is
   found but rarely. By far the greatest part of it is collected from
   among loose  soil, and gravel, and  sands,.,..especially from the
   gravel and sand of brooks in some mountainous countries, and
   from the soil which is near to such brooks.   Also in the soil of
   plains formed by the rivers into which such brooks empty them-
   selves, and in the sands of such rivers.
      And when we examine the gold found in these different places,
   we find reason to be satisfied, that it is brought down from the
   mountains by the gradual and long continued actionof water and
   the atmosphere on the materials through which  it is dispersed.
   The proofs  of  this are, that the nearer to the mountains it  is
   found, the grains  of it are in  general  so much  the larger, and
   the rougher or less  wofn;....while such of it as  is found at  a
;   distance  from the  mountains, or from  the highest parts of the
   country, always consist of grains smaller in their size,  and evi-
L  dently smoothed on their surface, and worn by the attrition they
£ have sustained  from the sand and gravel, during the great length
Jff- of time required for their being brought down so far. You have
V-'  examples of this general fact in the gold which  is found in the
av; sands of some of,the rivers#ff France,  of which an elegant and
h  entertaining account is given by Mr. Reaumur  in the memoirs
}  of the academy for the year 1718.
      We have also an example of the same fact in Scotland.  Gold
[,  is found at  Lead  Hills, and  in a district there  called Ettrick
I  Forest.   The gold  is all in the form of small grains, dispersed
I through  the gravel of the^brooks, and in/the  soil that is near
   them.   It was  thought an object of  value a.long time ago, when
   gold was dearer than now: and great numbers of  hands were
   employed in collecting it.   From some registers, it appears that-
   in one'year 48000/. sterling value of this gold was coined in the
   Scotch-mint.  The grains are in general the larger and rougher,
          VOl.. Tit.              3 C 
386      GOLD DUST....HOW  FORMED, he.

the higher up the country they are found.  The  farther we
descend, they are more dispersed  and of a smaller size, and
more worn and smoothed.   The same thing also was observed
by Baron Born  in  Hungary and Bohemia.  ^This points out
very  evidently from whence this  gold comes,  which  is thus
found in the soil, gravel, or sand,  of these particular districts
or rivers.   And there cannot be a doubt that the gold which
has been lately found  in  Ireland has had the same origin.  In
those hills that confine the valley and the brook around which
it is found, there are certainly mineral veins containing gold.
And they cannot be far distant, if I may judge from a specimen
I saw of the gold grains.  They are so rough, and have so little
appearance of being worn, that they cannot be far removed from
their original veins.
   From the manner in which gold  is deposited in sands, 8cc. it
will often appear to be accumulated in particular soils and sands
 into much richer collections than what can be found in the veins
themselves from which it descended. The deposits of this kind in
 some of the lately explored districts of Spanish America, as they
 have been described by the visitors,exceed all belief. According
 to some of them, a man can  gather to the value of 200/. sterling  .,
 in a day, by washing the common  soil in some of the valleys.
 The soil in which  it is found must be considered as the relics
 of the rubbish of mountains, deposited  upon mountains which"*
 have been demolished and  washed  away.  One of the strong
 proofs of  the great antiquity of this globe  is the considerable
 quantity of  gold found in the soils and sands of some districts.
 It is a clear proof of an operation  or process which  must have
 required a length of time that  is far too great for our compre-
 hension.                           "1,1;*           ' ^
   The  size of  the gold grains  is ejs?fremely various.  The
 greatest part of them are very small; some as large as the seeds
 of apples, and some touch larger.  The grains of the Irish gold
 are uncommonly large.  Reaumur  reports that  a  piece was
 shewn to the French Academy, said to weigh 56 marks, or 448m|
 ounces.  Feuillee  says he saw one in the cabinet of Antonio
 Portocarrero,  which  weighed  upwards  of 66 marks.  Both
 pieccswere a§sayed, and found of different fineness in different 
                GOLD....HOW  OBTAINED.     •      387

  parts of the mass.  One was of 23£ carats, 23, 22.   The other
  of 22, 21, 17-*-.  It is, however, rare to find pieces one ounce in
  weight.  The largest in the British Museum is only 15 penny-
  weights.  In Chili 5000 pound weight of the richest ore yields
  only 12 ounces, which is not quite one grain per pound.  Ore is
  wrought there without loss, if it contain one-sixth of this.   On
  the coast of Guinea, a man can gain seven shillings sterling per
  day by washing the common sands on the river banks.  From
  half a ton of the richest part of the soil at Lead Hills, washed
  under my inspection, the produce of gold was ll£ grains.
     In this manner, therefore,  is gold separated from its original
  matrix, and collected in certain places by nature.  It remains to
  describe how man provides this metal for himself, by imitating
  more or  less,  or  by completing this operation.  This descrip-
  tion will be extremely short; because the account already given
  of the peculiar properties of this metal, and  of the state of its
  ores, and of the  operations in metallurgy, requires  nothing but
  general indications of what is to be done.
     The  first operation  is an imitation of nature.   The native
  gold being  in small grains, either among the sands and gravel,
  or perhaps bedded in the stony  matters,  the  whole is pounded
  by mills: and then the sand so formed is agitated with much
  water  in buckets, or baskets, or  cisterns, by  stirring it  with
  rakes; and by a  sleight of hand, acquired by practice, the
  lighter sand,  occupying the upper part of the water, is dashed
  over the brim.    The  gold particles remain with  the heavier
rJ sand.  This is also dashed over,'after stirring: but it falls on a
 " long sloping table covered with rug.  The stream carries the
  lighter particles  over all the rug, and off the table. The heavier
  matter sticks in  the Ktg^i; and a few grains of gold are found
  towards  the upper end'of it.  These are shaken or  washed off
  from time to time, and added to the heavie^ particles which re-
  mained in the baskets  or cisterns.  Thus all the grains are at
  lagrcollected; but along with them much baser metals, or their
* ores, which are  also very heavy.
     The next operation is roasting this dust, to drive off-sul-
  phurous and arsenical matter which is  combined with  the.
  base metals. 
388         GOLD....HOW  OBTAINED.

   The whole is now triturated in tubs  with a quantity of
 mercury, which dissolves the gold  and silver,  and forms an
 amalgam.    This operation is expedited by adding a quan-
 tity of water and of common salt.   The  water facilitates
 the  labour, and also assists the mercury in throwing out the
 base metals.    The  common salt decomposes  the vitriolic
 salts which  were produced by the roasting and burning of
 the  sulphur.
   In the next place, the greatest part of the mercury is se-
 parated,  nearly pure,  by squeezing the  whole thin  paste
 .through porous leather.  The firm mass which remains con-
 tains all the  gold  and silver, and a good deal of mercury.
 The lact is got off by distillation.
   The last operation is the separation of the silver from the
 gold, and the refinement of  both, by such of the processes
 already described as is suited to the proportion  of the two
 metals, and the impurities wkh which they may be tainted.
   And when the  gold is found combined with the ores of
 other metals, that is, when ores of other metals  are treated
 for  the gold which they contain, processes must be employed  j
 for  scorifying these metals,  in one way or another, whether A
 by sulphurating them, or by lead till the gold  and silver are-  v.
 left  alone, to be treated  as now mentioned.   For  a  mo rested
 particular account I must refer you to Agricola, SchlutterH
 and  Born.


   GENUS  XV.....PLATINA, OR  PLATINUM.

   This metal was first brought to England in the year 174SJ jfl
 or 1750,  by Dr. Brownrigg,  who presented it to the Royal
 Society.  He  had received it from  Mr. Charles Wood, assay ^
 master in Jamaica, who told him it came  from some of  the
 Spanish province? in America;  and that it had several of  J
 the  qualities of gold, in consequence of which it was very dif f-^
 cult to separate it from that metal; and that the name given*
 to it by the Spaniards was  platina or platina  del Pinto,  and
 Juan bianco.    Platina is the diminutive of  Plata, silver :
 and  Pinto is supposed to bej the name  of a mountain, or river,
 or person. 
PLATINUM.
389
r*
  Soon after it was known in England, specimens of it were
brought to  other  parts  of  Europe :   and the attention of
many chemists was engaged by it.    They made many ex-
periments, and wrote dissertations on this metal;   of which
we  have examples in those published by Mr. Lewis in the
Philosophical  Transactions for the years 1754 and 1755, and
in  his  Commercium  Philosophico-technicum;  Mr.  Scheffer's
paper in the Transactions of the Swedish Academy for the
year 1752 ;  Mr.  Margraaf's dissertation in the Memoirs of
the Royal Academy of  Berlin for the year 1757, printed in
1759; and  a memoir by Macquer and Beaume, in the Me-
moirs of the  Royal Academy  of Sciences at Paris, for the
year  1758,  printed  in the year 1763 ; and many  more since
that time.
    Platinum is brought  from America, in loose grains of
the size of coarse  sand, most of them smooth on their edges
and sides, having the metallic opacity and lustre, and a dingy
white colour, not brighter than that of iron; and they are
 all attracted, more or less, by the magnet.   But,  intermixed
 with these  grains of the platinum, there are generally others
 of a smaller  size, which  are plainly iron ore, or iron sand.
 In some  specimens, also,  a few small grains of gold  are
found; apd Mr.  Lewis also  observed a little  quicksilver
 adhering to  the  gold.   Mr.  Lewis therefore conjectured
 that the platinum  is  obtained in washing some soils or sands
 for gold.
    By the numerous experiments that have been made with
 this  metal, it is  now ascertained, that in these grains it is
 intimately and strongly united with  about one-third of its
 weight of  iron,  and that it is not easily refined.    When
 rendered free  from all admixture,  it has a whiter  colour;
 and is the heaviest metallic substance known at present. Re-
 fined gold is little more  than nineteen times as heavy as wa-
 ter.    But refined platinum is twentyitwo times the weight
 of that fluid.   Even  in its natural state,  the specific gravity
 of it is  very uncommon.   It is sixteen or seventeen,  or,
 when the picked grains  are tried, eighteen times as heavy as
 water.                                        •
    When refined, it is also very malleable and ductile; al-
 though in its  natural impure state it has but a very small de-
 gree of malleability. 
 390   PLATINUM....ITS PROPERTIES, &c.

   One of the most extraordinary qualities of  this metal \s
 its resistance to the action of heat,  when  applied with  the
 purpose of melting it, without the addition of  other metals.
 Macquer and Beaume kept it in the greatest heat of a por-
 celain kiln,  and in a glass-house furnace, without  making
 any ehange on it.  The fusion of it was at last accomplished,
 however,. by Mr.  Macquer, by employing the intense heat
 of Vilette's speculum, and the great lense belonging to  the
 Academy, both of which exceed the best furnaces,  in  the
 intensity of  their heat.   Mr. Lavoisier also succeeded with
 the blow-pipe, and with  other  fuel, by employing  oxygen
.gas-
   It possesses another singular property   that of compact-
 ing or welding, by  the blows of  a hammer,  in the same man-
 ner as iron : and thus it may be  brought from the  spongy
 state in which it is left by the processes for refining,  to the
 utmost density and compactness.
   In the further prosecution  of these experiments with heat,
 and in those  that were made with solvents, platina was found
 to have the same degree of power to retain its metallic form   l
 and purity, and the same disposition to  recover them when
 lost, that silver and gold have.
   It suffers no change from the action of air and heat; nor
 is it affected by nitre  in the  fire.    Crude  platinum, or the
 grains in their natural state, are corroded and calcined  by
 melted nitre: but it is evidently the iron which they contain
 that is attacked by the nitre, and, when the platinum is onoe
 completely  refined, the  nitre has no power to  calcine  it.
 This metal also resists the calcining powers of  heat and air,
 in cupellation with lead.   It not  only  remains  unchanged,    j
 like silver and gold, while the  lead is changed into litharge,   'I
 but defends a portion  of  the lead from being calcined equal    }
 to about one-fifth of its own weight.
   Thus, by its resistance to the action of oxygen, it bears a
 resemblance to  silver and gold.   But,  upon the whole,  it "*fc
 agrees more with gold than with silver.
   It is  similar to  gold by resisting the  action of pure sul-
 phur, and consequently of the sulphuret of antimony, which
 can therefore be employed to assist  in refining it from iron.
 But the  metallic part of  the  antimony adheres to it after-
 wards very strongly. 
              GREATLY RESEMBLES GOLD.      391

     But, though the platinum cannpt be united with pure sul-  t
   phur, it can, like  gold, be dissolved by the melted sulphuret
   of potash, though not so easily.
     None of  the acids, in  their ordinary sta^e,  act on platina,
   in whatever manner they are applied, whether in their com-
   mon form,  or  that of hot and dry vapours, by cementation.
   Like gold,  it can only  be dissolved by oxygenated muriatic
   acid, or by aqua  regia;  commonly by aqua regia composed
   of  equal parts of aquafortis  and muriatic acid.  Such an
   aqua regia will dissolve about one-twelfth, or one sixteenth of
   its weight by digestion, or one-eighth by cohobation, accord-
   ing to Lewis.   It has little causticity : and it stains the skin
   an indelible brown.
      When this  solution is  evaporated for crystallization, it
   affords small crystals like grains of sand, of a deep yellow or
   red colour, and sometimes opaque.   Wherrthey are washed
   and dried,  they require more boiling water to dissolve them
   than five-hundred times  their weight.   The solution  is yel-
   low, and deposits a pale-coloured and very light sediment,
   supposed by Bergmann to be iron.
     The solution of platina shews also  very  particular pro-
   perties, when we add to it alkaline salts, in order to precipi-
   tate the platina.  Professor Bergmann made many accurate
   experiments  with it in this way ; and has  been  much more
   successful than Mr. Lewis in discovering the manner in which
f-„ alkalis act  on the solution of  platinum.    You may  see
'.  his account of these experiments in his  dissertation on this
I  metal.
>,     I shall at present mention only the most remarkable pro-
te  perties by which this solution  differs from that of gold.
W'~   1st, One remarkable difference is observed in the effect of
   sal ammoniac on  it.   The solution of sal ammoniac, or mu-
   riat of ammonia, in water, produces no perceptible effect on
   the solution of gold.   But when a saturated solution of this
   salt is adde4 to the solution of platinum, an orange-coloured
   precipitate is  instantly  formed,  wjjiich  experiments have
   shewn to be the  platinum, or \ part of  it,  combined with a
   small portion of the ammoniaical muriat.   This precipitate is
   still dissolvable, though  with "difficulty, in a large quantity of
   water. 
 392      PLATINUM....WITH METALS.

   2d, We find a difference between the solution of platinum,
 and that of gold, when we mix them with alcohol, aether, or the
 aromatic oils.   These fluids make the gold separate  sooner
 or later from the acid in  its bright metallic form.   But when
 they are added to the solution of platinum, no such effect is
 ever produced.
   3d, This solution also differs from the solution of gold, by
 the manner in which it  is affected by other metals,  or their
 solutions, particularly by the solution of the sulphat of iron,
 and the solution of tin.   Both of these precipitate gold : and
 the solution of tin, in particular, precipitates in the form of the
 fine purple for enamels.   But neither has any effect upon the
 solution of platinum.   These differences are the foundation
 of  the methods by which these two metals can be completely
 and exactly separated from one another.
   One of  the points  to which Mr. Lewis was most attentive
 in studying the nature of this metal,  was, to learn the conse-
 quences of mixing it with other metallic substances.   As it
 was not fusible alone, the only manner in which it could be
 applied to use, appeared  to be by mixing it with other metals,  ,
 which might have the power to dissolve it in the fire, and to
 unite with it, so as to form useful mixtures.   But he obtained.
no products that promise to be useful, except with copper, a
mixture of moderate toughness, extremely hard, and which
 does not tarnish ;  and with iron, a mixture of extraordinary
strength and hardness.
   Such mixtures, however, afford us the only means of manu-
facturing it.   They render  it  fusible :  and thus it  may be
moulded.  The other metals may then be  abstracted,  by  *,
various processes, leaving it  pure, but porous or  spongy.  In  *
this state  it may be compacted and rendered perfectly solid, M
by forging, and thus manufactured into any  shape.  By such  'j
processes platinum becomes  one of the most valuable  metals
that we know.
   It unites readily with bismuth ;  most easily of all whh .^
 tin, flowing very thin ;  also with lead ; and forms a metal
 which will not scorify, nor be.absorbed by the cupel.
   Dr. Lewis's principal purpose, by these mixtures,  was to
learn the consequences of mixing platinum with gold,  in dif-
ferent proportions. * 
            HOW SEPARATED FROM  GOLD.      393

      lhe reason of his having  this obje :t  in  view was, that
   the platinum  was considered  as  capable of  being mixed
   with  gold, so as to commit great  frauds  in  traffic,  without
   the possibility of detection by the common  trials  of >.l.\c
   purity of  gold, or of the quantity and nature of its al  j.
      He  therefore mixed it by fusion with gold,  in many uii-
   ferent proportions.   But,  in general, it debased the  colour
  . and the malleability of the gold so much, even when it was
   only one twenty-fourth part of  it, that he concluded that  no
   great frauds could  ever be committed  by  employing  the
   grains of  platinum  for the adulteration  of  gold.   And
   methods are  now well known,  by v/hich we can easily refine
   gold that  has  been adulterated with  platinum.  We can
   easil)' therefore detect such frauds, and learn the amount of
   them.  The best of these methods  is the one invented  by
   Mr. Scheffer of Sweden.   The adulterated gold  must  be
   dissolved  with its usual solvent, the nitro-muriatic.  And
   we must then add a solution of the sulphat of iron.   Every
   atom of the  gold  is quickly precipitated,  while every atom
   of the platinum  remains  dissolved.   We must then wait
 \i.. until  the  gold  has completely subsided :  and afterwards,
   pouring off  the liquor, we must wash the  precipitated gold
   with repeated  waters,  and great care to avoid loss.  And
   lastly, being dried, it is easily melted into a mass with a little
   borax and nitre.
      It  may be remarked, however, with respect to Mr. Lewis's
,:'•. experiments  on the mixtures of platinum with gold, that they
I?/are imperfect on this account;  he made use of  the platinum
f  in its native  state  ;  in which state  it is always mixed with
*  iron :  and  the gold which he  alloyed with platinum was
   therefore alloyed with iron at the same time.   Later experi-
   ments have  shewn that the quantity of iron in native  plati-
   num amounts to one-third of its weight.   And these metals
   are so strongly and closely  combined together, that it  is only
^* of late that methods have been discovered for separating  the
   iron.
      The  most successful methods that I have  heard  of are
   these :
      One way  is, to dissolve the grains  in  the nitro-muriatic
   solvent, and precipitate the  iron  from  the solution, with
       vol.  in.              3  n 
394  PLATINUM ...HOW MANUFACTURED.

Prussian alkali.  The prussiat of  soda is  the best for this
purpose.   This is a most effectual  precipitant of  iron;
and produces  no effect on the dissolved platina, provided no
more be used than enough to precipitate the iron.   The solu-
tion  of platina, thus freed from the  iron,  may next  be
evaporated to  dryness :  and the dry  matter,  exposed to a
violent heat, gives the platina pure.
  A second way is, after dissolving the grains of platina, to
precipitate the solution with a solution of sal ammoniac, and
then expose the orange-coloured precipitate to a violent heat,
by which the salts that adhere to it are evaporated, and along
With them any small portion of  the  iron which may adhere
to the precipitate.
   A third method which has  been practised with  success,
and  is  the cheapest,  is to refine it  with arsenic.  Platina,
white arsenic,  (or rather the arseniat of potash) and tartar,
in equal quantities, are melted by a violent heat, and form a
very brittle white  mixture,  of metallic lustre.  This is ex-
posed  to  heat and air under a muffle, which dissipate the
arsenic and the iron in vapour, leaving the platina pure, to be
compacted by the hammer.
   Fourthly,  Mr. Macquer  found  that it could  be refined
with lead by cupellation.  But a  most intense and long con-
tinued  heat is required  to evaporate the last portion of the
lead from it.   This method can only be applied in the refine-
ment of a very small quantity of it.   From a larger quantity
it would  be  impossible to evaporate the last of the lead.
(See Lewisys  Commercium Philosophico-iechnicum.)
   And lastly,  some  of Mr. Pelletier's experiments with
phosphorus point out another method of refining it, which he
says, is easily practicable.   He heated the grains of platinum
in a crucible, and  then  threw in some  bits of phosphorus.
The phosphorus instantly penetrated the grains, and  formed
a firsihle metallic  compound,....a phosphoret  of platinum.
If this compound be exposed to a strong heat for some time,
the phosphorus is gradually burnt,.and with it the iron, which
forms a scoria or slag with the melted acid of the phosphorus.
The platinum  is thus purified, but is no longer fusible :  and
it remains very spdr.gy,  with the scoria adhering to it, partly
r>n its surface, and partly in  its pores.   He therefore gives it 
 ITS  USES  AND VALUABLE PROPERTIES.  395

a strong heat, and suddenly compresses  it in that state with
the blows of a very heavy hammer, such as is employed in
the process of  refining iron.   This effectually compacts the
platinum, forces the scoria out of its pores, and makes the
parts of it unite together.*
   This method of compacting platinum, and uniting the parts
of it by percussion, when strongly heated, was first suggested
by  Mr. Beaume:  and it must be employed in every case in
which this metal is refined.   We cannot unite the parts of it
by fusion with  any heat  that furnaces can give.
   When by these processes platina has been purified from all
admixture,  it has  the colour of pure tin; is very malleable,
growing rigid by  the hammering ; but may be softened by
annealing.  In this state, its density  or specific  gravity is
from 20 to 22.
   It is  now to be hoped  that this metal will  be imported
more freely into Europe; and that the mining grounds in a
America  in which it is found will be opened  again.   The
Spanish  government at  first prohibited the collection and
importation of it, from apprehensions that it would embarrass
their commerce in gold, by giving opportunity for frauds not
easily detected.  But there is no reason  now for such appre-
hensions and precautions, since methods have been discovered
for detecting the smallest quantity of  platinum  mixed with
gold, and for easily separating these metals from one another.
And were the properties of platinum more fully investigated,
methods for working  it easily into  utensils might be dis-
covered:  and  then it  might justly be considered as one of
the most useful of the metallic substances.   Its resistance to
the action of fire, together with its incorruptibility and clean-
liness, would render it valuable for domestic purposes. The
chemists already  employ it  on account of these qualities
in  some of their nice experiments and  processes.   (See Note
66. at the end of the Volume.)

 * Would not cementation with charcoal and bone-ashes, or the stone men-
tioned in page 268, accomplish  this purpose,, without the expence of preparing
the phosphorus,... and thus afford a very easy method of manufacturing this
iiftpfu! nrMal <  iepi rott. 
I
*
CLASS  V.
OF WATERS.
   IN former parts of this course, we have had already op.
portunities to notice the important  and numerous uses of
water in the system of the  universe.
   It is  said of some of the ancient  philosophers, that  they
supposed all things derived their origin from water. And it
is  true  that the  existence of  all  the numerous tribes of
vegetables  and  animals depends upon it.   And when we
examine the  materials of  which they are  composed, water
is  always the principal part.    But  must  we  also suppose
that water  has given origin to the  more solid and durable
parts of this globe, the various earths and  stones, the rocks
and minerals of which the mountains and land are composed?
Have all these been produced from water?
   Whatever opinion we may form of the origin of these, it
is  at least certain,  that water has been the agent employed
to  give  the regular arrangement in which many of them are
found.
   The appearance of numerous relics of sea productions, and
other traces-of this fluid, are so frequent in the strata of which
this globe,  so far as we can observe,  is principally-composed,
that there  is no room to doubt that  the materials of these
strata have been  arranged  in that manner by the sea.   But
some have  rincluded from  these phenomena, and some other
facts, that water has even furnished the matttr of the  earthy
and stony bodies,....that water is actually convertible  into
earth. 
   IS WATER  CONVERTIBLE INTO  EARTH? 397

     The first author who has mentioned the convertibility of
  water  into earth is Mr. Boyle.   He writes, that a friend of
  his was in possession of three-fourths of an ounce of earth,
  produced from one  ounce of water by the action of a long
  continued heat.   And he relates some experiments made by
x himself, which convinced him that earth could be produced
  from the purest water by heat.
     I repeated Mr. Boyle's experiment, by boiling and circu-
  lating  boiling  water a lon^j time in a glass vessel luted up
  quite  close : and I  saw the appearance by which  he was
  deceived.
     Godfrey, the descendant of Mr. Boyle's  assistant, thought
  he converted  water  into  earth by triture.  Wallerius also
  relates, in the  Swedish  transactions, experiments in which,
  by triture, or agitation, or both, a quantity of siliceous matter
  was obtained from water. And Mr. Margraaf obtained it by
  distinction.
     Lavoisier's opinion is, that the earthy matter produced by
  boiling of water in glass vessels, is a part of the glass corroded
  by muriatic acid, present in all waters.
     My opinion is, that this matter is a part of the glass cor-
  roded or penetrated by the water itself, which alone has the
  power to  penetrate it, and even to dissolve it,  by length of
  time and  assistance of heat.   This  explains the form  and
  appearance of this matter, which is always in fine minute  and
  thin scales, and also the change observed in the  water, when
  the experiment has been continued a long time.  It is said to
  boil more like  oil than  like water.   This proceeds from its
  holding a  small portion of the  glass,  or of the alkali of the
  glass,  perfectly dissolved. By my observations on the Geyser
  springs of Iceland I found that water held siliceous eaith in
  solution.
     Another opinion, however,  has been lately formed with
  regard to it, which is of .greater consequence, as it enables us
  to understand and explain a number of chemical facts.  The
  opinion I mean is that  which  we have already adopted  and
  applied in former parts of  this course ; that  water is  not a
  simple elementary substance, but  a compound.
     This idea of the nature of wafer was suggested by Mr.
  Watt.  (Phil.  Trans.  17%f.J   Mr.   Cavendish, however. 
398
WATER.
 was the first who gave it solid foundation and credibility, by
 his accurate  examination of the consequences of setting fire
 to a mixture of hydrogen gas and oxygen gas, in a vessel in
 which they were confined.   Mr. Lavoisier and other French
 chemists, seeing the vast importance of this experiment in
 their  system,  immediately  repeated it, with  much larger
 quantities of the materials, and with an excellent apparatus
 and the  most  scrupulous  accuracy.   They added several
 Other  experiments, which concur to establish the opinion of
 the compounded nature of water.   They also soon  perceived
 and pointed  out the  important improvements  which might
 be deduced from this discovery in the explication of many
 chemical facts, which were thus set in the clearest light. And
 since  that time, the last finishing, we may say, has been given
 to this happy chain of experiments : and the  compounded
 nature of water has been still further illustrated, by the capital
 experiment of  the  Dutch society of chemical philosophers,
 who resolved water into its two  constituent parts,  without
 making any addition to it whatever, but the matter of heat,
 collected and condensed by electrical operations.*
    All this, however, has  been already noticed in the pre-
 ceding parts of this course.   At  present we  must confine
 ourselves  to  the   examination  of  the  variety  of waters
 found  in  nature,  and  to an account of the means which
 chemistry  furnishes  for  investigating  their  qualities  and
 contents.                                                   ,
    The natural  varieties of waters are produced by the union
 of various other substances,  in different proportions, com-
 monly very minute, with this fluid.   And it is never found
 perfectly  pure from these, though in some cases it  is  very
 nearly so.
   When  we have  occasion for water quite  pure, to  be  em-
 ployed in nice chemical operations, we  must procure it by

  * I observe some authors complimenting the sagacity of Sir Isaac Newton,
 by saying that he conjectured, from its great refracting powers, that it con-
tained an inflammable substance.  I have never met with  this  assertion bv
 Sir Isaac Newton :  and it is surely a mistake ; for the fact is, that water has
 the smallest refracting power of any liquid that we are acquainted with.  Sir
 Isaac indeed says, that the great refracting power of the diamond, makes him
 imagine that it contains inflammable matter.....editor 
      VARIETIES OF NATURAL WATERS.   399

art.   We must choose good spring water, or rain or snow-
water, collected at  a distance  from  the  smoke of many
houses, and distil it until we have got two-thirds, or three-
fourths, and reject the remainder.
   The varieties of  water found in nature may be all com-
prehended under the six denominations of
        1. Rain water.
       2. Fountain water, and well water.
        3. River water.
       4. Water of lakes.
        5. Water of marshes and shallow pools.
        6. Sea water.
   Of these natural waters, rain water, when properly col-
lected, comes nearest in purity to distilled water.  It is
water distilled by nature ; and would  be quite pure, but for
the vapours of the atmosphere.  To have it in the greatest
degree of purity of which it is capable, it must be collected
at a  distance  from the  smoke of  houses,  or other causes
which occasion vapours or effluvia to mix with the air.  The
rain water which runs from  roofs, however,  is very impure
and  sooty.   Sometimes too it has happened,  that showers
of rain have fallen  mixed with the  staminal  dust of plants,
which has been mistaken for sulphur.
   The waters of  springs and wells consist of rain water,
which has  soaked  through crevices and  the  more  porous
parts of  the earth,  until it  has been stopped in its progress
downwards,  by impenetrable  strata of clay or other matter,
and  breaks  out again in some  lower part  of  the  earth's
surface.
   The opinion which  was once formed by some philoso-
phers concerning the origin of springs, is  very absurd,....
that they are  fed  by the sea; that the sea water  filtrates
through the  pores of the  earth,  and ascends through the
interior parts of the high lands and mountains:  that the salt
is  separated from  it during this filtration ;    and that the
water breaks out at last to form the springs.  It is  absurd
to suppose that the water can ascend in  this  manner,  con-
trary  to  its  gravity, or that the salt can be separated by fil-
tration.   It is plain that rain  water  falls  most plentifully
upon the mountains and high lands: and as a  great part of it 
400          SPRING  WATERS, 8tc.
is  absorbed, and penetrates into the porous parts,of them,
it  is abundantly  sufficient  to 'account for  the origin of
springs.   And we have  a proof  from  the  experience of
miners.   The peeper they go, the less water they meet with.
   Spring water must therefore necessarily be less pure than
rain  water ; as the water may  find various substances in its
Way  through the earth, which it will dissolve and partake of.
Some springs, however, give a water remarkably pure.  Such
are those which are filtrated through sandy and gravelly soils,
or through mountainous countries, composed of  harder and
more undisodvable  stones.   Others  contain  a variety of
matters ;  and these sometimes in considerable quantity, and
of such  a nature as to give them medicinal efficacy.   For
this reason, after we shall have shortly considered the other
more general varieties of natural waters, we shall return to
the varieties of spring waters, and explain them more par-
ticularly,  with a view to point out the proper method of ex-
amining mineral springs, and for discovering the principles
they contain.
   The water of rivers is composed entirely of  the waters of
springs, and of such rain water as runs along the surface of
the ground, without sinking into it.   It is therefore various
in different places.   Thus the water of rivers which pass
through very large cities,  as the Thames does, becomes so
loaded with animal and vegetable matter, as to  be susceptible
of a high degree of corruption.   In general,  however, the
water of  those large rivers which are not exposed to such
causes of impurity, though often troubled with atoms of mud
and clay, when refined from these by r^st or filtration, are
rather more pure  and wholesome than the water of the
greater number of springs  or  wells.  The reason seems to
be, that thay are composed partly of rain water, which has
not penetrated the soil, partly of the water of springs, which,
while it runs a considerable way  along the surface to join
great rivers, becomes generally purer. Some of the principles
it  contains are volatile : a greater number are dissolved  in
the w.iter by means of those volatile  ones, and are deposited
when they  evaporate.   Whether  the. purity of river water
depends on these  circumstances or not, it is  certainly very
remarkable  in some cases. 
WATERS  OF RIVERS AND LAKES.    401
  The water of large lakes, having the same origin with
river  water, is equally pure,  except  in  a  few examples of
lakes  situated  in countries which abound with salt; and is in
general much  more transparent, in consequence of its stag-
nation, which  allows  all the muddy particles  to separate to
the bottom.   But small pools  and marshes, and other shal-
low collections of stagnating water, are in general very im-
pure and unwholesome.  The  heat of the  sun has a strong
effect  upon these, and occasions quick and multiplied suc-
cessions of animal and vegetable productions in them.  The
vulgar have been astonished and terrified at the sight of a red
colour which such waters sometimes assume, as if suddenly
changed into blood.   This arises from insects.  The putrid
damps which  arise  from  such waters in  hot climates, or
rather from the  marshes which  they  leave  when they dry
up, are causes of numerous diseases, agues, dysenteries, &c.
   The last variety of water which we enumerated, sea water,
is still farther removed from  the  state of purity than any
of the former.  Near the shores especially, it is not only
rendered impure by the muddy particles brought  into it by
the rivers, and those stirred up and kept afloat by the waves ;
but as it contains innumerable animals, these must contribute,
by their different excretions,  to its impurity.  The  admix-
ture,  however,  by which  it is the most remarkably distin-
guished from pure  water, is that of different  saline sub-
stances, which it contains in  very considerable quantity, in
 consequence of which it has a strong taste, and is totally
 unfit for the use of  man, and other land animals.
    The nature of these  salts,  and saline compounds, which
 sea water contains,  has been  investigated by different che-
 mists.
    First, Dr.  Gaubius of Levden, who made his experiments
 upon 50 pound of the sea water, and has published them in
 his Adversaria.....From 50 pound of  16 ounces Troy weight
 of sea water, Gaubius obtained,

                                           oz.  dr.  gr.
   Common salt, some of it impure          20   4    1
   Selenitc, and what he calls alumen munaticum 1   1    0
   Sal dictum  Glauberi    -    - •   -        2
    Vol.  jix-                 3 '■ 
402  SEA WATER....ITS MED.  QUALITIES.

   Bergmann examined sea water, taken up for him by  Mr-
Sparmann from a depth of 60 fathoms, in the latitude of the
Canary* Islands.   He obtained from it,

                                          02.  dr.  gr.
   Common salt     _     -    .     -    -    37   5    26|
   Magnesia muriata    -    -     -    -     10   2  ■  14
   Gypsum    ------11    44$

   He  examined it very scrupulously for magnesia vitriolata,
but found none.
   Dr. Higgins obtained from sea water of our climate,

                                           oz.  dr. gr.
   Common salt.....23   3    36
   Magnesia muriata     -    -    -    -    10   1    12
   Gypsum    ------11    44

   To  imitate sea water, suppose 50 pound of it to contain
25 Ounces of common salt, and 10 ounces of muriat of mag-
nesia.  Each gallon English will contain four ounces of com-
mon salt, and 13 drachms of muriat of magnesia; which 13
drachms, of muriated magnesia  will  probably be .contained
in 26  drachms of what is called oil of salt.
   Dr. Higgins  remarks that the magnesia salita appears to
be the most efficacious ingredient in  sea water.   The pro-
portion of it to the sea salt is as eight to 181.  And as persons
are cured of diseases by sea water, who  eat sea salt  every
day of their lives with their food, there is no  reason to im-
pute their recovery to the sea salt.
   It  is usual, therefore, in the practice of medicine, to imi-
tate sea water with a mixture of common salt and purgative
 salts  dissolved  together : and the solution may be made so
 strong that two spoonfuls, or a little more,  may prove a dose.
 But to resemble sea water, it should always be greatly diluted
 when  taken.
   Sea water proves a useful medicine in some cases, though
 taken in smaller quantities than what prove purgative.  It is
 thought, when taken in this  manner,  to have some efficacy  in
 removing obstructions and tumours of  the lymphatic glands. 
VARIETIES  OF SPRING WATER.      403
And some have imputed  these  effects to its septic  power,
whereby it dissolves concretions of the fluids/   It contains
less than Sir John Pringle's septic quantity of common salt.
But its medical efficacy does not appear to me in this light.
Putridity weakens the power of the vital or animal principle,
and increases all diseases.   I should rather impute  it to a
general stimulus, by which it promotes all the secretory mo-
tions in the body.  It  is certainly in some measure by a
stimulus exerted upon the skin, and  by  which it promotes
perspiration, that bathing in sea water has been so beneficial
in these and other diseases.
   Such is, therefore, the general  outline of the  variety of
natural waters.   To return now to the waters of springs.....
   In order to give you a general  view of the variety which
occurs among spring waters, I must, in the first place,  enume-
rate the different  substances  which  have been found  in
them by chemical experiments,  and mention some remarka-
ble qualities which some of them are known to possess.
   Thus, 1st, Some are warmer than the medium heat of  the
latitude in which they are found.
   The water of common springs always has at its source the
medium temperature of the climate  in  which it is found.
In Edinburgh, this medium temperature is 48° ;  in  London
52° ; about Paris 55° ;  farther south, higher.  But  springs
are found in many places, the heat of which is considerably
above  these  medium  temperatures:  and there  is  great
variety in respect of  this superior heat.  Some are boiling
hot ; others  scalding  hot;  others only tepid ; and so  on.
The most surprising particular in the history of these springs
is the amazing quantities of hot water which some of them
throw out, without the least apparent variation of this quan-
tity, or of the heat;  a certain proof that they  receive their
 supply of water and heat from a great depth.   Such are the
 springs at Bath.                                   . .
   The cause  of this  heat  is a  subject of many opinions.
 There are, doubtless,  chemical changes going on  in  many
 watery solutions in the bowels of- the earth, in which heat is
 extricated    But  I  cannot conceive any  such,  where  the
 result is pure water,  such as flows from  the Bristol hot well.
 In such cases,  the cause of the heat is certainly subterranean 
404    SUBSTANCES  FOUND IN SPRINGS.

fire.  No other cause is adequate to the effect: and  we know
that these fires exist, and  have existed at all times.  In agree-
ment with this opinion, hot springs are most frequent in volca-
nic countries. There are many in Italy and in Iceland. Geyser,
in the neighbourhood of Hecla, in Iceland,  emits  an immense
body of water by several openings.  Two of them are very re-
markable.   The one3  called the old Geyser,  throws out water
by a perpendicular pipe, nine feet in diameter: and it sometimes
throws the water up in the air 200 feet.  Sir Joseph Banks, &c.
saw it rise about 90; also Mr. Stanley.   Vide vol. ii. of Edin.
Trans.)  Some hot springs are  at a great distance from  vol-
canoes.  But how is subterranean fire supplied with air ? I may
answer, that water carries air with it to these fires, and is con-
verted into  air by  chemical operations ; some of which are
known to us, while others are equally certain, although our che-
mical knowledge cannot yet explain them.
   To proceed.  Beside this heat, found in some springs,  we
find also in many, as was  formerly observed,
   2do, Carbonic acid, the quantity of which is very various.
Some are so  much saturated with it, that it  comes out of them
as from some fermented liquors.   It is generally attended by
other admixtures.                                  #
   3tio,  The  fossil alkali is not uncommon, sometimes combin-
ed in part with  carbonic acid,  but much more frequently with
the muriatic.   Some authors also mention  the volatile alkali as
having occurred.  I believe, however, that if this ever happen,
it is exceedingly rare.
   4to, The sulphuric,  or the muriatic acid,  or both together,
are very often present  in  these waters:  but they  are always
combined with the fossil alkali, or with some alkaline earth, or
with a metallic substance.
   5to, The only alkaline earths hitherto discovered  in spring
waters are the calcareous and magnesia.  They are either in the
form  of carbonats, that  is,  dissolved in  the water by  means of
the carbonic  acid, or they  are  combined with the sulphuric or
muriatic acids.
   6to, The argillaceous earth is rarely found dissolved in  these
waters, but when it occurs, it is always  combined with the sul-
phuric acid. 
DIFFERENT  DENOMINATIONS, &c.     405
  7mo, Geyser is the only example known to me in which the
flinty earth is found in spring water.  It is dissolved by means
of fixed alkali.
  8vo, Of the inflammable substances, we sometimes find sul-
phur, or sulphurous gases, and more rarely,  some of the fossil
oils.  These last appear mostly in drops upon the surface of the
water.  The sulphur, when it occurs, is more intimately com-
bined or dissolved,  and this by means of fixed alkali, or of hy-
drogen, so as  to form inflammable gas.
  9no, Some  of the  metallic substances are  the last which we
need to enumerate among the  contents of spring waters.  And
no more  than two have, in my opinion,  been certainly demons-
trated in their composition,....iron and copper.
  Iron occurs very often; and is commonly dissolved in  the wa-
ter by the sulphuric acid, and sometimes, as is supposed,  by
fixed air.  Copper but rarely appears ; and is always dissolved
by the sulphuric  acid.
   Some  authors mention also zinc and arsenic as occurring some-
times : but I have not met with proofs of this. The ores of zinc
are not liable to that vitriolization by the action of air, to which
those of iron and copper are often disposed, and which converts
them into compounds of metals and sulphuric acid.  And as  for
arsenic,  though  of itself soluble in water, it does not dissolve
 without  boiling heat.  Were it ever to make its appearance in
 waters, the presence of it in their composition would be but too
 manifest by their pernicious effects.
   These are  the different substances which  have been plainly
 demonstrated in different spring waters.  And they are found in
 the different springs in great varieties of number and proportion,
 only that in general the proportion of them to the water is very
 small.   Those that predominate in any particular spring, give
 to the water particular qualities and a particular character, in
 consequence of which, the springs reckoned medicinal have been
 distinguished by physicians into a number of different kinds, and
 by different denominations, which I shall next explain.
   1st,  Those that are  warmer than the middle temperature
 of the' place where they are found, called hot  or tepid springs.....
  Thermet. 
406       NAMES OF  MINERAL WATERS.
  2d, Those in which carbonic acid predominates, so as to give
them a sourish aste, and briskness....,Acidulce.
  3d, Those that contain an alkaline salt not completely neutra-
lized with acid.....Fossil alkaline -waters.
  4th, Those which contain such a quantity or variety of saline
matters,  as render  them purgative.....Purging springs.
  5th, Chalybeate waters.
  6th, Sulphurous  waters.
  These are the general distinctions of medicinal springs among
physicians, who thus discriminate them by some of their sensible
qualities or medicinal powers.
  But some other qualities have been observed-in spring or well
waters, which have  occasioned other distinctions and denomina-
tions of them  among common observers.  Thus,
  7th, Some are  called hard,  or springs or wells of hard water.
These do not dissolve  soap well, but produce  a greasiness on
the  surface :  and they  are ill qualified for boiling  vegetables,
and  for penetrating and dissolving their soluble parts.   The in-
fusions of tea, or other  vegetables, in these are weak and bad.
They contain  a compound  of some fossil acid with  other mat-
ter,  by which it is  not so completely neutralized as  to prevent
its acting on the alkali of soap.
  8th, Some are  called petrifying xvatcrs.  They  contain cal.
careous earth dissolved by carbonic acid.   .
  9tJi, Some are  called  salt springs.  They yield common salt
with profit.
  10th, Coppery springs contain copper separable by iron.
  11th, Bituminous springs, are so called,....drops of bitumen
being commonly found floating on their surface.
  And now I have said enough to enable you  to form some ge-
neral notions of the variety of spring waters which occur in na-
ture. We shall next attend to the manner of examining them,
in order to learn which of these substances now enumerated, or
how many of them, they contain.
  In examining mineral springs,  lmo, Observe the situation of
the spring,  and nature  of the  soil and country around it, and
whether any  minerals are near it, or within  the distance of a
few miles.   They often receive some of their contents from a
mineral vein. 
 WATERS....HOW EXAMINED, IN GENERAL.  407

    2do, Observe its heat with a good thermometer, and also the
 colour, taste, smell,  and other sensible  and obvious qualities
 of the water.  Deep  glasses are the best for shewing colour or
 clearness.
    3tio, In order to thet examination of the mOre fixed ingredi-
 ents, evaporate  one or more gallons  of it with a gentle heat to
 dryness.  This evaporation may be performed, at last, in a small
 China bowl, that the extract of the water may be the better col-
 lected together, and the more easily taken out; and the bowl
 should be heated only with the steam of water.  The quantity
 of the dry  extract can be exactly ascertained by weighing the
 bowl before and after the  evaporation : and the different ingre-
 dients of it are to be investigated  by an analysis.
    We must next  investigate the materials  which compose this
  dry extract, by the application of different solvents and other
  agents, such as 1st,  Alcohol:  2d, Distilled water applied cold:
  3d, Distilled water applied hot: 4th,  Acids.  Alcohol dissolves
 the compounds  of magnesia or calcareous-earth with muriatic
  acid, but leaves untouched all other  compounds.   A moderate
 quantity of cold water dissolves  all the other saline compounds,
  except g> psum: and gypsum is  dissolved  and  separated from
 the mere earthy matter, by 500  times its weight of boiling wa-
4  ter, or that quantity of distilled water boiled with it some time.
    These different solutions may afterwards be evaporated for
  crystallization ; or  we may easily learn, by other  trials to be
  mentioned presently, what acid and what quantity of it they con-
  tain, and with what matter this acid  is joined.
    4to, A set of experiments are  to be made on  the water Itself
  in its entire state.   And they are made by adding different chc
  mical agents, which produce remarkable effects on the various
  substances which  the water contains, or are affected themselves
  remarkably by them, to such a degree that we are enabled in this
  manner to detect the most minute  quantity of these substances.
  Of these experiments  I shall mention some examples,  while  I
  describe the manner of invebtigating the  contents of  mineral
  waters. 
408         DETECTION OF  CARBONIC,
       I.....Experiments to discover the Carbonic  Acid.

   1.  Attend to the obvious qualities which it produces, viz.
briskness like that of a fermented liquor, and a pungent sourish
taste, both of which are lost by exposure to the air, especially
with  agitation.
   2.  It strikes  a  red colour with litmus, which  disappears by
exposure to the air for some time.
   3.  Lime-water, being mixed with such aerated water, preci-
pitates the lime, which will be redissolved if there be much of
the air, and if we have not employed enough of the lime-water.
   4.  To measure the  quantity, a bladder is tied to a bottle, and
the air is expelled by heat.
   This is the method which has been often practised, and which
may be practised when we cannot do better : but it is not exact.
A part of the air is very liable to escape at  those places where
the bladder is tied :  and some of  it penetrates through the blad-
der, or is absorbed by the water  with which it is  soaked.  A
more exact way is to fit a cork very close  to the mouth of the
bottle, and then,  making a  hole through the cork, fix in it a
bended glass tube.  The bottle being then quite  filled with the
water, put in the cork, and make the extremity of the bended
glass  tube dip into a cistern of quicksilver, in which stands in-
verted a cylindrical vessel,  also filled with  quicksilver.   The
air expelled from the water by heat, will rise through the tube
into this cylinder, and displace the quicksilver :  and thus it is
both collected and measured at the same time.  And in order
to learn the quality of it,  we may  apply caustic alkali, or lime
and water to it, to know how much of it is  carbonic acid gas,
which will be quickly absorbed;  and  we  may afterwards  ex-
amine the remainder.*

         II.....Experiments to discover Alkaline Salts.

   To learn, in the next place, whether or not there is any alkali
not completely neutralized with fossil acids,  or combined only
  * We may also learn its quantity with considerable accuracy, by the weight
of the precipitate which' it occasions from lime-water,....having taken care that
an excess of lime-water has been employed.  The air may he estimated at
eleven-twentieths of the dried precipitate., .editor. 
         SULPHURIC, AND MURIATIC  ACIDS.   409

  with the carbonic, we may use some of the vegetable tinctures,
  or infusions of flowers, that are the most easily affected by al-
  kalis.  The syrup of violets is that which  is commonly used:
  but I find an infusion of the flowers of .mallow more convenient.
  The colour is produced exactly the  same, whether the alkali be
  fixed  or volatile:  but  we  can easily distinguish which of the
  two it is, by a subsequent experiment with the muriat of quick-
  silver.  And if we  find it to be  a  fixed alkali, we are sure it
  must be the fossil alkali.   The quicksilver, when oxydated, has
  a remarkably strong attraction for volatile alkali,....a small por-
  tion of which unites with it in this case ; and forms with it,  and
  with a small part of  the muriatic acid, a mercurius dulcis, in-
  soluble in water.
    These  experiments, therefore, give indications  of alkaline
  salts not completely neutralized with fossil acids.  But if alkalis
  be present, combined  with one or  more  of these into neutral
  salts,  they are best discovered and  distinguished by examining
  the extract of the water  obtained by evaporation,  and the  dif-
  ferent saline  compounds into which it can be analysed.

         III.....Experiments to discover Sulphuric Acid.

    This is often  present, combined with  some other matter.
'  With whatever substance it be combined, it can always be de-
  tected by the muriat of nitrate of barytes, the barytes having
  the  strongest attraction for the  sulphuric  acid, with Which ir
  forms- a compound insoluble in water.   To make this experi-
  ment quite satisfactory, however, we must add a small quan-
  tity of nitric or muriatic acid,  perfectly pure, or free from sul-
  phuric acid;  for the barytes m>y be precipitated by a carbonat
  of alkali.   But if this happen, a small addition of pure aqua-
  fortis will redissolve it.
        IV...'..Experiments to discover the Muriatic Acid.
   This acid  can as certainly be discovered by the solution of «
 silver with excess of  acid.
   We do not learn, however,  by these trials, what matter these
 acids are combined with :  but  this appears,  either from some of
 the other trials we have to mention, or from the examination of
 the fixed m ..ter obtained by evaporation.
     VOL. III.                 "3 * 
410           DETECTION OF EARTHS.
  I observed before,  that these acids are hardly ever found in
the waters in a non-saturated or pure state ;  though this is said
by some authors, who have probably been imposed upon by the
taste and qualities of  the acidulae or aereal waters.   But turnsol
would detect them.
         V....-Detection of Earths in Mineral Waters.
  Earth,  wdien present, is  seldom  any other than  calcareous
earth,  or  magnesia,  or  both, combined  with  some  solvent,
either carbonic acid, or some of the fossil acids.  I have always
observed,  that in the  waters containing those carbonats, there is
also a quantity  of  the earth combined with some other of the
fossil acids.   The part dissolved by carbonic acid, is discovered
by boiling the water in a clean vessel.  The acid is expelled,
and the earth  precipitates.
   Bergmann says that '.he calcareous earth, suspended by aereal
acid, soon separate's  from the water by moderate boiling; but
that magnesia, in  the  same state, separates gradually, during
the whole time that the water is boiled or evaporated to dryness.
Water fully impregnated with  carbonic acid will dissolve more
than one-fortieth of its weight of  magnesia, every ounce hold-
ing above twelve grains.  The tufa formed by the evaporation of
such waters, has been generally considered as calcareous:  but
it always contains magnesia, and sometimes a great deal. Strata
of limestone  are  met  with, containing so  much that they are
unfit for manure,  and even pernicious.  This is the casein the
neighbourhood of  Doncaster.
   The nature of the earth which separates in this manner isde.
termined by combining it with the sulphuric acid.
   There is another method,  better fitted for detecting the small-
est quantity of earth  suspended by means of carbonic  acid-
This is done  by dropping into the water some solution of the
acetite of  lead.  The lead is  precipitated, and  the earth sus-
pended by the acetous acid.   But as the lead would also be pre-
cipitated  by a sulphat, we  must  add some more acetous acid.
This will redissolve the lead, if it has been separated by means
of  an earth.   But observe that saccharum saturni does not shew
a small quantity  of  earth, if  there  be much carbonic acid in
the water. 
              DETECTION OF  EARTHS.           411

  When the earth present in water is dissolved by some of the
fossil acids, it  may  be separated by carbonat of fixed alkali,
which however is best  added after the water has been evapo-
rated to one-fortieth, or one-fiftieth,  or rather after it has been
evaporated to dryness ; the soluble parts of the residuum being
redissolved with distilled water,  and the alkali added to this so-
lution".
  The nature of the earth is determined, 1st, By distilled vi-
negar applied  cold,  which will  dissolve  calcareous earth, or
magnesia,  but not argillaceous earth.
  2dly, By  sulphuric acid, which precipitates the  calcareous
earth from the vinegar in form of gypsum,  but with magnesia
forms a soluble compound.
  Professor Bergmann also recommends the oxalic acid, or the
acid of sugar,  as a means for detecting the smallest quantity of
the calcareous earth in particular, and in wha ever manner it be
dissolved.   It is sure to unite with this acid,  for which it has a
much stronger attraction than for any other, and always forms
an insoluble compound.  And this is perfectly true.   The preci-
pitation, however,  is not so quick, or  so remarkable, as in some
of the experiments already mentioned, especially with the ace-
tite of lead.
  If there be any  siliceous earth dissolved in the water, we
shall  be sure to find it in the matter which the water affords
when evaporated to dryness.   After  we have extracted the sa-
line  compounds and salts from that matter by alcohol, and by
distilled  water, applied  first cold, in moderate  quantity, and
afterwards  hot, in large  quantity,   mere earth will remain,
which must be treated first with distilled vinegar,  which will
dissolve calcareous earth or magnesia; afterwards with some of
the fossil acids, which will dissolve  the argillaceous earth, if
there be any.  But if a quantity of  tender, light and spongy
earth remain, on which the acids produce no more effect, there
is  reason to think that it is siliceous: and we can assure our-
selves that it is such, by mixing it  with  an equal weight, or
one-half of its weight, of dry carbonat of soda, and  heating
this mixture strongly with the blow-pipe in a platina spoon.   If
the earth is  siliceous, it will melt into glass. 
412          DETECTION OF SULPHUR.
                  VI....Detection  of Sulphur.

   Having now shewn the means for discovering the presence of
 salts and  of earths, in the composition of mineral waters, the
 means for detecting the presence of sulphur are next to be de.
 scribed.
   Sulphur has been found in two states in sulphurous waters:
 1st, Either  combined with an alkali, and forming an alkaline
 sulphuret, (this I believe is exceedingly rare) :  or, 2dly, In the
 state of a sulphuret of hydrogen, or sulphurous hydrogen gas,
 which, you know, is soluble in water.
   The nature of this compound was first investigated by Pro.
 fessor Bergmann.   He also shewed that  it can be prepared by
 art,  and so combined with water as  to form a sulphurous water
 of this volatile kind.
   The indications of a sulphurous mineral water are,
   1st, Odour of hepar sulphuris,  perceived on approaching the
 spring.  This  is a sure and nice indication.
   2dly,  A common  trial  is to put a piece of  silver into the
 water, which is quickly tarnished and  blackened.   I  find that
 other metals  are fitter, e. g. lead is quickly blackened.
  '3dly,  A mark made with acetite  of lead, or  tartrite  of bis-
 muth, on  paper, is exceedingly  effectual and sure.   A  true
 hydro-sulphuret, dissolved in water, (that is, a volatile sulphu-
 rous water) blackens these substances very speedily, even when
 brought very near them ; and they do this without suffering any
 decomposition,  indicated  by milkiness or turbidness.  But a
 sulphuret of  potash or soda dissolved in water, though it black.
 ens these substances as quickly, is always  decompounded by it.
 To learn the quantity  of the sulphur,
   Imo, If any part of the sulphur is  dissolved in  the water, and
 kept suspended by an alkaline substance, a little of the sulphuric
 or muriatic acid will precipitate the sulphur, which, being after-
 wards collected on a filtre, can be weighed by itself.   But these
 acids never  precipitate  the  whole  of  the sulphur  from such
 waters; a part  of it being combined with inflammable air, and
 dissolved in  consequence.   And many waters have all the sul-
phur which they contain dissolved  in this form.   In this  case 
SULPHUROUS WATERS.           413
 the sulphur cannot be precipitated by diluted sulphuric or mu-
 riatic acid.
    2do, But we have other acids that can precipitate the sulphur
• in this case, and  these are the  strong red nitrous acid, and the
 sulphurous acid.   The first was, recommended by Bergmann,
 and the second by the French chemists.   This precipitation  is
 supposed  to'be produced by the action of the oxygen of the acid
 on the hydrogen of the gas.  These two principles unite  toge-
 ther to form water, and the sulphur, when thus left alone, is not
 soluble in water.   But there is  a difficulty attending this account
 of the matter: for, if it be well  founded, we cannot find a reason
 for this inefficacy of the nitric and sulphuric acids to precipitate
 the sulphur equally well, or better, as they contain more  oxygen
 than the nitrous or the sulphurous acid.  Moreover, when the
 oxygen is taken from the sulphurous acid, why is not the sulphur
 which that acid contains precipitated also, along with that of the
 water?  As this does not happen, Mr. Berthollet and Fourcroy
 suppose that only a very small  portion of oxygen is taken from
 the sulphurous acid, or supplied by it: and accordingly, when the
 water is  examined after the precipitation of the sulphur, the
 sulphurous acid is found still existing in it.
    3tio, Several metallic oxyds also can be employed to attract
 the  sulphur  from  these waters,....cerussa,  or white lead,  for
 example.  Litharge also has the same power, and the oxyds of
 quicksilver, and some others, particularly white arsenic.  These
 oxyds act partly by their oxygen, which unites with the hydrogen
 of the gas, and partly by their own attraction for sulphur.
    4to, -Some solutions of  metals in acids are still more conve-
 nient  indicators,  as they enable us to  ascertain the quantity of
  the sulphur.   One of the best for this purpose is the solution of
  muriat of quicksilver.  An aethiops, or sulphuret of quicksilver,
  is produced, from which we can easily separate the quicksilver
  by acids, to have  the sulphur pure ; or we can first weigh accu-
  rately  the precipitate,  then revive the mercury,  and, by the
  quantity of it, know how much  sulphur was joined with it.  You
  know that the muriat of quicksilver contains this metal highly
  oxydated.  The oxygen unites with the hydrogen of the gas,
  and the quicksilver thus metallized unites with the sulphur. 
 414 BITUMINOUS AND METALLIC SPRINGS.

   f77.....The only other inflammable substance which has been
 found in waters, viz. bitumen, is obvious to the senses.
   VIII.....Metals  are the last of the substances we enumerated,
 as found in waters,....and iron is the most common.   It is often
 combined with  sulphuric acid, sometimes, however, with car.
 bonic acid.
   The possibility of dissolving iron in water by carbonic acid,
 or fixed air, was first discovered by Mr. Lane, and communicated
 in the  Philosophical Transactions of the Royal Society.
   In authors you will find the Prussian alkali  rtcommended for
 detecting metals in general,  and even  for distinguishing them.
 It precipitates iron blue, copper of a red or coppery colour, and
 zinc white.   There is, however, some uncertainty in the indica-
 tion of this  test.   It is a very  difficult chemical problem  to
 prepare this alkali altogether free from  iron.  .We have a better
 test  of this kind  by combining  the tinging  matter,  not with
 alkali, but with lime.   Lime-water, boiled a little on Prussian
 blue, will completely deprive about one-thirtieth of  its weight
 of all the colouring matter, without taking up any martial oxyd;
 and is a very sure and expeditious test, of the  presence of iron.
 For  this purpose,  it must  be carefully kept in well stopped
 phials, and even screened from the light.
   The appearance of ochre  in the channel of the little stream
 formed by the water flowing from the spring,  is also a very nice
 indication of iron.
   Astringent vegetable  matter, and especially the gall-nuts of
 the oak, will discover an astonishingly small quantity of iron in
 these waters.   It sometimes happens,  however,  that  the dark
 colour does not appear when the powdered galls are added to a
 water  which contains iron.   This proceeds from an  excess of
 acid, and is easily obviated, by adding a very  small quantity of
 alkali.  We can make the colour appear and disappear repeatedly,
in a mixture of this kind.
   As for copper or zinc, their appearance is very rare : and we
need not have recourse to this trial to discover them.  There are
others  that are better.
  For the art of imitating the different mineral waters which arc
esteemed in Europe, and made objects  of commerce, you may
consult Professor Bergmann, whose work on this subject,  and 
INDICATIONS OF  CHALYBEATE WATER.  415
on the manner of analysing mineral waters, is one of the most
valuable  he has left us.   More lately, Mr. Fourcroy has pub-
lished a laboured and accurate  analysis of a sulphurous water in
France, at  Enghien, in which he has given many judicious and
useful remarks on the  use of  precipitants in* examining these
waters.
END OF THE THIRD VOLUME-
  riUNTED BY B. GRAVES,
No. 40, North Fourth-streets 
 
NOTES  AND  OBSERVATIONS.
BY THE EDITOR.
                    [Note 46.  jfr.30.]

     IT will be of some service to us in our future consider-
ation of this subject,  to recollect the well known fact,  that
any  plant, the sugar  cane for  example, will  grow from a
minute  seed to maturity, yielding sugar and every other
production competent to its nature, if planted in pure sand,
fed with distilled water, and having a free  communication
with the air and light, and  a proper degree of warmth.  The
sand in which it grew is neither diminished  nor changed in
the smallest degree.   It would seem, therefore, that we must
expect nothing from alcohol but what is supplied from these
sources, viz. the water, the atmosphere, light, and heat; and
that it is to these that  we are to  look for the oxygens, hydro-
gen, azote, carbon, alkali, and every thing  that we obtain
from alcohol.

                     [Note 47. p. 35.]

   Dr. Black has attended to those circumstances only of the
process  which relate  to the preparation  of  aether.   It is
therefore proper  to mention, that, at the time  when  the
white cloud prescribes damping  the fire and changing the re-
ceiver, another singular product begins to form.  This drops
from the spout of the retort into the water  in the receiver;
    VOL. III.               3 G 
418       NOTES AND OBSERVATIONS.
and  is the sxveet  oil of wine, an oily,  fragrant, and sweet
tasted fluid.    With whatever care  the  process is now con-
ducted, the matter in the retort being now much hotter, the
vapours of sulphurous acid now rise, and must be allowed to es-
cape: more oil comes over, but horribly tainted with these va-
pours, and growing more and more thick  and dark coloured,...
at last quite dirty.    This is owing to a perfect charcoal, now
formed in the retort, so light as to rise with the vapours.  At
last,  the  matter in the retort becomes a dry, pitchy-like,
spongy mass.

                     [Note  48. p.  35.]

   It would never appear in the fluid form in these climates,
but in that of clastic vapour, did not the pressure of the air
keep its particles  from flying asunder.   This must bring to
our recollection Dr.  Cullen's experiments, which were of so
much use to Dr.  Black,  for establishing the doctrine of
latent heat.
   If a wide glass cylinder,  fitted with a piston, which is
put half way down, be filled with the pure vapour of *ther,
kept of such a  temperature that it  just balances  the  pres-
sure of the air, and if the piston  be then suddenly drawn
to  the top,  the c; Under will be filled  wirn  a  white cloud,
which  lasts  for  a second  or two, and  then disappears.
This shews that it is not merely capacity for heat which  fits
the vapour for appearing in its more expanded form.  This
form is the consequence, and not the cause, of the absorption
of heat.

                     [Note 49. p. 100.]

   I  cannot but  think that peat, or the black   moss of  the
moors, is an approximation to coal. Peat is not found in many
places; and no where abounds so  much as in  Scotland and
Ireland.   It is by no means enough  for the formation of
peat, that the place be a wet marsh, abounding in vegetable
matter.   In immense districts of Europe  and  America,
such situations are common; and we have impassable moras-
ses  and  swamps  of vast  extent.   But these are not filled 
NOTES  AND  OBSERVATIONS..    419
with peat; nor is  the mud which fills  them very inflammable.
Accustomed to the bogs of Scotland, and little informed in na-
tural h.uory, I was much surprised at  finding similar situations
in tae Canadian woods without  peat; and this made me exa-
mine With attention the matter contained in those bogs.  Even
wiiov the  vegetable remains  were  very abundant,  and consti-
tuted almost the whole mass,  I found it very  little inflammable,.
and altogether unfit for a fuel.  And what I took particular no-
tice of, the  smell in burning was altogether unlike the smell of
burning peat.  This is quite peculiar to peat.   I never saw peat
i.i any part of North America, except in the neighbourhood of
Louisburg: and there  it was but  a very scanty mixture of peat-
earth with the moorish soil.
   While the smell  of all burning peat has a character by which
it mav always be  known,  there are considerable varieties ; and
these varieties seem to me to be super-additions to the distinctive
smell  of peat.  This is considerably like that of the  most in-
flammable lean coal, and  still more  like to that of jet, but not
near so offensive.   The blackest, hardest,  heaviest peat, when
the matter is almost an impalpable pulp, is the most inflamma-
ble, and leaves the smallest quantity of ashes.  This kind of
peat has the heaviest sickening smell.   Such is  the peat at Ca-
nisbay, in the no4th extremity of Scotland, just by  John-a-
Groat's House.  This,  when  dried,  is so fine in its texture, as
to break with a sort of  polish,  like a jasper.  Its smell in burn-
ing is  not very distinguishable from that of cannel coal.  The
smell of the best Dutch turf, which is taken up from the bottom
of salt water, very much resembles  that of the peat now men-
tioned.
   I am inclined to think that a certain juice is necessary for the
formation of a bog into peat.   Perhaps this juice is the primi-
tive bitumen.  I suspect also that it is always accompanied by vi-
triolic matter.  Peat ashes always contain a very great propor-
tion of iron.  I have seen three places in  Russia, where there
is superficial peat  moss:  and  in all of them the vitriol is so
abundant as to effloresce.   One  in particular, adjacent to St.
Petersburg!!, shews it every morning  on the clods,  when the
dew has dried off. 
420        NOTES  AND  OBSERVATIONS.
   Peat  mosses form very regular  strata,  lying  indeed on the
 surface ; but if any operation of nature should cover this  with
 a deep load of other matter, it would be compressed,  and ren-
 dered verv solid ;  and remaining for ages in that situation, might
 ripen into a substance very like pit-coal.

                      [Note 50. p.  118.]

   Perhaps the fact would be more properly expressed by saying
 that  when the effervescence produces hydrogenous  gas, the
 French  chemists, combining their theory of combustion with
 Mr.  Cavendish's  discovery of the composition of water, infer
 that the metal acted only on the water, and,  attracting its oxy-
 gen,  sets the hydrogen at liberty. When azotic gas, or nitrous
 air,  is yielded by the  effervescence of a solution of  metal in
 nitric acid, they say that the metal acts on the acid, attracting its
  v,nrCn, and  thus liberating  the azote.  Before Mr.  Caven-
 -.lbh's discovery,  the solution of metals in the sulphuric  and
 muriatic acids presented  difficulties which greatly embarrassed
 the partizans of the new doctrine.  This accounts for their anx-
 ious and laborious repetition of the experiments of Mr. Caven-
 dish.  Till this doctrine was firmly and accurately established,
 the theory of acidification  was quite unsatisfactory.   Nor did
 even  the composition of water make it of extensive influence,
 till the proportion of the gases was exactly ascertained.
   It  must be acknowledged that the order in which metals ap-
 pear to attract the acids in solution corresponds pretty well with
 the order in which they are oxydated by the action of heat and
 air.   Zinc and iron  precipitate all  other  metals from the ni-
 trous acid: and these  metals are more calcinable than most
 others.   Tin, however, does not fall into its place in the order
 of solution:  it is very calcinable.  It is  also  pretty conforma-
ble to the same principle, tha* zinc, iron, and tin, produce in-
flammable air, that is, decompose water by their strong action
 on the oxygen.  But were  this the  sole efficient' cause of this
peculiarity of those metals, we should expect it in a much more
remarkable degree in cobalt, magnesium, and tungsten, which
calcine  so rapidly  by mere exposure to the atmosphere.  Nay,
 the white oxyd of magnesium should do it.  But none of these 
            NOTES  AND  OBSERVATIONS.       421

 substances produce, as far as I can learn, inflammable air from
 diluted sulphuric acid. &c.
   I would say farther that the application of this theory to the
 complicated cases of animal ahd vegetable substances  is,  in  a
 great measure, gratuitous, till  we shall have  ascertained, not
 only the  proportion of the ingredients, but also  their elective
 attractions in  all different temperatures.   This seems peculiarly
 necessary with respect to the basis of the  three gases, which
 act such important parts in these changes.  Till this knowledge
 be attained with considerable precision,  it will always be easy,
 by ringing the changes (so to speak) on oxygen, hydrogen, and
 azote, and by taking their several actions in any order of suc-
 cession that we please, it will, I say, be easy to explain any
 phenomenon  whatever.   I must add, that some of those  elec-
 tive attractions appear to me to be such as to render some of the
 favourite  explanations of these phenomena inadmissible.   I
 think that I shall be able  to give instances, before we arrive at
 the end of these lectures.


                      [Note 51. p. 124.]

   These Dutch gentlemen do not choose to consider these  facts
 as examples of combustion ;  because  they say that  there is no
 decomposition  or change  effected in either of the ingredients.
 It is a mixture, like that of sulphuric  acid and water,  in which
 also there is a vast extrication of calorique ; because the capa-
' city of the mixed is less than the sum of the  capacities of the
 ingredients while  separate.  Or it is. the extrication  of latent
 heat.  They  explain these facts in the same manner.  There is,
 indeed,  another case, in the mixture of metal  with sulphur,  in
 which this  explanation is very admissible, namely, the incan-
 descence (and  actual inflammation,  if in the  air) of mercury
 and sulphur,  in the preparation of cinnabar.  But in the Tacts
 mentioned above there are very essential differences of circum-
 stances.
   I have not  seen  the account which  the Dutch chemists have
 published of these experiments ; and have read only Van Mons's
 repetition of them, of. which a  very  distinct  abstract may be 
422        NOTES  AND OBSERVATIONS.

seen in the Analytical Review, for October 1795. I do not know,
therefore, the precise state of the compounds.   This is certain-
ly a chief circumstance, with respect to the theory of the phe-
nomenon.  It was surely a very unexpected circumstance, that
zinc should exhibit such an appearance of inflammation,  seeing
that this metal contracts no union with sulphur.
   We must at any rate conclude from these experiments, that
oxygen  gas is not the sole source of the  light and heat which
appear in the combustion  of bodies,  which seems to be a point
of doctrine in the antiphlogistic system of chemistry. The great
heats produced during the solution of metals in acids, notwith-
standing the eruption of much gas  containing oxygen, present,
I think,  a difficulty in this system.   It is somewhat lessened by
these Dutch experiments.   For wee see so much heat extricat-
ed as to produce ignition; and therefore may  more easily con.
ceive the change of capacity in  solution  to be adequate to the
production of the smaller heats which appear in that process.
   The  heat  and light also, in  all deflagrations with nitre, are
another indication of a great quantity of caloric combined with
oxygen and with azote in the nitre,  in their solid form.
   From such facts, it may perhaps be concluded, that the emis-
sion of heat  and light is more  copious in ordinary combustion
than in  the other cases before us, only by the  emission of what
was firther  combined  as indispensable articles of the gaseous
form in which oxygen and  azote exist in the atmosphere, that
is, bv the emission of the latent heat of Dr.  Black ; a state  of
the  caloric different from  that which requires a proper third
substance, along with a high temperature, to disengage it  by
superior affinity.
   But, although these considerations give a greater consistency
to the new doctrines, and lessen some of their difficulties, the
intelligent reader  must,  I  think, perceive  that the whole be-
comes hypothetical, and all the properties, affinities, and other
relations of these supposed bases of different kinds of gas, are
mere interpretations of the phenomena; or rather are accom-
modations and corrections of supposed properties, till the hypo-
thesis is made to tally at last with all the phenomena.  The hy-
 pothesis seems to have nearly the same rank in science with the 
           NOTES  AND OBSERVATIONS.        423

magnetical hypothesis of iEpinus.  Both are ingenious and ele-
gant,  in the highest degree; and  have such a comprehensive
resemblance to the phenomena, that the hypothetical principle
becomes an excellent  principle  of arrangement or classification
of the phenomena, almost equivalent to  a just theory, and, in
all probability,  extremely near  to it.   Other cases occur in the
subsequent lecture which will bring this subject again before us.

                     [Note 52. p.  183.]

   Dr. Black having only  given the  general conclusions which
have been drawn by these eminent chemists concerning this very
singular substance,  it seems necessary to mention the chief and
most simple facts by which these opinions are supported.
   If we boil the prepared  alkali, called the lixivium sanguinis,
or Prussian alkali, with a  diluted sulphuric acid, vapours come
off which are extremely volatile.  When the distillation is skil-
fully conducted, the first vapours are found much more volatile
than water; and cannot be  condensed, unless water be mixed
with them, or presented to them in the receiver.  This vapour
has a strong smell, not disagreeable, and is extremely inflam-
mable.
   This substance contains the colouring principle ; and the lixi-
vium  now possesses none.   Its  taste is  sweetish and astringent.
But as this  watery solution of it unites with all alkaline sub-
stances, and with metallic ox>ds, and may be detached from one
of them by means of another, in the same manner as acids, it is
considered,  chemically, as  an  acid, and has  been  called  the
Prussian, or Prussic Acid:  and its compounds  have been
called  Prussiates.   That compound, called the lixivium san-
guinis, prepared, or Prussian alkali, &c. is the Prussiate of
Potash.
   The prussic acid,  prepared in the way just now mentioned,
is but impure.  Dr.  Scheele procured  it in the greatest purity,
by first forming of this impure acid a prussiate of mercury, and
then putting some filings of iron into it and a small quantity of
sulphuric acid.   This instantly decomposed the mercurial prus-
siate,  and even greatly weakened the attraction of the  Prussic 
424         NOTES  AND OBSERVATIONS.

acid for the iron, by the excess of sulphuric acid.  The mixture
being now distilled with an extremely gentle heat, and the first
vapours only preserved, the result.was a prussic  acid perfectly
pure.  With this, or such as this,  all the experiments forascer-
taining its properties are tried.
   It combines,  as  I have  said, with all the  substances  which
combine with acids, with  various degrees of elective attraction.
Lime water digested on Prussian blue combines with this mat-
ter alone, without taking up ;my iron, as the solution of alkali
does.  It acquires  a yellow or straw colour, and  no longer ma-
nifests its alkaline qualities.  It does not affect the test paper. It
has lost its  alkaline taste, and  its attraction  for  carbonic acid.
This compound, called the prussiate of lime, is a much fitter test
of the presence of iron, than the lixivium sanguinis, or prussiate
of potash, because  it contains no iron.
   The union of this colouring matter with the various bases, is
exceedingly weak ; for every acid, even the carbonic, detaches
it from them all.   Nay, Scheele found  that carbonic acid ren-
dered blood incapable of imparting the  colouring quality to the
lixivium sanguinis. But, as observed by Dr. Black, the addition
of a small quantity of iron, either pure or very slightly calcir cd,
so fixes this acid in the lixivium sanguinis, that it now resists the
action of any diluted acid. It is found, however,  that strong sul-
phuric acid dissolves the blue precipitate, and forms with it a
brown liquor,....but it becomes blue by diluting with wat*.
   Mr. Berthollet has greatly augmented our knowledge of the
 prussic acid discovered by Scheele.  He found that in Scheele's
 decomposition  of the mercurial prussiate by means of iron, the
 iron took from it not only its prussic acid, but also its oxvgen ;
 for the iron was now an oxyd,  and the  mercury was  revived.
   His most curious observations related to the super-oxygena-
 tion of the prussic  acid.  He found that when mixed with ox-
 ygenated muriatic  acid, it reduced the muriatic  to its ordinary
 state, while the prussic had now acquired the abundant oxvgen
 of the other, and  its  properties  were  greatly changed.  It is  ,
 now much more volatile : and, if exposed to the sun's light, it  1
 acquires the smell of aromatic oil, and  even collects  into a slug-  •
 <jish  oil like liquor, heavier than  water;  and it is no longer 
            NOTES AND OBSERVATIONS.        425

inflammable, nor precipitates iron.  It is saturated with oxygen,
which is equivalent to its being burnt already.   In this  oxyge-
nated state, it does not form a blue, but  a green precipitate,
with the solution of vitriol. This is not owing to the mixture of
a really blue precipitate with yellow oxyd of iron ;  for muriatic
acid does not dissolve this  oxyd, nor change the colour.  It may
be brought back from this state bv sulphurous or volatile vitriolic
acid.  This is evidently by abstraction of part of the oxygen by
the sulphurous acid.   And, conformably with this  account of
it, we observe that the green precipitate mentioned just  now, is
made blue by  the volatile  vitriolic acid.  The  same effect  is
produced  by  exposure to  the light.   Now we know that in all
cases of  super-oxygenation, light detaches the  redundant ox-
ygen.
   Scheele's preparation  of Prussian alkali  by* means  of  sal
ammoniac, chalk, alkali, and charcoal, shews that volatile alkali,
or its component parts, hydrogen and azote, enter into the com-
position of the prussic acid.  And if caustic fixed alkali  or lime
be mixed with oxygenated prussic acid,  we have the  vapours of
caustic volatile alkali.  Moreover, if the alkali or lime  be now
detached  by sulphuric acid, we do not obtain the prussic acid
again :  it has been destroyed ,  and the  volatile alkali just now
mentioned has been part  of it.   But further, this addition of
sulphuric  acid produces effervescence of fixed air, or carbonic
acid.^  This was not seen before.   It  would seem, therefore,
that this  is the other ingredient of the  prussic acid; and that
it consists of volatile alkali and fixed air, or of their component
parts, hydrogen, azote, carbon and  oxygen.  Perhaps  the last
does not exist in it,  but is furnished by the water in the distil-
 lation of prussic acid, and in that process combines with the
 carbon, forming the  basis  of carbonic acid.
   After all the investigations of this eminent chemist,  there is
still a great uncertainty as to the real state of  things in Prussian
blue.  I think that there may be strong objections made to the ex-
istence ofanyti ;,;!<- compounds in chemistry; and that all the exam-
ples offered are really mixtures of the third, with atrue compound
of the ether two.  Mr. Berthollet says,  that there are two kinds
of the prussiate of iron.   One  is the common  Prussian blue,
 containing the iron or its oxyd, saturated with the tinging mat-
     vm . tit.                •"  II 
426       NOTES AND  OBSERVATIONS.

ter.   The other consists of oxyd not saturated, or precipitate
of iron with excess of oxyd.   We obtain this by  digesting
an alkali  on Prussian blue.   It evidently takes to itself part
of the colouring matter.   But the remainder  is not, as com-
monly thought, an ordinary oxyd;  for when an acid is poured
on it, we  obtain Prussian blue. '
   Alkali  prepared in  this manner, by digesting on  Prussian
blue by, the assistance of heat, contains a considerable quan-
tity  of the  second kind of precipitate.   It will, by cooling
for a considerable time, deposit this in form of a yellow calx.
When thus freed from it evaporated  to dryness,  and  then
redissolved  in  water,  it is called purified  Prussian alkali.
Mixture  with vitriol produces no blue,  if kept in  the dark.
But the light causes the blue precipitate to form gradually,
till the whole alkali is  decompounded.

                     [Note 53.  p. 183.]

   I forgot, when considering the  solution  of iron  in the
 muriatic  acid, to mention a curious observation of  the Duke
 D'Ayen.   When the, martial muriat  is  exposed to  a  mild
heat,  water only slightly  acidulated  is  disengaged,'....then
part  of  the  acid  rises,  in  almost incoercible  fumes,  but
 pure,....then a compound of  the  iron and acid rises, and con-
 denses in elegant lancet-shaped  crystals.   When  the more
 fixed matter which remains is urged by the most violent heat,
 there  rises a vapour  which  seems  truly metallic,  condens-
 ing in regular hexagonal crystals, having the full opacity
 and lustre  of polished steel, and strongly attracted  by the
 loadstone.
   This is unquestionably a volatilazation of the metal:  and
 I think points out some cementing processes,  such as with
 common salt, which should make us expect valuable results.
 If this sublimate be a pure iron, it is surely in a state that
 we  are not acquainted with.   I should wish that in this pro-
 cess of the Duke  D'Ayen, a magnet had been placed in the
 way of the vapours, or even applied externally by one of its
 poles, to the part of the receiver on which  the sublimate ap-
 pears to accumulate most speedily. 
NOTES  AND OBSERVATIONS.       427
                    [Note 54. p. 196.]

  These two remarkable masses of  malleable  iron  men-
tioned in the text have greatly puzzled  the  naturalists who
have attempted to account for them.  Both were found so
far from all traces of habitation, that there is  no suspicion
that they have been brought into that state by  the operation
of man.  And indeed the appearance of the Siberian mass
is such as could not have  been induced by our greatest heats
in our best furnaces.  The whole has been in a  state of most
violent  ebullition ;  there being many bladders in it larger
than an egg ; and the surface is all blistered.   The whole is
covered with a crust like iron-stone : but, internally, it is
good red-short malleable iron.   The  mass found in  South
America is  about fifteen tons weight,  and of  sijnilar  struc-
ture, but not so solid.   1 his, and another of still  larger
size,  and branched like a stumped tree,  found, in the same
woods,  three hundred miles from all appearances of  iron, or
even of stone, were lying on the surface of the earth.   (Phil.
Trans.  1788.)   A mass of  the  same  kind  and appearance,
near seven  tons weight,  was found under the pavement at
Aken near Magdeburg, and  is excellent iron.
   In all those instances, it is remarkable that the fusion has
been more  complete than we  can produce in  our best fur-
naces.  Also the glassy matter is transparent, and altogether
unlike the slags which are formed in our metallurgic opera-
tions. No appearances of sulphurous admixture are observed
in those masses.
  Professor Chladni, an author of great respectability, is much
disposed to  think that all  these  masses have  been portions
of those fire-balls which are often observed to move in our
atmosphere with immense velocity,....with a dazzling flashing
light, frequently with smoke,  making a rustling noise,  and
sometimes  bursting in pieces with a loud explosion.   The
Siberian Tartars worship the lump  above mentioned, as a
thing come  down from heaven.   Many accounts have been
given of red hot masses which have fallen through  the air:
and those which have been shewn as such, are^ll of the same
kind, consisting chiefly of malleable iron.  Chladni gives a 
428       NOTES  AND  OBSERVATIONS.

circumstantial account of three.   One example at Hraschina,
near  Agram, in  Hungary, is attested by many witnesses,
before the Bishop's consistory at Agram.  It was seen coming
from a great distance, with a brandishing unequal light, like
a long flaming chain : and it split into two pieces, which fell
about a mile asunder, making holes more than an ell wide,
and three fathoms deep.   One weighed seventy-one, and the
other sixteen pounds ;  and they  are now in the Emperor's
museum at Vienna.  They are  of  the  same kind exactly
with  those  already described.    That   such  trifling masses
should make si1, a  excavations, can be accounted  for, only
by supposing them  to be in a  state of continual  explosion
or deflagration, blowing in all directions,  like the instrument
of destruction called a  careasse, discharged  by  a mortar.
This  will  alro  give them a gre;.t apparent  diameter while
moving through  he air.   (Sec ChladnPs Dissertation  on the
Mass of Iron found in Siberia;  Leipzig,  1794: and the Art
of alining and  metallurgy,  by Mr. Stultz,   keeper  of the
mineral museum at Vienna,  1789.  See  also some valuable
papers by Mr.  Howard, in the Philosophical  Transactions,  j
1802, &c. or extracts from them in Nicholson's Philosophical !f]
Journal)  In these papers  every thing has  been collected
which has a relation to  the subject: and  Mr. Howard's ob-
servatipns'are eminently  ingenious and instructive.

                    [Note 55. p. 209.]

   Dr.  Black's notes contain no account of this process.   I
believe that it is not generally known :  and although Jars has
published what  he calls the process  carried on in  Sheffield,
we acquire little information from ii.  From the circum-
stance that the ores which afford  a metal  nearly in the state
of steel, are generally spathose, or  analogous to them, it seems
not unlikely that the carbon which it wanted to form steel
may be had  in the  fixed air.  Accordingly, many of the old
processes for case hardening iron,  and for making small  bits of
steel, employ crude calcareous earth.  The carburet (so  plum-
bago  is considered) burns  very slowly.   Perhaps   even
carbonic acid  may  be  decompounded  by iron, by  the help
of some double elective  attraction.  And the secret flux, of 
           NOTES AND OBSERVATIONS.       429

which  Mr. Jars speaks, may be a mixture containing lime-
stone,  and a proper re-agent.

                    [Note 56. p. 224.]

   I confess that this appears to me. to be an inaccurate, or
at least an imperfect account of the matter.   If indeed  it
relates only to the heat produced in the union of the nitrous
and the vital air, to form nitrous acid, it is satisfactory.  But
if it be meant to explain the  heat  which  is  observed in the
solution, when the  gases are forming, it is surely inaccurate.
Indeed this heat has always struck me as a very great diffi-
culty in the  whole theory.   Mr.  Lavoisier unquestionably
derives his explanation of the heat produced in combustion
from Dr.  Black's theory of fluidity and vapour ; and  sup-
poses that a gas consists of its radical, or distinguishing in-
gredient, combined with calorique, according to the ordinary
laws of chemical affinity.  This being supposed, the solution
of metal in  an acid, so far  from  producing or extricating
calorique, should absorb it from the  materials, and produce
a cold incomparably more intense than any of our freezing
mixtures.   For  such solutions, whether the  metal be  oxy-
dated  by  the acid or the water,  are always accompanied
by the eruption of gaseous fumes.   Iron in the diluted sul-
phuric acid  produces an immense  volume of gas.   Those
metals which are oxydated by decompounding the acid, pro-
duce gases which still contain much oxygen.  And  it may be
remarked, that,  in general,  those  solutions which produce
fumes most deficient in oxygen, produce the greatest heats.
This fact is favourable to Mr. Lavoisier's explanation.   The
oxygen remaining in its concrete form, does not expend any of
the calorique extricated by other  circumstances  of  the  pro-
cess.   Supposing that no  more latent heat is necessary  than
for the production of as much watery vapour as  should have
the same density, the quantity is very great, when compared
with that which occasions  the cold in  our freezing mixtures.
It  must  not  be said that the quantity  necessary  for  this
gaseous combination  may be  small;  for in this case,  we
should  often  have  gases  instead  of   ordinary  vapours;
whereas, we know that an  incomparably greater supply of 
430       NOTES  AND  OBSERVATIONS.

calorique is required for the formation of a gas.   Besides,
the Lavoisierian theory of combustion supposes a vast ac-
cumulation of heat in oxygenous gas ;  this being, according
to that celebrated philosopher,  the source of all the heat ex-
tricated in that operation of nature.  It must also be observed
here, that the oxygenous gas gives out this heat; and the oxy.
gen is  combined with the inflammable  body, in  a state very
similar to its condition  in the present experiment.   There-
fore, we-unquestionably have a prodigious quantity to account
for; the oxygen in  the dissolving  or combining substances
being unprovided  in the quantity necessary  for  its becom-
ing a source of heat in  some future combustion.
   I would no*'  ask  in what state is the calorique contained
in the  materials  of an acid and a metal, when they act on
each other ?  Some of the materials must contain it in a
state that is unnecessary for their appearance  in the state of
a  solution, of an  ox\ d, or of a metalline salt.   When all
this calorique  has  emerged, the oxygen in nitre still contains
a great store  of it,  seeing that  it  is extricated from it in
deflagration with  inflammable substances.   This  only  in-
creases the difficulty.  For this great store of calorique must
remain in  the solution, and in the metallic salt  which it
produces.   Heat is  extricated  in the solution, and gas con-
taining oxygen  is produced.    This gas,  by^ uniting with
vital air, again detaches calorique,  and produces  nitric acid.
This acid will dissolve  metal, and again detach  calorique.
This may  be continued without end.  This circumstance
alone  shoflld  convince  us  that  there is some error in our
theory ; because this endless generation of heat is impossi-
ble in  the nature of things.  We cannot say,  with any well
grounded confidence, whether  more calorique is extricated
from oxygen,  when, in  the gaseous form, it causes the  com-
bustion of  sulphur,  or  when,  as an ingredient of nitre, it
contributes  to the deflagration with the same  sulphur.  I
grant that I think  that more is extricated in  the first  case.
But it  should  be an  immense deal more.   For methods may
be found for transferring the oxygen of the sulphuric  acid,
formed in the  first case, to azote, and of thus forming  nitric
acid, and nitre, which will again deflagrate with sulphur. 
          NOTES  AND  OBSETVATIONS.       431

  All this is mysterious and intricate.   I do not say incom-
patible ; but  I  am not  able to reconcile them by means of
any known facts.   The same,  or greater difficulties,  occur
in almost all  the spotaneous inflammations ; in the deflagra-
tions of nitrous acid with essential oils ;  and in  man)  de-
tonations ;  and in particular the heat and light which we call
glow, or incandescence ;....especially such as  appears in the
Dutch experiments,  mentioned in page 335, on the mixture
of sulphur with several metals.   I acknowledge that I never
was  satisfied with   the  explanations given of  this  subject.
Indeed it is rather kept out  of  sight by the  French chemists.
I am informed that  Mr. Meunier,  who was one of Mr. La-
voisier's chief assistants, tried many experiments, in company
with Dr. Sommering of Mentz ;  and that they communicated
their observations to Lavoisier and the  chemists of Paris ;
and  that these gentlemen were  so little pleased with the
results, that  they were never mentioned in  the Academy.  I
am disposed to assign  a very different source of the heat
in all these operations :  and should this work have a second
edition,  I  may probably have  so far  matured  my ideas
on the subject as to think  them not unworthy of the pub-
lic attention.  At present  they  are  by  no  means in such a
state.

                     [Note  57. p. 229.]
           •
   The very ingenious Mr. Davy,  chemical lecturer in the
 Royal  Institution in London, has published, in  Nicholson's
 Philosophical Journal, vol. III. p. 515. and vol. V. p. 281. the
 outlines of  a  chemical  examination of  this  gas, which he
 very properly denominates  Nitrous oxyd.   He there men-
 tions, in very general terms, its relations to heat, water, acids,
 alkalis, inflammable substances,  &c. the methods  of produc-
 ing it, deduced from a due consideration of  those relations,
 and the appearances of  its compounds.   This  sketch is the
 performance of a sagacious observer and good reasoner.
   With regard to  its production,  his  experiments  confirm
 Dr.  Black's conjecture  very clearly.  He says  that the most
 uniform  and  expeditious  method  of  changing  nitrous air
 into nitrous oxyd is to expose it to the action of a sulphite 
432       NOTES AND OBSERVATIONS.

of potash or soda.  In an hour's time,  100 grains of dry
sulphite of potash converts 16  cubic  inches of nitrous air
into eight inches of nitrous oxyd; and is itself partly changed
into an ordinary sulphat.
   But the method of preparing this oxyd, which he found
the most convenient of  all, was by means of nitrous ammo-
niac, mixed with thrice its weight of sand.  This salt, the
nitrum flammans of the older chemists, notwithstanding the
singularity of  its most obvious properties,  has somehow
escaped the pertinacious  scrutiny of  the  chemists for a long
while.  Mr. Davy has made some  very judicious experi-
ments on  it ; and observed properties which are undoubtedly
of great value,  by the information they  seem to  give  con-
cerning the changes made on  the affinities of chemical  sub-
stances by a change of temperature.   If nitrous ammoniac
be kept steadily in a  temperature very little exceeding 320
of Fahrenheit, it melts, and decomposes  completely, resolv-
ing itself into water and the gas now under  consideration.
If raised much above  400°,  and approaching to 500°, the
constituent substances take other combinations, and produce
the Ordinary  nitrous gas,  and azotic gas,  not combined.
Probably,  a very nice management of the heat might deter-
mine it either to the one or the other of those products, along
with the water, which seems  to form in every temperature,
once  the salt has melted.  Should the temperature  rise to
700°, another combination takes place ;  the  oxygenous gas
is decomposed ; and  we have a detonation.   It must be re-
marked that the formation of nitrous gas and azotic gas is ac-
companied by a luminous appearance  in the vessels.   This
is probably analogous  to the low inflammation of phosphorus,
sulphur, and other inflammable substances; and should induce
us to examine those  phenomena, to see  whether  they also
are accompanied by such a change  in their gaseous produc-
tions.
   This is said to be  the process employed by the society of
chemists who have lately attracted so much notice by the em-
ployment of this gas  for medicinal and dietetical purposes.
Its effects, when breathed for some time, are very wonderful,
and were first discovered, I believe by Mr. Davy.   To those
who are not hurt by the sight of folly,  they  are  also very
amusing. 
NOTES AND OBSERVATIONS.       433
   Mr.  Davy  has also very ingeniously combined this gas
with alkalis.   He triturates a dry caustic alkali with a  sul-
phite, and exposes the mixture to the action of nitrous  gas.
In this way the  alkali acts on  the nitrous  oxyd, so as to
combine with it  in the very  instant of its formation.   He
had  found that  the oxyd, already in a gaseous state, con-
tracts no union  with  alkalis, if dry,  and scarcely if  in a
watery solution.   The compound tasted almost like a caustic
alkali, but with a very peculiar pungency.   The oxyd is ex-
pelled, in its genuine form, by any acid ; also by a tempera-
ture exceeding 400°.
   Inflammable substances decompound nitrous oxyd, much
in the same way  that they decompound nitrous acid: but the
decomposition requires a much higher temperature.   Sul-
phur burning  slowly, with its weak blue flame, is extinguish-
ed in it.  So  are charcoal and phosphorus, if in their lowest
temperature of combustion.  But  if any of those substances
be made to burn  briskly, producing a white light, they decom-
pound  nitrous oxyd with great rapidity, with  an enlarged
flame, and even  deflagration.  Therefore a candle burns with
an enlarged flame,  having a beautiful  rose-coloured light.
The  sulphurous  pyrophori burn vividly; but require a con-
siderable heat to begin the combustion.
   There is a peculiarity  attending the burning in this  gas.
Nitrous acid  is  produced.   Mr.  Davy imagines that this
arises from a new arrangement of principles, occasioned by
the  ignition of a part of the gas that is not immediately con-
tiguous to the flame.   He explains  in  the same wa>,  some
other phenomena which   distinguish  this gas  from nitrous
acid.
   By comparing a variety of appearances,  Mr.  Davy con-
cludes, that  100 parts of this  oxyd consist of thirty-seven
parts of oxvgen,  and sixty-three of azote, in a much 'denser
state than  that of their separate existence.

                    [Note 5ft. p. 244.]

   Mr. Howard  has communicated to the Royal Society of
London a very curious account  of  a preparation of mercury,
which explodes by a spark or an electrical shock, in the same
    vol. in.               " * 
434       NOTES AND OBSERVATIONS.
way as gunpowder, but with incomparably greater force, and
with some peculiarities, which are remarkable and instruc-
tive.   (See Phil. Trans. 1800. p. 204.)
   The red oxyd of mercury was mixed with.alcohol;  and
nitric acid was poured on it.  It dissolved the oxyd  before
it  acted  remarkably on  the  alcohol; and after some time
there was an ebullition, which sent forth  a  dense white
smoke, smelling strongly of sether.  The mixture  deposited
a precipitate, at first of a dark brown, and it gradually grew
whiter.   When separated by filtration,  it appeared  crystal-
lized.  -Sulphuric acid  was poured on this saline mass.   A
violent  effervescence ensued ;  and  the mixture  exploded.
When the sulphuric acid was much concentrated, the explo-
sion often happened at the first contact.
   Three or four grains of this salt in dry powder were  laid
on an anvil;  and were  struck with a smart blow with a ham-
mer, in  the manner  practised  by Fourcroy and Vauquelin
with several salts.   It detonated with great violence :  and
the faces of the anvil and hammer  were very sensibly in-
dented.   The  same  effects  were produced by sending  the
shock of an electrical battery through five or six grains of it,
The report of two grains is always as loud  as  that of a
musket.
   Two or three grains, lying in a sort of  cup of  tin-foil,
were thus made to float on some oil.   This was heated gra-
dually :  and the powder exploded when the temperature rose
to 368°.
   Mr. Howard then examined  the explosive or  expansive
power of this substance when fired in the chamber of a piece,
in the manner of gunpowder.  It burst the  barrel in which
it was fired  in  a very extraordinary manner.   Seventeen
grains of it, however, were fired in the chamber of  a fowl-
ing-piece, without destroying it.   There was no recoil  that
was remarkable.   The report was feeble ; and  the ball had
about half the force  which an ordinary charge, or 68 grains
of the best gunpowder, would have given .it.   When the ex-
periment was repeated with  34 grains,  the  barrel was  de-
stroyed, being torn into many pieces at the breech.
   The expansive power of this substance was compared with
that of gunpowder,  by firing half an  ounce  of each in  two 
           NOTES  AND OBSERVATIONS.       43$

 chambers, bored with the same tool, in two blocks of hard
 wood.   The gunpowder  split  the block into three pieces,
 driving them from each  other  till the  flame had room to
 escape.  The mercurial powder burst  its block in many
 directions,  but  without sensibly separating the fragments.
 The parts adjoining  to the powder were pounded to dust.
   A box of cast iron was made to fit exactly the chamber of
 a twelve-pound carronade.  It had a cavity which held three
 and a half ounces of the mercurial powder.  The box con-
 sisted of two parts,  firmly screwed together.  It was put
 into  the  carronade: and three twelve-pound balls were put
 above it.   The powder was fired through a small touch-hole.
 The fore part of the box  was blown out.   The other part
 was shivered into many pieces ;  so were the two undermost
 balls ;  and the uppermost  was cracked  through the centre.
 The report  was extremely feeble.   The entire ball struck
 the  mark with very little force.
   Ten grains of the mercurial powder were fired by an elec-
 trical shock,  in the centre of a glass ball seven inches in
 diameter, and half an inch thick. . The glass withstood the
 shock ; and  its inside  was coated with metallic mercury.
 Only  four  cubical  inches of  gas  were  found added  to
 the air  in the glass.   They were a  mixture of azote and
 carbonic acid.   Ten grains of gunpowder  were fired in the
 same manner : but no measure was taken of the gas. Indeed
 little could be inferred from the gases remaining when all is
 cold, because we are ignorant of what is absorbed.  What is
 most remarkable in this experiment is, that the inflammation
 which takes place in this explosion, will not inflame gunpow-
 der mixed with it in a loose state.
   Mr.  Howard  ascribes the great force  of the explosion to
 a greater rapidity of inflammation.  He  might have added,
 in all probability, a more complete inflammation; for some
 grains of the gunpowder were not inflamed.   Indeed there is
 usually  a  very great  portion  that is driven out of the way
 without inflaming,  when the  powder lies loose, as in  this
 r-ase  it did.
   The most important circumstance in the experiment is the
rapid diminution of the expansive force  by an enlargement
of bulk.  Jt seems irresistible, while the particles of the gas 
436       NOTES AND  OBSERVATIONS.

are very near each other ; but moderate, as soon as they have
receded to  a small  distance.   The effects of  gunpowder
agree very well with the  supposition  of a repulsive force
between the  particles,  and  acting  only  on the immediately
adjoining particles,  inversely proportional to their  distance.
Th- repulsion of the particles of this  mercuriated gas must
decrease much faster ;  and  mav perhaps  be as the  square of
the distance inversely.   But be it what it will, it has a dif-
ferent law;  and therefore is a different gas from that of gun-
powder, perhaps containing the  vapour  of  mercury  itself.
There are experiments, by which it appears that this vapour
is indeed  very expansive.   It  may  also  have very little
latent heat.
   This dissertation is full of the most acute observations; and
contains a most ingenious analysis of the phenomena, and
much chemical science.

                 [Note 59. p. 245.]

   As this is the first example which we have, in Dr. Black's
arrangement of the metals,  of the separation of one metal
by another, it may  not  be  improper to pay  a little  more at-
tention  to the general phenomena.
   The  first observation I have to  make  on it is, that there
is not such a violent-effervescence accompanying the solution
of the  added metal, as  when that metal is put into the pure
acid.   In some cases  there is  no effervescence whatever.
And in every case  the effervescence is  extremely slight.
   I may also observe, that the present example,  the precipi-
tation of  mercury  by copper,  is the first fact appealed to by
Dr.  Stahl, as a strong argument for his doctrine of phlogis-
ton.  He appeals to it as a fact long and well known.   There
are  many others equally distinct.   Thus, lead dissolved by
acetous acid is precipitated by zinc, in fine metalline crystals;
like sugar  candy.    Silver is precipitated  from the nitrous
acid by copper, also in metalline crystals.  This precipitation
forms  a very beautiful object, when viewed through  a mic-
roscope ; as it goes on in a drop of the solution, when a parti-
cle of copper is placed in contact with it.  The crystals  will be
seen starting, as it were,  into existence, or shooting out  in
• fine rami fixations. 
          NOTES AND  OBSERVATIONS.      437

  According to the doctrine of Stahl, when a metal is dis-
solved in an acid, the acid is supposed to unite with the calx,
and  expel  the  phlogiston.   Therefore,  when  an alkali is
thrown  into  the solution,  the precipitate must be con-
ceived to be a calx, perhaps combined with a portion of  the
acid, or the alkali, or both. But when one metal is employed
to precipitate  the  calx of another, the separation must be
ascribed to the superior attraction of the acid for the calx
of the added metal.  For when this metal is  dissolved in
the  pure acid, its  phlogiston  is supposed to esCape.   To
abide by the example in the text, the acid must be supposed
to have a stronger attraction for  the  calx of copper  than
for  that of mercury.    Therefore, when  mercury is  thus
separated by  copper, the phlogiston of the copper  m^st be
supposed to be  expelled from the calx.   It does not quit the
mixture, but unites with the precipitated  calx of mercury,
and changes it into a metal.
   Dr.  Stahl  accordingly asserted this  double exchange ;
and  says  that  it is confirmed by  the want of effervescence
in  most cases,  and by 'the very faint  effervescence in all.
This small effervescence he  accounts for in a manner suffi-
 ciently satisfactory, by saying that the precipitated metal did
not  require for its metallic form all the phlogiston which the
acid expelled from the other.
   Dr. Black, while he acquiesced in the doctrine of Stahl,
 did not content himself  with a mere expression of this ac-
 quiescence; but was accustomed to exhibit this doctrine as
not only plausible, but as extremely ingenious and elegant;
and was at some pains to obviate  the objections which were
made to it. He saw clearly that it clashed with no principles of
 philosophy, to say that a substance might be positively light.
 And when I  reminded him  of the  experiments on pendu-
 lums, by which Sir Isaac Newton proved that all sublunary
 matter  is cqualhf heavy,  he  considered these  experiments
 with care,  and thought that they were not susceptible of the
 accuracy necessary for  deciding the question;  because  he
 observed that the exact determination of the centre of oscil-
lation of such  pendulums  as  Newton must have employed,
was  a thing which could scarcely be accomplished.  It  was
this objection hv Dr.  Black which made me repeat Newton's 
438       NOTES  AND OBSERVATIONS.

experiments, in a form where the  position of the centre of
oscillation is of no consequence.   (See Encyl. Britan. Supp,
§ Astronomy.)
   Impressed with this favourable notion of the doctrine of
Stahl, Dr.  Black was much  offended by the  conteniptuous
terms in which more  than one or two French chemists, spoke
of  it,....calling it disgraceful to science, and what no man of
common sense could adopt for a minute.   He thought Stahl,
Margraaf, Cramer, and other German chemists, by no means
deficient in common sense;  and used to say, that the French
chemists forgot, in their dashing lessons to the  rest of Eu-
rope, that Macquer,  Geoffroi, Beaume, were their country.
men.   No man "had a higher opinion of the genius, pene-
tration, and sagacity of Mr.  Lavoisier,  than Dr. Black:
and I have often heard him lament the loss which science
su  tained by his death.   He admired particularly Lavoisier's
quick sight of the importance of Mr. Cavendish's discovery
of  the composition of water,  and his employing it imme-
diately,  not only to  get over the  difficulties which all the
acids, except  the nitrous, brought into view, but even to ex-
tend his doctrine far beyond the first conceptions of it. Dr.
Black adopted all Lavoisier's doctrines: but he did not like
the  officious (as  he  called ir) interference of some of his
coadjutors: and  he said that  Berthollet  was the only one of
them in whose judgment and caution he had full confidence.
With all this candour, he never would allow Stahl's doctrine
to be spoken of in a  slighting manner.
   But to return from this eulogy on Stahl:....We must ex-
amine the manner in which the separation of  one metal by
means of another is explained in the doctrine of the French
chemists.   It is extremely easy, and pretty satisfactory : but
it requires a little more thought and reflection to understand
the whole internal procedure :  and there are some  cases  in
which there are difficulties which  I do not think easily sur-
mounted.
   What is called the solution of a metal in an acid,  is  in
general,  rather the  solution  of a metallic oxyd:  and we
must regard this solution and the previous oxydation as two
separate  operations.    When a metal is  first oxydated, and
then dissolved in an acid, we do not see where the. one oper- 
          NOTES  AND OBSERVATIONS.       439

ation  terminates, and the other begins ;  the one operation
seems just the continuation of the other.   If we attempt to
resolve these questions by having recourse to attractions and
repulsions  and to conceive this  succession of changes in a
mechanical way, as is  done by  many who would be thought
philosophical chemists, we shall find ourselves immediately
put to a stand.   For  in  mechanism,  the law of continuity
suffers no exceptions.   But chemistry itself helps our con-
ceptions of this matter, by shewing us  other  cases, where a
similar succession of phenomena appears.   Thus, the con-
tinued addition of heat to a substance shews us first the solid,
then a fluid,....then a vapour.   And in each of these changes
of constitution and properties, there is a great absorption of
heat.   We  have another example still  more analogous.   By
gradually evaporating any  brine, we at last produce crystals
of salt, still consisting of  the  saline matter  combined with
water.   Here the formation of a saline crystal, by the pure
saltfirst attaching to itself the water of crystallization, which
it certainly  will do, if no  more water  be supplied to it,  and
then  its  subsequent solution in more water, are facts which
very  much resemble the formation of  an oxyd, and its sub-
sequent  solution  in more acid.  Careful observation may
discover many more examples of such a series, and it may
be known as  a very common  phenomenon,....as a general
though not universal law.  But this  is all  the explanation
that pure chemistry affords; and it is  by a  judicious obser-
vation and employment of such general laws, that it has be-
come so  comprehensive and important a department of  na-
tural knowledge.
  Being more familiarly acquainted with the crystalline and
briny froms of a salt, we seem  a  little entitled to reason
from  these to similar subjects which are less intimately known:
and   we  are led to  believe,  that the  oxygen which  forms
part of the oxyd, is more firmly united with the mercury,
than  what is afterwards combined with it as an ingredient of
the acid.   And  this  opinion  is confirmed by  observing,
that  in most cases,  we can easily detach the acid; but that
it is  very difficult to  detach the pure oxygen.    In  many
cases, the most intense heat will not detach this last.  Also,
although  we do not in the least  understand why or how  the 
440       NOTES  AND  OBSERVATIONS.

previous union of the oxygen with the azote of the nitrous
acid should make its disposition to combine with the mer-
cury any less, we know that this is a general fact in chemis-
try.   And lastly, though  ignorant of the efficient  reason,
we know that in proportion as more of an ingredient is al-
ready  united with  another,  all  subsequent additions are
made with less force,  and the union is less  firm,  or more
easily destroyed.
   Having these notions of  the affinities of substances, we
must suppose that the copper first attaches to itself  as much
oxygen as will render it an oxyd susceptible of union with
the nitrous acid.  This must certainly be  taken from the
mercurial nitrate, leaving the mercury still in the  state of
oxyd.    It must therefore be taken from the nitrous acid in
the mixture.   This must be the order of procedure, because
it  is  this portion of the oxygen that is  easiest detached.
The acid is already in the form of nitrous acid,  having been
decomposed  in  part when  dissolving the  mercury.   Or, if
we allow the  acid of solution to be nitric acid, the first effect
of the copper must still be to decompose some acid. The cop-
per oxyd is at length  formed: and now dissolves, by abstract-
ing,  not oxygen,  but nitrous or nitric acid  from the nitrate.
This it continues to do more and more, reducing  the mer-
cury to the state of  an oxyd,  and last of all leaving it in its
primitive form  of a metal.   This  order of procedure  is
confirmed by observing, that in some cases the metal is left
in the state  of an oxyd, or  in a  state  very  little removed
from it.
   Now this procedure has, I think, considerable difficulties.
We  do not see,  in any case, how the affinity of the copper
for acid or  oxygen, which continually diminishes  as it  at-
taches more to itself, is at last able to deprive  the  mercury
of that portion of oxygen that is  most  strongly attached to
it.  We cannot suppose the oxydation  of the mercury to be
the first thing effected, being already persuaded that the cop-
per, which can decompose  pure acid, will  more readily de-
compose it,  when the combination of the  parts of  the acid
is weakened  by  its union with the  mercurial oxyd.   It must
therefore take the oxygen  from the  acid,  and not from the
oxyd: and the  mercurial oxyd must be the last thing de- 
          NOTES  AND  OBSERVATIONS.       441

composed.   The firmest combination must be overcome by
the smallest force.
   Nor is it  without its difficulties, to conceive how a metat
becomes soluble in an acid, only by being already combined
with one  of its ingredients.   I  do not know any  similar
fact: and  1  have little confidence  in any other mode of che-
mical investigation, and least of all in reasonings depending
on the consideration of attractions and repulsions.
   Farther,  if the copper be oxydated  by decomposing the
nitric acid,  we should have an effervescence of nitrous  air
as strong as when topper  is put into pure acid.   We cannot
suppose that the  redundant azote unites with the oxygen of
the oxyd,  and changes it into nitric or nitrous acid; because
the mercury was  oxydated  by means of an affinity for.oxy-
gen, stronger than that of azote for  the  same oxygen.   I
think-that this effervescence should be  observed in  every
instance of  separating one metal by means of another ; even
when the  added metal is  oxydated  by decomposing the wa-
ter.   For I do not think that the redundant hydrogen will
unite with the oxygen of  the oxyd.   Now these phenomena
are not observed : what effervescence is observed is always
weak.   We have not  inflammable air in all the cases where
the added metal decomposes the water.  In such cases we are
led to think  that the hydrogen is expended during the decom-
position of  the oxyd of the dissolved metal.  But this also
obliges us to suppose that the decomposition of  one oxyd,
and the  formation  of the  other,  are the first  parts of the
whole process, a thing which does not agree with our notions
of the affinities.
   I do not  think it will be  difficult to decide these questions
by proper experiments : but none such have yet come in my
way.

                      [Not* 60. p. 253.]

   As the notes-found among Dr. Black's papers are  not in such
a condition that I can lay them before the reader, so as to answer
the  purposes mentioned in  the lecture,  I must content myself
■with giving the chemical arrangement of the medicinal prepa-
rations of mercury that was followed by him in his discourses,
     vol.  m.                 3 K 
442         NOTES  AND OBSERVATIONS.

with such of his observations on particular medicines as I thought
might be  of use.

 Table of the preparations of Mercury, as drawn out by Dr. Black.

            Hydrargyrus prxparatur ad usus medicos:

         L Destillatione, ut  purus fiat.

                Hydrargyrus purificatus.  Lond.

        II. Tritura, ut in atoinos invisibiles attenuetur.

            Merc, gummos. Plenckii.
             Pilulae Hydrargyri.  Ed. et Lond.
             Hydrargyrus cum creta.  Lond.
             Emplastrum Hydrargyri, sive cacrul.   Ed.
            Emplastrum Lithargyri cum Hydrurgyro.  Lond.
            Emplastrum ammoniaci cum Hydrargyro.  Lond.
            Unguentum Hydrargyri, sive ccerul.  Ed.
             Vnguentum Hydrargyri fortius et mitius.  Lond.

       III. Calcinatione ignis  ope et aeris.

            Hydrargyrus calcinatus. Lond.
                   Olim Mercurius prxcipitatus per vr

       IV. Viribus salium.

         1. Cum  acido vitriolico.

             Hydrargyrus vitriolatus flavus, vulgo tui-pethum minerale.  Ed.
             Hydrargyrus vitriolatus.  Lond.

         2. Cum  acido nitroso.
             Guttx albse Wardi.  (a)

   (a) Dr. Black has given the following account of the process for preparing
 this medicine, known by the name of Ward's white drop.-
   A mixture being made of sixteen parts of pure aquafortis, and seven of
 volatile sal  ammoniac, four parts of mercury are added for every sixteen of
 the mixture.- and the mercury being dissolved, as much more ii added as the
 liquor will dissolve.
   This is evaporated till a pellicle just appears on the surface.  It is now
 allowed to cool.
   When  cold, the  heavy, uncrystallized,  or fluid part, is drained off.  The
 crystallized salt is dissolved in thrice  its weight of rose water, which forms the
 white drop.  The dose is in two drops, each dose  containing half a grain of
 mercuiy. 
                 NOTES AND  OBSERVATIONS.         4413

                Unguent um Hydrargiri nitrati.   Ed. et Lond.   (b)
               Hydrargyrus nitratus ruber.  Ed. et Lond.

           3. Cum acido  muriatico.

               Hydrargyrus muriatus corrosivus.  Ed.
               Hydrargyrus muriatus.   Lond.
               Hydrargyrus muriatus raids.  Ed.
               Calomelas.   Lond.
               Hydrargyrus muriatus prxcipitatus.  Ed.>   r  .
               Hydrargyrus Muriatus mitis.   Lond.     S

           4.  Cum acido acetoso.

               Hydrargyrus acetatus.  Ed. et Lond.
                    PiluU Keyseri.  (d)

    (b)  A variety of this ointment is  used with success in the Manchester
 infirmary. It is prepared with the oil of butter, which has had no salt what-
 ever.  This preparation is found to preserve its  colour unchanged.

    (c) Dr. Black has written, on a copy of this table, an account of Scheele's
 process for this medicine, mid humida, as follows :
    Half a pound of mercury,  and as  much aquafortis, are put into a small
 matrass  or* cucurbit,  having a pretty long neck.  The mouth of it  being
 covered with a bit of paper, a digesting sand-heat is given to the mixture for
 some hours.   When the action of the acid becomes languid, the heat must be
 increased to  nearly a  boiling heat,  and continued three  or  four hours,....
 agitating the mixture from time to time.   At  last, make the solution boil
 gently, for a  quarter of an hour; at the find of which  there should remain a
 small quantity of mercury undissolved.
   While the  above is going on,  dissolve four and a half ounces of pure sea
 salt, in six or eight pounds of water.  Mix this solution, boiling hot, with the
 solution of mercury, also boiling,....stirring  violently while they are  mixed.
 Then allow the precipitate to settle ; and afterwards edulcorate it with repeated
 washings of hot water.....and dry it. We obtain a mercurius dulcis in impalpable
 powder, amounting to eight and a half ounces.
   The efficacy of this  process  is explained by Dr. Black, on the principles
 advanced in 4ne lecture, namely,  that the solution of mercury, made as here
 directed,  is a  sort of compound solution, containing .a quantity of the metal,
 not oxydated,  sufficient  completely to  saturate the muriatic acid.  In .proof
 of which, he  says that  this solution is precipitated  black  (a mark  of crude
mercury) by an alkali;  whereas if the  solution  has been  continued only till
the cessation of effervescence, an alkali  occasions a yellow precipitate, &c.

  (J.) Dr. Black refers for  the preparation  of  th's medicine to Observ. de
Medicine, de Mr. Rkl-wii.. a..  1 .-uvre, 1772; and to the Encyclopedic 
 444         NOTES AND OBSERVATIONS.

          S.  Dfturbatione ex acidis vi alkalinorum.
              Hydrargvrus praceipiratus cinereus.  Ed.}    -
                    Mercurius pr^cipitatus fuseus.     J
              Calx Hydrargiri alba.  Lond.  (f)
              Unguent, calcis Hydrargyri alb*.  Lond.

         V. Conjunctione cum sulphure.
              Hydrargyrus sulphuratus niger.  Ed.
              Hydrargyrus cum sulphure.   Lond.
              Hydrargyrus sulphuratus ruber.   Lond.
              Pilulj^ydrargyri muriati mitis, sive calomelanos, composite. £d.

                        . [Note  61. p.  262.]

    Medicamenta  parantur ex  antimonio,  vel  sulphurato,  vel
 sulphure privato.
                      Ex autimonio sulphurato. '
          I.  Tritura.
             Antimonium praeparatum.  Ed. et  Lond.

         II.  Ope ignis  et aeris.
                    Flores Antimonii sine addito.
             Vitrum antimonii.  Ed>.
             Antimonium vitrfcatum.  Lond.
             Vitrum antimonii ceratum.  Ed.

       III.  Vi salis  alkalini.
                    Hepar antimonii mitissimum.
                   Regulus antimonii medicinalis.
                    Hepar ad Kermes minerale  Geoffroii.

   (e) This,  as prepared in the shops, is said to be frequently very acrimonious,
which Dr. Black ascribes to impure aquafortis in the preparation.
   (f) This white precipitate may be made exactly similar to calomel, by using
plenty of volatile alkali for the precipitation, so much that the mixture  may
smell of it.   This alkali will  take from the metal  a considerable  quantityof
the muriatic  acid.   Also by its hydrogen it deprives the  quicksilver of the
oxygen  with,  which it  was combined.  The  precipitate is therefipe rendered
insoluble in water, and scarcely soluble  in vegetable acids.  It will be  very
different if we are sparing of the alkali.
   Dr. Black  remarks in this note, that the fossil alkali, though aerated, cannot
be made *o precipitate mercury from a solution  of corrosive sublimate,  of a
white colour, because  the quantity of it which is sufficient for saturating the
acid does not contain enough of air to saturate the mercurial precipitate,  and
render it white.  He confirms this explanation by numbers, stating according
to Mr. K"-".van'« esncrTients, the quantity necessary for this purpose. 
NOTES  AND OBSERVATIONS.        445
                  Hepar ad tincturam antimonii.
                  Kermes minerale.
            Sulphur antimonii pratcipitatum. Ed. et Lond.

      IV. Vi nitri salis.

                  Crocus antimonii mitissimus.
                  Vulgo Regulus Antimonii medicinalis.
            Crocus antimonii.  Ed. et Lond.
            Antimonii emeticum mitius.   Boerh.
            Antimonium ustum cum nitro, vulgo Calx antimonii nitrata. Ed.
            Antimonium calcinatum.  Lond.   Vulgo diaphoret.
            Antimonium calcareo-phosphoratum, sive Pulvis antimonialis.Ed
            Pulvis Antimonialis.  Lond.

       V. Viribus Acidorum.
                  Antimonium vitriolatum. Klaunig.
                  Antimonium catharticum.   Wilson.
        ..   Antimonium muriatum, vulgo  Butyrum antim.  Ed.           ,
            Antimonium muriatum.  Lond.
                  Pulvis Algerothi, sive Mercurius vitte.
                  Bezoardicum minerale.
            Antimonium tartarisatum, vulgo tartarus emeticuB.  Ed.
            Antimonium tartarisatum.  Lond.
            Vinum antimonii tartarisati.   Ed. et Lond.
            Vinum antimonii.  Lond.

                 Ex antimonio sulphure private

   Hoc metallum, prout  diversis modis liberatur a sulphure,
dicitur Regulus antimonii simplex, Regulus antimonii martialis,
Regulus Jovialis, &c. Ex eo parata  sunt;

        I. Ignis vi et a'e'ris.
                  Flores argentei, sive nix antimonii.

       II. Vi nitri salis.
                  Cerussa antimonii.
                  Stomachicum.  Poterii.
                  Antihecticum.   Poterii.
                  Cardiacum.  Poterii.
   Medicamenta ab antimonio nomen mutuantia, quae tajnen ejus
metalli vix quicquam retineat:
Cinabaris antimonii.
Tinctura antimonii. 
 446       NOTES AND  OBSERVATIONS.

                      [Note 62. p. 300.

   The grains of small shot made in this way are very often hol-
low, or have a deep pit in one side, which is frequently rugged
within,  it is owing to the sudden congelation of the outside by
the water.   This  forms a hard case,  while the interior is still
fluid; and, contracting as it cools, a part  is left empty.  As
this greatly hurts  the value  of the small shot, many  attempts
have been made to prevent it, which have been more or less suc-
cessful.  Some manufacturers have mixed other metals with the
lead,....others  have kept oil on  the water,....others receive the
lead into boiling hot water covered with melted tallow.   I be-
lieve that the most successful method has been that of the pa-
tent shot manufacture in Southwark,  London, where  the  fur-
nace is  at the top  of a very high tower, not less than one hun-
dred feet, and the shot is gradually cooled  as  it falls  through
the air.   The chief effect of this, however,  must be the incom-
parably .greater number of spherical grains.  I do not se.e  how
this will much prevent the hollowness  of the shot, even although
the tower were four times as high.  The shot would fall two hun-
dred and fifty feet in four seconds, and four hundred feet in
five seconds, neither  of which would sufficiently cool it.  Its
latent heat requires a much longer time  than this for its absorp-
tion by air.  The  pear-like shape is occasioned by the fluid lead
within breaking through the  crust, and freezing as it comes in
contact  whh the water.  Metals afford very curious forms, by
dropping them when fluid into water.   When this is done from
a very small height, the drops  descend slowly through the wa-
ter. The fluid within breaking the crust by  its great weight,
runs out,  freezing as  it goes down, and often leaves a pretty
round thin cup with a taper thing below it like an extinguisher.
Some metals thus form themselves  into nails with large heads,....
others take other shapes, very uniform, and very  unexpected.
Great differences  are produced  by different liquors instead of
water,  and by different heats of the metals,  and by the heights
from which they are poured,  Sec. 
             NOTES AND OBSERVATIONS.       447

                        [Note 63. p. 332.]

     It is by no means clear that the acid has increased its propor-
  tion of oxygen by deoxygenating the copper.   It is true that the
  copper  remaining in the retort scarcely needs any addition of
  inflammable  matter to reduce  it: but there is adhering to it a
  large  proportion of extinctive coaly matter, which  answers the
  same  purpose: and the  fact is, that when  this is urged by a
  strong heat, we obtain a great deal of fixed air.  Of this I have
  had repeated experience.   It is indifferent whether this be con-
  ceived as composed of  the oxygen of the cupreous oxyd or from
  the acid.   In neither case can the acid be said to have increased
  its proportion of oxygen  in any other way than by leaving be-
  hind a portion of carbon.  I see nothing that induces me to think
  even  this to be the  case,  or that there is not as much oxygen
  taken from the acid in  this operation as belongs to the extractive
  or carbonic matter.  Mr. Chaptal (Ann. de  Chymie,  vol. 28.)
  thinks that he sees plain differences between what he chooses to
  call acetous and acetic acid.   But thty appear to me very un-
  satisfactory.   The  superior acidity  of the  acid  obtained  by
*r the present process  is  sufficiently accounted for by  its  dephleg-
  mation  and freedom from  mucilaginous  and  other extractive
  matter.  At any rate,  this is by no means  the most eligible pro-
  cess for obtaining from this salt the greatest quantity of acetous
  or acetic acid, free from empyreuma:  and, as Dr. Black has not
  mentioned any  of the other methods of decompounding it, I
  trust that the  reader will not be displeased with some account of
  the most approved of them.
     The  simplest and most obvious of all is to employ the supe-
  rior affinity of another acid; and of these the  most fixed is to
  be preferred.   Concentrated sulphuric acid being poured on the
  acetite  of copper, it detaches  the acid with  great facility, and
  as agreeably  flagrant  as  the best of  the dry process,  or what
  comes over after the portion tinged with the copper, and before
  any empyreuma can be observed.   It is also  extremely strong,
  and of a pungent odour: and the last  portion is inflammable.
  This was first observed, I think, by Count de Lauragais: and
  he employed it to form an acetic aether, which exceeds others
  in fragrance.   There is generally some carbonated matter left 
448         NOTES AND OBSERVATIONS.

adhering to the sulphat: and this has been adduced as a proof
that the acetic acid, by depositing carbon, has become redundant
in oxygen.
   It will be said that the acid obtained by this process is not
in a state of complete dephlegmation,  as in the other.  But I
may observe here, that the other process cannot be easily con-
ducted without some water.   Without this addition, in order to
transmit the heat  more readily to the  centre of the mass, the
acid cannot be expelled from thence, without over-heating the
extejrior parts.
   A still better process is that of Mr. Lowitz.   He mixes three
parts of the acetite of copper with eight parts of a sulphat of
potash surcharged with acid, (prepared  by  distilling sulphuric
acid from potash, to dryness).  This mixture, in  dry powder,
Contains  as much  redundant sulphuric acid as is  sufficient for
saturating the copper or its oxyd, and for extricating the whole
of the acetous acid, with a very moderate heat.  He affirms that
in this way we  obtain it, with all the fragrance possible, from
this preparation.
   Nitric, or the oxygenated muriatic acid, or aqua regia, might
be employed,  with  proper  precautions, to  decompound the
cupreous acetite, and seem the fittest for enabling us to'judge
whether the acetous acid can be superoxygenated.

                     [Note 64. p. 357.]

   I must not omit this opportunity of making  some remarks on
this mode  of concretion of the silver.   It must happen in con-
sequence of an attraction which brings  together,  in a certain
determinate manner,  the minute atoms into which the silver is
divided.   The same thing is observable in numberless instances
of precipitation;  and is probably  universal.  * Often,  indeed,
the precipitate is a fine impalpable powder.  But each  particle
of this is a mountain, in comparison of the atoms  in their state
of separation, while chemically united with those of the solvent.
Often are  we able to  see with a microscope, that each of these
particles of powder it a group of minute regular forms or crys-
tals.   Nay, even when the precipitate  is  gelatinous,  as in luna 
             NOTES  AND OBSERVATIONS.        449

 eornea, I am  persuaded that its structure is not uniform, but
 plated or symmetrical.   This I  conclude, from observing that
 the formation of such jellies proceeds in a waj which resembles
 the more sensible  crystallizations.   When  a  solution is  just
 ready to shoot into crystals, if we touch it  with a particle of
 the crystal,  the change begins there,  and spreads from it as a
 centre.  I  observe  the same  thing in the formation  of some
 gelatinous concretions by  inspissation.  But, to return to this
 precipitation of silver ;....it is particularly to be remarked, that,
 although the concretion proceed, from  a basis sending out stems,
 from which proceed branches, which again produce subordinate
 ramifications,  and  the concretion has therefore been  called a
 Vegetation, it does not at all proceed in the manner of a growth,
 or a gradual protrusion from a parent trunk.   This trunk does
 not grow or  change at the same time.  Nor  does it appear to
 contribute any thing whatever to the increase or ramification. It
 remains of the same length:  the same distance remains between
 every branch:  and all the increment is plainly an accretion of
 external matter applied to its extremities, or to different parts of
 its surface in succession.  The additions are of matter previ-
ously  floating  about.   The  little shrub, therefore, is  not pro-
 duced by the gradual developement of a seminal body nor by
 the action of its organical structure on the fluid matter which it
 pumps along its canals, assimilating it as it goes along,  and se-
 creting or rejecting it according to fixed laws.  In the present
 case, every atom  seems to have  the  same powers, and to be
equally capable of becoming either the stem or any one of the
branches.  When we observe the gradual formation with atten-
tion, assisted by a microscope, we observe each little addition to
start into existence in a moment: and we can scarcely tell when
or where to expect the next.  They are all  accretions,....apposi-
tions, of silver previously floating about in the  solution.  Some-
times, indeed, a little branch employs a sensible  moment in at-
taining its full length : but even then,  I presume, that this is a
succession of many instantaneously formed plates; for we know
that all crystals are of a transversely plated structure.  I cannot
but think that the atoms of silver continue to be suspended, or to
float about for some  little time, after their separation from the
    vol. in.                3 h 
450        NOTES AND  OBSERVATIONS.
acid, in their individual and invisible form ; and that they are thus
carried to some distance from the copper (in contact of which
only they are detached from the acid) before they arrange them-
selves  in  some little symmetrical group, fitted  to form  a new
crystal, observing such a law of attraction, that it must attach to
those already formed, in one way, but not in another.   Or, shall
we say that there is a power resembling magnetism, electricity,
or galvanism, propagated from the central bit of copper?  This
last (galvanism) seems to offer the best means for illustrating the
phenomenon : tor it cannot be called an explanation ; but  it is
of  the same kind with all other explanations purely chemical.
None of  them aim at ascertaining the proximate cause, and its
manner of action.   It is thought a sufficient explanation, if we
 shew that the phenomenon is one of a great class already known,
 although  we arc- equally in the dark with respect to each of them.
 The philosophical chemist, indeed, frequently  attempts some.
 thing more  and to shew how the chemical attractions  operate
 in producing the phenomenon.  This is precisely the difficulty
 here.  The question is not chemical, but mechanical.   We are
 required to shew how certain centripetal, or centrifugal forces
 separate  certain particles, and bring  them together again in
 another determinate  manner.   The chemist  ascertains, from
 observation, the affinity, that is, the cases in which such separa-
 tions and  reuinons are invariably  effected.   When  he  goes
 further,  and speaks of his  greater and smaller attractions, of
 one attraction opposing another, &c. he speaks as a mechanician,
 and generally without any distinct conceptions of the  subject.
 In questions of this kind, the object before the mind is  an atom
 of moveable matter, under the influence of  a moving force: and
  all discussion  must now proceed on the acknowledged laws of
  motion.  I take it that the present phenomenon is one  of those
  which sets the insufficiency  of those usual modes of reasoning
  in the clearest light.  I cannot conceive any action between the
  copper and the adjoining acid, which can produce the deposition
  of a remote atom of silver from a remote atom of acid, which
  will not be produced by the action of the  already formed solid
  silver, adjoining to that particle of acid which deposits its silver.
   All that I can do, is to recollect that something very like  it hap- 
            NOTES AND  OBSERVATIONS.        451

 pens when I bring a magnet near a parcel of iron-filings, which
 ^tre lying confused, and without any mutual influence.  Every
 individual rag of iron becomes in an  instant active;  turns
 about;  and presents one extremity to one adjoining rag of iron
 and the other to another.  They adhere  together ; and when I
 draw one away, it drags another after  it, See.  And all  this
 activity is at an end, whenever I remove  the magnet.  Here
 then is  a considerable resemblance of effect:  but it is still very
 imperfect.  The mere presence of the copper is not enough:
 it must be in the very act of dissolving  in the  contiguous a-id.
 The galvanic  phenomena have a  much  closer resemblance to
 what we  are  now considering.   Indeed they  are almost  the
 same-   We have  at  one wire an oxydation going on; and a
 deoxydation going on at the other: and the two have an invaria-
 ble dependence on each  other.  The one cannot happen unless
 the other also happen:  and we  cannot  tell  which is the prior
 event.   But  this  is  only an  illustration:  and the  immediate
 actors and powers remain as much unknown as ever.   Can the
 phenomenon be conceived in  this way I  It is probable that an
 unsaturated solution of copper, and a saturated solution of silver
 in the same acid, may remain mixed together without changing.
 We know this to be true with saturated solutions of  silver and
 mercury.  When  copper is put into such a mixture, it may be
 that a greater  dose of it bting acquired  by the acid in contact
 wi h it, liberates some silver, (though I cannot tell how) which
 liberated silver floats off,  and is carried by the fluid till it meets
 with a crystal of silver already formed, acting with polar forces,
 like the particles of iron-filings; and there it settles  symmetri-
 cally.
  It is to be wished that chemists would endeavour to acquire
 some more precise notions than they seem to content themselves
 with at present, of those internal procedures.  Such unbounded
 use is made of the change of partners (so to express myself) be-
 tween oxygen, hydrogen, azote,  and carbon, in the  chemical
 phenomena of vegetable and animal substances, that «very tyro
 from the chemical  classes finds himself in a condition to write
a system of chemistry, which leaves nothing unexplained, and
admits of no  contradiction.   The author of a Pyrologia,  by 
452        NOTES AND  OBSERVATIONS.

bringing caloric into the chemical dance, finds himself qualified
to -Yvke a world.  It is time to check such unprofitable specula-
tions.   Dr. Black's maxim of  setting  one foot firm on ground
which we know familiarly, be'bre we  attempt to make another
step, is the only safe way of proceeding in this noble but difficult
science.   Av example, still more remarkable  and puzzling, oc-
curred to me very  lately.   I had set up a galvanic pile, of 420
pairs  of silver and zinc plates, having pieces of woollen cloth
soaked in :» saturated solution of sea salt. It stood on a table in
a warm room ;  and the evening sun shone on it.  Chancing to
look at it from the other side of  the room, I observed a most
beautiful nimbus  or  glory  surrounding a  great part of  the
 column, exhibiting fine prismatic colours.   I  went immediately
 to f:ke a nearer view  of it, and it vanished.  Returning to my
 chair, I saw it i'gain, but not if I moved my head much to either
 side.  I went to it again, and viewing it with a reading glass, I
 observed that each piece of  cloth had, all around, fine crystals
 standing out almost  horizontally.  They  were more slender
 than the finest human hair;  and many of them (no thicker than
 the re§t) were two  inches long.  They were  perfectly straight, •*•.
 except a small bending by their own weight.  I could perceive,
 by their manner of reflecting the light,  that  they were angular
 prisms, and that they were jointed transversly, like the equisetum
 lacustre.
    Now I would ask how these crystals of soda (for such they
 are) were formed ? I let some fib/es of cotton fall on them;  and
 could observe that the part beyond the fibre increased,  without
 the fibre itself being carried farther from the  soaked cloth by an
 increase of what was between them.....It is  very mysterious.

                       [Note 65. p. 371.]

    When we reflect on the manner in which it explodes, when
 lying loose  on a  plate of  metal, where  it  is perfectly open to
 expand upwards and  laterally, and on the very small portion of
 this small quantity of matter  that is hindered from  expanding
 downwards, and on  the impression  that it makes,  it  gives us
  some notion of the immense velocity with which it expands.  I 
           NOTES  AND  OBSERVATIONS.        453

found that seven grains, lying on a plate of brass, and exploding
by he at, made as great an impression as a piece of iron, two and
a half pounds weight, falling on it with the velocity of 25 feet in
a second.   .We cannot compute  the downward action at more
than one-fourth of the whole expansion.   We must therefore
calculate the velocity of 1| grains which will give as great a
blow  as the piece of iron, which weighed  17,500 grains.  We
shall  find this  velocity  to be 250,000 feet,  which is nearly 45
miles, in a second.   Yet this  is  probably very small in com-
parison with the velocity of expansion of the fulminating silver,
perhaps not the 100th part of it.   Thus we approach to  some
of those atonishing forces that operate in the emission and re-
fraction of light, and  many other phenomena of  nature.

                     [Note 66. p. 395.]

  No observations, made with any immediate purpose of em-
ploying them in the lecture, are to be found among Dr. Black's
papers, on several substances which seem to be pretty generally
admitted as metallic; namely, those called molybdenum, tellurium^
chromum, tungsten, uranium, titanium, &c.   It appears that he
did not consider the very imperfect knowledge acquired of them
as of importance enough to occupy any of the time allotted for
course of elementary instruction in the science of chemistry. The
few distinguishing properties established with respect to each of
them are  not such as have any extensive  influence, either on
doctrinal  points,  or the conduct of chemical processes, or the
improvement of the chemical arts.  Some  of them, particularly
the one called titanium,  seems to have engaged his  attention a
good deal.   But the state of his health precluded all labour on
his part to acquire a more perfect knowledge  of its properties.
F.ND OF THE NOTES TO VOL. HI 
INDEX.
                                 A.

                                                        7A.GZ. NOTES.
Adopters,      .....             i. 285.
Aggregation,      ....       .         i. 267.
Annealing of metals,              .      .      .       .   1. 133.
Apparatus, chemical,       .             .         •       i- 272.
Assay furnace,         .        i        .          .      i. 309.
Athanor furnace,        .        ...        .     i. 306.
Atmosphere, of the unequal temperature of the,         .       96.
Absorbent earths,      .....   «• 169.
Acetous  acid      .       .      .      •       .    .    11.  64.
——----ammoniac,      .                                 128.
Acids,......       u.  42.
Agate,      ...            •               "-32L
Alabasters.....                  u/ S18'
Alkali fossile acetatum,      ...              ". 128.
Alkalis,      .......       «• 215-
Alkaline earths,      .            •             • 16^. 171,215.
       ^ salts,                                          »  32-
— substances, affinities of,                         "• 260.
 .,,„                                  ...    286.
Alum,      .       •      •      •                       ..
Amianthus,       ......     »■ 314-
Ammoniacal salts,      .      •      ■       • •     •      "• 118
Aquafortis,                 •                            »•  f*
 A    ,                                                  11. 131.
Argal,                          •
Argillaceous earths,        .         •         •      »• i7^> 283
Abestos,        •        •        •        ■     '      I!' 313"
Atoms, elementary,        .                 .    .      h.    4.
 a   .„ „„=                      ...        «. 250.
Azotic gas,         •
Achromatic telescopes,      ....       «*• 309.

«*».      ;......."La ,£
jEthiops martiahs,       .      .       •       •
Affinity, or attraction, chemical,      .  i. 254, 265, i. 383 to 389.
Alcohol,             .....*»•  36 
INDEX.
	TAOC.
Amalgama,	iii. 249.
Amber, ....	90.
Ambergrise,	74.
Antimonial caustic,	. iii. 257, 273,
Antimonium muriatum,	267. 262.
	
——----tartarisatum,	276.
Antimony,	253.
--------, butter of,	257.
------■—, cinnabar of,	273. 260.
	
Aqua-regia,	iii. 368,
Arbor Dianz,	iii. 347.
Ardent spirits,	24.
Arsenic,	iii. 129.
	132. 133.
Arseniats,	
Assaying,	iii. 143.
Astringents, vegetable,	184.
Aurum fulminans,	iii. 370. 323.
B.
Bacon's (Lord Verulam) theory of heat,                    i.  29.
Beerhaave's definition of chemistry,      .      .           i.   8.
Blow-pipe,  .       .       .       .       .      .       .   i. 310.
--------.----- claim to the discovery of latent heat,       .  i. ——
Black's (Dr.) definition of chemistry,        .               i.   11.
-------------furnace,        .       .       .            .   i. 318.
Beccher's opinion on the principle of inflammability,   .     i. 223.
________general furnace,     .      .      .       .     .  i. 315.
Baths (chemical), vari'us kinds of,    .      .       .       i. 282.
Boyle's invention of spirit-of wine thermometers,    .       i.  51.
Braun's (Professor) experiments for producing artificial cold, i.  69.
Boilincr temperature in vacuo,       .      ..      .      .  i. 145.
-------------experiment on the cooling of bodies,      .    i.  84.
Balloons,        .        •        •        .      .     ii. 217.
Barytes,        ......       ii. 274.
Basaltes,       .           •             •       .     .    ii. 310.
Blue lijrhts (Chinese),                                 .   ii.  90.
.____________• nomenclature,                               ii. 147.
Bay-salt,       .      .       "      .      .       .       ii. 115.
Beaum^'s (M.) theory of crystallization,     .       .       ii.  27.
Bittern,       .      .       .       .       .               ii. 201.
 Bergman's nomenclature,    ..      -      ■           .   ii. 141 
INDEX.
                                                           FACE. NOTE?
Boiled salt,......". 116-
Borat of lime,      .       ......"   274.
Borax,       .       .       .       .       •       ,     ii. 70, 137.
Brownrigg's (Dr.) speculations on fixed air,    •     .     •  ii. 236.
Buffon's theory of the earth,.....ii. 164.
Benzoic acid,       .       -              ...    ni.  74.
Bitumens,    .......  «i.  89.
Bar-iron,      .       .    '   .      •      •             ™- 200.
Bleaching, new process of,        .      .      •         i»- 157.
Blind-coal,  .       .       .      .      •      •      •   "i.  23.
Bezoardicum minerale,       ...       .      iii- 274.,
Bismuth,     .      .       .      .       •           * "'«• 291.
Bolognian phosphorus,.......iii-  17-
Bronzes,      .........m- 339.
Balsams,    .....      ■       ni.
62.
Balsamum sulphuris crassum,        .         .        •   ...   fP'
Barilla,      .              .              .       .       in.
00.
Bees-wax,     ....... iii-  83
Capacity of bodies for the matter of heat,    .      .      i-   77.
Capillars attraction,       .       .       .       .       .    i. 251.
Cementation, chemical,......i- 270.
Cavendish's (Mr.) experiments on nitric acid,       .    .   ii.   98.
____________________________fixed air,                 ii. 234.
______     ■  discovery of nitrogen,      .      . .     .   ii. 249.
Carbone,     ........     ii. 261.
Calcareous earths,     .          .     .    .     .    ii. 172, 262.
m------------spar,......•    •  "•  172.
Calx extinto,     .     •    •    ...     .     •    •  ii-  184.
Carbonic acid,     .       .              >      .    .   ii.  242, iii.
_______'.-----, affinities of,......ii-  259.
Carnelian,       .      -      •             :       ■     "• 321.
Carbonated hydrogen,              .       •               i»-    5.
Case-hardening,     .       -     •    •    •           .in.  208.
Cast-iron,       ..."....      .   iii. 199.
Calcination of metals,           .       •       •       •    iii- 106.
Calomelas,    •  .      •      •      •      •      •    "i- 237.
Camphors,      .      ...      •             .    iii   66.
Canton's phosphorus,.......iii-  19.
Cahoutchouc,       ......  iii-  77.
 Calamine,......»             ni-  288.
Caster,       .       .       .       •       •       .     .   iii.  76.
 Caustic alkali,.....•  »•  191,198.
 Cerussa,      ......      iii.  305- 
INDEX.
\
                                                                  NO»TE»
   Chalcedony,
   Chamelion minerale,
   Charcoal,
   Chemical substances, arrangement of,              .       ii-   7.    415
   Chemistry, introductory remarks on,
   ' "     —, various definitions of,
   --------, general views of it as a science,
   Chert,       ....
   Chimney, causes and cure of smoaky,
   Cinnabar,
   ■-----■— of antimony;
   Circulation, chemical,
   Civet,       ....
   Cleghorn's (Dr.) theory of heat,
   Clays,    .......
   Coaks,      .....
   Coal, fossil,      ....
   Cobalt,
   Cohobation, chemical,
   Colcothar,      ....
   Cold,      ....
   Combination, (chemical), theories of,
ffiL-----------, rules for procuring,
  ^Combustion,    .....
   Common salt,
   Composition, attraction of,
   Congealing point of a body,
   Congelation, phenomena of,
   Copal,       ....
   Copper,
   Copperas,
   Corrosive sublimate,
   Cort's process of manufacturing bar-iron,
   Corundum,......
   Crawford's (Dr.) theory of inflammation,
   Cream of tartar,
   Crocus antimonii,
   Crucibles, different kinds of,
   Crude antimony,
   Crystallization,
   Cubic nitre,
   Cucurbits,       ....                   »•  284.
   Cullen's (Dr.) experiments on vaporization in vacuo,    .    i.  156.
   Cupellation of gold and silver,    .         .    iii. 349, 365,381-
PACK.	
ii	. 321.
iii	. 161.
i. 296, iii.	3, 10.
ii	7.
t i	1.
i	. 6.
i	11.
ii	297.
i	304.
iii	246.
iii.	273.
i.	278.
iii	76.
i. 32,	187.
ii.	283.
i. 297, iii	. 3.
i. 299, iii	91.
iii.	294.
i.	278.
iii.	170.
i. 26, 68.	
i.	246.
i-	259.
i.	218.
ii. 106	110.
i-	268.
i.	110.
i.	121.
iii.	73.
iii. 326,	340.
iii.	170.
iii.	237-
iii.	200.
ii.	327.
ii.	343.
ii.	131.
iii.	270.
i.	280.
iii.	260.
ii. 20	,26.
. . ii.	104.
VOL. III.
a  m 
INDEX.
D.
Dampers,    .                        .    .
Decrepitation of salts,      ....
Deflagration,      .                    .
Deliquescence,      .       .          .
De Lisle's scale for thermometers,    .         .
Dephlogisticated air,       ....
Dephlogistirated muriatic acid,
Derham's (Dr.) opinion as to the ascent of vapour,
Desagulier's (Dr.) ibid.
Detonation,       ...
Diamond,......    .
Diffusion,       .....
Digestion, chemical,       .       .       <
Digestive salt,.....••
Distillation,       .         .....
■ per ascensum,
-, furnace for,
Dolomieu's observations on quartz and precious stones,
Dressing the ore,                     :
Dulcified spirit of nitre,      .      .      .     •
Dyke in mining,     .       .      .      .
                                   E.
Earths,
-, various orders of,
Ebullition,......
Effervescence......
Efflorescence of salts,    .    .     .     .
Elective attractions,
-------------------, doub1*,
Electricity, as smeans of producing heat,
Eliquationln metallurgy,
Emetic tartar,     . .        .    ■     •
Empyreal air,    .    .  '•-..'   .    -1
Enamels and glazing for pottery,
Eudiometer,
Evaporation,    .    .     ...
______------, natural,     .       .
..             produces cold,
Expansion of bodies by heat,
Factitious gems,    .         .        •     .
Fahrenheit's scale for thermometers,
.,            experiments on the congelation of water,
Page, no	
i	305.
ii.	25.
ii.	86.
i.	240.
. i.	65.
ii. 56	i, S)4.
iii.	153.
i.	197.
i.	198.
i'-.	86.
324, iii.	13.
i.	241.
i.	279.
ii.	105.
i. 159,	281.
i.	284.
i.	314.
ii.	335.
iii.	140.
iii.	39.
ii.	159.
ii.	151.
ii.	169.
i.	146.
i.	239.
ii. 22, 25.	
i.	262.
i-	267.
i.	287. •".
iii,	260.
iii.	276.
ii.	94.
iii.	310.
iii	. 225. •
i. 19C	I, 281.
i	. 195.
. i	. 202.
i	. 35r
. ii	. 327.
i	.. 62.
■, . i.	122-
 
INDEX.
     F
Li-
te
                                                           JACK.  NOTK*.
Feldt spar,.......             ii.  304-
Fermentation, as a means of producing heat,         •      i •  289.
Finery cinder,                            .                iii.  201.
Fire-damp,              .             .      .      .     ii.  360.
Fixed air,       .....      ii. 220, 230,237.
---------—, affinities of,                                    ii.  259.
-----------, medical virtues of,                     .       ii-  239.
Flexible earths,.......ii.  170.
---------stones,                                   ^       ii.  313.
Flint,           .-...           .   ii.  297.
-----------glass,      .                     .            iii.  309.
Florentine academicians ; their invention of spirit-of-wine ther-
  mometers,       .       .       .       .      .     .     i.   50.
Flores martiales,     .....         iii. 188.
•       argentei        .       .       .       .            iii.  253.
     » antimonii,     .       .       .       .      .        iii. 263.
Fluat of lime,     .        .         .              .      ii. 266. ,
Fluidity produced solely by heat,     .      .      .      i. 102, 136.
F'uor, or flour mineralis,       .       .     .      .     .   ii. 266.
Fluoric acid,     .              .     .         ,      .       ii. 268.
Fossil acids,       .       .              .      •       .    ii.  42.
       —alkali,       .       .      .       .      .     .   ii.  36.
  burcroy's definition of chemistry,      .       .       .     i. * 10.
       — theory of heat,      .      •       •      •       i.   31.
French nomenclature,     .           ...        .   ii.  143.
Frigorific particles, erroueous supposition  of,       .        i- 104.
_____—--,— mixtures, explanation of the effects of,      .   i. 125.
Fuel; inflammation of it, as a  means of producing  heat,  i. 293,300.
Furnace,        .         , '      •           -        .  -   i. 302.
.............made of crucibles,                               »• 317.
Fusible earths,         .       .'        •        •         ii. 170.
....— stones.
30;
Gallic acid,       .'.''           . «  •          •           "»•  185-
Garnat,          .            -'■;     •          • ••        «•  3<*"
Gems......•      i?-321'
Geoffroy's table of elective attractions,         .              i.  264.
Glass,       ...       -,      •       ■  •           »-298
______.....furnace,          .         •           •          >•  312.
Glauber's salt,       .     ...             •   _      »■   81.
..................spirit of nitre,. #                           iii-   37.
Globe, great changes of the,         .       .        •       »•  160.
Gold,
duet,
iii.  345, 367.
    iii. 386. 
INDEX.
                                                          VICE.  KOTKS.
 Granite,       ...        .         ii. 306, 319.
 Gr.. I.           .                                        H. 295.
 Gra.''ation,     .            .      .        .       .       i. 251.
 Green vitriol,                              .         iii. 170, 193.
 Gum-resins,              .                        .      iii.  76.
 Gun-;>owder,        ...          .         ii.  89.
 Gypsum,      ...                  .         ii. 179,263.

                                   H.

 Hale's (Dr.) discovery of fixed air,        .       ,        ii. 208.
 Ha'.'ey's (Dr.) opinion as to the ascent of vapours,           i. 199.
 Hard earths,              .                                ii 170,
 Heat,        .                 ...        i. 21,  28.
 ----. various theories of,                                    i.  29.
 ----, expansion of bodies by,      .       ...        i.  35.
 —,—; whether it produces increase of weight by increasing
  the bulk of a body,                .        .       .        i.  45.     34L
 ........; distrbution of it among bodies,         .           i. 73,  94.     339.
 .........celerry «:f he communication of,         .           i.   81.     328-
 ........., the sole cause of fluidity,      .           i.  102.134,136.
 .„..„. (latent),        -           -         i.  131, 165, 341.357-
 ........f absorbed in ebullition, is separable by condensation,   i. 157.
 .........;  indications of it in vapour,           .         .    i. 163.
 ..........reflections on the union of'bodies with,      i.  184,191,232.
 Heat, the sole cause  of evaporation,         .    .           i. 201.
 .___connection of light and,         .        .       .     j. 208.
 ____t imperfect separation of compound bodies by,           i. 243.
 ____, various means of producing,        .         .        i 287.
 Heats (measurable), scale of,         .             .        i. 211.
 ----(sensible), table of,          .        •                 i- 212.
 Hellot's sympathetic ink,          .                 •      »i- 295.
 Hepar sulphuris,        •        •         •         •     "•   54-
 Hepatic gas,        •                                    "• 406-
 Hitches in mining,     •                  •                 "• 159-
 Hoffman's mineral anodyne liquor,        .         .       >ii.   43.
Homberg's phosphorus,             •             •        »»• *6.
 Hooke's (Dr.) remarks on inflammation,           .         i.         376.
 Hope's (Dr.) analysis of strontites,       .         .        ii. 277.
 Hornblende,        ...                   •         ". 308.
 Hutchin's (Mr.) experiments for producing artificial cold,     i.  71.
 Hutton's (Dr.) observations on saline solutions;      .      ii.  15.
._____________theory of the earth,        .        .        ii. 168.
 Hvdrargyrus muriatus,       ....      'm. 237.
 Hydrogenous gas,          .          •              .       ii. 375.
 Hydrcr-sulphuret,               ~  -              >         ii-  4°7- 
INDEX.
I.
James's  powder,
Jaquin's  (Professor) experiments on lime,
Jaspers,
Ice, Indian process for making,
Iceland crystal,
Ignition, or incandescence,
Inflammable substances,
—-------air,
---------——  exploded with vital air,
Inflammation, cause of,
Ink for writing,
Iron,
—, medicinal  virtues of,
---------theory of heat insufficient,
Iron mould,       .        .....
Iron, ores of,         .        .      .
Irvin's (Dr.) opinion of the capacity of bodies for heat,
      Kali acetatum,
t,i.;   Kelp,
' '■'   Kermes mineralis,
K.
L.
 I1CE.
iii.  272.
 ii.  217.
 ii.  320.
 i. 203.
 ii.  172.
 i.  207.
 ii.  341.
 ii.  376.
 ii.  368.
  i. 231.
iii.  185.
iii  164.
iii.  209.
 i.  186.
iii.  178.
iii.  196.
 i.  136.
 ii.  125.
  ii. 38\
iii.  267-
NOTKS.
380.
Labrador stone,        .         .         .         .
Lacca,         ....
Lakes (deep) ; cause why they are not frozen in winter,
Lamp-black,       ....
----furnace,      .       -      •              •      *•
Lapis lazuli,       •
----nephritif us,
Latent heat, examples of,        •      •      •
________in steam, measure of the,
________, theory of it,
Lava,       •                             '
Lavoisier's theory of inflammation,     •     •
______remarks on carbonic acid,
______experiments on airs,
_______theory of combustion and acidity,
 ..—.— decomposition of water,
..........theory of the calcination of metals,
Lead,
  ii. 319.
 iii.  76.
  i.  95.
 iii.  56.
306, 315-
  ii. 319.
  ii. 320.
  i. 131. 341,3*7.
  i. 165.
  i. 168.
  ii. 309.
  •i. 230.
  ii. 243.
  ii. 247.
  ii. 349.
  ii. 371.
  ii. 113.
 iii. 299. 
INDEX.
                                                           PAGE.  N«TK».
 Lead, ores and medicinal preparations of,        ;         iii. 315.
 Light, connection of hear  and,         .        .         i. 208.
 .........of the sun; its effect on vegetables,       .          i. 226.     372.
 Lime-mortar,          .            .              .       ii. 194.
 ------slaked,             .              .           184,218,221.
 ------, theories respecting,            .          .         ii. 197.
 Lime water,      .        .....      ii. 185.
 Liquefaction,     ....       .     .      .      i.  112.
 Liquor fumans Libavii,    ....     .     .iii. 321.
 Litharge,     .       .          .              .           iii.  302.
 Lithophyta,.........ii.  174.
 Lixivium sanguinis,    .     .         .         .     .     iii.  179.
 Lodes.......*     .     ..     ii.  158.
 Loriot's (M) preparation of mortar,              .        ii.  195.
 Lowitz's experiments with frigorific mixtures,         .     i.  130.
 Luna cornea,                        .               .iii. 355.
 Lunar cauBtic/,           .                            .     iii. 353.
 Lutes,         .                  .       .       .     .    i. 319,

                                   M.

 Macbride's (Dr.) speculations on fixed air,            .     ii. 233.
 Macquer's definition of chemistry,      .       .      .     i.   6.
 --------theory of heat,                 .                 i.   31.
 ----------------lime,       ...                 ii.  198.
 Magnesia alba,       ...           ii. 200,  212.
 Magnesium,       .'            .                         iii. 145.
 Manganese,        .                                 .iii. 145.
 Marbles,      .       .           .      .                 ii. 317.
 Margraaf's  experiments on lime,                           ii. 217.
 Marie,           .            ..                           ii.  175.
 Martial pyrites,      .          ;                   „  .'    iii. 192.
 Martin's (Dr.) experiments onthe capacities of bodies for
  heat,      .         ...                     i.   78.
 Mayhow's (Dr.) experiments on nitre,      .  .             ii.   85.
 Melting point of a body,      ....       i.  109.
 Menstruum,      .      .        .      .        .      .    i.  241.
 Mercury employed in thermometers,      .      .         i.   50.
 -------------, qualities of,    .        .              iii. 213,  251.
 Metallic substances,       .              .            .    iii.  101.
 ----------!---------; their solution in acids,               iii.  117.
 —-------------------------relation to the salts,    .   ,  iii.  120.
 —----          "——^—————— earths, and inflam-
  mables,               ....      iii.  123.
 Metallurgy,     ....         iii.  140.
Mica,     .        ........ii.  314 
INDEX.
Mineral acids,          ...
i    —— waters,        .        .
Mines, of the ventilation of,     ,
Minium,     ...
Mirrors, foiling of,
Mixture (frigorific),        .       .
——, general effects of,
———, as a means of producing heat,
Mocoe,       ....
Moon;  cause of her faint light,
Mountain cork,
Muffle of a furnace,
Muriat of silver,
Muriatic  acid,
             , process for obtaining,
-2rther,
Muschenbroeck's erroneous opinion as to the freezing of
  water,      .
Musk,       .             *
N.
  *AGK.  NOT**
  ii.   42.
 iii.  405.
   i   91.
 iii.  302.
  iii. 249.
  i.  125.
237, 245.
   i. 288.
  ii. 322.
   i. 209.
  ii. 315.
   i. 309.
  iii. 353.
ii. 58, 62.
  ii.  108.
  iii.  44.

   i.  104.
  iii.  76.
Newcomen's steam-engine,
Nickel,
Nitre,
    , natural history of,
----, mother ley of,
Nitrate of silver,
Nitric acid,
------xther,
Nitrous acid,
.--------ammoniac,
.--------gas,
—-----oxyd,
      i. 175-
     iii. 297.
      ii.  83.
      ii. 100.
      ii. 201.
     iii. 352.
 ■   ii. 60,97.
   .  iii.  40.
ii. 58, 60, 91.
      ii. 122.
iii. 223, 229.
     iii. 230.
Ochre,
Oils used as fuels,
_-----•, nature of,
.______-, aromatic,
—-----, drying,
__-  , empyreumatic,
Oils, essential,
      , expressed,
iii.	178
i.	294
iii.	56
iii.	60
iii.	83.
iii.	86.
iii.	60
iii.	78
 
INDEX.
                                                          TACE.
Oils, unctuous,               .                           iii.   78.
Onyx,                  ' .                .                ii.  322.
Opal,              ...               .             ibid.
Oxyd,        ....          iii.  114.
------, of azote,                         .         .        iii.  230.
Oxygen gas,             .           .         .           ii.   96.
Ogygenated muriatic acid,           .           .         iii. 154.
Oxy-muriatic acid,          . '          .           .         ibid.
Oxy-munats,            .           .           .        iii. 156.
         1    of tin,      .       .      ...         iii. 321.
Papin's digester-,
Pastes,           «           ...
Pearl white,
Peat,           .
Pellucid gems,        ....
Petrifying waters,
Petroleum,         .
Phlogisticated air,
Phlogiston,         .       .           .            i.
Phosphat of lime,                  ...
Phosphoric  acid,         .
Phosphorus,        .         ;         .
Pinchbeck,       .....
Pitch,      .....
Plants, similarity of the acids of,      -      .
Plastic earth*,
Platina,       .      •       .       .       ...
Plumbago,       ......
Pneumatic chemistry,       ...
Porcelain,        ....
Porphyry,         ....
Potash,       .      .       .       .       .  ■■     .
Precious stones,         .         .
Precipitation,
Pressure, effect of it on bodies  in changing their states,
Priestley's discovery of phlogisticated air,
--------experiments on airs,
        ■ eudiometer,
................discovery of oxygen,
Prussian alkali,
............blue,
Prussiat of potash,
Prussic acid,
i	143.
ii.	327.-
iii.	292.
m	
ii	322.
ii. 173	237.
iii	89.
ii. 55	,248.
222, ii	50.
ii.	271.
ii. 272,	387.
ii. 384,	398.
iii.	339.
iii.	88.
iii.	54.
ii.	283.
iii.	388.
iii.	169.
ii.	245.
ii.	329.
ii. 306,	318.
ii.	33.
ii.	316.
i.	244.
i.	142.
ii. 55,	94.
ii.	245.
iii.	225.
iii.	241.
ii. 179,	425.
iii.	180.
iii.	423.
	ibid.
 
INDEX.
                                                         PAGE.  yOTBI
Puddingstone,         .                            ii.  296, 319,
Pulse glass,        .                           .         i. 171.
Pulvis, fulminans,           .                      .        ii.  90.
............algerothi,                                 iii.  258, 274.
Pumice stone,                                            ii. 309.
Purple of Cassius,        .              .       .        iii. 376.
Puzzolana,                                   .            ii. 312.
Pyrophori,             .             .             .     iii. 7, 15

                                   Q.

Quartz,             •             -              *     ii.  335, 339.
QuickTime,             .              •         «• 182,  197, 252.

                                   R.

Reaumur's scale for thermometers,       .                 i.  64.
.-------porcelain,      .              .         .         ii. 301.
Red precipitate,         •                      •         1U- 233,
Reduction of metals,                 .         •      «i- HO, 142.
Refining,             .             •                    iii.  143.
Refrigeratory.       .              •            .        i.  284.
Regenerated tartar,           -              -             ii-  125.
Regulus of a metal,       .          •         •           »j-  110-
         antimonii,        -         •                    m-  279.
Resins,         .             ...       iii.  69.
Retorts,                           •                     }-  285-
Reverberatory,         •            •           .        i. 311,
Robison's (Professor) experiments on the effect of light in ve-
   getation,     .         •         •         •           1-  226, 372.
 _______________.__ remarks on Lavoisier's theory of acidity
   and combustion,      .            •            .    .    ii. 352.
        .                     the divellent affinities of
   metals,     .     •......         »>•          439
 Roasting an ore,     j  •
 Rocks; their demolition by the weather,

                                   s.

 Saccharum saturni,
 Sal ammoniac,
___. cartharticus amarus,       ...
 —- diureticus,
 ----martis,
»__-microcosmicum,
.___vegeto-minerale,
 Valine solutions,
      VOL. UT.               "   3 K
111.	
iii.	142
n.	157
iii.	305
ii.	122
ii.	201
ii.	125.
iii.	170.
ii.	272
ii.	128.
ii.	12.
 
INDEX.
rAGE.  NOTE*.
Saltpetre, "iz*r*-*.'-Z ' u '~^ ~ .'	ii. 83.
Salts, ' ;	ii. 9, 14.
----, compound or neutral,	ii. 72.
table of,	ii. 78.
	ii. 140.
Santorio's invention of air thermometers,	i. 49.
Sand-stone, . - •	ii. 295.
Saturation, .	i. 242.
Saussure's eudiometer,	iii. 225t
Scheele's discovery of phlogisticated air,	ii. 55, 94.
._________I------r fire-air, or empyreal air,	. ii. 94.
___----experiments on airs,	ii. 248.
_________discovery of the fluoric acid,	ii. 268.
_________theory of fire, heat, and light,	. ii. 344.
Schoerl, .	ii. 207.
Seas ; cause why they are not frozen in winter,	. ' i. 95.
Sea-salt, . . • • •	ii 11r.
----water,	iii. 401.
Sebacic acid,	iii. 58,
Sedative salt, .. . . ■	ii. 69.
Selenites,	ii. 179.
Semipellucid gems,	ii 321. ii- 318.
Serpentines,	
Shells,	ii. 174.
Silica,	ii. 292.
Siliceous earths,	ii. 170, 293.
,---------petrifactions and crystals,	ii. 298.
	. ii. 320.
Silver,	iii. 345,350.
——, ores of, •	. . iii. 362.
Smalt,	iii. 297.
Soap,	iii. 80. ii. 38.
Soda,	
.......pho^phorata,	ii. 397.
.......- vitriolata,	ii. 81.
Stahl's theory of the calcination of metals, ,	iii. H2r
Solution, • >	i. 240.
Soot,	iii. 56.
Spars,	ii. 172, 319.
Spelter,	iii. 281. iii. 83.
Spermaceti,	
Spirit of wine,	iii. 24.
	i. 294.
Spiritus Mindereri	ii. 128.
Stahl's opimon on the principle of inflammability,	i. 223.
	ii. 50.
	ii. 198.
 
INDEX.
                                                          FACE.  NOTES,
 Stalactites,         ,        t.         .          •          ii.  173.
 Stannum,     .    .         .         .        •           iii.  317.
 Steam cookery,             ...          i.  172.
 -------engines,           .                               i.  174.
 Steel,         .          .          .          .           iii-  204.
 Strontites,       '  .      .           .          •         ii-  277.
 Suber montanum,         .                    .           iii  315,
 Sublimation,        .           .           .          i. 190, 281.
 Subliming vessels,         .           .            .       i.  286.
 Sugar,             .        .  ■    .              •         iii-   50«
 ----, acid of,         .          .  .   .          •         >"•   52-
 Sulphat of potash,       ....        ii.   79.
" ——.------soda,       .                  •       •          "•   81.
 -----------lime,              .            •    ,      »• *79,  263.
 —----——mercury,             -             •          iii-  221.
 Sulphur,              •             •         •        ii- 54,  402.
 ------, flowers of,             .             •.             U.  412.
 ------, natural history of,          .            ..         ii-  409.
 ------, balsams of,              .              ■          ii-  412.
 ,.—---antimoniipnecipitatum,         •          •          iii-  266.
 Sulphurets,             .                      •          »"•  261.
         -of lime,            .       .  •         .     ,     ii.  189.
Sulphuric acid,              .              •           ii- 45, 413.
--------sether,             .             •               *"•  33>
Sulphurous acid,           .            •            "• 56. ii. 413.
Sun's rays, as a means of producing heat,         •          >■ 290.
Sympathetic inks,'              .            •        iii. 292, 295.
                                   T.
Talc,
ii. 314.
iii.  88.
■  ar,
  artar,             .            .                       ii. 130.
   rtarous acid,              •              •          "• «'» lJO-
 . irtarus solubilis,              •               •           »• 130.
  ivlor's (Dr.) experiments as to the expansion of fluids by
  heat,             •                          •          }  55'
 • erra foliata tartari,                                      "• 127.
 ---ponderosa,  .                                         u' 2'4-
         -                                                i   49
  hermometer,              •              •              _    'J'
  _______........s, imperfections of,             •           *•   ss-
  _______,........., various scales  for,         •         .     1.  62.
 ...................., extension of our  ideas of heat by means of, i.  66.
                                   v.
  aporization,  reasons for believing it universal,      .      i. 192.
  ipour and vaporization, general phenomena of,       .    x. 139. 
\^
INDEX.
Vapour, dangerous from burning fuel,
............s, opinions concerning the ascent of,
Vegetable alkali,
............acids,
.......-.....ammoniac,
Vegetation of salts,
Verdigrise,             .           .
Vermilion,
Vessels, chemical,
Vital air,
Vitrification of earthy bodies',
Vitriolated tartar,
Vitriolic acid,
.      ------; its action on inflammables,
———----ammmoniac,
Vitrum antimonii,
Volatile alkali (pungent),
Volcanoes,              .                  «.

                                   w.'

Walker's (Mr.) experiments with frigorific mixtures,
Water; expansion of it in congelation,
...------, boiling  in vacuo,
Water,  composition of,
-------s, of natural,
Water- bath, cause of the equality of heat from a,
-------blast,
Watt's (Mr.) steam engine,
-------———experiments on distillation in vacuo,
Wedgewood's thermometer,
Whinstone,
White lead,
Wilson's (Prof.) experiments on evaporation,
Wind-furnace,
Wine-stone,                   .       .       -
Wood as fuel,
Worcester's ("VI. of) steam engine,

                                    z.

Zaffre.
Z<"Jile,
Zinc,
Zoophvtu,
     PAGE.   NOTE:
     i, 298.
    i.  197.
    ii.  33.
    ii.  64.
    ii. 128.
    ii.  22.
    iii. 331.
   iii. 246.
     i. 274.
ii. 94, 248.
     i. 111.
    ii.  72.
    ii.  45
    ii.  48.
    ii. 119.
   iii. 264.
    ii. 188.
    iii. 194.
    i. 130.
i. 40, 325.
    i. 155.
   ii. 235.
  iii. 396.
    i.  94.
    i. 309.
    i. 176.
    i. 182.
    i. 214.
   ii. 296.
  iii. 305.
    i. 206.
    i. 307.
    ii. 13J.
    i. 299.
    i. 174.
iii.  294.
 ii.  308.
iii.  281.
 ii. I7i
FINIS. 
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