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TWO   LECTURES
                ON

     COMBUSTION:

        SUPPLEMENTARY TO A
   COURSE  OF  LECTURES
         ON CHEMISTRT.
      READ AT NASSAU-HALL.

              CONTAINING
    AN  EXAMINATION
Dr. PRIESTLEY'S CONSIDERATIONS ON THE;
      DOCTRINE OF PHLOGISTON,
                AND
    THE DECOMPOSITION OF WATER.
       BY  JOHN  MACLEAN,
PROFESSOR OF MATHEMATICS AND NATURAL PHILOSOPHY
        IN THE COLLEGE OF NEW-JERSEY.
"5JTTT
          PHILADELPHIA:
PRINTEP BY T. DOBSON, AT THE STONE-HOUSE, N° 4IS
           S. SECONP-STREET.
791- 
4DVERTISEMENT.
   Owing to other engagements, a
part only of the firfl: of thefe  lee--
tures was read to  the ftudents—*
They are now printed to fave the
young gentlemen  the  trouble  of
tranferibing them,
                           J.  M.

P. S.  // was not till after they were
  fent to the pre/s, that I was informed
  fyfr. Adet had publifhed an anfwef
  (g Dr. Priejlleys pamphlet. 
LECTURES
                   ON
      COMBUSTION.
 GENTLEMEN)

        ALTHOUGH  the  cofifequences of the
combination of different fubftances  have been ex-
plained in the le&ures which I have already had the
honour of reading to you ;  yet, as the appearances
attending  the  expofure of  inflammable bodies and
metals to the air at high temperatures,  are peculi-
arly finking, and have  occafioned much difputation
among philofophers,  it will be proper to confider
and compare the different opinions which have been
held refpeefting them;
   Becher  fuppofed  that  inflammable bodies con-
tained a fubftance,  which  he called inflammable
earth.
   Stahl thought they included a peculiar principle;
to this he gave the name  of Phlogifton.   He fup-
pofed the phenomena of combuflion were owing to 
                   (  4   )
its efcape, and the allies or refidue of a burnt body
was matter, by which the phlogifton had been con-
fined.  Thus, he thought, that in the combuftion
of fulphur,  the phlogifton  was merely  feparated
from the fulphuric acid.
   The difference among inflammable bodies, he at-
tributed  to the matter containing the phlogifton ;
and this opinion he confidered as confirmed, by the
compound of potafli and fulphuric acid being rea-
dily converted into one of potafti and fulphur, by
being mixed with powered charcoal,  and raifed  to
a high temperature: for he  fuppofed the charcoal
communicated to the fulphuric  acid the phlogifton
which it had  loft.
   As  all metallic  bodies became  converted into
earthy-like fubftances when placed in certain  cir-
cumftances, and as their original properties were re-
ftored on their being mixed with inflammable bo-
dies,  and raifed to a high temperature, Stahl con-
ceived that each metal confifted of phlogifton and a
peculiar earth or calx.
   It is eafy to perceive that Stahl did not attend to
the influence the air of the atmofphere has on every
ordinary procefs of combuftion.   He  was  ignorant
of the compofition  of the atmofphere :  he did not
know that one of its parts combines  with every
inflammable body and metal which is burnt  in  it ;
 that the new compound is  in many cafes aerial, or
 ^afeous, and  in all  exceeds in weight the combuf-
                                            tible 
                    (   s  )
tible fubftance;  that this excefs of weight corref-
ponds exactly to a like lofs fuftained by the atmo-
fphere ; that in fome cafes the whole, and in others
part, of the fubftance furnifhed by the  atmofphere,
may be feparated with all its diftinguiihing proper-
ties ;  that in every inftance the whole of it may be
detached by the aftiftance of other fubftances, which
have a  difpofition to combine with it ;  and that in
proportion as the feparation takes place, the inflam-
mable body, or metal, is recovered. In fine, it may
be  perceived, that  Stahl  was unacquainted  with
many of the phenomena,  and formed  a conjecture
to account for what he had obferved.
   By the difcovery of feveral of the circumftances
juft mentioned, Mr. Lavoifier,  a celebrated French
chemift, was induced to afcribe the change in the
properties of  inflammable bodies, and metals, by
combuftion, to their union with the oxygen of the
atmofphere, and the great increafe of temperature
which attends fome of thefe  combinations,  to tht.
fame  caufe that occafions a like phenomenon, during
the combination of other fubftances.
   Mr. Lavoifier  was foon fupported by feveral of
his countrymen,  who  were fatisfied there was na
occafion for fuppofmg the exiftence of fuch a  prin-
ciple  as phlogifton, to account for the phenomena.
Their doctrine has hence  been called antiphlogiitic.
   From its having arifen in confequence of the dif-
covery of feveral aerial or gafeous fubftances,  it  is 
                   (  6  )
alio name,1 the Pneumatic Do&rine-----It is the fyf-
icm in which you have been inftru&ed.
  At firft it was ftrenuouily oppofed by many phi-
lofophers, who,   although  they  admitted  Stahl's
theory was infuificient, yet thought the exiftence of
phlogifton was not incompatible  with the difcove^
ries which had given rife  to the antiphlogiftic doc-
trine, and was perhaps even neceffary for  the ex-
planation of forne, if not  of all, of the phenomena.
  In confequenccj many attempts were made to re^
concile  Stahl's notion with  thefe difcoveries ;  but
few phlogiftians  agreed about the nature of phlo-
gifton.  Some of them confidered it as  an immate-
rial principle; others thought it  was light ;  others
hydrogen gas, &c.;  nay, it was  not uncommon for
the fame perfon to waver between thefe  different
opinions.
  The event of the conteft has been highly honour-
able to the French chemifts.  All philofophers now
living, except Doctor Prieftley, have acceded  to
their doctrine.
  The Doctor has often  animadverted  on their ex-
periments  and conclufions, and being  perfuaded,
that what he has obferved  has not  been  properly
attended to,  or well underftood, he has lately  pub-
liftied a fmall pamphlet,  entitled, Confiderations on
the Doctrine of Phlogifton, and the Decompofition
of Water.   In it he has collected every thing  he
oonfiders as material, whether as objections to the
                                       pneumatic 
                    C   7  )
pneumatic  doctrine,  or as  arguments in favour  of
that to which he is attached.   An examination  of
thefe, while it will unfold to you his modification of
Stahl's theory, may ferve to put you on your guard
againft falling  into even that  temporary delufion,
which an erroneous  opinion is fo apt to produce,
when fupported by a celebrated name.
   The work confifts of  a  dedication, an introduce
tion, and three fections: but as the difcuflion of the
fubjeft is confined  to the feftions, it will be necef-
fary only to confider thefe.
   In the firft,  he  treats of the conftitution  of me-
tals ; in  the fecond,  of the decompofition of water ;
and in the third, of fuch objections to  the pneumatic
doctrine  as could not  conveniently be introduced
into either of the  other two.
   Although this arrangement is not very well fuited
to our purpofe, yet from an  anxiety to avoid mifre*
prefentation, I (hall retain it; and for the fame rea-
fon, inftead of giving an abridged view of the Doc-
tor's objections and arguments, I (hall read  his own
words;  but as he has  not adopted the nomenclature
In which you have been inftru&ed, I fliall  mention
 the names that correfpond with thofe  which he em-
 ploys.
    In the fection on  the  conftitution of metals, after
 giving  a very brief account of  the principles of
 Stahl and Lavoifier, he  fays,  " As a proof  that me-
 t< tals are firpple fubftances,  and  that  they become
                                          "  calces 
                    C   8  )
 " calces (oxyds) merely  by  imbibing air,  they al-
 " hge  the cafe of  mercury, which  becomes the
 " calx  called precipitate per fe (red oxyd of mer-
 " cury) by expofure to the atmofphere in a certain
 " degree of heat,  and which becomes running mer-
 <c cury  again by expofure to a greater degree of
 " heat.  They  therefore  think it impoflible not to
 " conclude,  that in all other  cafes of calcination,
 " as well as this,  the only difference between the
 e* calx (oxyd) and the metal, is that the  latter has
 " parted with the air which it had imbibed."
   This  is certainly a very inaccurate ftatement. The
 antiphlogiftians confider  metals as fimple,  becaufe
 they have  not  difcovered them to be compound;
 and they believe the fubftances, which the Doctor
 calls calces, are compounds of metals and one part
 ef the air,  which they  call  oxygen, becaufe they
 cannot be formed without  the prefence of oxygen ;
 they exceed in weight the metal, and this excefs,
 correfponds to an  equal lofs of oxygen ;  and the
 oxygen  may be  recovered entirely,  in the  ftate of
 gas, from the red oxyd of mercury, by fimply raif-
 irig its temperature ;  in  part  from the red oxyd of
 lead, and black oxyd of inanganefe by  treating
them in the fame way; and  may be wholly fepa-
rated from  every metallic  oxyd, by mixing  them
with inflammable fubftances, and  railing  the tem^
 perature of the mixture.
i
The 
                    C   9  )
  The  formation and  decompofition  of the  red
oxyd of mercury is afcribed to the oxygen  and
mercury attracting each  other, with different forces^
at different temperatures; the  partial  decompofi-
tion  of the oxyds  of lead and manganefe  is con-
fidered  as  being owing to thefe  metals  retaining
different proportions of oxygen with unequal force j
and the effect of the inflammable fubftances is attri-
buted to their  having a ftronger  difpofition, than
metals have, to combine with oxygen: All which
explanations are the more probable, from  their cor-
refponding with the laws of chemical combination,
difcovered  by  obferving the aeftion  of  different
bodies on each  other.
  After giving the forementioned account  of the
foundation of the antiphlogiftic opinion, the Doctor
attempts to fhew its infufiiciency.  "But this is
" the cafe  of only  this  particular  calk (oxyd; o(
" this metal, and there is another calx of the fame
" metal, viz.  that which remains  after expofing
" turbith mineral to a red heat, which cannot be
" completely revived by any degree of heat, but
" may  be  revived in inflammable  air (hydrogen
" gas), which  it  imbibes,  or  wheh  mixed with
gc charcoal, iron-filings,  or  other  fubftances fup-
u pofed to contain phlogifton.   And if this  calx of
u mercury, or  (fuppofing it  to  contain fome acid
" of vitriol,) [fulphuric acid,] this  fait neceffarily
«' requires  fome addition to conftitute  it a metal,
                        p                    " all 
                   (   1°  )
 " all mercury muft contain the fame.   For though
 •' with the fame  external  appearance,  the fame
 " metal  may  contain different  proportions of any
 " particular principle,  as phlogifton, they muft be
 " denominated different  fubftances, if fome fpeci-
 " mens contain this element and others be wholly
 " deftitute of it.   All, therefore,  that can  be in-
 " ferred from the  experiment with the precipitate
 " perfe (red oxyd of mercury) is,  that in this  par-
 " ticular  cafe, the mercury in becoming  that  calx
 " imbibed air, without parting with any, or very
 " little of its phlogifton j  and  if we judge by the
 " air expelled from the calces  of metals and other
 " circumftances, there are few, if any of them, but
 " contain more orlefs of phlogifton."
   From  the  following paffages in Fourcroy's Ele-
 ments of Chemiftry &c. it appears  the reafoning in
the paragraph juft read  is  founded on a miftake.
Turbith mineral "  when urged  with a  fire in a re-
" tort, at firft becomes of a deeper colour,  and  is
 " afterwards  reduced to  running mercury,  giving
 " out at the  fame  time a confiderable quantity of
" vital air (oxygen gas).   Kunckel mentions  this
" redu&ion.   It fucceeded  with Meffrs   Monnet,
" Bucquet, and Lavoifier,  who traced it  through
" all its circumftances.  I have repeated  it feveral
tc times with fuccefs.
   "  Perhaps  the  reafon  why Mr.  Baume did not
" obtain running mercury, which has  induced  him
                                           " to 
                   (   »  )
" to affert that this yellow oxide does not refume
" a metallic form unlefs fome combuftible fubftance
" be added, was  his not having applied to it a fuf-
" ficient heat."*
  Thefe are confirmed by later obfervations,f and
they fhew, the  mercury in turbith mineral, or any
fubftance into which it may be converted  by a red
heat,  does not require any addition to conftitute it
a metal.
  It is  true, the  prefence of hydrogen  gas,  and
other inflammable fubftances,  renders the  reduction
eafier; but this it is contended,  only proves, that
the fubftance is  decompofed more  readily, when
there is  a body  prefent,  which has a difpofition to
combine with one of its conftituent  parts, viz. the
oxygen, a  circumftance analogous to many other
chemical decompofitions.
  The antiphlogiftians are induced to believe the
hydrogen  gas is not imbibed  by the mercury, but
combines  with  the oxygen, becaufe, \Ji. Oxygen
gas may be colle&ed, when  an  oxyd of mercury-
is reduced by limply  raifing  its  temperature: %d.
When the reduction is performed in  hydrogen gas
this difappears,  no oxygen gas  is obtained, but a
quantity of water may  be colle&ed: And,  ^d. From
various  experiments it feems, that water is a  com-
pound of hydrogen and oxygen.
  * Fourcroy, Vol. II. p.  318.   London Edition, 1790.
  + Annates de Chimie, Tome iomc. p. 305.
                     b  2                   That 
                   C  "   )
  That a higher temperature  is neceflary  for the
decompofition of the fubftance from  turbith mine-
ral, than for that of the red oxyd of mercury, is
not at all furprifing; they are different bodies, and
muft therefore be acted on  by other agents, with
different forces.
  The  inference, which  the Doctor draws  from
the experiments with the red oxyd of mercury, and
from the gas  obtained from  the oxyds of other
metals,  cannot be  admitted, until  he proves  the
mercury and gas a&ually contain phlogifton.
  The Doctor proceeds—" I would obferve in this
" place, that it is afferted by fome  very able che-
" mifts, that if the  precipitate per fe (red  oxyd of
" mercury) be made with proper attention,  it  will
" be revived without yielding any air.  This is alfo
" the cafe  with minium (red  oxyd of lead) when
" frefti made.  But this is owing, I doubt not, to
*e their wanting ivater, which I deem to be effential
" to the conftitution of every kind of air  (gas) ; fo
" that they both contain the element of dephlogif-
" ticated  air (oxygen gas), though for want of
*6 water, it is not able to affume that form."
   I confers, I am  unacquainted  with the expert
ments, which have  led to the affertion alluded to in
this paragraph.—But, if water be effential to the
conftitution of every kind of air, and if mercury
and lead are  converted  into  their red  oxyds,  or
calges, by  uniting with the  element  of oxygen gas
                                              or 
                   (   >3  )
or dephlogifticated air, what precaution can prevent
the compounds  from imbibing  the water, if they
have a difpofition  to  do fo ? The Do&or  believes
they have fuch  a difpofition;  for  except to thefe
able chemifts, they  have always  afforded oxygen
gas or dephlogifticated air, and to do this they muft,
in his opinion, contain water.
  The next paragraph is as follows.   " That mer-
(C cury may have the fame external appearance and
" all its effential properties, and yet contain differ-
" ent proportions  of fomething that enters into it,
" is evident from  the phenomena of its folution in
" the nitrous acid, and  the revival of its calx in in-
" flammable air (hydrogen gas).   According to  the
" old theory, there is a lofs of fome part of its phlo-
'? gifton  in the  folution of mercury in the nitrous
e^ acid,  fince nitrous air  (gas) js  procured in  the
" procefs: And though it may be revived from its
" precipitates (oxyds) by mere heat, yet if it be
*' revived in a veffel of inflammable air (hydrogen
" gas), it will imbibe it in great quantities.  Mer-
" cury revived in  thefe circumftances muft contain
" more phlogifton than that which is revived from
" the fame calx by mere heat.  But though mer*
" cury reviyed  by mere  heat  after a folution in
*' nitrous acid muft have a deficiency of phlogifton,
ft and  when  it  is revived from precipitate  per fe
" (red oxyd of mercury)  in  inflammable air (hy-
« droeen gas) muft contain  a, redundancy of  the
                                         " fame 
                   (   14  )
" fame principle, yet there will hardly be a doubt
" but that, in all chemical proceffes,  it  would  ex-
" hibit the fame phenomena."
  I: two portions of matter exhibit the fiime pheno-
mena in all chemical operations, they ought moft
certainly to be confidered as  the  fame fubftance;
and as  mercury revived from its oxyds by a mere
increafe of temperature, poffeffes all the  properties
of that revived by the afiiftance of hydrogen gas,
&c. it cannot  be in any  refpecr. deficient.  It is in
vain to fay, that it muft be fo, becaufe " according
" to the old theory, there is a lofs of fome part of
" its phlogifton in  the folution of mercury in the
" nitrous acid," and if it be  revived in hydrogen
gas " it will imbibe  it in great quantities;"  it is
firft  incumbent to prove, that the old theory, as
iie calls it, is right, and that the  gas which  difap-
pears,  is  a&ually abforbed by the mercury:  but
thefe are juft the fubjects of difpute.
   Having faid fo much  on mercury he obferves.
"  In all other eafes of the calcination (oxydationj
"  of metals in air, which I have called the phlogifti-
"  cation of the air, it is not  only  evident that they
"  gain  fomething which adds to their weight, but
"  that  they  likewife  part with  fomething.    The
"  moft fimple of thefe proceffes is  the expofing iron
"  to the  heat of a burning lens in confined air, in
"  confequence of which  the  air  is diminiftied and
««  the  iron becomes a calx (oxyd).   But that there
                                             " is 
                    I   *5   )
*' is fomething emitted! from  the iron in this procefs
" is evident from the ftrong fmell which arifes from
" it.   If the procefs be continued, inflammable air
" [hydrogen gas] will be  produced, if  there be
" any moifture at hand to form the bafis of it. From
" this it is at leaft probable, that,  as the  procefs
" went  on in  an uniform manner,  the fame fub-
" ftance, viz. the bafis of inflammable air [hydrogen
" gas], was continually iffuing from it; and this  i>
" the fubftance, or  principle, to which we give the
" name of phlogifton."
   " That  the effect of this procefs  is not, as the
" antiphlogiftians affert,  the mere  feparation of the
" dephlogifticated from the phlogifticated air [the
" oxygen from the azotic gas] in that of the atmof-
" phere, I  have proved in a courfe of experiments,
" in which I have fhewn that a confiderable part
" of the phlogifticated air  [azotic gas]  that is found
" after this procefs,  is formed in the  courfe of it,
" by the union of the  phlogifton from  the iron
" with the dephlogifticated air [oxygen gas].  And
" if the  calcination of the  iron in  this procefs be
" always attended  with  the lofs of  fome confti-
" tuent part of it, the fame is, no doubt, the cafe
" with all other calcinations of the fame metal, and
" alfo thofe  of  all  other  metals.  And further,  if
" the metals be compound  fubftances, containing
" phlogifton united to  fome bafe,  the fame is  the
" cafe with fulphur and  pbofphorus, becaufe they
                                      (t become 
" become acids when they  are  ufed in the fame
" procefs."
   I do not know,  that a fmell arifes from pure iron
when heated in air:  but moft certainly there  are
other metals, from  which  no fmell  arifes,  when
placed in the fame circumftances ; and the Doctor
has faid, if the calcination of iron be attended with
the lofs  of fome  conftituent  part  of it,  meaning
phlogifton, the fame is no doubt the cafe with thofe
of all  other metals; and therefore even although
iron fliould afford  a  fmell,  it is no proof cf the ef-
cape of phlogifton.
   That  a  quantity  of hydrogen gas is obtained
when the iron or air is moift is moft certain: but this,
it is infilled,  is owing to the iron  uniting with the
oxygen of the water, while  the hydrogen  affumes
the form of gas or air.
   I have not been able  to  find  any  courfe of ex-
periments,  which proves, that azotic gas is formed
by expofing iron in confined  air to the rays of the
fun concentrated by a burning lens: but Dr. Prieftley
informs us, that on examining the  refiduum of fome
" pretty pure dephlogifticated air [oxygen gas]"
in which iron had been fired with  afliftance of a
lens, " it did not appear that any  phlogifticated
" air [azotic gas]  had been produced in the pro-
" cefs,"* and the fame thing has been obferved by

  * Experiments and Obfcrvations on Air, Vol. III. p. 481.
      *                                Lavoifier 
                    (   '7  )
Lavoifier,*  confequently azotic gas cannot be form-
ed by any thing from the iron uniting with oxygen,
and  the argument for the exiftence of phlogifton
drawn from its fuppofed formation is invalid.
.  From the effects of air at high temperorures, the
Doctor paffes  to thofe of acids or metals.   " Accor-
" ding  to the antiphlogiftic theory, the  inflamma-
" ble air [hydrogen  gas]  that  is produced  in the
" folution of metals in any acid, comes wholly from
" the water combined with it; and not at all from
" the metal diffolved.  But  the  advocates for this
" theory do not feem to have attended to one ne-
" ceffary confequence of this fuppofition.  Accor-
" ding  to their  own principles,  water confifts  of
" eighty feven parts of oxygen, to only thirteen of
" hydrogen in every hundred, which is nearly feven
" times as  much of the  former as of the  latter.
" Confequently fince nothing but  hydrogen efcapes
" in the procefs,  there muft remain, from this de-
" compofition of the water,  feven times as much
" oxygen in the folution.  But both Mr. Lavoifier
" and  Mr.  de la Place  fay  [Examination of  Mr.
" Kirwan's  Treatife, p.  197, 198,] what I  doubt

  * II eft  de mcrae extrerr.ement difficile d'obtenir du gaz
oxigine  parfaitement pur, il contient  prefque toujours une
petite portion de gaz azote,  mais elle ne trouble en iien le
refuhat de l'experience, & elle  fe retrouve a la fin en raerae
quantite  qu'au commencement.  Annales de Chimie, Tome
I. p. 26.
                        c                   " not 
                   r(   IS   )
" not is ftri&ly true, that after  the procefs the acid
" will faturate  exactly the fame quantity  (they do
" not fay more) of alkali, that it would have done
" before;  whereas, with the addition of  fo much
" oxygen, it ought  to faturate confiderably  more.
" If the oxygen from the decompofition of the  wa-
" ter do  not join that  in the  acid,  what  becomes
" of it ?"
  The anfwer  to this queftion is very eafy—Far
from  fuppofing  the oxygen  from the water joins
that in the acid, the antiphlogiftians believe it unites
with the metal,  to enable this to combine with the
acid.   They are of this belief,  becaufe the metal is
precipitated in  a ftate of oxyd when  an  alkali  is
added  to  the folution ;  while the acid requires the
fame quantity of alkali to faturate it, and forms the
fame fubftances  that it would have done before its
action on the metal.
  Perhaps it was from being aware of this anfwer
that the Doctor has faid, in the next  paragraph,
which concludes the fection,  " If this cafe be ana-
" logous to that of the  fuppofed decompofition of
" water by hot iron,  the oxygen ought  to be lodg-
" ed in the iron, and compofe finery cinder (black
<s oxyd of iron).  But this fubftance is  not foluble
" in vitriolic (fulphuric) acid, if that be employed
" in the experiment; and when it is diffolved in the
" marine (muriatic) acid, it does not dephlogifticate
" (oxygenate) it,  as  minium (red  oxyd  of lead)
                                          "  and 
                    (   '9  )
u and other  fubftances  containing  oxygen,  &c.
" It is evident, therefore,  that there is no addition
" of oxygen  in  this procefs, confequently no de-
" compofition of water in the cafe, and that the in-
" flammable air  (hydrogen  gas) muft come from
" the decompofition of the iron/'
  It  is rather furprifing the  Doctor fhould affert,
that finery cinder (black oxyd of iron) is not foluble
in fulphuric acid,  when,  in page 505 of the third
volume of his own experiments and obfervations,
it is faid, that of fixty grains of finery cinder put
into vitriolic  (fulphuric) acid, * fifteen  grains re-
mained undiffolved. Befides, there is the moft fatis-
factory evidence that  iron, after its folution in the
fulphuric acid,  is in a ftate  like that of the black
oxyd or  finery cinder.   This fubftance  diffolves  in
the acid  without effervefcence, f and if the precipi-
tate which  the folution of iron in the fulphuric acid
affords,  on the addition of an alkali, be collected  as
foon as it falls, and dried in clofe veffels, it will be
the black oxyd. J  There is no effervefcence during
the  folution, becaufe  there is no hydrogen gas
evolved; and this,  the  antiphlogiftians  believe,  is
owing to the iron  being previoufly combined with
enough of oxygen to  fuperfede the neceflity of de-

  * The quantity of acid is not fpecified.
  f  Lavoifier's Elements of Chemiftry, p.  8$.  Edinb.
Edition, 1790.
  + Fourcroy, Vol. II. p. 425.
                       c 2              compofing 
                    C  2°   )
compofing the water. The precipitate muft be dried
immediately, and in clofe veffels, becaufe, from its
minute divifion,  it  is very liable to be oxydated to
a greater degree.
   The other cirrumftance which he has adduced as a
proof, that the black oxyd does not contain oxygen,
is not more convincing.  It  certainly does not fol-
low,  becaufe  muriatic acid  can  feparate  a  certain
portion of oxygen from lead, when this is  combined
with  a great quantity of that  fubftance,  that  it
fliould likewife  feparate oxygen from iron, when
this is united to  a comparatively  fmall quantity.
   From  this firft fection of the Doctor's work it
feems, his objections to the opinion, that metals are
fimple, and become converted into earthy-like bo-
dies by an  union with oxygen, are,   \ft.  The fub-
ftance which remains after expofing turbith mineral
to a red heat, cannot be  made to yield its mercury,
unlefs it be mixed with bodies  fuppofed  to  contain
phlogifton.    id. When iron is fired in air it emits
a fmell, and if there be moifture at hand, inflamma-
ble air (hydrogen gas) is produced.-  $d. Phlogif-
ticated air  (azotic gas) is formed during  the com-
buftion of iron.   4th. If oxygen was feparated from
hydrogen during the folution of iron in acids, thefe
fhould acquire a proportional addition of ftren<nh.
And,  $th. Iron diffolved in the fulphuric acid is not
in the ftate  of the black oxyd.
   It alfo appears that the Doctor is of opinion,
                                     •   1. That 
                   (   21   )
   i. That metals contain phlogifton.
   2. That, in the formation of  precipitate per fe,
(red oxyd of mercury)  air is abforbed, and little or
no phlogifton emitted.
   3. That mercury revived from its calces (oxyds)
by  mere  heat contains lefs phlogifton than when
revived with the aftiftance of  inflammable air  (hy-
drogen gas.)
   4, That the fmell which arifes from heated iron,
is  owing to the  phlogifton which is efcaping, and
that the  inflammable  air (hydrogen gas) which is
produced when  moifture is  at hand, is  formed by
the union of the phlogifton with the water.
   5. That phlogifticated air (azotic gas) is formed
by the union of phlogifton with  dephlogifticated air
(oxygen gas.)
   6. That the inflammable air (hydrogen gas) emit-
ted during the folution of iron in acids, is owing to
the decompofition of the iron.   And,
   7. That finery  cinder (black  oxyd of iron)  does
not contain oxygen.
   But from the facts mentioned in the review of
the fection it follows,  1. The  fubftance into which
turbith mineral may be converted by a red  heat,
 affords its mercury by a fimple increafe of tempera-
 ture.
    2.  Mercury, revived from  its oxyds by a fimple
 increafe of temperature, does not differ from that
 revived  in hydrogen gas.
                                            1,  It 
                    (   «  )
   3. If a fmell arifes from  heated iron,  it is  no
 proof of the emiflion of phlogifton.
   4. Azotic gas cannot  be formed by the union of
 oxygen with any thing emitted from heated iron.
   And, 5. Iron, when diffolved  in fulphuric acid,
 is reduced to a ftate like that of the black oxyd.
   And further, if it can be proved that water is a
 compound of hydrogen and oxygen,  and fufceptible
 of decompofition,  as is infilled by  the  antiphlogif-
 tians, it muft alfo  follow, that hydrogen gas, and
 other inflammable fubftances,  affift  the reduction of
 metallic oxyds,  by combining with their  oxygen.
 And that the hydrogen gas obtained by  expofing
 heated iron to moifture,  or by diffolving iron in di-
 luted fulphuric acid, proceeds  from the decompofi-
 tion  of the water,  and not from that of the iron.
 —But the proofs of thefe will be exhibited in the
 examination of the fecond feclion.

   The  fecond fedtion of Dr.  Prieftley's  work is the
 moft important.   He  begins  it  with  obferving,
 "  The antiphlogiftic theory has received its greateft
 "  fupport from the  fuppofed difcovery,  that water
"  is refolvable into two principles ; one that of oxy-
"  gen, the  bafe of dephlogifticated air, and  the
"  other, becaufe it has no other origin  than water,
"  hydrogen, or that which,  with  the addition of
"  calorique, or the element of heat, conftitutes  in-
"  flammable air."
                                            The 
                   (   *3  )
  The term  hydrogen is derived  from craf, aqua,
and yurty.ni, gignor, and was.defigned to exprefs the
principle engendering water.  It has been criticifed
by fome, who maintain it  fignifies, engendered by
water, and this is  the fenfe  in  which Dr. Prieftley
feems inclined to  underftand it.  But, as has been
well obferved by  Mr.  Lavoifier, it may be ufed in
either of thefe acceptations; for where water is de-
compofed hydrogen is produced, and when hydro-
gen is combined with oxygen water is produced.
  After  giving an extract from a joint work by fe-
veral of  the antiphlogiftians, in which they declare
their firm belief in the formation, the decompofition,
and recompofition  of water, the Doctor fays,
  " Notwithftanding  the confidence thus ftrongly
" expreffed by thefe able and experienced chemifts,
" I muft take the liberty to fay,  that  the experi-
" ments  to  which they allude  appear to me to be
" very liable to exception, and that the doctrine of
" phlogifton  eafily accounts  for all that they ob-
" ferved.
  " Their proof that water is decompofed,  and re-
" folved into two  kinds of air,  is,  that when fleam
" is made to pafs over red-hot iron inflammable air
" is produced, and the iron acquires an addition of
" weight, becoming what is called finery cinder ;
" but what  they call oxide of iron,  fuppofing that
" there is lodged  in it the oxygen  which was one
" of the conftituent parts of the water expended in
                                           " the 
                    (  24  )
« the procefs, while the other part, or the  hydro-
" ^en, with the addition of heat, affumed the form
" of inflammable air."
  It ought to have been ftated, that in this experi-
ment there  is a lofs of water exactly equal to  the
joint weight of the  addition made to the iron,  and
of the hydrogen gas obtained.
  The antiphlogiftians fuppofe the addition made to
the  iron to be  oxygen,  becaufe the compound rc-
fembles, in every reipect, as the Doctor  himfelf al-
lows,  that  fubftance which is  formed by burning
iron in oxygen gas, or in atmofpherical air ; and this
they confider as an oxyd, becaufe,  \fl.  While it is
forming  the oxygen gas difappears, and  its  weight
is exactly equal to that of the iron and  the  oxygen
confumed: *-----And,  id. When  iron-filings  are
mixed with red oxyd of mercury,  and the  mixture
made nearly red-hot, the iron is converted into  the
fame black fubftance  as  in the laft  experiment,
while  the oxyd of  mercury is reduced, and  the
weight acquired by the iron correfponds to  the  ex-
cels of that of the red oxjyd above the mercury, f

  *  Onand on  a dormc a cette experience toute l'attention
qu'elle merite, l'air fe trouve diminue d'une quantite en poids
exafiement egale a ce'.le dont le fer eft augmente.  Annalcs
de Chimie, Tome I. p. 24..
  f  J'ai  nic e enfemble (fays  Mr.  Lavoifier), 450 grains
d'oxide rouge de mercure, par le feu, bien pur, & 100 grains
de limaille d'un fer tres doux, et qui n'etcit nullement atta-
       4.                                      <!"£ 
                     (,   25   )
   The hydrogen gas is fuppofed to come from the
 water, and not from the iron, becaufe it is not ob-
 tained when  the black oxyd is formed, without the
 aififtance of water; and, as will be fhewn, water may
 be formed by uniting oxygen with hydrogen.
   The Doctor  obferves,  on  the  experiment  with
 iron and  water,  " But in order to prove that this
 " addition of weight  to the iron is really  oxygen,
 " they ought to be  able to exhibit it in the form of
 " dephlogifticated air  (oxygen gas)  or fome other
 <c fubftance into which oxygen is allowed  to enter,
 " and this they have not done. Iron that has really
 " imbibed air, or the  common  ru/i of iron, has  a
 " very different appearance from this finery cinder
 " (black oxyd of iron) being red, and  not black;
 " and when  treated in  fimilar  proceffes,  exhibits
 " very different refults.   Mr. Fourcroy  fays (Exa-
 " mination of Kirwan, p. 251.) that this finery cin^
 " der is  ' iron partially oxygenated.'   But if that

 que de  rouille.  J'ai introduit ce melange dans une  petite
 cornue, &  J'ai fait chauffer jufqu'au moment feulment  ou les
 vaiffeaux ont commence obfcurement a rougir.  II ne s'eft
 degage aucun gaz pendant cette operation, fi ce n'eft une tres-
 mediocre quantite d'air  fixe ou acide catbonique aeriforme ;
 elle n'excedoit pas deux ou trois pouces cubiques.  II a paffe
 dans la diftillation  415 grains de  mercure  coulant;  ayant
 enfuite  cafse la cornue, J'ai trouve la limaille de fer dans I'etat
 d'un fer brul<, elle etoit friable, elle fe reduifoit aifement en
 poudre, elle  etoit dans I'etat d'un veritable ethwps (black
exyd) & pefoit  132 grains.  An. de Chimie,  Tome I. p. 28.
                        d                  " were 
                  (   26  )
" were the cafe, it would go on to attract more ox-
" ygen, and in time become a proper ruft of iron,
" completely oxygenated.   But  this is fo far from
" being the cafe, that finery cinder  never will ac-
" quire ruft ; which fliews, that the iron in this flate
" is  faturated  with fome very different principle,
" which even  excludes that which would have con-
" verted it into ruft."
  The evidence which has been given, feems to me
to be fufficient to prove the  addition made to the
iron muft be  oxygen ; but more will be given  in
the courfe of thefe lectures.
  Without doubt common ruft of iron is very dif-
ferent from the black oxyd  : but the Doctor is cer-
tainly miftaken in fuppofing this cannot acquire ruft ;
Mr. Fourcroy  fays,  it  rufts fooner than common
iron, and every apothecary knows it does fo.  Be-
fides, we  learn from  the  experiments  of Meffrs.
Joffe and Fourcroy, that if ruft be made red hot in
a retort, a quantity of carbonic  acid is  difengaged
from it, and the iron remains  in  the flate of black
oxyd.   The ruft therefore  is a carbonate of iron,
and muft  contain all the principles which compofe
the  black oxyd;  and this can  contain none capable
of  excluding that which would convert it into ruft.
   The Doctor then remarks, " However, neither
" this, nor any other calx of iron,  can be revived,
•" unlefs it be  heated in inflammable air (hydrogen
 -•' gas), which it eagerly imbibes, or in contact with
                                         " fome 
                    C  27   )
 " fome other fubftance which has been fuppofed to
 66 contain phlogifton.  The probability therefore is,
 " that the phlogifton then enters this calx of iron,
 " replacing that which had been expelled to form
 cc the inflammable air. Nor can any inflammable air
 " be procured in this procefs with fleam, but by
 " means of fome fubftance which has been fuppofed
 " to contain phlogifton.   Where then is the cer-
 " tain proof that water is decompofed in this pro-
 " cefs ?"
   The fuppofition that a  body contains  phlogifton
 is no proof that it does fo.
   " It  may be faid, that the oxygen imbibed by
 " this iron, being  expelled by heat  in contaft with
 " inflammable air (hydrogen gas), unites with that
 " air, and with it conftitutes the water  found af-
 " ter the procefs.  But for any thing that appears,
 " this  water may be that which the iron had im-
 " bibed,  and which can  only be expelled from it
 " by the entrance of that phlogifton which it  had
 " loft."
   Doubtlefs you will be furprifed to hear, that wa-
 ter is the fubftance  which  the  Doctor fuppofes is
 capable, when combined with iron, of excluding that
 which  would convert it into ruft ; and you will re-
collect that black oxyd of  iron can be formed with-
out the  affiftance of water.
   It is true,  the Doctor obferves on  the  formation
of the black oxyd in oxygen gas and atmofpherical
                      d  2,                  airT 
                   (  28   )
air, that " by far the greateft part of the weight
" of dephlogifticated air (oxygen gas; is water, and
" the air being decompofed  in the procefs, the wa-
" ter is  imbibed by the  iron, and the  acidifying
" principle (oxygen) contributes to form," accord-
ing to the publication now under review, phlogifti-
cated air (azotic gas, *) but by his experiments and
obfervations, " fixed air (carbonic acid gas), with the
" phlogifton which is at the fame time expelled from
" the iron." f
  It has been already fhewn, that no azotic gas is
formed by the combuftion of iron  in oxygen gas ;
and the quantity of carbonic acid which has been
found in the  remainder of  oxygen  gas,  in  which
iron has been burned, is very trifling, and is owing
partly to the gas containing fome before the ope-
ration,  and partly to plumbago contained  in  the
iron.  {
   But moreover, if the Doctor's explanation of the
 formation of the carbonic acid gas be accurately exa-
mined,  it will be found inconfiftent with many of his
 own principles.
   He believes water is a conftituent part of oxygen
 gas,  becaufe, from certain  experiments, he  has
 inferred it conftitutes one half of carbonic acid gas,

  * See P. 15.
  f Experiments and Obfervations, Vol. III.  p. 551.
   I Annales de Chimie, Tome III. p. 91—97.
and 
                   (   *9   )
and enters into the compofition  of all aerial fluids:
and from the quantity of water  obtained  on burn-
ing hydrogen in oxygen  gas,  he fuppofes it con-
ftitutes nine parts in ten of oxygen gas. *
  It will be fliewn in the next lecture, that his opinion
reflecting the compofition of gafes is not well found-
ed ;  but  for the fake  of argument, let it  for the
prefent be granted, that oxygen gas is compounded
as he fuppofes,  and that  carbonic acid gas confifts
" of about one half water,  and the other phlogif-
" ton and dephlogifticated air t (oxygen gas) in the
" proportion of one fourth of the former, to three
" fourths of the latter." J
   In page 159 of the firft volume of his Experiments
and Obfervations, he fays, " In fix ounce meafures
 " and a half of dephlogifticated air (oxygen gas),
 " I melted turnings of malleable iron till there re-
 " mained only an  ounce meafure  and one  third;
 " and of this twenty-feven thirtieths of an  ounce
 " meafure was fixed air (carbonic acid gas)." Confe-
 quently the oxygen gas  concerned in the formation
 of  the carbonic acid  gas, muft  have occupied the
 fpace of 6,06 ounce meafures. §
   *  Experiments and Obfervations, Vol. III. p. 535.
   f  He means what he calls the acidifying principle or ox-
 ygen.
   +  Experiments and Obfervations, Vol III. p. 536.
   §  The volume of gas that difappeared was 5,16 ounce
 meafures, and that of the carbunic acid  was ,9 of an ounce
 meafure.                                        . 
                    (   3°   )
   An ounce, meafure is equal to 1,8980 cubic inch,
and therefore 6,06  ounce meafures  are equal  to
11,501  cubic inches.
   A cubic inch of oxygen gas  weighs ,34211 of a
grain;* and  11,501  cubic  inches  weigh  3,9346
grains.
   The  weight of a cubic inch of carbonic acid gas
is  ,44108 of a grain ; f and that of ,9 of an ounce
meafure, or 1,7082 cubic inch is ,75345 of a grain.
   The 3,9346 grains of oxygen gas,  confumed  in
the experiment, confifted, according to the Doctor's
eftimation, of 3,54114 grains of water, and ,39346
of a grain  of  oxygen : and the ,752,4-5 of a grain
of carbonic acid gas confifted of ,37672 of a grain  of
water, ,09418 of a grain of phlogifton, and ,28254
of a grain of oxygen.   Therefore the oxygen ad-
mitted into the carbonic acid  gas was lefs than that
contained in the oxygen gas..   What became of the
reft?}
   But the infufficiency of the Doctor's  account  of
the formation  of  the  carbonic acid gas will more
clearly appear, on  comparing the combuftion of iron
with that of charcoal.

  * Lavoifier's Elements,  Edinb. edit. Appendix, p. 490.
  f Ibid.
  f The above calculation is  made on the fuppofuion that
all the caibonic acid was formed during the procefs, although
it is probab'e fome of it  was contained in the oxygen gas be-
fore the combv.i-ion of the  ircn.
                                      " I heated 
                   (  3*   )
  " I heated (fays he*) eight grains and a quarter
<c of perfect charcoal, in 70 ounce meafures of de-
" phlogifticated air (oxygen gas) of the ftandard of
" 0,46, when it ftill  continued 70 ounce meafures ;
" but after wafhing in water, it was reduced to 40
" ounce  meafures of the ftandard of 0,6, and the
" charcoal then  weighed a grain and a quarter."
  Suppofing this experiment to have been accurate,
which is not eafy to do, the quantity of oxygen gas
confumed was 19,47974 grains, and that of the car-
bonic acid obtained was 25,11509 grains.   Accord-
ing to the  Doctor,  the  firft confifted of 1,947974
grains of oxygen, and 17.531766 grains of water;
and the  fecond  of 9,418159  grains of oxygen,
3,139386  grains  of phlogifton, and  12,557545
grains of water.
  By this  ftatement, the carbonic acid gas did not
contain fo much water as the oxygen gas; yet there
is none of that fluid depofited when perfect charcoal
is burnt in  dry oxygen gas: the phlogifton in the
carbonic  acid was not half the weight of the con-
fumed  charcoal; although the  Doctor fays, page
166, Vol. I. of  his Experiments and Obfervations,
that charcoal is very nearly pure phlogifton ; the
oxygen in the carbonic acid gas was almoft five times
as much  as that  in the oxygen gas ; and from the
experiment  with iron,  the oxygen in  the oxygen

    * Experiments and Obfervaticns, Vol. III. p. 377.
                                            gas 
                    C  3^   )
 gas  ought to have formed 3,73023 grains of car-
 bonic acid gas, whereas  the quantity faid to have
 been obtained was 25,11509  grains.
   It is plain, therefore,  the  formation  of the car-
 bonic acid gas cannot be accounted for,  by fup-
 pofing the two gafes to be compounded in the man*
 ner alleged by the Doctor, and charcoal to be pure
 phlogifton.
   But he has faid in page 547 of the third Volume
 " that charcoal contains all the element  of fixed air
 " [carbonic acid gas], the acidifying principle as well
 " as phlogifton."-----However,  even  this  fuppo-
 fition will not be fufficient to remove the difficulty.
   It has been  already  mentioned,  that  of the
 25,11509 grains of  carbonic acid gas, 3,73023
 grains fhould on the Doctor's principles be formed
 by the affiftance of the oxygen  gas: the phlogifton
 fuppofed by him to be neceffary for this quantity
 is equal  to ,46627 of a grain, and ought to have
 been furnifhed by  the charcoal.  The remainder
 of the feven grains of charcoal fhould have confifted
of phlogifton  and oxygen, in a  proportion  fit for
making, on the addition of water, the carbonic acid
gas.   But the remainder is 6,53373 grams ;  and as
water is fuppofed to conftitute one half  of the car-
bonic acid gas,  it ought to have formed 13,06746
grains, and thefe with the 3,73023 grains are lefs
 than the quantity  faid to have  been formed by
 8,31740 grains.
       4                                  Now, 
                   C   33  )
   Now, as the formation of the  carbonic acid gas
by the combuftion of charcoal cannot be reconciled
to the fuppofed compofition of the two gafes, and
as the  explanation which the  Doctor has  given,
of the formation of  the fame gas by the combuftion
of iron  is founded on the fame principles,  it can-
not poffibly be juft.  And  further, as his opinion
of the  compofition  of finery cinder rcfts  on the
propriety of the explanation which he has given of
the formation of the azotic gas, or of that  of the
carbonic acid gas, and as both have been fhewn to
be wrong,  it alfo muft be groundlefs.
   In  confirmation of his opinion the  Doctor pro-
ceeds, " This is the more probable,  fince  when
"  any other fubftance, which is  certainly known to
"  contain oxygen, is  heated in the fame circum-
"  fiances, fixed air [carbonic acid]  (which  is al-
"  lowed to contain oxygen) is found, and  this is
"  not the cafe with this calx of  iron.   If for ex*
"  ample precipitate per fe, or minium  [the red
"  oxyds of mercury and lead] be heated in inflam-
<e  mable air, the  mercury and the lead will  be re-
"  vived, and a confiderable quantity of fixed air [car-
" bonic acid gas] will be produced at the fame time.
"  But if the  air be previoufly expelled  from the
"  minium which converts it into a yellow fubftance
"  called mafficot [yellow oxyd of lead] though the
"  lead will be revived,  no fixed air [carbonic acid
"'  gas] will be generated.  Since  therefore, the re-
                      e                  " fult 
                   (  34  )
" fult of treating finery cinder [black oxyd of iron]
" and  mafficot is  precifely  the  fame,  in  the fame
" circumftances, we are fully authorifed to conclude
" that the fubftances themfelves are fimilar, and
" confequently  that the finery  cinder contains  no
" more oxygen than mafficot."
  Together with  fome water,  a fmall  but not a
confiderable quantity of carbonic acid gas is com-
monly obtained,  when  the red oxyds  of mercury
and lead are revived in hydrogen gas.   In one ex-
periment made  with red oxyd  of mercury,  fent to
the Doctor by Mr. Berthollet, he obtained 0,04
of an ounce meafure  of  carbonic acid gas; and in
another, made with red oxyd of lead, he procured
0,028  of an ounce meafure.*
  Metallic oxyds are much difpofed to  unite with
carbonic acid, and therefore  the fmall quantity ob-
tained in the above inftances, might with fafety be
attributed, to their having  attracted  it  from  the
atmofphere and parted with it during the redueftion.
  But Mr. Berthollet informs us,f the oxyd which
he gave to the Doctor actually  did contain carbonic
acid:  On diftilling 50  grains  of it  and receiving
the gas over lime water,  although this was not at
firft  made turbid, after about a quarter of an hour
it depofited a confiderable precipitate.   The pre-
cipitate he afcribed to carbonic acid uniting with the

     '  Experiments and Obfervations, Vol.  I. p. 168.
     f Annales d^ Chimie, Tome III. p. 91.
                                           lime. 
                    (   35  )
lime; and its flow formation to the acid being held
in folution  by a great quantity of oxygen gas,  and
to the portions of  the carbonate of  lime  which
were firft formed being diffolved  by the unchanged
lime water.
   Dr. Prieftley obferves on this  experiment of Mr.
Berthollet,  " The  precipitate per  fe with  which
"  Mr. Berthollet furnifhed me,  he fays, contained
"  a confiderable quantity  of fixed air; and yet he
"  allows  that when  admitted to lime water, it did
"  not immediately make it turbid, which it is well
"  known a tenth part of the fixed air which I  pro-
"  cured would have made it inftantly and complete-
"  ly white.   The turbulency that came on after-
"  wards muft therefore have had fome other caufe, *'
"  probably  fome acid of vitriol  [fulphuric acid] in
"  the water of the trough in which the experiment
"  was made, and which gradually  infinuating itfelf
"  into  the lime water in his  tube,  would  make a
iCfelenite [fulphate of lime], a thing that  has  fre-
"  quently occurred in the courfe  of my own experi-
"  ments, and which for fome time puzzled me not a
"  little."*
   But although the carbonic acid gas which he ob-
tained would make a certain quantity of lime water
inftantly turbid, it is not well known that it would
do fo  when combined with feven or  eight cubical

    * Experiments and Obfervations, Vol. III. p. 559.
                      s 2                 inches 
                   (  36   )
inches of oxygen gas.  Mr. Berthollet does not fay,
that the water in the trough of his pneumato-che-
mical apparatus was different from that in the veffel
in which he received the oxygen gas ; and I  cannot
believe a man of his accuracy would think of filling
the trough, for fuch an experiment, with any other
than lime water.
   The  yellow  oxyd  of  lead  may be  formed by
making the red oxyd red hot,  or  by expofing lead
to the fame temperature and  in contact with  air.
It affords no carbonic acid gas when it is reduced in
hydrogen  gas, not from its being deftitute  of oxy-
gen, but from its containing no carbonic acid. The
temperature to which it has  been previoufly  fub-
mitted  is unfavourable  to its  union with carbonic
acid; but  if when cooled, it be expofed for a fhort
time to the air, it will imbibe that fubftance and
yield it when reduced in hydrogen gas.
   It will be readily allowed by the antiphlogiftians,
 that if yellow oxyd of lead does not contain  oxy-
 gen, the black oxyd of iron does  not do fo either :
 but the yellow oxyd cannot be made  without the
 prefence of oxygen gas or  atmofpherical air ;  it is
 heavier than the lead  in  its  compofition ;  and its
 not affording carbonic acid is no  proof that it  does
 not contain oxygen.
    The Do&or obferves  further  in fupport of his
 opinion,   " In another  important refpeeSl finery
 *c cinder [black oxyd of iron] and mafficot are  fimi-
                                           " lar. 
                   (   37  )
" lar.   They are both foluble in marine [muriatic]
" acid without  dephlogifticating [oxygenating] it,
" which minium  [red oxyd of lead] inftantly does.
" And  yet  Mr. Berthollet fays, (Annales de Chi-
" mie,  Vol. III.  p. 96,)  that « the heat by which
" minium becomes  mafficot cannot change its na-
" tare.'   What  is the evidence  of a change  in
" the nature of any thing, but a change of its pro-
" perties ? On  the whole, therefore,  the proba-
" bility  is,  that when iron is converted into  finery
" cinder, it lofes its phlogifton,  and  imbibes  only
" water; and  that  when  it is  reconverted into
" iron,  it parts with the water, and recovers  its
" phlogifton.  N. B. The experiment with the maf-
" ficot muft be tried prefently after it is made, fince
" it will very  foon  imbibe  air from the  atmo-
" fphere."
   The red contains more  oxygen  than the yellow
oxyd of lead.  Its parting with fome oxygen to the
muriatic  acid is only a  proof of  what has  been
already  noticed, that  the lead retains   different
quantities of oxygen with unequal force.
   The quotation from Mr. Berthollet is not  exact.
It is his  intention to exprefs, that the carbonic acid
and azote,  with which red oxyd  of lead is com-
monly contaminated,  may be feparated by a high
temperature, and yet  the  lead remain in  the flate
of an oxyd.
The 
                   (  38   )
  The reafon  why  the experiment with  mafficot
muft be  tried prefently after it is  made has been
already affigned.
  Now, confidering the manner in which the finery
cinder  and  mafficot are formed, and  that the dif-
ferent  circumftances  which  have been  alleged  as
proofs  of their not containing oxygen are incom-
petent, the probability is,  that  they do  not  confift
of water, and iron, and lead, deprived of phlogifton.
  The Doctor then  fays,  " In this place I  would
" obferve that, if it be admitted that there is a prin-
" ciple in inflammable air [hydrogen gas], which,
" being imbibed by the calx of a metal, converts it
" into  a metallic fubftance,  it will  follow that the
" fame principle is contained in charcoal, and other
" combuftible fubftances; becaufe they will all pro-
" duce the fame effect, and therefore that the prin-
" ciple of inflammability, or phlogifton, is the fame
" in them all."
  This will readily be admitted, but by the fame
mode of reafoning it muft follow, that if a fubftance
caufes  the reduction of a  metallic oxyd without
communicating any thing to it, there can be no oc-
cafion  for the addition of any principle, and confe-
quently no fuch  principle as phlogifton exifting.
  From  the decompofition, the Doctor paffes  to
the recompolition of water : but the  confideration of
his  obfervations  on this fubject  muft be deferred to
the next lecture,
                                       LECTURE 
LECTURE    II.
         Dr. PRIESTLEY is as much diffatisfied
 with the proofs of the recompofition, as with thofe
 of  the decompofition  of water.   " Another  pre-
 " tended proof [fays he] that water is compofed
 " of dephlogifticated and inflammable air [oxygen
 " and hydrogen gafes], is that when the latter is
 " burned flowly in the former, they both difappear,
 " and  a quantity  of water  is  produced,  equal  to
 " their weight.  I do not,  however,  find that it
 " was in more than a fingle experiment that water
 " fo produced  is faid to have been  entirely  free
 " from acidity, though  this experiment was on a
 " large fcale, not lefs than twelve ounces of water
 " being  procured.   But  the  apparatus  employed
 " does  not  appear to me to admit of fo  much  ae-
 " curacy as the conclufion  requires; and there is
 " too much of correction, allowance, and computa-
 " tion,  in  deducing the refult.  Alfo it  is, after
 " all, acknowledged that,  after  decompofing  this
" quantity of the two kinds  of  air, and making all
 " the  allowance they could for  the phlogifticated
" air,  or azote, in  the  dephlogifticated air,  they
" found  fifty one cubic inches of this kind of air
                                        " more 
                   (  4°   )
" more than they could well account for.   This
" quantity therefore, and perhaps fomething more
" (fince the  operators were  interefted to make it as
" fmall as poffiblej muft have been formed in the
" procefs.   And when this kind of air,  as well as
" inflammable [hydrogen  gas] is dccompofed to-
" gether with dephlogifticated  air [oxygen gas],
" nitrous acid is produced.  The probability there-
" fore is, that the acidifying principle, or  oxygen,
" in the dephlogifticated air which  they  decom-
" pofed,  was contained in  that phlogifticated air
" [azotic gas],  and that, had the procefs been con-
" ducted in  any other manner, it would have affum-
" ed the form of nitrous acid.   They acknowledge
" that, except when the inflammable  air [hydrogen
" gas]  was burned in the  flowed  manner, ths
" water they produced had more or lefs of acidity.''
  The Doctor,  at one time, believed that water
was compofed of oxygen and hydrogen. But as, on
repeating the experiment of burning hydrogen  in
oxygen gas, he could not collect: as much  water  as
was equal in weight to the  gafes confumed ; and  as
that, which  he did obtain was  mixed with nitrous
acid, he was induced to change his opinion, and  to
fuppofe the  water was not generated,  but depofited
by  the gafes during the combuftion, and  that the
body formed was the nitrous acid.*

  *  Experiments and Obf tyations, Vol. III. p. 43, et feq.
           2                               The 
                    (   4i  )
    The antiphlogiftians  alleged,  when  the  expert
 ment was performed on  a large fcale, the deficiency
 of water was very trifling, and never  more than
 might with propriety be attributed to the unavoid-
 able lofs to which fuch experiments were  liable ;
 and they fuppofed the  nitrous  acid, found in the
 water, proceeded from fome azotic gas having been
 contained in the  oxygen gas employed, and this the
 more efpecially,  as no way had been difcovered for
 procuring oxygen gas perfectly free from azotic gas.
   The experiment alluded to by  the Doctor, in the'
 paragraph laft read, juftifies the reafoning of the an-
 tiphlogiftians. An account of it is to be found in the
 eighth and ninth volumes of the Annates de Chimie.
   The  union of the two fubftances was  effected
 by filling a balloon with oxygen  gas, adding to it
 hydrogen gas in  a fmall  ftream,  and fetting  them
 on fire by palling the  ele&ric fpark through them.-
 To  the  balloon were  connected  refervoirs, called
 gazometers, containing the  two gafes.  By certain
 contrivances, thefe were made to fupply the balloon
 with frefli portions of the gafes, as fall as the com-
 bination took place*
   The experiment lafted  185 hours, and at the
end of it  there was  collected of  water  12 ounces
4 gros and  45 grains French weight,  and  there
remained in  the balloon a quantity of gas.
   By comparing the volume of the  two gafes be-
fore the combuftion, with  that of the gas remain-
                      F                      &>g 
                   (   42   )
ing in the balloon, and making every neceffary cor-
rection for the difference of  temperature  and pref-
fure,  it  appeared, that  12  ounces 4  g«» and
49,2270 grains of the  gafes had been confumed :
the difference between this weight and that of the
water is a mere trifle.
   The water was perfeftly pure :  yet this  was not
owing to the  oxygen gas being  free from admix-
ture ;  for by a  preliminary experiment  it was dif-
covered, that 100 cubic inches of it contained three
 of azotic gas ; and 467 French cubic inches of tins
 fubftance were found in the balloon, at the end of
 the experiment.
    The caufe of  the  purity of the  water  was  dif-
 covered  by Mr. Seguin to  be  the flownefs with
 which the combuftion was conduaed:  for he has
 afcertained,  that, with materials of the fame kind,
 the nitrous acid may be formed  merely by carry-
 ing on the combuftion quickly, and by that means
  railng the temperature to the point at which azotic
  and oxygen gafes aa on each other.
    This obfervation  of .Mr.  Seguin has been  con-
  firmed by Meffrs. Pelletier and Jacquin,* and alfo by
  Mr.  Van Marum ;t  fo that pure water has been ob-
  tained in more  than one experiment.
    * Annales de Chimie, Tome X. p. 140.
    t Ibid. Tome XII. p. 139-  Mr- Van-Marum's words are,
   '« Dans une de mes experiences la combuftion du gaz hydro-
   » gene ctait tres-lente, en employant trois heures et demie pour
   « 1? confumption  de mille pouces cubiqnss du gaz hydrogene,
                                                 & 
                   (   43   )
   But Dr. Prieftley fuppofes the oxygen and phlo-
gifton formed  azotic gas in Mr. Seguin's  experi-
ment.  Certain it is, there were 51,7440  French
cubic inches of azotic  gas  found in the balloon at
the end of the  experiment, above what had  been
found in the oxygen gas before the combuftion.
   This quantity was  fuppofed by Mr. Seguin to
have  been  owing to atmofpherical air  from  which,
the gazometers  could  not be completely emptied,
before they were filled with the other gafes : but
whether this be the true' reafon or not, for the  ap-
pearance of thefe  51,7440 cubic inches, they could
not poffibly  have been formed in the manner fup-
pofed by Dr. Prieftley,
   The  oxygen  gas confumed weighed 6209,869
grains and ought according  to the Doaor  to have
contained 620,9869 grains of oxygen or the acidify-
ing principle;  but 51,7440 French cubic inches of
azotic gas weigh only 22,9971 French grains. Nay
the whole  quantity of azotic gas, found in  the bal-
loon, was  equal only to 207,55348 French  grains ;
and'yet, befides oxygen, it ought to have contained
phlogifton and water,

" & l'eau produite par cette experience n'avoit abfolument
"point d'acide.   Une autre fois la  vitefle avec laquelle l'air
*«. entroit dans la ballon e'oit apeu pres d'un tiers plusgrande,
" & alors l'eau produite cor.tenoit de  l'aciJe foiblement fen-
m fible."
                          F2                  ]n 
                   (  44   )
  In addition to thefe ftriking proofs  of the incon-
fiftency of his principles, it may be remarked,  the
phlogifton of the inflammable air [hydrogen gas]
ought to have weighed more than the whole quan-
tity of azotic gas.
  In page 290  of Vol. I. of his Experiments  and
Obfervations, there is a calculation on the fuppofi-
tion that phlogifton compofes one half of hydrogen
gas: And in page 535 of Vol. III. he fays, " Wa-
" ter feems to conflitute about nine parts in ten of
" dephlogifticated air (oxygen gas), but there feems
" to be a much lefs proportion of it in inflammable
" air (hydrogen gas.)"
  The hydrogen gas expended in Mr. SeguiVs ex-
periment amounted to 1039,358 grains; and if the
phlogifton be eftimated at  only one  fifth of  that
weight, it will be 207,8716 grains, which is more
than the weight of the whole azotic gas.
   Since, therefore, the azotic gas could not have
been  formed by the oxygen and hydrogen, and fince
no  other produa was  obtained than water,  and
the weight of this correfponded to that of the two
gafes confumed, it may with fafety be inferred that
they formed water by their combination.
   But,  continues the Doaor, " The experiments
" which I made on  the decompofition of thefe two
" kinds of  air  in  clofe veffeh, appear to me to he
ff much lefs liable tp exception, and  the  concluficn
                                        " dr^wrj ( 
                   (   45  )
*c drawn from them  is the reverfe of that of the
" French philofophers."
  In what  refpea his experiments were lefs  liable
to exception than thofe  of  the French chemifts,,  is
what  I  cannot  comprehend.    Theirs  were per-
formed on  a very extenfive fcale;  great  care was
taken to afcertain the degree of  purity of the gafes
before combuftion ; and the apparatus was fo con^-
flruaed  that the refults could be determined with
the great eft nicety. The Doaor's, on the  contrary,
were made with very trifling quantities of materials ;
their  purity was not tried ; and their  weight was
not accurately determined.
   In one experiment, he employed fuch a quantity
of the gafes, as, he fays, ought  to have afforded a
grain  of water;  but he colleaed only  a quarter
of a grain:  in  another, he ought to have got two
grains,  whereas he obtained  only a grain and an
half.   And thefe are the experiments which he op-
pofes  to thofe  of the  French  chemifts,  and from
which he concludes,  the water is not equal  to the
weight of the gafes confumed! *
   Satisfied,  however, of the  fuperiority  of his ex-
 periments, the Doaor proceeds to give their refults,
   " When  dephlogifticated  and  inflammable  air
 *' (oxygen and hydrogen gafes),  in  the proportion
 *< of  a little  more than one meafure of the  former

    *  Experiments and Obfervations, Vol. III.  p. 45.
                                             $<to 
                    (  46   )
" to two of the latter, both fo pure as to contain no
" fenfible quantity of phlogifticated air (azotic gas;,
" arc inclofed in a glafs or copper  veffel, and de-
" compofed by  taking  an ekaric fpark in it, a
" highly phlogifticated nitrous acid is inftantly pro-
" duced ; and the purer the airs are, the ftronger
" is the acid found to be. If phlogifticated air (azo-
" tic gas) be purpofely introduced into this mixture
" of dephlogifticated  and inflammable air foxygen
c; and  hydrogen gafes), it  is  not afteaed by  the
" procefs ; though when there is a confiderable de-
" deficiency of inflammable air (hydrogen gas), the
" dephlogifticated air for want of it  will unite with
" the phlogifticated air, and, as in Mr. Cavendifh's
" experiment, form the Tame acid.   But fince both
*c the kinds of air, viz.  the inflammable and  the
" phlogifticated  (hydrogen  and azotic) contribute
" to form the fame acid, they muft contain the fame
" principle, viz. phlogifton."
  "  If there  be  a redundancy of inflammable air in
" this procefs, no acid  will  be produced, as  in the
" great experiment of the French chemifts; but in
" the  place of it there will be a quantity of phlo*
" gifticatcd air (azotic gas).   A confiderable quan-
" tity of water is always produced in thefe decom-
 c portions of air.  But this circumftance only proves
li that the greateft part of  the weight  of all kinds
*' of air is water.   I have, in my  experiments on
" terra ponderofa aerata (carbonate  of barytes) der
                                    " monftrated 
                    I   47  )
" monftrated  that water conftitutes about half the
" weight of fixed air (carbonic acid gas.)"
  It has been already fliewn, that hydrogen gas can
neither form  azotic gas nor nitrous acid ; but it may
be worth while to point out the reafons for thefe
refults.
  In the detail which is given of thefe experiments
in the third volume  of his Experiments  and Obfer-
vations, there is  no notice of any preliminary at-
tempts to afcertain the degree of purity of the gafes;
but it is there faid, the  oxygen gas ufed in the two
trifling  experiments  formerly  mentioned was got
from the oxyd of manganefe ;  and that employed in
other experiments, during which the explofions were
performed in a  copper veffel, was  fometimes got
from the  fame fource, and  at others from the red
oxyd of mercury by  the nitrous acid, and from the
red oxyd of lead.  Now  it  is  well known,  that all
thefe fubftances in general contain azote.—The firft
doe s fo, in fo remarkable a degree, that the firft por-
tions of gas which  it yields  on being heated are
frequently pure azotic gas. The fecond, being made
with the nitrous acid, alfo contains fome of it. And
the third  attra^ls  it from the atmofphere, as the
Doaor himfelf has difcovered.
   Mr.  Cavendifh afcertained  by his experiments,
that, if there be lefs  hydrogen ufed than is neceffary
for the faturation  of the oxygen, a quantity of ni-
trous acid is formed; and that, if azotic gas be ad-
                                             ded 
                   (  4»  ;
dcd to the mixture, cceteris paribus, the quantity of
acid is always increafed ; but, that  if there be a fu-
perabundance of hydrogen, no acid is produced.
   Hence the reafon why the  azotic gas was not a£-
feaed  in Dr. Prieftley's experiment, feems to have
been, he ufed  as much hydrogen as, with the azote
contained in the oxygen gas  and not attended  to,
was fufficient for the whole oxygen.
   It has been already made evident, that water can-
not enter into the compofition of oxygen and hy-
drogen gafes in the proportion alleged by the Doc-
tor ;  and by a  little  attention to  the  experiments
with the carbonate of barytes it will clearly appear,
there is not the fmalleft foundation for the opinion
that water  is neceffary for the conftitution of car-
bonic acid gas.
   The native carbonate of barytes was faid, by Dr.
Withering and  others, not to  yield its carbonic acid
at any temperature to which  it could  be  expofed:
but Dr.  Prieftley found, that when the vapour of
water was fent  over it when red hot in an earthen
tube,  it afforded carbonic acid gas with the greateft
rapidity,  and in an equal quantity as  when it was
diffolved  in  the muriatic acid; while at  the fame
time fome of the water difappeared. He hence con-
cluded, that water muft be  a conftituent part  of
carbonic acid gas.
   "  Attending," fays he,  " to the water expended
" in the procefs, I found that  I procured 330 ounce
     1                               " meafures' 
                   C   49  )
u meafures of fixed air (carbonic acid gas) with thd
" lofs of 160 grains of water.  According to this, as
" the air weighed 294  grains,  the  water in the
" fixed  air muft have been 80 parts of 147 of the
** whole.
  " In  another experiment, having previoxtfly found
" that three  ounces of the terra ponderofa (carbo-
" nate of barytes) yielded about 250 ounce meafures
" of fixed air (carbonic acid gas),  I attended only
" to the lofs of water in procuring it, and I found
"it to  be one  fifth of an ounce in two fucceffive
" trials. The quantity of fixed air (carbonic acid gas)
" would weigh  225 grains, and the water expend-
" ed about 100 grains, fo that in  this experiment
" alfo the  fixed air (carbonic  acid  gas) muft have
" contained about one half of its weight of wa-
ter." *
  This  calculation, however,  cannot be depended
Upon ;   for the lofs which the carbonate of barytes
fuftained was not examined, and the carbonic acid
gas muft have diffolved a quantity  of water which
it would depofite on returning  to the temperature
of the atmofphere.
  To thefe objeaions, which were firft made by Mr.
Berthollet, the Doaor has returned * " I found very
*' exaaiy how much fixed air [carbonic acid gas] a
" given quantity of  this fubftance [carbonate  of

    *  E.\periments and Obfertrationsi Vol.1, p. 131.
                        9             " JbarytesJ 
                   (  50   )
" barytes] would yield by  means of water, which
" appeared to be the very  fame that it  yielded  by
" folution in  fpirit of fait (muriatic acid), and that
" it yielded no air at all by mere heat without wa-
" ter.   It was quite fufficient therefore to find how
" much water was expended in procuring any quan-
" tity of fixed air (carbonic acid gas) from this fub-
" fiance.   And as there was  no other fource of lofs
" of water befides the fixed air (carbonic acid gas),
" it could not but be concluded, that it entered into
" its  compofition  as a neceffary part of it, and in
" the proportion which I afcertained." *
  In this anfwer, he has entirely overlooked the pro-
perty which carbonic acid gas has of  diffolving wa-
ter.   Every  chemift  knows  it  has that  property,
and in  a greater  degree at  a high than at  a low
temperature.   But the water is not neceffary to  the
conftitution of the gas, becaufe it exifts before  the
folution of the water; and it may be deprived of the
water,  by fulphuric acid  or any deliquefcent fub-
ftance,  and ftill remain carbonic acid gas.
   Befides, Dr.  Hope,  now Profeffor of Chemif-
try  in  the Univerfity  of Edinburgh, has  difco-
vered that the carbonic acid can be feparated from
the barytes,  by  expofing  the  compound to fuch  a
temperature  as can be raifed  in a fmith's forge, f

  * Experiments and Obf rvations, Vol. III. p. 557.
  t rdinbwgh Philofophical Tranfaelions.
                                              To 
  To be fure,  the difengagement of the carbonic
acid takes place  at a lower temperature when wa-
ter  is ufed;  but this is only a proof that the fepa-
ration is promoted by the tendency which carbonic
acid gas has to combine with water.
  Hence then the celebrated experiments with the
terra ponderofa aerata, or carbonate of barytes, af-
ford no fupport to the Doaor's principles.
  " The reafon, no doubt,"  fays  the Doaor, in a
note at  the end of the pamphlet, " why, in the ex-
" perimenjs of the French chemifts, the water they
" produced was  not without acidity, whenever the
" flame they made ufe of was too ftrong, was that,
" in that cafe, more of the dephlogifticated air [ox*
" ygen gas]  in proportion to the inflammable [hyr
ft drogen gas] was confumed,  than when the flame
te was weak ; fo that the refults  of  their  experi-
" ments exaaiy coincide  with thofe of mine."
   When his experiments are accurately examined,
they are found to confirm thofe  of the French che-
mifts ; but the reafoning in the note which has been
read cannot be admitted.
   The appearance of flame attends the combination
of an inflammable fubftance and oxygen, when both
are in the flate of gas:—it is  owing to their union
taking  place  at many points at the fame time ; but
zs the union depends as much on the one as on the
other,  a proportional  quantity of each muft be  as
 neceffary to exhibit a weak as a ftrong flame.
G 2
The 
                   (  5*  ;
   The Doaor further relates of his experiments,
tc When  the decompofition gf dephlogifticated and
" inflammable air  [oxygen and hydrogen gafes] is
^£ made in a glafs veffel, a peculiarly denfe vapour is
fe formed, which the eye can  eafily  diftinguifh not
*' to be mere vapour of water ; and  if the juice  of
" turnfole be put into the veffel, it immediately be-
" comes of a deep, red, whjch fhews that it was  an
" acid vapour,
   " Since the acid that I procured in this procefs
" was in confiderable quantity, and no phlogifticated
'* air [azotic gas]  was prefent, (for in the  laft  of
" my experiments  J did not even make ufe  of  an
c* air pump, but firft filled the veffel with water, and
6i then difplaced it by the mixture pf the airs), I  do
te not fee how it is poffible to account for the forma-
". tion of  this acid but from the union of the two
" kinds of air ; and it cap hardly be fuppofed that^
*6 in the very fame  procefs, the decompofition of the
" fame  fubftances  fhould compofe  others fo very
" different from each other as water and fpirit  of
" nitre [nitrous  acid].  I think I have fufliciently
" accounted for the refult of the experiments made
" by the French chemifts on the common hypothe-
" fis, which  fuppofes inflammable  air  to contain
*6 phlogifton; but I do not fee how it  is poffible for
■?c them to explain mine on theirs, according to which
" there  is no fuch  principle  in nature.   Upon the
*' whole,  it  does not appear to me that the evi-
f; dence? either for the compofition or the decompo*
                                        -J fitiptl 
                   i  53   )
" fition of water,  is at all  fatisfaaory;  and cer-
*' tainly the arguments in fupport of an hypothec's
" fo extraordinary, and fo novel, ought to be of the
" moft conclufive kind."
  Having in fome of his experiments emptied  tht.
veffel in which the explofions were made of common
air, by means of an air pump, the Doaor fuppofed
it might be objeaed, that he could not entirely ex-
hauft the veffel ;  and it is on that account he has,
mentioned, that in the laft of his experiments  he did
not ufe an air pump : but the azote which occafioned
the  produaion of the  denfe acid vapour was con*
tained in the oxygen gas which he employed.
  The objeaions contained in this  feaion  to the
conclufions drawn from the experiments which the
antiphlogiftians confider as proofs of the  decompo-
fition and recompofition of water, are,
   i.  Finery cinder [black oxyd of  iron]  does not
contain oxygen.
  ■2.  The weight of the water colleaed after burn-
ing inflammable and dephlogifticated  airs £hydrogen
and oxygen gafes] is not equal to that of the  airs
confumed.   And,
  3.  Either  the water fo obtained  is mixed with
nitrous  acid, pr  a quantity of phlogifticated air
[azotic gas] is formed.
  The Doaor is of opinion,
   1.  That finery cinder [black oxyd of iron] con,
$J$ pf water and iron deprived of phlogifton.
                                        2, Thaf 
                   C  54  )
   2.  That when a metallic calx  containing oxygen
is reduced in inflammable air [hydrogen gas], fixed
air [carbonic acid gas] is formed  by the union of
the oxygen with the  phlogifton  and water of the
inflammable air.  And,
   3.  That during the Combuftion of inflammable in
dephlogifticated air [hydrogen in oxygen gas], the
phlogifton  and oxygen form, according  to circum-
ftances, nitrons acid or phlogifticated  air [azotic
gas] ;  and  the water obtained by the procefs is not
generated, but from being a conftituent part  of the
two airs is depofited on their union.
   But from what has been ftated in the review of
this feaion it appears,
   1.  The  fame fubftance is formed by expofing
iron to the fleam of water, by burning iron in oxy-
gen gas, and by heating iron filings mixed with red
oxyd of mercury,
   2.  Hydrogen gas  is obtained when the iron is
changed by being expofed  to the vapour of water ;
but there is none afforded when  the change is efT
fefted by either of the other proceffes.
   3.  The  carbonic  acid,  which has been  found
after the reduaion of certain metallic oxyds in hy-
drogen gas, was previoufly contained in thefe oxyds.
   4.  The water which may be colleaed wlien hy-
drogen is burned in oxygen  gas is exaaiy  equal in
weight to the t\yo fubftances which difappear.
4. The 
                   C  55  1
  4. The azotic gas which has been found in the
refiduum was contained in  the gafes before the com-
buftion.
  6. The nitrous acid, formed when the combuf-
tion was  rapid,  was owing to the union of  azote
with oxygen.
  7. The experiments  with terra ponderofa do not
fhew that water is neceffary to the  conftitution of
the gafes.  And confequently from thefe it follows,
  That when water is  brought in contaa with red
hot iron  it is refolved  into two  fubftances, one of
which  combines with the  iron, while the other af-
fumes  the form of  gas—and, That water may be
reproduced by reuniting thefe fubftances.

  The third feaion begins as follows:
  " Having  confidered the evidence that has  been
" alleged in  fupport of the antiphlogiftic theory,
" and  found  it  to be infufficient,  I fhall in  this fec-
" tion mention  a few objeaions that may be made
" to it from other confiderations.
  " 1. If inflammable air, or hydrogen, be nothing
" more than a  component part of water, it could
" never be produced but  in circumftances in  which
" either water itfelf, or fomething  into which wa-
" ter is known to enter, is prefent.  But in my cx-
" periments  on  heating finery cinder [black  oxyd
" of iron] with  charcoal, inflammable air is pro-
" dueed, though, according to the new theory, no
                                        " water 
                   C   5&  )
14 water is  concerned.   According to this theory,
" finery cinder, called the oxyd of iron, confifts of
" nothing befides iron and oxygen;  and the char-
" coal, made with the greateft degree of heat that
" can be applied, is equally free from water ; and
" yet when thefe two fubftances are mixed together,
" and  expofed to heat, they yield inflammable air
" in the greateft abundance.
  " This  faa I  cannot  account for  on the  princi*
" pies  of the new theory ; but nothing is eafier oti
u thofe of the old. For  the finery cinder [the black
" oxyd] containing water, as one of  its  component
" parts, gives it out to any fubftance from  which
" it can receive phlogifton in return.  The  water,
u therefore, from the finery cinder [black oxyd of
" iron] uniting with the charcoal makes  the inflam^
" mable air [hydrogen gas], at the fame time that
" part of the phlogifton from  the  charcoal  contri-
" butes to revive the iron.   Inflammable air [hydro-
" gen gas] of the very fame kind is procured when
tfi fleam is made to pafs over red-hot charcoal."
  Although hydrogen be  a conftituent part  of wa-
ter  it enters  into the compofition of many other
bodies, and therefore the prefence of water  is not
neceffary to account for its produaiofl.
  The particulars of the experiment  are related in
page 279 of the firft volume of the Doaor's  Expe-
riments and  Obfervations.  " Having" fays he,
" made the feales of iron [black oxyd of iron], and
        1                                 " alfo 
                    C  57   )
6e alfo the powder of charcoal very hot, previous to
ce the experiment, fo that I was fatisfied that no air
" could be extraaetd from either of them feparately
" by any degree of heat; and  having mixed them
" together while  they were very hot, I put them
" into an earthen retort, glazed within and with-
" out, which was  quite impervious to air.   This I
" placed in a furnace, in which  I could give it a
" very ftrong heat; and conneaed it  with  proper
cc veffels to condenfe and collea the water which I
" expeaed to receive in  the  courfe of the procefs.
" But to my  great  furprife, not  one particle  of
" moifture came over, but a prochgious quantity  of
" air, and  the rapidity of its produaion aftonifhed
"me; fo that I had no doubt but  that the 'weight
" of the air would have  been equal  to the lofs  of
" weight both in the fcales [the black oxyd] and
" the charcoal; and when I examined the air which
" I repeatedly did, I found it to contain one tenth
" of fixed air  [carbonic acid gas] ;  and the  inflam-
" mable  air which remained when the fixed air was
" feparated from it,'was of a  very remarkable kind,
" being  quite as heavy  as common air.  The rea-
" fon of this was fufficiently  apparent when it was
" decompofed  by means of dephlogifticated air,
*< [oxygen gas] for the greateft part of it was fixed
« air."
   The Doaor now thinks this laft mentioned fixed
air was not a  conftituent part of  the  inflammable
                       **                    air, 
                   C   58  5
air, but formed by the  union of its phlogifton with
the dephlogifticated air.
  The reducing of wood to charcoal confifts in fepa-
rating the more volatile  from the lefs volatile parts.
This is done very imperfeftly in common charcoal.
The  hydrogen efpecially is retained  with  fo great
force that the coal muft be expofed to an intenfc
and long continued heat.
  It is not mentioned in the detail  of  the  experi-
ment, that the charcoal was previoufly expofed to
the greateft degree of heat that could be applied,
it is merely faid it was made very hot, and that was
very far .from being fufficient.
  Unglazed earthen veffels abforb  moifture from
the  atmofphere  very greedily, and  it is  fcarcely
poffible to glaze accurately the  infide of an earthen
retort; at all  events it is  quite impoffible, without
breaking  the  retort, to  know whether  it has been
perfeaiy done or not.
  The charcoal,  the iron fcales (black  oxyd), and
the  retort fliould  all have been expofed feparately
to an intenfe and long continued heat,  immediately
before being  ufed ; the weight of the charcoal and
iron before the experiment fhould have been com-
pared  with their  weight  after it;  and  the weight
of the gafes  obtained inftead of  being gueffed at,
fhould have been  accurately determined  and com-
pared  with the lofs fuftained by the mixture.   The
experiment is, in its prefent flate, of no value.
                                             Mr. 
                   «,   d9  )
  Mr. Berthollet, firft objeaed  to  the experiment
that hydrogen was with  great  difficulty  feparated
from carbone, and the Doaor in reply to him has
faid in  page 556 Vol. III. of his Experiments and
Obfervations, " How obftinately charcoal retains
" water, is eafily afcertained.  For  Mr. Berthollet
*' himfelf would fay,  that when any particular de-
tc gree of heat would not make charcoal yield any
" more inflammable air,  there was  no more water
" retained in it  than  the fame degree of heat was
sc able with  its  affiftance to decompofe.   But by
" the affiftance of finery cinder (black oxyd of iron)
" with even a much lefs degree of heat, it yields
" inflammable air very copioufly, juft as if fleam
" had been made to pafs over it in  that heat; and
" judging from evident appearances,  there can be
" no  doubt but  that with a fufficient quantity of
" finery  cinder,  to fupply it  with water,  all the
" phlogifton  in  the  charcoal,  exclufive  of that
" whjch -contributed to the revival of the iron, will
" be converted into inflammable air."
  From this anfwer, the Doaor feems to  have mif-
underftood Mr.  Berthollet.  He  has  not faid that
charcoal  retains  water obftinately,  his words are
" il paroit, par un grand  nombre d'experiences que
64 le charbon retient fortement de Thydrogcne ; aufli
" avons nous  diftingue  le principe  charboneux au
-' earbone du charbon ordinaire."
H 2
The 
                   C  60   >
  The refults of the Doaor's  experiment  may be
accounted for in this manner. The carbonic acid gas
was formed by the union of the oxygen in the oxyd
of iron with the carbone in the  charcoal;  and the
heavy inflammable  gas' proceeded from the folution
of fome carbone in hydrogen  gas furnifhed either
by the charcoal or moifture contained in  the retort.
  It can be no objeaion to this  explanation, that
the charcoal afforded an inflammable gas at a lower
temperature when  mixed  with oxyd of iron  than
when ufed by itfelf.   If the proportion of hydrogen
be very fmall in comparifon with that of  the car-
bone,  the compound is folid at  even a  very  high
temperature ; but when the proportion of hydrogen
is greater,  it is eafily made  gafeous.  In the  fore-
going  experiment  the  proportion of carbone was
diminifhed  by  the  union  of part of it with the
oxygen of the oxyd  of iron.
   At  all events  the explanation  offered  by the
Doaor cannot be a juft one.  It has been  already
fliewn the  fuppofition refpeaing  the compofition of
oxygen gas is unfounded, and that, even  after ad-
mitting that fuppofition, finery  cinder cannot*con-
fift of water and iron deprived  of phlogifton.
   2. " Though the new theory, fays the  Doaor,
 " difcards phlogifton, and  in this  refpea is more
 " fimple than  the  old, it  admits another new prin-
 " ciple, to which  its advocates give the name of
 ■* Carbone, which  they define  to be the fame  thing
                                         " with 
                      v.  oi   )
  '* with charcoal  free  from  earth, falts, and all
  " other  extraneous  fubftances; and  whereas we
  " fay that fixed air confifts of inflammable air and
  " dephlogifticated air or  oxygen,  they  fay  that it
  " confifts of  this carbone  diffolved in dephlogif-
  " ticated d\r,fee Examination of Mr. Kirwan, p. 79.
  " Mr. Lavoifier fays, Ibid.  p. 63,  that  ' wherever
  " fixed air  has been obtained, there  is charcoal.'
  tc They therefore call it the carbonic acid.  -
     " But in many of my experiments large quantities
  " of fixed air have been procured where  neither
  " charcoal, nor any thing containing charcoal, was
  " concerned,  or  none in quantity fufficient to ac-
  " count for it.  When the pureft  malleable iron is
  « heated in dephlogifticated air [oxygen gas]  or in
  " vitriolic  acid air  [fulphureous acid gas], a con-
  " fiderable quantity of fixed  air is formed.  It is
  " faid that plumbago is contained  in  iron.  But it
  " is not found in malleable iron, and leaft of  all in
   " the air  that is expelled from  it.   Fixed  air is
   " alfo produced by reviving minium  [red oxyd of
   " lead] in  inflammable air [hydrogen gas], and if
   " charcoal of copper be heated in  dephlogifticated
   " air, a quantity of fixed air equal to nine tenths of
   " the dephlogifticated air  will be formed.    More
   " than  thirty ounce meafures of  the pureft  fixed
   " air were by this means procured from fix grains
   " of this charcoal, which  is made by the union of
*   «« fpirit of  wine and this metal.
                                           «< Laftly, 
                   (  02   ■
  " Laftly, fixed air is  procured" in great aburJJ
" dance in animal refpiration.   It is true that fixed
" air is procured  by expofing lime  water  to atmo-
" fpherical air, but it is never  procured by this
" means in air confined in any veffel.  There muft,
" for this  purpofe, be an open communication with
" the atmofphere.   But  fixed air will be procured
" in great abundance by breathing air contained in
" the fmalleft receiver, and  efpecially if the air be
" dephlogifticated.  It muft therefore be formed
" by phlogifton,  or fomething emitted from the
" lungs, uniting with the dephlogifticated air which
" it meets  there.   It may be  faid that  fince  we
" feed in a  great  meafure  upon  vegetables- (and
" even animal food  is originally formed from them)
" and this principle of carbone is found in  all vege-
" tables, this may be the fubftance  that is exhaled
" from  the lungs.   But fince in this procefs, it
" forms the  fame  fubftance  that inflammable  air
" from iron does with  dephlogifticated air, or oxy-
" gen, it muft be the fame thing with it;  and then
" this carbone will only be another name  for phlo-
" gifton."
  The objeaion,  that  carbone is  a hypothetical
being, was formerly made by. Mr. Keir, and anfwer-
ed by Mr. Berthollet,  " If there was no  method,.
" fays he, of procuring diftilled water,  and that
" in the explanation of  phenomena which are ow-
** ing to that fluid,  it was confidered independently
                                           " of 
                   C  6r>
14 of the fmall quantity  of falts which it holds in
" folution, would Mr.  Keir look upon water as an
" hypothetical  being of which no idea could  be
" formed ? Charcoal which has been  well  urged
Ci by  the fire contains  fometimes lefs than an hun-
" dredth part of foreign matter which  has no in-
" fluence on its combinations; fometimes it contains
" much  more:  abftraaion  is made of that part
"' foreign to its properties,  and to avoid circumlo-
" cution, the name of carbone is given  to the char-
" coal confidered in a flate of purity."*
  Notwithftanding what the Doaor has afferted, it
is fcarcely  poffible to obtain iron  free from  plum-
bago ;  and this, from the quantity of carbone which
it contains,  can, with a due proportion of oxygen,
make nearly four times its weight of carbonic acid.
  The carbonic acid  gas procured by the revival of
the red oxyd of lead has been already accounted for.
  Charcoal of copper, as Dr. Prieftley calls it,  is
made by paffing the  vapour of alcohol  or of oil of
turpentine through a red hot copper tube: a great
quantity of hydrogen  gas is evolved and a black
fubftance colleas in the tube.  Of 446 grains  of this
black  fubftance obtained  in one" experiment,  28
grains were copper ;  and of 508 got by another, 19
grains  were copper: the remainder when burned
afforded carbonic acid gas.

        fc Annales de Chimie, Tome X. p.  145,
                                          Thefe 
                   (   ^4  )
  Thefe  experiments  prove that alcohol  or  fpirit
of wine and oil  of turpentine contain hydrogen and
carbone; and that  copper can  feparate the carbone
from the hydrogen.  Charcoal of copper, therefore,
is not a compound  of fpirit of wine and copper, but
of carbone and that metal.
  That carbonic acid is formed  during refpiration
is moft certain, and that  it is fo  by the addition of
fomething to the oxygen contained in the atmof-
phere is equally certain; but the Doaor has forgot
when he fays, " it forms the fame fubftance which
" infiammaable air  from iron  does with dephlogif-
** ticated air, or oxygen."
  In page 28 5 of the firft volume of his Experiments
and Obfervations, when fpeaking of  the carbonic
acid gas obtained  by burning the inflammable gas
which is procured  by paffmg  the vapour  of  water
over red hot charcoal, he fays in the text.  " That
" the fixed air [carbonic acid  gas] is not generated
" in this procefs, is evident from there  being no fixed
« air found after  the explofion of dephlogijlicated air
" {oxygen  gas~] and  inflammable  air  from  iron:*
 And in a note at the bottom of  the page he  ob-
 ferves, " When I wrote this paper, I imagined that
 " the fixed air, which was found on the decompofi-
 " tion of this  inflammable air with dephlogifticated
 £i air, had  been contained in the inflammable  air.
 " But it will appear, that it muft have been formed
 " by the union pf phlogifton [or inflammable air]
                                           "  and 
                   (  65   )
4i and dephlogifticated air, made by the expjofioli 1
" though it is remarkable that no fixed air is formed
" when the inflammable air from iron is ufed:''
  Befides in p. 562. Vol. III. he fays of inflamma-
ble air from iron, " that it may not only be wafhed
" in lime water, but even be wholly decompofed by
" being fired together with  dephlogifticated air,
" without difcovering any fixed air at all:*
  Therefore the identity of carbone and the fur>
pofed  phlogifton has  not  been eftablifhed.
  The third objealon is a repetition of what he has
faid before. " 3d. The  antiphlogiftians always fup-
•* pofe azote, or phlogifticated air, to be a fimple fub-
" fiance, though I think abundant evidence has been
" given (and more will  be found in my laft memoir,
" printed in the Tranfaaions of the Philofophical
"  Society at Philadelphia), that it is compofed of
"  phlogifton and dephlogifticated air."
   The abundant  evidence  which has been  given
amounts to, an afTertion  that he has fhewn in a feries
of experiments that azotic gas is formed during the
oxydation of iron; and thecircumftance of 51,744
cubic inches of azotic gas,- having been found in the
refiduumofthe great experiment made by Mr. Se-
guin and others, above what had been difcovered
in the oxygen gas before the combuftion.
   It is fcarcely  neceffary  to remind  you,  the firft
is contradiaed by  his own experiments and thofe of
Mr. Lavoifier ; and that the laft, cannot be account-
                       1                      e<3 
                  (   66  )
co for on his principles, even after granting a nun>
ber of unfounded fuppofitions.
  It is the Doaor's objea, in the memoir which is
to be publifhed in the fourth volume of the  Tranf-
aaions of the Philofophical Society of Philadelphia,
to prove, that there is a greater quantity of oxygen
in the atmofphere than  is fuppofed by the antiphlo-
giftians, and  was formerly believed by the  Doaor
himfclf; and that fome  of the azotic gas found after
the combuftion of certain fubftances in atmofpheri-
cal air, is formed by the union  of their phlogifton
with the oxygen of  the atmofphere.   But as the
Doaor has not favoured us with a detail of his ex-
periments, and as they  bear the moft ftriking marks
of not having been performed with accuracy,  I will
not take up  your time with a review  of them.
   The Doaor then remarks,
   " 4. As to the new nomenclature, adapted to the
 " new theory, no objeaion would be made to it, if
 " it were formed, as is  pretended,  upon a know-
 " ledge of  the real  conftitution of natural fub-
 " fiances; but we cannot adopt one, the principles
 " of which we conceive not to be fufficiently afcer-
 '- tained.  For  other  objeaions to  this nomencla-
 "  ture,  I  refer to the  Preface to Mr.  Keir's excel-
 "  lent Diaionary of Chemiftry.  However, whe-
 "  ther we approve of this new  language or not, it
 "  is now  fo generally adopted, that we are under
 " the neceffity of learning, though not of ufing it."
           1                            Although 
                   (   67  )
  Although  the  new  nomenclature is not ftriaiy
methodical,  and  its terms are rather uncouth and
harfli, yet as,  in as far as the ftate of our know-
ledge enables us to judge, it in general  expreffes ei-
ther the properties or compofition of bodies, I moft
heartily recommend it.
  The Doaor  fums up, " On the whole, I cannot
" help faying,  that it appears to me not a little ex-
" traordinary,  that a  theory  fo new,  and of fuch
" importance,  overturning every thing that was
" thought to be the  bell:  eftablifhed in chemiftry,
" fhould  reft on fo  very narrow and  precarious  a
" foundation,  the experiments adduced in fupport
" of it  being not only ambiguous, or explicable on
" either hypothefis, but exceedingly few.   I think
" I have recited  them  all, and that on which the
« greateft ftrefs is laid,  viz.  that of the formation
*' of water from the decompofition of the two kinds
" of air, has  not been fufficiently  repeated.  In-
" deed,  it requires fo difficult and expenfive an ap-
<c paratus, and fo many precautions in the ufe of it,
" that  the frequent repetition  of the experiment can-
" not be expeaed ; and in thefe circumftances the
" praaifed experimenter cannot help fufpeaing the
 fC accuracy of  the refult, and confequently the cer-
" tainty  of the conclufion.
    " But I check myfelf.  It does  not become one
 ►( of a minority, and efpecially of fo  fmall a mind-
 *c ritv,  to  fpeak or  write  with confidence; and
                        12              "  though 
                   C  68«  )
<e though I have endeavoured to keep my eyes open,
" and  to be as attentive as  I could to every thing
^ that has been done in this bufinefs,  I may have
" overlooked fome  circumftances which have im*
" preffed the minds of others,  and their fagacity i3
*£ at leaft equal to mine,
  " The phlogiftic theory is  not without its difficul-
" ties. The chief of them is,  that we are not able to
" afcertain the weight of phlogifton, or indeed that
" of the oxygenous principle.   But neither do any
" of us pretend to have weighed light, or the ele-
*' ment of heat, though we  do not  doubt but that
"they are iproipcr\y fubftances,  capable, by their ad*
*4 dition, or abftraaion, of making great changes in
" the properties of bodies, and of being tranfmitted
" from one fubftance to another."
  The experiments adduced  in fupport of the anti*
phlogiftic doarine are neither ambiguous, nor expli*
cable on either  hypothefis!9 nor few.—Thofe of the
French chemifts were performed  with  the greateft
care and nicety, and a few fuch are of more confe-
rence than thoufands made without  a due regard
to-accuracy and precifion ;  and if I miftake not it
fcas been fliewn r that they cannot be  explained on
jhe Poftor's  principles,  and that his numerous ex-*
periments con£rm. theirs,           - , ■
  The experiment of the formation of water has
foeen frequently repeated.   It has been performed
p£.a large fcale by Mr* Monge, by Meffrs, Lavoifier
                    .   .                     and 
                   (  69   )
and Meufnier, by Meffrs. Fourcroy, Vauquelin, anej
Seguin, by Meffrs Pelletier and Jacquin, and by Mr.
Van Marum.
   The Doaor deferves  credit for his candour; but
I confers I am rather furprifed, that after having cal-
culated the  weight of phlogifton and oxygen, and
fupported a theory on the fuppofition of the calcula-
tions being  right, he  fhould ftate, as the chief diffi-
culty attending that theory, the impoffibility of af-
certaining the weight of thefe  fuppofed fubftances.
   However, if thefe fubftances or principles did ac-
tually exift, one or both of them would have weight;
for charcoal, whether it be " very nearly pure phlo-
*' gifton," or contains " the acidifying principle as
*< well as phlogifton," can  be weighed.
   It has been fhewn, that the formation of carbo-
 nic acid gas by the burning of charcoal,  cannot be
 explained on the Doflor's principles, if both the
 phlogifton and the oxygen have weight; and it will
 be  found equally inexplicable if one of them be de*
 (litute of that property.
    Let it firft be fuppofed the  phlogifton has no
 weight;  and let it be again granted, that his expe-
 riment on the combuftion  of charcoal in oxygen gas
 was accurate.  The oxygen in the eonfumed char^
  coal could weigh np more than feven grains; and
 thefe, added to the tenth part of the weight of ox-
 ygen gas> would make 8,947974 grains.   One half
 pf the- weight of carbonic  acid gas is fuppofed to be
  «pater, and  cpnie^uently if the phlogifton has  no
                                          weight* 
                   (  7°   )
weight, the other half ought to be owing to the ox-
ygen.  But there could not  be more of this  oxygen
than 8,947974 grains, and thefe,  with  an equal
quantity  of  water,  ought   to  have  formed only
17,895948 grains  of carbonic acid gas, while the
quantity faid  to  have been  obtained was 25,1150
grains.
   On the other hand, if the oxygen be fuppofed  to
be deftitute of weight, and phlogifton to be heavy,
as the phlogifton could not  exceed feven grains, the
quantity of carbonic acid gas fliould have been four-
teen grains.
   Befides, the water in the oxygen gas ought,  in
either cafe, to have  exceeded that  fuppofed to  be
neceffary for  the conftitution of the  carbonic acid
gas.  What became  of this excefs ?  Why did it not
combine with the one grain and quarter of uncon-
fumed charcoal ?
   Although it is more than probable that light, and
the caufe  which excites in  us the fenfation  of heat
or caloric, are bodies; yet   their exjftence  as fuch
does not make a neceffary part of the antiphlogiftic
doarine.
   As the different parts  of this feaion have no im-
mediate  conneaion,  it is unneceffary to make any
recapitulation.
   The following note is fubjoined  to the  laft fec-
tion:  " N.  B.  For  anfwers to the objeaions  of
" Mr. Lavoifier and Mr. Berthollet to fome expe-
 Ci riments of mine relating to  this  fubjea,  I refer 
tl to the laft edition of  my Obfervations  on Air,
" Vol. III. p. 554."
  Such of thefe anfwers as were applicable to the
objeaions, which have been laid before you, have
been already confidered.
  I  have  now, Gentlemen,  finifhed the  reading
and  examination of Dr. Prieftley's  pamphlet. Per-
haps, from having been fo particular, I have almoft
exhaufted your patience ; but I truft you will ex-
cufe me, as  the fate of  feveral important  branches
of chemical fcience is involved in  that of this fubjea.
   From the view which has been given of the dif-
 ferent explanations of the phenomena of combuf-
 tion it appears, that Becher's is incomplete ; Stahl's,
 though ingenious, is defeaive ;  the antiphlogiftic is
 fimple, confiftent, and fufficient; while Dr. Prieft-
 ley's, refembling Stahl's but in  name, is  complica-
 ted, contradiaory, and inadequate.   You doubtlcfs
 therefore will be inclined  to prefer the antiphlogif-
 tic doarine : Indeed you may adopt it with fafety ;
 for from being a plain relation of fafts, it  is found-
 ed on no idealprradpk* on no creature of the ima-
 gination ; it is propt by  no vague fuppofition, by no
 random conjeaure; it is  dependent  upon  nothing
 whofe exiftence cannot aaually be demonftrated ;
 whofe properties  cannot be fubmitted to the moft
 rigorous  examination  ;  and whofe quantity cannot
 be determined by the tefts of weight and  meafure.
THE END. 
 
MecL.Hiit.

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MU33t
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