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                    ON
           CHEMISTRY,            J
In which the Elements of that Science are familiarly
           explained and illustrated
     BY EXPERIMENTS AND PLATES.
           TO WHICH ARE ADDED,            k^'
      Some late Discoveries on the subject of the       +4.
   FIXED ALKALIES,     ^
              BT H. DAVT, ESQ,.               ay*
          OF" THE ROYAL SOCIETY.
         A Description and Plate of the
        PNEUMATIC CISTOahy^
              OT ^fsSfftS?^ GENERAL'S Of-'f'JCE
                   j™   DEC-8—M01K
              A short Accqunt df*»  ~J **"" a
   ARTIFICIAL M:IN]
           In the United States.
            With an APPENDIX,
          Consisting of Treatises on           f-\
   DYEING, TANNING AND CURRYING.    *3
            (From etonee'* Upmt*              ^
 FOR ZNCREASE COOKE £5* CO.  BOOK-SELLERS, N. HJVBtT.  p^
                  1813.                    r.4
 

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PREFACE.
  IN venturing to offer to the public,  and more particularly t»
the female fex,  an Introduction to Chemiftry, the author, herfelf
a woman, conceives that fome explanation may be required :  and
fhe feels it the more neceffary to apologize for the prefent under-
taking, as her knowledge of the fubject is  but recent, and as fh«
can have no real claims to the title of chymift
  On attending for the firft time, experimental lectures, the au-
thor found it almoft impoffible to derive any clear or fatisfactory
information frem the rapid demonftrations which are ufually,  and
perhaps neceffarily crowded into popular courfes of this kind.  But
frequent opportunities  having afterwards occurred  of converfing
with a friend on the fubje«5t of chymiftry. and of repeating a va-
riety of experiments, fhe became better  acquainted with the prin-
ciples of that fcience, and began to feel highly interefted in its pur-
fuit.  It was then that fhe  perceived, in attending the excellent
lectures delivered at the Royal Inftitution,  by the prefent Profes-
sor of Chymiftry, the great advantage which her previous know-
ledge of the fubjedt, flight as it was,  gave her over others who
had not enjoyed the fame  means of private instruction.   Every
h£t or experiment, attracted her attention,  and ferved to explain
fomc  theory to which fhe was not  a total  ftranger; and fhe  had
the gratification to find that the numerous and elegant illustrations,
for which that fchool is fo much distinguifhed, feldom failed to  pro-
duce on her mind the effect for which they were intended.
   Hei.ce it was natural to infer,  that familiar converfation was in
ftudiei of this kind, a moft ufeful auxiliary fource of information  ;
and more efpecially to the female fex, whofe education is feldom
calculated to prepare their  minds for abflract ideas,  or fcientific
language.
   As, however, there  are but few women who have accefs to this
mcrie of instruction; and as the author  was not acquainted with
ary book that could prove a fubftitute for it, fhe thought that it
might be ufeful for beginners, as well as satibfr&ory to  herfelf, to-
trace  the fleps by which fhe had  acquired her little ftock of  chem-
ical knowledge, arid to record in the form of dialogue, thofe iikas
which fhe had firft derived from converfation.
   But to do this with fuflicicnt method, and to fix upon a mode of
arrangement, v.as an object of fome difficulty.   After much hefi-
tation, and a degree of embarrafsment. which, probably, the moft
competent chemical writers have  often  felt  in common with  the
moft fuperficial, a mode of divifion was adopted, which, though the
moft natural, does not always admit of being ftrictly purfued—it is
that of treating firft of the fimpleft bodies, and  then gradually ri-
ling to the moft intricate compounds
  It is not the author's  intention to enter into a minute vindication
of this plan.   But, whatever may be its advantages or inconvenien-
cies, the method adopted in this work is  fuch, that a young pupil, 
IV
FREFACE.
 who fhould occafionally recur to it, with a view to procure inform-
 ation on particular fubjedts, might often find it oblcure or  unintel-
 ligible; for its various parts are fb connected with each other as to
 form an uninterrupted chain offices and reafoninj-s, which will ap-
 pear sufficiently  clear and confident to thofe only who may  have
 patience to go through the whole work, or have previoufly devoted
i'ome attention to the fubjedk.
   It will, no dou'jt, be obferved, that in the course of thefe conver-
 sations remarks are often introduced,  which  appear  much too a-
 cu:e for tl.e younj pupils, b> whom they are suppofed to be made.
 Of this fault the author is fully aware.  But in order to avoid it, it
 would have been necefsary either to omit a variety of ufeful illuftra-
 tions, qr to fubmit to fuch minute explanations and frequent repe-
titions, as would have rendered the work much lefs  fuited to its
purpofe.
   In writing thefe pages, the author was more than once checked in
 her progrefs by the apprehenfion,  that fuch an attempt might be
 confidered by  fome, either as unfuited to the ordinary purfuitsof
her fex, or ill  j jftified by her own recent and  imperfect knowledge
 of the fubjedl.   But, on the  one hard, fhe felt encouraged by the
eftablifhment of thofe public inftltutions,  open to both fexes, for
the diffemination  of philosophical knowledge, which clearly prove,
that the general opinion no longer excludes women  from an ac-
quaintance with the elements of fcience; and, on the other, flatter-
ed herfelf, that whilft the imprtffions made upon her  mind, by the
wonders of Nature ftudied in this, new point of view, were ftill frefh
and ftrong, fhe might perhaps fucceed the better in communicating
 to others the fentiments fhe htrfclf experienced.
   It wiil be obferved, that, from the beginning of the work it is ta-
ken  for granted,  that the reader  has previoufly  acquired fome
flight knowledge of natural philofophy, .a circumftance, indeed,
which appears very defirable.   The author's original intention wai
 to commence this work by a ftnall tract, explaining, on a plan ana-
logous to this, the moft effential rudiments of that fcience    Thii
idea fhe has fince abandoned ;  but the manufcript was ready, and
might perhaps have been printed at fome future period, had n< t an
elementary work of a fimilar defcription, under the title of '■ Scien-
tific Dialogues,''  been lately pointed out t* her, which, on a rapid
 perufa!,fhe thought very ingenious, and well calculated to anfwer
 its intended object. 
COXTENTS.
        VOL I.---ON SIMPLE BODIES.

                   CONVERSATION I.                  i.
             On the general primiples of Chymhtry.
Connection  between Chymistry and  Natural Philosophy.   Im-
  proved State of modern Chymistry.   Its Use in the Art5.  The
  general Objects of Chymibtry.  Definition of Elementary Bo-
  dies.  Definition of Decompofition.  Integrant and Constituent
  Particles.  Distinction between Simple and  Compound Bodies.
  Of Chymical Affinity, or Attraction  of Compofition.  Exam-
  ples of Compofition and Decompofition.
                CONVERSATION II.                    10
                     On Light and Heat.
Light and Heat capable of being feparated. Dr Herfchel's Expe-
 riments.   Of Caloric. Its four Modifications.  Free Caloric. Of
 the three different States  of  Bodies, folid, fluid, and seriform.
 Dilation of Solid Badies.  Pyrometer. Dilation of Fluids.  Ther-
 mometer. Dilation of Elaftic Fluids.  Air Thermometer.   Cold,
 a Negative Quality. Profeffor Pictet's Experiments on the Reflec-
 tion of Heat.  Proftflor  Prevoft's  Theory of  the  Radiation of
 Heat.
                   CONVERSATION III.      -      -     26
                   Continuation of the Subjetl,
Of the  different  Power of Bodies to  conduct Heat.   Attempt to
  account for this Power.  Count Rumford's Theory of the Non-
  conducting Power of Fluids.   Phenomena of Boiling.  Of So-
  lution in general.  Solvent  Power of Water.  Difference  be-
  tween Solution and Mixture.  Solvent Power of Caloric.  Of
  Clouds, Rain, Dew, Evaporation,  &c.  Influence of Atmof-
  pherical  Prtffure  on  Evaporation.
                   CONVERS VTIONIV.                 46
        On Specific Heat, Latent Heat, and Chymual Heat.
 Of Specific Heat.   Of the Different  Capacities of Bodies  for
  Heat. Specific Heat not Perceptible b;- the Senfes  How tC
  be afcertained.  Of Latent Heat.   The Difference between La-
  tent and Specific  Heat.   Phenomena  attending the Melting of
  Ice and the Formation ot Vapour.  Phenomena attending  the
  Formation of Ice, and the Condensation  of Elaftic Fluids  In-
  ftances of Condenfation and confequent Difengagemcnt of Heat,
  produced by Mixtures, viz.  by the mixture of Sulphuric  \cid
  and Water, by the  Mixture of  Alcohol and  Water ;  by the
  Slakeing of Lime.  General  Remarks  on  Latent Heat.  Ex-
  planation of the Phenomena of Ether  boiling and Water freez-
  ing,  at the fame Temperature.   Calorimeter.   Meteorolog-
  ical Remarks.  Of Chymical Heat.
A 2 
CONTENTS.
                   CONVERSATION V.                 6-'-
                    On Oxygen and Nitrogen.

 The Atmosphere composed oFOxygen and Nitrogen in the State
   of Gas.  Definition of Gas.  Difference between Gas and Va-
   pour.  Oxygen essential to Combuftioo  and Respiration.  De-
   compofition of the Atmofphere by Combuftion. Nitrogen Gas
   obtained by this Procefs. Of Oxygenation  in general.   Of the
   Oxydation of Metals. Oxygen Gas obtained from Oxyd of Man-
   ganefe.  Defcription of a Water-Bath for collecting and prefer-
   ving Gasses.  Combuftion of Iron Wire in Oxygen Gas.   Fixed
   and volatile products of Combuftion.  Patent Lamps.  Decom-
   pofition of the Atmosphere by Refpiration.  Recompofition of
   the atmofphere.
                    CONVERSATION VI.                8a
                         On Hydrogen.

 Of  Hydrogen.  Of the Formation of Water by the Combuftion of
   Hydrogen.  Of the Decompofition of Water. Detonation of Hy-
   drogen Gas.   Description of Lavoisier's Apparatus for the For-
   mation of Water. Hydrogen Gas essential to the production of
   Flame.  Mufical Tones produced by the Combuftion of Hydro-
   gen Gas within a glafs Tube.  Combuftion of Candles explained.
   Detonation of  Hydrogen Gas in Soap Bubbles.  Air Balloons.
   Meteorological Phenomena afcribed to Hydrogen Gas.

                   CONVERSATION VII.                98
                   On Sulphur and Phosphorus.
 Natural Hiftory cf Sulphur.  Sublimation.   Alembic.  Combust-
   ion of Sulphur in Atmospheric/* ir. Of Acidification in general.
   Nomenclature of the  ..cids.  Combuftion of Sulphur in Oxygen
 ,  Gas,  Sulphuric .-.cid.  Sulphurous ^ cid.  Sulphurated Hydro-
   gen Gas. Harrowgate, or  Kydro-sulphurated  Waters.  Phos-
   phorus.   Hiftory of its Difcovery.   Its Combuftion  in Oxygen
♦  Gas.   Phofphoric   Acid     Phofphorus  /•cid.  Eudiometer.
   Combination of Phosphorus with Sulphur. Phosphorated Hy-
   drogen Ga».   Nomenclature of Binary Compounds.   Phofphor-
   tt of Lime burning under Water.

                  CON VERS VTION VIII.              m
                         On Car Lone.
 Method of obtaining pure Charcoal  Method of making common
   Charcoal.   Pure Carbone not to be obtained by Art. Diamond
   is Carbone in a State of perfect purity.  Properties of Carbone,
   Combuftion  of Carbone.  Production of  Carbonic  Acid Gas.
   Carbone fusceptible of only one Degree of  Acidification.   Gas-
   eous Oxyd of Carbone.  Of Seltzer Water and other Mineral
   Waters.  Effervescence-  Decompofition of Water by Carbone.
   Of Fixed and essential Oils. Of the combuftion of Lamps  and
   Candles. Vegetable Acids.  Of the power  of Carbone to revive
   Metals. 
                        CONTENTS.                       vil

                   CON VERS ATIONIX.                129
                         On Metals.

Natural History  of Metals.    Of  Roafting,  Smelting,   &c___
  Oxydation of  Metals by the Atmosphere-   Change  of Col-
  ours produced by different degrees of  Oxydation.  Combus-
  tion of Metals  Perfect Metals burnt by the Galvanic Fluid on-
  ly.   Some Metals revived by Carbone and other Combuftibles.
  Perfect Metals revived by Heat alone-   Of  the Oxydation of
  certain  Metals by the Decomposition of Water.   Power of
  Acids to promote this effect.   Oxydation of Metals  by Acids.
  Metallic Neutral  Salts.  Previous Oxydation  of the  Metal re-
  qusite.   Crystallization.  Solution  distinguifhed  from Diffolu-
  tion. Five Metals fufceptible  of Acidification   Falling Stones.
  Alloys, Soldering, Plating,  &c.  uf  Arfenic,  and of the Cauftic
  Effects of Oxygen.  Of Verdegris, Sympathetic Ink, &c.

                    CONVERSATION X-                150
                         On Alkalies.
Analogy between Earths and  Alkalies.   Ammonia proved to be a
  Compound : other Alkalies Suppose i to be fuch.   Their Combi-
  nation with  Acids.    Nomenclature  of the  Compound Salts.
  Potafh; its Natural Hiftory.  Woodafh.   Pearlafh.  Combina-
  tion of Potafh with Oils.   Soap.   Potafh contained likewise in
  the Mineral and Animal Kingdoms.  Carbonat of Potafh. Heat
  produced by the  folution of Potafh in Water   Of Glafs.  Of
  Nitre or Saltpetre. Change of Colours produced by Alkalies on
  Vegetable Blues.   Soda ; its  Refemblance to Potafh ; obtained
  from Sea  Salt, or from Marine Plants, \mmonia obtained from
  Sal Ammoniac.  Ammoniacal Gas readily abforbed by Witer,
  Compofition of Ammonia.   Liquid   Ammonia or Hartshorn.
  Heat produced by the condenfation of Ammoniacal Gas in Wa-
  ter ; and Cold produced by the Solution of this Gas in Ice.  Car-
  bonat of Ammonia.
                   CONVERSATION XL                164
                         On E.irths.
Nomenclature of  the Earths.   Their  Incombustibility-   Form the
  Bafis of all Mir.era's   Earths fufpected  to be oxydated Metals,
  Probability of their being Compounds.  Their Alkaline Proper-
  ties.  Silex; its properties and Uses in nature and in the • rts.
  Alumine  ; its U*es in Pottery, &c.  Alkaline Earths  Barytcs.
  Lime ;  its extenfivc Chymical Properties and Ufes in the Arts.
  Magnesia.  Strontian.

            VOL.11. ON COMPOUND BODIES.
                   CONVERSATION XII.               1S1
                 On the Attraction of Compofition.
Of the Laws which regulate the Phenomena of the Attraction of
  Compofition.  1.  It takes Place only between  Bodies of a differ-
  ent Nature,  a. Betwten the moft minute Particles only-  3. 
▼ill,                     *ONTENTS.
  Between a, 3,4,  or more Bodies.  4. Produces  a Change oi
  Temperature.   5. The Properties that  characterize  Bodies in
  their feparate State, deftroyed by Combination.   6. The Force
  of Attraction estimated by that which is  required by the Separ-
  ation of the Conftituents.  7. Bodies have amongft themfelves
  different Degrees of Attraction.   Of fimple elective and double
  elective Attractions,  Of quiefcent and divellent Forces.

                  CONVERSATION XIII,               188
                     On Compound Bodies.
Of the fimpleft clafs of Compounds. Of the various Combinations
  of Oxygen.  Of the undecompounded Acids.   Of the Classifi-
  cation  of Acids,  ift Clafs, Acids of fimple  and known Radi-
  cals,   zd Clafs, Acids of unknown Radicals.   3d Clafs, Acids of
  double  Radicals.   Of the Decompofition  of  Acids of the firft
  Clafs by combuftible Bodies.

                 CONVERSATION XIV.                195
Qn the Combinations rf Oxygen •with Sulphur and ivith Pbosphot us ; and
                 of the Sulphats and Pbosphats.
Of the Sulphuric Acid.  Combuftion of Animal or  Vegetable Bo-
  dies by this Acid.   Method  of  preparing it   The Sulphurous
  Acid obtained in the form of Gas.  May be obtained from Sul-
  phuric Acid.  May be reduced to Sulphur.  Is  abforbable by
  Water. Dellroys  Vegetable  Colours—Oxyd of Sulphur.  Of
  Salts in general.   Sulphats, Sulphat of Potafh or Sal Polychreft.
  Cold  produced by the melting of Salts,  Sulphat of Soda, or
  Glauber s Salt.   Heat evolved during the Formation of Sales.
  Crystallization of Salts.  Water of Crystallization   Efflores-
  cence and Deliquifcence of Salts.   Sulphat of Lime.   Gypfum
  or Plaifter  ot Paris-  Sulphat of Magnefia.  Sulphat  of Alu-
  mir.e,  or Allum.   Sulphat of Iron.  Of Ink.  Of the Phosphor-
  ic and Phosphorus Acids.  Phosphorus obtained from  Bones.
  Phosphat of Lime.

                   CONVERSATION XV.               205
 On  the Combinations of Oxygen ivith Nitrogen and -with Carbone ;  and
                 of the Nit rats and Carb  nats.
 Nitrogen fucceptible of various Degrees of Aiidification.  Of the
  Nitric Acid   Its Nature and  Compofitjon  discovered by Mr.
  Cavendifh.   Obtained from Nitrat of Potafh.   Aqua Fortis-
   Nitric  Acid may be  converted into  Nitrous  Acid.    Nitric
  Oxyd  Gas     Its conversion into  Nurous  -.cid  Gas-  Used
  as an  Eudiometrical left.   Gaseous Oxyd of Nitrogen, or txhil-
  irating Gas  obtained from Nitrat of  Ammonia.  Its Singular
  Effects on  being  respired.  Nitiats.  Of Nitrat ol Potafh Nitre
  or Saltpetre  Of Gunpowder.—Cau<,es  of D. tonation- D*-com-
  pofkion of Nitie. Deflagration- Nitrat of Ammonia. Nitrat of
   Silver. Of the Carbonic  Acid. pormtd  by the combuftion of
   Carbone. Constitutes a  component part of the Atmofphere, Ex- 
CONTENTS.
lx
   haled in fome Caverns. Grotto del Cane.  Great Weight of this
   Gas. Procured from calcareous Stones by Sulphuric Acid.  Dele-
   terious effects of  this Gas when respired.  Sources which keep
   up a fupply of this Gas in the Atmosphere  Its effects on Vege-
   tation. Of the Carbonats  of Lime, Marble,  Chalk, Shells,
   Spars, and calcareous Stones.

                  CONVERSATION. XVI.               aai
   On the Muriatic and  Oxygenated Muriatic Acids ; and on Mu-
                            riats.
Of the Muriatic Acid.  Obtained from Mnriats.  Its gaseous Form-
   Is absorbable by Water. Is fusceptible of a Stronger Degree of
   Oxygenation. Oxygenated  Muriatic Acid-   Its gaseous  Form
   and other Properties.  Combuftion of Bodies in this Gas. It dis-
   solves Gold.  Compofition of Aqua Regia. Oxygenated Muriatic
   Acid deftroys all  colours. Used for  Bleaching and for Fumiga-
   tions.  Its  offenfive Smell  &c,   Muriats.   Muriat of Soda,  or
   common Salt.  Muriat of  Ammonia.  Oxygenated Muriat  of
   Potafh. Detonates with Sulphur, Phosphorus,  &c  Experiment
   of burning Phosphorus under Water  by means of this Salt and
   of Sulphuric  Acid.

                  CONVERSATION XVII-              230
           On the Nature and Compcfition f Vegetables.
Of Organized Bodies. Of the  Functions of Vegetables. Of the El-
   ements of Vegetables. Of the Materials of Vegetables.  Analyfis
   of Vegetables. Of Sap.  Mucilage, or Gum. Sugar.  Manna.and
   Honey.  Gluten. Vegetable Oils.  Fixed Oils.  Linseed, Nut, and
   Olive Oils. Volatile Oils, forming Essences and Perfumes.  Cam-
   phor, Refins  and  Varnifhes. Pitch, Tar,  Copal,  Maftic, &c.
   Gum Resins-   Myrrh, Assafcetida,  &c.   Caoutchouc, or Gum-
   Elastic. Extractive colouring Matter; its ufe in the Arts of Dye-
   ing and Painting-  Tanning ; its ufe in the art  of preparing Lea-
   ther.  Woody Fibre. Vegetable Acids. The Alkalies  of Salts
   contained in Vegetables.

                CONVERSATION XVIII.               250
                On the Deccmpofition of Vegetables.
Of Fermentation in general. Ol the Saccharine Fermentation, the
   Product  of which is  Sugar. Of the Vinous Fermentation, the
   Product of which is Wine. Alcohol, or Spirit of Wine.  Analy-
   sis of Wine by Distillation. Of Brandy. Rum, Arack, Gin, &c.
  Tartrit of Potafh, or Cream of Tartar. Liqueurs Chymical Prop-
   erties of Alcohol.  Its Combustion.  Of  Ether,  Of the Acetous
   Fermentation, the  Product < f which is Vinegar.  Fermentation
  of Bread  Of the Putrid Fermentation,  which reduces Vegeta-
   ble' to their Elements  Spontareous succession of thefe  Fermen-
  tations   Of Vegetables laid  to  be  petrified.  Of Bitumens ;
  Naphtha. Afphaltum. Jet, Coal, Succin, or Yellow Amber,   Of
  Fossil Wood,  Peat, and  Turf. 
*                       contents-
                CONVERSATION XIX.                47*
                    Hijlary of Vegetation.

Connexion  between the Vegetable and Animal  Kingdoms.  Of
  Manures. Of Agriculture.  Inexhauftible Sources of Materials
  for the purposes of Agriculture.  Of Sowing Seed- Germination
  of the Seed.   Function of the Leaves of Plants.  Effects of  light
  and Air on Vegetation   Effects of Water on Vegetation.  Ef-
  fects of Vegetation on the Atmofphere.  Formation  of  Vegeta-
  ble Materials by the Organs of Plants.  Vegetable heat.  Of the
  Organs of Plants.   Of the Bark,  consifting of Epidermis, Par-
  enchyma, and Cortical Layers.   Of Alburnum  or  Wood.——
  Leaves, Flowers, and Seeds.  Effects of the Seasons on  Vegeta-
  tion. Vegetation of Evergreens in Winter.

                   CONVERS ATION XX,              290
                 On the Compufition of Animals.
Elements of Animals.  Of the Three principal Materials of Ani-
  mals,  viz. Gelatine, Albumen, Fibrine. Of Animal   cids.  Of
  Animal Colours, Prussian Blue, Carmine, and Ivory Black,

                  CONVERSATION XXI.               301
                    On the Animal Economy.
Of the principal *nimal Organs.  Of  Bones, Teeth, Horns, Liga-
  ments, and Cartilage. Of the Muscles, conftituting the organs
  of Motion  Of the  Vafcular System for the conveyance of
  fluids  Of the Glands for the Secretion of Fluids. Of the Nerves,
  conftituting the organs of Scnfation.  Of the Cellular Subftancs
  which connects the feveral Organs-  Of the Skin.

                 CONVERS  TION XXII.               311
           On Animalization, Nutrition, and Respiration.
D'geftion-  Solvent power of the Ga-rric Juice.   Formation of
  Chyle.  Its   ssimilation, or Converfion into Blood-   Of Respir-
  ation.  Mechanical Process of Respiration.  Chymical  Process
  of Respiration.  Of the circulation of the Blood.   Of the Func-
  tions of the  A rteries  the Veins and the Heart.  Of  the Lungs.
  Effects of Refpiration on the Blood-

                 CONVERS STION  XXIII.              323
        On Animal Heat; and of various Animal Products.

Of the Analogy of Combuftion and Respiration.    Animal  Heate-
  volvedin the Lungs   Animal Heat evolved in the Circulation.
  Heat produced by  Fever.  Perspiration. Heat produced by ex-
  ercise.  Equal Temperature of \nimals at all Seasons.  Power
  of the * nimal Body to resift the efivcts of Heat. Cold produced
  by Perfpiration.   Refpiration of Fifh, and of Birds.  Effects of
  refpiration on Muscular Strength  Of feveral Animal Products,
  viz, Milk, Butter, and Cheefe ; Spermaceti; Ambergris; Wax 5 
                        contents;
                                                      a




  *L* ConkLU.Sk; ^^ ^^  °f ^putHdFer»e„ta.





DaV7Uef,tcrian LeCtUrCj0n th^ Decompofition of the Fixed Alka-


Defcription of the Pneumatic Ciftern of Yale College,        f e r

Account of Mineral Waters                   s*        353

                     APPENDIX.                  35
                                            I


-on Currying,   -     .     .    .    .    I'l
-on Tanning, 
 
      CONVERSATIONS
                  ON

CHEMISTRY.
ON SIMPLE BODIES.
            Con&eraation i.
On the General Principles of Chemiftry.
Mrs. B.
   HAVING now acquired some elementary notions of
Natural Philosophy, I am going to propose to  vou
another branch of science to which I am particularly
anxious that you should  devote a share of your atten-
tion.  This  is Chemistry, which is so closely con-
nected with Natural Philosophy, that the study of the
one must  be incomplete without some knowledge of
the other ; for it  is obvious that we can derive but a
very imperfect idea of bodies from the study of the
general laws by which they are governed, if we  remain
totally ignorant of»heir intimate nature.
   Caroline.  To confess the truth,  Mrs.  B. I am  not
disposed to form a very favourable idea  of Chemistry,
nor do I expect to derive much entertainment from
it.  I  prefer those sciences that exhibit nature on a
grand scale, to those which are confined to the  mi-
nutiae of petty details.  Can the studies which we have 
2
 lately  pursued,  the general properties of matter, or
 the revolutions of the heavenly bodies, be compared to
 the mixing up of a few insignificant drugs ?
   Airs. B.   I rather imagine  that your want of taste
 for chemistry proceeds from the very limited idea  you
 entertain of its object  You confine the  chemist's  lab-
 oratory to the narrow  precints  of  the  apothecary's
 shop, whilst it is subsefvient to an immense  variety of
 other ustful pin poses.   Besides,  my dear,  chemistry
 is by no means confined to works of art.   Nature  also
 has her laboratory,  which  is  the  universe,  and there
 she is incessantly  employed  in chemical operations.
 You are surprised, Caroline ; butl assure you that the
most  wondeiful  and the most interesting phenomena
of nature are almost all of them  produced by chemical
powers.  Without entering therefore into the  minute
details  of  practial   chemistry, a  woman may obtain
such a knowledge of the science,  as will not only throw
an interest on the common occurrences of life, but will
enlarge the sphere  of her  ideas, and render the con-
templation  of Nature a source  of delightful instruc-
tion.
   Caroline.  If this  is the  ca?e,  I  have  certainly been
much mistaken in the notion I had formed of chemistry.
I own that 1 thought it was  chiefly  confined  to the
 knowledge and preparation of medicines.
   Mrs. B.   That is only a branch of chemistry, which
 is called Pharmacy ; and though the study of  it  is  cer-
;ainly of very great importance to  the world at large,
 it properly belongs  to professional men, and is therefore
 the last that I should advise you to study.
   Emily.  But did not  the  chemists  formerly employ
 saemselvesin search (;f the  Philosopher's Stone, or the
 secret of making gold ?
   Mrs. B.   Thcte  were a particular set of misguided
 philosophers, who  dignified themselves with  the name
 of Alchymists, to distinguish thcii  puihiiits from those
 of the common chemists, whose  studies  were confined
 to the know ledge of medicines.
   But, since that period, chemistry has undergone so
 complete a revolution, that  from  an obscure  and mys- 
3
terious  art, it is now become a regular and beautiful
science, to which art is entirely subservient.  It is true,
however, that we are indebted  to  the alchy mists  for
many very useful discoveries, which sprung from their
fruitless attempts to make gold, and which undoubtedly
have proved of infinitely greater  advantage to mankind
than all their chimerical pursuits.
   The modern chymists, far from directing their  am-
bition to the imitation of one of the least useful produc-
tions of inanimate nature, aim at copying almost  all her
operations,  and  sometimes even  form combinations,
the model of which is not to be  found in her own  pro-
ductions.   They have little reason to regret their ina-
bility to make gold (which is often but a false represen-
tation of riches,) whilst by their innumerable inventions
and discoveries, they have so greatly stimulated indus-
try, and facilitated  labour, as prodigiously to  increase
the luxuries as well as the necessaries of life.
   Emilxj.   But I do  not  understand  by  what  means
chemistry  can facilitate labour ; is not that rather the
province of the mechanic ?
   Mrs. B.   There are many  ways  by which  labour
may be rendered more easy, independently of mechan-
ics ; but even  the machine the most wonderful in its
effects, the steam  engine, cannot  be understood with-
out  the assistence of chemistry.   In  agriculture,  a
chemical knowledge of the nature of  soils, and of veg-
etation, is  highly useful; and in those arts which re-
late to the comforts and conveniencies of  life  it would
be endless  to  enumerate  the advantages  which result
from the study of this science.
   Caroline.  But, pray, tell us more  precisely in what
manner the discoveries of chemists have proved  so ben-
eficial to society.                       ...
   Mrs. B.  That  would be an unfair anticipation ; for
you would not comprehend the nature of  such  discov-
eries and  useful applications,  so Veil  as you  will do
hereafter.   Without a due regard to method, we can-
not expect to make any progress in chemistry.   I  wish
to direct your observation  chiefly to the chemical oper-
ations of Nature ; but those of Art are certainly of too. 
4
high importance  to pass unnoticed.  We shall there-
fore allow them also some share of our attention.
  Emily.   Well then, let us now set to work regularly,
I am very anxious to begin.
  Mrs. B.  The  object  of chemistry is to obtain a
knowledge of the intimate nature of bodies and of their
mutual action on each other.  You  find  therefore, Ca-
roline, that this is no narrow or confined science, which
comprehends every thing material within our sphere.
  Caroline.  On the contrary, it must be inexhaustible ;
and I am at a loss to conceive how  any proficiency can
be made in a science whose objects are so  numerous.
  Mrs. B.  If every individual substance was  formed
of different material's, the study of chemistry would in-
deed be endless ; but you must observe, that the vari-
ous bodies in nature are composed of certain elementary
principles, which are not very numerous.
  Caroline.  Yes ;  I know that  all  bodies are  com-
posed of fire, air, earth, and water;  I learnt  that many
years ago.
  Mrs. B.   But you must now endeavour to forget  it.
I have already informed you what a great change chem-
istry has under-one since it has become a regular sci-
ence.  Within tfrese thirty years especially,  it  has ex-
perienced an  entire revolution, and it  is now proved
that neither fire, air, earth  nor water, can be cahed ele-
mentary bodies.  For an elementary body is  one that
cannot be decomposed, that is to  say, separated into
other substances ; and fire, air, earth, and water, are all
of them susceptible of decomposition.
   Emily.   I  thought that  decomposing a body was di-
viding it into its minutest parts.  And if so, I do not un-
derstand why an elementary substance is not  capable  of
being decomposed, as well as any  other.
   Mrs. B.   You  have misconceived the idea of De-
composition ;  it is very  different from  mere divhion :
the latter simply re/J0ices a body into  parts, but the for
iner separates it into the various ingredients, or mate-
rials, of which it is composed.  If we  were to take a
loaf of bread, and separate  the several ingredients  of
which it is made, the flour, the yeast,  the  salt, and the 
3
water, it would be very different from cutting the loaf
into pieces, or crumbling it into atoms.
   Emily.   I  understand you now very Avell.  To de-
compose a body is to separate from each other the va-
rious elementary substances of which it consists.
   Caroline.   But flour, water, and the other materials
of bread, according to youi definition, are not elementary
substances ?
   Mrs. B.   No my dear; I mentioned bread rather as
a familiar comparison to illustrate the  idea, than as an
example.
   The  elementary substances of which a body is com-
posed, are called the constituent parts  of that body ; in
decomposing it, therefore, we  separate its constituent
parts.   If,  on the contrary, we divide a body by chop-
ping it to pieces, or even by giiading or pounding  it to
the finest powder, each of these small particles vvili
still consist of a portion of the  several constituent  parts
of the whole body :  these  we call the integrant parts ;
do you understand the  difference ?
   Emily.   Yes, I think, perfectly.   We decompose  a
body into its constituent parts  ;  and divide it into its inte-
grant parts.
   Mrs. B.   Exactly   so.   If therefore a body consists
of only one kind of substance,  though we may divide it
into its integrant parts, it is not possible to decompose it.
Such bodies  are therefore called simfile or  elementary,
as they are the elements of which all  other bodies are
composed.  Comfiound bodies  are  such  as  consist of
more than one of these elementary principles.
  Caroline.   But do not fire,  air, earth and water,  con-
sist, each of them, but of one kind of substance ?
   Mrs. B.   No, my dear : they are every one of them
susceptible of being separated  into  various simple bo-
dies. Instead  of four, chemists now  reckon upwards of
forty elementary substances.  Thase we shall first ex-
amine separately, and  aftervvardyconsid«r in their com-
binations with each other.
B2 
6
Their names are as follow :
LIGHT,	SILEX,		ZINC,
CALORIC,	ALLUMINE,		BISMUTH,
OXYGEN,/^"	YTTI'.IA,		ANTIMONY,
NITROGEN,	GLUCINA,		ARSENIC,
HYDROGEN,	ZIECON1A,		COBALT,
SULPHUR,	AGUSTINA,		MANGANESE,
PHOSPHORUS,	(25 Metals	■)	TUNGSTEN,
CARBONE,	GOLD.		MOLYBDNUM,
(2 Alkalies.)	PLATINA,		URANIUM,
POTASH,	SILVER,		TELLURIUM,
^ODA,	MERCURY,		TITANIUM,
(\0 Earths.)	COPPER,		CHROME,
LIME,	IRON,		OSMIUM,
MAGNESIA,	TIN,		IRIDIUM,
STRONT1TES,	LEAD,		PALLADIUM,
BARYTES,	NICKLE,		RHODIUM.
Caroline. This	is indeed a formidable list !		
   Mrs.  B.  Not  so much as you imagine ;  many of
 the names you are already  acquainted with, and  the
 others will soon become familiar to you.   But,  before
 we  proceed  farther it will  be necessary to give  you
 some idea of chemical attraction, a power on which  the
 whole science depends.
   Chemical Attraction, or the Attraction of Composition,
 consists in the peculiar tendency which bodies  of a  dif-
 ferent nature have to unite with each other.   It is by
 this force that all the compositions,  and decompositions,
 are effected
   Emily.  What is the difference between chemical at-
 traction,  and the attraction of cohesion,  or  of  aggrega-
 tion, which you often mentioned to us in former conver-
 sations ?
   Mrs. B.   The attraction of cohesion exists only  be-
tween particles of the  same nature, whether simple or
 compound; thus it uaites the  particles  of a  piece of
metal which  is a simple substance,  and  likewise  the
particles  of a  loaf of bread which is a compound.  The
attraction of  composition, on the contrary unites  and
maintains in  a st.-.te of combination particles  of a  dis-
similar nature ; it is this power that forms  each  of  the 
compound particles of which bread consists ; and it is
by the attraction of cohesion that all  these particles are
connected into a single mass.
  Emily.  The attraction of cohesion, then, is the pow-
er which unites the integrant particles of a body ;  the
attraction of composition that which  combines the con-
stituent particles.  Is it not so. ?
  Mrs. B. Precisely : and  observe  that the attraction
of cohesion unites particles of a similar nature, without
changing their original properties;  the  result of such
an union, therefore, is a body of the same kind  as the
particles of which it is formed ; whilst the attraction of
composition, by combining particles of a dissimilar na-
ture, produces new bodies, quite  different from any of
their constituent particles.   If, for instance, I pour on
the  piece of copper, contained in this  glass, some of
this liquid (which is called nitric acid) for which it has
a strong attraction, every particle of the copper will com-
bine with a particle of acid,  and together they will form
a new body, totally different either from  the copper or
acid.
   Do you observe the internal commotion that already
begins to take place ? It  is  produced by the combina-
tion of these two substances;  and yet the acid has in
this case  to overcome, not only the resistance which the
strong cohesion of the particles of copper oppose to its
combination with them, but also the weight of the  cop-
per which makes it sink to the bottom of the glass, and
prevents the acid from having such free access to it as
it would if the metal were suspended in the liquid,
   Emily.  The acid seems, however, to overcome both
 these obstacles without difficulty, and appears to be  very
 rapidly dissolving the copper
   Mrs B.  By  this means it reduces the copper into
 more minute parts, than could possibly  be done by any
 mechanical power.  But as the acid can act  only on the
 surface, of the metal, it will be sometime before the un-
 ion of these two bodies will be compleated.
   You m..y, however, already see  how totally different
 this compound is from either of its ingredients.  It  is
 neither colourless like the acid,  nor hard,  heavy, and 
8
  yellow, like the copper.  If you tasted it, you would no-
  longer  perceive  the sourness of the acid.   It has at
  present the appearance of a blue  liquid ; but when the
 union is completed, and the water with which the  acid
 is diluted is evaporated, it will assume the form of regu-
 lar chrystals, of a fine blue colour, and perfectly trans-
 parent.  Of these I can shew you  a specimen, as I have
 prepared some for that purpose.
   Caroline.  How very beautiful they are, in colour,
 form and transparency '
   Emily.   Nothing can be more  striking than this ex-
 ample of chemical attraction.
   Mrs.  B.  The term attraction  has been  lately intro-
 duced into chemistry as a substitute  for the word affin-
 ity,  to which some chemists  have objected, because it
 originated in the vague notion that chemical combina-
 tions depend upon a certain resemblance, or relationships
 between particles that are disposed to unite ; and this idea
 is not only imperfect, but  erroneous, as it is generally
 particles of the most dissimilar nature, that have  the
 greatest tendency to combine.
   Caroline   Besides, there seems to  be  no advantage
 in using a variety of terms  to express the same mean-
 ing : on the contrary it creates confusion : and as we
 are well acquainted with the term  of attraction in natu-
 ral philosophy, we had better adopt it in chemistry like-
 wise.
   Mrs. B.  If you have a clear idea of the meanings
 I shall leave you at liberty to express it in the terms you
 prefer.   For myself,  I  confess that I  think the word
 attraction best suited to the general law that unites the
 integrant particles of bodies ; and affinity better adapted
 to that which combines the constituent  particles, as it
 may convey an idea of the preference which some bod-
ies have for others, which the term attraction of composi-
 tion does not so well express.
   Emily.   So I think ; forjthough that preference may
not result  from any relationship or similitude,  between
the particles (as you say was once supposed), yet, as it
 really exists, it ought to be expressed.
   Mrs. B.  Well,  let it be agreed that  you may use 
9
the terms affinity, chemical attraction, and attraction of
composition,  indifferently,  provided you recollect that
they all have the same meaning.
  Emily.  I do not conceive how bodies can be decom-
posed by chemical attraction.   That this power should
be the means of composing them, is very obvious ; but
how it can at the same time produce exactly the contra-
ry effect, appears to me very singular.
  Mrs.  B.  To decompose a body, is, you know, to
separate its constituent parts, which, as we have just ob-
served,  can never be done by mechanical means.
   Emily.  No ; because mechanical  means separate
only the integrant particles ; they act  merely against
the attraction of cohesion.
   Mrs. B.  The  decomposition  of  a body, therefore,
can  only be performed by chemical powers.  If  you
present to a bodv composed only of two principles, a
third, which has a greater affinity for one of them than
the two first have lor each other, it will  be decomposed,
that is,  its two principles will be separated by means
of the   third  body.   Let  us call two ingredients, of
which a body is composed, A, and  B.   If we present
to it another ingredient C, which has a greater affinity
forB, than that which unites  A and B,  it necessarily
follows that  B will quit A to combine with C.  The new
ingredient,  therefore,  has  effected  a decomposition of
 the original body A B; A has  been  left alone, and a
new compound, B C, has been formed.
   Emily.  We might, I think, use the comparison of
 two friends, who wore very happy in each other's soci-
 ety, till a third  disunited them by the preference  which
 one of them gave to the new comer.
   Mrs. B.   Very well, I shall no\i show you how this
 takes place in chemistry.
   Let us suppose that we wish to decompose the com-
 pound  we have just formed by  the combination  of the
 two ingrelieuts, copper  and nitric acid :  we may do
 this by presenting to it a piece of iron, for which  the
 acid h.s a stronger attraction than for copper ; the acid
 will consequently quit the copper to combine with toe
 iron, and the  copper  will be what the chemist calls 
to
precipitated, that is to  say, it will return to its separate
state, and reappear in its simple form.
   In order to produce this effect, I shall dip  the blade
of this knife into the fluid, and when 1 U.ke it out, you
will observe that instead of being wetted with a  blueish
liquid like that contained in the glass, it will be covered
with a very thin pellicle of copper.
   Caroline.  So it is really ! But then is it not the cop-
per instead of the acid, that has combined with the iron
blade I
   Mrs. B.  No ; you are d2ceived by appearances  :
it is the acid which combines with the  iron,  and in so
doing deposiles the copper on the surface of the blade.
   Emily.  But cannot three or more substances com-
bine together, without any of them being precipitated ?
   Mrs. B.  That is  sometimes the case ; but in gene-
ral, the stronger affinity destroys the weaker : and it sel-
dom happens that the attraction of several  substances
for each other is so equally balanced as to produce such
complicated compounds.
   It is now time to conclude our conversation  for this
morning.  But before we part,  I must recommend you
to fix in your memory the names of the simple bodies^
against our next interview.



              Conservation  n.

                On Light and  Heat.
                     Caroline.

  We have learned by heart the names of all the sim-
ple  bodies,  which you have enumerated, and we are
now ready to enter on the examination of each of them
successively.   You will begin I suppose with light ?
  Mrs. B. That will not detain  us long : the nature of 
11
light,  independent of heat,  is so imperfectly knoWttj
that we have little more than conjectures respecting it.
   Emily.  But is it possible to separate light from heat;
I thought that they were only different degrees of the
same thing ?
   Mrs* B. They are certainly very intimately connect-
ed : yet it appears they are distinct substances, as they
can, under certain circumstances, be in a great mea-
sure separated :  the most striking instance of this was
pointed out by Dr. Herschel.
   This philosopher  discovered that  heat was  less re-
frangible  than light;  for in separating the different
coloured rays of  light by a prism (as we  did some time
ago), he found that the greatest  heat was beyond the
spectrum, at a little distance from the red rays, which
you may recollect are the least refrangible.
   Emily.  I should like so try that experiment.
   Mrs. B. It is  by  no means an easy one : the heat of
a ray of light, refracted by a  prism, is  so small that it
requires a very delicate thermometer to  distinguish the
difference of the degree of heat within and without the
spectrum.  For  in this experiment  the  heat is not to-
tally separated from the light, each coloured ray re-
taining a  certain portion of it, though  the  greatest
part is not sufficiently refracted to fall within the spec-
 trum.
   Emily.  I  suppose, then,  that those  coloured rays
which are the  least refrangible, retain the  greatest
 quantity of heat ?
   Mrs. B.  They do so.
   Caroline. Perhaps the different degrees of heat which
 the seven rays possess, may  in some unknown manner
 occasion  their variety  of colour.  I have  heard that
 melted metals change colour according to  the  different
 degrees of heat to which they are exposed ; might not
the colours of the spectrum be produced  by a  cause of
 the same  kind ?  Do let  us try if we cannot  ascertain
 this, Mrs. B ? I should like extremely to  make some dis-
 covery in  chemisty.
   Mrs. B Had we not better learn  first what is already
 known ? Surely you cannot seriously imagine that  be- 
12
fore you have acquired a single clear idea on chemistry,
you can  have any chance of discovering  secrets that
have eluded the penetration of those who  have spent
their whole lives in the study of that science.
  Caroline.   Not  much, to  be  sure   in the  regu^r
course of events ;  but a lucky chance sometimes hap-
pens.  Did not a child lead the way to the  discovery of
telescopes ?
  Mrs. B. There are certainly a few instances  of this
kind.   But believe me, it is infinitely wiser  to follow up
a pursuit regularly,  than to trust to chance for your
success.
  Emily  But to return to your subject.  Though I no
longer doubt that light and heat can be separated.  Dr.
Hercheil's experiment does not appear to me to afford
sufficient proof that  they are  essentially different ; for
light,  which you call a simple body, may  likewise be
divided into the various coloured rays ;  is it not  there-
fore possible that  heat  may  only be  a modification of
light ?
  Mrs. B    That is a supposition which, in the pre-
sent state of natural  philosophy, can  neither be posi-
tively affirmed nor denied :  it is generally thought that
light and heat are connected  with  each other as cause
and effect, but which is the cause, and which the effect,
it is extremely difficult to determine.   But it would be
useless to detain you any longer on this intricate sub-
ject.   Let  us now pass on to that of heat, with which
we are much better acquainted.
  Caroline.  Heat is not, I believe, amongst  the number
of the simple bodies ?
  Mrs.  B.  Yes, it is: but under  another  name—that
of caloric, which is nothing more than the principle,
or matter of heat.—We suppose caloric to be  a very
subtiie fluid, originally derived from the sun, and com-
posed of very minute particles, constantly  in agitation,
and moving in a  .manner similar to light, as long as they
meet with no obstacle.-  But when these rays come in
contact with the  earth  and the  various bodies  belong-
ing to it,pait of them are reflected from their surfaces
 according to certain laws, and part enters into them. 
13
  Carroline. These rays of heat,  or caloric, proceed-
ing from the same source, and following the same  di-
rection, as the rays of light, bear a very strong  resem-
blance to them.
  Mrs. B. So  much so that it often requires great at-
tention not to confound them.
  Emily.  I think there is no danger of that, if  we re-
collect one great distinction—light is visible, and calor-
ic is not.
   Mr*. B. Very  right.  Light affects  the sense  of
Sight ; Caloric that of Feeling : the one produces Visiont
the other the  peculiar sensation of Heat.
   Caloric is found  to exist  in a variety of forms, and
to be susceptible of certain  modifications, all of which
may be comprehended under the four following  heads ;
          1.  FREE CALORIC.
          2   SPECIFIC HEAf.
          3   LAtMNf HEAT.
          4.  CHEMICAL  HEAf.
   The first, or free caloric, is also called heat of
temperature ; it comprehends all heat which is per-
ceptible to the senses, and affects the thermometer.
   Emily.   You mean  such as the  heat of the  sun,  of
fire, of candles, of stoves ; in short of every thing that
burns ?
    Mrs.  B.  And likewise of things  that do not  burn,
as for instance, the warmth of the body ;  in a word, all
heat that is sensible, whatever may be its degree, or the
source from  which it is derived.
   Caroline.  What  then are the other modifications  of
caloric ? It must be a strange kind of heat that cannot
be perceived by our senses  ?
   Mrs. B. None of the modifications of caloric should
properly be called heal  ; for heat,  strictly  speaking, is
the  sensation, produced by caloric, on animated bodies,
and this word therefore should  be  confined  to  express
the sensation.   But custom has adapted it likewise to
inanimate matter,  and we say  the heat of an oven, the
heat of the sun, without any reference to the sensation
which they are capable of exciting.
G 
14
   it was in order to avoid the  confusion which arose
from thus confounding the cause and effect, that  mod-
ern chemists adopted the new word Caloric,  to express
the principle  which produces heat;  but they do not
yet limit the word heat (as they should do) to the ex-
pression of the sensation, since they still retain the hab-
it of connecting this  word with the three other  modifi-
cations of caloric.
   Caroline. But you  have not yet explained to us what
these other modifications of caloric are.
   Mr*.  B. Because  you  are not yet acquainted with the
properties of free caloric, and you know we have agreed
to proceed with regularity.
   One  of the  most remarkable properties of free calor-
ic is its power of dilating  bodies.   This fluid is  so ex-
tremely subtile, that  it  enters  and pervades all bodies
whatever, forces itself between their particles, and not
only separates them, but, by its repulsive power, drives
them asunder, frequently to  a considerable distance
from each other.   It is thus that caloric dilates  or ex-
pands a  body so  as to make  it occupy  a  greater  space
than it did before.
   Emily. The effect of caloric on bodies therefore,  is
directly contrary to  that of the attraction of cohesion  ;
the one draws the particles  together, the other drives
them asunder.
   Mrs. B  Precisely.   There  is a kind of continual
warfare between the attraction of aggregation and the
repulsive  power of caloric :  and from  the action  of
these two opposite forces, result  all the various forms
of matter, or degrees  of  consistence  from the solid
to the liquid and  aeriform state.   And accordingly, we
find that .nost bodies are capable of passing from one
of these forms to the other,  merely in consequence  of
their receiving  different quantities of  caloric.
   Caroline. This is very curious ;  but  I think I under-
stand the reason  of  it.   If a great quantity  of caloric is
added to a  solid  body, it introduces  it elf between the
particles in such a manner as to overcome in a  consid-
erable degree, the attraction of cohesion ; and the body
from a  solid, is then  converted into a fluid. 
15
  Mrs. B. This is the case whenever a body is  melt-
ed ; but if you add caloric to a liquid, can you tell ma
what is the consequence ?
  Caroline. The  caloric forces itself in greater  abun-
dance between the particles of  the  fluid,  and drives
them to such  a distance from each  other,  that their
attraction of aggregation is wholly  destroyed  ; the li-
quid is then transformed into vapour.
  Airs. B. Very well ; and this is precisely the case
with boiling water, when it is converted into steam or va-
pour.
   But each of these various states,  solid,  liquid,  and
aeriform, admit of many different  degrees  of density,
or consistence, still arising  v partly at least) from the
different quantities of caloric the bodies contain.  Solids
are  of various degrees of density, from  that of gold,
to that ol a thin jelly.  Liquids  from the  consistence
of  melted  glue, or  melted metals,  to that  of^ ether,
whreh-is.the lightest of all liquids.   The different elas-
tic fluids (with'which you are nof acquainted)  admit of
no less variety in their degrees of density.
   Emily. But does not every individual  body also ad-
mit  of different degrees ol consistence,  without chang-
ing its state ?
   Airs. B. Undoubtedly ;  and this I can immediately
show you by a very  simple experiment.   This  piece
of iron now exactly fits the frame or ring, made  to re-
ceive it, but if heated red hot, it will no longer  do so,
for its dimensions will be  so much increased by the
caloric that has penetrated into it, that it  will  be  much
too large for the frame.
   The iron is now red hot ; by applying it to the  frame,
we  shall see  how much it is dilated.
   Emily.  Considerably so indeed!  I  knew  that  heat
had this effect on bodies, but I did not imagine that it
could be made so conspicuous.
   Mrs.  B. By means  of this instrument (called a Py-
 rometer) we  may estimate,  in the most exact manner,
 the various dilatations  of any solid body by heat.  The
 body we are  now going to submit to trial is this small- 
iron bar ;  I fix it to this apparatus, (Plate 1.  Fig.  \.)
and then heat it by lighting three  lamps  beneath it :
when the bar dilates, it increases in length as well as
thickness  ;  and, as one end  communicates Avith  this
wheel-work, whilst the other end is fixed and  immove-
able,  no sooner does it begin to  dilate than it presses
against the wheel-work; and sets in motion the index,
which points out the degrees of dilation on the dial-
plate.
   Emily.  This is  indeed a  very  curious  instrument j
but I do not understand the use of the wheels ; would
it not be more simple, and answer  the purpose equally
well, if the bar pressed against the  index, and put it in
motion without the intervention of the wheels ?
  Mrs. B. The use  of the  wheels is merely to mul-
tiply the motion, and  therefore render the effect of the
caloric more  obvious : for if the index moved no more
than  the  bar increased in length, its motion would
scarcely be perceptible : but by means of the wheels  it
moves in  a much greater proportion which  therefore
renders the variations much more  conspicuous.
  By submitting different bodies to the test of the py-
rometer, it is found that they  are  far  from dilating in
the same proportion.   Different metals expand in dif-
ferent degrees, and other kinds of solid bodies vary  still
more in this  respect.  But  this different susceptibility
of  dilation is still  more remarkable in fluids  than in
solid bodies, as I shall show you.  I have here  two glass
tubes,  terminated  at one end by  large bulbs.   We
shall fill the bulbs, the one with spirit of wine, the oth-
er with water.   I have coloured both  liquids,  that  the
effect may be more  conspicuous.   The spirit of wine,
you see, dilates  merely by the warmth of my  hand,  as
I hold the  bulb.
  Emily.  It certainly dilates,  for I see it is rising into

                      Plat*  I.

  Fig. i. A A.  Bar of metal.  143. Lamps burning. B B.
Wheel work*  C'  Index.
  Fig; a   A Ai Glas9 tubes with  bulbs.  B B.  Glasses of wa-
ter in  which they are immersed- 
'late I.
Page-10
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       the tube.   But water, it seems, is not so easily affected
       by the heat ; for no apparent change is produced on it
       by the warmth of the hand.
        Mrs. B.   True ; we shall now plunge the bulbs into
       hot water, (Plate  1. Fig. 2.)  and you will see both li-
       quids rise in the tubes ; but the spirit of wine will begin
       to ascend first.
        Caroline.  How rapidly it dilates !  Now  it has nearly
       reached the top of the tube, though the water has  not
       yet began to rise.
         Emily.   The water now begins to dilate.   Are  not
       these glass tubes, with liquids rising within them, very
       like thermometers ?
         Mrs. B.  A Thermometer is constructed  exactly
       on the same principle, and these tubes  require only a
       scale to answer the purpose of thermometers : but they
       would be rather awkward in their dimensions.  The
       tubes and  bulbs  of  thermometers, though of various
       sizes, are in general much smaller  than these ;  the
       tube too  is hermetically closed, and the air excluded
       from it.   The fluid most generally used in thermome-
       ters is mercury, commonly  called quicksilver, the di-
       lations  and contractions of which correspond  more
       exactly to the additions, and  substractions, of caloric,
       than those of any other fluid.
         Caroline.  Yet I have often seen  coloured  spirits of
       wine used in thermometers.
         Mr*.  B.  The  dilations and  contractions  of  that
t      liquid are  not  quite so uniform  as those of mercury ;
       but in cases in which it is not requisite to ascertain  the
       temperature with   great precision, spirit  of wine will
       answer the  purpose equally well, and  indeed  in  some
       respects better, as  the expansion of the latter is great-
       er and therefore more conspicuous.  This fluid is used
       likewise in situations and experiments in which mercu-
       ry would be frozen ; for mercury  becomes a solid body,
       like a piece of lead or any other metal,  at a certain  de-
       gree of cold : but no degree of cold has  ever been known
       to freeze spirits of wine.
         A thermometer therefore  consists  of a tube with a •
C 2 
18
bulb, such as you see  here, containing a fluid whose
degrees of dilation and  contraction are indicated  by a
scale to which the tube is fixed.  The  degree which
indicates the  boiling point, simply  means  that, when
the fluid is sufficiently dilated to rise to this  point, the
heat is such, that  water  exposed to  the same tempera-
ture will boil.  When on the other hand, the fluid  is so
much  condensed as to  sink to the  freezing point, we
know that water will freeze at that temperature.  The
extreme points of the scales are not the same in  all
thermometers, nor are  the degrees always  divided in
the same manner.  In different countries philosophers
have chosen to adopt different scales  and divisions.  The
two thermometers most used are those of Fahrenheit,
and of Reaumur ; the first is generally preferred by the
English, the latter by the French.
   Emily.  The variety of scales must be very inconven-
ient, and  I  should think liable to occasion  confusion,
when French and English experiments are compared.
   Mrs. B.  This inconvenience is but very trifling, be-
cause the different graduations of the scales  do not af-
fect the principle upon which thermometers are con-
structed.  When we know, for instance, that Fahren-
heit's scale is  divided into 212  c-grees in which 32*
correspond with  the freezing point, and 212° with the
point of boiling water;  and that Reaumer's is divided
only into 80 degrees, in  which 0Q denotes the  freezing
point, and 80° that, of boiling water, it is easy  to com-
pare the  two scaies together, and reduce the one into
the  other.  But  for greater convenience,  thermome-
ters are sometimes constructed with both these scales,
one on either side of the tube ; so that  the  correspon-
dence of the different degrees of the two scales, is thus
instantly seen.  Here is one of these  scales  (Plate II.
Fig. 3.) by which you  can at once  perceive that  each
degree of Reaumer's corresponds to 2  1-4 of Fahren-
heit's division.
   Emily.  Are spirits of wine,  and  mercury, the only
fluids used in the construction of thermometers ?
   Mrs.  B. ' I believe they are the only liquids now  in
 use, though some others, such  as linseed oil, would 
ri*e It
 
20
   Caroline.   Now I comprehend it  very well ? nothing-
 explains a thing so clearly as a comparison.
   Emi'y.  But will  thermometers  bear any degree of
 heat ?
   Mr*. B.   No ;  for if the temperature be much above
 the highest degree  marked on the scale of the ther-
 mometer, the  mercury would  burst the tube in an at-
 tempt  to ascend.  And  at any rate, no  thermometer
 can be applied to temperatures higher than  the boiling
 point of the  liquid used in its construction.  In furnaces,
 or whenever any very high temperature is to be measu-
 red, a pyrometer,  invented by Wedgewood,  is used for
 that purpose.   It  is made of a certain composition  of
 baked  clay,  which has  the peculiar property of con-
 tracting by  heat,  so  that the degree of contraction  of
 this substance  indicates the temperature to which it has
 been exposed.
  Emily.  But is  it possible for a body to  contract by
 heat ?  I thought that heat dilated all bodies whatever.
  Mrs. B.   That  is,  I believe, true.  Yet  heat,  fre-
quently diminishes the bulk of a body by evaporating
some of  its particles ; thus, if  you dry a wet sponge
before  the  fire, the heat, though  it must,  according to
the general law of nature, dilate the particles of the
sponge, will  very considerably contract its bulk by evap-
orating its moisture.
  Caroline.   And   how do you ascertain the  degrees of
contraction by this pyrometer ?
  Mr*. B.   The  dimensions of  a  piece  of clay are
measured by the  bore of a graduated jconical tube in
which  it is placed ; the more it  is contracted by  the
heat, the lower  it descends into the narrow part  of the
tube.
  Let  us now proceed to examine  the other  properties ■
of free caloric.
  Free caloric always tends to an equilibrium ; that
is to say, when two  bodies are of different tempera-
tures,  the warmer gradually parts with its  heat to the
colder, till they are both brought to the same tempera- -
 ture. 
   Emily.  Is cold then nothing but  a negative quality,
 simply implying the absense of heat ?
   Mrs. B.   Not the total absence, but a diminution of
 heat ; for we know of no  body in which some caloric
 may not be discovered.
   Caroline.   But when I lay my hand on  this marble
 table,   I feel it positively cold, and cannot conceive that
 there is any caloric in it.
   Mrs. B.  The cold you experience consists in the
 loss of caloric that your hand sustains in an attempt to
 bring its temperature to an equilibrium with the mar-
 ble.   If you  lay a piece of ice upon  it,  you will  find
 that  the contrary effect will take  place ; the ice will
 be melted by the heat which it abstracts  from the  mar-
 ble.
   Caroline.   Is it not in this case the  air of the room,
 which being warmer than the marble, melts the ice ?
   Airs. B.   The air certainly acts on the surface ex-
 posed to it, but the table melts that part which is in con-
 tact with it.
   Caroline.   But why does caloric tend  to an equilibri-
 um ? It cannot be on the same principle as  other fluids,
 since it has no weight ?
   Mrs. B.   Very true, Caroline, that is an excellent
 remark.  The tendency of caloric to  an equilibrium is
 best explained by a supposed repulsive force of its par-
 ticles, which having  a constant tendency  to  fly  from
 each other, diffuse themselves wherever there is  a de-
 ficiency of that fluid, and thus  gradually restore  an
 equilibrium of  temperature.   But it is not only bodies
 which contain a greater proportion of caloric that part
 with it to those  that contain less :  in order to explain
 all the phenomena of heat and cold, we must suppose
 that a mutual exchange of caloric takes place between
 all bodies, of  whatever temperature, and that  the rays
of caloric, in passing from one body to another,  are sub-
 ject to all the laws of reflection and refraction, the same
 as those of light.   This theory was  first suggested  by
 Professor Prevost,  of Geneva, and is now, I  believe,
 pretty generally adopted.   Thus you may  suppose  all
 bodies whatever constantly radiating caloric : those that 
23'
are of the same temperature give out  and reciye equal'
quantities,  so that no change of temperature is produ-
ced in.them ; but when one'body contains more free ca-
loric than another, the exchange is always in favour  of
the colder body, until an equilibrium  is effected ; this
you found to be the case when the marble table cooled
your hand, and when it melted the ice.
  Caroline.  This surprises me extremely : I  thought
from what  you first said, that the hotter bodies  alone
emitted rays of caloric which were absorbed by the cold-
er,  for it seems unfair that a hot  body should  receive
any caloric from a cold one, even though it should  re-
turn a greater quantity.
  Mr*.  B.  It may at first appear  so,  but it is no more
extraordinary than that a candle should send forth  rays
of light  to the  sun, or  that a stone  in falling, should at-
tract the earth, as you know it does from the law of grav-
itation.
  Caroline.  Well, Mrs. B  since  you have all nature
to oppose  me, 1  believe  that  I  must  give   up the
point.   But I wish I could see these rays of caloric,  I
should then have  greater faith in them.
  Mr*.  B.  Will you give no crec'it  to  any sense but
that of sight ?  You  may feel the rays  of caloric which
you  receive from  any body of a  temperature higher
than your own : the loss of the caloric you part with
in return,  it is true is not perceptible ;  for as you  gain
more than you lose, instead of  suffering a  diminution,
you  are really  making  an acquisition of caloric.  It is
therefore  only  when  you are parting with it to a body
of a lower temperature, that you are sensible of the sen-
sation of cold, because you then  sustain an absolute loss
of caloric.
  Emily.   And in  this case we cannot be  sensible  of
the small quantity of heat  we receive in enchange from
the colder  body, because it serves  only to diminish the.
loss.
  Mr*.  B   Very well, indeed, Emily.   Professor Pic-
tet of Geneva,  has made some  very interesting experi-
ments to  prove that  caloric radiates  from ail bodies
whatever,  and that these rays may be reflected, ac- 
 
Plate II f
P<u/v  23
M' PIC JETS APPASAT(rs  FOB THE REFLECTION OF HEAT
JJmwn lp tiu.titHiw
/.,,,  .tveii far lur i-c.-jsc Coolu: IcC!Jl'"/r Havens. 
23
cording to  the  laws of optics, in the same manner as
light.  I wish I  could repeat these experiments before
you, but  the difficulty of procuring mirrors fit for the
purpose puts it  out of my power ;  you must therefore
be satisfied with an account of them, illustrated by this
diagram : (Plate III. Fig. 4.)—He placed an iron bul-
let, about two inches in  diameter, and  heated to a de-
gree not sufficient to render it luminous, in the focus of
a large metallic mirror.   The rays of heat which fell
on this mirror were reflected, agreeably to the property
of concave mirrors, in a parrallel direction, so as to fall
on a similar mirror, which was placed opposite the fust,
at a distance of about  twelve feet  : thence  they con-
verged to the focus of the second mirror, in which the
bulb of a thermometor  was placed, the consequence ot
which was, that  the thermometer immediately rose sev-
ral degrees.
   Emily.   But  would not the same effect have taken
place, if the rays of caloric  from the heated bullet had
fallen directly on the thermometer, wniiout the  assist-
ance of mirrors  ?
   Mr*. B.   The effect would  in that  case  have been
so  trifling, at the distance at which the bullet and the
thermometer were from each other, as would probably
have  rendered  it imperceptible.    The  mirrors, you
know, greatly increase the  effect, by collecting a large
quantity of rays  into a focus ; but their principal use was
to prove that the calorific emanation was reflected in the
same manner as light.
   Caroline.  And  the  result I think  was very  con-
clusive.
   Mr*.  B.  The experiment was afterwards repeated
with a wax  taper instead of the bullet* with a view  of

                      Plate III.

   A A. and B B  Concave mirrors fixed on stands.  C.   heated
bullet placed in the focus of the  mirror A, D,   The thermome-
ter with its bulb placed in the focui-of the mirror B.   1*34.
Rays of caloric radiating from the bullet and  failing  on the mir-
ror  , 5678   rhe same rays reflected from the mirror •* to
mirror B,  9 10 n 13. The same rays reflected by the mirror B
to the thermometer. 
24
separating the light from the caloric.   For this purpose
a transparent plate of glass was interposed between  the
mirrors; for light you know passes with great  lecility
through glass, whilst the transmission of caloric  is con-
siderably  impeded  by  it.  It was  found  however,
in this experiment, that some of the calorific rays pas-
sed through the glass together with the  light, as the
thermometer rose a few degrees ;  but as soon as the
glass was removed, and a free passage left to the calor-
ic, it rose immediately double the number of degrees.
   Emily.   This  experiment, as well as that of  Dr.
Hersehell's proves that light and heat may be separa-
ted ; for in the latter experiment the separation was
not perfect, any more than in that of Mr Pictet.
   Caroline.   I should like to repeat Mr. Pictet's exper-
iments,  with the difference of substituting a cold body
instead of a hot one, to see whether cold  would not be
reflected as well as heat.
   Mr*. B.   That experiment was proposed to Mr.
Pictet by an incredulous philosopher like  yourself, and
he immediately tried it by substituting a piece of ice  in
the place of the heated bullet.
   Caroline.  Well, Mrs B. and what was the result i
   Mr#.  B.  The thermometer fell considerably.
   Caroline.  And does not that prove that  cold is not
 merely a negative quality, implying  simply an inferior
 degree of heat ? The cold must be positive,  since it  is
 capable of reflection.
    Mr*.  B.  So it at first appeared ;  but upon a  little
 consideration it was found that it afforded only an addi-
 tional proof of the reflection of heat : this I shall endea-
 vour to explain to you.
    We suppose that all bodies whatever radiate caloric ;
 the thermometer used in these  experiments therefore
 emits calorific  rays in the same manner  as any other
 substance.  When its temperature  is in  equilibrium
 with that of the surrounding bodies, it receives as much
 caloric as it parts with, and no change of temperature
 is produced.   But when we introduce a body of a low-
  er temperature, such  as a  piece of ice, which  parts 
2S
 with less caloric than it receives, the  consequence is,
 that its temperature is raised, whilst  that of the  sur-
 rounding bodies is  proportionably lowered;  and  as,
 from the effect of the mirrors, a more  considerable ex-
 change of rays takes  place between the ice  and the
 thermometer, than between these and  any of the  sur-
 rounding bodies, the temperature of the thermometer
 must be more  lowered than that  of any other adjacent
 object.
   Caroline.   I do not perfectly  understand your expla-
 nation.
   Mr*. B.   This  experiment is exactly similar to that
 made with the  heated  bullet:  for, if we  consider the
 thermometer as the hot body (which  it certainly is in
 comparison to the ice),  you may then easily understand
 that it is by the loss of the calorific rays which the ther-
 mometer sends to the  ice,  and not by any cold rays
 received from it, that the fall  of  the mercury is occa-
 sioned ;  for  the ice, far from  emitting rays  of cold,
 tends forth rays of caloric, which diminish the loss  sus-
 tained by the thermometer.
   Let us say,  for instance, that the  radiation of the
 thermometer towards the ice  is  equal to 20,  and that
 of the ice towards the thermometer to 10 ; the exchange
 in favour of the ice is as 20 is to  10, or the thermome-
 ter absolutely loses 10, whilst the ice gains 10.
   Caroline.   But if the ice  actually sends rays of ca-
 loric to the thermometer, must not the latter  fall  still
 lower when the ice is removed ?
   Mr*.  B. No; for the air which will fill the space
that the ice occupied, being of the same  temperature
 as the thermometer,  will emit and receive an equal
 quantity of caloric, so that no alteration of  temperature
 will be produced.
   Caroline.   I  must confess that you  have explained
 this in so satisfactory a manner that I cannot help being
 convinced that cold has no real claim to the rank of a
 positive being,   bo now we  may  proceed  to the other
 modifications of caloric.
                        D 
■»'•
  Mrs. B.  We have  not  yet  concluded our observa-
tions on free caloric.  But  1 shall defer,  till our next
meeting, what  I  have further  to say  on this subject,
as I believe it  will afford  us ample conversation  for
another interview.
Contocttfation  in.
Continuation of the Subject.
                      Mrs. B.

   In our last conversation, we began to examine the
constant tendency of free caloric to restore an equilibri-
um of temperature.  This property, when once well
understood,  affords the  explanation of a great variety
of facts which appeared formerly unaccountable.  You
must observe, in the first place, that the effect of this
tendency is  gradually to  bring  all bodies that  are in
contact,  to  the same  temperature.   Thus,  the fire
which burns in the grate, communicates its heat from
ene object  to another, till every part of the room has
an equal proportion of it.
   Emily.   And yet this book is not so cold as the table
en which it lies, though both are  at an equal distance
from the fire, and actually in contact with each other,
so that, according to your theory, they should be exact-
ly of the same temperature ?
   Caroline.   And the hearth, which is much nearer the
fire than the carpet, is certainly the colder of the two.
   Mrs. B,   If you ascertain the temperature of these
several bodies by a thermometer (which is a much more
accurate test than  your feeling), you will find that it i»
 exactly the same. 
27
  Caroline.  But if they are of the same temperature,
why should the one feel colder than the other ?
  Mr*. B.   The hearth and  the table feel colder than
the carpet or the book, because the  latter are not such
good conductors of  heat as the former.   Caloric finds a
more  easy  passage  through marble and wood,  than
through leather and worsted ; the two former will there-
fore absorb heat  morejrapidly from your hand, and con-
sequently give it a stronger sensation of cold than the
two latter, although  they are all of them really of th«
same temperature.             •
  Caroline.  So, then, the  sensation  I feel on touching  '
a cold body, is in proportion  to the rapidity with which
my hand yields its  heat to that body ?
  Mrs. B.  Precisely ;  and, if you lay your hand suc-
cessively on every  object in the room, you will discover
which  are good, and which are bad conductors of heat,
by the different degrees of cold you feel. But in order
to ascertain  this  point, it is necessary that the  several
substances should  be of the  same temperature, which
will not  be. the case with  those that are very near the
fire, or those  that  are exposed to a  current of cold air
from a window or  door.
  Emily.  But what is the reason that some bodies are
better  conductors of heat than others ?
  Mrs. B  That is a point not well ascertained.   It is
conjectured that a certain union or adherence takes place
between the caloric and the particles of the body through
which  it passes.   If  this adherence be strong,  the body
detains the  heat, and parts with it slowly and reluctant-
ly :  if slight, it propagates it freely and rapidly.   The
conducting power  of  a body is  therefore, inversely,  as
its tendency to unite with caloric.
  Emily.   That is to say, that the best conductors arc
those that have the least affinity for caloric.
  Mrs. B.  Yes; but I object to the term affinity in this
case, because  as that word is used to express a chem-
ical attraction  (which can be  destroyed only by decom-
position), it cannot be applicable to the   slight and tran-
«ient  union that  takes place between free  caloric and
the bodies through which it passes : an  union which is 
28
 so weak, that it constantly yields to the tendency which
 caloric has to an equilibrium.  Now you clearly under-
 stand, that the passage  of caloric, through bodies that
 are gocd conductors,  is much more rapid than through
 those that are bad conductors, and that the former both
 give and receive it more quickly,  and therefore,  in a
 given  time,  more abundantly,  than bad conductors,
 which makes them feel either hotter or colder, though
 they may be in fact, of the same temperature.
   Caroline.   Yes, I understand it now : the table,  and
 the book lying upon«it,  being really of the same tem-
 perature, would each receive in the same space of time,
 the same quantity of heat from my hand, were their
 conducting powers equal; but as the  table is the best
 conductor of the two,  it  will  absorb the heat  from my
 hand more rapidly, and consequently produce a stronger
 sensation of cold than the book.
   Airs. B.   Very well, my dear ;  and observe, like-
 wise,  that  if you  were  to heat the table and  the book
 an equal  number of degrees above  the temperature
 of your body, the  table which before felt the colder,
 would now feel the hotter of the two  ; for as in  the first
 case it took the heat  more rapidly from your  hand, so
 it will  now impart heat most rapidly to it.  Thus  the
 marble table, which seems to us colder than the mahog-
 any one, will prove the hotter of the two to the ice ; for
 if it takes heat more rapidly from our hands, which are
 warmer,  it will give out heat more rapidly to the ice,
 which is colder.  Do you understand the reason of these
 apparently opposite effects ?
  Emily.  Perfectly.   A body that is a good conductor
 of caloric, affords it a free passage  ;  so that it  pene-
 trates through  that  body more rapidly than through
 one which is  a bad conductor; and,  consequently, if
 it is coi k r than your hand, you lose more caloric, and
 if it is hotter, you gain more  than with a bad conductor
 of the same temperature.
  Mrs. B.  But you must observe that this is the case
 only when the conductors are either hotter or colder
than your hand ; for, if you heat different conductors
 to  the temperature  of  your body,  they  will all feel
equally warm, since the exchange of radiation between 
2f
 •odies of the  same temperature is equal.  Now, cat
you tell me why flannel clothing, which is a very bad
conductor of heat, prevents our feeling cold ?
  Caroline.  It prevents the cold from penetrating.
  Mrs. B.  But you forget that cold is only a negative
quality.
  Caroline.  True; it only  prevents the heat of our
bodies from escaping so rapidly as it would  otherwise
 do.
  Mrs. B.  Now  you have  explained it right: th«
flannel rather  keeps in the heat,  than keeps out the
cold.   Were the  atmosphere of a  higher temperature
than our bodies, it would be equally efficacious in pre-
serving them of an uniform temperature, as it would
prevent the free access  of the  external heat, by the
difficulty with  which it conducts it.
  Emily.  This, I think, is very clear.   Heat, whether
external or  internal,  cannot easily penetrate  flannel %
therefore  in cold weather it keeps us warm;  and if
the vieather was hotter than our bodi«s, it would keep
 us cool.
  Airs. B.  For the  same reason,  glass  windows,
 which are very bad  conductors of heat, keep a room
 warm in winter and cool in summer, provided the sun
 does not  shine upon them.  The most dense bodies
 are, generally speaking, the best conductors of heat.
 At the temperature of the atmosphere a piece of metal
 will feel  much colder than a piece of wood, and the
 latter than a piece of woollen cloth :  this again will feel
 colder than flannel;  and down, which is one of tlie
 lightest, is  at the same time, one of the warmest
 bodies.
   Caroline.   This is, I suppose,  the  reason that the
 plumage  of birds preserves them so  effectually from
 the iufluence of cold in winter ?
   Mrs. B. • Yes;  but though feathers in general are
 an  excellent preservative against  cold, down is a kind
 of plumage peculiar to aquatic birds, and covers their
 chest,  which is the part exposed  to the  water;  for
 though the surface of the water is not of a lower tem-
 perature  than  the  atmosphere, yet, as  it is a  bette."
                        D 2 
30
conductor of heat, it feels much colder, consequently
the chest of the bird  requires a warmer covering than
any other part of its body.
   Most Animal  substances,  especially  those  which
Providence has assigned as a covering for animals, such
as fur, wool, hair, skin,  Sec.   are  bad conductors of
heat, and are, an  that account  such excellent  preserva-
tives against the inclemency of winter, that our warm-
est apparel is made of these materials.
   In fluids of different densities, the power of conduct-
ing  heat, varies no  less remarkably ; if you dip your
hand into this vessel  full of mercury, you will scarcely
conceive that its temperature is not lower than that oi
the atmosphere.
   Caroline.  Indeed  I can  hardly believe it, it feels so
extremely cold.—But we  may easily  ascertain its true
temperature  by the thermometer.—It  is really  not
colder than  the  air  ;—the apparent difference then is
produced merely by the difference  of the conducting
power in mercury and in air ?
  Mrs. B.  Yes ; hence you may judge how little  the
sense of feeling is to  be relied on as a test of the tem-
perature of bodies, and how necessary a thermometer
is for that purpose.
  But I must not forget to tell  you,  that it  has been
doubted whether fluids have  the  power of conducting
caloric  in  the same manner as  solid bodies.   Count
Rum ford a very few years since  attempted  to prove,
by a  variety of experiments, that  fluids, when at rest,
were not at all endowed with this property.
  Caroline.  How is that possible, since they  are capa-
ble of imparting  cold or heat to us ; for if they did not
conduct heat, they would neither take it from,  nor give
it to us ?
  Airs. B.  Count Rumford did not mean to say that
fluids do not communicate their heat to solid bodies  ;
but only that heat does not  pervade fluids, that  is to say,
is not transmitted from one particle of a fluip to another,
in the same manner as in solid bodies.
  Emily.  But when you  heat a  vessel of water over
the fire, if the particles of water  do not communicate 
51
heat  tt  each other, how does  the water become hoi
throughout.
   Mr*. B.   By constant agitation.  Water as you have
seen, expands by  heat in the  same  manner  as  solid
bodies; the heated particles of water  therefore at the
b)t;o>n of the vessel, become specifically lighter than
the  rest of the liquid, and consequently ascend to the
surface where, parting with some of their heat to the
colder atmosphere, they are condensed, and give way
to a  fresh succession of heated particles  ascending
from the bottom,  which having thrown  off* their heat
at the surface, are  in their turn displaced.  Thus every
particle is successively heated av the bottom, and  cool-
ed at the surface of the liquid ; but as the fire commu-
nicates heat more  rapidly han the atmosphere cools the
succession of surface, the whole of the liquid in time be-
comes heated.
   Caroline.   This  accounts most ingeniously for the
propagation of heat upwards.  But suppose you  were
to heat the upper surface of a liquid, the particles being
specifically  lighter  than  those below, could not des-
cend : how therefore would the heat be communicated
downwards ?
   Msr. B.   Count Rum ford assures  us, that  if there
was no agitation to force the heated surface dowdward,
the heat would not descend.  In proof of this, he suc-
ceeded in  making  the upper surface of a  vessel of wa-
ter boil and evaporate,  whilst a cake of ice remained
frozen at the  bottom.
   Caroline. That is very extraordinary indeed !
   Mrs. B.   It appears so, because we  are  not accus-
tomed to  heat  liquors by  their  upper surface,  but you
will understand this theory better if I shew you the in-
ternal motion that  takes place in liquids when they ex-
perience a change of  temperature.  The motion of the
liquid itself is indeed invisible from the extreme minute-
ness of its particles : but if you  mix with it any colour-
ed dust, or powder,* of nearly the same specific gravity
as the liquid, you may judge of the internal motion  of
the latter by that of the coloured dust  it  contains.   Do
you see the small pieces of amber moving about in the
liquid contained in  this phial. 
:;♦
   Caroline.  Yes, perfectly.
   Mrs. B.   We shall now immerse the phial in a glass
 •f hot water, and the motion of the liquid will be shown,
 by that which it communicates to the amber.
   Emily.  I see two currents, the one  rising along the
 sides of the phial, the other descending into the centre j
 but  I do not understand the reason of this.
   Mrs. B.   The hot water communicates its caloric,
 through the medium of the phial, to the particles of the
 fluid nearest to the glass ; these dilate and ascend late-
 rally to the  surface,  where,  in parting with their heat,
 they are  condensed, and in descending, form the cen-
 tral  current.
   Caroline.  This is indeed a very clear and satisfactory
 experiment ; but how much slower the currents now
 move than they did at first ?
   Airs. B.  It is because the circulation of particles hat
 nearly produced an equilibrium of temperature between
 the liquid in the glass and. that in the phial.
   Caroline.   But these  communicate laterally,  and  t
 thought  that heat in liquids  could  be propagated only
 upwards ?
   Mrs. B.  You do not take notice that the heat  is im-
 parted from one  liquid to the other, through the med-
 ium of the phial itself, the external surface of which re-
 ceivesj the heat from the water in the glass,  whilst its
 internal surface transmits it to the liquid it contains.-—
 Now take the phial  out of the hot water, and observe
 the effects of its cooling.
   Emily.   The  currents are  reversed : the external
current now descends, and the internal one  rises.   I
 guess the reason of this  change :—the phial  being in
contact  with cold air instead of hot water, the external
particles are cooled instead of being heated ; they there-
fore  descend and force up the  central particles, which
 being warmer are consequently lighter.
   Mrs. B.  It is just so.   Count Rumford infers from
hence, that no alteration of temperature can take  place
in a fluid,  without an internal  motion  of its particles,
and as this motion is produced  only  by the comparative
kvity of the  heated particles, heat  cannot be propagatedi
downwards. 
35
   This theory explains the reason of the cold  that  is
 found to prevail at the bottom of the lakes in Switzer-
 land, which are fed  by rivers issuing from the snowy
 Alps.   The  water of these rivers being colder and
 therefore more dense than that of the lakes, subsides  to
 the bottom, where it connot be affected by the warmer
 temperature  of the surface ; the motion of the waves
 may communicate this temperature to some little depth,
 but it can descend no farther than the agitation extends.
   Emily.  But when the atmosphere is colder than the
 lake, the colder surface of the water will descend for
 tlie very reason that the warmer will not ?
   Mrs. B.   Certainly; and it is on this  account  that
 neither a lake nor any body of water whatever,  can be
 frozen until every particle of the water has risen to the
 surface to give off its caloric to the colder atmosphere ;
 therefore the deeper a body of water is, the longer will
 be the time it requires to be frozen.
   Emily.  But if the temperature of the whole body of
 water is brought clown to the freezing point, why is only
 the surface frozen ?
   Mrs. B.   The temperature of the whole body is low-
 ered, but not to the freezing point.   The dimunition of
 heat as you know, produces a contraction in the bulk
 of fluids, as well as of solids.  This effect however does
 not take place in  water below the temperature of forty
 degrees, which is eight  degrees  above  the freezing
 point.   At that temperature,  therefore,  the  internal
 motion, occasioned by the increased specific gravity
 of the condensed particles,  ceases ; for when the water
 at the surface no longer condences, it will no longer de-
 scend, and leave a fresh surface  exposed to the atmos-
 phere : this surface alone,  therefore, will be further
 exposed to its severity, and will soon be brought down
 to the freezing point, when it becomes ice, which being
 a bad conductor of heat, preserves the water beneath  a
long time from being affixed by the external cold.
  Caroline.   And  the sea  does not freeze, I  suppose,
because its depth is so great, that a frost never lasts long
enough to bring down the temperature of such a great
b.ody of water to forty degrees ? 
34
   Mrs. B.   No, that is not the case; for salt water is
 m exception to this law, as it condenses even many de-
 grees below the freezing point.  When  the caloric of
 fresh water therefore is imprisoned by the ice, the ocean
 •till continues  throwing  off heat into the atmosphere,
 which is a most signal dispensation of Providence to mo-
 derate the intensity of the cold in winter.
   Emily.   I admire this theory extremely ;* but allow
 me to ask you one  more  question  relative to it.  You
 •aid that when water was heated over the fire, the par-
 ticles at the bottom of the vessel ascended as soon  as
 heated, in consequence of their specific levity  ;  why
 does not the same effect continue when the water boils,
 and is converted into steam ?  and why  does the  steam,
 rise from the surface instead of the bottom of the liquid?
   Airs. B.  The steam or vapour does ascend from the
bottom, though it seems to arise from the surface of the
liquid. We  shall boil some water in this Florence flask j.
 (Plate IV. Fig, V.) you will then see through the glass,
 that the vapour rises in bubbles from the bottom.  We
 •hall make  it  boil by means of a lamp, whiclvis more
 convenient for this purpose than the chimney fire.-——
   Emily.  I see some small bubbles ascend, and a great
many appear all over the inside  of the flask ; does the
 water begin to boil already ?
   Mrs. B.  No ;  what you now see are bubbles of air
which were  either enclosed in the water, or attached to
 the inner surface of the  flask, and which, being rarefied
 by the heat, ascend in the water.

                     PLATE IV.
  Fig. 5. Boiling water in a flask over a patent lamp.
  Fig. 6. Ether evaporated and water frozen in the air pump.
A. A phial of ether.   B, Glafs  vessel containing water.   C.  C.
Thermometers, one in the ether, the other in the water.

  * This theory of the non-conducting power of fluids, notwith-
 standing all its plaufibility, has been found,  by a variety of fubse-
 qucnt experiments, to have been  carried by Count Rumford, ra-
 ther too far; and it is  now  generally admitted that fluids are not
 entirely deftitute of conductibility, though they  propagate  heat
 chiefly by motion, in the manner juft explained, and possess the
 conducting power but in a very imperfect degree. 
f ft.
5   1
=SH
$ 
 
15
  Emily  But the heat which rarefies the air enclosed
•n the water, must rarefy the water at the same time ;
therefore, if it  could  remain  stationary in  the water
when both were cold, I do not understand why it should
not when both are equally heated ?
  Mrs. B.  Air  being much less dense than water, it
more easily rarefied ;  the former therefore expands to
a greater extent,  whilst the latter continues to  occupy
nearly  the same space; for water dilates comparatively
but very little without changing its state and becoming
vapour.  Now that the water in the flask begins to boil,
observe what large bubbles rise from the bottom of it.
  Emily.   I see  them perfectly ; but  I wonder  that
they have sufficient power to force themselves  through
the water.
   Caroline.  They must rise, you know, from their spe-
cific levity.
   Mrs.  B.  You are right, Caroline; but vapour has
not in  all liquids (when brought to.the degree of vapor-
ization) the power of overcoming the  pressure of the
less heated surface ;  therefore no vapour will ascend
from them till the degree of heat which is necessary to
form it has reached  the surface ; that is to say till the
whole of the liquid  is brought to the  boiling point.
 This is the case with all metals, mercury alone excep-
 ted.
    Emily.   I have observed that steam, immediately is-
 suing from the spout of  a tea-kettle, is less visible than
 at a further distance from it; yet it must be more dense
 when it first evaporates than when it begins to diffuse it-
 self in the air.
    Mrs. B.  Your objection is a very natural one ; and
 in order to answer it, it will be necessary for me  to en-
 ter into some explanation respecting the nature of solu-
 tion.  Solution takes place whenever  a body is melted
 in a fluid.   In  this operation the body is reduced to such
 a  minute  state  of division  by the  fluid, as to become
 invisible in it,  and to  partake of its fluidity : but this
  happens without any decomposition, the body being on- 
36
 ly divided into its integrant particles by  the fluid  in
 which it is melted.
   Caroline.  Is it then a mode of destroying  the a1 trac-
 tion of aggregation ?
   Airs.  B.  Undoubtedly—The two principal solvent
 fluids are water and caloric.  You may  have observed
 that if you melt salt in  water, it totally disappears, and
 the water remains clear and transparent as before  ; yet
 though the union of these two bodies appears so per-
 fect, it is not produced  by any chemical combination  ;
 both the salt and the water remain unchanged ; and if
 you were to separate  them by evaporating  the latter,
 you would find the salt in tne same state as before.
   Emily.  I suppose that water is a solvent for solid boi
 dies, and caloric for liquids ?
   Mrs. B.  Liquids of course can only be  converted
 into vapour by caloric.  But the solvent power of this
 agent is not at  all  confined to that class of bodies ;  a
 great variety of solid substunces are dissolved  by heat:
 thus metals, which are insoluble in water,  can be  dis-
 solved  by intense heat, being first fused or  converted
 into a liquid, and then rarefied  into an invisible vapour.
 Many other bodies, such as salts,  gums, kc. yield to
 either of these solvents.
   Caroline.  And that, no doubt, is the reason why hot
 ?,ater will melt them so much better than cold water ?
   Airs.  B.  It is so.  Caloric may indeed be consider-
 ed as having, in every instance, some share in the so-
 lution of a body by water, since all water, however low
its temperature may be, always contains more or less
 caloric.
   Emily.   Then  perhaps  water owes its solvent power
merely to the caloric it contains ?
   Mrs.  B.  That probably would be carrying the spec-
ulation tro far; I should rather think that water  and
caloric unite their efforts to dissolve a body, and that the
difficulty or facility  ol effecting this, depends  both on
the degree of attraction of aggregation to  be  over-
 come and  on the arrangement of the  panicles which
 are more or less disposed to be divided and penetrated
 by the solvent. 
37
   Emily. But have not all liquids the same solvent pow-
' er as water ?
   Mr*.  B.   The solvent power of other liquids  varies
 accord.ng to  their nature,  and that of the  substance
 submitted to their action.   Most  of these solvents, in-
 deed differ essentially from water, as  they  do  not
 merely separate  the intregrant particles of the bodies,
 which they dissolve, but attack their constituent princi-
 ples by  the power of chemical attraction,  thus  produ-
 cing a true  decomposition   These  more  complicated
 operations,  which may be  distinguished by  the name
 of chemical solutions, we must consider  in another place,
 and confine our attention at present to  the  simple solu-
 tions by water and caloric.
   Caroline.  But there are a variety of substances which,
 when dissolved in water, make it thick and muddy,  and
 destroy its transparency.
   Airs.  B.  In this case it is not a solution, but  simply
 a mixture.   I shall show you the difference between  a
 solution  and a mixture, by putting some common  salt
 into one glass of water, and some  powder of chalk into
 : nother ; both these substances are white, but their ef-
 fect on the water will be very different.
   Caroline.  Very different indeed !  the  salt  entirely
 disappears and leaves the water transparent, whilst  the
 chalk changes it into an opake liquid like  milk.
   Emily.  And would lumps of chalk  and  salt pro
 similar effects on water ?                         c]uoe
   Mr*. B.  Yes, but not so rapidly ; salt is  indeed soon
melted though in  a lump, but chalk which does  not
mix so   readily  with water,  would  require a much
 greater length of time ; I therefore preferred showing
 you the  experiment with both substances reduced to
 powder, which does not in any  respect alter  their  na-
 ture, but fecilitates the operation merely  by presenting
a greater quantity of surface to the water.
   I must not forget to mention  a  very  curious circum-
stance  respecting solutions, which is, that a fluid is  not
increased in bulk  by holding a body in solution.
   Caroline.  That seems impossible  ; for two bodies
cannot exist together in the same  space.
E 
38
   Mr*.  B.   That  is true,  my  dear ; but two bodies
 may,  by  condension,  occupy  the same space which
 one of them  filled  before.  It is supposed  that there
 are pores or  interstices,  in which the  salt lodges, be-
 tween the  minute  particles of  the water.  And these
 6paccs are so small that the body  to be dissolved must
 be divided into very minute particles in order  to be con-
 tained in them ; and it is this state of very great division
 that renders them invisible.
   Caroline.   I can  try this experiment immediately.
 —It is exactly so—the water in this glass, which I fill-
 ed to the brim,  is  melting a considerable quantity of
 salt without overflowing.   I shall try  to add  a little
more.—But now, you see, Mrs.  B.  the water runs
 over.
  Mrs.  B.  Yes; but observe  that the last quantity of
salt you put in remains solid at the bottom, and displaces
the water ;  for it has already melted all the salt it is
capable of holding in solution.  This is called  the point
of saturation ; and the water is now said to be saturated
with salt.
   Emily.  This happens, I suppose, when  the inter-
stices between the particles  of the liquid are completely
filled ?
   Mr*.  B.  Probably.  But these remarks,  you must
observe,  do not apply to a  mixture ; for any  substance
which does not dissolve, increases the bulk  of  the  li-
quid.
   Emily.  I  think  I now understand the solution of a
solid body by  water perfectly :  but I have not so clear
an idea of the  solution of a liquid by caloric.
   Mr*.  B.   It is precisely of the same nature ; but
as caloric is an invisible fluid,  its action as a  solvent is
not so obvious as that of water.  Caloric dissolves water,
and converts it into vapour by the  same process  as wa-
ter dissolves salt;  that is  to say, the particles of water
aie so minutely divided by the caloric as to become in-
visible   Tims you are now  enabled  to  understand
why the vapour of boiling water, when it  first  issues
 from the spout of a kettle, is invisible ;  it \z so. because
 it is then completely dissolved by  caloric.  But the  air 
w
 with which it comes in contact, being much colder than
 the vapour, the latter yields to it a quantity of its ca-
 loric.   The particles  of vapour being thus in a great
 measure  deprived of their  solvent, gradually collect
 and become visible in the form of steam, which is water
 in a state of imperfect solution ; and if you were fur-
 ther to deprive it of its caloric, it would return to its o-
 riginal liquid state.
   Caroline.   That I understand very well; but in what
 state is the steam, when it again becomes invisible by
 being diffused in the air ?
   Mrs. B.   It is carried off* and again dissolved by the
 air.
   Emily.  The air then has a solvent power, like water
 and caloric ?
   Mrs. B.   Its solvent power proceeds chiefly, if not
 entirely, from  the caloric  contained in it, the  atmos-
 phere acting only  as a vehicle.  Sometimes the watery
 vapour diffused in the atmosphere  is but imperfectly
 dissolved, as is the case in the formation  of clouds and
 fogs ;  but  if it gets  into  a region of air sufficiently
 warm, it becomes  perfectly invisible.
   Einily.   Does the air ever dissolve water, without its
 being previously converted into vapour by boiling.
   Mrs. B.   Yes,  it does.   Water when heated to the
 boiling point, can no longer exist in the form of water,
 and must necessarily be converted  into vapour, what-
 ever may be the state and temperature of  the surround-
 ing medium ; but  the air  (by means probably of  the
 caloric  it contains)  can  take up a  certain portion  of
 water  at any  temperature, and hold it in a state of so-
 lution.  Thus the  atmosphere is continually carrying off
 moisture from the earth, until it is saturated with it.
   The  tendency of free  caloric to an equilibrium, to-
 gether with its  solvent power, are  likewise connected
with the  phenomena of  rain, of dew, &c.   When a
cloud of a certain temperature happens to pass through
a colder region of  the atmosphere,  it parts with a por-
tion of its heat to the surrounding air ; the quantity  of
caloric therefore,  which served to keep the cloud in a
state of vapour, being diminished, the watery particles 
40
approach  each other, and form themselves into drops
of water,  which being heavier than the atmosphere,
descend to the earth.   There are also  other circum-
stances, and particularly  the variation  in  the  weight ot
the atmosphere, which may contribute to the formation
of rain.   This  however, is  an intricate subject,  into
which we cannot more fully enter at present.
  Emily.   But in what manner do you account for the
formation of dew ?
  Airs.  B. During the heat of the  day the air is  able
to retain a greater quantity of vapour in  a  sta~e of so-
lution, than either  in the morning or  evening.    As
soon, therefore, as a diminution of heat takes place to-
wards  sun-set, a  quantity  of vapour condenses, and
falls to  the ground  in form of dew.   The  morning
dew, on the contrary, rises from  the earth ;  but  when
the sun  has emitted a sufficient quantity of caloric  to
dissolve it,  it  becomes  invisible in the atmosphere.
When once the dew, or any  liquid  whatever,  is  per-
fectly dissolved by the air, it occasions no humidity ; it
is only when in a state of imperfect solution, and  float- .
ing in the form of watery vapour in the atmosphere, that
it produces dampness.
  Caroline.  I have often observed, Mrs.  B. that when
I walk out in frosty weather, with a veil over my  face,
my breath freezes upon it.   Pray what is the reason  of
that ?
  Mrs. B  It is because the cold air immediately seizes
on the caloric of your breath, and  reduces  it, by  rob-
bing it of its  solvent, to  a  denser fluid, which is the
watery vapour that settles on your  veil, and there it
continues parting with its caloric till it is brought down
to the temperature of the atmosphere, and  assumes the
form of ice.
  You may, perhaps, have observed that the breath of
animals, or rather the moisture contained in it, is  visi-
ble  during a frost, but not in warm weather.*  In the
latter case, the air  is capable of retaining  it in a  state

  * Unless in very damp weather, when the atmosphere is al-
ready saturated with moisture- 
4!
of solution,  whilst in the former, the cold condenses it
into visible vapour; and for the same reason, the steam
arising from water that is warmer than the atmosphere,
is visible.  Have you never taken notice of the vapour
rising from your hands after having dipped them into
warm water ?
  Caroline.  Often, especially in frosty weather ?
  Mr*.  B.   When a bottle of wine is taken fresh from
the cellar (in summer particularly), it will soon be cov-
ered with dew ; and even the glasses in which the wine
is poured will be moistened with a similar vapour. Let
me hear if you can account for this ?
  Emily. The bottle is colder than the surrounding air,
therefore it must absorb caloric  from it ; the  moisture
which that air held in solution must become  visible, and
form the dew which is deposited on the bottle.
   Mr*.  B.  Very well, Emily. Now, Caroline, can
you tell me why, in  a warm room, or  close  carriage,
the contrary effect takes place ; that is to say, that the
inside of the windows are covered with vapour  ?
  Caroline.   I  have  heard that it proceeds  from the
breath of those within the carriage : and I suppose it is
occasioned by the windows  which,  being colder than
the breath, deprive it of part of  its caloric, and by this
means convert it into a watery vapour.
  Mrs.  B.   Very  well, my  dear  :  I am  extremely
glad to find that you both understand the subject so well.
  We have already observed that pressure  is  an obsta-
cle  to evaporation :  there  are liquids that  contain so
gveat a quantity of caloric, and whose particles conse-
quently adhere so  slightly together, that they may be
converted into vapour without any elevation of tempera-
ture, merely by taking  off the weight of the atmos-
phere.   In such liquids,  you perceive, it is the  pres-
sure of the atmosphere alone that connects  their parti-
cles and keeps them in a liquid state.
  Caroline.   I do not well understand why the  particles
of such fluids should  be  disunited and converted  into
vapour,  without any addition of heat, in spite of the
attraction of cohesion ?
E  2 
42
   Mrs. B.   It is because the quantity of calouc which
 enters into the formation of these fluids  is sufficient to
 overcome  their  attraction  of cohesion.  Ether is of
 this description ;  it will boil and be converted into va-
 pour, without any application of heat,  if the pressure of
 the atmosphere be taken off.
   Emily.   I thought that ether would evaporate with-
 out either taking away the pressure of the atmosphere,
 or applying  heat, and  that it was for  that reason so
 necessary to keep it carefully corked up.
   Mr*. B.   That is true ; but in this case it  will evap-
 orate but  very slowly.  I am going to show you  how
 suddenly the ether in this phial will be  converted into
vapour, by means of the air pump.—Observe with what
rapidity the  bubbles  ascend, as I take off the pressure
of the atmosphere.
   Caroline.   It positively boils : how  singular to see a
liquid boil without heat!
   Airs. B.   Now I shall place the  phial of ether in
this glass, which  it nearly fits, so  as to leave only a
small space,  which I  fill with water : and in this state
I put it again under the receiver.   (Plate IV. Fig. q.)"
—You will observe, as  I exhaust the  air from it,  that
whilst the ether boils, the water freezes.
  Caroline.    It is indeed wonderful to see water freeze
by means of a boiling fluid !
   Emily.   There is another circumstance which I  am
unable to account for.   How can the ether change to a
stats of vapour,  without an  addition of caloric  ; for  it
must contain more caloric in a state of vapour, than in
a state of liquidity ;  and  though you say  that it is the

  * Two pieces of thin glafs tubes, fealed at one  end, might
answer this purpose better- The experiment however,  as here
described, is difficult, and  requires a very nice apparatus.  But
if instead of phials or tubes, two watch-glasses be uftd, water
may be frozen almost instantly in the same manner.  The  two
glasses are  placed over one another, with a few drops of water
interposed between them,  and the uppermost glass is filled with
ether. After working the pump for a minute or two, the glasses
are found to adhere flrongly together, and a  thin layer  of ic e  is
teen between them. 
'■                   43
 ; ressure of the atmosphere  which condenses it into a
 liquid, it must be, I suppose, by forcing out part of the
 caloric that belongs to it when in an aeriform state ?
   Mr*.  B.  You are right   Ether,  in a  liquid state,
 does not contain a sufficient quantity of caloric to become
 vapour.   I have therefore, two difficulties  to  explain ;
 first, from whence the ether obtains the caloric neces-
 sary to convert it into vapour when it is relieved  from
 the  pressure of the  atmosphere;  and, secondly, what
 is the reason that the water, in which the bottle of ether
 stands, is frozen ?
 ^ Caroline.   Now I think I can ansv/er both these ques-
 tions.   The ether obtains the addition of caloric requir-
 ed from the water in the glass ;  and the loss of caloric,
 which the latter sustains,  is the occasion of its freezing.
   Mrs B.   You are perfectly right ; and  if  you look
 at the thermometer  which I have placed in the water,
 whilst I am working the pump, you will see that every
 time bubbles of vapour are produced,  the mercury de-
 scends ;  which proves that the heat of the water dimin-.
 ishes in equal proportion as the ether boils.
   Emily.   This I understand now very well; but if the
 water freezes in  consequence of yielding its caloric to
 the ether, the equilibrium of heat must in this case, be
 totally destroyed.  Yet you have told us, that bodies of
 a different temperature aie always communicating their
 heat to each other, till it becomes every where  equal ;
 and  besides, I do not see why the water, though origi-
 nally of the same temperature as the ether,  gives out
 caloric to it, till the water is frozen and the ether made
 to boil.
   Mr*. B.   I suspected that you would make these ob-
 jections ;  and in order to remove them, I enclosed two
 thermometers in the air-pump ;  one of which stands in
 the glass of water, the other in the phial of ether; and
 you  may see that the equilibrium of temperature is  not
destroyed ; for as the thermometer descends in the wa-
ter, that in the ether sinks in the same manner ; so that
both thermometers  indicate the  same temperature,
though one of them is in a boiling, the other in a freez-
ing liquid. 
44
   Emily.  The ether then becomes  colder as it boils i
 This is so contrary to common experience, that I con-
 fess it astonishes me exceedingly.
   Caroline.  It is indeed, a most extraordinary circum-
 stance.   But pray how do you account for it ?
   Mrs.  B.   I  cannot satisfy your curiosity at  present ;
 for before we can attempt to explain this apparent par-
 adox, we must become acquainted with the subject  of
 latent heat ;  and that I think we must defer till our
 next interview.
   Caroline.  I believe Mrs. B. that you are glad to put
 off the explanation ;  for it must be a  very difficult point
 to account for.
   Mr*.  B.   I hope however, that I shall do it to  your
 complete satisfaction.
   Emily.  But before  we  part give  me leave to  ask
 you one question.  Would not water, as well  as etheri
 boil with  less heat, if the  pressure  of the atmosphere
 were taken off ?
   Mr*. B.   Undoubtedly.  You must always recollect
 that there are two forces to overcome, in order to make
 a liquid boil, or evaporate ; the  attraction of  aggrega-
 tion, and ihe weight of  the atmosphere.  On the sum-
 mit of a high mountain (as  Mr. De Sausure ascertained
 on  Mount Blanc) less heat is required to make water
 boil  than in the plain,  where the weight of the atmos-
 phere is greater.  But I can show you a very pretty ex-
 periment, which proves the effect of the pressure of the
 atmosphere in this respect.
   Observe, that this Florence flask is  about half full of
 water, and the upper half of invisible vapour, the water
 being in the act of boiling.—I take it from the lamp and
 cork  it  carefully—the  water  you   see, immediately
 ceases boiling.—I shall now wrap a cold wet cloth round
 the upper part of the flask*-----
  Caroline.   But look, Mrs. B. the water begins to boil

   • Or the whole  flask may be dipped in a basin of cold water.
In order to (how how much  the water cools whilst it is boiling, a
thermometer, graduated on the tube itself, may be introduced in-
to the bottle through the cork. 
 again,  although the  wet cloth  must rob it  more and
 more of its caloric ! What can be the reason of that ?
   Mr*. B.   Let us examine its  temperature.   You see
 the thermometer immersed in it remains stationary  at
 180 degrees, which is about 30 degrees below the boil-
 ing point.   When I took the flask from the lamp, I ob-
 served to you that the upper part^of it was filled with
 vapour ; this being compelled to yield its caloric to the
 wet cloth, was again converted into water—What then
 filled the  upper part of the flask ?
   Emily.   Nothing ;  for it was.too well corked for the
 air to gain admittance, and therefore the upper  part of
 the flask must be a vacuum.
   Mr*. B.   If the upper part of the flask be a vacuum,
 the water below no longer sustains the pressure of the
 atmosphere, and will  boil at a much lower temperature.,
 Thus, you  see,  though it  has lost many degrees  of
 heat, it began boiling again the instant the vacuum was
 formed above it.  The boiling has now ceased ;  if it had
 been  ether, instead of water, it would  have  continued
 boiling  much longer ; but water  being a more dense
 fluid, requires a more considerable quantity of caloric to
 make it evaporate, even when the pressure of the at-.
 mosphere is removed.'
   Emily.   But if the pressure of the atmosphere keeps
 the particles of ether  together,  why does it  evaporate
 when exposed to the  air ?  Nay, does not even water,
 the particles of which adhere so strongly together, slow-
 ly evaporate in the atmosphere ?
   Mr*.  I',.  I have already  told  you that air has the
power of keeping a certain quantity of vapour in solu- .
tion at any known temperature; and  being constantly
in a state of  motion, and incessantly renewing itself on
the surface  of the liquid, it  skims off, and  gradually
dissolves  new r uantities of vapour.  Water also has
the power of absorbing a certain  quantity of air, so that
their action on each other is reciprocal ; the air thus
enclosed in water is that which  you see evaporate in
bubbles  when water is heated previous to its boiling.
   Emily.  What proportion  of vapour  can  air  contain .
in a state of  solution. 
46
   Mr*. B.  I do not know whether it has been exactly
ascertained by experiment;  but at any rate this  pro-
portion must varv,  both  according to the temperature
and the weight of the atmosphere; for the lower the
•temperature,  and the greater the pressure, the small-
er must be the proportion of vapour that air can  con-
tain in a state of solution.  But we have dwelt so  long
on the subject of free caloric, that we must reserve the
other modifications  of that fluid to our next meeting,
when we shall endeavour to proceed more rapidly.
           Contoergation iv.

On Specific Heat, Latent Heat, and Chemical Heat.
                     Mrs.  B.
  We are now to examine the three other modifica-
tions of caloric.
  Caroline.  I am very curious to know of what nature
they can be ;  for I have no notion of any kind  of heat
that is not perceptible to the senses.
  Mr*.  B.  In order to enable you to understand them
it will be necessary to enter into some previous expla-
nations.
  It has been  discovered by  modern  chemists,  that
bodies of a different nature, heated to the same tempe-
rature, do not contain the same quantity of caloric.
  Caroline.  How could that be ascertained ?
  Mr*.  B.  It was found that,  in  order to raise the
temperature of different bodies the same number of de-
grees, different quantities of caloric were required for
each of them.  If, for instance, you place a pound  of 
47
had, a pound of  chalk, and a pound of  milk, in a hot
oven, they will be gradually heated to the temperature
of the oven ; but the lead will attain it first,  the chalk
next, and the milk last.
   Emily.  As they were all of the same weight,  and
exposed to the same  heat, I  should  have thought that
they would have attained the  temperature of  the oven
at the same time.
   Caroline.   And how is it that they do not ?
   Airs. B.  It is supposed to be on account of the differ-
ent capacities of these bodies for caloric.
   Caroline.   What do you mean by the  capacity of a
body for caloric  ?
   Mrs.  B.  I mean a certain  disposition of bodies to ad-
mit more or less caloric between their minute particles.
Let us put as many marbles into this glass as it will con-
tain, and pour some sand over them—observe  how  the
sand penetrates and lodges between them.   We shall
now fill  another glass with  pebbles of  various  forms
—you see that they arrange themselves in a more com-
pact manner than the marbles,  which being globular,
can touch each other by a single point only.   The peb-
bles, therefore,  will not admit so much  sand between
them ;  and consequently one of these  glasses will  ne-
cessarily contain more sand than the other, though both
of them be equally full.
   Caroline.   This I  understand  perfectly.  The mar-
bles and  the pebbles represent two bodies of different
kinds, and the sand the  caloric contained in them : and
it  appears very  plain, from this comparison,  that one
body may admit of more caloric between its particles
than another.
   Mrs. B.   If you understand this; you  can no longer
be surprised that bodies of a different capacity for calor-
ic should require different proportions  of that fluid to
raise their temperatures equally.
   Emily.  But I do not understand why the body that
contains  the most caloric should not be of the highest
temperature ; that is to say, feel hot in proportion to the
quantity of caloric it contains ? 
48
    *Mrs. B.   The caloric that is employed in filling the
 capacity of a body, is not free caloric :  but it is impri-
 soned as it were in the body, and is therefore impercep-
 tible ;  for we  can feel  only the free radiating caloric
 which  the body  parts with,  and not that which  it re-
 tains.
    Caroline.   It appears to me very extraordinary that
 heat should be confined in a body  in  such a  manner  as
 to be imperceptible.
    Mrs. B.  If you lay your hand on a hot body, you
 feel  only the caloric which leaves it, and  enters your
 hand ;  for it is impossible that you should be sensible
 of that  which remains'in the body.   The thermometer
 in the same manner, is  affected only by the free caloric
 which a body transmits to it, and not at all by that which
 it does not  part with.  You see therefore, that the tern-
 perature of bodies  can  be raised only by free ridiating
 caloric.
   Caroline.  I  begin to  understand  it : but I confess
 that the idea of insensible  heat is so new and strange to
 me, that it requires some time to render it familiar.
   Airs. B.  Call it-insensible caloric, and the difficulty
 will appear much less formidable.  It is indeed a sort
 of contradiction to call it heat, when it is so situated as
 to be incapable of producing that sensation.
   Emily.   Yet  is it not  this modification  of caloric
 which is called specific heat ?
   Mr*  B.   It is so ;  but  it certainly would  have  been
more correct to have calicd it specific  caloric.
   Emily.   I do not understand how the term specific ap-
plies to  this modification of caloric ?
   Mr*  B.   It expresses the relative  quantity of calor-
ic  which different bodies of the same  weight and  tem-
perature are capable of  containing.  This modification
is  also frequently called heat of capacity, a term perhaps
preferable,  as it explains better its own meaning.
   You now understand,  I suppose, why  the  milk and
chalk required a longer time than the  lead to raise their
temperature to that of the oven ?
   Emily.  Yes ; the milk and  chalk  having a greater 
49
  capacity for caloric than the lead,  a greater proportion
  of that fluid became insensible to those bodies ;  and
  the more slowly, therefore, their temperature was rai-
  sed.
    Mrs. B. You are quile right.  And could we mea-
  sure the heat communicated by tlie oven to these three
  bodies, we  should  find  that though they have all ulti-
  mately reached the same temperature, yet they  have
  absorbed different quantities of heat according to their
  respective capacities for caloric ;  that is  to  say,  the
  milk most, the chalk next, and the lead least.
    Emily.   But supposing that these three bodies were
  made much hotter,  would heat continue  to become in-
  sensible  in  the in., or is there  any point beyond which
  the capacity of bodies for caloric is so completely filled,
  that their heat of temperature can alone be increased ?
    Airs. B.  No: there is no such point;  for the capa-
 city jf bodies for caloric always increases  or diminishes
 in proportion to their  temperature ;  so that whenever
 a body is exposed to an elevation of temperature,  part
 of the  caloric   it receives  is  detained in an insensible
 state, in order to fill  up its increased capacity.
   Emily.  The more dense a  bjdy is, I  suppose, the
 less is its capacity for caloric.
   Mr*. B.   That is the case with  every  individual
 body  ;  its capacity is  least when solid, greater when
 melted and most considerable when converted into va-
 pour.   But this does not always hold good with respect
 to bodies  of different  nature ;  iron, for instance, con-
 tains  more specific  heat  than ashes, though it is cer-
 tainly much  more dense.  This  seems to show that
 specific heat does not merely depend  upon the  inter-
 stices between the particles; but, probably, also upon
 some peculiar  power of  attraction  for caloric.   The
 word  capacity  therefore, which is generally used,' is
 not perhaps strictly  correct ; but until we are better
 acquainted with  the nature and cause of specific heat,
 we cannot adopt a  more appropriate term.
   Emily.    But, Mrs. B.  it would appear to me  more
proper  to compare bodies by measure,  rather than by
weighty in order to estimate  their specific heat.   Why, 
                        50
          *.
for instance, should  we not compare pints  of milk, of
chalk  and of lead, rather than pounds of those substan-
ces ; for equd weights may be composed of veryditler-
cnt quantities ?
   Mrs. B. You are mistaken, my dear : equal weights
must contain equal quantities of matter ; and when we
wish to know  what  is the relative quantity of caloric,
which  substances of various kinds are capable  of con-
taining, under the same temperature, we  must com-
pare equal weights, and not  equal  bulks of those sub-
stances.  Bodies of the same weight may undoubtedly
be  of  very  different dimensions ;  but that does not
change the real quantity of matter.   A pound of feath-
ers does not contain  one atom  more than a pound of
load.
   Caroline.   I have  another difficulty to propose.  It
appears to me, that if the temperature of the  three
bodies  in the oven did not rise equally, they  would nev-
er reach  the  same degree  ; the lead  would  always
keep its advantage over the chalk, and milk, and  would
perhaps be  boiling before the others had attained the
temperature of the oven.  I think you  might  as well
say that, in the course of time, you and I should be of
the same age ?
   Mrs. B.    Your comparison is not correct, my dear.
As soon  as the lead reached the temperature of the
oven, it would remain stationary ; for it would then give
out as much heat as it would receive. You should le-
collect  that  the exchange of  radiating heat, between
two bodies of equal temperature, is equal ;  it  would
be impossible, therefore, for  the lead  to  accumulate
heat after having attained the temperature of the oven  ;
and that of the chalk and milk therefore would ultimate-
ly arrive at the same standard.   Now I fear that this
will not hold good with  respect to our ages, and that,
as long as I live, I shall never cease to keep my advan-
tage over  you.
   Emily.  I think  that I have  found a comparison for
specific heat,  which is very applicable.   Suppose that
two men of  equal weight and bulk,  but who  required
Afferent quantities of food to satisfy their appetites, sit 
 down  to dinner,  both equally hungry ; the* one would
 consume a much greater quantity  of provisions  than
 the other, in order to be equally  satisfied.
   Mr*.  B.  Yes, that is very fair;  for the quantity of
 food  necessary to  satisfy  their respective appetites,
 varies in the same manner as the quantity of caloric
 requisite to raise  equally the temperature of different
 bodies.
   Emily.  The thermometer, then, affords no indication^
 of the specific heat of bodies ?
   Mr*.  B.  None at all : no more than satiety is a test
 of the quantity  of food  eaten.  The thermometer,  as  I
 have repeatedly said, can be  affected  only by free or
 radiating caloric, which alone raises the temperature of
 bodies.
   Emily.  And is there no method  of measuring the
 comparative quantities of caloric absorbed in the oven by
 the lead, the chalk, and the  milk ?
   Mr*.  B.  It may be done by cooling  them to the
 same  degree in an apparatus adapted to receive and
 measure the caloric which they give out.    Thus, if you
 plunge them into  three equal quantities of water, each
 at the same temperature, you  will be able to judge  of
 the relative quantity of caloric  which the three bodies
 contained, by that, which, in  cooling, they communi-
 cated to their  respective  portions  of water ; for the
 same quantity of caloric which they each absorbed to
 raise their temperature, will abandon them in lower-
 ing it ;  and on examining the three vessels of water,
 yon will  find the one in  which you immersed the  lead
 to be the least healed ;  <hat which contained the chalk
 wiil be the next ; and  t.iat which" contained the  milk
 will be heated the most of all.   The celebrated Lavoi-
 sier has invented a machine to estimate, upon this pii>
ciple, the  specific  heat  of  bodies in  a  more perfect
manner ; but I  cannot  explain it to you, till you are ac-
quainted vv'-w'i the next modification of caloric, which is
called latent heat,
   Caroline.  And  pray what kind of heat is that ?
   Airs.  R. It is so analogous to  specific heat, that most
chemists make  no distinction between them ;  but  Mv. 
Si
 Pictet, in  his essay on fire, has so  judiciously discrimi-
 nated  them, that I think his view of the subject  may
 contribute to render it clearer. We therefore call latent
 heat (a name that was first used by Dr. Black) that por-
 tion of insensible caloric  which is employed  in  chang-
 ing  the stxte  of bodies  ; that is  to say, in converting
 solids into liquids, or liquids  irto  vapour.   The  heat
 which performs these changes  becomes fixed in the
 body which it has transformed, and, as it is  perfectly
 concealed from our senses, it has obtained the name of
 latent heat.
   Caroline.   I think it would be much more correct to.
 call  this  modification latent  caloric,  instead  of latent
 heat, since it does not excite the sensation of heat.
   Mrs. B.   The remaik is equally applicable to  both
 the  modifications of specific and latent heat; but we
 must not presume (unless amongst ourselves in order
 to explain the subject) to alter  terms which are  still
 used by much  better chemists  than ourselves.  And,
 besides, you must not suppose that the  nature of heat
 is altered by being variously  modified : tor if latent heat,
 and specific heat, do not  excite the same  sensations  as
 free caloric, it is owing to their being in a state of  con-
 finement, which prevents them  from acting  upon our
 organs : and consequently, as soon as they are extrica-
 ted from the body in which  they are imprisoned, they
 return to their state of free caloric.
   Emily.  But I do not yet clearly see in what respect
 latent heat diners from specific heat; for they arc  both
 of them imprisoned and concealed in bodies ?
   Airs. B.  Specific heat is that which is employed in
 filling the capacity of a body for  caloric,  in the state  in
 which  this body actually exists  ;  while  latent beat  is
that  which is employed only in  eflecting a change of
 state, that is, in converting bodies from a solid  to a
 liquid, or from a liquid to  an aeriform state. But I think
that, in a  general point  of  view,  both these  modifica-
tions might be comprehended under the n.ime of heat
 of capacity, as in both cases the caloric is equally enga-
ged  in filling the capacities of bodies.
   I  shall  now show you an experiment  which I hope 
wfi1 give you a clear idea of what is understood by latent'
heat.
   The snow which yon  see in this phial, has been cool-
ed by a certain chemical means (which I cannot well
explain to you at present), to 5 degrees below the freez*
ing point, i s you wil' find indicated by the thermometer,
which  is  placed i.i it.   We shall expose it to the heat
of a lamp, and  you will see  the thermometer gradually
rise, till it reaches the freezing point-----
   Emily.  But there the thermometer  stops,  Mrs.  B.
and yet the lamp burns just as well as before.  Why is
not its heat communicated to the thermometer ?
   Caroline.  And the snow begins to melt, therefore it
must be rising above the freezing point ?
   Mr*. B.-  The heat no longer affects the thermome-
ter, because it is wholly  employed in converting: the ice
into water.   As  the ice  melts, the caloric  becomes
latent in  the new formed liquid, and therefore cannot
raise its temperature ; and  the thermometer will con-
sequently remain stationary, till the whole of the ice be
melted.
   Caroline.  Now it is all melted, and the thermometer
begins to rise again.
   Mr*. B.  Because the  conversion  of  the  ice into
water being  completed,  the caloric no longer becomes
latent ; and  therefore the heat  which  the water now
receives raises its temperature, as  you find the ther-
mometer indicates. •
   Emily.  But I  do not think  that the thermometer
rises so quickly in the   water, as it did  in the ice, pre-
vious to  its  beginning to melt, though  the lamp burns
equally well ?  '■
   Mrs. B.  That is owing to the different  specific heat
of ice and water.  The capacity of water for caloric
being greater than tint  of ice,  more heat is required
to raise its temperature,  and therefore the thermometer
rises slower in the water than in ice.
   Emily.  True ; you said  that a solid body always in-
creased its capacity for heat by becoming fluid ; and this
is an instance of it.
F 2 
54
  Mr*. B.   But be careful  not  to confound  this with
latent heat.
  Emily.  On the contrary,  I think that  this example
distinguishes them extremely  well; for though they
both go into an insensible state, yet  they differ in this
respect, that the  specific heat fills the capacity  ol the
body in the  state  in  which it exists, while  latent heat
changes that Ftate, and is afterwards employed in main-
taining the body in its new form
  Caroline.  Now, Mrs  B. the water begins to boil, and
the thermometer is again stationary.
  Mrs.  B.  Well, Caroline, it is your  turn  to explain
the phenomenon.
  Caroline.  It is wonderfully curious.   The caloric is
now busy in  changing  the water into steam, in which
it hides itself and  becomes insensible.  This is another
example of latent heat,  producing  a change of form.
At  first it converted a solid  body into a liquid, and now
it turns the liquid into vapour !
  Mrs. B.  You see,  my  dear, how easily  you have
become acquainted with these modifications of insensi-
ble  heat,  which  at first  oppeared so  unintelligible.
If, now, we were to reverse these changes, and con-
dense the vapour into  water, and the water  into ice,
the latent heat would re-appear entirely, in the form  of
free caloric,
  Emily.  Pray do let us see the effect  of latent heat
returning to its natural form.
  Mrs. B.  For the  purpose of shewing  this, we need
simply conduct the vapour through this tube  into this
vessel of cold water, where it  will part with its latent
heat and return to its liquid  form.
   Emily.  How rapidly the steam heats  the water !
   Mrs. B.   That is because it does not merely impart
its  free caloric to the water,  but likewise  its latent heat.
This method  of heating liquids  has been turned to ad-
vantage, in several  economical  establishments.  At
Leeds,  for instance, there is a large dye-house, in which
a great number of coppers are kept boilir.g by means of
a  single one,  which is situated without the  building,
and which alone is heated by fire.   The  steam  of this 
ss
last is conveyed through pipes into the bottom of each
of the other coppers, and it appears extremely singular
to see all these coppers boiling,  though there  is not a
particle of fire in the place.
  Caroline.    This is an admirable contrivance, and I
wonder that it is not in common use.
  Airs. B.    The steam kitchens, which are getting
into such general use, are upon  the  same principle.
The steam  is  conveyed through  a pipe in a similar
manner, into the vessels which contain the provisions
to be dressed, where it communicates to them its*latent
caloric, and returns to the state of water.   Count Rum-
ford makes great use of this principle in  many  of  his
fire-places : his great maxim is to avoid all unnecessary
waste  of caloric,  for  which  purpose he confines  the
heat in such a manner, that not a particle of it shall  un-
necessarily  escape ; and while he  economises the free
caloric, he takes care also to turn the latent heat to  ad-
vantage.  It is thus that he  is enabled to produce a  de-
gree of heat superior to that which is obtained in com-
mon  fire-places, though he employs but  half the quan.
tity of fuel,
  Emily.   When  the advantages of such contrivances
are so  clear and plain, I cannot understand why they
are not universally used.
  Mrs. B.   A long time is always required before in-
novations, however useful,  can be reconciled with  the
prejudices of the vulgar.
  Emily.   What a pitv it is that there should be a pre-
judice against new inventions ; how much more rapid-
ly the world would improve, if such useful discoveries
were immediately, and universally adopted!
  Mrs. B.   1 believe, my dear, that there are as manv
novelties attempted to be  introduced, the adoption of
which would be prejudicial to  societies, as there  are of
those which would be beneficial to it   The well inform-
ed,  though by no means exempt  from error, have  an
unquestionable advantage over the illiterate, in judging
what is likely or not to prove servicable ; and therefore
vye  find the former more ready to adopt such  discove-
ries as promise to be really advantageous, than the lat- 
56T
 ter, who having no other test of the  value of a  noveitjr
 but time and experience,  at first oppose its introduc-
 tion   The well  informed are.  however, frequently dis-
 appointed  in their most sanguine expectations, and the
 prejudices of the vulgar though  they  often  retard the
 progress of knowledge, yet sometimes, it must be ad-
 mitted,  prevent the propagation of error.—But  we are
 deviating from our subject.  We have converted steam
 into water, and are now to change water into ice, in cr-
 der to render the latent  heat  sensible, as  it  escapes
 from the water on its becoming solid.  For this purpose
 We must produce a degree of cold that will make water
 freeze.
   Caroline.  That must be very difficult to  accomplish
 in this warm  room.
   Mrs. B.  Not so much  so as you  think.   There are
 certain chemical mixtures which produce a rapid change
 from the solid to the  fluid  state, or the  reverse,  in the
 substances combined, in consequence of which change
 latent heat is eicher extricated or absorbed.
   Emily.   I do not qtnte understand you.
   Mrs. B.  This snow and salt, which  you see me
 mix  together, are melting  rapidily ; heat,  therefore,
 must be absorbed by the mixture, and cold produced.
   Caroline.  It feels even colder than ice, and yet the
 snow is melted.   This is very extraordinary.
   Mrs. B.  The cause of the intense cold of the mix-
 ture is to be attributed to the change from a solid  to a
 fluid state.   The union of the snow and salt produces a
 new arrangement of their partieles,  in consequence of
 which they become liquid,  and  the quantity  of caloric
 required to effect this change is seized upon by the mix-
 ture wherever it can  be obtained.   I his eagerness of
 the mixture for caloric, during its liquefaction, is  such,
that it converts part of its own  free caloric  into latent
heat, and it is thus that its temperature is lowered
  Emily.   Whatever you  put into this  mixture there-
 fore, would freeze ?
  Mrs. B.  Yes; at least any fluid that is succeptible
of freezing  at that temperature ; for  the exchange of
radient heat would always be in favour of the cold mix- - 
57
  ture, until an equilibrium of temperature was ertablish-
  ed;  therefore unless the body  immersed  contained
  more free caloric than would become latent in the mix-
  ture during its conversion into a liquid, the former must
  ultimately give  out its  latent heat till  it cools down to
  the temperature of the  latter.  I have prepared  this
  mixture of salt and snow for the purpose of freezing the
  water from which  you are desirous of seeing the latent
  heat escape.   I have put a thermometer in the glass of
  water that is to be frozen, in order that you may observe
  how it cools-----
    Caroline.   The thermometer descends,, but the heat
  which the water is now losing, is its free, not its latent
  heat?
    Mr*. B.   Certainly ; it does not  part with its latent
  heat till it changes its state and is converted into ice.
    Emily.  But here is a very extraordinary circum-
  stance 1  The thermometer is fallen below the freezing
  point, and yet the water is not frozen.
    Mrs.  B.   That is always  the  case previous to the
  freezing of water when it is in a state of rest.   Now it
  begins to congeal, and you may observe that the ther-
  mometer again rises to the freezing point.
    Caroline.  It appears  to me very strange that the
  thermometer should rise  the very moment that the wa-
  ter freezes ; for it seems  to imply that the water was
*  colder before it froze than when in the act of freezing.
    Mrs.  B.   It is so ; and after our long dissertation on
  this circumstance,  I did not think that it would  appear
  so surprising  to you.   Reflect a little, and I think you
  will discover the reason of it.
    Caroline.  It must  be,   no  doubt,  the extrication of
  latent heat, at the instant the water  freezes,  that raises
  the temperature.
    Mrs. B.   Certainly ; and if you  now  examine  the
  thermometer, you will find that its rise was but tempo-
  rary,  and lasted only during the disengagement of the
  latent heat;  it has since fallen and will continue  to  fall
  till the ice and mixture are of  an equal temperature. 
5J8
  Emily.   And can you  show us any experiments in
which liquids, by being mixed, become solid, and disen-
gage latent heat ?
  Airs  B.   I could show you several ; but you are not
yet sufficiently advanced to understand  them  well.   I
shall, however,  try one which will afford you a striking
instance  of the fact.   The fluid which you  see in this
phial consists of a quantity of a certain salt called muriat
of lime,  dissolved in water.  Now if I pour into it a few
drops of this other fluid, called sulphuric acid, the whole
or  very nearly the whole,  will be instantaneously con-
verted into a  solid mass.
  Emily.   How white it  turns !  I  feel the latent heat
escaping, for the bottle is warm, and the  fluid is chan*
ged to a solid white substance like chalk !
  Caroline   This is indeed  the most curious  experi-
ment we have seen  yet.   But pray what is  that white
vapour that ascends from the mixture ?
    Mrs. B  You are not yet enough of a chemist to
understand that.  But, take  care,  Caroline do not ap'
proach too near it, for it smells extremely  strong.
  The  mixture of  spirit  of wine and  water affords
another striking example  of the extrication of latent
heat.  The particles of these liquids, by penetrating
each other, change their arrangement, so  as to become
more dense,  and vif I may use the expression),  less
fluid, in consequence of which they part with a quanti-
ty of latent heat.
  Sulphuric  acid and water  produce  the  same effect
and even in a much greater degree.   We shall try both
these experiments,  and you will feel how much heat
which was in a  latent state, is set at liberty.—Now each
of you take hold of one  of these glasses.-----
  Caroline.   1 cannot hold mine ; I am sure  it  is as hot
as boiling water
  Airs.  B.   Your glass,  which  contains the sulphuric
acid and water, is indeed, of  as high  a tempen.'ure as
boiling water ;  but  you do not find yours so hot Emily ?
  Emily.   Not qu're.  Hut why  are  not  these liquids
converted into  solids by the  extrication of their latent.
heat ? 
ST9
  Mr*. B.  Because they part  only with a portion of
that heat, and therefore they suffer only a diminution
of their liquidity.
  Emily.  Yet they appear as perfectly liquid as they
did before they were mixed.
  Mr*  B.  They arc however  considerably condens-
ed.   I  shall repeat the experiment  in a  graduated
tube, and you will see that the two liquids, when mix-
ed, occupy less space than they did separately.   This
tube is graduated by cubit inches, and this  little mea-
sure contains  exactly one cubit  inch ; therefore, if I
fill it twice,  and pour its  contents into  the tube, they
should fill it up to the second mark.
   Caroline.  And so they do exactly.
   M?-*. B. Because I put two  measures of the same
liquid into the tube ? but we shall now try it with one of
water and one of sulphuric acid ; observe  the  differ-
ence—
   YLmily  The  two measures,   this  time,  evidently
lake up less space, though the fluid does not appear to
have suffered any change in its liquidity.
   Mrs. B.  The two liquids, however, have undergone
some degree  of  condensation from the new arrange-
ment of their particles ;  they  have  penetrated each
other, so as to form  a closer substance, and  have thus,
as it were, squeazed out a portion of their latent heat.
But this change ot state is certainly much less striking,
and  less complete,  than  when  liquids are converted
into solids.
   The slakeing of lime is another curious instance of
the extrication of latent heat.  Have you never  obser-
ved how quick-lime smokes when water is poured upon
it, and how  much heat it produces ?
   Carroline.   Yes ; but I do not understand what change
of state takes  place in the lime that ocoasions its  giving
out latent heal; for  the quick-lime,  which  is solid, is
(if I recollect right) reduced to  powder by this  opera-
tion, and is therefore rather expanded than  condensed.
   Mrs. B.  It is from the water, not  the lime, that
the  latent heat  is  set free.  The  water incorporates
with, and becomes  solid in the lime; in  consequence 
60
 of which the heat,  which kept  it in a liquid state, is
 disengaged and escapes into a sensible form.
   Caroline.  1 always thought that the  heat originated
 in the lime.   It  seems  very strange that  water,  and
 cold water too,  should contain so much  heat.
   Emily.   After this extrication of caloric, the  water
 must exist in a state of ice in the lime, since it parts
 with the heat which kept it liquid ?
   Airs.  B.  It cannot properly be called ice,  since ice
 implies a degree of cold, at least equal to the freezing
 point.   Yet as  water,  in  cotqbining  with lime,  gives
 out more heat  than  in freezing,  it must  be in a state of
 still greater solidity  in the lime, than it  is in the form
 of ice ;  and you may have  observed that it  does  not
 moisten  or liquefy the lime in the smallest degree.
   Emily   But, Mrs. B. the  smoke that rises is white ;
 if it was only  pure  caloric which escaped, we  might
 feel, but could  not see it.
   Mrs. B.   This white  vapour  is formed by  some of
 the particles of lime, in a state of fine dust,  which are
 carried off by the caloric.
   Emily.  In all changes of state, then, a body either
 absorbs or disengages latent heat ?
   Airs. B.   You cannot exactly say absorbs latent heat,
 as the  heat becomes latent only  on  being confined in
 the body ; but you may say that bodies, in passing from
 a solid to a liquid form, or from the liquid state to that
 of vapour,  absorbs  heat;  ami that  when the  reverse
 takes place heat is disengaged.*   We have seen like-
 wise,  that a body may part with some of its latent heat
 without completely changing  its form, as was the case
 with the mixtures of sulphuric  acid and  water, and
 spirit of wine  and water ;  but here  you must  observe,
that the condensation  which forces  out a  portion  of
their latent heat, is occasioned by a new arrangement
of the  particles, produced by mixing the liquids, they
therefore undergo  a change  of state, though  no very
sensible difference takes place in their form.

  * This rule, if not univerfal, admits  of very few exceptional 
61
   Caroline.  All solid  bodies, I  suppose,  must have
parted with the whole of their latent heat ?
   Mr*. B   We cannot precisely say that;  for solid
bodies are most of them susceptible of being brought
to different degrees  of density,  during which  opera-
tion a qu.ntity  of heat is disengaged ; as it  happens in
the hamnieringof  metals,  the boring of cannon, and
in s^eneral whenever bodies are exposed to considerable
friction or violent presrtue.
   It has been much disputed, however, to what modi-
fication of heat caloric thus extricated belongs,  though
in general it has been considered as latent heat; but it
 dees not seem  strictly entitled to that name, as its ex-
trication produces no other change in the body than an
increase  of density.  .
   Emily.  And may  not the same objection be made
to the heat extricated from the mixtures we have just
witnessed ? for the only alteration that is produced by
it is a greater density.
   Mrs. B.  But F observed to you, that the density was
produced by a new arrangement of the particles, owing
to the mixing of two different  substances ; this  cannot
be the case,  whenjflkat is extricated from solid  bodies
by mere mechanical force,  such as hammering  me-
tals ;  no  foreign   particles  are  introduced,  and ex-
cept  a closer  union, no change  of arrangement can
take place.   The*caloric, thus extricated,  seems there-
fore to have a still  more dubious title to the modification
of latent heat, than  that produced by mixtures.  I know
no other way of settling this difficulty than by calling
them both heat of capacity, a title to which we have
 agreed that specific heat, and latent heat, have an equal
 claim
   Emily.  We can now, I think, account for the ether
boiling, and the water  freezing in vacuo, at the same
temperature
   Mr*. B.  Let me  hear  how you explain it ?
   Emily.   The latent heat, which the water gave out
in freezing,  was immediately  absorbed  by the ether,
during its conversion  into vapour;  and therefore, from
                          G 
62
alalcnt state in one liquid, it passed  into a latent state
in the other.
   Mr*. B.   But this only  partly accounts for the  ex-
periment ;  it remains to  be explained why the tempe-
rature  of the ether, while in a state of  ebullition, is
brought down to the freezing temperature of the water.
It is because the ether, during its evaporation, reduces
its own temperature, in the same proportion as that of
the water, by converting its free caloric into latent heat;
so that, though one liquid boils,  and the other freezes,
their temperatures remain in a state of equilibrium.
   Having advanced so far on  the subject of heat, I
may now give you an account of the calorimeter, an in-
strument invented by  Lavoisier, upon  the principles
just  explained,  for the purpose  of  estimating  the  spe-
cific heat of bodies.  It consists of a vessel, the inner
surface of which is lined with ice, so as to form a  sort
of hollow globe of ice, in the midst of which the body,
whose  specific heat is to be ascertained, is placed. The
ice absorbs caloric from  this body, till  it has brought
it down to the freezing point: this caloric converts in-
to water a  certain  portion of the  ice which  runs  out
through  an  aperture at the bottom  of the machine ;
and the quantity of ice changed to water is  a  test of
the  quantity of caloric  which the body has given  out
in descending from a certain temperature to the freez-
ing point.
   Caroline.   In this apparatus, I suppose, the milk,
chalk,  and lead, would melt different  quantities  of  ice,
in proportion to their diff'eient capacities for caloric  ?
   All's. B.   Certainly ; and thence we  are able to as-
certain, with precision, their respective capacities for
heat.   But  the calorimeter affords  us no more  idea
■of the absolute quantity of heat contained in a body,
than the thermometer ; for though by means  of it we
extricate both the free and  confined caloric, yet we ex-
tricate them only to a certain  degree, which is  the
freezing point .* and we know not  how much they con-
tain of either below that point.
   Emily.   According  to this theory  of latent heat, it
appears  to  me the weather  should  be warm when it 
&
freezes, and cold in a thaw ;  for latent heat is liberated
from every  substance  that freezes,  and such  a large
supply of heat must warm  the atmosphere ;  whilst,
during a thaw, that very quantity of free heat must be
taken from the atmosphere, and return to a latent state
in the bodies which it thaws.
  Mr*. B.  Your observation is very natural ; but con-
sider, that in a frost the atmosphere is so much colder
than the earth, that all the caloric  which it takes from
the freezing bodies is insufficient to raise its tempera-
ture above the freezing point  ; otherwise the frost must
cease.  But if the quantity  of latent heat extricated
does  not destroy the frost,  it serves to moderate the
suddenness  of the change of temperature of the atmos-
phere,  at the  commencement both of a frost, and of a
thaw.   In the first instance,  its extrication  diminishes
the severity of the cold ;  and, in the  latter,  its absorb*
tion moderates the  warmth  occasioned by a thaw: it
even sometimes produces a discernable chill, at the
breaking up of a  frost.
   Caroline.   But what are the general causes that pro-
duce those  sudden changes  in the weather, especially
from hot to  cold, which we often experience ?
   Mrs. B.   This question would lead us into meteoro-
logical discussions, to which I  am  by no means com-
petent   One cii cumstance,  however, we can easily un-
derstand.   When the  air  has passed over cold coun-
tries, it will probably arrive here, at a temperature much
below our own, and then  it must absorb lieat from every
object it meets with  which will produce a general fall
of temperature.
   But  I  think we have now sufficiently  dwelt on  the
subject of  latent heat ;   we  may therefore proceed to
the  last modification, which  is chemical heat.  In
this state we consider caloric as one of the  constituent
parts of bodies.   Like any other  substance, it is sub-
ject to the attraction of composition,  and is thus capa-
ble of being chemically combined.
   Emily.   In this case, then, it neither affects the th< r-
mometer, nor the calorimeter,  since principles united 
64
by the attraction of composition can  be separated only
by the decomposition of a body.
   Mrs. B.   You are perfectly right.   We may consid-
er free caloric as  moving constantly  through  the inte-
grant particles of a body ; specific and latent  heat, as
lodging between  them, and  being there detained by a
mere mechanical union;  but  it is chemical heat alone
that actually combines, in consequence of a true chemi-
cal  affinity,  with  the constituent particles  of bodies ;
and  this union cannot  be dissolved without a decomposi-
tion  produced by superior attractions.
   Caroline.   But  it this kind of heat is so perfectly con-
cealed in the body, pray how is it known to exist ?
   Mr*. B.   By being freed from its imprisonment; for
when the body in  which it exists is decomposed, it then
returns to the state of free caloric.  This caloric, how-
ever, seldom  shews itself entirely, as part of it gene-
rally enters  into  new combinations with some of  the
constituent parts of the decomposed body,  and is thus
again concealed under the form of latent heat.
   But it will be better to defer saying any thing further
of this modification of heat at  present.   When we
come to analyse compound bodies, and resolve them in-
to their continent parts, we shall have many opportu-
nities of becoming better acquainted with it.
   Caroline.   Caloric  appears to me a most  wonderful
element :  but 1 cannot reconcile myself to the  idea of
its being a substance ; for il  seems to be constantly ac-
ting in opposition, both to  the attraction of  aggregation
and  the laws of gravity ;  and yet you  decidedly class it
amongst the simple bodies.
   Mrs. B.   You  are  not at all singular in the  doubts
you entertain, my dear, on  this point ;  for although ca-
loric is now  generally  believed to be  a real  substance,
yet  there are certainly  some  strong  circumstances
which seem to militate against this doctrine.
   Caroline.   But  do you, Mrs. B. believe it to be a sub-
stance ?
   Mrs. B   Yes,  I do :  but I am inclined to  think,
that its levity is,  in  all probability, only reLtive, like 
6o
that of vapour which ascends through the heavier me-
dium, air.
  Caroline.  If that be the case, it would not ascend in
a vacuum.         •
  Mr*. B   In an absolute vacuum, perhaps it would
not.   But as the most complete cacuum we can obtain
is never perfect,  we may always imagine the existence
of some unknown invisible fluid, which  however light
and subtile, may be heavier than caloric, -and will grav-
itate in it.  The  fact has not,  I believe,  been yet de-
termined by very decisive experiments ; but it appears
from some  made  by  Professor Pictet, mentioned in
his' Essay on Fire,' that heat has a tendency to as-
cend in the  most complete vacuum which we are able
to obtain.
  Emily.  But if there exists such a subtile fluid as you
imagine, do you  not think that chemists would  have dis-
covered it by some of its properties?
  Mr*.  B.   It  has been  conjectured that light might
be such a fluid ; but I confess that I do not think it prob-
able : for as it appears by Dr. HerchelPs experiment
that heat is less refrangible than light, I should be rath-
er inclined  to think it  the heavier of the two.  But,
while you have so many well ascertained facts to learn,
I shall not perplex you with  conjectures. We have
dwelt on the subject of caloric  much longer than I in-
tended, and I fear you will find it difficult to remember
so long a lesson.  At our next meeting we shall examine
the nature of oxygen and nitrogen, two substances with '
which you must now be made acquainted.



               Con&ergation v/

              Oh Oxygen and Mtrogen,'


                      Mr*.  B.
   To-day we shall examine the chemical properties of
the atmosphere.
                      ©2 
66
   Caroline.  I  thought you  said that we were to learn
the nature of oxygen and nitrogen, which come next
in our table of simpic bodies ?
   Airs. B.   And so you shall : ihe atmosphere is com-
posed of these  two principles :  we shall therefore ana-
lyse it, and consider its component parts separately.
   Emily.   I always thought that  the  atmosphere had
been a very complicated fluid, composed of all the vari-
ety of exhalations from the earth.
   Mrs. B.  In a general point of view, it may be said
to consist of all the substances capable of existing, in
an aeriform state, at the common temperature  of our
globe.   But, laying aside these heterogi nous and ac-
cidental substances (which rather  float in  the  atmos-
phere  than form any ot i's component parts , it con-
sists of an elastic fluid  called atmospherical air,
which is composed of two gasses,  kiov n by the names
Of OXYGEN GAS and NITKOGKN 01' AZOTIC GAS.
   Emily.   Pray what is a gas ?
   Mrs. B.  The name ol 'gas is given to  any'neriform
fluid,  which  consists of some substances rhemia i!y
combined with  caloric, and capable of existing con-
stantly in an aeriform state, under the pressure,  and  at
the temperature of the atmosphere   Every  individual
gas is the re foe composed of two parts :  1st, the par-
ticular substance tb.it i> converted  into a gas, by calor-
ic ; this is called the busis of the gas. as it is horn it
that the gas derives  all iti  specific and characteristic
properties: and 2dly, the  caloric, winch, by its chem-
ical combination with the basis,  constitutes  it a gas,  or
permanently eh.siic fluid.
   Emily.   When  you speak  then of the simple sub-
stances, oxygou and  nitro^ei, you mean to express,
those substances which are tue  basis of the two gasses,
independently of caloric  ?
   Mrs. B.   Yes,  in strict propriety ;  and they should
be culled gasses, only when brought, by their combina-
tion with caloric, to an  aeriform state.
   Caroline.   Is not water, or any other substance, when
evaporated by heat, called also  a gas ? 
67
  Mrs. B.  No, my dear; vapour is indeed, an elas-
tic fluid, and bears  so strong  a resemblance to a gas,
that there is some danger of confounding them ; there
are however, several points  in which they es->en'ial!y
differ, and by which you  may  always  distinguish them.
   Vapour  is  nothing more  than the solution, or me-
chanical divi ion, of any substance whatevei in caloric.
Thj c-tloric, in this case, becomes latent  in the vapour ;
but its union with it is very slight, and as we have seen
in a variety ofinstanc.es. it is necessary  only to lower
the tempeiatme in  order to  separate them.   But,  to
foi m a gas or permanently elastic fluid, a chemical com-
bination must take place  between the caloric and the
substance, at the ti  it of its being converted into a gase-
ous state ;  it is necessary therefore, that there should
be  an  afli.'ity between them,  and hence  their  combina-
tion can..ot  be destroyed by a  mere chimge of tempera-
ture,  or Uy any chemical agents, except such as have
a stronger affiniy. for either  of the constituents  of the
gas, an.1 oy that  . ens effect  its decomposition.
   Caroline.  Indeed,  I ought not to have forgotton that
caforic, in  vapour, is only latent,  and not chemically
com';iiicd.   But pray,  Mrs. B.  what kinds of sub-
 stances aie oxygen and  nitrogen, when not in  a gaseous
 State ?
   Mr*. B.  We have never been able  to obtain these
 substances  in their pure  simple st.ite, because we can-
lui separate them entirely  eitier iroin caloric or from
 theoti.cr bocies witli which  we end them united ; it is
 therefore ouiy  by their elVecls in combining with other
 substance- tha  we are acquainted with them.
   Caroline.  How  much more satisfactory it  would  be
if we could see  tliein !
   Emily    In  what proportions are they  combined in
the al.uosphere ?
   Airs. B.   The  oxygen gas constitutes  about one
 fourth, and the nitrogen gas three-fourths.  When sep-
 arated thty are found to  possess qualities tot. i.y  differ-
 ent from eicii  other.  Pure oxygen gas is essential both
 to  respiration and combustion,  while neither  ol these
 processes can be performed in nitrogen gas. 
68
   Caroline.  But since nitrogen gas is unfit for respira'
 tion, how does  it happen that the three fourths of this
 gas, which enter into  the composition of the atmos-
 phere, are not a great impediment to breathing ?
   Mr*.  B.  We should breathe more freely than our
 lungs  could  bear,  if we  respired oxygen gas  alone.
 The nitrogen is no impediment either to respiration,
 or combustion; it appears to be merely passive in
 those functions ; but it serves as it were, to dilate and
 weaken the oxygen while  we breathe, as you  would
 weaken  the wine that you drink, by diluting it with
 water.
   Emily.  And by what  means  can the  two gasses, •
 which composed the atmospheric air,  be separated ?
   Airs.  B.  There are many ways of analysing the at-
 mosphere  ; the two gasses can  be separated first by
 combustion.
   Emily.  How is it possible  that rombustion should
 separate them ?
   Mr*. B.  I must first tell you,  that all  bodies, ex-
 cepting the earth and alkalies, have so strong an affini-
 ty for oxygen, that they will, in  certain circumstances,
 attract and absorb it from the atmosphere ; in this case
 the nitrogen gas remains alone, and we thus obtain  it in •
 its simple gaseous state.
   Caroline.  I do not understand how a gas can be  ab-
 sorbed ?
   Mr*.  B. The gas is not absorbed, but decomposed ;
 and it is oxygen only, that is to say, the basis of the gas,
 which is  absorbed..
   Caroline.   What  then becomes of the caloric of the
 oxygen gas, when it is deprived of its basis ?
   Airs. B.  We shall make this piece of dry wood ab-
 sorb oxygen from the atmosphere, and you will see what
 becomes of the caloric.
   Caroline.  You are joking, Mrs. B. you do not mean
 to decompose the atmosphere with a piece of stick  ?
   Mrs.  B.  Not the whole body of the atmosphere, -
 certainly  ; but if we can  make this stick  absorb any ■
 quantity of oxygon from it, will not a proportional quan-
tity of atmospherical air Le decomposed ? 
69
   Caroline.  Undoubtedly ; if the wood has so strong-
 an affinity for oxygen, as to attract it from the caloric
 with which it is combined in the atmosphere, why does
 it not decompose the atmosphere spontaneously ?
   Mrs. B  Because the attraction of aggregation of
 the particles of the wood, is an obstacle to their combi-
 nation  with the oxygen ;  for you know that the oxygen
 must penetrate the wood in order  to  combine with its
 particles, and forcibly separate them indirect opposition
 to the attraction  of aggregation.
   Emily.   Just as caloric penetrates bodies ?
   Mrs B.   Yes ; but caloric being a much more sub-
 tile fluid than oxygen,  can penetrate substances much
 more easily.                             .
    Caroline.  But if the attraction  of cohesion between
 the particles of a body, counteracts its affinity for oxy-
 gen, I do not see how  that body can decompose the at-
 mosphere ?                             .
    Mr*.  B.  That is now the difficulty  which we have
4 to remove with regard to the piece of wood.-—Can you
 'think of no method of diminishing the  attraction of co-
 hesion ?                       .,,,...    .  ,,
    Caroline.  Heating  the wood, I should think, might
 answer the purpose :  for the caloric would separate the
 particles, and.make room for the oxygen.
    Mrs  B  Well, we shall try your method ; hold the
  stick close to the  fire—closer still, that  it may imbibe
  the caloric plentifully  ; otherwise the attraction of cohe-
  sion between its particles will not  be  sufficiently over-
  come--                           _       ,    . T  -,; ,
    Caroline.  It has actually  taken fire, and yet I did
 not let it touch the coals ; but I held it  so  very close,
  that I suppose it caught fire  merely from the intensity
  of the heat.                    .               ,    ,
    Mrs. U.  Or you might say, in other words, that the
  heat so far overcome  the attraction of cohesion of the
  wood, that it was enabled to absorb oxygen very rapidly
  from the atmosphere.                          .  .
     Emily.  Does the wood  absorb oxygen while it is
  burning ? 
ro
  Airs.  B.  Yes ;  and the heat and light are produced*■
by the caloric of the  oxygen gas, which being set at
liberty by the oxygen uniting with the wood, appears in
its sensible form.
  Caroline.  You  astonish me  ! Is it possible that  the
heat of a burning body should be produced by the at-
mosphere, and not the body itself.
  Mr*.  B.  It is not precisely ascertained whether apy
portion of the caloric is furnished by the combustible bo-
dy ; but there is no doubt that by far the most consider-
able part of it is disengaged from the oxygen gas, • when
its basis combines with the combustible body.
  Emily.  I have not yet met with any thing in chemis-
try that  has surprised or  delighted me so  much as this
explanation of combustion.   I  was at first wondering
what  connection there could be between the affinity of
a body of oxygen and its combustibility ; but I think I
understand it now perfectly.
  Mr*.  B.  Combustion then,  you see, is  nothing more
than the rapid absorption of the basis of oxygen gas, by
a combustible body, attended by the  disengagement of
the light and heat,  which were combined with the ox-
ygen when in its gaseous stale.
  Emily.   But are there no combus'ible  bodies whose
attraction for oxygen is  so stiong, that they  will  over-
come the  resistance of the attraction of aggregation,
without the application of heal ?
  Caroline.  That  cannot be ;  otherwise we should see
bodies burning spontaneously.
  Mr*.  B.  This  indeed, sometimes happens, (and
for  the  very reason which Emily as-signs), as I shall
show you at some future time.  But  in general, all  the
combustions that could occur spontaneously, ai the tern-
terature of the atmosphere, having already taken place ;
therefore new combustions cannot happen  without rais-
ing the temperature  of  the  body.  Some bodies,
however, will burn at a much lower  temperature than
others.
  Emily.   The elevation of temperature, required to
make a body burn, must, I suppose depend entirely upon
the force of aggregation  to be overcome I 
71
  'Mrs. B.   That is one point;  but you must likewise
•recollect, that there must be a stronger affinity between
 the body  and oxygen,  than between the latter and its
 caloric : otherwise the oxygen will not quit its gaseous
 form to combine with the body.  It is  this degree of
 affinity for oxygen that constitutes  a combustible body.
 The earths and alkalies have no such an affinity for oxy-
 gen, and are therefore  incombustible.  But  in order
 to make a combustible body burn, you see that it is ne-
 cessary to give the first impulse to combustion by the
 approach of a hot or burning body, from which it may
 obtain a sufficient quantity of caloric to raise its temper-
 ature.
    Caroline.   But the common way of burning a body is
 not merely to approach it to one already on fire, but rath-
 er to put on the  one in  actual contact with the other, as
 when I burn this piece of paper by holding it in the flame
 .of the fire.
    Mrs.  B.  The closer it is in contact with the source
  of caloric, the sooner will its temperature be raised to
  the degree necessary  for  it to burn.  If you  hold  it
  near the fire, the same effect will be produced ; but
  more time will be required, as you found  to be the case
  with the piece of stick.
    Emily.   But why is it not necessary to continue ap-
  plying caloric throughout the process of combustion,
  in order to prevent the attraction of aggregation  from
  recovering its ground and impeding the absorption  of
  the oxygen ?
     Mrs.  B.   The caloric, which is gradually disengag-
  ed, by the decomposition of the oxygen  gas, during
  combustion, keeps up the temperature of the burning
  body ; so that when once combustion has begun, no furth-
  er application of caloric is required.
 "*   Caroline.   Since I  have learnt this wonderful theory
  of combustion, 1 cannot take my eyes from the  fire ;
  and I can scarcely conceive that the heat and light which
  I always supposed to proceed from the coals, are really
  produced by the atmosphere, and that the coals are  on-
  ly the instruments by which the  decomposition of the
  oxygen gas is effected. 
72
   Emily.  When you blow the fire, you increase  the
combustion, I suppose, by  supplying the  coals  with  a
greater quantity of oxygen gas ?
  Mrs. B.  Certainly;  but  of course no blowing will
produce  combuation,  unless the temperyture  of the
coals be first raised.  A  single spark, however, is some-
times sufficient to produce that effect; for as I said be-
fore, when <nce combustion  has commenced, the ca-
loric disengaged is sufficient  to elevate the temperature
of the rest of the body, provided that  there be  a free
access of oxygen.  There  are, therefore, three things
required  in order to produce  combustion ; a combusti-
ble body, oxygen, and a  temperature at which the one
will combine with the other.
   Emi.y.  You said that the combustion  was  one me-
thod oi decomposing the atmosphere, and obtaining the
nitrogen  gas in its simple state : but how do you secure
this gas, and prevent it from mixing with the rest of the
atmosphere ?
   Mr*. B.  It is necessary  for this purpose to burn
the body  within a close  vessel, which is easily done.—
We shall introduce a small lighted taper (Plate V. Fig.
7.) under  this glas receiver,  which  stands in a basin
over water, to prevent ail communication  with the ex-
ternal air.
   Caroline.    How dim  the  light burns already !  It is
now extinguished.
   Mr* B   Can you tell us why it is extinguished ?
   Caroline.  Let me consider—The  receiver  was full
of atmospherical air ;  the taper  in  burning within it,
must have absorbed t'pe oxygen  contained in that air,
and the caloric that was disengaged produced the light
of the  taper.   But when the whole ol the oxygen was
abs itbed, the  whole of this caloric  was  disengaged ;
consequently the taper  ceased to burn, and the flame  '
was extinguished.
   M> *. B.  Your explanation is perfectly correct.
   Emily.  The two constituents ol the oxygen gas be-
ing thus  disposed of, what remains under the receiver
must be  pure nitrogen gas ?
   Airs. B.  There are some circumstances which pre- 
73
■verit the nitrogen gas, thus obtained, from being per-
fectly pure ;  but we may easily try whether the oxygen
has disappeaied by putting another lighted taper under
it.__You  see how  instantaneously the flame is extin-
guished for want of the oxvgen ; and were you to put an
animal under the  receiver,  it would immediately be
suffocated.   But that  is an experiment which  I suppose
your curiosity will not tempt you to try.
   Emdif.  It must be very  cruel indeed !—-But look,
Mrs. B.  the receiver is full of a thick  white  smoke.
Is that nitrogen gas ?
   Mrs B.   No,  my dear, pure nitrogen  gas  is per-
fectly   transparent,  and  invisible,  like  common air.
This cloudiness proceeds from a variety of exhalations,
 which arise from the burning taper, and the  nature  of
 which you cannot yet understand.
   Caroline.  The  water  within the receiver has now
 risen a little above its level in the bason.   What is the
 reason of this ?
    Mr*. B.  With a little reflection, I  dare say, you
 would  have  explained  it  yourself   The  water rises
 m  consequence of the oxygen gas within  it having been
 destroyed or rather decomposed, by the combustion of
 the taper ;  and the water  did not rise immediately be-
 cause the heat of the taper whilst burning, produced a
 dilatation of the air  in the vessel,  which counteracted
 this effect.                     .                   .
    Another means of decomposing the  atmosphere is
 the oxygenation of certain metals.  This process is very
 analogous to combustion; it  is, indeed, only  a more
 general  term to  express the combination of a body
 with oxygen.                           .  ,.«.  r
    Caroline.   In what respect, then, does it differ from
 combustion ?                                ,   .
    Mr* B.  The combination of oxygen in combustion
 is  always accompanied by  a  disengagement  of light
 and heat: whilst this circumstance  is not  a  necessary
 conse.uence of simple oxygenation.
    Caroline.  But how can a body absord oxygen with-
 out disengaging  the  caloric of the gas ?
    Mr*  B   Oxygen does not always present itseli in a
                          H 
74
 gaseous state ;  it is a constituent part of a vast number
 of bodies, both solid and liquid, in which it exists in a
 much denser state than in the atmosphere ; and from
 these bodies it may be obtained without any disengage-
 ment of caloric.   It  may likewise, in some cases, be
 absorbed from the  atmosphere  without  any sensible
 production of light  and heat;  for  if the process be
 slow, the caloric is disengaged in  small  quantities, and
 so gradually, that it  is not capable of producing either
 light or heat.   In this case, the  absorption of oxygen
 is called oxygenation or oxydation, instead of combustion,
 as the disengagement of sensible light and heat is es-
 sential to the latter.
  Emily.  I wonder that metals can unite with oxygen ;
 for,  as they are very dense,  their attraction of aggre-
 gation must be very  great, and I should have thought
 that oxygen could never have penetrated such bodies.
  Mrs. B.  Their  strong attraction for oxygen coun-
 terbalances this obstacle   Most  metals, however, re-
 quire to be made  red  hot before they are capable of at-
 tracting oxygen in any considerable  quantity.  By  this
 process  they lose most of their metallic'properties,
 and fall into a kind of powder,  formerly called calx, but
 now much more  properly termed an oxyd; thus we
 have oxyd of lead, oxyd of iron, &c.
  Caroline.  The word oxyd, then, simply means  a
 metal combined with oxygen ?
  Mrs. B.  Yes; but the term is not confined to me-
 tds, though chiefly applied to  them.  Any body what-
 ever, that has combined with a certain quantity of oxy-
 gen, either by  means of  oxydation or  combustion, is
called an oxyd, and is said  to be oxydated or oxygenated.
  This black powder is an oxyd of manganese, a metal
which has so strong  an attraction for  oxygen, that  it
absoibs that  substance  from  the atmosphere  at  any
known temperature :  it is therefore never  found in its
 metallic form, but always in that of  an oxyd, in which
state, you iee, it has very  little of the appearance of  a
metal.  It is now heavier than it was before oxydation,
 in consequence  of the addiuonal weight  of the oxygen
 with which it has combined. 
»
D
t 
Plau. V.
Page. 75.
Fiff. «?.
             /"/>. J>.





Prf/jitnilitn  of ojcyt/cii tfal
raw it $r th* Author
DwBeteSc
i,'/W/i/iW fyr Ji!ir..;r( ..ok.: £•('? .Yen  ."•',•„, 
75
  Caroline.   I am very glad to hear that; for I confes'*
I could not help having some doubts  whether oxygen
was really 3 substance, as it is not to be obtained in a
simple and palpable  state  :  but  its weight is, I think,
a decisive proof of its being really a body.
   Mrs. B.   It is easy to estimate its weight,  by separ-
ating it from  the manganese, and finding how much the
latter has lost.
  Emily.   But if you  can  take the oxygen  from  the
metal, shall we not then have it in its  palpable simple
state ?
  Mrs. B.   No  : for I can only separate the oxygen
from  the manganese, by  presenting to it some  other
body  for which  it has a greater  affinity  than for the
manganese.  Caloric possesses such a  superior affinity
for oxygen,  provided the-temperature of the  metal
be sufficiently raised ;  if,  therefore,  I heat  this oxyd*
of manganese to a certain  degree, the caloric  will com-
bine with the oxygen,  and carry it off in the form of
gas.
   Er\Uy.   But you said just  now,  that manganese
would attract oxygen from  the atmosphere  in which
it is combined with  caloric ; how,  therefore, can  the
oxvgen have  a superior affinity for caloric, since it aban-
dons the latter to combine with the  manganese ?
   Mrs. B.   1 give you credit for this objection, Emily ;
and the only answer I can make to it is. that the mutu-
al affinities of metals for oxygen and of oxygen for ca-
loric, vary  at different temperatures ;  a certain degree
of heat will, therefore,  dispose a  metal  to combine
with  oxycren. whilst  on the contrary,  the former  will
be compelled to pirt with the latter when the tempera-
ture is  further increased.   I have put some oxyd  of
manganese into a retort, which is an ear-then vessel with
a bent neck,  such as you  sec here (Plate V.  Fig. S.J
                      Plate V.
  Fig. 7. Combustion of a taper under a receiver.  Fig. 8.  A re-
tort on a stand. Fig.  9.  A furnace.  B Earthen  retort in the
furnace.  C. water bath   D. Receiver.  E E.  Tube conveying
the gas from the retort through the water into the receiver-  F,
F. F.  Shelf perforated  on which the receiver stands. Fig.  10.
Combustion of  iron wire in oxygen gas 
76
 —The retort containing the manganese you cannot sec,
 as I have enclosed it in this furnace,  where  it is now
 red hot.  But in order to  make you sensible of the es-
 cape of the gas, which is itself invisible, I have  con-
 nected the neck of the retort with this bent tube,  the
 extremity of which is immersed in this vessel of vvaler
 (Plate V.  Fig. 9.)—Do you see the bubbles of air rise
 through the water ?
   Caroline.   Perfectly.  This, then   is  pure  oxygen
 gas ;  what a pity  it should be lost ! Could you not pre-
 serve it ?
   Airs. B.  We shall collect it in this receiver.—For
 this  purpose,  you  observe, I first fill it with water,  in
 order to exclude the atmospherical air ; and then place
 it over the bubbles that issue from the retort, so as to
 make  them rise through the water to the upper part of
 the receiver.
   Emily.   The bubbles of oxygen gas rise, I  suppose,
 from their specific levity ?
   Airs. B.  Yes ; for  though  oxygen forms  rather a
 heavy  gas, it is light compared  to water.  You see how
 it gradually displaces the water from the  receiver.  It is
 now full of gas, and I may leave it inverted in water on
 this shelf, where I can keep the gas  as long as  I choose
 for future experiments.   This  apparatus (which is in-
 dispensable in all experiments in which gasses are con-
 cerned) is called a  water-bath.
   Caroline.  It is  a very clever contrivance,  indeed ;
 it is  equally simple and useful.  How convenient the
 shelf is for the receiver to rest  upon underwater,  and
 the holes in it for the gas to  pass  into  the receiver !  I
 long to make some experiments with this apparatus.
   Mr*. B.  I shall try your skill that way, when you
 have a little more experience.  I  am now  going  to
 show you an experiment, which proves, in a very strik-
ing manner,  how  essential  oxygen is to combustion.
You will see that iron itself will burn in this gas, in the
 most rapid and brilliant manner.
  Emily.  Really  ! 1 did  not know  that it was possible
 to burn iron.
  Mrs. B.  Iron is eminently combustible in pure oxy- 
7T
gen gas, and what will surprise you still  more, it can
be set on fire without any very great rise of temperature.
¥ou sec this spiral iron wire—I fasten it at one end to
this cork, which is made to fit an  opening  at the top of
the glass receiver (Plate V.  Fig.  10 )—
  Emily.  I see the opening  in the receiver; but it is
carefully closed by a ground glass stopper.
  Airs. B.  That is in order to prevent the  gas from
escaping; but I shall take out  the stopper, and put in
the cork, to which  the wire hangs.—.Now  I mean to
burn this wire in the oxygen gas, but 1 must fix a small
piece of lighted tinder to the extremity  of it, in order
to give the  first impulse to combustion;  for however
powerful oxygen is in promoting combustion,  you must
recollect that it cannot take place without a certain eleva-
tion of temperature.   I  shall now  introduce the wire
into the receiver, by quickly changing the stoppers.
  Caroline.   Is  there  no danger of the gas escaping
while you change the stoppers ?
  Airs. B.   Oxygen  gas is a little heavier tfian atmos-
pherical air, therefore It will  not mix with  it very rapid-
ly ; and if I do not  leave the  opening uncovered we
shall not lose any-----
  Caroline.   Oh, what a brilliant  and beautiful flame !
  Emily.   It  is as  white, and  dazzling as the sun !—
Now a piece  of the melted wire  drops  to the bottom :
I fear it is extinguished; but no,  it  burns again as
bright as ever
  Mrs B.   It will burn  till the wire  is  entirely con*
sumed, provided the  oxygen  be not  first expended;
for you know it can burn only while there is oxygen to
combine with it
  Caroline.   1 never saw a more  beautiful light.  My
eyes can hardly bear it!  How astonishing to think that
all this caloric was contained in the small quantity of
gas that was enclosed in the receiver ; and that,  without.
producing any sensible heat!
  Mrs. B.   The caloric  of the oxygen gas  could not
produce any sensible  heat before the combustion took
place,  because it was not  in a free state.  You  can tell
                        H2 
rs
me, I hope, to what modification of heat this caloric  is
to be referred ?
   Caroline  Since it is combined with the basis of the
gas, it must be chemical heat.
   Emily,  Chemical heat is then extricated in all com-
bustions ?
   Mrs.  B.  Certainly.   By the decomposition of the
gas, the caloric, returns to its free state, and  thus pro-
duces a quantity of sensible heat, proportional to the
rapidity ol that decomposition.
   Caroline.  How wonderfully quick combustion goes
on in.pure oxygen  gas! But pray are these drops of
burnt iron as heavy  as the wiie was before ?
   Airs.  B.  They  are even heavier; for tlie iron  in
burning, has acquired exactly the weight of the oxy-
gen which has disappeared, and is now combined with
it.  It has become an oxyd of iron.
   Caroline.   I do not know what you mean  by saying
that the oxygen has disappeared, Mrs. B. for it was al-
ways invisible.
   Mrs.  B.  True,  my dear; the expression was  in-
correct    But though you could not see the oxygen gas,
I believe you had no doubt of its presence,  as the effect
it produced on the wire was sufficiently evident.
   Caroline.   Yes, indeed;  yet you  know  it was the
caloric of the gas, and not the oxygen gas  itself, that
dazzled us so much.
   Mrs. B  You are not quite correct in your turn,  in
saying the caloric dazzled you ; for caloric is invisible ;
it  affects  only the sense of feeling ; it was  the  light
which dazzled you.
   Caroline.  True ;  but light and caloric are such con-
stant  companions, that  it is difficult to separate them,
even in  idea.
   Mr*. B.   The easier it is to confound them the more
careful you should be in making the  distinction.
   Caroline.  But why has the w ater now risen, and fill-
ed part of the receiver ?
   Mrs. B.   Indeed, Caroline, I did not think you would 
79
have asked such  a  question !  I am sure, Emily, you-
can answer it.
  Emily.   Let me reflect...........The. oxygen
has combined with the wire ; the caloric has escaped ;
consequently nothing can remain in the receiver,  and
the water will rise to fill the vacuum.
   Caroline.  I wonder that I did not think of that   I
wish that we had weighed the  wire and the oxygen gas
befoie comousiion ;  we might then have found wheth-
er the weight of the oxyd was equal to that of both.
   Airs. B.  You might try the experiment if you par-
ticularly wished it ; but I can assure you, that, if ac-
curately performed, it never fails  to show that  the  ad-
ditional weight of the oxyd is precisely equal to that of
 the oxygen absorbed, whether the process has been  a
 real combustion, or a simple oxygenation
   Caroline.  But this cannot be the case with combus-
 tions in general,  for when  any  substance is burnt in the
 common air, so far from increasing in weight, it is evi-
 dently diminished, and sometimes entirely consumed.
   Mr*.  B.   But what do you mean by the expression.
 Consumed ? You cannot suppose that the smallest parti-
 cle of any substance in nature can be actually  destroy-
 ed    A compound body is decomposed by combustion ;
 some of its constituent parts fly off in  a gaseous form,
 whi.e others remain in a concrete state ; the former are
 called the volatile, the latter the fixed products of  com-
 bustion.   But if we collect the whole of them, we shall
 always find tnat they exceed the weight of the combus-
 tible  body, by that of the oxygen which has combined
 with  them during  combustion.
    Emily.  In the combustion of a coal fire, then, I sup-
 pose  that the ashes are  what would be called the fixed
 product .' and the smoke  the volatile product ?
     Mr*. B.  Yet when the fire burns best, and the quan-
  tity of volatile products should be the greatest,  there is
  no smoke ; how can you account for that ?
     Emily.  Indeed  1 cannot  ; therefore I suppose that
  I was not right in  my conjecture.
     Airs. B.  Not quite :  ashes  as you supposed,  are a
  fixed product of combustion ;  but  smoke,  properly 
80
 speaking, is not one of the volatile  products, as it con-
 sists of some minute undecomposed particles of the coals-
 that are carried off by the caloric without  being burnt,
 and are  either deposited in the  form of soot or dis-
 persed by the wind.   Smoke therefore, ultimately be-
 comes one of the fixed products of combustion.  And
 you may easily conceive that the stronger the fire is,
 the less smoke  it produces, because the  fewer particies
 escape combustion.  On this principle depends the in-
 vention of Argaud's patent lamps ; a current of air is
 made to pass through the cylindrical wick  of the lamp,
 by which means it is so  plentifully  supplied  with oxy-
 gen, that not a particle of oil escapes combustion, nor
 is an atom of smoke produced.
  Emily.   But what then.are  the  volatile products of
 combustion ?
  M?-*. B.  Various new compounds, with which you
 are not yet acquainted, and  which being converted by
 caloric, either  into vapour, or gas, arc  invisible  ; but
 they can  be collected, and we shall examine  them, at
 some future period.
  Caroline.  There are  then other gasses, besides the-
 oxygen and nitrogen gasses ?
  Mr*. B.  Yes,  sevt ral :  any substance that has a
 sufficient affinity for caloric to combine with it, and as-
 sume and maintain the  form of an elastic  fluid at the
 temperature of the atmosphere, is capable of being con-
verted into a gas.  We  shall examine the several gas-
 ses in their respective places ; but we must now confine
our attention to those that compose  the atmosphere.
  I shall  show you another method of decomposing the
atmosphere, which is very simple.  In breathing we
retain a portion  ofthe oxygen, and  expire the nitrogen
gas ; so that if we breathe in a closed vessel,  for a cer-
tain length of time, the air within it vill be deprived of
its oxygen  gas.  Which of you will make  the  experi-
ment ?
  Caroline.  I should be very glad to try it.
  Airs. B.  Very well ; breathe several times through'.
 this glass tube into the  receiver  with which it  is con-
 nected, until you feel that your breath is exhausted— 
81
  Caroline.  I am quite out of breath already 1
  Mrs. B. Now  let us try the gas with a lighted taper.
  Emily.   It is very pure nitrogen gas, for the taper is
immediately extinguished.
  Mrs. B.  That is not a proof of its being pure, but
only of the absence of oxygen, as it is that principle
alone that can produce combustion, every  other gas
being absolutely incapable of it.
  Family.   In the methods which you have shewn  us,
for decomposing  the  atmosphere, the  oxygen  always
abandons the nitrogen :  but is there no way  of taking
the nitrogen from the oxygen, so as to obtain the latter
pure from the atmosphere ?
  Airs. B.  You must  observe, that whenever  oxygen
is taken from the atmosphere, it is by decomposing  the
oxygen gas : we cannot do the same with the nitrogen
gas, because nitrogen has a stronger affinity for caloric
than for any other known principle  : it appears  impos-
sible  therefore to separate it from the atmosphere, by
the power of affinities.   But if we cannot obtain the oxy-
gen gas by this means, in its separate state, we have  no
difficulty (as you have seen) to procure it in its gaseous
form,  by taking it from those  substances that have  ab-
sorbed it from the atmosphere.   This is done by com-
bining the oxygen, at a high tempeiature, with  caloric,
as we did with the oxyd of manganese.
   Emily.   Can atmospherical  air be rccomposed  by
mixing due proportions of oxygen and nitrogen gasses ?
   Mr*. B.  Yes : if about one-fourth of oxygen gas be
mixed with  three fourths  of  nitrogen gas, atmospher-
ical air is produced.
   Emily.   The air then must be an oxyd of nitrogen ?
   Mr--. B.  No, my dear ; for there must be a  chemi-
cal combination between oxygen and nitrogen in order
to produce an oxyd ; whilst in the atmosphere these two
substances are separately combined with caloric, form-
ing two distinct gasses, which are simply mixed in  the
formation of'he atmosphere.*
   • Thi«, at least, seems to be the prevailing opinion.  Yet it has
been queftioned by some chemists, particularly of late, whether the
union of oxygen and nitrogen in  the  atmosphere be not a  true
chemical combination. 
82
I shall say nothing more of oxygen and nitrogen at pre-
sent, as we  shall continually have  occasion to  refer  to
them in our future conversations.  They are both  very
abundant in nature ;  nitrogen is the most plentiful in the
atmosphere, and exists also in all  animal substances ;
oxygen forms a constituent part, both of animal and veg-
etable kingdoms, from which it may  be obtained by a
variety of chemical means.  But  it is now time to con-
clude our lesson.  I  am afraid you have learnt  more to
day than you will be  able to remember.
  Caroline.   I assure you that I  have  been too much
interested in it, ever  to forget it;  as for nitrogen, there
seems to be but little to remember about it  : it makes
a very insignificant figure in  comparison to oxygen, al-
though it composes a much larger portion of the atmos-
phere.
   Mr*. B.   It will not appear so insignificant when you
are better ^acquainted  with it; for though it seems to
perform but a passive part in the  atmosphere, and  has
no very striking properties when considered in its sepa-
rate state, yet you will see by and by what a very im-
portant agent it becomes,  when  combined with other
bodies.   But no more of this  at present ; we must re-
serve it for its proper place..
CoMjenrntion  vi.
    On Hydrogen.
    he  next  simple body we come to is  iiydkogkn.
vible ?V     kHKl °f a suUtance« th*t i  is it also invi- 
B3
   Mr*.  B.  Yes;  we cannot  obtain hydrogen in its
pure concrete state.   We are  acquainted with it only
in its gaseous form, as we are with oxygen and nitro-
gen.
   Caroline.  But in its gaseous state it cannot be called
a simple substance, since it is combined with caloric.
     Airs.  B.  True-, my dear ; but as we do not know
in nature of any substance which is not more or  less
combined with caloric, we are apt to say, (rather incor-
rectly indeed) that a substance is in its pure state, when
combined with caloric only.
   Hydrogen is derived  from two Greek words,  the
meaning of which is to produce water.
   Emily.  And how does hydrogen produce  water  ?
   Mrs.  B.  Water is composed of 85 parts, by weight,
t)f oxygen, chemically combined with  15 parts of hy-
 drogen  gas,  or (as it was formerly called)  inflamable
air.
   Caroline.  Really ! is  it possible that water should
be a combination of two gasses, and  that one  of them
 should be  inflamable  air ?   It must be a most extra-
 ordinary gas, that will produce both fire and water  !
   Mrs. B.   Hydrogen, I assure you, though  a consti-
tuent part of water, is one of the most combustible  sub-
stances in  nature.
   Emily.   But I thought  you  said that combustiow
 could take place in no gas but oxygen ?
   Airs.  B. ^ Do you recollect what the process of com-
bustion consists in ?
   Emily.  In the combination of a body with oxygen,
 with disengagement of light and heat.
   Mrs.  B.  Therefore,  when I  say that hydrogen is
 combustible, I mean that it has an affinity for oxygen  ;
 but like all other combustible substances, it  cannot
 burn  unless  supplied with  oxygen, and heated  to a
 proper temperature.
   Curoline.  But  I cannot conceive how, by mixing
 fifteen parts of it, with eighty-five parts  of oxygen  gas,
 the two gasses can be converted into water. 
84
    Mrs. B.   The  simply mixing these  proportions of
  oxygen and hydrogen gasses, will not produce water ;
  because the great quantity of caloric to which they owe
  gaseous form would prevent their bases from coining
  into contact,  and entering  into chemical combination ;
  besides, water is a much  denser fluid  than gas, and
  therefore it is necessary, in order to reduce these gasses
  to a liquid, to diminish the quantity of caloric.  Can you
  think of any means of accomplishing this ?
    Caroline.  By putting a colder body in contact  with
 the gasses, which  would take some of  their caloric
 from them.
    Mr*.  B.  That would lower the temperature of the
  gas ; but could not affect the  caloric that is chemically
 combined  with the basis.
    Caroline   True  ; I forgot, that in order to separate
 caloric from a body with which it is chemically combin-
 ed, a decomposition must take place ; but I cannot ima-
 gine how this is effected.
   Mrs. B.  A decomposition can be effected only by
 superior attractions  which produce new combinations.
 At a certain temperature, oxygen will abandon its ca-
 loric to  combine  with  hydrogen ; if, therefore, we
 raise it to  that temperature, the  oxygen  will combine
 with the hydrogen, and set its own caloric at liberty ;
 and it is thus that the combustion of hydrogen gas pro.
 duces water.
   Caroline.  You love to deal in paradoxes to-day, Mrst
 B.—Fire then produces water  !
   Mr*  B.  The combustion of hydrogen gas certain-
 ly  does; but  you do not seem  to have  remembered
 the theory of combustion so well  as  you  thought you
 would   Can you tell me what happens in the combus-
 tion of hydrogen gas ?
   Caroline.  The hydrogen gas combines with the basis
of the oxygen gas, and the caloric of the latter is disenga-
ged.--Yes, I think, 1 understand it now  : the caloric of
the oxygen gas being set at liberty, and the basis of the
two gasses coming into contact, they combine,  and con-
dense into a liquid. 
85
  Emily.  But  does all the caloric, produced by  the
combustion of hydrogen gas, proceed from the oxygen
gas?
  Mr*. B  That  is a doubtful point; but I rather  be-
lieve that in this,  as probably in every o'her instance of
combustion, some portion of heat and light is disengag-
ed by the combustible itself.
  Emily.  Water then, I suppose, when it evaporates
and incorporates  with the  atmosphere, is  decomposed
and converted into hydrogen and oxygen gasses ?
  Mr*. B.  No my dear; there you  are quite mis-
taken : the decomposition of water is  totally different
from  its evaporation ;  for  in  the  latter case  (as  you
should recollect) water is only  in a state of very minute
division; and is merely suspended in the atmosphere,
without  any  chemical combination, and without  any
separation of its  constituent parts.   As long as these
remain combined, they form water, whether in a state
of liquidity,  or in that of an elastic fluid, as vapour, or
under the solid form of ice.
  In our experiments on latent heat, you may recollect
that we caused water successively to pass through these
three  forms, merely by an increase or diminution of
caloric, without employing any power  of attraction, or
 effecting any decomposition.
  Caroline.   But are there no means  of decomposing
water ?
  Airs. B.   Yes, several: charcoal, and metals, when
heated red hot, will attract the oxygen from water in
the same manner, as they will from the atmosphere ;
but in this process there is no disengagement of calor-
ic,  as that which the oxygen  abandons, instead of be-
coming  sensible, combines immediately with the  hy-
drogen,  which it converts  into gas, and carries  off in
that form.
  Caroline.   So,  then, the quantity of  caloric that  was
employed in maintaining the combined substances in a
liquid form,  is just  sufficient  to convert the hydrogen
singly, into a gas.
  Mrs. B.   That is a very ingenious inference;  but
I doubt whether it is strictly accurate,  as the hot body 
16
 (whether charcoal  or  metal)  by means of which  the
 water is  decomposed, supplies, in cooling,  a  portion
 of the caloric which enters into the formation of  the
 gas.
   Emily.  Water,  then, may be resolved  into a solid
 substance and a gas; the oxyen being  condensed into
 a solid,  by  the  loss of caloric,  and the hydrogen  ex-
 panded into a gas, by the acquisiton of it.
   Mr*.  B.   Very well; but remember that the basis
 of the oxygen gas, or what you call solid oxygen,  can
 never be obtained alone ; it can be separated from  the
 hydrogen only by combining it with some other body
 fonwhich it has a greater affinity.
   Caroline.   Hydrogen,  I see, is like nitrogen, a poor
 dependant friend of oxygen, which is continually for-
 saken for greater favourites.
   Mr*. JB. The connection, or friendship, as you choose
 to call it,' is much more  intimate between  oxygen and
 hydrogen, in the state of water, than between  oxygen
 and nitrogen, in the atmosphere ;  for in the iirst  case,
 there is a chemical union and  condensation of the two
 substances ;  in the latter  they are simply mixed  to-
 gether in their gaseous state.  You will find,  however,
 that, in some cases, nitrogen is quite as  intimately con-
 nected with  oxygen, as  hydrogen is.—But this is for-
 eign to our present subject.
   Emily.  Water,  then, is an oxyd, though  the  at-
 mospherical  air is not ?
   Mrs. B.   It is not commonly called an oxyd, though
 according to our definition, it may, no doubt, be refer-
 red to that class of  bodies.
   Caroline.   I should like extremely to see  water  de-
 composed.
   Mrs. B.   I  can  easily  gratify  your  curiosity by a
 much more easy  process than  the oxydation of  char-
 coal  or metal;  the decomposition of water by  these
 latter means, take up a great  deal of time, and is  at-
 tended with much trouble ; for it is necessary that  the
 charcoal or metal should  be made red hot in a furnace,
that the water should pass over them in a state of  va- 
/Vft/r  VI
PaffC 87
Brairvby the. Author
DoelMfoJo
Enyrarrd /or Increase Cook &cC?JVeu' Haverv. 
 
87
pour, that the gas formed should be collected over the
water-bath, kc.   In short it is a very complicated affair.-
But the same effect may be produced with the  great-
est facility, by adding some suljbhuric acid (a substance
with the nature of which you are not yet acquainted), to
the water which the metal is to decompose.   The acid
disposes the metal to combine with the oxygen of  the
water so readily and abundantly, that no heat is requir-
ed to hasten the process.   Of this I  am going to show
you an instance.—I put into this bottle the water that is
to be decomposed, the metal that  is to effect that  de-
composition by combining with the  oxygen, and  the
acid which is to facilitate the combination of the metal
 and the oxygen.  You will see with what violence these
 will act on each other.
    Caroline.   But what metal  is it that you employ tor
 this purpose ?                  #       .            .
    Mrs.  B.  It  is iron ; and it is used in the state ot
 filings, as  these present a greater surface to the  acid
 than a solid piece of metal.   For, as it  is the surface
 of the metal which is I'.cted upon by the acid, and is dis-
 posed to receive the oxygen produced by the decompo-
 sition of the water, it necessarily follows that the great-
 er is the surface, the more  considerable is the effect.
 The hubbies which are now rising are hydrogen gas—
    Caroline.  How disagreeably it smells 1
    Mrs. B.  It is indeed  unpleasant,  but not unwhole-
  some.  We shall not,  however,  suffer any more to es-
  cape, as it  will be wanted for  experiments.  I  shall
  therefore  collect it in a glass  receiver, by making it
  pass through this bent tube,  which will conduct it into
  the water-baih.  (Plate VI.  Fig.  11.)            .  .
     Emily:  How very  rapidly the  gas escapes,  it is
PLATE VI.
  Fig  xi. Apparatus for preparing and collecting hydrogen gas.
Fie 12  Receiver full of hydrogen  gas inverted over  water.
Fig 13'. Slow combuftion of hydrogen gas.  Fig. 14-  Appara-
tus for illuflrating the  formation of water by the combuftion of
hydrogen  gas.   Fig  15-  Apparatus  for producing harmonic
founds by the combuftbn of hydrogen gas. 
88
perfectly transparent, and without any colour whatever
—Now the receiver is full—
  Airs.  B.  We shall therefore remove it and substi-
tute another in its place.  But  you must observe, that
when the receiver is full, k h necessary to  keep  it in-
verted with the mouth under water, otherwise the gaa
would escape.   And in order that it may not be in the
way, I introduce within  the bath  under the  water, a
saucer, into which I slide the  receiver, so  that  it can
be taken out of the bath and conveyed any  where, the
water in the saucer  being equally effectual in prevent-
ing its escape as that in the bath. (Plate VI. Fig. 12.)
  Emily.  I am quite surprised to see what a large
quantity of hydrogen gas can  be produced by such a
small quantity of water, especially as oxygen is the
principal constituent of water.
  Mrs.  B.  In weight it is : but not in volume.  For
though  the proportion,  by weight, is nearly six parts
of oxygen to  one of hydrogen, yet  the  proportion of
the volume of the gasses, is about  one part of oxygen,
to two of hydrogen ;  so  much heavier is  the former
than the latter.
  Caroline.  But why is the vessel in which the  water
is decomposed so hot ? As the  water  changes from a
liquid to a gaseous form, cold should be produced in-
stead of heat.
   Mr*.  B.  No ; for if one of the constituents of water
is converted into a gas, the other becomes solid in com-
bining with the metal; and the  caloric which the oxy-
gen loses by being thus rendered solid, is just sufficient
to transform the hydrogen into a gas.
   Emily.   In this case, neither heat nor cold would be
produced ; for the caloric disengaged from the oxygen,
being immediately combined with the hydrogen, can-
not become sensible ?
   Mrs. B.  That is very true ; but the sensible heat
which is disengaged in this operation is not owing  to
the decomposition of the water, but  to an extrication
of latent heat produced by the  mixture of water and
sulphuric acid, as you saw in a former experiment.
   If I  now set  the hydrogen gas, which  is  contained 
89
in this receiver, at liberty all at once, and kindle it as
soon as it comes in contact with the atmosphere,  by
presenting it to a candle, it will so suddenly and rapid-
ly decompose the oxygen gas,  by combining with its
basis,  that an explosion, or a  detonation (as chemists
commonly call it), will be produced.  For this purpose
I need only take up  the  recsiver,  and quickly present
its open  mouth to the candle-----so.....
  Caroline.  It produced only  a sort of hissing noise,
with a vivid flush of light.  I  had expected  a much
greater report.
   Mr*.  B  And so it would have been, had the gasses
been closely confined at the moment they were made
to explode.   If for instance, we were to put in this bot-
tle a mixture of hydrogen gas and atmospheric air :
and  if, after corking the bottle, we should kindle the
mix'ure  by a very small orifice, from the sudden dilata-
tion of the gasses at the moment of their combination,
the bottle must either fly to pieces, or the cork be blown
out with  considerable violence.
   Caroline.   But in  the experiment which we have just
seen,  if you did not kindle  the hydrogen gas, would it
not equally combine with the oxygen ?
   Mrs.  B   Certainly not ; have I not just explained
to you the necessity of the oxygen and hydrogen gasses
being burnt together, in order to combine  chemically
and produce water ?
   Caroline   That is true ; but  I thought this was a dif-
ferent combination, for I see no water produced
   Mrs.  B.  The water produced by this detonation was
 so small in quantity, and in such a state of minute divi-
 sion,  as to be  invisible.   But water certainly was pro-
 duced ;  for oxygen is incapable of combining with hy-
drogen in any  other proportions than those that form
water;  therefore water must  always be the result of
their combination
   If,  instead of  bringing the hydrogen gas into sudden
contact with the atmosphere [as we  did just now") so as
to make  ihe whole of it explode the moment it is kind-
led, we  allow  but  a very small surface of gas to burn
in contact with  the  atmosphere,  the combustion goes
                       I 2 
90
 on quietly and gradually at the point of contact, without
 any detonation,  because the surfaces brought together
 are too small for the immediate union of gasses.  The
 experiment is a  very easy one.   This phial with a nar-
 row neck (Plate  VI. Fig. 13J,   is full of  hydrogen
 gas, and  is carefully corked.  If I take out  the  cork,
 without moving the  phial, and quickly approach the
 candle to the orifice, you will see how different the re-
 sult will be—
   Emily.   How prettily it burns,  with a blue flame !
 The flame is gradually sinking within the phial—now
 it has entirely disappeared.   But does not this combus-
 tion likewise produce water ?
   Mr* B.  Undoubtedly.  In order to  make the for-
 mation of water  sensible to you,  I shall procure a  fresh
 supply  of hydrogen gas, by putting  into this bottle
 (Plate VI. Fig.  \4.)  iron filings, water, and  sulphuric
 acid, materials similar to those which we have just used
 for the same purpose.   I shall then  cork up the lxittle,
 leaving only a small orifice  in the cork, with apiece of
 glass tube fixed to  it, through which the gas  will issue
 in a continued rapid stream.
   Caroline.  I hear already the hissing of  the gas,
 through the tube, and I can feel a strong current against
 my hand.
   Mrs. B.  This  current  I am going  to kindle with
 the candle—see  how vividly it burns—
   Emily.   It bums like a candle with a long flame.—
 But why does this combustion last so much longer than.
 in the former experiment ?
   Mr*. B.  The combustion goes  on  uninterruptedh/
as long as the new  gas continues to be produced.   Now
if I invert this receiver over the flame, you will soon
perceive its internal surface covered with a  very fine
dew, which is pure water—
   Caroline  Yes, indeed ;  the glass is now  quite dim
with moisture ! How glad I am that we can see the vva»
ter produced by this combustion.
   Emily.  It is exactly what 1 was anxious to see  ; for
1 confess I was a little incredulous. 
91
   Mr*. B.   If I had not  held the glass-bell over the
 flame, the water would have escaped in the state of va-
 pour, as it djd in the  former experiment.  We have
 here, of course, obtained but a very small quantity of
 water ;  but the difficulty of procuring a proper appara-
 tus, with  sufficient quantities of gasses, prevents my
 shewing it to you on a large scale.
   The composition of water was discovered about the
 same period, both  by Mr.  Cavendish,  in this country,
 and by the celebrated French chemist Lavoisier-  The
 latter invented a very perfect and ingenious apparatus
 to perform w ith  great accuracy, and upon a large scale,
 the  formation of water by the combination of oxygen
 and hydrogen gisses.  Two tubes, conveying due pro-
 portions,  the one  of oxygen, the other  of hydrogen
 gas, are  inserted  at opposite sides of a large globe of
 glass, previously exhausted of air  ; the  two streams of
 gas are  kindled within the globe, by the electric  spark,
 at the point where they come in contact; they burn to~
 gether,  that is to say, the hydrogen gas combines with
 the basis of the oxygen gas,  the caloric of which  is set
 at liberty  ; and a quantity of water is produced, exactly
 equal in weight to that of the two  gasses introduced into'
 the globe.
   Carroline.   And what was the greatest quantity of wa-
 ter ever formed in this apparatus  ?
   Mr*. B.   Several  ounces ; indeed, very  near  a
pound, if I recollect right; but the  operation lasted many
 days.
   Kmily   This experiment  must  have convinced all
 the  world of the truth of the discovery.  Pray,  if im-
 proper  proportions of the gasses were mixed and set
 fire to, what would be the result ?
   Mrs.  B.   Water would be equally formed, but there
would be  a residue of either one or other of the gasses,
because as I have already told you, hydrogen and oxy-
gen will combine only in the proportions  requisite for
the formation of water.
   There is another curious effect  produced by the com-
bustion  of hydrogen gas,  which  1  shall shew you,
though I must acquaint you first, th.it 1 cannot well ex- 
92
plain the cause of it, for this purpose, I  must puj«ome
more materials into our apparatus, in order to obtain  a
stream of hydrogen gas, just as  we have done before.
The process is already going on, and the gas is rushing .
through the tube—I shall now kindle it with the taper.
  Emily.   It burns exactly as it did before-----What is
the curious effect which you were mentioning ?
  Airs. B.   Instead of the receiver, by mean of which
we  have just seen  the drops of water form,  we shall in-
vert overt the flame this piece  of twbe, which  is about
two feet in length,  and one inch in diameter  (Plate  VI.
Fig. \5.) but you must observe that it is open at both
ends.
  Emily.   What a strange noise it makes !  something
like the jEolian  harp, but not so sweet.
   Caroline.  It  is  very  singular,  indeed; but  I think
rather too powerful to be pleasing.   And is  not  this
sound accounted for ?
   Mr*. B.  That the percussion of glass, by  a rapid
 stream of gas, should produce a sound, is not  extraor-
dinary ; but  the sound is here so peculiar, that no oth-
er  gas has a similar effect  Perhaps it is  owing to  a
brisk  vibratory  motion ol the glass occasioned  by  the
successive formation and  condension of small drops
of  water  on the  sides of the  glass tube, and the air
rushing in to replace the vacuum formed.*
   Caroline.  How very much this  flame resembles the
burning of a candle !
   Mrs. B.  The burning of a candle is produced by
much the same means.   A great deal of hydrogen  is
contained in candles, whether  of tallow or wax.  This
hydrogen being  converted into gas by the heat of the can-
dle combines with the oxygen of the  atmosphere, and
flame and water  result from this combination.   So  that,
in iact, tlie flame of a candle  is nothing but the com-
bu  1 .n of hydrogen gas.  An elevation of temperature,
sueh as is produced by a lighted match or taper, is re-
quired to give the  first impulse  to the combustion ; but 
93
afterwards it goes on of itself, because the candle  finds-
a supply of caloric in the successive quantites of chem-
ical heat which becomes  sensible by the combination of
the two gasses.   But there are other accessary circum-
stances connected with the combustion of candles and
lamps, which I cannot explain to you till you  are ac-
quainted with carbone,  which is one ef their constituent
parts.   In general, however, whenever you  see flame,
you may infer that it is owing to the formation and burn-
ing of hydrogen gas ;  for flame is the peculiar mode
of burning of hydrogen gas ; which, with only one or
two apparent exceptions, does not belong to any other
combustible.
   Emily.  You astonish  me ! I understood that flame
was the caloric abandoned by the basis  of the  oxygen
gas, in all combustions whatever ?
   Mr*. B. Your error proceeded from your vague and
incorrect idea of flame ; you have  confounded it  with
Jight and caloric  in  general.  Flame always implies
caloric, since it is produced by the combustion ofhodro-
gen gas;  but all caloric does not imply flame.  Ma-
ny bodies burn  with  intence heat without  producing
flame.  Coals,  for instance,  burn with flame until all
the hydrogen which they  contain is  evaporated  ; but
when they afterwards  become red hot, much more ca-
loric is disengaged than when they produce flame.
   Caroline.   But the iron wire, which you burnt in ox-
ygen gas, appeared to me to emit flame ; yet as it was
a simple metal, it could contain no hydrogen ?
   Mr*. B   It produced a sparkling dazzling blaze of
light, but no realflame.
   Emily.   And what  is the cause of the regular shape
of the flame of a candle ?
   Mr*. B. The regular stream of hydrogen gas which -
exhales from its combustible matter.
   Caroline.   But the hydrogen gas must from its  great
levity, ascend into the  upper regions of the atmosphere;
why therefore does  not the flame  continue to  accompa-
ny it ?
   Airs. B.   The combustion  of the hydrogen gas is
completed at the point where the flame terminates; 
94
it then ceases to be hydrogen gas, as it is converted by
its combustion into watery vapour ; but in a state of such
minute division as to be invisible.
  Caroline.  I do not understand what is the use of the
wick of a candle ;  since the hydrogen gas burns so well
without it ?
  Mr*. B.  The combustible matter of the candle must
be decomposed in order to emit the hydrogen gas,  and
the wick  is instrumental in effecting this  decomposi-
tion. Its combustion first melts the combustible matter,
and......
   Caroline.  But in lamps the combustible matter is al-
ready fluid, and yet they also require wicks ?
   Mrs B.  I was going to add  that,  afterwards, the
burning wick (by the power of capillary attraction) grad-
ually draws up the fluid to the point where  combustion
takes place ; for you must have observed, that the wick
does not burn quite to the  bottom.
   Caroline.  Yes  ; but I do not understand why it does
not.
   Mr*. B.  Because the air has not so free an access
to that part of the  wick which is immediately in contact
with the  candle, as to that part just above, so that the
heat there is not sufficient to produce its decomposition;
the combustion therefore begins a little above this point.
But we dwell too long on a subject which you cannot
yet thoroughly understand —I have another experiment
to shew you with  hydrogen gas, which I think will en-
tertain you.  Have you ever blown bubbles with soup
and water ?
   Emily.  Yes, often, when I was  a child ;  and I used
to make them float in the air by blowing them upwards.
   Mr*. B.  We  shall fill  some such bubbles with hy-
drogen gas, instead  of atmospheric air, and you  will
see with  what ease and rapidity they will ascend, with-
out the assistance  of blowing, from the lightness of the
gas—Will you mix some  soap and water  whilst I fill
this bladder with the  gas contained in the receiver which
stands on  the shelf in the water-bath  ?
   Caroline.  What is the  use of the brass stopper and
turn-cock at the top of the receiver ? 
 
P/a/r III
Pftt/e 95
Ij 1.1 if n M- /'-■  tin her.
/:'"•/■■ !iiW '. •/■  In iv;ise Cool  <i; C° .Yew tLivritr.
~*  DsoUmtSc 
                        95

  Mrs. B. It is to afford a passage to the gas when re-
quired.  There is, you see, a similar stop-cock  fasten-
ed to  this bladder, which  is made to fit that on  the re-
ceiver.  I screw them one on the other, and now turn
the two cocks, and open  a communication between the'
receiver and the bladder ; then, by sliding the receiver
off the shelf, and gently sinking it into the bath, the
water rises in the receiver and forces the gas into the
bladder.   (Plate VII. Fig.  \5.)
   Caroline.  Yes, 1  see the bladder swell as the water
rises in the receiver.
   Mr*.  B.  1  think  that we have already a sufficient
 quantity  in the bladder for our purpose ; we must be
 careful to stop both the cocks  before we separate the
 bladder from the receiver, lest the gas should escape.—
 Now  1 must fix a pipe  to the  stopper of the bladder,
 and, by dipping its mouth into the soap and water, take
 up a few drops ; then I again turn th« cock, and squeeze
 the bladder in order to force the gas into the soap and
 water at the mouth  of the pipe   (Plate Vll Fig. \7.)  t
   Emily.   There is a bubble—but it  burns before it
 leaves the mouth of the pipe
   Mrs.  B.  We must have patience  and try  again ;
 it is not  so easy to blow bubbles by means of a  bladder,
 as simply with the breath.
    Caroline.  Perhaps there is  not  soap enough in the
 water ;  1 should have had warm water, it would have
 dissolved the soap tetter.
    Emily.  Does not some of the gas  escape  between
 the bladder and the pipe ?
    Mrs.  B.   No, they are perfectly air-tight ; we shall
  succeed presently,  I dare say.
    Caroline   Now a bubble ascends; it moves with the
  rapidity  of a balloon.  How beautifully it  refracts the
  light !
    Emily.  It has  burst against the ceiling—you  suc-

                      PLnTE VII.


    Fig. 16.  / pparatus for transferring gasses from a receiver in-
  to a bladder. Fig, 17.  Apparatus for blowing s«ap bubbles. 
96
  ceed now wonderfully ; but why do they all ascend and
  bust against the ceiling ?
  - Mr*. B.   Hydrogen gas is so much lighter than at-
  mospherical air,  that it ascends  rapidly with its very
  light envelope, which is burst  by the force with which
  it strikes the ceiling.
    Air balloons arc filled with this gas, and ifthey  car-
  ried no other weight than their covering, would ascend
  as rapidly as these bubbles ?
    Caroline.   Yet their covering must be much heavier
  than that of these bubbles ?
    Mrs.  B.  Not in proportion to the quantity of gas
  they contain.  I   do not  know whether you have ever
  been present at the filling of a large balloon.  The ap-
  paratus for the purpose is very simple.   It consists of
  a number of vessels, either jars or barrels, in which the
  materials for the formation of the gas are mixed, each
  of these being furnished with a tube, and  communica-
  ting with a  long flexible pipe, which conveys the gas in-
i  to the balloon.
    Emily.  But the fire balloons which were first invent-
  ed,  and have been since abandoned, on account of their
  beingso dangerous, were constructed, I suppose on a dif-
  ferent principle.
    Mr*. B.   They were filled  simply with atmospheri-
  cal  air, considerably rarefied, and  the  necessity of hav-
  ing a fire underneath the balloon, in order to preserve
  the  rarefaction of the air within it, was the circumstance
  productive of so much danger.
    If you are not  yet tired of experiments, I have ano-
  ther to show you.  It  consists in filling soap bubbles
  with a mixture of hydrogen and oxygen gasses, in the
  proportions that form water: and afterwards setting fire
  to them.
    Emily.  They will detonate, I suppose ?
    Mr*.  B.   Yes,  they will.  As you have  seen  the
  method of transferring  the gas from the  receiver  into
  the  bladder it is  not necessary to repeat it.  I  have
  therefore provided a bladder which contains a due  pro-
  portion of oxygen and hydrogen gasses, and we have
  only to blow bubbles with it. 
9f
  Caroline.  Here is  a fine large bubble rising—shall
I set fire to it with the candle ?
  Mr*. B.  If you please.
  Caroline   Bless me,  what  an explosion 1—It was
like  the repoit of a gun :  I confess it  frightened me
much.  I  should never have  imagined  it  could be so
loud.
  Emily.   And the flash was as vivid lightning.
  Mrs. B  The combination of the  two gasses takes
place during that instant of time that you see the flash,
and hear the detonation.
  Emily.   This  has a strong resemblance  to thunder
and lightning.
  Mrs. B.  These phenomena,  however,  are most
probably  of an  electrical nature.  Yet various  meteo-
rological effects may be attributed to accidental detona-
tions of hydrogen gas in the atmosphere ;  for nature a-
bounds with hydrogen ; it constitutes  a  very consider-
able portion of" the whole mass of water belonging to our
globe, and from that  source, almost  every  other body
obtains it.  It enters into the composition of all animal
substances, and of a greater number of minerals ; but it
is most abundant in vegetables. From this immense va-
riety of bodies, it is often spontaneously disengaged  ;
its great levity makes it rise into the superior  regions
of the atmosphere, and when, either by an electric spark,
 or any casual  elevation of temperature,  it  takes fire, it
 may produce  such meteors or luminous appearances as
are  occasionally seen in the atmosphere  Of this kind
are  probably those broad flashes which we often see on
 a summer evening, without hearing any detonation.
   Emily.  Every flash I suppose, must produce a quan-
 tity of water ?
   Caroline.  And this water, naturally descends  in  the
 form of rain ?
   Airs. B.  That probably is often the case, though it
 is not a necessary consequence; for the water may be
 dissolved by the atmosphere, as it descends towards the
 lower regions, and remain there in the form of clouds.
 But pray do not question me too closely on this subject, 
98
for the phenomena of the atmosphere arc  nor yet well-
understood ; and even with the little that is known I am
but imperfectly acquainted,
©
CoMiergation vii,
            On Sulphur and Phosphorus.

                     Mrs.  B.
  Si_LPuuKis the next simple substance that comes
under our consideration.  It differs in one essential point
from the preceding, as it exists in a solid form at  the
temperature of the atmosphere.
  Caroline.  I am glad that we have at last a solid body
to examine ; one that we can see and touch.   Pray, is
it not with sulphur that the points of matches are cover-
ed to make them easily kindle ?
  Airs.  B.  Yes, it is ; and you therefore already know
that sulphur is a very combustible substance.   It is sel-
dom discovered in nature in a pure unmixed state ; so
great is its affinity for other substances, that it  is almost
constantly found combined with some  of them.  It  is
most commonly united  with metals, under various forms,
and is separated  from  them by a very simple  process.
It exists likewise in many mineral  waters, and some
vegetables  yield  it in various  proportions, especially
those of the cruciform  tribe.   It is also found in animal
matter ; in short, it may be discovered in greater or less
quantities, in  the mineral, vegetable, and animal king-
dom.
  Emily.  I have heard of flowers of sulphur,  are they
the produce of any plant ?
  Mr*.  B. By no means : they consist of nothing mare 
 
?titte Vi/j
       Fn/.1S.




Si//> 7////«//e//t  of Sulphur
I'rtr/r ff.O
                  Fiff.2(?.




/Jfcmiptwiiou of' wutcr far Gir&eHit.
t;v tii^tuth^i: 
99
than common sulphur reduced to a very fine powder by
a process called sublimation.—You see some of it in this
phial; it is exactly the same substance as this lump of
sulphur, only its colour is  a paler yellow, owing to its
state of very minute division.
   Emily.  Pray what is sublimation ?
   Airs.  B.  It is the  evaporation,  or, more properly
 speaking, the volatilization of solid substances, which, in
 cooling, condense again in a concrete form.   The  pro-
 cess, in  this  instance, must be performed in a closed
 vessel, both to prevent  combustion, which  would  take
 place, if the access of  air was not carefully precluded,
 and likewise in order to collect the substance after  the
 operation.  As it is rather a slow process, we shall not
 try the experiment now ; but you will understand it per-
 fectly if I show you the apparatus used for the purpose
 (Plate  VIII. Fig.  \8.)   Sovne lumps of sulphur are
 put into a receiver of this kind which is called a cucurbit.
 Its shape, vou see, somewhat resembles that of a pear,
 and  is  open at the top  so  as  to  adapt itself exactly
 to a kind of conical  receiver of this sort called the head.
 The cucuioit, thus covered  with its head,  is  placed
 over a sand bath ;  .'.is  is nothing more than a vessel
 full of sand, which  is kept heated  by a furnace,  such
 as you see  here, so as to preserve the apparatus  in  a
 moderate and  uniform  temperature.   The  sulphur
 then soon begins to melt, and immediately after this a
 thick white smoke rises,  which  is gradually deposited
 witbii the head, or upper part of the apparatus, where
 it condenses against the  sides, somewhat  in the form
 of  a  vegetation, whence it  has obtained the name  of
 flowers of  sulphur.  This apparatus,  which  is called
 an alembic,  is highly useful  in all  kinds of distillations,
 ns you  will nee  when we come to treat of those^ opera-
 tion?.  Alembics are  not commonly made  of  glass,
 like  this, which is applicable only to distillations upon
                      PLATE VIII.
    Fig. 18. A. Alembic.  B. Sand-bath.  C. Furnace.  Fig. 19.
  Fudiometer,  Fig. ao- A Retort containing water.  B- Lamp to
 heat the water. C. C. Porcelain tube containing Carbone.  D.
  Furnace through which the tube passes.  E. Receives for the ga*
 produced. F.  Water-hath. 
100
 a very small scale.  Those used in manufactures are
 generally made of copper, and are of course  consider-
 ably  larger.  The principal construction, however, is
 always the same,  although their shape admits of some
 variation.
   Caroline.   What is the use of that neck,  or tube,
 which bends down from the upper piece of the appara-
 tus ?
   Mr*. B.   It is of no use in sublimations ; but in dis-
 tillations (the general object of which is to evaporate,
 by heat, in closed  vessels, the volatile parts  of a com-
 pound body, and to condense  them again into a liquid}
 it serves to carry off the condensed  fluid,  which other-
 wise would fall back into the cucurbit.   But this is rath-
 er foreign to our present subject.  Let us return to the
 sulphur.  You  now  perfectly understand, I  suppose,
 what is meant by sublimation ?
   Emily.  I believe I do.   Sublimation appears to con-
 sist in destroying, by means of heat, the attraction of
 aggregation of the particles of a  solid body, which are
 thus volatilized; and  as soon as they  lose the caloric
 which produced that  effect, they are deposited in the
 form of a fine powder.
   Caroline.   It seems to me to be somewhat similar to
 the transformation  of water into vapour, which returns to
 its liquid state when deprived of caloric.
   Emily.  There  is this difference, however,  that the
 sulphur does not return to its former state, since, instead
 of lumps, it changes to a fine powder.
   Mr*.  B. Chemically speaking, it is exactly the same
 substance, whether in  the form of lump or powder.  For
 if this powder be melted again by heat, it will  in  cool-
 ing, be restored to  the same solid state in which it was
 before its sublimation.
   Caroline.   But  if there be no real change produced
by the sublimation of the sulphur, what is the use of
that operation ?
   Mrs. B. It divides the sulphur into very minute parts,
and thus disposes it to enter  more  readily into condi-
tion with other bodies.  It is used also as a means of
purification. 
101
  Caroline.  Sublimation appears to me like the begin-
ning of combustion, for the  completion of which  one
circumstance only is wanting, the absorption of oxygen.
  Mr*  B   But that circumstance is everything.  No
essential alteration is produced in sulphur by sublima-
tion ;  whilst in combustion it combines with the oxygen
and forms  a new compound totally  different  in every
respect from sulphur in its pure  state.—We shall now
burn some sulphur,  and you will see  how very  differ-
ent the result will be.  For this  purpose I put a small
quantity of flowers  of sulphur into this cup,  and place
it in a dish, into which I  have poured a little water ; 1
now set  fire to the sulphur with the point of this hot
wire;  for its combustion will not begin unless  its tem-
perature be considerably raised.—You see that it burns
with a faint blueish flame ;  and as I invert over  it this
receiver, white fumes arise from the sulphur and fill the
vessel—You will soon perceive that  the water is rising
within the receiver, a little above its level in the plate.
__Well, Emily, can you account for this ?
   Emily.   I suppose that the sulphur has absorbed the
oxygen from the atmospherical air within the receiver ;
and that we shall find some oxygenated sulphur in the
cup.   And for the white smoke, I am quite at a loss to
 guess what it may be
   Mrs. B.  Your first conjecture is very right; but you
 are quite mistaken in the  last ; for nothing will be left
in the cup.   The white vapour  is the oxygenated sul-
phur which assumes the form  of an elastic fluid  of a
pungent and offensive smell, and is a powerful acid.
 Here  you  see  a chemical combination  of oxygen and
sulphur, producing a  true gas, which  would  continue
 such under the pressure and at  the temperature of the
atmosphere, if it did  not unite with the  water in the
plate, to which it imparts its-acidJtaste and  ail its acid
properties.—You see, now,  with what curious  effects
 the combustion of sulphur is attended.
   Caroline.  This is something quite new ;  and  I  con-
 fess that I do not perfectly understand why the sulphur
 turns  acid
   Mr*.  B.  It is because it unites with oxygen, which
?* the general acidifying principle.   And,  indeed, the 
102
word oxygen, is derived from two Greeks words signi-
fying toproduce an acid*
   Caroline.   Why  then is not  water, which contains
such a quantity of oxygen, acid ?
   Mrs. B.  Because hydrogen, which is the other con-
stituent of  water,  is not susceptible of acidification.
I believe it  will be necessary, before we proceed fur-
ther, to say a few words of the general nature of acids,
though it is rather a deviation from our plan of examin-
ing the simple bodies  separately,  before we consider
them in a state of combination.
   Acids may be considered as a peculiar class of burnt
bodies, which  during their  combustion,  or combina-
tion,  with  oxygen, have acquired very characteristic
properties.   They are chiefly discernable by their sour
taste,  and by turning red most  of the blue vegetable
colours.  These  two properties are common  to the
whole class  of acids :  but each of them is distinguished
by other peculiar  qualities. Every acid consists of some
particular substance which constitutes its bases, and is
different in each), and of oxygen, which is common  to
them all.
   'Emily.   But I  do not clearly see the difference be-
tween acids and oxyds ?
   Mr*. B.   Acids were, in fact, oxyds, which, by tlie
addition of  a sufficient quantity of oxygen,  have been
converted into  acids.   For acidification,  you must ob-
serve, always implies previous  oxydation,  as a body
must have combined with the quantity of  oxygen requi-
site to constitute it an oxyd, before it can  combine  with
the greater  quantity that is necessary to render it  an
acid.
   Caroline.   Are all oxyds capable of being converted
into acids  ?
   Mr*. B.   Very far from it; it is only certain sub-
stances which villi enter into that peculiar kind of union
with oxygen that  produces acids, and the  number  of
these is proportionally very small; but all burnt bodies
may be considered as belonging either to the class  oi
oxyds, or to that of acids.  At a future period, we shall
enter more at  large upon this subject.  At present, I 
                        103

have but one circumstance  further to point out to your
observation  respecting acids: it is, that most of them
are susceptible of two degrees of acidification, accord-
ing to  the  different quantities of oxygen with which
their  basis combines.
   Emily.  And how are these two degrees of acidifica-
 tion distinguished ?
   Mr*  B   By the peculiar properties that result from
 them.   The acid we have just made is the first or weak-
 est degree of acidification,  and is called sulphurous acid;
 if it were fully saturated with oxygen,  it  would be call-
 ed sulphuric acid.  You must therefore remember, that
 in this,  as in all acids, the first degree of acidification
 is expressed by the termination in ow«; the stronger,
 by the termination in ic.
   Caroline.   And how is the sulphuric acid made ?
    Mrs.  B.   By  burning sulphur in pure oxygen  gas,
 and thus rendering its combustion much more complete.
 I have provided some oxygen gas for  this purpose ; it
 is in that bottle, but we must first decant the gas into
 the glass receiver which stands on the shelf in the bath,
 and  is full of water.
   Caroline.  Pray, let me try to do it,Mrs  B. ?
    Mrs. B.  It requires some little dexterity—hold the
 bottle completely under  water,  and  do not turn  the
  mouth upwards, till it is immediately under the aper-
  ture in the shelf,  through which the gas is to pass  into
  the  receiver, and then turn it up gradually.—Very well,
  you have only let a few bubbles escape,  and that must
  be expected at a first trial—Now I shall put this piece
  of sulphur into  the receiver, through the opening at
  the top, and  introduce  along with it a small piece of
  lighted tinder to set fire to it.  This  requires being
  done  very quickly, lest  the atmospherical  air should
  get in,  and mix with the pure o ygen gas.
    Emily.   How beautiiully it bums 1
    Caroline.   But it is  already  buried in the thick va-
  pour.   This I suppose is sulphuric acid  ?
    Emily.   Are these acids always in a gaseous state ?
    Mr*. B-   Sulphurous acid,  as we  have already ob-
  served, is a permanent  gas, and can be obtained  in a 
trJ*
 liquid form only by condensing it in water. _ In its p'jr?
 Btate,  the sulphurous acid is invisible,  and it appears in
 the form of white smoke, only from its combining with
 the moisture.   But the vapour of sulphuric acid,  which
 you have just  seen to rise during the combustion, is not
 a gas, but only a  vapour, which condenses into  liquid
 sulphuric acid, merely by losing its caloric.   And this
 condensation is much hastened and promoted by receiv-
 ing the vapour into cold water ; which may afterwards
-be separated from the acid by evaporation.
   Before we quit the subject of sulphur, I must tell you
 that it is susceptible of combining with a great variety
 of  substances,  and  especially  with  hydrogen,  with
 which you are already acquainted.   Hydrogen gas can
 dissolve a small portion of it
   Emily.  What; can a gas dissolve a solid substance ?
   Mr*  B.   Yes ; a solid substance may be so minute-
 ly divided by heat, as to become soluble in a gas ; and
 there are several  instances of it.  But you must ob-
 serve that, in  this case, a chemical solution, that is  to
 say,  a combination of the sulphur  with the  hydrogen
 gas, is produced.  In order to effect this,  the sulphur
 must be strongly heated in  contact with the gas: the
 heat reduces the sulphur to such  a  state of extreme
 division, and diffuses it so thoroughly through the gasj
 that they combine and incorporate together.   And  as
 a proof that there must be  a  chemical  union between
 the sulphur and the  gas, it is  sufficient to remark, that
 they are not separated when the sulphur loses the  ca-
 loric by which it was volatilized.   Besides,  it is evi-
dent,  from the peculiar fetid smell of this gas, that it
 is a new compound  totally different from  either of its
constituents ; it is called sulphurated hydrogen  gas, and
is contained in great  abundance  in  sulphurous mineral
waters.
  Caroline.  Are not the  Harrogate waters of this na-
ture ?
  Mrs  B.   Yes ;  they are naturally impregnated with
sulphurated  hydrogen gas,  and  there  are  many  other
springs of the same kind ; which shews that  this gas
must  often be  formed  in  the  bowels of the earth by
spontaneous processes of nature. 
105
  Caroline.  And could not such waters be made artifi-
cially by impregnating common water with this gas ?
  Mr*. B.  Yes ; they can be so well imitated as per-
fectly to resemble the Harrogate waters.
  Sulphur combines likewise with phosphorus,  and
with  the alkalies, and alkaline earths, substances with
which you are yet unacquainted.  We cannot therefore
enter into these combinations at present.  In our next
lesson we shall treat of phosphorus
  Emily.  May we not begin that subject to-day ;  this
lesson has been so short ?
  Mrs. B.  I have no objection, if you are not tired.
What do you say, Caroline ?
  Caroline.   I am as desirous as Emily of  prolonging
the  lesson to day,  especially as  we are to enter on a
new subject ;  for I confess that sulphur has not appear-
ed to me  so interesting as the other simple bodies.
   Mrs. B.   Perhaps you may  find phosphorus more
entertaining.  You must not, however,  be discouraged
when you meet with some parts of a study less amus-
ing than others ;  it would answer no good purpose to
select the most pleasing parts, since,  if we did not pro-
ceed with some method, in order to acquire a general
idea of the whole, we could scarcely expect to take in-
terest in any particular subjects
                 PHOSPHORUS.

  Phosphorus is a simple substance that was former-
ly unknown. It was first discovered by Brandt, a chem-
ist of Hamburgh, whilst employed in researches  after
the philosopher's stone ; but the method of obtaining it
remained a secret till it  was a second time discovered
both by  Kunckel and Boyle,  in  the year  1680.  You
sec a specimen of phosphorus in this phial; it is gen-
erally moulded into small sticks of a yellowish colour,
as you find it here. 
106
  Xlaroline.  I do not understand in what the discovery
consisted ; there may  be a secret method of making a
composition, but a simple body cannot be made, it can
only he found.
  Airs. B.  But a body may exist in nature so closely
combined with other substances, as to  elude the obser-
vation of chemists,  or render it extremely difficult to
obtain it in its simple state.  This is the case with phos-
phorus, which is always so intimately combined with
other substances, that its existence remained unnoticed
till  Brandt  discovered the means  of obtaining it free
from all combinations.  It is found in all animal sub-
stances, and  is  now chiefly extracted from bones, by a
chemical process.   It  exists also  in some plants, that
bear a strong analogy to animal mailer in their chemical
composition.
  Emily.  But is it never found in its simple state  ?
  Mr*. B.   Never, and this is the reason of its having
remained so long undiscovered.
  Emily.  It is possible, then, that in course or time
other new simple bodies may be discovered ?
  Airs. B.  Undoubtedly : and we may  also learn that
some of those, which we now class among  the simple
bodies,  may, in fact,  be compound ; indeed, you will
soon find that discoveries, of this kir.o. are by no means
unfrequent.
  Phosphorus is eminently combustiuio ; it nie'ls and
takes fire at the temperature of  1C0°;  andabsoibsin
its combustion nearly once and a half ns own weight  of
oxygen.
  Caroline.  What! will a  pounci  of phosphorus con-
sume a pound and a half »-f oxygen r
  Mrs. B.  '-oh appears from accurate experiments.
lean show you  with v\hat violence it  combines  with
oxygen, by burning some of it  in  that gas.   We must
manage the experiment in the same manner as we did
the combustion of sulphur.—-You see I am obliged  to
cut this little bit  of phosphorus under water, otherwise
there would be danger of its taking fire by the heat  of
my fingers —I now put it into the receiver, and kindle
it by means  of a hot wire. 
107
  Emily.  What a blaze ! I can  hardly look at it.  f*
never saw any thing so brilliant.  Does it not hurt your
eyes, Caroline ?
  Caroline.  Yes; but still I  cannot  help  looking  at
it.   A prodigious quantity of oxygen must indeed be
absorbed,  when  so  much light and caloric are disen-
gaged !
  Mrs. B.  In the combustion of a pound of phospho-
rus, a sufficient  quantity  of caloric is art free to melt
upwards of a  hundred pounds of ice ;  thi.-; has been
computed by direct experiments with the calorimeter.
  Emily.  And  is the result of this  combus ion, like
that of sulphur,  an acid ?
  Mrs. B.  Yts; phosphoric acid.   And  had we du-
ly  proportioned the phosphorus and the oxygen, they
would have  been completely converted into phosphoric
acid, weighing  together,  in  this  new  state,  exactly
the sum of their weights sepau.iely.  The water would
have ascended into the receiver, on account of the va-
cuum formed  and would hove filled it entirely.   In
this case, as in the  combustion  of sulphur, the  acid
vapour formed is absorbed and condensed in the water
of the receiver.   But when this combustion is perform-
ed  without  any water or moisture being present, the
acid then appears in the form of concrete whitish flakes,
which are, however,  extiemely ready to melt upon the
least admission  of moisture.
   Emily.   Does phosphorus, in burnjng in  atmospher-
ical air, produce, like sulphur, a weaker  sort of the
same acid ?
   M, s. IJ.  No ; for it burns in atmospherical air near-
ly  at  the same  temperature, as in  pure oxygen gas;
and it is, in both cases, so strongly  disposed to com-
bine with  the oxygen, that the combustion is perfect,
and the product similar ; only in atmospherical  air, be-
ing less rapidly supplied  with oxygen, the process is
performed in a slower manner.
   Caroline.   But !s there no method of acidifying phos-
phorus in a slighter manner ; so as to form phosphorus
acid ?
   Mr*. B.   Yes, there is.   When  simply exposed tc 
108
 the atmosphere, phosphorus undergoes a kind of slow
 combustion at any temperature above zero.
   Emily.  But is not the process in this case, rather an
 oxydation than a combustion ? For if the oxygen is too
 slowly absorbed  for a sensible quantity of light and heat
 to be disengaged, it is not a true combustion.
   Mrs. B.   The  case is not as you suppose ; a  faint
 light is emitted  which is very discernible in the dark ;
 but the heat evolved is not sufficiently strong to be sen-
 sible ; a whitish vapour-arises from this  combustion,
 which uniting with water,  condenses into  liquid phos-
 phorus acid.
   Caroline.   Is  it not very  singular that phosphorus
 should  bum  at  so low a temperature in atmospherical
 air,  whilst it does not burn in pure oxygen without the
 application of heat ?
   Airs. B.   So it at first appears.   But this circum-
 stance seems to be owing to the r.itrogen gas of the
 atmosphere.   This gas dissolves small particles of phos-
 phorus, which being thus minutely divided and diffus-
 ed in the atmospherical air. combines with  the oxygen,
 and undergoes this slow combustion.   But the same ef-
 fect does not take place in oxygen gas, because it is not
 capable of dissolving phosphorus ;  it is therefore ne-
 cessary, in this case, that heat should be applied to ef-
 fect  that division of particles, which, in  the former in-
 stance, is produced by the nitrogen.
  Emily.   I have# seen letters written with phosphorus,
 which are invisible  by day-light, but may be  read in
the dark by their own light.   They look as if they were
 written with fire  ; yet they do not seem to burn.
  Mrs. B.  But they do really burn  ; for it is by their
 slow combustion that the  light is emitted ; and phos-
 phorus acid is the result of this combustion.
  Phosphorus is sometimes  used as a test  to estimate
 the  purity  of atmospherical air.  For this purpose, it
 is burnt in a graduated tube called an eudiometer, (Plate
 VIII. Fig  \9.)  and from the} quantity of air which
 the  phosphorus  absorbs, the prepcrtion of oxygen in
 the air examined, is deduced ;  for the phosphorus will
 absord all the oxygen, and the  nitrogen alone  will re-
 main. 
109
   Emily.   And  the more oxygen is contained in the
atmosphere, the purer I suppose it is esteemed ?
   Mrs.  B.   Certainly.   Phosphorus, when melted,
combines with a  great variety of substances.  With
sulphur it forms a'compound  so extremely combusti-
ble, that it immediately takes fire on coming in contact
with the air.   It is with this composition that the phos-
phoric  matches are prepared, which kindle as soon as
they are taken out  of their case and are  exposed to the
air.
   Emily.  I have a box of these curious matches ; but
I  have observed, that in  very cold weather, they  will
not take fire without being previously rubbed.
   Airs. B.   By rubbing them you raise their  tempera-
ture ; for you know, friction is  one of the means of ex-
tricating heat.
   Emily.  Will phosphorus combine  with hydrogen
gas, as sulphur does ?
   Mrs. B.   Yes;  and the compound gas which re-
sults from this combination has a smell still more  fetid
than the sulphurated hydrogen ? it  resembles that of
garlic.
   The phos/i/iorated hydrogen  gas has this remarkable
peculiarity, that it  takes  fire  spontaneously in the at-
mosphere at any temperature.  It is thus that are pro-
duced those transient flames, or flashes  of light, called
by the vulgar Will-of-the-Wisp, or more properly Ignes-
Fatui, which are often seen in  church yards, and places
where the putrefaction of animal matter exhales phos-
phorus and hydrogen gas.'
   Caroline.   Country people,  who are so much  fright-
ened by those appearances, would  soon be reconciled
to them, if they knew from what a simple cause  they
proceed.
   Airs. B.   There  are other combinations of phospho-
tus that have also very singular properties, particularly
that which results from its union with lime.
   Emily.  Is there any name to distinguish the com-
bination of two simple substances, like phosphorus  and
lime, neither  of which are oxygen, and which there-
fore can produce neither an oxyd nor an acid ?
                         L 
no
  Mrs. B.  The names of such combinations are com-
posed  from those of their ingredients,  merely  by a
slight change in their termination.  Thus we call  the
combination of sulphur with jime a sulphuret, and that
of phosphorus, a phosphor-et of lime.   This latter  com-
pound, 1 was  going to say, has the  singular property
of decomposing water, merely by being thrown  into
it.  It effects this by absorbing  the oxygen of water,
in consequence  of which  bubbles of hydrogen gas  as-
cend, holding in solution a small quantity of phospho-
rus
  Emily.   These bubbles then are jihosphorated hydro-
gen gas ?
  Mr*. B.  Yes ; and they produce  the singular ap-
pearance of a flash of fire ussuing ffom water, as the
hubbies kindle and detonate on the surface of the water,
at the instant that they come in contact with the atmos-
phere.
  Caroline.  Is not this effect nearly similar to that pro-
duced by the combination of phosphorus and sulphur,
or, more properly speaking, the phosphoret of sulphur ?
  Mrs. B.  Yes;  but  the phenomenon appears more
extraordinary in this case,  from the presence  of water
and  from  the gaseous form -of the combustible  com-
pound.  Besides the experiment surprises by its great
simplicity.  You only throw  a piece of phosphoret of
lime into a glass of water, and bubbles of fire will im-
mediately  issue from it.
  Caroline. Cannot we try the experiment ?
  Mr*. B. Very easily ; but we must do it in the open
air ;  for the smell of the  phosphorated  hydrogen  gas
is so extremely fetid, that it wcukl be intolerable in the
house.   But before we leave the  room, we may pro-
duce, by another process, some  bubbles of the  same
gas, which are much less offensive.
   There is in this little glass retort a solution of pot-
ash in water  ;  I add to it a small piece of phospho-
rus.   We must now heat the retort over the lamp, af-
ter having engaged its neck under water—you  see it
begins to boil;  in a few  minutes bubbles  will appear, 
lit
which take fire and detonate as they  issue from tire

  Caroline.  There is one—and another.  How curi-
ous It is '.—But I do not understand how this is produ-
cccK ?
  Mr*. B.  It is the consequence of a.display  of affin-
ities too complicated, I fear, to be made perfectly intel-
ligible to you at present.
   In a few words, the reciprocal action of the potash,
phosphorus, caloric, and water,  are such that  some of
the  water is decomposed, and  the hydrogen thereby
formed carries off some minute particles of phospho-
rus, with which it forms phosphorated hydrogen gas,
a compound which spontaneously takes fire at almost
 any temperature.                              ...
   Emily.  What is that  circular ring of smoke which
 slowly  rises from each bubble after its detonation .
   Mrs. B.   It consists of water and phosphoric acid in
 vapour, which  are produced by the combustion of  the
 hydrogen and phosphorous.
            Conservation  viil

                   On Carbone,




                     Caroline.

  To-day, Mrs. B.—I believe we are (o learn the  na-
ture and properties of  car hone  This  substance js
quite new to me ; I never heard it mentioned before.
  Mr*. B.  Not so new as you imagine ; for carbone
is nothing more than charcoal in a state  of perfect  pu>
my.- 
112
  Caroline.  B Jt charcoal is made by art, Mrs. B.  and
a body consisting  of one simple substance  cannot be
fabricated ?
  Airs.  B.  You again confound the idea of making
a simple body, with that of separating it f.om  a com-
pound  The chemical process by which a simple body
is obtained in a state of purity,  consist in unmaking the
compound in which it is contained,  in order to separate
from it the simple substance in question.   The  meth-
od by which charcoal  is usually obtained,  is,  indeed,
commonly called making it ;  but, upon examination,
you will find this process to consist simply in separating
it from other substances with which  it is found combi-.
ned in nature.
   Carbone forms a considerable part of the  solid mat*
ter of all organized  bodies;  but  it is  most abundant
in the vegetable creation,  and it is  chiefly obtained
from wood.   When the oil and water (which are other
constituents of vegetable matter) are evaporated,  the
black, porous, brittle substance that remains is char-
coal.
   Caroline.   But if heat be applied to the wood  in or^
der to evaporate the oil and water, will not the  tempe-
rature of the charcoal be raised so as to make it  burn ;
and  if it  combines with oxygen can we any   longer
 call  it pure ?
   Mrs. B.  I was going to say, that in this operation,,
 the  air must be excluded.
   Caroline.   How then can the vapour of the  oil and
 water fly off ?
   Airs.  B.   In order to produce charcoal in its purest
 state (which is, even then,  but a less imperfect  sort of
 carbone), the operation should be performed in an earth-
 en retort.  Heat being applied  to the body of the re-.
 tort, the evaporable  parts  of the  wood   will  escape
 through, its neck, into which no  air can penetrate as
 long as the heated vapour  continues to fill  it.   And if
 it be wished to collect these volatile products of the
 wood, this can easily be done by introducing the  neck
 of the retort  into the water-bath apparatus, with which,
 you  are acquainted.   But the preparation  of.commoni 
113
eharcoaT, such as is used in kitchens and manufactories
is performed on a much larger scale, and  by an  easier
and less expensive process.
  Emily   I have seen the process of making commot*
charcoal   The wood is ranged on the ground in a pile
of a  pyramidical form, with a fire undeme  th  ; the
whole is then covered with clay, a few holes only being
left for the circulation of air.
   Mrs. B. These holes are closed as soon as the wood
is fairly lighted, so that  the combustion is checked,  or
at least continuesbut in a very, imperfect  manner; but
the heat produced by it is sufficient to force out and vola-
 tilize, through the earthly cover, most part of the oily
 and watery  principles of the wood, although  it cannot
 reduce it to ashes;
   Emily-   Is pure carbone as black as charcoal f
   Mr*. B.  The more charcoal is purified, that  is to'
  say, the nearer it approaches  to the state of simple*
  carbone, the deeper its black colour appears ; but the
  utmost efforts of chemical art, are not able to bring it
  to its perfect  elementary state ; for in that state it is
  both colourless and transparent, and as different in ap-
  pearance from charcoal as any substance can possibly
  be.  This ring which I wear on my finger, owes its bril-
  liancy to a small piece of carbone.
    Caroline.  Surely you are jesting, Mrs. B;
    Emily.   I thought that your ring was diamond  ?
    Mrs. B.  It is so. But diamond is-nothing more than
  carbone in its purest and most perfect state
    Emily    That is astonishing ! Is  it possible to  see
  two things apparently more different than  diamond and
  oharcoal ?                               .
    Caroline.  It  is, indeed, eurtous to think  that wc
  adorn ourselves with jewels of charcoal ?
     Mr*. B.  When you are better acquainted with the
  nature of chrystalization, in which state bodies are gen-
  erally the  purest,  you will  more readily  conceive the
  possibility of  carbone  assuming the transparency and:
  brilliancy of diamond.                   <  m.
     There are many other substances, consisting  chiefly
                           L 2 
m
 ©f carbone, that are remarkably white.  Cotton, for in-
 stance! is almost wholly carbone.
   Caroline.   That I own, I never could have imagin-
 ed !—But pray, Mrs. B   since it is known of what  sub-
 stance diamond and cotton are  composed, why should
 they not be manufactured, or imitated,  by some chem-
 ical process, which would render them much  cheaper
 and more plentiful  than the present mode of obtaining
 them ?
   Airs. B.   You might as well my dear  propose  that
 we should make  flowers and  fruit, nay perhaps  even-
 animals by a chemical process ; for it is known of what
 these bodies consist, since every thing which we are
 acquainted with in  nature, is formed from the various
 simple substances that we have enumerated.  But  you
 must not suppose that a knowledge of the component
 parts of a body will in every case  enable us to imitate
 it.  It is much less difficult to decompose bodies,  and
 discover of what materials they  are made, than  it is to
 recompose them.   The first of these processes is call-
 ed analysis, the last synthesis   When  we are able to
 ascertain  the nature of a substance by both these  me-
 thods, so that the result  of one  confirms that of  the
 other, we obtain the most complete  knowledge of it
 that we are capable of acquiring.  This is the case
 with water,  with  the atmosphere, with  most  of. the
 oxyds,  acids, and neutral salts, and  with  many  other
 compounds.   But  the more complicated combinations
 of nature, even in the mineral kingdom, are in gene-
 ral beyond our reach, and any attempt to imitate organ-
 ized bodies must ever prove fruitless ;  their formation
 is a secret that rests in the bosom  of the Creator.   You
 sec, therefore, how vain it would be to attempt the form-
 ation of cotton by chemical means.    But,  surely, we
 have no reason to regret our inability* in this instance,
 when nature has so clearly pointed a  method of obtain-
 ing it in perfection and abundance.
   Caroline.   I did  not  imagine that the  principle of
 life could be  imitated by the aid of chemistry ; but it
did not appear to me ridiculous to suppose that chemists
might attain a perfect imitation of inanimate nature.
   Mrs.  B.   They have succeeded in  this point in a- 
res
variety  of iustances ; but, as you  justly observe,  the-
principle of life,  or even the minute and intimate  or-
ganization of the  vegetable kingdom, are secrets that
have almost entirely eluded the researches of philoso-
phers ; nor do I  imagine that human art will  ever be
capable of investigating them with complete success.
   Emily..  But diamond, since it consists merely of one
simple unorganized substance,  might b«t one would.
think,  perfectly imitable by art ?
   Mrs. B.   It is sometimes as much beyond our power
to obtain a simple body in a state of perfect purity, as it
is to imitate a complicated combination ; for the opera-
tions by which nature decomposes bodies are frequent-
ly as inimitable as those which she uses for their com-
bination.   This is the  case with carbone; all the ef-
forts of chemists to separate it entirely from other sub-
stances, have been fruitless, and in the purest state in
which it can be obtained by art, it still retains a portion
of oxygen, and probably of some other foreign ingre-
dients.  It is in the diamond alone, as I have observed
hefore, that carbone is  supposed to exist  in its perfect
form ;  we are ignorant of  the means which nature em-
ploys to bring it to that state ; it may probably be the
work of ages, to purify, arrange,  and unite the  parti*
cles of carbone in the form of diamond.   And with re-
 gard to our artificial carbone, which  we  call charcoaV
 we must consider it as an oxyd of carbone ; since, what-
 ever may  be the means employed for obtaining it, it
always retains a  small portion of oxygen.   Here is
some  charcoal in the purest state we can procure it:
you see that it is a very  black,  brittle, light, porous
substance, entirely  destitute of cither taste or smell.
 Heal,  without air, produces no alteration in it, as it is
not volatile; but on the contrary,  it invariably remains
at the  bottom of the  vessel after all  the  other parts of
the  vegetable are evaporated.
   Emily.  Carbone is, no  doubt, combustible,  since
ypu say that charcoal  would absorb oygen if air was
admitted during its preparation ?
   Caroli?ie.   Unquestionably.  Besides, you know, Em-
ily,  how much it is used in cooking.   But pray what is 
116
fhe reason that charcoal burns without smoke, whilst &>
wood fire smokes so much ?
   Mr*. B.  Because, ip the conversion' of wood  into
ehavcoal/ the volatile particles of the former have been
evaporated'.
   Caroline.  Yet I have frequently seen charcoal bu m
with flame;  therefore  it  mu it, irr that case,  contain
some hydrogen-.
   Mr*. B.  Very true ; but you must recollect that
charcoal,  especially that  which is used for commoni
purposes, is very far from being pure.   It generally re-
tains, as  we have  seen, not only a small  quantity of
oxygen,  but also some remains of the various other
component parts of vegetables, and hydrogen particu-
larly, which accounts for the flame in  question.
   Caroline.  But what  becomes of the  carbone itself
(luring its combustion ?
   Mrs. B.   It gradually combines with the oxygen 06
the atmosphere, in the same way as sulphur and phos-
phorus, and, like those substances, it  is converted into*
a  peculiar acid,  which flies off in a  gaseous  form.
There is this difference, however, that tbe  acid is not*
in this instance,  as in the two cases just mentioned, a
mere condensable vapour, but a permanent elastic fluid,.
which always  remains in  the' state  of gas, under any
pressure and*at any temperature-.  The nature of this,
acid was first ascertained by Dr. Black,  of Edinburgh ;.
and, before the  introduction of the new nomenclature,
it  was called fixed air:  It is now distinguished  by  the
more appropriate name of carbonic acid gas,
   Emily.  Carbone, then) can be volatilized by burn-
ing, though, by heat alone, no such effect is produced ?
   Mr*. B.  Yes; but then  it is no longer  simple car-
bone, but an> acid of which  carbone  forms the basis.
In this  state, carbone retains no  more  appearance of
solidi.y or corporeal form,  than  the basis of any other
gas.   And you may,  I think, from this instance, de-
rive a more clear idea of the basis of the oxygen, hy-
drogen, and nitrogen  gasses, the existence of which,
as  real bodies,  you seemed to doubt, because they were
Rot to be obtained simply m a solid form. 
117
  "Emily.  That is true ; we may conceive the basis of
the oxygen, and of the other gasses, to be solid, heavy
substances, like carbone ; but so much expanded by ca-
loric, as to become invisible.
   Can-oline. But does not the carbonic acid gas partake
of the blackness of charcoal ?
   Mrs. B.  Not in the least.   Blackness, you know,
does not appear to be essential to carbone, and it is pure
carbone, and not charcoal, that  we must consider as
the basis of carbonic acid.  We shall make some car-
Ixinic acid, and, in opder to hasten the process, we shall
burn the carbone in oxygen gas.
   Emily.  But how can you make carbonic acid, unless
you can burn  diamond; since that alone is pure car-
bone ?
   Mr*. B.  Charcoal will answer the purpose still bet-
ter ; for the carbone being, in  that state,  already com-
bined with some portion of oxygen, it will require less of
that principle  to comple its oxygenation.
   Caroline.  But is it possible to burn diamond ?
   Mr*. B.  Yes, it is ; and, in order to effect  this com-
bustion, nothing more is required than to apply a suffi-
cient degree of heat by means of the blow-pipe, and of'
a stream of oxygen gas.  Indeed it is by burning  dia-
mond that its  chemical nature has been ascertained. It-
is long since  it has  been known, as a combustible sub-
stynrc, but it  is  within these few years only that  the
product of its  combination has been proved to be pure
carbonic acid.   This discovery is due to Mr,. Tenant.
But still more recent  experiments  have shown, that
diamond requires a greater proportion  of oxygen than
charcoal to be converted into carbonic acid.  It appears
that 15 parts of diamond require  85 parts of oxygen to
form 100  parts of carbonic acid ; whilst 28 parts of char-
coal take up  only  72  parts of oxygen to produce  100
parts of carbonic acid ;  from which it is naturally infer-
red that carbone, in the state of charcoal, is already com-
bined with a portion of oxygen.
   Now let us  try to make some carbonic acid___Will
you, Emily, decent  pome oxygen gas from  this large
jar into the receiver in which we are to burn the  oar>- 
118
bone; and I shall introduce this small piece of char-
coal, with a little lighted tinder, which will be necessa-
ry to give  the first impulse to the combustion.
  Emily.   I cannot conceive  how so small a piece of
tinder, and that but just lighted, can  raise the temper-
ature of the carbone sufficiently to set fire to it; for it
can produce scarcely any  sensible heat, and it hardly
touches the carbone.
   Mr*. B.  The tinder thus kindled has only heat e-
nough to  begin its own combustion, which, however,
soon becomes so rapid in the oxygen  gas, as to raise the*
temperature of the charcoal sufficiently for this to burn
likewise, as you see is now the case.
   Emily.   I am  surprised that the combustion of  car-
bone is not more brilliant; it does not disengage near
so much  light or caloric as phosphorous, or sulphur.
Yet, since it. combines with so much oxygen, why is
not a proportional quantity of light and heal disengaged
from the decomposition of the oxygen gas ?
   Mrs. B,  It is not surprising that less light and heat
should be disengaged in this than in almost  any other
combustion, since the oxygen,  instead of entering into
a solid or a liquid combination, as it  does in  the phos-
phoric and sulphuric acids, is employed in forming a-
nother elastic fluid.
   Emily.   True;  and on second consideration,  it ap-
pears, on the contrary,  surprising  that  the  oxygen
should, in its  coronation with eiuboue-  icU.in  a suffi-
cient portion of caloric to nn.niuir-. both substances iii.a
gaseous state.
   Caroline.  We may then judge of the degree  of so-
lidity in which oxygen is-com! ined in.a burnt body, by
the quantity of caloric lib-rate .1 during its combustion  ?.
   Mrs. B.  Yes ;  provided mat y~'i take into the  ac-
count the quantity of oxygen abs? ; oed by the combus-
tible body, and observe the proportion which the caloric
bears to it.
   Caroline.  But why should the water, oiler the com-
busiion of caiboite,  rise in the  receiver  since the ga*
within it retains an aeriform stat* I   ■ 
TX9
   TVJr*.  B.  Because carlxmic acid gas is more dense,
■and consequently occupies less space than oxygen gas;
 the water therefore rises to fill the vacuum formed by
 the diminution of volume of the gas.
   Caroline.  That is very clear : and the condensation
 of the new gas depends, I  suppose,  on the quantity of
 caloric that has been disengaged*
   Mrs.  B.  The gas must be decreased in volume,
 from that circumstance,  in a certain  proportion ;  but
 its density is still further increased by the addition of the
 carbone.   But besides this condensation, there is in our
 experiment another cause of the diminution of volume,
 which is, that carbonic acid gas, by standing over water,
 is gradually absorbed by it, an effect which is produced
 by shaking the receiver.
   Emily.  The charcoal is now extinguished,  though
 it is not nearly consumed ; it has such  an extraordinary
 avidity for oxygen, I suppose, that the  receiver  did  not
 contain enough to satisfy the whole.
   Airs. B.  That is certainly the case ; for if the com-
 bustion was performed in the exact proportions of 28
 parts of carbone to 72 of oxygen, both these ingredients
 would disappear, and  100 parts of carbonic acid would
 be produced.
   Caroline.  Carbonic acid must be a very strong acid,
 since it contains so  great a proportion  of oxygen ?
   Airs. B.  That is a very natural inference; yet it is
 erroneous.  For  the  carbonic is the weakest of all the
 acids.   The strength of an acid  seems to depend upon
 fhe nature of its basis  and its mode of  combination, as
 well as upon the proportion of the acidifying principle.
 The same quantity of oxygen that will convert some
 bodies into strong acids, will only be  sufficient simply to
 oxydate others.
   Caroline- since this acid is so weak, I think chem-
ists  should have called it the carbonous, instead of the
carbonic acid.
   Emily.   But, I suppose, the  carbonous acid is still
weaker, and is formed by burning carbone in atmosphe-
rical air.
   Mr*.  B.  No,  my  dear.   Carbone does not ap- 
120
pear to be susceptible of more than  one  degree of
acidification, whether burnt in oxygen gas or atmosphe-
rical air.  There is therefore no carbonous acid.
  It has indeed been lately discovered, that carbone may
be converted in a gas, by  uniting with a smaller pro-
portion of oxygen ; but as this gas does not  possess any
acid properties, it is  no more than an oxyd  ; and in or-
der to distinguish it from charcoal, which contains a still
smaller proportion of oxygen, it  is  called gaseous oxyd
of carbone
  Caroline.   Pray is not carbonic acid a very whole-
some gas to breathe, as it contains so much oxygen ?
  Mr*. B.   On the  contrary, it is extremely  perni-
cious.  Oxygen, when  in  a state  of combustion with
other substances, loses, in almost  every  instance its
rcspirable properties, and the salubrious effects  which
it has on the animal economy  when in its uncombined
state. Carbonic acid is not onjy unfit for respiration, but
extremely deleterious if taken into the lungs.
  Emily.   You know Caroline, how very unwholesome
the fumes of burning charcoal are reckoned.
  Caroline.   Yes ;  but to confess the truth, I  did  not
consider that  a charcoal  fire produced  carbonic acid
gas.—Pray, can this gas be condensed into a liquid ?
   Mr*. B.  No: for, as I told you before, it is a perma-
nent elastic fluid.   But water can absorb a certain quan-
tity of this gas, and  can  even be impregnated with it,
in a very strong degree, by the assistance of agitation
and pressure, as I am going to show you.   I  6hall de-
cant  some  carbonic  acid  gas into this bottle,  which I
fill first with water, in order to exclude the  atmospher-
ical  air ; the gass is then introduced through the water,
which you see  it displaces, for it will not mix with it in
any quantity  unless strongly agitated, or allowed to
stand  over for some time.  The bottle  is now about
half full of carbonic acid gas, and thejother half is  still
occupied  by the water.  By corking the bottle,  and
then  violently   shaking it, in  this way, 1 can  mix the
gas and water together.—Now will you taste it ?
  Emily.   It has a distinct  acid taste.
  Caroline.   Yes, it is sensibly  sour, and appears full
of little bubbles. 
121
  Mr*. B.  It possesses likewise all the other  proper-
ties of acids,  but of course in a  less degree than the
pure carbonic acid gas,  as it is so much diluted by wa-
ter.
  This is a kind of artificial  Seltzer water.   By analy-
sing that which is produced by nature, it was found to
contain scarcely  any thing  more  than common water
impregnated with a certain  proportion of carbonic acid
gas.   We are, therefore, able  to imitate it, by mixing
those  proportions of water, and carbonic acid.  Here,
my dear,  is an instance, in  which,  by a chemical pro-
cess, we can exactly copy the operations of nature ; for
the artificial  Seltzer waters can be made in every res-
pect  similar to those of nature : in one point, indeed,
the former have an advantage, since they  may be pre-
pared stronger, or weaker,  as occasion requires.
   Caroline.  I thought I had tasted such water before.
But what renders it so brisk and sparkling ?
   Mrs. B.  This sparkling, or effervescence, as  it is
called, is always occasioned by the action of an elastic
fluid escaping from a liquid ; in the artificial Seltzer wa-
ter it  is  produced  by  the  carbonic acid,  which being
lighter than the water in which it was  strongly conden-
sed, flies off with great rapidity the instant the bottle is
uncorked ; this makes it necessary to  drink it immedi-
ately.  The bubbling that took place in this bottle was
but trifling, as the water was but very  slightly  impreg-
nated with carbonic acid.   It requires a particular ap-
paratus to prepare the gaseous artificial mineral waters.
   Emily.  If,  then, a bottle of Seltzer water remains
for any length of time uncorked, I suppose it returns to
the state of common water  ?
   Mr*. B. The whole  of the carbonic acid gas, or very
nearly so, will soon  disappear ;  but there is likewise in
Seltzer water a very small quantity of soda, and of a few
other  saline or earthy ingredients, which  will remain
in the water, though it should be kept uncorked for any
length of time.
   Caroline.  I have often heard of people drinking soda
 water, pray what sort of water is that ?
M 
,122
   -Mrs. B.  It is a kind of artificial Seltzer water, hold-
 ing in solution,  besides the gaseous  acid, a particular
 saline substance, called soda, which imparts to the wa-
 ter certain medicinal qualities.
   Caroline..  But how can these  waters be so  whole-
 some, since carbonic acid is so pernicious ?
   Airs. B.  A  gas we may conceive though very pre-
 judicial to breathe, may be beneficial to the stomach.—
 But it would be of no use to attempt explaining this more
 fully  at present.
   Caroline.  Are waters never impregnated with other
 gasses ?
   Mr*.  B.  Yes ; there are several  kinds of gaseous
 waters.   I forgot to tell you that waters have for some
 years past been prepared, impregnated both  with oxy
 gen and hydrogen gasses.  These are not  an imitation
 of nature, but are altogether obtained by artificial means.
 They have been lately used medicinally,  particularly
 abroad, where,  I understand, they have acquired some
 reputation.
   Emily.  If I recollect right, Mrs. B  you told us that
 carbone was capable of decomposing water ;  the affin-
 ity between oxygen and carbone must therefore be grea-
 ter than between oxy gen and hydrogen  ?
   Airs.  B.  Yes ; but this is not the rase unless their
 temperature be  raised to a certain degree.  It is only
 when carbone is red hot, that it is capable of separa-
 ting the oxygen from the hydrogen.   Thus, if a small
 quantity of water be thrown on a red hot fire, it will in-
 crease, rather than extinguish the combustion ; for the
 coals or  wood (both of which contain a great quantity
 of carbone) decompose the water, and thus supply the
 fire both with oxygen and hydrogen gasses.  If,  on the
 contrary,  a large mass of water be thrown over the fire,
 the diminution of  heat thus produced  is such that the
 combustible matter loses the power of decomposing the
 water, and the fire is extinguished.
   Emily.   I  have  heard that fire engines sometimes
 do more harm than good, and th-..t they actually increase
 the fire when they cannot throw  water enough  to ex-
tinguish it.  It must be owing no doubt, to the deccnv 
123
position of the water by the carbone during the confla-
gration.
   Mr*. B.  Certainly.—The apparatus which you see
here (Plate VIII  Fig.  20 J may be used to exemplify
what we have just said.   It consists in a kind of open
furnace, through  which a  porcelain  tube,  containing
charcoal, passes.  To one end of the tube is adapted a
glass retort with water in  it; and the other end  com-
municates with a receiver placed on the water bath.  A
lamp being applied to the retort, and the water made
to boil, the  vapour is  gradually conveyed through the
red hot charcoal, by which it is decomposed ;  and the
hydrogen gas which results from this decomposition is
cofllcted in the receiver.   But the  hydrogen thus ob-
tained is far from being pure ; it retains in  solution  a
 minute portion of carbone, and contains  also a quantity
 of carbonic acid.  This  renders it  heavier  than pure
 hydrogen gas, and gives it some peculiar properties :
 it is distinguished by the  name of carbonated hydrogen
 gas.
.   Caroline.  And whence  does it obtain the  carbonic
 acid that is mixed with it ?
   Emily.   I believe  I can answer that question,  Carol-
 ine—From the union of the oxygen (proceeding from
 the decomposed water) with the  carbone,  which, you
 know, makes  carbonic acid.
    Caroline.  True ;  I  should  have recollected that.—
 The product of the decomposition of water by red hot
 charcoal, therefore,  is carbonated  hydrogen  gas  and
 carbonic acid gas.
    Mr*.  B. You are perfectly right now.
    C.irbone is frequently  found combined with hydrogen
 in a  state of solidity, especially in coals, which owe
 their combustible nature to these two principles.
    Emilu.   Is it the  hydrogen, then; that produces the
 flame of coal a ?
    Mrs. B.  It  is so;  and when all the  hydrogen is
 consume!, the  carbone  continues  to bum  without
 flame.   But again the  hydrogen gas produced by the
 combustion of coals is not pure ; for,  during the com-
 bustion, particles of carbone are successively volatilized 
124
 with the hydrogen, with which they form what is called
 a hydro-carbonate,  which is the essential combustion.
   Carbone  is a very  bad conductor  of heat; for  this
 reason it is  employed (in conjunction with other ingredi-
 ents) for coating furnaces and other chemical apparatus.
   Emily.   Pray what is the use of coating furnaces ?
   Mr*. B.   In most cases, in which a furnace is used,
 it is necessary to produce and preserve a great  degree
 of heat, for which purpose every possible means are
 used to prevent the heat from escaping by communica-
 ting with other bodies, and this object is attained by
 coating over the inside of the furnace with a kind of
 plaster, composed of materials that are bad conductors
 of heat.
   Carbone combined with a small quantity of iron, forms
 a compound called plumbago, or black lead, of which
 pencils are made.  This substance,  agreeably to  the
 nomenclature,  is a carburet of iron.
   Caroline.   Why, then, is it called black lead ?
   Mrs. B.  I really cannot say; but it is certainly a most
 improper name for it,  as there is not a particle of lead
 in the composition.  There is another  carburet of iron
 though united only to  an  extremely  small  proportion
 of carbone,  acquires very remarkable properties ;  this
 is steel.
   Caroline.   Really ;  and yet steel is much harder than;
 iron ?
   Mr*. B.   But carbone is not ductile, like iron,  and
 therefore may render the steel more  brittle, and pre-
 vent its bending so easily.  Whether it is that the  car-
 bone  by introducing itself into the pores of the iron,
 and by filling them, makes the metal both harder  and
 heavier; or whether  this change depends upon some
 chemical cause, I cannot pretend to decide   But there
 is a  subsequent operation, by which  the hardness of
 steel is very much increased, which simply consists in
heating the  steel till it is red hot, and then plunging it
into cold water.
  Carbone besides the  combination just mentioned,  en-
ters into the composition of a vast number  of natural
 productions, such, for instance, as all the various kinds 
125
of oils, which result from the combination of carbone?
hydrogen, and caloric, in various proportions
  Emily.   I thought  ihnt carbone, hydrogen, and ca-
loric  formed  carb mated hydrogen gas ?
  Mrs B.  That is  the  case when a small  portion of
carbonic acid  gas is  held  in solution by hydrogen gas.
Different proportions of the  same principles, together
w'nh  the circumstances  of their union, produce  very
different combinations ; of this you will see  innumera-
ble examples.  Beride-, we are not now talking of gas-
ses, but of carbone and hydrogen, combined  only  wi:h
a •  uantity of caloric sufficient to bring them to the con-
sistency of oil or fat.
   Caroline.   But the oil and fat are not of the same con-
sistence ?                                           .
   Mrs. B    Fat is only congealed oil ; or oil,  melted
fat   The one requires a  little more heat to maintain  it
in a fluid state, than the other   Hwe  you  never ob-
served the fat of meat turned to oil by the caloric it has
imbibed from the fire ?
   Emily   Yet oils in general, as salad oil, and la mp oil,
 do not turn to fat when cold ?
    Mrs. B.   Not at the common temperature of the at-
 mosphere, because they retain too much caloric to con-
 geal at that temperature  ; but if exposed to  a sufficient
 degree of co.d, their latent heat is extricated, and  they
 become  solid tat substances.  Have you never seen sal-
 ad oil frozen  in winter?
    Emily.   Yes ; but it appeals to me in a state very dii-
 fereot from animal fat.
    Mr*. B   Ti.e essential  cons ituent parts of  either
  vegetable or  animal oils are the same, carbone  and hy-
  drogen ;  the variety arises from  the  different  propor-
  tions of these substances, and from other accessary in-
  gredients that may be mixed with them.   The oil of a
  whale, and the oil  of'rases, are,  in their essential con-
  stituent parts, the same ;  but the one is impregnated
  with the offensive particles of animal matter, the other
  with the delicate perfume of a flower.
    The difference of fixed  oils, and volatile  or essential-
  oils, consist  also in the  various proportions of caibone
                       H2 
126
and hydrogen. Fixed oils are those which will not evap-
orate without being decomposed ; this is the case  with
all common oils, which contain a greater proportion of
carbone than  the  essential oils.   The essential  oils
(which comprehend the whole  class  of essences  and
perfumes)  are  lighter; they contain more equal pro-
portions of  car'ione and hydrogen, and are volatilized or
evaporated  without being decomposed.
  Emily.   When you say that one kind of oil will evap*
orate, and the  other be decomposed, you mean, I sup-
pose, by the application of heat ?
  Airs. B.   Not  necessarily ;  for there are oils that
will evaporate  slowly  at the common temperature of
the atmosphere ;  but for a more rapid volatilization, or
for their decomposition, the assistance of heat is requir-
ed.
  Caroline.  I  shall now remember,  I think,  that  fat
and oil are really the same substances, consisting both
of carbone  and hydrogen ; that in fixed oils the carbone
preponderates,  and heat produces  a decomposition ;
while, in essential  oils, the proportion of  hydrogen is
greater, and heat produces  volatilization only.
  Emily.   I suppose the reason why  oil burns so well
in lamps, is because  its two constituents are so  com-.
bustile ?
  Mr*. B.  Certainly ; the  combustion of oil  is just
the same as that  of a candle; if  tallow, it is  only oil
in a concrete  state ; if wax, or spermaceti, its  chief
chemical ingredients are still hydrogen and carbone.
  Emily.   I wonder, then,  there should be so great a
difference between tallow and wax ?
  ilfrs. B.  I must again repeat that the same substan-
ces, in different proportions, produce results that have
sometimes scarcely  any resemblance to each other.
But this is  rather a general remark that 1 wish to im-
press upon  your mind, than one which is applicable to
the present case ; for tallow and wax  are  far from  be-
ing very dissimilar ;  the chief difference consists in
the wax being a purer compound of carbone and hy-
drogen  than the  tallow, which retains more  of the
gross particles of animal matter.   The combustion of 
127
a candle, and that of a lamp, both produce water and
carbonic acid gas.  Can  you  tell me how  these are
formed ?
  Emily.   Let me think.....Both the candle and
lamp burn  by means of fixed oil—.this is decomposed
as the combusUon goes on ; and  the constituent parts
of the oil being thus separated, the carbone unit us to
a portion of oxygen from  the atmosphere to form  car-
bonic acid  gas,   whilst the  hydrogen  combines with
another portion of oxygen,  and forms wiui it water.
The products therefore, of the combustion of oils, are
water and carbonic acid gas.
   Caroline   But we see neither water nor carbonic  a-
 cid produced by  the combustion of a candle ?
   Mr*.  B.  The carbonic acid gas, you know is invisi-
 ble, and the water being in a state of vapour, is  so like-
 wise.   Emily is perfectly correct in her explanation,
 and I am very much pleased with it.
   All  the vegetable acids consist of various proportions
 of carbone  and hydrogen, acidhVd  by oxygen.  Gums,
 sugar, and starch,, are likewise composed of these in-
 gredients ; bin as the oxygen which they  contain is not
 sufficient to  convert them into acids, they are classed
 with the oxyds, and called vegetable oxyds.
   Emily.  I am  very  much delighted with all these
 new ideas ;  but  at the same time, I cannot help being
 apprehensive that I may forget many of them.
   Airs. B.  I wruld advise you to take notes, or, what
 would answer better still, to write  down, after  every
 lesson, as  much  of it as you  can recollect.   And, in
 order to give  you a little assistance,  I shall lend you
 the beads or index, which  I occasionally consult  for
 the hakeof preserving some method and arrangement
 in  these conversations.   Unless you follow some such
 pi ah,  you  cannot  expect  to retain nearly all  that you
 learn, how great  soever be the impression it may make
 on you at first.
   Emily.  I will certainly follow your advice.—Hither-
 to I have  found that I recollected  pretty well what you
 have taught  us ;  but the history of carbone  is  a  more 
128
 extensive  subject than any of the simple bodies we
 have yet examined.
   Mr* B  I have little more to say on carbone at pre-
 sent, but hereafter you will see that it  performs a con-
 siderable part in most cbemic il operations
   Caroline.  That is, I suppose,  owing to its enteting
 into tlie composition of so great a  variety of substances ?
   Mr*. B.  Certainly ; it is the- basis, you  have seen,
 of all vegetable matter ;,and you will find  that it is very
 essential to the process of aniinahzation. But in the min-
 eral  kingdom also, particularly in its form of carbonic
 acid, we shall often discover it combined  with  a great
 variety of Mibstances.
   In  chemical operations, carbone is particularly use-
 ful, from its very great attraction for oxygen, as it will
 absorb this substance from  many oxygenated or burnt
 bodies, and thus deoxygenate, or unburn them, and res-
 tore them to their original state.
   Caroline.  I do not understand how a body can be
 unburnt, and restored to its original state.  This piece
 of tinder, for  instance, that  has been  burnt, if by any
 means the oxygen was extracted from it, would not be
 restored to its former state of linnen ;  for its texture is
 destroyed by burning, and lhat must be the  case with
 all organized or manufactured substances, as you obser-
 ved in a former conversation.
   Mrs. B.   A compound body is decomposed by com--
 bustion, in a way which generally precludes the  possi-
 bility of restoring it to its former state ;  tlie oxygen, for
instance, does not become  fixed in the tinder, but it
 combines  with its  volatile parts,-and flies off'  in  the
 shape of gas. or watery vapour.  You see therefoie,
 how  vain  it would be to attempt the recomposition of
 such  bodies.  But with regard to simple bodies, or at
 least bodies whose constituents are not  disturbed by the
 process of oxygenation or  deoxvgenation, it is often
 possible to restore them, after combust ion to their ori-
 ginal  state—The metals, for instance,  undergo  nooth--
 er alteration by  combustion than a combination with
oxygen ; therefore,  when  the oxygen is taken from
 thwm,they return to their pure metalhc sute.   But L 
129
shall say nothing further of this at present, as the me-
tals will furnish ample subject for another morning; and
they are the class of simple bodies that come next un-
der our consideration.
Condensation ix.
                    On  Metals..

                     Mrs. B.

  The  metals,  which we are now to examine, are
bodies of various different nature from those which we
have hitherto considered.   They do not, like  the ele-
ments of gasses, elude  the immediate observation of
our senses :  for  they are the most brilliant, the  most
ponderous, and the most palpable substances in nature.
  Caroline.  I doubt, however, whether the metals will
appear to us so interesting, and give us so much enter-
tainment as  those mysterious elements which conceal
themselves from our view.  Besides, they  cannot af-
ford so much novelty  ; they are bodies  with which we
are already so well acquainted.
  Mr*. B.  But the acquaintance, you will soon per-
ceive, is but very superficial ; and I trust that  you will
find both novelty and entertainment in considering the
metals in a chemical point of view.   To treat of this
subject fully, would require a whole course of lectures ;
for  metals form  of themselves a most important branch
of practical  chemistry.   We must, therefore, confine
ourselves to a general view of them.   These bodies
are seldom found naturally in their metalic form ;  they
are generally more or less oxygenated or combined with
sulphur, earths  or acids, and are often blended  with
each other.   They  are  found  buried in the bowels  of 
fhe earth in  most parts of the globe,  but chiefly irt'
mountainous  districts, where the surface of the globe
has suffered  from  earthquakes, volcanoes, and other
convulsions of nature.  They are there spread in strata
of beds, called veins, and these veins are  composed of
a  certain  quantity  of  metal, combined with  various
earthy substances, with  which they form minerals of
different nature and appearance, which are called ores.
   Caroline.  I am now  amongst  old acquaintance, for
my father has a lead  mine in Yorkshire,  and  I have
heard  a great deal about veins of ore, and  of the roast-
ing and smelting of the lead ; but, I confess, that I do
not understand in what these operations consist.
   Mr*. B.  Roasting is the process by which the vola-
tile parts of the ore are evaporated ; smelting, that by
which the pure metal is  afterwads separated from the
earthy remains of the ore.  This is done by throwing
the whole  into  a furnace,  and mixing with it  certain
substances, that will combine with the earthy parts, and
other foreign ingredients of the ore  ; the metal being
the heaviest falls to the bottom, and  runs out by  proper
openings, in its pure metalic state.
   Emily.   You told us in a preceding lesson that me-
tals had a strong  affinity for  oxygen.  Do they  not,
therefore, combine with oxygen, when strongly heated
in the furnace, and run out in the state of oxyds  ?
   Mr*. B.   No ;  for the scoriae, or oxyd,  which soon
forms on the surface of the fused metal, when it is
oxydable, prevents tlie air from having any further in-
fluence on the mass ;  so  that neither combustion nor
oxygenation can take place.
   Caroline.   Are all metals combustible ?
   Mr* B.  Yes, without exception ;  but  their attrac-
tion for oxygen varies extremely :  there are some that
will combine with it  only at a very high temperature,
or by the assistance of acids ; whilst  there are others
that oxyclate of themselves very  rapidly,  even at the
lowest temperature,  as manganese,   which  scarcely
ever exists in its metallic state, as it immediately absorbs
oxygen on being exposed to the air, and crumbles to an-
oxyd in the course of a few hours. 
1S1
  Emtly.   Is it not from that oxyd that  you extracted
ihe oxygen gas ?
  Airs. B.  It is ;  so that, you see, this metal attracts
oxygen at a low temperature, and parts with it  when
 strongly heated.
  Emily.   Is there any other metal that oxydates at the
temperature of the atmosphere ?
   Mr*.  B.  They all do, more or less, excepting gold,
 silver, and platina.
   Copper, lead, and iron, oxydate slowly in the air, and
 cover themselves with a  sort of rust, a process  which
depends on the gradual conversion of the surface into
an oxyd.   This  rusty  surface  preserves the interior
 metal from oxygenation, as it prevents the air from com-
 ing in contact with it.   Strictly speaking, however the
 word rust applies ooly to the oxyd, which forms on the
 surface  of iron,  when  exposed  to  air and  moisture,
 which oxyd appears to be mined  with a small  portion
 of carbonic acid.
   Emily.  When metals oxydate from the atmosphere
 without an elevation of temperature, some  light and
 heat, I suppose, must be disengaged,  though not in suf-
 ficient quantities to be sensible.
   Mr*.  B.   Undoubtedly ;  and,  indeed, it is not sur-
 prising  that in this case the light and heat  should not
 be sensible, when you consider how extremely slow,
 and, indeed,  how  imperfectly, most metals oxydate
 by mere exposure  to the atmosphere.  For the  quan-
 tity of oxygen with which metals are capable of com-
 bining, generally depends  upon  their  temperature ;
 and the absorption  stops at various points of oxydation,
 according to the degree to which their temperature  is
 raised.
   Emily.   That seems very  natural ; for the  greater
 the  quantity of caloric introduced  into a metal, the fur-
 ther its particles are separated from one  another, and
 the more easily, therefore, can they attract the  oxygen
 and combine with  it.
   Airs. B.   Certainly ;  and besides, in proportion  as
 the resistance diminishes on one  hand, the affinity in-
 creases on the  other.  When the metal oxygenates 
1-3V
 with sufficient rapidity for light and heat to become sen-
 sible, combustion actually takes place.  But this  hap-
 pens only at  very  high temperatures, and  the product
 is nevertheless an oxyd ; for though, as I have just said,
 metals will combine with different proportions  of oxy-
 gen, yet, with the exception of only five of them,  they
 are not susceptible of acidification.
   Metals change colour during the different degrees of
 oxydation which they  undergo.   Lead, when heated in
 contact with the  atmosphere, first becomes grey  ; if its
 temperature be  then raised, it turns yellow, and a still
 stronger heat changes it to  red.   Iron becomes succes-
 sively a green, brown, and white oxyd.   Copper chang-
 es from brown to blue, and lastly green.
  Emily.   Pray, is  the  white lead  with which  houses
 are painted prepared by  oxydating lead ?
  Mr*. B.  Yes ;  almost all the  metallic  oxyds are
 used as paints.  Red lead is another oxyd  of that me-
 tal.  The various sorts of ochres chiefly consist of iron
 more or less oxydated.  And it is a remarkable circum-
 stance, that if you burn metals rapidly, the light or flame
 they emit during  combustion partakes of the colours
 which the oxyd successi. ely assumes.
  Caroline.  How  is that accounted for, Mr. B. ?  For
 light, you  know, does not  proceed from the burning
 body, but from the decomposition of the oxygen gas  ?
I hope you have  a satisfactory answer to give  me, for
 I am under some apprehensions for my favourite theo-
 ry of combustion ;  and for the world 1 would not have
it overthrown.
  Mr*. B.  Do  not be  alarmed, my dear; I  do not
 think it was ever supposed to be in danger from this cir-
cumstance.  The  corresiondence of the  colour of the
light with that of the oxyd which emits it, is, in all prob-
ability,  owing to some particles of the metal which are
volatilized and carried of by  the caloric.
  Caroline.  Is this then a sort of metalic  gas.
  Emily.  Why is it reckoned so  unwholesome to
breathe the air of a place in  which metals  are melting ?
  Mr*. B.  For this  double reason, that  most metals
in melting oxydate more or less at their surface, and 
 
Apparatus for ths com//MtioH of





metals Iry means  of ojcy/?en  </M







                            fit/. U-A.
 
I 33
 thereby diminish the purity of the air ;  but move es-
 pecially because the particles of the oxyd that are vola-
 tilized by the heat, and breathed with the  air of the
 room are very noxious.   This is particulaaly the  case
 with lead and arsenic.   Besides the large  furnaces  that
 are requited for these fusions, contribute also materially
 to alter the salubrity of the air in  those  places where
 the process is carried on.
   I must shew you some instances of the combustion
 of metals;  it would require the heat  of a  furnace to
 make them burn in the  common air, but if we supply
 tin ;u  with a  stream of  oxygen gas, we may easily ac-
 complish it.
   Caroline.   But it will still, I  suppose, be  necessary
 in son.c degree to raise their temperature  ; for the oxy-
 gen will not be able to penetrate such dense substances,
 unless the caloric forces a passage for'it.
   Mr*.  B.    This, as you  shall see,  is very easily done,
 particularly  if the  experiment be tried upon a small
 scale.—I begin by  lighting this piece  of charcoal with
 the  candle,  and then increase the  rapidity of its com-
 bustion by  blowing upon  it with a  blow-pipe.  (Plate
 IX. Fig. 21.;
   Emily.   That I  do not understand ; for it is not eve-
 ry kind of air, but merely oxygen  gas, that  produces
 combustion.  Now  you said that in breathing we  in-
 spired, but  did not expire, oxygen gas.   Why, there-
 fore, should the air which  you breathe through  the
 blow-pipe,  promote the combustion of the  charcoal ?
   Mrs. B.   Because the air, which has but once pass-
 ed through  the lungs, is yet but little altered, a small
 portion only of its oxygen  being destroyed;  so that a
 great deal more is gained by increasing the rapidity of
 the current,  by means of the blow-pipe,  than is lost in
 consequence of the  air passing once through the lungs,
 as you shall  see—

                    PLATE IX.

  Fig. 21.  Igniting charcoal with a taper and blow-pipe.  Fig.
32. Combuftion of metals by means of a blow-pipe conveying a
 ft ream of oxygen gas from a gas-holder.
                         N 
134
  Emily.  Yes, indeed;  it makes the charcoal burn
much brighter.
  Mrs.  B.  Whilst it is red hot, I shall drop some iron
filings on it, and supply them with a current of oxygen
gas, by  means of this apparatus (Plate IX. 'Fig.  22.)
which consists simply of a closed tin cylindrical vessel,
full of oxygen  gas, with two apertures and stop-cocks,
by one of" which a stream of water is thrown into the
vessel through a long funnel, whilst by the other the
gas is forced out through a blow-pipe adapted to it, as
the water gains admittance.—Now  that I pour water
into the funnel, you may hear the gas issuing from the
blow  pipe—I  bring the charcoal close  to the  current,
and drop the filings upon it.—
   Caroline.  They emit much fhe same  vivid light as
the combustion of thelron wire in oxygen gas.
   Airs.  B.  The process is, in fact, the same ; there
is only some diffeience in the mode of conducting it.
Let us  burn some tin in the same manner—you see
that it is equally combustible—Let us now try some cop-
per—
   Caroline.  This burns with a greenish flame ; it is I
 suppose,  owing to the  colour of the oxyd ?
   Emily.   Pray, shall we not also burn some gold ?
   Mr*. B.  This is not in our power, at least in this
 way.  Gold, silver,  and platina, are incapable ol being
 oxydated  by the greatest heat that we can produce by the
 common  method.   It is from this circumstance  that
 they have been called perfect metals.  Even these, howe-
 ver, have an affinity for oxygen ; but their oxydation or
 combustion can only be performed  by means  of elec-
 tricity.   The  spark given out by the Galvanic Pile pro-
 duces in  the point of  contact a greater degree of heat
 than any  other process ; and it is at this veiy high tem-
 perature  only that the  affinity of these metals for oxygen
 will enable them to act on each  ther.
    I am sorry that I cannot shew you the combustion of
 the perfect metals by  this process, but it requires a con-
 siderable Galvanic  Battery.   You  will,  however, see
 these experiments performed in the most perfect man-
I 
                          135

 »er, when you attend the chemical lectures of the Roy-
 al Institution.                                      '
    Caroline.   I think you said that  the oxyds of metals
 could be restored to their metallic state ?
    Mrs. B.   Yes ; this is called reviving a metal.   Me-
 tals are m general capable of being revived by charcoal,
 when heated red hot, charcoal having, at  that tempera-
 ture, a greater  attraction foi oxygen than the metals.
 You need only therefore, decompose, or unburn the ox-
 yd, by depriving it of its oxygen, and the  metal will he
 restored to its  pure state.
    Emily.   But will  the caibone, by this  operation, be
 burnt, and be converted into carbonic acid ?
    Mrs. B.  Certainly.  There are other combustible
 substances to which  metals  at a high  temperature will-
 part with their oxygen.  They will also yield it to each
 other, according to  their  several  degrees of attraction
 for it; and if the  oxygen goes into a more dense state
 in the metal  which it enters, than it existed in that which
 11 quits, a proportional disengagement of caloric  will
 take place.
   Caroline.^  And cannot the oxyds of gold,  silver, and
 platina, which  are formed by means of the electric fluid
 be restored to  their metallic  state ?
   Mr*  B.  Yes,  they may ; but the intervention of a
 combustible  body is not required ; heat alone will take
 the oxygen from them, convert it into a gas,  and revive
 thenrutal
 _  Emily.  You said that rust was an oxyd of iron ; how
 is it, then, that water, or  merely dampness,  produces.
 it, which, you know, it very frequently does on steel
 grates, or any iron instruments.
   Mr*. B.   In that  case  the metal  decomposes  the
 water, or dampness (which is nothing but water in  a
 state of vapour), and obtains the oxygen from it.
   Caroline. I thought  that it was necessary to bring me-
 tals  to a very high temperature to enable  them to de-
 compose water.
   Airs. B   It is so, if it  is  required that the process
should  be  performed rapidly, and if any considerable
quantity is to  be decomposed.  Rust you know is some^ 
136
times months  in forming, and  then it is only the sur-
face of the metal that is oxydated.
  Emily.  Metals, then,  that do not rust,  arc incapa-
ble  of spontaneous oxydation, either by air or water ?
  Mm. B.   Yes ; and this is the case with the perfect
metals,  which on that account,  preserve their metallic
lustre so well.
  Caroline.   When metals are oxydated by  means of
water, is there no sensible disengagement of light and
heat ?
  Mr*.  B.   No ; because the oxygen exists already in
a dense state in water ; and the portion  of caloric  that
it parts with combines  with the hydrogen to convert it
into a gas.
  Emily. Are all metals capable of decomposing waterr
provided their temperature be  sufficiently raised ?
  Mr*. B.  No ; a certain degree of attraction is re-
quisite, besides the assistance of heat.   Water you re-
collect,  is  composed of  oxygen and hydrogen ;  and
unless the affinity of the metal for oxygen be stronger
than that of hydrogen, it is  in  vain  that we raise its
temperature, for  it cannot take the oxygen  from the
hydrogen.   Iron, zinc, tin, and antimony, have a strong-
er  affinity  for oxygen than  hydrogen has, therefore
these four metals are  capable of decomposing water.
But hydrogen having an advantage over all the  other
metals with respect to its affinity for  oxygen, it not only
withholds its oxygen from  them, but is  even capable
in certain circumstances, of taking the oxygen from the
oxyd  of these metals.
  Emily.  I confess that I do not quite understand why
hydrogen can  take oxygen from those metals that do
not decompose water.
  Caroline.  Now I think I do perfectly.   Lead for in-
stance will not decompose water, because it has not so
strong an attraction for oxygen, as hydrogen has.  Well,
then, suppose  the  lead  be in a state  of oxyd ;  hy-
drogen  will take the oxygen  from  the lead,  and unite
with it to form water, because  hydrogen has a stronger
attraction for oxygen, than oxygen has for lead ; and it 
13T
is the same with all the other metals which do not de*-
compose  ^ater.
  Emily.   1 understand  your evplanation.  Coroline,
very well;  and I ini igine that it is because  lead can-
not decompose water that v iM so much employed for
pipes for conveying that fluid.
  Mrs. B   Ceriainly ; lead is, on that account, par-
ticularly appropriate to such purposes ; whilst, on the
contrary,  this metal, if it was oxydable by water,  would
impart to it very no ions qualities, as all oxyds of le..d
•re  more or less perm. ions.
  Bui,  with n-gard to the oxydation of metals, there
is a mode of effecting it more powtiful than  either of
the former, which is by means of acids.   These, you
know,  contain a  much greater proportion of o-:ygen
than either air or water; and will, most of them, easi-
ly yield it to metals.  Have you never observed,  that if
you drop  vinegar,  lemon, or any  acid,  on the  blade of
a knife, or on a pair of scissars, it will immediately pro-
duce a spot  of rust ?
  Caroline.  Yes,  cften;  and  I am very careful now
to wipe off the  acid  immediately to prevent the rust
from foi uiing.
  Emily.   Metals have, then, three ways of  obtaining
oxygen;  from the atmosphere, from water,  and from
acids.
  Mr*. B.  The two first you have already witnessed,
and I shall now show  you how  metals take the oxygen1
from an acid.  This bottle contains nitric acid ; 1 shall
pour some of it over this piece of copper-leaf ......
  Caroline.   Oh,  what a disagreeable smell!
  Emily.  And what  is it that produces the  efferves-
cence and that thick yellow vapour?'
  Airs. B.   It is the acid, which being abandonrd by
the  greatest part  of  iti oxygen,  is converted into  a
weaker acid, which escapes in the form of gas.
  Caroline.   And whence proceeds this heat ?
  Mr*.  B.  Indeed, Caroline,  I think you might now
be able to answer that question yourself.
  Caroline.  Perhaps it is that the oxygen enters im©
                        N  2 
138
the metal in a more solid state than it existed in the acid,
in consequence of which caloric is disengaged.
   Mr*  ii.   You have found it out, you sec,  without
much difficulty.
   Emily.   The effervescence is over ;  therefore I sup-
pose that the metal is now oxydated.
   Mrs. B.  Yes.  But there is another important con-
nection between metals and acids,  with which I m ust
make  you  acquainted.  Metals  when  in  the state  of
oxyds, are capable of being dissolved by acids    In this
operation they enter  into a chemical combination with
the acid, and form an entirely new compound.
   Caroline.   But what difference is there between the
bxydation and  the dissolution of a metal by an acid ?
   Airs. B.   In  the first case, the metal merely com-
bines  with a portion  of oxygen taken  from the acid,
wh cli is thus  partly deoxygenated, as  in  the  instance
you have just  seen ;  in the second case, the metal after
being  previously oxydated, is actually  dissolved in the
acid, and enters into a chemical combination  with  it,
Without producing any further  decomposition or effer-
vescence.—This complete combination of an oxyd and
an acid forms a peculiar and important class  of com-
pound salts.
   Emily.  The difference between an oxyd and a com-
pound salt, therefore, is very obvious : the one consists
of a metal and oxygen ;  the other of an oxyd and acid.
   Mrs  B.  Very well;  and you will  be  careful to re-
member that the metals are incapable  of entering into
this combination with acids,  unless they are previously
oxvdated; therefore, whenever  you bring a  metal  in
contact  with an acid, it will be first oxydated and after-
wards  dissolred,  provided  that there  be a  sufficient
quantity of acid for both operations
   There are  some metals, however, whose solution is
more  easily accomplished, by diluting the acid in water ;
and the metal will,  in this case, be oxydated, not  by
the acid, but  by the  water, which it will  decompose.
But m proportion as the  oxygen of ihe water oxydaies
the surface  o4'  the  metal, the  acid combines  with it,
 washes it off, and leaves a fresh surface for the  oxygen 
lay
to act upon :  then other coats of oxyd are successively
formed, and rapidly dissolved by the  acid,  which con-
tinues combining with the new-formed surfaces of the
oxyd till the whole of the metal is  dissolved.   During
this process the hvdrogen gas of the water is disengag-
ed and  flies off with effervescnce.
   Emily.  Was not this the manner in which the sul-
phuric  acid assisted the iron fillings in decomposing wa-
ter ?
   Mrs. B. Exactly ; and it is thus that several metals,
which are incapable alone  of decomposing water,  are
enabled to do it by the assistance of an acid, which, by
continually washing off the covering  of oxyd,  as  it is
formed, prepares a fresh surface of meial to act upon the
water
   Caroline.  The acid here seems to act a part not very
 different from  that of a  scrubbing-brush—But pray
 would  not this be a good method of cleaning giates and
 metallic utensils ?
    Airs. B.   You forget that acids have the power of
 oxydating metals, .<s well as tnat of dissolving their ox-
 yds ; so that by cleaning a grate in  this way, you would
 create  more rust than  you could destroy.
    Caroline.   True ; how  thoughtless I was to forget
 that !  Let us watch the dissolution of the copper in the
 nitric acid ; for4 am very impatient to see  the salt that
 is to r< suit from it.  The  mixture is now of a beautiful
 blue colour ; but there is no appe  .ranee of the forma-
 tion of a salt  , it seems to be a tedious operation.
    Airs.  B.    The  chrystallization of the  sail  requires
 some length of time to be completed ;  if, however, yon   \
 are so  impatient, I  can easily  shew you a metallic salt
 already formed
    Caroline.   But that would not  satisfy  my curiosity-
  half so well as one of our own manufacturing.
    Mrs.  B.   It is  one of our  own  preparing that I
 mean  to shew you. When we decomposed water a few
 days since, by the oxydation of iron filings, through the
 assistance of sulphuric acid, in what did tlie process con-
  sist ? 
r*u
  Caroline.  In proportion as the water yie'dod its ox-
ygen to the iron,the acid combined with the new-form-
ed oxyd, and the hvdrogen escaped alone
  Mr*. B.  Very'well : the result,  therefore* was a
compound salt, formed by the combination  of sulphuric
acid with oxyd of iron.   It still remains in the vessel in
which the experiment was  performed.  Fetch it, and
we  shall examine l.
  Emily.   What a variety of processes the decomposi-
tion of water, by a metal and an acid, implies !   1st
The decomposition of the water ; 2dly, ths oxydation
of the metal;  and idly, the formation of  a compound
salt.
  Caroline.  Here it is, Mr?. B —What beautiful green«
crystals !  But we do not perceive ai>y crystals in  the
solution of copper in nitrous acid ?
  Mrs. B.   Because the salt is now  suspended in  the
water which the  nitrous acid contains, and will remain
so till it is deposited in consequence of rest and cooling.
  Emily.   I  am surprised  that a body so opaque as
iron can be converted into, such transparent crystals.
  Airs  B.   It is the union with the acid that produces
the  transparency ; for  if the pure  metal was  melted,
and afterwards permitted to cool and crystallize, it would
be found just  as opaque as before.
  Emily.  1 do not understand the exact meaning of
crystallization ?
  Mrs. B.   You  reccollect that when a solid body is
dissolved either by water or caloric, it is not decompo-
sed ; but that  its integrant parts are  only  suspended in
the solvent.  When the solution is made in water,  the
integrant particles of the body will, on the  water being
evaporated, again unite into a solid mass,  by the force
of their mutual attraction.  But  when the  body is  dis-
solved by caloric alone, nothing  more is  necessary, in
ordjr to make its particles reunite, than  to reduce its
temperature.   And, in  general,  if the solvent, wheth-
er water or caloric, be slowly separated by evaporation
or by cooling, and  care taken that the particles be  not
agitated during their reunion, they will arrange thenv 
141
selves in regular masses, each individual substance  as-
suming a peculiar form  or  arrangement; and  that is
what is called crystallization.
  Emily.   Crystallization, therefore, is simply  the  re-
union of the particles  of a solid body that has been dis-
solved in a fluid.                      , m
   Mrs. B.   That is a very good definition of it.   ttut
I must not forget to observe, that heat^ and water may
unite their solvent powers ; and  in  this case, crystalli-
zation may be hastened  by  cooling, as well as by eva-
porating the liquid.
   Caroline..  But if the body dissolved be  of  a  volatile
nature, will it not evaporate with the fluid  ?
   Mr*.  B.  A crystallized body, held  in  solution only
by water,  is scarcely ever  so volatile as the fluid  itself,
and care must be taken  to manage the heat,  so that it
may be sufficient to evaporate  the water only.
   I should not omit to mention that bodies, in  crystal-
lizing from their watery solution, always retain  a  small
portion of water, which remains confined  in the crystal.
in a solid form, and does not reappear, unless the body
loses its crystalline state.  This is called the  water of
 crystallization.
    It is also necessary that you should here more par-
 ticularly remark the difference, to which we have  for-
 merly alluded,  between the simple solution of  bodies
 either in water or  in caloric, and the solution of  metals
 in acids ;  in the  first case, the  body is merely divided,
 by the solvent  into its   minutest parts.   In  the  latter,
 a similar effect is,  indeed, produced ;  but it is by  means
 of a chemical combination between the metal and  the
 acid, in which both lose their  characteristic  properties.
 The first is a mechanical operation, the second a  chem-
 ical process.  We may, therefore, distinguish  them by
 calling the first a simple solution, and  the  other a chemi-
 cal solution.  Do you understand this difference ?
    Family.  Yes  ;  simple solution can  affect only  the at-
 traction of aggregation.  But chemical solution implies
 also an altractioii~of composition, that is to  say, an ac-
 tual combination between  the solvent  and the body  dis-
 solved. 
142
  Mr*. B.  You have expressed your id«a very  well'
indeed.  But you must observe, also, that whilst a bo-
dy  may be separated from its solution in water or ca-
loric, simply by cooling, or by evaporation, an  acid  can
be taken from a metal with which it  is combined,  only
by stronger affinities,  which produce a decomposition.
  Emily.  I think that you have rendered the difference
between these two kinds of solution so obvious, that we
can never confound  them.
  Mrs. B.  Nothwithstanding, however, the  real dif-
ference which  there appears to be between these  two
operations, they are  frequently confounded.   Indeed,
several modern  chemical writers, of great eminence,
have even thought proper to generalize the idea of so-
lution, and  to suppress entirely the distinction introdu-
ced by the great Lavoisier, which I have taken so much
pains to explain, and which I confess appears to me to
render the subject much clearer.
  ^ Emily.   Are the perfect metals susceptible  of being
dissolved and converted into compound salts by acids ?
   Mrs.  B.   Gold is acted upon by only one acid,  the
oxygenated  muriatic,  a  very remarkable acid,  which,
when in its  more concentrated state, dissolves  gold or
any other metal, by burning them rapidly.
   Gold can, it  is trae, be dissolved likewise  by  a  mix-
ture of two acids, commonly called aqua regia ; but this
mixed solvent  derives  that property from containing
the peculiar acid which 1 have, just mentioned.   Platina
is also acted upon by this acid only ; but silver is dissol-
ved by several of them—
   Caroline.   I think you said  that vome of the metals
might be so strongly oxydated as to become acid ?
   Mrs. B.   There are five metals, arsenic,  molybde-
na, chrome, tungsten, and  columbiuin,*  which are sus-
ceptible, of con:bluing with a sufficient quantity of  oxy-
 gen to be convened into acids
   Caroline.   Acids are connected with metals in such a
variety of ways, that I am afiaid of some  confusion in
     Co'umbium  which has not long  fince been discovered byi
Mr. H rctiett, was inadvertently omitted in the enumeration of the
simple  bodi«3 given in the first conversation. 
143
remembering them —In the first place, acids will yield
their oxygen to metals.  Secondly, they  will combine
with them in  their state of oxyds, to form compound
salts ; and lastly, several of the metals are themselves
susceptible of acidification.
   Mr*.  B.  Very  well ; but though metals have so
great an affinitv for acids, it is not with that class of bo-
dies alone that  they  will combine.  They are most of
them  in their simple state, capable of uniting with sul-
phur,  with phosphorus, with caibone, and with each
oiher  ; these  combinations,  according to the  nomen-
clature which  was explained to you on a  former occa-
sion, are called sulphurets, phosphorets, carburets. &c.
    The  metallic phosphorets offer nothing  very re-
markable.  The sulphurets  form the peculiar kind of
 mineral called pyrites, from which certrin kinds ol mi-
neral  waters, as those of Hirrogate, derive  their chief
chemical properties.   In this combination, the sulphur,
 together with the iron, have so strong an attraction for
 oxygen, that they obtain it both from the air and from
 water, and by condensing it in a solid form, produce the
 heat which raises the temperature of the water in such
 a remarkable degree.
   Emily.  But if pyrites obtain oxygen from water,
 that water must suffer a decomposition, and hydrogen
 gas be evolved ?
   Airs.  B.  That is actually the case in the hot springs,
 alluded to, which give out an extremely fetid gas, com-
 posed of hydrogen impregna'ed with sulphur.
   Caroline.  If I recollect right,  steel and plumbago,
 which you mentioned in the last lesson,  are both car-
 burets of iron ?
    Airs. B.   Yes ;  and they are the only carburets of
 much consequence.
    A curious combination of metals has lately very much
 attracted  the  attention of the scientific world :  I mean
 the stones that fall  from the atmosphere.  They fll
 consist principally of native or pure iron which is never
 foimed in that state in the bowels  of  the earth ; and
 contain also  a small  quantity of nickle and chtome, a
 combination likewise new in the mineral kingdom. 
144
  These circumstances have led many scientific persons
to believe that those substances have  fallen from the
moon or some other planet,  while others are of opinion
either that they are formed in the atmosphere, or arc
projected into it by some unknown volcano on the sur-
face of our globe.
  Caroline.   I have heard much of these stones,  but  I
believe many people are of opinion that they  are fo med
on the earth, and laugh at their pretended celestial ori-
gin.
  Airs. B.   The fact  of their falling is so  well ascer-
tained, that I think no person who has at all investiga-
ted the subject, can now entertain any doubt of it.  Spe-
cimens of these stones have been discovered in all parts
of the world, and to each of them has some tradition or
story of its fall been found connected.    And as the ana-
lysis of all the specimens  afford precisely  the  same
results, we have tnus a very strong proof that they all
proceed  from the same source.  It  is to Mr. Howard
that philosophers are indebted, for having first analysed
these stones and directed their attention to this interest-
ing subject.
  But we must not suffer this digression to take up  too
much of our time.
   The combinations of metals with  each other are cal-
led alloys ; thus brass is  an alloy of copper  and  zinc;
bronze, of copper and tin, &c.
  Emily    And is not pewter also a combination of me-
tal ?
  Mr*. B.   It is.   The  pewter made in this country,
is mostly composed of tin, with a very  small  proportion
of zinc and lead.
  Caroline.   Block-tin is a kind of pewter, I believe ?
  Mr*. B.   No ;  it is iron  plated with tin, which ren-
ders it more durable, as tin  will not so easily rust.  Tin
alone, however, would be too soft a metal to be wor-
ked for common use, and all the tin vessels  or  utensils
are in fact  nuid of plates of iron thinly coated with tin,
which prevents the  iron from rusting.
  Caroline.   Say rather oxydating, Mrs. B.__.Rust is a
word that should be exploded in chemistry. 
                        145

  Airs. B.   Take care, however, not to introduce  the
word oxydate instead of rusi, in general  conversation ;
for  either you will not be  understood, or you  will be
laughed at for your conceit.
  Caroline.   1  confess that  my attention is, at present,
so much engaged by chemistry, that it sometimes leads
me into ridiculous observations.  Every thing in nature
I refer to cbemisiry,  and have often been laughed at
for my continual allusions to it.
   Mr*. B.   You must be more cautious and discreet in
this respect, my dear, otherwise your enthusiasm, al-
though proceeding from a sincere admiration of the sci-
ence, will be attributed to pedentry.
   Metals differ very much in their affinity for each  oth-
er , some will  not  unite at all, others readily combine
together, and on this property of  metals the art of sold-
ering depends.
   Emily.   What is soldering ?
   Airs.  B.  It  is joining two pieces of metal together,
 by heating them, with a thin plate of a more fusible me-*
tal interposed between them.   Thus tin is a  solder for
 lead ; brass, gold, or silver, are solder for iron, &c.
  ' Caroline.  And is not plating metals something of the
 same nature ?
   Airs. B.  In the operation of plating, two metals are
 united, one being covered with the other, but  without
 the intervention of a third ; iron or tin may be thus cov-
 ered with gold or silver.
   Emily.   Mercury appears to  me of a very different
 nature from the other metals.
   Mr*.  B   One of its greatest peculiarities is  that it
 retains a  fluid  state  at the temperature of the atmos-
 phere.   All metals are fusible  at different degrees of
 heat, and they have likewise each the  property of  free-
 zing or becoming solid at a  certain fixed temperature.
 Mercury congeals only at 72° below the freezing point.
   Emily.   That is to  say, that in order to freeze, it re-
 quires a temperature  72° colder than that at which wa-
 ter freezes.
   Airs.  B.  Exactly  so.
                           O 
146
    Caroline.   But is the  temperature of the atmosphere
  ever so low as that?
    Mrs. B.   Scarcely ever, at least in an inhabited part
  of the globe ; therefore mercury is never  found solid
  in nature, but it  may be congealed by artificial cold ; I
  mean such intense cold as can  be produced by some
  chemical  mixtures.
    Caroline.   And  can mercury be made to boil and e-
  vaporatc ?
    Mrs. B.   Yes, like any other  liquid ;  only it requires
  a  much greater degree of heat.   At the temperature
  of 600°, it begins to boil and  evaporate iike water.
    Mercury   combines with gold,  silver, tin, and with
  several  other metals ; and, if mixed with any of them
  in a sufficient proportion, it penetrates the solid  metal,
  softens  it, loses its own fluidity,  and forms an amalgam,
  which is the name given to the combination of any me-
  tal with mercury,  forming a substance more or less so-
  lid, according as the mercury or the other metal pre-
  dominates.
    Emily.  In the  list of metals there  are some  whose
  names 1 have never before heard mentioned.
    Airs. B.   There are several that have been recently
  discovered, whose properties  arc yet  but little known,
V as for instance, titanium which was discovered by  the
  Rcvd.  Mr. Gregor, in the tin mines of Cornwall ; co-
  lumbium, which  has lately  been discovered by Mr.
  Hatchett ; and osmium, iridium, palladium,  and rhodi-
  um, all of which Dr. Woolaston and Mr. Tennant found
  mixed with crude  platina
    Caroline.   Arsenic  has been mentioned amongst the
  metals ; I had no notion that  it belonged to that class of
  bodies, for 1 had never seen it  but as a powder, and never
  thought of it but as a most deadly poison.
    Mr*  B   In  its pure metallic  state, I believe, it is
  not so poisonous ;  but it has so great an  affinity for oxy-
  gen, that it absorbs it from the atmosphere at its natu-
  ral temperature ; ycu have seen it therefore, only in its
  state of oxyd, when, from its  combination with oxygen,
  it  has acquired its very poisonous properties. 
147
  Caroline.  Is it possible that oxygen can  impart poi-
sonous qualities ? That valuable  substance which pro-
duces light, and fire, and which all bodies in nature are
so eager to obtain !
   Mr*. B.  Most of the metallic oxyds are poisonous,
and derive this property from their union  with  oxygen.
The white lead, so much used in paint,  owes its per-
nicious effects to oxygen.  In general oxygen, in a con-
crete state, appears  to  be particularly destructive in  its
effects on flesh or any  animal matter ; and those oxyds
are most caustic that have an acrid burning taste, which
proceeds  from the metal having but a slight affinity for
oxygen,  and therefore easily yielding  it  to the flesh
which it corrodes and destroys.
   Emily.  What is the meaning of the word causti?,
which you have just used ?
   Mr*.  B.  It expresses that property which  some
bodies possess, of disorganizing and destroying animal
matter, by operating  a kind of combustion, or at least
a chemical decomposition.   You must often have heard
of caustics used to burn warts, or other animal excrescen-
ces ; most of these bodies owe their destructive power
to the  oxygen with which they are combined.  The
common caustic, called lunar caustic, is a compound for-
med by the union of nitric acid and silver ; and it is sup-
posed to owe its caustic qualities to the  oxygen contain*
ed in the nitric acid.
   Caroline. But, pray, are  not acids still more caustic
than oxyds, as they contain a greater proportion of  ox-
ygen ?
   Mr*.  B. Some of the acids  arc ; but the caustic
property  of a body depends not oniy upon  the  quantity
■of oxygen, which it contains, but  also upen its slight af-
finity for that principle, and the consequent facility with
which it yields it.
   Emily.   Is  not this  destructive property of oxygen
a'"Oun!t-d for ?
   Mr*  B.  It  proceeds probably from the strong at-
traction of oxygen for  hydrogen ; for if the one rapidly
absorbs the other from the animal fibre,  a  disorganiza-
f;vn of the substance must eoyi.e. 
148
   Emily.  Caustics arc then very properly said to burn
 the flesh, since the combination of oxygen and hydro-
 gen is an actual combustion.
   Caroline.   Now, I think,  this effect would be  more
 properly termed an oxydation, as there is no disengage-
 ment of light and heat.
   Mr*.  B.  But there really is a sensation of heat pro-
 duced by live action of caustics ; and the caloric that is
 disengaged must,  I  think,  partly, if not wholly pro-
 ceed from ihc  oxygen which the caustic yields to the
 flesh.
   Caroline.   Yet the oxygen of a caustic  is not in a
 gaseous state, and can therefore have no caloric to part
 with ?
   Mr*. B.  In whatever state oxygen exists, we may
 suppose that, like every other body in nature, it retains
fiornc portion of caloric ; and if, in combining with the
 hydrogen of the flesh, it becomes more dense than  it
 previously was in the caustic, it must part with caloric
 whilst  this change is taking place.   I believe I  have
 once before observed that we may, in a great measure,
judge of the comparative degree  of solidity  which ox-
ygen assumes in a body, by the  quantity of caloric lib-
 erated during its combination ; and when we find, that
in its passage from one body to another, heat is evolved,
 we may be certain that it exists in a more solid state in
the latter.
   Emily.  But if oxygen  is so caustic, why  does not
 that contained in the atmosphere burn us ?
   Mrs  B.  Because it is in a gaseous state, and has a
 greater attraction for its caloric than for the hydrogen of
our bodies.  Besides, shou d the air be slightly caustic,
we are in a great measure sheltered from its effects by
the skin ; you  all know how much a wound, however
trifling, smarts on being exposed to it.
   Caroline.   It is a curious idea,  however,  that  we
should live in a slow fire.  But, if the air was caustic,
would it not have an acrid taste  ?
   Mrs. B. It possibly might have such a taste ; though
in so slight a degree, that custom has remlerd  i{ insen-
sible. 
149
   Caroline.  And why is not water caustic ?   When I
dip my hand into water, though cold, it ought to  burn
me from the caustic nature of its oxygen
   Mrs. B.  Your hand docs not decompose the water ;
the oxvgen in  that state  is much  better supplied  with
hydrogen than  it would be by animal matter,  and  if its
causticity depends on its affinity for that principle, it will
be ve y far from quitting its state  of water to  act upon
your hand.   You must not forget that oxyds are caustic
in proportion as the oxygen adheres slightly to them
   Emily.   Since the oxyd of arsenic is poisonous,  its
acid, I suppose,is fully as much so ?
   Airs. B.  Yes ; it is one of the strongest poisons in
nature
   Emily.   There is a poison  called verdigris, which
forms on brass and copper when not kept very clean ;
and this,  I have heard, is an objection  to these metals
being made into kitchen utensils.   Is this poison  like-
wise occasioned by oxygen ?
   Airs. B.  It is produced by the intervention of oxy-
gen ; for verdigris is a compound salt  formed by the
union of vinegar and copper : it is of a  beautiful green
colour, and  much used in painting.
   Emily.   But, I believe, verdigris is often formed  on
eopper when no vinegar has been in contact with it.
   Mr*   B  Not real verdigris,  but compound  salts,
somewhat  resembling it, may be produced by the action
of an acid on copper.
   There is a beautiful green salt produced  hy  the com-
bination of cobalt with muriatic  acid,  which has  the
singular property of forming what  is called sympathetic
ink.  Characters written with this solution are invisible
when cold, but  when a gentle heat is applied,  they at«
suuie a  fine blueish green colour.
   Caroline.  I  think one might draw very curious land-
scapes with the assistance of this ink; I would first make
a water colour  drawing of a winter scene, in which  the
trees shall  be leafless and the grass scarcely  green ; J
would then trace all the verdure with the invisible ink.
and whenever 1 choose to create spring, I  should hold
                      O 2 
150
it before the fire, and its warmth woukl cover the land-
scape with a rich verdure.
  Mrs. B.   That will be a very amusing experiment,
and I advise you by all means to try it.—I must now,
however, take my leave of you ; we  have had a very
long lecture, and I hope you will be able to remember
it.  Do not  forget to write down all  you can recollect
of this conversation, for the subject is of  great import-
ance, though it  may not appear at first very entertain-
ing.

              Conversation x.
On Alkalies.
                     Mrs. B.

  After, having taken a general view of combustible
bodies, we now come to the alkalies, and the earths,
which compose the class of incombustibles ;  that is to
say, of such bodies as do not combine  with oxygen at
any known temperature.
  Caroline.  I am afraid that the incombustible  sub-
stances will not be near so interesting as the others ; for
I have found nothing in chemistry that has pleased me
ao much as the theory of combustion.
  Mrs. B.  Do not however depreciate the  incombus-
tible bodies before you are acquanted  with them ; you
will find they  also possess properties highly  important
and interesting.
  Some of the earths bear so strong a resemblance in
their properties to the alkalies, that it is a difficult point
to know under what head to place them.  The celebrat-
ed French chemist, Fourcroy, has classed two of them
(Barytes and Strontites) with the alkalies ; but, as lime 
151
and magnesia have almost an equal title to that rank, I
think it better not to separate them,  and therefore have
adopted the common method of classing them with the
earths, and of distinguishing them by the name oialka-
line earths.
   We shall first take a review of the alkalies,  of which
there are three species \. potash, soda, and ammonia,
The two first are called fixed alkalies,  because they ex-
ist in a solid form at the temperature of the atmosphere,.
and require a great heat to be volatilized.  The third,
ammonia,  has  been distinguished by the name of i;o/c-
tile alkali, because  its natural form is that of gas.
   Caroline.  Ammonia ? I  do not recollect that name
 in the  list of simple bodies.
   Mrs.  B.  The reason why you do not find it there is,
 that it  is a compound ; and if I introduce  it to your ac-
 quaintance now. it is  on  account of its close connec-
 tion with the two other alkalies,  which it resembles es-
 sentially  in its nature and properties.   Indeed it is not
 long since ammonia has resigned its place among the
 simple bodies, as it was not, till lately, supposed to be a
 compound ; nor is it improbable that potash and soda
 may some day undergo the same fate, as they are strong-
 ly suspected of being compounds also.
   The  general properties  of  alkalies are,  an acrid
 burning taste,  a pungent smell,  and a caustic action on
 the skin and flesh.
   Caroline.  How san  they be  caustic,  Mrs. B. since
 they do not contain oxygen ?
   Mr*. B.  Whatever substance  has an affinity for any
 one of the  constituents of animal matter,  sufficiently
 powerful to decompose it, is entitled to the appellation
 of caustic.  The  alkalies, in their pure state, have a
 very  strong attraction for water, for hydrogen, and for
 carbone,  which, you know, are the constituent princi-
 ples of oil, and it  is  chiefly by absorbing these substan-
 ces from  animal matter, that they effect  its decomposi-
 tion :  for, when  diluted with  a  sufficient  quantity  of
 water, or  combined  with any oily subsunce, they lose
 their causticity. 
152
   But, to return to the general properties of alkalies—
 they change the colour of  syrup of  violets,  and other
 blue vegetable infusions,  to green ; and have,  in gene-
 ral, a very gre .t tendency to unite wi'h acids, although
 the respective  qualities of these two classes of bodies
 form \ remarkable contrast.
   We shall examine the result of the combination of
 acids and alkalies more particularly when we have com-
 pleted  our general view  of the simple  bodies.  It will
 be  sufficient at present to  inform you, that whenever
 acids  are  brought in contact with alkalies, or alkaline
 earths, they unite with a remarkable eagerness, and
 form compounds perfectly different from either of their
 constituents;  these compounds are  called neutral or
 compound salts.
   Caroline.  Are they  of the same  kind as the salts
 formed by the combination of a metal and an acid ?
   Mr* B.   Yes  ; they are analogous in their nature,
 although different in many of their properties.
   A methodical  nomenclature,  similar to that  of the
 acids, has been  adopted for  the compound salts.  Each
 individual salt derives it name from its constituents, so
 that every name implies a knowledge of the composition
 of the salt.
   The three alkalies,  the alkaline earths, and the me-
tals, are called  salifiable bases or radicals, and the acids,
salifying principles  The name of each salt is compos-
 ed both of that of  the acid and the salifiable base ; and
it terminates in at or it, according to the degrees of oxy-
 genation of the acid.  Thus, for instance,  all those
salts  which are  formed by the combination of the  sul-
phuric acid with any of the salifiable bases, are  called
sulpliats, and the name -of  the radical is added for the
specific distinction of the  salt ; if  it  be potash,  it will
compose a sulphat of potash ;  if ammonia,  sulphat of
ammonia, U.C.
  Emily.  The chrystals  which  we obtained from the
combination of iron and  sulphuric acid, were thereforej
sulphat of iron ?
  Mrs. B.  Precisely ; and those which we prepared
by dissolving copper in nitric acid, nitrat of copper^  and 
153
so on.   But this is not all;  if the salt be formed by that-
class of acids which ends in ous (which you know, in-
dicates a less degree of oxygenation),  the  termination
of the name of the salt will be in it, as sulphit of pot-
ash, sulplut of ammonia,  See.
   Emily.   Thjre must be an immense number of com-
pound salts, since there is so great a variety of salifia-
ble radicals, as well of salifying principles.
   Mrs. B.  Their real number cannot be  ascertained,
since  it  increases every day  as the science advances.
But,  before we  proceed farther in the investigation o£
the compound salts,  it is necessary that we should ex-
amine the nature of the ingredients from which they.
are composed.   Let us therefore return to  the alkalies.
The dry white powder which you see in  this phial is
pure caustic potash  ; it is very difficult to preserve it in
this state, as it attracts with extreme avidity the mois-
ture from the atmosphere,  and if the air were not per-
fectly excluded, it would in a very short time be actually.
melted.
   Emily.   It is then,. I suppose,  always found in a li-
quid state ?
   Airs. B.   No; it exists in nature in a great variety
of forms and combinations, but is never  found in its
pure separate stale ;  it is combined with carbonic acid,
with which it exists in every part of the vegetable king-
dom,  and is most  commonly obtained  from the ashes
of vegetables,  which compose the substance that re-
mains after all the other parts have been volatilized by
combustion.
   Caroline.   But you once said, that after the volatile
parts of a vegetable were evaporated, the substance
that remained was charcoal ?
   Mr*. B.   What, my dear ? Do you  still confound the
processes of simple  volatilization and  combustion ?  In
order to procure charcoal we evaporate such  parts as
can be reduced to vapour by  heat alone ; but when we
burn the vegetable, we volatilize  the  carbone also, by
converting it into carbonic acid gas.
   Caroline.  That is true ;  I hope I shall make no  more
mistakes in my favourite theory of cambustion. 
154
  Mr*. B.  Potash derives its name from the pots in
which the vegetables from which it was obtained  used
formerly to be bur t; the alkali remained mixed with
the ashes at the bottom, and was thence called potash.
  Caroline.  There is some good sense in this name as
it will always remind  us of the operation, and of the
general source from which this alkali is derived.
  Emily.  The ashes of a  wood fire, then, are potash,
since they are vegetable ashes ?
  Mr*. B.   They always contain more or less  potash,
but are very far from consisting of that substance alone,
as they are a mixture of various earths and salts which
remain after the combustion  of vegetables,  and  from
which  it is not easy to separate  the alkali in its pure
form.  The process by which potash is obtained,  even
in the imperfect state  in which it is used in the  arts, is
much  more complicated than simple combustion.  It
was once deemed impossible to separate it entirely from
all foreign substances, and it is only  in chemical labora-
tories that it is to be met with in the state of purity in
which  you find it in this phial.  Wood ashes are,  how-
ever, valuable for the alkali which they contain, and
are used for some purposes without  any further prepar-
ation.  Purified in a certain degree, they make what is
commonly called pearl ash, which is of great efficacy in
taking out grease, in washing linen,  Sec. for potash
combines readily with oil  or  fat, with which it forms
■a compound well known, to you under the name of soap.
   Caroline.   Really !  Then I should think it would be
better to wash all linen with pearl ash  than  with  soap,
as, in  the latter case,  the alkali, being  already  com-
bined  with oil, must  be less  efficacious  in extracting
grease.
   Mr*.  B.   Its effect would  be too powerful  on fine
linen,  and would injure its texture ;  pearl-ash is there-
fore only used for that which is of a strong coarse kind.
For the same reason you cannot wash your hands with
plain potash ; but, when mixed with oil in the  form of
soap, it is soft as well as cleansing, and is therefore  much
better adapted to the purpose.
   Caustic potash, as  we  already observed, acts on the 
155
skin, and  animal fibre,  in  virtue of its attraction  for
water and oil, and converts all animal matter into a kind
of saponaceous jelly.
   Emily.   Are vegetables the only source from wnich
potash can be derived ?
   Airs. B.  No :  for though far. most abundant in  ve-
getables,  it is  by no means confined to that class of bo-
dies, beins found also on the surface of the earth mixed
with various minerals, especially with earths and stones,
whence  it is  supposed to be conveyed into vegetables
bv the roots of the plant.   It is  also met with, though
in very small  quantities,  in some animal substances.
The most common state of potash is that of carbonat ; I
 suppose you understand what that ib ?
    Emily.  1 believe so ; though 1 do not recollect that
 you ever mentioned the word before   If I am not mis-
 taken, it must be a compound salt formed by the union
 of carbonic acid with potash.
    Mr*. B.  Very true ;  you  see how  admirably  the
 nomenclature of modern  chemistry is  adapted to assist
 the memory ; when you hear the name of a compound,
 you  necessarily learn  what are its constituents;  and
 when you are acquainted with the constituents,  you can
 immediately  name ihe compound th«t  they form
    Caroline.   Prav,  how were  bodies arranged  and dis-
 tinguished before this nomenclature was introduced ?
    Mrs.  B.   Chemistrv was then a much more difficult
 study ;  for everv  substance  has an arbitrary name,
 which'it derived'either  from  the person who discover-
  ed it, as Glaubt r's salts for instance, or  from some oth-
  er circumstance  relative to it,  though quite unconnect-
  ed with its real nature, as potash.                 #
    These names have been retained for some of the sim-
   ple bodies ;  for as this class is not numerous, and there-
   fore can earily lie remembered, it has not been thought
  necessary to change them.
    Emily.  Yet I think it would have  rendered  the new
   nomenclature more complete to have  methodized the
   names  of the elementary as well as of the compound
   bodies, though it could not have been done in the same
   manner.  But the names of the simple substances might 
136
have indicated  their nature, or at least,  some of their
principal properties; and if, like the acids and com-
pound salts, all the simple bodies had a similar termin-
ation, they would have been immediately known as such.
So complete and regular a nomenclature  would 1 think,
have given  a clearer and more comprehensive view of
chemi-strv, than  the present, which is a  medley of the
old and new torms.
   Airs, B.   But you are not aware of the difficulty of
introducing into science an entire set  of new tciins; it
obliges all the  teachers and professors to go to school
again ; and if some of the old names, that art least ex-
ceptionable, were not left as an introduction to the new
ones,  few people would have had industry and perseve-
rance enough to submit to the study of a completely new
language ; and the inferior classes of arti-.ts,  who can
only act from  habit ard routine, would,  at least, for a
time, have  felt material inconvenience from a total
change of their habitual terms.  From these consider-
ations, Lavoisier and  his colleagues, who invented the
new nomenclature, thought it most prudent to leave a
few links of the old chain, in order to connect it with
the new  one.   Besides, you  may easily conceive the
inconvenience which might arise from giving a regular
nomenclature to substances, the simple nature  of which
is always uncertain ;  for the  new  names might,  per-
haps, have proved to have been founded in error.   And,
indeed, cautious as the inventors of the modern chemi-
cal  language have been, it has already been found ne-
cessary to modify it in may respects.  In those few ca-
ses, however, in which new  names have been adopted
to  designate simple bodies, the  names  have  been  so
contrived as to indicate one  of the chief properties of
the  body in question ; this  is the case with oxygen,
which, as I explained to you, signifies to produce acids;
iwd hydrogen,  to produce water.
   But to return  to the alkalies   We shall now try to
melt some of this caustic potash  in a little water,  as a
circumsiance occurs during its  solution very worthy of
observation—Do you feel the heat that  is produced?
   Caroline.  Yes, I  do ; but is not this directly  con-
trary to our theory of caloric, according  to which heat 
157
is disengaged when  fluids  become solid,  and cold pro-
duccd when solids are melted ?
   Mrs. B.   The latter is  really the case in all solu-
tions ; and if the solution of caustic alkalies seems to
make an exception to the rule, it does not, I believe,
form any solid  objection to  the theory.  The  matter
may be explained thus: When water first comes in
contact with  the potash, it produces an effect similar to
the  slakeing  of lime,  that is, the water is solidified in
combining with  the potash,  and thus loses its latent
heat; this is the heat  that you now feel, and which is,
therefore,  produced not by the melting of the solid
but  by the solidification of the fluid   But when there
is more water than the potash can absorb  and solidify,
the  latter then yields to the solvent power of the water ;
and if we do  not perceive the cold produced by its melt-
ing, it is because it is counterbalanced by the heat pre-
viously dis-ngaged* [Sec note page 16*4.]
   A very remarkable property  of potash  is the forma-
tion of glass by its fusion  with silicious earth.   You
aie  not yet acquainted with  this last  substance further
than its being in the list of simple bodies.   It is suffi-
cent, for the  present, that you should know what sand
and  flint are chiefly composed  of it; alone it is infusi-
ble ; but  mixed with potash, it melts when  exposed to
the  heat  of a furnace, combines with the  alkali, and
runs into glass.
   Caroline.   Who would ever have supposed that the
same substance  that converts transparent oil into such
an opaque body  as soap, should transform that opaque
substance, sand,  into transparent glass !
   Mrs. B.   The transparency,  or opacity  of bodies,
does not,  I conceive, depend so much upon their  inti-
mate nature,  as upon  the arrangement of their parti-
cles ;  we cannot have a more striking instance of this,
than  that which is  afforded by the drfferent states of
carbone, which, though it commonly appears in  the
form of a black opaque body, sometimes assumes the
most dazzling transparent form in nature, that of dia-
mond, which, you  recollect, is  nothing  but  carbone,
and which, in all probability, derives its beautiful trans- 
158
parency from the peculiar arrangement of its particles
during their crystallization.
  Emily.  I never should have supposed  that the for-
mation of glass was so simple a process as you describe
it.
  Mrs. B.  It is  by no  means  an easy operation  to
make perfect glass ; for if the  sand, or flint, from which
the silicious earth is obtained be mixed with any metal-
lic particles, or other substance winch cannot be vitri-
fied, the glass will be discoloured, or defaced by opaque
specks.
  Caroline.  That I suppose is the reason why objects
so often appear irregular and thapeless through a com-
mon glass window.
  Mr*  B.  This species of  imperfection proceeds,  I
believe, from  another cause   It is extremely difficult
to prevent the lower  part of the vessels in  which the
materials  of glass  are  fused, from  containing a more
dense vitreous matter than the upper, on account of the
heavier ingredients  falling to  the bottom.   When this
happens, it occasions the appearance of veins or waves
in the glass, from the difference of density in  its seve-
ral parts, which produces an irregular refraction of the
rays of light that pass through it.
  Another  species of imperfection sometimes arises
from the fusion not being continued for a length of time
sufficient to combine the two ingredients completely,
or from the due proportion of  potash and  siiex (which
are as two to  one),*not being carefully observed; the
glass, in those  cases, will  be liable lo alteration from
the action of the air, of salts, and  especially  of acids,
which will effect its decomposition  by combining  with
the potash and forming compound salts.
  Emily.   What an  extremely  useful substance pot-
ash is 1                                          •
  Mrs. B.  Besides the great importance of  potash in
the manufactures of glass and soap, it is  of very  con-
siderable utility  in many  of the other arts, and  in its
combination with several acids, particularly the nitric,
with which it forms saltpetre. 
159
  Caroline.  Then saltpetre must be a nitrat of potash 9
But we are not yet acquainted with the nitric acid ?
  Mrs. B.  We shall, therefore, defer entering into
the particulars of these combinations, till we come to a
general review  of the  compound salts.  In order to
avoid confusion, it will be better at present to confine
ourselves to the alkalies.
  Emily.   Cannot you  shew  us the change of colour
which you said the alkalies produced on  blue vegetable
infurions ?
  Mr* B.  Yes ; very easily.  I shall dip a  piece of
white paper into this syrup of violets, which, you see,
is of a deep blue, and dyes the  paper of the same co-
lour.—As soon as it is dry, we  shall dip it  into a solu-
tion  of potash,  which, though  itself colourless, will
turn the paper green—
  Caroline.   So it has indeed !  And do the other  alka»
lies produce a similar effect ?
  Mr*. B.  Exactly the same.—We  may now proceed
to Soda, which, however important, will detain us but
a very short  time ;  as in all its general properties it
very  strongly resembles potash ;  indeed, so great is
their similitude, that they have  been  long confounded,
and they can  now scarcely be distinguished except by
the difference of the salts which they form with acids.
  The grei.t source of this  alkali  is the  sea, where,
combined with  a  peculiar acid, it  forms the  salt with
which the waters of  the ocean are so  strongly impreg-
nated.
  Emily.   Is not that the common  table salt ?
  Airs. B.  The very same ; but again we must post?
pone  entering  in'o the particulars of this  interesting
combination, till we treat  of the neutral salts.  Soda
may  be  obtained  from common salt; but the easiest
and most u^ual method of procuring it,  is by the com-
bustion of  marine plants, an operation perfectly analor
gous to that by which potasli  is  obtained from vegcta*
bles.
  Emily.   From what does soda derive its name ?
  A Ira. B.   From a  plant called by  us soda,  and by the 
160
Arabs kali; which  afford it in  great abundance.  Kali
has, indeed,  given its name to the alkalies in generaF.
   Caroline.   Does soda form glass  and soap, in the
same manner as potash ?
   Mr*.  B.  Yes,  it does;  it  is of equal importance
in the arts, and it is even  prefered to potash for some
purposes ; but you will not be able to distinguish  theif
properties, till  we examine the compound sahs which
they  form with acids ; we must therefore  leave soda
for the present, and proceed  to Ammonia, or the vol-
atile alkali.
   Emily.   I  long to hear something of this alkali; is
it not of the same nature as hartshorn ?
   Airs. B.  Yes,  it is,  as you will see by and by.   This
alkakli is seldom found in nature in its pure state ; it is
most commonly extracted  from a compound salt called
sal ammoniac, which was formerly imported  from  Am*
monia, a region of Lybia,  from which both the salt and
the alkali, derive their names.   The crystals contained
in this bottle are specimens of this salt,  which consists
of  a combination of ammonia and muriatic acid.
   Caroline.   Then it should be called muriat of ammo-
nia ; for though lam  ignorant  what muriatic acid is,
yet I know that its combination with ammonia cannot
but be so  called ;  and I am surprised to see sal ammo-
niac inscribed on the label.
   Mrs. B.   That is the name  by which it has been so
long known, that the modern chemists have not yet suc-
ceeded in banishing it altogether; and it is still sold
under that name  by druggists,  though  by scientific
chemists it is more properly called muriat of ammonia.
   Emily.   By what means can  the ammonia  be separ-
ated irom the muriatic acid ?
   Mr*. B.   By a display  of  chemical attractions  ; but
this operation is  too complicated for  you to understand,
till  you are better acquainted  with the agency of affini-
ties.
  Emily.   And when  extracted from the  salt,  what
kind of substance is ammonia ?
  Mr*.  B.   Its natural form  at the temperature of the
atmosphere,  when  free  from combination, is that of 
161
 gas ; and in this state it is called ammoniacal gas.  But
 it mixes very readily  with  water,  and can be thus ob-
 tained in a liquid fotm.
   Caroline.  You said that ammonia was a compound ;
 pray, of what principles is it composed ?
   Mrs. B.  It was discovered  a few  years since, by
 Berthollet, a celebrated French  chemist, that it consist-
 ed of about one part of hydrogen  to four parts of nitro-
 gen.  Having heated ammoniacal gas under a receiver,
 by causing the electrical spark to pass  repeatedly thro'
 it,  he found that it increased considerably in bulk  lost
 all its alkaline  properties,  and was actually  converted
 into hydrogen and nitrogen gasses.
   Emily.   Ammoniacal gas must, I suppose,  be very
 heavy, since it expands so much when decomposed ?
   Mrs B.   Compared  with hydrogen  gas,  it certain-
 ly is ; but it is considerably lighter than oxygen gas,
 and only about half the  weight of atmospherical air.
 It possesses  most  of the  properties of the fixed alka-
 lies;  but cannot be of so much use in  the arts on ac-
 count  of  its  volatile  nature.  It is, therefore,  never
 employed  in  the  manufacture  of glass,  but it forms
 soap with oils equally as well as potash and soda ; it re-
 sembles them likewise in its strong attraction for water ;
 for which reason it  can be  collected in  a receiver over
 mercury only.
   Caroline.  I do not understand this ?
   Mr*. B.   Do you  recollect  the method  which we
 used to collect  gasses in a glass receiver over water ?
   Caroline.   Perfectly.
   Mr*. B.   Ammoniacal gas has so strong a  tenden-
 cy to unite with water, that, instead of passing through
 that fluid, it would be instantaneously  absorbed by it.
 We can  therefore neither use water .for that  purpose,
 nor  any  other  liquid  of which  water is a component
 part ;  so that, in order to collect.this gas, we are oblige
 ed to have recourse to mercury (a  liquid which has no
 action upon it), and  we use a mercurial bath, instead of
 a water bath, as we did on former occasions.  Water
impregnated  with this gas, is  nothing  more than the
■fluid which you mentioned  at the beginning of the con-
                       P  2 
162
versation—hartshorn ; it is the ammoniacal gas escap-
ing from the water which gives it so powerful a smell.
  Emily   But there is no appearance of effervescence
in hartshorn ?
  Mrs. B  Because the particles of gas that rise from
the water are  too subtile and minute for their effect to
be visible.
  Water diminishes in density by being impregnated
with  ammoniacal gas ; and this augmentation of bulk
increases its capacity for caloric
  Emily.   In  making hartshorn,  then, or  impregnat-
ing water with ammonia, heat must be absorbed,  and
cold produced ?
   Mr*.  B.  That effect would take place if it was not
counteracted by another circumstance ; the gas is lique-
fied by incorporating with the water, and gives  out ils
latent heat.   The condensation of the  gas  more than
counterbalances the expansion of the water ; therefore,
upon the whole, heat is produced.—But rf you dissolve
ammoniacal gas with ice or snow,  cold is produced.—
Can you account for that ?
   Emily.  The gas, in being condensed into a liquid,
must give out heat  ; and, on the other  hand, the snow
or ice, in being rarefied into a liquid must absorb heat ;
so that, between the opposite effects, 1 should have sup-
posed the original temperature would  have been pre-
served.
   Mr*.  B.  But you have forgotten to take into the ac-
 count the rarefaction of the water (or melted  ice) by
the impregnation of the gas ;  and this is the cause of
the cold which is ultimately produced.
   Caroline.   Is ihe  sal volatile (the smell of which so
strongly resembles hartshorn) likewise a preparation of
 ammonia ?
   Mr*  B.   It is carbonat of ammonia dissolved in wa-
 ter ; and which, in its concrete s.ate, is commonly  call-
 ed salts of hartshorn,   Ammonia is caustic like the fiv
 ed alkalies, as you  may judge by the  pungent  effects
 of hartshorn,   which  cannot be taken internally or ap-
 plied to delicate external parts, without being plentiful- 
163
ly diluted with water—Oil and acids are very excellent'
antidotes for alkaline poisons ; can you guess why ?
  Caroline.  Perhaps, because  the oil combines with
the alkali, and forms soap, and thus  destroys its caustic
properties ;  and the acid converts it into  a compound
salt, which I suppose, is  not so pernicious as caustic al-
kali.
Airs. B.  Precisely so^
  Amnioniacal  gas, if it he mixed  with atmospherical
aiv, and a burning taper repeatedly plunged into it,  will
burn with a large flame  of a peculiar yellow colour.
  Emily.  I  thought that  all the alkalies  were incom-
bustible.
  Caroline.   Besides, you say that flame is produced by
the combustion of hydrogen only ?
   Mr*  B.   And is not hydrogen gas one of the con-
stituents of ammoniacal gas ? Therefore,  though gen-
erally speaking, the alkalies are incombustible, yet  one
of the  constituents  of ammonia is eminently  combus-
tible.
  Emily.  I  own I had  forgotten that ammonia  was a
compound.   But pray tell me, can ammonia be pro-
cured from this Lybian salt only ?
   Mr*.  B.   So far from it, that it is contained in,  and
may be extracted from,  all animal substances whatever.
Hydrogen and nitrogen are two of the chief constitu-
ents of animal matter :  it  is therefore not surprising
that they should occasionally meet and combine in those
proportions that compose ammonia.   But this alkali  is
more frequently generated by the spontaneous decom-
position of animal substances ; the hydrogen and nitro-
gen gasses that arise from putrified bodies combine, and
form the volatile alkali.
   Muriat  of ammonia, instead  of being exclusively
brought from Lybia, as  it originally was,  is now chief-
ly prepared in Europe,  by chemical processes.  Am-
monia, although principally extracted from this salt,
can  only be produced by a great variety of other sub-
stances.  The horns of cattle,  especially those of the
deer, yield  it in abundance, and it is from this circum-
stance  that a solution of ammonia  in  water has been 
164
 called  hartshorn.   It may  likewise be procured  from
 wool, flesh and bones ; in a word, any animal substance
 whatever yields it by decomposition.
   We  sh..ll now lay aside the alkalies, however import-
 ant the subject may be, till we treat of their combination
 with  acids.   The next time we  meet we shall examine
 the earths,  which will complete our review of the class
 of simple bodies, after which we shall  proceed to  their
 several combinations.

   • If. however, this defence of the general theory be true, it ought
 to be found, on accurate elimination, that a certain quantity of
 heat ultimately disappears. or should this explanation be rejected,
 the phenomenon might be accounted for by supposing that a solu-
 tion of alkali in water has less capacity for heat than either water
 or alkali in their separate state.



              Conservation xi.

                     On Earths.


                      Mrs. B.
   The earths, which we are to-day to examine are ten
 in number:
        SILEX,                   STRONTITES,
        ALUMINE,                YTTUIA,
        BAKYTES,                GLUCINA,
        LIME,                   EIKCONIA,
       MAGNFCIA,               GARGONIA.
   The  five last  are of a very late discovery ; their pro-
 perties  are  but  imperfectly known ;  and as thty have
 not yet  been applied to  use, it will be unRecessary to
 enter into any  particulars respecting  them  ; we  shall
confine  our  remarks, therefore, to  the  six  first.   The
earths in general  are, like the  alkalies, incombustible
 substances.
   Caroline.   Yet I have  seen turf burnt in the country,
and it makes an  excellent fire ;  the earth becomes red
hot, and produces a very great quantity of heat. 
165
  Mrs. B.  It is not the earth that burns my dear, but'
the roots, grass, and other remnants of vegetables that
are intermixed with it.  The caloric, which is  produ-
ced by the combustion of these substances, makes the
earth red hot,  and this being  a bad conductor of  heat,
retains its caloric a long time ; but were you to examine
it when cooled, vou would find  that it had not absorbed
one particle of oxygen, nor suffered any alteration  from
the fire.   Earth is,  however, from the  circumstance
just mentioned, an  excellent refiecter of heat, and  owes
its utility when mixed with fuel, solely to that property.
It is in this point of view that Count Rutnford has re-
commended balls of incombustible substances to be ar-
ranged in  fire-places, and mixed  with  the  coals, by
which means the caloric disengaged by the combustion
of the latter, is more perfectly reflected into the room,
and an expense of fuel is saved.
   Earth,  you know,  was supposed to be one  of the
four elements ; but now that a variety of elements have
been discovered and clearly discriminated, no single one
can be exclusively called an  element; and as none of
them  have been decomposed, they  have an equal title
to the rank of simple bodies, which are the  only elements
that we now acknowledge. It is from these earths, eith-
er in their  simple  state, or mixed together and combi-
ned with other minerals, that the solid part of  our globe
is formed.
   Emi.'y.   When  I think of the great  variety of soils, I
am  astonished that there are not a greater number o£
earihs to form  them.
   Mr*.  B   You  might, indeed,  almost confine that
number to  four ;  for barytes, strontites, and the others
of late discovery,  act  hut so sm.ll a part is this  great
theatre, tiiat they cannot be reckoned as essential to the
general  formation  ol the glooe.   And you  must not
cu.itiiie your idea of earths to the formation of soil ; for
reck, marble, chalk, slate, sand, flint, and all kinds of
stones, from the precious jewel to the commonest peb-
bles ; in a word all ihe immense variety of mineral pro-
ducts, may be referred to some, of these earihs, cither in>
a simple state, or combined the one with the other, o*
blended with other ingredients. 
166
  Caroline.  Precious stones composed of earth !  That
seems very difficult to conceive.
  Emily.  Is it  more extraordinary than that the most
precious of all jewels, diamond, should be composed of
carbone ? But diamond forms an exception, Mrs.  B—;
for, though a stone, it is not composed of earth.
  Mrs.  B.   I did not specify the exception, as I knew
you were so well acquainted with it    Besides, I would
call diamond a mineral rather than a  stone, as the lat-
ter term always implies the presence  of some earth.
  Caroline.  I cannot conceive how such coarse mate-
rials can be converted into such beautiful productions.
  Mrs. B.  We  are very far from  understanding all
the secret resourses of nature ; but I do  not think the
spontaneous formation of the crystals, which we call
precious stones,  one of the most difficult phenomena to
compound.
  By the slow and  regular work of  ages, perhaps of
hundreds of ages,  these earths may  be  gradully  dis-
solved by water, and as  gradually deposited by their
solvent in the slow and undisturbed process of crystal-
lization.  The  regular arrangement of their particles,
during their reunion in a  solid niuss,  gives them that
brilliancy, transparency, and beauty,  for which  they
are so much admired : and renders them in appearance
so totally different from their rude and primitive ingre-
dients.
  Caroline   But how does it happen that they are spon-
taneously dissolved, and afterwards crystalized ?
  Airs. B.  The scarcity of many kinds of crystals, as
rubies, emeralds, topazes, Sec. shows  that their forma-
tion is not an operation very easily carried on in nature.
But cannot  you  imagine that when  water, holding in
solution some particles of earth, filters through the cre-
vices of hills or mountains, and at length dribbles into
some cavern, each successive drop may be slowly eva-
porated,  leaving behind it the particle of earth  which
it held in solution ?  You know that cryitalization is
more regular and  perfect, in proportion as the  evapor-
ation of the solvent is slow and uniform ; Nature, there*
fore, who knows no Umit of time, has, in all works of 
i6r
this kind, an infinite advantage over any artist who at-
tempts to imitate such productions.
  Emily.   I can now conceive that the arrangement of
the particles of earth,  during crystallization, may be
such as to occasion transparency, by admitting a  free
passage to the rays  of light; but I cannot understand
why crystallized earths should asssume such beautiful
colours as most of them do.  Sapphire, for instance, is
of a celestial blue ;  ruby, a deep red ; topaz, a brilliant
yellow ?
  Mr*  B.  Nothing  is more  simple than to suppose
that the arrangment of their  particles  is  such, as to
transmit some of the coloured rays of light, and to re-
flect others, in which case the stone must  appear of
the colour of the  rays which it reflects   But, besides,
it frequently happens, that the colour of a stone is  ow-
ing to a mixture of some metallic matter.
  Caroline.  Pray, are the different kinds of precious
stones each composed  of one individual earth, or  are
thev formed ofa combination of several earths ?
  Airs. B  A great variety of materials enters  into
the combination of most of them ; not  only several
earths, but son climes salts and  metals.   The  earths,
however,  in their  simple state, frequently form very
beautiful crystals ; and,  indeed, it is in that state only
that they can be obtained perfectly pure.
  Emily.  Is not the Derby shire spar produced  by  the
crysta.lization of Garths, in the way you have just  ex-
plained ? I have been in some of the  subteraneous cav-
erns where it is found, which are such as you  have des-
cribed.
  Mr*.  B  Yes ;  but  this spar is  a  very imperfect
specimen of crystallization ; it consists of a great vari-
ety  of ingredients confusedly blended together, as  you
may judge by its opacity, and by the various colours and
appearances which it  exhibits.
  But, in examining  the  earths in their  most perfect
and agreeable   form,  we must not lose sight of that
state in  which they  are  most commonly found,  and
which, if less pleasing to the eye,  is far more interest-
ing;by its utility. Before we proceed further,  however,
I should  observe, that although the earths are consid- 
168
 ered as simple substances (as chemists  have not  suc-
 ceeded in decomposing them) yet there  is considerable
 reason to suppose that they, as well as the alkalies,  are
 compound  bodies.   From the circumstance of their
 being incombustible, it has  been conjectured with some
 plausibility, that they may possfoly be Ixxlies  that have
 already  been  burnt, and  which being  saturated with
 oxygen, will not combine with  any additional quantity
 of that principle.
   Caroline.  But if they have  been burnt, they must
 contain oxygen, which .would easily be discovered ?
   Airs.  B.  Not if their attraction  for  it be so strong
 that  they  will  yield to no other substance ; for, dur-
 ing the state of combination, the properties of oxygen
 mav be so altered,  as to  be concealed entirely from
 our'observation  ; and it is possible that this may be the
 case  with  the  earths.  Let  us suppose them, for  in-
 stance, to have  heen originally some peculiar metals,
 whose affinity for oxygen was  so  great, that they  at-
 tracted  it  from every  substance,  and consequently
 would yield it 'o none ;  such metals must ever exist in
 the state of oxyds ; and, as we  should not have known
 them under their metalic form,  we  cou'd not consider
 them as metals, but  should distinguish them by  some
 specific  name,  as we have  done  with  regard 10  the
 earths.
   Caroline.   That,  indeed, seems  very  probable ; for
 metals, when oxydated, become  to all appearance a kind
 of earthly substance.
   Emily.  But Have the earths any of the properties of
 the metallic oxyds ?
   Mrs. B.  Their strongest  feature of resemblance is
 their property of combining with the acids to form com-
 pound salts.
  You must not, however, consider the idea of earths
 being burnt bodies, as any, thing more than mere con-
jecture ; for whatever may be  their contituents, until we
 succeed in decomposing them, we cannot consider them
in any other li^ht than as simple bodies.
   Emily  Pray which of the earths are endued with al-
 kaline properties ? 
169
  Mrs. B.   All of them, more or less ;  but there  are
four,  barytes, magnesia, lime, and  strontius,  which
are called alkaline earths, because they possess those
qualities in  so great a degree, as to  entitle them,  in
most  respects, to the rank of alkalies.  They  combine
and form compound  salts with acids in  the same way
a> .Ikalies ; they are, like them, susceptible of a con-
siderable  degree of causticity and are similarly acted
upon by chemical tests—The other earths,  silex and
alumine,  with one 01 two others of late discovery,  are
in some degree mere earthy,  that is to say. they pos-
sess more completely the properties common to all the
earths, which are, insipidity,  dryness,  unalterableness
in the fire, infusibility, &c.
   Caroline.   Yei, did you wot tell us that silex, or sili-
cious earths, when mixed with an alkali,  was fusible
and ran into  glass ?
   Mrs B.   Yes, my dear ;  but the characteristic pro-
pel ties of earths,  which I have mentioned, are to  be
considered as belonging to them in a state of purity on-
ly ;   a state  in  which they are very seldom to be met
with in nature.—Besides these general properties, each
earth has its own specific  characters, by  which it is dis-
tinguished from  any other substance.   Let us there-
fore review them separately.
   Silfx, or silicia, abounds in flint, sand, sondstone,
agate, jasper, &c.  It forms the basis of many precious
stones, and  particularly of those that strike fire with
steel.  It is  rough  to the touch, scratches and wears
away metal ; it is acted upon by no acid  but the fluoric,
and  is not soluble in water by any known process; but
nature certainly dissolves it by means  with which we
are  unacquainted,  and  thus produces a variety of sili-
cions  crystals, and amongst  these rock  crystal, which
is the purest specimen of this earth.   Silex appears to
have been intended by Providence to form the solid ba-
sis of the globe, to serve as a foundation for the origin-
al mountains and give them that hardness and dura-
bility which has enabled them to resist the various rev-
olutions which the surface of the earth has successively
undergone.    From  these  mountains silicious locks
have, during the course of ages, been gradually  detach- 
170
ed  by torrents of water, and brought  down  in  frag-
ments ; these, in the violence and rapidity of their des-
cent, are sometimes crumbled to sand, and in thit state
form the beds of rivers and of the sea, chiefly composed
ofsilicious  materials.  Sometimes  the  fragments are
broken without being pulverised by  their fall,  and as-
sume the  form  of pebbles,  which  gradually  become
rounded and polished.
  Emily.   Pray what is the true colour of silex, which
forms such a variety of different coloured substances ?
Sand is brown, flint is nearly black, and precious stones
are of all colours ?
  Airs. B.  Pure silex, such as is found only in the
chemist's laboratory, is  perfectly white,  and  the  vari-
ous  colours which it assumes, in the different substan-
ces you have just mentioned,  proceed from the differ-
ent ingredients with which it is mixed in them.
  Caroline.  I wonder that silex is not more valuable,
since it forms the basis of so many precious stones.
  Airs. B.  You must not forget that the value we set
upon precious stones, depends in a L,reat measure  upon
the scarcity with which nature affords them ; for were
those productions either common, or perfectly iroitable
by  art, they  would no  longer, notwithstanding  their
beauty, be so highly  esteemed.  But the real value of
siheious earth, in many of the most useful arts, is very
extensive.   Mixed with cliy, it forms the basis  of all
the  various kinds of earthen ware, from the most com-
mon utensils to the most refined ornaments
   Emily.  And we  must not forget ils importance in
the  formation (if glass with potash.
   Airs. B.   Nor should we omit to mention,  likewise,
many other important uses of silex, such as being the
chief ingredient of some of the most durable  cements,
of mortars, &c.
   I said before, that silicious earth combined  «vith no
 acid but the fluoric :  it is for this reason that  glass is
 liable to bj ullackccl by that acid only,  which,  from its,
strong affinity for sitex.  forces that substance  from its
 combination with the potash, and thus destroys the glass.
   We will now  hasten to proceed to the  other earths,.
 for  I am rather  apprehensive of your growittg  weary
 of this part of our subject. 
m
  Caroline.  The history of earths is not quite so enter*
taining as that of the other simple substances.
  Mr*. B.   Perhaps not; but it is absolutely indispens-
able that you should know something of them ; for they
form the  basis of so many interesting and important
compounds, that their total omission  would throw great
obscurity on our general outline  of chemical science.
We shall, however, review them in as cursory a manner
as the subject will  admit of
  Alumi ne derives its n »me from a compound salt cal-
led  alum, of which  it forms the basis.
  Caroline.   But it ought to be just the contary,  Mr?.
B.   The simple body should give, instead of taking  its
name from the compound.
  Mrs.  B.   Yery true, my  dear  ; but as the  com-
pound salt  was known long before its basis was  discov-
ered, it  was natural enough when  the  earth  was  at
length separated from the acid, that it should derive  its
name from the compound from which it was obtained.
However, to remove your scruples, we will call the salt
according  to the new nomenclature, salphat  of Allumine..
From this  combination, allumine may be obtained in its
pure sute ; it is then soft to the  touch,  makes  a  paste
with water, and  hardens in the  fire.  In nature, it is
found chiefly in clay, which contains a  considerable
proportion of this earth ; it is very abundant in fuller's
earth, slate, and a variety of other mineral productions.
There is indeed scarcely any  mineral substance  more
useful to'mankind than alumine.  In the siate of clay,
it fcrms  large  strata of the earth, gives consistency to
the soil of vallics, and of i.ll low  end  damp spots, such
as  swamps and marshes.   The  beds of lakes. ponds,;
and springs arc almost entirely  of clay ;  instead  of
allowing of the filtration of water, as sand does, it forms
an  impenetrable brttom, and by this means water is
ac  umulMed in the caverns of  the earth, producing
those reservoirs whence springs issue, and spout oui at
the surface.
  Emily.   I always thought that these subterraneous
reservoirs of water were beaded by some hard stone, or
s;ock, which the water could not penetrate.
  Afre. B.   Tnis is not the case  ; for in the  course of 
172
time water would penetrate, or wear away silex, or any
other kind  ofMone, while is is effectually  stopped by
c'av or allumine.
  The solid compact soils, such as are fit for corn,  owe
their consistence in a great measure to alumine  ;  this
earth  is therefore used to improve sandy or chalky soils,
which do not retain a sufficient quantity of water for the
purpose of vegetation
  Alumine is  the mosf essential ingredient in all potte-
ries   It enters  into the  composition of briek, as well
as ihat  of  the finest china ; the  addition of silex and
water hardens it.  renders it susceptible of a degree of
vitrification, and makes it perfectly fit for its  various
purposes.
  Caroline. I can  scarcely conceive that  brick  and
china could be made of the same materials.
  Mrs. B.  Brick  consists  almost entirely of baked •
clay ; but a certain proportion of silex is essential to
the formation  of earthen or stone  ware.   In common
potteries sand is used for that purpose  ; a  more pure
silex is, I b litve necessary for the composition of por-
celain, as well  as a finer kind of clay ; and these mate-
rials are, no doubt, more  carefully prepared, and curi-
ously  wrought, in the one cise than in the other.  Por-
celain  owes its beautiful  semi-transparency  to  a com-
mencement of vitrification.
  Emily.   But the commonest earthen ware,  though
not transparent, is covered with a  kind of glazing
  Mrs. B   That precaution is equally necessary  fou
Use as for beauty, as the ware would be liable to be spoiU
ed and corroded  by a variety  of substances, if not  cov-
ered with  a coating ol this kind.   In porcelain it con*
sists  of enamel,  which is a fine  white opaque glass,
formed of  metalic  oxyds, sand, salts,  and  such other
materials as are susceptible of vitrification.  The glazing
of common  earthen ware  is made  chiefly  of oxyd
of lead, or sometimes merely of salt,  which when
thinly  spread over earthen  vessels, will, at a certain
heat, run into opaque  glass.
  Caroline. And of what nature are the colours which
are used for painting china ? 
17 a
  Mrs. B.   They are all composed of metallic oxyds,
so that these colours, instead of receiving injury from
the application of fire, are strengthened and developed
by its action, which  causes them to undergo different
degrees of oxydation.
  Alumine and silex are not only often  combined  by
art, but they have in  nature a very strong tendency to
unite,  and are found combined, in different proportions,
in various gems and other minerals.  Indeed, many of
the precious  stones,  such as ruby, oriental sapphire,
amethyst, 8cc  consist chiefly of Alumine.
  We may now proceed to the alkaline earths.  I shall
say but a few words on Barytes, #*- it is hardly ever
used, except in chemical laboratories.   It is remarka-
ble for  its great weight,  and its ?'ror g alkaline proper-
ties,  such as  destroying animal substances,  turning
green some blue vegetable colours, and shewing a pow-
erful attraction for acids ; this last property it possesses
to such a degree, particularly  with regard to the sul-
phuric acid, that it will always detect its presence in any
substance or  combination whatever,  by immediately
uniting with it and forming a sulphat of barytes.   This
renders it a  very valuable  chemical test.  It is found
pretty  abundantly in nature in the state of carbonat,
from which the pure  earth can be easily separated.
  The  next earth we have to consider is  Lime.—.This
is a substance  of too great and general importance to
be passed over so slightly as the last.
  Lime is strongly alkaline.   In nature  it is not met
with in its simple state, as its affinity for water and car-
bonic acid is so great, that it is always found combined
with these substances, with which it forms the common
lime-stone ; but it is separated in the  kiln from these
ingredients, which are volatilized whenever a sufficient
degree of heat is applied.
  Emily.  Pure lime then is nothing  but  lime-stone,
which has been deprived in the kiln, of its water, and
carbonic acid ?
  Mrs. B.   Precisely ;  in this state it is  called quick-
lime, and  is so caustic, that it is capable of decompos-
ing the dead bodies of animals very rapidlv, without
                         Q2 
'*,
their undergoing the process of putrefaction.—I have
here some quick-lime, which is kept carefully corked
up in a bottle  to prevent the  access of air ; for were it
at all exposed to the atmosphere, it  would absorb both
moisture and  carbonic acid gas from it,  and be soon
slaked.   Here is also some lime-stone—we shall pour
a little water on each, and  observe the effects that  re-
sult  from it.
  Caroline.  How quick the lime hisses !  It is become
excessively hot!—It swells, and now it bursts and crum-
bles  to powder, while the water on the lime-stone  ap-
pears to produce no kind of alteration.
  Mr*. B   Because the lime-stone is already saturat-
ed with water, whilst the quick-lime, which has been
deprived of it in the kiln, combines with  it with very
great avidity, and produces this  prodigious disengage-
ment of heat,  the cause of which I formerly explained
to you ; do you recollect it ?
  Emily.   \es ;  you said that the heat did not proceed
from the lime, but from the water which was solidified,
and  thus parted with its heat of liqudity.
  Mr*. B.  Very well.   If we continue to add succes-
ive quantities of water to the  lime after being slaked
and crumbled  as  you see, it will then gradually be  dif-
fused in the water, till it will at length be dissolved in it,
and entirely disappear ; but for this purpose it requires
no less that 7i<0 time its  weight of water..  This solui
 icr.is called lime-water.
  Caroline.  How very small, then, is the proportion
of lime dissolved.
  Mrs. B.  Barytes is still of more difficult solution ;
it dissolves only in 900 times its weight of water:  but
it is  much more soluble in the state of crystals.  The
liquid contained in this bottle is lime-water ;  it is often
used as a medicine,  chiefly, I believe, for the purpose
of combining  with,  and neutralizing the  super-abun-
dant  acid which it meets with in the stomach.
  Emily.   I am surprised that it  is so perfectly clear :.
it does not at all partake of the whiteness of lime.
  Mr*. B.  Have you forgotten that, in solutions,  the
solid body is so minutely subdivided by the fluid, as to
become invisible, and therefore will not in the least  de-
gree impair the transparency of the  solvent. 
175    '
  1  sard that the attraction  of lime for carbonic  acid
was  so strong, that it would absorb  it from the atmosr
phere.   We may see this effect by exposing a glass of
lime-water to the air ; the lime  will  then separate  from
the water,  combine with the  carbonic acid, and  re-ap-
pear on the surface in the form  of a white film, which is
carbonet of lime, commonly called chalk.
   Caroline.  Chalk is then a  compound salt ?  I never
should have supposed that those immense beds of chalk
that  we see in many parts of the country,  were a  salt.
Now, the white film begins to appear on the surface  of
the  water;  but it is far  from  resembling hard  solid
chalk.
   Mrs. B   That is owing to its state of extreme divis-
ion ; in a little time it will collect into  a more  compact
mass, and subside at the bottom of the glass.
   If you  breathe into  lime-water, the carbonic acid,
which is mixed  with the air that you expire,  will  pro-
duce tlie same effect.   It is an  experiment easily made
—I  shall pour some lime-water into this glass tube, and,
by breathing repeatedly into it, you will soon  perceive
a precipitation of chalk—.
   Emily.   I see already a small white cloud formed.
   Mrs.  B.   It is composed of  minute particles of
chalk ; at  present it floats in  the water, but it will  soon
subside..
   Carbonet of lime, or chalk,  you see, is insoluble  in
water,  since  the lime which  was dissolved re-appears
when converted into chalk ; but you must  take notice of
a very singulai  circumstance which is,  that chalk is so-
luble in water impregnated with carbonic  acid.
   Caroline.   It  is very curious, indeed,  that carbonic a-
cid gas srr|#ild render'lime soluble in one  instance, and
insoluble in the other !
   Mr*.  B-  I have here a little bottle of Seltzer water,
which, you know, is strongly impregnated with carbon*
ic acid—let us pour a little of it into a glass of  lime wa-
ter.   You  see that it immediately forms a precipitation
of carbonat of lime !
   Emily.  Yes, a white cloud appears.
   Mr*. B.  I shall now pour an additional.quantity  oi
the Seltzer water into the lime water— 
176
   Emily.  How singular!  The  cloud  is re-dissolved,
 and the liquid is  again transparent.
   Mrs. B.   All the mystery depends upon this circum-
 stance, that carbonat of iime is soluble in carbonic acid,
 whilst it is insoluble in water ; the first  quantity  of car-
 bonic  acid,  therefore, which  I introduced into  the
 lime water, was employed  in forming the carbonat of
 lime, which remained visible, until an additional quan-
 tity of carbonic acid dissolved it.   Thus, you see, when
 the lime and carbonic acid are in proper proportions to
 form chalk, the white cloud appears, but when the acid
 predominates, the chalk is  no sooner  formed than it is
 dissolved.
   Caroline.   That is now the case ; but  let us try whe-
 ther a further addition of lime water will again precip-
 itate the chalk.
   Emily.   It does, indeed ! the  cloud re-appears, be-
 cause, I suppose, there is now no more of the carbon-
 ic acid than is necessary to form chalk  : and, in order
 to dissolve the chalk, a superabundance of acid  is re-
 quired.
   Airs. B.  We have, I think, carried this experiment
 far enough  ; every  repitition would  but exhibit the
 same appearances.
   Lime combines with most of the acids, to which the
 carbonic (being the weakest) readily yields it  ;  but
 these combinations we shall have an opportunity of no-
 ticing  more  particularly  hereafter.   It unites with
phosphorus, and with  sulphur,  in  their simple state ;
in short, of all the earths, lime is that which nature em-
ploys most frequently and most abundantly, in its innu-
 merable combinations.  It is the basis of all calcareous
 earths and stones ; we find it likewise in  the'1 animal and
 the vegetable creations.
   Emily.  And in  the arts is not lime of a very great
 utility ?
   Mr*.  B.  Scarcely  any  substance more  so ; you
know that it is  a most essential requisite in building as
it constitutes the basis of all cements,  such as mortars,
 stucco, plaster, &c.
   Lime is also of infinite importance in agriculture ;  it
lightens and warms, soils that are too cold, and com- 
177
pact in consequence of too great a proportion of clay.
But it would be endless to enumerate the various pur-
poses for which it is employed ; and you know  enough
of it to form some idea of its importance : we  shall,
therefore, now proceed to the third alkaline earth, Mag-
kesca.
   Caroline   I  am already pretty well acquainted with
that earth, it is a medicine.
   Mr*. 13.  It is  in the state of carbonat that magnesia
is  usually  employed  medicinally ;  it then differs but
little in appearance from its simple  form, which is that
of a very fine light white powder.   It dissolves in  2000
times  its  weight of water,  but  forms with acids ex-
tremely soluble salt?.   It  has not so great  an attrac-7
tion for acids as lime, and consequently yields them to
the latter.   It  is  found in  a great  variety of mineral
combinations, such as slate, mica, amianthus, and  more
particularly  in a certain lime-stone, which  has lately
been discovered by  Mr. Tennant to contain  it in  very
great quantities  It does not attract  and  solidify water,
like lime ,• but  when mixed  with water, and exposed to
the atmosphere, it slowly absorbs carbonic acid  from
the latter, and thus loses its causticity.  Its chief use in
medicine is, like that of lime, derived from its readiness
to combine  with, and neautralize,  the  acid which  it
meets  wilh in the stomach.
   Emily.   Yet,  you said it was taken in the state of
carbonat, in  which case it is already combined with an
acid ?
   Airs. B.   Yes ;  but the carbonic is the last of all the
acids in the order  of  affi lities ; it  will  therefore yield
the magnesia to any of the others.   It is, however, fre-
quently taken in its caustic state as  a remedy for  flatu-
lence.   Combined with sulphuric acid, magnesia lorms
another and more powerful medicine, commonly called
epsom  salt.
   Caroline.   And properly,  sulphat of magnesia, I sup*
pose ;  Pray why  was it ever called Epsom salt?
   Mr*. B. Because there is a spring in the neighbor-
hood of Epsom, which contains this salt  in great abun-
dance. 
17*
  The last alkaline earth which we have to mention is
Strontian or  Strontites. discovered by Dr. Hope,
a few years ago.   It so strongly  resembles barytes in
its properties, and is so spa ii-gly found in nature,  and
of so little use in the arts, that it will not be necessary
to enter into any particulars respecting it.   One of the
most  remarkable characteristic properties  of strontites,
is. that its salts, when dissolved in  spirit of wine, tinge
the flame of a deep red, or blood colour.
  We shall here conclude this lecture  ; and at our next
Meeting, you will be introduced  to a subject totally dif-
ferent from any of the preceding. 
    Contoettfations
         ON
  CHEMISTRY,

     VOLUME II.

ON COMPOUND BODIES. 
\ 
        Conversational
               ON

CHEMISTRY.
€N COMPOUND  BODIES.
             ConDergation xn.

        •y THE AffRJCflON OF C03lPOSlfIOH.

                    Mrs.  B.

  HAVING completed our examination of the simple
-or elementary bodies, we are now to proceed  to those
of a compound nature ; but before we enter on this ex-
tensive  subject, it will be necessary to make you ac-
quainted with  the principal laws by which  chemical
•combinations are governed.
   You recollect, I hope, what we have formerly said of
the nature of the attraction of composition, or  chemical
attraction, or affinity, as it is also called ?
   Emily.  Yes, I think perfectly ; it is the  attraction
that subsists between bodies of a different nature, which
occasions them to combine and form a compound, when
they come in contact.
   Mrs.  B.  Very well :  your definition comprehends
 the first law of chemical attraction, which is, that it takes
place r>nbi between bodies of a different nature ; as,  for in-
 stance, between an acid and an alkali; between oxygen
and a metal, &c.
                        R 
184
. Caroline.   That we understand of course;  for the
attraction between particles of a similar nature is that of
aggregation, or cohesion, which is independant of any
chemical power.
  Mrs. B.   The second law of chemical  attraction,  is
that it takes place only between the most minute fiartides  of
bodies ;  therefore, the more  you divide the particles  of
the bodies to be combined, the more readily they act
upon each other.
  Caroline.   That is again a circumstance which we
might have  supposed ; for the finer the particles of the
two substances are, the more easily and perfectly they
will come in contact  with each other, which must great-
ly facilitate their union.   It was for this purpose, you
said, that you used iron filings  in  preference  to wires
or pieces of iron, for the decomposition of water.
  Mr*. B.   It was  once supposed that  no mechanical
power could divide bodies into particles sufficiently min-
ute for them to act  upon each other; and that, in or-
der to produce the extreme division requisite for a che-
mical action, one,  if  not both of the bodies, should be
in a fluid state.  There are, however, a few instances,
in which two solid bodies very  finely pulverized, exert
a chemical  action on one another; but such exceptions
to the general  rule are very rare indeed.
  Emily.   In all  the combinations that we have hither-
to  seen, one of the constituents has, 1  believe, been
either liquor or aeriform.  In combustions, for instance,
the oxygen is taken from the atmosphere, in which it
existed in the state of gas ; and whenever we have seen
acids combine with metals  or with alkalies, they were
eithid in a liquid or an aeriform state.
   Mr*.  B.  The third law  of chemical attraction  is,
that it can take place  between two, three, fourt  or even a
greater number of bodies.—Can  you recollect any exam-
ples  of these double, triple, and  quadruple combina-
tions  ?
  Caroline.   Oxyds and acids are  bodies composed  of
two eonstituents ; compound salts of three : but I   re-
collect no instance of the combination of four principles,
unless  it be amongst  the earths in  the formation  of
stones. 
1SS
  Mr*. B.  Such examples  very frequently  occur a'
tnongst the earths ; but you might have quoted,  as  in-
stances of quadruple  compounds, all  those  that result
from the combination of acids with  ammonia,  or vola-
tile alkali.
  Caroline.  True.  As ammonia is itself a compound,
hs union with the  acids, which  are also composed of
two principles, must form a quadruple combination.
  Mrs. B.  You will soon become acquainted with a
great  variety  of these complicated compounds.   The
fourth law of chemical attraction is, that a change of tem-
perature always takes place at the moment of combination.
This is occasioned by the change of capacity for heat,
which takes place  in bodies, when passing from a sim-
ple to a combined state.   Do you recollect any instance
of this, Emily ?
   Emily.  Yes  ; when lime, or any of the alkalies, or
alkaline  earths, combine  with,  and solidify  water, the
whole of its heat of liquidity is set at  liberty.
   Airs. B.  I had rather that you had chosen any oth-
er instance, as the union of water with the alkalies and
alkaline earths is  not,  strictly  speaking, a chemical
combination ;  for the water remains in the stale of wa-
ter tho' condensed and solidified in the alkali ;  and can
be  separated from  it and restored to  its fluid state, mere-
ly by the restitution of its heat of liquidity.
   1 am going to show  you a very striking  instance of
the change  of  temperature arising from the combina-
tion of different bodies —I shall pour  some nitrous acid
on this small quantity of oil of turpentine—the oil will
instantly combine with the oxygen of the acid, and pro-
duce a considerable change of temperature.
   Caroline.   What a bh.ze \  The temperature  of the
oil  and the acid  must be elevated,  indeed, to  produce
such violent combustion.
   Mr*. B.  There is.  however, a peculiarity in this
combustion, which I, that the oxygen, instead  of being
derived from the atmosphere alone, is principally sup-
plied  bv the acid itself.
  Emily,   And are not all combustions instances of the 
184
change of temperature produced by the chemical  com-
bination of two bodies ?
  Airs.  B.  Undoubtedly ;  when oxygen loses its gas-
eous form in order to  combine with a solid body, it be-
comes condensed, and the caloric evolved produces the
elevation of temperature.  The specific gravity of bo.
dies is at the  same time altered by chemical combina-
tion ; for in consequence of a change  of capacity for
heat, a change of density must be produced.
   Caroline.   That was the case with the sulphuric acid
and water, which by being mixed together, gave  out  a
great deal of lieat, and proportionally increased in den-
sity.
   Mr*.  B.   I do not think the instance to which  you
refer is quite in point; for there does not appear  to be
what we have called  a  true  chemical  combination be-
tween sulphuric acid and water, since they  are only
mixed  together, and undergo no other change  than  a
lo^s  of caloric, so that they may  he separated again
from each other merely by evaporating the water.  Yet
you have truly observed in this instance that  the parti-
cles of the two fluids  so far penetrate each other,  as to
form a  more compact substance,  in  consequence  of
 which a quantity of latent heat is forced out, and  there.
 is an increase of specific gravity.
    The 5th law  of chemical  attraction is, that the pro-
perties which characterise bodies when separated, are altered
 or destroyed  by their combination.
    Caroline.   Certainly  ; what, for instance, can  be  so
 different from water as the  hydrogen and oxygen gas-
 es ?
    Emily.   Or  what more unlike sulphat of iron, than
 iron or sulphuric acid  ?
    Caroline.   But of all metamorphoses, thai of sand and
 potash into glass, is the most striking 1
    Mr*.  B.  Every chemical combination is an illustra-
 tion of this rule.   But  let us proceed—
    The 6ih law is, that the force of  chemical  affinity;  be-
  tween the constituents of a body, is estimated by that  which.
 is required for their separation. This force is by no means
  proportional to the facility with which bodies unite ;  for 
185
  manganese, for instance,  which,  you know,  has  st
  great an attraction for oxy gen, that it is  never  found in
  a metallic state, yields it more easily than any other me-'
  tal.
    Caroline.  And likewise  lime, which has a great at-
  traction for caibonic acid, yields it to any of the other
  acids, and even to heat alone.
    Emily.   But,  Mrs. B.  you speak of estimating the
  force of attraction between  bodies, by the force requir-
  ed  to separate them ; how can you measure these for-
  ces T
   Mrs. B.   They  cannot  be  precisely measured, but
  they are comparatively  ascertained by experiment, and
  can be represented by numbers which express the reia--
  tive degrees of attraction.
   The 7th law is, that  bodies  have amongst themselves
  different degrees of attraction.   Upon this law (which
  you may have discovered  yourselves  long  since), the
  whole  science  of chemistry depends; for it is by means
 of the various degrees  of affinity which bodies  have
 for  each other,  that all the chemical compositions and
 decompositions are  effected.  Thus if  you pour sul-
 phuric acid on soap,  it  will  combine with the alkali  to
 the  exclusion of the oil,  and form a  sulphat of potash.
 Every chemical fact or experiment is an instance  of the
 same kind ;  and whenever the decomposition of a body
 is performed bv the addition  of any single new sub-
 stance, it is said to be effected by simple elective attrac-
 tions.  But it often happens,  that no simple  substance
 will  decompose a body, and that, in order to effect  this,
 you  must offer to  the compound a body which is  itself
 composed of two, or sometimes three principles,  which
 would not, each separately, perform the decomposition.
 In this case there are two new compounds formed in'
 Consequence of a reciprocal decomposition and recom-
 position.  All instances  of this  kind are called double'
 elective attractions.
  Caroline.   I confess I do not Understand this clearly.
  Mrs.  B.  You will easily comprehend it by the as-
sistance of this diagram, in  which the reciprocal forces'
of attraction are represented by numbers:
                        R 3 
186
       Original Compound.
        Sulphat of Soda.
v    Soda   8 Sulphuric Acid.-'
X           O              v
  Result X7 Divellertt Attractions6$ 136    itoufr
  Nitrat  o            ^              v   Sulphat
 of  Soda, x            2              I   oF Lime'
         x            5.              e

         &            5              ft
         X            *   .           0
         XNitric Acid 4 Lime.        <(

         i           72              t
         X            '^              A
               Original Compound.
                  Nitrat of Lime.

  We here suppose  that we are to decompose sulphat
of soda; that is to separate the acid from  the alkali :
if, for this purpose we add some lime, in order to make
it combine with the acid, we shall fail in our attempt, be-
cause the soda and the sulphuric acid attract each oth--
erby a force which is (by way of supposition^ repre-
sented by the number 8 ; while the lime tends to unite
with this acid by an affinity equal to the number  6. It
is plain, therefore, that the sulphat  of soda will not be
decomposed, since  a force equal to 8  cannot be over-
come by a force equal only to 6.
  Caroline.  So far, this appears very clear.
  Mrs. B.  If, on the other hand,  we endeavour to de-
compose this salt by  nitric acid, which tends to combine-
with  soda, we  shall be  equally unsuccessful, as nitric
acid tends to unite with the alkali by a force  equal only
to 7.
  In neither of these cases  of simple elective attrac-
tion,  therefore, can  we accomplish our purpose.   But
let  us previously combine together  the lime and  nitric
 acid, so as  to form  a nitrat of  lime, a compound salt, 
187
the constituents of which are united by a poorer equal
to 4.  If then we present this compound to the sulphat
of soda,  a  decomposition will ensne, because the sum
of the forces  which tend to preserve the two salts in
their actual state, is not equal to that of the forces which
tend to decompose them, and to form new combinations.
The nitric  acid, therefore, will combine with the soda,
and the sulphuric acid with the lime.
   Caroline.  I understand  you  now very well.  This
double effect takes place because the numbers 8 and 4,
which represent the degrees of attraction of the con-
stituents of the two original salts, make a sum less than
the numbers 7 and 6,  which represent the degrees of
attraction of the two new compounds that will in conse-
quence be formed.
   Mr*.  B.  Precisely so.
   Caroline.  But what is the meaning  of quiescent and
divellant forces, which are written in the diagram ?
   Mr*.  B.  Quiescent forces are those which  tend to
preserve compounds in a state of rest, or such as they
actually are : divellant forces are those  which tend to
destroy that state of combination, and to form new com-
 pounds.
   These are the principal circumstances relative to the
 doctrine of chemical attractions, which have been laid
down as rules by modern chemists 't a few others might
be mentioned respecting the same theory, but of less
importance, and  sudh *as would take us too far from our
plan.   I should,  however, not omit to mention that Mr.
 Berthollet, a celebrated French  chemist,  has shewn,
that whenever in chemical operations there is a display
 of contrary attractions, the combinations  which  take
 place depend not only upon the affinities,  but also, in
 some degree, on the proportions of the substances con-
 cerned. 
          1-83

aTonbewatton  xm.
On Compound Bodies.
                      Mrs. B.

   Having now  given  you  some idea of the laws by
 which chemical attractions  are governed, we may pro-
 ceed to the  examination of bodies that are formed in
 consequence of  these attractions.
   The first class of compounds that present themselves
 to our notice, in our  gradual ascent to the most com-
 plicated combinations, are bodies composed of only two
 principles.  The sulphurets,  phosphorets,  carburets,
 &c.   are  of this description;  but the most numerous
 and important of these compounds are the combinations
 of oxygen with the  various  simple substances with
 which it has a tendency to unite.  Of these you  have
 already acquired some knowledge, and I hope you will
 not be at a loss to tell me the general  names by which
 the combinations of oxygen with other substances are
 distinguished  ?
  Emily.  I believe you told us that all the combina--
 tions of oxygen produced either oxyds or acids ?
  Mrs. B.  Very right; and with what  simple bodies
 will oxygen combine, Caroline !
  Caroline.  With all  the elementary substances, ex-
 cepting the earths and  alkalies.
  Mrs. B. Very well, my dear; we may now, there-
 fore, come to the oxyds and acids.  Of the metallic
oxyds, you have  already some general notions.  This
subject, though highly interesting in its details, is not of
sufficient importance to our concise view of chemistry,
to be particularly treated of;  but it is absolutely  ne-
cessary that you should be better acquainted with  th«^ 
189
stents, and likewise with their combinations with' the al-
kalies, which  form the triple compound called Neu-
tral Salts.
   You have, I believe, a clear idea of the nomencla-
ture by which the base (or radical) of the acid, and the
various degrees of acidification, are expressed ?
   Emily.  ' Yes, I think so;  the acid is distinguished
by the name of its base, and its degree of acidity by the
termination of that name in ous or ic ; thus sulphurous
acid is that formed by the smallest proportion of oxygen
combined with sulphur ; sulphuric  acid is  that which
results from the combination  of sulphur with the great-
est quantity of oxygen.
   Mr*. B.  A still greater latitude may, in many cases,
be allowed  to the proportions of oxygen than  can be
combined with acidifiable radicals ;  for several of these
radicals are susceptible of uniting with a quantity of ox-
ygen so small as to be insufficient to give  them the
properties of acids; in these cases therefore, they are
converted  into oxyds.   Such is  sulphur, which by ex-
posure to the  atmosphere with a degree of heat inad-
equate to  produce inflammation,  absorbs a small pro-
portion of oxygen, which colours it red or brown.  This
therefore is the first degree of oxygenation of sulphur *
the 2d converts it into sulphurous acid ;  the Sd into sul-
phuric acid'; and, 4thly, it it was found capable of com-
bining with a  still larger proportion of oxygen, it would
then be termed super-oxygenated sulphuric acid.
   Emif.   Are these  various degrees  of oxygenation
 common to all acids ?
   Mr*.  B.  No  ; they vary much in this respect; some
 are susceptible  of  only  one degree of oxygenation;
 others, of two, or  three ; there are but very few that
 will admit of more.
   Caroline.  The  modern nomenclature  must be  of
 immense advantage in  pointing out so easily the nature
 of the acids,  and their  various degrees of oxygenation*
    Mrs  B.  Certainly.   But great a,  are the^ advan-
 tages of the new nomenclature in this respect, it is not
 possible to apply it in its full extent to all the acids, be-
 cause the radicals or bases of some of them are still un-
 known. 
190
  Caroline.  If you are acquainted with the acid, I can-
sot understand how its bases can remain unknown ; you
have only to separate the oxygen  from it by  elective
attractions, and the bases must remain alone ?
  Mr*. B.  This is not always so easily accomplished
as you imagine ;  for there are some acids  which no
chemist has hitherto been able  to decompose by any
means whatever.  It appears  that  the bases of  these
undecompounded acids have so strong an attraction for
oxygen,  that they will yield it to no other substance ;
and in that case, you  know, all the efforts of the chem-
ists are vain.
   Emily.   But if these acids have never been  decom--
posed, should they not be  classed with the simple bo-
dies :  for you have repeatedly told  us that the simple
bodies are rather suGh as chemists are unable to decom-
pose, than such as are really supposed to consist of on-
ly one principle ?
   Mrs. B.   Analogy affords  us so  strong a proof of
the compound  nature of  the  undecompounded acids,
that I could never reconcile myself  to classing them
with  the  simple  bodies, though this  division-has  been
adopted  by several  chemical  writers.  It is certainly
tlie most  strictly regular ; but,  as a systematical ar-
rangement is of use only to assist the  memory in retain-
ing facts,  we may, I think be  allowed to deviate from
it when there is danger of producing confusion by  fol-
lowing it too closely :—and this, I believe,  would be
the case, if you  were taught to consider the undecom-
pounded acids as elementary bodies.
   Emily.   I am sure you would not deviate from the
methodical  arrangement  wiihout  good  reason.   But
pray  what are the names of  these  undecompounded
acids I
  Airs. B.   There are  three of that description :
       The Aluriutic acid.
       The Boracic acid.
       The Fluoric acid.
  Since  these  andi cannot derive their  names from
their radicals, they are called  after the compound sub-
stances irom which they are extracted. 
m
  Caroline.  We have heard of a great variety of acids;
pray how many are there in all ?
  Mr*. B.  I believe there  are reckoned at present
thirty-four, and  their number is constantly increasing,
as the science improves; but the most  important, and
those to which  we shall almost entirely confine our at-
tention, are but few.  I shall, however, give you a gen-
eral view of the whole ; and then we shall more partic-
ularly examine those that are the most essential.
   This class of bodies was formerly divided into mine-
ral,  vegetable, and animal acids, according to the sub-
stances from which they were extracted
   Caroline.   That I should think must have  been an
excellent arrangement; why was it altered ?
   Mr*.  B.   Because in many cases it produced con-
fusion.   In which  class,  for instance, would you  place
carbonic acid I
   Caroline.   Now I see the difficulty.   I should be at
a loss where to place it, as you have told us  that it ex-
ists in the animal, vegetable, and mineral kingdoms.
   Emily.  There would  be  the same  objection with
respect  to phosphoric  acid,  which, though  obtained
chiefly  from bones, can also, you said, be found in small
quantities in siones, and likewise in some plants
   Mr*. B.  You see, tlierefore, the propi iety of chang-
ing this mode  of classification.   These  objections do
not exist in the  present  nomenclature; for  the  com-
position and nature of each individual acid is in some de-
gree pointed rut,  instead of the class of bodies from
which it is extracted ; and, with  regard  to  the  more
 general division  of acids, they are classed under these
four heads :
   1st.  Acids of known and simple bases,  which  art
formed by the union of these  bases with oxygen.
   They are the  following :
        The Sulphuric    "\
            Carbonic
            .A itric         j
           Phosphoric    )>  Acids of known and sim-
            Arstnical      |        pie bases.
            Tungstenic    }
            Molybdenic    J 
192
   2dly. Those of unknown bases :
   The Muriatic       ")
       horacic          > Acids of unknown bases.
       Fluoric         J
   These two classes comprehend the most anciently
known and most important acids.   The  sulphuric, ni-
tric, and muriatic, were toirneily,and are still frequent-
ly, called mineral acids.
   3dly. Acids that have double or  binary radicals,  and
which consequently  consist of triple combinations.—
These are the vegetable  acids whose common  radical
is a compound of hydrogen and carbone.
   Caroline.  But if t!-c bases of all the vegetable acids
be the same, it sho> Id form but one acid ; it may in-
deed combine with different proportions of oxygen,  but
the nature of the acid must be the same ?
   Mr*. B.  The only difference  that exists in the  ba-
ses of vegetable acids, is the various proportions of hy-
drogen anil carbone from  which it is composed.  But
this is enough to produce a number of acids apparently
very dissimilar.  That  they do not,  however, differ
essentially, is proved by  their susceptibility  of being
converted into each other, by the  addition or subtraction
•f a portion of hydrogen or of carbone.
   The names of these acids  are,
       The Acetic
            Oxalic
            Tartarou*
           Curie
            Malic               Acids of double bases,
           Gallic           ^     being of vegetable
           Mucous                   origin.
           Benza'c
           Succinic
           Camiphoric
            Suberic
   The 4th class of acids consists of  these  which have
triple radicals, and  are  therefore  ol a still more com-
pound nature.   This class  comprehends  the animal
acids, which are: 
193
       The Lactic
           Prussic
           Formic
           Bombic       J>   Acids of triple bases, or
           Sebacic               animal acids.
           Zoonic
           Lithic
  I have given this summary account or enumeration
of the acids, as you may find it more satisfactory to
Imve at once an outline, or general notion of the extent
of the subject ; but we  shall  now confine ourselves to
the two first classes, which require our more immediate
attention ; and defer the remarks which  we shall have
to make on the others, till we  treat of the chemistry of
the animal and vegetable kingdoms.
  The acids of simple  and known radicals are all ca-
pable of being decomposed by combustible bodies, to
which they yield their oxygen  If, for instance I pour
•a drop of sulphuric acid on this piece of iron, it will pro-
duce a spot of rust ; you know what that is ?
  Caroline.  Yes, it is an oxyd,  formed by the oxygen
of the acid combining with the iron.
  Mrs. B.  In this case you  see the sulphur deposits
the oxygen by which it was acidified on the metal.—
And again, if we pour some acid on a compound combus-
tible substance, (we shall try  it on this piece of wood)
it will combine with one or more of the constituents of
that substance, and occasion a  decomposition.
  Emily.  It has changed the  colour of the wood to
black.  How is that ?
  Mrs. B.  The  oxygen  deposited by the acid has
burnt it;  you know that wood in burning becomes black
before it is reduced to ashes.  Whether  it derives the
oxygen which bums it from the atmosphere, or  from
any other source, the chemical effect on the wood is
the same.   In  the  case of real combustion, wood be-
comes black because it is reduced to the  state of char-
coal by the evaporation  of its other constituents.   But
can you tell me the reason why wood  turns black when
burnt by  the application of an acid ?
                          o 
194
  Caroline.   First  tell me what are the ingredients f«
wood ?
  Mr*  B.  Hydrogen and carbone are the chief con-
stituents of wood, as of all other vegetable' substances.
  Caroline.  Well, then, I suppose that the oxygen of
the acid combines  with the hydrogen of the wood, to
form  water ; and that the  carbone of the wood,  re-
maining alone, appears of its usual black colour.
  Mr*.  B.  Very well, indeed, my dear ;  that is cer-
tainly the most plausible explanation.
  Emily.   Would not this be a good method of making
charcoal ?
  Mr*.  B.  It would  be an extremely expensive, and
I believe, very imperfect  method ;  for  the action of the
acid on the wood, and the heat produced by it. are  far
from sufficient to deprive the wood of  all its evaporable
parts.
  Caroline.  What is the reason  that  vinegar, lemon,
and  the acids  of fruits, do not produce this effect  on
wood ?
  Mrs.  B.  They are vegetable acids whose bases are
composed of hydrogen and carbone ; the oxygen, there-
fore, will not be disposed to quit this radical, where it
is already united with hydrogen.  The  strongest  of
these may, perhaps, yield  a little of  their oxygen  to
the wood, and produce a stain upon it ;  bin the  caibone
will not be  sufficiently uncovered to assume its  black
colour.  Indeed,  the  several mineral  acids themselves
possess  this power of charring wood in very different
degrees.
  Emily. Cannot vegetable acids be decomposed by any
combustibles ?
  Airs.  B.  No ; because their radical is composed of
two substances which have a greater attraction for oxy-
gen than any known body.
  Caroline   And  are those strong acids which burn and
decompose wood, capable of producing similar effects on
the skin and fie- h of animals ?
  Mrs.  B.   Yes  ; all the mineral  acids,  and  one  of
them more especially, possess powerful caustic quali-
ties.  They actually corrode and destroy the skin and 
195
flesh : but th ey do not produce upon these exactly  the
same alteration as they  do on wood,  probably because
there is a great proportion of nitrogen and  other sub-
stances in animal matter, which prevents the separation
of carbone from being so conspicuous.
®
             Co nfe evsation xiv.

Of the Sulphuric and Phosphoric Acids: or the combination*
  of Oxygen with Sulphur  and Phosphorus ; and of the
  Sulphats and Phosphats.
                      Mrs. B.

   In  addition to the  general  survey which we  have
taken of acids, I think you will find it interesting to ex-
amine individually a few of the most important of them,
and likewise some of their principal combinations with
the nlkalies, alkaline earths, and metals.   The first of
the acids, in point of importance, is the sulphuric for-
merly called oil of vitriol.
   Caroline.  I have known it a long time by that name,
but had no idea that it was the same fluid as sulphuric
acid.   What resemblance or connection  can there be
between oil of vitriol and this acid ?
   Mr*. B.  Vitriol is the common name for sulphat of
iron, a salt which is formed by the combination of  sul-
phuric acid and iron ;  the sulphuric acid was formerly
obtained by distillation from this salt, and it very natur-
ally received its name from the substance which afford-
ed it.
   Caroline.  But it is still usually called oil of vitriol ?
  Mrs.  B.  Yes; a sufficient length of time has  not 
196
yet elapsed, since the invention of the new nomencla-
ture, for it to be generally disseminated ; but as it  is
adopted by all scientific chemists,  there is every reason
to suppose that it will gradually become universal. When
I received this bottle from the chemist's, the name writ-
ten on the label was oil of vitriol; But, as I  knew you
were very punctilious in regard to the nomenclature, I
changed it, and substituted the modern name.
  Emily.  This acid has neither  colour nor smell, but
it appears much thicker than the waler.
  Mrs.  B.  It is twice as heavy as water, and has, you
see, an oily consistence.
  Caroline.  And it is probably from this circumstance
that it has been  called an oil,  for it  can have no real
claim to that name, as it does not  contain  either hydro-
gen or carbone, which are the essential constituents to
oil.
  Mr*.  B.  Certainly ; and therefore it would be the
more absurd to retain a name which owed its origin to
such mistaken analogy.
  Sulphuric acid in its purest  state, would be  a  con-
crete substance, but its attraction for water is such, that
it is impossible to preserve it in that state ; it is, there-
fore, always  seen in a liquid form, such  as you  here
find it.  One of the most striking properties of sul-
phuric acid is that of evolving a considerable quantity of
heat when mixed  with water ; this 1 have already shewn
you.
   Emily.  Yes, I recollect it;  but what was the degree
of heat  produced  by that mixture ?
   Mr*. B.  The thermometer may be raised by it  to
300, which is considerably above  the degree of boiling
water.
  Caroline.  Then water might be made to boil in that
mixture.
   Mr*  B.  Nothing more easy, provided that you em-
ploy sufficient quantities of acid  and of  water, and  in
the due propoiiions.  The  greatest heat is  pioduced
by a mixture  of one part  of water to four of the acid:
we shall make a mixture of these proportions,  and im-
merse this thin  glass tube, which is full of water, into
it. 
197
  Caroline. The vessel feels extremely hot, but the wai?
ter does not boil yet.
   Mrs. B.  You must allow some time for the heat to<
penetrate the tube, and raise the temperature of the wa-
ter to the boiling point.—
   Caroline.  Now  it boils—and  with increasing  vio-
lence.
   Mr*. B.  But  it will not continue boiling long ;  for
the mixture gives out heat only while the particles of
the water and  the acid are mutually penetrating each
other :  as soon as the new  arrangement of those parti-
cles is  effected, the mixture will gradually cool, and the
water return to its former temperature.
   You  have  ssen the manner in which sulphuric acid
decomposes all  combustible  substances, whether ani-
mal, vegetable, or mineral, and burns them by means of
its oxygen ?
   Caroline.   I have  very unintentionally repeated the
experiment on my gown, by letting a drop of the acid fall
upon it, and it  has made a  stain, which, I suppose, will
never wash out.
   Mr*. B.  No, certainly ; for, before  you can put it
into water, the spot  will become a hole, as the acid has
literally burnt the muslin.
   Caroline.   So it has indeed ! Well, I  will fasten the
stopper and put the bottle away, for it is a dangerous sub-
stance—Oh, now I have done worse still, for I have spilt
some on my hand 1
   Airs. B.  It  is  then burned, as well as*your gown,
for you know that oxygen destroys animal as well as veg-
etable  matter; and,  as  far as the decomposition of the
skin of your finger is effected, there is no remedy ; but,
by washing it immediately in water, you will dilute the
acid, and prevent any further injury.
   Caroline.   It feels extremely hot, I assure you.
   Airs.  B.   You have now  learned, by  experience,
how cautiously this acid must be used.   You will soon
become acquainted with another acid,  the  nitric, which
though it produces less lieu on the skin, destroys it still
quicker,  and  makes upon it  an indelible stain.   You
should never  handle any substances of this kind, with-
                         S 2 
198
out previously dipping your fingers in water,  which
will  weaken  their caustic effects.—But since you  will
not repeat the experiment, I must put in  the  stopper,
for the acid attracts the moisture from the atmosphere,
which would  destroy its strength and purity.
   Emily.  Pray how can sulphuric acid be extracted
from  sulphat  of iron by distillation ?
   Airs. B.   The process of distillation, you know, con-
sists in separating substances from one anothsr by means
of their different degrees of volatility,  and by the  intro-
duction of a new chemical agent, caloric.   Thus,  if sul-
phat of iron be exposed in a retort to a proper degree of
heat,  it will be decomposed, and the sulphuric acid  will
be volatilized.
   Emily.  But now that the process of forming acids
by the combustion of their  radicals is known, why should
not this method be used for making sulphuric arid ?
   Mrs. B. This is actually done in most manufactures ;
but the usual method of preparing sulphuric acid does
not consist in  burning the sulphur in oxygen gas, (as we
formerly did  by way of experiment),  but in heating it
together  witii another substance, nitre, which yields ox*
ygen  in sufficient abundance  to render the  combustion
in common air rapid and complete.
   Caroline.   This substance, then, answers the same
purpose as oxygen gas ?
   Mrs. B.   Exactly.   In manufactures the combustion
is performed in a leaden  chamber,  with  water  at the
bottom, to receive the vapour, and assists its condensa-.
tion.  The combustion is,  however, never so  perfect,
but that a quantity of sulphurous acid is formed at the
same time ;   for you recollect that the sulphuious acid
differs from the sulphuric  only by containing less oxy-
gen.
 ^ From its own powerful properties,  and from the va-
rious  combinations into which it enters,  sulphuric acid
is of great importance in many of the arts.
   It is used also as a medicine in a state of great dilu-
tion ;  for were it taken internally, in a concentrated
state,  it would prove  a most dangerous poison.
   Caroline.  I am sure  it would burn the throat and sto*
mach. 
199
  Mr*. B.   Can you think of any thing  that Would
prove an antidote to this poison ?
  Caroline.   A large draught of water to dilute it.
  Mr*. B.   That would certainly weaken the power ot
the acid, but it would increase the  heat  to an  intolera-
ble degree.   Do you. recollect nothing that would de-
stroy its deleterious properties more effectually ?
   Emily.   An alkali might, by combining  with it; but
then,  a pure alkali is itself a poison, on account of its
causticity.
   Mr*. B.   There is no necessity that the alkali should
be  caustic.   Soap, in which it is combined with oil: or
magnesia, either in a state of carbonat, or mixed  with
water, would prove the best antidotes.
   Emily.  In those cases, then, I suppose, the potash
 and the magnesia would quit their combinations to form
 salts with the sulphuric acid ?
    Mrs. B.   Precisely.
    We may now  make a few observations on the sul-
 phurow* acid,  which we have found to be the  product of
 sulphur slowly and imperfectly burnt —This acid is dis-
 tinguished by its pungent smell,  and its gaseous form.
    Caroline.   Its aeriform state is, I  suppose,  owing to
 the  smaller proportion of oxygen,  which  renders  it
 lighter than sulphuric acid ?
    Mrs. B   Probably;  for by adding oxygen to the
 weaker acid, it may be converted into the stronger kind.
 But this change of state may also be connected with a
 change of affinity with regard to caloric.
    Emily.   And may sulphurous acid be obtained  from
 sulphuric acid by a diminution of oxygen ?
    Mr*. B.   Yes: it can be done by bringing any com-
 bustible substance in contact with the  acid.   This de-
 composition is most  easily performed by some of the
 metals ; these absorb a portion of the oxygen from the
 sulphuric acid, which is thus converted into the sulphu-
 rous, and flies off in its gaseous form.
    Caroline.   And cannot the sulphurous acid itself be
 decomposed and reduced to sulphur ?
    Mr*. B.   Yes;  if this gas be  heated in contact with 
200
 charcoal, the oxygen of the acid will combine with it,.
 and the pure sulphur be regenerated.
   Sulphurous acid is readily  absorbed by water;  and
 in this liquid state it is found particularly useful in bleach-
 ing linen and woollen cloths, and is much used in man-
 ufactures for those purposes.   I can shew you its effect
 in destroying colours, by taking out any iron mould, or
 vegetable stain—I think I see a spot on your gown, Em-
 ily, on which we may try the experiment.
   Emily.  It is the stain of mulberries ;  but I shall be
 almost afraid of exposing  my gown to the experiment,
 after  seeing the effect which the sulphuric acid produc-
 ed on that of Caroline—
   Mr*.  B   There is no such danger from the sulphur-
 ous ;   but  the  experiment must be  made  with great
 caution ! for, during the formation of sulphurous acid
 by combustion,  there  is always  some sulphuric pro-
 duced.
   Caroline.  But where is  your sulphurous acid ?
   Airs. B.  We may  easily prepare  some ourselves,
 simply by burning a match ; we must first wet the stain
 with a little water, and  now hold it in this  way,  at a lit-
 tle distance, over the lighted  match:  the vapour  that
 arises from it is sulphurous acid, and the stain, you see,
 gradually disappears.
   Emily.  I have frequently  taken out stains by this
 means, without understanding  the nature of the  pro-
 cess.   But why  is it  necessary to wet the stain before
 it  is exposed to the acid fumes ?
   Mr*. B.   The moisture attracts and absorbs the sul-
 phurous acid ; and it serves likewise to dilute any par-
 ticles  of sulphuric acid  which might injure the linen.
   Sulphur is susceptible of a third combination with
 oxygen,  in  which the  proportion of the  latter is  too
 small  to render the sulphur acid.  It acquires this slight
oxygenation  by  mere  exposure  to  the  atmosphere,
without any elevation of temperature :  in this case,  the
sulphur does not change  its natural form,  but is only
discoloured, being changed to red or brown ; and in'
this state it is an oxyd of sulphur.
   Before we take leave  of the sulphuric acid,  we shall 
201
say a few words of its principal combinations.   It unites
with all the alkalies, alkaline earths, and metals, to form.
compound salts.
   Caroline   Pray, give me leave to interrupt you  for
a moment; you have never mentioned any other salts
than the compound or neutral  salts j  is there no other
kind?
   Mr*.  B.   The term  salt has  been used, from time
immemorial, as a kind of general name,  for any sub-
stance  that has savour,  odour, is  soluble in water, and;
crystallizable, whether it be of an acid,  an  alkaline, or
compound nature ; but the compound salts  alone retain
that appellation in modern chemistry.
   The most important of the salts, formed  by the com-
bination of the sulphuric acid, arc,  fii st, sulphat of pot-
ash, formerly called salpolychrest ;  this is a very bitter
salt, much used in medicine ; it is found in  the ashes of
most vegetables, but it may be prepared artificially by
tlie immediate  combination  of sulphuric acid and pot-
ash.   This salt is easily soluble  in  boiling  water.  So-
lubility is, indeed, a property, common to all salts ; and.
they always produce cold in melting.
   Emily.  That  must he owing to  the caloric whiclv
they absorb in  passing from a solid to a  fluid form.
   Airs. B.   That is, certainly, the most probable ex-
planation.
   Sulphat of soda, commonly called Glauber's salt,  is
another mccf cimd salt,  which is  still more bitter than
the preceding.   We must prepare some of these com-
pounds,  that you may  observe the phenomena  which
takes  place  during  their  formation.   We need only
pour sume sulphuric acid over the soda  which I put in*
to this glass.
   Caroline.   What an amazing  heat is  disengaged.  I
thought you said that cold was produced by  the melting
of salts !
   Mr*. B.   But  you must observe  that we are now
making not melting a salt.  Heat is disengaged during
the formation of compound salts, because the acid goes
into a more dense state in the salt than that  in  which it
existed before.  A faint light is also emitted, which
may sometimes be perceived in the dark. 
202
   Emily.   If the oxygen, in combining with the  alka-
li, disengages light and heat, an actual combustion lakes
place.
   Airs. B.   Not so fast, my dear ;  recollect that the
alkalies are incombustible substances, and incapable of
combining with oxygen singly.  They are not acted on
by this  principle, unless it  presents  itself in a state of
union with another body ; and, therefore,  the combina-
tion of  an acid with an alkali cannot be called combus-
tion.
  Caroline   Will this sulphat of soda become solid ?
   Mr*. B.   We have not, I suppose,  mixed the acid
and the alkali in the exact proportions that are  requir-
ed for the formation of the salt, otherwise the mixture
would have been almost immediately changed to  a so-
lid mass ;  but, in  order to obtain it in crystals,  as you
see it in this  bottle, it would be necessary first to dilute
it  with  water, and afterwards evaporate the water, du-
ring which operation the salt  would gradually crystal-
lize.
  Caroline.   But of what use is the addition of water, if
it is afterwards to be evaporated ?
  Mrs. B.   When ruspended in water,  the acid and
the alkali are more at liberty to act on each other, their
union is more complete, and the salt assumes the regu-
lar form of crystals during the slow evaporation of its
solvent.
   Sulphat of soda liquefies by heat,  and effloresces in
the air.
  Emily.   Pray what  is the meaning of the word efflo-
resces ? I do not recollect your having mentioned it be-
fore.
   Mr*. B.  A salt is f.aid to effloresce when it loses its
water of crystallization on being exposed to the atmos-
phere, and is thus gradually converted into a dry pow-
der : you may observe that these crystals of  sulphat of
soda are  far  from  possessing the transparency which
belongs to their crystalline state ;  they  are covered
with a white  powder, occasioned  by their having  been
exposed to the atmosphere,  which has deprived thrir
surface  of its  lustre, by absorbing its water of  cryslalli- 
203
nation.  Salts are, in general, either efflorescent or de-
liquescent ; this latter property is precisely the reverse
of the former ; that is to say, deliquescent salts absorb
water  from  the  atmosphere, and  are  moistened  and
gradually melted by it.  Muriat of lime is un instance
of great deliquescence.
   Emily.   But are  there no  salts that  have the same
degree of attraction for water as the atmosphere,  and
that will consequently not be affected by it ?
   Mrs. B.   Yes ; there are  many  such  salts;  as, for
instance,  common  salt, sulphat of  magnesia,  and  a
variety of others.
   Sulphat of lime is  very frequently  met with in nature,
and constitutes the  well known substance called gyp-
sum, or plaster of Paris.
   &ul[ihut of magnesia,  commonly called Epsom salt,  is
another very bitter medicine, which is obtained from
sea-water and from  several springs, or may be prepar-
ed by  the direct combination of its ingredients.
   \Ve have formerly mentioned sulphat of Alumine  as
constituting  ti.e common alum; it  is iound in nature
chiefly in  the neighborhood of volcanos, and is particu-
larly useful in the arts, from its strong  astringent qua-
lities.   It is chiefly employed by dyers and calico-pvint-
ers to  fix  colours ; and is used also  in the manufacture
of leather.
   Sulphuric acid combines also with the metals.
   Caroline.   One of these combinations, sulphat of iron
we are already well  acquainted with.
   Mr*. B.   That is the most  important  metallic salt
formed by sulphuric acid, and the only  one that we
shall  here notice.   It  is of great use in the arts ; and
in  medicine, it affuids  a very valuable tonic :  it  is  of
this salt that most of those preparations called sttil me-
dicines are composed.
   Caroline.   But  does  any  carbone enter into these
compositions to form steel ?
   Alr^. B.  Not  an atom ; they are, therefore, very
improperly called  steel; but it  is  the vulgar appella-
tion, and medical  men themselves often comply with
the general costom. 
204
   "Sulphat of iron may be prepared, as you have  seen,
 T)y dissolving iron in sulphuric acid ;  but it is generally
 obtained from  the natural production  called Pyrites,
 which, being a  sulphuret  of  iron, requires only expo-
 sure to the atmosphere to be  oxydated,  in  order to
 form  the  salt;  this, therefore, is much the most easy
 wav of procuring it on a large scale.
   Emily.  I am  surprised to  find that both acids and
 compound salts  are generally obtained from their vari-
 ous combinations,  rather  than  from  the  immediate
 union of their ingredients.
   Mr*.  B.  Were the  simple bodies  always at hand,
 their combination would  naturally be the most conve-
 nient  method of forming  compounds ; but  you must
 consider that, in most instances, there is great difficulty
 and expense  in  obtaining the simple ingredients from
 their combinations ; it is, therefore, often  more expe-
 dient to procure compounds from the decomposition of
 other compounds.  But to return  to the sulphat of iron.
 There is  a  certain vegetable acid called  Gallic acid,
 which has the  remarkable property  of precipitating
 this salt black.—I shall pour a few drops of the gallic
 acid into this  solution  of  sulphat of iron—
   Caroline.  It is become as black as ink !
   Mrs. B   And  it is  ink in reality  Common writing
 ink is a precipitate of sulphat of iron by gallic acid;
 the black calour is owing to the formation of  gL.ll.it  of
 iron,  which being insoluble, remains suspended in the
 fluid.
   This acid  has  also  the property of  altering the co-
 lour of iron in its  metallic state.   You may  frequently
 see its effects on the blade of a knife that  has been
 used to cut certain kinds of fruits.
   Caroline.  True ; and that is perhaps the reason that
 a silver knife is preferred to cut fruits ;  the gallic acid,
 I suppose,  does not act upon silver.—Is this acid found
in all fruits ?
   Mr*.  B.  It is  contained, more or  less  in  the  rind
of most  fruits and roots,  especially the  radish,  which
if scraped  with a  steel or iron knife, has its bright red
colour changed to a deep  purple, the knife being at the 
*05
name rime blackened.  But the vegetable substance i»
which tue gallic acid most abounds is nutgall, a kind of
excrescence  that  grows on oaks. «md fiom which the
acid is commonly obtained for its vaiious purposes.
   jlfr*. B.   We now  come  to  the r-HrspHOBic and!
phosphorous acids.   In ireating  of pi.o.-q horns, you
have seen how these acids may be obtained from it by
combustion ?
   Emily.  Yes ; but I should be much surprised if it
was the usual method of obtaining  them, since it is so
very difficult to procure phosphorus in its pure state.
   Mr*. B    You are  right,  my dear ;  the  phosphoric
acid,  for general purposes,  is extracted from bones,
in which it is contained in the state of phosphat of lime ;
from this salt the phosphoric acid is separated by means
of the sulphuric, which combines with the lime.  In its
pure state, phosphoric acid is either liquid or solid,  ac-
coiding to its degree of concentration.
   Amongst  the salts formed by this acid, phosphat of
lime is the only one that affords much  interest; and this,
we have already observed, constitutes the basis of all
bones.  It is also found in very small  quantities in soma
\egetables.


             Conservation;* xv.

Of the nitric and carbonic acids ; or the combinations of ox-
   ygen  with nitrogen and carbone ;  and qfthe nitrats and
   carbonats.

                      Mrs. B.

   I am almost afraid of introducing the subject of the
nithic  acid, as I am sure  that 1 shall  be  blamed by
Caro.ine, for not having made her acquainted with it b«-
forc
   Caroline.   Why so, Mrs. B.—?
                        T 
£06
   Mrs, B.  Because you have long known its radical,
 Which is nitrogen or azote ; and, in treating of that ele-
 ment, I did not even  hint that it  was the basis of an
 acid.
   Caroline.  Indeed, that appears  to me a great omis-
 sion ; for you have made us acquainted with all the oth-
 er acids, in treating of their radicals.
   Emily.  I would advise you not to be too hasty in
 your censure, Caroline  ;  for 1 dare say  that Mrs.  B.
 had some very good reason for not mentioning this acid
 sooner.
   Mrs. B.  I do not know whether you will think the
 reason sufficiently good to acquit me ; but the omission,
 I assure  you, did not proceed from negligence.  You
 hiay recollect that nitrogen was one of the first simple
 bodies which  we  examined; you were  then ignorant
 bf the theory of combustion, which I believe was, for
 the  first time mentioned in that  lesson ; and  therefore
 it would have been in vain, at  that time, to  have attempt*
 ed to explain the nature and formation of acids       \
   Caroline.  I wonder, however, that it never occurred
 fo us to inquire whether njtrogen could be acidified ; for,
 as we know it was classed amongst the combustible bo-
 dies, it was natural to suppose that it might produce  an
 hcid.
   Mrs. B.   That is not a necessary consequence ; for
 it might  combine with oxygen  only in the degree  re-
 quisite to form an oxyd.   But you will find that nitro-
 gen  is susceptible  of various decrees  of oxygenation,
 some of which convert it  merely into an oxyd, and oth-
 ers give it all the acid properties.
   The acids,  resulting from the  combination of oxygen
 with nitrogen, are called the nitrous and  nitric acids.
 We  will begin with the nitric,  nAvhich  nitrogen is in
 the highest state of oxygenation.   This acid  naturally
 exists in the form of gas j but it is so extremely soluble
in water,  and  has so great an affinity  lor it, that one
 graiii of water will absorb and  condense  ten grains of
acid gas, and form the limpid  fluid which you see  in this
bottle.
  Caroline.  What a strong offensive smell it has ! 
aor
   Mr*. B.   This acid contains a greater abundance of
 oxygen than  any other, but it retains it with very little
 force.
   Emily.  Then  it must be a powerful caustic, both
 from the facility with which it parts with its oxygen, and
 the quantity which it affords ?
   Mrs. B.   Very well,  Emily ; both cause and effect
 are exactly such as you describe:  nitric acid burns and
 destroys all  kinds of organized  matter.  It even  sets
 fire to some of the most combustible substances.   We
 shall pour a little of it over this piece of dry  warm char-
 coal—you see it inflames it immediately ;  it would do
 the same with oil of turpentine,  phosphorus, and seve-
 ral  other very combustible bodies.  This  shews  you
 how easily this acid is decomposed by combustible bo-
 dies, since these effects must depend upon  the absorp-
 tion of oxygen.
   Nitric acid has been used in the arts from time im«
 memorial, but it is not more than twenty five years that
 its chemical nature has been ascertained.  The cele*
 brated   Mr.  Cavendish discovered that it consisted  of
 about 10 parts of nitrogen, and 25 of oxygen.*   These
 principles, in their gaseous state, combine at a  high
 temperature ; and this may be effected  by repeatedly
 passing the electrical  spark through a mixture of the
 two gasses.
   Emily.  The nitrogen and oxygen gasses, that com»
 pose the atmosphere, do not combine,  I suppose, be-
 cause their temperature is not sufficiently elevated ?
   Caroline.   But  in a thunder storm,  when the  lightr
 ning repeatedly passes through them,  may  it not pro-
 duce nitric acid ; we should be in a strange  situation if
 a violent storm should at once  convert the atmosphere
 into nitric acid.
   Mrs.  B.   There is no danger of it my  dear  ;  the
 lightning can  affect but a very small portion of the at-
 mosphere, and though it were occasionally to produce
 a little nitric  acid, yet this never could happen  to such
 extent as to be perceivable.

  *  Fhe proportions stated by Mr, Davy, in hit Chemical Re-
searches, are as I to *.   389. 
2oa
   Emily.   But how could the nitric acid be known, and
used, before the method of combining its constituents
Was discovered ?
   Mr*. U   Before that period the nitric acid was ob-
taiiied, and  it is indeed still extracted  for the commcn
purposes of art, from the compound salt which it formi
Wi:u potash, commonly called ?iitre.
   Caroline   Why is it called so ?  Pray, Mrs.  B. let
these old unmeaning  names  be entirely given up, by
us at least; and let us call this salt nitrat of potash.
   Mrs. B.  With all my heart; but it is necessary that
I should, at least, mention the old names, and more es-
pecially those that are  yet in  common  use ;. otherwise,
when you  meet with them, you would not be able to un«
derstand their meaning.
   Emily.   And how is the acid obtained from this salt ?
   Mr*. B.  By the intervention of sulphuric acid, which
combines  with the  potash,  and sets the nitric acid at
liberty.  This I can easily shew you, by mixing some
nitrat of  potash and  sulphuric acid in this  retort and
heating it over a lamp ; the  nitric acid will come  over
in the lorn of vapour, which we shall collect in a glass
bell.  This acid diluted in water is commonly  called
aquafortis, if Caroline will allow  me  to mention that
name.
   Caroline.   I have often heard that aqua fortis will dis-
solve almost all metals ;  it is  no doubt because it yields
its oxygen so easily.
   Mrs.  B.  Yes ; and from this powerful solvent pro*
periy, it derived the name of  aqua fortis, or strong wa-
ter.   Do you  not  recollect that we oxydated, and after-
Wards dissolved some copper  in this acid ?
   Emily.   If I remember right, the nitrat of copper.
was the first instance  you gave us of a compound salt ?
   Caroline.   Can the nitric acid be completely decom-
posed and converted into nitrogen and oxygen ?
   Emily.   That cannot be the case, Caioline, since the
acid can be  decomposed only  by the  combination of its
constituents with other bodies.
   Mrs. B.  True ; but caloric is sufficient forthis pur-
 pose.  By  making the acid pass through a red hot por- 
20*
•elain  tube,  it is decomposed ;  the nitrogen and oxy-
gen regain the  caloric which they  had lost  in combi-
ning, and are thus both restored to their gaseous state.
   The nitric acid may also be partly decomposed, and
is by this means converted into nitrous acid.
   Caroline.   This conversion must be easily effected,
as the  oxygen is so slightly combined with the nitrogen.
   Mrs.  B.   The partial decomposition of nitric acid is
readily effected by most metals;  but  it is sufficient to
expose the nitric acid, to a very strong light to make it
give out oxygen gas, and thus be converted into nitrous
acid.   Of this acid there are various degrees, accord-
ing to the proportions of oxygen  which it  contains ;
the strongest and that into which the nitric acid is first
converted, is of a yellow colour, as you  see it in this bot-
tle.
   Caroline.   How it fumes when the stopper is  taken
out.
   Mrs.  B. The acid exists naturally in a gaseous state,
and is here so strongly  concentrated in water that it is
constantly escaping.
   Here  is another bottle  of nitrous acid, which, you
see is  of an orange red colour ;  this acid is weaker, the
nitrogen being combined with a  smaller quantity of ox-
ygen ; and with a still less proportion of oxygen it is
an olive  green colour, as it appears in this third  bottle.
In short, the weaker the acid, the deeper is its colour.
   Nitrous acid acts still more powerfully on some inflam-
mable substances  than the nitric.
   Emily. I am surprised at that, as it contains less oxy-
gen.
   Mr*.  B.  But, on the other hand, it parts with its oxy-
gen much more readily : you may recollect that we once
inflamed oil with this acid.
   The next combinations of oxygen and nitrogen form
only oxyds  of nitrogen, the first  of which is common-
ly called nitrous air: or more properly nitric  oxyd gas.
This may be obtained from nitric acid, by exposing
the latter to the action of metals, as in dissolving  them
it does not yield the whole of its oxygen, but retains a
portion of this principle sufficient to convert it into this
                        T 3 
2110
peculiar  gas,  a specimen of which I have prepared,..
and preserved within this inverted glass bell.
  Emily.   It is a perfectly invisible elastic fluid.
  Mr*  B   Yes; and  it may be kept any length  of
time in this  manner  over water, as it is not, like the
nitric and nitrious acids,, absorbable by it.   It is  rather
heavier than atmospherical air, and is incapable of sup-
porting either combustion or respiration.   I am going
to incline the glass gently on one side, so as to let  some
of the gas escape—
  Emily.   How very curious !—It  produces orange
fumes like the nitrous acid 1  that is the more extraordi-
nary, as the gas withing the glass is perfectly invisible.
  Airs. B.   It would give me much pleasure  if you-
could make out the reason of this curious change  wiih-
out requiring any further explanation.
  Caroline.   It seems,  by the  colour and  smell, as if-
it were converted into nitrous acid gas ;  yet that cannot
be, unless it  combines  with  more  oxygen ; and how
can it obtain oxygen the very minute it escapes from the
glass ?
  Emily.   From the atmosphere^ do doubt. Is it not so,.
Mrs. B?
  Mrs. B.   You  have guessed it ; as soon as itcon.es
in contact with the atmosphere it absorbs from it the ad-
ditional quantity of oxygen necessary  to convert  it into
nitrous acid gas.  And, if 1 now remove the bottle en-
tirely from the water, so as to bring at once the  whole
of the  gas into contact with the atmosphere,  this con-
version will appear still  more striking.
  Emily.   Look, Caroline,  the whole capacity  of the
bottle is instantly tinged of an orange colour 1
  Mr*. B.   Thus you  see it is the  most easy process
imaginable to convert nitrous oxyd gas into nitrous acid
gas.  The property of attracting oxygen from the at-
mosphere, without any  elevation  of temperature, has
occasioned this gaseous oxyd being used as a test  for
ascertaining the degree of purity of the  atmosphere.
I am going to show you how it is applied to this purpose
>—You see this  graduated glass lube, which is  closed
at one end; (Plate VIII. Fig.  19J—I  first fill it with 
211
water, and then introduce a certain measure of nitrous*
gas, which, not being absorbable by water, passes thro*
it, and occupies the upper part of the lube.   I  must
now add rather above two thirds of oxygen gas, which
will just be sufficient lo convert the nitric oxyd gas in-
to nitrous acid gas.
   Caroline.   So is has !—I saw it turn of an orange co-
lour ; but it immediately afterwards disappeared entire-
ly, and the water,  you see,- hasrisen, and almost filled
the tube.
   Mr*. B.   That is because the acid gas is absorbable
by water, and in proportion as the gas impregnates the
water, the latter rises in  the tube.  When the oxygeiv
gas is very pure, and the required proportion of nitric
 oxyd gas very exact,  the whole is absoibed by the wa-
ter;  but  if any other gas be  mixed with the oxygen,
instead of combining with the nitric oxyd, it will remain
 and occupy the upper part of the tube ;  or, if the gas-
 ses be not in the due proportion,  there will be a residue
 of that which predominates.—Before we leave this sub-
ject, I must not forget to remark, that nitric  acid may
 be formed by dissolving nitric oxyd gas in nitric acid.
 This solution may be effected simply by making bubbles
 of nitric  oxyd gas pass through nitric acid.
    Emily.   That is to say, that nitrogen, at its-highest
 degree of oxygenation, being mixed with nitrogen at
 its lowest degree of oxygenation, will produce a kind of
 intermediate substance, which is nitric acid.
    Mr*. B.   You have stated the fact with great  preci-
 sion.—There are various other methods of preparing
 nitrous oxyd, and of obtaining  it from compound bodies ;
 but it is  not necessary to enter into these particulars; It
 remains for me only to mention  another curious modifi-
 cation of oxygenated nitrogen,  which has been  distin-
 guished by the name of gaseous oxyd of nitrogen.  It is
 but  lately that  this gas has been accurately examined,
 and its properties have been chiefly investigated by Mr.
 Davy.   It has obtained  also  the name of exhilirating
  gas, from the very singular property which that gentle-
 man has discovered in it, of elevating the animal spirits,.
  when inhaled into the lungs, to a degree sometimes re-
 sembling delirium or intoxication. 
212
    Caroline.  It is respirable, then ?
    Mrs. B.  It can scarcely  be called respirable, as it
 would  not support  life for any length of time; but it
 may be breathed for a few moments without any other
 effects, than the  singular exl iliration of spirits I have
 just mentioned.  It affects different people, however,
 in a very different manner.  Some become violent, even
 outrageous: others experience a languor, attended with
 faintness; but  most agree  in opinion, that  the sensa-
 tions it excites are extremely pleasant.  "
   Caroline.  I think I should like to  try it—how do you
 breath it ?
    Mr*. B.  By collecting the gas in a bladder, to which
 a short tube with a stop-cock is adapted ; this is applied
 to the mouth with one hand, whilst the nostrils are kept
 closed with the other, that the common air may have
 no access.  You  then alternately inspire, and expire
 the gas, till you perceive its effects.   But I cannot con-
 sent to your making the experiment; for  the nerves
 are sometimes  unpleasantly affected  by it, and I would
 Hot run any risk of that kind.
   Emily.   I should like,  at  least,  to see somebody
 breathe it;  but pray by what means  is this curious gas
 obtained ?
   Mrs. B.  It is procured from nitrat of ammonia, an
 artificial salt, which yields this  gas  on the application
 of a gentle heat—I have put some of the salt into a
 retort  and by the aid of a lamp the  gas will  be extri-
 cated—
   Caroline.  Bubbles of air begin to escape through the
 neck of the retort into the water apparatus ; will you
 not collect them ?
   Mrs. B.  The gas that first comes over is never pre-
 served, as it consists  of little more than the common
 air which  was  in the retort; besides, there is always
 in this  experiment a quantity of watery vapour which
 must come away before the nitrous oxyd appears.
   Emily.   Watery vapour!  Whence does  that pro-
 ceed ?  there is no water in nitrat  of ammonia !
   Mrs. B.  You must recollect that there is in every
«alt a quantity of water of crystallization which may be 
218
evaporated by] heat alone.  But, besides this, water 'ik
actnally generated in this experiment,  as you will see
presently.  But  first tell me, what are the  constituent
parts of nitrat of ammonia ?
  Emily.   Ammonia, and nitric acid:  this  salt, there-
fore,  contains three different  elements, nitrogen and
hydrogen, which produce the  ammonia; and oxygen,
which, with nitrogen, forms the acid
  Mrs. B.   Well, then, in this process the ammonia
is decomposed ;  the hydrogen quits the nitrogen to com-
bine with some of the  oxygen of the  nitric acid, and
forms with it the watery vapour which is now coming
over.  When that is effected, what will you expect to
find?                                ...
   Emily.  Nitrous acid instead of nitric  acid, and ni!>
sogen instead of ammonia.
   Mrs.  B.  Exactly so ; and  the nitrous acid, and  nir
trogen combine, and form the gaseous oxyd of nitro-
 gen, in which the proportion of oxygen is  37  parts to
 63 of nitrogen.
   You may have observed, that for a little while no bub-
bles of air have come over, and we have perceived oi>
 ly  a stream of vapour condensing as it issued into the
 water.—Now bubbh-s of air again  make their appear-
 ance, and I imagine that  by  this time all the wutery
 vapcur is come away, and  that we may begin to collect
 the gas.  We may try whether it is  pure by filling a
 phial with it, and pHinging a taper into it—yes, it will
 do now,  for the taper burns brighter than  in the com-
 mon air, and with a greenish flame.
    Caroline.   But  how is that ?  I thought no gas would
 support combustion but oxygen.
    Airs.  B.   Or any gas that  contains ovypen, and is
 ready to vield it,  which is the case with this in a con-
 siderable'degree  ; it is not, therefore, surprising that
 it should accelerate the  combustion of the taper.
    You see that the gas is  now produced in great abun-
 dance ;  we  shall collect a large quantity of it, and I
 dare say we  shall find some of the family who will be
 curious to make the experiment of respirirg it   Whilst
 Ihis procees is going on, we may take a general survey; 
su
•f the most important combination of the nitric and ni-
trous acids with the alkalies.
  The first of these is nitrat of potash,  commonly call-
ed nitre, or saltpetre.
  Caroline.  Is not that the salt with which gunpowder
is made ?
  Mr*. B.  Yes.  Gunpowder  is  a mixture  of fiv«
parts of nitre to one of sulphur, and one of  charcoal.—
Nitre from  its great proportion of  oxygen, and  from
the  facility with which it yields it, is the basis of most
detonating compositions.
  Emily.  But what is the cause of the violent  detona-
tion of gunpowder when set fire to ?
  Mr*. B.  Detonation may proceed from two causes ;
the sudden formation or  destruction of  an elastic fluid.
In the first case, when either a solid or liquid is instan-
taneously converted into an elastic fluid, the prodigious
and sudden expansion of the body strikes the air with
great violence, and this concussion produces the sound
called detonation.
  Caroline.  That I  comprehend very well ; but how
can a similar effect be produced by the destruction of a
gas?
  Mr*. B.  A gas can be destroyed only by condens-
ing it to a liquid or solid state ; when  this  takes place
suddenly,  the gas, in assuming a new and more com-
pact form, produces, a vacuum into which the surround-
ing air rushes with great impetuosity ; and it is  by that
rapid and  violent motion  that the sound is produced.—
In all detonations, therefore, gasses are  either  sudden-
ly formed, or destroyed.  In that  of gunpowder,  can
you tell me which of  these two  circumstances takes
place ?
  Emily.   As gunpowder is a solid,  it must, of course,
produce the gasses in its detonation ; but h^w,  1 can-
not tell.
  Mr*  B.  The constituents  of   gunpowder,  when
heated to a certain degree, enter into a number of new
combinations, and are  instantaneously converted into a
variety of passes, the sudden expansion  of wluch gives
jise to the detonation. 
215
  Caroline.  And in what instance does the destruction
or condensation of gasses produce detonation ?
  Mr*. B.  I can give  you one with  which you are
well acquainted ; the sudden combination of the oxygen
and hydrogen  gasses
  Caroline.  True ; I recollect perfectly that hydrogen
detonates with oxygen when the two gasses are conver-
ted into water.
  Mr*.  B  But let  us return  to the nitrat of potash.
This salt is decomposed when exposed to heat,  and
mixed  with any combustible body,  such  as carbone,
sulphur, 01 metals, these substances oxydating rapidly
at the expense of the nitrat. I must shew you an in-
stance of this —I expose to the fire some of the salt in
a small iion ladle, and when it is sufficiently heated,
add to it some powdered charcoal: this wi'l attract the
oxygen from  the salt, and be converted into carbonic
acid—
  Emily.  But what occasions that crackling noise, and
those vivid flashes that accompany it ?
  Mrs. B.   The rapidity with which the carbonic acid
gas is  formed, occasions a succession of small detona-
tions,  which,  together with the emission of flame, is
called  deflagration.
  Nitrat  of ammonia we have already noticed, on ac-
count ot the gaseous oxyd of nitrogen which is obtained
from it.
  Nitrat of silver  is the lunar caustic, so remarkable
for its  property of destroying animal fibre,  for which
purpose it is often used by surgeons.—We have said
so much on a former occasion, on the mode in which
caustics act on animal matter, that I shall not detain you
any longer on this  subject.
  We  now come  to the carbonic  acid, which we
have aire dy had many opportunities of noticing.  You
recollect that this acid may be formed by the combus-
tion of carbone whether in  its imperfect state of char-
coal, or in its purest form  ol  diamond.  And it is not 
216
necessary,  for  this purpose, to burn the carbone in
pure oxygen gas, as we did in a preceding lecture ; for
you need only lis;lit a piece of charcoal and  suspend it
under  the  receiver on the water  bath   The charcoal
will soon be extinguished, and  the air in the receiver
will be found mixed with  carbonic  acid, the process,
however, is much more expeditious if the combustion
be performed in  pure on ygen gas.
  Caroline    But how  can  y ou separate the carbonic
acid, obtained in this manner, from the air with  whfoh
it>s mixed?
  Mrs. B.   The  readiest  mode is to introduce under
the receiver, a  quantity of  caustic lime, or  caustic al-
kali, which soon attracts the whole of the carbonic acid
to form a carbonat.—The alkali is found increased in
weight,  and the  volume of the air is diminished by a
■quantity equal to that of the carbonic  acid which was
mixed  with it.
  Emily.  Pray  is  there no method of obtaining pure
carbone from carbonic acid ?
  Mr*. B.   For a long time it was supposed that car-
bonic acid was  nov decomposable ;  but Mr Tennant
discovered, a few years ago, that this acid may  be de-
composed by burning  phosphorus in a closed  vessel
with carbone of  soda or carbonat of  lime : the  phos-
phorus  absoibs  the oxygen  from the carbonat,  whilst
the caibone i? separated in the form of a black powder.
  Caroline.  Cannot we make that experiment ?
  Airs. B.   Not easily ;  it  requires being performed
with extreme nicety,  in order to obtain any sensible
quantity of carbone, and the experiment is  much too
delicate  for  me  to attempt it.  But there  can be no
doubt of the  accuncy of Mr.  Tennant's results ; and
all chemists now agree,  that  100 parts of carbonic acid
gas consist of about 28 parts of carbone to 72 of oxygen
gas.
  Carbonic acid  gas is found very abundantly in  nature,
it is supposed to form about  a hundredth part of the
atmosphere, and is constantly produced by the respira-
tion of  animals ;  it esists in a great variety of combina-
tions, and is  exhaled from many natural compositions. 
sir
 It is contained in a state of great purity in certain caves,
 'such as the Grotto del Cane, near Naples.
    Emily.  I recollect having read an  account  of that
  grotto, and i f the cruel expt rimtnts  nuicie on the poor
  dogs,  to  pdily  the curicsity  of strangers.   But 1 un-
  derstood that the vapour exhaled by this cave was call-
  ed fixed air
    Mrs. B.  That is the name by which carbonic acid
  was know before its chemical composition was  discov-
  ered.— This gas is  more destructive of life  than any
  other ; and if  the  poor animals that are submitted to
  its effects, are  not  plunged into cold water as soon as
  they become senseless, they do not recover.  It extin-
  guishes flame instantaneously.   I  have collected some
  in this glass, which I will pour over the candle.
    Caroline.  This  is  extremely singular—it seems to
  extinguish it as it were by enchantment,  as the  gas is
  invisible.   I should never have imagined  that  a gas
  could have been poured like a liquid.
    Airs B.  It can be done with carbcrtiic acid only, as
'  no other gas is sufficiently  heavy to be susceptible of be-
  ing poured out in the atmospherical air, without mixing
  with it
    Emily.  Pray by  what means did you obtain this gas '
    Airs.  B.  I procured it from marble.   Carbonic acid
  gas has so strong an  attraction for all  the alkalies and
  alkaline earths, that these are always  found in nature in
  the state of carbenats.   Combined  with lime  this acid
  forms chalk, which may be considered as the basis of
  all kinds of marble  and calcareous stones.  From these
  substaBf es carbonic acid is easily  separated, as it ad-
  heres so slightly to its combinations, that the  carbonats
  are all decomposable by any of the other acids.   I can
  easily shew  you how I obtained this gas ; I poured some
  diluted sulphuric acid over pulverized marble in this bot-
  tle (the same which  we used the other day to prepare
  hydrogen  gas),  and the gas escaped  through the tube
  connected with it;  the operation still  continues, as you
  may easily perceive—
    Emily.  Yes. it  does; there is a great fermentation
  mi the glass vessel.   What singular commotion is exci- 
218
 led by the sluphuric acid taking possession of the lime,
 and driving out the carbonic acid ?
   Caroline. But did the carbonic acid exist in a gaseous
 state in the marble ?
   Mr*. 13.  Of course not ; the acid when in a state of
combination, is capable of existing in a solid form.
   Caroline.   Whence,  then, does it obtain the caloric
necessary to convert il into  gas ?
   Airs. B.  It may  be supplied in this case from  the
mixture of sulphuric acid  and  water, which produces
an evolution of heat, even greater than is required for
the purpose ;  since,  as you may perceive by touching
the glass vessel, a considerable quantity of the caloric
disengaged becomes sensible.   But a supply of caloric
may be obtained also from  a diminution of capacity for
heat occasioned by the new combination which takes
place  ; and, indeed, this must be the case  when other
acids are  employed  for the disengagement  of carbonic
acid gas, which do not, like  the  sulphuric, produce  feat
on being mixed with water.   Carbonic acid  may like-
wise be disengaged from its combinations by heat alone,
which restores it to its gaseous state.
   Caroline.  It appears to me  very extraordinary  that
the same  gas, which  is produced by burning of wood
and coals, should erist also  in stones, marble, and chalk,
which are incombustible substances.
   Airs. B.  I will not answer that objection, Caroline,
because I think I can put you in a way of doing it your-
self.   Is carbonic acid combustible ?
   Caroline.  Why, no—because it is a body that  has
been already burnt, it is carbone only, and nut the  acid,
that is combustible.
   Airs. B.  Well, and what inference do you draw from
this?
   Caroline.  That carbonic acid cannot render  the bo-
dies in which  it is contained combustible ; but that sim-
ple carbone does, and that it is  in this elementary  state
that  it exists in wood, coals, and a great variety  of oth-
 er combustible bodies.— Indeed, Mrs. B   yc u are  very
 ungenerous ;  you are not satisfied with convincing me 
219
that my objections are frivolous, but you oblige me ta
prove them so my self.
   Mr*. B.   You must confess,  however,  that  I make
ample amends for the detection of error, when I enable
you 10 discover the truth. You understand, now, I hope,
that carbonic acid is equally produced  by the decompo-
sition of chalk, or by the combustion of charcoal. These
processes are certainly of a very different nature ; in the
first case the acid is already formed, and requires noth-
ing more than heat to restore  it to its gaseous state  ;
whilst in the latter, the acid is actually formed by the
process of combustion.
   Caroline.   1 understand it now perfectly.   But I have
just been  thinking of another difficulty, which  I hope
you will excuse my not being able  to remove  myself.
How  does the  immense quantity of calcareous earth,
which is spread all over the  globe, abtain the carbonic
acid which is combined with it ?
   Airs. B.   This question is, indeed, not very easy to
answer; but I  conceive that  the general carbonization
of calcareous matter may have been the effect of a gen-
eral combustion,  occasioned by some  revolution of ou»
globe, and  producing an immense supply of carbonic
acid, with which the calcareous matter became impreg-
nated  ; or that tnis may  have been effected by a gradu-
al  absorption of carbonic acid from the atmosphere.—
But this subject would lead us to discussions which we
cannot indulge in, without deviating too much from our
subject.
   Emily.   II »w does it happen that we do not perceive
the pernicious  effects of the  carbonic acid that is float-
ing in the atmosphere ?
   Mr*. B.   Becau-w  of the state of very great  dilution
in which it  exists there.  But can you tell me, Emily,
what are  the sources  which keep the  atmosphere  con-
stantly supplied with this acid ?
   Emily.   I suppose the combustion of wood, coals, and
other substances, that contain carbone.
   Mr*. B.   And also the breath of animals.
   Caroline.   T've breath  of animals!  I  thought  you
said that this gas \as not at all respirable, but, on the
contrary, extremely poisonous. 
220
    Mrs. B.   So it is ;  but  although animals cannot
 breathe in carbonic  acid gas, yet,  in the process of re-
 spiration,  they  have the power of forming this gas in.
 their lungs ;  so that the air which we  expire, or  reject,
 from the lungs, always contains a greater proportion of
 carbonic acid, which is much greater than that which
 is commonly  found in the atmosphere.
   Caroline.   But  what is it that renders carbonic acid
 such a deadly poison ?
   Mr*.  B.  The  manner in which this gas destroys
 life, seems to be  merely by preventing the access to
 respirable  air ; for carbonic acid gas, unless very much
 diluted with common air, does not penetrate into the
 lungs, as the windpipe actually contracts, and refuses
 it admittance.—But we must dismiss this subject at pre-
 sent, as we  shall have an opportunity  of treating of re-
 spiration much more fully, when we come to the chem-
 ical functions of animals.
   Emily.  Is carbonic acid as destructive to the life of
 vegetables, as it is  to that of animals ?
   Mrs. B.   If a vegetable be completely immersed in
 it. I believe it generally proves fatal to it ; but mixed in.
 certain  proportions with atmospherical air, it is on the
 contrary, very favourable to vegetation.
   You remember, I suppose, our mentioning the  min-
 eral waters, both  natural and artificial, which contain
 carbonic acid  gas ?
   Caroline.  You  mean the Seltzer water ?
   Mr*. B.  That  is one  of those which are most used ;,
 there are, however, a variety of others ino which car-
 bonic acid enters as an ingredient ; all these waters are
 usually distinguished by the name of acidulous or gase-
 ous mineral waters.
   The class of salts called carbonats is the  most numer-
ous in nature ; we  must pass over them in  a very cur-
sory manner, as the subject is far too  extensive for us
to enter on  in detail.   The state  of carbonat is the natu-
ral state of  a vast number of minerals, and particularly
of the  alkalies and alkaline earths,  as  they  have so
great an attraction  for the carbonic  acid,  that they  are 
221
almost always found combined with it ; and you may
recollect that it is only by separating them from this
acid, that they acquire that causticity and those striking
qualities which 1  have formerly described   All mar-
bles, chalks, shells, calcareous spars, and  lime-stones
of every description,  are  neutral salts, in  which lime,
their common basis, has lost all  its characteristic pro»
perties.
   Emily.   But if all these  various substances are form-
ed by  the union of lime with  carbonic acid, whence a-
rises their diversity of form and appearance ?
   Mrs. B.   Both from the different proportions of their
component parts, and from a variety of foreign ingre-
dients which may occasionally be mixed  with them :
the veins and coloui s of marble, for instance, proceed
from a mixture of metallic substances ; silex  and alu-
mine  also frequently  enter  into these  combinations.
 The various carbonats therefore, that I have enumerat-
ed, cannot be considered as pure unadulterated neutral
 salts, although they certainly belong to that class of bo-
 dies.
®
             eontoettfation xvi.

On the muriatic and oxygenated muriatic acids ; and on
                     muriats.
                      Mrs. B.

  We come now to the undecompounded acids.—The
muriatic, formerly called the makine  acid,  is the
only one that requires our particular attention.
  The basis of this acid, as I have told you before, is un-
known, all attempts to decompose it haying hitherto
                       ¥3 
222
jtfoved fruitless ; it is, therefore, by analogy only, that
we suppose it to consist of a certain substance or radical,.
combined with oxygen.
   Caroline.  It can then never be formed by the com-
bination  of simple bodies,  but must always be  drawn
from its compounds.
   Emily. Unless the acid should be found in nature tin-
combined with other substances.
   Mr*. B.  1 believe that is never (he case.  Its prin-
cipal combinations are with soda, lime, and magnesia.
Muriat of soda,  is the common sea salt,  and from  this
substance the acid  is usually  disengaged by means  of
the sulphuric acid.  The natural state of the muriatic
acid, is that of an invisible  permanent gas at the com-
mon temperature of the atmosphere ; but it has  an ex-
tremely strong attraction for  water, and assumes ihe
form  of a whitish cloud, whenever  it meets with any
moisture to combine with.  This acid is remarkable for
its peculiar, and very  pungent smell,  and possesses,  in
a powerful degree, most of the acid  properties.  Here
is a bottle containing muriatic acid in a liquid state.
   Caroline..   And  how is it liquified ?
   Mr*.  B.   By impregnating water with it ; its strong
attraction for  water  makes it very easy to obtain it in
a liquid form.  Now, if 1 open the phial, you may ob-
serve a kind of vapour rising from it, which is muriatic
acid gas, of itself invisible, but made apparent  by com-
bining with the moisture of the atmosphere.
   Emily..  Have you not any of the pure muriatic acid
Sas •
   Airs.  B   This jar is full of that acid in its gaseods
state—it is inverted over mercury instead of water, be-
cause, being absorbable by water, this gas cannot  be
confined by it—I shall now raise  the jar a litlle on one
side, and suffei some of the gas to  escape.—You  see
that it immediately becomes visible in  the form  of a
cloud.
   Emily.  It must be, no doubt, from  its uniting with
the moisture of the atmosphere, that it is converted,  in-
to this dewy vapour. 
22.?
  Mr*. B.  Certainly ;  and for  the same reason, that?
is to say, its ex'.re 11c eagerness  to  unite with water,.
this gas will cause snow to tnelt a s rapidly as an intense
fire.
   Emily.  Since  this  arid cannot  be decomposed, I
suppose that it is not  susceptible of  different degrees
of oxygenation ?
   Airs.  B.  You  are mistaken in  your conclusion ;  for
though we cannot deoxygenate this acid, yet we may
add oxygen to it.
   Caroline.  Why then is not the least degree of  ox-
ygenation of the  acid,  called the muriatous,  and  the
 higher degree the mariatic acid ?
   Mr*. B.  lkcause,  instead of becoming, like other
 acids, more dense,  and more acid by  an addition ot  ox-
 ygen, it is rendered on the contrary  more volatile, more
 pungent, but less acid, and  less absorbable by  water.
 These circumstances, therefore, seem to indicate  the
 propriety of making an exception to the nomenclature.
 The highest degree of oxygenation of this  acid has been
 distinguished  by  the additional epithet of oxygenated,
 or, for the sake of brevity, oxy,  so that it is called the
 oxygenated^  oxy-muriatic  acid.   This likewise exists
 in a  gaseous form, at the temperature of the atmos-
 phere ;  it is also susceptible of being absorbed by water,
 and can be congealed, or  solidified, by a certain degree
 of cold.
    Emily.  And  how  do  you obtain  the  oxy-muriatic
 acid ?
    Mr*. B.  By  distilling liquid muriatic acid over ox-
 yd of manganese, which  supplies the acid with the ad-
 ditional oxygen.  One part of the acid being put into
 a retort, with too parts of the oxyd of manganese,  and
  the heat of a lamp applied, the gas is soon disengaged*
  and may be received  over water, as it is  but sparingly
 absorbed by it.   I hate collected some in this j*.«r—
    Caroline.   It is  not invisihler like the  generality of
  gasses ; for it is  of a yellowish  colour.
  *   Mr*.  B.  The  muriatic  acid  extinguishes flame,
  whilst,  on  the contrary, the oxy-muriatic makes the
  flame larger, and gives it a dark red colour.  Can joa
  account foj? this difference in the two acids i 
224
   Emily.  Yes, I think so; the muriatic acid  cannot
be decomposed, and therefore will not supply the flame
with the oxygen necessary for its support ;  but when
this  acid is farther oxygenated it will part with its ad-
ditional quantity of oxygen, and in  this way support
combustion.
   Mr*. B.   That is  exactly the case ; indeed the ox-
ygen, added to the muriatic acid, adheres so slightly
to it, that it is separated by mere exposure to the sun's
rays.   This acid  is decomposed also by combustible
bodies,  many of which it burns, and actually inflames,
without any previous increase of temperature.
   Caroline.  That is extraordinary, indeed ! I hope you
mean to indulge us with some of these experiments ?
   Mr*. B.   I have prepared several  glass jars  of oxy-
muriatic acid  gas, for that purpose   In the first we
shall introduce some Dutch gold leaf—Do you observe
that it takes fire ?  .
   Emily.  Yes, indeed it  does—-how wonderful it is !
it became immediately red hot, but was soon  smother-
ed in a thick vapour.
   Caroline   Good heavens ! what a disagreeable smell.
   Mrs. B.   We shall try the same  experiment  with
phosphorus in another jar of this acid —You had better
keep your handkerchief to your nose  when I open it—
now let us drop into it this little piece of  phosphorus—
   Caroline.   It bums really : and almost as brilliantly as
in oxygen gas ! But what  is most extraordinary, these
combustions take place without  the metal or  phospho-
rus being previously lighted, or even in the least heated.
   Mr*. B.   All these  curious effects are owing to the
very great  facility with which  this acid yields oxygen
to such bodies as are strongly disposed to combine with
it.  It appears extraordinary indeed to see bodies, and
metals in particular, melted down and inflamed, by a
gas,  without any increase of temperature,  either  of
the  gas or  of the combustible.  The  phenomenon,
however, is, you see,  well accounted for.
   Emily.  Why did  you burn a piece of Dutch gold-
leaf  rather than a piece of any other  metal ?
   Mr*, B.  Because, in the first place, it is a compo- 
225
sition of  metals  consisting chiefly  of copper,  whicHi
burns readily ;  and I use a thin metallic leaf in prefer-
ence to a lump of metal, because it offers to the action.
of the gas but a small quantity of matter under a large
surface.__Filings, or shavings, would  answer the pur-
pose nearly as well; but a lump of  metal,  though the
surface would  oxydate with great rapidity, would not
take fire.  Pure  gold  is not inflamed  by  oxy-muriatic
acid gas, but it is rapidly  oxydated, and  dissolved by
it; indeed, this acid is the only one  that will dissolve
gold.
   Emily.  This, I suppose, is what is  commonly called
aqua regia, which you know,  is the only thing that will
act upon  gold.                         ,
   Mrs.  B. That is not exactly the case either ; for aqua
regia is composed of a mixture of muriatic and nitric.
acid.   But,  in  fact,  the result of this mixture is no-
thing more than oxy-muriatic acid, as the muriatic acid
oxy genates itself at the expense of the nitric ;  this mix-
ture, therefore, though  it bears the name of nitro mu-
riatic acid, acts  on gold merely  in virtue  of the oxy-
muriatic acid which it contains.
   Sulphur,  volatile oils, and many other substances,
 will burn in the same  manner in oxy-muriatic acid gas ;;
 but I have  not  prepared a  sufficient quantity of it,  to
 shew you the combustion of all these  bodies.
    Caroline.  Yet tneie are several jars  of the gas re-
 maining.
    Mr*.  B.  We must reserve these for other experi-
 ments.    The oxy-muriatic  acid does not, like  other
 acids,  redden  the blue vegetable colours ; but it totally
 destroys any colour,  and tuins all vegetables perfectly
 white.   Let us  collect some  vegetable substances to
 put into this glass which is full of gas.
    Emily.  Here is a sprig of mvrtle—
    Caroline.   And here some coloured paper—
    Airs.  B.  We shall also put in this piece of coque-
  licot ribbon, and a rose—               >
    Emily.  Their colours begin  to fade immediately-
  But how doe? the gas produce this t ffect ?
    Airs.  B.  The oxygen combines with the colouring, 
226
 matter of these substances, and destroys it;  that is to
 say,  destroys the property  which these colours had  of
 reflecting only one kind of rays, and  renders  them ca-
 pable of reflecting them all,  which, you  know,  will
 make them appear white   Old prints may  be cleaned
 bv this acid, for the paper will be whitened without in-
 juring the impression, as printer's ink is made of  mate-
 rials  (oil and lamp black) which are not acted upon by
 acids.
   This property of the  oxy-muriatic acid has  lately
 been  employed  in manufactories in a variety of bleach-
 ing processes ;  but for  these purposes the gas must be
 dissolved in water, as the acid is thus rendered much
 milder and  less powerful in its effects ; for, in a  gase-
 ous state, it would destroy the texture,  as  well as the
 colour, of the substance  submitted to its action.
   Caroline.   Look at the things whit h we put into the
 gas ;  they have now entirely lost their colour !
   Mrs. B.   The effect  of the acid is almost completed
—and, and  if we were to examine the quantity that re-
mains, we should find it consist chiefly of muriatic acjd.
   The oxy-muriatic acid has been used to purify the
air in fever  hospitals and prisons, as  it burns and des-
troys  putrid uffluvia of  every kind.   The  infection of
the small pox is likewise destroyed  by this gas, and mat-
ter that has been submitted to its influence will no longer
generate that disorder.
   Caroline.  Indeed, I think the remedy must be near-
ly as bad as the disease ; the oxy-muriatic acid has such
a dreadful suffoc .ting smell.
   Airs  B.  It is  certainly  extremely offensive ;  but,
by keeping  the mouth  shut, and  wetting the nosnils
with liquid ammonia,  in order to neutralize  the vapour
 as it reaches the nose, its prejudicial  effects may be in
some  degree  prevented.  Ai any  rate, however, this
mode of disinfection can hardly be used in pi. ces  that
are inhabited.   And as the vapour of nitric acid, which
is scarcely  less  efficacious for this putpose.  is not at all
prejudicial, it is usually preferred on such occasions.
   Amongst  the ronu>oui<d  salts formed by  muriatic
acid,  the muriat of soda, or common  salt, is the most 
                        227

interesting.  The uses and properties of this salt are
too well known  to require much comment   Besides
the pleasant  flavour it imparts to  the food, it  is  very
wholesome,  when not used to excess, as it greatly as-
sists the process of digestion.
   Sea-water is the  great source from which the muriat
of soda is extracted by evaporation.   But it is found also
in large solid masses in the bowels of the earth, in Eng-
land, and in many other parts of the world.
   Emily.   1  thought that salts, when solid were always
in a state  of crystals ; but the common table s..lt is in
the form of a coarse white powder.
   Mrs. B.   Crystallization c.epcnds, as you may recol-
lect, on the, slow and  regular reunion of puriicies  dis-
solved in a fluid ; common sea salt  is only in a state of
imperfect crystallization, because the process bv which
it is ptepared is not favorable to the formation of regu-
lar crystals.   But, if you meit it, and afterwards evapo-
rate the water siowly, you win obtain a regular crystal-
lization.
   Muriat of ammonia is another combination of this acid,
which  we  have already  mentioned  as the  principal
source from which  ammonia is derived.
   1 can at  once shew  you  the formation of this salt by
the immediate combination of muriatic acid with an ino-
rii.— fhe^e two glass  jars contain, the one muriatic
a* id gas, the other ammoniacal gas, both of which are
peric-ctiy  invisible—now,  if 1 mix them together, you
 see they immediately form an opaque white cloud like
 smoke.  If  a  thermometer were placed in the jar in
which these gasses are mixed, you  wtulcl perceive that
 some heat is at the same time pioduced.
   Emily.   The  effects of chemical combinations  are,
 in< eed, wondeiful—how extraordinary  it  is that two in-
 visible  bodies should become visible by th< ir union.
   Mr* B    This strikes you with wonder because it is
a phenomenon  which  nature  seldom exhibits to our
view ;  but the most common of her operations are as
wonderful, and it is their  frequency on y that prevents
our  regarding  them  with  equal admiration.  What 
228
 would be more surprising for instance, than combustion)
 wen.- it not rendered so familiar by custom ?
   Emily.   That is true.—But pray,  Mrs.  B.  is  this
 white cloud tlie salt that produces ammonia ? How diff-
 erent it is from the solid muriat of ammonia which you
 once shewed us !
   Mr*.  B.  it  is :he  same substance  which first ap-
 pears in the state of vai.'iir, but  will soon be  condens-
 ed, by cooling agan st the  sides of ihe jar, in the form
 of very minute crystals.
   We  may now proceed to the oxy-muriats.   In this
 class of salts the oxy-muriat of potash is ihe most wor-
 thvof our attention, for its striking properties.   The
 acid, in this state of combination,   contains a still great-
 er proportion of oxvgen than when aione.
  Caroline. But how can the oxy  muriatic acid acquire
 an increase of oxygen by combining  with potash ?
  Mr*  B.  It does  not really acquire an addiiional
 quantity of oxygen, but it  loses son.e ol the  niurh.tic
 acid, which produces the same effect, as the  acid that
 remains is projiortionably super-oxvgenaled.
  If  this salt be mixed, and merely  rubbed  together
 with  sulphur,  phosphorus,  charcoal, or  indeed any
other combustible, it explodes strongly.
  Caroline  Like gunpowder, 1 suppose, it is sudden-
 ly converted into elastic fluids ?
  Mr*. B.  Yes ; but with this remarkable difference,
 that  no increase  of temperature,  ai.y  lurtl.tr than is
 produced by the gentle friction, is requiu d in this in-
 stance.   Can you tell  me  v hat gasses  arc generated
 by the detonation of this salt with charcoal ?
  Emily.   Let me  consider.......The  oxv muri-
 atic acid parts with  its excess of  oxygen to the  char-
coal, by which means  it ib  converted into n.uriaic  pcid
 gas ;  whilst the charcoal,  btii-.g burnt by the oxygen,
 is changed to carbonic acid  gas—What becomes of  the
 potash I cannot tell.
  Alt s. B.  That is  a fixed  product that  remains in
 the vessel.
  Caroline.  But since  the potash does  not enter into
 the new combinations, I do not understand of vthat use 
229
it is in  this operation.  Would  not  the  oxy-muriatic
acid  and the charcoal produce the same effect without
it?
   Mr*.  B.   No ; because there would not he that very
great concentration of oxygen which the combination
with the potash produces, as 1 have just explained.
   I mean to shew you this experiment,  but I would ad-
vise you not to repeat it alone  ; for if care be not taken
to mix only very small quantities at a time, the detona-
tion  will be extremely violent, and may be  attended
with dangerous effects.   You see I mix an exceedingly
small quantity of the salt with a little powdered charcoal,
in this Wedgwood mortar, and rub them together with
the pestle—
   Caroline.   Heavens ! How can such a loud explosion
be produced by so small a quantity of matter ?
   Mr*.  B.   You must consider that an extremely small
quantity of solid substance  may produce a  very great
volume  of  gasses; and it is  the  sudden evolution of
these which occasions the sound.
   Emily. Would not oxy-muriat of potash make strong-
er gunpowder than nitrat of potash ?
   Mr*. B.   Yes ; but the preparation as well as the
use of this salt, is attended with so much  danger, that
it is never employed for that purpose.
   Caroline.   There  is no cause to regret it, I think;
for the common gunpowder is quite sufficiently destruc-
tive.
   Mrs. B.   I  can shew you a very curious experiment
with this salt;  but it must  again  be on condition that
you will  never attempt to  repeat it by yourselves.  I
throw a small piece of phosphorus into this glass of wa-
ter ;  then a little oxy-muriat of potash; and,  lastly, I
pour in, by  means of this  funnel, so as to bring it in
contact with the two other ingredients in the bottom of
the glass, a small quantity of sulphuric acid—
   Caroline.   This is  indeed,  a beautiful experiment!
the phosphorus takes  fire and burns from the bottom of
the water.
   Emily.  How wonderful it  is to see flame bursting 
230
©ut under water, and rising  through it! Prayj how is
this accounted for ?
  Mr*. B.  Cannot you find it out, Caroline ?
  Emily.  Stop—I think I  can  explain it.   Is it  not
because the sulphuric acid decomposes the  salt by com-
bining with  the  potash, so as to liberate the  oxy-muri-
atic acid gas by which the phosphorus is set on fire ?
  Airs. B.   Very well, Emily ;  and with  a little more
reflection you would have discovered another  concur-
ring circumstance, which is, that an increase -of tem-
perature is produced by the mixture of the sulphuric
acid and water, which assists in promoting  the combus-
tion of the phosphorus.
   We have now examined such of the acids and salts as
I  conceived  would appear to you most interesting.—
I  shall not  enter  into any  particulars respecting the
metallic acids, as  they offer nothing sufficiently strik-
ing for our present purpose.
      Contoergation xvn
On the nature and composition of vegetable*.
                     Airs. B.

  We have hitherto treated only of the simplest com-
binations of elements,  such as oxyds, acids, compound
salts,  stones,  &c. all of which  belong to  the  mineral
kingdom.  It is time now to turn our attention to a more
complicated class of compounds,  that  of  Organized
Bodies, which will furnish us with a new  source of in-
strucion and amuse.nent.
  Emily.  By  organized  bodies, I suppose you mean 
231
the vegetable and animal creation? I  have, however,
but a very vague idea of the  word organization,  and 1
have  often  wished to know more precisely  what it
means.
   Mrs. B.  Organized bodies  are such as are endow-
ed by nature with various parts, peculiarly constructed
and adapted to perform  certain  functions connected
with life.   Thus  you may observe, that mineral com-
pounds" are formed by the simple effect of mechanical
or chemical attraction, and may appear to some  to  be,
in a great measure,  the productions of chance ;  whilst
organized bodies  bear  the most striking  marks of de-
sign, and are eminently distinguished by that  unknown
principle called life,  from which the various organs de-
rive the power of exercising their respective functions.
   Caroline.  But in what  manner does life enable these
organs to perfom their  several functions ?
   Mrs. B.  That is a  mystery which, I fear, is envel-
oped in too profound darkness  for us to  hope that we
shall ever be able to  unfold it   We must content our-
selves with examining the effects of this  principle ; as
for the cause, we  have been able only to give it a name,
without attaching any other meaning to it than the vague
and unsatisfactory idea of an unknown agent.
    Caroline   And yet  I think  I can form a very clear
 idea of life.
    Airs. B.  Pray let us hear how you would  define it.
    Caroline.  It is perhaps more easy to conceive  than
 to express—let me consider—fs not life the power which
 enables both the  animal anu vegetable  creation to  per-
 form the  various functions which nature has assigned to
 them ?
    Airs.  B.  I have nothing to object to your definition ;
 but you will allow me to observe, that you have only men-
 tioned the  effects which the unknown cause  produces,
 without giving us any notion of the cause  itself.
   Emily.   Yes,  Caroline, you have told us  what life
 does, but you have not told us  what it  is.
   Mrs.  B. We  may study its operations,  but we should
puzzle ourselves to no  purpose by atte mpting to form
an idea of its real nature. 
2S2
  We shall begin with examining its effects in the veg-
etable  world, which constitutes the  simplest  class of
organized bodies;  these  we shall  find distinguished
from the mineral creation, not only by their more com-
plicated  nature, but by the power which  they possess
within themselves, of forming new chemical arrange-
ments of their constituent parts, by means of appro-
priate organs.  Thus,  though  all vegetables are ulti-
mately  composed of hydrogen,  carbone,  and oxygen*
(with a few other occasional ingredients), they separate
and  combine these principles by their  various  organs
in a thousand ways, and form with them, different kinds
of juices and solid parts, which -exist  ready made in
vegetables, and may, therefore, be considered as their
immediate materials.
       These are  :
          Sap           Resins,
          Alucilage       Gum Resins,
          Sugar,         Balsams,
          Fecula,         Caoutchouc,
          Gluten,         Extractive colouring matters
          Fixed Oilr      Tannin,
          Volatile Oil,    Woody Fibre,
          Camphor,      Vegetable Acids, is"c.
  Caroline.   What a long list of names  ! I did not sup-
pose that a vegetable was  composed of half so many
ingredients.
  Mr*. B.   You must not  imagine that  every one of
these materials is formed in each  individual plant.  I
only mean to say, that they are  all derived exclusively
from the vegetable kingdom.
  Emily.  But does each particular  part of the plant,
such as the root,  the bark, the stem,  the seeds,  the
leaves,  consist of one of these  ingredients only, or of
several of them combined together ?
  Mrs.  B.  1 believe there is no part of a plant which
can  be said  to consist solely of any one  particular in-
gredient  ; a  certain  number  of vegetable materials
must always  be combined for the formation of any par-
ticular part,  (of a seed, for instance), and these' com-
binations are carried on by sets of vessels,  or minute 
233
organs, which select  from ether parts, and bring t6*
gethe-, the several principles required for the de-\elope-
ment and growth of those particular parts which ihey
are intended to form and to maintain.
   Emily.   And are not these combinations always reg-
ulated by the laws of chemical attraction ?
   Airs. B.   No  doubt;  the  organs  of plants cannot
force principles to combine that  have no attraction for
each other ;  nor can they  compel superior attractions
to yield to those of  inferior  power ; they probably  act
rather mechanic illy, by bringing into contact such prin-
ciples, and in such proportions, as will by their chemical
combination, form the  various vegetable products.
   Caroline.  We may then consider each  of these or-
gans as a curiously constructed  apparatus, adapted for
the performance  of a variety of chemical processes.
   Mr*  B   Exactly so. As long as the plant lives and
thrives, the carbone, hydrogen, and oxygen,  (the chief
constituents of its immediate materi Is),  are  so balanc-
ed and connected together, that they are not susceptible
of entering into other combinations ; but no sooner does
death  take place,  than this state of equilibrium is  de-
stroyed, and new combinations produced.
   Emily.  But why should death destroy it ; for these
principles  must  remain  in  the same proportions,  and
consequently,  I should suppose,  in the  same order of
attractions ?
   Mrs. B.   You must remember, that in the vegeta-
ble, as well as in the animal kingdom, it is  by the prin-
ciple of  life  that the organs are enabled to act; when
deprived of that agent  or stimulus,  their power ceases,
and  an order  of attractions succeeds similar  to  that
which would take place in mineral or unorganized mat-
ter.
   Emily.   It is this new  order  of attractions, I sup-
pose,  that destroys the organization of  the plant after
death ; for if  the same combinations still  continued to
prevail, the plant would  always remain in the state in
which it died.
   Mr*. B.  And that you  know is never the case ;
plants may be partially preserved  for some time after
                        V 2 
234
death, by drying; but in the natural course of events they
all return to the state of  simple elements ; a  wise and
admirable  dispensation of Providence,  by which dead
plants are  rendered fit to enrich the soil, and become
subservient to the nourishment of living vegetables.
   Caroline.   But we  are talking of the  dissolution of
plants, before we have examined them  in their living
state.
   Mr*.  B.  That is true, my dear.  Bat I  wished to
give you a general idea of the nature of vegetation, be-
fore we entered into particulars.   Besides, it is not so
irrelevant as you suppose to talk of vegetables in their
dead state, since we cannot analyse them without de-
stroying  life ; and  it is only  by hastening  to submit
them to examination, immediately after they have ceas-
ed to live, that we can anticipate their natural decompo-
sition.   There are two kinds of  analysis of which veg-
etables  are susceptible; first,  that which  separates
them into their immediate materials, such as sap, resin,
mucilage, 8tc. 2dly, that which decomposes  them in-
to their primitive elements,  as carbone, hydrogen, and
 oxygen.
    Emily.   Is there not a third kind of analysis of plants,
 which consists in separating their various parts,  as the
 stem, the leaves, and the several  organs of the flower ?
    Mr*.  B.  That, my  dear, is rather  the department
 of the botanist: we  shall consider these  different parts
 of plants, only as the organs  by which the various se-
 cretions or separations are performed: but  we must
 first examine the nature of these secretions.
    The sap may be considered as the principal material
 of vegetables,  since it contains  the  ingredients that
 nourish every part  of   the plant.  The basis  ol  this
 juice,  which the roots suck up  from the soil is water ;
 this holds in solution the various other ingredients  re-
 quired by the several parts of the plant, which are grad-
 ually secreted from the sap by  the different organs ap-
 propriated to that purpose, as it passes through them in
 circulating through the plant.
    Mucus or mucilage is a vegetable substance, which
 like all the others, is secreted  from the sap ; when in
  excess,it exudes from trees in the form of gum. 
235
  Caroline.  Is that the gum so frequently used instead
of paste or glue ?
  Mrs. B.  It is; almost all fruit-trees yield some sort
of gum, but that most commonly used in the arts is ob-
tained from a species of acacia-tree  in Arabia, and is
called gum Arabic : it foims the chief nourishment of the
natives of those parts, who obtain it in great quantities
from incisions which they make in the trees.
  Caroline.   I did not know that gum was eatable.
  Mr*. B.   I should not imagine that it would be eith-
er a pleasant or a particularly eligible diet to those who
have not, from their birth, been  accustomed  to it.  It
is, however, frequently taken medicinally, and consid-
ered as very nourishing.  Several  kinds of vegetable
 acids may be obtained, by particular processes, from
 gum or mucilage, the  principal of which is called the
 mucous acid.
   Sugar  is not found in its simple state in plants, but is
 always mixed with gum, sap, or other ingredients ; it
 is to be found in every  vegetable, but abounds  most in
 roots, fruits, and particularly the  sugar-cane.
   Emily.  If all vegetables contain  sugar, why is it ex-
 tracted exclusively from the sugar-cane  !
    Mr*.  B.   Beci.use  it is both most abundant in that
 plant, and most easily obtained from  it.
    During  the  late troubles  in the  West-Indies, when
 Europe was but imperfectly supplied  with sugar,  seve-
 ral attempts were made  to extract it from other vege-
 tables, and very good sugar was  obtained from parsnips
 and from carrots ; but the process was too expensive to
 carry on this enterprise to any extent.
    Airs.  B.  I should think that sugar might  be  more
 easily extracted from  sweet fruits, such as figs,  dates
  &c.
    Mrs.  B.  Probably ; but it would be still more ex-
 pensive from the high price of those fruits.
    Emily.  Pray in what manner is sugar obtained from
  the sugar-cane ?
    Mrs.  B.  The juice of this  plant is first expressed
  by passing it between two cylinders of iron.   It is then
  boiled with lime water, which makes a  thick scum rise 
236
 to  the  surface.   The  clarified liquor  is let off below
 and evaporated to a very small quantity, after which ic
 is suffered to crystalize by standing in a vessel, the bot-
 tom of which is perforated with holes, that are imper-
 fectly stopped,  in order that the syrup may drain  off.
 The sugar obtained by this process is  a coarse brown
 powder, commonly called raw or moist  sugar; it under-
 goes another operation to be refined and converted into
 loaf sugar.  For this  purpose  it is dissolved in water,
 and afterwards purified by an animal fluid, called  albu-
 men.  White of eggs  chiefly consist of this fluid, which1
 is also one of the constituent  parts of blood ;  and conse-
 quently eggs, or bullock's blood, are commonly used for
 this purpose.
    The  albuminous fluid being diffused  through the
 syrup, combines with  all the solid impurities contained
in it, and rises with them to the surface, where it forms'
 a thick scum ; the clear liquor is then again evaporated
to a proper consistence, and poured into moulds, in
which, by  a confused crystallization,  it forms loaf  su-
 gar.  But an additional  process  is required  to whiten
h ; to this effect the mould is inverted, and its open base
is covered with clay, through  which water is made to*
pass ; the water slowly trickling through the sugar, com-
bines with, and carries of the colouring  matter.
  Caroline.  I am very glad to hear that the blood that
 is used to purify sugar  does not remain  in it, it would be
 a disgusting idea.
  Enuly.   And pray how is sugar-candy and  barley su-
 gar prepared ?
  Mr*.  B.  Candied  sugar  is nothing more than the
 regular crystals, obtained by slow evaporation from a
 solution  of sugar.   Barley  sugar is sugar melted by
 heat, and afterwards cooled in moulds of a spiral form.
  Sugar may be decomposed by  a red  heat ; and,  like
 all  other vegetable substances, resolved into carbonic
 acid and hydrogen.  The formation and the decomposi-
 tion of sugar afford  many very  interesting particulars,
 which we shall fully examine  after having gone through
 the other materials of vegetables.—We shall find there
is reason  to suppose  that sugar is not, like the other
materials, accreted from the sop by appropriate orrr.ns ♦ 
237
but that it is formed by a peculiar process with which
you are not yet acquainted.
  Caroline.  Pray is not honey of the tame nature as
sugar ?                        „         ,
  Mrs. B.  Honey is a mixture of sugar and gum.
  Emily   I thought that honey was in some  measure
an animal substance, as it is prepared by the bees ?
   Mrs. B.  It is rather collected by them from Mow-
 ers, and conveyed to their storehouses, the hives.—It is
 the wax only that undergoes a real alteration in the bo-
 dy of the bee, and is thence converted into an animal sub-
 stance.                                 ,
   Emily.  Cannot sugar be obtained from honey, since
 it is so simple a compound ?
   Mrs.  B.  No mode has yet been discovered to effect
 this ;  it is supposed, however, to have been done by the
 ancients, who were unacquainted with the sugar-cane,
 but the process is now unknown.
   Manna is a compound of sugar, gum, and a nauseous
 extractive matter, to which  last it owes its peculiar
 taste and colour. It exudes like gum from various trees
 in hot climates, some of which have their leaves  glazed

    The next of the vegetable materials is/e«*/a ;  this is
  the  general  name given  to  the farinaceous substance
  contained in all seeds, and in some roots, as the  potato,
  parsnip, Sec.  It is intended by nature for the first ali-
  ment of the young vegetable ; but that of one particular
  grain is  become a favourite and a most common iood ot
  a large part of mankind.                       .   .
    Emily.  You allude,  I  suppose, to bread, which is
  made of wheat flour ?                        .
    Airs.  B.  Yes.  The fecula of wheat contains also
  another vegetable substance, which seems peculiar to
  that seed, or at  least has not as yet been obtained  from
  any other.   This  is  gluten, which is  of a sticky,  ropy,
  elastic nature ; and it is supposed to be owing to  the vic-
  ious  qualities of this  substance, that wheat  flour forms a
  much better paste than any other.
    Emily.   Gluten, by  your  description, must be very
  like gum. 
2*3 ff
  Mrs. B.  In their sticky nature they  certainly have
some resemblance : but gluten  is essentially different
from gum in other points, and especially in its being in-
soluble in water, whilst gum you know is extremely so-
luble.
  The oils contained in vegetables all consist of hydro-
gen and carbone in various proportions.   They are of
two kinds, fixed and volatile, both of which we formerly
mentioned.  Do you remember in what the difference
between fixed and valatile oil consists ?
  Emily.  If I recollect right,  the former are decom-
posed by heat, whilst  the latter are  merely volatilized^
by it.
  Mr*. B.  Very well.   Fixed oil is contained only in
the seeds of plants, excepting in the olive, in which it is
produced, and expressed from the fruit.   We  have al-
ready observed that seeds contain also fecula;  these
two substances, united  with a little mucilage, lorm the
white  substance  contained in  the seeds or kernels of
plants, and is destined for the nourishment of the young
plant, to which  the seed gives birth.  The  milk  of al-
monds, which is expressed  from the seed of that namej
is composed of these three substances.
  Emily.  Pray of what nature is  the linseed  oil which
is used in painting ?
  Mr*. B.  It is a fi^ed oil oblained from the seed of
flax.  Nut oil, which is frequently  used for the same
purposes is expressed from walnuts.
  Olive oil is that which is best adapted to culinary pur-
poses
  Caroline.   And what are the oils used for burnii g ?
  Mrs, B.   Animal oils most commomy ;  but the pre-
ference given to them is owing to their being less ex-
pensive ;  for  vegetable oils burn equally well, and are
more pleasant, as their smell is  not offensive.
  Emily. Since oil is so good a combustible, what is the
reason that lamps so frequently  require trimming?
   Mr*.  B.   This sometimes proceeds from the  con-
struction of the lamp, which  may  not be suflkiently fav-
ourable to a perfect combustion ;  but there is  certainly
a defect in the nature of oil itself, which renders  it ne* 
239
■ccssary for the best constructe d lamps to be occasion-
ally trimmed.  This  defect arises from a portion of
mucilage which  it is extremely  difficult  to  separate
from the oil, and which  being a  bad combustible, ga-
thers round the wick, and thus impedes its  combustion,
and consequently dims the light
   Caroline.  But will not oil burn without a wick ?
   Mr*.  B.  Not unless their temperature be elevated
to 400°  ; the wick answers this  purpose, as 1 think  I
 once before explained to you.  The oil rises between
 the fibres of the cotton by capillary attraction, and the
 heat ol  the burning wick  volatilizes  it, and  brings it
 successively to the temperature at which it is combus-
 tible.
    Emily.   I  suppose the  explanation which you have
  given with regard to the necessity of trimming lamps,
  applies also to candles which so often require snuffing ?
    Mr*. B.   1 believe it does ; at least in some degree.
  But beside  the  circumstance just explained,  the com-
  mon sort of oils are not very combustible, so that the
  heat produced by a  candle,  which is a coarse kind of
  animal oil, being insufficient to volatilize them com-
  pletely a quantity of soot is gradually deposited on the
  wick, which dims the light and retards the combustion.
    Caroline.  Wax candles then  contain no incombusti-
  ble matter, since they do not require snuffing ?
     Mr*. B.  Wax is a  much belter combustible than
  tallow, but still not  perfectly so, since it likewise con-
  tains some particles that are unfit  for burning ;  but
  when these  gather  round the  wick (which in  a wax
  light is comparatively small) they weigh it down on one
  side, and fall  off together with the burnt part  of the
  wick.
     Caroline.  As oils are such good combustibles, I won-
  der that  they   should require so great an elevation of
  temperature before  they begin to burn.
     Mr*. B.  Though fixed oils will not enter into actual
  combustion below the  temperature ol about 400°,  yet
   they will slowly absorb oxygen  at the common tempe-
  rature  of the atmosphere.   Hence arises a variety of
  changes in oils which modify their properties and  uses
  in the  arts. 
240
   If oil simply absorbs, and combines with oxygen,  it
 thickens and changes to a kind of wax.   This change
 is observed to take place on the  external  parts  ot cer-
 tain vegetables, even during their life.   But it happens
 in many instances that the oil does not  retain all the ox-
 ygen which it attracts, but that part of it combines with,
 or burns the hydrogen of the oil, thus forming a quan-
 tity  of water which gradually goes  off by evaporation.
 In this case the alteration of the  oil consists not only in
 the addition of a certain quantity of oxygen, hut in the
 diminution of  the hydrogen.   These  oils  are  distin-
 guished by the name of drying  oils.   Linseed,  poppy,
 and nut-oils are of this description.
   Emily.   I am well acquainted with drying oils, as  I
 continually use  them in painting.   But 1  do not under-
 stand why the acquisition  of oxygen on one hand, and
 loss of hydrogen on the other, should render them dry-
 ing ?
   Mr*. B.  This I conceive, may arise from two rea-
 sons ; either from tlie oxygen which is added being less
 favourable  to the state  of fluidity  than the hydrogen,
 which is substacted ; or from this additional quantity of
oxygen giving rise to new combinations, in consequence
of which the most fluid parts of the oil are liberated and
 volatilized.
   For the purpose of painting, the drying quality of oil
is farther increased by adding a quantity of oxyd  of lead
to it, by which means it is more rapidly  oxygenated.
   The rancidity of oils is likewise owing to their oxy-
 genation.  In this case a new order of  attraction takes
place, from which a peculiar acid is formed, called the
sebacic acid.
   Caroline.  Since the nature  and composition of oil is
 so well  known, pray could not oil be actually made) by
 combining its principles ?
   Mrs. B.  That is by no means a necessary  conse-
 quence ; for there are innumerable varieties of com-
 pound bodies which  we can decompose,  although we
 are  unable to reunite their ingredients.  This, howev-
 er, is not the case with oil, as it has very  lately been
 discovered, that it is  possible to form oil, by a peculiar 
241
"process, from the action of oxygenated muriatic acid
 gas on hydro-carbonate.
   We now pass to the volatile or essential oils.   These
 form the basis of  all  the  vegetable perfumes,  and are
 contained, more or less, in every part of the plant ex-
 cepting the seed; they are,  at least, never found in
 that part of the seed which contains the embrio plant.
   Emily.  The smell of flowers then, proceeds from
 volatile oil ?
   Mr*. B.  Certainly ; but this oil is often most abun-
 dant in the  rind of fruits, as  in oranges, lemons,  &c.
 from  which it may be extracted by the  slightest pres-
 sure ; it is found also  in the leaves of plants, and even
 in the wood.
   Caroline.   Is it not very plentiful in the leaves of
 mint,  and of thyme, and all the sweet-smelling herbs I
   Mrs. B.   Yes,  remarkably so;  and in geranium
 leaves also,  which have  a much more powerful odour
 than the flowers.
   The perfume of sandal fans is an instance of its ex-
 istence in  wood.   In short, all  vegetable odours, or per-
 fumes, are produced by the evaporation of particles of
 these  volatile oils.
   Emily.   They are,  I suppose very light, and of very
 thin consistence, since they are so volatile ?
   Mrs.  B.  They vary very much in this respect, some
 of them being as  thick as butter, whilst others are  as
 fluid as water.  In order to be prepared for perfumes,
 or essences, these oils »re first properly purified, and
 then either distilled with alcohol, as is the case with lav-
 ender water, or simply  mixed with a large  proportion
 of water, as is often done with regard to peppermint.
 Frequently also, these odoriferous waters are prepared
 merely by soaking the plants in water, and distilling.
 The water then comes over impregnated with the vola-
 tile oil.
   Caroline.   Such waters are  frequently used  to take
 spots of grease out of  cloth, or silk j  how do they pro-
duce that effect ?
   Mr*. B.   By  combining  with the  substance that
forms these stains; for volatile oils dissolve wax, tallowj 
242
 spermaceti,  and resins ;  if therefore the spot proceeds
 from any of these substances it will remove it
   Insects of all kinds have a  great  aversion  to  per-
 fumes ;  so that volatile oils are employed with success
 in museums for the preservation of stuffed birds and
 other species of animals.
   Caroline.  Pray does not the powerful smell of cam-
 phor proceed from a volatile oil ?
   Mr*.  B.  Camphor seems to be  a substance of its
 own kind, remarkable by many peculiarities.   But if
 not exactly of the  same  nature as  volatile oil,  it is at
 least very analogous to  it.  It  is obtained chiefly from
 the camphor tree, a species of laurel which grows in
 China, and the  Indian isles, from the stem aud roots of
 which it is extracted.  Small quantities have also been
 distilled  from thyme, sage, and other aromatic plants ;
 and  it is deposited in preity large quantities by some
 volatile oils after long stanc'ing.   It  is extremely vola-
 tile and inflammable.  It is  insoluble  in  water,  but is
 soluble  in oils,  in which state, as  well as  its solid
 form, it  is frequently applied to medicinal purposes.
 Amongst the particular  properties of camphor, there
 is one too singular to be passed over in silence.    If you
 take a small piece of camphor, and place  it on the sur-
face of a bason of pure water,  it will immediately begin
 to move  round and round with threat rapidity ; but if you
 pour into the bason a single drop of any odoriferous flu-
id, it  will instantly put a stop to this motion.  You can
 at any time try this very simple  experiment; but  you
 must not expect thtt I shall be able to account for this
 phenomenon,  as nothing  satisfactory has yet been ad-
vanced for its explanatkn.
  Caroline.   It is very singular  indeed ; and I will cer-
tainly  try the experiment.  Pray what are resins, which
you just now mentioned ?
  Airs.  B.   They are volatile oils,  that have been act-
 ed on,  and peculiarly modified,  by oxygen.
  Caroline   They  ate, therefore, oxygenated volatile
 oils ?
  Mr*.  B.  Not exactly ; for the process does not ap-
pear to consist so  much in the  oxygenation of the oil,
 its in the combustion  of a portion of its hydrogen,  and 
243
a small portion of its carbone.  For when resins are
artificially made by the combination of volatile oils with
oxygen, the  vessel in which the process is performed
is bedewed with water, and the air  included within is
loaded with carbonic acid
  Emily.   This process must be, in some respects sim-
ilar to that for preparing drying oils.
   Mr*. U.   Yes ;  and  it is by this operation that both
of them acquire a greater degree of consistence.  Pitch,
tar, and turpentine, are the most common resins ; they
exude from the pine and fir trees.  Copal, mastic, and
frankincense, are also of this class  of vegetable sub-
stances.
   Emily.  Is it of these resins that  the mastic and co-
pal varnishes, so much used in painting, are made ?
   Airs. B.  Yes.  Dissolved either in oil or in alcohol,
resins form varnishes.  From these solutions they nlay
be precipitated by water, in which they are insoluble.
This  1 can easily shew you   If you will pour some
water into this glass of mastic varnish, it will combine
with the  alcohol  in which the resm is dissolved, and
 the latter will  be precipitated in the form of a white
cloud-r-
   Emily.  It is so.  And yet how is it that pictures 9*
 drawings, varnished with  this  solution, may safely be
 Washed with water ?
   Mrs.  B  As  the  varnish dries,  the alcohol evapo-
 rates, and the dry varnish or resin  which remains, not
 being soluble in water, will not be acted on by it.
   There is a class of compound resins called gum re-
 sins, which are precisely what their name denotes, that
 is to say, resins combined with mucilage.   Myrrh and
 ass.tfoetida are of this description.
   Caroline.  Is it  possible that a substance of so disa-
 greeable a smell as assaieetida can  be formed from a
 volatile oil ?
   Mr*.  B   The odour of volatile oils is  by no  means
alvvays grateful.  Onions  and garlic derive  their smell
from volatile oils,  as well as roses and lavender.
   There is still another form under which volatile oils
 present themselves, which is  that of balsams.-*These 
244
 •onsists of resinous juices combined with a peculiar acid
 called the benzoic acid.  Balsams appear to have been
 originally  volatile oils,  the oxygenation of  which has
 converted one part into a resin and the other part into
 an acid, which,  combined together,   form a balsam.;
 such arc the balsams of Peru, Tolu. &c.
   We shall now take leave, of the oils and their various
 modifications, and proceed to the next vegetable sub-
 stance,  which is caoutchouc.   This is a  white  milky,
 glutinous fluid,  which acquires consistence, and black-
 ens  in drying,  in  which state it forms the substance
 with which you  are so well acquainted, under the name
 of gum elastic.
   Caroline.   I  am  surprised to  hear that gum-elastic
 was  ever white,  or ever fluid ! And from what vegetable
 is it  procured ?
  ;Mr*. B   It  is obtained from two or three different
 species of trees in the East Indies, and South Ameri-
 ca, by making incisions in the stem.  The juice is col-
 lected as it trickles from thess incisions, and moulds of •
 clay,  in the form of little bottles of  gum-elastic,  are
 dipped into  it.   A layer of this  juice adheres to the
 clay and dries on it ; and several layers are successive--
 ly added by repeating this till the bottle is of  sufficient
 thickness.  It is then  beaten  to break down the clay,..
 which is  easily  shaken  out.—The natives of the coun-
 tries where this substance is produced,  sometimes
 make shoes and boots of it by a similar process, and
 they  are said to be extremely pleasant and serviceable,,
 both from their  elasticity, and from their being water-
 proofi                            .              ,.
   The  substance that comes next in our enumeration
 of the  immediate ingredients of vegetables, is extrac-
 tive matter.  This is a term, which, in a general sense,
 may be applied  to any substance extracted from vege-
 tables ; but it is more  particularly understood to relate
 to the extractive colouring matter  of plants.  A great
 variety  of colours  are  prepared  from  the vegetable
kingdom, both for the purposes of painting and of dy-
 ^g ; all the colours  called lakes are of this descrip-
  *n : but they  are  less durable than mineral colours, 
245
ibr, by long  exposure to the  atmosphere, they eithe?
darken or turn yellow.
   Emily.   1  know that in painting the lakes are reck-
oned far less durable colours than the ochres ; but what
is the reason of it ?
   Airs. B.   The change which takes place in  vegeta-
ble colours is  owing chiefly  to the  oxygen  of the at-
mosphere slowly burning their hydrogen, and leaving
in some measure the blackness of the carbone expos-
ed.  Such a change cannot  take place  in ocre which
is altogether a mineral substance.
   Vegetable colours have a stronger affinity for animal
than for vegetable substances, and  this  is supposed to
be owing to a small  quantity of  nitrogen  which they
contain.  Thus,  silk and worsted will take a much finer
vegetable die than linen and cotton.
   Caroline.   Dyeing,  then, is quite a  chemical pro-
cess ?
   Airs.  B.   Undoubtedly.  The condition required  to-
form a good die is,  that the colouring  matter should
be precipitated, or fixed, on the substance to be dyed,
aud should form a compound  not soluble in the liquids
to which it will  probably  be exposed.   Thus, for in-
stance, printed or dyed  linens or cottons must be able
to resist the action of soap and water, to which they must
necessarily be  subject in washing; and woolens and
silks should withstand the action of grease and acids, to
which they may  be accidentally exposed.
   Caroline.  But if linen and cotton have not a sufficient
 affinity for colouring matter,  how are they made to re-
 sist the  action of  washing, which they always do when
 they are well printed ?
   Mr*. B.   When the substance to  be dyed has either
 no affinity for the  colouring matter,  or not sufficient
 power  to retain it,  the  combination  is  effected,  or
 strengthened,  by the intervention of a third substance,
 called&a mordant, or basis.  The mordant must have a
 strong affinity both for the  colouring matter and  the
 substance to be dyed,  by which  means  it causes them
 to combine and adhere together
   Caroline.  And what are the substances that  perform
                        W2 
246
the office of thus reconciling the two  adverpe  parties?
   Mr*. B.  The  most common mordant is sulphat of
alumine, or alum.   Oxyds of tin andiron,  in the state
of compound salts, are likewise used for that purpose.
   Tannin is another vegetable ingredient of great  im-
portance in the arts.  It  is obtained chiefly from  the
ba> k of trees ; but it is found  also in nut-galls and in
so nc other vegetables.
   Emily.   Is  that the  substance commonly called  tan
which is used in hot-houses ?
   Mr*.  B.  Tan is the prepared bark in which the pe-
culiar substance, tannin, is contained.  But the use of
tan in hot-houses is of much less importance than in the
operation of tanning, by  which skin is  converted into
leather.
   Emily.  Pray, how is this operation performed ?
   Airs. B.  Various methods are employed for this
purpose, which all consist in exposing skin to the action
of the tannin, or of substances containing this princi-
ple, in sufficient quantities  and disposed to yield it to the
skin.   The most usual  way is to infuse coarsely pow-
dered oak  bark in water,  and to keep the skin immer-
sed in this  infusion  for a certain length of time.   Dur-
ing this process, which is slow and gradual, the skin is
found to have increased in  weight, and to have acquired
a considerable tenacity and impermeability  to  water.
This  effect may be much accelerated by using strong
saturations of the  tanning principle (which can  be  ex-
tracted from bark), instead of employing  the bark it-
self.  But this quick mode of preparation docs not  ap-
pear to make  equally good leather.
   Yannin is contained in  a great variety of astringent
vegetable substances, as galls, the  rose-tree, and wine ;
but it  is no where so plentiful as in  bark.  All these
substances  yield it  to water, from which it may be  pre-
cipitated by a  solution of isinglass, or glue, with which
it strongly  unites  and forms an  insoluble compound.
Hence its  valuable  property of  combining with  skin
(which consists chiefly of glue), and of enabling it to re-
sist the action of water,
  Emily.   Might we not  see that effect by pouring a 
247
little melted isinglass into a glass of wine, which you say
contains tannin ?
   Airs. B.  Yes.   I  have prepared a solution of isin-
glass for that very purpose.—Do you observe the thick
muddy precipitate ?—Tnat is the tannin combined with
the isinglass.
   Caroline.  This precipitate must then be of the same
nature as leather ?
   Mr*.  B.  It is composed of the  same  ingredients;
but the organization and the texture of the skin being
wanting, it has neither the consistence nor the tenacity   ,
of leather.
   Caroline.  One might suppose that  men who  drink
large quantities of red wine, stand  a chance of having
the coats of their stomachs converted into leather, since
tannin  has so strong an affinity for skin.
   Mr*. B.  It is not impossible but that  the coats of
their  stomachs may  be, in some measure, tanned,  or
hardened by  the constant use of this  liquor ; but you
must  remember that  where a number of other chemi-
cal agents are concerned, and, above all, where life ex-
ists, no certain chemical inference can  be drawn.
   I must not dismiss this subject, without  mentioning
a very recent discovery of Mr. Hatchett,  which relates
to it.  This gentleman found that a substance very sim-
ilar to tannin,  possessing  all its  leading properties, and
actually capable of tanning leather, may  be pioduced
by exposing carbone, or any substance containing car-
bonaceous matter, whether vegetable, animal, or  min-
eral, to the action of nitric acid.
   Caroline.   And is not this discovery very likely to be
of great use to manufactures ?
   Airs. B.   That is jety doubtful;  because  tannin,
thus artificially prepared, must probably slways be more
expensive than that which is obtained  from bark.  But
the  fact is extremely curious,  as it affords one of those
very rare instances of chemistry, being able to imitate
the  proximate principles of organized  bodies.
   The last of the vegetable materials is  woody fibre ;
it is the hardest part of plants.   The chief source  from
which this substance is derived is wood,  but it  is also 
248
 contained, more or less, in every solid part of the  plant.
 It forms a kind of skeleton of the part to which it belongs.
 and retains  its shape after all the other materials have
 disappeared.  It consists chiefly of carbone united with
 a small proportion  of salts and  the other constituents
 common to  all vegetables.
   Emily.   It is of a woody fibre, then, that the common
 charcoal is made ?
   Mrs. B.   Yes.  Charcoal, as you may recollect, is
 obtained from wood, by the separation of all its  evapo*
 rable parts.
   Before  we  take leave of the vegetable materials, i t
 will be proper, at least, to enumerate the several vege-
 table acids which we either have had, or may have occa-
 sion to mention.   I believe I  have formerly  told you
 that their basis, or  radical, was uniformly composed of
 hydrogen  and  carbone, and that their difference consist-
ed only in the  variousproportions of oxygen which they
contained.
  The following is  the names of the vegetable acids :
  The Mucous Acid, obtained from gum, or mucilage ;;
Suberic	from cork ;
Camphoric,	from camphor ;
Benzoic,	from balsams :
Gallic,	from galls, bark, &c.
Alalic,	from ripe fruits ;
Citric,	from lemon juice j
Oxalic,	from sorrel ;
Succinic	from amber ;
Tartarous .	frc m tartrit of potash ;
Acetic,	from vinegar.
   They are all decomposable by heat, soluble in waterj
and turn vegetable blue colouft fed.   The  succinic, the
tartarous,  and the acetous acids, are the products of the
decomposition of vegetables ;  we shall, therefore, re-
serve their examination for a future period.
   The oxalic acid, distilled from sorrel, is  the highest
term of vegetable acidification ; for, if more oxygen be
added to it, it loses its vegetable nature, and is resolved
into carbonic acid and water ; therefore, though  all the
ether acids may be converted into the oxalic by an ad- 
249
dition of oxygen, the oxalic itself is not susceptible of«
farther degree of oxygenation ; nor can it be made, by
any chemical process, to return to  a state of lower acid-
ification.
   To conclude this subject, I have only to add  a few
words on the gallic acid ....
   Caroline.  Is not this the same acid before mentioned,
which  forms ink, by precipitating  sulphat of iron from
its solution ?
   Mr*. B.  Yes.  Though it is usually extracted from
galls, on account of its being most  abundant in that ve-
getable substance,  it may also be obtained from a great
variety of plants.  It constitutes what is called the  as-
tringent principle of vegetables ; it is generally combi-
ned with tannin, and you will  find that an infusion of
tea, coffee, bark, red wine, or any  vegetable  substance
that contains the astringent principle, w » make a black
precipitate with  a solution of sulphat of iron.
   Caroline.  But pray what are gills ?
   Mr*. B.  They are excrescences which  grow on the
bark of young oaks, and are occasioaed by an insect
which  wounds the bark of trees, and lays its egg in the
aperture.  The  lacerated  vessels of the tree then dis-
charge their contents,  and form an excrescence, which
affords a defensive covering for these eggs. The fnsect,
when come to  life,  first feeds on this excrescence,
and  some time  afterwards eats its way out, as it ap-
pears from a hole  found  in all  gall-nuts that no longer
contain an insect. It is in hot climates only that strong-
ly astringent gall-nuts are found ; those which are us>ed
for the purpose  of making ink  are brough  from Alep-
po.
   Emily.  But are not the oak-apples which grow on
the leaves of  the  oak in this country, of a similar na-
ture  ?
   Airs. B.  Yes ; only  they are an inferior species of
galls, containing less of the astringent  principle, and
therefore less applicable to useful purposes
  Caroline.  Are the vegetable acids never found but
in their pure uncombined state ?
   Mr*. B.   By no means ; on the contrary, they arc 
250
frequently met  with in  the  state of compound salts ;
these, however, are in general not  fully saturated with
the salifiable bases, sol hat the acid predominates, and
in this state they are called acidulous salts.  Of this kind
is the salt called cream of tartar.
  Caroline.  Is not the salt of lemon commonly used to
take out ink spots and stains, of this nature ?
  Mrs  B.  No ; that salt consists merely of the citric
acid reduced to the state of crystals.
  Caroline.  And  pray how does it take out ink spots ?
  Mrs. B.  By decomposing the black precipitate, and
rendering it soluble in water   But the display  of at-
tractions by which this is performed is, I believe, not
exactly ascertained
  Besides  the vegetable materials which we have enu-
merated, a variety  of other substances, common to the
three kingdoms, are found in vegetables, such as pot-
ash, which was formerly supposed to belong exclusive-
ly to plants, and was in consequence called the vegeta-
ble  alkali.
  Sulphur, phosphorus, earths,  and a variety of me-
tallic ovyds, are also found in vegetables, but nnly in
small quantities.   And we meet sometimes with  neu-
tral salts formed by the combination of these ingredi-
ents.
®
  Confcettfation  xvm.
On the decomposition of Vegetables.
                     Caroline,

  THE account which you  have given us, Mrs. B. of
the materials of vegetables, is doubtless, very instruct- 
251
ive ; but it does not completely satisfy mv curiosity.—
I wish to know how plants obtain the principles  from
which their various materials are  formed ;  by  what
means these are convened into vegetable matter, and
how they are connected with the lile of the plant ?
   Mr*. B.  This implies nothing less than a complete
history of the  chemistry and physiology of vegetation,
subjects on which we have yet  but  very imperfect no-
tions.  Still 1  hope that I shall be able, in some  mea-
sure, to satisfy  your curiosity.  But in order to render
the subject more intelligible, I must first make you ac-
quainted with the various changes which vegetables un-
deigo, when the vital power no longer enables them to
resist the common laws of chemical attraction.
   The composition of vegetables being  more compli-
cated than that of minerals, the former more  reatlily
undergo cheniical  changes than the  latier :  for the
greater the variety of attractions, the more easily is the
equilibrium destroyed,  and  a new older of combinations
introduced.
   Emily.  I am surprised that vegetables should be so
easiiy susceptible ol decomposition ; for the  preserva-
tion  of the vegetable kingdom is certainly far more im-
portant than that of minerals.
   Mr*.  \\.   You  p.ust  consider, on  the  other  hand,
how much more easily the former is renewed than the
latter.   The decomposition of the vegetable takes place
only  fer the death of the plant, which, in the conin on
course ol nature, happens when it has yielded fruit and
seeds to propag..te its species.  If instead of thus finish-
ing its career, < ach plant was to retain its form and veg-
etable state, it would become  an useless bun-en to ti.e
c.rth  and its  inhabitants.— When vegetables,  there-
fore, cease to  be  productive,  they cease to live, and
Nature then begins her process of decomposition, m or-
der  to dissolve them into  their cheniical constituents,
hydroiren,  carbone, and oxygen  ;  those simple and
p unitive ingredients which she keeps in store  for all
her combinations.
   Emily.  But since no system of combination can be
destroyed, except by the establishment of another or- 
252
 <3er of attractions, how can the decomposition of veget-
 ables reduce them to their simple elements ?
   Airs. B.  It is a  very  long process, during which
 a variety of new combinations are successively  esta-
 blished  and successively destroyed ; but,  in each  of
 these changes, the ingredients of vegetable matter tend
 to unite in a more simple order of compounds, till  they
 are  at length -brought to their elementary state, or at
 least, to their most simple order of combinations.  Thus
 you will find that vegetables are  in the end almost  en-
 tirely reduced to water and carbonic  acid ;  the hydro-
 gen  and carbone dividing  the oxygen between them,
 so as to form with  it these two substances.   But  the
 variety of intermediate combinations that  take place du-
 ring the several stages of the decomposition  of vegeta-
 bles, present us with a new set of compounds, well wor-
 thy of our examinaion
   Caroline.   How is it possible that vegetables,  while
 putrefying, should produce any  thing worthy of observa-
 tion ?
   Mr*.  B.  They are susceptible of undergoing cer-
 tain charges before they arrive at the state of putrefac-
 tion, which is the final term  of decomposition ;  and of
 these changes we avail ourselves for particular and  im-
 portant purposes.  But, in order to make you under-
 stand this subject, which is of considerable importance,
 I must explain it more in detail.
   The decomposition  of vegetables is always attended
 by a violent internal motion, produced by the disunion
 of one order of particles, and the combination of aro-
 ther   This is called fermentation.—There are several
 periods at which fermentation stops, so that  a state of
 rest appears to be restored, and  the new order of com-
 pounds fairly established.   But unless means be used
to secure these new combinations in their actual state,
their duration will be  but transient, and a new fermenta-
tion will take place, by which the compound last formed
will be destroyed ; and another, and less complex order
will succeed.
   Emily.  The fermentation, then, appears  to be"only
the successive  steps by which a vegetable descends ta
its final dissolution ? 
258
    Mr*.  B.   Precisely so.  Your definition is perfectly
  correct.
    Caroline.  And how many fermentations, or new ar-
  rangements, does a vegetable  undergo  before it is re-
  duced to its simple ingredients ?
    Airs. B. Chemists do not exactly agree in this point;
  but there are, I think, four distinct fermentations, or
  periods, at which the decomposition of  vegetable mat-
  ter stops and changes its course.  But every kind of
  vegetable matter is not equally susceptible ot  undergo-
  ing all these fermentations
    There are likewise several circumstances required
  to produce fermentation.   Water, and n certain degree
  of heat are both essential  to this process, in order to se-
  parate the particles, and thus weaken their force of co-
  hesion, that the new  chemical affinities may be brought
 into action.
    Caroline.  In frozen climates, then, how can the spon-
  taneous decomposition of vegetables take place ?
    Mrs. B.  It certainly cannot ;  and, accordingly, we
 find scarcely any vestiges of vegetation where a constant
 frost prevails.
    Caroline.  One would imagine  that, on the  contrary,
 such spots would be covered with vegetables ;  for, since
 they  cannot be decomposed,  their numbers must always
 increase.
   Airs. B.   Bui, my dear, heat and water are  quite as
 essential  to the formation  of vegetables  as they  are to
 their decomposition.  Besides, it  is from the  dead  ve-
 getables reduced to  their  elementary  principles, that
 the rising generation is supplied with sustenance.  No
 young plant, therefore, can grow, unless its predeces-
 sors contribute both  to its formation and  support ; and
 these  not only furnish the seed  from which  the new
 plant springs, but likewise the food by which it is nour-
ished.
  Caroline.  Under the torrid zone, therefore, where
water is never frozen, and the heat is very great, both
the processes of vegetation, and fermentation  must, I
suppose, be extremely rapid ?
                        X 
254
    Mr*. B.  Not so much as you imagine ; for in such
'climates great part of the water which is requisite for
 these processes is in an aeriform state, which is scarce-
 ly more conducive either to the growth or formation
 of vegetables than that of ice.  In those latitudes, there-
 fore, it is only in  low damp situations,  sheltered by
 woods from  the sun's rays, that the smaller tribes of
 vegetables can grow and  thrive  during the dry season,
 as dead vegetables  seldom retain water enough to pro-
 duce fermentation,  but are, on the contrary, soon dried
 up by the heat of the sun, which enables them to  resist
 that process ; so that it is not till the  fall of the autum-
 nal rains (which are very violent in such climates), that
 spontaneous fermentations can take place.
   The several fermentations derive their names from
 their principal products.   The first is called the saccha-
 rine fermentation, because its product is sugar.
   Caroline.  But sugar, you have told us, is  found in all
 vegetables ; it cannot, therefore, be the product of their
 decomposition.
   Mrs.  B.   It is true that this fermentation is not con-
 fined to the  decomposition of vegetables, as it contin-
 ually takes place during their life ;  and indeed this cir-
 cumstance has, till  lately, prevented it from  being  con-
 sidered as one of the fermentations.   But the process
 appears so  analogous to  the other  fermentations, and
 the formation of sugar, whether in living or dead veget-
 able matter, is so evidently a new compound, proceed-
 ing from the destruction of the previous order of com-
 binations, and essential to the subsequent fermentations,
 that it is row esteemed the first  step, or necessary pre- •
 liminary, to decomposition, if not an actual commence-
 ment of that process.
   Caroline.  I recollect your hinting to us that sugar was
 supposed not to be secreted from the sap, in the same
 manner as mucilage, fecula, oil, and the other ingredients
of vegetables.
   Airs.  B.  It is rather from these materials, than from
the sap  itself, that sugar is formed ;  and it is developed
at  particular periods,  as  you may  observe in fruits,
which become sweet in ripening, sometimes even after 
255
they have  been gathered.  Life, therefore, is  not es-
sential to the formation of sugar, whilst on the contra-
ry, mucilage, fecula, and the other vegetable  materials
that are secreted from the sap by appropiate  organs,
whose powers immediately  depend on the vital princi-
ple, cannot be produced but during the existence of that
principle.                     ,              .
   Emily.   The ripening of fruits is, then, their first
step to destruction, as well as their last towards perfec-
tion ?
   Mr*. B.   Exactly so.—-The saccharine fermentation
frequently takes place also during the cooking of veget-
ables.   This is the  case with parsnips, carrots,  pota-
toes, &c.  in  which, sweetness is developed by heat and
moisture ; and we know that if we carried the process
a little farther, a  mora complete decomposition would
ensue,  fhe same process takes place also in  seeds
previous to their sprouting*
   Caroline.  How do you reconcile this to your theory,
Mrs. B. ? Can you suppose that a decomposition  is the
necessary precursor of life ?
   Mrs. B.   That is  indeed the case.  Tlie materials
of the seed  must be  decomposed, and the seed dis-
organized, before a  plant c..n sprout from it.—Seeds,
• besides the embryo plant, contain (as we have already
 observed), fecula, oil,  and  a  little  mucilage.  These
 substances are destined  for the nourishment of the fu-
 ture  plant ; but they must undergo some change be-
 fore they can be fit for this function.  The seeds, when
 buried in the earth, with  a certain  degree of moisture
 and of temperature, absorb water, which dilates  them,
 separates their particles, and introduces a new order of
 attractions, of which sugar is  the product.  The sub-
 stance of the seed is thus softened, sweetened, and con-
 verted into a sort of white milky pulp,  fit for the nour-
 ishment of the embryo plant.
   The saccharine fermentation of seeds  is artificially
 produced  for the purpose of making malt, by the fol-
 lowing process :  A quantity of bailey is  first soaked in
 water for two  or three diys ; the water being after-
 wards drained off, the gra.n heats spontaneously, svvelia. 
256
 bursts, sweetens, shews a disposition to germinate,  and
 would actually sprout, if the process  was not stopped
 by putting it into a kiln, where it is well dried at a  gen-
 tle heat. l In this state it is crisp and friable, and consti-
 tutes  the  substance called malt, which is the principal
 ingredient of beer.
   Emily.  But I hope you will tell us how malt is made
 into beer ?
   Airs.  B.  Certainly ; but I must first explain to you
 the nature of the second fermentation, which is essen-
 tial to that operation.  This is called the vinous fermen-
 tation, because its product is wine.
   Emily.  How very different the decomposition of ve-
 getables is from what  I  had  imagined.    The  pro-
 ducts  of their disoi ganization appear  almost  superior
 to those which they yield during their state of life and
 perfection.
   Mr*.  B.   And  do you not at the same time, admire
 the beautiful  economy of Nature, which,  whether she
 creates, or whether she destroys, directs all her opera-
 tions to some  useful and benevolent purpose ?  It ap-
 pears that  the saccharine fermentation is  essential, as
 a previous step, to  the vinous fermentation ; so  that
 if sugar be not developed during the life of the plant,
 the saccharine fermentation must be artificially produc-
 ed before the vinoub  fermentation can take place.  This
 is the case with barley, which does not yield any sugar
 until  it is made into malt  ;  and  in that state only
it is susceptible of undergoing the vinous  fermentation
by which it is converted into beer.
  Caroline.   But if the product of the vinous fermenta-
tion is always wine, beer cannot have  undergone that
process ; for beer is certainly not wine.
  Mrs. B.   Chemically speaking, beer may  be con-
sidered as the wine of grain.   For it is the product of
the fermentation of malt, just as wine is that of the fer-
mentation of grapes, or other fruits.
  The  consequence  of the vinous fermentation is the
decomposition ol the saccharine matter, and the form-
ation  of spirituous liquor from the  constituents of the
sugar.  But, in order to promote  this fermentation,. 
257
not only water and a certain degree of heat are necessa-
ry, but also some other vegeuble ingredients, besides
the sugar, as  fecula,  mucilage,  acids, salts, extractive
matter, &c all of which seem to contribute to  this pro-
cess.
   Emily   It is,  perhaps, for this reason, that wine is
 not obtained from tie tern entailer cl \ i u n ^ai ;  bu
that fruits are chosen for that purpose, as they contain
not only sugar, but likewise the other  vegetable  ingre-
dients which are requisite to promote the vinous fermen-
tation.
   Mr*. B.  Certainly   And you must  observe also,
that the relative quantity of sugar is  not  the only cir-
cumstance to be considered in the choice of vegetable
juices for the  formation of wine ;  otherwise  the  sugar-
cane would be  best  adapted  for that purpose.   It is
rather the manner and proportion in which the sugar is
mixed with other vegetable ingredients that influences
the production and qualities of wine.   And  it is found
that the  juice of the grape not only  yields the most
considerable proportion of wine, but that  it likewise af-
fords it of the most grateful flavour.
   Emily.  I h ive seen a vintage in Switzerland, and I
do not recollect that heat was applied, or water  added,.
to produce the fermentation of the grapes.
   M'-s.  B.   Tne common temperature  of the atmos-
 phere, in the  cellars, in which the juice of the grape
 is  fermented, is sufficiently warm for this purpose ;
 and, as  the juice contains an ample supplv of  water,.
 there is  no occasion  for any addition of it—But when
 fermentation is produced in dry malt, a quantity  of  wa-
 ter must necessarily be added.
   Emily.  But what are precisely the changes that hap-
 pen during the vinous fermentation ?
   Mrs.  B.   The sugar is decomposed^ and its constitu-
ents are  recombitied into two new substances ; the one
 a peculiar  liquid substance, called  alcohol  or spirit of'
 wine, which  remains in the fluid ; the other, carbonic
acid gis, whicu escapes during the fermentation.  Wine,
therefore,ii x g3ier.il p >i;it of  view, miy be consider-
ed as a liquid ot winch ale i'ioI  constitutes the essential
                         X2 
258
part.   And the varieties of strength and flavour  of the
different kinds of wine are to be attributed to the dif-
ferent qualities of the fruits from which they are obtain-
ed, independently of the sugar, without  which no wine
can be produced.
   Caroline.  I am astonished  to hear that so powerful
a liquid as spirits of wine should be obtained  from so
mild a substance as sugar !
   Airs. B.  Cm you tell me in what the principal dif-
ference consist between alcohol and sugar ?
   Caroline.  Let me reflect ....  Sugar consists of
carbone, hydtogen, and oxygen.  If carbonic acid  be
substracted  from it, during  the formation of alcohol,
the latter will contain less carbone and oxygen than su-
gar does ; therefore hydrogen must be the prevailing
principle of alcohol.
   Mr*. B.   It is exactly so.  And this very large pro-
portion of hydrogen accounts for the  lightness and com-
bustible property of alcohol, and of spirits in general, all
of which consist of alcohol variously modified.
   Emily.   And can sugar be recomposed from the com-
bination of alcohol and carbonic acid  ?
   Mrs. B.  Chemists have never been able to succeed
in effecting this ; but from analogy,  I   should suppose
such  a recomposition possible.  Let  us  now observe
more particularly the phenomena that take  place dur-
ing the vinous  fermentation.  At the commencement
of this process, heat is  evolved, and the  liquor swells
considerably from the  formation of the carbonic acid,.
which is disengaged in such prodigious quantities as  to
be often prejudicial to the vintagers.   If the fermenta-
tion be stopped by putting the liquor  into barrels, be-
fore the whole of the carbonic acid is evolved, the wine
is brisk, like Champagne, from the carbonic  arid im-
prisoned in it, and it tastes sweet like cider, from the su-
gar not being completely decomposed.
   Emily.   But I do not understand why heat should be
evolved during this operation.  For as there is a con-
 siderable formation of gas, in which  a proportionable
quantity of heat must become insensible, 1 should have
imagined that cold, rather than heat, would have been
 produced. 
 
Page 1J3.
Flat,J
, \ *f«-r
£,~„.,,y,S For  I».f»ie Cooke* C? M* Mr*en 
259
    Mr*. B.   It appears  so on first consideration ; but
 you must recollect that fermentation  is a complicated
 chemical process; and that, during the decompositions
 and recompositions attending it, a quantity of chemical
 heat may be disengaged,  sufficient both to develope
 the gas,  and to  effect an  increase of temperature—
 When the fermentation  is completed, the liquid cools
 and subsides, the effervescence  ceases, and the thick
  sweet, sticky juice of the fruit is converted into a clear
  transparent spirituous liquor called wine.
    Emily.  How  much I  regret  not  having been  ac-
 quainted  with the nature  of the vinous fermentation,
  when I had an opportunity of seeing the process !
     Mr*. B.  You have  an easy  method  of satisfying
  yourself in  that  respect  by  observing  the process of
  brewing,  which, in  every essential circumstance, is
  similar to that of making wine, and is really a very cu-
  rious chemical operation.
     Although I cannot perform the experiment of mak-
  ing wine, it  will be easy to shew you the mode  of ana-
  lyzing it.  This is done by distillation.  When wine of
  any kind is  submitted to this operation, it  is found to
  contain brandv,  water, tartar, extractive colouring mat-
  ter, and some vegetable acids.  1 have put  a little port
  wine into this glass alembic (Plate X. Fig. 23.J and on
  placing the lamp under it, you will soon see these pro-
  ducts successively come over—
     Emily.  But you do not mention alcohol amongst the
  products of the distillation of wine;  and yet that is its
  most essential ingredient.
     Mrs.  B.   The  alcohol is contained in  the brandy
  which is now coming over, and  dropping from the still.
  Brandy is nothing more than a  mixture of  alcohol  and
  water; and in  order to obtain  the alcohol pure,  we
  must again distil it from brandy.
     Caroline.   I have  just taken a drop on  my finger;

                        PLATE X.
?■    Fig. 23. A. Alrmbic  B. Lamp.  C. Wine glass.
     Fig  *4-  Alcohol blow-pipe.  D  The Lamp.  E. The  ves-
  sel In which the alcohol is boiling. F  A fafety valve.  G.  The
  inflamed jet or ftream of alcohol directed towards a glass tube H. 
260
it tastes  like strong brandy, but it  is without colour;
whilst brandy is of a deep yellow
   Mr*.  B.  It  is not so  naturally ;  in its pure  state
brandy is colourless, and it obtains the  yellow tint you
observe by extracting the colouring matter  from the
new oaken casks in which it is kept.
   But if it does not acquire the usual tinge this way, it is
the custom to colour the  brandy  used in  this country
artificially,  in order to give it the  appearance of having
been long kept.
   Caroline.  And is rum also distilled from wine ?
   Mr*.  B.  By no means ;  it is distilled from the su-
gar-cane, a plant which contains so great a quantity of
sugar, that it yields more alcohol  than almost any  other
vegetable.   Previous to the distillation of the  spirit, the
sugar-cane is made to undergo the vinous fermentation,
which the other ingredients of the plant are just  suffi-
cient to promote.
   The spirituous  liquor  called arack,  is  in  a  similar'
manner distilled from the product oi the vinous fermen--
tation of  rice.
   Emily.  But rice has no sweetness ; does  it  contain.
any sugar?
   Mrs.  B.  Like  barley and most other seeds, it is in-
sipid until it has undergone  the  saccharine  fermenta--
tion ;  and this, you must recollect,  is always a previ-
ous step  to the  vinous fermentation in those vegetables
in which sugar  is not already formed.   Brandy may in
the same manner be obtained from malt.
   Caroline.  You mean from beer, I suppose; for the
malt must  have previously undergone the vinous fer-
mentation.
   Mrs. B.  Beer is not  precisely the product of the
vinous fermentation of malt  For hops are a necessary
ingredient for the formation of tha! liquor ; whilst bran-
dy is distilled from pure  fermented n.alt.   But brandy.
might, no doubt, be distilled from beer as well as from:
any other liquor that has undergone the vinous fermen-
tation ; for since the basis of brandy is alcohol, it may
be obtained from any liquid that contains that spirituous
substance. 
261
   Emily.   And pray, from what vegetable is the favor*
, ite spirit of the lower orders of people, gin, extracted ?
   Airs. B.  The spirit (which is the same in all fer-
 mented  liquors) may be  obtained  from  any kind  of
 grain ; but the peculiar flavour which distinguishes gin,
 is ihat of juniper berries, which  are  distilled together
 with the grain—           .....
    1 think  the brandy contained in  the wine which we
  j.re distilling, must, by this  time,  be all  come  over..
  Yes—taste the fluid that is  now dropping  from  the
  alembic—
    Caroline,   It is perfectly insipid,  like water.
    Mrs.  B.   It is water, which, as I was telling you, is
  the second product of wine,  and  comes  over after  all
  the spirit, which is the lightest part,  is distilled   The
  tartar and extractive colouring matter we shall  find in a
  solid form at the bottom of the alembic.
     Emily.  They look very like the lees of wine.
     Mrs  B.  And in many respects they are of a simi-
  lar nature ; for lees of wine  consist chiefly of tartrit of
  potash, a salt  which exists in the juice of the grape,
  and in many other vegetables, and is developed only by
  the vinous  fermentaticn.  During this  operation  it is
  precipitated, and  deposits itself on the internal surface
   of the cask in  which the  wine  is contained.   It is
   much use.fl  in medicine under  the  name of  cream of
   tartar,  and it n from this salt that the tartarous  acid is
   obtained.                                       .  .
     Caroline.   But the  medicinal cream of tartar is in
   appearance  quite  different  from these dark  coloured
   drees ;  it is perfectly colourless.
      Mrs  B    Because  it consists of the pure salts only,
   in its crystallized form ;  whilst in the  instance before
   us it is mixed with the deep-coloured extractive matter
   and other foreign ingredients,     _
     Emily.   Pray cannot we now obtain pure alcohol from
   the brandv which we have distilled ?
      Mr*   B   We might:  but  the  process would be
   tedious: for in ^der to obtain alcohol perfectly  free
   from water, it is necessary  to distil, or a> the distillers
   call it rectify it several times.  You must therefore aU 
                        262

low  me  to  produce a bottle of alcohol that has been
thus purified.  This  is  a  very important ingredient,
which has many striking properties, besides its forming
the basis of all spirituous liquors.
  Emily.   It is alcohol, 1 suppose, that produces intox-
ication ?
  Mr*. B.   Certainly ; but the stimulus and moment-
ary energy it gives to the system, and  the  intoxication
it occasions  when taken in  excess, are circumstances
not yet accounted for.
  Caroline.   1 thought that it produced these effects by
increasing the rapidity of the  circulation of the blood ;
for drinking wine of spirits, 1 have heard always quick-
ens the pulse.
  Mrs. B.   No doubt; the  spirit by stimulating the
nerves, increases the action of  the muscles ; and the
heart,  which is one of the strongest muscular organs,
beats with augmented vigour and propels the blood with
accelerated quickness.   After  such strong excitation
the frame naturally suffers  a proportional degree of de-
pression, so that a state of dehility and  langour are the
invarible consequences of  intoxication.  But though
these circumstances are  well ascertained,  they are iar
from explaining why alcohol should produce  such ef-
fects.
   Emily.   Liqueurs are the only kind of spirits which
I think pleasant.  Pray of what do they consist ?
   Mr*.  B.  They are composed of alcohol, sweetened
with syrup, and flavored  with volatile oil.
   The different kinds of odoriferous spirituous waters
are likewise solutions of volatile  oil in alcohol, as laven-
der water, eau de Cologne, &c.
   The chemical properties of alcohol are important and
numerous.   It is  one of tlie most powerful  chemical
agents,  and is particularly  useful in dissolving a variety
 of  substances which are soluble neither  by water nor
 heat.
   Emily.   We have seen it dissolve copal and mastic
 to form  varnishes ; and these  resins  are  certainly not
 soluble  in  water, since water  precipitates them from.
 their solution in alcohol. 
263
  Mr*. B.  I am happy to find that you recollect these
circumstances so well.  The same experiment affords
also an instance of another property of alcohol, its ten-
dency to unite with water ; for the resin is precipitated
in consequence of losing the alcohol,  which abandons
it from its preference for water.  We  do not, however,
consider the union of alcohol and  water,  as the effect
of chemical  combination, but rather as a simple solu-
tion, similar to that of sulphuric acid  and water ;  it is
attended also,  as you may recollect, with the same pe-
culiar circumstance of a disengagement of heat and con-
sequent diminution of bulk, which we have supposed
to be produced by a mechanical penetration of particles
by  which latent heat is forced out.
  Alcohol unites thus readily not only with resins and
with water, but with oils and balsams ;  these compounds
form the extensive class of elixers, tinctures,  quintes-
sences. &c
  Emily.  I suppose  that alcohol must be highly com-
bustible, since it contains so large a proportion of hy-
drogen ?
  Mr*. B.  Extremely so  ; and it will burn at a very
moderate temperature.
  Caroline.   1 have often  seen  both brandy and spirit
of wine burnt  ; they pn<luce a great deal ol flame, but
not a proportional quantity of heat, and no smoke what-
ever.
  Airs.  B.   The last circumstance arises from their
combustion being comp'ete ; and the  disproportion be-
tween the flame and heat shows you that these are by
no  means synonimous.
  The great quantity of flame proceeds from the com-
bustion of the hydrogen,  to  which,   you  know, that
manner of burning is peculiar.— Have you not remarked
also, that brandy and alcohol will burn  without a wick?
They take fire at so low a temperature, that this assist-
ance  is not required to concentrate the heat and  vola-
tilize the fluid.
  Caroline.   I have sometimes seen  brandy  burnt by
merely heating it in a spoon.
  Mr*.  B.   The rapidity of the combustion of alcohol 
264
may, however, be prodigiously increased by volatilizing
it.  An ingenious  ins rument has been constructed on
this principle  to  answer the purpose of  a  blowpipe,
which may be  used for melting glass or other chemical
purposes.  It consists of a small metallic vessel (Plate
X. Fig.  24.)  of a  sperical  shape, which contains
the alcohol,  and  is heated by  the lamp beneath it;
as soon as the alcohol is volatilized,  it passes through
the spout of the vessel, and issues just above the wick
of the lamp, which immediately  sets fire to the  stream
of vapour, as I  shall shew you—
  Emily.   With what amazing violence it burns ! The
flame of alcohol in  the state of vapour, is, I  fancy, much
hotter than when the spirit is merely burnt  in a spoon !
  Mr*. B. Yes ;  because in this way the combustion
goes on much cpjicker, and, of course, the heat is pro-
portionally increased.—Observe its effect on this small
glass tube, the middle of which I  present to the extrem-
ity of the flame, where the heat is greatest.
  Caroline.  The glass, in that spot, is become red hot,
and bends from its own weight.
  Mrs. B.  I have now drawn it asunder, and am go-
ing to blow a ball at one of the heated ends ; but  I must
previously close it  up, and flatten it with a little metal-
lic instrument, otherwise the breath would pass through
the tube without dilating any part of it.  Now, Caroline,
will you blow strongly into the tube  whilst  the closed
end is red hot ?
  Emily.   You blowed too hard  ; for the ball suddenly
dilated to a great size, and then burst in pieces.
  Mrs  B.  You  will be more  epert  another time ;
but I must caution you, should you ever use this blow-
p'pe, to be very careful that the combustion of the alco-
hol does not go on with  too great violence, for I have
seen the flame sometimes dart  out  with such force as
to reach the opposite wall of the room, and set the paint
on fire.   There  is, however, no danger  of the vessel
bursting, as it is provided with a safety tube, which af-
fords an additional vent for the vapour of alcohol when
required.
   The products of the combustion of alcohol consist in 
265
a -great proportion of water, and a small quantity of car-
bonic acid.  There is no smoke or fixed remains what*
ever.  How do you account for that,  Emily ?
   Emily   1  suppose that  the oxygen which the alco-
hol absorbs in burning, converts  its hydrogen into wa-
ter,  and its carbone into carbonic acid gas ;  and thus it
is completely  consumed
   Mr*. B.  Very well.—Ether,  the lightest of all flu-
ids,  and with which you are well acipjainted, is obtained
from alcohol, of which it  forms the lightest and most
volatile part
   Emily.   Ether,  then, is to alcohol, what alcohol is
to brandy ?
   Airs. B.  No: there is an essential difference.  In
order to obtain alcohol from  brandy, you need only de-
prive the latter of its water; but for the formation of
ether, the alcohol must be decomposed, and one of its
constituents partly substracted.   I leave  you to  guess
which of them it is-—
   Emily,  it  cannot be hydrogen, as ether is more vo-
latile than alcohol, and hydrogen is the  lightest of all
its ingredients :  nor do I suppose that it can be  oxygen,
as alcohol contains so small a proportion of that princi-
 ple  ; it is therefore, most probably carbone, a diminu?
 tion of which would not fail to  render the new com-
 pound  more  volatile.
   Mr*. B.   You are perfectly  right.  The formation
 of ether  consists simply in subtracting from the  alco-
 hol a certain  proportion of carbone ; this  is effected by
 the action of  the sulphuric, nitric, or muriatic acids on
 alcohol.  The acid and carbone remain at the bottom
 of the vessel, whilst the decarbonized alcohol flies off
 in the form of a condensable vapour, which is  ether.
   Ether is the most inflamable of all fluids, and burns
 at so low  a  temperature that the heat evolved during
 its  combustion is more than is required for its support,
 so that a quantity of ether  is  volatilized,  which takes
 fire, and gradually increases the violence of the com-
 bustion.
   This spirituous fluid  is so light that it evaporates at
 the common  temperature of the atmosphere, it is there'
                          Y 
266
  fore necessary to keep it confined by a veil ground glass
  stopper.   No degree of cold known has ever frozen it.
    Caroline.   Is it not often taken medicinally ?
    Mr*. B.  Yes ; it is one  of the most effectual antis-
  pasmodic medicines, and the quickness of its effects,
  as such,  probably depends on its  being instantly con-
  verted into vapour by the heat of the stomach, through
  tlie intervention  of which it acts on the nervous system.
  But the  frequent use of ether,  like that of spirituous
  liquors, becomes prejudicial, and, if taken to excess,
.  it produces effects similar to those of intoxication.
    We may now take our leave of the vinous fermenta-
  tion, of which I hope,  you have accpiired a clear idea;
  as well as of the several products that are derived from
  it.
    Caroline.   Though this process appears at first sight
  so much complicated,  it may, I think,  be summed up
  in few words,  as it consists simply in the conversion of
  sugar  into alcohol and carbonic  acid, which gives rise
  both to the formation of wine, and of all kinds of spirit-
  uous liquors.
     Mrs.  B.  We shall now proceed to the acetous fer-
  mentation, which is thus called, because it converts wine
  into  vinegar,  by the  formation  of the acetous acid,
  which is the basis or radical of vinegar.
    Caroline.  But is  not  the acidifying principle of the
  acetous  acid the same as that of  all other acids, oxy-
  gen ?
     Mr*.  B.  Certainly ;  and on that account the con-
  tact of air is essential to this fermentation, as it affords
  the necessary supply of oxygen.  Vinegar,  in order to
  obtain pure acetous acid from it,  must be distilled and
  rectified by certain processes; and  the more frequent-
  ly this operation is  repeated, the more perfect the acid
  will be.
     Emily.   But  pray,  Mrs. B. is not the  acetous  acid
  frequently  formed  without  this fermentation  taking
  place  ? Is it not, for instance,  contained in acid fruits,
  and in every substance that becomes sour ?
     Mrs.  B.  No, not in fruits;  you  confound it  with
   the  citric,  the  malic, the  oxalic, and other  vegetable 
26r
adds, to which living vegetables owe their acidity.  But
whenever a vegetable substance tuins sour, after it has
ceased to live, the acetous  acid is developed by means
of the acetous fermentation, in which the substance ad-
vances a step towards its final decomposition
   Amongst the various  instances of acetous fermenta-
tion, that of bread is usually classed.
   Carotine.  But the fermentation of bread is produced
by yeast;  how does that effect it ?
   Mr*. B.  It  is found by experience  that any  sub-
stance that has already undergone a fermentation, will
readily excite it in one that is susceptible of that process.
If, for instance, you mix a little vinegar  with wine that
is intended to be acidified,  it will absorb oxygen  more
rapidly, and the  process  be completed  much  sooner
than if left to ferment spontaneously.   Thus, ^ yeast,
 which is a product of  the fermentation of beer, is used
 to excite and accelerate the fermentation of malt, which
 is  to be converted  into beer, as well as that of paste
 that is to be made into bread.
    Caroline.  But if bread undergoes the acetous fermen-
 tation,  why is it not sour ?
    Mrs. B.  It acquires a certain savour which corrects
 the heavy insipidity  of flour, and may be reckoned a
 first degree of acidification ; for if the process was car-
 ried farther, the bread would become decidedly acid.
    There are,  however, some chemists who do not con-
 sider the fermentation of bread as being of the acetous
 kind,  but suppose  that it is a process of fermentation
 peculiar to that substance
    The putrid fermentation is the final operation of Na-
 ture, and her last step towards reducing organized  bo-
 dies to their  simplest combinations.   All vegetables
 spontaneously  undergo this  fermentation  after  death,
 provided there be a sufficient degree of heat and mois-
 ture, together with access of air ;  for it is well  known
 that dead plants may  be preserved by drying, or by the
 total exclusion of air.
    Caroline.  But do dead plants undergo the other fer-
 mentations previous  to this last; 01 do they immedi-
 ately sufl'cr the putrid fermentation? 
                        2 S3

   Mr*. B.  That depends on a variety of circumstan-
ces,  such as the degrees of temperature and of moist-
ure,  the nature of the plant itself, See.  But, if you
were carefully to follow and examine the decomposition
of plants from their death to their final dissolution, you
would generally find a sweetness developed in the seeds,
and a spirituous flavour in the fruits, (which have under-
gone the saccharine fermentation), previous to the to-
ut! disorganization and separation of the parts.
   Emily.   I have sometimes remarked a kind of spi-
rituous taste in fruits that were over  ripe,  especially
oranges ; and this was  just before they became rotten.
   Mrs. B.  It was then the vinous fermentation which
had succeeded  the  saccarine,  and  had you followed up
these changes attentively, you would probably  have
found the spirituous taste  followed by acidity, previous
to the fruit  passing to the state of putrefaction.
   When  the leaves fall from the trees in autumn, they
do not (if there  is no great moisture  in the atmosphere)
immediately undergo a decomposition,  but are first dri-
ed and withered ; as soon, however, as  the rain  sets in,
fermentation commences,  their gaseous products are
imperceptibly evolved into  the atmosphere, and their
fixed remains mixed with their kindred earth.
   Wood, when exposed  to  moisture, also undergoes
the putrid fermentation and becomes rotten.
   E?nily.   But I  have  heard that the dry rot, which is
so liable to destroy the beams of houses,  is  prevented
by a current of air ; and  yet you said that air  was es-
sential to  the putrid fermentation ?
   Mr*. B.  True ; but it must not be in such a pro-
portion to  the moisture as  to dissolve the latter,  and
this is  generally  the case when the rotting of  wood is
prevented or stopped by the free access of air.—What
is commonly dry rot, however, is not, I believe, a true
process of putrefaction.   It is supposed to depend on a
peculiar  kind of  vegetation,  which, by feeding on the
wood, gradually destroys it.
   Straw and all other kinds of vegetable matter under-
go the putrid  fermentation  much  more rapidly when
mixed with animal matter.  Much  heat is evolved dur- 
269
ing this process,  and a variety of volatile products ard
disengaged, as carbonic acid and  hydrogen gas, the
latter of which is frequently either sulphurated or phos-
phorated.  When all these gasses have been evolved,
the fixed products consisting  of carbone, salts,  potash,
&c. form a kind of vegetable earth, which makes very
fine manure, as it is composed of those elements which
form the immediate materials of plants.
   Caroline.   Pray are not vegetables sometimes  pre-
served from decomposition by petrefaction ? I have seen
very curious specimens of petrified vegetables, in which
state they perfectly preserve their form and organiza-
tion, though in appearance they are changed to stone.
   Mrs.  B.   That is a kind of metamorphosis, which,
now that you are tolerably well versed in history of min-
eral and vegetable substances, I leave to your judgment
to explain.   Do  you  imagine that vegetables can be
converted into stone ?
   Emily.  No certainly ; but they might perhaps be
 changed to a substance in appearance resembling stone.
   Mr*.  B.  It is not so. however, with the  substances
 that are called petrified vegetables ; for these are real-
 ly stone, and generally of the hardest kind,  consisting
 chiefly of silex.  The case  is this ;  when a vegetable
 is buried under water, or in  wet earth, it is  slowly and
 gradually decompo-ed.   As each successive particle of
 the  vegetable is destroyed, its place is supplied by a
 partible of Vicious earth, conveyed thither by the water.
 In thtTOurse of time the vegetable is entirely destroyed,
 but the silex has completely replaced it, having assum-
 ed its form and apparent texture,  as if the vegetable it-
 self were changed to stone.
    Caroline.   That is very curious ! and I suppose that
 petrified animal substances are of the same nature ?
    Mr*.  B.   Precisely. It is equully impossible for eith-
 er animal or vegetable substances  to be converted into
 stone.  They may be reduced, as we find they are, by
 decomposition, to  their constituent elements,  but  can-
 not be  changed  to  elements, which  do not enter int»
  their composition.
                         Y2 
2ro
  There are, however, circumstances  which frequent-
ly prevent the regular and final decomposition of vege-
tables ;  as, for instance,  when they are buried either
in the sea,  or in the earth, where they  cannot undergo
the putrid fermentation for want of air.  In these cases
they are subject  to a  peculiar change,  by  which they
are converted into a new  class of  compounds,  called
bitumens.
  Caroline.   These are substances I never heard of  be-
fore.
  Mrs. B   You will find, however, that some of them
are very familiar to you.  Bitumens are vegetables so far
decomposed  as  to retain  no organic appearance ;  but
their origin is easily detected by their oily nature, their
combustibilty, the products of their analysis, and  the
impressions of the forms of  leaves, grains,  fibres of
wood, and even of animals, which they  frequently bear.
  They are sometimes of an  oily liquid consistence, as
the substance called naphtha, which is a  fine transparent
colourless fluid, that issues out of clays  in some parts of
Persia.  But more frequently they are solid  as asphaltum,
a smooth hard  brittle substance,  which easily  melts,
and forms, in its  liquid state, a beautiful dark brown
colour for oil painting.  Jet, which is of a still harder
texture, is a peculiar bitumen, susceptible of so fine a  po-
lish that it is used for many ornamental purposes.
   Coal is also a bituminous substance,  to the composi-
tion of which both  the  animal and mineral kingdoms
seem to concur.   This most useful mineral appears to
consist  chiefly of vegetable  matter,   mixed  with  re-
mains of marine animals  and marine  salts, and  occa-
sionly containing a quantity of sulphuret of iron,  com-
monly called pyrites.
  Emily.   It is, I suppose, the earthy, the  metallic,
and the saline parts of coals, that compose the cinders
or  fixed products of their combustion  ; whilst the  hy-
drogen and the carbone, which they derive from vege-
tables, constitute their volatile  products.
   Caroline.   Pray is not coak (which  I have  heard is
much used in some manufactories;  also a bituminous
substance ? 
271
  Mrs. B. It is a kind of fuel artificially prepared from
coals.  It consists of coals reduced to a substance anal-
ogous  to charcoal, by the evaporation of their volatile
parts.  Coak, therefore, is composed of carbone, with
some earthy and saline ingredients.
   Suctin or yellow  amber, is a bitumen which the  an-
cients  called electrum, from whence the word electricity
is deiived, as that substance is peculiarly, and  was once
supposed to be exclusively electric.   It is found either
deeply buried in the bowels of 'he earth, or floating  on
the  sea, and is supposed to be a resinous body which
has  been acted on  by  sulphuric acid,  as  its analysis
shews it to consist of an oil and an acid.  The  oil is call-
ed oil of amber, the acid the succinic.
   Emily.  That oil I have sometimes used in  painting,
as it is reckoned to change  less than the other kinds of
oils.
   Mrs.  B.  The last class of vegetable substances that
have  changed their  nature are fossil wood,  peat,  and
turf.  These are composed of wood and roots  of shrubs,
that are partly decomposed by being exposed to mois-
ture underground, and yet, in some measure,  preserve
their form and organic appearance.   The peat, or black
 earth  of the  moors, retains  but few vestiges of the roots'
 to which it owes  its richness and combustibility, these
 substances being in the course of time reduced  to  the
 state of vegetable earth.  But in turf the roots of plants
 are still diseernable, and it  equally answers the purpose
 of fuel.  It is the combustible used by the poor  in heathy
 countries, which supply it abundantly
   It is too late this morning to  enter upon the history of
 vegetation.  We shall reserve  this  subject,  therefore,
 for our next interview, when 1 expect that it will furnish
 us with ample matter lor another conversation. 
272
Confcettfation xix
History  of Vegetation,
                     Mrs. B.

  The Vegetable Kingdom may be considered as  the
link  vvhic.i unites the mineral and animal creation into
one common chain of beings ; for it is through the means
of vegetation alone that mineral substances are introdu-
ced into the animal system, since generally speaking, it
is  from vegetables that all animals ultimately  derive
their sustenance.
  Caroline.  1 do not understand that; the human spe-
cies  subsist as much on animal as on vegetable food,
and there are some carnivorous animals that will eat  on-
ly animal food.
  Mrs.  B.  That is  true ; but  you  do not consider that
those that  live on animal food derive their sustenance
equally, though not so immediately, from vegetables.
The moat that  we eat is formed from the herbs  of  the
field,  and  the  prey  of carnivorous animals proceeds,
either directly or indirectly, from the same source.  It
is  therefore through this  channel that the simple ele-
ments become a part of the animal frame.  We should
in vain  attempt to derive nourishment from  carbone,
hydrogen, and  oxygen, either in their  separate  state,
or combined in the mineral kingdom ; for it is only by
being united in  the form of vegetable combination that
they become capable of conveying nourishment.
  Emily.  Vegetation then, seems to be the method
which nature employs to prepare the food of animals ?
  Mrs.  B.  That is certainly its principal object.—The
vegetable creation does not exhibit more wisdom in that
admirable system of organization, by which it is enab-
led to answer its own immediate ends of preservation, nu-
trition, and propagation, than in its grand and ultimate 
t)f-n
object of forming those arrangements and combinations
of principles, which are so well adapted for the nourish-
ment of animals.
  Emily.   But I am very curious to know whence veg-
etables  obtain those principles, which form their imme-
diate materials ?
  Mr*. B.   This.is a point on which  we are yet  so
much in the dark, that I cannot hope fully to satisfy
your curiosity ; but what little I know on this subject, I
will endeavour to explain to you.
  The  soil, which, at first view, appears to be the ali-
ment of vegetables, is found, on a closer investigation, to
be little more than the channel through which they  re-
ceive their nourishment  ; so that it  is very possible  to
rear plants without any earth or soil.
  Caroline.   Of that we have an instance in the hya-
cinth and other bulbous roots, which  will, grow and blos-
som beautifully  in glasses of water.  But  I  confess  I
should thihk it would be difficult to rear trees  in a simi-
lar  manner.
  Airs. B.   No doubt it would, as it is the burying  of
the roots in the earth  that supports the stem of the tree.
But this office, besides that  of  affording a vehicle  for
food, is far the most important  part  which the earthy.
portions of the  soil perform in the process of vegetation ;
for we can discover by analysis but an extremely  small
proportion of earth in vegetable compounds.
  Caroline.   But  if earths  do not afford nourishment,.
why is  it necessary to be so attentive to the preparation
of the soil ?
  Airs. B.  In order to impart to  it   those  qualities
which  render it  a proper vehicle for  the  food of the
plant.  Water is the  chief nourishment of vegetables-;
if, therefore, the soil  be too sandy, it will not retain  a
quantity of water sufficient  to supply the roots of the
plants.  If, on  the contrary,  it  abounds too much with
clay, the water will lodge in such quantities  as  to threa-
ten  a decomposition of the roots.—Calcareous  soils are
upon the whole, the most  favourable to the growth of
plants,  fiom their containing in great abundance car--
bonic acid,  which is  one of.the most essential ingredi* 
274
ents of  vegetation.   Soils are, therefore, usually im-
proved by  chalk, which you may recollect  is a  car-
bonat of lime.  Different vegetables,  however require
different kinds of soils.   Thus rice demands a moist, re-
tentive soil ; potatoes a soft  sandy soil ; wheat a firm and
rich soil    Forest trees grow better in a fine sand than
in a stiff clay ; and a light feruginous soil is best suited
to fruit trees.
   Caroline.   But pray what is the use of manuring the
soil?
   Mr*. B.   Manure consists of all kinds of substances,
whether  of vegetable or  animal origin, which have un-
dergone the putrid fermentation and are consequently
decomposed, or  nearly  so,  into their elementary  prin-
ciples.  Now, I ask you what is the utility of supplying
the soil with these decomposed substances ?
   Caroline.^  It is, I suppose, in order to furnish vege-
tables with the principles which enter into their com-
position   For manures not only contain carbone, hy-
drogen, and oxygen, but by their  decomposition sup-
ply the  soil with these principles in their  elementary
form.
   Mr*. B.   Undoubtedly ; and it is for this reason that
the finest crops are produced in fields that were former-
ly covered with woods, because their soil  is composed
of a rich mould, a kind of vegetable earth  which a-
bounds in these principles.
   Emily.   This accounts  for the  plentifulness of the
crops produced in America, where the country was but
a few years since covered with wood.
   Caroline.  But how is it that animal substances are
reckoned to produce the best manure  ? Does  it  not ap-
pear much more natural that the decomposed elements
of vegetables should  be the  most appropriate to  the for-
mation of new vegetables ?
   Mr*. B    The addition of a much greater proportion
of nitrogen, which constitutes the chief difference be-
tween animal and vegetable matter, renders the  com-
position  of the  former more  complicated, and conse-
quently more favourable to decomposition.  The use
of animal substances is chiefly to give the first impulse 
275
to the fermentation of the vegetable ingredients that en-
ter into the composition of manures.  The manure of
a farm-yard is of that description ; but there is  scarcely
any substance susceptible  of undergoing the putrid fer-
mentation that will not make good manure.  The heat
produced by  the fermentation of manure is another
circumstance  which is extremely favourable to veget-
ation ;  yet  this  heat would  be too great if the manure
was laid on the  ground in the  height of fermentation  ;
it is used in this state only for hot-beds, to produce mel-
ons, cucumbers, and such  vegetables as require a very
 high temperature.
   Caroline    A difficulty  has just occurred to me which
 I do not know how to remove—Since  all organized
 bodies are, in the  common course ot  nature, ultimately
 reduced to  their elementary state, they must  necessa-
 rily in that siate enrich the soil, and afford food for ve-
 getation.   How is it then that  agriculture, which  can-
 not increase the quantity of these elements that are re-
 cpjired to manure the earth, can increase its produce so
 woderfully, as is  found to be tlie case in all cultivated
 countries  ?
   Mrs. B.  It is by suffering none of these principles
 to  remain inactive, and by employing them to the best
  advantage.   This object is attained by a judicious pre-
  paration of the soil, which  consists  in fitting it either
  for the  general purposes of vegetation, or for that of the
  particular  seed which is to be sown.  Thus,  if the soil
  be  too cold, it  may be warmed by slacking lime  upon
  it ; if loo loose  and  sandy, it may be rendered  more
  consistent and  retentive of water by the  addition of clay
  or  loam ;  if too  poor, it may be enriched by chalk  or
  any kind of calcareous earth.   On soils thus  improved,
  manures will act with double efficacy, and if attention
  be paid to spread them  on the ground at a proper sea-
  son of the year, to mix them with the soil so that they
  may be generally diffused  through it,  to destroy the
  weeds  that might appropriate these nutritive principles
  to  their own usesto remove the stones which would im-
  pede the growth of the plant, Sec. we may obtain a pro-
  duce  an  hundred fold  more abundant than the  earth
 would spontaneously supply. 
276
   Emily.  We have a very striking instance of this in
 the scanty produce of uncultivated commons, compared
 to the  rich  crops  of meadows which are occasionally
 manured.
   Caroline.   But, Mrs.  B.  though  experience, daily
 proves the advantages of cultivation, there is still a diffi-
 culty which  I  cannot get over.   A certain quantity of
 elementary principles exist in nature, which  it is  not
 in the  power of man either to augment or diminish.
 Of these principles you have taught us that both the an-
 imal and vegetable creation are composed.   Now  the
 more of them is  taken  up by the vegetable kingdom,
 the less it would seem,  will  remain for animals  ; and
 therefore' the more populous the earth becomes, the less
 it will produce.
   Airs. B.   Your reasoning is very plausible ; but ex-
 perience every where  contradicts the inference yon
 would draw  from it: for  we find that the animal and
 vegetable  kingdoms, instead of thriving as you would
 suppose, at each other's ex pence, always increase and
 multiply together.  Indeed, you must allow that your
 conclusion would be valid only if every particle of the
 several principles  that could possibly be spared from
 other purposes were employed in the animal and vege-
 table  creations.  Now we have reason to believe, that
 a much greater proportion  of these principles  than is
 required for such purposes remains, either in  an ele-
 mentary  state, or engaged in a  less useful mode  of
 combination  in the  mineral kingdom.   Possessed  of
 such immense resources  as  the atmosphere and the
 water affords us, for  oxygen, hydrogen,  and carbone,
 so far from being in danger of working up all our sim-
 ple  materials, we cannot suppose  that we shall  ever
 bring agriculture to such a degree of perfection as to re-
 quire the whole of what these resources could supply.
  Nature, however,  in thus furnishing us with an in-
exhaustible stock of raw materials,  leaves  it in some
 measure to the ingenuity of man to appropriate them
 to his own purposes.  But, like a kind parent,  she sti-
 mules him to  exertion, by setting  ths  example and
 pointing out the way.  For it  is on the  operations  of
nature that all the improvements of art are founded.-— 
tT7
The art ofagriculture Consists, therefore, in discovering
the readiest method of obtaining the several principles,
either from their grand sources, air and water, or from
the decomposition, of organized bodies; and in appropri-
ating them in the best manner to the purposes of vege-
tation.
   Emily.  But, among the  sources of nutritive princi-
ples,  I am surprised that you do not mention the earth
itself, as il contains abundance of coals which are chiefly
composed of carbone.
   Mr*.  B.  You must recollect that coals are, principal-
ly, if not entirely, of vegetable origin ;  and therefore, the
earth should  he  considered rather as the vehicle thro'
which  decayed organized matter is gradually brought
to the state of coals, than as the original source of that
valuable  combustible.   Besides,  you  know, that tho'
coals abound in carbone, they cannot on account of their
hardness and impermeable texture,  be immediately
subservient to the purposes of vegetation.
   Emily.  No ; but by their combustion  carbonic  acid
is  produced ; and this entering  into various combina-
tions on the surface  of the earth, may perhaps assist  in
promoting vegetation.
   Mr*. B. Probably it may in some degree ; but at any
 rate  the quantity of nourishment, which vegetables may
 derive  from  that source, can be  but very trifling, and
 must entirely depend on local circumstances.
   Caroline.   Perhaps the smoky atmosphere  of London
 is the reason  why vegetation is so forward and so rich in
 its vicinity ?
    Mrs. B.   I rather believe that this circumstance pro-
 ceeds from the very ample supply of manure,  assisted
 perhaps by the warmth and shelter which the town af-
 fords.   Far from attributing any good to the smoky at-
 mosphere of London, I confess, I  Kke to  anticipate
 the time when  we shall  have made  such progress  in
 the art of managing combustion, that every particle  of
 carbone  will be consumed, and the  smoke destroyed
 at the moment of its  production.  We  may then ex-
 pect to  have the satisfaction of seeing the atmosphere
of London as clear as that of the country.—But to re- 
278
turn to our subject : I hope that you arc now convinced
that we shall not easily  experience a  deficiency of nu-
tritive elements to fertilize the earth, and that,  provided
we are but industrious in applying  them to the best ad-
vantage by improving the art of aggriculture, no limits
can be assigned to the fruits that we may expect to reap
from our labours !
   Caroline.  Yes ; I am perfectly satisfied in that re-
spect, and can assure you that 1 feel already much more
interested in the progress and  improvement ofagricul-
ture.
   Emily.   I have often thought that the culture of the
land  was not considered as a concern of sufficient im-
portance.  Manufactures always  take  the lead  ;  and
health and innocence  are  frequently sacrificed to the
prospect of a more profitable employment. It  has often
grieved me to see the  poor manufacturers crowded to-
gether in close rooms,  and confined for the whole  day
to the most uniform and sedantary employment, instead
of being engaged in that innocent and salutary kind of
labour, which nature seems to have assigned to man for
the immediate acquirement of comfort, and for the pre-
servation of his existence.   I am  sure that you agree
with me in thinking so, Mrs. B.
    Mr*.  B.   I am entirely of your opinion, my dear, in
 regard to the  importance of agriculture ; but I am far
from wishing to depreciate manufactures; for as the
labour of one  man is sufficient to produce food for sev-
eral,  those  whose  industry is not  required  in tillage
must do something in return for the food that is provided
for them. They exchange consequently, the accom-
modations for the necessaries of life.   Thus the carpen-
ter and the weaver lodge and clothe the peasant, who
supplies  them with their  daily  bread.  The greater
stock of provisions, therefore, which the husbandman
produces, the greater is the quantity of accommodation
which the artificer prepares.  Such  are  the happy ef-
fects which naturally result  from civilized society.  It
would be wiser, therefore, to endeavour to impi ove the
situation of those who areengagedin manufactures, than
to indulge in vain  declamations on the hardships to
which they are often exposed. 
 
 
279
  But we must not yet take our leave  of the subject of
agriculture ; we have prepared the soil, it remains for us
now to sow the seed. In this operation we must be care-
ful not to bury it too deep into the ground, as the access
of air is absolutely necessary to its germination ; the
earth therefore must lie loose and light over it, in order
that the air might penetrate.—Hence the use of plough-
ing  and digging, harrowing  and raking, ^cc.   A  cer-
tain degree of heat and moisture, such as usually takes
place in  the spring, is likewise necessary.
   Caroline.   One  would imagine you were going to
describe the decomposition of an old plant, rather  than
the formation of a new one ; for j*)U have enumerated all
the  requisites for fermentation.
   Mrs. B.   Do  you forget, my dear, that the young
plant derives its existence  from the destruction of the
seed, and that it is actually by the saccharine fermenta-
 tion that the  latter is decomposed ?
   Caroline.   True ; I wonder that  I did  not  recollect
 that. The  temperature  and  moisture required for the
 germination of  the seed, is then  employed in producing
 the saccharine fermentation within it.
   Mrs. B.   Certainly.  But, in order to  understand
 the ,natiire  of  germination, you should  be acquainted
 with the different  parts  of which the seed is composed.
 The external covering  or envelope* contains,  besides
 the germ of the future plant, the substance which  is to
 constitute its first nourishment ;  this substance, which
 is called the parenchyma, consists  of fecula, mucilage,
 and oil, as we formerly observed.
    The   seed  is  generally divided into two  compart-
 ments,  called lobes or cotyledons, as is  exemplified  by
 the bean,  (Plate XI.  Fig. 25J—the dark coloured
  kind of string which divides the lobes, is called the rad-

                      PLATE XI.
   Fig 2j. Bean.
   Fig. 26  A B.  Cotyledons.  C   Envelope.    D. Radicle.
   Fig 27  A  B  Cotyledons.  C  Plumula.    D. Radicle.
   Fie 28   \  B.  Cotyledons.  C.  Plumula.    D Radicle.
   Fig. 29. A A  Glass bell.   B Bladder representing the lung*
  C.  Bladder reprcnting the diaphragm. 
280
cle, as it forms the root of the plant, and it is from a
contiguous substance called plumula, which is enclosed
wiihin the lobes, that the stem arises.   The figure and
size of the seed depend  very much upon the cotyle-
dons ; these vary in number in different seeds  ; some
have only one, as wheat, oats, barley, and all the grasses;
some have three,  others  six.  But most seeds, as  for
ins(ance,all the variety of beans, have  two cotyledons.
When the seed is buried in the earth, at any tempera-
ture above 4-0° it imbibes water, which softens and swells
the lobes ; it then absorbs oxygen which combines with
some of its carbone, and is  returned in  the form of car-
bonic acid.  The loss of carbone increases the compar-
ative proportion of hydrogen and oxygen in  the seed,
and excites the saccharine fermentation, by which the
parenchymatoas matter is converted into a kind of sweet
emulsion.   In  this form it  is carried into the radicle by
vessels for  that purpose ; and in the mean time,  the
fermentation having caused the seed to burst,  the co-
tyledons  are  rent asunder, the radicle strikes into the
ground and becomes the root of the plant, and hence
the fermented  liquid is conveyed to the plumula, whose
vessels have been  previously  distended by the  heat of
the fermentation.   The plumula being thus swelled, as
it were by the emulsive fluid, raises itself and springs up
to the surface  of the earth, bearing with it the cotyle-
dons, which as soon as they come  in  contact with  the
air, spread themselves, and are transformed into leaves'—
If we go into the garden,  we shall probably find some
seed in that state which I have described—
   Emily.  Here are some lupines that are just  making
their appearance above ground.
   Mr*.  B.  We will take up several of them to observe
their different degrees of progress in vegetation. Here
is one that has  but recently burst its envelope—do you
see the little radicle striking downwards ? (Plate  XI.
Fig  26.) In this the plumula.is not  yet visible.  But
here is another in  a greater state  of forwardness—the
plumula, or  stem,  has risen out of the ground, and  the
cotyledons are  converted into seed leaves, (Plate XI.
Fig.  21).                                y
   Caroline.  These leaves  are  very thick and clumsy, 
281
and unlike the other leaves which I perceive are just be=
ginning to appear.
   Mrs. B.  It is because they retain the remains of
the parenchyma, with which they still continue to nou-
rish the young plant, as it has not yet sufficient roots, and
strength to provide  for its sustenance  from the soil.—
But, in this third lupine, (Plate XI. Fig. 2B.) the ra-
dicle had sunk deep into the earth, and sent out several
shoots, each of which is furnished with a mouth to suck
up nourishment from the soil ; the function of the ori-
ginal leaves, therefore, being no longer required,  they
are  gradually decaying, and the plumula is become a
regular stem, shooting out small branches and spreading
its foliage.
   Emily.   There seems to be a very  striking  analogy
between a seed and an egg ; both  require  an elevation
of temperature to be brought to life ;  both at first  sup-r
ply with aliment  the organized being which they  pro-
duce ; and as soon as this has attained sufficient strength
to procure its  own nourishment,  the egg-shell breaks,
whilst in the plant the seed-leaves fall off.
   Mr*. B.   There  is certainly some resemblance  be-
tween  these  processes ;  and when you  become  ac-
quainted with animal chemistry, you will frequently be
struck with  its analogy to that of the  vegetable king-
dom.
   As soon as the  young plant feeds from the soil, it re-
quires the assistance of leaves, which are the organs by
Which the plant throws off its superabundant fluid ; this
secretion is much more plentiful in the vegetable  than
in the animal creation, and the great extent of surface
of the foliage of plants is admirably calculated for car-
rying it on  in  sufficient  quaniites.   This transpired
fluid consist of little more than water.  The sap, by this
process, is  converted into a  liquid of  greater  con-
sistence, which  is fit to be  assimulated to its several
parts.
   Emily.   Vegetation, then, must be essentially injur*
ed by destroying the leaves of the plant ?
   Mr*.  B.   Undoubtedly ;  it not  only diminishes the
transpiration, but also the absorption by the roots ; foe
                       Z 2 
282
 the quantity of sap absorbed, is alvvays in proportion to
 the quantity of fluid thrown off by transpiration.   You
 sec therefore the necessity that  a young  plant should
 unfold its leaves as soon as it begins to derive its  nou-
 rishmeni from the soil;  and accordingly you will find
 that those lupines which have dropped their seed leaves,
 and are no longer fed by the parenchyma, have spread
 their foliage, in order to  perform the office just descri-
 bed.
   But I  should inform you that  this  function of trans-
 piration seems to be combined to tlie upper surface  of
 the leaves,  whilst on  the contrary, the lower  surface
 which is more rough and uneven, and  lurnished with a
 kind of hair or down, is destined to absorb moisture, or
 such other ingredients as the plant derives from the at-
 mosphere.
   As soon as a young plant makes its appearance above
 ground,  light  as well as air becomes necessary to its
 preservation.   Light  is  essential to the developement
 of the colours and to the thriving of the plant.  You may
 have  often observed what a predilection vegetables have
 for the light.  If you make any plants grow in a room,
 they  all  spread  their leaves and extend their branches
 towards the windows.
   Caroline.   And many plants close up their flowers as
 soon  as it is dark.
  Emily.  But may not this be owing to the  cold  and
 dampness of the evening air ?
   Airs.  B.   That does not appear to be the case  ; for
 in a course of curious experiments, made by Mr. Sene-
 bier, of Geneva, on plants which  may be reared by lamp
 light, he  found  that  the flowers closed  their petals
 whenever the lamps were extinguished.
  Emily.  But pray, why is air essential to vegetation ;
 plants do not breathe it like animals ?
   Airs. B.  At least not m the same manner ; but they
certainly derive some principles  from the  atmosphere,
and yield others to it.   Indeed,  it is chiefly owing to
theac ion oftht atmosphere and the vegetable kingdom
on each other, and the air continues always fit for  res-
piration.   But you will understand this better when I
have e^iaincd the effect of water on plants. 
283
  I have  said that water forms the chief nourishment
of plants ; it is the basis not only of the sap, but of al[
the vegetable juices.  Water is the vehicle which car-
ries into the plant the various salts and other  ingredi-
ents required for the formation and support of the veg-
etable system   Nor is this all ; great part of the water
itself is decomposed by the organs of the plant; the hy-
drogen becomes a constituent part  of oil,  of extract, of
colouring matter, See. whilst a portion of the oxygen
enters into the formation of mucilage, of fecula, of su-
gar, and  of vegetable acids.  But the greater part of
the oxygen,  proceeding from the decomposition of the
water, is converted into a  gaseous state by the  caloric,
disengaged from the hydrogen during its condensation
in the formation of the  vegetable* materials.   In  this
slate the  oxygen is transpired by  the leaves of plants
when exposed to the sun's rays.   Thus  you find  that
the decomposition of water, by the organs of the plant,
is nut only a means of supplying it with its chief ingre-
dient, hydrogen, but at the same  time of replenishing
the atmosphere with oxygen, a principle which requires
continual renovation, to make up for the great consump-
tion of it occasioned by the numerous oxygenations,
 combustions, and resp'uations, that are constantly ta-
king place on the surface of the globe
   Emily.  What a striking  instance of the harmony of
 nature !
   ATrs.  B.   And how admirable  the design of Provi-
 dence,  who makes every different part  of the  creation
 thus contribute to  the support and renovation of each
 other 1                                   ,
    But the intercourse of the vegetable and animal king-
 doms through the medium of the atmosphere extends
 still farther.   Animals,  in breathing, not only consume
 the oxygen of the air,  but load  it with  carbonic acid,
 which,  if accumulated in  the atmosphere, would,  in a
 short time, render it totally unfit for respiration.  Here
 the vegetable kingdom again interferes ; it attracts and
 decomposes the carbonic acid, retains the carbone for
 its own  purposes,  and  returns the oxygen  for  ours.
 This process,  however, is only  carried on during the
 day, and a contrary one seems to take place during the 
284
night; for the leaves then absorb oxygen and emit car-
bonic acid.   The absorption of carbonic acid during the
day, is, however,  far from balanced by  the  quantity
emitted during the night.
  Caroline.  How  interesting  this  is !  I do not know a
more beautiful illustration of the wisdom  which is dis-
played in the laws of nature
  Mrs. B.   Faint and imperfect as are the ideas which
our limited  perceptions  enable  us to form of Divine
Wisdom, still they cannot fail to  inspire  us with awe
and admiration. What then would be our feelings were
the complete system of nature at once displayed before
us !  So magnificent a scene would  probably be too great
for our limited and imperfect comprehension, and it is,
no doubt, amongst the wise dispensations of Providence,
to veil  the  splendour of a glory with which we should
be overpowered.—But it is well suited to the nature of
a rational being to explore, step by step,  the works of
the creation ;  to endeavour to connect them into har-
monious systems ; and. in a word, to trace, in the chain
of beings, the kindred ties and benevolent designs which-
unite its various links, and secure its preservation.
   Caroline.   But of what nature are these organs of
plants which are endued with such wonderful powers ?
   Mrs. B.   They are so minute,  that their structure,
as well as the mode in which they  perform their  func-
tions, generally elude our examination ;  but we may
consider them as so many vessels  or apparatus appro-
priated to perform, with the assistance of  the principle
of life, certain chemical processes, by means of which
these vegetable compounds are  generated.  We may,
however, trace the tannin, resins,  gum, mucilage, and
some other vegetable materials in the organized arrange-
ment of plants, in which they form the bark, the wood,
the leaves, flowers, and seeds.
   The bark is composed of the epidermis, the paren-
thyma,  and  the cortical layers.
   The epidermis  is the external covering of the  plant.
It is a thin transparent membrane  consisting of a num-
ber of slendes fibres  crossing each other, and  forming
& kind of net-work.   When of  a white glossy nature, 
285
as in several species  of trees, in the stem* of corn and
of seeds, it is composed of a thin coating of silicious
earth, which accounts for the strength and hardness of
those long and slender stems.  Mr. Davy  was led to
the discovery of the silicious nature of the epidermis ot
such plants, by observing the singular phenomenon ot
sparks of fire emitted by the collision of rattan canes
with which two boys were  fighting in a dark  room.—
On analysing the epidermis of the cane,  he found it to
be almost entirely silicious.
   Caroline.  With iron  then, a cane I suppose, will
strike fire  very easily ?
   Mrs.  B.  I understand  that  it  will—In evergreens
 the epidermis is mostly  resinous,  and  in some few
 plants is formed of  wax.  The resin, from its want ot
 affinity for water, tends to  preserve the plant from the
destructive effects of violent rains, severe climates, or
 inclement seasons,  to which this species ol vegetables
 is peculiarlv exposed.                .
   Enuly.   Resin must preserve wood just like a vai-
 nish, as it is the essential  ingredient  of varnishes.
   Mr*.  B.  Yes, and by  this means it prevents like-
 wise all unnecessary expenditure of moisture.
   The parenchyma is immediately beneath the epider-
 mis ; it is  that  green  rind which appears when you
 strip a branch of any tree  or shrub of its external coat
 of bark.  The parenchyma is not confined to  the stem
 or branches, but extends  over  every part of the plant.
 It forms  the  green matter of  the leaves, and is com-
 posed of tubes filled with a peculiar juice.
    The cortical layers are  immediately in  contact with
 the wood  ; they abound with tannin and gallic acid, and
 consist  of small vessels,  through which the sap de-
 scends after being elaborated in the leaves.   1 he corti-
 cal layeis arc  annually renewed, the old bark being
 converted into wood.
    Emily.   But  through  what  vessels does the sap as-

   '^■Mrs B.  That  function  is performed by  the tubes
 of'the  albunum or wood, which is immediately  be-
  neath the cortical layers.   The  wood  is composed ot 
286
woody fibres, mucilage, and resin.  The  fibres aw
disposed in  two ways ; some of  them longitudinally,
and these form  what is called the silver grain of the
wood.  The others,  which are  concentric, are called
the spurious grain.  These last are disposed in layers,
from the number of which  the age of the tree  may be
computed, a new  one being produced  annually by the
conversion of the bark into wood.   The oldest, and con-
sequently most internal part of the alburnum, is called
heart-wood  ; it appears to be  dead,  at  least  no vital
functions are discernible in it.  It is through the  tubes
of the living alburnum that the sap rises.   These,
therefore, spread into the  leaves, and there communi-
cate with the extremities of the vessels of the cortical
layers, into which  they pour their contents.
   Caroline.   Of what use then are the tubes of the pa-
renchyma,  since neither the ascending nor descending
 sap passes through them ?
   Mrs. B.   They are supposed to perform the impor-
 tant function of secreting from the sap the peculiar jui-
 ces from which the plant more immediately derives its
 nourishment.  These juices are very conspicuous,  as
 the vessels  which contain  them are much larger than
 those through which  the sap circulates.  The peculiar
 juices of plants differ much in  their nature, not only in
 different species of vegetables, but frequently in differ-
 ent parts of the same  individual plant.   They are some-
 times saccharine as in the sugar-cane, sometimes resi-
 nous, as in  firs and evergreens, sometimes of  a milky
 appearance, as in  the laurel.
   Emily.   I have often observed, that  in  breaking a
 young shoot, or  in bruising a leaf of laurel,  a  milky
juice will ooze out in  great abundance.
   Mrs.  B.   And it is by making incissions in the bark,
 that pitch,  tar, and  turpentine are obtained from fir
trees   The durability of this species of wood is chiefly
owing to the resinous nature of its peculiar juices.  The
volatile oils have in a great measure,  the same preser-
ative effects, as they defend the parts with  which they
are connected, from  the attack of insects.   This tribe
 seems to have as  great an aversion to perfumes,  as the 
2sr
.Hi'ii.m species lake delight in them.  They  scarcely
ever attack any odoriferous parts of plants, and it is not
uncommon to see every leaf of  a tree  destroyed by a
blight, whilst the blossoms remain untouched.  Cedar,
sandel, and all aromatic  woods, ai e on this account of
great durability.
  Emily.   But the wood of the oak,  which is  so much
esteemed for its durability has I believe, no smell.----.
Does it derive this quality from its hardness alone ?
  Mr*. B.   Not entirely ; for the chesnut, though con-
siderably  harder and firmer than the oak, is not so
lasting.  The durability of the oak is, 1 believe, in a
great measure  owing to its having very  little heart-
wood, the alburnum preserving its vital functions long-
er than in other  trees.
  Caroline.  If  incisions  are made  into the alburnum
and cortical layers, may not the ascending and descend-
ing sap be procured in  the same manner as the pecu-
liar juice is from the vessels of the parenchyma ?
  Mrs. B.   Yes ; but in  order to obtain specimens of
these fluids,  in any quantity, the experiment must le
made in the spring,  when the sap  circulates with the
greatest  energy.  For this purpose  a small bent glass
tube should  be  introduced into the incision, through
which the sap may flow without  mixing with any of the
other juices of  the tree.   From tlie bark  the sap will
flow much more plentifully than from the wood, as the
ascending sap  is much  more liquid, more abundant,
and more rapid  in its motion than that which descends;
for the latter having been deprived by the operation of
the leaves of a considerable part of its moisture, con-
tains a much greater proportion of  solid matter which
retards its motion.  It does not appear that there  is
any of descending sap, as none  ever exudes  from the
roots of plants ; this process, therefore,  seems to be
carried on only  in proportion to the  wants  of the plant,
and the sap descends no further and in no greater quan-
tity than  is required to nourish the several  organs.—
Therefore, though the sap rises and descends in the
plant, it does not appear to undergo a real circulation.
   The last of the organs of plants is the flower or blos-
som, which produces the fruits and  seed.   These may 
288
 be considered as the ultimate purpose of nature  in the
 vegetable creation.   From fruits and seeds animals de-
 rive both a plentiful source of immediate nourishment,
 and an ample provision for the reproduction of the same
 means of subsistence.
   The seed, which forms the final product of  mature
 plants we have  already examined,  as constituting the
 first rudiments of future vegetation.
   These are  the principal  organs of vegetation,  by
 means of which the several chemical processes, which
 are carried on  during the life of the plant,  are perform-
 ed.
 ;  Emily.   But how  are the several principles which
 enter into the  composition of vegetables,  so combined
 by the organs of the plant as to be converted into veget-
 able matter ?
   Mrs. B.  By chemical processes, no doubt,  but the
 apparatus in which they are performed is  so extremely
 minute as completely to elude our examination.  We
 can  form an opinion,  therefore, only by  the result  cf
 these operations.  The sap is evidently  composed of
 water absorbed by the roots, and holding in solution the
 various principles which it derives from the soil.   From
 the roots the sap ascends through the tubes of  the al-
 burnum into the stem, and thence branches out to every
 extremity of the plant.   Together with the sap circu-
 lates  a certain  quantity of carbonic acid, which is grad-
 ually  disengaged from the former by the  internal heat
 of the plant.
   Caroline.   What!  have  vegetables a peculiar heat
 analogous to animal heat  ?
   Mr*  B.   It is a circumstance that has long been
 suspected; but  late  experiments have decided beyond
 a doubt, that vegetable heat is considerably above that
 of unorganized  matter in winter, and below it in sum-
 mer.   The wood of a tree is about  60° when  the ther-
 mometer is 70^ or 80°.  And the bark, though so much
 exposed, is seldom below 40 in winter
  It is from the sap, after it has been elaborated by the
leaves, that vegetables derive their  nourishment ;  in
its progress through the plant, from the leaves to the 
28 J
r*ets,  it deposites in  the  several sets  of vessels witb
which it communicates, the  materials on which the
growth  and nourishment of each  part depends.   It is
thus that the  various  peculiar juices, saccharine, oily,
mucous, acid, and colouring, are formed ; as also the
more solid  parts of fecula, woody fibre, tannin, resins,
concrete salts : in a word, all  the immediate materials
• of vege tables, as  well as the  organized  parts of plants,
which latter, besides the.power of secreting these from
the sap,  for the  general purpose of the plant, have also
that of applying them to their own particular nourish-
ment.
   Emily.  But  why should the process of vegetation
take place only at one season of the year, whilst a total
inaction  prevails during the other ?
   Mr*.  B.  Heat is such an important chemical agent,
that its  effect, as such, might perhaps alone account
for the impulse which the  spring gives to vegetation.
But, in order to explain the mechanism Of that opera-
tion, it has been supposed that the warmth of the spring
dilates the  vessels  of plants, and produces  a kind of
vacuum, into which the  sap (which had  remained in  a
state of inaction in the trunk during the  winter) rises ;
this is followed by the ascent of the sap contained in the
roots, and room is thus made for fresh sap, which the
roots, in their turn pump up from the soil.  This pro-
cess  goes on till the  plant blossoms and  bears  fruit,
which terminates its  summer career ;  but  when the
cold weather set6 in, the fibres and vessels contract, the
leaves wither, and are no longer able to perform their
office of transpiration ; and, as this secretion stops, the
roots cease to absorb sap  from the  soil.—If the plant
be an annual, its life then terminates  ; if not, it remains
in a state of torpid inaction during the winter ; or the
only internal motion that takes place is  that of a small
quantity of resinous juice, which slowly  rises  from the
stem into the branches, and enlarges  their buds during
4he winter.
   Caroline.  Yet, in evergreens,  vegetation must con-
•tinue throughout the year.
   Mr*.  B.  Yes ; but in winter it goes on in a very im-
                        A a 
290
 perfect manner, compared  to the vegetation of spring
 and summer.
   We have dwelt much longer on the history of vege-
 table chemistry than I had intended ; but we  have at
 length, I think brought the subject to a conclusion.
   Caroline.  I  rather wonder that you did not reserve
 the account of the fermentations for the conclusion ; for
 the decomposition of vegetables naturally follows their
 death, and can hardly, it  seems,  be introduced with so
 much propriety at any other period.
   Mrs. B.  It is difficult to determine at what point
 precisely it may be most eligible to enter on the history
 of vegetation ;  every part of the subject  is  so closely
 connected, and forms such an uninterrupted chain, that
 it is by  no means easy to divide it.   Had I begun with a
 germniation of the  seed, which, at first view, seems  to
 be the most proper arrangement,  I could  not have ex-
 plained  the nature and fermentation of the  seed, or have
 described the changes which manure must undergo, in
 order to yield the vegetable elements.   To undei stand
 the nature of germination, it is necessary,  I think, pre-
 viously to decompose the parent plant,  in order to be-
 come acquainted with  the materials required for  that
 purpose.  I hope, therefore, that, upon  second consider-
 ation, you will find that the order which I have adopted,
 though apparently less correct, is in fact the best calcu-
lated for the elucidation of the subject.
  CottJettfation xx.

On the Composition of Animals.
                      Mrs. B.
  WE are now come to the last branch  of chemistry,
which comprehends the most complicated order of com-
pound beings.  This is the animal creation, the history 
2$1
of which cannot but excite the highest  degree of curi-
osity and interest, though we often fail in attempting to
explain the laws by which it is governed.
  Emily.   But since all animals ultimately derive their
nourishment from vegetables, the chemistry of this or-
der of beings must consist merely in the conversion of
vegetable into animal matter ?
  Mr*. B. Very true ; but the manner in which this is
effected is, in a great measure, concealed from  our  ob-
servation.  This process is called animalization, and is
performed by peculiar organs.  The difference of the
animal and vegetable kingdoms  does not, however,  de-
pend merely on a different arrangement of combinations.
A new principle abounds in the animal kingdom, which
is but rarely and in very  small quantities found in veg-
etables ; this is nitrogen.  There is likewise in animal
substances a greater and more constant proportion of
phosphoric  acid,  and other saline matters.  But  these
are not essential to the formation of animal matter.
  Caroline.  Animal compounds contain then four fun-
damental principles,  oxygen, hydrogen,  carbone,  and
nitrogen.
  Mr*. B.   Yes ; and these form the immediate mate-
rials of animals, which are gelatine, albumen, and fibrinc.
  Emily.   Are those  all ? I am surprised that animals
should be composed of fewer kinds  of materials than
vegetables ; for they appear much more complicated in
their organization.
  Mr*. B.  Their  organization is certainly more per-
fect and intricate,  and the ingredients that occasionally
enter into their  composition  are more numerous.   But
notwithstanding the wonderful variety observable in the
texture of the animal organs, we find  thtt the original
compounds, from which all the varieties of animal mat-
ter  arc derived, may be reduced to the three heads just
mentioned.   Animal substances being  the most com-
plicated of all natural  compounds, are most easily sus-
ceptible  of  decomposition, as the  scale of attractions
increases in proportion  to the number  of constituents.
Their  analyses is, however, both difficult and imper-
fect ;  for as they cannot be examined in their living 
2*2
 state,  and are  liable  to alteration  immediately after
 death, it is probable that, when submitted to the inves-
 tigation of a chemist, they are always more or less al-
 tered in  combinations and properties, from what they
 were whilst they made part of the living animal.
   Emily   The mere diminution of temperature, which
 they experience by the privation  of animal heat, must,
 I should  suppose, be sufficient to derange the  order of
 attractions that existed during life.
   Mr*.  B.   That is one  of the causes, no doubt : but
 there are many other  circumstances which prevent us
 from studying the nature of living animal substances.
 We must therefore, in a considerable degree,  confine
 our researches to the phenomena of these compounds
 in their inanimate state.
   These three kinds of animal matter, gelatine, albu-
 men, and fibrine, form the basis of all the various parts
 of the animal system ; either solid, as the shin, flesh,
 nerves, membranes, cartilages, and  bones  ;  or fluids, as
 blood, chyle, milk, the  gastric, and pancreatic juices, bile,
perspiration, saliva, tears, &c.
   Caroline.   Is it not surprising that so great a variety
 of substances, and so  different in  their nature,  should
 yet all arise from so few materials, and from the same
 original elements ?
   Mr*.  B.   The difference  in the  nature of various'
bodies depends, as I have often observed to you, rather
on their state of combination, than  on the  mateiials of
which they are composed.   Thus, in considering  the
chemical nature of the creation in  a general point of
view, we observe that it is throughout composed of a ve-
ry small number of elements. But when we divide it in-
to the three kingdoms, we  find that, in the mineral, the
combinations seem to result from the union of elements
casually brought together ;  whilst in the vegetable and
animal kingdoms,  the attractions are peculiarly and
regularly produced by appropriate organs, whose action,
depends on the vital principle.   And we  may further
observe, that  by means of certain spontaneous changes
and  decompositions, the elements of one kind  of mat-
ter become subservient to the production of another •
so that the three kingdoms are intimately connected', 
29S
and constantly contributing to the preservation of each'

  Emily.   There  is, however,  one very considerable
class of elements,  which  seem to be  confined  to the
mineral kingdom : I mean metals.
  Mrs. B.   Not entirely ;  they are found, though in
very minute quantities, both in the vegetable and  ani-
mal kingdoms.  A small  portion of earth and sulphur
enters also into the composition of organized  bodies.
Phosphorus, however, is almost entirely confined to the
animal  kingdom ;   and  nitrogen, but with few excep-
tions, is extremely scarce in vegetables.,
  Let us now proceed to examine the nature of the three
principal materials of the animal system.
   Gelatine or jelly, is the chief ingredient of skin, and
of all the membranous parts of animals.  It may be ob-
tained from  these substances under the  forms of glue,
size, isinglass, and transparent jelly.
  Caroline.  But these are of a very different nature  ;
they cannot therefore be all pure gelatine.
  Mr*. B.  Not entirely, but very nearly so.'  Glue is
extracted from  the skin of animals    Size  is obtained
either from the skin in its natural state, or frorn leather.
Isinglass is gelatine procured from a particular species
of  fish ;  it is, you know, of this substance that the
finest jelly is made, and this is done by merely  dissolv-
ing the isinglass in boiling water, and allowing  the so-
lution to congeal.
  Emily.  The wine, lemon, and spices, are, I suppose, j
added only to flavour the jelly ?
   Airs. B.  Exactly so.
   Caroline.  But jelly is often made of  hartshorn shav-
ings, and of calves'feet;  do these substances  contain;
 gelatine ?
   Mr*. B.  Yes.   Gelatine may be obtained from al-
most  any animal substances, as it enters more  or less
into  the  composition of all  of them.   The process  of
obtaining  it is extremely  simple, as it  consists merely
in boiling  the substance that contains it with water. The
 gelatine dissolves in water, and  may be obtained of any
degree of consistence or strength,  by evaporating thjs
                        A a a- 
2:94
solution.  Bones in particular produce it very plentiful-
ly,  as they  consist  of phosphat  of lime combined  or
cemented by gelatine.  Horns which are a species  of
bone, will yield abundance  of gelatine.  The horns  of
the hart are reckoned to produce gelatine of the  finest
quality ;  they are reduced to the  state of shavings in
order that the jelly  may be more  easily extracted  by
the water   It is of hartshorn  shavings that the jellies
for invalids are usually made, as they are of very easy di-
gestion.
  Caroline,  It  appears singular  that hartshorn, which
yields such a powerful ingredient as ammonia, should
at the same time produce so mild  and insipid a substance
as jelly ?
  Mrs. B.  And, what is  more surprising, it  is from
the gelatine of bones that  ammonia is produced.—You
must observe,  however, that the processes by which
these two substances are obtained from bones  are very
different.  By the simple action of water, and heat, the
gelatine is separated ; but in order  to procure the am-
monia, or what is commonly called hartshorn, the  bones
must be distilled, by which means the gelatine is de-
composed, and hydrogen and nitrogen combined in the
form of ammonia.  So that the first operation is a mere
separation of ingredients, whilst  the second requires a
chemical decomposition.
  Caroline*  But when jelly is made from  hartshorn
shavings, what  becomes of the phosphat of lime which
constitutes the other part of bones ?
  Mrs.  B.   It  is  easily separated by straining.  But
the jelly is afterwards more perfectly  purified, and ren-
dered transparent by adding white of egg, which  being
coagulated by heat, rises to the surface along with any
impurities.
   Emily.  I  wonder that bones are not used by the com-
mon people to make  jelly ; a great deal of wholesome
nourishment might, I should suppose, be procured from
them, though the jelly would  perhaps  not be quite  so
good as if made from hartshorn shavings ?
   Mr*. B.   There is a kind of prejudice  among the
poor against a species of food that is usually thrown te 
295
      fte- dogs;  and as we cannot expeot them to enter int»
      chemical consideration, it is in some degree excusable.
      Besides, it requires a prodigious quantity of fuel to dis-
      solve bones and obtain the gelatine  from- them.
         The solution of bones  in water is greatly promoted
      by an accumulation of heat.  This may be effected  by
      means of an extremely strong metallic vessel, called
      Papin's digestery in which the bones and water are en-
      closed,  without any possibility of the steam making .its
      escape.  A heat can thus be applied much superior to
      that of boiling water; and bones, by this means, are
      Completely reduced  to. a pulp.  But  the process still
      consumes too much fuel  to be generally adopted among
      the lower classes.
         Caroline.  And why should not a manufacture be  es-
      tablished  for grinding or macerating bones, or at least
      for reducing them to the state  of shavings, when I
      suppose they would dissolve  as  readily  as hartshorn
k      shavings ?.
         Mrs. B.  Indeed I see  no objection to this plan, if
      the  prejudices of the vulgar  could be overcome;  but
      this would be-a difficult matter, for I have even heard
      it objected to Papin's digester, that by the  use of food
      thus prepared,, the flesh of those feeding upon it would
      become ossified.
         Caroline.  But  these prejudiced people might easily
       see that the flesh  of dogs, who feed chiefly on bones, is
      not ossified..  Besides it  would not be difficult to con-
      vince them %at the real bony matter, the phosphat of
      lime, is deposited and forms no part of the jelly.
         Emily.   And when, jelly  is made of. isinglass,, does it
      leave no sediment ?'
         Mrs. B.  No.; nor does it  so.much require clarify-
      ing, as it consists almost entirely  of pure  gelatine, and
      any foreign  matter that  is  mixed with it,  is thrown  off
      during  the boiling in the  form  of scum.  These  are
      processes which you may  see performed in great per-
      fection  in  the culinary  labratory,  by  that very and
      most useful chemist the cook.
         Caroline.  To what an immense variety of purposes
      themistry  is  subservient 1 
296
   Emily.  It appears in that respect, to have  an  ad-
vantage over most other arts and  sciences ;  for  these
very  often have a tendency to confine the imagination
to their own particular object, whilst the pursuit ot chem-
istry  is so extensive and diversified, that it inspires a
general curiosity, and a desire of inquiring into the na-
ture of every object.
   Caroline.   I suppose that soup is likewise composed
of gelatine ;  for when cold,  it often assumes the con-
sistence of jelly ?
   Mrs. B.  Yes ; all soups contain a quantity of gela-
tine obtained from meat, and dissolved in water.  And
the various kinds  of portable soups  consist almost en-
tirely of concentrated jelly, which,  in order to be made
into soup, requires only to be dissolved in water.
   Gelatine,  in its solid state,  is a semiductile  transpar-
ent substance, without either taste or smell.—When
exposed to heat, in contact with air and water, it first
swells, then fuses, and finally burns.  You  may have
seen the  first part of this operation performed in the
carpenter's glue-pot.
   Caroline.  But you said that gelatine had no smell,-
and glue has a very disagreeable one
   Mrs. B.  Glue is not  purely gelatine ; but like size,
the smell of which  is  still more offensive,  it retains
some other particles of animal matter.
   Gelatine may  be precipitated from its solution in wa-
ter by alcohol.—We shall try this experiment with a
glass  of warm jelly.—You see that the gjplatine subsides
by the union of the alcohol and the water.—
   Emily.  How is it, then, that jelly is flavoured with
wine, without producing any  precipitation ?
   Airs. B.   Because the alcohol contained  in wine is
already combined with water  and other ingredients, and
is therefore not at liberty to act upon the jelly as when
in its separate state.   Gelatine is soluble both in acids
and in alkalies ;  the  former,  you know, are frequently
used to season jellies.
   Caroline.  Among the combinations of gelatine we
must  not forget one which you formerly  mentioned :
that with tannin, to form leather. 
297
  Mr*.  B.  True ; but you must observe that leather
•an be' produced only by gelatine in a  membraneous
state;  for  though pure gelatine and tannin will pro-
duce a substance chemically  similar to leather, yet the
texture  of  the skin is requisite to make it answer the
useful purposes of that substance.                #
  The  next  animal substance we are to examine is al-
bumen-, this,  although constituting part of most of the
animal compounds, is frequently found insulated in the
animal system ; the white of egg, for instance, con-
sists almost entirely of albumen;   the  substance that
composes the nerves* the serum, or white part of the
blood, and the  curds of milk, are  little  else than albu-
men variously modified.                   m
   In its most simple state, albumen  appears in thelorm
 of  a  transparent viscous fluid, possessed of ■ no distinct
 taste or smell; it coagulates at the low  temperature of
 165°,  and when once solidified, it  will  never return to
 its  fluid state.
   Sulphuric  acid and alcohol are eaeh of them capable
 of coagulating albumen  in the same manner  as heat, as
 I am going to shew you—                    .
   Emily.  Exactly so.—Pray, Mrs. B. what kind oF<
 action  is-there between albumen  and  water?  I have
 sometimes observed, that if the spoon with which I eat
 an egg happens to be wetted, it becomes tarnished.
    Mr*. B.  It is because the white of egg (and indeed-
 albumen in general) contains a little sulphur, which, at
 the temperature of an egg  just boiled,  will  decompose
 the drop of water  that wets the spoon, and produce sul-
 phurated hydrogen gas, which has the  property of. tar-
 nishing silver.                         .....,
    We may now proceed to Fibrine. This is an insipid
 and  inodorous substance, having somewhat the appear-
 ance of fine white threads adhering together ;  it is the
 essential  constituent of muscles or flesh,  in which it is
 mixed with and  softened by gelatine.   It  is insoluble
 both in water and alcohol,  but sulphuric acid converts
 it  into a substance very analagous to gelatine.
    These  are  the essential  and general ingredients, ot
  animal matter ;  but there are other substances, which,. 
298
though not peculiar to the animal system, usually enter
into its composition, such as nils, acids, salts, he.
  Animal Oil is the chief constituent  of  fat; it is con-
tained in abundance in the cream of milk, whence it is
obtained in the form of butter.
  Emily.  Is animal oil the  same in its composition as
vegetable oils ?
  Mrs.  B.  Not the same,  but very  analogous.   The
chief difference is  that animal oil contains nitrogen, a
principle that seldom enters  into the composition of ve-
getable oils, and never in  so large a proportion.
  There are  a few animal  acids, that is to say, acids
peculiar to animal matter, from which they are almost
exclusively obtained.
  The animal acids have triple bases  of hydrogen, car-
bone, and nitrogen.  Some  of them are found native in
animal matter ; others are produced during its decom-
position.
  Those that we find ready  formed arc :
  The bombic  acid, which is obtained  from silkworms.
  The formic acid,  from ants.
  The lactic acid, from the whey of milk.
  The sebacic from oil or fat.
  Those produced during the decomposition of animal'
substances by  heat, are the prussic and zonic acids.—
This last is produced  by the roasting of meat,  and
gives it a brisk flavour.
  Caroline.  The class of animal acids is not very ex-
tensive.
  Airs. B.  No;  nor  are  they,  generally speaking,
of great importance.  The prussic acid is, I think, the
only one  sufficiently  interesting to require any further
comment.   It  can be formed by an artificial process,
without the presence of any animal matter ; and it-may
likewise be obtained from a variety of vegetables, par-
ticulatly those of the narcotic kind, such as poppies, lau-
rel.  Sec.  But  it is  commonly obtained from  blood, by
strongly heating  that  substance  with caustic potash ;
 the  alkali  attracts the acid from the blood, and forms
 with it  a prussiat of potash.   From this state of combi- 
                        4VV

nation the prussic acid can  be obtained pure by means
of other substances which have the power of separating
it from the alkali.
   Emily.  But if this acid does not exist ready formed
in blood, how can the alkali attract it from it ?
   Mr*. B.  It is the triple bases only of this  acid that
exists in the  blood ; and this is developed and brought
to the state of acid, during the combustion.   The acid
therefore  is first formed,  and it afterwards combines
with the potash.
   Emily.  Now  I comprehend it.  But how can  the
prussic acid be artificially made ?
   Mr*. B.  By  passing ammoniacal gas over red  hot
charcoal ; and hence we learn that  the  constituents of
this acid are hydrogen, nitrogen,  and carbone.   The
two first are derived from  the volatile alkali, the  last
from the combustion of the charcoal
   Caroline.  But this does not accord  with  the system
of oxygen being  the indispensable principle of acidity ?
   Mrs. B.  It  is true ; and this circumstance, togeth-
er with some others of the same kind, has led several
chemists to suspect that oxygen may not be the sole
generator of acids, and that  acidity may possibly depend
rather on the arrangement  than on ihe presence of any
particular principles.
   Caroline.   I do not  like  that  idea.  For if it were
 founded, all our theory  of chemistry must be erroneous.
   Mr*. B.  The objection is yet so  new and uncon-
 firmed by common  experience,  that I confess I  do not
feel inclined to distrust the  general  doctrine of acidifi-
cation  which  we have  hitherto adopted.  But we have
not  yet  done with the prussic acid.  It has  a strong
affinity  for  metallic oxyds,  and precipitates  the solu-
tion of iron in acids of a blue colour.  This is the prus-
sianbiue,  orprussiat of iron, so much used in the arts,
and with which I think you  must be acquainted.
   Emily.  Yes,  I am ;  it is much used  in  painting,
both in oil and in water colours ; but it is not reckoned
a permanent oil  colour.
   Mrs. B.  That defect arises,  I believe,  in  general,
from its being badly prepared, which  is the case when 
300
 the iron is not so fully oxydated as to  form a red oxyd.
 For a  solution  of green oxyd of iron (in which the
 metal is more slightly  oxydated) makes  only  a pale
 green,  or even a  white precipitate,  with  prussiat of
 potash: and this gradually changes to blue by being
 exposed to the air, as I can immediately shew you.
   Caroline.  It  already begins to assume a pale blue
 colour.   But how does the air produce this change ?
   Mr*. B.  By oxydating the  iron more perfectly.  If
 we pour some nitrous acid on  it,  the prussian blue co-
 lour  will be immediately  produced,   as  the acid will
 yield its oxygen to the precipitate, and fully saturate it
 with this principle—as you shall see—
   Caroline.  It is very curious to  see a colour change
 so instantaneously.
   Mrs. B.  Hence you perceive that prussian  blue
 cannot  be a permanent colour unless prepared with
 red oxyd of iron,  since by exposure to the atmosphere
 it gradually darkens, and in a short time is no  longer
 in harmony with the other colours of the painting.
   Caroline.  But it can never become darker, by expo-
 sure  to the atmosphere, than  the true prussian blue,
in which the oxyd is perfectly saturated ?
   Mrs, B. Certainly not.  But  in painting, the art-
 ist not reckoning upon partial alterations in his colours,
 gives his blue tints that particular shade which harmon-
 izes with the rest of the picture.  If, afterwards those
 tints become darker, the harmony of the colouring must
 necessarily be destroyed.
   Caroline.  Pray, of what nature is  the  paint  called
 carmine ?
  Mrs. B.  It is an animal colour, prepared from co-
 chineal, an insect, the infusion of which produces  a very
beautiful red.
   Caroline.  Whilst  we are on the subject of colours,
 I should like to learn what ivory black is ?
  Mr*. B.   It is a carbonaceous substance obtained by
the combustion of  ivory.  A more common  species of
black is obtained from the burning of bone.
  Caroline.   But  during the combustion of ivory or 
301
bone, the carbone I should have imagined, must be
converted into carbonic acid gas, instead of this black
substance !
  Mrs. B.  In this, as in most combustions, a consid-
erable part  of the carbone is simply volatilized by the
heat, and again obtained concrete  on  cooling—This
colour, therefore, may be called the soot produced by
the burning  of ivory or bone.



             Conversation xxi.

               072 the Animal Economy.
                     Mrs. B.

  We have now acquired some idea of the various ma-
terials that compose the animal system;  but if you are
curious to know  in what manner these  substances are
formed by the  animal organs, from vegetable, as welL f
as from animal substances, it will be necessary to have
some previous knowledge of the nature and  functions
of these organs, without which it is impossible to form
any distinct idea of the processes of animalization and
nutrition.
  Caroline.  I do not  exactly understand the meaning
of the  word animalization ?
  Mr*. B.  Animalization is the process by which the
food is assimilated,  that is to say, converted into animal
matter; and nutrition is  that by which  the  food  thus
assimilated is  rendered subservient to the purposes of
nourishing and maintaining the animal system.
  Emily.   This, I am sure, must be the most inter-
esting of all the branches of chemistry
  Caroline,  So I think ;  particularly as I expect  that
                       B b
V 
302
we shall hear something of the nature of respiration,
and of the circulation of the blood ?
   Mrs. B.   These  functions  undoubtedly occupy a
most important place in the history of the animal econ-
omy.   But I must previously give you a very short ac-
count of the principal organs by which the various ope-
rations of the animal system  are performed.—These
are :
                The Bones,
                     Aluscles,
                     Blood vessels,
                     Lymphatic vessels,
                     Glands, and
                     Nerves.
   The bones are the most solid part of the animal frame,
and in a great measure  determine  its form and dimen-
sions.   You recollect, I suppose,  what are  the ingre-
dients which enter into their composition?
   Caroline.   Yes ; phosphat of lime, cemented by ge-
latine.]
   Mr*. B.   During the earliest  period of animal life
they consist almost entirely of a gelatinous membrane
of the form of the bones, but of a loose spongy texture,
the cells or cavities of which are  destined to be filled
with phosphat of lime; it  is  the  gradual acquisition of
this salt which  gives to the  bones their subsequent hard-
ness and durability.  Infants first receive it from their
mother's milk, and afterwards derive it from all animal
and from most vegetable  food, especially farinaceous
substances, such as wheat flour,  which  contain it in
sensible quantities.   A  portion of the phosphat after the
bones of the infant have been sufficiently expanded and
solidified, is  deposited  in  ihe teeth, which consist at
first of  only a gelatinous membrane  or case, fitted for
the reception of this salt; and which, after acquiring
hardness within  the gum, gradually portrude lrom it.
 # Caroline.  How very curious this is :  and how inge-
niously nature has first provided for the solidification of
such  bones as are immediately wanted, and afterwards
for the formation of the teeth, which would not only be
useless, but detrimental in infancy I 
20o
  Mr*. B.  In quadrupeds the phosphat of lime is de-
posited likewise in  their horns, and in the hair or wool
with which they are generally clothed
  In  birda it  serves also to  harden the beaks and the
quills  of their feathers.
  When animals are arrived  at a state of maturity,  and
their bones have acquired  a  sufficient degree of solid-
ity, the phosphat of lime  which is taken with the food
is seldom assimilated, excepting when the female nour-
ishes her young ; it is then all secreted into the milk,
as a provision for the tender bones of the nursling.
  Emily.   So that whatever becomes superfluous to
one being, is immediately wanted by another ; and the
child acquires strength  precisely by the species of nour-
ishmet which is no longer  necessary to the  mother.
Nature is, indeed, an admirable ecoromist!
   Caroline.  Pray, Mrs.  B.  does not the disease in the
bones of children,  called the rickets, proceed from  a
deficiency of  phosphat  of  lime ?
   Airs.  B.  I have heard that this  disease may arise
from  two  causes; it is sometimes occasioned by the
growth of the muscles  being too rapid in proportion to
that of the bones.  In this case the weight of the flesh
is  greater than the bones can support, and presses up-
on them so as to produce a swelling of the joints which
is the great indication of the rickets.   The  other cause
 of this disorder is an imperfect digestion and assimila-
 tion of the food, attended with an excess of acid, which
 counteracts the formation of phosphat of lime.  In both
 instances, therefore, care should be taken  to alter the
 child's diet, not merely  by  increasing the  quantity of
 aliment containing phosphat  of lime, but also by avoid-
 ing all food that is apt  to  turn acid on the stomach and
 produce indigestion.  But the best preservative against
 complaints of this kind is, no  doubt, good nursing;
 when a child has plenty of air and exercise, the diges-
 tion  and assimilation will be properly  performed, no
 acid  will be produced  to interrupt these functions,  and
 the muscles and bones  will  grow together in -just  pro-
 portions.
   Caroline.   I have often heard the rickets attributed to 
304
 bad nursing, but I never could have guessed what con-
 nection there was between exercise and the formation
 of the bones.
   Airs. B.  Exercise is generally beneficial to all the
 animal functions.   If man is  destined to labour for his
 subsistence,  the bread that he  earns is scarcely more
 essential to his health  and preservation than the exer-
 tions by wliich he obtains it.  Those whom the gift of
 fortune have placed above the necessity of bodily labour,
 are compelled to take exercise in  some mode  or other,
 and when they cannot  convert  it  into  an  amusement,
 they must submit to it as a task,  or their health will soon
 experience the effects of their indolence.
   Emily.   That will  never be my case :   for exercise,
 unless it  becomes fatigue, always gives me  pleasure ;
 and,  so far from being a task,  is to me a source of dai-
 ly enjoyment.   I often think what  a blessing it is, that
 exercise which is so conducive to  health,  should be so
 delightful, whilst  fatigue which is  rather hurtful, in-
 stead of pleasure occasions painful sensations.   So that
 fatigue, no doubt, was  intended  to moderate our bodily
 exertions, as satiety puts a limit to our appetites ?
   Mrs. B.   Certainly.—But let us not deviate too far
 from our subject.—The bones are connected together
 by ligaments, which consist of  a  white thick,  flexible
 substance, adhering to their  extremities,  so far as to
 secure the joints firmly, though without impeding their
 motion.  And the  joints are  moreover covered  by a
 solid smooth, elastic, white substance,  called cartilage,
 the use of which is to allow, by its smoothness and elas-
 ticity, the bones to  slide easily over one another, so that
 the joints may perform their office  without difficulty or
 detriment.
   Over the bones the muscles  are  placed ;  they consist
of bundles of fibres which terminate in a kindof string,
or ligament, by which they are. fastened to the bones.
The muscles are the organs of motion ; by their power
of dilation and contraction they  put  into action  the
bones, which act as leavers in  all the motions of the
body, and  form the solid support of its various parts.
The muscles are of various degree:? of strength or con- 
305
sistence in different species of animals.  The mammif-
erous tribe,  or those that suckle their young, seem in ■
this  respect to occupy an  intermediate place between
birds and cold-blooded animals, such as reptiles and
fishes.
  Emily.  The different  degrees of firmness and  so-
lidity in the muscles  of these several species of ani-
mals proceed,  I imagine, from the different nature of
the food on which they subsist ?
  Mr*. B.  No ; that is  not supposed to be the case :
for  the human species, who are of the mammiferous
tribe, live on more  substantial food than birds, and  yet
the latter exceed them  in muscular  strength.—We
shall hereafter attempt to account for  this difference ;
bat let us now proceed in  the examination of the animal
functions.
  The next class of organs is that of the vessels of the
body, the office of which  is to convey the  various fluids
throughout  the frame.   These vessels are innumera-
ble.   The most considerable of them are those thro'
which the blood circulates, which are  of two kinds:
the arteries,  which convey it from  the heart to the ex-
tremities of the  body, and the veins, which bring it
back into the heart.
  Besides these,  there are a  numerous set of small
transparent vessels,  destined to absorb and convey dif-
ferent fluids into the blood ; they are generally called
the absorbent or lymphatic vessels : but it is to a portion
of them only  that the function of conveying into the
blood the fluid called lymph is assigned-
  Emily.  Pray what is the nature of that fluid ?
  Mrs. B.  The nature and use of the lymph have, I
believe, never been perfectly ascertained ;  but it is sup-
posed to consist of  matter that has been previously  an-
imalized, and  which, after answering the purpose for
which it was intended,  must in regular rotation make
way for the fresh  supplies produced by  nourishment.
The lymphatic vessels  pump  up this fluid from every
part of  the system, and  convey it into the veins to be
mixed with the blood  which runs through them,  and -
which is commonly  called venous blood.
                      Bb2 
306
  Caroline.  But does it not again enter Into the animal
system through that channel ?
  Mrs. B.  Not entirely ; for the  venous blood does
not return into the circulation  until it  has undergone a
peculiar change, in which it throws off whatever is  be-
come useless.
   Another set of absorbent vessels pump up the chyle
from the stomach  and intestines, and convey it, after
many  circumvolutions, into the great vein  near  the
heart.
   Emily.   Pray what is chyle ?
   Mr*. B.   It is the substance into which food is con-
verted by digestion.
   Caroline.   One  set  of the  absorbent vessels,  th^-n,
is employed in  bringing away  the  old materials that
are no longer fit for use ;  whilst the other set is busy
in conveying into the blood the new materials that  are
to replace them.
  Emily.   What  a great  variety of ingredients  must
enter into the composition of the blood !
   Mrs. B.  You must observe that there is also a great
variety of substances to be  secreted from it.   We may
compare the Wood to a general recepticle or store-
house for all kinds of commodities which are afterwards
fashioned, arranged, and  disposed of  as circumstances
require.
   There is another set of absorbent vessels in females
which is destined to secrete milk for the  nourishment
of the young.
  Emily.   Pray is not  milk very analogous in its  com-
position to  blood ; for, since the nursling derives its
nourishment from  that  source  only, it must contain eve-
ry principle which the animal system requires ?
  Mrs. B.  Very true.  Milk is found, by its analysis,
to contain all the principal materials of  animal matter,
gelatine, albumen, oil,  and phosphat of lime ; so that
the  suckling has but little trouble to digest and assimi-
late this nourishment.  But we shall examine the com-
position of mild more fully afterwards.
   In many parts of the body numbers of small vessels. 
30?
are collected together in little bundles called glands,
from a  Latin word meaning acorn, on account of the
resemblance  which some of them bear in shape to that
fruit   The function of the glands is to secrete, or sep-
arate certain  matters from the blood.
   Tne secretions are  not only  mechanical, but chem-
ical  separations from the bloood ; for the substances thus
formed, though contained in  the blood, are  not  ready
combined  in that fluid.   The secretions are of two
kinds  those  which form peculiar animal fluids, as bile,
tears, saliva,  &c and those which produce the general
materials  of the animal system, for the purpose  of re-
 cruiting and  nourishing the several organs of the  body ;
 such as albumen, gelatine, and fibrine  ; the  latter may
 be distinguished by the name of nutritive secretions.
   Caroline.  1 am quite astonished to hear  that all the
 secretions should be derived from the blood
   Emily.  I thought that the bile was produced  by the
 liver ?
   Mr*. B.  So it is ; but the liver is nothing more than
 a very  large gland, which  secretes the bile from the
 blood.
   The last of the animal organs which we  have men-
 tioned are the nerves ; these are the vehicles of sensa-
 tion, every other part of the body being, of itself totally
 insensible.
    Caroline.  They, must then be spread throughout eve-
 ry  part of the frame, for we are every where susceptible
 of feeling.
    Emily.  Excepting the nails and hair.
    Mr*.  B.   AnU those  are almost the  only parts in,
 which nerves  cannot be  discovered.  The common
 source of all the nerves is the brain ; thence they de-
  scend,  some  of them through different  holes of the
  skull, but the  greatest part through the back bone, and
 extend themselves by inumerable ramifications through-
 out the  whole  body.   They  spread themselves over
 the muscles,  penetrate the gland,  wind round the  vas-
  cular system, and even pierce into the interior of the
  bones.   It  is most probably through them that the com-
  munication is carried on between the  mind  and the otl> 
308
 er parts of the body ; but in what manner they  are act-
 ed upon by the mind, and made to re-act on the  body,
 is still a profound secret.  Many hypothesis have been
 formed on this very obscure subject, but they are all
 equally improbable, and it would be useless for us  to
 waste our time in conjectures on  an inquiry which in
 all probability, is beyond the reach of human capacity.
   Caroline.   But you have not mentioned  those par-
 ticular nerves that  form the senses of  hearing, seeing
 smelling, and tasting ?
   Mrs. B.  They are considered as being of the same
 nature as those which are dispersed over every part o f
 the  body, and canstitute the general sense of  feeling.
 The different sensations  which they produce arise from
 their peculiar situation and connection  with the several
 organs of taste, smell, and hearing.
   Emily. But these senses appear totally different from
 that of feeling ?
   Mrs. B.   They are, all of them sensations, but var-
 iously modified according to the nature of the different
 organs  in which  the nerves are situated.   For, as we
 have formerly observed,  it is  by contact only that the
 nerves are affected.   Thus odoriferous particles must
 strike upon the nerves of the nose in  order to excite
 the sense of smelling, in the same manner that taste
 is produced by the particular substance  coming in con-
 tact with the nerves of the palate.  It is thus also that
 the sensation of sound is produced by the concussion of
 the air striking against the  auditory nerve ; and  sight
 is the effect of the light falling upon  the optic nerve.
 These various  senses, therefore, are affected only  by
 the actual contact of particles of matter, in the same
 manner as that of feeling.
   The different organs of the animal body, though ea-
 sily separable and perfectly  distinct, are  loosely con-
nected together by a kindof spongy substance, in tex-
ture somewhat  resembling net-work, called the cellu-
 lar membrane ; and the  whole  is covered by the skin.
   The skin, as well as the bark of vegetables, i* form-
ed of three coats.   The external one is called the cuti-
 cle, or epidermis ; the second, which  is called the mu-
 cous membrane, is of a thin soft texture,  and  consists of 
auy
a mucous substance, which in negroes is black, and is
the cause of their skin appearing of that colour
   Caroline.  Is then the external skin  of negroes white

UkM0r*!'SB   Yes ; but as the cuticle is transparent, as
weU Z porus,the' blackness  of the: mucous ™^J«£
is visible through it.  The extremities of the> ncm*are
spread over the* skin, so that the *™f™J*«f^*
transmitted through the cuticle.  The inte.nal cover
ing of the muscles, which is proper y the skin, is the
thfckest, the toughest, and most resisting o ^e whole
-it is this membrane that is so essential in the arts, by
 forming leather when combined with tannin.
   The skin which covers the animal body, as well  as
 those membranes that form the coats of the vessels, con-
 sist almost exclusively of gelatine ; and are capable of
 being converted into glue, size, or jelly-
    The  cavities between the muscles and the skin are
 usually filled with fat, which lodges in the cells of the
 membranous net before mentioned, and gives to the ex-
 ™rr?al form (especially in the human  figure) that round-
 ness  smoothness, and softness, so essential to beauty.
    Em7y   And the skin itself is, I think, a very  orna-
 mental part of the human frame, both  from the: finess
 of its texture, and the variety and delicacy of its tints
    Mr*  B  This variety and harmonious gradation ot
  colours', proceed, not so much from the skin itself, as
  from the internal organs which transmit  their several
 coZrs through it, these being only softened and blend-
  ed by the colour of  the skin,  which is uniformly of a

  ^Ss'iVodified, the darkness of the veins appears of
  a pale  blue  colour, and the floridness of the arteries is
  changed  to  a  delicate  pink.  In the most transparent
   parts8,  the skin exhibits the bloom  of the rose,  whilst
  vriiere it is more opaque its own colour predominates ;
  and at  tl e joints  where the bones are  most prominent,
  the v h tenJcss is often discernable    In a word  every
    art of he human frame seems to contribute to its ex-
   ernal  grace ; and this not  merely  by  producing  a
  pleasing varie y of tints, but by a peculiar kjnd of beau. 
310
ty which belongs to each individual part.   Thus it is t»
the solidity and arrangement of the bones that  the  hu-
man figure owes  the  grandeur of its stature, and its
firm and dignified deportment.   The muscles delineate
the form, and stamp it with energy and grace ;  and the
soft substance which is spread over them smooths their
ruggedness, and gives to the  contours the gentle un-
dulations of the line of beauty.   Every organ of sense
is a peculiar and separate  ornament ;  and the skin,
which polishes the  surface and gives  it that charm of
colouring so inimitably by art, finally conspires to ren-
der the whole the fairest work of the creation.
   But now that we have seen in what manner  the ani-
mal frame is formed, let us observe how it  provides
for its support, and how the  several organs,  which
form so complete a whole, are nourished and maintain-
ed.
   This will lead  us to a more particular explanation of
the internal organs :  here  we shall not meet with so
much apparent beauty,  because these parts were not
intended by  nature to be exhibited to view ;  but the
beauty of design, in the internal organization of the ani-
mal frame, is, if possible, still more striking than that of
the external part.
   We shall defer this subject until our next interview. 
311
       Conservation xxn.

On Animalization, Nutrition, and Respiration.
                     Mrs. B.

  We have now learnt of what materials the animal
system  is composed,  and have formed  some  idea of
the nature of its organization.  In order to complete the
subject, it remains for us to examine in what manner it
^s nourished and supported.
  Vegetables we have observed, obtain their nourish-
ment from various substances, either in their elementa-
ry  state, or in a very simple state of  combination  ;
as carbone, water, and salts, which they pump up from
the soil ;  and carbonic  acid and oxygen, which they
absorb from the atmosphere.
   Animals, on the contrary, feed on substances of the
most complicated  kind : for  they derive their suste-
nance,  some from  the animal creation, others from the
vegetable kingdom, and some from both.
   Caroline.   And there is  one species of  animals,
 which, not satisfied with enjoying either kind of food in
 its simple state, has invented  the  art  of  combining
 them together  in a thousand ways, and of rendering
 even the mineral kingdom  subservient to their refine-
 ments.
    Emily.   Nor is this all ; for our delicacies are collec-
 ted from the various climates of the earth, so  that the
 four quarters of the globe are often obliged to contribute
 to the preparation of our simplest dishes.
    Caroline.   But the very complicated substances which
 constitute the nourishment of animals, do not, I suppose,
 enter into their system in their actual state of combina-
 tion.
    Airs. B.   So far from it, that they not only undergo
 a  new  arrangement of their parts, but a selection  is 
312
  made of such as are most proper for the nourishment of
  the body, and those only enter into the system and are
  animalized.
    Emily.   And by what organs is this process perform-
  ed ?
    Mr*. B.   Chiefly by the stomach, which is the or-
  gan of the digestion, and the prime regulator of the ani-
  mal frame.
    Digestion is the first step towards nutrition.  It con-
  sists in reducing  into one homogenous mass the vari-
  ous substances that are taken as nourishment; it is per-
 formed by first chewing and mixing the  solid aliment
 with the saliva, which  reduces it to a soft mass, in which
 state it is conveyed into the  stomach, where it is more
 completely dissolved by the  gastric juice.
    This fluid (which is secreted into the stomach by ap-
 propriate glands) is so  powerful a solvent that scarcely
 any substance will resist its action.
   Emily.  The coats of the  stomach however cannot be
 attacked by it, otherwise we  should be in danger of hav-
 ing them destroyed when the stomach was  empty.
   Mrs.  B.  They are probably not subject to its ac-
 tion ; as long at least as life continues.   But it appears,
 that when the gastic juice has no foreign substances to
 act upon, it is capable of occasioning a degree of irrita-
 tion in the coats of the stomach, which produces the sen-
 sation of hunger.  The gastric juice together with the
 heat and muscular action  of the stomach,  converts  the
 aliment into a uniform pulpy mass called  chyme.  This
 passes into the intestines, where it meets with the bile
 and some other  fluids,  by the agency of which, and by
 the operation of other causes  hitherto  unknown,  the
 chyme is changed into  chyle, a much thinner substance,
 somewhat  resembling  milk, which is pumped out by
immense numbers ofsmall absorbent vessels spread over
the internal surface of the intestines.  These, after ma-
ny circumvolutions, gradually meet and unite into large
branches, till they at length  collect  the chyle into one
vessel, which pours its contents into the great vein near
the heart, by which means the food, thus prepared en-
ters into the circulation. 
313
  Caroline.  But I do not  yet  clearly understand how
the blood, thus formed, nourishes the body and supplies
all the secretions.
  Mrs. B.   Before this can be explained to you, you
must first  allow me  to complete the formation of the
blood.  The chyle may indeed be considered as form-
ing the chief ingredient of blood ; but this fluid is not
perfect until it has passed through the lum;*,  and un-
dergone (together with the blood that has already cir-
culated) certain necessary changes that are effected by
BRSriRATION.
   Caroline.  I am very glad that you are going to ex-
plain the nature of respiration  s  I have often longed  to
understand it,  for though we talk incessantly of breath-
 ing,  I never knew precisely what purpose it answered.
   Airs. />'.  It is  indeed  one  of the most interesting
 processes imaginable ; but in  order  to understand this
 function well,  it will  be  necessary  to enter into some
 previous explanations.  Tell me,  Emily,  what do you
 understand by respiration ?
   Emily.   Respiration, I  conceive, consists simply  Hi
 alternately inspiring air into the lungs, and cxpirivg it
 from them.
    Mr*. B   Your answer wiil do very well as a gener-
 al definition.   But,  in order to form a tolerably clear
 notion of ihe  various phenomena of respiration,  there
 iu-e  many  circumstances to be taken into consideration.
    In the first place, there are two tbir.^ to be distin-
 guished in respiration, the mcchankui and the chemical
 part of the process,
    The mechanism of breathing depends on the alter-
 nate expansions and contractions of the chest, in which
 the lungs are contained.   When the chest dilates the
 cavity is enlarged, and the air rushes in at the mouth,
  to  fill  up the vacuum formed by this  dilatation } when
 it contracts, the cavity is diminished, and the air for-
  ced out again              t
    Co-wlinc.   1 thought that it was the lungs that con-
  tracted unci expanded in breathing ?
    Airs. B.   They  do likewise 5 but their  action is on-
  ly the consequence of that of the chest.   The lungs,
                          C c 
314
together with the heart  and the largest blood vessels,
in a manner fill up the cavity of the chest; they  could
not, therefore,  dilate if the chest did not previously ex-
pand ; and,  on the other hand, when the chest  con-
tracts, it compresses  the lungs and forces  the air out
of them.
   Caroline.   The lungs, then, are like  bellows, and
the chest is the power that works them.
   Mrs. B.   Precisely so.  Here is a curious little  fi-
gure  (Plate XI. Fig 29), that will assist me in explain-
ing the mechanism of breathing.
   Caroline.   What a droll  figure ! a  little  head fixed
upon  a glass bell, with  a bladder tied over the bottom
of it!
   Mrs. B.   You must observe that there  is  another
bladder within  the glass, the neck of which communi-
cates  with the mouth of the  figure—this represents the
lungs  contained  within the  chest; the other bladder,
which you  see is  tied loose,  represents a  muscular
membrane,  called the diaphragm,  which separates the
chest from the lower  part oi the body.  By  the chest,
therefore, I mean that large cavity in the upper part
of the body  contained within the ribs, the  neck, and
the diaphragm ;  this membrane is muscular and capa-
ble of contraction and dilation.  The  contraction may
be imitated by drawing the bladder tight over the bot-
tom of the receiver, when the air,  in the bladder which
represents the lungs, will  be forced  out  through the
mouth of the. figure—
   Emily.  See, Caroline, how it blows the flame of the
candle in breathing!
   Mrs. B.   By  letting  the bladder  loose  again, we
imitate the dilatation of the diaphragm, and the eavity
of the chest being enlarged, the lungs expand,  and the
air rushes in to fill them.
   Emily.   This figure, I think, gives a very clear idea
of the process of breathing.
   Mr*. B.   It  illustrates tolerably well  the action of
the lungs and diaphragm ; but those are not the only
powers that are concerned in enlarging or diminishing
the cavity of the chest;  the ribs are also possessed  of 
SIS
a muscular motion  for the same purpose ;  they are al-
ternately drawn in edgeways to assist  the  contraction,
and stretched  out, like  the hoops  of a  barrel,  to con-
tribute to the dilatation of the chest.
  Emily.   I  always supposed  that the elevation and
depression of the ribs  were the consequence,  not the
cause, of breathing.
  Mr*. B.  It is exactly the reverse.   The muscular
action of the diaphragm, together with that of the ribs,
are the causes  of the contraction and expansion of th»
chest; and the air  rushing into, and  being  expelled
from the lungs,  are only consequences of those actions.
  Caroline.   I confess that I thought the act of breath-
ing began by opening the mouth for the air to rush in,
and that it was the  air alone, which, by  alternately
rushing in  and  out, occasioned the dilatations and con»-
tractions of the lungs and chest.
  Mrs. B.   Try  the  experiment  of merely opening
your mouth ; the air will not rush in,  till by an interior
muscular  action you  produce a vacuum—yes, just so,
your diaphragm is now  dilated, and the ribs expanded.
But you will not be able to keep them long in that stale.
Your lungs and chest are already resuming their former
state,  and  expelling the air with  which they had just
been  filled.  This mechanism goes  on more or less
rapidly, but in  general, a person at rest and  in health
will breathe between fifteen and twenty-five times in a
minute.
   We may now proceed to the chemical effects of res-
piration ; but, for this purpose, it is necessary that you
should previously have some notion of the circulation of
the  blood.  Tell  me,  Caroline,  what  do you under-
stand by the circulation of the  blood ?
   Caroline.   I am delighted that you come to that sub-
ject, for it is  one that has long excited my curiosity,—
But I cannot conceive how it is connected with respira-
tion.   The idea I have of the circulation is, that the
blood runs from the heart through the veins all over the
body, and back again to the heart.
  Airs. B.   I could hardly have  expected a better de-
finition from you;  it  is,  however, not quite correct, 
316
for you do not distinguish the arteries from theyeinty
which,  as wo have already observed, are two  distinct
sets of vessels, eac'i having its own particular functions.
The arteries convey the blood from the heart to the ex-
tremities of the body j und the veins bring it back to the
heart.
   This sketch will give you  an  idea of the manner in
which some of the principal veins and arteries of the
human body branch  out of tlie heart, which  may be
considered as a common centre  to both sets of  vessels.
The heart is a kind of strong clastic bag, or muscular
cavity,  which possesses a power of  dilating and con-
tracting itself, for the purpose of  alternately receiving
and expelling the blood, in  order to carry on the pro*
cess of circulation.
   Emily.   Why are the arteries in this drawing paint-
ed red, and the veins purple ?
   Mr*. B.  It is to point out the difference of  the co-
lour of the blood in these two sets of vessels.
   Caroline.  But if it is the same blood that flows from
the arteries into the veins, how can its colour be chan-
ged?
   Mr*. B.  This change arises from various circum-
stances.  In  the first place, during its passage through
the arteries,  the blood  undergoes a considerable  alter-
ation,  some of its constituent parts being gradually se-
parated from it for tue purpose of nourishing the  body,
and of supplying the  various secretions.   The conse-
quence of this is, that the florid arterial colour of the
blood  changes by degrees to a  deep purple, which is
its constant  colour in  the veins.  On the other  hand,
the blood  is recruited  during  its  return through the
veins by the fresh chyle,  or imperfect blood,  which
has been produced by food ; and it receives also lymph
from  the absorbent vessels, as we have before mention-
ed.   In consequence of  these   several changes, the
blood returns to the heart in a state very  different from
that in which it left it.   It is  loaded whh a greater pro-
portion of hydrogen  and carbone,  and is no longer
fit for the nourishment of the body or  other purposes of
circulation. 
sir
  Emily.   And in this state  does it mix  in the heart
with the pure florid blood that runs into the arteries ?
  Mr*. B  No. The heart is divided into two cavities or
compartitions, called the right and left ventricles.   The
left  ventricle is  the receptible  for  the pure  arterial
blood previous  to its circulation ; whilst the venous, or
impure blood,  which returns to the heart after having
circulated, is received into the right  ventricle,  previous
to its purification, which I  shall presently  explain.
  Caroline.   For my part, I always thought that the
same blood  circulated again  and again through the bo-
dy,  without undergoing any change.
   Mr*.  B.  Yet you  must have  supposed  that the
blood circulated for  some purpose ?
   Caroline.   I  knew that  it  was indispensable to life,
but  had no idea of its real functions.
   Mrs.  B.   But now that  you understand that the blood
 conveys nourishment  to every purt of the  body, and
 supplies the various secretions,  you must be sensible
that it  cannot  constantly answer these objects without
being renovated and purified.
   Caroline.  But does  not the  chyle answer this pur-
 pose ?
   Mr*. B.  Only  in  part.   It renovates the nutritive
 principles of the blood,  but does not relieve it from the
 superabundance of hydrogen and carbone with which
 it is incumbered.
   Emily.   How then is this effected ?
   Mr*  B.   By Respiration.    This is one of the
 grand  mysteries'which modern chemistry has disclos-
 ed.   When the venous blood  enters the left ventricle
 of the heart, it  contracts  by its  muscular power, and
 throws the blood through a  large vessel into  the lungs,
 which are  contiguous,  and  through which it  circulates
 by millions of small ramifications.   Here it  comes  in
 contact with the air which  we  breathe.  The action of
 the air on  the blood in the lungs is indeed  concealed
 from our immediate observation ;  but we are able  to
 form a tolerably accurate judgement of it from the cuan-
 ges which  it effects not only in the blood, but also  on
 the air expired.         C c 2- 
318
   This air is found to contain all the nitrogen inspired;
but to have lost part of its oxygen,  and to  have acqui*
red a portion of watery  vapour.  Hence it  is inferred,
that when  the air  comes in contact with the venous
blood in the lungs,  the oxygen  attracts  from it the su-
perabundant quantity  of hydrogen and carbone  with
which  it has impregnated itself during the circulation ;
and that one part of that oxygen combines with the hy-
drogen,  in the  form of^ watery vapour, whilst another
part combines with the carbone, which  it  converts into
carbonic acid.   The  whole  of these  products being
then expired, the blood is restored  to its former purity,
that is, to  the state of arterial  blood, and is thus again
enabled to perform its various functions.
   Caroline.  This is truly wonderful !  Of all  that we
have yet learned,  I do not recollect any thing that has
appeared io ine so curious and interesting.   I almost
believe that I should like to study anatomy now, though
I have hitherto had so disgusting an idea of it.  Pray,
to whom are we indebted for  these beautiful discover-
ies ?
   Mrs. B.  Crawford, in this country, and Lavoisier,
in France, are the principal inventors of the theory of
respiration.  But the still more important and more ad-
mirable discovery  of the circulation of the blood was
made long before by our immortal countryman, Hervey.
   Emily.  Indeed  I  never  heard  any  thing that de-
lighted me so much as this theory  of respiration.  But
I hope, Mrs. B. that you will enter a  little more into
particulars before  you dismiss  so interesting a subject.
"We left the blood in  the lungs to undergo the  salutary
change.  But how does it thence spread to all the  parts
of the body ?
   Mrs. B.   After circulating  through the  lungs, the
blood  is collecied into four  large  vessels,  by  which it
is conveyed into the left ventricle of the heart, whence
it  is propelled to all the different parts of the body by a
large artery which gradually ramifies  into millions of
small arteries through the whole frame.  From the ex-
tremities of these little ramifications the blood is trans-
mitted to the veins, which bring it back to the  heart 
313
and lungs, to go round again and again  in the manner
we have just described.   You see  therefore, that  the
blood  actually  undergoes two circulations ; the one*
through  the lungs, by which it is converted into pure
arterial blood ;  the other, or  general circulation, by
which nourishment is conveyed to every part of the bo-
 dy ; and these are both equally indispensible to the sup-
 port of animal life
   Caroline.   Do we expire all  the air that  we inspire,
 besides the addition of hydrogen and carbone which are
 taken up from the blood ?
   Airs. B.   Yes,  excepting  small portions  of the ox-
 ygen, and of the nitrogon, which, as they do not reap- '
 pear, are supposed to  be absorbed  by tne blood for
 some purposes which have not yet  been  clearly  ascer-
 tained.   The general opinion, however,  with   regard
 to oxygen, is, that it serves to stimulate  the heart and
 keep up its muscular action.   As to the nitrogen, it was
 supposed to  be  expired from the  lungs, without any
 change or diminution.   But  it was  proved  a few years
 ago,  by some of Mr. Davy's  experiments, which have
 been since confirmed by those of Professor Plaffof Kiel,
 that a small quantity of nitrogen disappears in respira-
 tion, and combines with  the system in  a manner which
 is not yet well understood.
    Emily.  But whence proceeds the hydrogen and car-
 bone with which the blood is impregnated when it comes.
 into the lungs ?                        .  .
    Mrs.  B. Both hydrogen and carbone exist in  a great-
  er proportion in blood than in organized animal  matter.
    The blood,  therefore, after supplying its various  se-
 cretions, becomes loaded with an excess of these princi-
 ples, which is carried off by respiration.  But, besides
  this, the formation of a new chyle affords a constant sup-
  ply of carbone and hydrogen.
    'Caroline.  Pray,  how does the  air  come in  contact
  with the blood in the lungs  ?           .    . .
    Mr*  B.  I cannot answer this question without  en-
  tering  into' an explanation  of ihe nature  and structure
  of the  lungs.   You recollect that  the venous blood on
   being   expelled  from the right ventricle, enters  the 
320
  lungs to go through what we may call the lesser  circu-
  lation ;  the large trunk or vessel that  conveys it, bran-
  ches out, at its entrance into the lungs, into an infinite
  number of  very fine  ramifications.—The  windpipe,
  which conveys  the air from the mouth  into the lungs,
  likewise spreads out inioa corresponding number of air
  vessels, which follow the same course  as the blood ves-
  sels, forming millions of very minute air cells.—These
  two setts of vessels are so interwoven as to form a sort of
  net-work, connected into a kind of spongy mass, in which
  every particle of  the blood must necessarily  come in
  contact with a particle of air.
   Caroline.  But since the  blood  and the air  are con-
 tained in different vessels, how can they come  into con-
 tact ?
   Mrs. B.   They  act on each other through the mem-
  brane which forms the coats of these vessels; for al-
 though this membrane prevents the blood and  the  air
 from mixing together in the lungs, yet it is no impedi-
 ment to their chemical action on each other.
   Emily.   Are  the lungs composed  entirely of blood
 vessels and air vessels ?
   Mr*. B.  I believe they are with the addition only of
 nerves and of a small  quantity of the cellular substance
 before mentioned, which connects the whole into an uni-
 form mass.
   Emily.   Pray, why are the lungs always spoken of in
 the plural number ? Is there more than one ?
   Mrs. B   Yes ; for though they form but one organ,
 they really  consist of two compartments called lobes,
 which are  enclosed in separate membranes or bags,
 each occupying one side of the chest, and being in close
 contact  with  each  other, but without communicating
 together.  This is a beautiful provision of nature in con-
 sequence of which, if one of the lobes be  wounded, the
 other performs the whole process of respiration till the
 first is healed.
   But, before we proceed further, I must inform you
that  the  chemical  theory  of respiration, with which
you just have been made acquainted, simple  and beau-
tiful as it is, has  appeared to many philosophers insuf- 
321
ficient to explain all the phenomena of respiration.  A-
mongst the various  modifications proposed with a view
to improve this theory, that suggested by La Grange,
Hassenfratz, and some other eminent chemists, uppeurs
to be the most important.   These philosopher* suppose
the oxygen, which disappears in respiration, is absorbed
by the blood, and carried with it into the circulation, du-
ring which it gradually combines with the hydrogen and
carbone that are  successively added to the circulation,
forming the water and carbonic acid which are expelled
from the lungs at each expiration.   Thus the process,
instead of being completed in the lungs, as  the former
theory supposes, only begins in that organ, and  contin-
ues throughout the  circulation.
   According to thu theory, the florid colour of arterial
blood depends upon the addition of oxygen,  so that this
colour gradually vanishes as the blood passes from  the
arterial to the  venous state, that is to say, as the oxygen
enters into combination with the hydrogen and carbone
during circulation.
   Caroline.  There does not appear to me to  be any
very essential  difference in these two theories, since in
both the oxygen purifies  the blood by combining with
and carrying off the matter which had accumulated in it
during circulation.
   Mr*. B.  Yes ; but, in medical, or rather phisiologi-
cal seience, it must be a question of great importance
whether the oxygen actually enters the  circulation,  or
whether it proceeds no further than the lungs.
   The blood thus completed, forms the most complex
of all animal compounds, since it contains not  only the
numerous materials necessary to form the various secre-
tions, as saliva, tears, &c.  but likewise all  those that are
required to nourish the several parts of the frame, as the
mnsc!es, bones, nerves, glands, Sec.
   Emily.  There seems to be a singular analogy be-
tween the blood of animals, and the sap of vegetables ;
for each of these fluids contain the several materials des-
tined  for the nuiritioi- of the numerous class of bodies
to which they respecthely belong. 
                        322

  Mrs. B.   Nor is the production  of these fluids in
the animal and  vegetable systems entirely different ;
fur the absorbant vessels, which pump up the  chyle,
from the stomach and intestines, may be compared to
the absorbants of the roots of plants, which suck up the
nourishment from the soil.  And the  analogy between
the sap and the blood may be still further traced, if  we
follow  the latter  in the course of its circulation ;  for in
the living  animal,  we find  every where organs which
are possessed of a power to secrete from the blood and
appropriate to themselves the ingredients requisite for
their support.
  Caroline.   But whence does these organs derive their
respective powers ?
  Mr*. B.   From peculiar organization, the secret of
which  no one has yet ever been able to unfold.  But it
must be ultimately by means of the vital principles that
both their mechanical and chemical powers are brought
into action.
   I cannot dismiss the  subject of circulation without
mentioning perspiration, a secretion which is immediate-
ly connected  with it, and acts a most important part in;
the animal economy.
   Caroline.   Is not this secretion likewise made by ap-
propriate glands ?
  Mrs. B.   No ; it is performed by the extremeties of
the arteries, which penetrate through the skin and ter-
minate under the cuticle, through the pores of which the
perspiration issues.   When this fluid is not secreted in
excess, it is insensible, because it is dissolved by  the  air
as it exudes  from  the pores ;  but when it  is secreted
faster than it can be dissolved, it becomes sensible, as it
assumes its liquid state.
  Emily.  This secretion bears a striking  resemblance
to  the transpiration of the sap of plants.  They both
consist of the most fluid part, and both "exude from  the
surface by the extremities of the vessels through which
they circulate.
  Mrs. B.   And the analogy does not stop there ; for,
since it has been ascertained that the  sap returns  into
the roots ol the plants, the  resemblance between the 
823
animal and vegetable circulation is become still more
obvious.   The latter, however, is far from being com-
plete, since, as we have observed before, it consits only
in a rising and descending of the sap, whilst  in animals
the blood actually  circulates through every part  of the
system.
   We have now, I think, traced the process of nutri-
tion from the introduction of the food into the stomach to
its finally  becoming a constituent part of the animal
frame.   This will, therefore, be a fit period to conclude
our present conversation.   What further remarks we
have to make on the animal economy shall be reserved
for our next interview.
®
Contoettfation xxm.
On animal heat: and on various Animal Products.
                      Emily.

  Since our last interview, I have been thinking much
of the theory of respiration ;  and I  cannot  help being
struck with the resemblance  which  it appears to bear
to the process of combustion    For in respiration, as in
most cases of combustion, the air suffers a change, and
a portion of  its oxygen  combines with hydrogen and
carbone, producing carbonic acid and water.
  Mr*.  B.   I am much  pleased that  this idea has oc-
curred to you : these two processes appear so very anal-
ogous-, that it has been supposed that a kind of combust-
ion actually  tak«;s place in the  lungs ;  not of the bloock,
but of the superfluous hydrogen and carbone which the
oxygen  attracts from it. 
324
  Caroline.  A combustion in our lungs ! that is a Curi-
ous idea indeed ! But, Mrs. B.  How can you call  the
action of the air on the blood in the lungB,  combustion,
when neither light nor heat are produced by it ?
  Emily.  I was going to make the same objection.
Yet I do not conceive how the  oxygen can combine with
the hydrogen and carbone, and produce water and car-
bonic acid, without disengaging heat ?
  Mrs. B.  The fact is, that  heat is  disengaged.
Whether  any  light be evolved, I cannot pretend  to de-
termine ; but that heat is produced in considerable and
very sensible quantities is certain, and this is the princi.
pal, if not the only source of animal  heat.
  Emily.  How wonderful! that the very process which
purifies and elaborates the blood, should afford an inex«
haustible supply of internal heat!
  Airs. B.  This is the theory of animal heat in its ori-
ginal simplicity, such as it was first proposed by  Black
and Lavoisier.   It is equally  clear and ingenious ; and
was at first generally adopted.  But it was objected, on
second consideration, that if the whole of the animal
heat was  evolved in  the lungs, it would necessarily be
much  less in the extremities  of the bo:ly, than immedi-
ately at its source, which is  not found to  be the case.
This objection, however, which was by no  means frivo-
lous, is now satisfactorily answered by means of the im-
proved theory of respiration  which I mentioned last.
According to this hypothesis,  you recollect the changes
which  the blood undergoes in consequence of respira«
 tion only begin in the lungs and  gradual!)  continue du-
 ring circulation.  Therefore  the animal heat, which is
 the  consequence of those changes, likewise begins in
the  lungs, and afterwaixls continues during the whole
circulation j and heat is thus uniformly diffused through-
out every  part of the body.
   Caroline.   More and more admirable J
   Mr*. B.  Now let me hear whether you can explain
how animal heat is produced   You, Caroline, tell me in
what manner it is first evolved in the lungs  ?
   Caroline,  part of the  oxygen gas inspired, imme«
diately combines in the  lungs  with the loose caibone 
and hydrogen of the venous blood ; and the caloric evolv-
ed during this combination, becomes animal heat.
   Mrs. B.  Very well;  but  you must  observe, that
the whole of the oxygen inspired at a breath is not con-
sumed by one respiration ; a considerable part of it is
expired, so that we  may breathe the same portion of
air several times before the whole of the oxygen is ex-
pended.—Now, Emily, will  you explain to mc in what
manner  an  uniform degree  of heat is kept up through-
out the body ?                         .
   Emily.  A quantity of oxygen enters into the  circu-
lation dining which it gradually combines with the hy-
drogen and 'carbone of ihe blood, thus producing  a con-
stant disengagement of  heat throughout every part of
the body.                        ,r   ,          c
   Mrs.  B.  Very  well,  indeed.  You have in  a few
words stated nearly all that  can be said on the subject.
 I must, however, mention another circumstance  which
 may contribute  to account for the gradual evolution of
 animal heat.   It appears, from some experiments, that
 the blood,  in consequence of the successive changes it
 undergoes during circulation (by which  it is gradually
 converted from  arterial into venous  blood), has  its  ca-
 pacity for caloric diminished.   What must be the con-
 sequence of this '.
    Emily  That heat of course, must be disengaged.
    Mrs  B   Exactly so ; and  thus  an additional quan-
 tity of animal heat must be  generated.   However,  the
 heat produced in this way is but trifling,  and could  on-
 ly account for a very small portion of the animal tern-

 PeSroflne  The  cause of animal  heat was  always a
 nerfect mystery to me, and  I am delighted with  its ex-
 P?t nation.-But pray, Mrs.  B.  can you tell me what is
 the  reason of the increase of heat that takes place in a

 ^Emily.  Is it not because we then breathe quicker, and
 therefore more heat is disengaged in the system ?
    * Ir*  B That may be one reason : but I should think
 that the principal cause of  the heat experienced in fe-
 vers, is, that there is no vent for the caloric which is
                       D  d 
326
generated in the body.  One of the most considerable
secretions  is  the insensible perspiration ; this is con-
stantly carrying off caloric in a latent state ;  but during
the hot stage of a fever,  the  pores are so contracted
that all perspiration ceases, and the accumulation of cal-
oric in the  body occasions those burning sensations that
are so painful.
   Emily.   This is, do doubt, the reason why the perspi-
ration that often succeeds the hot stage of a fever affords
so much relief.  If I had  known this theory of animal
heat when  I had a fever last summer, I think I should
have found some amusement in watching the  cheniical
processes that were going on within me.
   Caroline.   But exercise likewise produces animal
heat and that must be quite in a different manner.
   Mrs. B.   Not so much as you think ; for the more
exercise you take, the  more the body is stimulated, and
requires recruiting.   For this purpose  the  circulation
of the blood is quickened, the breath proportionably ac-
celerated, and consequently a greater quantity of caloric
evolved.
   Caroline.   True ; after running very fast,  I  gasp for
breath, my respiration is quick and hard, and it is just
then that I begin to feel hot.
   Emily.   It  would  seem, then, that violent exercise
should produce fever.
   Mr*. B. Not if the person is in a good state of health;
for the additional caloric is then carried off by ihe  per-
spiration which  succeeds.
   Emily.   What admirable resources nature  has  pro-
vided for us ! By the production of animal heat she has
enabled us  to keep up  the  temperature of our  bodies a-
bove that of inanimate objects ; and whenever this source
becomes too abundant, the excess is carried off by pers-
piration.
   Mr*. B.  It is by the same law of nature that we are
enabled, in  all climates, and in all seasons, to  preserve
our bodies of an equal temperature, or at least very near-
ly so.
   Caroline.  You cannot mean to say that our bodies are
of the same temperature  in  summer and in winter  in
England and in the West Indies ? 
Z2T
  Mrs. B.  Yes, I do; at least if you speak of the tem-
perature of the blood, and the internal parts of the body;
for those parts th it are immediately in contact with the
atmosphere, such as  the hands and face, will occasonally
get warmer or colder, than  the  internal or more shel-
tered parts.   But if you put the bulb of a thermometor
in your mouth, which is the best way of ascertaining the
real temperature of your body, you will  scarcely per-
ceive any difference in its indication, whatever may be
the difference of temperature of the atmosphere.
   Caroline.  And  when I feel overcome by heat, I am
really not hotter than when  l»m shivering with cold ?
   Mrs.  B.  When a person in health feels very hot,
whether from internal heat, from  violent exercise, or
from the temperature of the atmosphere, his body is
certainly a little warmer than when he feels very cold  ;
but this difference is much smaller than our sensations
would make us believe : and the natural standard is soon
restored by rest and perspiration   1 am sure you will
be surprised to hear that  the internal temperature of
the body scarcely ever descends below 95° or 96°, and
hardly ever  attains 104° or 105", even  in the most vio-
lent fevers.
   Emily.  The greater quantity  of caloric, therefore,
that we receive from the atmosphere in summer, cannot
raise the temperature of our bodies,  beyond certain lim-
its, as it does that of inanimate bodies, because an excess
of caloric is carried off by perspiration.
   Caroline.   But the temperature of the atmosphere,
and consequently that of inanimate bodies, is surely nev-
er so high as that of animal heat ?
   Airs. B.   1  beg your pardon  Frequently in the East
and West Indies, and sometimes, in the southern parts
of Europe, the atmosphere is above 98°, which is the
common temperature of animal heat.—Indeed,  even in
this country, it  occasionally happens that the sun's rays,
setting full  on  an object, elevate its temperature above
that point.
   In  illustration of the power which our  bodies  have to
resist the effects of external heat, Sir Charles Blagden,.
with some other gentlemen, made several very curious
experiments.   He remained for some time in an oven. 
328
  heated to a temperature not much inferior to that of boil-
  ing water, wiihout suffering any  other incenvenience
  than  a profuse perspiration, which he supported  by
  drinking plentifully.
    Emily.  He could scarcely consider the perspiration
  as an inconvenience, since it saved him from being ba-
  ked, by giving vent to the excess of caloric.
    Caroline.  I always thought, I confess, that it was
  from the  heat of the perspiration, that we suffered in
  summer.
    Mrs. B. You now find that you were quite  mistaken.
  Whenever evaporation takes place, cold, you  know, is
 produced in consequence of a quantity of caloric being
 carried off in a latent state ;  this is the case  with per-
 spiration, and it is in this way that it affords relief.  It
 is for the  same reason that tea  is otten refreshing  in
  summer, though it appears to heat you at the moment
  you drink it.
   Emily.   And in winter, on the  contrary,  tea is pleas-
ant on account of its heat.
   Mr*. B.  Yes;  for  we have then  rather  to  guard
 against a deficiency than an excess of caloric, and you
 do not find that tea will excite perspiration in winter, un-
 less after dancing, or any other violent exercise.
   Caroline.  What is the reason that it is dangerous to
 eat ice after dancing, or to di ink any tiling cold when one
 is very hot ?
   Mr*. B.  Because the loss of heat arising  from the
 perspiration, conjointly with  the chill occasioned by the
 cold draught, produces more cold than can be borne with
 safety, unless you continue to use  the same exercise af-
 ter drinking that you did before ;  for the heat  occasion-
 ed by the exercise will counteract the effects of the cold
 drink, and the danger will be removed. You may, how-
 ever,  contrary  to the  common notion, consider it as a
 rule, that cold liquids may at all  times, be drunk with
 perfect safety, however hot you may feel, provided you
 are not at the moment in a state  of great perspiration,
 and on condition that you keep yourself in gentle exer-
 cise afterwards.
    Emily.   But  since we are  furnished with such re-
 sources against the extremes of  heat or cold, I should. 
520
nave thought that all climates would have been equally
wholesome.
   Mrs. B.  That is true, in a certain  degree, with re-
gard to those who have been accustomed to them from
birth ; for  we find that the natives of those  climates
which we consider as the most deleterious, are  as heal-
thy as ourselves ; and if such climates are unwholesome
to those who are habituated to a more moderate tempe-
rature, it is because the animal economy does not easily
accustom itself to considerable changes.
   Caroline.  But pray, Mrs. B. if the circulation pre-
serves the  body of an uniform temperature, how does it
happen, that animals are sometimes frozen ?
   Mrs. B.  Because  if more heat is carried off by the
atmosphere than the circulation can  supply, the cold
will finally prevail, the heart will cease to  beat, and the
animal will be frozen.  And likewise, if the body re-
mained long exposed to a degree of heat, greater than
the perspiration could carry off, it  would at last lose the
power of resisting its destructive influence.            »
   Caroline.  Fish, I suppose, have no animal heat, but
partake of the temperature of inanimate objects ?
   Emily.  And their coldness, do doubt, proceeds from
their not breathing ?
   Mr*. B.  All kinds of fish, I believe, breathe  more
or less, though in a much smaller  degree  than land ani-
mals.  Nor are they  entirely destitute of animal heat,
though for the same reason they are  much colder than
other creatures.   They have comparatively but  a very
small quantity of blood, therefore but little oxygen is re-
 quired, and a proportionally small quantity  of animal
 heat is generated.
   Caroline.  But how ean fish breathe under water ?
   Mr*. B.  Some of them raise their heads above the
water to breathe ; and others are supposed to be endow-
 ed by nature with the power of decomposing water and
 absorbing oxygen from it.  Besides, water always con-
 tains air mixed with it which the fish may possibly  ap-
 ply to the purposes ot respiration.   Whatever the case
 may be, it is certain that several kinds of fish  have  re-
 servoirs of air, or air bags, from which they have  prob--
                       Dd2 
330
abhy the means of supplying the gills, an organ which.
in the respiration of fish, answers the double purpose of
mouth and lungs.
  Caroline.   Are there any species  of  animals  that
breathe more than we do ?
  Mr*. B. Yes;  birds, of all animals, breathe the great-
est  quantity of air  in proportion to their size ; and  it is
to this that they are supposed to owe the peculiar firm-
ness and  strength of their muscles, by which they are
enabled to support the violent exertion of flying.
  This difference betwetn birds and  fish,  which  may
be considered, as the two extremes of the scale of mus-
cular strength,  is  well worth observing.   Birds resid-
ing constantly in  the atmosphere,  surrounded by  oxy-
gen,  and  respiring it in a  greater proportion  than any
other species of animals,  are endowed with a superior
degree of muscular strength, whilst the muscles of fish,
on the contrary, are flaccid and oily ; these animals are
comparatively  slow  and  feeble in their motions, and
their temperature is scarcely above that of the water in
which they live.  This  is, in all probability,  owing to
their imperfect respiration ; the quantity of hydrogen
and carbone, that is in consequence accumulated in their
bodies, forms  the oil  which is strongly  characteristic
of that species of animals,  and which  relaxes  and  soft-
ens the small  quantity of fibrine which  their muscles
contain.
  Caroline.  But, Mrs. B. there  are some species of
birds that frequent both elements, as, for instance ducks
and other water fowl.  Of what nature  is  the flesh of
these ?
  Mrs. B.  Such birds, in general, make but little use
of their wings ; if they fiy, it is but feebly, and only to a
short distance.   Their flesh too partakes of the oily na-
ture, and  even in taste sometimes resembles that offish.
This is the case not only with the various kinds of water
fowls, but with  all other amphibious animals,  as  the ot-
ter, the crocodile, the lizard, Sec,
  Caroline.   And what is the reason that reptiles arc so
deficient in muscular sirength ?
   Mrs.   B.    It  is  because they usually live under
ground, and seldom come into the atmosphere___They. 
331
have  imperfect, aud  sometimes no discernible organs
of respiration, they partake  therefore of the soft oily
nature of fish ; indeed, many of them are amphibious,
as frogs, toads, and snakes, and  very few of them find
any difficulty in remaining a length of time  under wa-
ter.   Whilst, on the  contrary, the insect tribe that are
so strong in proportion to their size, and alert in  their
motions, partake of the nature of birds, air being  their
peculiar element,  and their organs of respiration being
comparatively larger than in other classes of animals.
   1  have now  given  you a short account of  the princi-
pal animal functions.   However interesting the subject
may  appear to you,  a fuller investigation of it would,
I fear,  lead us too far from our object.
   Emily.  Yet I shall not quit it without much regret;
for of all the branches of chemistry, it is certainly the
most curious and  most interesting.
   Caroline.  But,  Mrs.  B.  1 must remind you that
you promised to give us  some account of the nature of
milk,
   Mrs.  B.  True.  There  are several  other  animal
productions ihat deserve likewise to be mentioned.  We
shall begin with  milk, which is certainly the most im-
portant and most interesting of all the animal  secretions.
   Milk,  like all other  animal  substances,  ultimately
yields  by analysis,  oxygen,  hydrogen,  carbone, and
nitrogen.  These are combined in it under the forms
of albumen, gelatine, oil, and  water.  But  milk con-
tains, besides,  a considerable  portion of phosphat  of
 lime, the purposes of which,  1 have already pointed
out.
   Caroline.  Yes ; it is  the salt which  serves  to nou-
 rish the tender bones of the  suckling?
   Mrs. B.   To  reduce  milk to its elements would be
 a very  complicated, as  well as useless operation ; but
 this fluid, without any chemical assistance, may be de-
 composed into three  parts,  cream,  curds, and  whey—
 These constituents of milk have but a very slight affin-
ity to each other, and you  find  accordingly  that cream
 separates from  milk by mere standing.   It consists
 chiefly of oil,  which being lighter than the  other parts 
332
 ©f the milk, gradually rises to the surface.   It is of this,
 you know, that butter is made,  which is nothing more
 than oxygenated cream.
   Caroline   Butter,  then, is somewhat analogous to
 the waxy substance formed by the oxygenation of veg-
 etable oils.
   Mr*   B.   Very much so.
   Emily.  But is the cream oxygenated by churning ?
   Mr*.  B.   Its oxygenation commences  previous  to
 churning, merely  by standing exposed to  the  atmos-
 phere, from  which  it absorbs oxygen.   The process
 is afterwards completed by churning; the  violent mo-
 tion which this  operation  occasions,  brings every par-
 ticle of  cream in  contact  with the  atmosphere, and
 thus facilitates its oxygenation.
   Caroline.   But the  effect of churning, I  have often
 observed in  the dairy, is  to separate the  cream into
 two substances, butter, and butter-milk ?
   Mr*.  B.  That  is  to say,  in proportion  as the oily
 particles of the cream become oxygenated,  they sepa-
 rate from the other constituent parts of the cream in
 the form of butter.   So by churning you produce, on
 the one  hand, butter, or oxygenated  oil; and,  on the
 other, butter-milk, or cream  deprived of oil.—But  if
 you make butter by churning new milk instead of cream,
 the butter-milk  will then be  exactly  similar in its pro-
 perties to creamed or skimmed milk.
   Caroline   Yet butter-milk is  very different from
 common skimmed milk.
   Mrs.  B.  Because you  know  it is customary, in
order to save time  and labour, to make butter froR>
cream alone.  In this case, therefore, the butter-milk
is deprived of the creamed milk,  which contains both
the curd  and the  whey.   Besides, in consequence of
the milk remaining exposed to the atmosphere  during
the separation of the cream, the latter becomes more
or less acid, as well as the  butter-milk which  it yields
in churning.
   Emily.  Why should not the butter be equally acidi-
fied by oxygenation ?
   Mrs.  B.  Animal oil is not so easily acidified  as the- 
333
other ingredients  of  milk.   Butter, therefore, though*
usually made of sour cream, is not sour itself, because
the oily part of the cream had not been  acidified.   But-
ter,  however, is susceptible of  becoming acid by  an
excess of oxygen ; it is then said  to be rancid, and pro-
duces the sebacie acid, the same  which is obtained from
fat.
   Emily.  If that be the case, might not rancid butter
be sweetened by  mixing with it some substance that
would take the acid from it ?
 •• Airs. B.   This idea has been  suggested by Mr. Da-
vy, who supposes,  that if rancid butter were well wash-
ed in  an alkaline solution, the alkali would separate the
acid from the butter.
   Caroline.  You said just now that creamed milk con-
sisted of curd and whey. Pray how are these separa-
ted ?
   Airs. B.   They may be  separated by standing for a
certain length of time exposed to the atmosphere ; but
this decompositon may be  almost  instantaneously  ef-
fected by the chemical agency of a variety of substan-
ces.   Alkalies, rennet,* and indeed almost all animal
substances, decompose  milk by combining  with the
curds.
   Acids and  spirituous liquors, on the other hand, pro-
duce a decomposition by combining with tlie whey.  In
order therefore  to obtain the whey pure, rennet, or
alkaline substances, must be used  to  attract the curds
from it.
   But if it be wished to obtain the curds pure, the whey
must  be separated by acids, wine,  or other spiiituous
liquors.
   Emily.  This is a  very useful  piece of information ;
for  I find white  wine whey,  which I  sometimes take
when 1 have a cold,  extremely  heating ; now, if the
whey were separated by  means  of an alkali instead of
wine, it could not produce that effect.

  * Rennet is the name given to a ivatery infusion of  the
coats of the stomach of a sacking calf.  Its remarkable ef-
ficacy in promoting coagulation is supposed to drpend on.
the gastric juice with which it is impregnated. 
334
  Mrs. B.  Perhaps not.  But I would strenuously ad-
vise you not to place too much  reliance  on your slight
chemical knowledge in medical matters.   I do not know
why whey is not separated from curd by rennet, or by
an  alkali, for the purpose which you mention ;  but I
strongly suspect there must be some  good reason why
the preparation by means  of wine is generally prefer-
red.  I can,  however, safely point out to you a method
of obtaining  whey  without either alkali, rennet,  or
wine ; it is by substituting lemon juice,  a very small
quantity of which will separate it from the curds.
  Whey, as an article of diet, is very wholesome ; it
is the most nutritive part of the milk,  and the lightest
of digestion.  But its effect, taken medicinally, is chief-
ly,  I  believe, to excite  perspiration, by being drunk
warm on going to bed.
  It appears that the nutritive particles of whey may be
obtained in crystals  by evaporation;  in  this state they
are called salts, or more commonly sw,§-cr of milk.  This
salt is sweet to the taste,  and in  its composition is so
analogous to  sugar, that it is susceptible of undergoing
the vinous fermentation.
  Caroline  Why then is  not wine,  or alcohol, made
from whey ?
  Mrs. B.   The  quantity of sugar  contained in milk
is so trifling that it can  hardly answer for that purpose.
I have heard of only one instance of  its  being used for
the production of a  spirituous  liquor, and  this is  by
the Arabs ;  their abundance of horses as  well as  their
scarcity of fruits,  has introduced the fermentation of
mare's  milk, by  which they  produce  a liquor called
fcoumiss.   Whey  is likewise susceptible of being acidi-
fied by  combining with oxygen from the atmosphere.
It then produces the lactic acid, which you may recol-
lect is mentioned amongst the animal acids, as the acid
of milk.
  Let us now see what are the properties of curds.
  Emily.  I know that they are made into cheese ;  but
I have heard that for  that purpose they are  separated
from the vvhey by rennet, and yet this you have just told
us is not the method of obtaining pure curds ?
  Mr*. B.   Nor are pure curds so well adapted for th# 
335
formation of cheese.   For the nature and flavour of the
cheese depends, in a great measure, upon the cream
or oily matter which is left in the curds ; so that if eve-
ry particle of cream be removed from the curds, the
cheese  is  scarcely   eatable.   Rich cheeses,  such as
cream and Stilton cheeses, derive their excellence from
the quantity, as well as the quality of the cream that en-
ters into their composition.
   Caroline.  I had no idea that milk was such an  inter-
esting compound.   In many respects there appears to
me to be a very striking analogy between  milk and the
contents of an egg> both in respect to their nature  and
their use.  They  are, each of them, composed of the
various substances necessary for the nourishment of the
young animal, and equally destined for  that purpose.
   Mr*.  B.  There  is. however, a  very  essential dif-
ference.   The young animal is formed, as well as nour-
ished by the content*  of the egg-shell ; whilst milk
serves as nutriment to the suckling, only after it is born.
   There are several  peculiar  animal substances which
do not enter into the general enumeration of animal
compounds, and  which, however, deserve to  be men-
tioned.
   spermaceti  is  of  this class ; it is a kind of oily sub-
stance obtained from the head of the whale,  which
however, must undergo a certain preparation before it
is in a fit state to be made into candles.  It is not much
more combustible than tallow, but is more pleasant  to
burn, as it is less fusible and less greasy.
   Ambergris is another peculiar substance derived from
a species  of whale.   It  is, however, seldom  obtained
from the animal itself, but is generally found floating on
the surface of the sea.
    Wax, you know, is a concrete oil, the peculiar  pro-
duct of the bee, part of the constituents of which  may
probably be  derived from flowers, but so prepared by
the organs of the  bee, and so nixed with its own  sub-
 stance, as to be decidedly an  animal product.   Bees'-
wax is naturally of a yellow colour, but it is bleached
 by long exposure to the atmosphere, or may be instan-
taneously  whitened  by the  oxy-muriatic acid.   The
 combustion of wax is far more perfect than that  of tal- 
336
  low,  and consequently produces a greater quantity of
  light and heat.
    Lac is a substance very similar  to wax in the man-
  ner of its formation ; it is the product of an insect which
  collects its ingredients from flowers, apparently for the
  purpose of protecting its eggs from injury   It is form-
  ed into cells fabricated with as  much  skill as those of
  the honey-comb, but differently arranged.  The prin-
  cipal  use of lac is in the manufacture of sealing-wax, and
  in dying scarlet.
    Alusk, civet, and  castor, are other particular produc-
  tions, from different species of quadrupeds   The two
  first are very powerful perfumes ;  the latter has a nau-
  seous smell and taste, and is only useful medicinally.
    Caroline.   Is it from this substance that castor oil is
  obtained ?
    Mr*. B.   No.  Far from it, for castor oil is a  veget-
  able oil, expressed from the seeds of a particular plant;
  and has not the least resemblance to the medicinal sub-
  stance obtained from the castor.
    Silk is  a peculiar secretion of the silk  worm, with
 which it builds  its  nest  or cocoon.   This insect was
 originally brought to Europe from China.  Silk, in  its
 chemical nature, is very similar to the hair and wool of
 animals.  The moth ol the silk worm ejects a  liquor
 which appears to contain  a particular acid, called bom-
 bic, the properties of which are very little known.
   Emily   Before we conclude  the subject  of the ani-
 mal economy, shall  we not learn by what steps animals
 return to their elementary state ?
   Airs.  B.  Animal matter, although the most com-
 plicated of all natural substances, returns to its elemen-
 tary state by one  single  spontaneous process, the putrid
fermentation.   By this,  the  gelatine, albumen,  and  fi-
 brine,  are slowly reduced  to the state of oxygen, hy-
 drogen, nitrogen, and carbone  ; and thus the circle  of
 changes  through which  thehe principles have  passed
 is finally completed.   They first quitted  their elemen-
 tary form, or their combination with unorganized mat-
 ter, to enter  into the vegetable system.—Hence they
 were transmuted to  the  animal kingdom; and from 
33Y
"this they return again to their primitive simplicity, soon
 to re-enter the sphere of organized existence.
   When all  the  circumstances  necessary  to  produce
 fermentation  do not take place, animal, like vegetable
 matter, is liable to a partial or imperfect decomposition,
 Which converts  it into a combustible substance very
 like spermaceti I expect Caroline, who is so fond of an-
 alogies, will  otnsider this as a kind of animal bitumen.
   Caroline.   And why should  I not, since the  process-
 es, that produce these substances are so similar.
   Airs. B.   There  is, however, one considerable dif-
 ference :  the state of bitumen  seems permanent, whilst
 that of  animal substances,  thus  imperfectly decompo-
 sed,  is only transient; and, unless precautions lie taken
 to preserve  them in that state, a total dissolution in-
 fallibly ensues.  This circumstance, of the occasional
 conversion of animal matter into a kind of spermaceti,
 is ol late discovery.   A manufacture has in consequence
 been established  near  Bristol, in which by  exposing
 the carcases of horses and other animals for  a length
 of time  under water, the muscular parts are converted
 into this spermaceti-like substance.   The bones after-
 wards undergo a different process to produce  harts-
 horn,  or, more properly,  ammonia, and phosphorus;
 and the skin is prepared for leather.            %
   Thus art contrives to enlarge the sphere  of  useful
 purposes, to  which the elements were intended by na-
 ture ;  and the productions of the several kingdoms are
 frequently arrested in their course, and variourly  modi-
 fied, by human skill, which compels them to contribute,
 under new forms, to the necessities or luxuries of man.
   But all  that we enjoy, whether produced  by  the
 spontaneous operations of nature, or the ingenious ef-
 forts of art, proceed alike from the goodness of Pro-
 vidence.—To GOD alone man owes the admirable
 faculties which enable  him to  improve and modify the
 productions of nature, no less than those productions
 themselves.   In  contemplating the works of the  crea-
 tion, or studying  the inventions of art, let us, there-
 fore,  never forget the Divine Source from which they
 proceed ; and  thus every acquisition of knowledge will
 prove a lesson of piety and virtue.
          E e          END  OF THE  LONDON COPY. 
338
 '■i  abridgement of the Bakerian Lecture on the decompo-
  sition of the fixed alkalies and the exhibition of the new
  substances which  constitute their bases ; by Humphrey
  Davy,  esq. secretary of the Royal Society.

  The researches I had made on the decomposition  of
iicids, and of alkaline and earthy  neutral  compounds,
proved that the  powers  of  electrical  decomposition
were proportional to the strength of the opposite elec-
tricities in the circuit, and to the conducting power and
degree of concentration of the  materials  employed.
In the first attempts I made on the decomposition  of
the fixed alkalies, I acted  upon aqueous solutions  of
potash and soda, saturated at common temperatures, by
ihe highest electrical power I  could  command, and
which was  produced by a combination of voltajc batte-
ries, belonging to the Royal Institution, containing 24
plates  of  copper and zinc of 12 inches square, 100
plates of 6  inches, and 150 of 4 inches  square,  charg-
ed with solutions of alum and nitrous acid ; but in these
cases, though there was a high intensity  of action, the
water of the solutions alone was effected, and Hydrogen,
s»nd oxygen disengaged with  the production  of much
heat and  violent effervescence.  The presence  of wa-
ter app^ring thus to prevent any decomposition, 1 used
potash m igneous fusion.  By means of a stream of oxy-
gen  gas from a  gasometor applied to the flame of a
spirit lamp, which was thrown on a  platina spoon con-
taining potash, this alkali was kept for some minutes
in a strong red  heat, and in a state of  perfect fluidity.
 The  spoon was preserved in communication with  the
 positive  side of the battery,  and the power of 100 of inch-
 es, highly charged ; and the  connection from the neg-
 ative side  vuis  made by a platina wire   By  this  ar-
 rangement some biilium  phenomena vrere  produced.
 The potash appeared a conductor,  in a high  degree,
 and as long as the communication was preserved, a most
 intense  light was exhibited  at the negative wire, and
 a column of flame, which seemed to be owing to the  de-
 velopement of combustible matter, arose from the point
 of contact.  When the order was changed, so that  the
 platina spoon was made negative, a vivid, constant light 
                        339

appeared at the  opposite point.  There was no effect
of inflammation  round it, but aeriform globales,  which
inflamed in the  atmosphere, rose through the  potash.
The platina, as might have been expected,  was con-
siderably  acted  upon ;  and in  the cases when  it  had
been negative in the highest degree.
   The  alkali was  apparently dry in this experiment ;
and it seemed probable, that  the  inflammable  matter
arose from its decomposition.   The  residual potash
was unaltered;  it contained, indeed^ a number of dark
grey metallic particles,  but these proved to be  derived
from the platina.
   I tried  several  experiments on the electrization of
potash, rendered fluid by heat,  with the hopes of being
able to collect the  combustible  matter, but without suc-
cess ;   and I only attained  my object, by employing
electricity, e.s the common agent for  fusion and  decom-
position.   Though potash, perfectly dried by  ignition,
is a non-conductor, yet it is rendered a conductor by a
very slight addition of moisture,  which docs not  per-
ceptibly destroy its aggregation ; and in this state it rea-
dily fuses and decomposes by  strong electrical  powers.
   A small piece  of pure potash, which  had been ex-
posed a few seconds  to the atmosphere,  so as  to  give
 conducting power to the surface, was placed  upon an
 insulated disc of  platina, connected with the  negative
 side of the battery, of fhe power of two hundred and
 fifty of six and  four,  in a state of intense activity ; and
 a platina wire communicating with the positive side, was
 brought in contact with the upper surface of the alkaki.
 The whole apparatus was in the open atmosphere.
    Under these circumstances, a vivid action  was soon.
 observed to take  place.  The potash began to fuse  at
 both its points  of electrization.  There was a violent
 effervescence, at  the upper surface :  at the  lower or
 negative  surface,  there was no liberation of elastic flu-
 id ; but small  globules, having a high  metalic lustre,
 and  being  precisely similar, in visible characters to
 quicksilver, appeared ; some  of which burnt with ex-
 plosion, and bright flame, as  soon as they were form-
 ed, others remained, and were merely tarnished, and
 finally covered  by a white film, which formed on their 
340
v.irfaces.  These globules, numerous experiments soon
showed to be the substance I was in search of, and  a
peculiar inflammable principle the basis of potash.   I
found that the platina was in no way connected with the
result, except as  the medium of exhibiting the elec-
trical powers of decomposition ;  and a substance of the
same kind was produced, when pieces of copper, silver,
gold*plumbago, and even charcoal  were employed for
completin g the circuit.   The phenomenon was inde-
pendent of the presence of air.  I found  that it took
place when the alkali was in the vacuum of an exhaust-
ed  receiver.   The substance was  likewise produced
from potash fused by means of a lamp, in glass  tubes
confined by mercury, and  furnished with hermetically
inserted platina wires, by which  the  electrical action
was transmitted.  But this operation could not be car-
ried on for any considerable time ;  the glass was rapid-
ly dissolved by the action of the alkali,  and this sub-
stance soon penetrated through the body of the tube.
  Soda, when acted upon in the same manner as  pot-
ash, exhibited an analogous  result;  but'the-decompo-
sition demanded greater intensity of action  in the  bat-
teries, or the alkali was required to be  in much thinner
and smaller pieces.  \Villi  the battery of one hundred
of six  inches in full activity, I  obtained  good results
from pieces  of potash weighing from forty to seventy
grains, and of a thickness  which made the distance  of
the electrified metallic surfaces nearly a quarter of an
inch ; but with a similar  power it  was impossible  to
produce the effects of decomposition on pieces of  soda
of more than  fifteen and twenty  grains iu weight, and
that only when the distance between  the wires was  a-
Lout one eighth or tenth of an inch.
  The substance produced from potash remained  fluid
at the  temperature  of the atmosphere at the  time  of
its production ; that from soda,  which was fluid in the
degree of heat of the alkali during its formation, became
t>olid on cooling,  and  appeared  having the  lustre  of
silver
  When the power of two hundred and fifty was  used
with a very high charge for the  decomposition of soda,
the globules often burnt at the moment of their forma. 
341
tion  and sometimes violently exploded and separated
into  smaller  globules,  which flew with great  velocity
through the air, in a state of vivid combustion, producing
a beautiful effect of continued jets of fire.
III.   Theory of the Decomposition of the fixed Alkalies ;
           their Composition and Production.

  As in all decompositions of compound substances
which I had previously examined at the same time,
that combustible bases were developed at the negative
surface in the electrical circuit, oxygen was produced
and evolved or  carried into combination at the positive
surface; it was reasonable to conclude that this substance
was generated in a  similar manner  by the electrical
action upon the alkalies, and a number of experiments
made above mercury, with the apparatus for excluding
external air, proved that this was the case.
  When solid potash, or soda  in its  conducting state,
was included  in  glass tubes firnished with electrified
platina wires, the new substances were generated at the
negative surfaces; the gas given out at the other surface
proved, by this most delicate examination, to be pure ox-
ygen ; and unless an excess of water was present, no gas
was evolved from the negative surface.
  In the synthetical experiments, a perfect coincidence
likewise will be found.
  I mentioned that the metallic lustre of the substance
from  potash immediately became destroyed in  the at-
mosphere, and that a  white crust formed upon it.  This
crust \ soon.found to  be pure potash, which immediate-
ly deliquesced, and new quantities were formed, which
in their turn attracted  moisture from the atmosphere, till
the whole globule disappeared, and assumed the form of
a saturated solution of potash.
  When  globules were placed in appropriate tubes,
containing common  air  or oxygen  gas,  confined  by
mercury, an absorption of oxygen took place ;  a crust
of alkali instantly formed upon the globule ; but from
                       E e2 
342
 the want of moisture for  its solution the  process smp-
 pcd, the interior being defended from  the action of the
 gas-
   With the substances from soda the appearances av.d
 effects were analogous.  When the  substances were
 strongly heated, confined in given portions of oxygen,
 a rapid combustion with a brilliant white flame was pro-
 duced, and the metallic globules  were found converted
 into a white and solid mass, which, in the case of the sub-
 stance from potash, was found to be potash, and in  the
 case of that from soda, soda.
   Oxygen  gas  was absorbed in this  operation, and
 nothing emitted which effected the purity of the resi-
 dual air.   The  alkalies produced were apparently dry,
 or at least contained no more moisture than might well
 be conceded to exist in the  oxygen gas absorbed ; and
 their weights considerably exceeded those of the com-
 bustible matters consumed.   The processes on which
 these conclusions are found  will be fully described here-
 after, when the  minute details which are necessary will
 be explained, and  the proportions of oxygen and of the
 respective inflamable substances which enter into union
 to form the fixed alkalies will be given.
  It appears, then, that in these facts there is the same
 evidence for the decomposition of potash and  soda into
oxygen and two peculiar substances, as there is for the
decomposition   of  sulphuric and phosphoric acids and
ihe metallic oxyds into oxygen and their respective com-
bustible bases.
  In the analytical experiments, no substances capable
 of decomposition   are present, but the alkalies and a
 minute portion  of moisture  ; which seems in no other
 way essential to the result, than in rendering them con-
 ductors at the suiface : for  the new substances are not
 generated till the interior, which is dry, begins to be  fu-
 sed ; they explode then in rising through the  fused  al-
 kali ;  they come in contact  with the heated moistened
 surface ; they cannot be produced from crystallized  al-
 kalies, which contain much  water ; and the effects pro-
 duced by the electrization of ignited potash, which con-
 tains no sensible quantity of water, confirm the opinion
 of 'heir formation independently cf the pescnse of this
 substance^ 
343
  The combustible bases of the fixed alkalies seemtfo-'
be repelled as other  combustible substances, by posi-
tively electrified  surfaces, and  attracted by negatively
electrified surfaces ; and the oxygen follows the con-
trary order ; or the oxygen being naturally possessed
of the negative energy,  and the  bases of  the positive
do  not remain in combination  when either of them is
brought into an electrical state opposite  to its natural
one.   In the synthesis,  on the  contrary,  the natural
energies  or attractions  come in  equilibrium with each
other ;  and when these are in a low state at common
temperatures, a slow  combination is effected ; but when
 ihey are exalted by heat,  a  rapid union  is the result
 as in oilier like cases with the production of fire.
   A number of circumstances relating to  the agencies
 of  the  bases will be immediately stated,  and  will be
 found to offer confirmations to these general conclusions.

 IV. On the Properties and Nature of the Basis of Potash.
   After 1 had detected  the bases of the fixed alkalies,
 I had  considerable difficulty  to preserve  and  confine
 them  so as to examine their properties, and submit
 them  to experiments ;  for, like  the alkahests imagin-
 ed by the alchemists, they  acted more or less upon al-
 most every body to which they were exposed.
    The fluid substance  a mongst all those  I have tried,
 on  which I find they have least effect,  is recently dis-
 tilled  naphtha.  In this material,* when excluded from
 the air, they remain for many days without considera-
 bly changing, and their physical properties may be
 easily  examined in  the atmosphere when they are co-
 vered by a thin film of  it.  The basis of potash at 60°
 Fahrenheit, the temperature in  which I first examined
 it, appealed,  as I have already  mentioned, in small
 globules possessing  the metallic lustre,   opacity  and
 general appearance of mercury  ; so that  when a  glo-
 bule of mercury was placed near a globule of the pecu-
 liar substance, it was not possible to detect a difference
 by the eye.
    At 6©«  Fahrenheit it is, however, only imperfectly
  fluid, for it  does readily run into a globule  when its 
344
shape is altered ;  at 70° it becomes more fluid ;  and at
100°  its  fluidity is perfect,  so  that different globules
may be easily made to run into one.   At 50°  Fahren-
heit it becomes  a soft and malleable solid,  which has
the lustre of polished silver ; and at about the freezing
point of  water it becomes harder and brittle ; and,
when broken in fragments,  exhibits a crystallized tex-
ture,  which,  in the  microscope, seems composed of
beautiful  facets of a perfect whiteness and high metallic
splendour.
  To be  converted into vapour, it  requires a tempera-
ture approaching that of the red heat;  and when the
experiment is conducted under proper circumstances,
it is found unaltered after distillation.
  It is a perfect conductor of electricity.   When a
spark  from the  voltaic battery of an  hundred  of six
inches is taken upon a large globule in the atmosphere,
the light is  green, and  combustion takes place at the
point of  contact only.   WThen  a small  globule is used
it is completely dissipated with  explosion, accompanied
by  a  most vivid  flame, into alkaline fumes.  It is an
excellent conductor of heat.  Resembling the metals
in all these sensible properties,  it is, however, remark-
ably different from any of them in specific gravity.   I
found  that  it rose to the  surface of naphtha distilled
from petroleum,  and of which  the specific gravity was
eight hundred and sixty-one, and it did not sink in dou-
ble distilled naphtha, the specific gravity of which was
about  seven  hundred and seventy, that of water being
considered as one.  The small quantities  in which it
is produced by the highest electrical powers, rendered
it very difficult to determine this qpality with minute
precision.  I endeavored to gain approximations on the
subject by comparing the weights of perfectly equal
globules of  the  basis of  potash and mercury.    I
use . the very delicate balance of the Royal Institution,
which, when, loaded  with  the  quantities  I  employed,
and of which the  mercury  never exceeded  ten grains,
is sensible, at least, to the         of a grain.   Taking
the mean  of four experiments, conducted  with great
care, its specific  gravity at 62° Fahrenheit, is to that
of  mercury as 10 to  223,  which  gives a  proportion 
345
to that of water  nearly as  6  to  10 ; so that  it is the
lightest fluid body known.  In  its solid form it is a
little heavier; but even in this state, when cooled to
40s Fahrenheit, it swims in the double distilled naphtha.
   The chemical relations of the basis of potash are
still more extraordinary than its physical ones.
   I  have already mentioned  its  alkalization and  com-
bustion in oxygen gas.  It combines with oxygen  slow-
ly and without flame  at  all temperatures that I  have
tried below that of its evaporation.  But  at this tempe-
rature  combustion  takes  place, and the. light is  of  a
brilliant whiteness,  and the heat intense.  When  heat-
ed slowly in a quantity of  gas  not sufficient for its  com-
plete conversion  into  potash,  and at a temperature in-
adequate  to its inflammation, 400° Fahrenheit for in-
stance,  its tint changes to that  of a red  brown, and
when the heat is  withdrawn, all the oxygen is found to
be absorbed, and a solid is formed of a greyish colour,
which partly consists of potash,  and partly  of  the basis
of potash in a lower degree of oxygenation, and which
becomes potash by being  exposed to water, or  by  being
again heated in fresh quantities of air.  The substance
consisting of the basis of  potash  combined with an un-
der proportion cf oxygen, may likewise be formed by
fusing dry  potash and its basis together under proper
circumstances.   The  basis rapidly loses  its metallic
splendour;  the two substances unite into  a compound
of a red  brown  colour when  fluid, and of a dark grey
hue when solid ; and  this compound  soon absorbs its
full proportion of oxy yen when exposed to the air, and
 is wholly converted into potash.
   And the same body is  often formed in the analytical
 experiments when the action of the electricity  is in-
tense, and the potash much heated.     _  0
   The basis of potash, when introduced into  oxymuri-
a;ic acid gas,  burns spontaneously with a bright red
light, and a white salt, proving to  be muriat of potash,
 is formed.
   Wiitn a  globule is healed in  hydrogen at  a degree
 below its point of vaponzation,  it  seems to dissolve in
 it, for the globule  diminishes in volume, and the gas
explodes  with  alkaline fumes and  bright light, when, 
346
suffered to pass into the air ; but by cooling, this spon-
taneous detonating property is destroyed, and the basis
is either wholly or principally deposited.
  The action of the basis of potash on water exposed
to the atmosphere is connected with some beautiful phe-
nomena.   When it is thrown upon water, or when it is
brought into contact with a drop of water at common
temperature, it decomposes it with great violence, an
instantaneous explosion is produced with brilliant flame,
and a solution of pure potash is the result.
  In experiments of this kind, an appearance often oc-
curs similar to that produced  by the  combustion  of
phosphorated hydrogen ;  a white ring of smoke, which
gradually extends as it rises into the air.
  When water is made to act upon the basis of potash
out of the contact of air,  and preserved by means of a
glass tube under naphtha, the decomposition is violent;
and there i*. much heat and noise but no luminous ap-
pearance :  and the gas evolved, when examined in the
me" uri?  or water pneumatic apparatus, is found to be
pure n^arogen.
   Whc-i a globule  of  the basis of potash is placed up-
on ice, it instantly burns with a bright flame, and a deep
hole is made in the ice, which is lound to contain a so-
lution of potash.
   The theoiy of  the action of the basis of potash upon
water exposed  to the atmosphere, though complicated
changes occur, is far from  being obscure.  The phe-
nomena seem to depend  on the strong attractions of the
basis for  oxygen and  of the potash formed for water.
The heat which arises from two causes, decomposition
and combination,  is  sufficiently intense  to produce the
inflammation.  Water is a bad  conductor of heat; the
 globule sterns  exposed to air ;  a part of it, there is the
 greatest reason to  believe, is dissolved by the heated
nascent hydrogen ;   and  this substance being capable of
spontaneous inflammation, explodes  and communicates
 the  effect of combustion to any of the basis that may-
 be yet uncombined.
   When a globule confined out of the contact  of air  is
 acted upon by water, the theory of decomposition  is 
347
very simple ;  the heat produced is rapidly carried  off,
so that there is no ignition ;  and a high temperature be-
ing requisite for  the solution of the basis in hydrogen,
this combination probably does not take place, or at least
it may have a momentary existence only.
   The production of alkali in the decomposition of wa-
ter by the basis of potash,  is demonstrated in a very
simple and  satisfactory manner by dropping a globule
of it upon moistened paper tinged with termeric  At
the moment that the glooule comes  into contact with
the water, it burns, and moves  rapidly upon the paper,
 as if in search of moisture,  leaving  behind it a deep
 reddish-brown trace, and  acting  upon the paper pre-
 cisely as dry caustic potash.
   So strong is the attraction of the basis of potash for
 oxygen, and so great the energy of its action upon wa-
 ter, that it discovers and decomposes the small quanti-
 ties of water contained in alcohol and ether, even when
 they are  carefully purified.
   In ether this decomposition  is  connected with an in-
 structive result   Potash is insoluble in  this fluid ; and
 when the basis of potash is  thrown into it, oxygen is
 furnished to it, and hydrogen disengaged, and the alka-
 li, as it forms, renders the ether white and turbid.
    In both these  inflammable compounds the energy  of
 its action is proportionable to the quantity of water  they
 contain,  and hydrogen and  potash  are the constant re-
 sult.
    The basis of potash,  when thrown into solutions  of
 the mineral  acids, inflames and burns on the surface.
 "When it is  plunged by proper means beneath the sur-
 face enveloped in potash, surrounded by naphtha, it acts
  upon the oxygen with the  greatest intensity,  and all its
  effects are such as may be explained from its strong af-
  finity for this substance.   In sulphuric acid a  white sa-
  line substance,  with a  yellow coating,  which is, proba-
  bly, sulphat of  potash  surrounded by  sulphur,  and a
  gas which has the smell of sulphurous acid, and which,
  probably, is a mixture  of that substance with hydrogen
  gas, are formed.   In nitrous acid, nitrous gas is disen
  gaged, and r.itrat of potash formed.
    The basis of potash readily combines  with the sirn- 
343
pfc inflammable solids, and with the metals ;  with phos-
phorus and  sulphur it forms compounds similar to the
metallic  phosphorets and  sulphurets.   When it  is
brought  in  contact with a  piece of  phosphorus  and
pressed upon, there is a considerable  action :  they be-
come fluid together,  burn,  and produce phosphoiat of
potash.  When the experiment is made under naphtha,
their combination takes place  without the liberation  of
any elastic matter,  and they form a compound which
has a considerably higher point of fusion than  its two
constituents,  and which remains a soft solid in boiling
naphtha   In its appearance it perfectly agrees with a
metallic phosphoret ;  it is of the colour of  lead, and,
when spread out, has a lustre similar to polished lead.
When exposed to air at  common temperatures it slow-
ly combines with  oxygen,  and becomes phosphat of
potash.  When heated  upon a plate of platina, fumes
exhale from it, and it does not burn till it  attains  the
temperature of the rapid  cor.ibustion of the  basis  of
potash.  W7hen the basis of potash is brought in  con-
tact with sulphur in fusion,  in  tubes filled  with the va-
pour of naphtha, they combine rapidly with the evolution
of heat and light, and a  grey substance, in appearance
like  artificial sulphuret  of iron,  is formed,  which,   if
kept in fusion, rapidly  dissolves the glass, and becomes
bright  brown.   When this  experiment is made in a
glass tube hermetically sealed, no gas is liberated  if
the tube is opened under mercury ; but when it is made
in a tube connected  with a mercurial apparatus, a small
quantity  of  sulphurated hydrogen is evolved,  so that
the phenomena  are  similar to those produced by  the
union of  sulphur with the metals in which sulphurated
hydrogen is  likewise disengaged, except that the igni-
tion is stronger.
  Copper filings and powdered sulphur, in weight in
the proportion of three to one,  rendered  very dry, were
heated together in a retort, connected with a mercurial
pneumatic apparatus.   At the  moment of combination
a quantity of elastic  fluid was  liberated, amounting to
nine or ten  times  the volume of materials employed,
and  which consisted  of sulphurated  hydrogen mixed
with sulphureous acid.  The first mentioned product, 
349
there is every reason to believe, must be referred to the
sulphur ; the last probably to  the copper, which,  it is
easy to conceive, may have become slightly and super-
fioially oxydated during the processes of filing and dry-
ing by heat.
   When the union  is effected in the atmosphere, a
great inflammation takes place,  and sulphuret of potash
is formed.   The sulphurated  basis likewise gradually
becomes oxygenated by exposure to the air, and is fi-
nally converted into sulphate.  The new substance pro-
duces some  extraordinary and beautiful  results  with
mercury.  When one part of it is added to eight or
ten parts of mercury in volume at 60° Fahrenheit, they
instantly unite and form a substance exactly like mercu-
ry in colour, but which seems  to have less coherence ;
for  small portions  of it appear  as  flattened spheres.
"When a globule is made to touch a globule of mercury
about twice  as  large, they combine with considerable
heat; the  compound is fluid at the temperature of its
formation ; but, when cool, it appears as a solid metal,
similar in colour to silver.   If the quantity of the basis
of potash is  still farther increased,  so as to be about
one thirtieth  the weight  of the mercury, the amalgam
increases in  hardness and becomes more brittle.  The
solid amalgam, in  which the basis is in the  smallest
proportion, seems to consist of about one part in weight
of basis,  and seventy parts of mercury, and is very
soft and malleable.
   When these compounds are exposed to air,  they ra-
pidly absorb oxygen ;  potash, which  deliquesces, is
formed, and in a few  minutes the mercury  is found
 pure and unaltered.
   When a globule of the amalgam is thrown  into wa-
ter it rapidly decomposes it, with a hissing noise ; pot-
ash is  formed,  pure hydrogen is disengaged, and  the
mercury remains free.
   The fluid amalgam of  mercury and  this substance
 dissolves all the metals I have exposed to it; and in
this  state  of union  mercury acts on iron  and  platina.
"When the basis of potash is heated  with  gold, or  sil-
ver, or copper, in a close vessel of pure glass,  it ra-
 pidly acts upon them;  and when the compounds  arg 
350
thrown  into water, this fluid is decomposed, potash
formed, and the metals appear to be separated unalter-
ed.
   The  basis of potash combines with fusible  metal,
and forms an alloy with it, which has a higher point of
fusion than the fusible metal.
   The action of the basis of potash upon the inflamma-
ble oily compound bodies, confirms the other facts  of
the strength of its attraction for oxygen.
   On naphtha, colourless  and recently distilled, as I
have already said, it has  very little power of action;
but in naphtha that has been exposed to the air, it soon
oxydates, and alkali is formed, which  unites with the
naphtha into a brown soap that collects round the glob-
ule.
   On the concrete oils, (tallow, spermaceti, wax, for in-
stance)  when heated it acts slowly, coaly matter is de-
posited, a little gas is evolved, and  a soap is formed ;
but in these cases it is  necessary that a large quantity of
the oil be employed.   On the fluid fixed oils it produces
the same effects,  but more slowly.
   By heat  likewise it  rapidly decomposes the volatile
oils ; alkali is formed,  a small quantity of gas is  evolv-
ed, and charcoal is deposited.
   When the basis of potash is thrown into camphor in
fusion, the camphor soon  becomes  blackened, no gas
is liberated in the process of decomposition, and a sapo-
naceous compound is  formed ; which seems to show
that camphor contains no more oxygen than the volatile
oils.
   The  basis of potash readily reduces metallic oxyds
when heated in contact with them.  When a small quan-
tity of the oxyd  of iron was  heated with it, to a tem-
perature approaching its point of distillation,  there was
a vivid action ; alkali and grey metallic particles, which
dissolved with effervescence in muriatic acid,  appeared.
   The  oxyds of lead  and the oxyds of tin were revi-
ved  still more rapidly ; and  when the basis of potash
was in  excess, an alloy was  formed  with the revived
metal.
   In consequence of this  property the basis of potash
readily  decomposes  flint  glass,  and green glass,  by a 
351
gentle heat; alkali is immediately formed by oxygca
from  the oxyds, which dissolves the  glass,  and a new
surface  is soon exposed to the  agent.  At a red heat
even the purest glass is altered by the basis of potash :
the oxygen in the alkali of the glass seems to be divid-
ed  between the two bases, the basis oi potash and the
alkaline basis in the glass and oxyds, in the first degree
of  oxygenation, are the  result.   When  the  basis of
potash is heated in  tubes made of plate glass, filled
with  vapour  of naphtha, it first acts  upon the small
quantity of oxyds of cobalt and manganese in the inte-
rior surface of the glass, and a portion of alkali is form-
ed.   As the  heat approaches to redness it begins to
rise in vapour, and condense in  the colder parts of the
tube ; but at the point, where the heat is strongest, a
part  of the vapour  seems to penetrate the  glass, ren-
dering it a deep red-brown colour ; and by repeatedly
distilling and heating the substance in a close tube of
this kind, it finally loses its metallic form, and a  thick
 brown crust, which slowly decomposes water, and which
combines with  oxygen when exposed to air, forming
 alkali, lines the interior of the tube, and in  many parts
 is  found penetrating through its substance.
    The basis of soda,  is solid at common temperatures.
 It  is  white opaque, and when  examined under a film of
 naphtha has the lustre and general appearance of silver.
 It is exceedingly malleable.   Its specific gravity is less
 than that of water about 9 to  10, or, 9348 to 1.
    The basis of soda has a much higher point of fusion
 than  the basis of potash, its chemical phenomena are
 analogous to those pioduced by the basis of potash.
    The proportions of the  peculiar basis, and oxygen
 in potash and soda are,  about six parts basis and one of
 oxygen in potash,  and seven parts of basis and two of
 oxygen in soda.
    PNEUMATIC CISTERNof Yale College.
  An instrument has been for several years used in the
laboratory of Yale College, for experiments in the large
way, on the gases which water does not rapidly adsorb,. 
352
which has been found to be more convenient and com-
plete than any other arrangement of apparatus  for si-
milar  purposes.  The only  instrument  of the kind
which has ever been  constructed,  was  manufactured
in New-Haven.   [See  Frontispiece.]   Being calculated
for an extensive course of  public lectures, delivered in
a laboratory where  there  is plenty of room, its dimen-
sions are larger than might be worth  while in establish-
ments on a smaller scale   It forms that of a parallel-
opipedon, 7 1-8 feet long, 3 feet wide, and 2 feet 2  inches
deep, without allowing for the two inch pine plank of
which this part of the instrument is constructed   The
several planks and parts are connected by grooves and
tongues, and bound together by  iron rods, passing lat-
erally through them, and terminating in screws furnish-
ed with nuts.   The interior part is  furnished with two
shelves, [A.A.A.A.] each two feet six inches long, for
sustaining air-jars  and bell-glasses; the middle  space
between these is one foot.eight inches wide, and forms
a well j_H] for immersing the bell-glasses ; across this
well is placed  a sliding shelf, [G] with three inverted
shallow tin funnels beneath it, corresponding with as
many holes for receiving and transferring gases.  Thus
far, it is obvious that the instrument is only a very ex-
tensive pneumatic cistern, and has no superiority over
those commonly in use, except from its affording ample
space for a veiy  important and interesting class  of ex-
periments, which are much more impressive and con-
vincing to a large audience, when performed on a large
scale.   There are, however, a  number  of additional
contrivances.  Beneath each of the shelves are two in-
verted rectangular boxes,  [shm-n by dotted lines at I. I.
i nd under A.A.A.A.] made of thin pine plank, dovetail-
ed together at the angles,  entirely open below, and at-
tached to the inferior  side of the shelves by tongues,
grooves, and wood-screws.  These boxes are twelve
inches deep, of  the capacity of about 12 gallons each,
and occupy the whole space beneatn the shelves except
7,5  inches  at  each end of the cisK-rn, and nine  inches
between the bottom  of the boxes and the bottom  of the
cistern. This latter space is reserved to give room  for the
action of three pair of hydrostatic  bellows.  [15. B] They
are made of leather, nailed to the bottom of the cistern 
353
distended by circular iron rings,  and attached by nails
to a thick circular plank which serves as a top, and which
is moved up and down by an  iron rod connected with
an iron lever, [C.C.C.j which rests on a forked iron sup-
port, attached to the upper edge of the end of the cistern.
The bellows are so placed, that nearly one half projects
beneath  the boxes, which we may call reservoirs ; the
other part is beneath the open space which lies between
the end  of  the reservoirs and  the  end of the  cistern,
and the rod of  the bellows perforates the  shelf imme-
diately at the termination of the box and contiguous to
it, but  does not pass through the box, which must be
air-tight.  At the  edge of that part of  the  bellows
which projects beneath the ieservoir, is a valve open-
ing upward ;  in the centre of the bellows  and on
the bottom  of  the cistern,  which is  also the bottom of
the bellows, is another valve opening upwards, covering
an orifice which is connected with a duct, leading out,
laterally, through the plank, edgewise, to the atmos-
phere.   Into this duct is inserted a copper tube, [D.D.]
consisting of two parts,  one of  which forms merely a
portion of the duct,  being driven into it so that it forms
a perfectly  tight connection ; the other part is soldered
to this at right angles, and ascends in close contact with
the outside of the cistern, till it rises two inches higher
than its upper edge, and there it  opens in  an orifice
somewhat dilated.   Each of the four reservoirs may be
considered  as furnished with the apparatus of  bellows,
duct, valves, and tube ; although in the instrument to
which this description refers, there are in fact but three
bellows, &c. one reservoir being destitute of them   It
remains to be remarked, that each reservoir is  furnish-
ed with a stop-cock, which lies horizontally  upon the
shelf and partly imbedded in it, and passes into the re-
servoir by a short tube of copper, soldered at right an-
gles  with the cock.  The cocks of the two  contigious
reservoirs are placed parallel  to each other and to the
sides of the cistern, and immediately contiguous to the
partition which  separates the reservoirs, and they are
connected by a third stop-cock soldered to each of them
opening into both by proper orifices, and thus serving,.
when occasion requires, to connect the reservoirs,  and.
 in fact, to convert two into one.   Through each of the
                        Ee2 
354
shelves, at the angles of the two reservoirs which are
contigiousat once to that side of the cistern which may
be regarded as its back  part,  and to ihe well, a hole is
bored into the  reservoir for the insertion of a copper
tube [E.E.]  for a blow-pipe.  These tubes are so  form-
ed, that while one part is pressed firmly into the hole so
as to be air-tight, another part, at right angles with the
first, and bending in a pretty large  curve, terminates in
a trumpet like orifice, adapted to the insertion of a  cork.
Immediately beneath these two orifices is a table, [F.]
attached  by hinges  to the side of the cistern, to sustain
a lamp for the blow-pipe ; when not in use, it hangs by
the side  of the cistern, and is raised occasionally,  as it
is wanted.
   To an intelligent chemist, it will be obvious from an
attentive perusal of the description,  that this  instru-
ment will afford  all the following advantages.
   1. It is an extensive pneumatic  cistern,  with  every
common convenience, on a large scale.
   '<j. By the bellows and their  appendages, common
air may be thrown  into the  reservoirs, by which means
the height of the water on the shelves may be increas-
ed at pleasure, when it is too low.
   3. By  permitting a portion of this air to escape, by
opening one of the horizontal cocks, the  height of the
water on the shelves may  be  diminished at pleasure ;
thus we  have means of graduating the  height of the
water precisely to our purpose, without lading it out or
in.
   4. We have  four capacious air-holders in the  very
place where the gases are produced, viz. in the pneu-
matic cistern ; thus, four different kinds of gases may
be stored away  under water in a space otherwise use-
less.  For instance, common air, for regulating the
height of the water, or, for  the blow-pipe, may  be in
one reservoir ; oxygen gas in  a second,  hydrogen gas
in a thud, and olefiant gas in a fourth, and they may
be thus reserved for future use.
   5. The gases may  be drawn off f r use into bell-
glasses,  merely by  bringing those bell t-lasses,  filled
with water,  over the horizontal cocks
   i. It is obvious that the four reseryoiis are in fac* 
355
four large gasometers ; they want nothing  to entitle
them to this character, e  cepiascalc which a  moderate
share of ingenuity would easily adapt to them  ; the gas-
ses may be delivered into them at once by crooked tubes
passing from the gas-bottles, and any gas contained in a
bell-glass may  be thrown into a reservoir, by a single
stroke of the  bellows.  For this purpose a crooked  tube
connected with that which leads to the bellows and ter-
minating in the well beneath an air jar, is  all that is ne-
cessary.  Or, by baring the arm, the gas may be thrown
up by the hand, into the reservoirs, the jar being pushed
down through the water.
   7  It affords an excellent blow-pipe for common pur-
poses and for  the fine experiments with oxygen gas ;
and, by fitting to it Mr. Hare's very ingenious apparatus
of the silver cylinder, it becomes the compound blow-pipe,
for the invention and application of which  he deserves
so much credit. By the same contrivance  water is form-
 ed with  the  greatest facility by burning the two gasses
 as they come from their respective reservoirs, and issue
 at the common orifice, covering the flame with a recei-
 ver.
   8. The inflammable gasses being confined beneath the
 pressure of water, will issue  at any orifices, where they
 are permitted, and thus all the  ornamental  as well as
 useful purposes  to which the combustion of these  gas-
 es is applied,  may be exhibited ;  particularly, the  gas
 from fossil coaL may be made to burn in revolving  jets,
 stars, and other fanciful and useful forms, merely  by
 substituting for a blow-pipe tube,  the apparatus proper
 for this exhibition.
    All these purposes, this instrument has fully answer-
 ed during several years ; and it  may  be  confidently re-
 commended to lecturers on chemistry, and, on a small-
 er scale would be very valuable  to a private chemist.
 A forcing pump might be substituted for the bellows,
 with the saving of the space which the bellows occupy,
 but it would be  probably less convenient in practice.
    This first idea of this instrument was  suggested by
 Mr  Hare's compound  blow-pipe.  Being  mentioned
 to that  gentleman,  the subject was prosecuted in com-
 mon, and so far matured that it was afterwards executed
 by  the writer, B. Silliman. 
35(5
    A1ANUFACTURE of AIINERAL  WATERS,

   The extensive utility of many of the natural mineral
 waters has been long established by the experience of
 mankind, and sanctioned by the opinions of the first
 medical practitioners of every  enlightened  country.—.
 The  accurate  analyses  of all the most important and
 most celebrated mineral waters has been accomplished,
 by men competent to the task ; and  we are thus in-
 formed not only concerning the nature, but  the propor-
 tion of  the  ingredients which  they contain.   They
 are either solid substances, such  as  water can  dis-
 solve, or gases capable of being combined with this
 fluid.  To both of these the  mineral waters owe their
 medicinal powers, and to the  latter alone, and chiefly to
 the carbonic  acid, the peculiar activity, briskness and
 pungency.
   In  the manufacture of artificial mineral  waters, the
 original  water  is perfectly imitated, by the  addition of
 all the ingredients in the proper proportions;  and the
 gas, by  a peculiar and very powerful apparatus is after-
 wards forced in,  till the waters  acquire  a degree of
 briskness and activity far surpassing any thing which
 they  ever  exhibit in nature  The impression enter-
 tained by some, that a perfect imitation  of the native
 mineral waters is impossible, is therefore equally con-
 trary  to the decision of good sense, as it is repugnant
 to experience ; for in London, in Paris, and in many
 other great  towns, artificial  mineral  waters are thus
 fabricated ; and used to a great extent.
   In the artificial waters, we always have it in our pow-
 er, to leave out noxious, or  useless  ingredients ;  to
 substitute others, and to vary the proportions at pleasure.
  Every  species of mineral waters whatever, can be
 prepared by art, but the principal ones that have  been
attempted in this country, are the  Ballstown, Soda, and
the Seltzer waters.

             BALLSTOWN WATER.

 ^  The  Ballstown  water is well known in the  United
States as a gentle cathartic,—an active diuretic,—a re- 
357
medy against gravelly complaints,—a  tonic to  the
stomach, and generally to the system ;—not to mention
its efficacy against rheumatic, and cutaneous complaints,
when applied externally, as well as internally  It re-
mains to  be  added,  only, that  the artificial  Ballstown
water is found by experience to produce the effects of
the  natural water :  it is however more powerful, and
therefore  an  equal  quantity produces more marked
effects.
                 SODA WATER.

   The Soda water is not an exact imitation of any natu*
 ral water, but has been directed by medical  men as a
 remedy in a number of common and troublesome com-
 plaints.   It is ordered in the  pharmacopeias and dis-
 pensatories, and their  prescriptions should be followed
 in this manufacture.  It is a  complete  remedy against
 sourness  of  the  stomach, commonly called  heartburn,
 and in most cases of indigestion and weakness of the
 stomach it is very useful; gradually  restoring the appe-
 tite, and  with it the tone of the organ ; it is a prevent-
 ative, of many of the diseases of the  stomach and bow-
 els. which proceed from acidity, and for the  same  rea-
 son it often removes or prevents the sick headache.
   As a palliative, and even a remedy, in some cases of
 urinary calculi and gravelly complaints, it is  preferable
 to tlie Ballstown  vvater.  It may prevent, arrest, retard,
 or remove the complaint according to circumstances.
   The Soda water is also very  refreshing, and to most
 persons a very grateful drink, especially after heat and
 fatigue, and-may be made a complete substitute for the
 beverages of which ardent spirits form a part.—With
 wine and sugar it is very grateful.

                SELTZER  WATER.
   The Seltzer* water has long been known, and is one  i
 the most famous of the natural mineral waters of Eu-
 rope   On  ccount of its agreeable taste, and exiiillira-
 liiv effects, it is largely used at table, and as  a beverage
 at all hour*.  It  is a diuretic, and possesses  contiMcra-
 bletflicacy  in ncphictic and urinary  complains ; it is
 very usctul ag..iii?t bilious and dyspeptic affections, and
 in many cases of cutaneous eruptions. 
358
  It possesses a peculiar power of allaying feverish  ir-
ritation, and has done much service in slow hectic fevers;
it mixes well with milk, and is thus used with advantage
by hectic patients.—It is used also with sugar & wine.
  The  manufacture  of mineral  waters  upon  correct
chemical principles was undertaken  in  New-Haven,.
Connecticut, about three years ago ; and during the last
summer, a public  establishment  for this purpose was
opened in ihe same town, under the direction of Profes-
sor Silliman.
  An establishment of  the same kind, and  under the
same direction was effected in  New-York in April  of
this year, (1809) by Noyes Darling 8c Co   Fountains
of Ballstown, Soda, and Sheltzer waters were opened in
the bar of the Tontine Coffee House.   The cisterns are
placed in the cellar, and the waters are conveyed into
the bar in block-tin tubes, which pass up into mahogony
pillars, crowned with gilt urns, lettered with  the names
of the respective waters.  The pillars, with their urns,
stand a foot  apart, and  the middle one is raised above
the others ; silver stop-cocks inserted into the sides  of
the pillars, give the whole  much neatness and richness
of appearance.
  The proprietors of this establishment intend, as we
understand, to open fountains at the City Hotel, in the
month of May, in a spacious room, fitted  up and orna-
mented in a handsome style, and adopted to the  accom-
modation of ladies as well  as  gentlemen.
  The  Ballstown  and Seltzer waters are prepared ac-
cording to an accurate analyis ; and in order to give the
Soda water its proper efficacy, it is made with the full
proportion of Soda directed by the dispensatories.
  The waters are bottled for  exportation, in any quan-
tity demanded.
  Soda water has been made  in New-York by Mr.
Usher, for a year or more, and  has had a good  reputa-
tion  and an  extensive sale.  It  has  been  sold  fiom a
fountain, and  in stone bottles.   We understand that he
is about to extend his establishment.
  There have been,  for some time, manufactories  of
mineral waters in the city  of Philadelphia, and we are
informed that these waters have been  extensively used. 
 
 
APPENDIX.



  DYEING.
                Principles of Dyeing.

   The  substances  commonly employed for clothing
 may be reduced to four ; namely, wool, silk, cotton, and
 linen.
   Permanent alterations in the  colour of cloth can only
 be induced two ways ; either by producing a  chemical
 change in the cloth, or  by covering its fibres with some
 substance which possesses the wished for colour.  Re-
 course can seldom or never be had to the first method,
 because  it is haidly possible  to  produce a  chemical
 change in the  fibre of cloth without spoiling its texture
 and rendering  it  useless.  The dyer, therefore, when
 he wishes to give a new colour to cloth, has always re-
 course to the second method.
   The substances employed for this purpose are called
 colouring matters, or dye stuffs.   They are for the most
 part extracted  from animal and vegetable  substances,
 and have  usually the colour which they intend to give
 to the cloth.
   Since the  particles  of colouring matter with which
 cloth, when  dyed,  is  covered, are transparent, it  fol-
 lows, that all the light  reflected from dyed cloth must
 be reflected, not by the dye stuff itself, but by the fibres
 of the cloth below the dye stuff.   The colour  therefore
 does not  depend upon the  dye  alone, but also upon the
 previous colour of the cloth.  If the cloth  be black, it
is clear that  we cannot  dye it any other colour whatev-
 er ; because  as no light in that case is  reflected, none
 can be transmitted, whatever dye stuff we employ.   If
 the clo'h were red, or blue, or yellow, we could not dye
 it any other colour except  black ; because, as  only  red
or  blue, or yellow  rays were reflected, no other could
                       G  g 
be transmitted.  Hence the importance of a fine white
colour, when cloth is to receive bright dyes.   It then
reflects all the rays in abundance, and therefore any
colour may be given, by covering it with a dye stuff
which transmits only some particular rays.
   If the colouring  matters were  merely spread over
the surface of the   fibres of  cloth by the dyer, the
colours produced might be very bright, but  they could
not be permanent ; because the colouring matter would
be very soon rubbed off ;  and would  totally disappear
whenever the cloth was washed, or even barely expos-
ed to the  weather.   The  colouring matter then, how-
ever perfect a colour it posseses, is of no value, unless
it also adheres so firmly to the cloth  that none of the
substances usually applied to cloth, in order to  clean  it,
&c. can displace  it   Now this can only happen,  when
there is a strong affinity between the colouring matter
and the cloth, and when they are actually combined  to-
gether in consequence of that affinity.
   Dyeing then is merely a chemical process, and con-
sists in combining a certain colouring matter with  fibres
of cloth.   This process can in no instance be perform-
ed, unless the dye  stuff be first reduced to its integrant
particles  ; for the attraction of aggregation  between
the particles of dye stuffs, is too great to be  overcome
by the affinity between them and the  cloth,  unless they
could be brought within much smaller distances than
is possible while they both remain in  a  solid form.   It
is necessary, therefore, previously to dissolve the colour-
ing matter in some liquid or other, which has a weak-
 er affinity for it than the cloth  has.  When the cloth is
 dipped into this solution, the colouring matter,  reduc-
 ed by this contrivance to a liquid state,  is  brought with-
 in the attracting distance ; the  cloth therefore acts upon
 it, and from its stronger affinity, takes  it from the  sol-
 vent and  fixes it upon itself.   By  this  contrivance  too,
 the equality of the  colour is in some  measure secured,
 as every part of the cloth has an  opportunity  of attract-
 ing  to itself the  proper proportion  of colouring parti-
 cles.
    The facility with which cloth imbibes a dye, depends
 iupon two things; namely, the affinity between the cloth 
3
 and the dye  stuff, and the affinity between the dye-stuff
 and its solvent.   It  is directly as the former, and in-
 versely as the latter.  It  is of importance  to preserve
 a due proportion between these two affinities, as upon
 that proportion much  of the accuracy of dying depends.
 If  the affinity  betwen the colouring matter  and  the
 cloth be too great, compared  with the affinity between
 the colouring matter and the solvent, the cloth will take
 the dye too rapidly, and it will be scarcely possible to
 prevent  its colour from  being unequal.   On the other
 hand, if the affinity  between  the colouring matter and
 the solvent  be too great, compared with that betvteen
 the colouring matter and the  cloth, the cloth will either
 not take the colour at all, or it will take it very slowly
/and very faintly.
    Wool has the strongest affinity for almost all colour-
 ing matters ; silk the next strongest, cotton a conside-
 rably weaker affinity, and linen the weakest affinity of
 all.  Therefore in order to dye cotton  or  linen, the dye
 stuff should in  many cases be dissolved in a substance
 for wliich it has a weaker affinity  than for  the  solvent
 employed in the dyeing of wool or silk.  Thus we may
 use oxyd of iron dissolved in sulphuric acid, in order to
 dye wool ; but  for  cotton or linen, it is better to dis-
 solve it in acetous acid.
    Were it  possible  to procure  a sufficient number of
 colouring matters,  having a  strong affinity for cloth, to
 answer all the purposes of dyeing, that art would be ex-
 ceedingly simple and easy.   But this is by no means
 the case ; if we except indigo, the dyer is scarcely pos-
 sessed ofadve stuff which yields of  itself a good colour,
 sufficiently  permanent to deserve the name of dye.
    This  difficulty,  which at first sight appears insur-
 mountable,  has been obviated by a very  ingenious  con-
 trivance.  Some substance is pitched upon, which has a
 strong affinity, both for the cloth and the colouring mat-
 ter.  This  substance is previously combined with cloth,
 which is then dipped into the solution containing the dye
 stuff.  The dye  stuff combines  with the intermediate
 substance, which, being firmly combined with the cloth,
 secures the permanence of  the  dye.   Substances  em-
 ployed for this purpose are denominated mordants,- 
                                  1 T™W^

                         4

   The most important part of dyeing, is undoubtedly the
proper choice, and the  proper application of mordants,
as upon them, the permanency of almost every dye de-
pends.  Every tiling which has been said respecting the
application of colouring matters, applies equally to the
application of mordants.  They must previously be dis-
solved in  some liquid  which has a weaker affinity to
them than the cloth has to which they are to be applied;
and the cloth must be dipped, or even steeped in this so-
lution, in order to  saturate itself with the mordant.
   Almost tlie only substances used as  mordants, are
earths, metalic oxyds, tan, and oil.
   Of earthy  mordants, the most important,  and most
generally used, is alumine.  It is  used  either in the
state of common alum, in which it is combined with sul-
phuric acid, or in that of acelite of alumine.
   Alum, when used as a mordant, is dissolved in water,
and  very frequently a quantity of tartar is dissolved
along with it.  Into this solution the cloth is put, and
kept in it till it has absorbed as much allumine as is ne-
cessary.  It is then taken out,  and for the most part
washed and dried.  It is now a good deal heavier than
it was before, owing to the allumine which has combined
with it.  The tartar  serves  two purposes ; the potash
which it contains  combines  with the sulphuric  acid of,
the  alum, and thus  prevents that very corrosive rub-
stance from injuring the texture of the cloth, which oth-
erwise might happen ; the tartareous acid, on the other
hand, combines with part of the alumine, and forms  a
tartrit of alumine, wliich is more easily decomposed by
the cloth than alum.
   Acetite of Alumine  has been but lately introduced into.
dying.   This mordant is now prepared by pouring ace-
tite of lead into a  solution of alum ;  a double decompo-
sition takes place, the  sulphurious  acid combines with
the lead, and the compound precipitates in the form of an
insoluble powder, while the  alumine combines with the
acetous acid, and remains dissolved in the liquid.  This
mordant is employed for cotton  and linen, which have
a weaker affinity than wool  for  alumine.   It answers
much better than  alum ; the cloth is more easily  satur-
ated with alumine, and takes in consequence, both a rich-
 er  and a more permanent colour. 
5
   Besides alumine, lime is sometimes used as a mordant;
Cloth has a strong enough affinity for it; but, in gene-
ral, it does not answer so well, as it does not give so good
a colour.  When used, it is either in the state of lime
water, or of sulphat of lime dissolved in water.
   Almost all the metalic oxyds have an affinity for cloth,
but only two of them are extensively used as mordants,
namely, the oxyds of tin, and of iron.
   The oxyd of tin was first introduced into dyeing  by
Kuster, a German chemist, who brought the secret to
London in 1543.  This period forms an era in the his-
tory of dyeing.   The oxyd of tin has enabled the  mod-
erns greatly to surpass the ancients in the finess of their
colours ; by means of it alone, scarlet, the  brightest of
all colours is produced
   Tin, as Proust has proved, is  capable of two degrees
of oxydation   The  first oxyd  is composed  of 0.  70
parts of tin,  0. 30 of oxygen ; the second, or white oxyd,
of o. 60 parts of tin, and O. 40 of oxygen. The first oxyd
absorbs oxygen with very great facility, even from the
air, and is rapidly converted into white oxyd.  This fact
makes it certain, that it is the white oxyd  of tin alone,
which is the real mordant; even  if the other oxyd were
applied to cloth, as it probablv  often is, it must soon be
converted into  white oxyd, by absorbing  oxygen  from
the atmosphere-
   Tin is used as a mordant in three states ;  dissolved
into nitro muriatic acid, in acetous acid, and in a mixture
of sulphuric and muriatic  acids.  Nitro  muriat of tin
is the common mordant used by  dyers.  They prepare
it by dissolving  tin in diluted nitric acid, to which a cer-
tain proportion of muriat of soda, or of ammonia is ad-
ded.  Part  of the nitric acid decomposes  these  salts,
combines with their base, and sets the  muriatic acid at
liberty  1'hey prepared it at first, with  nitric acid alone,
but that mode was very defective,because the nitric acid
very readily converts tin to white oxyd, and then is  in-
capable of dissolving it.   The  consequence  of which
was, the precipitation of the whole of the tin.  To rem-
edy this defect,  common salt, or salt ammoniac, was ve-
ry soon added ;  muriatic acid  having  the  property of
dissolving white oxyd of tin very readilyt   A conside-
                       Gg 2 
6
T
rable saving of nitric acid might be obtained by employ--
ing as much sulphuric acid as is just sufficient to satu-
rate the base of the common salt, or  sal ammoniac em-
ployed.
   When the nitro muriat of tin is to be used as a mor-
dant, it is dissolved in a large quantity of water, and the
cloth is dipped in the solution, and allowed to remain till
sufficiently saturated.  It is then taken out and washed   i
and dried.  Tartar is usually  dissolved  in  the water
along  with  the nitro muriat.  The consequence of this
is a double decomposition, the nitro muriatic acid com-
bines with the potash of the tartar, while the tartareous
acid dissolves the  oxyd  of tin.   When tartar is used,
therefore, in any considerable quantity, the mordant is
not a nitro muriat but a tartrit of tin.
   Iron, like tin, is capable of two degrees of oxyda-
tion ;  but the green oxyd  absorbs oxygen  so readily,
from the atmosphere, that  it is  very soon converted
into the red oxyd.  It is only  this last oxyd  which is
really used as a mordant in dyeing   The green oxyd
is indeed, sometimes applied to cloth ; but it very  soon
absorbs oxygen, and is converted into the red oxyd.—
This oxyd has a  very  strong affinity for all kinds of
cloth.  Tfyepermanency of the iron spots on  linen and "
cotton is a sufficient proof of this.   As a mordant, it is
used  in  two  states : in that of sulphat of  iron,  and
acetite of iron   The  first is commonly used  for wool.
The salt is dissolved in water,  and the cloth dipped in
it.   It  may be used  also  for cotton, but in most cases
acetite of iron is preferred.   It is prepared by dissolv-
ing iron, or its oxyd, in vinegar, sour beer, Sec. and the
longer it is kept, the  more  it is preferred.   The  rea-
son is, that this mordant succeeds best when the iron is
in the state of  red oxyd.  It would be  better then to
oxydate the iron,  or  convert it inio rust, before using
it; which might easily be done, by keeping  it  for some
time in a moist place, and sprinkling it occasionally  with
water.
   Tan has a  very strong affinity for cloth, and for se-
veral colouring matters ; it is therefore very  frequently
employed as a mordant   An  infusion  of nut-galls, or
of  auv,.acht  or any other  substance containing tan, i> 
7
made in water, and the cloth  is dipped in this infusion,.
and allowed to remain  till it  has absorbed a sufficient,
quantity  of tan.  Silk is  capable of absorbing a  very
great proportion of tan, and by that means acquires  a
great increase of weight.  Manufacturers sometimes
employ this method of increasing the weight of silk.
   Tan is often employed also, along with other  mor-
dants, in order to produce a  compound mordant.   Oil
is also used  for the same purpose, in the dyeing of
cotton and  linen.   The mordants with which tan  most
frequently is combined,  are alumine and oxyd of iron.
   Besides  these mordants, there are several other sub-
stances frequently  used as auxiliaries, either to  facili-
tate the combination  of the mordant with the cloth, or
to alter the shade of colour; the  chief of these are,
tartar, acetite of lead,  common  salt, sal ammoniac, sulphat
or acetite of copper, Sec.
   Mordants not only render the dye  permanent, but
have also  considerable influence on the colour produ-
ced.   The same colouring matter produces very dif-
ferent dyes, according as the mordant is changed.   Sup-
pose,  for instance, that the colouring matter be cochi-
neal ;  if we use  the  aluminous mordant, the cloth will
acquire a crimson colour ; but the oxyd of iron produ-
ces with it a black.
   In dyeing then  it is not only necessary to procure a
mordant which has a sufficiently strong affinity for the
colouring matter and the cloth, and a colouring matter
which possesses the wished  for colour in perfection,
but we must procure a mordant and a colouring matter
of such  a  nature, that  when combined together,  they
shall possess the wished  foi colour in perfection.  It  is
evident too, that a great variety of colours may be pro-
duced with a single dye stuff, provided we  can change
the mordant sufficiently.
   The colouring matter with which the cloth is  dyed,
does not  cover every portion of its surface ; its parti-
cles attach themselves to the cloth  at certain distances
from each other ; for the cloth may be dyed different
shades of  the same  colour, lighter or darker, merely
by varying the  quantity of  colouring  matter.   With
■x small quantity, the shade  is  light j and it becomes 
8
deeper  as the  quantity increases;  now  this would be
impossible, if the dye stuff covered the whole of the
cloth.
  That the particles of colouring matter, even  when
the shade  is deep,  are at some  distance, is  evident
from this well known fact, that cloth may be dyed two
colours  at  the same  time.   All  those  colours to
which the dyers give the name of compound, are in
fact two different colours applied  to the cloth  at once.
Thus cloth gets a green colour, by being dyed first
blue and then yellow.
  The  colours  denominated by dyers simple,  because
they are the foundation of all their other processes, are
four; namely,  first, blue;  second,  yellow;  third, red;
fourth,  black.   To these they usually add a fifth, under
the name of root or brown colour.

                   Of Dyeing Blue.
  The  only colouring matters employed in dying blue,
are woad and indigo.
   Woad is a plant cultivated in  this kingdom, and even
growing wild in some parts of England.
  Indigo  is a blue powder, extracted from a species
of plants  which is  cultivated for that purpose in  the
East and West Indies.  These plants contain a pecu-
liar green pollen, which in that state is soluble in water.
This  pollen has a strong affinity lor oxygen, which it
attracts greedily from the atmosphere ; in consequence
of which it assumes a blue colour, and becomes insolu-
ble in water.
  Indigo  has a very  strong affinity for wool, silk, cot-
ton and linen.   Every kind of cloth,  thereiore,  may
be dyed with it, without the assistance of any  mordant
whatever.  The  colour thus induced  is very perma-
nent ; because  the  indigo is already saturated  with ox
yge"  and because it is not liable to be decomposed by
those substances, to the action of which the cloth is ex-
posed.  But  it can  only be applied to cloth in a  state
of solution ; and the only solvent known being sulphu-
ric acid, it would seem at first sight,  that the sulphu-
ric acid solution is the only state in which indigo can be
employed as a dye. 
9
  The sulphat of indigo is  indeed  often used to dye
wool  and silk blue; but it can scarcely  be  applied
to cotton and  linen, because the affinity of these sub-
stances  for  indigo is not great enough to enable them
readily to decompose the sulphat.  The colour given
by  sulphat  of indigo is exceedingly beautiful;  it  is
known by the name  of  Saxon blue.

                 Of Dyeing Yellow.
  The  principal colouring  matters for dyeing yellow
are weld, fustic, and quercitron bark.
   Weld is a plant which grows in this country.
  Fustic is the wood of a large tree which grows in the
West Indies.
   Quercitron is a tree growing naturally in North Amer-
ica, the bark of which  contains colouring matter.
   The yellow dyed by means of fustic is more perma-
nent, but not so beautiful as that given by weld, or quer-
citron.   As  it is permanent,  and not much injured by
acids, it is often used in dyeing compound colours, where
a yellow is required. The mordant is alumine. When
the mordant is oxyd of iron, fustic dyes a good perma-
nent drab colour.
   Weld and quercitron bark, yield nearly ihe same kind
of colour ;  but as the bark yields colouring matter in
much greater abundance, it is much more convenient,
and upon the whole  cheaper than weld.   It is probable,
therefore, that it will gradually  supercede the use of
that  plant.   The  method  of using each  of these dye
stuffs is nearly the same.

                   Of Dyeing Red.
   The colouring matters employed for dyeing red, are
kermc:--, cochineal, archil, madder, carthamus, and Brazil-
wood.
   Kcrmes is a species  of insect, affording a red colour
by solution in water  ; but it  is not so beautiful  as cochi-
neal, which is likewise an insect found  in America.—
The decoction of cochineal  is a very beautiful crimson
colour   Alum brightens the colour of the decoction,
and occasions a crimson precipitate.  Muriat of tin gives
a copious flue red precipitate. 
10
  Archil, is a paste formed of a species of lichen pound-
ed,  and kept moist for some time with stale urine.
  Madder is the root of a well known plant.
  Carthamus is the flower of a plant cultivated in Spain
and the Levant.  It contains two colouring matters ; a
yellow, which  is soluble in water, and a red. insoluble in
water, but soluble  in alkaline carbonats.   The  red cob
ouring matter of  carthamus, extracted by carbonat of
soder, and precipitated by lemon juice, constitutes the
rouge used by  ladies as a paint.   It is afterwards ground
with a certain  quantity of talc.   The fineness- of the talc,
and the proportion of it mixed with the carthamus, oc-
casion the difference between the  cheaper and dearer
kinds of rouge.
  Brazil wood, is the wood of a tree growing in Amer-
ica  and the  West Indies.  Its  decoction is a  fine red
colour.
  None of the red colouring matters have so strong an
affinity for cloth as to produce a permanent red, without
the assistance of mordants.  The mordants employed
are alumine, and oxyd of tin ; oil, and tan, in certain pro-
cesses, are also used ; and tartar and muriat of soder
are frequently called in t.s auxiliaries.
  Wool  may  be dyed scarlet, the most splendid of all
colours,  by first  boiling it in a solution of murio sul-
phat of tin, then dying it  pale yellow with quercitron
bark,  and afterwards  crimson,  with cochineal :  for
scarlet is a compound colour consisting of crimson mix-
ed with a little yellow.
  Silk is usually  dyed red with cochineal, or cartha-
mus, and  sometimes with Brazil wood.   Kermes does
not answer for silk ; madder is scarcely ever  used for
that purpose,  because it  does not yield a colour bright
enough.   Archil is employed to give  silk a bloom ; but
it is  scarcely  used by itself, unless when the colour
wanted is lilac.
  Silk may be dyed crimson by steeping it  in a solu-
tion of alum,  and then dying it in the usual way in  a
cochineal bath.
  Silk cannot be dyed a  full scarlet ; but a colour ap-
proaching to scarlet may  be given it, by first impregna* 
ting the stuff with murio sulphat of tin, and afterwards
dyeing it in a bath, composed of four parts of cochineal,
and four parts of quercitron bark.  To give the colour
more body, both  the  mordant and the dye may be re-
peated.  A colour approaching scarlet may be  also
given to  silk,  by first dying it crimson,  then dying it
with carthamus,  and lastly, yellow without heat.   Cot-
ton and linen are dyed red with  madder.  The process
was borrowed from the East.  Hence, the colour is of-
ten called Adrianople, or Turkey red   The cloth is
first impregnated with oil, then with galls,  and lastly
with alum.  It is then boiled for an hour in a decoction
of madder, which is commonly  mixed with a quantity
of blood.  After the cloth is dyed, it is  plunged into a
 soda ley,  in order to brighten  the  colour.   The  red
 given by  this process,  is very permanent,  and when
 properly  conducted,  it is exceeding beautiful.   The
 whole difficulty consits in the application of the mor-
 dant,  which  is by far the most complicated employed
 in the whole art of dying.

                   Of Dyeing Black.
    The substances employed to give a black colour to
 cloth are, red oxyd  of iron, and tan.  These two sub-
 stances  have a strong affinity for each other ;  and when
 combined, assume a deep black colour,  not liable to be
 destroyed by the action of air or light.
    Logwood is usually employed as an  auxiliary, be-
 cause it communicates lustre,-and adds considerably to
 the fullness of ihe black.   It is  the wood of a tree which
 is a native of several of the West India islands, and of
 that part of Mexico which surrounds the Bay of Hon-
 duras.  It yields its  colouring  matter  to  water.   The
 decoction is at first a fine red, bordering on violet;  but
 if left to  itself, it  gradually  assumes a black colour.
 Acids give it a  deep red colour ; alkalies a deep violet,
 inclining to brown ;  sulphat of iron renders it as black
 as ink. and occasions a precipitate of  the same colour.
    Wool  is  dved black by the  following process: It is
  boiled for two  hours in a decoction of nut-galls,  and af-
  terwards kept for two hours more in a bath composed
 of logwood  and sulphat of iron, kept during the whole 
12
 time at a scalding heat, but not boiled.   During the op-
 eration it must be frequently exposed to  the air ; be-
 cause the green oxyd of iron, of  wliich the sulphat  is
 composed, must be converted into red oxyd by absorb-
 ing oxygen,  before the cloth can acquire a proper col-
 our.  The common proportions are five parts of galls,
 five of sulphat of iron, and thirty of logwood,  for every
 hundred of cloth.  A little  acetite of  copper, is com-
 monly  added to the sulphat of iron, because it is thought
 to improve the colour.
    Silk is dyed nearly in the same manner.  It is capable
 of combining with a great deal of tan ; the quantity giv-
 en is varied at the pleasure of the artist, by allowing the
 silk to  remain a longer or shorter time in the decoction.

              Of Dying Compound Colours.
   Compound colours are produced by mixing together
 two simple ones ; or,  which is the same thing,  by dy-
 inpj cloth  first one simple colour,  and then another,-—
 These colours vary to infinity, according to the propor-
 tions of the ingredients employed.   They may  be ar-
 ranged under the following classes :
   Mixtures of 1. Blue and yellow ; 2.  Blue and  red;
 3.  Yellow and red ; 4. Black, and other colours.
   Alixturcs  of blue  and yellow.    This  forms green,
 which is distinguished by dyers into a variety of shades,
 according to the depth of the shade, or the prevalence
 of  either  of  the component parts.   Thus we  have
 sea-green, grass-green, pea-green, &c.
   Wool,  silk, and  linen,  are  usually  dyed  green,
 by  giving them first a blue colour,  and afterwards dy-
 ing them  yellow ; because, when the yellow is first
 given, several inconveniences4bllow :  the yellow part-
 ly separates  again in the blue vat,  and communicates
 a green colour to it,  and thus  renders it useless for ev-
 ery other purpose, except dying green.   Any  of the
 usual processes for dying blue and  yellow  may be fol-
 lowed,  taking  care  to  proportion the depth of the
 shades to  that  of the green required.   When  sulphat
 of indigo is  employed, it is usual to mix all the ingre-
 dients together, and to dye the cloth at  once ; this pro-
 duces what is known by ihe name of Saxon, or English
green. 
13
   Mixtures of  Blue and  red.  These form  different
 shades of violet, purple, and lilac.   Wool is generally
 first  dyed blue, and  afterwards  scarlet, in the usual
 manner.  By means of cochineal mixed with  sulphate
 of indigo, the process may be performed at once.   Silk
 is first dyed crimson, by means of cochineal,  and then
 dipped into the indigo vat   Cotton and linen are first
 dyed  blue, then  galled,  and soaked in a decoction of
 logwood ; but a more  permanent  colour  is  given by
 means of oxyd of iron.
   Mixtures of yellow and red.   This produces orange.
 When blue is combined with red and yellow  on cloth,
 the  resulting colour is  olive.  Wool  may be dyeU  or-
 ange, by first dyeing it scarlet, and then yellow. When
 it is dyed first with madder, the result is cinnamon col-
 our.
   Siik is dyed orange by means of carthamus ;  a cin-
 namon colour by logwood, Brazil-wood, and fustic mix-
 ed together.
   Cotton and linnen receive a cinnamon colour by means
 ol weld  and madder ; and an olive  colour, by being
 passed through a blue, yellow, and then a madder bath.
   Alixtures of black with other colours.  These consti-
 tute greys, drabs, and  browns   If cloth be previously-
 combined with brown oxyd of iron,  and afterwards dved
 yellow with  quercitron bark, the result will be a drab
 of different shades, according to the proportion  of mor-
dant employed.  When the proportion is  small, the
colour inclines to olive or yellow ; on the contrary, the
drab may be deepened or saddened, as the dyers term
it, by mixing a little sumach with the bark.
                    TANNIAXZ.
   Tanning is the art of converting the  raw skins of
animals into Leather.  Skins are the general term for the
skins of calves, seals, hogs, dogs,  &c.  As  the meth-
ods of tanning in  general use have been found tedious
and  expensive in their  operation,  various schemes, at
different  times,  have been  suggested to shorten the
process and lessen the expense.
                       G g 
14
   Much light has been  thrown by  modern chemists
 upon the theory of tanning.   M. Seguin,  in  France,
 has particularly distinguished himself  by his researches
 on this  subject,  and  much  improved the art in  his
 country.
   A few years since W. Lesmond  obtained a patent
 for practising Seguin's method in England.  He  ob-
 tained the tanning principle by digesting oak bark, or
 other proper materials, in cold water, in  an apparatus
 nearly similar to that used in the saltpetre works :——.
 That is to  say, the water which has  remained upon  the
 powdered  bark a certain time, in one vessel, is drawn
 off by a cock, and poured upon fresh tan—this  is again
 to be drawn oft", and poured  upon other fresh tan ; and
 in this way the process is to be continued to the fifth ves-
 sel.   The  liquor is  then highly coloured,  and marks
 from six to  eight degrees  upon  the  hydrometer for
 salts.  This he calls the tanning lixivium.   The crite-
 rion for ascertaining its strength,  is the quantity of the
 solution of gelatine which a  given  quantity of it will
 precipitate.  Isinglass is used for this purpose,  being
 intirely composed of  gelatine.  And here it  may be
 observed, that this is the mode of ascertaining the quan-
 tity of tanning principle in any vegetable substance, and
 consequently how far ihey may be used as a substitute
 for oak bark.
   The hides, after being prepared in the  usual way,
 are immersed for some hours in a weak tanning lixivi-
 um of only one or two degrees ; to obtain which,   the
 latter portions of the  infusions are set apart,  or  else
 some of  that which has been partly  exhausted by  use
in tanning.   The  hides  are then to be  put into a strong-
er lixivium, where, in a few days, they will be  brought
to the same degree of saturation with the liquor in which
they are  immersed.   The strength of the  liquor  will
by this means be considerably  diminished, and must
therefore be renewed.  Wfien the hides are by  this
means completely saturated, that is  to say, perfectly
tanned, they are to be removed, and slowly dried in the
 shade.
  The length of time necessary  to tan leather com-
pletely, according to the old process,  is certainly a ve- 
LO
ry great inconvenience ; and there is no doubt but that
it may be much shortened by following the new meth-
od.  It has been found,  however, that the  leather so
tanned has not been so durable as that which has been
formed by a slower process.
  The public is much indebted to Mr. Davy, professor
of chemistry in the Royal  Institution, for the attention
which he has paid to the subject. From his excellent pa-
per " on the constituent parts of astringent vegetables,"
in the Philosophical Transactions, we present the read-
er with the following extract.—
  " The different qualities of leather  made  with the
same kind of skin, seem to depend  very much upon
the different quantities of extractive matter it contains.
The leather obtained  by means of infusions of  galls,  is
generally found harder,  and more liable to crack, than
the leather  obtained  from the infusions of barks ; and
in all cases it contains a much larger proportion of tan-
nin, and  a smaller proportion of extractive matter.
   •' When skin is very slowly tanned in weak solutions
of the barks, or of catechu, it combines with a consid-
erable proportion of  extractive matter ;  and in  these
cases, though  the  increase of weight of the  skin  is
comparatively  small, yet it is rendered perfectly inso-
luble in water,  and  is found soft,  and at the same time
strong.  The saturated  astringent infusions of  barks
contain much less extractive  matter in  proportion  to
the  tannin, than the weak infusions ; and when skin
is quickly  tanned in them, common  experience shews
that it produces leather less durable than the leather
slowly formed.
   "  Besides, in the case of quick tanning by means of
infusions of barks,  a quantity of vegetable extractive
matter is lost to  the manufacturer,  which might have
been made to enter into the composition of his leather.
These observations shew, that there is some foundation
for the  vulgar opinion of  workmen, concerning what
is technicr.lly called the feeding of leather in the slow
method of  tanning ;  and though the processes of the
art may in some  rases be protracted for an unnecessary
length of  time, ye', in general, they appear to have
arrived,  in  consequence of  repeated practical experi- 
1(3
ments, at a degree of perfection which cannot be very
far extended  by means of any elucidations  of theory
that have as yet been known.'''
  It was first suspected by  Sir Joseph Banks, and af-
terwards confirmed  by the experiments of Professor*
Davy, that a substance called catechu or terra Japonica,
brought from the East Indies contained a vast quanti-
ty of tannin ; so much so that it far excels every other
known substance in this respect.   Owe pound of catechu
contains as much tannin as eight or ten pounds of com-
mon oak bark, and would consequently tan proportion*
ately  as  much more leather.   It is an extract made
from the wood of a  species of mimosa,  by decoction
and subsequent evaporation.
  Oak bark being a very expensive article in the  pro-
cess of tanning, various substances have been proposed
as substitutes for it.   All the parts of vegetables which
are of an astringent nature, contain tannin (which may
be known by their giving precipitates with gelatine,
insoluble in water), and  will answer this purpose.   The
leaves, branches, fruit, flowers,  of a  vast number of
plants ; every part of the oak, as the leaves and acorns,
oak saw-dust, and the barks of almost all trees, contain
mure or less tannin..
                   CURRY IYG.
   Currying is the art of dressing cow-hides, calves-
skins, Sec   The principal object in this process,  is to
soften and supple cow and calfskins, which are usually
employedin makingupper-leaihers and quartersof shoes
the covers of saddles,  coaches,  Sec.  As soon as these
skitis are  brought  from the tanner's yard,  the currier
first soaks them for  some time in common water, when
he tti.es them out,  stretches them on a smooth wooden
horse, scrapes off with a paring knife all the superfluous
flesh, and immerses them again.  They are next put
on a  wet hurdle,  and trampled with the heels, till  they
become soft and pliant, when they are steeped in train-
oil, and afterwards spread out on large tables, and their
ends tightly secured.  There, by means of  a pummel. 
17
(an instrument consisting of a thick piece of wood, the
lower side of which is full of furrows,  or teeth, cros-
sing each other), the currier folds, squares,  and moves
the skins in various directions, to render them supple.
This operation is properly called  currying ;  and,  with
a few immaterial exceptions, is that now  generally fol-
lowed.
   After the skins are thus dressed, they  are coloured,
black,  white, red,  green,  8cc.  which  process  is per-
formed either on the flesh or grain side  ; that on the
former, by skinners,  and  that on the grain or hair side,
by curriers ;  these, when a skin  is to be made white,
rub it  with chalk,  or white-lead,  and  afterwards with
pumice-stone.  But,  when  a black  colour  is wanted)
the skin must be first oiled and dried, then passed over
a puff,  dipped in water impregnated with iron, when it
is immersed in another water prepared with soot,  vine-
gar, and gum-arabic  Thus it gradually acquires a
deep dye, and the operations are repeated  till it becomes
of a shining black.   The grain and wrinkles, which
contribute to the pliancy of calves  and cows leather, are
made by the  reiterated folds given to the skin in every
direction, and by the great care taken  to scrape off ev-
ery excrescence and  hard place on the grain? or colour-
 side. 
INDEX.
              A

   Absorbents,  306
Acetous fermentation,  266
———acid, 248  266
Acidulous   gaseous   mineral
   waters, 220
-  - - - ■  salts. 250
Acids, 101. 191
Affinity,  8
Agate, 173
Agriculture, 274
Air  66
Albumen, 291, 297
Alburnum. 285
Alchemists, 3
Alcohol, or spirit of wine, 257
Alembic  99
Alkalies  ijo
Alkaline earths, 151,  173
Alloys  144
Alum, or sulphat of alumine,
   hi  203
Alumine, 171
Amalgam, 146
Ambergris, 335
Amethyst, 173
Amianthus, 177
Ammonia, or volatile alkali,
   152.  160
Ammoniacal gas,  163
Analysis, 114
Animals, 291
Animal acids,  192 298
------heat, 324
------oil  332
/nimaiization   291.  3OI
Antimony, 6  136
Aqua fortis, 208
------regia, 14a
Areck, 261
Arganos'- la up, 80
Arsenic,  6
Ashphaltum,  270
Assafcetida, 243
A stringent principle, 249
Atmosphere,  65
Atmospherical air,  66
Attraction  of aggregation,  or
  cohesion, 14
------of composition,  6. 181
Azote, or nitrogen, 206
Azotic gas, 65

              B

Balloon!>, 96
Balsams,  232
Bark, 204
Barytes,  i65
Basis of acids, 102
_ -  -  . - gasses, 66
- -  -  . - salts, 152
Beer,  255
Benzoic acid, 19a
Bile, 291, 3°7
Birds,  30 '->
Bismuth, 6
Bitumens, 270
Black lead, or plumbago, 114
Bleaching,  H4>  "3
Biock tin, 14a
Blood, 292
Boiling water 34
Bombic acid,  193  336
Bone-, 292  302
Boracic acid,  190
Brandy,  265
Brass.  144
Bread, 273
Bricks 16a
Butter 334
Butter-milk, 334
              C
Calcareous earths,  175 
ISSDEX.
..... ftones, 175
Caloric. 13
Calorimeter, 63
Camphor, 232
Camphoric acid.  19a
Caoutchouc, 232
Capacity for heat,  47
Carbonats, 221
Carbonat of ammonia, 16a
......  lime,  175
.....  magnesia,  176
.... -  potash, 154
Carbonated  hydrogen gas, 125
Carbone,  111
 Carbonic acid,  117.  2lj
Carburet of iron, 124
 Carmine, 300
 Castor, 336
 Cellular membrane, 309
 Caustics, 147
 Ch*lk 175
 Charcoal, 11a
 Cheese, 335
 Chemical attraction,  6
 .....heat  78
 ..... folution> 141
 Chemistry, 3
 Chest, 306
  China, 16a
  Chroma,  . 14°
  Chyle, 292. 3°7
  Chyme. 306
  Citric acid, 19a
  Circulation of  the blood, 307
  Civet  336
  Clay, 161
  Coak, 270
  Coal. 270
  Cobalt, 6
  Cochineal, 30Q
             by ©xy-muriirtic
 acid, 22
          of carbone, HI
          of coals 80
         of charcoal by nitric
 acid, ao6
          of candles, 83
          of iron, 130
          of lamps.  80
          of metals, 130
          of oils 231
          of oil of turpentine
  by nitrous  acid, 183
          of phosphorus.  105
           of  sulphur, 100
Compound bodies, 6
Compound, or neutral salts,
  15*
Conductors of heat, %"]
Constituent parts, 5
Copper, 13a
Copal  a43
Cortical layers, 284
Cotyledons,  or lobes, 279
Cream, 331
Cream of tartar, or tartit of pot*
   ash, 250
Crystals, 174
Crystallization, 141
 Cucurbit, 99
 Curd, 334
 Cuticle, or epidermis,  309
De composition, s
             of vegetables, 250
Deflagration, 230
Deliquescence, 291
Detonation, 89
Dew, 40
^
Cold, 18                          -
Colours of metallic oxyds, 13a  Diamond,  115
Columbium,  6.  146           Diaphragm, 306
Combustible  bsches,  7a        Digeftion,  305
Combustion,  73               D.velent forces,  186
  _______.....  volatile products Dissolution of metals, 138
    r  .g                      Distillation, 99
____'________fixed products of               of red wine 260
   «6                         Div sion, 5
„_________..  of amoiuacal gas, Drying oils, 241
   16a 
Dyeing, 233
Earths, 164
Earthen ware, 173
Effervescencf,  iaa
Efllorescence, 193
Elective attractions, 98
Elementar  bodies, 6
NDEX.

   Fuller's earth, HO"

                 G

   Galls, ao4
   Gallat of iron, 204
   Gallic acid, 19a. 2o4
   Galvanic electricity, 135
   Gas. 66
   Gaseous  oxyd  of carbone,
1
Elixirs, tinctures, or quintescen-                  nitrogen
  ceS) »6a                    Gastric juice, 292
129
an
Enamel, 16a
Epidermis of  vegetables, 384
Epsom salts,  175
Equilibrium of caloric, 18
Essences, 281
Essential, or  volatile oils, I2J
Ether. 263
Evergreens, 287
Eudiometer,  108
Expansion of caloric, 14
Extractive colouring matter,
   33 a. 3JO
Gelatine, or jelly. 293
Germination, 290
Gin. 261
Glands, 307
Glass  157
Glauber's salts, or  sulphat  of
   soda, 155. 186
Glazing, 162
Glucina, i64
Glue, 393
Gluten,  336
Gold,  134
Gum,  33J
     arabic, 33^
     resins.  333
 Gunpowder, 228
 Gypsum, or plaister of Paris,
   or sulphat of lime, 303
H
Falling (tones, 143
Fat, 125
Feathers, 304
Fecula, 33a
Fermentation, 306
Fibrine, 397
Fifh, 133               ..     .    t
Fixed air, or  cabonic acid, 116 Hair, 307
   zjj                        Harrowgate water, 10*
     alkalies, 151              Hartshorn, 160
     oils,  laj. 33a            Heart, 319
     products of combuftion, 80 Heat, ia
Flame, 90                         of temperature, 12
Flint, 176                    Honey, 337
Fluoric acid, 109              Horns, 305
Food of animals, 31 r          Hydro-carbonate ia5
Formic acid. 193              Hydrogen, 8a  1
Fossil wood, 371                        gas, 84
Free caloric, or heat of temper-
   ature, 13
Freezing mixtures, 56         Jasper, 173
 Frank.1 >ccnse, 343              Ice,  '•>$
 Friction, 61                   JeUy» *93
 Frost, 63                     Jet,  370 
Igni fatui, 109
Incombustible bodies, 160
Ink, 204
Infects, 132
Integrant  parts,  5
Iridium, 6.
Isinglass,  293
Ivory black,  300
Kali,  261
K
Lac, 336
Lactic  acid, 173
Lakes, colours, 233
Latent heat, j 1
Lavender water,  231
Lead,  136
Leaves,  a/>8
Life, 331
Ligaments, 306
Light,  106
Lightning, 101
Lime, 173
Lime water, i64
 Limestone, 163
 Linseed oil,  236
 Liqueurs, 262
 Liquids,  17
 Lobes,  279        .        ..
 Lunar, caustic,  or nitrat of sil-
   ver,  147  '
 Lungs, >i7
 Lymph,  06
 Lymphatic vessels, ~o6

               M.

  Magnesia,  161
  Malic acid.  19a
  Malt,  25 1
  Manganefe  76
  Mauna,  235
  Manure, 27*       .  .    .,
  Marine acid, or muriatic acid,
     222
  Ma«'-ic,  2  ;
  Membrane, 29a
Mercury,  1I5
Metallic oxyds, r4>
Metals, 6  129
Mica,  175
Milk.  29a.  33i
Mineral acids, 19a
Molybdena, 6.
Mortar,  175
Mucilage, 23a
Mucous  acid, 19a
Muriatic acid, or marine acid',
   190
Muriat of ammonia,  160 227
            of soda, or common
   salt, 333
Muscles of animals, 2o6
Musk, 336
 Myrrh, 2*3
              N
Naphtha, 270
Nerves, 3oa
Neutral, or compound salts,
   15*
Nickel, 6
Nitre,  or  nitrat of  potasb, or-
   salt petre.  300
Nitric acid, 205
Nitrogen,  or azote, 66
            gas, 66
 Nitro-muriatic acid, or aqua re-
   gia, 225
. Nitrous acid gas,  2IO
 Nitrat of  ammonia, 212
       of potash, or nitre,  or salt
   petre, 208 2i4
        of silver, or lunar caulUc,
   315
 Nut-^alls 205
 Nut-oil 236

                O

  Ochres, i"a
  Oil of amber,  271
      of vitriol,  or sulphuric acid,.
    19 s
  O' ve oil, 2  2
  Omi.iuh. 6
  Oxalic acid,  193 
INDEX.
©xyd of iron i36
     of lead, 136        1
Oxygen, 66
Oxy-muriatic acid, 233
Oxy muriats, 228
Oxy-muriat of potash, 338
Palladium, 6
Papin's digefter.  395
Parenchyma, 379
Pearlash,  154
Peat, 370
Perfumes,  3j4
Perspiration  292
Peppermint water,  3jI
Pewter 144
Pharmacy, 3
Phosphat  of lime, 2o5
Phosphorated hydrogen gas,
   109
Phosphoric acid, 205
Phosphorous acid,  191
Phosphorus,  105
Thosphorct of lime,  no
              of sulphur, no
Pitch, 232
Platina, 136
Plating,  1 5
Plumula,  280
Porcelain, 176
Potash, 151
Prussiat  of  iron,   or  prussian
   blue, 191
Prussic acid, 19'j
Putrid fermentation, 3f6
Pyrites, 2o4
Pyrometer, 15

              Q_

Quick lime, 175
Quiescent forces, 186
Radiation of caloric, 22
Radical, 152
Radicle.' or root, 380
Rain, J9
Rectification, 261
Reflection of caloric, 25
Resins, 232
Respiration, 316
Rhodium, 6
Roasting metals, 13o
Rum, 263
              S

Saccharine fermentation, 26*
Sal ammoniac, or sulphat of am*
  monia 160
— polychrest, or sulphat of pot-
  afh, 201
— volatile, or carbonat of am-
  monia, 162
Saltpetre, or nitre, or  nitrat  of
  potash, 159
Salt, 212
Sap of plants, 3o3
Sapphire, 16 3
Saturation,  08
Sebacic acid, 19a.
Secretions. 307
Seltzer water, 122
Silex, or silicia, 161
Silk. 336
Simple bodies, 5
Size, 308
Skin, 292
Smelting metals,  130
Smoke, 80
Soap.  154
Soda,  151.  159
        water,  122
Soils, 175
Soldering, 145
Simple solution  141
Specific heat, 48. 13
Spermaceti.  33^
Spirits, 266
Steam, 39
Steel, 130
Stucco. 176
Strontites. 165.  178
Suberic acid, 192
Sublimation, 99
Succin. or yellow amber. 270
Succinic acid, 193.
Sugar, 233 
of milk,  334
Tungsten, 6
Sulphats,  201                        V
Super-oxygenated sulphur- Vapour, 67
  ic acid, 195            Varnishes, 195
Sulphat of alumine, or alum Vegetables, 232
  202                   Vegetable acids, 232
Sulphat of barytes,  163------colou.s, 228
------of iron, 152       ------he:.t, 195
        ol'lime, or gypsum,—----oils, 332
  or plaster of Paris,  203 Veins. 316
----of magnesia, or Epsom Verdigris, 149
  salt, 177               Vinou» fermentation, 256
----of potash,  or sal poly- Vital air, -or oxygen gas, 77
  chrest, 201            Vitriol,ofsulphatofiron, 152
_—of soda, or Glauber's                          -
  sails,  176. 186                     U
Sulphur  98
Sulphurated hydrogen gas, Undecompounded acids, 190
  109
Sulphurous acid, 103
Sulphuric acid, 103
Symphathetic ink,  149
Synthesis, 114
Uranium, 6
W
Water, 86
Wax, 335
Whey, 334
Wine, 259
Tan, 246
Tannin, 232
Tar, 232
Tartarous acid, 192
Tartrit of potash, 254
Teeth, 293
Tellurium, 6
Thermometers,  17
Thunder, 98
Tin, 145
Titanium, 6
Turf, 271
Turpentine, 232
Transpiration of plants, 291
Yeast, 338
Yttria, 164
Zinc, 136
Zirconia, 164
Zoonic acid, 193 
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