Education Library 
 
CONVERSATIONS 
 
 ON 
 
 CHEMISTRY ; 
 
 IN WHICH 
 
 THE ELEMENTS OF THAT SCIENCE 
 
 ARE 
 
 FAMILIARLY EXPLAINED 
 AND 
 
 ILLUSTRATED BY EXPERIMENTS, 
 
 AND SIXTEEN COPPER-PLATE ENGRAVINGS. 
 
 I" HE EIGHTH AMERICAN FROM THE SIXTH LONDON EDITION, RE 
 VISED, CORRECTED AND ENLARGED. 
 
 TO WHICH ARE NOW ADDED, 
 
 EXPLANATIONS OP THE TEXT QUESTIONS FOR EXERCISE DI- 
 RECTIONS FOR SIMPLIFYING THE APPARATUS, AND A VO- 
 CABULARY OF TERMS TOGETHER WITH A LIST OP 
 
 INTERESTING EXPERIMENTS. 
 
 BY DR. J. L. COMSTOCK. 
 
 HERTFORD: 
 
 OLIVER D. COOKE. 
 
 4822. 
 
c*^ 
 
 DISTRICT OF CONNECTICUT, M. 
 
 BE IT REMEMBERED, That on the twenty ninth day 
 L. S. of December, in the forty sixth year of the Independence of 
 the United States of America, Oliver D. Cooke of the said 
 District hath deposited in this office the title of a Book, the right 
 whereof he claims as proprietor, in the words following;, to wit, 
 "Conversations on Chemistry : in which the elements of that science 
 are familiarly explained arid illustrated by experiments, and sixteen 
 copperplate engravings. The eighth American from the sixth London 
 edition, revised, corrected and enlarged. To which are now added, 
 explanations of the text, questions for exercise, directions for simpli- 
 fying the apparatus, and a vocabulary ol terms ; together with a list of 
 interesting experiments. By Dr. J. L. Comstock." In conformity 
 to the act of the Congress of tbe United States, entitled, " An act for 
 the encouragement of learning, by securing the copies of Maps, Charts 
 and Books, to the authors and proprietors of such copies, during the 
 times therein mentioned." 
 
 CHAS.A.INGERSOLL, 
 Clerk of the District of Connecticut. 
 A true copy of Record, examined and sealed by me, 
 
 CHAS. A INGERSOLL, 
 Clerk of the District of Connecticut. 
 
 P. B. GOQDSE&L, PRINTER. 
 
QD * 
 W3& 
 
 ADVERTISEMENT 
 
 l4itUC 
 
 OF THE AMERICAN EDITOR. / 
 
 THE familiar and agreeable manner in which the " Conversations on 
 Chemistry" are written, renders this one of the most popular treatises 
 on the subject rvhich has ever appeared. The elegant and easy style 
 also, in which the authoress has managed to convey scientific instruction 
 is peculiarly adapted to the object of the work. 
 
 In some respects, however, the English edition may be considered as 
 objectionable. A book designed for the instruction of youth, ought if 
 possible to contain none but established principles. 
 
 Knowa and allowed facts are always of much higher consequence 
 than theoretical opinions. To youth, particularly, by advancing as 
 truths, doctrines which have arisen out of a theory not founded ou 
 demonstration, we run a chance of inculcating permanent error. 
 
 In these respects we think that iVIrs. Bryan has not been sufficiently 
 guarded. The brilliant discoveries of Sir Humphrey Davy, and his 
 known eminence as a Chemical Philosopher, seem in many instances 
 to have given his opinions an authority, which, in the mind of the wri- 
 ter, superseded further investigation. Indeed inferences are sometimes 
 JrawD from these opinions which they hardly warrant. Under this 
 view of the- subject, a part of the notes are designed to guard the pupil 
 against adopting opinions which he will find either contradicted, or 
 merely examined by most chemical writers. In addition to this, I 
 fcave made such explanations of the text as I thought would assist the 
 pupil in understanding what he read. 
 
 In attempting to make this science popular, and of general utility, 
 it is of great importance that the experiments come within the use of 
 such instruments as are easily obtained. I have therefore given such 
 directions on thh subject as my former experience, as a lecturer, 
 with a small apparatus, taught me to believe would be of service. 
 
 The questions. I believe, will be found to involve whatever is most 
 important to be known throughout the work. 
 
 The list of experiments was chiefly made up without referring to 
 books ; some few of them, however, are copied from Parke, Accum, 
 c. 
 
 HARTFORD. CT. Jan. 1, 1822. 
 
 M289981 
 
N venturing to offer to the public, and more particularly to 
 the female sex, an introduction to Chemistry, the author, her- 
 self a woman, conceives that some explanation may be required ; 
 and she feels it the more necessary to apologise for the present 
 undertaking, as her knowledge of the subject is but recent, and 
 as she can have no real claims to the title of chemist. 
 
 On attending for the first time experimental lectures, the au- 
 thor found it almost impossible to derive any clear or satisfacto- 
 ry information from the rapid demonstrations which are usual- 
 ly, and perhaps necessarily, crowded into popular discourses of 
 this kind. But frequent opportunities having afterwards oc- 
 curred of conversing with a friend on the subject of chemistry, 
 and of repeating a variety of experiments, she became better 
 acquainted with the principles of that science, and began to feel 
 highly interested in its pursuit. It was then that she perceiv- 
 ed, in attending the excellent lectures delivered at the Royal 
 Institution, by the present Professor of Chemistry, the great 
 advantage which her previous knowledge of the subject, slight 
 as it was, gave her over others who had not enjoyed the same 
 means of private instruction. Every fact or experiment at- 
 tracted her attention, and served to explain some theory to 
 which she was not a total stranger ; and she had the gratifica- 
 tion to find that the numerous and elegant illustrations, for 
 which that school is so much distinguished, seldom failed to 
 produce on her mind the effect for which they were intended. 
 
 Hence it was natural to infer, that familiar conversation was ; 
 In studies of this kind, a most useful auxiliary source of informa- 
 tion ; and more especially to the female sex, whose education is 
 seldom calculated to prepare their minds for abstract ideas, or 
 scientific language. 
 
 As, however, there are but few women who have access to 
 this mode of instruction ; and as the author was not acquainted 
 with any book that could prove a substitute for it, she thought 
 that it might be useful for beginners, as well as satisfactory to 
 herself, to trace the steps by which she had acquired her little 
 stock of chemical knowledge, and to record, in the form of dia- 
 logues, those ideas which she had first derived from conversa- 
 tion. 
 
 But to do this with sufficient method, and to fix upon a mode 
 of arrangement, was an object of some difficulty. After much 
 hesitation, and a degree of embarrassment, which, probably, the 
 most competent chemical writers have often fell in common 
 with the most superficial, a mode of division was adopted, 
 which, though the most natural, does not always admit of being 
 
PREFACE. v. 
 
 strictly pursued it is that of treating first of the simplest bodies, 
 and then gradually rising to the most intricate compounds. 
 
 It is not the author's intention to enter into a minute vindica- 
 tion of this plan. But whatever may be its advantages or in- 
 conveniences, the method adopted in this work is such, that a 
 young pupil, who should only recur to it occasionally with a 
 view to procure information on particular subjects, might often 
 find it obscure or unsatisfactory ; for its various parts are so 
 connected with each other as to form an uninterrupted chain of 
 facts and reasonings, which will appear sufficiently clear and 
 consistent to those only who may have patience tor go through 
 the whole work, or have previously devoted some attention to 
 the subject. 
 
 It will, no doubt, be observed, that in the course of these 
 Conversations, remarks are often introduced, which appear 
 much too acute for the young pupils, by whom they are suppo- 
 sed to be made. Of this fault the author is fully aware. But, 
 in order to avoid it, it would have been necessary either to omit 
 a variety of useful illustrations, or to submit to such minute ex- 
 planations and frequent repetitions, as would have rendered the 
 work tedious, and therefore less suited to its intended purpose. 
 
 In writing these pages, the author was more than once check- 
 ed in her progress by the apprehension that such an attempt 
 might be considered by some, either as unsuited to the ordinary 
 pursuits of her sex, or ill-justified by her own imperfect know- 
 ledge of the subject. But, on the one hand, she felt encouraged 
 by the establishment of those public institutions, open to both 
 sexes, for the dissemination of philosophical knowledge, which 
 clearly prove that the general opinion no longer excludes wo- 
 men from an acquaintance with the elements of science ; and, 
 on the other, she flattered herself, that whilst the impressions 
 made upon her mind, by the wonders of Nature, studied in this 
 new point of view, were still fresh and strong, trfie might per- 
 haps succeed the better in communicating to others the senti- 
 ments she herself experienced. 
 
 The reader will soon perceive, in perusing this work, that he 
 is often supposed to have previously acquired some slight know- 
 ledge of natural philosophy, a circumstance, indeed, which ap- 
 pears very desirable. The author's original intention was to 
 commence this work by a small tract, explaining, on a plan 
 analogous to this, the most essential rudiments of that science. 
 This idea she has since abandoned, an elementary work on 
 Natural Philosophy having appeared just as the first edition of 
 the " Conversations on Chemistry" was preparing for the press. 
 Her intended tract, however, was actually written, and subsequent 
 considerations have lately induced her to offer it to the public- 
 
CONTENTS. 
 
 ON SIMPLE BODIES. 
 
 CONVERSATION I. 
 
 Page 
 
 ON THE GENERAL PRINCIPLES OF CHEMISTRY. i 
 
 Connection between Chemistry and Natural Philosophy. Improved 
 State of modern Chemistry. Its Use in the Arts. The general ob- 
 jects of Chemistry. Definition of Elementary bodies. Definition of 
 Decomposition. Integrant and Constituent Particles. Distinction 
 betvyeen Simple and Compound Bodies. Classification of Simple 
 Bodies. Of Chemical Affinity, or Attraction of Composition. Ex- 
 amples of Composition and Decomposition. 
 
 CONVERSATION II. 
 
 CN LIGHT AND HEAT. 14 
 
 Light and heat capable of being separated. Dr. HerschcPs Experi- 
 msuts. Phosphorescence. Of Caloric. Its two .viodifications. 
 Free Caloric. ...Of the three different States of Bodies, solid, fluid, and 
 aeriform. Dilatation of s^lid Bodies Pyrometer Dilatation of 
 Fluids. Thermometer. Dilatation of Elastic Fluids. Air Ther- 
 mometer. Equal Diffusion of Caloric. Cold a Negative Quality. 
 Professor Prerosfs Theory of the Radiation of Heat. Profes- 
 sor Pictet's Experiments on the Reflection of Heat. Mr. Leslie's 
 Experiments on the Radiation of Heat. 
 
 CONVERSATION III. 
 
 CONTINUATION OF THE SUBJECT. 34 
 
 Of the different Power of Bodies to conduct Heat. Attempt to ac- 
 count for this Power. Count Rumlord's Opinion respecting tho non- 
 conducting Po^ er of Fluids. Phenomena of Boiling. of Solution 
 in general. Solvent Po-.ver of Water. Difference between Solu- 
 tion and iixture. Solvent power of Caloric. Of Clouds, Rain, 
 Dr. Wells' Theory of Dew, Evaporation, &c. Influence of Atmos- 
 pherical Pressure on evaporation. Ignition. 
 
 CONVERSATION IV. 
 
 N COMBINED CALORIC, COMPREHENDING SPECIFIC HEAT AND LA- 
 TEST li-EAT. 57 
 
 Of Specific Heat. Of the different Capacities of Bodies for Heat. 
 Specific Heat not perceptible by the Seoses. How to be ascertain- 
 
CONTENTS. VII. 
 
 eti. Of Latent Heat. Distinction between Latent and Specific 
 Heat Phenomena attending the Melting of Ice and the Formation 
 of Vapour. Phenomena attending the Formation of Ice, and the 
 Condensation of Elastic Fluids Instances of Condensation, and 
 consequent Disengagement of Heat, produced by Mixtures, by the 
 Slacking of Lime. General Remarks on Latent Heat. Explana- 
 tion of the Phenomena of Ether boiling, and Water freezing, at tne 
 same i emperature. Of the Production of Cold by Evaporation. 
 Calorimeter. Meteorological Remarks 
 
 CONVERSATION V. 
 
 OS THE CHEMICAL AGENCIES OF ELECTRICITY. 74 
 
 Of Positive and Negative Electricity. Galvaui's Discoveries. Volta- 
 ic Battery. Electrical Machine. Theory of Voltaic Excitement, 
 
 CONVERSATION VI. 
 
 ON OXYGEN- AND NITROGEN, 84 
 
 The Atmosphere composed of Oxygen and Nitrogen in the State of 
 Gas. Definition of Gas Distinction between Gas and Vapour. 
 Oxygon essential to Combustion and Respiration. Decomposition 
 of the Atmosphere by Combustion. Nitrogen Gaa obtained by this 
 Process Of Oxygenation in grm-ial. Ot the Oxydation of vletals. 
 Oxygen Gas obtained from Oxyd of vianganese.. Description of 
 a Water-Bath for collecting and preserving Gases. Combustion of 
 Iron Wire in Oxygen Gas. Fixed and volatile Products of Com- 
 bustion.- -Patent Lamps. Decomposition of the Atmosphere by 
 Respiration. Recomposition of the Atmosphere. 
 
 CONVERSATION VII. 
 
 ON P YDROGEN. 98 
 
 Of Hydrogen. Of the Formation of Water by the Combustion of 
 Hydrogen. Of the Decomposition of Water. Detonation of Hy- 
 drogen Gas. Description of Lavoisier's Apparatus for the forma- 
 tion of Water. Hydrogen Gas essential to the Production of Flame. 
 Musical Pone? produced by the Combustion of Hydrogen Gas 
 within a Glass Tube.- Combustion of Candles explained. -Gas 
 lights. ---Detonation of Hydrogen Gas in Soap Bubbles --Air Bal- 
 loons.-- Meteorological Phenomena ascribed to Hydrogen Gas. 
 Miner's Lamp. 
 
 CONVERSATION VIII. 
 
 ON SULPHUR AZVD PHOSPHORUS. 116 
 
 Natural History of Sulphur -Sublimation.- Alembic. Combustion 
 of -ulphur in Atmospheric Air Of Acidification in general. No- 
 menclature of the Acids. Combustion of Sulphur in Oxygen Gas, 
 Sulphuric Acid. Sulphurous Acid. Decomposition of s>ulphur.-~- 
 
VHI. CONTENTS. 
 
 -, Phosphorus 
 
 With Sulphur. Phosphorated Hydrogen Gas.- Nomenclature of 
 Binary Compounds. Phosphcret of Lime burning under Water. 
 
 CONVERSATION IX. 
 
 Oft" CARBON. 128 
 
 Method of obtaining 1 pure Charcoal". Method of making common 
 Charcoal. Pure -Carbon not to he obtained by Art. Diamond. 
 Properties of Carbon. Combustion of Carbon. Production of 
 Carbonic Acid Gas. Carbon susceptible of only one Degree of 
 Acidification. Gaseous Oxyd of Carbon Of Seltzer Water, and 
 other Mineral Waters. Effervescence, Decomposition of Water 
 by Carbon. Of Fixed and Essential Oils. Of the Combustion of 
 Lamps and Candies. Vegetable Acids Of the Power of Carbon 
 to revive Aietais. 
 
 CONVERSATION X. 
 
 OJV MKTALS. 141 
 
 .Natural History of Metals. Of Roasting, Smelting, &c. Oxydation 
 of metals by the Atmosphere. Change of Colours produced' by dif- 
 ferent degrees of Oxyduriou. Combustion of Metals. Perfect Met- 
 als burnt by Electricity only.- Some Metals revived by Carbon and 
 other Combustibles. Perfect Metals revived ly Heat alone. Of 
 the Oxydation of certain Metals by the Decomposition of VVater. 
 Power of Acids to promote this Effect. Oxydution of Metals by 
 Acids. Metallic Neutral Salts. Previous oxyclaiion of the Meta! 
 requisite. Ciystallisatioii. Solution distinguished from Dissolu- 
 tion. Five metals susceptible of acidification. Meteoric Stones. 
 Alloys, Soldering, Plating, &c.-- Of Arsenic, and of the caustic 
 Effects of Oxygen. Of Verdigris, Sympathetic Ink, &c.~ Of the 
 new Metals discovered by Sir H. Davy. 
 
 ON COMPOUND BODIES. 
 
 CONVERSATION XIII. 
 
 ON THE ATTRACTION OF COMPOSITION. 16J 
 
 OF the Lawe which rrgulate the Phenomena of the Attraction of 
 Composition.---!. It takes place only between Bodies of a diflerent 
 Nature.---^. Between the most minute Particles only. 3. Between 
 2, 3,4, or more rJodies. Of Compound or Neutral Salts. 4. Pro- 
 duces a Change of Temperature 5. The Properties which char- 
 acterise Bodies in their separate State, destroyed by Combination. 
 '-6. The Force of Attraction estimated by that which is required" 
 
CONTENTS. IX. 
 
 >y the Separation of the Constituents. 7. Bodies have amongst 
 themselves different Degrees of Attraction. Of simple elective 
 and double elective Attractions. Of quiescent and divellent Forces. 
 ---Law of definite Proportions. -Decomposition of Salts by Volta- 
 ic Electricity. 
 
 CONVERSATION XIV. 
 
 ON ALKALIES. 173 
 
 Of the Composition and general properties of the Alkalies. Of the 
 new discovered Alkali or Lition. Of Potash. Manner of pre- 
 paring iuPearlash. Soap. -Carbonat of Potash.- Chemical No- 
 menclature.--- Solution of Potash. Of Glass. Of Nitrat of Pot- 
 ash or Saltpetre. Effect of Alkalies on Vegetable Colonrs. Of 
 Soda. Of Ammonia or Volatile Alkali Muriat of Ammonia. - 
 Ammoniacal Gas. ---Composition of Ammonia. Hartshorn and Sal 
 Volatile. Combustion of Ammoniacal Gas. 
 
 CONVERSATION XV. 
 
 ON EARTHS. 183 
 
 Composition of the Earths. Of their Incombustibility. Form the 
 Basis ol all Minerals. Their Alkaline Properties, Silex ; its 
 Properties and Uses in the Arts. Alumine ; its Uses in Pottery, 
 &c. Alkaline Earths. Barytes. Lime ; its extensive chemical 
 Properties and Uses in the Arts. Magnesia. Strontian. 
 
 CONVERSATION XVI. 
 
 ON ACIDS. 1#6 
 
 Nomenclature of the Acida. Of the Classification of Acids. 1st 
 Class Acids of simple aim known Radicals, or Mineral Acids. 
 ~d Class Acids ot double Radicals, or Vegetable Acids. 3d Ulass 
 Acids of triple Radicals, or Animal Acids. Ol the Decomposi- 
 tion, of Acids of the 1st Class by Combustible Bodies. 
 
 CONVERSATION XVII. 
 
 OJ? THE SULPHURIC AND PHOSPHORIC ACIDS: OR, THE COMBI- 
 NATION'S OF OXYGEN VVITi, SULPftUJR AND WITH PHOSPHO- 
 RUS, AND OF THE SULPHATS AND PHOSPHATS. 201 
 
 Of the Sulphuric Acid. Combustion of Animal or Vegetable Bodies 
 by this Ac i*d. .uethod of preparing it. i he fculphurous Acid ob- 
 tained in the Form of Ga?. /(ay be obtained i'rorn oulphuric Ac- 
 id. May be reduced to i^uipijur ,'s absorbable by Water. De- 
 stroys Vegetable Colours. -)xyd of r'ulphur, Of Halts in general. 
 Sulphate. SuJ^hat of Potash, orSai Poiychrest. <>ld produced 
 by the malting 01 alts. ulphat of Soda, or Jiruher's Salt. 
 Heat evlvea during the Formation of Salt*. Crystallisation of 
 Salts. Water of Crystallisation. Efflorescence and Deliquescence 
 
X. CONTENTS. 
 
 of Salts. Sulphat of Lime, Gypsum or Plaister f Paris. Suiphat 
 
 of Magnesia. Suiphat of Alumine, or Alum. Suiphat of Iron. 
 
 Of Ink. Of the Phosphoric and Phosphorous Acids. Phosphorus 
 obtained from Bones. Phosphat of Lime. 
 
 CONVERSATION XVIII. 
 
 F THE NITRIC AND CARBONAIC ACIDS: OR, THE COMBINATION 
 OF OXYGEN WITH NITROGEN AND WITH CARBON AND OF THE 
 NITRATS AND CARBONATS. 209 
 
 Nitrogen susceptible of various Degrees of Acidification. Of the 
 Nitric Acid. Its Nature and Composition discovered by Mr. Cav- 
 endish Obtained from Nitrat of Potash. Aqua Fortis. Nitric 
 Acid may be converted into Nitrous Acid. Nitric Ox yd Gas. Its 
 Conversion into Nitrous Acid Gas. Used as an Eudiometrical Test. 
 Gaseous Oxyd of Nitrogen, or exhilarating Gas, obtained from 
 Nitrat of Ammonia Its singular Effects on being respired. Ni- 
 trats. Of Nitrat of Potash, Nitre or Saltpetre. Of Gunpowder. 
 Causes of Detonation. Decomposition of Nitre. Deflagration. 
 Nitrat of Ammonia. Nitrat of Silver. Of the Carbonic Acid. 
 Formed by the Combustron of Carbon. Constitutes a component 
 Part of the Atmosphere. Exhaled in some Caverns. Grotto del 
 Cane. Great Weight of this Gas Produced from calcareous 
 Stones by Sulphuric Acid. Deleterious Effects of this Gag when 
 respired. Sources which keep up a Supply of this Gas in the At- 
 mosphere. Its Effects on Vegetation. Of the Carbonats of Lime : 
 Marble, Chalk, Shells, Spars", and calcareous Stones. 
 
 CONVERSATION XIX. 
 
 ff THE BORACIC, FLUORIC, MURIATIC, AND OXYGENATED MU- 
 RIATIC ACIDS ; AND ON MURIATS. 223 
 
 On the Boracic Acid, Its Decomposition by Sir H. Davy. Its Basis 
 Boracium. Its Recoroposition. Its Uses in the Arts. Borax or 
 Borat of Soda. Of the Fluoric Acid. Obtained from Fluor ; cor- 
 rodes Siliceous Earth ; its supposed Composition. Fluorine ; its 
 supposed Basis. Of the Muriatic Acid. Obtained from Muriats. 
 Its gaseous Form. Is absorbable by Water. Its Decomposition. 
 I< susceptible of a stronger Degree of Oxygenation. Oxygena- 
 ted Muriatic Acid. Its gaseous Form and other Properties. Com- 
 bustion of Bodies in this Gas. It dissolves Gold- Composition of 
 Aqua Regia. Oxygenated Muriatic Acid destroys all O lours - 
 Sir H. Davy's TheVryof the Nature of Muriatic and Oxymuriatic 
 Arid. Chlorine. Used for Bleaching and for Fumigation'?. 1*9 of- 
 fensive Smell, &c. Muriate. Vluriat of Soda, or common Salt. 
 Muriat of Ammonia.. ..Oxygenated Muriat of Potash.. Detonates 
 with Sulphur, Phosphorus, Sic. ...Experiment of burning Phospho- 
 rus under Water by means of this Salt and of Sulphuric Acid. 
 
CONTENTS. XI. 
 
 CONVERSATION XX. 
 
 ON THE NATURE AND COMPOSITION OF VEGETABLES. 236 
 
 Of organised Bodies. Of the Functions of Vegetables. Of the ele- 
 ments of Vegetables. Of the Materials of Vegetables. Analysis 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. Resins and Varnishes. Pitch, Tar, Copal, Mastic, &c. 
 Gum Resins Myrrh, Assafoetida, fcc. Caoutchouc, or Gum Elas- 
 tic. Extractive colouring Matter ; its use in the Arts of Dyeing and 
 Painting. Tannin; its Use in the Art of preparing Leather. 
 Woody Fibre. Vegetable Acids. The Alkalies and Salts contain- 
 ed ia Vegetables. 
 
 CONVERSATION XXI. 
 
 ON THE DECOMPOSITION OF VEGETABLES. 254 
 
 Of Fermentation in general. Of the Saccharine Fermentation, the 
 
 Product of which is sugar. Of the Vinous Fermentation, the 
 
 Product of which is Wine. Alcohol, or Spirit of Wine. Analysis of 
 Wine by Distillation. Of Brandy, Rum, Arrack, Gin, &c. Tar- 
 trit of Potash, or Cream of Tartar. Liqueurs. Chemical Proper- 
 ties of Alcohol. Its Combustion. Of Ether. Of the Acetous Fer- 
 mentation, the Product of which is Vinegar. Fermentation of Bread. 
 Of the Putrid Fermentation, which reduces Vegetables to their 
 Elements. Spontaneous Succession of these Fermentations. Of 
 Vegetables said to be petrified. Of Bitumens: Naphtha. Asphal- 
 tum, Jet, Coal, Succin, or Yellow Amber. Of Fossil Wood, Peat, 
 and Turf. 
 
 CONVERSATION XXII- 
 
 HISTORY OP VEGETATlONi 272 
 
 Connection between the Vegetable and Animal Kingdoms. Of Ma- 
 nures. Of Agriculture. Inexhaustible Sources of Materials for the 
 Purposes of Agriculture. Of sowing Seed. Germination of ths 
 Seed. Function of the Leaves of Plants. Effects of Light and Air 
 on Vegetation. Effects of Water on Vegetation Effects of Vegeta- 
 tion on the Atmosphere.-r-Formation of Vegetable Materials by the 
 Organs of Plants, Vegetable Heat. Of the Organs of Plants. Of 
 the Bark, consisting of Epidermis, Parenchyma, and Cortical Lay- 
 ers. Of Alburnum, or Wood. Leaves, Flowers, and Seeds. Effects 
 of the Season on Vegetation. Vegetation of Evergreens in Winter. 
 
 CONVERSATION XXIII. 
 
 N THE COMPOSITION OF ANIMALS. 288 
 
 Eieaaenfs f animals. Of the principal Materials of Animals, viz. GeJ- 
 atine, Albumen, Fibrine, Mucus. Of Animal Acids. Of Animal C- 
 tewrs, Prussian Blue, Caraaine, and Ivory Black. 
 
XJi. CONTENTS. 
 
 CONVERSATION XXIV 
 
 ON THE ANIMAL ECONOMY. 297. 
 
 Of the principal Animal Organs. Of Bones, Teeth, Horns, Ligaments, 
 and Cartilage. Of the Muscles, constituting the Organs of Motion. 
 ...Of the Vascular System, for the Conveyance of I luiris. Ol the 
 Glands, for the ^ecr-.-tion of Fluids. Of the Nerves, constituting the 
 Organs of Sensation. Of the Cellular Substance which connects the 
 several Organs. Of the Skin. 
 
 CONVERSATION XXV. 
 
 OK ANIMALISATION, NUTRITION, AND RESPIRATION. 3Q5 
 
 Digestion. Solvent Power of the Gastric Juice. Formation of a 
 Chyle. Its Assimilation, or Conversion into Blood. Of Respira- 
 tion. Mechanical Process of ttespiration. Chemical Process of 
 
 Respiration Of the Circulation of the Blood. Of the Functions 
 
 of the Arteries, the Veins, and the Heart. Of the Lungs. Effects 
 of Respiration on the Blood. 
 
 CONVERSATION XXVI. 
 
 ON ANIMAL HEAT ; AND OP VARIOUS ANIMAL PRODUCTS. 315 
 
 Of the Analogy of Combustion and Respiration. Animal Heat evolv- 
 ed in the Lungs Animal Heat evolved in the Circulation. Heat 
 produced by Fever. Perspiration. Heat produced by Exercise- 
 Equal Temperature of Animals at all Seasons. Power of the Animal 
 Body to resist the Effects of Heat. Cold produced by Perspiration. 
 Respiration of Fish and of Birds. Effects of Respiration on Mus- 
 cular Strength. Of several Animal Products, viz. Milk, Butter, and 
 Cheese; Spermaceti; Ambergris; Wax; Lac; Silk; Musk; Ci 
 ret; Castor.- Of the putrid Fermentation. Conclusion. 
 
CONVERSATIONS 
 
 ON 
 
 CHEMISTRY. 
 
 CONVERSATION I. 
 
 ON THE GENERAL PIUNCIPLES OF CHEMISTRY. 
 
 Mrs. B. As you have now acquired some elementary no- 
 tions of NATURAL PHILOSOPHY, 1 am going to propose to you 
 another branch of science to whicri 1 am particularly anxious 
 that you should devote a share of your attention. This is 
 CHEMISTRY, which is so closely connected with Natural Philos- 
 ophy, that the study of the one must be incomplete without 
 some knowledge of the other ; for, it is obvious that we can de- 
 rive 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 their intimate nature. 
 
 Caroline. To confess the truth, Mrs. B., I am not disposed 
 to form a very favourable idea of chemistry, nor do 1 expect to 
 derive much entertainment from it. 1 prefer the sciences which 
 exhibit nature on a grand scale, to those that are confined to 
 the minutiae of petty details. Can the studies which we have 
 lately pursued, the general properties of matter, or the revolu- 
 tions of the heavenly bodies, be compared to the mixing up of 
 a few insignificant drugs ? I grant, however, there may be en- 
 tertaining experiments in chemistry, and should not dislike to 
 try some of them : the distilling, for instance, of lavender, or 
 rose water 
 
 Mrs. B. I rather imagine, my dear Caroline, tnat your want 
 of taste for chemistry proceeds from the very limited idea you 
 entertain of its object. You confine the chemist's laboratory 
 to the narrow precincts of the apothecary's and perfumer's 
 shops, whilst >it is subservient to an immense variety of other 
 useful purposes. Besides, my dear, chemistry is by no means 
 confined to works of art. Nature also has her laboratory^ 
 
 VOL. i. ! 
 
24 GENERAL, PRINCIPLES 
 
 which is the universe, and there she is incessantly employed in 
 chemical operations. You are surprised, Caroline ; but i as- 
 sure you that the most wonderful and the most interesting phe- 
 nomena of nature are almost all ot them produced by chemic- 
 al powers. What Bergman, in the introduction to his history 
 of chemistry, has said of this science, will give you a more just 
 and enlarged idea of it. The knowledge of nature may be 
 divided, he observes, into three periods. The first is that in 
 which the attention of men is occupied in learning the external 
 forms and characters of objects, and this is called Natural His- 
 tory. In the second, they consider the effects of bodies acting 
 on each other by their mechanical power, as their weight and 
 motion, and this constitutes the science of Natural Philosophy. 
 The third period is that in which the properties and mutual ac- 
 tion of the elementary parts of bodies are investigated. This 
 last is the science of CHEMISTRY, and I have no doubt you will 
 soon agree with me in thinking it the most interesting. 
 
 \ou may easily conceive, therefore, that without entering in- 
 to the minute details of practical chemistry, a woman may ob- 
 tain 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 contemplation of nature a 
 scene of delightful instruction. 
 
 Caroline. If this is the case, I have certainly been much mis- 
 taken in the notion 1 had formed of chemistry. I own that I 
 thought it was chiefly confined to the knowledge and prepara- 
 tion of medicines. 
 
 Mrs. B. That is only a branch of chemistry which is called 
 Pharmacy; and though the study of it is, no' doubt, of great 
 importance to the world at large, it bt longs exclusively to pro- 
 fessional men, and is therefore the last that I should advise you 
 to pursue. 
 
 Emily. But, did not the chemists formerly employ them- 
 selves in search of the philosopher's stone, or the secret of 
 making gold ?* 
 
 *The Alchymists had in view three great objects of discovery, viz. 
 1st. The Elixir of health; by the use of which the lives of men mignt 
 be protracted to any desirable length, or their mortality prevented. 
 '2nd. The universal solvent, or a liquid which should dissolve every 
 other substance This it was supposed would lead to the grand dis- 
 covery, viz. 3rd. The making of gold, or finding the philosophers slone. 
 That men of sound and discriminating minds on other subjects, should 
 imve spent their whole lives in pursuits so chimerical, is to us wonder- 
 ful indeed. But our wonder ceases in some degree, when we are told 
 that the doctrine of transmutation, kc. wns founded on a Theory, 
 which, in the 12th century, was considered as plausible, as we coosid- 
 
OP CHEMISTRY. o 
 
 Mrs. B. These were a particular set of misguftled philoso- 
 phers, who dignified themselves -with the name of \lchemists, 
 to distinguish their pursuits from those of the common chemists, 
 whose studies were confined to the knowledge of medicines. 
 
 But since that period, chemistry has undergone so complete 
 a revolution, that, from an obscure and mysterious art, it is now 
 become a regular and beautiful science, to which art is entirely 
 subservient. Tt is true, however, that we are indebted to the 
 alchemists for many very useful discoveries, which sprung 
 from their fruitless attempts to make gold, and which, undoubt- 
 edly} have proved of infinitely greater advantage to mankind 
 than all their chimerical pursuits. 
 
 The modern chemists, instead of directing their ambition to 
 the vain attempt of producing any of the original substances in 
 nature, rather aim at analyzing and imitating her operations, 
 and have sometimes succeeded in forming combinations, or ef- 
 fecting decompositions, no instances of which occur in the 
 chemistry of Nature. They have little reason to regret their 
 inability to make gold, whilst, by their innumerable inventions 
 and discoveries, they have so greatly stimulated industry and 
 facilitated labour, as prodigiously to increase the luxuries as 
 well as the necessaries of life. 
 
 Emily. But I do not understand by what means chemistry 
 can facilitate labour; is not that rather the province of the me- 
 chanic ? 
 
 Mrs. B. There are many ways by which labour may be 
 rendered more easy, independently of mechanics ; but mechan- 
 ical inventions themselves often derive their utility from a chem- 
 ical principle. Thus that most wonderful of all machines, the 
 Steam-engine, could never have been invented without the as- 
 sistance of chemistry. In agriculture, a chemical knowledge of 
 the nature of soils, and of vegetation, is highly useful ; and. in 
 those arts which relate to the comforts and conveniences of life, 
 it would be endless to enumerate the advantages which result 
 from the study of this science. 
 
 er many of ours at. the present day, viz. T^hat a perfect metal'consist- 
 ed nf quicksilcer and sulphur; these, when pure and united, formed 
 gold. Tha. a:l oth-.-r m -tais contained a quantity of dross, which 
 pr v nt.ed the particles of these two substances from uniting. If 
 therefore, this dross could he got rid of in the other metals, gold would 
 be the result. They believed also, that nature herself favoured this 
 operation. Thus Friar lloger Bacon, in his Mirror of Alchymy, say?, 
 "I must tell you, that nature ahvaies inlendeth and striueth to the per- 
 fection of gold ; hut many accidents comraing between, change the met- 
 fcc " S-e his Book printed in 1697, Chap. ii. C. 
 
4 GENERAL PRINCIPLES 
 
 Caroline. But pray, tell us more precisely in what manner 
 the discoveries of chemists have proved so beneficial to so- 
 eiety ? 
 
 Mrs. B. That would be an injudicious anticipation ; for 
 you would not comprehend the nature of such discoveries and 
 useful applications, as well as you will do hereafter. Without 
 a due regard to method, we cannot expect to make any pro- 
 gress in chemistry. I wish to direct your observations chiefly 
 to the chemical operations of Nature ; but those of Art are cer- 
 tainly of too high importance to pass unnoticed. We shall 
 therefore 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, Caroline, that this is no nar- 
 row or confined science, which comprehends every thing mate- 
 rial 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 were formed of differ- 
 ent materials, the study of chemistry would, indeed, be endless ; 
 but you must observe that the various bodies in nature are com- 
 posed of certain elementary principles, which are not very nu- 
 merous. 
 
 Caroline. Yes ; I know that all bodies are composed 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 chemistry has under- 
 gone since it has become a regular science. Within these thir- 
 ty years especially, it has experienced an entire revolution, and 
 it is now proved, that neither fire, air, earth, nor water, can be 
 called elementary bodies. For an elementary body is one that 
 has never been decomposed, that is to say, separated into oth- 
 er substances ; and fiiv, air, earth, and water, are all of them 
 susceptible of decomposition. 
 
 Emily. I thought that decomposing a body was dividing it 
 into its minutest parts. And if so, I do not understand why an 
 elementary substance is not capable of being decomposed, a,s 
 well as any other. 
 
 Mrs. B. You have misconceived the idea of decomposition ; 
 it is very different from mere division. The latter simply re- 
 duces a body into parts, but the former separates it into the va- 
 rious ingredients, or materials, of which it is composed. If we- 
 
OF CHEMISTRY. 
 
 to take a loaf of bread, and separate the several ingredi* 
 ents of which it is made, the -flour, the yeast, the salt, and the 
 water, it would be very different from cutting or crumbling the 
 loaf into pieces. 
 
 Emily. I understand you now very well. To decompose a 
 body is to separate from each other the various elementary sub- 
 stances of which it consists. 
 
 Caroline. But flour, water, and other materials of bread, ac- 
 cording to your definition, are not elementary substances. 
 
 Mrs. B. JNo, my dear ; I mentioned bread rather as a famil- 
 iar comparison, to illustrate the idea, than as an example. 
 
 The elementary substances of which a body is composed are 
 called the constituent parts of that body ; in decomposing it, 
 therefore, we separate its constituent parts. If, on the contra- 
 ry, we divide a body by chopping it to pieces, or even by grind- 
 ing or pounding it to the finest powder, each of these small par- 
 ticles will still consist of a portion of the several constituent 
 parts of the whole body: these are called the integrant parts j 
 do you understand the difference ? 
 
 Emily. Yes, I think, perfectly. We decompose a body in- 
 to its constituent parts ; and divide it into its integrant parts. 
 
 Mrs B. Exactly so. If therefore a body consists of only 
 one kind of substance, though it may be divided into its inte- 
 grant parts, it is not possible to decompose it. Such bodies are 
 therefore called simple or elementary, as they are the elements 
 of which all other bodies are composed. Compound bodies are 
 such as consist of more than one of these elementary principles. 
 
 Caroline. But do not fire, air, earth, and water, consist, each 
 of th 3 m, but of one kind of substance ? 
 
 Mrs. B. No, my dear ; they are every one of them sucepti- 
 ble of being separated into various simple bodies. Instead of 
 four, chemists now reckon upwards of forty elementary substan- 
 ces. The existence of most of these is established by the clear- 
 est experiments ; but, in regard to a few of them, particularly 
 the most subtle agents of nature ; heat, light, and electricity , 
 there is yet much uncertainty, and I can only give you the opin- 
 ion which seems most probably deduced from the latest discov- 
 eries. After I have given you a list of the elementary bodies, 
 classed according to their properties, we shall proceed to exam- 
 ine each of them separately, and then consider them in their 
 combinations with each other. 
 
 Excepting the more general agents of nature, heat, light, and 
 2* 
 
% GENERAL PRINCIPLES 
 
 electricity, it would seem that the simple form of bodies is that 
 of a metal.* 
 
 Caroline. You astonish me ! I thought the metals were only 
 one class of minerals, and that there were besides, earths, 
 stones, rocks, acids, alkalies, vapours, fluids, and the whole of 
 the animal and vegetable kingdoms. 
 
 Mrs. B. You have made a tolerably good enumeration^ 
 though I fear not arranged in the most scientific order. All 
 these bodies, however, it is now strongly believed, may be 
 \iltimately resolved into metallic substances.! Your surprise 
 at this circumstance is not singular, as the decomposition of 
 some of them, which has been but lately accomplished, has exci- 
 ted the wonder of the whole philosophical world. 
 
 But to return to the list of simple bodies these being usually 
 found in combination with oxygen, I shall class them according 
 to their properties when so combined. This will, I think$ fa- 
 cilitate their future investigation. 
 
 Emily. Pray what is oxygen ? 
 
 Mrs. B. A simple body ; at least one that is supposed to be 
 so, as it has never been decomposed. It is always found united 
 with the negative electricity. It will be one of the first of the 
 elementary bodies whose properties I shall explain to you, and, 
 as you will soon perceive, it is one of the most important in 
 nature ; but it would be irrelevant to enter upon this subject at 
 present. We must now confine our attention to the enumera- 
 tion and classification of the simple bodies in general. They 
 may 'be arranged as follows : 
 
 CLASS I. 
 
 Comprehending the imponderable agents, viz. 
 
 HEAT OR CALORIC, 
 
 LIGHT, 
 
 ELECTRICITY. 
 
 * No actual discovery makes this probable. It is supposing that alt 
 Ihe gases, as oxygen, hydrogen, <kc. as well as phosphorus, sulphur, 
 and carbon and several other substances are in part composed of a 
 metal, and yet not one among this number are known to have metallic 
 bases. C. 
 
 * Three of the alkalies only are known to have metallic base?, 
 
OP CHEMISTRY, 
 
 CLASS II. 
 
 Comprehending agents capable of uniting with inflammable, 
 bodies, and in most instances of effecting their combustion* 
 
 OXYGEN, 
 CHLORINE, 
 
 IODINE.* 
 
 CLASS III. 
 
 Comprehending bodies capable of uniting with oxygen, and 
 forming witli it various compounds. This class may be di- 
 vided as follows : 
 
 DIVISION I. 
 
 water. 
 
 DIVISION 2. 
 
 Bodies forming acids. 
 NITROGEN, . . . forming nitric acid. 
 SULPHUR, . . . forming" sulphuric acid. 
 PHOSPHORUS, . . forming phosphoric acid. 
 CARBON, .... forming carbonic acid. 
 BORACIUM, . . . forming boracic acid. 
 FLUORiuivi, . .. . forming fluoric acid. 
 MURIATIUM, . . forming muriatic acid^ 
 
 DIVISION 3. 
 
 Metalic bodies forming alkalies. 
 POTASSIUM, . . . forming potash. 
 
 SODIUM, forming soda. 
 
 AMMONIUM, . . . forming ammonia- 
 LITHIUM, .... forming lithina.t 
 
 DIVISION 4. 
 
 Metallic bodies forming earths. 
 CALCIUM, or metal forming lime. 
 MAGNIUM, .... forming magnesia, 
 BARIUM, forming barytes. 
 
 * A majority of the most learned Chemists, it is believed, have 
 Joubted whether Chlorine and Iodine were supporters of combustion, 
 any farther than they contain oxygen. C 
 
 t This fourth alkali was discovered by Mr, Arfimdflon, a Swedish 
 Chemist, so recently as the year 1818* 
 
8 GENERAL PRINCIPLES 
 
 STRONTIUM, . . . forming strontites 
 SILICIUM, .... forming silex. 
 ALUMIUN, .... forming aluinine, 
 YTTRIUM, .... forming yttria. 
 GLUCIUM, .... forming glucina. 
 ZIRCONIUM, . . . forming zirconia.* 
 
 DIVISION 5. 
 
 Metals, either naturally metallic, or yielding their oxygen to 
 carbon or to heat alone. 
 
 Subdivision 1. 
 
 Malleable metals. 
 
 GOLD, COPPER, 
 
 PLATINA, IRON, 
 
 PALLADIUM, LEAD, 
 
 SILVER,f NICKEL, 
 
 MERCURY,!): ZINC, 
 
 TIN. CADMIUM.^ 
 
 Subdiv. 2. 
 Brittle metals. 
 
 ARSENIC, ANTIMONY, 
 
 BISMUTH, ' MANGANESE, 
 
 TELLURIUM, URANIUM, 
 
 COBALT, COLUMBIUM Or TAN- 
 TUNGSTEN, TALIUM, 
 
 MOLYBDENUM, IRIDIUM, 
 
 TITANIUM, OSMIUM, 
 
 CHROME, RHODIUM, 
 CERIUN.JI 
 
 * Of all these earths, three or four only have as yet been distinctly 
 decomposed. 
 
 t These first four metals have commonly been distinguished by the 
 appellation of perfect or noble metals, on account of their possessing the 
 characteristic properties of ductility, malleability, inalterability, and 
 great specific gravity, in an eminent degree. 
 
 ^ Mercury, in its liquid state, cannot, of course, be called a mallea- 
 ble metal. But when frozen, it possesses a considerable degree of mal- 
 leability. 
 
 $ \ metal resembling tin; which was discovered in 1817, in an ore 
 of zinc, by Mr. Mromeyer. 
 
 j| These last four or five metallic bodies are placed under this class 
 for the sake of arrangement, though" some of their properties have not 
 yet fully investigated. 
 
5F CHEMISTRY. 
 
 Caroline. Oh, what a formidable list ! you will have much 
 to do to explain it, Mrs. B. ; for 1 assure you it is perfectly un- 
 intelligible to me, and I think rather perplexes than assists me. 
 
 Mrs. B. Uo not let that alarm you, my dear ; I hope that 
 hereafter this classification will appear quite clear, and, so far 
 from perplexing you, will assist you in arranging your ideas, 
 It would be in vain to attempt forming a division that would 
 appear perfectly clear to a beginner ; for you may easily con- 
 ceive that a chemical division being necessarily founded on 
 properties with which you are almost wholly unacquainted, it 
 is imposssible that you should at once be able to understand its 
 meaning or appreciate its utility. 
 
 But, before we proceed further, 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, con- 
 sists in the peculiar tendency which bodies of a different 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 attraction, 
 and the attraction of cohesion, or of aggregation, which you of- 
 ten mentioned to us, in former conversations ? 
 
 Mrs. B. The attraction of cohesion exists only between par- 
 ticles of the same nature, whether simple or compound ; thus it 
 unites the particles of a piece of metal which is a simple sub- 
 stance, 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 state of combination, particles of a 
 dissimilar nature; it is this power that forms each of the com- 
 pound particles of which bread consists ; and it is by the attrac- 
 tion of cohesion that all these particles are connected into a 
 single mass. 
 
 Emily. The attraction of cohesion, then, is th^ power which 
 unites the integrant particles of a body : the attraction of com- 
 position that which combines the constituent particles. Is it 
 not so ? 
 
 Mrs. B. Precisely : and observe that the attraction of cohe- 
 sion 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 nature, produces compound bodies, quite different 
 from any of their constituents. If for instance, I pour on the 
 piece of copper, contained in this </Iass, some of this liquid 
 (which is called nitric acid,) for which it has a strong attrac- 
 
10 GENERAL PRINCIPLES 
 
 tion, every particle of the copper will combine with a particle 
 of acid, and together they will form a new body, totally differ- 
 ent from either the copper or the acid. 
 
 Do you observe the internal commotion that already begins 
 to take place ? It is produced by ihe combination 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 opposes to their combination with it, but also to over- 
 come the weight of the copper, which makes it sink to the bot- 
 tom of the glass, and prevents the acid from having such fr-ee 
 access to it as it would if the metal were suspended in the li- 
 quid. 
 
 Emily. The acid seems, however, to overcome both these 
 obstacles without difficulty, and appears to be very rapidly dis- 
 solving the copper. 
 
 Mrs. B. By this means it reduces the copper into more mi- 
 nute parts than could possibly be done by any mechanical pow- 
 er. But as the acid can act only on the surface of the metal, it 
 will be some time before the union of these two bodies will be 
 completed. 
 
 You may, however, already see how totally different this 
 compound is from either of its ingredients. It is neither colour- 
 less, like the acid, nor hard, heavy, and 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 
 arid is diluted is evaporated, the compound will assume the form 
 of regular crystals of a fine blue colour, and perfectly transpar- 
 ent.! Of these I can show you a specimen, as I have prepar- 
 ed some for that purpose. 
 
 Caroline. How beautiful they are, in colour, form, and trans- 
 parency ! 
 
 Emily. Nothing can be more striking than this example of 
 chemical attraction. 
 
 Mrs. B. The term attraction has been lately introduced into 
 chemistry as a substitute for the word aflmity,to which some 
 
 * This hardly explains the process. A part of the oxygen of the ni- 
 tric acid unites with the copper ; and in consequence of this loss of ox- 
 ysren, the nitric acid is converted into nitrous gas. It is the escape of 
 this gas through the water as it is formed that occasions the commo- 
 tion. C. 
 
 t These crystals are more easily obtained from a mixture of sulphu- 
 ric with a little nitric arid 4 
 
 t ' h -se crystals are su.'phate of copper, or what is commonly knowr 
 nnder the name of blue vitriol. C, 
 
OP CHEMISTRY. 1 
 
 chemists have objected, because it originated in the vague notion 
 that chemical combinations depended upon a certain resem- 
 blance, or relationship, between particles that are disposed to 
 unite 5 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 meaning; on the con- 
 trary it creates confusion; and as we are well acquainted with 
 the term Attraction in natural philosophy, we had better adopt 
 it in chemistry likewise. 
 
 Mrs. B. If you have a clear idea of the meaning, 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 constit- 
 uent particles, as it may convey an idea of the preference which 
 some bodies have for others, which the term attraction of com- 
 position does not so well express. 
 
 Emily. So I think ; for though that preference may not re- 
 sult 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 the terms 
 affinity, chemical attraction, and attraction of composition^ 
 indifferently, provided you recollect that they have all the same 
 meaning. 
 
 Emily. I do not conceive how bodies can be decomposed by 
 chemical attraction. That this power should be the means of 
 composing them, is very obvious ; but that it should, at the same 
 time, produce exactly the contrary 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 observed, cannot 
 be done by mechanical means. 
 
 Emily. No : because mechanical means separate only the 
 integrant particles ; they act merely against the attraction of co- 
 hesion, and only divide a compound into smaller parts. 
 
 Mrs. B. The decomposition of a body is performed by 
 chemical powers. If you present to a body composed of two 
 principles, a third, which has a greater affinity for one of 
 them than the two first have for each other, it will be decompo- 
 sed, that is, its two principles will be separated by means of 
 the third body. Let us call two ingredients, of which the body 
 is composed, A and B. If we present to it another ingredient 
 
12 GENERAL PRINCIPLED 
 
 C, which has a greater affinity for B 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 were very happy in each other's society, till a 
 third disunited them by the preference which one of them gave 
 to the new-comer. 
 
 Mrs. B. Very well. I shall now show you how this takes 
 place in chemistry. 
 
 Let us suppose that we wish to decompose the compound we 
 have just formed by the combination of the two ingredients, 
 copper and nitric acid ; we may do this by presenting to it a 
 piece of iron, for which the acid has a stronger attraction than 
 for copper: the acid will, consequently quit the copper to com- 
 bine with the iron, and the copper will be what the chemists call 
 precipitated, that is to say, it will be thrown down in its sepa- 
 rate state, and re-appear in its simple form. 
 
 In order to produce this effect, I shall dip the blade of this 
 knife into the fluid, and, when I take it out, you will observe, 
 that, instead of being wetted with a bluish liquid, like that con- 
 tained in the glass, it will be covered with a thin coat of cop- 
 per. 
 
 Caroline. So it is really ! but then is it not the copper, in- 
 stead of the acid, that has combined with the iron blade ? 
 
 Mrs. J3. No ; you are deceived by appearances : it is the 
 acid which combines with the iron, and, in so doing, deposits or 
 precipitates the copper on the surface of the blade. 
 
 Emily. But, cannot three or more substances combine to- 
 gether, without any of them being precipitated ? 
 
 Mrs. B. That is sometimes the case ; but, in general, the 
 stronger affinity destroys the weaker ; and it seldom happens 
 that the attraction of several substances for each other is so 
 equally balanced as to produce such complicated compounds.* 
 
 Caroline. But, pray, Mrs. B., what is the cause of the chem- 
 ical attraction of bodies for each other ? It appears to me more 
 extraordinary or unnatural, if I may use the expression, than 
 the attraction of cohesion, which unites particles of a similar 
 nature. 
 
 Mrs. B. Chemical attraction may, like that 0f cohesion or 
 
 * Such compounds are quite numerous. They are called triple salt?. 
 Alum is one. It is composed of Alumine, potash, and sulphuric acid. 
 Tartar Emetic is another. It is composed of tartaric acid, potash and 
 antimony. C. 
 
OF CHEMISTRY. 
 
 gravitation, be one of the powers inherent in matter, which, in 
 our present state of knowledge, admits of no other satisfactory 
 explanation than an immediate reference to a divine cause. 
 Sir H. Davy, however, whose important discoveries have open- 
 ed such improved views in chemistry, has suggested an hypo- 
 thesis which may throw great light upon that science. He sup- 
 poses that there are two kinds of electricity, with one or other 
 of which all bodies are united. These we distinguish by the 
 names of positive and negative electricity ; those bodies are 
 disposed to combine, which possess opposite electricities, as 
 they are brought together by the attraction which these electri- 
 cities have for each other. But, whether this hypothesis be 
 altogether founded on truth or not, it is impossible to question 
 the great influence of electricity in chemical combinations. 
 
 Emily. So, that we must suppose that the two electricities 
 always attract each other, and thus compel the bodies in which 
 they exist to combine ?* 
 
 Caroline. And may not this be also the cause of the attrac- 
 tion of cohesion ? 
 
 Mrs. B. No, for in particles of the same nature the same 
 electricities must prevail, and it is only the different or opposite 
 electric fluids that attract each other. 
 
 Caroline. These electricities seem to me to be a kind of 
 chemical spirit, which animates the particles of bodies, and 
 draws them together. 
 
 Emily. If it is known, then, with which of the electricities 
 bodies are united, it can be inferred which will, and which will 
 not, combine together ? 
 
 Mrs. B. Certainly. I should not omit to mention, that some 
 doubts have been entertained, whether electricity be really a 
 material agent, or whether it might not be a power inherent in 
 bodies, similar to, or perhaps identical with, attraction, 
 
 * There seems to be an objection to this theory as explained here. 
 When two bodies, one in the positive, the other in the ^egative state of 
 electricity are presented to each other, a mutual attraction takes 
 pla.ce, until they touch, or come within the striking distance, so 
 that the electric fluid can pass from the positive to the negative body. 
 When this is effected, they are said to be in a state of equilibrium, or 
 in the same state of electricity, and consequently neither attract nor 
 repel each other. If therefore, chemical attraction depends on the 
 different electrical states of the particles, w.e are still at a loss how t 
 account for their adhesion even after they are united. The celebrated 
 Kepler accounted for the affinity of particles by supposing each to have 
 its likings audits antipathies, and the power of choosing accordingly. 
 This theory only wants our belief to make it satisfactory. C, 
 
 3 
 
 
** L10HT. 
 
 Emily. But what then would be the electric spark which is 
 visible, and, must therefore be really material ? 
 
 Mrs. B. What we call the electric spark, may, Sir H. Davy 
 says, be merely the heat and light, or fire produced by the 
 chemical combinations with which these phenomena are always 
 connected. We will not, however, enter more fully on this 
 important subject at present, but reserve the principal facts 
 which relate to it to a future conversation. 
 
 Before we part, however, I must recommend you to fix in 
 your memory the names of the simple bodies against our next 
 interview. 
 
 CONVERSATION II. 
 
 ON LIGHT AND HEAT, OR CALORIC. 
 
 Caroline. WE have learned by heart the names of all the 
 simple 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. Respecting the nature of light we have little more 
 than conjectures. It is considered by most philosophers as a 
 real substance immediately emanating from the sun, and from 
 all luminous bodies, from which it is projected in right lines 
 with prodigious velocity. Light, however, being imponderable, 
 it cannot be confined and examined by itself; and therefore it 
 is to the effects it produces on other bodies, rather than to its 
 immediate nature, that we must direct our attention. 
 
 The connection between light and heat is very obvious j 
 indeed, it is such, that it is extremely difficult to examine the 
 one independently of the other. 
 
 Emily. But, is it possible to separate light from heat ; I 
 thought they were only different degrees of the same thing, fire ? 
 
 Mrs, B. I told you that fire was not now considered as a sim- 
 ple element. Whether light and heat be altogether different a- 
 gents, or not, I cannot pretend to decide ; but, in many cases, light 
 may be separated from heat. The first discovery of this was 
 made by a celebrated Swedish chemist, Scheele. Another very 
 striking illustration of the separation of heat and light was 
 Jong after pointed out by Dr. Herschell. This philosopher 
 discovered that these two agents were emitted in the rays of the 
 u.n 3 and that heat was less refrangible than light ; for, in sep?.~ 
 
LIGHT. id- 
 
 rating the different coloured rays ofjpight 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 to 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 experi- 
 ment the heat is not totally separated from the light, each col- 
 oured ray retaining a certain portion of it, though the greatest 
 part is not sufficiently refracted to fall within the spectrum.; 
 
 Emily. I suppose, then, that those coloured rays which are 
 the least refrangible, retain the greatest quantity of heat f 
 
 Mrs. B. They do so. 
 
 Emily. Though I no longer doubt that light and heat can 
 be separated, Dr. Herschell 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 divi- 
 ded into the various coloured rays. 
 
 Mrs. B. No doubt there must be some difference in the va- 
 rious coloured rays. Even their chemical powers are different. 
 The blue rays, for instance, have the greatest effect in sepa-v 
 jatin oxygen from bodies, as v/as found by Scheele ; and there 
 exist also, as Dr. Wollaston has shown, rays more refrangible 
 than the blue, which produce the same chemical effect, and, 
 what is very remarkable, are invisible.* 
 
 Emily. Do you think it possible that heat may be merely a 
 modification of light ? 
 
 Mrs. B. That is^a supposition which, in the present state of 
 natural philosophy, can neither be positively affirmed nor de- 
 nied. Let us, therefore, instead of discussing theoretical 
 points, be contented with examining what is known respecting 
 the chemical effects of light. 
 
 Light is capable of entering into a kind of transitory union 
 with certain substances, and this is what has been called phos- 
 phorescence. Bodies that are possessed of this property, after 
 being exposed to the sun's rays, appear luminous in the dark. 
 The shells of fish, the bones of land animals, marble, limestone, 
 
 * The violet rays have the power of imparting the magnetic virtue 
 to steel. The process consists in intercepting all the rays except this, 
 and of throwing this, being first collected into a focus by a lens, on 
 the middle of a needle, and tarrying it towards the extremity. This 
 is to be done many times, and always towards the same extremity. 
 After a while the needle acquires polarity. C 
 
1O LIGHT. 
 
 and a variety of combinations of earths, are more or kss pow* 
 er fully phosphorescent. 
 
 Caroline. I remember being much surprised last summer 
 with the phosphorescent appearance of some pieces of rotten 
 wood, which had just been dug out of the ground ; trwy shone 
 so bright that I at first supposed them to be glow-worms. 
 
 Emily. And is not the light of a glow-worm of a phospho- 
 rescent nature ? 
 
 Mrs. B. It is a very remarkable instance of phosphorescence 
 in living animals ; this property, however, is not exclusively 
 possessed by the glow-worm. The insect called the lanthorn- 
 fly, which is peculiar to warm climates, emits light as it flies, 
 producing in the dark a remarkably sparkling appearance. 
 But it is more common to see animal matter in a dead state pos- 
 sessed of a phosphorescent quality ; sea-fish is often eminently 
 so.* 
 
 Emily. I have heard that the sea has sometimes had the ap- 
 pearance of being illuminated, and that the light is supposed t 
 proceed from the spawn of fishes floating on its surface. 
 
 Mrs. B. This light is probably owing to that or some other 
 animal matter. Sea water has been observed to become lumi- 
 nous from the substance of a fresh herring having been immers- 
 ed in it; and certain insects, of the Medusa kind, are known to 
 
 produce aimnw. ' ' 
 
 But the strongest phosphorescence is produced by cnemicai 
 compositions prepared for the purpose, the most common of 
 which consists of oyster-shells and sulphur, and is known by 
 the name of Canton ? s Phosphorus.! 
 
 Emily. I am rather surprised, Mrs. B., that you should have 
 said so much of the light emitted by phosphorescent bodies 
 without taking any notice of that which is produced by burn- 
 ing bodies. 
 
 Mrs. B. The light emitted by the latter is so intimately con- 
 nected with the chemical history of combustion, that I must de- 
 fer all explanation of it till we come to the examination of that 
 process, which is one of the most interesting in chemical scr- 
 ence. 
 
 * The phosphorescence of dead animals is owing to the escape of 
 phosphorus in the form of phosphoretted hydrogen. This is set free 
 from its combination with the substance of the animal by the putre- 
 factive fermentation C. 
 
 t To prepare this, mix 3 parts of oyster shells calcined for an hour 
 and pulverized with 1 part of sulphur. This is to be rammed into a 
 crucible, which is to be kept at a red heat for one hour. On exposing 
 ome of this to the sun's rays, it absorbs light, and will shine in the 
 dark* This shows that light can be separated Jrorn heat. C. 
 
FREE CALORIC. If 
 
 Light is an agent capable of producing various chemical 
 changes. It is essential to the welfare both of the animal and 
 vegetable kingdoms ; for men and plants grow pale and sickly 
 if deprived of its salutary influence. It is likewise remarkable 
 for its property of destroying colour, which renders it of great 
 consequence in the process of bleaching. 
 
 Emily. Is it not singular that light, which in studying optics 
 we were taught to consider as the source and origin of colours^ 
 should have also the power of destroying them ? 
 
 Caroline. It is a fact, however, that we every day experi- 
 ence; you know how it fades the colours of linens and silks. 
 
 Emily. Certainly. And I recollect that endive is made to 
 grow white instead of green, by being covered up so as to ex- 
 clude the light. But by what means does light produce these 
 effects ? 
 
 Mrs. B. This I cannot attempt to explain to you until you 
 liave obtained a further knowledge of chemistry. As the chem- 
 ical properties of light can be accounted for only in their refer- 
 ence to compound bodies, it would be useless to detain you any 
 longer on this subject ; we may therefore pass on to the exami- 
 nation of heat, or caloric, with which we are somewhat better 
 acquainted. 
 
 HEAT and LIGHT may be always distinguished by the differ- 
 ent sensations they produce. Light affects the sense of sight ; 
 Caloric that of feeling; the one produces Vision, the other the 
 sensation of Heat. 
 
 Caloric is found to exist in a variety of forms or modifica- 
 tions, and I think it will be best to consider it under the two fol- 
 lowing heads, viz. 
 
 1. FREE OR RADIANT CALORIC. 
 
 2. COMBINED CALORIC. 
 
 The first, FREE or RADIANT CALORIC, is also called HEAT 
 OF TEMPERATURE; it comprehends all heat which is percepti- 
 ble 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. tt. And likewise of things that do not burn, as, for in- 
 stance, 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 r 
 It must be a strange kind of heat that cannot be perceived bv 
 ur senses. 
 
 3* 
 
18 FREE CALORIC 
 
 Mrs. B. None of the modifications of caloric should pro p - 
 erly be called heat ; for heat, strictly speaking, is the sensati on 
 produced by caloric, on animated bodies ; this word, therefore, 
 in the accurate language of science, should be confined to ex- 
 press the sensation. But custom has adapted it likewise, to in- 
 animate 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. 
 
 It was in order to avoid the confusion, which arose from thus 
 confounding the cause and effect, that modern chemists adopted 
 the new word caloric, to denote the principle which produces 
 heat; yet they do not always, in compliance with their own 
 language, limit the word heat to the expression of the sensa- 
 tion, since they still frequently employ it in reference to the oth- 
 er modifications of caloric which are quite independent of sen- 
 sation. * 
 
 Caroline. But you have not yet explained to us what these 
 other modifications of caloric are. 
 
 Mrs. B. Because you are not acquainted with the properties 
 f free caloric, and you know that we have agreed to proceed 
 with regularity. 
 
 One of the most remarkable properties of free caloric is its 
 power of dilating bodies. This fluid is so extremely subtle, 
 that it enters and pervades all bodies whatever, forces itself be- 
 tween their particles, and not only separates them, but fre- 
 quently drives them asunder to a considerable distance from 
 each other. It is thus that caloric dilates or expands a body so 
 as to make it occupy a greater space than it did before. 
 
 Emily. The effect it has 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 continual struggle between 
 the attraction of aggregation, and the expansive power of calo- 
 ric ; 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 most bodies are capable of passing from one of these forms 
 to the other, merely in consequence of their receiving different 
 quantities of caloric. 
 
 * If I touch a body at a higher temperature than my hand. I imme- 
 diately receive a quantity of caloric from it, and at the same instant 
 feel 'h- sensation called heat. The caloric then is the cause of this 
 teasation, and heat the effect of caloric passing into my hand. C, 
 
FREE CALORIC. 19 
 
 Caroline. That is very curious ; but I think I understand 
 the reason of it. If a great quantity of caloric is added to a 
 solid body, it introduces itself between the particles in such a 
 manner as to overcome, in a considerable degree, the attraction 
 of cohesion ; and the body, from a solid, is then converted into 
 a fluid. 
 
 Mrs. B. This is the case whenever a body is fused or melted ; 
 but if you add caloric to a liquid, can you tell me what is the 
 consequence ? 
 
 Caroline. The caloric forces itself in greater abundance be- 
 tween the particles of the fluid, and drives them to such a dis- 
 tance from each other, that their attraction of aggregation is 
 wholly destroyed : the liquid is then transformed into vapour. 
 Mrs. B. Very well ; and this is precisely the case with 
 boiling water, when it is converted into steam or vapour, and 
 with all bodies that assume an aeriform state. 
 
 Emily. 1 do not well understand the word aeriform ? 
 Mrs. B. Any elastic fluid whatever ; whether it be merely 
 vapour or permanent air, is galled aeriform. 
 
 But each of these various Sates, solid, liquid, and aeriform, 
 admit of many different degrees of density, or consistence, still 
 arising (chiefly at least) from the different quantises of caloric 
 the bodies contain. Solids are of various degrees of density, 
 from that of gold, to that of a thin jelly. Liquids, from 
 the consistence of melted glue, or melted metals, to that of 
 ether, which is the lightest of all liquids. The different elas- 
 tic fluids (with which you are not yet acquainted) are sus- 
 ceptible of no less variety in their degrees of density. 
 
 Emily. But does not every individual body also admit of 
 different degress of consistence, without changing its state ? 
 
 Mrs. B. Undoubtedly; and this I can immediately show 
 you by a very simple experiment. This piece of iron now ex- 
 actly fits the frame, or ring, made to receive it 5 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 fra -e. 
 
 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 Pyrometer) 
 we may estimate, in the most exact manner, the various dilata- 
 tions 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 appara- 
 
20 FREE CALORIC, 
 
 tus, (PLATE I. Fig. 1.) and then heat it by lighting the three 
 lamps beneath it : when the bar expands, it increases in length 
 as well as thickness ; and, as one end communicates with this 
 wheel- work , whilst the other end is fixed and immoveable, no 
 sooner does it begin to dilate than it presses against the wheel- 
 work, and sets in motion the index, which points out the de- 
 grees of dilatation on the dial- plate. 
 
 Emily. This is, indeed, a very curious instrument ; 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 in dila* 
 ting, 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 multiply the mo- 
 tion, 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 scaicely be perceptible; but by means of the 
 wheels it moves in a much greater proportion, which therefore 
 renders the variations far more conspicuous. 
 
 By submitting different bodies to, the test of the pyrometer, it 
 is found that they are far from dffating in the same proportion. 
 Different metals expand in different degrees, and other kinds of 
 solid bodies ^arf 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 other with water. I 
 have coloured both liquids, in order that the effect may be more 
 conspicuous. The spirit of wine, you see, dilates by the 
 warmth of my hand as I hold the bulb.* 
 
 Emily. It certainly does, for I see it is rising into the tube. 
 But water, it seems, is not so easily affected by heat ; for scarce- 
 ly any change is produced on it by the warmth of the hand. 
 
 Mrs. b. True ; we shall now plunge the bulbs into hot water, 
 (PLATE I. Fig. 2.) and you will see both liquids rise in the 
 tubes ; but the spirit of wine will ascend highest. 
 
 Caroline. How rapidly it expands ! Now it has nearly reach- 
 ed the top of the tube, though the water has hardly begun to 
 rise. 
 
 Emily. The water now begins to dilate. Are not these glass 
 tubes, with liquids rising within them, very like thermometers ? 
 
 * In the absence of glass tubes terminated by bulbs, procure a pair 
 of tin cannisters, 3 inches high and 2 wide, soldered up all round. la 
 the middle of the top of each, have inserted a circular tin spout, and in- 
 fo these cement glass tubes about J2 inches high. These will answer 
 every purpose, C. 
 
FREE CALORIC. 21 
 
 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 thermometers is mercury, 
 commonly called quicksilver, the dilatations and contractions of 
 which correspond more exactly to the additions, and subtrac- 
 tions, of caloric, than those of any other fluid. 
 
 Caroline. Yet I have often seen coloured spirit of wine used 
 in thermometers. 
 
 Mrs. B. The expansions and contractions of that 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 pre- 
 cision, spirit of wine will answer the purpose equally well, and 
 indeed in some respects better, as the expansion of the latter is 
 greater, and therefore more conspicuous. This fluid is used 
 likewise in situations and experiments in which mercury would 
 be frozen ; for mercury becomes a solid body, like a piece of 
 lead or any other metal, at a certain degree of cold ; but no 
 degree of cold has ever been known to freeze spirit of wine.t 
 
 A thermometer, therefore, consists of a tube with a bulb, 
 such as you see here, containing a fluid whose degrees of dila- 
 
 *r\ which the 
 canon anu cumittcuon are ^indicated by a Scale v~ 
 
 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 
 temperature 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 scale must be very inconvenient, and 
 
 * 
 
 * The tube is closed by holding the end over a spirit lamp until the 
 glass is melted. This wora is derived from Hermes, the Greek name 
 forAiertury. He is said to have been the mventer of chemistry ; 
 hence this is sometimes called the Hermetic art, and hermetically, 'or 
 chemically closed, is closed by heat or melting. C. 
 
 t Spiiit of wine is stated to have been frozen in England by some 
 process which the author has preferred to keep secret. C. 
 
tfKEE CALORIC. 
 
 1 should think liable to occasion confusion, when French and 
 English experiments are compared. 
 
 Mrs. B. The inconvenience is but very trifling, because the 
 different gradations of the scales do not affect the principle up- 
 on which thermometers are constructed. When we know, for 
 instance, that Fahrenheit's scale is divided into 212 degrees, 
 in which 32 U corresponds with the freezing point, and 212 
 with the point of boiling water; and that Reaumur's is divided 
 only into 80 degrees, in which denotes the freezing point, 
 and 80 that of boiling water, it is easy to compare the two 
 scales together, and reduce the one into the other. But, for 
 greater convenience, thermometers are sometimes constructed 
 with both these scales, one on either side of the tube ; so that 
 the correspondence of the different degrees of the two scales is 
 thus instantly seen.. Here is one of these scales, (PLATE II. 
 Fig. l.) by which you can at once perceive that each degree of 
 Reaumur's corresponds to 2 1-4 of Fahrenheit's division. But 
 I believe the French have, of late, given the preference to what 
 they call the centigrade scale, in which the space between the 
 freezing and the boiling point is divided into 100 degrees. 
 
 Caroline. That seems to me the most reasonable division, 
 and I cannot guess why the freezing point is called 32, or 
 what advantage is derived from it. 
 
 Mrs. B. There really is no advantage in it 5 anditQiigina- 
 ted in mistaken opinion of the instrument-maker, Fahrenheit, 
 who first constructed these thermometers. He mixed snow and 
 salt together, and produced by that means a degree of cold 
 which he concluded was the greatest possible, and therefore 
 made his scale begin from that point. Between that and boil- 
 ing water he made 212 degrees, and the freezing point was 
 found to be at 32o. 
 
 Emily. Are spirit of wine, and mercury, the only liquids 
 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 make tolerable thermom- 
 eters: but for experiments in which a very quick and delicate 
 test of the changes of temperature is required, air is !he fluid 
 sometimes employed. The bulb of air thermometers is filled 
 with common air only, and its expansion and contraction are* 
 indicated by a small drop of any coloured liquor, which is sus- 
 pended within the tube, and moves up and down, according as 
 the air within the bulb and tube expands or contracts. But in 
 general, air thermometers, however sensible to changes of tem- 
 perature, are by no means accurate in their indications. 
 
 I can, however, show you an air thermometer of a very pe- 
 
PLATE //. 
 
 TIIKRAtOMEJ'KR . 
 
TREE CALORIC. 
 
 ouliar construction, which is remarkably well adapted for some 
 chemical experiments, as it is equally delicate and accurate in 
 its indications. * 
 
 Caroline. It looks like a double thermometer reversed, the 
 tube being bent, and having a large bulb at each of its extremi- 
 ties. (PLATE 11. Fig. 2.) 
 
 Emily. Why do you call it an air thermometer ; the tube 
 contains a coloured liquid ? 
 
 Mrs. b* But observe that the bulbs are filled with air, the li- 
 quid being confined to a portion of the tube, and answering on- 
 ly the purpose of showing, by its motion in the tube, the com- 
 parative dilatation or contraction of the air within the bulbs ? 
 which afford an indication of their relative temperature. Thus 
 if you heat the bulb A, by the warmth of your hand, the fluid 
 will rise towards the bulb B, and the contrary will happen if 
 you reverse the experiment. 
 
 But if, on the contrary, both tubes are of the same tempera- 
 ture, as is the case now, the coloured liquid, suffering an equal 
 pressure on each side, no change of level takes place. 
 
 Caroline. This instrument appears, indeed, uncommonly 
 delicate. The fluid is set in motion by the mere approach of 
 my hand. 
 
 Mrs. B. You must observe, however, that this thermometer 
 cannot indicate the temperature of any particular body, or of 
 the medium in which it is immersed ; it serves only to point 
 out the difference of temperature between the two bulbs, when 
 placed under different circumstances. For this reason it has 
 been called differential thermometer. You will see hereafter 
 to what particular purposes this instrument applies. 
 
 Emily. But do common thermometers .indicate the exact 
 quantity of caloric contained either in the atmosphere, or in any 
 body with which they are in contact ?t 
 
 * Students in chemistry may amuse themselves with air thermome- 
 ters of their own construction. Procure a flat vial, or inkstand with 
 a wide inouth; also a broken thermometer tube, the bulb being entire. 
 Fit a cork air tight to the vial, and pierce it in the middle with a hot 
 iron to admit the tube Fill the vial about hair' full of some coloured 
 liquid. Warm the bulb of the tube by holding it in the hand, and in 
 this state introduce the small end through the cork nearly to the bot- 
 tom of the vial. The hand being removed f-om the bulb, the fluid 
 will rise in the tube. The fluid will afterwards rise or fall as heat is 
 applied to the vial or bulb. C. 
 
 t The thermometer indicates the exact quantity of free caloric pres- 
 ent at the time and place of the experiment. Thus if a certain quantity 
 of heat is required to raise the mercury 0, double this quantity will 
 raise it to 40. AH bodies contain a quantity of heat not appreciable 
 
24 . FREE CALORIC. 
 
 Mrs. B. No : first, because there are other modifications ol 
 caloric which do not affect the thermometer ; and, secondly, 
 because the temperature of a body, as indicated by the ther- 
 mometer, is only relative. When, for instance, the thermome- 
 ter remains stationary at the freezing point, we know that the 
 atmosphere (or medium in which it is placed, whatever it may 
 be) is as cold as freezing water ; and when it stands at the boil- 
 ing point, we know that this medium is as hot as boiling water ; 
 but we do not know the positive quantity of heat contained either 
 in freezing or boiling water, any more than we know the real ex- 
 tremes of heat and cold ; and consequently we cannot deter- 
 mine that of the body in which the thermometer is placed. 
 Caroline. I do not quite understand this explanation. 
 Mrs. /'. Let us compare a thermometer to a well, in which 
 the water rises to different heights, according as it is more or 
 less supplied by the spring which feeds it ; if the depth of the 
 well is unfathomable, it must be impossible to know the abso- 
 lute quantity of water it contains ; yet we can with the greatest 
 accuracy measure the number of feet the water has risen or 
 fallen in the well at any time, and consequently know the pre- 
 cise quantiiy of its increase or diminution, without having the 
 least knowledge of the whole quantity of water it contains.* 
 
 Caroline. Now I comprehend it very well ; nothing appears 
 to me to explain a thing so clearly as a comparison. 
 
 Emily. But will thermometers bear any degree of heat ? 
 Mrs. B. No ; for if the temperature were much above the 
 highest degree marked on the scale of the thermometer, the 
 mercury would burst the tube in an attempt to ascend. And at 
 any rate, no thermometer can be applied to temperatures high- 
 er than the boiling point of the liquid used in its construction, 
 for the steam, on the liquid beginning to boil, would burst the 
 tube. In furnaces, or whenever any very high temperature is 
 to be measured, a pyrometer, invented by Wedgwood, is used 
 for that purpose. It is made of a certain composition of baked 
 
 by the thermometer, or sensible to the touch. This is called Jixed or 
 latem heat. This can sometimes be set fiee, as when we hammer a 
 piece of cold iron it becomes hot. Thus the latent caloric is squeezed 
 out of the iron by the contraction of its pores under the hammer, and it 
 then becomes/ree caloric. C. 
 
 * This passage may be expounded as follows. The unfathomable 
 depth of the well signifies the absolute quantity of caloric, and which 
 the thermometer does not measure ; because all bodies however cold, 
 still contain caloric. Thus mercur3 r freezes at 40 below zero, but 
 Still contains caloric, and so on. The rising and falling of the water 
 signifies the greater or less quantity of free caloric as indicated by the 
 thermometer. C. 
 
FREE CALORIC. 25 
 
 clay, which has the peculiar property of contracting 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 t I 
 thought that heat dilated all bodies whatever. 
 
 Mrs. B. This is not an exception to the rule. You must re- 
 collect that the bulk of the clay is not compared, whilst hot, 
 with that which it has when cold 5 but it is from the change 
 which the clay has undergone by having been heated that the 
 indications of this instrument are derived. This change con* 
 sists in a beginning fusion which tends to unite the particles 
 of clay more closely., thus rendering it less pervious or spon- 
 gy-* " 
 
 Clay is to be considered as a spongy body, abounding in in- 
 terstices or pores, from its having contained water when soft. 
 These interstices are by heat lessened, and would by extreme 
 heat be entirely obliterated. 
 
 Caroline. And how do you ascertain the degrees of contrac- 
 tion of Wedgwood's pyrometer ? 
 
 Mrs. B. The dimensions of the piece of clay are measured by 
 a scale graduated on the side of a tapered groove, formed in a 
 brass ruler 5 the more the clay is contracted by the heat, the 
 further it will descend into the narrow part of the tube. 
 
 Before we quit the subject of expansion, I must observe to 
 you that, as liquids expand more readily than solids, so elastic 
 fluids, whether air or vapour, are the most expansible of all bod- 
 ies. 
 
 It may appear extraordinary that all elastic fluids whatever, 
 undergo the same degree of expansion from equal augmenta- 
 tions of temperature. 
 
 Emily. I suppose, then, that all elastic fluids are of the same 
 density ? 
 
 Mrs. B. Very far from it ; they vary in density, more thaw 
 either liquids or solids. The uniformity of their expansibility, 
 which at first may appear singular, is, however, readily accoun- 
 ted for. For if the different susceptibilities of expansion of 
 bodies arise from their various degrees of attraction of cohe- 
 sion, no such difference can be expected in elastic fluids, since 
 in these the attraction of cohesion does not exist, their particles 
 being on the contrary possessed of an elastic or repulsive pow-r 
 
 * According to the calculation's of Saussure, the temperature necessa- 
 ry to melt this clay is 1575 Wedgwood, which is a degree of heat 
 greatly beyond our common furnaces. It is therefore most probable 
 that the clay contracts at lower temperatures by the los? of mois- 
 ture, C. 
 
 4 
 
-6 FREE CALO&IC. 
 
 er ; they will therefore all be equally expanded by equal de- 
 grees of caloric. 
 
 Emily. True ; as there is no power opposed to the expan- 
 sive force of caloric in elastic bodies, its effect must be the same 
 in all of them. 
 
 Mrs. B. Let us now proceed to examine the other properties 
 of free caloric. 
 
 Free caloric always tends to diffuse itself equally, that is to 
 say, when two bodies are of different temperatures, the warm- 
 er gradually parts with its heat to the colder, till they are 7 both 
 brought to the same temperature. Thus, when a thermometer 
 is applied to a hot body, it receives caloric ; when to a cold one, 
 it communicates part of its own caloric, and this communica- 
 tion continues until the thermometer and the body arrive at the 
 same temperature. 
 
 Emily. Cold, then, is nothing but a negative quality, simply 
 implying the absence 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 dis- 
 covered. 
 
 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 calo- 
 ric that your hand sustains in an attempt to bring its tempera- 
 ture to an equilibrium with the marble. 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 it abstracts from the 
 marble. 
 
 Caroline. Is it not in this case the air of the room, which 
 being warmer than the marble, melts the ice ? 
 
 Mrs. B. The air certainly acts on the surface which is ex- 
 posed to it, but the table melts that part with which it is in 
 contact. 
 
 Caroline. But why does caloric tend to an equilibrium ? It 
 cannot be on the same principle as other fluids, since it has no 
 weight ? 
 
 Mrs. B. Very true, Caroline, that is an excellent objection. 
 You might also, with some propriety, object to the term equi- 
 librium being applied to a body that is without weight ; but I 
 know of no expression that would explain my meaning so well. 
 You must consider it, however, in a figurative rather than a 
 Iheral sense : its strict meaning is an equal diffusion. We 
 Cannot, indeed, well say by what power it diffuses itself equally, 
 though it is not surprising that it should go from the parts 
 
FREE CALORIC. 27 
 
 which have the most to those which have the least. This sub- 
 ect is best explained by a theory suggested by Professor Pre* 
 vost of Geneva, which is now, I believe, generally adopted. 
 
 According to this theory, caloric is composed of particles 
 perfectly separate from each other, every one of which moves 
 with a rapid velocity in a certain direction. These directions 
 vary as much as imagination can conceive, the result of which 
 is, that there are rays or lines of these particles moving with 
 immense velocity in every possible direction. Caloric is thus 
 universally diffused, so that when any portion of space hap- 
 pens to be in the neighbourhood of another, which contains 
 more caloric, the colder portion receives a quantity of calorific 
 rays from the latter, sufficient to restore an equilibrium of tem- 
 perature. This radiation does not only take place in free 
 :>pace, but extends also to bodies of every kind.* Thus you 
 may suppose all bodies whatever constantly radiating caloric : 
 those that are of the same temperature give out and absorb 
 equal quantities, so that no variation of temperature is produced 
 in them ; but when one body contains more free caloric than 
 another, the exchange is always in favour of the colder body, 
 until an equilibrium is effected 5 this you found to be the case 
 when the marble table cooled your hand, and again when it 
 melted the ice. 
 
 Caroline. This reciprocal radiation surprises me extremely ; 
 I thought, from what you first said, that the hotter bodies alone 
 emitted rays of caloric which were absorbed by the colder \ 
 for it seems unnatural that a hot body should receive any calor- 
 ic from a cold one, even though it should return a greater quan- 
 tity. 
 
 Mrs. B. It may at first appear so, but it is no more extraor- 
 dinary than that a candle should send forth rays of light to the 
 sun, which, you know, must necessarily happen. 
 
 Caroline. Well, Mrs. B , Ibelieve'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. 
 
 Mrs. B. Will you give no credit 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 per- 
 ceptible ; for as you gain more than you lose, instead of suffer- 
 ing a diminution, you are really making an acquisition of calo- 
 
 * This is true when applied to inanimate matter. But if a live ani- 
 mal is exposed to a degree of heat above the temperature of its own. 
 body, it has the power of resistance ; a<id though the heat he 100 de- 
 grees above that of the animal, it scarcely affects its temperature. C. 
 
'28 FREE CALOBltr. 
 
 ric. It is, therefore, only when you are parting with it to 
 body of a lower temperature, that you are sensible of the sen- 
 sation of cold, because you then sustain an absolute loss of ca- 
 loric. 
 
 Emily. And in this case we cannot be sensible of the small 
 quantity of heat we receive in exchange from the colder body, 
 because it serves only to diminish the loss. 
 
 Mrs. B. Very well, indeed, Emily. Professor Picket, oi 
 Geneva, has made some very interesting experiments, which 
 prove not only that caloric radiates from all bodies whatever, 
 but that these rays may be reflected, according to the laws of 
 optics, in the same manner as light. I shall repeat these ex- 
 periments before you, having procured mirrors* fit for the pur- 
 pose ; and it will afford us an opportunity of using the differen- 
 tial thermometer, which is particularly well adapted for these 
 experiments. I place an iron bullet, (PLATE III. Fig. 1.) 
 about two inches in diameter, and heated to a degree not suffi- 
 cient to render it luminous, in the focus of this large metallic 
 concave mirror. The rays of heat which fall on this mirror 
 are reflected, agreeably to the property of concave mirrors, in 
 a parallel direction, so as to fall on a similar mirror, which, 
 you see, is placed opposite to the first, at the distance of about 
 ten feet; thence the rays converge to the focus of the second 
 mirror, in which I place one of the bulbs of this thermometer. 
 Now, observe in what manner it is affected by the caloric which 
 is reflected on it from the heated bullet. The air is dilated in 
 the bulb which we placed in the focus of the mirror, and the 
 liquor rises considerably in the opposite leg. 
 
 Emily. But would not the same effect take place, if the rays 
 of caloric from the heated bullet fell directly on the ther- 
 mometer, without the assistance of the mirrors ? 
 
 Mrs. B. The effect would in that case be so trifling, at the 
 distance at which the bullet and the thermometer are from each 
 uther, that it would be almost imperceptible. The mirrors, 
 you know, greatly increase the effect, by collecting a large 
 quantity of rays into a focus ; place your hand in the focus of 
 the mirror, and you will find it much hotter there than when 
 you remove it nearer to the bullet. 
 
 Emily. That is very true ; it appears extremely singular to 
 
 * Mirrors made of common tinned iron show this experiment very 
 well. They may be 10 or 12 inches in diameter, and about 2 inches 
 deep. They must be planished with a hammer having a convex face, 
 and afterwards polished with a piece of buckskin, and a little whi- 
 ting. C. 
 
( 01 
 
 ?M 
 
 -< 
 
 III 
 
 
 lit 
 
 ^ i * 
 <-J^ 
 
S'AEE CALORIC. 29 
 
 feel the heat diminish in approaching the body from which it 
 proceeds. 
 
 Caroline. And the mirror which produces so much heat, by 
 converging the rays, is itself quite cold 
 
 Mrs. B. The same number of rays that are dispersed over 
 the surface of the mirror are collected by it into the focus j 
 but if you consider how large a surface the mirror presents to 
 the rays, and, consequently, how much they are diffused in 
 comparison to what they are at the focus, which is little more 
 than a point, I think you can no longer wonder that the focus 
 should be so much hotter than the mirror. 
 
 The principal use of the mirror in this experiment is, to 
 prove that the calorific emanation is reflected in the same man- 
 ner as light. 
 
 Caroline. And the result, T think, is very conclusive. 
 
 Mrs. tt. The experiment may be repeated with a wax taper 
 instead of the bullet, with a view of separating the light from 
 the caloric. For this purpose a transparent plate of glass must 
 be interposed between the mirrors ; for light, you know, passes 
 with great facility through glass, whilst the transmission of cal- 
 oric is almost wholly impeded by it. We shall find, however, 
 in this experiment, that some few of the calorific rays pass 
 through the glass together with the light, as the thermometer 
 rises a little ; but, as soon as the glass is removed, and a free 
 passage left to the caloric, it will rise considerably higher. 
 
 Emily. This experiment, as well as that of Dr. ilersdiell's, 
 proves that light and heat may be separated ; for in the latter 
 experiment the separation was not perfect, any more than in 
 that of Mr. Pictet. 
 
 Caroline. I should like to repeat this experiment, 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. 
 
 Mrs. H. That experiment wfcs proposed to Mr. Pictet by an 
 incredulous philosopher like yourself, and he immediately tried 
 it by substituting a piece of ice in the place o> th^ heated bullet. 
 
 Caroline. Well, Mrs. B., and what was the result ? 
 
 Mrs. B. That we shall see ; I have procured some ice for 
 the purpose. 
 
 Emily. The thermometer falls 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. 
 
 Mrs. w. So it at first appeared to Vlr. Pictet ; but upon a 
 Httle consideration he found that it afforded only an additional 
 
 4* 
 
SO PEEE CALORIC* 
 
 proof of the reflection of heat : this I shall endeavour to explain 
 to you. 
 
 According to Mr. Prevost's theory, we suppose that all bo- 
 dies 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 lower temperature, such as 
 a piece of ice, which parts with less caloric than it receives., 
 the consequence is, that its temperature is raised, whilst that of 
 the surrounding bodies is proportionally lowered. 
 
 Emily. If, for instance, I was to bring a large piece of ke 
 into this room, the ice would in time be melted, by absorbing 
 caloric from the general radiation which is going on throughout 
 the room ; and as it would contribute very little caloric in re- 
 turn for what is absorbed, the room would necessarily be cool- 
 ed by it. 
 
 Mrs. B. Just so ; and as in consequence of the mirrors, a 
 inore considerable exchange of rays takes place between the 
 ice and the thermometer, than between these and any of the 
 surrounding bodies, the temperature of the thermometer must 
 be more lowered than that of any other adjacent object. 
 
 Caroline. I confess I do not perfectly understand your ex- 
 planation. 
 
 Mrs. 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 thermometer sends to the ice, and not by any 
 cold rays received from it, that the fall of the mercury is oc- 
 casioned : for the ice, far frorr emitting rays of cold, sends 
 forth rays of caloric, which diminish the loss sustained by the 
 thermometer. 
 
 Let us say, for instance, that the radiation of the thermome- 
 ter 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 thermometer absolutely loses 10, whilst the 
 ice gains 10. 
 
 Caroline. But if the ice actually sends rays of caloric to the 
 thermometer, must not the latter fall still lower when the ice is 
 removed ? 
 
 Airs. B. No ; for the space which the ice occupied, admits 
 vays from all the surrounding bodies to pass through it ; and 
 those being of the same temperature as the thermometer, will 
 
FREE CALORIC. 81 
 
 not affect it, because as much heat now returns to the thermom- 
 eter as radiates from it. 
 
 Caroline. I must confess that you have explained this in so 
 satisfactory a manner, that I cannot help being convinced now 
 that cold has no real claim to the rank of a positive being. 
 
 Mrs. B. Before I conclude the subject of radiation I must 
 observe to you, that different bodies (or rather surfaces) possess 
 the power of radiating caloric in very different degrees. 
 
 Some curious experiments have been made by Mr. Leslie on 
 this subject, and it was for this purpose that he invented the 
 differential thermometer; with its assistance he ascertained that 
 black surfaces radiate most, glass next, and polished surfaces 
 the least of all. 
 
 Emily. Supposing these surfaces, of course, to be all of the 
 same temperature. 
 
 Undoubtedly. I will now show you the very simple and 
 ingenious apparatus, by means of which he made these experi- 
 ments. This cubical tin vessel, or canister, has each of its 
 sides externally covered with different materials ; the one is 
 simply blackened ; the next is covered with white paper ; the 
 third with a pane of glass, and in the fourth the polished tin 
 surface remains uncovered. We shall fill this vessel with hot 
 water, so that there can be no doubt but that all its sides will be 
 of tiie same temperature. Now let us place it in the focus of 
 one of the mirrors, making each of its sides front it in succes- 
 sion. We shall begin with the black surface.* 
 
 Caroline. It makes the thermometer which is in the focus of 
 the other mirror rise considerably Let us turn the paper sur- 
 face towards the mirror. The thermometer falls a little, there- 
 fore of course this side cannot emit or radiate so much caloric 
 as the blackened side. 
 
 Emily. This is very surprising ; for the sides are exactly of 
 the same size, and must be of the same temperature. But let 
 us try the glass surface. 
 
 Mrs. B. The thermometer continues falling, and with the 
 plain surface it falls still lower ; these two surfaces therefore 
 radiate less and less. 
 
 Caroline. I think I have found out the reason of this. 
 
 Mrs. a. I should be very happy to hear it, for it has not yet 
 (to my knowledge) been accounted for. 
 
 * The radiating power of different surfaces may be shown thus. Take 
 a common half pint tin cup, scour one side bright, and paint or smoke 
 the other black. Place this in the focus of the mirror, and the thermo- 
 meter will rise or fall as its sides are changed. U. 
 
FflEE CALORIC. 
 
 Caroline. The water within the vessel gradually cools, and 
 the thermometer in consequence gradually falls. 
 
 Mrs. B. It is true that the water cools, but certainly in much 
 less proportion than the thermometer descends, as you willper- 
 eeive if you now change the tin surface for the black one. 
 
 Caroline. I was mistaken certainly, for the thermometer ri- 
 ses again now that the black surface fronts the mirror. 
 
 Mrs. B. And yet the water in the vessel is still cooling, 
 Caroline. 
 
 Emily. I am surprised that the tin surface should radiate the 
 least caloric, for a metallic vessel filled with hot water, a silver 
 tea-pot, for instance, feels much hotter to the hand than one of 
 black earthenware. 
 
 Mrs. B. That is owing to the different power which various 
 bodies possess for conducting' caloiic, a property which we 
 shall presently examine. Thus, although a metallic vessel 
 feels warmer to the hand, a vessel of this kind is known to 
 preserve the heat of the liquid within, better than one of any 
 other materials ; it is for this reason that silver tea-pots make 
 better tea than those of earthen ware. 
 
 Emily. According to these experiments, light-coloured dress- 
 es, in cold weather, should keep us warmer than black clothes, 
 since the latter radiate so much more than the former. 
 
 Mrs. B. And that is actually the case. 
 
 Emily. This property, of different surfaces to radiate in dif- 
 ferent degrees, appears to me to be at variance with the equilib- 
 rium of caloric ; since it would imply that those bodies which 
 radiate most, must ultimately become coldest. 
 
 Suppose that we were to vary this experiment, by using two 
 metallic vessels full of boiling water, the one blackened, the 
 other not ; would not the black one cool the first ? 
 
 Caroline. True ; but when they were both brought down to 
 the temperature of the room, the interchange of caloric between 
 the canisters and the other bodies of the room being then equal, 
 their temperatures would remain the same. 
 
 Emily. I do not see why that should be the case ; for if dif- 
 ferent surfaces of the same temperature radiate in different de- 
 grees when heated, why should they not continue to do so when 
 cooled down to the temperature of the room ? 
 
 Mrs. B. You have started a difficulty, Emily, which cer- 
 tainly requires explanation. It is found by experiment, that 
 the power of absorption corresponds with and is proportional 
 to that of radiation ; so that under equal temperatures, bodies 
 compensate for the greater loss they sustain in consequence of 
 their greater radiation by their greater absorption ; so that if 
 
KREE CALORIG. 33 
 
 you were to make your experiment in an atmosphere heated 
 like the canisters, to the temperature of boiling water, though 
 it is true that the canisters would radiate in different degrees, no 
 change of temperature would be produced in them, because 
 they would each absorb caloric in proportion to their respective 
 radiation. 
 
 Emily. But would not the canisters of boiling water also ab- 
 sorb caloric in different degrees in a room of the common tem- 
 perature ? 
 
 Mrs. B. Undoubtedly they would. But the various bodies 
 in the room would not, at a lower temperature, (urnish either 
 of the canisters with a sufficiency of caloric to compensate for 
 the loss they undergo ; for, suppose the black canister to ab- 
 sorb 400 rays of caloric, whilst the metallic one absorbed only 
 200 5 yet if tine former radiate 800, whilst the latter radiates 
 only 400, the black canister will be the first cooled down to the 
 temperature of the room. But from the moment the equilibri- 
 um of temperature has taken place, the black canister, both 
 receiving and giving out 400 rays, and the metallic one 200, no 
 change of temperature will take place. 
 
 Emily. I now understand it extremely well. But what be- 
 comes of the surplus of calorific rays, which good radiators 
 emit and bad radiators refuse to receive : they must wander 
 about in search of a resting-place ? 
 
 Mrs. B. They really do so ; for they are rejected and sent 
 back, or, in other words, reflected by the bodies which are 
 bad radiators of caloric : and they are thus transmitted to other 
 bodies which happen to lie in their way, by which they are eith- 
 er absorbed or again reflected, according as the property of re- 
 flection, or that of absorption, predominates in these bodies. 
 
 Caroline. I do not well understand the difference between 
 yadiating and reflecting caloric, for the caloric that is reflected 
 from a body proceeds from it in straight lines, and may surely 
 be said to radiate from it ? 
 
 Mrs. B. It is true that there at first appears to be a great 
 analogy between radiation and reflection, as they equally con- 
 vey the idea of the transmission of caloric. 
 
 But if you consider a little, you will perceive that when a 
 body radiates caloric, the heat which it emits not only pro- 
 ceeds from, but has its origin in the body itself. Whilst when 
 a body reflects caloric, it parts with none of its own caloric, 
 but only reflects that which it receives from other bodies. 
 
 Emily. Of this difference we have very striking examples 
 before us, in the tin vessel of water, and the concave mirrors 5 
 
34 FilEE CALORIC. 
 
 the first radiates its own heat, the latter reflect the heat which 
 they receive from other bodies. 
 
 Caroline. Now, that I understand the difference, it no longer 
 surprises me that bodies which radiate, or part with their own 
 caloric freely, should not have the power of transmitting with 
 equal facility that which they receive from other bodies. 
 
 Emily. Yet no body can be said to possess caloric of its 
 own, if all caloric is originally derived from the sun. 
 
 Mrs. B. When I speak of a body radiating its own caloric, 
 I mean that which it has absorbed and incorporated either im- 
 mediately from the sun's rays, or through the medium of any 
 other substance. 
 
 Caroline. It seems natural enough that the power of absorp- 
 tion should be in opposition to that of reflection, for the more 
 caloric a body receives, the less it will reject. 
 
 Emily. And equally so that the power of radiation should 
 correspond with that of absorption. It is, in fact, cause and 
 effect 5 for a body cannot radiate heat without having previous- 
 ly absorbed it 5 just as a spring that is well fed flows abun- 
 dantly. 
 
 Mrs. B. Fluids are in general very bad radiators of caloric ; 
 and air neither radiates nor absorbs caloric in any sensible de- 
 cree 
 
 !5 CC ' 
 
 We have not yet concluded our observations on free caloric. 
 But I shall defer, till our next meeting, what I have further to 
 say on this subject. I believe it will afford us ample conversa- 
 tion for another interview. 
 
 COiWERSATION III. 
 
 CONTINUATION OF THE SUBJECT. 
 
 Mm. B. IN our last conversation, we began to examiin the 
 tendency of caloric to restore an equilibrium of temperature. 
 Tnis property when once well understood, affords the explana- 
 tion of a great variety of facts which appeared formerly unac- 
 countable. You must observe, in the first place, that the ofli'd 
 of this tendency is gradually to bring all bodies that are in con- 
 tact to the same temperature. Thus the fire which burns in 
 the grate, communicates its heat from one 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 on 
 
 
FREE CALORIC. 35 
 
 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 exactly df 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 is exactly the same. 
 
 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 car- 
 pet 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 therefore absorb heat more rapidly from 
 your hand, and consequently give it a stronger sensation of cold 
 than the two latter, although they are all of them really of the 
 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 successively 
 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 which 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 ? 
 
 ]\Irs. B. This is a point not well ascertained. It has been 
 conjectured that a certain union or adherence takes place be- 
 tween 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 reluctantly ; if slight, it propa- 
 gates 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 are those that 
 have the least affinity for caloric. 
 
 Mrs. B. Yes ; but the term affinity is objectionable in this 
 case, because, as that word is used to express a chemical at- 
 traction (which can be destroyed only by decomposition,) it 
 cannot be applicable to the slight and transient union that takes 
 place between free caloric and the bodies through which it pass- 
 
36 FREE CALORIC 
 
 es ; an union which is so weak, that it constantly yields to tiit 
 tendency which caloric has to an equilibrium. Now you 
 clearly understand, that the passage of caloric, through bodies 
 that are good 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 
 cither hotter or colder, though they may be, in fact, both of the 
 same temperature. 
 
 Caroline. Yes, I understand it now ; the table, and the book 
 lying upon it, being really of the same temperature, 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. 
 
 Mrs. jB. Very well, my dear; and observe, likewise, 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 most rapidly from your 
 hand, so it will now impart heat most rapidly to it. Thus the 
 marble table, which seerns to us colder than the mahogany 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 un- 
 derstand the reason of these apparently opposite effects ? 
 
 Emily. Perfectly. A body which is a good conductor of 
 caloric, affords it a free passage ; so that it penetrates through 
 that body more rapidly than through one vyhich is a bad con- 
 ductor ; and consequently, if it is colder 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. ij. 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 bo- 
 dy, they will all feel equally warm, since the exchange of cal- 
 oric between bodies of the same temperature is equal. Now, 
 can you tell me why flannel clothing, which is a very bad con- 
 ductor 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. 
 
 . B> Now you have explained it right ; the flannel rather 
 
FREE CALORIC, 37 
 
 keeps in the heat, than keeps out the cold. Were the atmos- 
 phere of a higher temperature than our bodies, it would be 
 equally efficacious in keeping their temperature at the same 
 degree, 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 exter- 
 nal or internal, cannot easily penetrate flannel ; therefore in 
 cold weather it keeps us warm, and if the weather were hotter 
 than our bodies, it would keep us cool. 
 
 Mrs. B. The most dense bodies are, generally speaking, the 
 best conductors of heat ; probably because the denser the body 
 the greater are the number of points or particles that come in 
 contact with caloric. At the common temperature of the at- 
 mosphere, 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 
 the lightest, is at the same time one of the warmest bodies.* 
 
 Caroline. This is, I suppose, the reason that the plumage 
 of birds preserve them so effectually from the influence 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 most 
 exposed to the water ; for though the surface of the water is not 
 of a lower temperature than the atmosphere, yet, as it is a bet- 
 ter conductor of heat, it feels much colder, consequently the 
 chest of the bird requires a warmer covering, than any other 
 part of its body. Besides, the breasts of aquatic birds are ex- 
 posed to cold, not only from the temperature of the water, but 
 also from the velocity with which the breast of the bird strikes 
 against it ; and likewise from the rapid evaporation occasioned 
 in that (Jart by the air against which it strikes, after it has been 
 moistened by dipping from time to time into the water. 
 
 If you hold a finger of one hand motionless in a glass of wa- 
 ter, and at the same time move a finger of the other hand 
 swiftly through water of the same temperature, a different 
 sensation will be soon perceived in the different fingers.f 
 
 Most animal substances, especially those which Providence 
 has assigned as a covering for animals, such as fur, wool, hair, 
 
 * One reason why fur, down, &c. conduct heat so badly, is, that 
 they contain a targe quantity of air, which is a worse conductor than 
 the materials themselves. G. 
 
 t f he reason seems to be, that the finger, when it is still, warms the 
 water in contact with it : while the one that is stirring is constantly 
 exposed to fresh applications of cold. C. 
 
 5 
 
i& FREE CALORIC, 
 
 skin, &c. are bad. conductors of heat, and are, on that account, 
 such excellent preservatives against the inclemency of winter, 
 that our warmest apparel is made of these materials. 
 
 Emily. Wood is, I dare say, not so good a conductor as me- 
 tal, and it is for that reason, no doubt, that silver tea-pots have 
 always wooden handles. 
 
 Mrs. ti. Yes ; and it is the facility with which metals con- 
 duct caloric that made you suppose that a silver pot radiated 
 more caloric than an earthen one. The silver pot is in fact hot- 
 ter to the hand when in contact with it ; but it is because its 
 conducting power more than counterbalances its deficiency in 
 regard to radiation. 
 
 We have observed that the most dense bodies are in general 
 the best conductors ; and metals, you know, are of that class. 
 Porous bodies, such as the earths and wood, are worse conduct- 
 ors, chiefly, I believe, on account of their pores being filled 
 with air ; for air is a remarkably bad conductor. 
 
 Caroline. It is a very fortunate circumstance that air should 
 be a bad conductor, as it tends to preserve the heat of the body 
 when exposed to cold weather. 
 
 Mrs. B. It is one of the many benevolent dispensations of 
 Providence, in order to soften the inclemency of the seasons, 
 and to render almost all climates habitable to man. 
 
 In fluids of different densities, the power of conducting 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 of the atmosphere. 
 
 Caroline. Indeed I know not how to believe it, it feels so 
 extremely cold. But we may easily ascertain its true tempera- 
 ture by the thermometer. It is really not colder than the air: 
 the apparent difference then is produced merely by the differ- 
 ence 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 temperature of bodies, 
 and how necessary a thermometer is for that purpose. 
 
 It has indeed been doubted whether fluids have the power 
 of conducting caloric in the same manner as solid bodies. 
 Count Rumford, a very few years since, attempted to prove, 
 by a variety of experiments, that fluids, when at rest, were 
 not at all endowed fvith this property. 
 
 Caroline. How is that possible, since they are capable 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 ? 
 
 ji.rs. . . Count Rumford did not mean to say that fluids 
 would not communicate their heat to solid bodies j but only 
 
FREE CALORIC. 3$ 
 
 -/at heat does not pervade fluids, that is to say, is not transmit- 
 ted from one particle of a fluid to another, in the same manner. 
 as in solid bodies. 
 
 Emily. But when you heat a vessel of water over the fire, it 
 the particles of water do not communicate heat to each other^ 
 how does the water become hot throughout ? 
 
 Mrs. 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 bottom of the vessel, be- 
 come specifically lighter than the rest of the liquid, and conse- 
 quently 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 at the bottom, and cooled at the surface of the liquid ; 
 but as the fire communicates heat more rapidly than the atmos- 
 phere cools the succession of surfaces, the whole of the liquid 
 in time becomes heated. 
 
 Caroline. This accounts most ingeniously for the propaga- 
 tion of heat upwards. But suppose you were to heat the up- 
 per surface of a liquid, the particles being specifically lighter 
 than those below, could not descend : how therefore would the 
 heat be communicated downwards? 
 
 Mrs. B. If there were no agitation to force the heated sur- 
 face downwards, Count Rumford assures us that the heat would 
 not descend. In proof of this he succeeded in making the up- 
 per surface of a vessel of water boil and evaporate, while a 
 cake of ice remained frozen at the bottom.* 
 
 Caroline. That is very extraordinary indeed ! 
 
 Mrs. B. It appears so, because we are not accustomed to 
 heat liquids by their upper surface ; but you will understand 
 this theory better if I show you the internal motion that takes 
 place in liquids when they experience a change of temperature. 
 The motion of the liqnid itself is indeed invisible from the ex- 
 treme minuteness of its particles ; but if you mix with it any 
 coloured dust, or powder, of nearly the same specific gravity as 
 the liquid, you may judge of the inteinal motion of the latter 
 by that of the coloured dust it contains. Do you see the small 
 
 *Dr. Thomson says " All fluids, however, are capable of conduct- 
 ing caloric ; for when the source of heat is applied to their surface, 
 the caloric gradually makes its way downwards, and the temperature 
 of every stratum gradually diminishes from the surface to the bottom 
 cf the liouid." C, 
 
40 FUSE CALORIC. 
 
 piece of amber moving about in the liquid contained in this 
 phial ? 
 
 Caroline. Yes, perfectly. 
 
 Jl-rs. B. We shall now immerse the phial in a glass of 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 in the centre ; but I do not un- 
 derstand 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 laterally to the surface, 
 v here, in parting with their heat, they are condensed, and in 
 descending, form the central current. 
 
 Caroline. This is indeed a very clear and satisfactory exper- 
 iment ; but how much slower the currents now move than they 
 Uid at first ? 
 
 Mrs. B. It is because the circulation of particles has nearly 
 produced an equilibrium of temperature between the liquid in 
 the glass and that in the phial. 
 
 Caroline. But these communicate laterally, and I thought 
 that heat in liquids could be propagated only upwards. 
 
 Mrs. B. You do not take notice that the heat is imparted 
 from one liquid to the other, through the medium of the phial 
 itself, the external surface of which receives 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 effect 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 therefore descend and force up the central parti- 
 cles; which, being warmer, are consequently lighter. 
 
 Mrs. tt. It is just so. Count Rumford hence infers, 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 levity of the heated particles, heat 
 cannot be propagated downwards. 
 
 But though I believe that Count Rumford's theory as to 
 heat being incapable of pervading fluids is not strictly cor- 
 rect, yet there is, no doubt, much truth in li.s observation, 
 tha the communication is materially promoted by a motion 
 of the parts ; and this accounts for the cold that is found to 
 prevail at the bottom of the lakes in Switzerland, which are 
 fed by rivers issuing from the snowy Alps, The water of 
 
CALORIC. 41 
 
 these rivers being colder, and therefore more dense than that of 
 She lakes, subsides to the bottom, where it cannot 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 further than the agitation extends. 
 
 Emily. But when the atmosphere is colder than the lake, the 
 colder surface of the water will descend, for the very reason 
 that the warmer will not. 
 
 Mrs. 6. Certainly ; and it is on this account that neither a 
 lake, nor any body of svater whatever, can be frozen until every 
 particle of the water has risen to the surface to give off its calo- 
 ric 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 
 be brought down to the freezing point, why is only the surface 
 frozen ? 
 
 Mrs. B. The temperature of the whole body is lowered, but 
 not to the freezing point. The diminution of heat, as you 
 know, produces a contraction in the bulk of fluids, us well as 
 of solids. This effect, however, does not take place in water 
 below the temperature of 40 degrees, which is 8 degrees above 
 the freezing point. At that temperature, therefore, the inter- 
 nal motion, occasioned by the increased specific gravity of the 
 condensed particles, ceases ; for when the water at I he surface 
 no longer condenses, it will no longer descend, and leave a 
 fresh surface exposed to the atmosphere : 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 be- 
 neath a long time from being affected 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 body of water to 
 40 degrees ? 
 
 Jllrs. H. That is one reason why the sea, as a large mass of 
 water, does not freeze. But, independently of this, salt water 
 does not freeze till it is cooled much below 32 degrees, and 
 with respect to the law of condensation, salt water is an ex- 
 ception, as it condenses even many degrees below the freezing 
 point. When the caloric of fresh water, therefore, is impris- 
 oned by the ice on its surface, the ocean still continues throw- 
 ing offbeat into the atmosphere, which is a most signal dispen- 
 sation of Providence to moderate the intensity of the cold in 
 winter. 
 
 Caroline. This theory of the non-conducting power ef & 
 
42 FREE CALORIC. 
 
 quids, does not, I suppose, hold good with respect to air, 
 otherwise the atmosphere would not be heated by the rays of 
 the sun passing through it ? 
 
 Mrs. B. Nor is it heated in that way. The pure atmosphere 
 is a perfectly transparent medium, which neither radiates, ab- 
 sorbs, nor conducts caloric, but transmits the rays of the sun 
 to us without in any way diminishing their intensity. The air 
 is therefore not more heated, by the sun's rays passing through 
 it, than diamond, glass, water, or any other transparent me- 
 dium.* 
 
 Caroline. That is very extraordinary ! Are glass windows 
 not heated then by the sun shining on them ? 
 
 Mrs. B. No; not if the glass be perfectly transparent. A 
 most convincing proof that glass transmits the rays of the sun 
 without being heated by them is afforded by the burning lens, 
 which by converging the rays to a focus will set combustible 
 bodies on fire, without its own temperature being raised. 
 
 Emily. Yet, Mrs. B., if I hold a piece of glass near the fire, 
 it is almost immediately warmed by it ; the glass therefore must 
 retain some of the caloric radiated by the fire ? Is it that the 
 solar rays alone pass freely through glass without paying trib- 
 ute? It seems unaccountable that the radiation of a common 
 fire should have power to do what the sun's rays cannot accom- 
 plish. 
 
 Mrs. B. It is not because the rays from the fire have more 
 power, but rather because they have less, that they heat glass 
 and other transparent bodies. It is true, however, that as you 
 approach the source of heat the rays being nearer each other, 
 the heat is more condensed, and can produce effects of which 
 the solar rays, from the great distance of their source, are inca- 
 pable. Thus we should find it impossible to roast a joint of 
 m-^at by the sun's rays, though it is so easily done by culinary 
 h at. Yet calorie emanated from burning bodies, which is 
 commonly called culinary heat, has neither the intensity nor the 
 velocity of solar rays. All caloric, we have said, is supposed 
 to proceed originally from the sun; but after having been incor- 
 porated with terrestrial bodies, and again given out by them, 
 though its nature is not ess nfially altered, it retains neither the 
 intensity nor the velocity with which it first emanated from 
 that luminary; it has therefore not the power of passing through 
 
 * To show still better that transparent media are not heated by the 
 ays of the sun, throw the focus of a hurnine; lens into a vessel of clear 
 water. ISo effect on the temperature will be produced; but if an 
 spake body, as a piece of cork be introduced under the focus, the nra- 
 ter at this point instantly begins to boih C. 
 
CALORIC. 43 
 
 transparent mediums, such as glass and water, without being 
 partially retained by those bodies. 
 
 Emily. I recollect that in the experiment on the reflection of 
 heat, the glass skreen which you interposed between the burn- 
 ing taper and the mirror, arrested the rays of caloric, and suf- 
 fered only those of light to pass through it. 
 
 Caroline. Glass windows, then, though they cannot be heat- 
 ed by the sun shining on them, may be heated internally by a 
 fire in the room ? But, Mrs. B., since the atmosphere is not 
 warmed by the solar rays passing through it, how does it obtain 
 heat ; for all the fires that are burning on the surface of the 
 earth would contribute very little towards warming it ? 
 
 Emily. The radiation of heat is not confined to burning bod- 
 ies ; for all bodies, you know, have that property ; therefore 
 not only every thing upon the surface of the earth, but the 
 earth itself, must radiate heat ; and this terrestrial caloric, not 
 having, I suppose, sufficient power to traverse the atmosphere, 
 communicates heat to it. 
 
 Mrs. 13. Your inference is extremely well drawn, Emily ; 
 but the foundation on which it rests is not sound : for the fact 
 is, that terrestrial or culinary heat, though it cannot pass through 
 the denser transparent mediums, such as glass or water, without 
 loss, traverses the atmosphere completely ; so that all the heat 
 which the earth radiates, unless it meet with clouds* or any 
 foreign body to intercept its passage, passes into the distant re- 
 gions of the universe. 
 
 Caroline. What a pity that so much heat should be wasted ! 
 
 Mrs. B. Before you are tempted to object to any law of na- 
 ture, reflect whether it may not prove to be one of the number- 
 less dispensations of Piovidence for our good. If all the heat 
 which the earth has received from the sun, since the creation 
 hud been accumulated in it, its temperature by this time would, 
 no doubt, have been more elevated than any human being could 
 have borne. 
 
 Caroline. I spoke indeed very inconsiderately. But, Mrs. 
 B , though the earth, at such a high temperature, might have 
 scorched our feet, we should always have had a cool refreshing 
 air to breathe, since the radiation of the earth does not heat the 
 atmosphere. 
 
 Emily. The cool air would have afforded but very insufficient 
 
 * Every one has observed how oppressive the heat is on a foggy, o? 
 cloudy day in the summer. The moisture of the f')g absorbs the heat- 
 which the earth radiates, and throws it back, upon the earth again, 
 and upon us. C, 
 
44 FREE CALORIC, 
 
 Jrefreshnaent, whilst our bodies were exposed to the burning fa* 
 diation of the earth. 
 
 Mrs. B. Nor should we have breathed a cool air ; for though 
 it is true that heat is not communicated to the atmosphere by 
 radiation, yet the air is warmed by contact with heated bodies, 
 in the same manner as solids or liquids. The stratum of air 
 which is immediately in contact with the earth is heated by it ; 
 it becomes specifically lighter and rises, making way for another 
 stratum of air which is in its turn heated and carried upwards ; 
 and thus each successive stratum of air is warmed by coming in 
 contact with the earth. You may perceive this effect in a sultry 
 day, if you attentively observe the strata of air near the surface 
 of the earth; they appear in constant agitation, for though it is 
 true the air is itself invisible, yet the sun shining on the vapours 
 floating in it, render them visible, like the amber dust in the wa- 
 ter. The temperature of the surface of the earth is therefore the 
 source from whence the atmosphere derives its heat, though it 
 is communicated neither by radiation, nor transmitted from one 
 particle of it to another by the conducting power ; but every 
 particle of air must come in contact with the earth in order to 
 receive heat from it. 
 
 Emily. Wind then by agitating the air should contribute to 
 cool the earth and warm the atmosphere, by bringing a more 
 rapid succession of fresh strata of air in contact with the earth, 
 and yet in general wind feels cooler than still air? 
 
 Mrs. B. Because the agitation of the air carries off heat 
 from the surface of our bodies more rapidly than still air, by 
 occasioning a greater number of points of contact in a given 
 time. 
 
 Emily. Since it is from the earth and not the sun that the at- 
 mosphere receives its heat, I no longer wonder that elevated 
 regions should be colder than plains and valleys ; it was always 
 a subject of astonishment to me, that in ascending a mountain 
 and approaching the sun, the air became colder instead of being 
 more heated. 
 
 Mrs. B. At the distance of about a hundred million of miles, 
 which we are from the sun, the approach of a few thousand feel 
 makes no sensible difference, whilst it produces a very consid- 
 erable effect with regard to the warming the atmosphere at the 
 surface of the earth. 
 
 Caroline. Yet as the warm air arises from the earth and the 
 cold air descends to it, I should have supposed that heat would 
 have accumulated in the upper regions of the atmosphere, and 
 that we should have felt the air warmer as we ascended ? 
 
 Mrs. j?. The atmosphere, you know, diminishes in density. 
 

II 
 
 *i 
 
 II-S 
 
 
 
FREE CALORIC. 43 
 
 und consequently in weight, as it is more distant from the earth ; 
 the warm air, therefore, rises till it meets with a stratum of air 
 of its own density ; and it will not ascend into the upper regions 
 of the atmosphere until all the parts beneath have been previ- 
 ously heated. The length of summer even in warm climates 
 does not heat the air sufficiently to melt the snow which has ac- 
 cumulated during the winter on very high mountains, although 
 they are almost constantly exposed to the heat of the sun's rays, 
 being too much elevated to be often enveloped in clouds. 
 
 Emily. These explanations are very satisfactory ; but allow 
 me to ask you one more question respecting the increased levity 
 of heated liquids. You said that when water was heated over 
 the fire, the particles 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 ? 
 
 Mrs. 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, (PLATE IV. Fig. 
 1.) in order that you may be well acquainted with the process 
 of ebullition ; you will then see, through the glass, that the 
 vapour rises in bubbles from the bottom. We shall make it 
 boil by means of a lamp, which is 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 dissolved in the water, or attached to the inner sur- 
 face of the flask, and which, being rarefied by the heat, ascend 
 in the water. 
 
 Emily. But the heat which rarefies the air inclosed in 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, is more easily 
 ram lormer, therefore, expands to a great extent, 
 
 whilstWe 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, 
 
46 FREE CALORIC. 
 
 Caroline. They must rise, you know, from their specific lev- 
 ity. 
 
 Mrs. B. You are right, Caroline ; but vapour has not in all 
 liquids (when brought to the degree of vaporization) the power 
 of overcoming the pressure of the less heated surface. Metals, 
 for instance, mercury excepted, evaporate only from the sur- 
 face ; 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 a state of 
 ebullition. 
 
 Emily. I have observed that steam, immediately issuing 
 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 evap- 
 orates, than when it first begins to diffuse itself in the air. 
 
 Mrs. /> ; . When the steam is first formed, it is so perfectly 
 dissolved by caloric, as to be invisible. In order however to 
 understand this, it will be necessary for me to enter into some 
 explanation respecting the nature of SOLUTION. 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 flu- 
 id, as to become invisible in it, and to partake of its fluidity ; 
 but in common solutions this happens without any decomposi- 
 tion, the body being only divided into its integrant particles by 
 the fluid in which it is melted. 
 
 Caroline. It is then a mode of destroying the attraction of 
 aggregation. 
 
 Mrs. 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 perfect, it is not produced by any chem- 
 ical combination ; both the salt and the water remain unchang- 
 ed ; and if you were to separate them by evaporating the latter, 
 you would find the salt in the same state as before. 
 
 Emily. I suppose that water is a solvent for solid bodies, 
 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 ofjgo^d sub- 
 stances are dissolved by heat : thus metals, which aMBnsolu- 
 ble in water, can be dissolved by intense heat, being first fused 
 or converted into a liquid, and then rarefied into an invisible 
 vapour. Many other bodies, such as salt, gums, &c. yield to 
 <-hher of these solvents. 
 
FREE CALORIC. 47 
 
 Caroline. And that, no doubt, is the reason why hot water 
 will melt them so much better than cold water? 
 
 Mrs. B. It is so. Caloric may, indeed, be considered as 
 having, in every instance, some share in the solution of a body 
 by water, since 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 contained in it. 
 
 Mrs. B. That, probably, would be carrying the speculation 
 too far; I should rather think that water and caloric unite their 
 efforts to dissolve a body, and that the difficulty or facility of 
 effecting this, depend both on the degree of attraction of ag- 
 gregation to be overcome, and on the arrangement of the par- 
 ticles which are more or less disposed to be divided and pene- 
 trated by the solvent. 
 
 Emily. But have not all liquids the same solvent power as 
 water ? 
 
 Mrs. B. The solvent power of other liquids varies according 
 to their nature, and that of the substances submitted to their 
 action. Most of these solvents, indeed, differ essentially from 
 water, as they do not merely separate the integrant particles of 
 the bodies which they dissolve, but attack their constituent 
 principles by the power of chemical attraction, thus producing 
 a true decomposition. These more complicated operations we 
 must consider in another place, and confine our attention at 
 present to the solutions 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. 
 
 Mrs. B. "in this case it is not a solution, but simply a mix- 
 ture. 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 another ; both these substances 
 are white, but their effect on the water will be very different. 
 
 Caroline. Very different indeed ! The salt entirely disap- 
 pears and leaves the water transparent, whilst the chalk chan- 
 ges it into an opaque liquid like milk. 
 
 Emily. And would lumps of chalk and salt produce similar 
 effects on water ? 
 
 Mrs. 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 sub- 
 stances reduced to powder, which does not, in any respect alter 
 
48 FREE CALORIC. 
 
 their nature, but facilitates the operation merely by presenting 
 a greater quantity of surface to the water. 
 
 I must not forget to mention a veiy curious circumstance 
 respecting solutions, which is, that a fluid is not nearly so 
 much increased in bulk by holding a body in solution, as it 
 would by mere mixture with the body. 
 
 Caroline. That seems impossible; for two bodies cannot 
 exist together in the same space. 
 
 Mrs. B. Two bodies may, by condensation, occupy less 
 ?pace when in union than when separate, and this I can show 
 you by an easy experiment. 
 
 This phial, which contains some salt, I shall fill with water, 
 pouring it in quickly, so as not to dissolve much of the salt ; 
 and when it is quite full I cork it. If I now shake the phial 
 till the salt is dissolved, you will observe that it is no longer 
 full. 
 
 Caroline. I shall try to add a little more salt. But now, you 
 see, Mrs. B., the water runs over. 
 
 Airs. 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 wa- 
 ter in this case is said to be saturated with salt. 
 
 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 solu- 
 tion of a liquid by caloric. 
 
 Mrs. B. It is probably of a similar nature ; but as caloric is 
 an invisible fluid, its action as a solvent is not so obvious as that 
 of water. Caloric, we may conceive, dissolves water, and con- 
 verts it into vapour by the same process as water dissolves salt- 
 that is to say, the particles of water are so minutely divided by 
 the caloric as to become invisible. Thus, you are now enabled 
 to understand why the vapour of boiling water, when it first is- 
 sues from the spout of a kettle, is invisible; it is so, because it 
 is then completely dissolved by caloric. But the air wi f h which 
 it comes in contact, being much colder than the vapour, the 
 latter yields to it a quantity of its caloric. The particles of va- 
 pour being thus in a great measure deprived of their solvent, 
 gradually collect, and become visible in the form of stenro, whi h 
 is water in a state of imperfect solution; and if you were I'ur- 
 ther to deprive it of its caloric, it would return to its original li- 
 quid state. 
 
 Caroline. That I understand very well. If you hold a cold 
 plate ov^r a tea-urn, the steam issuing from it will be immedi- 
 ately converted into drops of water by parting with its calorir 
 
FREE CALORIC. 4$ 
 
 to the plate 5 but in what state is the steam, when it becomes 
 invisible by being diffused in the air ? 
 
 Mrs. B. It is not merely diffused, but is again dissolved by 
 the air. 
 
 Emily. The air, then, has a solvent power, like water and 
 caloric ? 
 
 Mrs. B. This was formerly believed to be the case. But it 
 appears from more recent enquiries that the solvent power of 
 the atmosphere depends solely upon the caloric contained in it. 
 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 sufficiently warm, it be- 
 comes perfectly invisible. 
 
 Emily. Can any water dissolve in the atmosphere without 
 its being previously converted into vapour by boiling ? 
 
 Mrs. B. Unquestionably ; and this constitutes the difference 
 between vaporization and evaporation. Water, when heated 
 to the boiling point, can no longer exist in the form of water, 
 and must necessarily be converted into vapour or steam, what- 
 ever may be the state and temperature of the surrounding me- 
 dium; this is called vaporization. But the atmosphere, by 
 means of the caloric it contains, can take up a certain portion of 
 water at any temperature, and hold it in a state of solution. 
 This is simply evaporation. Thus the atmosphere is contin- 
 ually carrying off moisture from the surface of the earth, until 
 it is saturated with it. 
 
 Caroline. That is the case, no doubt, when we feel the ati 
 mosphere damp 
 
 Mrs. B. On the contrary, when the moisture is well dissol- 
 ved it occasions no humidity : it is only when in a state of im- 
 perfect solution and floating in the atmosphere, in the form of 
 watery vapour, that it produces dampness. This happens 
 more frequently in winter than in summer ; for the lower the 
 temperature of the atmosphere, the less water it can dissolve ; 
 and in reality it never contains so much moisture as in a dry 
 hot summer's day. 
 
 Caroline. You astonish me ! But why, then, is the air so dry 
 in frosty weather, when its temperature is at the lowest ? 
 
 Emily. This, I conjecture, proceeds not so much from the 
 moisture being dissolved, as from its being frozen j* is not that 
 the case ? 
 
 * [n cold climates, when there is not a cloud to be seen, and the sun 
 rises in all his glory, the air is sometimes full of little particles of ice* 
 glistening in every'direction, and forming a most beautiful spectacle. 
 This is owing to the condensation, and freezing of the pai tides of wav 
 ter iqt the air, by the intense cold. C. 
 
 6 
 
50 FREE CALORIC. 
 
 Mrs. B. It is ; and the freezing of the watery vapour which 
 the atmospheric heat could not dissolve, produces what is call- 
 ed a hoar frost ; for the particles descend in freezing, and attach 
 themselves to whatever they meet with on the surface of the 
 earth. 
 
 The tendency of free caloric to an equilibrium, together with 
 its solvent power, are likewise connected the phenomena of rain, 
 of dew, &c. When moist air of a certain temperature hap- 
 pens to pass through a colder region of the atmosphere, it parts 
 with a portion of its heat to the surrounding air ; the quantity 
 of caloric, therefore, which served to keep the water in a state 
 of vapour, being diminished, the watery particles approach 
 each other, and form themselves into drops of water, which be- 
 ing heavier than the atmosphere, descend to the earth. There 
 are also other circumstances, and particularly the variation in 
 the weight of the atmosphere, which may contribute to the for- 
 mation of rain. This, however, is an intricate subject, into 
 which we cannot more fully enter at present. 
 
 Emily. In what manner do you account for the formation of 
 dew ? 
 
 Mrs. B. Dew is a deposition of watery particles or minute 
 drops from the atmosphere, precipitated by the coolness of 
 the evening. 
 
 Caroline. This precipitation is owing, I suppose, to the cool- 
 ing of the atmosphere, which prevents its retaining so great a 
 quantity of watery vapour in solution as during the heat of 
 the day. 
 
 Mrs. B. Such was, from time immemorial, the generally re- 
 ceived opinion respecting the cause of dew ; but it has been 
 very recently proved by a course of ingenious experiments of 
 Dr. Wells, that the deposition of dew is produced by the cool- 
 ing of the surface of the earth, which he has shown to take 
 place previously to the cooling of the atmosphere 5 for on ex- 
 amining the temperature of a plot of grass just before the dew- 
 fall, he found that it was consideiably colder than the air a few 
 feet above it, from whieh the dew was shortly after precipitated. 
 
 Emily. But why should the earth cool in the evening sooner 
 than the atmosphere ? 
 
 Mrs. B. Because it parts with its heat more readily than the 
 air ; the earth is an excellent radiator of caloric, whilst the at- 
 mosphere does not possess that property, at least in any sensi- 
 ble degree. Towards evening, therefore, when the solar heat 
 declines, and when after sunset it entirely ceases, the earth 
 rapidly cools by radiating heat towards the skies ; whilst the 
 air has no means of parting with its heat but by corning into 
 
FREE CALORIC. >1 
 
 contact with ihe cooled surface of the earth, to which it com- 
 municates its caloric. Its solvent power being thus reduced, 
 it is unable to retain so large a portion of watery vapour, and 
 Deposits those pearly drops which we call dew. 
 
 Emily. If this be the cause of dew, we need not be appre- 
 hensive of receiving any injury from it ; for it can be deposi- 
 ted only on surfaces that are colder than the atmosphere, which 
 is never the case with our bodies. 
 
 Mrs. B. Very true ; yet I would not advise you for this rea- 
 son to be too confident of escaping all the ill effects which may 
 arise from exposure to the dew ; for it may be deposited on 
 your clothes, and chill you afterwards by its evaporation from 
 them. Besides, whenever the dew is copious, there is a chill in 
 the atmosphere which it is not always safe to encounter. 
 
 Caroline. Wind, then, must promote the deposition of dew, 
 by bringing a more rapid succession of particles of air in con- 
 tact with the earth, just as it promotes the cooling of the earth 
 and warming of the atmosphere during the heat of the day ? 
 
 Mrs. B. Yes ; provided the wind be unattended with clouds, 
 for these accumulations of moisture not only prevent the free 
 radiation of the earth towards the upper regions, but themselves 
 radiate towards the earth; under these circumstances much 
 less dew is formed than on fine clear nights, when the radiation 
 of the earth passes without obstacle through the atmosphere to 
 the distant regions of space, whence it receives no caloric in 
 exchange. The dew continuesto be deposited during the night, 
 and is generally most abundant towards morning; when the 
 contrast between the temperature of the earth and that of the 
 air is| greatest. After sunrise the equilibrium of temperature 
 between these two bodies is gradually restored by the solar 
 rays passing freely through the atmosphere to the earth ; and 
 later in the morning the temperature of the earth gains the as- 
 cendency, and gives out caloric to the air by contact, in the same 
 manner as it receives it from the air during the night. 
 
 Can you tell me, now, why a bottle of wine taken fresh from 
 the cellar (in summer particularly,) will soon be covered with 
 dew ; and even the glasses into which the wine is poured will 
 be moistened with a similar vapour? 
 
 Emily. The bottle being colder than the surrounding air, 
 must absorb caloric from it; the moisture therefore which that 
 air contained becomes visible, and forms the dew which is de- 
 posited on the bottle. 
 
 .< 7 rs. '?. Very well, Emily. Now, Caroline, can you inform 
 me why, in a warm room, or close carriage, the contrary effect 
 
52 FREE CALORIC. 
 
 takes place ; that is to say, that the inside of the windows it- 
 covered with vapour ? 
 
 Caroline. I have heard that it proceeds from the breath oi 
 those within the room or the carriage ; and I suppose it is occa- 
 sioned by the windows which, being colder than the breath, de- 
 prive it of part of its caloric, and by this means convert it into 
 watery vapour. 
 
 Mrs, B. You have both explained it extremely well. Bod- 
 ies attract dew in proportion as they are good radiators of ca- 
 loric, as it is this quality which reduces their temperature be- 
 Jow that of the atmosphere; hence we find that little or no dew 
 is deposited on rocks 5 sand, water; while grass and living veg- 
 etables, to which it is so highly beneficial, attract it in abund- 
 ance another remarkable instance of the wise and bountiful 
 dispensations of Providence. 
 
 Emily. And we may again observe it in the abundance of 
 dew in summer, and in hot climates, when its cooling effects are 
 so much required; but I do not understand what natural cause 
 increases the dew in hot weather ? 
 
 Mrs. B. The more caloric the earth receives during the day. 
 the more it will radiate afterwards, and consequently the more 
 rapidly its temperature will be reduced in the evening, in com- 
 parison to that of the atmosphere. In the West Indies espe- 
 cially, where the intense heat of the day is strongly contrasted 
 with the coolness of the evening, the dew is prodigiously abun- 
 dant. During a drought, the dew is less plentiful, as the earth 
 is not sufficiently supplied with moisture to be able to saturate 
 the atmosphere. 
 
 Caroline. I have often observed, Mrs. B., that when I walk 
 out in frosty weather, with a veil over my face, my breath free- 
 zes upon it. Pray what is the reason of that ? 
 
 Jkrs. B. It is because the cold air immediately seizes on the 
 caloric of your breath, and by robbing it of its solvent, reduces 
 it 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 as- 
 sumes the form of ice. 
 
 You may, perhaps, have observed that the breath of animals, 
 or rather the moisture contained in it, is visible in damp weath- 
 er, or during a frost. In the former case, the atmosphere being 
 over-saturated with moisture, can dissolve no more. In the lat- 
 ter, the cold condenses it into visible vapour; and for the same 
 reason, the steam arising from water that is warmer than the at- 
 mosphere, becomes visible. Have you never taken notice of 
 
CALORIC. 53 
 
 the valour rising from your hands after having dipped them 
 into warm water ? 
 
 Caroline. Frequently, especially in frosty weather. 
 
 A'irs. <. We have already observed that pressure is an ob- 
 stacle to evaporation : there are liquids which contain so great 
 a quantity of caloric, and whose particles consequently auhei'e 
 so slightly together, that they may be rapidly converted into va- 
 pour without any elevation of temperature, merely by taking off 
 the weight of the atmosphere. In such liquids, you perceive, 
 it is the pressure of the atmosphere alone that connects their 
 particles, and keeps them in a liquid stale. 
 
 Caroline. I do not well understand why the particles of 
 such fluids should be disunited and converted into vapour, with- 
 out any elevation of temperature, in spite of the attraction of 
 Cohesion. 
 
 Mrs. B. It is because the degree of heat at which we usually 
 observe these fluids is sufficient to overcome 'their attraction of 
 cohesion. Ether is of this description ; it will boil and be con- 
 verted into vapour, at the common temperature of the air, if 
 the pressure of the atmosphere be taken oft'. 
 
 Emily 1 thought that ether would evaporate without either 
 the pressure of the atmosphere being taken a way, or heat appli- 
 ed ; and that it was for that reason so necessary to keep it care- 
 fully corked up? 
 
 JV,rs. -''. It is true it will evaporate, but without ebullition ; 
 what 1 am now speaking of is the vaporization of ether, or its 
 conversion into vapour by tailing. 1 am going to shoiv you 
 how suddenly the ether in this phial will be converted into va- 
 pour, by means of the air-pump. Observe with what rapidity 
 the bubbles ascend, as I take off the pressured the atmosphere. 
 
 Caroline. It positively boils : how singular 10 see a liquid 
 boil without rieat! 
 
 Mrs. B. Now I shall place the phial of ether in this glass, 
 which it nearly fits, so as to leave only a small sp;ice, which I 
 fill with water; and in this state I put it again under the receiv- 
 er. (PLATE IV. Fig. 1.)* You will observe, as 1 exhaust the 
 air from it, that whilst the ether boils, the water freezes. 
 
 * Two pieces of thin ,e;U<s.s tubes, Si aled alone end nrsuit. answer this 
 purpose better. The experiment, however, as here fit-sen' bed, Is diffi- 
 cult, and requires a very nice apparatus. But ir, instead oi im;a!s or 
 tubes, two watch glasses be used, wator may i>r frciZ -n almosi instant- 
 ly in the same manner. The two Classes are placed over one another, 
 w th a few drops of water interposed between thc-in. r n4 the uppermost 
 glass is (illed with ether. After working the pump \> r a mumtt; or 
 two, the glasses are found to adhere strongly together, and a thin lay- 
 ?r of ice is seen between them. 
 
 6* 
 
54 #BEE CALORIC. 
 
 Caroline. It is indeed wonderful to see water freeze in con- 
 tact with a boiling fluid ! 
 
 Emily. I am at a loss to conceive how the ether can pass to 
 the state of vapour without an addition of caloric. Does it not 
 contain more caloric in a state of vapour, than in a state of li- 
 quidity ? 
 
 Mrs. B. It certainly does ; for though it is the pressure of 
 the atmosphere which condenses it into a liquid, it is by forcing 
 out the caloric that belongs to it when in an aeViform state. 
 
 Emily. You have, therefore, two difficulties to explain, Mrs. 
 B. First, whence the ether obtains the caloric necessary to 
 convert it into vapour when it is relieved from the pressure of 
 the atmosphere; and, secondly, what is the reason that the wa- 
 ter, in which the bottle of ether stands, is frozen ? 
 
 Caroline. Now, I think, 1 can answer both these questions. 
 The ether obtains the addition of caloric required, from the 
 water in the glass; and the loss of caloric, which the latter sus- 
 tains, is the occasion of its freezing. 
 
 Mrs. B. You are perfectly right ; and if you look at the 
 thermometer which 1 have placed in the water, whilst I am 
 working the pump, you will see that every time bubbles of va- 
 pour are produced, the mercury descends; which proves that 
 the heat of the water diminishes in 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 the exchange of caloric between two 
 bodies of equal temperature, was always equal; how, then, is 
 it that the water, which was originally of the same temperature 
 as the ether, gives out caloric to it, till the water is frozen, and 
 the ether made to boil ? 
 
 Mrs. B. I suspected that you would make these objections ; 
 and, in order to remove them, I enclosed two thermometers in 
 the air-pump ; one of which stands hi the glass of water, the 
 other in the phial of ether; and you may see that the equilib- 
 rium of temperature is not destroyed; for as the thermometer 
 descends in the water, that in the ether sinks in the same man- 
 ner; so that both thermometers indicate the same temperature, 
 though one of them is in a boiling, the other in a freezing li- 
 quid. 
 
 Emily. The ether, then, becomes colder as it boils ? This is 
 So contrary to common experience, that I confess it astonishes 
 me exceedingly. 
 
FREE CALORIC, 55 
 
 Caroline. It is, indeed, a most extraordinary circumstance* 
 But pray, how do you account for it ? 
 
 Mrs. ti. I cannot satisfy your curiosity at present; for be- 
 fore we can attempt to explain this apparent paradox, it is 
 necessary to become acquainted with the subject of LATENT 
 HEAT ; and that, I think, we must defer till our next interview. 
 
 Caroline. I believe, Mrs. B., thai you are glad to put off the 
 explanation ; for it must be a very difficult point to account for. 
 
 Mrs. 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 ether, boil with less 
 heat, if deprived of the pressure of the atmosphere? 
 
 Mrs. 8. Undoubtedly. You must always recollect that there 
 are two forces to overcome, in order to make a liquid boil or 
 evaporate; the attraction of aggregation, and the weight of the 
 atmosphere. On the summit of a high mountain (as Mr. I>e 
 Saussure ascertained on Mount Blanc) much less heat is requi- 
 red to make water boil, than in the plain, where the weight of 
 the atmosphere is greater.* Indeed if the weight of the atmos- 
 phere be entirely removed by means of a good air-pump, and 
 if water be placed in the exhausted receiver, it will evaporate 
 so fast, however cold it may be, as to give it the appearance of 
 boiling from the surface. But without the assistance of the 
 air pump, I can show you a very pretty experiment, which 
 proves the effect of the pressure of the atmosphere in this re- 
 spect. 
 
 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 dip 
 the flask into a bason of cold water. t 
 
 Caroline. But look, Mrs. B., the hot water begins to boil 
 again, although the cold water must rob it more and more of 
 its caloric r What can be the reason of that ? 
 
 Mrs. B. Let us examine its temperature. You see the ther- 
 mometer immersed in it remains stationary at 150 degrees, 
 which is about 30 degrees below the boiling point. When I 
 took the flask from the lamp, I observed to you that the upper 
 
 * On the top of Mount Blanc, water boiled when heated only to 
 187 degrees, instead of 212 degrees. 
 
 t f.'he same effect may be produced by wrapping a cold wet linen 
 cloth round the upper part of the flask. In order to. show how much 
 the water cools whilst it is boiling, a thermometer, graduated on the 
 tube itself, may be introduced into the bottle through the cork* 
 
56 FREE CALORIC. 
 
 part of it was filled with vapour ; this being compelled to yield 
 its caloric to the cold water, was again condensed 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. 
 
 Mrs. h. The water below, therefore, no longer sustains the 
 pressure of the atmosphere, and will consequently boil at a much 
 lower temperature. Thus, you see, though it had lost many de- 
 grees of heat, it began boiling again the instant the vacuum was 
 formed above it. The boiling has now ceased, the tempera- 
 ture of the water being still farther reduced ; if it had been 
 ether, instead of water, it would have continued boiling much 
 longer, for ether boils, under the usual atmospheric pressure, at 
 a temperature as low as 100 degrees; and in a vacuum it boils 
 at almost any temperature; but water being a more dense fluid, 
 requires a more considerable quantity of caloric to make it evap- 
 orate quickly, even when the pressure of the atmosphere is re- 
 moved. 
 
 Emily. What proportion of vapour can the atmosphere con- 
 tain in a state of solution ? 
 
 Mrs. B. I do not know whether it has been exactly ascer- 
 tained by experiment ; but at any rate this proportion must va- 
 ry, both according to the temperature and the weight of the at- 
 mosphere ; for the lower the temperature, and the greater the 
 pressure, the smaller must be the proportion of vapour that the 
 atmosphere can contain. 
 
 To conclude the subject of free caloric, I should mention 
 Ignition, by which s meant that emission of light which is pro- 
 duced in bodies at a very high temperature, and which is the 
 sffect of accumulated caloric. 
 
 Emily. You mean, I suppose, that light which is produced 
 by a burning body ? 
 
 Mrs. B. No: ignition is quite independent of combustion. 
 Clay, chalk, and indeed all incombustible substances, may be 
 made red hot. When a body burns, the light emitted is the 
 effect of a chemical change which takes place, whilst ignition 
 is the effect of caloric alone, and no other change than that of 
 temperature is produced in the ignited body. 
 
 All solid bodies, and most liquids, are susceptible of ignition, 
 6r, in other words, of being: heated so as to become luminous ; 
 and it is remarkable that this takes place pretty nearly at the 
 same temperature in all bodies, that is, at about 800 degrees of 
 Fahrenheit's scale, 
 
OMB1NED CALORIC. (){ 
 
 Emily. But how can liquids attain so high a temperature, 
 without being converted into vapour ? 
 
 Mrs B. By means of confinement and pressure. Water 
 confined in a strong iron vessel (called Papin's digester) can 
 have its temperature raised to upwards of 400 degrees. Sir 
 James Hall has made some very curious experiments on the ef- 
 fects of heat assisted hy pressure; by means of strong gun- 
 barrels, he succeeded in melting a variety of substances which 
 were considered as infusible; arid it is not unlikely that, by 
 similar methods, water itself might be heated to redness. 
 
 Emily. I am surprised at that : for I thought that the force 
 of steam was such as to destroy almost all mechanical resist- 
 ance. 
 
 Mrs. B. The expansive force of steam is prodigious ; but in 
 order to subject water to such high temperatures, it is prevent- 
 ed by confinement from being converted into steam, and the 
 expansion of heated water is comparatively trifling. But we 
 have dwelt so long on the subject of free caloric, that we must 
 reserve the other modifications of that agent to our next meet* 
 ing, when we shall endeavour to proceed more rapidly. 
 
 6ONVERSATION IV. 
 
 ON COMBINED CALORIC, COMPREHENDING SPECIFIC 
 AND LATENT HEAT. 
 
 Mrs. B. WE are now to examine the other modifications of 
 Galoric. 
 
 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 per- 
 ceptible to the senses. 
 
 Mrs. B. In order to enable you to understand them, it will 
 be necessary to enter into some previous explanations. 
 
 It has been discovered by modern chemists, that bodies of a 
 different nature, heated to the same temperature, do not con- 
 tain the same quantity of caloric. 
 
 Caroline. How could that be ascertained ? Have you not 
 told us that it is impossible to discover the absolute quantity of 
 caloric which bodies contain ? 
 
 Mrs. B. True ; but at the same time I said that we were 
 enabled to form a judgment of the proportions which bodies 
 bore to each other in this respect. Thus it is found that, in 
 order to raise the temperature of different bodies the sanre 
 
)S COMBINED CALORIC. 
 
 number of degrees, different quantities of caloric are required 
 for each of them. If, for instance, you plac^ a pound of lead, 
 a pound of chalk, and a pound of milk, in a hot oven, they will 
 be gradually heated to the temperature of the oven 5 but the 
 lead will attain it first, the chalk next, and the milk last. 
 
 Caroline. That is a natural consequence of their different 
 bulks ; the lead, beingthe smallest body, will be heated soonest, 
 and the milk, which is the largest, will require the longest 
 time. 
 
 Mrs. B. That explanation will not do, for if the lead be the 
 least in bulk, it offers also the least surface to the caloric, the 
 quantity of heat therefore which can enter into it in the same 
 space of time is proportionally smaller. 
 
 Emily. Why, then, do not the three bodies attain the tem- 
 perature of the oven at the same time ? 
 
 Mrs. B. It is supposed to be on account of the different 
 capacity 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 require 
 more or less caloric for raising their temperature to any degree 
 of heat. Perhaps the fact may be thus explained : 
 
 Let us put as many marbles into this glass as it will contain, 
 and pour some sand over them observe how the sand pene- 
 trates and lodges between them. We shall now fill another 
 glass with pebbles of various forms you see that they arrange 
 themselves in a more compact manner than the marbles, which, 
 being globular, can touch each other by a single point only. 
 The pebbles therefore, will not admit so much sand between 
 them ; and consequently one . of these glasses will necessarily 
 contain more sand than the other, though both of them be 
 equally full. 
 
 Caroline. This I understand perfectly. The marbles 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. You can no longer be surprised, therefore, that bod- 
 ies of a different capacity, for caloric should require different 
 proportions of that fluid to raise their temperatures equally. 
 
 Emily. But I do not conceive 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. 
 
 Mrs. B. The caloric that is employed in filling the capacity 
 
COMBINED CALORIC, 5$ 
 
 of a body, is not free caloric ; but is imprisoned as it were in 
 the body, and is therefore imperceptible : for we can feel only 
 the 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 imper- 
 ceptible. 
 
 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 im- 
 possible 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. 
 
 Caroline. I begin to understand it : but I confess that the 
 idea of insensible heat is so new and strange to me, that it re- 
 quires some time to render it familiar. 
 
 Mrs. B. Call it insensible caloric, and the difficulty will ap- 
 pear much less formidable. It is indeed a sort of contradic- 
 tion to call it heat, when it is so situated as to be incapable of 
 producing that sensation. Yet this modification of caloric is 
 commonly called SPECIFIC HEAT. 
 
 Caroline. But it certainly would have been more correct to 
 have called it specifiic caloric. 
 
 Emily. I do not understand how the term specific applies to 
 this modification of caloric ? 
 
 Mrs. B. It expresses the relative quantity of caloric which 
 different species of bodies of the same weight and temperature 
 are capable of containing. This modification is also frequently 
 called heat of capacity, a term perhaps preferable, as it ex- 
 plains better its own meaning. 
 
 You now understand, I suppose, why the milk and chalk re- 
 quired a longer portion of time than the lead to raise their tem- 
 perature to that of the oven ? 
 
 Emily. Yes : the milk and chalk having a greater capacity 
 for caloric than the lead, a greater proportion of that fluid be- 
 came insensible in those bodies : and the more slowly, therefore f 
 their temperature was raised. 
 
 Caroline. But might not this difference proceed from the dif- 
 ferent conducting powers of heat in these three bodies, since 
 that which is the best conductor must necessarily attain the 
 temperature of the oven first ? 
 
 Mrs. B Very well observed, Caroline. This objection 
 would be insurmountable, if we could not, by reversing the ex- 
 periment, prove that the milk, the chalk, and the lead, actually 
 absorbed different quantities of caloric, and we know that if the 
 
60 COMBINED CALORIC. 
 
 different time they took in heating, proceeded merely from their 
 different conducting powers, they would each have acquired an 
 equal quantity of caloric. 
 
 Caroline. Certainly. But how can you reverse this experi- 
 ment ? 
 
 Mrs. B. It may be done by cooling the several bodies to the 
 same degree in an apparatus adapted to receive and measure 
 the caloric which they give out. Thus, if you plunge them in- 
 to 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 com- 
 municated to their respective portions of water : for the same 
 quantity of caloric which they each absorbed to raise their tem- 
 perature, will abandon them in lowering it ; and on examining 
 the three vessels of water, you will find the one in which you 
 immersed the lead to be the least heated ; that which held the 
 chalk will be the next ; and that which contained the milk will 
 be heated the most of all. The celebrated Lavoisier has inven- 
 ted a machine to estimate, upon this principle, the specific heat 
 of bodies in a more perfect manner ; but 1 cannot explain it to 
 you, till you are acquainted with the next modification of ca- 
 loric. 
 
 Emily. The more dense a body is, I suppose, the less is its 
 capacity for caloric ? 
 
 Mrs. B. This is not always the case with bodies of different 
 nature ; iron, for instance, contains more specific heat than tin, 
 though it is more dense. This seems to show that specific heat 
 does not merely depend upon the interstices between the parti- 
 cles ; but, probably, also upon some peculiar constitution of 
 the bodies which we do not comprehend. 
 
 Emily. But, Mrs. B., it would appear to me more proper to 
 compare bodies by measure, rather than by weight, in order to 
 estimate their specific heat. Why, for instance, should we 
 not compare pints of milk, of chalk, and of lead, rather than 
 pounds of those substances : for equal weights may be compo- 
 sed of very different quantities ? 
 
 Mrs. B. You are mistaken, my dear ; equal weight must 
 contain equal quantities of matter ; and when we wish to know 
 what is th^ relative quantity of caloric which substances of va- 
 rious kinds are capable of containing under the same tempera- 
 turn, we must compare equal weights, and not equal bulks of 
 those substances. Bodies of the same weight may undoubtedly 
 be of very different dimensions ; but that docs not change 
 their real quantity of matter. A pound of feathers does n at 
 Contain one atom more than a pound of lead. 
 
COMBINED CALORIC. (jt. 
 
 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 never 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 at- 
 tained 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, Caroline. As soon 
 as the lead reached the temperature of the oven, it would re- 
 main stationary ; for it would then give out as much heat as it 
 would receive. You should recollect that the exchange of ra- 
 diating 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 ultimately 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 nev- 
 er cease to keep my advantage 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 different quantities of food 
 to satisfy their appetites, sit down to dinner, both equally hun- 
 gry; the one would consume a much greater quantity of provi- 
 sions than the other, in order to be equally satisfied. 
 
 Mrs. B. Yes, that is very fair; for the quantity of food ne- 
 cessary to satisfy their respective appetites, varies in the sume 
 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 ? 
 
 Mrs. B. None at all : no more than satiety is a test of the 
 quantity of food eaten. The thermometer, as I have repeat- 
 edly said, can be affected only by free caloric, which alone rai- 
 ses the temperature of bodies. 
 
 But there is another mode of proving the existence of spe- 
 cific heat, which affords a very satisfactory illustration of that 
 modification. This, however, I did not enlarge upon before, 
 as I thought it might appear to you rather complicated. If 
 you mix two fluids of different temperatures, let us say the one at 
 50 degrees, and the other at 100 degrees, of what temperature 
 do you suppose the mixture will be ? 
 
 Caroline. It will be no doubt the medium between the two s 
 that is to say, 75 degrees. 
 
 Mrs, B. 'That will be the case if the two bodies happen tc 
 
 r 
 
OH COMBINED CALORIC. 
 
 have the same capacity for caloric; but if not, a different re- 
 sult will be obtained. Thus, for instance, if you mix togeth- 
 er a pound of mercury, heated at 50 degrees, and a pound of 
 water heated at 100 degrees, the temperature of the mixture, 
 instead of being 75 degrees, will be 80 degrees ; so that the wa- 
 ter will have lost only 12 degrees, whilst the mercury will have 
 gained 38 degrees ; from which you will conclude that the ca- 
 pacity of mercury for heat is less than that of water. 
 
 Caroline. I wonder that mercury should have so little spe- 
 cific heat. Did we not see it was a much better conductor of 
 heat than water ? 
 
 Mrs. B. And it is precisely on that account that its specific 
 heat is less. For since the conductive power of bodies de- 
 pends, as we have observed before, on their readiness to receive 
 heat and part with it, it is natural to expect that those bodies 
 which are the worst conductors should absorb the most caloric 
 before they are disposed to part with it to other bodies. But 
 let us now proceed to LATENT HEAT. 
 
 Caroline. And pray what kind of heat is that ? 
 
 Mrs. Jl. It is another modification of combined caloric, 
 which is so analogous t specific heat, that most chemists make 
 no distinction between them ; but Mr. Pictet, in his Essay on 
 Fire, has so clearly discriminated them, that I am induced to 
 adopt his view of the suhject. We therefore call latent heat 
 that portion of insensible caloric which is employed in changing 
 the state of bodies; that is to say, in converting solids into li- 
 quids, or liquids into vapour. When a body changes its state 
 from solid to liquid, or from liquid to vapour, its expansion oc- 
 casions a sudden and considerable increase of capacity for heat, 
 in consequence of which it immediately absorbs a quantity of 
 caloric, which becomes fixed in the body 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. This modification of heat was discovered and na- 
 med by Dr. Black long before the French chemists introduced 
 lhe term caloric, and we must not presume to alter it, as it is 
 still used by much better chemists than ourselves. Besides, 
 you are not to suppose that the nature of heat is altered by be- 
 ing variously modified : for 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 confinement, which prevents them from ac- 
 ting upon our organs 5 and consequently, as soon as they are 
 
COMBINED CALORIC. 
 
 ^xtricated from the body in which they are imprisoned, they re- 
 turn to their state of free caloric. 
 
 Emily. But I do not yet clearly see in what respect latent 
 ;ieat differs from specific heat ; for they are both of them im- 
 prisoned and concealed in bodies. 
 
 Mrs. B. Specific heat is that which is employed in filling the 
 < ap-icity of a body for caloric, in the stale in which this body ac- 
 lually exists; while latent heat is that which is employed only 
 in effecting u 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 modifications 
 might be comprehended under the name of heat of capacity, as 
 in both cases the caloric is equally engaged in filling the capaci- 
 ties of bodies. 
 
 I shall now show you an experiment, which I hope will give 
 you a clear idea of what is understood by latent heat. 
 
 The snow which you see in this phial has been cooled by 
 certain chemical means (which I cannot well explain to you at 
 present,) to five or six degrees below the freezing point, as you 
 will find indicated by the thermometer which is placed in 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 it stops, Mrs. B., and yet the lamp burns 
 ust 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 ? 
 
 Mrs. B. The heat no longer affects the thermometer, because 
 it is wholly employed in converting the ice into water. As the 
 ice melts, the caloric becomes latent in the new-formed liquid, 
 ;nd therefore cannot raise its temperature; and the thermome- 
 ter will consequently remain stationary, till the whole of the ice 
 be melted. 
 
 Caroline. Now it is all melted, and the thermometer begins 
 to rise again. 
 
 Mrs. ft. Because the conversion of the ice into water being 
 completed, the caloric no longer becomes latent; and therefore 
 he heat which the water now receives raises its temperature, as 
 you find the thermometer indicates. 
 
 Emily. LJi.it I do not think that the thermometer rises so 
 quickly in the water as it did in the ice, previous to its begin- 
 ning 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 that of ice, more heat is required to raise its temperature, 
 
$4 COMBINED CALORIC. 
 
 and therefore the thermometer rises slower in the water than in 
 the ice. 
 
 Emily. True ; you said that a solid body always increased 
 its capacity for heat by becoming fluid ; and this is an instance 
 of it. 
 
 Mrs. B. Yes ; and the latent heat is that which is absorbed 
 in consequence of the greater capacity which the water has for 
 heat, in comparison to ice. 
 
 I must now tell you a curious calculation founded on that 
 consideration. I have before observed to you that though the 
 thermometer shows us the comparative warmth of bodies, and 
 enables us to determine the same point at different times and 
 places, it gives us no idea of the absolute quantity of heat in 
 any body. We cannot tell how low it ought to fall by the pri- 
 vation of all heat, but an attempt has been made to infer it in 
 the following manner. It has been found by experiment, that 
 (.he capacity of water for heat, when compared with that of 
 ice, is as 10 to 9 5 so that, at the same temperature, ice con- 
 tains one-tenth of caloric less than water. By experiment also 
 it is observed, that in order to melt ice, there must be added to 
 it as much heat as would, if it did not melt it, raise its temper- 
 ature 140 degrees.* This quantity of heat is therefore absorb- 
 ed when the ice, by being converted into water, is made to 
 contain one-ninth more caloric than it did before. Therefore 
 140 degrees is a ninth part of the heat contained in ice at 30 
 degrees ; and the point of zero, or the absolute privation of 
 heat, must consequently be 1260 degrees below 32 degrees.f 
 
 This mode of investigating so curious a question is ingenious, 
 but its correctness is not yet established by similar calculations 
 for other bodies. The points of absolute cold, indicated by 
 this method in various bodies, are very remote from each other ; 
 it is however possible, that this may arise from some imperfec- 
 tion in the experiments. 
 
 Caroline. It is indeed very ingenious but we must now at- 
 tend to our present experiment. The water begins to boih 
 and the thermometer is again stationary. 
 
 * That is, water contains 140 degrees of heat more than is indica- 
 ted by the thermometer. C. 
 
 t This calculation was made by Dr. Irvine. Dr. Crawford after- 
 wards placed the real zero at 1500 degrees below the of Fahrenheit. 
 Still later Mr. Dalton has turned his attention to the same subject. 
 The mean of his experiments places the real zero 6000 decrees below 
 the freezing point. All this goes to show that very little has yet been 
 demonstrated on this difficult question. C, 
 
COMPOUND CALORIC. 65 
 
 Mra. . Well, Caroline, it is your turn to explain the phe- 
 nomenon. 
 
 Caroline. It is wonderfully curious ! The caloric is now bu- 
 sy 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 bo- 
 dy into a liquid, and now it turns the liquid into vapour ! 
 
 Mrs. B. You see, my dear, how easily you have become ac- 
 quainted with these modifications of insensible heat, which at 
 first appeared so unintelligible. If, now, we were to reverse 
 these changes, and condense the vapour into water, and the wa- 
 ter into ice. the kitent 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 free state. 
 
 Mrs. B. For the purpose of showing this, we need simply 
 conduct the vapour through this tube into this vessel of cold wa- 
 ter, 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 he-it. This method 
 of heating liquids, has been turned to advantage, in several 
 economical establishments. The steam-kitchens, which are 
 getting into such general use, are upon the same principle. The 
 steam is conveyed through a pipe in a simitar manner, into the 
 several 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 princi- 
 ple in many of his fire-places : his grand rnaxira 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 unnecessa- 
 rily escape; and while he economises the free caloric, he takes 
 tare also to turn the latent heat to advantage. It is thus that 
 he is enabled to produce a degree of heat superior to that which 
 is obtained in common fire-places, though he employs loss fuel. 
 
 Emily. When the advantages of such contrivances are so 
 clear and plain, I cannot understand why they are not univer- 
 sally used. 
 
 Mrs. B. A long time is always required before innovations, 
 however useful, can be reconciled with the prejudices of the 
 vulgar. 
 
 Emily. What a pity it is that there should be a prejudice 
 against new inventions j how much more rapidly the world 
 
 7* 
 
COMBINED 
 
 would improve, if such useful discoveries were immediately and 
 universally adopted ! 
 
 Mrs. B. 1 believe, my dear, that there are as many novelties 
 attempted to be introduced, the adoption of which would be 
 prejudicial to society, as there are of those which would be 
 beneficial to it. The well-informed, though by no means ex- 
 empt from error, have an unquestionable advantage over the 
 illiterate, in judging what is likely or not to prove serviceable ; 
 and therefore we find the former more ready to adopt such dis- 
 coveries as promise to be really advantageous, than the latter, 
 who having no other test of the value of a novelty but time and 
 experience, at first oppose its introduction. The well-inform- 
 ed, however, are frequently disappointed in their most san- 
 guine expectations, and the prejudices of the vulgar, though 
 they often retard the progress of knowledge, yet sometimes, it 
 must be admitted, 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 order to render the latent heat sensible, as it 
 escapes from the water on its becoming solid. For this purpose 
 tye 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 as you think. There are certain 
 liemical mixtures which produce a rapid change from the solid 
 Co the fluid state, or the reverse, in the substances combined, in 
 consequence of which change latent heat is either extricated or 
 absorbed. 
 
 Emily. I do not quite understand you 
 
 Mrs. B. This snow and salt, which you see me mix togeth- 
 er, are melting rapidly ; 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 mixture is to 
 be attributed to the change from a solid to a fluid state. The 
 nnion of the snow and salt produces a new arrangement of 
 their particles, in consequence of which they become liquid ; 
 and the quantity of caloric, required to effect this change, is 
 seized upon by the mixture wherever it can be obtained. This 
 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 in this mixtuse, therefore,, would 
 freeze ? 
 
COMBINED CALORIC, 
 
 Mr*. B. Yes 5 at least any fluid that is susceptible of freezing 
 at that temperature. 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 ther- 
 mometer in the glass of water that is to be frozen, in order 
 that you may see how it cools. 
 
 Caroline. The thermometer descends, but the heat which 
 the water is now losing, is its free, not its latent heat. 
 
 Mrs. ti. 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 circumstance ! The 
 thermometer has fallen below the freezing point, and yet the 
 water is not frozen.* 
 
 Mrs. />'. 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 thermometer again rises to the 
 freezing point. 
 
 Caroline. It appears to me very strange that the thermome- 
 ter should rise the very moment that the water 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 cir- 
 cumstance, I did not think 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 extrications of latent 
 heat, at the instant the water freezes, which raises the temper- 
 ature. 
 
 JWrs. B. Certainly ; and if you now examine the thermome- 
 ter, you will find that its rise was but temporary, and lasted on- 
 ly during the disengagement of the latent heat now that all the 
 water is frozen it falls again, and will continue to fall till the ice 
 and mixture are of an equal temperature. 
 
 Emily. And can you show us any experiments in which li- 
 quids, by being mixed, become solid, and disengage latent heat ? 
 
 Mrs. B. I could show you several ; bat you are not yet suf- 
 ficiently 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, 
 
 * To make this experiment striking, the glass containing the water 
 and thermometer ought to he kept perfectly still until the mercury 
 sinks below the freezing point Then agitate the water, or drop into 
 it a small piece of ice, and it instantly shoots into crystal 3 . anHI tfi< 
 thermometer rises. . 
 
68 COMBINED CALORlfc. 
 
 if I pour into it a few drops of this other fluid, called sulphuric 
 acid, the whole, or very nearly the whole, will be instantane- 
 ously converted into a solid mass. 
 
 Emily. How white it turns ! I feel the latent heat escaping, 
 for the bottle is warm, and the fluid is changed to a solid white 
 substance like chalk !* 
 
 Caroline. This is, indeed, the most curious experiment we 
 have seen yet. But pray what is that white vapour, which as- 
 cends from the mixture ? 
 
 Mrs. B. You are not yet enough of a chemist to understand 
 that. But take care, Caroline, do not approach too near it, for 
 it has a very pungent smell. 
 
 I shall show you another instance similar to that of the wa- 
 ter, which you observed to become warmer as it froze. I have 
 in this phial a solution of a salt called sulphat of soda or Glau- 
 ber's salt, made very strong, and corked up when it was hot, and 
 kept without agitation till it became cold, as you may feel the 
 phial is. Now when I take out the cork and let the air fall upon 
 it (for being closed when boiling, there was a vacuum in the up- 
 per part) observe that the salt will suddenly crystalize. . . . 
 
 Caroline. Surprising ! how beautifully the needles of salt 
 have shot through the whole phial ! 
 
 Mrs. B. Yes, it is very striking but pray do not forget the 
 object of the experiment. Feel how warm the phial has be- 
 come by the conversion of part of the liquid into a solid. 
 
 Emily* Quite warm I declare ! this is a most curious expe- 
 riment of the disengagement of latent heat. 
 
 Mrs. B. The slakeingof lime is another remarkable instance 
 of the extrication of latent heat. Have you never observed 
 how quick-lime smokes when water is poured upon it, and how 
 much heat it produces ? 
 
 Caroline. Yes ; but I do not undeistand what change of state 
 takes place in the lime that occasions its giving out latent heat ; 
 for the quick-lime, which is solid, is (if I recollect right) re- 
 duced to powder, by this operation, 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 of which the heat, which 
 
 * The sulphuric acid by its stronger affinity for the lime, takes it 
 from the muriatic acid, unites with it, and forms sulphate of lime. The 
 solidity is owing to the insolubility of this last substance in water. 
 The experiment succeeds well if the water is, saturated with the in- 
 riate. C 
 
COMBINED CALORIC. 69 
 
 kept it in a liquid state, is disengaged, and escapes in a sensible 
 form. 
 
 Caroline. I 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. 
 
 Mrs. ':>. It cannot properly be called ice, since ice implies a 
 degree of cold, at least equal to the freezing point. Yet as wa- 
 ter, in combining with lime, gives out more heat than in free- 
 zing, it must be in a stale of still greater solidity in the lime, 
 than it is in the forrn 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 parti- 
 cles 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 
 r disengages latent heat ? 
 
 Mrs. B. You cannot 'exactly say absorbs latent heat, as the 
 heat becomes latent only on being confined in the body ; but. 
 you may say, generally, that bodies, in passing from a solid to 
 a liquid form, or from the liquid state to that of vapour, absorb 
 heat ; and that when the reverse takes place, heat is disenga- 
 ged.* 
 
 Emily. We can now, I think, account for the ether boiling, 
 and the water freezing in vacuo, at the same temperature.t 
 
 Mrs. B. Let me hear 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 a latent state in one liquid, it 
 passed into a latent state in the other. 
 
 Mrs. B. But this only partly accounts for the result of the 
 experiment ; it remains to be explained why the temperature 
 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 ca- 
 
 ''" This rule, if not universal, admits of very few exception., 
 
70 COMBINED CALORIC. 
 
 loric into latent heat ; so that, though one liquid boils, and tht 
 other freezes, their temperatures remain in a state of equilibri- 
 um. 
 
 Emily. But why does not welter, as well as ether, reduce its 
 own temperature by evaporating ? 
 
 Mrs. B. The fact is that it. does, though much .'ess rapidly 
 than ether. Thus, for instance, you may often have observed, 
 in the heat of summer, htfw much any particular spot may be 
 cooled by watering, though the water used for that purpose be 
 as warm as the air itself. Indeed so much cold may be produ- 
 ced by the mere evaporation of water, that the inhabitants of 
 India, by availing themselves of the most favourable circum- 
 stances for this process which their warm climate can afford, 
 namely, the cool of the night, and situations most exposed to 
 the night breeze, succeed in causing water to freeze, though 
 the temperature of the air be as high as 60 degrees. The wa- 
 ter is put into shallow earthern trays, so as to expose an exten- 
 sive surface to the process of evaporation, and in the morning, 
 the water is found covered with a thin cake of ice, which is col- 
 lected in sufficient quantity to be used for purposes of luxury. 
 
 Caroline. How delicious it must be to drink liquids so cold 
 in those tropical climates ! But, Mrs. B., could we not try that 
 experiment ? 
 
 Mrs . B. If we were in the country, I have no doubt but 
 that we should be able to freeze water, by the same means, and 
 under similar circumstances. But we can do it immediately, 
 upon a small scale, in this very room, in which the thermome- 
 ter stands at 70 degrees. For this purpose we need only place 
 some water in a little cup under the receiver of the air-pump 
 PLATE. V. fig. 1.,) and exhaust the air from it. What will be 
 the consequence, Caroline ? 
 
 Caroline. Of course the water will evaporate more quickU . 
 ,-.ince there will no longer be any atmospheric pressure on it 
 surface : but will this be sufficient to make the water freeze ? 
 
 Mrs. B. Probably not, because the vapour will not be car- 
 ried off fast enough j but this will be accomplished without dii- 
 ficulty if we introduce into the receiver (fig. 1.,) in a saucer, 01 
 other large shallow vessel, some strong sulphuric acid, a sub- 
 stance which has a great attraction for water, whether in the 
 form of vapour, or in the liquid state. This attraction is such 
 that the acid will instantly absorb the moisture as it rises from 
 the water, so as to make room for the formation of fresh va- 
 pour; this \v-ll of course hasten the process, and the cold pro- 
 iiuce-i from the rapid evaporation of the water, will, in a few 
 
1L4TE 77 
 
 e air pump &rtc*u>tr /or Mr. Leth'es experiment. C<r saucer tJif/i vnfp/iur/c 
 aeid. B a afafs or eartfttn cu/> cmrtamuy toater*. D a stand /Gr fa ru* uit/i its 
 k#s mat/t ^&us. A a Thermometer. Ft?. 2. Dr. JMaatM* Cryvpfams. Fy. . Dr. 
 farsstf 7,ux e/*Mi>i?dt CryvjJu>n<t.Ftj.&&4; t/is aii/% rent part? o/ftj.S. .rtenftfarate. 
 
6OMBINEU CALORIC. 71 
 
 minutes, be sufficient to freeze its surface.* We shall now ex- 
 haust the air from the receiver. 
 
 Emily. Thousands of small bubbles already rise through 
 the water from the internal surface of the cup ; what is the rea- 
 son of this ? 
 
 Mrs. B. These are bubbles of air which were partly attach- 
 ed to the vessel, and partly diffused in the water itself; and 
 they expand and rise in consequence of the atmospheric pres- 
 sure being removed. 
 
 Caroline. See, Mrs. B. ; the thermometer in the cup is sink- 
 ing fast ; it has already descended to 40 degrees ! 
 
 Emily. The water seems now and then violently agitated on 
 the surface, as if it were boiling ; and yet the thermometer is 
 descending fast ! 
 
 Mrs. B. You may call it boiling if you please, for this ap- 
 pearance is, as well as boiling, owing to the rapid formation of 
 vapour $ but here, as you have just observed, it takes place 
 from the surface, for it is only when heat is applied to the bot- 
 tom of the vessel that the vapour is formed there. Now crys- 
 tals of ice are actually shooting all over the surface of the water* 
 
 Caroline. How beautiful it is ! The surface is now entirely 
 frozen, but the thermometer remains at 32 degrees. 
 
 Mrs. B. And so it will, conformably with our doctrine of 
 latent heat, until the whole of the water is frozen ^ but it will 
 then again begin to descend lower and lower, in consequence of 
 the evaporation which goes on from the surface of the ice. 
 
 Emily. This is a most interesting experiment ; but it would 
 be still more striking if no sulphuric acid were required. 
 
 Mrs. B. I will show you a freezing instrument, contrived by 
 Dr. Woilaston, upon the same principle as Mr. Leslie's experi- 
 ment, by which water may be frozen by its own evaporation 
 alone, without the assistance of sulphuric acid. 
 
 This tube, which, as you see (PLATE V. fig. 2.,) is ter- 
 minated at each extremity by a bulb, one of which is half full 
 of water, is internally perfectly exhausted of air ; the conse- 
 quence of this is, that the water in the bulb is always much dis- 
 posed to evaporate. This evaporation, however does not 
 proceed sufficiently fast to freeze the water ; but if the empty 
 ball be cooled by some artificial means, so as to condense qiu>k- 
 ly the vapour which rises from the water, the process may be 
 thus so much promoted as to cause the water to freeze in the 
 
 * This experiment was first devised by Mr. Leslie, and has since 
 been modified in a variety of form*. 
 
72 COMBINED CALORIC. 
 
 other ball. Dr. Wollaston has called this instrument Crt/o- 
 phoras. \or Frostbearer. C.] 
 
 Caroline. So that cold seems to perform here the same pail 
 which the sulphuric acid acted in Mr. Leslie's experiment ? 
 
 Mrs. B. Exactly so; but let us try the experiment. 
 
 Etti.ily. How will you cool the instrument ? You have nei- 
 ther ice nor snow. 
 
 Mrs. H. True ; but we have other means of effecting this.* 
 You recollect what an intense cold can be produced by the evap- 
 oration of ether in an exhausted receiver. We shall inclose the 
 bulb in this little bag of fine flannel (fig. 3.), then soak it in 
 ether, and introduce it into the receiver of the air-pump, fig. 5.) 
 For this purpose we shall find it more convenient to use a cry- 
 ophorus of this shape (fig. 4.), as its elongated bulb passes easi- 
 ly through a brass plate which closes the top of the receiver, 
 If we now exhaust the receiver quickly, you will see, in less 
 than a minute, the water freeze in the other bulb, out of the 
 receiver. 
 
 Emily. The bulb already looks quite dim, and small drops 
 of water are condensing on its surface. 
 
 Caroline. And now crystals of ice shoot all over the water. 
 This is, indeed, a very curious experiment! 
 
 Mrs. B. You will see, some other day, that, by a similar 
 method, even quicksilver may be frozen. But we cannot at 
 present indulge in any further digression. 
 
 Having advanced so far on the subject of heat, I may now 
 give you an account of the calorimeter, an instrument invented 
 by Lavoisier, upon the principles just explained, for the purpose 
 of estimating the specific 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 freez- 
 ing point ; this caloric converts into 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 descend- 
 ing from a certain temperature to the freezing point. 
 
 Caroline. In this apparatus, I suppose, the milk, chalk, and 
 lead, would melt different quantities of ice, in proportion to their 
 different capacities for caloric ? 
 
 * This mode of making the experiment was proposed, and the par- 
 ticulars detailed, by Dr. Marcet. in the "34th vol. of Nicholson's Jour- 
 ntd, p. 119. . 
 
COMBINED CALORlo. 7'3 
 
 Mrs. B. Certainly: and thence we are able to ascertain, with 
 precision, their respective capacities for heat. But the calo- 
 rimeter 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 combined caloric, 
 yet we extricate them only to a certain degree, which is the 
 freezing point ; and we know not how much they contain of 
 either below that point. 
 
 Emily. According to the theory of latent heat, it appears to 
 me that the weather should be warm when it freezes, and cold 
 in a thaw : for latent heat is liberated from every substance 
 that it 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. 
 
 Mrs. B. Your observation is very natural ; but consider 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 insuffi- 
 cient to raise its temperature above the freezing point ; other- 
 wise the frost must cease. But if the quantity of latent heat ex- 
 tricated does not destroy the frost, it serves to moderate the sud- 
 denness of the change of temperature of the atmosphere, at the 
 commencement both of frost, and of a thaw. In the first in- 
 stance, its extrication diminishes the severity of the cold ; and, 
 in the latter, its absorption 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 produce those 
 sudden changes in the weather, especially from hot to cold, 
 which we often experience ? 
 
 Mrs. B. This question would lead us into meteorological 
 discussions, to which I am by no means competent. One cir- 
 cumstance, however, we can easily understand. When the air 
 has passed over cold countries, it will probably arrive here at a 
 temperature much below our own, and then it must absorb 
 heat from every object it meets with, which will produce a gen- 
 eral fall of temperature. 
 
 Caroline. But pray, now that we know so much of the effects 
 of heat, will you inform us whether it is really a distinct body, 
 or, as I have heard, a peculiar kind of motion produced in bod^ 
 ies? 
 
 Mrs. B. As I before told you, there is yet much uncertain- 
 ty as to the nature of these subtle agents. But I am inclined 
 to consider heat not as a mere motion, but as a separate sub- 
 stance. Late experiments too appear to make it a compound 
 
 5 
 
74 ELECTRO-CHEMISTRY. 
 
 body, consisting of the two electricities, and in our next con- 
 versation I shall inform you of the principal facts on which that 
 opinion is founded. 
 
 CONVERSATION V. 
 
 ON THE CHEMICAL AGEN IE^ OF ELECTRICITY.* 
 
 Mrs. B. BEFORE we proceed further it will be necessary to 
 give you some account of certain properties of electricity, which 
 have of late yeais been discovered to have an essential connec- 
 tion with the phenomena of chemistry. 
 
 Caroline. It is FLECTRICITY, if I recollect right, which comes 
 next in our list of simple substances ? 
 
 Mrs. B. I have placed electricity in that list, rather from 
 the necessity of < lassing it somewhere, than from any convic- 
 tion that it has a right to that situation, for we are as yet so igno- 
 rant of its intimate nature, that we are unable to determine, not 
 onlv whether it is simple or compound, but whether it is in fact 
 a rhaterial agent ; or, as Sir H. Davy has hinted, whether it 
 may not be merely a property inherent in matter. As, howev- 
 er, it is necessary to adopt some hypothesis for the explanation 
 of the discoveries which this agent has enabled us to make, I 
 have chosen the opinion, at present most prevalent, which sup- 
 poses the existence of two kinds of electricity, distinguished by 
 the names of positive and negative electricity. 
 
 Caroline. Well, I must confess, I do not feel nearly so in- 
 terested in a science in which so much uncertainty prevails, as in 
 those which rest upon established principles ; I never was fond 
 of electricity, because, however beautiful and curious the phe- 
 nomena it exhibits may be, the theories, by which they were 
 explained, appeared to me so various, so obscure and inade- 
 quate, that 1 always remained dissatisfied. I was in hopes 
 that the new discoveries in electricity had thrown so great a 
 light on the subject, that every thing respecting it would now 
 shave been clearly explained. 
 
 Mrs. B. That is a point which we are yet far from having 
 attained. But, in spite of the imperfection of our theories, you 
 will be amply repaid by the importance and novelty of the sub- 
 iect. The number of new facts which have already been as- 
 
 * The electricity extricated by the metals is commonly called Gn^ 
 yftnism. C- 
 
ELECTRO-CHEMISTRY. 
 
 curtained, and the immense prospect of discovery which has 
 lately been opened to us, will, I hope, ultimately lead to a per- 
 fect elucidation of this branch of natural science ; but at pres- 
 ent you must be contented with studying the effects, and in 
 some degree explaining the phenomena, without aspiring to a 
 precise knowledge of the remote cause of electricity. 
 
 You have already obtained some notions of -electricity : in 
 our present conversation, therefore, I shall confine myself to 
 that part of the science which is of late discovery, and is more 
 particularly connected with chemistry. 
 
 It was a trifling and accidental circumstance which first gave 
 rise to this new branch of physical science. Galvani, a pro- 
 fessor of natural philosophy at Bologna, being engaged (about 
 twenty years ago) in some experiments on muscular irritabili- 
 ty, observed, that when a piece of metal was laid on the nerve 
 of a frog, recently dead, whilst the limb supplied by that nerve 
 rested upon seme other metal, the limb suddenly moved, on a 
 communication being made between the two pieces of metal. 
 
 Emily. How is this communication made ? 
 
 Mrs. tt. Either by bringing the two metals into contact, or 
 by connecting them by means of a metallic conductor. But 
 without subjecting a frog to any cruel experiments, I can easily 
 make you sensible of this kind of electric action. Here is a 
 piece of zinc, (one of the metals I mentioned in the list of ele- 
 mentary bodies) put it under your tongue, and this piece of 
 silver upon your tongue, and let both the metals project a little 
 beyond the tip of the tongue very well now make the pro- 
 jecting parts of the metals touch each other, and you will in- 
 stantly perceive a peculiar sensation. 
 
 Emily. Indeed I did, a singular taste, and I think a degree 
 of heat ; but I can hardly describe it. 
 
 Mrs. B. The action of these two pieces of metal on the 
 tongue is, I believe, precisely similar to that made on the nerve 
 of a frog. I shall not detain you by a detailed account of the 
 theory by which Galvani attempted to explain this fact, as it 
 was soon overturned by subsequent experiments, which proved 
 that Galvanism (the name this new power had obtained) was 
 nothing more than electricity. Galvani supposed that the vir- 
 tue of this new agent resided in the nerves of the frog, but Vol- 
 ta, who prosecuted this subject with much greater success, 
 showed that the phenomena did not depend on the organs of the 
 frog, but upon the electrical agency of the metals, which is ex- 
 cited by the moisture of the animal, the organs of the frog be- 
 ing only a delicate test of the presence of electric influence. 
 
 Caroline. I suppose, then, the saliva of the mouth answers 
 
ELECTRO-CHEMISTRY. 
 
 the same purpose as the moisture of the frog, in exciting tht 
 electricity of the pieces of silver and zinc with which Emily 
 tried the experiment on her tongue. 
 
 Mrs. B. Precisely. It does not appear, however, necessa- 
 ry 'hat the fluid used for this purpose should be of an animal 
 nature. Water, and acids very much diluted by water, are 
 found to be the most effectual in promoting the developement of 
 electricity in metals; and, accordingly, the original apparatus 
 which Volta first constructed for this purpose, consisted of a 
 pile or succession of plates of zinc and copper, each pair of 
 which was connected by pieces of cloth or paper impregnated 
 with water; arid this instrument, from its original inconvenient 
 structure and limited strength, has gradually arrived at this 
 present state of poxver and improvement, such as is exhibited 
 in the Voltaic battery. In this apparatus, a specimen of which 
 you see before you (PLATE VI fig. 1.,) the plates of zinc and 
 copper are soldered together in pairs, each pair being placed 
 at regular distances in wooden troughs and the interstices being 
 filled with fluid. 
 
 Caroline. Though you will not allow us to inquire into the pre- 
 cise cause of electricity, may we not ask in what manner the 
 fluid acts on the metals so as to produce it ? 
 
 Mrs. B. The action of the fluid on the metals, whether wa- 
 er or acid be used, is entirely of a chemical nature* But wheth- 
 er electricity is excited by this chemical action, or whether it is 
 produced by the contact of the two metals, is a point upon 
 which philosophers do not yet perfectly agree. 
 
 Emily. But can the mere contact of two metals, without any 
 intervening fluid, produce electricity ? 
 
 Mrs. B. Yes, if they are afterwards separated. It is an es- 
 tablished fact, that when two metals are put in contact, and af- 
 terwards separated, that which has the strongest attraction for 
 oxygen exhibits signs of positive, the other of negative electrici- 
 ty- 
 
 Caroline. It seems then but reasonoble to infer that the pow- 
 er of the Voltaic battery should arise from the contact of the 
 plates of zinc and copper. 
 
 Mrs. B. It is upon this principle that Volta and Sir H. Da- 
 vy explain the phenomena of the pile ; but notwithstanding 
 these two great authorities, many philosophers entertain doubts 
 on the truth of this theory. The chief difficulty which occurs 
 in explaining the phenomena of the Voltaic battery on this prin- 
 ciple, is, that two such plates show no signs of different states 
 of electricity whilst in contact, but only on being separated af- 
 ter contact. Now in the Voltaic battery, those plates that are 
 
. 3 . 
 a/ Machine. 
 
 .&A tie Cylinder.^ the Conductor.-^ fa Xtttfr.. -C ^ Cfa'm. 
 
ELECTRO-CHEMISTRY. 77 
 
 m contact always continue so, being soldered together: and 
 they cannot therefore receive a succession of charges. Be- 
 sides, it" we consider the mere disturbance of the balance of 
 electricity by the contact of the plates, as the sole cause of the 
 production of Voltaic electricity^ it remains to be explained how 
 this disturbed balance becomes an inexhaustible source of elec- 
 trical energy, capable of pouring forth a constant and copious 
 supply of electrical fluid, though without any means of replen- 
 ishing itself from other sources. This subject, it must be own- 
 ed, is involved rn too much obscurity to enable us to speak very 
 decidedly in favour of any theory. But, in order to avoid per- 
 plexing you with different explanations, I shall confine myself 
 to one which appears to me to be least encumbered with difficul- 
 ties, and most likely to accord with truth.* 
 
 This theory supposes the electricity to be excited by the chem- 
 ical action of the acid on the zinc ; but you are yet such novi- 
 ces in chemistry, that I think it will be necessary to give you 
 some previous explanation of the nature of this action. 
 
 All rnetals have a strong attraction for oxygen, and this ele- 
 ment is found in great abundance both in water and in acids. 
 The action of the diluted acid on the zinc consists therefore in 
 its oxygen combining with it, and dissolving its surface. 
 
 Caroline. In the same manner I suppose as we saw an acid 
 dissolve copper? 
 
 Mrs. B Yes; but in the Voltaic battery the diluted acid is 
 not strong enough to produce so complete an effect ; it acts on- 
 ly on the surface of the zinc, to which it yields its oxygen, for- 
 ming upon it a film or crust, which is a compound of the oxy- 
 gen and the metal. 
 
 Emily. Since there is so strong a chemical attraction between 
 oxygen and metals, I suppose they are naturally in different 
 states of electricity ? 
 
 Mrs. B. Yes; it appears that all metals are united with the 
 positive, and that oxygen is the grand source of the negative 
 electricity. 
 
 * This m. de of explaining the phenomena of the Voltaic pile is call- 
 ed the chemical theory of electricity, because it ascribes the cause of 
 these phenomena to certain chemical changes which take place during 
 their appearance. The mode which is here sketched was long since 
 suggested hy Dr. Bostock, who has lately (1818) published " An Ac- 
 count of the History and present State of Galvanism ;" which con- 
 tains a fuller and more complete statement 01 his opinions, and those of 
 other writers on the subject, than any of his former papers, 
 
 8 * 
 
78 ELECTRO-CHEMhTItV, 
 
 Caroline. Does not then the acid act on the plates of cop- 
 per, as well as on those of zinc ?* 
 
 Mrs. B. No ; for though copper has an affinity for oxygen, 
 it is less strong than that of zinc ; and therefore the energy of 
 the acid is only exerted upon the zinc. 
 
 It will be best, I believe, in order to render the action of the 
 Voltaic battery more intelligible, to confine our attention at first 
 to the effect produced on two plates only. (PLATE VI. fig. 2.) 
 
 If a plate of zinc be placed opposite to one of copper, or 
 any other metal less attractive of oxygen, and the space between 
 them (suppose of half an inch in thickness,) be filled with an 
 acid or any fluid capable of oxydating the zinc, the oxydated 
 surface will have its capacity for electricity diminished, so that 
 a quantity of electricity will be evolved from that surface. 
 This electricity will be received by the contiguous fluid, by 
 which it will be transmitted to the opposite metallic surface, the 
 copper, which is not oxydated, and is therefore disposed to re- 
 ceive it; so that the copper plate will thus become positive, 
 whilst the zinc plate will be in the negative state. 
 
 This evolution of electrical fluid however will be very limi- 
 ted; for as these two plates admit of but very little accumula- 
 tion of electricity, and are supposed to have no communication 
 with other bodies, the action of the acid, and further develope- 
 ment of electricity, will be immediately stopped. 
 
 Emily. This action, I suppose, can no more continue than 
 that of a common electrical machine, which is not allowed to 
 communicate with other bodies? 
 
 Mrs. B. Precisely ; the common electrical machine, when 
 excited by the friction of the rubber, gives out both the. positive 
 and negative electricities. (PLATE VI. Fig. 3.) The posi- 
 tive, bv the rotation of the glass cylinder, is conveyed into the 
 conductor, whilst the negative goes into the rubber. But^unless 
 there is a communication made between the rubber and the 
 ground, a very inconsiderable quantity of electricity can be ex- 
 cited ; for the rubber, like the plates of the battery, has too 
 small a capacity to admit of an accumulation of electricity. 
 Unless therefore the electricity can pass out of the rubber, it 
 will not continue to go info it, and consequently no additional 
 accumulation will take place. JNow as one kind of electricity 
 cannot be given out without the other, the developement of the 
 positive electricity is stopped as well as that of the negative, 
 
 * The acid acts upon the copper, but not so strongly as on the zinc. 
 Any two metals, cue of which nas a stronger attraction for oxygen than 
 the other, will form the galvanic series. C. 
 
feLEOTRO-CHEMISTRY". 7$ 
 
 and the conductor therefore cannot receive a succession of char- 
 ges. 
 
 Caroline. But does not the conductor, as well as the rubber, 
 require a communication with the earth, in order to get rid of 
 its electricity? 
 
 Mrs. B. No; for it is susceptible of receiving and contain- 
 ing a considerable quantity of electricity, as it is much larger 
 than the rubber, and therefore has a greater capacity; and this 
 continued accumulation of electricity in the conductor is what 
 is called a charge. 
 
 Emily. But when an electrical machine is furnished with two 
 conductors to receive the two electricities, I suppose no commu- 
 nication with the earth is required ? 
 
 Mrs. B. Certainly not, until the two are fully charged; for 
 the two conductors will receive equal quantities of electricity. 
 
 Caroline. I thought the use of the chain had been to convey 
 the electricity from the ground into the machine ? 
 
 Mrs. B. That was the idea of Or. Franklin, who supposed 
 that there was but one kind of electricity, and who, by the 
 terms positive and negative (which he first introduced,) meant 
 only different quantities of the same kind of electricity.* The 
 chain was in that case supposed to convey electricity />ow the 
 ground through the rubber into the conductor. But as we have 
 adopted the hypothesis of two electrics, we must consider the 
 chain as a vehicle to conduct the negative electricity into the 
 earth. 
 
 Emily. And are both kinds produced whenever electricity 
 is excited ? 
 
 Mrs. B. Yes, invariably. If you rub a tube of glass with 
 a woolen cloth, the glass becomes positive, and the cloth nega- 
 tive. t If, on" the contrary, you excite a stick of sealing-wax 
 by the same means, it is the rubber which becomes positive, and 
 the wax negative. 
 
 * The idea of Dr. Franklin, was, that the positive state consisted iu 
 the presence, or accumulation of the electric fluid, and that the nega 
 tive was merely its absence or diminution. Hence the terms used by 
 him to indicate these states ware positive and negative. In this chap- 
 ter Mrs. B. has used these terms of the American Philosopher improp- 
 erly, for plus and minus were never msant to signify two sorts of elec- 
 tricity, but only its presence, or absence. Where authors have adop* 
 te<d Dufay^ theory, of two electricities, thf-yhave used the, terms, vi- 
 freous and resinous. C. 
 
 t Most probably, because the glass takes the electric fluid from the 
 cloth. Indeed we conceive there is about the same reason for believing 
 that the; negative state, is the absence of the electric fluid, as there i? 
 for beliering that cold is the absence of heat. C. 
 
SO ELECTRO-CHEMISTRY. 
 
 But with regard to the Voltaic battery, in order that the acid 
 may act freely on the zinc, and the two electricities be given 
 out without interruption, some method must be devised, by 
 which the plates may part with their electricities as fast as they 
 receive them. Can you think of any means by which this 
 might be effected ? 
 
 Emily. Would not two chains or wires, suspended from either 
 plate to the ground, conduct the electricities into the earth, and 
 thus answer the purpose? 
 
 Mrs. B. It would answer the purpose of carrying off the 
 electricity, I admit ; but recollect, that though it is necessary to 
 find a vent for the electricity, yet we must not lose it, since it is 
 the power which we are endeavouring to obtain. Instead, 
 therefore, of conducting it into the ground, let us make the 
 wires, from either plate, meet: the two electricities will thus 
 be brought together, and will combine and neutralize each oth- 
 er; and as long as this communication continues, the two plates 
 having a vent for their respective electricities, the action of the 
 acid will go on freely and uninterruptedly. 
 
 Emily. That is very clear, so far as two plates only are 
 concerned ; but 1 cannot say I understand how the energy of 
 the succession of plates, or rather pairs of plates, of which 
 the Galvanic trough is composed, is propagated and accumu- 
 lated throughout a battery ? 
 
 JVIrs. B. In order to show you how the intensity of the 
 electricity is increased by increasing the number of plates, we 
 will examine the action of four plates; if you understand these, 
 you will readily comprehend that of any number whatever. 
 In this figure (PLATE VI. fig. 4.,) you will observe 'hat the 
 two central plates are united ; they are soldered together, (as 
 we observed in describing the Voltaic trough,) so as to form 
 but one plate which offers two different surfaces, the one of 
 copper, the other of zinc. 
 
 Now you recollect that, in explaining the action of two plates^ 
 we supposed that a quantity of electricity was evolved from 
 the surface of the first zinc plate, in consequence of the action 
 of the acid, and was conveyed by the interposed fluid to the 
 copper plate, No. 2, which thus became positive. This cop- 
 per plate communicates its electricity to the contiguous zinc 
 plate, No. 3, in which, consequently, some accumulation of 
 electricity takes place. When, therefore, the fluid in the next 
 cell acts upon the zinc plate, electricity is extricated from it in 
 larger quantity, and in a more concentrated form than before. 
 This concentrated electricity is again conveyed by the fluid to 
 the next pair of plates, No. 4 and 5, when it is farther increased 
 
ELECTRO-CHEMISTRY. 81 
 
 by the action of the fluid in the third cell, and so on, to any 
 number of plates of which the battery may consist ; so that the 
 electrical energy will continue to accumulate in proportion to 
 the number of double plates, the first zinc plate of the series 
 being the most negative, and the last copper plate the most 
 positive. 
 
 Caroline. But does the battery become more and more 
 strongly charged, merely bv being allowed to stand undisturb- 
 ed ? 
 
 Mrs. B. No, for the action will soon stop, as was explained 
 before, unless a vent be given to the accumulated electricities. 
 This is easily done, however, by establishing a communication 
 by means of the wires (Fig. 1.,) between the two ends of the 
 battery: these being brought into contact, the two electricities 
 meet and neutralize each other, producing the shock and other 
 effects of electricity ; and the action goes on with renewed 
 energy, being no longer obstructed by the accumulation of the 
 two electricities which impeded its progress, 
 
 Emily. Is it the union of the two electricities which produ- 
 ces the electric spark ? 
 
 Mrs. B. Yes ; and it is, I believe, this circumstance which 
 gave rise to Sir H. Davy's opinion that caloric may be a com- 
 pound of the two electricities. 
 
 Caroline. Yet surely caloric is very different from the elec- 
 trical spark ? 
 
 Mrs. B. The difference may consist probably only in inten- 
 sity ; for the heat of the electric spark is considerably more in- 
 tense, though confined to a very minute spot, than any heat we 
 can produce by other means. 
 
 Emily. Is it quite certain that the electricity of the Voltaic 
 battery is precisely of the same nature as that of the common 
 electrical machine ? 
 
 Mrs. B. Undoubtedly ; the shock given to the human body, 
 the spark, the circumstance of the same substances which are 
 conductors of the one being also conductors of the other, and 
 of those bodies, such as glass and sealing-wax, which are non- 
 conductors of the one, being: also non-conductors of the other, 
 are striking proofs of it. Besides, Sir H. Davy has shewn in 
 his Lectures, that a Leyden jar, and a common electric battery, 
 can be charged with electricity obtained from a Voltaic battery, 
 the effect produced being perfectly similar to that obtained by 
 a common machine. 
 
 Dr. Wollaston has likewise proved that similar chemical de- 
 compositions are effected by the electric machine and by the 
 
82 ELECTRO-CHEMISTRY. 
 
 Voltaic battery; and has made other experiments which ren- 
 der it highly probable, that the origin of both electricities is es- 
 sentially the same, as they show thnt the rubber of the common 
 electrical machine, like the zinc in the Vohaic battery, produces 
 the two electricities by combining: with oxygen. 
 
 Caroline. But I do not see whence the rubber obtains oxygen, 
 for there is neither acid nor water used in the common machine, 
 and I always understood that the electricity was excited by the 
 friction. 
 
 Mrs. B. It appears that by friction the rubber obtains oxygen 
 from the atmosphere, which is partly composed of that ele- 
 ment. The oxygen combines with the amalgam of the rubber, 
 which is of a metallic nature, much in the same way as the 
 oxygen of the acid combines with the zinc in the Voltaic bat- 
 tery, and it is thus that the two electricities are disengaged. 
 
 Caroline. But, if the electricities of both machines are simi- 
 lar, why not use the common machine for chemical decomposi- 
 tion ? 
 
 Mrs. B. Though its effects are similar to those of the Voltaic 
 battery, they are incomparably weaker. Indeed Dr. Wollas- 
 ton, in using it for chemical decompositions, was obliged to 
 act upon the most minute quantities of matter, and though the 
 result was satisfactory in proving the similarity of its effects to 
 those of the Voltaic battery, these effects were too small in ex- 
 tent to be in any considerable degree applicable to chemical de- 
 composition. 
 
 Caroline. How terrible, then, the shock must be from a 
 Voltaic battery, since it is so much more powerful than an elec- 
 trical machine ! 
 
 Mrs. B. It is not nearly so formidable as you think ; at least 
 it is by no means proportional to the chemical effect. The 
 great superiority of the Voltaic battery consists in the large 
 quantity of electricity that passes ; but in regard to the rapidi- 
 ty or intensity of the charge, it is greatly surpassed by the 
 common electrical machine. It would seem that the shock or 
 sensation depends chiefly upon the intensity ; whilst, on the 
 contraiy, for chemical purposes, it is quantity which is requi- 
 red. In the Voltaic battery, the electricity, though copious, is 
 so weak as not to be able to force ?t-> way through the fluid 
 which separates the plates, whilst that of a common roach;: e 
 will pass through any space of water. 
 
 Caroline. Would not it be possible to increase the intensi<y 
 of the Voltaic battery till it should equal that of the common 
 machine ? 
 
 Mrs. B. It can actually be increased till it imitates a 
 
ELECTRO-CHEMISTRY. 83 
 
 electrical machine, so as to produce a visible spark when accu- 
 mulaied in a Leyden jar. But it can never he raised sufficiently 
 to pa>s tliiongh any considerable extent of air, because of the 
 ready communication through the fluids employed. 
 
 By increasing the number of plates of a battery, you in- 
 crease its intensity, whilst, by enlarging the dimensions of the 
 plates, you augment its quantity ; and, as the superiority of 
 the battery over the common machine consists entirely in the 
 quantity of electricity produced, it was at first supposed that it 
 was the size, rather than the number of plates that was essen- 
 tial to the augmentation of power. It was, however, found 
 upon trial, that the quantity of electricity produced by the 
 Voltaic battery, even when of a very moderate size, was suffi- 
 ciently copious, and that the chief advantage in this apparatus 
 was obtained by increasing the intensity, which, however, still 
 falls very short of that of the common machine. 
 
 1 should not omit to mention, that a very splendid, and, at 
 the same time, most powerful battery, was, a few years ago, 
 constructed under the direction of Sir H. Davy, which he re- 
 peatedly exhibited in his course of electro-chemical lectures. It 
 consists of two thousand double plates of zinc and copper, of 
 six square inches in dimensions, arranged in troughs of Wedg- 
 wood-ware, each of which contains twenty of these plates. 
 The troughs are furnished with a contrivance for lifting the 
 plates out of them in a very convenient and expeditious man- 
 ner.* 
 
 Caroline. Well, now that we understand the nature of the 
 action of the Voltaic battery, I long to hear an account of the 
 discoveries to which it has given rise. 
 
 Mrs. B. You must restrain your impatience, my dear, for I 
 cannot with any propriety introduce the subject of these disco- 
 veries till we come to them in the regular course of our studies. 
 But, as almost every substance in nature has already been ex- 
 posed to the influence of the Voltaic battery, we shall very soon 
 have occasion to notice its effects. 
 
 * A model of this mode of construction is exhibited in PLATE XIII. 
 Fig. I. 
 
 Note. In consequence of the discoveries of Prof. Hare, of Phila- 
 delphia, the present theory of galvanism must probably undergo a 
 radical change. This gentleman has invented a new method of extri- 
 cating the Voltaic influence, by so connecting the plates, that in ef- 
 fect only two great surfaces of the metals are presented to each other. 
 By this arrangement, the galvanic action on different substances, has 
 presented some new phenomena. The calorific principle is immensely 
 increased, while the electric shock is hardly to be perceived. Prof, 
 Hare has named this new apparatus caiorimotor, or heat mover. 
 
$4 OXYGEN AND NITROGEN. 
 
 CONVERSATION VI. 
 ON OXYGEN AND NITROGEN. 
 Mrs. B. TODAY we shall examine the chemical properties oi 
 
 the ATMOSPHERE. 
 
 Caroline. I thought that we were first to learn the nature of 
 OXYGEN, which conies next in our table of simple bodies ? 
 
 Mrs. B. And so you shall 5 the atmosphere being composed 
 of two principles, OXYGEN and NITROGEN, we shall proceed to 
 analyse it, and consider its component parts separately. 
 
 Emily. I always thought that the atmosphere had been a ve- 
 ry complicated fluid, composed of all the variety of exhalations 
 from the earth. 
 
 Mrs. B, Such substances may be considered rather as hetero- 
 geneous and accidental, than as forming any of its component 
 parts ; and the proportion they bear to the whole mass is quite 
 inconsiderable. 
 
 ATMOSPHERICAL AIR it composed of two gases, known by 
 the names of OXYGEN GAS and NITROGEN or AZOTIC GAS. 
 
 Emily. Pray what is a gas ?* 
 
 Mrs. B. The name of gas is given to any fluid capable of 
 existing constantly in an aeriform state, under the pressure and 
 at the temperature of the atmospheres 
 
 Caroline. Is not water, or any other substance, when evap- 
 orated by heat, called gas ? 
 
 Mrs. B. No, my dear ; vapour is, indeed, an elastic fluid, 
 and bears a strong resemblance to a gas ; there are, however, 
 several points in which they essentially differ, and by which 
 you may always distinguish them. Steam, or vapour, owes 
 its elasticity merely to a high temperature, which is equal to that 
 of boiling water. And it differs from boiling water only by 
 being united with more caloric, which, as we before explained, 
 is in a latent state. When steam is cooled, it instantly returns 
 to the form of water; but air, or gas, has never yet been ren- 
 dered liquid or solid by any degree of cold. 
 
 The new views which he has been induced to offer, seem to be confir- 
 med by the action ol' the colorimotor, viz. that galvanism is a com- 
 pound of electricity and caloric. This theory, it is obvious, will set 
 aside many of the principles laid down in the, foregoing chapter. An 
 account of this theory, with a description of the calorimotor, is pub- 
 lished in ."illiman's Journal, with Observations by the Editor ; also in 
 Hare's edition of Henry s Chemistry. C. 
 
 * All kinds of air differing from the atmosphere, are called by this 
 name. C. 
 
OXYGEN AND NITROGEN. &l< 
 
 Emily. But does not gas, as well as vapour, owe its elasticity 
 to caloric ? 
 
 Airs. B. It was the prevailing opinion ; and the difference 
 between gas and vapour was thought to depend on the different 
 manner in which caloric was united with the bases of these two 
 kinds of elastic fluids. In vapour it was considered as in a 
 latent state ; in gas, it was said to be chemically combined, 
 But the late researches of Sir H. Davy have given rise to a new 
 theory respecting gases ; and there is now reason to believe 
 that these bodies owe their permanently elastic state, not solely 
 to caloric, but likewise to the prevalence of either the one or the 
 other of the two electricities.* 
 
 Emily. When you speak, then, of the simple bodies, oxygen 
 and nitrogen, you mean to express those substances which are 
 the basis of the two gases ? 
 
 Mrs. B. Yes, in strict propriety, for they can properly^be 
 called gases only when brought to an aeriform state. 
 
 Car(,line. In what proportions are they combined in the at 
 mosphere ? 
 
 Mrs. B. The oxygen gas constitutes a little more than one- 
 fifth, and the nitrogen gas a little less than four-fifths.t When 
 separated, they are found to possess qualities totally different 
 from each other. For oxygen gas is essential both to respira- 
 tion and combustion, while neither of these processes can be 
 performed in nitrogen gas. 
 
 Caroline. But if nitrogen gas is unfit for respiration, how 
 does it happen that the large proportion of it which enters into 
 the composition of the atmosphere is not a great impediment to 
 breathing ? 
 
 Mrs. B. We should breathe more freely than our lungs could 
 bear, if we respired oxygen gas alone. The nitrogen is no im- 
 pediment to respiration, and probably, on the contrary, answers 
 some useful purpose, though we do not know in what manner it 
 acts in that process. 
 
 Emily. And by what means ran the two gases, which com- 
 pose the atmospheric air be separated ? 
 
 Mrs. B. There are many ways of analysing the atmosphere: 
 the two gases may be separated first by combustion. 
 
 * This wants further proof. The former theory, that the gases owe 
 their elasticity to caloric combined with their bases, we think accounts 
 equally well for this property, and at the same time is more simple, 
 and better proved. C. 
 
 t In 100 parts of atmospheric air, there is 21 of oxygen and 79 of 
 nitrogen. C. 
 
 9 
 
36 OXYGEN AND NITROGEN. 
 
 Emily. You surprise me ! how is it possible that combustion 
 should separate them ? 
 
 J\.;rs. b. I should previously remind you that oxygen is sup- 
 posed to be the only simple body naturally combined with neg- 
 ative electricity. In all the other elements the positive electri- 
 city prevails, and they have consequently, all of them, an at- 
 traction for oxygen.* t 
 
 Caroline. Oxygen the only negatively electrified body ! that 
 surprises me extremely ; how then are the combinations of the 
 other bodies performed, if, according to your explanation of 
 chemical attraction, bodies are supposed only to combine in 
 virtue of their opposite states of electricity ? 
 
 Mrs. B. Observe that I said, that oxygen was the only sim- 
 ple body, naturally negative. Compound bodies, in which ox- 
 ygen prevails over the other component parts, are also nega- 
 tive, but their negative energy is greater or less in proportion 
 as the oxygen predominates. Those compounds into which 
 oxygen enters in less proportion than the other constituents, are 
 positive, but their positive energy is diminished in propor- 
 tion to the quantity of oxygen which enters into their composi- 
 tion. 
 
 All bodies, therefore, that are not already combined with 
 oxygen, will attract it, and, under certain circumstances, will 
 absorb it from the atmosphere, in which case the nitrogen gas 
 will remain alone, and may thus be obtained in its separate 
 state. 
 
 Caroline. I do not understand how a gas can be absorbed ? 
 
 Mrs. B. It is only the oxygen, or basis of the gas, which is 
 absorbed ; and the two electricities escaping, that is to say, the 
 negative from the oxygen, the positive from the burning body, 
 unite and produce caloric. 
 
 * If chlorine or oxymuriatic gas be a simple body, according to Sir 
 H. Davy's view of the subject, it must be considered as an exception 
 to this statement; hut this suhject cannot be discussed till the proper- 
 ties and nature of chlorine come under examination. 
 
 t the hypothesis that combustion, as well as chemical affinity are 
 electrical phenomena, was first proposed by Berzelius, of Stockholm. 
 The theory is shortly this. In all cases, where the particles of bodies, 
 have a chemical attraction for each other, they are in opposite states 
 of electricity, and the force of their union is in proportion to the inten- 
 sity of these electrical states, since it is this which forces them te 
 unite. Thus the particles of an acid, and an alkali unite, because one 
 is strongly negative, and the other strongly positive. In cases of com- 
 bustion, these different states are still more intense, oxygen always be- 
 ing in the negative state, and the combustible in the positive, and M'he 
 a union takes place, heat and lieht is the consequence. This theory- 
 is not well proved, nor generally adopted. C. 
 
OXYGEN AND NITROGEN. 
 
 Emily. And what becomes of this caloric ? 
 
 Mrs. B. We shall make this piece of dry wood attract oxy- 
 gen 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 dry stick ? 
 
 Mrs. B. Not the whole body of the atmosphere, certainly ; 
 out if we can make this piece of wood attract any quantity of 
 oxygen from it, a proportional quantity of atmospherical air 
 will be decomposed. 
 
 Caroline. If wood has so strong an attraction for oxygen, 
 why does it not decompose the atmosphere spontaneously ? 
 
 Mrs. B. It is found by experience, that an elevation of tem- 
 perature is required for the commencement of the union of the 
 oxygen and the wood. 
 
 This elevation of temperature was formerly thought to be 
 necessary, in order to diminish the cohesive attraction of the 
 wood, and enable the oxygen to penetrate and combine with it 
 more readily. But since the introduction of the new theory of 
 chemical combination, another cause has been assigned, and it 
 is now supposed that the high temperature, by exalting the elec- 
 trical energies of bodies, and consequently their force of attrac- 
 tion, facilitates their combination. 
 
 Emily. If it is true, that caloric is composed of the two elec- 
 tricities, an elevation of temperature must necessarily augment 
 the electric energies of bodies. 
 
 Mrs. B. I doubt whether that would be a necessary conse- 
 quence ; for, admitting this composition of caloric, it is only by 
 fts being decomposed that electricity can be produced. Sir H. 
 Davy, however, in his numerous experiments, has found it to be 
 an almost invariable rule that the electrical energies of bodies are 
 increased by elevation of temperature. 
 
 What means then shall we employ to raise the temperature 
 of the wood, so as to enable it to attract oxygen from the atmos- 
 phere ? 
 
 Caroline. Holding it near the fire, I should think, would an- 
 swer the purpose. 
 
 Mrs. B. It may, provided you hold it sufficiently close to 
 the fire ; for a very considerable elevation of temperature is re- 
 quired. 
 
 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. 
 
 '. >5. B Or you might say, in other words, that the caloric 
 which the wood imbibed, so much elevated its temperature, and 
 
38 OXYGEN AND NITROGEN. 
 
 exalted its electric energy, as to enable it to attract oxygen very 
 rapidly from the atmosphere. 
 
 Emily. Does the wood absorb oxygen while it is burning ? 
 
 Mrs. B. Yes, and the heat and light are produced by the un- 
 ion of the two electricities which are set at liberty, in conse- 
 quence of the oxygen combining with the wood. 
 
 Caroline. You astonish me ! the heat of a burning body 
 proceeds then as much from the atmospere as from the body 
 itself? 
 
 Mrs. B. It was supposed that the caloric, given out during 
 combustion, proceeded entirely, or nearly so, from the decom- 
 position of the oxygen gas ; but, according to Sir H. Davy's 
 new view of the subject, both the oxygen gas, and the combus- 
 tible body, concur in supplying the heat and light, by the union 
 of their opposite electricities. 
 
 Emily. 1 have not yet met with any thing in chemistry 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 for oxygen and its com- 
 bustibility ; but I think I understand it now perfectly. 
 
 Mrs. B. Combustion then, you see, is nothing more than the 
 rapid combination of a body with oxygen, attended by the dis- 
 engagement of light and heat. 
 
 Emily. But are there no combustible bodies whose attraction 
 for oxygen is so strong, that they will combine with it, without 
 the application of heat ? 
 
 Caroline. That cannot be ; otherwise we should see bodies 
 burning spontaneously. 
 
 Mrs. B. But there are some instances of this kind, such as 
 phosphorus, potassium, and some compound bodies, which I 
 shall hereafter make you acquainted with. These bodies, how- 
 ever, are prepared by art, for in general, all the combustions 
 that could occur spontaneously, at the temperature of the at- 
 mosphere, have already taken place .5 therefore new combus- 
 tions cannot happen without the temperature of the body being 
 raised. Some bodies, however, will burn at a much lower tem- 
 perature than others. 
 
 Caroline. But the common way of burning a body is not 
 merely to approach it to one already on fire, but rather to put 
 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 wKl its temperature be raised to the degree necessary 
 for it to burn. If you hold it near the fire, the same effect wilt 
 
1 
 
OXYGEN AND NITROGEN. 89 
 
 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 applying ca- 
 loric throughout th'.' process of combustion, in order to keep up 
 the electric energy of the wood, which is required to enable it to 
 combine with the oxygen ? 
 
 Mrs. B. The caloric which is gradually produced by the two 
 electricities during combustion, keeps up the temperature of the 
 burning body, so that when once combustion has begun, no 
 further application of caloric is required. 
 
 Caroline. Since I have learnt this wonderful theory of com- 
 bustion, I cannot take my eyes from the fire ; and I can scarce- 
 ly conceive that the heat and light, which I always supposed to 
 proceed entirely from the coals, are really produced as much 
 by the atmosphere. 
 
 Emily. When you blow the fire, you increase the combustion, 
 I suppose, by suyplying the coals with a greater quantity of 
 oxygen gas ? 
 
 Mrs. B. Certainly ; but of course no blowiug will produce 
 combustion, unless the temperature of the coals be first raised. 
 A single spark, however, is sometimes sufficient to produce that 
 effect ; for, as I said before, when once combustion has com- 
 menced, the caloric disengaged is sufficient to elevate the tem- 
 perature of the rest of the body, provided that there be a free 
 access of oxygen. It however sometimes happens that if a fire 
 be ill made, it will be extinguished before all the fuel is consum- 
 ed, from the very circumstance of the combustion being so slow 
 that the caloric disengaged is insufficient to keep up the tempe- 
 rature of the fuel. You must recollect that there are three 
 things required in order to produce combustion ; a combustible 
 body, oxygen, and a temperature at which the one will combine 
 with the other. 
 
 Emily. You said that combustion was one method of decom- 
 posing the atmosphere, and obtaining the nitrogen gas in its 
 simple state; but how do you secure this gas 5 and prevent it 
 from mixing with the rest of the atmosphere ? 
 
 Mrs. 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 VII. Fig. 1.) under this glass 
 receiver, which stands in a bason over water, to prevent all 
 communication with the external air.* 
 
 '* To make a taper, melt some bees wax, and dip into it a strip of 
 cotton cloth about ah inch wide, and before it is cold, twist it pretty 
 hard. Gotten wick does better than the cloth, A quart tumbler make* 
 
 9* 
 
90 OXYGEN AND 
 
 Caroline. How dim the light burns already ! It is now ex- 
 tinguished. 
 
 Mrs. B. Can you tell us why it is extinguished ? 
 
 Caroline. Let me consider. The receiver was full of at- 
 mospherical air 5 the taper, in burning within it, must have 
 combined with the oxygen contained in that air, and the caloric 
 that was disengaged produced the light of the taper. But when 
 the whole of the oxygen was absorbed, the whole of its electrici- 
 ty was disengaged ; consequently no more caloric could be pro- 
 duced, the taper ceased to burn, and the flame was extinguished. 
 
 Mrs. B. Your explanation is perfectly correct. 
 
 Emily. The two constituents of the oxygen gas being thus 
 disposed of, what remains under the receiver must be pure ni- 
 trogen gas ? 
 
 Mrs. B. There are some circumstances which prevent the 
 nitrogen gas, thus obtained, from being perfectly pure ; but we 
 may easily try whether the oxygen has disappeared, by putting 
 another lighted taper under it. You see how instantaneously 
 the flame is extinguished, for want of oxygen to supply the ne- 
 gative electricity required for the formation of caloric ; and 
 were you to put an animal under the receiver, it would imme- 
 diately be suffocated. But that is an experiment which I do not 
 think your curiosity will tempt you to try. 
 
 Emily, Certainly not. But look Mrs. B., the receiver is full 
 of a thick white smoke. Is that nitrogen gas ? 
 
 Mrs. />. No, my clear ; nitrogen gas is perfectly transparent 
 and invisible, like common air. This cloudiness proceeds from 
 a variety of exhalations, which arise from the burning taper, 
 fhe 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 ? 
 
 Mrs. B. With a moment's reflection, I dare say, ^ou would 
 have explained it yourself. The water rises in consequence of 
 the oxygen gas within it having been destroyed, or rather de- 
 composed by the combustion of the taper. 
 
 Caroline. Then why did not the water rise immediately 
 when the oxygen gas was destroyed? 
 
 Mrs. B. Because the heat of the taper, whilst burning, pro- 
 duced a dilatation of the air in the vessel, which at first counter- 
 acted this effect. 
 
 Another means of decomposing the atmosphere is the oxyge- 
 
 A good receiver. Two or three inches of the taper can be fastened to 
 a piece of wire, bent so that it will etand up. Thus the experiment i* 
 easily made. C, 
 
OXYGEN AND NITROGEN. 91 
 
 nation 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. 
 
 Caroline. In what respeet, then, does it differ from combus- 
 tion ? 
 
 Mrs. B. The combination of oxygen in combustion is always 
 accompanied by a disengagement of light and heat ; whilst this 
 circumstance is not a necessary consequence of simple oxygen- 
 ation. 
 
 Caroline. But how can a body absorb oxygen without the 
 combination of the two electricities which produce caloric ? 
 
 Mrs. H. Oxygen does not always present itself in a gaseous 
 form ; it is a constituent part of a vast number of bodies, both 
 solid and liquid, in which it exists in a state of greater density 
 than in the atmosphere; and from these bodies it may be ob- 
 tained without much disengagement of caloric. It may like- 
 wise, 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 such 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 oxygena- 
 tion or oxydation, instead of combustion, as the production of 
 sensible light and heat is essential to the latter. 
 
 Emily. I wonder that metals can unite with oxygen ; for, as 
 they are so dense, their attraction of aggregation must be very 
 great ; and I should have thought that oxygen could never have 
 penetrated such bodies. 
 
 Airs. B. Their strong attraction for oxygen counterbalances 
 this obstacle. Most metals, however, require to be made red- 
 hot before they are capable of attracting oxygen in any consid- 
 erable quantity. By this combination 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.* 
 
 Emily. And in the Voltaic battery, it is. 1 suppose, an oxyd 
 f Zinc, that is formed by the union of the oxygen with that 
 metal ? 
 
 Mrs. B. Yes, it is. 
 
 Caroline. The word oxyd, then, simply means a metal com- 
 bined with oxygen ? 
 
 Mrs. B. Yes; but the term is not confined to metals, though 
 chiefly applied to them. Any body whatever, that has combi- 
 ned with a certain quantity of oxygen, either by means of oxy- 
 
 * Red had and rust of iron, C- 
 
02 OXYViEN AND NITROGEtf- 
 
 dation or combustion, is called an oxyd, and is said to be oxydcf^ 
 ted or oxygenated. 
 
 Emily. Metals, when converted into oxyds, become, I sup- 
 pose, negative ? 
 
 Mrs. B. Not in general ; because in most oxyds the positive 
 energy of the metal more than counterbalances the native en- 
 ergy of the oxygen with which it combines. 
 
 This black powder is an oxyd of manganese, a metal which 
 has so strong an affinity for oxygen, that it attracts that sub- 
 stance 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 see, it has very little of the appear, 
 ance of a metal. It is now heavier than it was before oxyda. 
 tion, in consequence of the additional weight of the oxygen with 
 which it has combined. 
 
 Caroline. I am very glad to hear that ; for I confess I could 
 not help having some doubts whether oxygen was really a sub- 
 stance, 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 a real 
 body. 
 
 J\!rs. B. It is easy to estimate its weight, by separating it 
 from the manganese, and finding how much tho 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 ? 
 
 Airs. 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.affording 
 the two electricities is decomposed, and one of them uniting 
 with the oxygen, restores it to the aeriform state. 
 
 Emily. But you said just now, that manganese would attract 
 oxygen from the atmosphere in which it is combined with the 
 negative electricity ; how, therefore, can the oxygen have a su- 
 perior affinity for that electricity, since it abandons it to com- 
 bine with the manganese ? 
 
 Mrs. 13. I give you credit for this objection, Emily ; and the 
 only answer I can make to it is, that the mutual affinities of me- 
 tals for oxygen, and of oxygen for electricity, vary at different 
 temperatures ; a certain degree of heat, will, therefore, dispose 
 a metal to combine with oxygen, whilst, on the contrary, the 
 former will be compelled to part with the latter, when the tem- 
 perature is further increased. I have put some oxyd of manga- 
 nese into a retort,* which is an earthen vessel with a bent neck, 
 
 *" To collect oxygen gas, take an oil flask and having fitted a cork 
 
0XYGEN AND NITROGEN. 
 
 such as you see here. (PLATE VII. Fig. 2.) The retort con- 
 taining the manganese you cannot see, as I have enclosed it in 
 this furnace, where it is now red-hot. But, in order to make 
 you sensible of the escape of the gas, which is itself invisible, 
 I have connected the neck of the retort with this bent tube, the 
 extremity of which is immersed in this vessel of water. 
 (PLATE VII. Fig. 3.) Do you seethe bubbles of air rise through 
 the water ? 
 
 Caroline. Perfectly. This, then, is pure oxygen gas; what 
 a pity it shoujd be lost ! Could you not preserve it ? 
 
 Mrs. B. We shall collect it in this receiver. For this pur- 
 pose, you observe, I first fill it with water, ia order to exclude 
 the atmospherical air ; and then place it over the bubbles which 
 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? 
 
 Mrs. B. Yes; for though oxygen forms rather a heavy gas 5 
 it is light compared to water. You see how it gradually displa- 
 ces the water from the receiver. It is now f u 1 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 ap- 
 paratus (which is indispensable in all experiments in which 
 gasses are concerned) is called a water-bath.* 
 
 Caroline. It is a very clever contrivance, indeed ; equally 
 simple and useful How convenient the shelf is for the receiver 
 to rest upon under water, and the holes in it for the gas to pass 
 into the receiver! I long to make some experiments with tins 
 apparatus. 
 
 Mrs. /5. I shall try your skill that way, when you have a lit- 
 tle more experience. I am now going to show you an experi- 
 ment, which proves, in a very striking 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. 
 
 Caroline. Really ! I did not know that it was possible t 
 burn iron. 
 
 to it, pierce the cork so as to admit a bent glass tube ; (the bending 
 is done-over a spirit lamp.) Pus into the fl^sk some black oxyd of m m- 
 ganese, and pour on sulphuric acid enough to make it into a paste. 
 Then put in the cork and tube, and having connected the other end of 
 the tube with a receiver, in the tub ot water, apply the heat of an ar- 
 gand lamp. C. 
 
 * A common large sized wash tub, with a board 4 or 5 inches wide 
 fixed through the middle, and about 6 inches from the top, and filled 
 wit!i water, will answer very well lor a great variety of experiments on 
 the gases, C, 
 
4 OXYGEN AND NITROGEN. 
 
 Emily. Iron is a simple body, and you know, Caroline, that 
 all simple bodies are naturally positivej and therefore must have 
 an affinity for oxygen. 
 
 Mrs. B. Iron will, however, not burn in atmospherical air 
 without a very great elevation of temperature ; but it is eminent- 
 ly combustible in pure oxygen gas ; and what will surprise you 
 still more, it can be set on fire without any considerable rise of 
 temperature. You see 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 VII. Fig.4.) 
 
 Emily. I see the opening in the receiver ; but it is carefully 
 closed by a ground glass-stopper. 
 
 Mrs. 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 I must fix a small piece of lighted tinder to the extremity of 
 it, in order to give the first impulse to combustion 5 for, howev- 
 er powerful oxygen is in promoting combustion, you must re- 
 collect that it cannot take place without some elevation of tem- 
 perature. 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 ? 
 
 Mrs. B. Oxygen gas is a little heavier than atmospherical 
 air, therefore it will not mix with it very rapidly; 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 apiece 
 of the melted wire drops to the bottom : I fear it is extinguish- 
 ed ; but no, it burns again as bright as ever. 
 
 Mrs. B. It will burn till the wire is entirely consumed, pro- 
 vided the oxygen is not first expended : for you know it can 
 burn only while there is oxygen to combine with it. 
 
 Caroline. I never saw a more beautiful light. My eyes cart 
 hardly bear it ! How astonishing to think that all this caloric 
 was contained in the small quantity of gas and iron that was 
 enclosed in the receiver ; and that, without producing any sen- 
 sible heat ! 
 
 Emily. How wonderfully quick combustion goes on in pure 
 
 * The combustion of steel, as a watch spring, is ranch more vivid 
 than that of iron. This affords a very beautiful experiment, and is 
 easily made aftvrthe oxygen is collected. A bottle of white glass of a 
 . A n... j ii -,,,->;,. loch of water at the bot- 
 
 quart capacity does well as a receiver, 
 torn will prevent its breaking. C. 
 
OXYGEN AND NITROGEN. $5 
 
 oxygen gas ! But pray, are these drops of burnt iron as heavy 
 as the wire was before ? 
 
 Mrs. B. They are even heavier ; for the iron, in burning, has 
 acquired exactly the weight of the oxygen which has disap- 
 peared, 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 always invisible. 
 
 Mrs.B. True, my dear; the expression was incorrect. But 
 though you could not see the oxygen gas, 1 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, 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 constant com- 
 panions, that it is difficult to separate them, even in idea. 
 
 Mrs. B. The easier it is to confound them, the more careful 
 you should be in making the distinction. 
 
 Caroline. But why has the water now risen, and filled part 
 of the receiver? 
 
 Airs. B. Indeed, Caroline, I did not suppose you would have 
 asked such a question ! I dare say, 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 before co n- 
 bustion ; we might then have found whether the weight of the 
 oxyd was equal to that of both. , 
 
 Mrs. B. You might try the experiment if you particularly 
 wished it ; but I can assure you, that, if accurately performed, 
 it never fails to show that the additional weight of the oxyd is 
 precisely equal to that of the oxygen absorbed, whether the pro- 
 cess has been a real combustion, or a simple oxygenation. 
 
 Caroline. But this cannot be the case with combustions in 
 goneral; for when any substance is burnt in the common air, 
 so far from increasing in weight, it is evidently diminished, and 
 sometimes entirely consumed. 
 
 Mrs. B. But what do you mean by the expression consumed? 
 You cannot suppose that the smallest particle of any substance 
 in nature can be actually destroyed. A compound body is de* 
 
96 OXYGEN AND NITROGEN. 
 
 composed by combustion ; some of its constituent parts fly oil 
 in a gaseous form, while others remain in a concrete state ; the 
 former are called the volatile, the latter the fixed products oi 
 combustion. But if we collect the whole of them, we shall 
 always find thnt they exceed the weight of the combustible bo- 
 dy, by that of the oxygen which has combined with them du- 
 ring combustion. 
 
 Emily. In the combustion of a coal fire, then^I suppose that 
 the ashes are what would be called the fixed product, and the 
 smoke the volatile product? 
 
 Mrs. B. Yet when the fire burns best, and the quantity of 
 volatile products should be the greatest, there is no smoke; how 
 can you account for that ? 
 
 Emily Indeed I cannot ; therefore I suppose that I was not 
 right in my conjecture. 
 
 Mrs. B. Not quite; ashes, as you supposed, are a fixed pro- 
 duct of combustion ; but smoke, properly speaking, is not one 
 of the volatile products, as it consists of some minute undecom- 
 posed particles of the coals which are carried off by the heat- 
 ed air without being burnt, and are either deposited in the form 
 of soot, or dispersed by the wind. Smoke, therefore, ultimate- 
 ly, becomes one of the fixed products of combustion. And 
 you may easily conceive that the stronger the fire is, the less 
 smoke is produced, because the fewer particles escape combus- 
 tion. On this principle depends the invention of Argand's 
 Patent Lamps; a current of air is made to pass through the 
 cylindrical wick of the lamp, by which means it is so plentiful- 
 ly supplied with oxygen, that scarcely a particle of oil escapes 
 combustion, nor is there any smoke produced. 
 
 Emily. But what then are the volatile products of combus- 
 tion ? 
 
 Mrs. B. Various new compounds, with which you are not 
 yet acquainted, and which being converted by caloric either in- 
 to vapour or gas, are invisible ; but they can be collected, and 
 we shall examine them at some future period. 
 
 Caroline. There are then other gases, besides the oxygen 
 and nitrogen gases. 
 
 Mrs. B. Yes, several : any substance that can assume and 
 maintain the form of an elastic fluid at the temperature of the 
 atmosphere, is called a gas. We shall examine the several 
 gases in their respective places : but we must now confine our 
 attention to those which compose the atmosphere. 
 
 I shall show you another method of decomposing the atmos- 
 phere, which is very simple. In breathing, we retain a portion 
 of the oxygen, and expire the nitrogen gas ; so that if we breathe 
 
OXYGEN AND NITROGEN. 97 
 
 in a closed vessel, for a certain length of time, the air within it 
 will be deprived of its oxygen gas. Which of you will make 
 the experiment ? 
 
 Caroline. I should be very glad to try it. 
 
 Mrs. B. Very well ; breathe several times through this glass 
 tube into the receiver with which it is connected, until you feel 
 that your breath is exhausted. 
 
 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 immedi- 
 ately 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 which can pro- 
 duce combustion, every other gas being absolutely incapable of 
 it.* 
 
 Emily. In the methods which you have shown us, for decom- 
 posing the atmosphere, the oxygen always abandons the nitro- 
 gen; but is there no way of taking the nitrogen from the oxy- 
 gen, so as to obtain the latter pure from the atmosphere ? 
 
 Mrs. 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 princi- 
 ple : it appears impossible therefore to separate it from the at- 
 mosphere by the power of affinities. But if we cannot obtain 
 the oxygen 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 absorbed it from 
 the atmosphere, as we did with the oxyd of manganese. 
 
 Emily. Can atmospherical air be recom posed, by mixing 
 due proportions of oxygen and nitrogen gases ? 
 
 Mrs. B. Yes : if about one part of oxygen gas be mixed with 
 about four parts of nitrogen gas, atmospherical air is produ- 
 ced.t 
 
 Emily. The air, then, must be an oxyd of nitrogen ? 
 
 Mrs. B. No, my dear ; for it requires a chemical combina- 
 tion between oxygen and nitrogen in order to produce an ox- 
 yd; whilst in the atmosphere these two substances are separate- 
 ly combined with caloric, forming two distinct gases, which 
 are simply mixed in the formation of the atmosphere. 
 
 I shall say nothing more of oxygen and nitrogen at present, 
 
 * This does not a^ree with the opinion that chlorine, and iodine are 
 simple bodies, since they are both supporters of combustion." C. 
 
 t The proportion of oxygen in* the atmosphere varies from 21 to 22 
 per cent, 
 
 10 
 
98 HYDRO GEN. 
 
 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 the animal and vegetable kingdoms, from which it may be 
 obtained by a variety of chemical means. But it is now time to 
 conclude 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. In regard to nitrogen there seems to be 
 but little to remember; it makes a very insignificant figure in 
 cor p \rison to oxygen, although it composes a much larger por- 
 tion of the atmosphere. 
 
 Mrs. i~j. Perhaps this insignificance you complain of may 
 arise from the compound nature of nitrogen, for though I have 
 hitherto considered it as a simple body, because it is not known 
 in any natural process to be decomposed, yet from some exper- 
 iments of Sir H. Davy, there appears to be reason for suspecting 
 that nitrogen is a compound body as we shall see afterwards. 
 But even in its simple state, 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 separate state, yet 
 you will see by-and bye what a very important agent it becomes, 
 when combined witli other bodies. But no more of this at pres- 
 ent; we must reserve it for its proper place. 
 
 CONVERSATION VII. 
 
 ON HYDROGEN. 
 
 Caroline. THE next simple bodies we come to are CHLORINE, 
 and IODINE. Pray what kinds of substances are these; are 
 they also invisible ? 
 
 Mrs. B. No ; for chlorine, in the state of gas, has a distinct 
 greenish colour, and is therefore visible ; and iodine, in the same 
 state, has a beautiful claret-red colour. The knowledge of these 
 two bodies, however, and the explanation of their properties, 
 imply various considerations, which you would not yet be able 
 to understand ; we shall therefore defer their examination to 
 some future conversation, and we shall pass on to the next sim- 
 ple substance, HYDROGEN, which we cannot, any more than ox- 
 ygen, obtain in a visible or palpable form. We are acquainted 
 
HYDROGEN. 
 
 with it only In its gaseous state, as we are with oxygen and nK 
 trogen. 
 
 Caroline. But in its gaseous state it cannot be called a sim- 
 ple substance, since it is combined with heat and electricity ? 
 
 Mrs. B. True, my dear ; but as we do not know in nature of 
 any substance which is not more or less combined with caloric 
 and electricity, we are apt to say that a^substance is in its pure 
 state when combined with those agents only. 
 
 Hydrogen was formerly called inflammable air, as it is ex- 
 tremely combustible, and burns with a great flame. Since the 
 invention of the new nomenclature, it has obtained the name of 
 hydrogen, which is derived from two Greek words, the meaning 
 of which is to produce water. 
 
 Emily. And how does hydrogen produce water ? 
 Mrs. B. By its combustion. Water is composed of eighty- 
 nve parts, by weight, of oxygen, combined with fifteen parts of 
 hydrogen ; or of two parts, by bulk of hydrogen gas, to one 
 part of oxygen gas. 
 
 Caroline. Really ! is it possible that water should be a com- 
 bination of two gases, and that one of these should be inflamma- 
 ble air ! Hydrogen must be a most extraordinary gas that wiU 
 produce both fire and water- 
 
 Emily. But I thought you said that combustion could take 
 place in no gas but oxygen ? 
 
 Mrs. B. Do you recollect what the process of combustion 
 consists in ? 
 
 Emily. In the combination of a body with oxygen, with dis- 
 engagement 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 ox- 
 ygen, and also heated to a proper temperature. 
 
 Caroline. The simply mixing fifteen parts of hydrogen, with 
 eighty-five parts of oxygen gas, will not, therefore, produce 
 water ? 
 
 Mrs. B. No ; water being a much denser fluid than gases, 
 in. order to reduce these gases to a liquid, it is necessary to di- 
 minish the quantity of caloric or electricity which maintains 
 them in an elastic form. 
 
 Emily. That I should think might be done by combining the 
 oxygen and hydrogen together; for in combining they would 
 give out their respective electricities in the form of caloric, arid 
 by this means would be condensed. 
 
 Caroline. But you forget, Emily, that in order to make the 
 oxygen and hydrogen combine, you must begin by elevating 
 
100 HYDROGEN.' 
 
 their temperature, which increases, instead of diminishing, then 
 electric energies. 
 
 Mrs. B. Emily is, however, right; for though it is necessary 
 to raise their temperature, in order to make them combine, as 
 that combination affords them the means of parting with their 
 electricities, it is eventually the cause of the diminution of 
 electric energy. 
 
 Caroline. You love to deal in paradoxes to-day, Mrs. B. - 
 Fire, then, produces water ? 
 
 Mrs. B. The combustion of hydrogen gas certainly, does 5 
 but you do not seem to have remembered the theory of com- 
 bustion so well as you thought you would. Can you tell me 
 what happens in the combustion of hydrogen gas ? 
 
 Caroline. The hydrogen combines with the oxygen, and 
 their opposite electricities are disengaged in the form of caloric. 
 Yes, I think I understand it now by the loss of this caloric, 
 the gases are condensed into a liquid. 
 
 Emily. Water, then, I suppose, when it evaporates and in- 
 corporates with the atmosphere, is decomposed and converted 
 into hydrogen and oxygen gases ? 
 
 Mrs. B. No. my dear there you are quite mistaken ; the 
 decomposition of water is totally different from its evapora- 
 tion ; for in the latter case (as you should recollect) water is on- 
 ly in a state of very minute division; and is merely suspended 
 in the atmosphere, without any chemical combination, and with- 
 out any separation of its constituent parts. As long as these 
 remain combined, they form W\TER, whether in a state of li- 
 quidity, or in that of an elastic fluid, as vapour, or under the 
 solid form of ice. 
 
 [n 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 employ- 
 ing any power of attraction, or effecting any decomposition. 
 
 Caroline. But are there no means of decomposing water ? 
 
 Mrs. 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. 
 
 Caroline. Hydrogen, I see, is like nitrogen, a poor dependent 
 friend of oxygen, which is continually forsaken for greater fa- 
 vourites. 
 
 Mrs. B. 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 atmos- 
 phere ; for, in the first case, there is a chemical union and con- 
 densation of the two substances 5 in the latter, they are simply 
 

HY&R6GEN. 101 
 
 mixer! together in their gaseous state. You will find, however, 
 that, in some cases, nitrogen is quite as intimately connected 
 with oxygen, as hydrogen is. But this is foreign to our present 
 subject. 
 
 Emily. Water, then, is an oxyd, though the atmospherical 
 air is not ? 
 
 Mr*. B. It is not commonly called an oxyd, though, accor- 
 ding to our definition, it may, no doubt, be referred to that class 
 of bodies. 
 
 Caroline. I should like extremely to see water decomposed. 
 
 Mrs. B. I can gratify your curiosity by a much more easy 
 process than the oxydation of charcoal or metals : the decom- 
 position of water by these latter means take up a great deal of 
 time, and is attended 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 the.Ti in a state of vapour, that the 
 gas formed should be collected over the water bath, &c. In 
 short, it is a very complicated affair. But the same effect may 
 be produced with the greatest facility, by the action of the 
 Voltaic battery, which this will give me an opportunity of ex- 
 hibiting. 
 
 Caroline. I am very glad of that, for I longed to see the 
 power of this apparatus in decomposing bodies. 
 
 Mrs. B. For this purpose I fill this piece of glass-tube 
 (PLATE VIIL Fig. 1.) with water, and cork it up at both ends; 
 through one of the corks I introduce that wire of the battery 
 which conveys the positive electricity ; and the wire whick con- 
 veys the negative electricity is made to pass through the other 
 cork, so that the two wires approach each other sufficiently 
 near to give out their respective electricities. 
 
 Caroline. It does not appear to me that you approach the 
 wires so near as you did when you made the battery act by it* 
 self. 
 
 Mrs. B. Water being a better conductor of electricity than 
 air, the two wires will act on each other at a greater distance in 
 the former than in the latter. 
 
 h/mily. Now the electrical effect appears : I see small bub- 
 bles of air emitted from each wire. 
 
 Mrs. B. Each wire decomposes the water, the positive hy 
 combining with its oxygen which is negative, the negative by 
 combining with its hydrogen which is positive. 
 
 Caroline. That is wonderfully cuiious ! But what are the 
 small bubbles of air ? 
 
 V/rs. B. Those that appear to proceed from the positive 
 wire, are the result of the decomposition of the water by that 
 
 10* 
 
102 HYDROGEN. 
 
 wire. That is to say, the positive electricity having combined 
 with some of the oxygen of the water, the particles of hydro- 
 gen which were combined with that portion of oxygen are set at 
 liberty, and appear in the form of small bubbles of gas or air. 
 
 Emily. And I suppose the negative fluid having in the same 
 manner combined with some of the hydrogen of the water, the 
 particles of oxygen that were combined with it, are set free, and 
 emitted in a gaseous form. 
 
 Mrs. B. Precisely so. But I should not forget to observe, 
 that the wires used in this experiment are made of platina, a 
 metal which is not capable of combining with oxygen ; for 
 otherwise the wire would combine with the oxygen, and the hy- 
 drogen alone would be disengaged. 
 
 Caroline. But could not water be decomposed without the 
 electric circle being completed ? If, for instance, you immersed 
 only the positive wire in the water, would it not combine with 
 the oxygen, and the hydrogen gas be given out ? 
 
 Mrs. B. No ; for as you may recollect, the battery cannot 
 act unless the circle be completed; since the positive wire will 
 not give out its electricity, unless attracted by that of the nega- 
 tive wire. 
 
 Caroline. I understand it now. Bat look, Mrs. B , the de- 
 composition of the water which has now been going on for some 
 time, does not sensibly diminish its quantity what is the rea- 
 son of that ? 
 
 Mrs. B. Because the quantity decomposed is so extremely 
 small. If you compare the density of water with that of 
 the gases into which it is resolved, you must be aware that a sin- 
 gle drop of water is sufficient to produce thousands of such small 
 bubbles as those you now perceive. 
 
 Caroline. But in this experiment, we obtain the oxygen and 
 hydrogen gases mixed together. Is there any means of procu- 
 ring the two gases separately ? 
 
 Mrs. B. They can be collected separately with great ease, 
 by modifying a little the experiment. Thus if instead of one 
 tube, we employ two, as you see here(c, d, PLATE VIII. fig. 2,) 
 both tubes being closed at one end, and open at the other ; and 
 if after filling these tubes with water, we place them standing in 
 a glass of water (e), with their open end downwards, you will 
 see that the moment we connect the wires, (a, b) which proceed 
 upwards from the interior of each tube, the one with one end 
 of the battery, and the other with the other end, the water in the 
 tubes will be decomposed ; hydrogen will be given out round 
 the wire in the tube connected with the positive end of the bat- 
 tery, and oxygen in the other ; and these gases will be evolved 
 exactly in the proportions which I have before mentioned, name- 
 
HYDROGfiNV 103 
 
 ly, two measures of hydrogen for one of oxygen. We shall now 
 begin the experiment, but it will be some time before any sensi- 
 ble quantity of the gases can be collected. 
 
 Emily. The decomposition of water in this way, slow as it is, 
 is certainly very wonderful ; but I confess that I should be still 
 more gratified, if you could show it us on a larger scale, and by 
 a quicker process. I am sorry that the decomposition of water 
 by charcoal or metals is attended with so much inconvenience. 
 
 Mrs. B. Water may be decomposed by means of metals 
 without any difficulty : but for this purpose the intervention of 
 an acid is required. Thus, if we add some sulphuric acid (a 
 substance with the nature of whieh 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 required to hasten the process. 
 Of this I am going to show you an instance. I put into this bot- 
 tle the water that is to be decomposed, as also the metal that is. 
 to effect that decomposition 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 for this pur- 
 pose? 
 
 Mrs. B. It is iron ; and it is used in the state of 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 acted up- 
 on by the acid, and is disposed to receive the oxygen produced 
 by the decomposition of the water, it necessarily follows that 
 the greater is the surface, the more considerable is the effect. 
 The bubbles which are now rising are hydrogen gas 
 
 Caroline. How disagreeably it smells ! [Pure hydrogen is 
 inodorous. Q.J 
 
 Mrs. fi. It is indeed unpleasant, though, I believe, not par- 
 
 * To obtain hydrogen, fit a corK. air tight to an oil flask, and pierce 
 it with a burning iron, to admit a tube. The tube may be of glass, 
 lead, or tin, bent to a convenient shape, and put into the opening made 
 by the hot iron. Pour into the flask about a gill of water, and drop in- 
 to it about an ounce of zinc, granulated by melting, and pouring it in- 
 to cold water. Then pour in half an ounce by measure of sulphuric 
 acid, and immediately put the cork into its place, and plunge the oth- 
 er end of the tube under a receiver, or large tumbler, filled with water, 
 and inverted in the water-bath. The flask grows hot and the gas be- 
 gins to rise, the instant the acid is poured in ; a place therefore must 
 previously be prepared to set it ; and if nothing better is at hand, a 
 bowl, with a cloth in it, to prevent breaking the flask, and set at a 
 convenient height will do very well. C, 
 
104 HYDROGEN, 
 
 4 
 
 ticularly hurtful. We shall not, however, suffer any more to 
 escape, as it will be wanted for experiments. 1 shall,' therefore, 
 collect it in a glass-receiver, by making it pass through this bent 
 tube, which will conduct it into the water-bath. (PLATE VIII. 
 fig. 3.) 
 
 Emily. How very rapidly the gas escapes ! it is perfectly 
 transparent, and without any colour whatever. Now the re- 
 ceiver is full 
 
 Mrs. B. We shall, therefore, remove it, and substitute anoth- 
 er in its place. But you must observe, that when the receiver 
 is full, it is necessary to keep it inverted with the mouth under 
 water, otherwise the gas 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 preventing its escape as 
 that in the bath. (PLA/TE VIII. fig. 4.) 
 
 Emily. I am quite surprised to see what a large quantity of 
 hydrogen gas can be produced by such a small quantity af wa- 
 ter, 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 gases, 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 decom- 
 posed so hot ? As the water changes from a liquid to a gaseous 
 ibrm, cold should be produced instead of heat. 
 
 Mrs. B. No ; for if one of the constituents of water is con- 
 verted into a gas, the other becomes solid in combining with the 
 metal. 
 
 Emily. In this case, then, neither heat nor cold should be 
 produced ? 
 
 Mrs. B. True ; but observe that the sensible heat which is 
 disengaged in this operation, is not owing to the decomposition 
 of the water, but to an extrication of heat produced by the mix- 
 ture of water and sulphuric acid. I will mix some water and 
 sulphuric acid together in this glass, that you may feel the sur- 
 prising quantity of heat which is disengaged by their union 
 now take hold of the glass 
 
 Caroline. Indeed I cannot ; it feels as hot as boiling water. 
 I should have imagined there would have been heat enough dis- 
 engaged to have rendered the liquid solid. 
 
 * Hydrogen is about thirteen times lighter than atmospheric air. C 
 
HYDROGEN. 105 
 
 Mrs. B. As, however, it does not produce that effect, we 
 cannot refer this heat to the modification called latent heat. 
 We may, however, I think, consider it as heat of capacity, since 
 the liquid is condensed by its loss; and if you were to repeat 
 the experiment, in a graduated tube, you would find that the 
 two liquids, when mixed, occupy considerably less space than 
 they did separately. But we will reserve this to another op- 
 portunity, and attend at present to the hydrogen gas which we 
 have been producing. 
 
 If I now se,t the hydrogen gas, which is contained in this re- 
 ceiver, 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 rapidly 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 pur- 
 pose, I need only take up the receiver, and quickly present its 
 open mouth to the candle so ....... 
 
 Caroline. It produced only a sort of hissing noise, with a 
 vivid flash of light. I had expected a much greater report. 
 
 Mrs. B. And so it would have been, had the gases been 
 closely confined at the moment they were made to explode. If,' 
 for instance, we were to put in this bottle a mixture of hydro- 
 gen gas and atmospheric air 5 and if, after corking the boillC, 
 we should kindle the mixture by a very small orifice, from the 
 sudden dilatation of the gases at the moment of their combina- 
 tion, 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 com- 
 bine with the oxygen ? 
 
 Mrs. B. Certainly not ; for, as I have just explained to you, 
 it is necessary that the oxygen and hydrogen gases be burnt to- 
 gether, in order to combine chemically and produce water. 
 
 Caroline. That is true; but I thought this was a different 
 combination, for I see no water produced. 
 
 Mrs. B. The water resulting from this detonation was so 
 small in quantity, and in such a state of minute division, as to 
 be invisible. But water certainly was produced 5 for oxygen 
 is incapable of combining with hydrogen in any other propor- 
 tions than those which form water ; therefore water m ust al- 
 ways 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 the 
 whole of it explode the moment it is kindled, we allow but a 
 very small surface of gas to burn in contact with the atmosphere, 
 
106 t HYDROGEN. 
 
 the combustion goes on quietly and gradually at the point of CG& 
 tact, without any detonation, because the surfaces brought to- 
 gether are too small for the immediate union of gases. The 
 experiment is a very easy one. This phial, with a narrow 
 neck, (PLATE VIII. fig 5.) is full of hydrogen gas, and is care- 
 fully 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 result will be* 
 
 Emily. How prettily it burns, with a blue flame ! The flame 
 is gradually sinking within the phial now it has entirely disap- 
 peared. But does not this combustion likewise produce water? 
 
 Mi's. B. Undoubtedly. In order to make the formation of 
 the water sensible to you, I shall procure a fresh supply of. hy- 
 drogen gas, by putting into this bottle (PLATE VIII. fig. 6.) 
 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 bottle, leaving only a small orifice in the cork, with 
 a piece 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 lam going to kindle with the candle 
 see how vividly it burns 
 
 Emily. It burns like a candle with a long flame. But why 
 does this combustion last so much longer than in the former ex- 
 periment ? 
 
 Mrs. B. The combustion goes on interruptedly as long as the 
 new gas continues to be produced. Now if I invert this recei- 
 ver over the flame, you will soon perceive its internal surface 
 covered with a very fine dew, which is pure water 1 
 
 Caroline. Yes, indeed ; the glass is now quite dim with mois- 
 ture ! How glad 1 am that we can sec the water produced by 
 this combustion. 
 
 Emily. It is exactly what I was anxious to see; for I confess 
 I was a little incredulous. 
 
 Mrs. B. If I had not held the glass-bell over the flame, the 
 water would have escaped in the state of vapour, as it did in the 
 
 * T"he levity of hydrogen is such, that if a vessel he filled with it, 
 and kept inverted, it may be carried ;<bout the room, without its es- 
 caping. The above experiment therefore may be nu.de by bringing 
 a small jar, or tumbler of the gas over a lighted lamp. C. 
 
 t The burning of a candle, lamp, wood &c. always produces water. 
 The tallow and oil cuntain hydrogen, and during combustion, it unites 
 with the oxygen of the atniosphere. Hold a wide tul-e over a lamp, 
 and it is soon covered v;ith moisture. Wood contains hydrogen. C 
 
HYDROGEN, 107 
 
 [periment. We have, here, of course, obtained but a 
 very small quantity of water; but the difficulty of producing a 
 proper apparatus, with sufficient quantities of gases, prevents 
 my showing it you on a larger scale. 
 
 The composition of water was discovered about the same pe- 
 riod, both by Mr Cavendish, in this country, and by the cele- 
 brated French chemist, Lavoisier. The latter invented a very 
 perfect and ingenious apparatus to perform, with great accura- 
 cy, and upon a large scale, the formation of water by the com- 
 bination of oxygen and hydrogen gases. Two tubes, convey- 
 ing due proportions, the one of oxygen, the other of hydrogen 
 gas, are inserted at opposite sides of a large globe of glass, pre- 
 viously exhausted of air; the two streams of gas are kindled 
 within the globe, by the electrical spark, at the point where 
 they come in contact ; they burn together, that is to say, the hy- 
 drogen combines with the oxygen, the caloric is set at liberty, 
 and a quantity of water is produced exactly equal, in weight, to 
 that of the two gases introduced into the globe. 
 
 Caroline. And what was the greatest quantity of water ever 
 formed in this apparatus ? 
 
 Mrs. B. Several ounces ; indeed, very nearly a pound, if I 
 recollect right ; but the operation lasted many days. 
 
 Emily. This experiment must have convinced all the world 
 of the truth of the discovery. Pray, if improper proportions 
 of the gases were mixed and set fire to, what would be the re- 
 sult ? 
 
 Mrs. B. Water would equally be formed, but there would be 
 a residue of either one or other of the gases, because, as I have 
 already told you, hydrogen and oxygen will combine only in 
 the proportions requisite for the formation of water. 
 
 Emily. Look, Mrs. B., our experiment with the Voltaic bat- 
 tery (PLATE VIII. fig. 2.) has made great progress; a quanti- 
 ty of gas has been formed in each tube, but in one of them there 
 is twice as much as in the other. 
 
 Mrs. B. Yes ; because, as I said before, water is composed 
 of two volumes of hydrogen to one of oxygen and if we should 
 now mix these gases together and set fire to them by an electric- 
 al spark, both gases would entirely disappear, and a small quan- 
 tity of water would be formed. 
 
 There is another curious effect produced by the combustion 
 of hydrogen gas, which I shall show you, though I must ac- 
 quaint you first, that I cannot well explain the cause of it. For 
 this purpose, I must put some materials into our apparatus, in 
 order to obtain a stream of hydrogen gas, just as we have done 
 before. The process is already going or ; and the gas is rush- 
 ing through the tube I shall now kindle it with the taper 
 
108 HYDROGEN. 
 
 Emily* It burns exactly as it did before What is the cu- 
 rious effect which you were mentioning? 
 
 Mrs. B. Instead of the receiver, by means of which we have 
 just seen the drops of water form, we shall invert over the flame 
 this piece of tube, which is about two feet in length, and one 
 inch in diameter (PLATE VIII. fig. 7.;) 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 ? 
 
 Mrs. B. That the percussion of glass, by a rapid stream of 
 gas, should produce a sound, is not extraoidinary : but the 
 sound here is so peculiar, that no other gas has a similar effect. 
 Perhaps it is owing to a brisk vibratory motion of the glass, oc- 
 casioned by the successive formation and condensation of small 
 drops of water on the sides of the glass tube, and the air rush- 
 ing 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 in- 
 to gas by the heat of the candle, combines with the oxygen of 
 the atmosphere, and flame and water result from this combina- 
 tion.t So that, in fact, the flame of a candle is owing to the 
 combustion of hydrogen gas. An elevation of temperature, 
 such as is produced by a lighted match or taper, is required to 
 give the first impulse to the combustion ; but afterwards it goes 
 on of itself, because the candle finds a supply of caloric in the 
 successive quantities of heat which results from the union of 
 the two electricities given out by the gases during their combus- 
 tion. But there are other circumstances connected with the 
 combustion of candles and lamps, which I cannot explain to 
 you till you are acquainted with carbon, which is one of 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 :J for flame is the peculiar mode of burn- 
 
 * This ingenious explanation was first suggested by Dr. Delarive. 
 See Journals of the Royal Institution, vol. i. p 259. 
 
 t The candle also contains carbon, which gives brilliancy to the 
 flame, and the product of the combination besides flame and water is a 
 quantity of carbonic acid. . 
 
 $ Or rather hydro- carhonat, a gas composed of hydrogen, and carbon, 
 which will be noticed under the head Carbon. 
 
HYDROGEN. 109' 
 
 ing hydrogen gas, which, with only one or two apparent excep- 
 tions, does not belong to any other combustible. 
 
 Emily. You astonish me ! 1 understood that flame was the 
 caloric produced by the union of the two electricities, in all 
 combustions whatever ? 
 
 Mrs. H. Your error proceeded from your vague and incor- 
 rect idea of flame; you have confounded it with light and calo- 
 ric in general. Flame always implies caloric, since it is produ- 
 ced by the combustion of hydrogen gas ; but all caloric does 
 not imply flame. Many bodies burn with intense 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 caloric is disengaged 
 than when they produce flame. 
 
 Caroline. But the iron wire, which you burnt in oxygen cas, 
 appeared to me to emit flame; yet, as it was a simple metal, it 
 could contain no hydrogen ? 
 
 Mrs. B. It produced a sparkling dazzling blaze of light, but 
 no real flame. 
 
 Caroline. And what is the cause of the regular shape of the 
 flame of a candle ? 
 
 Mrs. 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 there- 
 fore does not the flame continue to accompany it ? 
 
 Mrs, B. The combustion of the hydrogen gas is completed 
 at the point where the flame terminates; it then ceases to be 
 hydrogen gas, as it is converted by its combination with oxygen 
 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 ? 
 
 Mrs. B. The combust ble matter of the candle must be de- 
 composed in order to emit the hydrogen gas, and the wick is 
 instrumental in effecting this decomposition. Its combustion 
 
 first melts the combustible matter, and 
 
 Caroline. But in lamps the combustible matter is already 
 fluid, and yet they also require wicks ? 
 
 Mrs. B. I am going to add that, afterwards, the burning wick 
 
 (by the power of capillary attraction) gradually 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 bottoms 
 
 Caroline. Yes ; but I do not understand why it does not. 
 
 Mrs. B. Because the air has not so free an access to that 
 
 11 
 
110 HYDROGEN. 
 
 part of the wick which is immediately in contact with the can- 
 dle, as to the part just above, so that the heat there is not suffi- 
 cient to produce its decomposition; the combustion therefore 
 begins a little above this point.* 
 
 Caroline. But, Mrs. B. in those beautiful lights, called gas- 
 ligids., which are now seen in many streets, and will, I hope, be 
 soon adopted every where, I can perceive no wick at all. How 
 are these lights managed ? 
 
 Mrs. B. I am glad you have put me in mind of saying a few 
 words on this very useful and interesting improvement. In this 
 mode of lighting, the gas is conveyed to the extremity of a 
 tube, where it is kindled, and burns as long as the supply con- 
 tinues. There is, therefore, no occasion for a wick, or any 
 other fuel whatever. 
 
 Emily. But how is this gas procured in such large quanti- 
 ties ? 
 
 Mrs. B. It is obtained from c0al, by distillation. Coal, 
 when exposed to heat in a close vessel, is decomposed ; and hy- 
 drogen, which is one of its constituents, rises in the state of gas, 
 combined with another of its component parts, carbon, forming 
 a compound gas, called IJydro-carbonat, the nature of which 
 we shall again have an opportunity of noticing when we treat 
 of carbon. This gas, like hydrogen, is perfectly transparent, in- 
 visible, and highly inflammable; and in burning it emits that 
 vivid light which you have so often observed. 
 
 Caroline. And does the process for procuring it require no- 
 thing but heating the coals, and conveying the gas through 
 tubes ? 
 
 Mrs. B. Nothing else ; except that the gas must be made to 
 pass, immediately at its formation, through two or three large- 
 vessels of water,! in which it deposits some other ingredients, 
 and especially water, tar, and oil, which also arise from tin 
 distillation of coals. The gas-light apparatus, therefore con- 
 sists simply in a large iron vessel, in which the coals are expo- 
 sed to the heat of a furnace, some reservoirs of water, in 
 
 * Tn the burning of a candle, the reason why ccmhustion does not 
 take place in immediate contact with the tallow is, that the caloric 
 is here employed in converting; a solid into a fluid, as explained in 
 the conversation of free caloric. In the burning 01 a lamp if the 
 same thing takes place, it is because the metallic tube through which 
 .the wick passes, conducts off the heat. C. 
 
 t The gas is passed through one vessel of slacked lime and water to 
 absorb the carbonic acid gas, with which it is always more or less mix 
 ed, whea first distilled. C. 
 
HYDROGEN. Ill 
 
 which the gas deposits -its impurities, and tubes that convey 
 it to the desired spot, being propelled with uniform velocity 
 through the tubes by means of a certain degree of pressure 
 which is made upon the reservoir. 
 
 Emily. What an admirable contrivance ! Do you not think, 
 Mrs. B., that it will soon get into universal use ? 
 
 Airs. B. Most probably, for the purpose of lighting streets, 
 offices, and public places, as it far surpasses any former inven- 
 tion for that purpose; but in regard to the interior of private 
 houses, this mode of lighting has not yet been sufficiently tried 
 to know whether it will be found generally desirable, either with 
 respect to economy or convenience. It may, however, be con- 
 sidered as one of the happiest applications of chemistry to the 
 comforts of life; and there is every reason to suppose that it 
 will answer the full extent of public expectation. 
 
 I have another experiment to show you with hydrogen gas, 
 which I think will entertain you. Have you ever blown bub- 
 bles with soap and water ? 
 
 Emily. Yes, often, when I was a child ; and I used to make 
 them float in the air by blowing them upwards. 
 
 Mrs. B. We shall fill some such bubbles with hydrogen gas, 
 instead of atmospheric air, and you will see with what ease and 
 rapidity they will ascend, without 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 re- 
 ceiver 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 ? 
 
 Mrs. B. It is to afford a passage to the gas when required. 
 There is, you see, a similar stop-cock fastened to this bladder, 
 which is made to fit that on the receiver. I screw them one on 
 the other, and now turn the two cocks, to open a communica- 
 tion between the receiver and the bladder; then, by sliding the 
 receiver oft* the shelf, and gently sinking it into the bath, the 
 water rises in the receiver and forces the gas into the bladder. 
 (PLATE IX. fig. 1.) 
 
 Caroline. Yes, I see the bladder swell as the water rises in 
 the receiver. 
 
 Mrs. B. I think that we have already a sufficient quantity in 
 the bladder for our purpose ; we riuist be careful to stop both 
 ihe cocks before we separate the bladder from the receiver, lest 
 the gas should escape. Now I must fix a pipe to the stopper 
 of the bladder, and by dipping its mouth into the soap and wa- 
 ter, take up a few drops then I again turn the cock, and 
 
112 
 
 HYDROGEN. 
 
 squeeze the bladder in order to force the ?as into the soap aim 
 water at the mouth of the pipe. (PLATE ! X. fig. 2.) 
 
 Emily. There is a bubble but it bursts before it leaves the 
 mout;i ot'ihe i>ipe. 
 
 Mrs. IL We must have patience and try again ; it is not so 
 easy to blow bubbles by means of a >! idder. as simply with the 
 breath. 
 
 Caroline. Perhaps there is not soap enough in the water ; I 
 should l iave na( ] W ann water, it would have dissolved the soar) 
 b ter. 
 
 Emily. Does not some of the gas escape between the blad- 
 der 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 rapidi- 
 ty of a balloon. How beautifully it refracts the light ! 
 
 Emily. It has burst against the ceiling you succeed now 
 wonderfully ; but why do they all ascend and burst against the 
 ceiling ? 
 
 Mrs. B. Hydrogen gas is so much lighter than atmospherical 
 air, that it ascends rapidly with its very light envelope, which is 
 burst by the force with which it strikes the ceiling. 
 
 Air-balloons are filled with this gas, and if they carried 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 con- 
 tain. I do not know whether you have ever been present at 
 the filling of a large balloon. The apparatus for that 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 communi- 
 cating with along flexible pipe, which conveys the gas into the 
 balloon. 
 
 Emily. But the fire-balloons which were first invented, and 
 have been since abandoned, on account of their being so dan- 
 gerous, were constructed, I suppose, on a different principle. 
 
 J\1rs. /..'. They were filled simply with atmospherical air, 
 considerably rarified by heat 5 and the necessity of having a 
 fire underneath the balloon, in order to preserve the rarefaction 
 of the air within it, was the circumstance productive of so much 
 tlanper. 
 
 If you are not yet tired of experiments, I have another to 
 show you. It consists in filling soap-bubbles with a mixture of 
 
HYDROGEN* J 1^ 
 
 
 
 hydrogen and oxygen gases, in the proportions that form water; 
 and afterwards setting fire to them. 
 
 Emily. They will detonate, 1 suppose? 
 
 J\Jrs. i>. 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 proportion of oxygen and hydrogen gases, 
 and we have only to blow bubbles with it. 
 
 Caroline. Here is a fine large bubble rising shall I set fire 
 to it with the candle ? 
 
 Mrs. B. If you please. 
 
 Caroline. Heavens, what an explosion!* It Was like the 
 report of a gun : I confess it frightened me much. I never 
 should have imagined it could be so loud. 
 
 Emily. And the flash was as vivid as lightning. 
 
 Mrs. R. The combination of the two gases takes place du- 
 ring that instant of time that you see the flash, and hear the de- 
 tonation. 
 
 Emily. This has a strong resemblance to thunder and light- 
 ning.t 
 
 Mrs. R. These phenomena, however, are generally of an 
 electrical nature. Yet various meteorological effects may be at- 
 tributed to accidental detonations of hydrogen gas in the atmos- 
 phere; for nature abounds with hydrogen : it constitutes a very 
 considerable 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 great number of minerals; but it is most abundant in 
 vegetables. From this immense variety of bo-lies, it is often 
 spontaneously disengaged ; its great levity makes it rise into the 
 superior regions of the atmosphere ; and when, either by an 
 electrical 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 w** often see on a summer- 
 evening, without hearing any detonation. 
 
 Emily. Every flash, I suppose, must produce a quantity of 
 water ? 
 
 * In making this experiment, always be careful to turn the stop-cock, 
 or detach the bubble completely from the pipe before it is set fire to ; 
 otherwise a sad accident may happen from the gas taking fire in the 
 bladder. C. 
 
 t The report is owing to the air, rushing in io fill the vacuum, cau- 
 sed by the condensation of the two gasses aad the heat extricated at 
 Ihe same instant. C, 
 
 11* 
 
114 HYDROGEN. 
 
 Caroline. And this water, naturally, descends in the form of 
 rain ? 
 
 Mrs. 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 re- 
 main there in the form of clouds. 
 
 The application of electrical attraction to chemical phenom- 
 ena is likely to lead to many very interesting discoveries in me- 
 teorology ; for electricity evidently acts a most important part 
 in the atmosphere. This subject however is, as yet, not suffi- 
 ciently developed for me to venture enlarging upon it. The 
 phenomena of the atmosphere are far from being well under- 
 stood ; and even with the little that is known, I arn but imper- 
 fectly acquainted. 
 
 But before we take leave of hydrogen, I must not omit to 
 mention to you a most interesting discovery of Sir H. Davy, 
 which is connected with this subject. 
 
 Caroline. You allude, I suppose, to the new miner's lamp, 
 which has of late been so much talked of? I have long been 
 desirous of knowing what that discovery was, and what pur- 
 pose it was intended to answer. 
 
 Mrs. B. It often happens in coal-mines, that quantities of the 
 gas, called by chemists kydro-carbonat, or by the miners fire- 
 damp, (ihe same from which the gas-lights are obtained,) ooze 
 Out from fissures in the beds of coal, and fill the cavities in 
 which the men are at work ; and this gas being inflammable, 
 the consequence is, that when the men approach those places 
 with a lighted candle, the gas takes fire, and explosions happen 
 which destroy the men and horses employed in that part of the 
 coll'ery, sonriftimes in great numbers. 
 
 Emily- What tremendous accidents these must be ! Bufc 
 whence does that gas originate ? 
 
 Mrs. B. Being the chief product of the combustion of coal, 
 no wonder that inflammable gas should occasionally appear in 
 situations in which this mineral abounds, since there can be no 
 doubr that processes of combustion are frequently taking place 
 at a ereat depth under the surface of the earth ; and therefore 
 thosf accumulations of gas may arise either from combustions 
 actually going on, or from former combustions, the gas having 
 perhaps been confined there for ages. 
 
 Caroline. And how does Sir H. Davy's lamp prevent those 
 dreadful explosions? 
 
 Mrs. B. By a contrivance equally simple and ingenious ; 
 and one which does no less credit to the philosophical views 
 from which it was deduced, than to the philanthropic motive? 
 
HYDROGEN. 11 3 
 
 Irom which the enquiry sprung. The principle cf the lamp is 
 shortly this : It was ascertained, two or three years ago, both 
 by Mr. Tenant and by Sir Humphrey himself, that the combus- 
 tion of inflammable gas could not be propagated through small 
 tubes ; so that if a jet of an inflameable gaseous mixture, issu- 
 ing from a bladder or any other vessel, through a small tube, 
 be set fire to, it burns at the orifice of the tube, but the flame 
 never penetrates into the vessel. It is upon this fact that Sir 
 Humphrey's safety lamp is founded. 
 
 Emily. But why does not the flame ever penetrate through 
 the tube into the vessel from which the gas issues, so as to ex- 
 plode at once the whole of the gas ? 
 
 Airs. B. Because, no doubt, the inflamed gas is so much cool- 
 ed in its passage through a small tube as to cease to burn be- 
 fore the combustion reaches the reservoir. 
 
 Caroline. And how can this principle be applied to the con- 
 struction of a lamp ! 
 
 Mr*, h. Nothing easier. You need only suppose a lamp 
 enclosed all round in glass or horn, hut having a number of 
 small open tubes at the bottom, and others at the top, to let the 
 air in and out. Now, if such a lamp or lanthorn be carried in- 
 to an atmosphere capable of exploding, an explosion or com- 
 bustion of the gas will take place within the lamp; and al- 
 though the vent afforded by the tubes will save the lamp from 
 bursting, yet, from the principle just explained, the combustion 
 will not be propagated to the external air through the tubes, so 
 that no farther consequence will ensue. 
 
 Emily. And is that all the mystery of that valuable lamp? 
 
 Mrs. B. No; in the early part of the enquiry a lamp of this 
 kind was actually proposed ; but it was but a rude sketch com- 
 pared to its present state of improvement. Sir H. Davy, after 
 . a succession of trials, by which he brought his lamp nearer and 
 nearer to perfection, at lasi conceived the happy idea that if the 
 lamp were surrounded with a wire-work or wire-gauze, of a 
 close texture, instead of glass or horn, the tubular contrivance I 
 have just described would be entirely superseded, since each of 
 the interstices of the gauze would act as a tube in preventing the 
 propagation of explosions ; so that this previous metallic cover- 
 ing would answer the various purposes of transparency, of per- 
 meability to air, and of protection against explosion. This 
 idea, Sir Humphrey immediately submitted to the test of expr- 
 iment, and the result has answered his most sanguine expecta- 
 tions, both in his laboratory and in the collieries, where it has 
 already been extensively tried. And he has now the happiness 
 of thinking that his invention will probably be the means of sa- 
 
116 SULPHUR, 
 
 ving every year a number of lives, which would have been lost 
 in digging out of the bowels of the earth one of the most \Hilua- 
 ble necessaries of life. Here is one of these lamps, everv part 
 of which you will at once comprehend. (See PLATE X. fig. 1.) 
 
 Caroline. How very simple and ingenious ! But I do not 
 yet well see why an explosion taking place within the lamp 
 should not communicate to the external air 'around it, through 
 the interstices of the wire? 
 
 Mrs. 8. This has been and is still a subject of wonder, even 
 to philosophers ; and the only mode of explaining it is, that 
 flame or ignition cannot pass through a fine wire-work, because 
 the metallic wire cools the flame sufficiently to extinguish it in 
 passing through the gauze. This property of the wire-gauze is 
 quite similar to that of the tubes which I mentioned on introdu- 
 cing the subject ; for you may consider each interstice of the 
 gauze as an extremely short tube of a very small diameter. 
 
 Emihj. But I should expect the wire would often become 
 red-hot, by the burning of the gas within the lamp ? 
 
 Mrs. B. And this is actually the case, for the top of the 
 lamp is very apt to become red-hot. But, fortunately, inflam- 
 mable gaseous mixtures cannot be exploded by red-hot wire, 
 the intervention of actual flame being required forthat purpose; 
 so that the wire does not set fire to the explosive gas around it. 
 
 Emily. I can understand that; but if the wire be red-hot, 
 how can it cool the flame within, and prevent its passing 
 through the gauze ? 
 
 Mrs. h. The gauze, though red-hot, is not so hot as the flame 
 by which it has been heated ; and as metalic wire is a good con- 
 ductor, the heat does not much accumulate in it, as it passes off 
 quickly to the other parts of the lamp, as well as to any contig- 
 uous bodies. 
 
 Caroline. This is indeed a most interesting discovery, and 
 one which shows at once the immense utility with which science 
 may be practically applied to some of the most important pur- 
 poses. 
 
 CONVERSATION VIII. 
 
 ON SULPHUR AND PHOSPHORUS. 
 
 ^ 
 
 Mrs. B. SULPHUR is the next substance that comes under oui 
 consideration. It differs in one essential point from the prr 
 
.A.. f7if fiftfrn. containing tfu ait '._B. 1/u rtin or 
 <ff*/ir/'.> y u7itf& /fit ^atuze capf if /KWO? to die ns-tern .Q. 
 
 t'rip <?/7._E.# Kin; &r tritmmry&e wit& D __ T1//4" wine gauze eyfaiJrr. 
 
 (s. 
 
 ^/?__B. t/tt 
 

K 
 
 
SCJLHHUR. 117 
 
 Ceding, as it exists in a solid form at the temperature of the at- 
 mosphere. 
 
 Caroline. lam glad that we have at last a solid body to ex- 
 amine ; one that we can see and touch. Pray, is it not with 
 sulphur that the points of matches are covered, to make them 
 easily kindle ? 
 
 Jftrs. B. Yes, it is ; and you therefore already know that 
 sulphur is a very combustible substance. It is seldom discov- 
 ered in nature in a pure unmixrd 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 sim- 
 ple 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 quantity, in the 
 mineral, vegetable, and animal kingdoms.* 
 
 Emily. I have heard oi'fowers qf sulphur, are they the pro- 
 duce of any plant ? 
 
 Mrs. B. By no means : they consist of nothing more than 
 common sulphur, reduced to a very fine powder by a process 
 called sublimation. You see some of it in this phial ; it is ex- 
 actly 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 ? 
 
 Mrs. B. It is the evaporation, or, more properly speaking, 
 the volatilisation of solid substances, which, in cooling, con- 
 dense again in a concrete form. The process, in this instance, 
 must be performed in a closed vessel, both to prevent combus- 
 tion, which would take place if the. access of air were not care- 
 fully 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 
 XI. fig. 1.) Some lumps of sulphur are put into a receiver of 
 this kind, winch is called a cucurbit. Its shape, you see, some- 
 what 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 cucurbit, thus covered with its head, is 
 placed over a sand-bath : this is nothing more than a vessel 
 lull of sand, which is kept heated by a furnace, such as you see 
 
 * The sulphur of commerce is chiefly obtained in the vicinity of 
 volcanoes, or in volcanic countries, where it is brought up from the 
 how ] <>f the t-nrlh by sublimation. An inferior kind is obtained by 
 (lie distillation of pyrites. C 
 
118 SULPHUR. 
 
 here, so as to preserve the apparatus in a moderate and unifonu 
 temperature. The sulphur then soon begins to melt, and im- 
 mediately after this, a thick white smoke rises, which is gradu- 
 ally deposited within 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 ilowers of sul- 
 phur. This apparatus, which is called an alembic, is highly 
 useful in all kinds of distillations, as you will see when we come 
 to treat of those operations. Alembics are not commonly made 
 of glass, like this, which is applicable only to distillations upon 
 a very small scale. Those used in manufactures are generally 
 made of copper, and are, of course, considerably larger. The. 
 general construction, however, is always the same, although 
 their shape admits of some variation. 
 
 Caroline. What is the use of that neck, or tube, which bend? 
 down from the upper piece of the apparatus? 
 
 Mrs. B. it is of no use in sublimations ; but in distillations 
 (the general object of which is to evaporate, by heat, in closed 
 vessels, the volatile parts of a compound body, and to condense 
 them again into a liquid,) it serves to carry off the condensed 
 fluid, which otherwise would fall back into the cucurbit. But 
 this is rather 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 consist in 
 destroying, by means of heat, the attraction of aggregation of 
 the particles of a solid body, which are thus volatilised ; and as 
 soon as they lose the caloric which produced that effect, they 
 are deposited in the fumi of a fine powder. 
 
 Caroline. It seems to me to be somewhat similar to the trans- 
 formation 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. 
 
 Mrs. B. Chemically speaking, it is exactly the same sub- 
 stance, whether in the form of lump or powder. For if this 
 powder be melted again by heat, it will, in cooling, 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? 
 
 A!rs. '}. It divides the sulphur into very minute parts, and 
 thus disposes it to enter more readily into combination with 
 other bodies. It is used also as a means of purification. 
 
SULPHUR. Hi) 
 
 Caroline. Sublimation .appears to me, like the beginning ot' 
 combustion, for the completion of which one circumstance only 
 is wanting, the absorption of oxygen. 
 
 Mrs. B. But that circumstance is every thing. No essential 
 alteration is produced in sulphur by sublimation ; whilst in com- 
 bustion it combines with the oxygen, and forms a new com- 
 pound totally different in every respect from Sulphur in its pure 
 state. We shall now burn some sulphur, and you will see how 
 very different 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 : I now set fire to 
 the sulphur with the point of this hot wire ; for its combustion 
 will not begin unless its temperature 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. As for the white 
 smoke, I arn quite at a loss to guess what it may be. 
 
 Mrs. B. Your first conjecture is very right ; but you are 
 mistaken in the last ; for nothing will be left in the cup. The 
 white vapour is the oxygenated sulphur, which assumes the form 
 of an elastic fluid of a pungent and offensive smell, and is a pow- 
 erful acid. Here you see a chemical combination of oxygen and 
 sulphur, producing a true gas, which would continue such un- 
 der 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 
 acid taste, and all its acid properties. You see, now, with 
 what curious effects the combustion of sulphur is attended: 
 
 Caroline. This is something quite new ; and I confess that 
 T do not perfectly understand why the sulphur turns acid. 
 
 Mrs. B. It is because it unites with oxygen, which is the 
 acidifying principle. And, indeed, the word oxygen is deriv- 
 ed from two Greek words, signifying to produce an acid. 
 
 Caroline. Why, then, is not water, which contains such a 
 quantity of oxygen, acid ? 
 
 Mrs. B. Because hydrogen, which is the other constituent of 
 water, is not susceptible of acidification. I believe it will be 
 necessary, before we proceed further, to say a few words of the 
 general nature of acids, though it is rather a deviation from our 
 plan of examining the simple bodies separately, before we con- 
 sider them in a state of combination. 
 
1:2(3 SULPHUR. 
 
 Acids may be considered as a peculiar class of burnt* bodies, 
 which during their combustion, or combination with oxygen, 
 have acquired very characteristic properties. They are chiefly 
 discernible 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 basis, and is different in each,) 
 and of oxygen, which is common to them all. 
 
 Emily But I do not clearly seethe difference between acids 
 and oxyds. 
 
 Mrs. B. Acids were, in fact, oxyds, which, by the addition 
 of a sufficient quantity of oxygen, have been converted into 
 acids. For acidification, you must observe, always implies 
 previous oxydation, as a body must have combined with the 
 quantity of oxygen requisite to constitute it an oxyd, before it 
 can combine with the greater quantity which is necessary to 
 render it an acid. 
 
 Caroline. Are all oxyds capable of being converted into 
 acids ? 
 
 Mrs. B. Very far from it ; it is only certain substances which 
 will enter into that peculiar kind of union with oxygen that pro- 
 duces acids, and the number of these is proportionally very 
 small ; but all burnt bodies may be considered as belonging ei- 
 ther to the class of oxyds, or to that of acids. At a future pe- 
 riod, we shall enter more at large into this subject. At present, 
 I have but one circumstance further to point out to your obser- 
 vation respecting acids : it is, that most of them are suscepti- 
 ble of two degrees of acidification, according to the different 
 quantities of oxygen with which their basis combines. 
 
 Emily. And how are these two degrees of acidification dis- 
 tinguished ? 
 
 Mrs. B. By the peculiar properties which result from them. 
 The acid we have just made is the first or weakest degree of 
 acidification, and is called sulphureous acid ; if it were fully 
 saturated with oxygen, it would be called sulphuric acid. You 
 must therefore remember, that in this, as in all acids, the first 
 degree of acidification is expressed by the termination in ous : 
 the stronger, by the termination m ic. 
 
 Caroline. And how is the sulphuric acid made ? 
 
 * This might mislead the student. Tlif acids am not all of them 
 form PC! by bunau^. AH th<-> vogvt^ble aciiU. as theatric, malic, e. 
 exist ready formed ; some of th; : m are contained in fruits, as in lo- 
 apples, &c. C. 
 
SULPHUR. I2t 
 
 Mrs. B. By burning sulphur in pure oxygen gas, and thus 
 rendering its combustion much more complete. I have provi- 
 ded 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, iMrs. B. 
 
 Mr*. 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 aperture 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 bub- 
 bles escape, and that must be expected at 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 oxygen gas. 
 
 Emily. How beautifully it burns ! 
 
 Caroline. But it is already buried in the thick vapour. This, 
 I suppose, is sulphuric acid ? 
 
 Emily. Are these acids always in a gaseous state ? 
 
 Mrs. B. Sulphureous acid, as we have already observed, is a 
 permanent gas, and can be obtained in a liquid form only by 
 condensing it in water. In its pure state, the sulphureous acid 
 is invisible, and it now appears in the form of a white smoke, 
 from its combining with the moisture. But the vapour of sul- 
 phuric acid, which you have just seen to rise during the com- 
 bustion, is not a gas, but only a vapour, which condenses into 
 liquid sulphuric acid, by losing its caloric. But it appears from 
 Sir H. Davy's experiments, that this formation apd condensa- 
 tion of sulphuric acid requires the presence of water, for which 
 purpose the vapour is received into cold water which may after- 
 wards be separated from the acid by evaporation. 
 
 Sulphur has hitherto been considered as a simple substance; 
 but Sir H. Davy has suspected that it contains a small portion 
 of hydrogen, and perhaps also of oxygen. 
 
 On submitting sulphur to the action of the Voltaic battery, 
 he observed that the negative wire gave out hydrogen ; and the 
 existence of hydrogen in sulphur was rendered still more proba- 
 ble by his observing that a small quantity of water was produ- 
 ced during the combustion of sulphur. 
 
 Emily. And pray of what nature is sulphur when perfectly 
 pure? 
 
 Mrs. B. Sulphur has probably never been obtained perfectly 
 free from combination, so that its radical may possibly possess 
 
 12 
 
122 SULPHUR. 
 
 properties very different from those of common sulphur. It 
 has been suspected to be of a metallic nature 5 but this is mere 
 conjecture. 
 
 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 ac- 
 quainted. Hydrogen gas can dissolve a small portion of it. 
 
 Emily. What ! can a gas dissolve a solid substance ? 
 
 Mrs. B. Yes 5 a solid substance may be so minutely divided 
 by heat, as to become soluble in gas : and there are several in- 
 stances of it. But you must observe, that, in this case, a chem- 
 ical union or 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 gas 7 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 caloric by 
 which it was volatilized. Besides, it is evident, from the pecu- 
 liar fetid smell of this gns, that it is a new compound totally dif- 
 ferent from either of its constituents ; it is called sulphuretted 
 hydrogen gas, and is contained in great abundance in sulphu- 
 reous mineral waters. 
 
 Caroline. Are not the Harrogate waters of this nature ? 
 
 Mrs. B. Yes ; they are naturally impregnated with sulphu- 
 retted hydrogen gas, and there are many other springs of the 
 Same kind, which shows that this gas must often be formed in 
 the bowels of the earth by spontaneous processes of nature. 
 
 Caroline. And could not such waters be made artificially by 
 impregnating common water with this gas? 
 
 Mrs. B. Yes ; they can be so well imitated, as perfectly to 
 resemble the Hai rogate waters. 
 
 Sulphur combines likewise with phosphorus, and with the al- 
 kalies, and alkaline earths, substances with which you are yet 
 unacquainted. We cannot, therefore, enter into these combi- 
 nations at present. In our next lesson we shall treat of phos* 
 phorus. 
 
 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. \ 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 appeared to me so interesting as 
 the other simple bodies. 
 
PHOSPHORUS. 123 
 
 Mrs. B. Perhaps you may find phosphorus more entertain- 
 ing. You must not, however, be discouraged when you meet 
 with some parts of a study less amusing than others ; it would 
 answer no good purpose to select the most pleasing parts, since, 
 it" we did not proceed 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 considered as a simple body ; though, like 
 sulphur, it has been suspected of containing hydrogen. It was 
 not known by the earlier chemists. It was first discovered by 
 Brandt, a chemist of Hamburgh, whilst employed in researches 
 after the philosopher's stone ; but the method of obtaining it re- 
 mained a secret till it was a second time discovered both by 
 Kunckel and Boyle, in the year 1680. You see a specimen of 
 phosphorus in this phial ; it is generally moulded into small 
 sticks of a yellowish colour, as you find it here. 
 
 Caroline. I do not understand in what the discovery consist- 
 ed ; there may be a secret method of making an artificial com- 
 position, but how can you talk of making a substance which 
 naturally exists ? 
 
 Mrs. B. A body may exist in nature so closely combined 
 with other substances, as to elude the observation of chemists, 
 or render it extremely difficult to obtain it in its separate state. 
 This is the case with phosphorus, which is always so intimate- 
 ly combined with other substances, that its existence remained 
 unnoticed till Brandt discovered the means of obtaining it free 
 from other combinations. It is found in all animal substances, 
 and is now chiefly extracted from bones, by a chemical process. 
 I: exists also in some plants, that bear a strong analogy to ani- 
 mal matter in their chemical composition. 
 
 Emily. But is it never found in its pure separate state ? 
 
 Mrs. B. Never, and this is the reason that it remained so 
 long undiscovered* 
 
 Phosphorus is eminently combustible ; it meltsand takes fire 
 at the temperature of one hundred degrees, and absorbs in its 
 combustion nearly once and a half its own weight of oxygen. 
 
 Caroline. What ! will a pound of phosphorus consume & 
 pound and a half of oxygen ? 
 
 Mrs. B. So it appears from accurate experiments. I can 
 show you with what violence it combines with oxygen, by burn- 
 ing some of it in that gas. We must manage the experiment 
 in the same manner as we did the combustion of sulphur. Von 
 
124 PHOSPHORUS. 
 
 see I am obliged to cut this little bit of phosphorus under wa- 
 ter, 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. 
 
 Emily. What a blaze ! I can hardly look at it. I never saw 
 any thing so brilliant. Does it not hurt your eyes, Caroline ? 
 
 Caroline. Yes ; but still 1 cannot help looking at it. A 
 prodigious quantity of oxygen must indeed be absorbed, when 
 so much light and caloric are disengaged ! 
 
 Mrs. B. In the combustion of a pound of phosphorus, a suf- 
 ficient quantity of caloric is set free to melt upwards of a hun- 
 dred pounds of ice 5 this has been computed by direct experi- 
 ments with the calorimeter. 
 
 Emily. And is the result of this combustion, like that of sul- 
 phur, an acid ? 
 
 Mrs. B. Yes ; phosphoric acid. And had we duly propor- 
 tioned 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 separately. 
 The water would have ascended into the receiver, on account 
 of the vacuum formed, and would have filled it entirely. In 
 this case, as in the combustion of sulphur, the acid vapour form- 
 ed is absorbed and condensed in the water of the receiver. But 
 when this combustion is performed without any water or mois* 
 lure being present, the acid then appears in the form of con- 
 crete whitish flakes, which are, however, extremely ready to 
 melt upon the least admission of moisture. 
 
 Emily. Does phosphorus, in burning in atmospherical air 2 
 produce, like sulphur, a weaker sort of the same acid ? 
 
 Mrs. B. No : for it burns in atmospherical air, nearly at the 
 same temperature as in pure oxygen gas ; and it is in both ca- 
 ses so strongly disposed to combine with the oxygen, that the 
 combustion is perfect, and the product similar ; only in atmos- 
 pherical air, being less rapidly supplied with oxygen, the pro~ 
 eess is performed in a slow manner. 
 
 Caroline. But is there no method of acidifying phosphorus 
 in a slighter manner, so as to form phosphorous acid.? 
 
 Mrs. B. Yes, there is. When simply exposed to the atmos- 
 phere, phosphorus undergoes a kind of slow combustion at any 
 temperature above zero. 
 
 Emily. 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 
 
IOSPHORUS* 125 
 
 emitted which is very discernible in the dark ; but the heai 
 evolved is not sufficiently strong to be sensible; a whitish va- 
 pour arises from this combustion, which, uniting with water, 
 condenses into liquid phosphorus acid. 
 
 Caroline. Is it not very singular that phosphorus should 
 burn at so low a temperature in atmospherical air, whilst it 
 does not burn in pure oxygen without the application of heat ? 
 
 Mrs. B. So it at first appears. But this circumstance seems 
 to be owing to the nitrogen gas of the atmosphere. This gas 
 dissolves small particles of phosphorus, which being thus mi- 
 nutely divided and diffused in the atmospherical air, combines 
 with the oxygen, and undergoes this slow combustion. But the 
 same effect does not take place in oxygen gas, because it is not 
 capable of dissolving phosphorus ; it is therefore necessary, in 
 this case, that heat should be applied to effect that division of 
 particles, which, in the former instance, is produced by the ni- 
 trogen. 
 
 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 j yet 
 they do not seem to burn. 
 
 Mrs. B. But they do really burn ; for it is by their slow com- 
 bustion that the light is emitted ; and phosphorus acid is the re- 
 sult of this combustion. 
 
 Phosphorus is sometimes used as a test to estimate the puri- 
 ty of atmospherical air. For this purpose, it is burnt in a gra- 
 duated tube, called an Eudiometer (PLATE XI. fig. 2.), and 
 from the quantity of air which the phosphorus absorbs, the pro- 
 portion of oxygen in the air examined is deduced ; for the phos- 
 phorus will absorb all the oxygen, and the nitrogen alone will 
 remain. 
 
 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 combustible, that it immediately takes 
 fire on coming m contact with the air. It is with this compo- 
 sition that phosphoric 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. 
 
 Jtfrs. '3. By rubbing them you raise their temperature 5 for ? 
 you knowj friction is one of thf means of extrcating heat, 
 
 12* 
 
126 PHOSPHORUS. 
 
 Emily. Will phosphorus combine with hydrogen gas, as sul- 
 phur does ? , 
 
 Mrs. B. Yes; and the compound gas which results from 
 this combination has a smell still more fetid than the sulphuret- 
 ted hydrogen ; it resembles that of garlic. 
 
 The phospkoretted hydrogen gas has this remarkable pecul- 
 iarity, that it takes fire spontaneously in the atmosphere, at any 
 temperature. It is thus, probably, that are produced those 
 transient flames, or flashes of light, called by the vulgar Will- 
 of-the-Whisp) or more properly Ignesfatvi, which are often 
 seen in church-yards, and places where the putrefactions of 
 animal matter exhale phosphorus and hydrogen gas. 
 
 Caroline. Country people, who are so much frightened by 
 those appearances, would soon be reconciled to them, if they 
 knew from what a simple cause they proceed. 
 
 Mrs. B. There are other combinations of phosphorus that 
 have also very singular properties, particularly that which re- 
 sults from its union with lime. 
 
 Emily. Is there any name to distinguish the combination of 
 two substances, like phosphorus and lime, neither of which 
 are oxygen, and which cannot therefore produce either an ox- 
 yd or an acid ? 
 
 Mrs. B. The names of such combinations are composed from 
 those of their ingredients, merely from a slight change in their 
 termination. Thus the combination of sulphur with lime is 
 called a sulphuret, and that of phosphorus, a phosphuret of 
 lime.* This latter compound, I was going to say, has the sin- 
 gular 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 ascend, holding 
 in solution a small quantity of phosphorus. 
 
 * Phosphuret of lime is a very curious substance. To make it, 
 take a thin glass tube, 6 or 8 inches long, and less than half an inch 
 in diameter ; if it is closed at one end, so much the better, but a cork 
 will do. Near the closed end put a piece of phosphorus half an inch 
 long. Then put in by means of a stick or wire, holding the tube hori- 
 zontally, thirty or forty pieces of newly burned quick-lime, about the 
 size of split peas, letting the lowest remain 2 or 3 inches from the phos- 
 phorus. Then stop the other end of the tube loosely, and place the 
 part containing the quick-lime, in a bed of charcoal, so contriving it 
 that a candle or red hot iron can be brought under the part where the 
 phosphorus lies. Kindle a fire by means of bellows, and heat the lime 
 red hot, without melting the phosphorus, which may be kept cool by a 
 wet rag ; when this is done, bring the hot iron or candle under the 
 phosphorus, so as to make it pass through the quick-lime in the form 
 of vapour. Cork up the phosphuret of lime for use. C, 
 
PHOSPHORUS. 127 
 
 Emily. These bubbles then are phosphoretted hydrogen 
 gas ? 
 
 Mrs. B. Yes ; and they produce the singular appearance of 
 a flash of fire issuing from the water, as the bubbles kindle and 
 detonate on the surface of the water, at the instant that they 
 come in contact with the atmosphere. [If the water is icarm, 
 the experiment is more apt to succeed. C.] 
 
 Caroline. Is not this effect nearly similar to that produced 
 by the combination of phosphorus and sulphur, or, more pro- 
 perly speaking, the phosphuret of sulphur? 
 
 Mrs. B. Yes ; but the phenomenon appears more extraordi- 
 nary in this case, from the presence of water, and from the 
 gaseous form of the combustible compound. Besides, the ex- 
 periment surprises by its great simplicity. You only throw a 
 piece of phosphuret of lime into a glass of water, and bubbles 
 of fire will immediately issue from it. 
 
 Caroline. Cannot we try the experiment ? 
 
 Mrs. B.' Very easily ; but we must do it in the open air ; for 
 the smell of the phosphoretted hydrogen gas is so extremely fe- 
 tid, that it would be intolerable in the house. But before we 
 leave the room, we may produce, by another process, some 
 bubbles of the same gas, which are much less offensive. 
 
 There is in this little glass retort a solution of potash in wa- 
 ter $ I add to it a small piece of phosphorus. We must now 
 heat the retort over the lamp, after having engaged its neck 
 under water You see it begins to boil ; in a few minutes bub- 
 bles will appear, which take fire and detonate as they issue from 
 the water. 
 
 Caroline. There is one and another. How curious it is .' 
 But I do not understand how this is produced. 
 
 Mrs. B. It is the consequence of a display of affinities too 
 complicated, I fear, to be made perfectly intelligible to you at 
 present. 
 
 In a few words, the reciprocal action of the potash, phos- 
 phorus, caloric, and water, are such, that some of the water 
 is decomposed, and the hydrogen gas thereby formed carries 
 off some minute particles of phosphorus, with which it forms 
 phosphoretted hydrogen gas, a compound which spontaneously 
 takes fire at almost any temperature. 
 
 Emily. What is that circular ring of smoke which slowly ri- 
 ses from each bubble after its detonation ? 
 
 Mrs. B. It consists of water and phosphoric acid in vapour ; 
 which are produced by the combustion of hydrogen and phos- 
 phorus. 
 
128 CARBON. 
 
 CONVERSATION IX. 
 
 ON CARBOS. 
 
 Caroline. TO-DAY, Mrs. B., I believe we are to learn the 
 nature and properties of CARBON. This substance is quite new 
 to me ; I never heard it mentioned before. 
 
 Mrs. B. Not so new as you imagine ; for carbon is nothing 
 more than charcoal in a state of purity, that is to say, unmix- 
 ed with any foreign ingredients. 
 
 Caroline. But charcoal is made by art, Mrs. B., and a body 
 consisting of one simple substance cannot be fabricated ? 
 
 Mrs. B. You again confound the idea, of making a simple 
 body, with that of separating it from a compound. The che- 
 mical processes by which a simple body is obtained in a state of 
 purity, consist in unmaking the compound in which it is con- 
 tained, in order to separate from it the simple substance in 
 question. The method by which charcoal is usually obtained, 
 is, indeed, commonly called making it ; but, upon examina- 
 tion, you will find this process to consist only in separating it 
 from other substances with which it is found combined in na- 
 ture. 
 
 Carbon forms a considerable part of the solid matter of all 
 organised bodies ; but it is most abundant in the vegetable cre- 
 ation, 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 charcoal. 
 
 Caroline. But if heat be applied to the wood in order to 
 evaporate the oil and water, will not the temperature 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 fiy 
 off? 
 
 Mrs. B. In order to produce charcoal in its purest state, 
 (which is, even then, but a less imperfect sort of carbon,) the 
 operation should be performed in an earthen retort. Heat be- 
 ing applied to the body of the retort, the evaporable part of the 
 wood will escape through its neck, into which no air can pene- 
 trate as long as the heated vapour continues to fill it. And if it 
 b* wished to collect these volatile products of the wood, ihis 
 can easily be done by introducing the neck of the retort into the 
 
CARBON. 
 
 water-bath apparatus, with which you are acquainted. But 
 the preparation of common charcoal, such as is used in kitch- 
 ens and manufactures, is performed on a much larger scale, 
 and by an easier and less expensive process. 
 
 F.mily. I have seen the process of making common charcoal. 
 The wood is ranged on the ground in a pile of a pyramidical 
 form, with a fire underneath ; the whole is then covered wijh 
 day, a few holes only being left open for the circulation of air. 
 
 Mrs. B. The holes are closed as soon as the wood is fairly 
 lighted, so that the combustion is checked, or at least contin- 
 ues but in a very imperfect manner ; but the heat produced by 
 it is sufficient to force out and volatilize, through the earthy co- 
 ver, most part of the oily and watery principles of the wood, 
 although it cannot reduce it to ashes. 
 
 Emily. Is pure carbon as black as charcoal ? 
 
 Mrs. B. The purest charcoal we can prepare is so ; but 
 chemists have never yet been able to separate it entirely from 
 hydrogen. Sir H. Davy says, that the most perfect* carbon 
 that is prepared by art contains about five per cent of hydro- 
 gen ; he is of opinion, that if we could obtain it quite free 
 from foreign ingredients, it would be metallic, in common with 
 other simple substances. 
 
 But there is a form in which charcoal appears, that I dare 
 say will surprise you. This ring, which I wear on my finger, 
 owes its brilliancy to a small piece of carbon. 
 
 Caroline. Surely, you are jesting, Mrs. B. ? 
 
 Emily. I thought your ring was diamond ? 
 
 Mrs. B. It is so. But diamond is nothing more than carbon 
 in a crystalizecl state. 
 
 Emily. That is astonishing ! Is it possible to see two things 
 apparently more different than diamond and charcoal ? 
 
 Caroline. It is, indeed, curious to think that we adorn our- 
 selves with jewels of charcoal ! 
 
 Mrs. B. There are many other substances, consisting chiefly 
 of carbon, that are remarkably white. Cotton, for instance, is 
 almost wholly carbon. 
 
 Caroline. That, I own, I could never have imagined ! But 
 pray, Mrs. B., since it is known of what substance diamond 
 and cotton are composed, why should they not be manufactur- 
 ed, or imitated, by some chemical process, which would render 
 them much cheaper, and more plentiful than the present mode 
 of obtaining them ? 
 
 Mrs. . You might as well, my dear, propose that we should 
 make flowers and fruit, nay, perhaps even animals, by a chem- 
 kai process ; for it is known of what these bodies consist, since; 
 
130 CARBON. 
 
 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 called analysis, the last synthesis. 
 When we are able to ascertain the nature of a substance by 
 both these methods, 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 com- 
 plicated combinations of nature, even in the mineral kingdom, 
 are in general beyond our reach, and any attempt to imitate or- 
 ganised bodies must ever prove fruitless ; their formation is a 
 secret tjiat rests in the bosom of the Creator. You see, there- 
 fore, ho*v vain it would be to attempt to make cotton by chemi- 
 cal means. But, surely, we have no reason to regret our ina- 
 bility in this instance, when nature has so clearly pointed out a 
 method of obtaining 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 absurd to suppose that chemists might attain a perfect imi- 
 tation of inanimate nature. 
 
 Mrs. B. They have succeeded in this point in a variety of 
 instances; but, as you justly observe, the principle of life, or 
 even the minute and intimate organisation of the vegetable 
 kingdom, are secrets that have almost entirely eluded the re- 
 searches of philosophers; nor do I imagine that human art will 
 ever be capable of investigating them with complete success. 
 
 Emily. But diamond, since it consists of one simple unor- 
 ganised substance, might be, one would think, perfectly imitable 
 by art r 
 
 Mrs. B. It is sometimes as much beyond our power to ob- 
 tain a simple body in a state of perfect purity, as it is to imi- 
 tate a complicated combination ; for the operations by which 
 nature separates bodies are frequently as inimitable as those 
 which she uses for their combination. This is the case with 
 carbon; all the efforts of chemists to separate it entirely from 
 other substances have been fruitless, and in the purest state in 
 which it can be obtained by art, it still retains a portion of hy- 
 drogen, and probably of some other foreign ingredients. We 
 are ignorant or the m^ans which nature employs tojcrystalize it. 
 It may probably be the work of ages, to purify, arrange, and 
 
CARBON. 131 
 
 unite the particles of carbon in the form of diamond. 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 either taste or smell. Heat, 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 oth- 
 er parts of the vegetable are evaporated. 
 
 Emily. Yet carbon is, no doubt, combustible, since you say 
 that charcoal would absorb oxygen if air were admitted during 
 its preparation ? 
 
 Caroline. Unquestionably. Besides, you know, Emily, how 
 much it is used in cooking. But pray what is the reason that 
 charcoal burns without smoke, whilst a wood fire smokes so 
 much ? 
 
 Mrs. B. Because, in the conversion of wood into charcoal, 
 the volatile particles of the former have been evaporated. 
 
 Caroline. Yet I have frequently seen charcoal burn with 
 flame ; therefore it must, in that case, contain some hydrogen. 
 
 Mrs. B. Very true ; but you should recollect that charcoal, 
 especially that which is uled for common purposes, is not per- 
 fectly pure. It generally retains some remains of the various 
 other component parts of vegetables, and hydrogen particular- 
 ly, which accounts for the flame in question. 
 
 Caroline. But what becomes of the carbon itself during its 
 combustion ? 
 
 Mrs. B. It gradually combines with the oxygen of the atmos- 
 phere, in the same way as sulphur and phosphorus, and, like 
 those substances, it is converted into a peculiar acid, which flies 
 off in a gaseous form. There is this difference, however, that 
 the acid is not, in this instance, as in the two cases just men- 
 tioned, a mere condensible vapour, but a permanent elastic flu- 
 id, which always remains in the state of gas, under any pres- 
 sure and at any temperature. The nature of this acid was first 
 ascertained by Dr. Black, of Edinburgh ; and, before the intro- 
 duction of the new nomenclature, it was called Jixed air. It 
 is now distinguished by the more appropriate name of carbonic 
 acid gas. 
 
 Emily. Carbon then, can be volatilized by burning, though, 
 by heat alone, no such effect is produced ? 
 
 Mrs. B. Yes ; but then it is no longer simple carbon, but an 
 acid of which carbon forms the basis. In this state, carbon re- 
 tains no more apearance of solidity or coporeal form, than the 
 basis of any other gas. And you may, I think, from this in- 
 stance, derive a more clear idea of the basis of the oxygen, hy- 
 'trogen, and nitrogen gases, the existence of which, as real bo* 
 
132 CARBON. 
 
 dies, you seemed to doubt, because they were not to be obtain- 
 ed simply in a solid form. 
 
 Emily. That is true ; we may conceive the basis of the oxy- 
 gen, and of the other gases, to be solid, heavy substances, like 
 cai bors ; but so much expanded by caloric as to become invisible. 
 
 Caroline. 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 carbon, and it is pure carbon, and not 
 charcoal, that we must consider as the basis of carbonic acid. 
 We shall make some carbonic acid, and, in order to hasten the 
 process, we shall burn the carbon in oxygen gas. 
 
 Emily. But do you mean then to burn diamond ? 
 
 Mrs. B. Charcoal will answer the purpose still better, being 
 softer and more easy to inflame; besides the experiments on 
 diamond are rather expensive. 
 
 Caroline. But is it possible to burn diamond? 
 
 Mrs. B. Yes, it is; and in order to effect this combustion, 
 nothing more is required than to apuly a sufficient degree of 
 heat by means of the blow-pipe, and of a stream of oxygen gas. 
 Indeed it is by burning diamond that its chemical nature has 
 been ascertained. It has long been known as a combustible 
 substance, but it is within these few years only that the product 
 of its combustion has been proved to be pure carbonic acid. 
 This remarkable discovery is due to Mr. Tennant. 
 
 Now let us try to make some carbonic acid. Will you, 
 Emily, decant some oxygen gas from this large jar into the re- 
 ceiver in which we are to burn the carbon ; and I shall intro- 
 duce this small piece of charcoal, with a little lighted tinder, 
 which will be necessary to give the first impulse to the com- 
 bustion. 
 
 Emily. I cannot conceive how so small a piece of tinder, and 
 that but just lighted, can raise the temperature of the carbon 
 sufficiently to set fire to it : for it can produce scarcely any sen- 
 sible heat, and it hardly touches the carbon. 
 
 Mrs. B. The tinder thus kindled has only heat enough to be- 
 gin its own combustion, which, however, soon becomes so rap- 
 id in the oxygen gas, as to raise the temperature of the char- 
 coal sufficiently for this to burn likewise, as you see is now the 
 case. 
 
 Emily. lam surprised that the combustion of carbon is not 
 more brilliant ; it does not give out n'ar so much light or caloric 
 as phosphorus, or sulphur Yetsinre it combines with so muck 
 oxygen, why is not 4 proportional quantity of light and heat 
 
CARBO.N. 133 
 
 disengaged from tiie decomposition of the oxygen gas, and the 
 union of its electricity with that of the charcoal ? 
 
 Mrs. B. It is not surprising that less light and heat should 
 be liberated in this than in almost any other combustion, since 
 the oxygen, instead of entering into a solid or liquid combina- 
 tion, as it does in the phosphoric and sulphuric acids, is em- 
 ployed in forming another elastic fluid ; it therefore parts with 
 less of its caloric. 
 
 Emily. True; and, on second consideration, it appears, on 
 the contrary, surprising that the oxygen should, in its combina- 
 tion with carbon, retain a sufficient portion of caloric to main- 
 tain both substances in a gaseous state. 
 
 Caroline. We may then judge of the degree of solidity in 
 which oxygen is combined in a burnt body, by the quantity of 
 caloric liberated during its combustion ? 
 
 Mrs. B. Yes 5 provided that you take into the account the 
 quantity of oxygen absorbed by the combustible body, and ob- 
 serve the proportion which the caloric bears to it. 
 
 Caroline, But why should the water, after the combustion of 
 carbon, rise in the receiver, since the gas within it retains an 
 aeriform state ? 
 
 Mrs. B. Because the carbonic acid gas is gradually absorbed 
 by the water ; and this effect would be promoted by shaking 
 the receiver. 
 
 Emily. The charcoal is now extinguished, though it is not 
 nearly consumed ; it has such an extraordinary avidity for ox~ 
 ygen, I suppose, that the receiver did not contain enough to sat- 
 isfy the whole. 
 
 Mrs. B. That is certainly the case ; for if the combustion 
 were performed in the exact proportions of 28 parts of carbon 
 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 ? 
 
 Mrs. B. That is a very natural inference ; yet it is errone- 
 ous. For the carbonic is the weakest of all the acids. The 
 strength of an acid seems to depend upon the nature of its basis, 
 and its mode of combination, as well as upon the proportion of 
 the acidifying principle. The same quantity of oxygen 
 will convert some bodies into strong ackls, will 01*13 oe su.u- 
 cient simply to oxydate others. 
 
 Caroline. Since this acid is so weak, I think chemists 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 carbon in atmospherical air. 
 
 13 
 
134 CARBON- 
 
 Mrs. B. It has been lately discovered, that carbon may be 
 converted into a gas, by uniting with a smaller proportion 01* 
 oxygen ; but as this gas does not possess any acid properties, 
 it is no more than an oxyd 5 it is called gaseous oxyd of car- 
 bon. 
 
 Caroline. Pray is not carbonic acid a very wholesome gas 
 to breathe, as it contains so much oxygen? 
 
 Mrs. B. On the contrary, it is extremely pernicious. Oxy- 
 gen, when in a state of combination with other substances, loses, 
 in almost every instance, its respirable properties, and the salu- 
 brious effects which it has on the animal economy when in its 
 unconfirmed state. Carbonic acid is not only unfit for respira- 
 tion, 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. Can this gas 
 be condensed into a liquid ? 
 
 Mrs. B. No : for, as I told you before, it is a permanent elas- 
 tic fluid. But water can absorb a certain quantity of this gas, 
 and can even be impregnated with it, in a very strong degree, 
 by the assistance of agitation and pressure, as 1 am going to 
 show you. I shall decant some carbonic acid gas into this bot- 
 tle, which I fill first with water, in order to exclude the atmos- 
 pherical air; the gas is then introduced through ihe water, 
 which you see it displaces, for it will not mix with it in any 
 quantity, unless strongly agitated, or allowed to stand over it 
 for some time. The bottle is now about half full of carbonic 
 acid gas, and the other half is still occupied by the water. By 
 corking the bottle, and then violently shaking it, in this way, I 
 can mix the gas and water together. INow will you taste it ? 
 
 Emily. It has a distinct acid taste. 
 
 Caroline. Yes, it is sensibly sour, and appears full of little 
 bubbles. 
 
 Mrs. B. It possesses likewise all the other properties of acids, 
 but of course, in a less degree than the pure carbonic acid gas. 
 as it is so much diluted by water. 
 
 This is a kind of artificial Seltzer water. By analysing 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 
 process, we can exactly copy the operations of nature ; for the 
 artificial Seltzer waters can. be made in every respect similar t- 
 
CARBON. 135 
 
 those of nature; in one point, indeed, the former have an ad- 
 vantage, since they may be prepared stronger or weaker, as oc- 
 casion 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 al- 
 ways occasioned by the action of an elastic fluid escaping from 
 a liquid ; in the artificial Seltzer water, it is produced by the 
 carbonic acid, which being lighter than the water in which it 
 was strongly condensed, flies off with great rapidity the instant 
 the bottle is uncorked ; this makes it necessary to drink it im- 
 mediately. The bubbling that took place in this bottle was 
 but trifling, as the water was but very slightly impregnated with 
 carbonic acid. It requires a particular apparatus 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 com- 
 mon water ? 
 
 Mrs. 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 
 ingredient, 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 ? 
 
 Airs. B. It is a kind of artificial Seltzer water, holding in so- 
 lution, besides the gaseous acid, a particular saline substance, 
 called soda, which imparts to the water certain medicinal quali- 
 ties. 
 
 Caroline. But how can these waters be so wholesome, since 
 carbonic acid is so pernicious ? 
 
 Mrs. B. A gas, we may conceive, though very prejudical 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 gases? 
 
 Mrs. 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 oxygen and hydrogen gases. 
 These are not an imitation of nature, but are altogether obtain- 
 ed by artificial means. They have been lately used medicinal- 
 ly, particularly on the continent, where, I understand, they have 
 acquired some reputation. 
 
 Emily. If I recollect right, Mrs. B., you told us that carbon 
 was capable of decomposing water ; the affinity between oxy- 
 
136 -CARBON. 
 
 gen and carbon must, therefore., be greater than between oxy 
 gen and hydrogen ? 
 
 Mrs. B Yes ; but this is not the case unless their tempera 
 Jure be raised to a certain degree. It is only when carbon b 
 red-hot, that it is capable of separating the oxygen from the hy- 
 drogen. Thus, if a small quantity of water be thrown on a red- 
 hot fire, it will increase rather than extinguish the combustion , 
 for the coals or wood, (both of which contain a quantity of car- 
 bon,) decompose the water, and thus supply the fire both with 
 oxygen and hydrogen gases. 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 that they actually increase the fire when 
 they cannot throw water enough to extinguish it. It must be 
 owing, no doubt, to the decomposition of the water by the car- 
 bon during the conflagration. 
 
 Mrs. B. Certainly. The apparatus which you see here 
 (PLATE XI. fig 1 . 3.), 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 oth- 
 er end communicates 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 re- 
 sults from this decomposition is collected in the receiver. But 
 the hydrogen thus obtained is far from being pure ; it retains in 
 solution a minute portion of carbon, and contains also a quanti- 
 ty of carbonic acid. This renders it heavier than pure hydro- 
 gen gas, and gives it some peculiar properties 5 it is distinguish- 
 ed 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, Caroline. 
 From the union of the oxygen (proceeding from the decomposed 
 water) with the carbon, which, you know, makes carbonic acid. 
 
 Caroline. True ; I should have recollected that. The pro- 
 duct of the decomposition of water by red-hot charcoal, there- 
 fore, is carbonated hydrogen gas, and carbonic acid gas. 
 
 Mrs. B, You are perfectly right now. 
 
 Carbon is frequently found combined with hydrogen in a state 
 of solidity, especially in coals, which owe their combusribV 
 nature to these two principles. 
 
CARBON. 1 37 
 
 Emily. Is it the hydrogen, then, that produces the flame of 
 coals ? 
 
 Mrs. B. It is so ; and when all the hydrogen is consumed, 
 the carbon continues to burn without flame. But again, as I 
 mentioned when speaking of the gas-lights, the hydrogen gas 
 produced by the burning of coals is not pure : for, during the 
 combustion, particles of carbon are successively volatilized 
 with the hydrogen, with which they form what is called a 
 hydro carbonai, which is the principal product of this com- 
 bustion. 
 
 Carbon is a very bad conductor of heat ; for this reason, it 
 is employed (in conjunction with other ingredients) for coating 
 furnaces and other chemical apparatus. 
 
 Emily. Pray what is the use of coating furnaces ? 
 
 Mrs. B. In most cases, in which a furnace is used, it is ne- 
 cessary to produce and preserve a great degree of heat, for 
 which purpose every possible means are used to prevent the 
 heat from escaping by communicating 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. 
 
 Carbon, 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. 
 
 Emily. Why, then, is it called black-lead ? 
 
 Mrs. B. It is an ancient name given to it by ignorant peo- 
 ple, from its shining metallic appearance 5 but it is certainly a 
 most improper name for it, as there is not a particle of lead in 
 the composition. There is only one mine of this mineral, 
 which is in Cumberland.* It is supposed to approach as near- 
 ly to pure carbon as the best prepared charcoal does, as it con- 
 tains only five parts of iron, unadulterated by any other for- 
 eign ingredients. There is another carburet of iron, in which 
 the iron, though united only to an extremely small proportion 
 of carbon, acquires very remarkable properties ; this is steel. 
 
 Caroline. Really ; and yet steel is much harder than iron ? 
 
 Mrs. B. But carbon is not ductile like iron, and therefore 
 may render the steel more brittle, and prevent its bending so 
 easily. Whether it is that the carbon, 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 up- 
 
 * She means in England. Black lead is found in a great variety of 
 places in this country. C, 
 
 13* 
 
138 
 
 on some chemical cause, I cannot pretend io decide. Bn ? 
 there is a subsequent operation, by which the hardness of stee? 
 is very much increased, which simply consists in heating the 
 steel till it is red-hot, and then plunging it into cold water. 
 
 Carbon, besides the combination just mentioned, enters into 
 the composition of a vast number of natural productions, such, 
 for instance, as all the various kinds of oils, which result from 
 the combination of carbon, hydrogen, and caloric, in various 
 proportions. 
 
 Emily. I thought that carbon, hydrogen, and caloric, formed 
 carbonated hydrogen gas ? 
 
 Mrs. B. That is the case when a small portion of carbonic 
 acid gas is held in solution by hydrogen gas. Different propor- 
 tions of the same principles, together with the circumstances of 
 their union, produce very different combinations ; of this you 
 will see innumerable examples. Besides, we are not now talk- 
 ing of gases, but of carbon and hydrogen, combined only with 
 a quantity of caloric, sufficient to bring them to the consistency 
 of oil or fat. 
 
 Caroline. But oil and fat are not of the same consistence ? 
 
 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. Have you never observed the fat of meat turned to 
 oil by the caloiic it has imbibed from the fire ? 
 
 Emily. Yet oils in general, as salad-oil, and lamp-oil, do not 
 turn to fat when cold ? 
 
 Mrs. B. JNot at the common temperature of the atmosphere, 
 because they retain too much caloric to congeal at that tem- 
 perature ; but if exposed to a sufficient degree of cold, their 
 latent heat is extricated, and thy become solid fat substances* 
 Have you never seen salad-oil frozen in winter ? 
 
 Emily. Yes ; but it appears to me in that state very differ- 
 ent from animal fat. 
 
 j\irs. B. The essential constituent parts of either vegetable 
 or animal oils are the same, carbon and hydrogen ; their vari- 
 ety arises from the different proportions of these substances, 
 and from other accessory ingredients that may be mixed with 
 them. The oil of a whale, and the oil of roses, are, in their es- 
 sential constituent 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 Jixed oils, and volatile or essential oils, 
 consists also in the various proportions of carbon and hydro- 
 gen. Fixed oils are those which will not evaporate without 
 being decomposed ; this is the case with all common oils, which 
 
CARBON, 189 
 
 contain a greater proportion of carbon than the essential oils. 
 The essential oils (which comprehend the whole class of essen- 
 ces and perfumes) are lighter 5 they contain more equal propor- 
 tions of carbon and hydrogen, and are volatilized or evapora- 
 ted without being decomposed. 
 
 Emily. When you say that one kind of oil will evaporate^ 
 and the other be decomposed, you mean, I suppose, by the 
 application of heat ? 
 
 Mrs. B. Not necessarily ; for there are oils that will evapo- 
 rate slowly at the common temperature of the atmosphere ; 
 but for a more rapid volatilization, or for their decomposition; 
 the assistance of heat is required.* 
 
 Caroline. I shall now remember, I think, that fat and oil are 
 really the same substances, both consisting of carbon and hy- 
 drogen ; that in fixed oils the carbon preponderates, and "heat 
 produces a decomposition ; while, in essential oils, the propor- 
 tion of hydrogen is greater, and heat produces a volatilization 
 only. 
 
 Emily. I suppose the reason why oil burns so well in lamps 
 is because its two constituents are so combustible ? 
 
 Mrs. 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 carbon, 
 
 Emily. I wonder, then, there should be so great a difference 
 between tallow and wax ? 
 
 Mrs. B. I must again repeat, that the same substances, in 
 different proportions, produce results that have sometimes 
 scarcely any resemblance to each other. Bat this is rather a 
 general remark that I wish to impress upon your minds, than 
 one which is applicable to the present case ; for tallow and wax 
 are far from being very dissimilar ; the chief difference con- 
 sists in the wax being a purer compound of carbon and hydro- 
 gen than the tallow, which retains more of the gross particles 
 f animal matter. The combustion of 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 reflect .... Both the candle and lamp burn 
 by means of fixed oil this is decomposed as the combustion 
 
 * The volatile or essential oils evaporate when exposed to the air. 
 Hence the odor which oil 01 lavender, peppermint, c. give out. The 
 animal oils, and what are called expressed oils, as that of castor, c. 
 do not evaporate. Hence a good test of the purity of essential oil, 
 is, to let a drop fall on paper. If a grease-spot remains after a few 
 minutes, it is adulterated with some fixed oil, C. 
 
140 CARBONS 
 
 goes on ; and the constituent parts of the oil being thus sepa- 
 rated, the carbon unites with a portion of oxygen from the at- 
 mosphere to form carbonic acid gas, whilst the hydrogen com- 
 bines with another portion of oxygen, and forms with it water. 
 The products, therefore, of the combustion of oils are water and 
 carbonic acid gas 
 
 Caroline. But we see neither water nor carbonic acid pro- 
 duced by the combustion of a candle. 
 
 Mrs. B. The carbonic acid gas, you know, is invisible, and 
 the water being in a state of vapour, is so likewise. E roily is 
 perfectly correct in her explanation, and I am very much plea- 
 sed with it. 
 
 All the vegetable acids consist of various proportions of car- 
 bon and hydrogen, acidified by oxygen. Gums, sugar, and 
 starch, are likewise composed of these ingredients ; but, as the 
 oxygen which they contain is not sufficient to convert them into 
 acids, they are classed with the oxyds, and called vegetable 
 oxyds. 
 
 Caroline. I am very much delighted with all these new ideas ; 
 but, at the same time, 1 cannot help being apprehensive that 
 I may forget many of them. 
 
 Mrs. B. I would 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 heads or index, which I occa* 
 sionally consult for the sake of preserving some method and 
 arrangement in these conversations. Unless you follow some 
 such plan, 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. Hitherto I have 
 found that I recollected pretty well what you have taught us ; 
 but the history of carbon is a more extensive subject than any 
 of the simple bodies we have yet examined. 
 
 Mrs. />'. I have little more to say on carbon at present; but 
 hereafter you will see that it performs a considerable part in 
 most chemical operations. 
 
 Caroline. That is, I suppose, owing to its entering into the 
 composition of so sfreat a variety of substances ? 
 
 *i/r. ". Certainly ; it is the basis, you have seen, of all veg- 
 etable matter ; and you will find that it is very essential to the 
 process of animalization. But in the mineral kingdom also, 
 particularly in its form of carbonic acid, we shall often discov- 
 er it combined with a great .variety of substances. 
 
 In chemical operations, carbon is particularly useful, from 
 its very great attraction for oxygen, as it will absorb this sub- 
 
MET.VLS. 141 
 
 stance i'rom many oxygenated or burnt bodies, and thus deoxy- 
 genate, or unburn them, and restoie them to their original com- 
 bustible state. 
 
 Caroline. I do not understand how a body can be unburnt* 
 and restored to its original state. This piece of tinder, for in- 
 stance, that has been burnt, if by any means the oxygen were 
 extracted from it, would not be restored to its former state of 
 linen ; for its texture is destroyed by burning, and that must be 
 the case with all organized or manufactured substances, as you 
 observed in a former conversation. 
 
 Mrs. B. A compound body is decomposed by combustion in 
 a way which generally precludes the possibility of restoring it 
 to its former state; the 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, 
 therefore, how vain it would be to attempt the recomposition of 
 such bodies. But, with regard to simple bodies, or at least bod- 
 ies whose component parts are not distributed by the process of 
 oxygenation or .deoxygenation, it is often possible to restore 
 them, after combustion, to their original state. The metals, 
 for instance, undergo no other alteration by combustion than a 
 combination with oxygen ; therefore, when the oxygen is taken 
 from them, they return to their pure metallic state. But! shall 
 say nothing further of this at present, as the metals will furnish 
 ample subject for another morning ; and they are the class ol 
 simple bodies that come next under consideration. 
 
 CONVERSATION X, 
 
 ON METALS. 
 
 Mrs. B. THE METALS, which we are now to examine, are 
 bodies of a very different nature from those which we have 
 hitherto considered. They do not, like the bases of gases, 
 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 entertainment as those 
 mysterious elements which conceal themselves from our view. 
 Besides, they cannot afford so much novelty ; they are bodies 
 with which we are already so well acquainted. 
 
 Airs. B. You are not aware, my dear, of the interesting dis 
 
142 METALS. 
 
 coveries which were a few years ago made by Sir H. Davy re- 
 specting this class of bodies. By the aid of the Voltaic batte- 
 ry, he has obtained from a variety of substances, metals before 
 unknown, the properties of which are equally new aud curious. 
 We shall begin, however, by noticing those metals with which 
 you profess to be so well acquainted. But the acquaintance, 
 you will soon perceive, is but very superficial 5 and 1 trust that 
 you will find both novelty and entertainment in considering 
 the metals in a chemical point of view. To treat of this sub- 
 ject fully, would require a whole course of lectures ; for metals 
 form of themselves a most important branch of practical chem- 
 istry. We must, therefore, confine ourselves to a general view 
 of them. These bodies are seldom found naturally in their 
 metallic 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 the 
 earth in most parts of the world, but chiefly in mountainous 
 districts, where the surface of the globe has been disturbed by 
 earthquakes, volcanoes, and other convulsions of nature. They 
 are spread in strata or beds, called veins, and these veins are 
 composed of a certain quantity of metal, combined with vari- 
 ous earthy substances, with which they form minerals of dif- 
 ferent nature and appearance, which are called ores. 
 
 Caroline. I now feel quite at home, for my father has a 
 lead- mine in Yorkshire, and I have heard a great deal about 
 veins of ore, and of the roasting and smelting of the lead ; 
 but, I confess, that I do not understand in what these operations 
 consist. 
 
 Mrs. B. Roasting is the process by which the volatile parts 
 of the ore are evaporated ; smelting, that by which the pure 
 metal is afterwards 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 met- 
 al being the heaviest, falls to the bottom, and runs out by prop- 
 er openings in its pure metallic state. 
 
 Emily. You told us in a preceding lesson that metals had a 
 great affinity for oxygen. Do they not, therefore, combine 
 with oxygen, when strongly heated in the furnace, and run out 
 in the state of oxyds ? 
 
 Mrs. K. No ; for the scoriae, or oxyd, which soon forms on 
 the surface of the fused metal, when it is oxydable, prevents 
 the air from having any farther influence on the mass j so that 
 neither combustion nor oxygenation can take place. 
 
 Caroline. Are all the metals equally combustible ? 
 
METALS. 143 
 
 Mrs. B. No ; their attraction 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 oxydate spontaneously and with great rapidity, even 
 at the lowest temperature 5 such is in particular manganese, 
 which scarcely ever exists in the metallic state, as it immedi- 
 ately absorbs oxygen on being exposed to the air, and crumbles 
 to an oxyd in the course of a few hours. 
 
 Emily. Is not that the oxyd from which you extracted the 
 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 temper- 
 ature of the atmosphere ? 
 
 Mrs. 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 oxydation, as it pre- 
 vents the air from coming in contact with it. Strictly speaking, 
 however, the word rust applies only to the oxyd, which forms 
 on the surface of iron, when exposed to air and moisture, 
 which oxyd appears to be united with a small portion of car- 
 bonic 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 sufficient quantities to be 
 sensible. 
 
 Mrs. B. Undoubtedly ; and, indeed, it is not surprising 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 quantity 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 quan- 
 tity of caloric introduced into a metal, the more will its positive 
 electricity be exalted, and consequently the stronger will be 
 its affinity for oxygen. 
 
 Mrs. B. Certainly. When the metal oxygenates with suf- 
 ficient rapidity for light and heat to become sensible, combus- 
 tion actually takes place. But this happens only at very high 
 temperatures, and the product is nevertheless an oxyd ; for 
 
t44 METALS. 
 
 though, as I have just said, metals will combine with different 
 proportions of oxygen, yet with the exception of only five of 
 ^hem, they are not susceptible of acidification. 
 
 Metals change colour during the different degrees of oxyda- 
 tion 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 successively a green, brown, and white 
 oxyd. Copper changes from brown to blue, and lastly green. 
 
 Emily. Pray, is the white lead with which houses are pain- 
 ted prepared by oxydating lead ? 
 
 Mrs. B. Not merely by oxydating, but by being also united 
 with carbonic acid. It is a carbonat of lead. The mere oxyd 
 of lead is called red lead. Litharge is another oxyd of lead, 
 containing less oxygen. Almost all the metallic oxyds are used 
 as paints. The various sorts of ochres consist chiefly of iron 
 more or less oxydated. And it is a remarkable circumstance, 
 that if you burn metals rapidly, the light or flame they emit du- 
 ring combustion partakes of the colours which the oxyd succes- 
 sively assumes. 
 
 Caroline. How is that accounted for, Mrs. B., since light 
 does not proceed from the burning body, but from the decom- 
 position of the oxygen gas ? 
 
 Mrs. B. The correspondence of the colour of the light with 
 that of the oxyd which emits it, is, in all probability, owing to 
 some particles of the metal which are volatilised and carried off 
 by the caloric. 
 
 Caroline. It is then a sort of metallic gas. 
 
 Why is it reckoned so unwholsome to breathe the uir of a 
 place in which metals are melting ? 
 
 Mrs. B. Perhaps the notion is too generally entertained* 
 But it is true with respect to lead, and some other noxious met- 
 als, because, unless care be taken, the particles of the ox- 
 yd which are volatilized by the heat, are inhaled in with the 
 breath, and may produce dangerous effects. 
 
 I must show 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 them with a stream of oxy- 
 gen gas, we may easily accomplish it. 
 
 Caroline. But it will still, I suppose, be necessary in some 
 degree to raise their temperature ? 
 
 Mrs. B. This, as you shall see, is very easily done, particu- 
 larly if the experiment be tried upon a small scale. I begin by 
 lighting this piece of charcoal with the candle, and then in- 
 

Fig 1 fimi'tiry charfoaZ with a tatper IC&ka-jfjjpc. Flff. 2. Combustion of mf faff 
 by fnfatif or a &/CW-THIX conveying a strftutt of" oxygen gra-f from a 
 
METALS. 145 
 
 crease the r^idity of its combustion by blowing upon it with a 
 blow-pipe. (PLATE XII. fig. 1.) 
 
 Emily. That I do not understand ; for it is not every kind of 
 air, but merely oxygen gas, that produces combustion. Now 
 you said that in breathing we inspired, but did not expire 
 oxygen gas. Why, therefore, 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 passed 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 
 ncreasing the rapidity of the current, by means of the blow- 
 pipe, than is lost in consequence of the airj^ssing once through 
 the lungs, as you shall see '* 
 
 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 cm rent of oxygen gi.*, by means 
 of this apparatus, (PLATE XII. fig. 2.) 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. I\ow 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 up*- 
 on it 
 
 Caroline. They emit much the same vivid light as the com- 
 bustion of the iron wire in oxygen gas. 
 
 Mrs. B. The process is, in fact, the same; there is only some 
 difference 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 copper 
 
 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 ? 
 
 Mrs. #. That is not in our power, at least in this way. - 
 Gold, Silver, and platina, are incapable of 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, however, have an affinity for oxygen ; 
 but their oxydation or combustion can be performed only by 
 me.ans of acids or by electricity. 
 
 The spark given out by the Voltaic battery produces at the 
 point of contact a greater degree of heat than any other pre- 
 14 
 
146 METALS. 
 
 cess ; and it is at this very high temperature onl^hat the af- 
 finity of these metals for oxygen will enable them to act on each 
 other. 
 
 I am sorry that I cannot show you the combustion of the 
 perfect metals by this process, but it requires a considerable 
 Voltaic battery. You will see these experiments performed in 
 the most perfect mariner, when you attend the chemical lec- 
 tures of the Royal Institution. But in the mean time I can, 
 without difficulty, show you an ingenious apparatus lately con- 
 trived tor the purpose of producing intense heats, the power of 
 which nearly equals that of the largest Voltaic batteries. It 
 simply consists, you see, in a strong box, made of iron or cop- 
 per, PLATE X iig.^^) to which may be adapted this air-syringe 
 or condensing-pum^P^md a stop-cock terminating in a small 
 orifice similar to that of a blow-pipe. By working the conden- 
 sing syringe, up and down in this manner, a quantity of air is 
 accumulated in the vessel, which may be increased to almost 
 any extent t so that if we now turn the stop-cock, the conden- 
 sed air will rush out, forming a jet of considerable force ; and 
 if we place the flame of a lamp in the current, you will see how 
 violently the flame is driven in that direction. 
 
 Caroline. It seems to be exactly the same effect as that of 
 a blow-pipe worked by the mouth, only much stronger. 
 
 Emily. \es ; and this new instrument has this additional ad- 
 vantage, that it does not fatigue the mouth and lungs like the 
 common blow-pipe, and requires no art in blowing. 
 
 Mrs. B. Unquestionably ; but yet this blow-pipe would be 
 of very limited utility, if its energy and power could not be 
 greatly increased by some other contrivance. Can you imagine 
 any mode of producing such an effect ? 
 
 Emily. Could not the reservoir b'e charged with pure oxy- 
 gen, instead of common air, as in the case of the gas-holder ? 
 
 Mrs. B. Undoubtedly ; and this is precisely the contrivance 
 I allude to. The vessel need only be supplied with air from a 
 bladder full of oxygen, instead of the air of the room, and 
 this, you see, may be easily ^one by screwing the bladder on 
 the upper part of the syringe, so that in working the syringe the 
 oxygen gas is forced from the bladder into the condensing ves- 
 sel. 
 
 Caroline. With the aid of this small apparatus, therefore, 
 we could obtain the same effects as those we have just produced 
 with the gas-holder, by means of a column of water forcing the 
 gas out of it ? 
 
 Mrs. B. Yes ; and much more conveniently so. But therr 
 is a mode of using this apparatus by which more powerful ef- 
 
METALS. 147 
 
 fects still may be obtained. It consists in condensing in the 
 reservoir, not oxygen alone, but a mixture of oxygen and hy- 
 itvjen in the exact proportion in which they unite to produce 
 water ; and then kindling the jet formed by the mixed gases. 
 The heat disengaged by this combustion, without the help of 
 my lamp, is probably the most intense of any known; and va- 
 rious effects are said to have been obtained from it which ex- 
 ceed all expectation. 
 
 Caroline. But why should we not try this experiment ? 
 
 Mrs. B. Because it is not exempt from danger 5* the com* 
 bustion (notwitstanding various contrivances which have been 
 resorted to with a view to prevent accident) being apt to pene- 
 trate into the inside of the vessel, and to produce a dangerous 
 and violent explosion. We shall, therefore, now proceed in our 
 subject. 
 
 Caroline. I think you said the oxyds of metals could be re- 
 stored to their metallic state ? 
 
 Mrs. B. Yes ; this is called reviving a metal. Metals are 
 in general capable of being revived by charcoal, when heated 
 red hot, charcoal having a greater attraction lor oxygen than 
 the metals. You need only, therefore, decompose, or unburn 
 the oxyd, by depriving it of its oxygen, and the metal will be 
 restored to its pure state. 
 
 Emily. But will the carbon, 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 oxy- 
 gen. They will also yield it to each other, according to their 
 several degrees cf attraction for it ; and if the oxygen goes' i"t" 
 a more dense state in the metal which it enters, than it existed 
 in that in which it quits, a proportional disengagement of calo- 
 ric will take place. 
 
 Caroline. And cannot the oxyds of gold, silver, and platina, 
 which are formed by means of acids or of the electric fluid, be 
 restored to iheir metallic state ? 
 
 Mrs. B. Yes, they may ; and the intervention of a combust- 
 
 * Hydrogen and oxygon may be burned together with the most per- 
 fect safety by means of the compound blow-pipe, an instrument invent- 
 ed by Prof. Hare, of Philadelphia. Instead of mixing the gases in the 
 L^ame reservoir, they are kept separate until they meet at the point of 
 combustion. An account of this blow-pipe is given by Prof. Sillitnan, 
 in his edition of Henry's chemistry, together with a list of experi- 
 ments made with it on various substances. This was the first notice 
 of any experiment made by burning the two gases together, for the 
 ;>vrpose of obtaining an intense heat, C, 
 
148 METALS. 
 
 able body is not required ; heat alone will take the oxygen front 
 them, convert it into a gas, and revive the metal. ' 
 
 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 in- 
 struments ? 
 
 Mrs. B. In that rase the metal decomposes the wa\ter, 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 metals- to 
 ;i very high temperature to enable them to decomposed water. 
 
 Mrs. B. It is so, if it required that the process should be 
 performed rapidly, and if any considerable quantity is to be 
 decomposed. Rust, you know, is sometimes months in form- 
 ing, and then it is only the surface of the metal that is oxyda- 
 ted. 
 
 Emily. Metals, then, that do not rust, are incapable of spon- 
 taneous oxydation, either by air or water ? 
 
 Mrs. B. Yes ; and this is th case with the perfect metals ; 
 which, on that account, preserve their metallic lustre so well. 
 
 Emily. Are all metals capable of decomposing water, pro- 
 vided their temperature be sufficiently raised ? 
 
 Mrs. B. No ; a certain degree of attraction is requisite, be- 
 sides the assistance of heat. Water, you recollect, is compo- 
 sed 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 
 stronger 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, under certain circumstances, of ta- 
 king the oxygen from the oxyds of these metals. 
 
 Emily. I confess that I do not quite understand why hydro- 
 gen can take oxygen from those metals that do not decompose 
 water. 
 
 Caroline. Now I think, I do perfectly. Lead, for instance ? 
 will not decompose water, because it has not so strong an at- 
 traction for oxygen as hydrogen has. Well, then, suppose .the 
 lead to be in a'state of oxyd ; hydrogen will take the oxygen 
 from the lead, and unite with it to form water, because hydro- 
 gen has a stronger attraction for oxygen, than oxygen has for 
 iead ; and it is the same with all the other metals which do no? 
 decompose water, 
 
METALS. 149 
 
 B tnily. \ understand your explanation, Caroline, very well ; 
 and I imagine that it is because lead cannot decompose water 
 that it is so much employed for pipes for conveying that fluid.* 
 
 J\lrs. B . Certainly ; lead is, on that account, particularly 
 appropriate to such purposes ; whilst, on the contrary, this 
 metal, if it was oxydable by water, would impart to it very 
 noxious qualities, as all oxyds of lead are more or less perni- 
 cious. 
 
 But, with regard to the oxydation of metals, the most pow- 
 erful mode of effecting it is by means of acids. These, you 
 know, contain a much greater proportion of oxygen than either 
 air or water; and will, most of them, easily yield it to metals. 
 Thus, you recollect, the zinc plates of the Voltaic battery are 
 oxydated by the acid and water, much more effectually than by 
 water alone. 
 
 Caroline. And I have often observed that if I drop vinegar, 
 lemon, or any acid on the blade of a knife, or on a pair of scis- 
 sors, it will immediately produce a spot of rust. 
 
 Emily. Metals have, then, three ways of obtaining oxygen ; 
 from the atmosphere, from water, and from acids. 
 
 Mrs. B. The two first you have already witnessed, and I 
 shall now show you how metals take the oxygen from an arid. 
 This bottle contains nitric acid ; I 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 effervescence anc 
 that thick yellow vapour ? 
 
 Mrs. B. It is the acid, which being abandoned by the great- 
 est part of its oxygen, is converted into a weaker acid, which 
 escapes in the form of gas. 
 
 Caroline. And whence proceeds this heat ? 
 
 Mrs. B. Indeed, Caroline, I think you might now be able te 
 answer that question yourself. 
 
 Caroline. Perhaps it is that the oxygen enters into the metal 
 in a more solid state than it existed in the acid, in consequence 
 of which caloric is disengaged. 
 
 Airs. B. If the combination of the oxygen and the metal re- 
 sults from the union of their opposite electricities, of course 
 caloric must be given out. 
 
 Emily. The effervescence is over; therefore I suppose that 
 the metal is now oxydated. 
 
 * Lead is capable of decomposing water, and when sufffied to stanch 
 'long in a vessel uflliis metal, it becomes poisonous. When used 
 y to convey water, there is but little danger. C, 
 
 14* 
 
150 METALS* 
 
 Mrs. B. Yes. But there is another important connection 
 between metals and acids, with which I must now 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 oxy ela- 
 tion and the dissolution of the metal by an acid ? 
 
 Mrs. B. In the first case, the metal merely combines with a 
 portion of oxygen taken from the acid, which is thus partly de- 
 oxygenated, as in the instance you have just seen ; in the second 
 case, the metal, after being previously oxydated,is actually dissol- 
 ved in the acid, and enters into a chemical combination with it, 
 without producing any further decomposition or effervescence. 
 This complete combinati n of an oxyd and an acid forms a 
 peculiar and important class of compound salts. 
 
 Emily. The difference between an oxyd and a compound 
 salt, therefore, is very obvious ; the one consists of a metal and 
 oxygen ; the other of an oxyd and an acid. 
 
 Mrs. B. Very well : and you will be careful to remember 
 that the metals are incapable of entering into this combination 
 with acids, unless they are previously oxydated ; therefore., 
 whenever you bring a metal in contact with an acid, it will be 
 first oxydated and afterwards dissolved, provided that there be 
 a sufficient quantity of acid for both operations. 
 
 There are some metals, however, whose solution is more ea- 
 sily accomplished, by diluting the acid in water; and the metal 
 will, in this case, be oxydated, not by the acid, but by the wa- 
 ter, which it will decompose. But in proportion as the oxygen 
 of the water oxydates the surface of the metal, the acid corn- 
 bines with it, washes it off, and leaves a fresh surface for the 
 oxygen to act upon : then other coats of oxyd are successively 
 'formed, and rapidly dissolved by the acid, which continues 
 combining with the new-formed surfaces of oxyd till the whole 
 of -the metal is dissolved. During this process the hydrogen 
 gas of the water is disengaged, and flies off with effervescence. 
 
 Emily. Was not this the manner in which the sulphuric acid 
 assisted the iron filings in decomposing water ? 
 
 Airs. 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 sur- 
 face of metal to act upon the water. 
 
 Caroline. The acid here seems to act a part not very differ' 
 
METALS. 151 
 
 ent from that of a scrubbing-brush. But pray would not this 
 be a good method of cleaning metallic utensils ? 
 
 Mrs. B. Yes ; on some occasions a weak acid, as vinegar, 
 is used for cleaning copper. Iron plates, too, are freed from 
 the rust on their surface by diluted muriatic acid, previous to 
 their being covered with tin. You must remember, however 5 
 that in this mode of cleaning metals the acid should be quickly 
 afterwards wiped off, otherwise it would produce fresh oxyd. 
 
 Caroline. Let us watch the dissolution of the copper in the 
 nitric acid ; for I am very impatient to see the salt that is to re- 
 sult from it. The mixture is now of a beautiful blue colour 5 
 but there is no appearance of the formation of a salt; it seems 
 to be a tedious operation. 
 
 Mrs. B. The crystallisation of the salt requires some length 
 of time to be completed ; if, however, you are so impatient, I 
 can easily show 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 show 
 you. When we decomposed water a few days since, by the 
 oxydation of iron filings through the assistance of sulphuric 
 acid, in what did the process consist ? 
 
 Caroline. In proportion as the water yielded its oxygen to 
 the iron, the acid combined with the new-formed oxyd, and the 
 hydrogen escaped alone. 
 
 Mrs. 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 it. 
 
 Emily. What a variety of processes the decomposition of wa- 
 ter, by a mutfll and an acid, implies : 1st, the decomposition of 
 the water ; 2d)y, the oxydation of the metal; and 3dly, the 
 formation of a compound salt. 
 
 Caroline. Here it is, Mrs. B. What beautiful green crys- 
 tals ! But we do not perceive any 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 de- 
 posited in consequence of rest and cooling. 
 
 Emily. I am surprised that a body so opaque as iron can be 
 converted into such transparent crystals. 
 
 Mrs. B. It is the union with the acid that produces the trans* 
 parency ; for if the pure metal were melted, and afterwards 
 permitted to cool and crystallise, it would be found just as 
 opaque as before. 
 
152 METALS, 
 
 Emily. I do not understand the exact meaning of crystallisa- 
 tion. 
 
 Mrs. B. You recollect that when a solid body is dissolved 
 either by water or caloric it is not decomposed ; but that its in- 
 tegrant parts are only suspended in the solvent. When the so- 
 lution 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 order to 
 make its particles re-unite, than to reduce its temperature. And, 
 in general, if the solvent, whether water or caloric, be slowly 
 separated by evaporation or by cooling, and care taken that 
 the particles be not agitated during their re-union, they will ar- 
 range themselves in regular masses, each individual substance 
 assuming a peculiar form or arrangement; and this is what is 
 called crystallisation. 
 
 Emily. Crystallisation, therefore, is simply the re-union of 
 the particles of a solid body which has been dissolved in a 
 fluid.* 
 
 Mrs. B. That is a very good definition of it. But I must 
 not forget to observe, that heat and water may unite their sol- 
 vent powers 5 and, in this case, crystallisation may be hasten- 
 ed by cooling, as well as by evaporating the liquid. 
 
 Caroline. But if the body dissolved is of a volatile nature, 
 will it not evaporate with the fluid ? 
 
 Mrs. 13. A crystallised 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 evapo- 
 rate the water only 
 
 I should not omit also to mention that bodies, in crystallising 
 from their watery solution, always retain a small portion of 
 water, which remains confined in the crystal in a solid form, 
 and does not re-appear un^es the body loses it crystalline state. 
 
 This is called the water of crystallisation. But you must 
 observe, that whilst a body may be separated from its solution 
 in water or caloric 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 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 oxygena- 
 
 * Not exactly, because the particles of the fluid make a part of the 
 crystal. Crystallisation is that process by which the particles of ! 1?v 
 flies unite to form solids, of certain, and regular shapes. C. 
 
METALS. 15^ 
 
 fed muriatic, a very remarkable acid, which, when in its most 
 concentrated state, dissolves gold vsr any other metal, by burn- 
 ing them rapidly. 
 
 Gold can, it is true, be dissolved likewise by a mixture of 
 two acids, commonly called aqua regia ; but this mixed solv- 
 ent derives that property from containing the peculiar acid 
 which I have just mentioned. Platina is also acted upon by 
 this acid only ; silver is dissolved by nitric acid. 
 
 Caroline. I think you said that some of the metals might be 
 so strongly oxydated as to become acid ? 
 
 Mrs. B. There are five metals, arsenic, molybdena, chrome, 
 tungsten, and columbium, which are susceptible of combining 
 with a sufficient quantity of oxygen to be converted into acids. 
 
 Caroline. Acids are connected with metals in such a varie- 
 ty of ways, that I am afraid of some confusion in remembering 
 them. In the first place, acids will yield their oxygen to met- 
 als. Secondly, they will combine with them in their state of 
 oxyds, to form compound salts; and lastly^ several of the met- 
 als are themselves susceptible of acidification. 
 
 Mrs. B. Very well ; but though metals have so great an af- 
 finity for acids, it is not with that class of bodies alone that they 
 will combine. They are most of them in their simple state ? 
 capable of uniting with sulphur, with phosphorus, with carbon, 
 and with each other; these combinations, according to the no- 
 menclature which was explained to you on a former occasion, 
 are called sulphurets, pkosphoretg, carburets, &c. 
 
 The metallic phosphorets offer nothing very remarkable. 
 The sulphurets form the peculiar kind of mineral called pyrites^ 
 from which certain kinds of .mineral \vaters> as those of Ilarro 
 2;ate, derive their chief chemical properties. In this combina- 
 lion, the sulphur, together with the iron, have so strong an at- 
 traction 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 re- 
 markable degree. 
 
 Emily. But if pyrites obtain oxygen from water, that water- 
 must suffer a decomposition, and hydrogen gas be evolved. 
 
 Mrs. B. That is actually the case in the hot sgrings alluded 
 to, which give out an extremely fetid gas, composed of hydro* 
 gen impregnated with sulphur. 
 
 Caroline. If I recollect right, steel and plumbago, which 
 you mentioned in the last lesson, are both carburets of iron ? 
 
 Mrs. B. Yes ; and they are the only carburets of much con- 
 sequence. 
 
 \ curious combination of metals has lately very much at- 
 
154 METALS. 
 
 tracted the attention of the scientific world : I mean the mete 
 oric stones which fall from the atmosphere. They consist prin- 
 cipally of native or pure iron, which is never found in that state 
 in the bowels of the earth* and contain also a small quantity of 
 nickel and chrome, a combination likewise new in the mineral 
 kingdom* 
 
 These circumstances have led many scientific persons to be- 
 lieve 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 are projected into it by some un- 
 known volcano on the surface of our globe. 
 
 Caroline. I have heard much of these stones, but I believe 
 many people are of opinion that they are formed on the surface 
 of the earth, and laugh at their pretended celestial origin. 
 
 Mrs. B. The fact of their falling is so well ascertained, that 
 1 think no person who has at all investigated the subject, can 
 now entertain any doubt of it. Specimens of these stones have 
 been discovered in all parts of the world, and to each of them 
 some tradition or story of its fall has i>cen found connected. 
 And as the analysis of all those specimens affords precisely the 
 same results, there is strong reason to cor.jrcture that they all 
 proceed from the same source. It is to Mr, Howard that phi- 
 losophers are indebted for having firs-t analysed these stones, 
 and directed their attention to this interesting subject. 
 
 Candine. But pray, Mrs. B., how can solid masses of nick- 
 el be formed from the atmosphere, which consists of the t\\ c 
 airs, nitrogen and oxygen ? 
 
 Mrs. B. I really do not see how they could, ^and think it 
 much more nrobable that they fall from tb* "on. or some oth- 
 er celestial body. But we must not suffer this digression to 
 take up too much of our time. 
 
 The combinations of metals with each other are called alloys j; 
 
 * This seems to be a mistake. Several localities of native iron, 
 found in veins are pointed out by auihors. In several instances large 
 blocks of native iron have been found on the surface of the earth. Onp 
 found by Prof. Pallas in Siberia weighed loUU Jus. Another found in 
 South America is sad to weigh 30,000 Ibs. &c. Those have been sus- 
 pected to be of meteoric origin, though nothing is known, which inak^s. 
 this certain. Those stones which are known beyond a doubt to have 
 fallen from the atmosphere, have a very different composition. These 
 generally contain the following ingredients, viz. iron, nickel chrome, 
 oxide of iron, sulphur, silex, lime, mugnesia, and alumine. The iron 
 rarely amounts to a quarter of the whole. Accounts are recorded of 
 the falling of stones, sulphur, &c. in every age since the Christian era, 
 and in almost every part of the world.- C. 
 
METALS. 155 
 
 thus brass is an alloy of copper and zinc ; bronze, of copper 
 and tin, &c. 
 
 Emily. And is not pewter also a combination of metal ? 
 
 Mrs.' B. It is. The pewter made in this country is most- 
 ly composed of tin, with a very small proportion of zinc and 
 lead. 
 
 Caroline. Block-tin is a kind of pewter, I believe ? 
 
 Mrs. B. Properly speaking, block-tin means tin in blocks, 
 or square massive ingots ; but in the sense in which it is used 
 by ignorant workmen, it is iron plated with tin, which renders 
 it more durable, as tin will not so easily rust. Tin alone, how- 
 ever, would be too soft a metal to be worked for common use, 
 and all tin vessels and utensils are in fact made 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. 
 
 Mrs. li. Take care, however, not to introduce the word ox- 
 y el ate, instead of rust, in general conversation ; for you would 
 probably not be understood, and you might be suspected of af- 
 fectation. 
 
 Metals differ very much in their affinity for each other ; some 
 will not unite at all, others readily combine together, and on 
 this property of metals the art of soldering depends. 
 
 Emily. What is soldering ? 
 
 Mrs. />. It is joining two pieces of metal together, by a more 
 fusible metal 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 ? 
 
 Mrs. B. In the operation of plating, two metals are uni'ed, 
 one being covered with the other, but without the intervention 
 of a third ; iron or copper may thus be covered with gold or 
 silver. 
 
 Emily. Mercury appears to me of a very different nature 
 from the other metals. 
 
 Mrs. B. One of its greatest peculiarities is, that it retains a 
 fluid state at the temperature of the atmosphere. All metals 
 are fusible at different degrees of heat, and they have likewise 
 each the property of freezing or becoming solid at a certain fix- 
 ed temperature. Mercury congeals only at seventy-two degrees 
 below the freezing point. 
 
 Emily. That is to say, that in order to freeze, it requires a 
 temperature of seventy-two degrees colder than that at which 
 water freezes. 
 
 Mrs. B. Exactly so. 
 
15 METALS. 
 
 Caroline. But is the temperature of the atmosphere ever sw 
 low as that ? 
 
 Mrs. B. Yes, often in Siberia ; but happily never in this 
 part of the globe. Here, however, mercury may be congealed 
 by artificial cold ; I mean such intense cold as can be produced 
 by some chemical mixtures, or by the rapid evaporation of 
 ether under the air pump.* 
 
 Caroline. And can mercury be made to boil and evaporate ? 
 
 Mrs. /). Yes, like any other liquid j only it requires a much 
 greater degree of heat. At the temperature of six hundred 
 degrees, it begins to boil and evaporate like water. 
 
 Mercury combines with gold, silver, tin, and with several oth- 
 er metals ; and, if mixed with any of them in a sufficient pro- 
 portion, it penetrates the solid metal, softens it, loses its own flu- 
 idity, and forms an amalgam, which is the name given to the 
 combination of any metal with mercury, forming a substance 
 more or less solid, according as the mercury or the other metal 
 predominates. 
 
 Emily. In the list of metals there are some whose names I 
 have never before heard mentioned. 
 
 Mrs. B. Besides those which Sir H. Davy has obtained, 
 there are several that have been recently discovered, whose 
 properties are yet but little known, as for instance, titanium, 
 which was discovered by the Rev. Mr. Gregor, in the tin-mines 
 of Cornwall ; columbium or tantalium, which has lately been 
 discovered by Mr. Hatchett ; and osmium, iridium, palladium, 
 and rhodium, all of which Dr. Wollaston and Mr. Tennant 
 found mixed in minute quantities with crude platina, and the 
 distinct existence of which they proved by curious and delicate 
 experiments. More recently still Professor Parhelius has dis- 
 covered in a pyritic ore, at Fahlun, in Sweden, a metallic sub- 
 stance, which he has called selenium, and which has the singu- 
 lar peculiarity of assuming the form of a yellow gas when heat- 
 ed in close vessels. In some of its properties this substance 
 seems to hold a medium between the combustibles and the met- 
 als. It bears in particular a strong analogy to sulphur. 
 
 Caroline. Arsenic has been mentioned amongst the metals, I 
 had no notion that it belonged to that class of bodies, for I had 
 never seen it but as a powder, and never thought of it but as a 
 most deadly poison. 
 
 .--.rs. B. In its pure metallic state, I believe, it is not so poi- 
 sonous; but it has such a great affinity for oxygen, that it ab- 
 
 * By a process analogous to that described, page 72, of thie yol- 
 
Mhl'ALs. 15 
 
 b-urbs it iVom tiie atmosphere at its natural temperature : you 
 have seen it, therefore, only in its state of oxyd, when, from its 
 combination with oxygen, it has acquired its very poisonous 
 properties. 
 
 Caroline. Is it possible that oxygen can impart poisonous 
 qualities ? That valuable substance which produces light and 
 iire, and which all bodies in nature are so eager to obtain ? 
 
 Mrs. B. Most of the metallic oxyds are poisonous, and de- 
 rive this property from their union with oxygen. The white 
 lead, so much used in paint, owes its pernicious effects to oxy- 
 gen. In general, oxygen, in a concrete state, appears to be 
 particularly destructive in its effects on flesh or any animal mat- 
 ter ; and those oxyds are most caustic that have an acrid burn- 
 ing taste, which proceeds from the metal having but a slight af- 
 iinity for oxygen, and therefore easily yielding it to the flesh s 
 which it corrodes and destroys. 
 
 Emily. What is the meaning of the word caustic, which you 
 have just used ? 
 
 Mrs. B. It expresses that property which some bodies pos- 
 sess, of disorganizing and destroying animal matter, by ope- 
 rating a kind of combustion, or at least a chemical decomposi- 
 tion. You must often have heard of caustic used to burn warts, 
 or other animal excrescences ; 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 form- 
 ed by the union of nictric acid and silver : and it is supposed 
 to owe its caustic qualities to the oxygen contained in the nitric 
 acid. 
 
 Caroline. But, pray, are not acids still more caustic than 
 oxyds, as they contain a greater proportion of oxygen ? 
 
 Mrs. l<. Some of the acids are ; but the caustic property of 
 a body depends not only upon the quantity of oxygen which it 
 contains, but also upon its slight affinity for that principle, and 
 the consequent facility with which it yields it. 
 
 Emily. Is not this destructive property of oxygen accounted 
 for? 
 
 Mrs. B. It proceeds probably from the strong attraction of 
 oxygen for hydrogen ; for if the one rapidly absoib the other 
 from the animal fibre, a disorganization of the substance must 
 ensue. 
 
 Emily. Caustics are, then, very properly said to burn the 
 flesh, since the combination of oxygen and hydrogen is an ac- 
 tual combustion. 
 
 Caroline. Now, I think, this effect would be more properly 
 
158 METALS. 
 
 termed an oxydation, as there is no disengagement of light and 
 heat. 
 
 Mrs. B. But there really is a sensation of heat produced by 
 the action of caustics. 
 
 Emily. If oxygen is so caustic, why does not that which is 
 contained in the atmosphere burn us ? 
 
 Mrs. B. Because it is in a gaseous state, and has a greater 
 attraction for its electricity than for the hydrogen of our bodies.' 
 Besides, should the air be slightly caustic, we are in a great 
 measure sheltered from its effects by the skin ; you 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 may have such a taste, though in so 
 slight a degree, that custom has rendered it insensible. 
 
 Caroline. And why is not water caustic ? When I dip ray 
 hand into water, though cold, it ought to burn me from the 
 caustic nature of its oxygen. 
 
 Mrs. B. Your hand does not decompose the water; the ox- 
 ygen in that state is much better supplied with hydrogen than 
 it would be by animal matter, and if its causticity depend on 
 its affinity for that principle, it will be very 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 likewise occasioned by oxygen ? 
 
 Mrs. B. It is produced by the intervention of oxygen ; 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 copper 
 when no vinegar has been in contact with it. 
 
 Mi's. B. Not real verdigris, but other salts, somewhat re- 
 sembling it, may be produced by the action of other acids on 
 copper. 
 
 The solution of copper in nitric acid, if evaporated, affords 
 a salt which produces an effect on tin that will surprise you, 
 
METALis* 15 
 
 and I have prepared some from the solution we made before, 
 that I might show it to you. -I shall first sprinkle some water on 
 this piece of tin-foil, and then some of the salt. Now observe 
 that 1 fold it up suddenly, and press it into one lump. 
 
 Caroline. What a prodigious vapour issues from it and 
 sparks of fire I declare ! 
 
 Mrs. B. I thought it would surprise you. The effect, how- 
 ever, I dare say you could account for, since it is merely the 
 consequence of the oxygen of the salt rapidly entering into a 
 closer combination with the tin. 
 
 There 4s also a beauttful green salt too curious to be omitted; 
 it is produced by the combination of cobalt with muriatic acid, 
 which has the singular property of forming what is called sym- 
 pathetic ink. Characters written with this solution are invisi- 
 ble when cold, but when a gentle heat is applied, they assume a 
 fine bluish green colour. 
 
 Caroline. I think one might draw very curious landscapes 
 with the assistance of this ink ; I would first make a water-col- 
 our drawing of a winter-scene, in which the trees should be 
 leafless, and the grass scarcely green ; I would then trace all 
 ihe verdure with the invisible ink, and whenever I chose to cre- 
 ate spring, I should hold it before the fire, and its warmth 
 would cover the landscape with a rich verdure. 
 
 Mrs. i>. That will be a very amusing experiment, and I 
 advise you by all means to try it. 
 
 Before we part, I must introduce to your acquaintance the 
 curious metals which Sir H. Davy has recently discovered. 
 The history of these extraordinary bodies is yet so much in its 
 infancy, that I shall confine myself to a very short account of 
 them 5 it is more important to point out to you the vast, and 
 apparently inexhaustable, field of research which has been 
 thrown open to our view by Sir H. Davy;s memorable discov- 
 eries, than to enter into a minute account of particular bodies or 
 experiments. 
 
 Caroline. But I have heard that these discoveries, however 
 splendid and extraordinary, are jiot very likely to prove of any 
 great benefit to the world, as they are rather objects of curiosi- 
 ty than of use. 
 
 Mrs. E. Such may be the illiberal conclusions of the igno- 
 rant and narrow-minded ; but those who can duly estimate the 
 advantages of enlarging the sphere of science, must be convinc- 
 ed that the acquisition of every new fact, however unconnect- 
 ed it ma}' at first appear with practical utility, must ultimately 
 prove beneficial to mankind. But these remarks are sc ircely 
 applicable to the present subject ; for some of the new metals 
 
160 PETALS. 
 
 have already proved eminently useful as chemical agents, ana 
 are likely soon to be employed in the arts. For the enumera- 
 tion of these metals, I must refer you to our list of simple bod- 
 ies; they are derived from the alkalies, the earths, and three 
 of the acids, all of which h.id been hitherto considered as un- 
 decompoundable or simple bodies. 
 
 When Sir H. Davy first turned hs attention to the effects of 
 the Voltaic baitery, he tried its power on a variety of compound 
 bodies, and gradually brought to light a number of new and in- 
 teresting facts, which led the way to more important discove- 
 ries. It would be highly interesting to trace his steps in this 
 new department of science, but it would lead us too far from 
 our principal object. A general view of his most remarkable 
 discoveries is all that I can aim at, or that you could, at present, 
 understand. 
 
 The facility with which compound bodies yielded to the 
 Voltaic electricity, induced him to make trial of its effects on 
 substances hitherto considered as simple, but which he suspect- 
 ed of being compound, and his researches were soon crowned 
 with the most complete success. 
 
 The body which he first submitted to the Voltaic battery, 
 and which had never yet been decomposed, was one of the fix- 
 ed alkalies, called potash. This substance gave out an elastic 
 fluid at the positive wire, which was ascertained to be oxygen, 
 and at the negative wire, small globules of a very high metallic 
 lustre, very similar in appearance to mercury; thus proving 
 that potash, which had hitherto been considered as a simple 
 incombustible body, was in fact a metallic oxyd ; and that its 
 incombustibility proceeded from its being already combined 
 with oxygen. 
 
 Emily- I suppose the wires used in this experiment were of 
 platina, as they were when you decomposed water ; for if of 
 iron, the oxygen would have combined with the wire, instead of 
 appearing in the form of gas. 
 
 Mrs. B. Certainly : the metal, however, would equally have 
 been disengaged. SirH. Davy has distinguished this new sub- 
 stance by the name of POTASSIUM, which is derived from that 
 of the alkali, from which it is procured. I have some small 
 pieces of it in this phial, but you have already seen it, as it is 
 the metal which we burnt in contact with sulphur. 
 
 Emily. What is the liquid in which you keep it ? 
 
 Mrs. J3. It is naptha, a bituminous liquid, with which I shall 
 hereafter make you acquainted. It is almost the only fluid in 
 which potassium can be preserved, as it contains no oxygen, 
 
METALS. 101 
 
 and this metal has so powerful an attraction for oxygen, that 
 it will not only absorb it from the air, but likewise from water, 
 or any body whatever that contains it. 
 
 Emily. Tiiis, then, is one of the bodies that oxydates spoit- 
 laneousiy without the application of heat ? 
 
 Mrs. B. Yes ; and it has this remarkable peculiarity, that 
 it attracts oxygen much more rapidly from water than from air j 
 so that when thrown into water, however cold, it actually bursts 
 into flame. I shall now throw a small piece, about the size of 
 a pin's head, on this drop of water. 
 
 Caroline. It instantaneously exploded, producing a little flash 
 of light ! this is, indeed, a most curious substance ! 
 
 Mrs. B. By its combustion it is re-converted into potash ; and 
 as potash is now decidedly a compound body, I shall not enter 
 into any of its properties till we have completed our review of 
 the simple bodies; but we may here make a few observations 
 on its basis, potassium. If this substance is left in contact with 
 air, it rapidly returns to the state of potash, with a disengage- 
 ment of heat, but without any flash of light. 
 
 Emily. But is it not very singular that it should burn better 
 in water than in air? 
 
 Caroline. I do not think so : for if the attraction of potas- 
 sium for oxygen is so strong that it finds no more difficulty in 
 separating it from the hydrogen in water, than in absorbing it 
 from the air, it will no doubt be more amply and rapidly sup- 
 plied by water than by air. 
 
 Mrs. B. That cannot, however, be precisely the reason, fot 
 when potassium is introduced under water, without contact of 
 air, the combustion is not so rapid, and indeed, in that case, 
 there is no luminous appearance; but a violent action takes 
 place, much heat is excited, the potash is regenerated, and hy- 
 drogen gas is evolved. 
 
 Potassium is so eminently combustible, that instead of requi- 
 rins, like other metals, an elevation of temperature, it will f.urii 
 rapidly in contact with water, even below the freezing poifif. 
 This you may witness by throwing a piece on this lump of ice. 
 
 Caroline. It again exploded with flame, and has made u 
 Jeep hoi* 3 in the ice. 
 
 Mrs. B. This hole contains a solution of potash ; for the al- 
 kali being extremely soluble, disappears in the wat^r at the in- 
 stant it is produced. Its presence, however, may be easily as- 
 certained, alkalies having the property of changing paper 5 
 stained with turmeric, to a red colour ; if you dip one end of 
 this slip of paper into the hole in the ice you will see i< 
 
 15* 
 
162 METALS, 
 
 colour, and the same, if you wet it with the drop of water in 
 which the first piece of potassium was burnt. 
 
 Caroline. It has indeed changed the paper from yellow to 
 red. 
 
 Mrs. B. This metal will burn likewise in carbonic acid gas, 
 a gas that had always been supposed incapable of supporting 
 combustion, as we were unacquainted with any substance that 
 had a greater attraction for oxygen than carbon. Potassium, 
 however, readily decomposes this gas, by absorbing its oxy- 
 gen, as I shall show you. This retort is filled with carbonic 
 acid gas. I will put a small piece of potassium in it ; but for 
 this combustion a slight elevation of temperature is required, 
 for which purpose I shall hold the retort over the lamp. 
 
 Caroline. Now it has taken fire, and burns with violence ! 
 It has burst the retort. 
 
 Mrs. B. Here is the piece of regenerated potash ; can you 
 tell me why it has become so black ? 
 
 Emily. No doubt it is blackened by the carbon, which, when 
 its oxygen entered into combination with the potassium, was 
 deposited on its surface. 
 
 Mrs. B. You are right. This metal is perfectly fluid at the 
 temperature of one hundred degrees; at fifty degrees it is solid, 
 but soft and malleable ; at thirty-two degrees it is hard and brit- 
 tle, and its fracture exhibits an appearance of confused crystal- 
 lization. It is scarcely more than half as heavy as water; its 
 specific gravity being about six when water is reckoned at ten ; 
 so that this metal is actually lighter than any known fluid, even 
 than ether. 
 
 Potassium combines with sulphur and phosphorus, forming 
 sulphurets and phosphurets , it likewise forms alloys with sev- 
 erul metals, and amalgamates with mercury. 
 
 Emily. But can a sufficient quantity of potassium be obtain- 
 ed, by means of the Voltaic battery, to admit of all its proper- 
 ties and relations to other bodies being satisfactorily ascertain- 
 ed? 
 
 Mrs. B. Not easily ; but I must not neglect to inform you 
 that a method of obtaining this metal in considerable quanti- 
 ties has since been discovered. Two eminent French chem- 
 ists, Thenard and Gay Lussac, stimulated by the triumph 
 which Sir H. Davy had obtained, attempted to separate potas- 
 sium from its combination with oxygen, by common chemical 
 means, and without the aid of electricity. They caused red 
 hot potash in a state of fusion to filter through iron turnings in 
 an iron tube, heated to whiteness. Their experiment was 
 crowned with the most complete success ; more potassium was: 
 
METALS. 13 
 
 obtained by this single operation, than could have been collect- 
 ed in many weeks by the most diligent use of the Voltaic bat- 
 tery. 
 
 Emily. In this experiment, I suppose, the oxygen quitted its 
 combination with the potassium to unite with the iron turnings ? 
 
 Mrs. B. Exactly so; and the potassium was thus obtained 
 in its simple state. From that time it has become a most con- 
 venient and powerful instrument of deoxygenation in chemical 
 experiments. This important improvement, engrafted on Sir 
 II. Davy's previous discoveries, served but to add to his glory, 
 since the facts which he had established, when possessed of on- 
 ly a few atoms of this curious substance, and the accuracy of 
 his analytical statements, were all confirmed when an opportu- 
 nity occurred of repeating his experiments upon this substance, 
 which can now be obtained in unlimited quantities. 
 
 Caroline. What a satisfaction Sir H Davy must have felt, 
 when by an effort of genius he succeeded in bringing to light 
 and actually giving existence, to these curious bodies, which 
 without him might perhaps have ever remained concealed 
 from our view ! 
 
 Mrs. H. The next substance which Sir H. Davy submitted 
 to the influence of the Voltaic battery was Soda, the other fix- 
 ed alkali, which yielded to the same powers of decomposition 5 
 from this alkali too, a metallic substance was obtained, very 
 analogous in its properties to that which had been discovered 
 in potash; Sir H. Davy has called it SODIUM. It is rather 
 heavier than potassium, though considerably lighter than wa- 
 ter; it is not so easily fusible as potassium. 
 
 Encouraged by these extraordinary results, Sir II. Davy 
 next performed a series of beautiful experiments on Ammonia^ 
 or the volatile alkali, which, from analogy, he was led to sus- 
 pect might also contain oxygen. This he soon ascertained to 
 be the fact, but he has not yet succeeded in obtaining the basis 
 of ammonia in a separate state ; it is from analogy, and from 
 the power which the volatile alkali has, in its gaseous form, to 
 oxydate iron, and also from the amalgams which can i?e obtain- 
 ed from ammonia by various processes, that the proofs of that 
 alkali being also a metallic oxyd are deduced. 
 
 Thus, then, the three alkalies, two of which had always 
 been considered as simple bodies, have now lost all claim to 
 that title, and I have accordingly classed the alkalies amongst 
 the compounds, whose properties we shall treat of in a future 
 conversation. 
 
 Emily. What are the other newly discovered metals which 
 you have alluded to in your list of simple bodies? 
 
1 64 METALS. 
 
 Mrs. B. They are the metals of the earths which became 
 next the object of Sir H. Davy's researches ; these bodies had 
 never yet been decomposed, though they were strongly suspect- 
 ed not only of being compounds, but of being metallic oxyds. 
 From the circumstance of their incombustibility it was con- 
 jectured, with some plausibility, that they might possibly be 
 bodies that had been already burnt. 
 
 Cardine. And metals, when oxydated, become, to all ap- 
 pearance, a kind of earthy substance. 
 
 Mrs. B. They have, besides, several features of resemblance 
 with metallic oxyds ; Sir H. Davy had therefore great reason 
 to be sanguine in his expectations of decomposing them, and he 
 was not disappointed. He could not, however, succeed in ob- 
 taining the basis of the earths in a pure separate state ; but me- 
 tallic alloys were formed with other metals, which sufficiently 
 proved the existence of the metallic basis of the earths. 
 
 The last class of new metallic bodies which Sir H. Davy 
 discovered was obtained from the three undecompounded acids, 
 the boracic, the fluoric, and the muriatic acids; but as you are 
 entirely unacquainted with these bodies, I shall reserve the ac- 
 count of their decomposition till we come to treat of their prop- 
 erties as acids. 
 
 Thus in the course of -two years, by the unparalleled exer- 
 tions of a single individual, chemical science has assumed a 
 new aspect. Bodies have been brought to light which the hu- 
 man eye never before beheld, and which might have remained 
 eternally concealed under their impenetrable disguise. 
 
 It is impossible at the present period to appreciate to their 
 full extent the consequences which science or the arts may de- 
 rive from these discoveries ; we may, however, anticipate the 
 most important results. 
 
 In chemical analysis we are now in possession of more ener- 
 getic agents of decomposition than were ever before known. 
 
 In geology new views are opened, which will probably ope- 
 rate a revolution in that obscure and difficult science. It is al- 
 ready proved that all the earths, and, in fact, the solid surface 
 of this globe, are metallic bodies mineralized by oxygen, and as 
 our planet has been calculated to be considerably more dense 
 upon the whole than it is on the surface, it is reasonable to sup- 
 pose that the interior of the earth is composed of a metallic 
 mass, the surface of which only has been mineralized by the at- 
 mosphere. 
 
 The eruptions of volcanos, those stupendous problems of na- 
 
ON THE ATTRACTION OF COMPOSITION. 105 
 
 ture, admit now of an easy explanation.* For if the bowels of 
 the earth are the grand recess of these newly discovered inflam- 
 mable bodies, whenever water penetrates into them, combus- 
 tions and explosions must take place ; and it is remarkable that 
 the lava which is thrown out, is the very kind of substance 
 which might be expected to result from these combustions. 
 
 I must now take my leave of you ; we have had a veiy long 
 conversation to-day, and I hope you will be able to recollect 
 what you have learnt. At our next interview we shall enter on 
 a new subject. 
 
 CONVERSATION XHi. 
 
 ON THE ATTRACTION OF COMPOSITION. 
 
 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 extensive sub- 
 ject, it will be necessary to make you acquainted with the prin- 
 cipal laws by which chemical combinations are governed. 
 
 You recollect, I hope, what we formerly said of the nature of 
 the attraction of composition, or chemical attraction, or affini- 
 ty, as it is also called ? 
 
 Emily. Yes, I think, perfectly ; it is the attraction that sub- 
 sists between bodies of a different nature, which occasions them 
 to combine and form a compound, when they come in contact, 
 and, according to Sir II. Davy's opinion, this effect is produced 
 by the attraction of the opposite electricities, which prevail in 
 bodies of different kinds. 
 
 Mrs. B. Very well ; your definition comprehends the first 
 law of chemical attraction, which is, that it takes place only 
 between bodies of a different nature ; as, for instance, between 
 an acid and an alkali ; between oxygen and a metal, &c. 
 
 Caroline. That we understand of course ; for the attraction 
 
 * It is always easy to form a theory. But an explanation of these 
 " stupendous problems of nature,' 1 we believe has not yet been de- 
 monstrated to the satisfaction of all. though great learning and im- 
 mense labor has been bestowed on the subject. If the " easy explana- 
 tion 1 ' is founded on the data here proposed, viz. that the solid surface 
 of our globe consists of nothing except metals and oxygen such a 
 theory in the present state of knowledge, must chiefly consist of suppo- 
 sition piled on supposition : there being as yet no proof that the crnst 
 of 1h- r.arth is foioied only of thess two elements. 0. 
 
i66 ' ON THE ATTRACTION 
 
 between particles of a similar nature is that of aggregation,, o 
 cohesion, which is independent ot'.nnv ""hf. : iaical power. 
 
 Mrs. B. The 2d law of chemical attraction is, that it take's 
 place only between the most minute particles of bodies ; there- 
 fore, the more you divide the particles of the bodies to be com- 
 bined, 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 i\,uiact with 
 each other, which must greatly facilitate then union. It was 
 for this purpose, you said, that you used iron filings, in prefer- 
 ence to wires or pieces of iron, for the decomposition of water. 
 
 Airs. B. It was once supposed that no mechanical power 
 could divide bodies into particles sufficiently minute for them to 
 act on each other ; and that, in order to produce the extreme 
 division requisite for a chemical 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, ex- 
 ert 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 hitherto seen 5 
 one of the constituents has, I believe, been either liquid 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 either in a liquid or an aeriform state. 
 
 Mrs. B The 3d law of chemical attraction is, that it can 
 fake place between two, three, four, or even a greater number 
 of bodies. 
 
 Caroline. Oxyds and aeids are bodies composed of two con- 
 stituents $ but 1 recollect no instance of the combination of a 
 greater number of principles. 
 
 Mrs. B. The compound salts, formed by the union of the 
 metals with ncids, are composed of three principles. And thero 
 are salts formed by the combination of the alkalies with the 
 Earths which are of a similar d^scriprion. 
 
 Caroline. Are they of the same kind as the metallic salts ? 
 
 Mrs. V. Yes; they are very analogous in their nature, al- 
 though different in rnanv of their properties. 
 
 A methodical nomenclature, similar to that of the acids, has 
 been adopted for the compound salts. Each individual salt de- 
 rives its name from its constituent parts, so thate very name im- 
 plies a knowledge of the composition of the salt. 
 
 '] hi? j the c^c )'/i<h nujriate of arr;m >nia and quicklime. C. 
 
OF COMPOSITION. 16? 
 
 'The three alkalies, the alkaline earths, and the metals, are 
 called salifiable bases or radicals ; and the acids, salifying 
 principles. The name of each salt is composed both of that of 
 the acid and the salifiable base; and it terminates in at or zV, 
 according to the degree of the oxygenation of the acid. Thus, 
 for instance, all those salts which are formed by the combina- 
 tion of the sulphuric acid with any of the salifiable bases are 
 nailed sulphats, 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^ &c. 
 
 Emily. The crystals which we obtained from the combina- 
 tion of iron and sulphuric acid were therefore sulphat of iron ? 
 
 .\Irs.B. Precisely; and those which we prepared by dis- 
 solving copper in nitric acid, nitrat ofcopper, and soon. But 
 this is not all : if the salt be formed by that class of acids which 
 ends in ous, (which you know indicates a less degree of oxygen- 
 ation,) the termination of the name of the salt will be in it, as 
 sulphit of potash, sulphit of ammonia^ &c. 
 
 Emily. There must be an immense number of compound 
 salts, since there is so great a variety of salifiable radicals, as 
 well as of salifying principles. 
 
 Mrs. B. Their real number cannot be ascertained, since it 
 increases every day. But we must not proceed further in the 
 investigation of the compound salts, until we have completed 
 the examination of the nature of the ingredients of which they 
 are composed. 
 
 The 4th law of chemical attraction is, that a change of tem- 
 perature always takes place at the moment of combination. 
 This arises from the extrication of the two electricities in the 
 form of caloric, which always occurs when bodies unite ; and 
 also sometimes in part from a change of capacity of the bodies 
 for heat, which always takes place when the combination is at- 
 tended with an increase of density, but more especially when 
 the compound passes from the liquid to the solid form. I shall 
 now show you a striking instance of a change of temperature 
 from chemical union, merely by pouring some nitrous acid on 
 this small quantity of oil of turpentine the oil will instantly 
 combine with the oxygen of the acid, and produce a considera- 
 ble change of temperature. 
 
 Caroline. What a blaze ! The temperature of the oil and 
 the acid must be greatly raised, indeed, to produce such a vio- 
 lent combustion. 
 
 Mrs. B. There is, however, a peculiarity in this combustion, 
 which is, that the oxygen, instead of being derived from the at- 
 mosphere alone, is principally supplied by the acid itself. 
 
168 ON THE ATTRACTION 
 
 Emily. And are not all combustions instances of the change 
 of temperature produced by the chemical combination of two 
 bodies ? 
 
 Mrs* B. Undoubtedly; when oxygen loses its gaseous form, 
 in order to combine with a solid body, it becomes condensed, 
 and the caloric evolved produces the elevation of temperature. 
 The specific gravity of bodies is at the same time altered by 
 chemical combination ; for in consequence of a change of capa- 
 city for heat, a change of density must be produced. 
 
 Caroline. That was the case with the sulphuric acid and wa- 
 ter, which, by being mixed together, gave out a great deal of 
 heat, and increased in density. 
 
 Mrs. B. The 5th law of chemical attraction is, that the pro- 
 perties lohich characterise bodies, when separate, are altered 
 or destroyed by their combination. 
 
 Caroline. Certainly ; what, for instance, can be so different 
 from water as the hydrogen and oxygen gases ? 
 
 Emily. Or what more unlike sulphat of iron than iron 01 
 sulphuric acid ? 
 
 Mrs. B. Every chemical combination is an illustration of 
 this rule. But let us proceed 
 
 The 6th law is, that the force of chemical affinity between 
 the constituents of a body is estimated by that which is requir- 
 ed for their separation. This force is not always proportional 
 to the facility with which bodies unite ; for manganese, for in- 
 stance, which, you know, is so much disposed to unite with ox- 
 ygen that it is never found in a metallic state, yields it more 
 easily than any other metal. 
 
 Emily. But, Mrs. B., you speak of estimating the force of at- 
 traction between bodies, by the force required to separate them ; 
 how can you measure these forces ? 
 
 J.TS. B. They cannot be precisely measured, but they are 
 comparatively ascertained by experiment, and can be represent- 
 ed by numbers which express the relative degrees of attraction. 
 
 The 7th law is, that bodies have amongst themselves differ- 
 ent 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. Every chemic- 
 al fact or experiment is an instance of the same kind ; and 
 whenever the decomposition of a body is performed by the ad- 
 dition of any single new substance, it is said to be effected by 
 simple elective attractions. But it often happens that no sin> 
 pie substance will decompose a body, and that, in order to ef~ 
 
Ot 1 COMPOSITION. 
 
 169 
 
 ecfc 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 re- 
 ciprocal decomposition and recomposition. 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 assistance of 
 this diagram, in which the reciprocal forces of attraction are 
 represented by numbers : 
 
 Original Compound 
 Sulpbat of Soda. 
 
 Result 
 
 Nitrat 
 
 ofSoda 
 
 Result 
 Sulphat 
 of Lime 
 
 Soda 8 Sulphuric Acid 
 
 i 
 
 7 Divellent ^Attractions 6-13 
 
 I 
 
 Nitric Acid 4 Lime 
 
 
 
 12 
 
 *^* V~ ' "*-'' 
 
 Original Compound 
 ISitrat 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, because the soda and the sulphuric 
 acid attract each other by a torce which is superior, and (by 
 way of supposition) is represented by the number 8 ; while the 
 lime tends to unite with this arid by an affinity equal only 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 eadeayour to decompose 
 16 
 
170 ON THE ATTRACTION 
 
 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 attraction, there- 
 fore, 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, the constituents of which are united by 
 a power equal to 4. If then we present this compound to the 
 sulphat of soda, a decomposition will ensue, 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, there- 
 fore, will combine with the soda, and the sulphuric acid with 
 the lime.* 
 
 Caroline. I understand you now very well. This double ef- 
 fect takes place because the numbers 8 and 4, which represent 
 the degrees of attraction of the constituents of the two original 
 salts, make a sum less than the numbers 7 and 6, which repre- 
 sent the degrees of attraction of the two new compounds that 
 will in consequence be formed. 
 
 Mrs. B. Precisely so. 
 
 Caroline. But what is the meaning of quiescent and divel- 
 lent forces, which are written in the diagram ? 
 
 Mrs. B. Quiescent forces are those which tend to preserve 
 compounds in a state of rest, or such as they actually are : di- 
 vellent forces, those which tend to destroy that state of combi- 
 nation, and to form new cdmpounds. 
 
 These are the principal circumstances relative to the doctrine 
 of chemical attractions, which have been laid down as rules by 
 modern chemists ; a few others might be mentioned respecting 
 the same theory, but of less importance, and such as would 
 take us too far from our plan. I should, however, not omit to 
 mention that Mr. Berthollet, a celebrated Fremch chemist, has 
 questioned the uniform operation of elective attraction, and has 
 advanced the opinion, that, in chemical combinations, the chan- 
 ges which take place depend not only upon the affinities, but 
 
 * Suppose we say thus. The sulphuric acid attracts soda with a 
 stronger force than it does /me, andsorfa has a stionger affinity foi sul- 
 phuric acid than it has for nitric acid. It is plain then, that neither 
 lime nor nitric acid alone will decompose the sulphat of r soda. Now 
 if we unite the nitric acid and lime, we form nitrate of lime. But the 
 nitric acid has not so strong an affinity for the lime as it has for soda. 
 On mixing the two salts in solution, therefore, the nitric acid quits the 
 lime, and combines with the soda. This leaves the sulphuric acid and 
 the lime free and uncombined ; they then unite and form sulphat o* 
 lime. C. 
 
OP COMPOSITION. 171 
 
 also, in some degree, on the respective quantities of the substan- 
 ces concerned, on the heat applied during the process, and 
 some other circumstances. 
 
 Caroline. In that case, I suppose, there would hardly be 
 two compounds exactly similar, though composed of the same 
 materials ? 
 
 Mrs. B. On the contrary, it is found that a remarkable uni- 
 formity prevails, as to proportions, between the ingredients of 
 bodies of similar composition. Thus water, as you may re- 
 collect to have seen in a former conversation, is composed of 
 two volumes of hydrogen gas to one of oxygen, and this is al- 
 ways found to be precisely the proportion of its conitituents, 
 from whatever source the water be derived. The same uni- 
 formity prevails with regard to the various salts 5 the acid and 
 alkali, in each kind of salt, being always found to combine in 
 the same proportion. Sometimes, it is true, the same acid, and 
 the same alkali are capable of making two distinct kinds of 
 salts ; but in all these cases it is found that one of the salts con- 
 tains just twice, or in some instances, thrice as much acid, or 
 alkali, as the other.* 
 
 Emily. If the proportions in which bodies combine are so 
 constant and so well defined, how can Mr. Berthollet's remark 
 be reconciled with this uniform system of combination ? 
 
 Mrs. B. Great as that philosopher's authority is in chemis- 
 try, it is now generally supposed that his doubts on this subject 
 were in a great degree groundless, and that the exceptions he 
 
 * The student already understands, that in chemical combinations 
 the union takes place only between the particles, or atoms, of substan- 
 ces. These atoms, it is supposed are indivisible, being the ultimate 
 particles of which bodies are composed. In chemical combinations, 
 then, where substances are capable of uniting in only one proportion, 
 this must be atom to atom. Thus oxygen and hydrogen unite only in 
 the proportions of 100 of the former to 750 of the latter by weight, 
 Here an atom of oxygen unites to an atom of hydrogen to form water ; 
 but the atoms of oxygen are seven and an half times heavier than those 
 of hydrogen. 
 
 When substances unite in several proportions, the second and third 
 are always multiples of the first. Thus 100 parts of manganese, will 
 unite to 14, 28, 42, or 56 of oxygen, but not with any intermediate 
 quantity, as with 12, 20, 60, &c. This la\r of definite proportions, 
 so far as is known, holds good, where the resulting compound differs 
 widely from either of the substances of which it is composed, as in the 
 salts, compound minerals, &c. The theory of definite proportions is 
 explained by supposing that a substance which, we shall call A, unites 
 with another substance B, atom to atom, and that this forms a certain 
 compound. When they unite in the second proportion, two atoms of 
 B unite to one of A, and this forms another compound, and so on, un 
 til the atoms of A can unite to no more of B. C. 
 
172 ON THE ATTRACTION OP COMPOSITION. 
 
 has observed in the laws of definite proportions, have been on- 
 ly appaient, and may be accounted for consistently with those 
 laws. 
 
 Caroline. Pray, Mrs. B., can you decompose a salt by 
 
 means of electricity, in the same way as we decompose water? 
 
 JWrs. Li. Undoubtedly ; and I am glad this question occurred 
 
 to you, because it gives me an opportunity of showing you 
 
 some very interesting experiments on the subject. 
 
 If we dissolve a quantity, however small, of any salt in a 
 glass of water, and if we plunge into it the extremities of the 
 wires which proceed from the two ends of the Voltaic battery, 
 the salt will be gradually decomposed, the acid being attracted 
 by the positive, and the alkali by the negative wire. 
 
 Emily. But how can you render that decomposition per- 
 ceptible ? 
 
 Mrs. B. By placing in contact with the extremities of each 
 Wire, in the solution, pieces of paper stained with certain veget- 
 able colours, which are altered by the contact of an acid or an 
 alkali. Thus this blue vegetable preparation called litmus be- 
 comes red when touched by an acid ; and the juice of violets 
 becomes green by the contact of an alkali. 
 
 But the experiment can be made in a much more distinct 
 manner, by receiving the extremities of the wires into two dif- 
 ferent vessels, so that the alkali shall appear in one vessel and 
 the acid in the other. 
 
 Caroline. But then the Voltaic circle will not be completed j 
 how can any effect be produced ? 
 
 Mrs. B. You are right ; I ought to have added that the two 
 vessels must be connected together by some interposed sub- 
 stance capable of conducting electricity. A piece of moistened 
 cotton-wick answers this purpose very well. You see that the 
 cotton (PLATE XIII. fig. 2. c.) has one end immersed in one 
 glass and the other end in the other, so as to establish a com- 
 munication between any fluids contained in them. We shall 
 now put into each of the glasses a little glauber salt, or sulphat 
 of soda, (which consists of an acid and an alkali,) and then 
 we shall fill the glasses with water, which will dissolve the salt. 
 Let us now connect the glasses by means of the wires (e, d,) 
 with the two ends of the battery, thus .... 
 
 Caroline. The wires are already giving out small bubbles ; 
 is this owing to the decomposition of salt ? 
 
 Mrs. B. No ; these are bubbles produced by the decompo- 
 sition of the water, as you saw in a former experiment. In or- 
 der to render the separation of the acid from the alkali visible, 
 I pour into the glass (a.) which is connected with the positive 
 

 J. Titrate Battery of* iinprvt'fd ccmtirtcfton vith tht Ptates otif oft&c Cels- 
 3 SO 'tin* fences df tfiam'ral ttecvntpofitien 3>\" tfie Teltaic Jtaffery. 
 

ALKALIES. 173 
 
 wire, a few drops of a solution of litmus, which the least quan- 
 tity of acid turns red ; and in the other glass (b,) which is con- 
 nected with the negative wire, I pour a few drops of the juice 
 of violets .... 
 
 Emily. The blue solution is already turning red all round 
 the wire. 
 
 Caroline. And the violet solution is beginning to turn green. 
 This is indeed very singular ! 
 
 Mrs. B. You will be still more astonished when we vary the 
 experiment in this manner : These three glasses (fig. 3. f, g, 
 h,) are, as in the former instance, connected together by wetted 
 cotton, but the middle one alone contains a saline solution, the 
 two others containing only distilled water, coloured as before 
 by vegetable infusions. Yet, on making the connection with 
 the battery, the alkali will appear in the negative glass (h,) and 
 the acid in the positive glass (f,) though neither of them con- 
 tained anly saline matter. 
 
 Emily. So that the acid and the alkali must be conveyed 
 right and left from the central glass, into the other glasses, by 
 means of the connecting moistened cotton ? 
 
 Mrs. B. Exactly so ; and you may render the experiment 
 still more striking, by putting into the central glass (k, fig. 4.) 
 an alkaline solution, the glauber salt being placed into the nega- 
 tive glass (1,) and the positive glass (i) containing only water. 
 The acid will be attracted by the positive wire (m,) and will 
 actually appear in the vessel (i,) after passing through the alka- 
 line solution (k,) without combining with it, although, you 
 know, acids and alkalies are so much disposed to combine. 
 But this conversation has already much exceeded our usual 
 limits, and we cannot enlarge more upon this interesting sub- 
 feet at present. 
 
 CONVERSATION XIV. 
 
 ON ALKALIES. 
 
 Mrs, B. HAVING now given you some idea of the laws by 
 which chemical attractions are governed, we may proceed to 
 the examination of bodies which are formed in consequence of 
 these attractions. 
 
 The first class of compounds that present themseVes to our 
 notice, in our gradual ascent to the most complicated combina- 
 tions, are bodies composed of only two principles. The sul- 
 
174 ALKALIES, 
 
 phurets, phosphurets, carburets, &c. are of this description ; 
 but the most numerous and important of these compounds are 
 the combination of oxygen with the various simple substances 
 with which it has a tendency to unite. Of these you have al- 
 ready acquired some knowledge, but it will be necessary to en- 
 ter into further particulars respecting the nature and properties 
 of those most deserving our notice. Of this class are the AL- 
 KALKS and the EARTHS, which we shall successively examine. 
 
 We shall first take a view of the alkalies, of which there are 
 three, viz. POTASH, SODA, and AMMONIA. The two first are 
 called Jixed alkalies,* because they exist in a solid form at the 
 temperature of the atmosphere, and require a great heat to be 
 volatilised. They consist, as you already know, of metallic 
 bases combined with oxygen. In potash, the proportions are 
 about eighty-six parts of potassium to fourteen of oxygen ; and 
 in soda, seventy-seven parts of sodium to twenty-three of oxy- 
 gen. The third alkali, ammonia, has been distinguished by 
 the name of volatile alkali, because its natural form is that of 
 gas. Its composition is of a more complicated nature, of which 
 we shall speak hereafter. 
 
 Some of the earths bear so strong a resemblance in their 
 properties to the alkalies, that it is difficult to know under which 
 head to place them. The celebrated French chemist, Four- 
 sroy, had classed two of them (barytes and strontites) with the 
 alkalies; but as lime 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 of alkaline 
 earths. 
 
 The general properties of alkalies are, an acrid burning 
 taste, a pungent smell, and a caustic action on the sk n and flesh j 
 
 Caroline. I wonder that they should be caustic, Mrs. B.,' 
 since they contain so little oxygen. 
 
 Mrs. B. Whatever substance has an affinity for any one of 
 the constituents of animal matter, sufficiently powerful to de- 
 compose it, is entitled to the appellation of caustic. The alka- 
 lies, in their pure state, have a very strong attraction for water, 
 for hydrogtn, and for carbon, which, you know, are the con- 
 
 * It has already been stated that a third fixed alkali has lately been 
 discovered by Mr. Aifoiedson, which has been called lilhion. It 
 was first found in a Swedish mineral called petalite ; but has since 
 teen detected in some other miners'?. Though this alkali resembles 
 potash and soda in its general properties, yet it is decidedly an alka- 
 linp substance 01 its own, capable of forming different salts with the 
 acids, and having in particular the property of combining with 
 greater proportions of acid than the other alkalies. 
 
POTASH. If5 
 
 stituent principles of oil, and it is chiefly by absorbing these 
 substances from animal matter that they effect its decomposi- 
 tion ; for, when diluted with a sufficient quantity of water, or 
 combined with any oily substance, they lose their causticity. 
 
 But, to return to the general properties of alkalies they 
 change, as we have already seen, the colour of syrup of vio- 
 lets, and other blue vegetable infusions, to green ; and have, 
 in general, a very great tendency to unite with acids, although 
 the respective qualities of these two classes of bodies form a 
 remarkable contrast. 
 
 We shall examine the result of the combination of acids and 
 alkalies more particularly hereafter. It will be sufficient at 
 present to inform you, that whenever acids are brought in con- 
 tact with alkalies, or alkaline earths, they unite with a remark- 
 able eagerness, and form compounds perfectly different from 
 either of their constituents 5 these bodies are called neutral or 
 eompound salts. 
 
 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 moisture from the atmos- 
 phere, and if the air were not perfectly excluded, it would, in a 
 very short time, be actually melted. 
 
 Emily. It is then, I suppose, always found in a liquid state? 
 
 Mrs. B. No ; it exists in nature in a great variety of forms 
 and combinations, but is never found in its pure separate state 5 
 it is combined with carbonic acid, with which it exists in every 
 part of the vegetable kingdom, and is most commonly obtained 
 from the ashes of vegetables, which are the residue that remains 
 after all the other parts have been volatilised by combustion. 
 
 Caroline. But you once said, that after all the volatile parts 
 of a vegetable were evaporated, the substance that remained 
 was charcoal ? 
 
 Mrs. B. I am surprised that you should still confound the 
 processes of volatilisation and combustion. In order to pro- 
 cure charcoal, we evaporate such parts as can be reduced to va- 
 pour by the operation of heat alone ; but when we burn the 
 vegetable, we burn the carbon also, and convert it into carbonic 
 acid gas. 
 
 Caroline. That is true ; I hope I shall make no more mis- 
 takes in my favourite theory of combustion. 
 
 Mrs. B. Potash derives its name from the pots in which the 
 vegetables, from which it was obtained, used formerly to be 
 burnt ; the alkali remained mixed with the ashes at the bot- 
 tom, and was thence called potash. 
 
 Emily. The ashes of a wood-fire, then, are potash, since 
 they are vegetable ashes ? 
 
17 POTASH. 
 
 Mrs. 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 com- 
 bustion 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 for- 
 eign substances, and it is only in chemical laboratories that it 
 is to be met with in the state of purity in which you find it in 
 this phial. Wood-ashes are, however, valuable for the alkali 
 which they contain, and are used for some purposes without 
 any further preparation. Purified in a certain degree, they 
 make what is commonly called pearl-ash, which is of great ef- 
 ficacy in taking out grease, in washing linen, &c. ; for potash 
 combines readily with oil or fat, with which it forms a com- 
 pound 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 combined with oil, must be less 
 efficacious in extracting grease. 
 
 Mrs. R. Its effect would be too powerful on fine linen, and 
 v/ould injure its texture ; pearl-ash is therefore 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 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 which potash 
 can be derived ? 
 
 Mrs. B. No : for though far most abundant in vegetables, it 
 is by no means confined to that class of bodies, being found al- 
 so on the surface of the earth, mixed with various minerals, es- 
 pecially with earths and stones, whence it is supposed to be 
 conveyed into vegetables by the roots of the plant. It is also 
 met with, though in very small quantities, in some animal sub- 
 stances. The most common state of potash is that of carbo' 
 not y I suppose you understand what that is ? 
 
 Emily. I believe so ; though I do not recollect that you ever 
 mentioned the word before. If I am not mistaken, it must be 
 a compound salt, formed by the union of carbonic acid with 
 potash. 
 
 Mrs. B. Very true j you see bow admirably the nomencla- 
 
POTASH. 177 
 
 ture of modern chemistry is adapted to assist the memory 5 
 when you hear the name of a compound, you necessarily learn 
 what are its constituent parts; and when you arc acquainted 
 with these constituents, you can immediately name the com- 
 pound which they form. 
 
 Caroline. Pray, how were bodies arranged and distinguish- 
 ed before this nomenclature was introduced ? 
 
 Mrs. B. Chemistry was then a much more difficult study ; 
 for every substance had an arbitrary name, which it derived 
 either from the person who discovered it, as Glauber's salts 
 for instance; or from some other circumstance relative to it, 
 though quite unconnected with its real nature, as potash. 
 
 These names have been retained for some of the single bod- 
 ies; for as this class is not numerous, and therefore can easily 
 be remembered, it has not been thought necessary to change 
 them. 
 
 Emily. Yet I think it would have rendered the new nomen- 
 clature more complete to have methodised the names of th<. 1- 
 ementary, 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 have indicated their nature, or, at least, 
 some of their principal properties ; and if, like the acids and 
 compound salts, all the simple bodies had a similar termination, 
 they would have been immediately known as such. So com- 
 plete and regular a nomenclature would, I think, have given a 
 clearer and more comprehensive view of chemistry than the 
 present, which is a medley of the old and new terms. 
 
 Mrs. B. But you are not aware of the difficulty of introduc- 
 ing into science an entire set of new terms ; it obliges all the 
 teachers and professors to go to school again, and if some of the 
 old names, that are least exceptionable, were not left as an in- 
 troduction to the new ones, few people would have had indus- 
 try and perseverance enough to submit to the study of a com- 
 pletely new language; and the inferior classes of artists, who 
 can only act from habit and routine, would, at least for a time, 
 have felt material inconvenience from a total change of their 
 habitual terms. From these considerations, 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 con- 
 nect it with the new one. Besides, you may easily conceive 
 the inconvenience which might arise from giving a regular nom- 
 enclature to substances, the simple nature of which is always 
 uncertain ; for the new names might, perhaps, have proved to 
 have been founded in error. And, indeed, cautious as the in- 
 ventors of the modern chemical language have been, it has al- 
 
178 POTASH. 
 
 ready been found necessary to modify it in many respects. Iu 
 those few cases, however, in which new terms have been adopt- 
 ed to designate simple bodies, these names have been so con- 
 trived as to indicate one of the chief properties of the body in 
 question ; this is the case with oxygen, which, as 1 explained 
 to you, signifies generator of acids ; and hydrogen generator of 
 water. If all the elementary bodies had a similar termination, 
 as you propose, it would be necessary to change the name of 
 any that might hereafter be found of a compound nature, which 
 would be very inconvenient in this age of discovery. 
 
 But to return to the alkalies. We shall now try to melt 
 some of this caustic potash in a little water, as a circumstance 
 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 contrary to our 
 theory of latent heat, according to which heat is disengaged 
 when fluids become solid, and cold produced when solids are 
 melted. 
 
 Mrs. B. The latter is really the case in all solutions ; and if 
 the solution of caustic alkalies seems to make an exception to 
 the rule, it does not, 1 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 slaking of lime, that is, the water is solidified in combi- 
 ning with the potash, and thus loses its latent heat ; this is the 
 lieat 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 wa- 
 ter ; and if we do not perceive the cold produced by its melting, 
 it is because it is counterbalanced by the heat previously dis- 
 engaged.* 
 
 A very remarkable property of potash is the formation of 
 glass by its fusion with siliceous earth. You are not yet ac- 
 quainted with this last substance, further than its being in the 
 list of simple bodies. It is sufficient for the present, that you 
 should know that sand and flint are chiefly composed of it; 
 alone, it is infusible, but mixed with potash, it melts when ex- 
 posed to the heat of a furnace, combines with the alkali, and 
 runs into glass. 
 
 Caroline. Who would ever have supposed that the same sub- 
 
 * This defence of the general theory, however plausible, is liable to 
 some obvious objections. The phenomenon might perhaps be better 
 accounted for by supposing that a solution of alkali in water has less 
 capacity for heat than either water or alkali in their separate state. 
 
POTASH. 179 
 
 stance which converts transparent oil into such an opaque body 
 as 50-tp, 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 intimate nature, as upon 
 the arrangement of their particles: we cannot have a more 
 striking instance of this, than is afforded by the different states 
 of carbon, which, though it commonly appears in the form of a 
 black opaque body, sometimes assumes the most dazzling trans- 
 parent form in nature, that of diamond, which, you recollect, is 
 carbon, and which, in all probability, derives its beautiful trans- 
 parency from the peculiar arrangement of its particles during 
 their crystallisation. 
 
 Emily. I never should have supposed that the formation 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 siliceous earth is 
 obtained, be mixed with any metallic particles, or other sub- 
 stance, which cannot be vitrified, the glass will be discoloured, 
 or defaced, by opaque specks. 
 
 Caroline. That, I suppose, is the reason why objects so of- 
 ten appear irregular and distorted through a common glass- 
 window. 
 
 Mrs. 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 bot- 
 tom. 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 retraction of the rays of 
 Light which pass through it. 
 
 Another species of imperfection sometimes arises from the 
 fusion not being continued for a length of time sufficient to com- 
 bine the two ingredients completely, or from the due propor- 
 tion of potash and silex (which are as two to one) not being 
 carefully observed; the glass, in those cases, will be liable to 
 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 potash is ! 
 
 Mrs. B. Besides the great importance of potash in the man- 
 ufactures of glass and soap, it is of very considerable utility in 
 many of the other arts, and in its combinations with several 
 particularly the nitric, with which it forms saltpetre. 
 
180 SODA. 
 
 Caroline. Then saltpetre must be a nitrat of potash ? But 
 we are not yet acquainted with the nitric acid ? 
 
 Mrs. K. We shall therefore defer entering into the particu- 
 lars of these combinations till we come to a general review of 
 the compound salts. In order to avoid confusion, it will be bet- 
 ter at present to confine ourselves to the alkalies. 
 
 Emily. Cannot you show us the change of colour which you 
 said the alkalies produced on blue vegetable infusions ? 
 
 Mrs. B. Yes, very easily. I shall dip a piece of white pa- 
 per into this syrup of violets, which, you see, is of a deep blue, 
 and dyes the paper of the same colour. As soon as it is dry, 
 we shall dip it into a solution of potash, which, though itself 
 colourless, will turn the paper green * 
 
 Caroline. So it has, indeed ! And do the other alkalies pro- 
 duce a similar effect ? 
 
 Mrs. 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 pot- 
 ash ; 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 great 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 impregnated. 
 
 Emily. Is not that the common table salt ? 
 Mrs. B. The very same ; but again we must postpone en- 
 tering into the particulars of this interesting combination, till 
 we treat of the neutral salts. Soda may be obtained from com- 
 mon salt ; but the easiest and most usual method of procuring 
 it is by the combustion of marine plants, an operation perfectly 
 analogous to that by which potash is obtained from vegetables. 
 Emily. From what does soda derive its name ? 
 Mrs. B. From a plant called by us soda, and by the Arabs 
 Icali, which affords it in great abundance. Kali has, indeed, gi- 
 ven its name to the alkalies in general. 
 
 Caroline. Does soda form glass and soap in' the same man- 
 ner as potash ? 
 
 * A very pretty experiment on the change of colours may be made 
 as follow? : Make a tincture, by pouring Lolling water on red cab- 
 bage and let it stand a while. Put it into a vial. The colour will be 
 purple. Take two wine glasses, and into one put a few drops of sul- 
 phuric acid, and into the other the same quantity of a strong solution 
 of potash. So little of either will do, that the glasses may he inverted 
 for a moment. Then pour the tincture int- each, and the one contain- 
 ing the acid will appear a most beautiful red, and the other as beauti- 
 ful a green. C. 
 
AMMONIA. 181 
 
 Mrs. B. Yes, it does ; it is of equal importance in the arts, 
 and is even preferred to potash for some purposes; but you 
 will not be able to distinguish their properties till we examine 
 the compound salts which they form with acids ; we must 
 therefore leave soda for the present, and proceed to AMMONIA 
 
 Or the VOLATILE ALKALI. 
 
 Emily. I long to hear something of this alkali ; is it not of 
 the same nature as hartshorn ? 
 
 Mrs. ft. Yes it is, as you will see by-and-bye. This alkali 
 is seldom found in nature in its pure state ; it is most commonly 
 extracted from a com pound salt, cal led sal ammoniac, which was 
 formerly imported from Ammonia, a region of Libya, from 
 which both these salts and the alkali derive their names. The 
 crystals contained in this bottle are specimens of this salt, 
 which consist of a combination of ammonia and muriatic acid. 
 
 Caroline. Then it should be called muriatic of ammonia ; 
 for though I am ignorant what muriatic acid is, yet I know that 
 its combination with ammonia cannot but be so called ; and J 
 am surprised to see sal ammoniac 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 succeeded in 
 banishing it altogether ; and it is still sold under that name by 
 druggists, though by scientific chemists it is more properly call- 
 ed muriat of ammonia. 
 
 Caroline. Both the popular and the common name should 
 be inscribed on labels this would soon introduce the new no- 
 menclature. 
 
 Emily. By what means can the ammonia be separated from 
 the muriatic acid ? 
 
 Mrs. B. By chemical attraction ; .but this, operation is too 
 complicated for you to understand, till you are better acquaint- 
 ed with the agency of affinities. 
 
 Emily. And when extracted from the salt, what kind of sub- 
 stance is ammonia ? 
 
 Mrs. B. Its natural form, at the temperature of the atmos- 
 phere, when free from combination, is that of gas ; and in this 
 state it is called animoniacal gas. But it mixes very readily 
 with water, and can be thus obtained in a liquid form. 
 
 Caroline. You said that ammonia was more complicated in 
 its composition than the other alkalies ; pray of what principles 
 does it consist ? 
 
 Mrs. tf. It was discovered a few years since, by Berthollet, a, 
 celebrated French chemist, that it consisted of about one part 
 of hvdrogen to four parjs of nitrogen. Having heated ammo- 
 niacal gas under a receiver, by causing the electrical spark to 
 
 17 
 
1 82 AMMONIA. 
 
 pass repeatedly through it, he found that it increased consider- 
 ably in bulk, los>t all its alkaline properties, and was actually 
 converted into hydrogen'and nitrogen gases ; and from the latest 
 and most accurate experiments, the proportions appear to be, 
 one volume^ef nitrogen gas to three of oxygen gas.* 
 
 Caroline. Ammonia, therefore, has not,, like the two other 
 alkalies, a metallic basis ? 
 
 j\>rs. ti. It is believed that it has, though it is extremely dif- 
 ficult to reconcile that idea with what 1 have just stated of its 
 chemical nature. But the fact is, that although this supposed 
 metallic basis of ammonia has never been obtained distinct and 
 separate, yet both Professor Berzelius, of Stockholm, and Sir 
 H. Davy, have succeeded in forming a Combination of mercu- 
 ry with the basis of ammonia, which has so much the appear- 
 ance of an amalgam, that it strongly corroborates the idea of 
 ammonia having a metallic basis.t But these theoretical points 
 are full of difficulties and doubts, and it would be useless to 
 dwell any longer upon them. 
 
 Let us therefore return to the properties of volatile alkali. 
 Ammoniacal pas is considerably lighter than oxygen gas, and 
 only about half the weight of atmospherical air. It possesses 
 most of the properties of the fixed alkalies ; but cannot be of so 
 much use in the arts on account of i<& 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 ; foi 
 which reason it can be collected in a receiver over mercury 
 only. 
 
 Caroline. I do not understand this ? 
 
 Mrs. ;.. iJo you recollect the method which we used to col- 
 lect gases in a glass receiver over water ? 
 
 Caroline. Perfectly. 
 
 A.rs. t'. Ammouiacal gas has so strong a tendency to unite 
 with water, that, instead of passing through that fluid, it would be 
 instantaneously absorbed by it. We can therefore neither use 
 \vuter for that purpose, nor any other liquid of which water is 
 a component part; so that, in order to collect this gas, we are 
 
 - * It ought to be hydrogen gas. C. 
 
 " t 'I his amalgam is easily obtained, by placing a globule of mercury 
 upon a piece of muriat, or carbonat of ammonia, and electrifying this 
 globule by the Voltaic battery. The globule instantly begins to ex- 
 pand to three or tour times' it3 former size, and becomes much less 
 fluid, though without losing its metallic lustre, a change which is as- 
 cribed to the metallic basis of 'ammonia uniting with the mercury,. 
 This is an extremely curious experini< 
 
AMMONIA. 183 
 
 obliged to have recourse to mercury, (a liquid which has no ac- 
 tion upon it,) and a mercurial bath is used instead of a water 
 bath, such as we employed on former occasions. Water im- 
 pregnated with this gas is nothing more than the fluid which 
 you mentioned at the beginning of the conversation hartshorn ; 
 it is theammoniacal gas escaping from the water which gives it 
 so powerful a smell.* 
 
 Emily. But there is no appearance of effervescence in harts- 
 horn. 
 
 Mrs. B. Because the particles of gas that rise from the wa- 
 ier are too subtle 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 impregnating water 
 with ammonia, heat must be absorbed, and cold produced ? 
 
 Mrs. B. That effect would take place if it was not counter- 
 acted by another circumstance ; the gas is liquefied by incorpo- 
 rating with the water, and gives out its latent heat. The con- 
 densation of the gas more than counterbalances the expansion 
 of the water ; therefore, upon the whole, heat is produced. But 
 if you dissolve ammoniacal gas with ice or snow, cold is produ- 
 ced. 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, I should have supposed the original tempera- 
 ture would have been preserved. 
 
 Mrs. B. But you have forgotten to take into the account the 
 
 * To obtain ammoniacal gas, mix together equal parts of muriate 
 of ammonia, and dry burnt lime; af'er pulverizing each separately, 
 :ub them together in a mortar ; put them into a retort and apply the 
 ijfeat of a ia.mp. Or, the common spirit of sal. ammoniac may be heat- 
 ed in a retort in the same way. To collect and retain.the gas without 
 :t mercurial bath, fix a receiver or bottle in an inverted position, and 
 -onnect to the retort a tube, which introduce up into the receiver so 
 'hat it nearly reaches the bottom. A* the gas comes over, its levity 
 is such, that it fills the upper part of the receiver first, gradually dat- 
 ing out the air. and taking its place. To keep it for any considerable 
 lime, the receiver must be stopped. A pretty experiment may be 
 made by introducing up into the receiver with the ammonia, some mu- 
 riatie gas. Both gases are invissible until they arc; brought tog-ether, 
 when they unite, forming a dense white cloud, and fall down ia the 
 solid form of muriate of ammonia. The muriatic gas is obtained by 
 pouring sulphuric acid on common salt, and applying the heat of a 
 lamp. It may be sent up into the receiver in the way above described 
 or ammonia. C. 
 
184 AMMONIA. 
 
 rarefaction of the water (or melted ice) by the impregnation o? 
 the gas ; and this is the cause of the cold which is ultimately 
 produced. 
 
 Caroline. Is the sal volatile (the smell of which so strongly 
 resembles hartshorn) likewise a preparation of ammonia ? 
 
 Mrs. B. It is carbonat of ammonia dissolved in water; and 
 which, in its concrete state, is commonly called salts of harts- 
 horn. Ammonia is caustic, like the fixed alkalies, as you may 
 judge by the pungent eflects of hartshorn, which cannot be ta- 
 .ken internally, nor applied to delicate external parts, without 
 being plentifully 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 alkalf, 
 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 alkali. 
 
 Mrs. B. Precisely so. 
 
 Ammoniacal gas, if it be mixed with atmospherical air, and 
 a burning taper repeatedly plunged into it, will burn with a 
 large flame of a pecular yellow colour. 
 
 Emily. But pray tell me, can ammonia be procured from 
 this Lybian salt only ? 
 
 Mrs. 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 constituents 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 de- 
 composition of animal substances ; the hydrogen and nitrogen 
 gases 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 chiefly prepared in Eu- 
 rope, by chemical processes. Ammonia, although principally 
 extracted from this salt, can also be produced by a great varie- 
 ty of other substances. The horns of cattle, especially those of 
 deer, yield it in abundance, and it is from this circumstance that 
 a solution of ammonia in water has been called hartshorn. It 
 may likewise be procured from wool, flesh and bones ; in a 
 word, any animal substance whatever yields it by decomposi- 
 tion. 
 
 We shall now lay aside the alkalies, however important the 
 subject may be, till we treat of their combination with acidr- 
 The ne,xt time we meet we shall examine the earths, 
 
EARTHS. 185 
 
 CONVERSATION XV. 
 
 ON EARTHS. 
 
 Mrs. B. THE EARTHS, which we are to-day to examine, are 
 nine in number : 
 
 SILEX, STRONTITES,* 
 
 ALUMINE, YTTRIA, 
 
 BARYTES,* GLUCINA, 
 
 LIME,* Z1RCONIA. 
 MAGNESTA ; * 
 
 The last three are of late discovery; their properties are but 
 imperfectly known ; and, as they have not yet been applied to 
 use, it will be unnecessary to enter into any particulars respecting 
 them ; we shall confine our remarks, therefore to the first five. 
 They are composed, as you have already learnt, of a metallic 
 basis combined with oxygen ; and, from this circumstance, are 
 incombustible. 
 
 Caroline. Yet I have seen turf burnt in the country, and it 
 makes an excellent fire; the earth becomes red hot, and produ- 
 ces a very great quantity of heat. 
 
 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 produced 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, you would find that it had not ab- 
 sorbed one particle of oxygen, nor suffered any alteration from 
 the fire. Earth is, however, from the circumstance just men- 
 tioned, an excellent radiator df heat, and owes its utility, when 
 mixed with fuel, solely to that property. It is in this point of 
 view that Count Rum ford has recommended balls of incombus- 
 
 * There is less evidence that these four earths a e composed of 
 metallic bases than there is in the case of ammonia, which it will be 
 remembered \\jas supposed in have formed an amalgam \yith mercury, 
 and on this account was supposed to have had a metallic basis. Of 
 the other earths, no one except Dr. Clarke of Cambridge, Enf. has 
 pretended to offer any but conjectural evidence of their metallic nature. 
 This gentleman, on subjecting them to the heat of the blow-pipe, charg 
 ?d with oxygen and hydrogen, was led to believe he had obtained 
 their metallic bases. But as his experiments have been repeated at 
 the Royal Institution without success, it is now understood that the Dr, 
 must have been mistaken. C. 
 
186 
 
 tible substances to be arranged in fire-places, and mixed witii 
 the coals, by which means the caloric disengaged by the com- 
 bustion of the latter is more perfectly reflected into the room, 
 and an expense of fuel is saved. 
 
 Emily. I expected that the list of earths would be much 
 more considerable. When I think of the great variety of soils, 
 I am astonished that there is not a greater number of earths to 
 form them. 
 
 Mrs. B. You might indeed, almost confine that number to 
 four; for barytes, strontites, and the others of late discovery, 
 act but so small a part in this great theatre, that they cannot be 
 reckoned as essential to the general formation of the globe. 
 And you must not confine your idea of earths to the formation 
 of soil ; for rock, marble, chalk, slate, sand, flint, and all kinds 
 of stones, from the precious jewels to the commonest pebbles ; 
 In a word, all the immense variety of mineral products may be 
 referred to some of these earths, either in a simple state, or com- 
 bined the one with the other, or blended with other ingredients. 
 
 Caroline. Precious stones composed of earth ! That seems 
 very difficult to conceive. 
 
 E-nily. Is it more extraordinary than that the most precious 
 of ail jewels, diamond, should be composed of carbon ? But di- 
 amond 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 wel' a quainted with it. Besides, I would call a diamond a 
 tnineirl rather than a stone, as the latter term always implies 
 the presence of some earth. 
 
 Caroline. I cannot conceive how such coarse materials can 
 be converted into such beautiful productions. 
 
 Mrs. B. We are very far from understanding all the secret 
 resources of nature ; but I do not think the spontaneous forma- 
 tion of the crystals, which we call precious stones, one of the 
 Most difficult phenomena to comprehend. 
 
 By the slow and regular work of ages, perhaps of hundreds of 
 ages, these earths may be gradually dissolved by water, and as 
 gradually deposited by their solvent in the undisturbed process 
 of crystallisation. The regular arrangement of their particles, 
 during their re-union in a solid mass, gives them that brilliancy, 
 transparency, and beauty, for which they are so much admired ; 
 and renders them in appearance so totally different from their 
 lude and primitive ingredients. 
 
 Caroline. But how does it happen that they are spontane- 
 ously dissolved, and afterwards crystallised r 
 
 ./km*. B. The scarcity of many kinds of crystals, as rubies. 
 
EARTHS. 187 
 
 emeralds, topazes, &c. shows that their formation is not an ope- 
 ration very easily carried on in nature. But cannot you ima- 
 gine that when water, holding in solution some particles of earth, 
 filters through the crevices of hills or mountains, and at length 
 dribbles into some cavern, each successive drop may be slowly 
 evaporated, leaving behind it the particle of earth which it held 
 in solution? You know that crystallisation is more regular and 
 perfect, in proportion as the evaporation of the solvent is slow 
 and uniform; nature, therefore, who knows no limit of time, 
 has, in all works of this kind, an infinite advantage over any 
 artist who attempts to imitate such productions. 
 
 Emily. I can now conceive that the arrangement of the par- 
 ticles of earth, during crystallisation, may be such as to occa- 
 sion transparency, by admitting a free passage to the rays of 
 light ; but I cannot understand why crystallised earths should 
 assume such beautiful colours as most of them do. Sapphire, 
 for instance, is of a celestial blue ; ruby, a deep red ; topaz, a 
 brilliant yellow ? 
 
 Mrs. B. Nothing is more simple than to suppose that the ar- 
 rangement of their particles is such, as to transmit some of the 
 coloured rays of light, and to reflect 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 
 owing to a mixture of some metallic matter. 
 
 Caroline. Pray, are the different kinds of precious stones 
 each composed of one individual earth, or are they formed of a 
 combination of several earths ? 
 
 Mrs. B. A great variety of materials enters into the compo- 
 sition of most of them ; not only several earths, but sometimes 
 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 Derbyshire spar produced by the crystalli- 
 sation of earths, in the way you have just explained ? I have 
 been in some of the subterraneous caverns where it is found, 
 which are similar to those you have described. 
 
 Mrs. B. Yes; but this spar is a very imperfect specimen of 
 crystallisation ;* it consists of a variety of ingredients confused- 
 ly bleded 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 agree- 
 
 * The Derbyshire spar is composed of lime and fluoric acid: hence 
 it is called Jluate of li/ne. The colours are owing to intermixture with 
 metallic oxides. It is a very beautiful rain- ral, and instead of being 
 opake it is generally translucent, or nearly transparent. C. 
 
188 SILEX. 
 
 able form, we must not lose sight of that state in which they 
 are commonly found, and which, if less pleasing to the eye, is 
 far more interesting by its utility. 
 
 All the earths are more or less endowed with alkaline prop- 
 erties ; but th*ere are four, barytes, magnesia, lime, and stron- 
 tites, 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 as alkalies ; they 
 are, like them, susceptible of a considerable degree of causticity, 
 and are acted upon in a similar manner by chemical tests. The 
 remaining earths, silex and aiumine, with one or two others of 
 late discovery, are in some degree more earthy, that is to say, 
 they possess more completely the properties common to all the 
 earths, which are, insipidity, dryness, unalterableness in the 
 fire, in fusibility, &c. 
 
 Caroline. Yet, did you not tell us that silex, or siliceous 
 earth, when mixed with an alkali, was fusible, and run into 
 glass ? 
 
 Mrs. B. Yes, my dear ; but the characteristic properties of 
 earths, which I have mentioned, are to be considered as belong- 
 ing to them in a state of purity only ; 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 distinguished from any other substance. Let us therefore 
 review them separately. 
 
 SILEX. or SILICA, abounds in flint, sand, sand-stone, agate, 
 jasper, &e. ; it forms the basis of many precious stones, and 
 particularly of those which strike fire with steel. It is rough 
 to the touch, scratches and wears away metals ; it is acted up- 
 on 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 
 ef siliceous crystals, and amongst these rock crystal^ which is 
 the purest specimen of this earth. Silex appears to hfcve been 
 intended by Providence to form the solid basis of the globe, to 
 serve as a foundation for the original mountains, and give them 
 that hardness and durability which has enabled them to resist 
 the various revolutions which the surface of the earth has suc- 
 cessively undergone. From these mountains siliceous rocks 
 have, during the course of ages, been gradually detached by 
 torrents of water, and brought down in fragments ; these, in 
 the violence and rapidity of their descent, are sometimes crum- 
 bled to sand, and in this state form the beds of rivers and of 
 the sea, chiefly composed of siliceous materials. Sometiis 
 
SILEX. 189 
 
 the fragments are broken without being pulverised by their 
 fall, and assume 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. 
 
 Mrs. B. Pure silex, such as is found only in the chemist's la- 
 boratory, is perfectly white, and the various colours which it 
 assumes, in the different substances you have just mentioned, 
 proceed from the different 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.* 
 
 Mrs. B. You must not forget that the value we set upon pre- 
 cious stones depends in a great measure upon the scarcity with 
 which nature affords them; for, were those productions either 
 common or perfectly imitable by art, they would no longer, 
 notwithstanding their beauty, be so highly esteemed. But the 
 real value of siliceous earth, in many of the most useful arts, is 
 very extensive. Mixed with clay, it forms the basis of all the 
 various kinds of earthern ware, from the most common uten- 
 sils to the most refined ornaments. 
 
 Emily. And we must recollect its importance to the forma- 
 tion of glass with potash. 
 
 Mrs. B. Nor should we omit to mention, likewise, many 
 other important uses of silex, such as being the chief ingredi- 
 ent of some of the most durable cements, of mortar, &c. 
 
 I said before that siliceous earth combined with no acid but 
 the fluoric ; it is for this reason that glass is liable to be attack- 
 ed by that acid only, which, from its strong affinity for silex, 
 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 growing weary of this part of our 
 subject. 
 
 Caroline. I confess that the history of the earths is not quite 
 so entertaining as that of the simple substances. 
 
 Mrs. B. Perhaps not ; but it is absolutely indispensable 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 out-. 
 
 * The bases of some of the most costly gems, as sapphire, ruby ami 
 j are alumine. C, 
 
190 ALUMINE. 
 
 line of chemical science. We shall, however, review them in 
 as cursory a manner as the subject can admit of. 
 
 ALUMINE derives its name from a compound salt called alum 9 
 of which it forms the basis. 
 
 Caroline. But it ought to be just the contrary, Mrs. B. ; the 
 simple body should give, instead of taking, its name from the 
 compound. 
 
 Mrs. B. That is true ; but as the compound salt was known 
 long before its basis was discovered, it was very natural that 
 when the earth was at length separated from the acid, it should 
 derive its name from the compound from which it was obtain- 
 ed. However, to remove your scruples, we will call the salt 
 according to the new nomenclature, sulphat of aiumine. From 
 this combination, alumioe may be obtained in its pure state ; 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 con- 
 tains a considerable proportion of this earth ; it is very abun- 
 dant in fuller's earth, slate, and a variety of other mineral pro- 
 ductions. There is indeed scarcely any mineral substance more 
 useful to mankind than aiumine. In the state of clay, it forms 
 large strata of the earth, gives consistency to the soil of valleys, 
 and of all low and damp spots, such as swamps and marshes. 
 The beds of lakes, ponds, t and springs, are almost entirely 
 of clay ; instead of allowing of the filtration of water, as sand 
 does, it forms an impenetrable bottom, and by this means 
 water is accumulated in the caverns of the earth, producing 
 those reservoirs whence springs issue, and spout out at the sur- 
 face. 
 
 Emily. I always thought that these subterraneous reservoirs 
 of water were bedded by some hard stone, or rock, which the 
 water could not penetrate. 
 
 Mrs. B. That is not the case ; for in the course of time wa- 
 ter would penetrate, or wear away silex, or any other kind of 
 stone, while it is effectually stopped by clay, or aiumine. 
 
 The solid compact soils, such as are fit for corn, owe their 
 consistence in a great measure to aiumine ; this earth is there- 
 fore used to improve sandy or chalky soils, which do not retain 
 a sufficient quantity of water for the purpose of vegetation. 
 
 Aiumine is the most essential ingredient in all potteries. It 
 enters into the composition of brick, as well as that of the finest 
 porcelain : 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 should 
 be made of the same materials* 
 
BARYTfiS. 191 
 
 Mrs. B. Brick consists almost entirely of baked clay ; but 
 a certain proportion of silex is esset.t al to the formation of 
 earthen or stone ware. In common potteries sand is used for 
 that purpose ; a more pure silex is,* I believe, necessary for 
 the composition of porcelain, as well as a finer kind of clay ; 
 and these materials are, no doubt, more carefully prepared, 
 and curiously wrought, in the one case than in the other. Por- 
 celain owes its beautiful semi-transparency to a commencement 
 of vitrification. 
 
 Emily. But the commonest earthen-ware, though not trans- 
 parent, is covered with a kind of glazing. 
 
 Mrs. B. That precaution is equally necessary for use as for 
 beauty, as the ware would be liable to be spoiled and corroded 
 by a variety of substances, if not covered with a coating of this 
 kind. In porcelain it consists of enamel, which is a fine white 
 opaque glass, formed of metallic oxyds, sand, salts, and such 
 other materials as are susceptible of vitrification. The gla- 
 zing 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. 
 
 Car<line. And of what nature are the colours which are us- 
 ed for painting porcelain ? 
 
 Mr*. 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, < &c. consist chiefly of al- 
 umine. 
 
 We may now proceed to the alkaline earths. I shall say 
 but a few words on BARYTES, as it is hardly ever used, except 
 in chemical laboratories. It is remarkable for its great weight, 
 and its strong alkaline properties, such as destroying animal 
 substances, turning green some blue vegetable colours, ;md 
 showing a powerful 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 sub- 
 
 * Porcelain clay, of which china ware is made, is found among gra- 
 nite rocks, and seems to owe its oriei'i to the decomposition of a min- 
 eral calle d feldspar. Its composition i? silex and alumine, silex being 
 the predominant ingredient. C. 
 
 t The amethyst is almost entirely composed of imex. C. 
 
192 LIME. 
 
 stance 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 na- 
 ture 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 sub- 
 stance 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 carbonic 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 volatilised when- 
 ever 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 ? 
 
 j\irs. ft. Precisely : in this state it is called quick-lime, and 
 it is so caustic, that it is capable of decomposing the dead bo- 
 dies of animals very rapidly, without their undergoing the pro- 
 cess of putrefaction. 1 have here some quick-lime, which is 
 kept carefully corked up in a bottle, to prevent the access of 
 air ; for were it 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 result from it. 
 
 Caroline. How the quick-lime hisses ! It is become exces- 
 sively hot ! It swells, and now it bursts and crumbles to pow- 
 der, while the water appears to produce no kind of alteration 
 on the lime-stone. 
 
 Mrs. />". Because the lime-stone is already saturated 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 disengagement of heat, the cause of 
 which I formerly explained to you ; do you recollect it ? 
 
 Emily. Yes 5 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 liquidity. 
 
 Mrs. B. Very well. If we continue to add successive quan- 
 ties of water to the lime after being slaked and crumbled as you 
 see, it will then gradually be diffused in the water, till it will at 
 length be dissolved in it, and entirely disappear ; but for this 
 
 * The native carbonate of barytes is a rare mineral. It is a virulent 
 poison. The sulphate of barytes is found in considerable abundance 
 
LIMfc. i<}3 
 
 purpose it requires no less than 700 times its weight of water. 
 This solution is called lime water.* 
 
 Caroline. How very small, then, is the proportion of lime 
 dissolved ! 
 
 J\-frs. IB. Barytes is still of more difficult solution 5 it dis- 
 solves 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 neutralising, 
 the superabundant acid which it meets with in the stomach. 
 
 bmity. I am surprised that it is so perfectly clear; it does 
 not at all partake of the whiteness of the lime. 
 
 Mrs. B. Have you forgotten that, in solutions, the solid bo- 
 dy is so minutely subdivided by the fluid as to become invisi- 
 ble, and therefore will not in the least degree impair the trans- 
 parency of the solvent? 
 
 I said that the attraction of lime for carbonic acid was so 
 strong, that it would absorb it from the atmosphere. We may 
 see this etfect by exposing a glass of lime-water to the air ; the 
 lime will then separate from the water, combine with the car- 
 bonic acid, and re-appear on the surface in the form of a white 
 fii.ii, which is carbonatof 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 < ateV ; but it is far from 
 resembling hard solid chalk. 
 
 Mrs. B. That is owing to its state of extreme division ; 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, \vi!l produce the same ef- 
 fect. It is an experiment very easily made ; I shall poui 
 some lime-water into this glass tube, and, by breathing repeat- 
 edly 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 pres- 
 ent it floats in the water, but it will soon subside. 
 
 Carbonat of lime, or c^ialk, you see, is insoluble in water,, 
 since the lime which was dissolved re-appears when converted 
 
 * To make lime water, take a piece of' well burned lime about the 
 size of a heiPs egg, put it into au earthen dish, and sprinkle water oa 
 it. till it falls into powder : Then pour on two quarts of boiling 1 water, 
 and sir it several times, alter the lime ha? settled, ; pour off the clear 
 water and cork it up tor use. C. 
 
 18 
 
194 LIME. 
 
 into chalk ; but you must take notice of a very singular circum- 
 stance, which is, that chalk is soluble in water impregnated with 
 carbonic acid. 
 
 Caroline. It is very curious, indeed, that carbonic acid gas 
 should render lime soluble in one instance, and insoluble in the 
 other ! 
 
 Mrs. B. I have here a bottle of Seltzer water, which, you 
 know, is strongly impregnated with carbonic acid : let us 
 pour a little of it into a glass of lime-water. You see that it im- 
 mediately forms a precipitation of carbonat of lime ? 
 
 Emily. Yes, a white cloud appears. 
 
 Mrs. B. I shall now pour an additional quantity of the Selt- 
 zer water into the lime-water 
 
 Emily. How singular ! The cloud is re-dissolved, and the 
 liquid is again transparent. 
 
 Mrs. B. All the mystery depends upon this circumstance, 
 that carbonat of lime is soluble in carbonic acid, whilst it is in- 
 soluble in water ; the first quantity of carbonic acid, therefore, 
 which I introduced into the lime-water, was employed in form- 
 ing the carbonat of lime, which remained visible, until an addi- 
 tional quantity 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 predom- 
 inates, the chalk is no sooner formed than it is dissolved. 
 
 Caroline. That is now the case; but let us try whether a 
 further addition of lime-water will again precipitate the chalk. 
 
 Emily. It does, indeed! The cloud re appears, because, I 
 suppose, there is now no more of the carbonic acid than is ne- 
 cessary to form chalk; and, in order to dissolve the chalk, a 
 superabundance of acid is required. 
 
 Mrs. B. We have, I think, carried this experiment far 
 enough ; every repetition would but exhibit the same appear- 
 ances. 
 
 Lime combines with most of the acids, to which the carbo- 
 nic (as being the weakest) readily yields it; but these combina- 
 tions we shall have an opportunity of noticing more particular- 
 ly hereafter. It unites with phosphorus, and with sulphur, in 
 their simple state; in short, of all the earths, lime is that which 
 nature employs most frequently, and niost abundantly, in its in- 
 numerable combinations. It is the basis of all calcareous earths 
 and stones ; we find it likewise in the animal and the vegeta- 
 ble creations. 
 
 Emily. And in the arts is not lime of very great utility ? 
 
 Mrs. B. Scarcely any substance more so; you know that it- 
 
MAGNESIA. 19$ 
 
 is a most essential requisite in building, as it constitutes the ba- 
 sis of all cements, such as mortar, stucco, plaster, &c. 
 
 Lime is also of infinite importance in agriculture; it lightens 
 and warms soils that are too cold and compact, in consequence 
 of too great a proportion of clay. But it would be endless to 
 enumerate the various purposes 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- 
 NESIA. 
 
 Caroline. I am already pretty well acquainted with that 
 earth ; it is a medicine. 
 
 Mrs. B. It is in the state of carbonat that magnesia is usual- 
 ly employed medicinally; it then differs but little in appear- 
 ance 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 extremely soluble salts It has not so 
 great an attraction 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, and amianthus, and more 
 particularly in a certain lime-stone, which has lately been dis- 
 covered by Mr. Tennant to contain it in very great quantities. 
 It does not attract and solidify water, like lime : but when mix- 
 ed 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 read- 
 iness to combine with, and neutralise, the acid which it meets 
 with in the stomach. 
 
 Emily. Yet, you said that it was taken in the state o4* carbo- 
 nat, in which case it has already combined with an acid ? 
 
 Mrs. B. Yes; but the carbonic is the last of all the acids in 
 the order of affinities; it will therefore yield the magnesia to 
 any of the others. It is, however, frequently taken in its caus- 
 tic state as a remedy for flatulence. Combined with sulphuric 
 acid, magnesia forms another and more powerful medicine, com- 
 monly called EpKoni salt. 
 
 Caroline. And properly, sulphat of magnesia, I suppose ? 
 Pray why was it ever called Kpsorn salt? 
 
 Mrs. :?. Because there is a spring in the neighbourhood of 
 Epsom which contains this salt in great abundance. 
 
 The last alkaline earth which we have to mention is STRON- 
 TIAN, or STRONTITES, discovered by Dr. Hope a few years ago. 
 It so strongly resembles barytes in its properties, and is so spar- 
 ingly 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 remarkable characteristic properties of strontites is, 
 
that its sails, when dissolved in spirit of wine, tinge the flame o*' 
 a deep red, or uiood colour. 
 
 CONVERSATION XVI. 
 
 ON ACIDS, 
 
 Mrs. B. WE may now proceed to the acids. Of the metallic 
 oxyds, you have already acquired some general notions. This 
 subject, though highly interesting in its details, is not of suffi- 
 cient importance to our concise view of chemistry, to he partic- 
 ularly treated of; but it is absolutely necessary that you should 
 be better acquainted with- the acids, and likewise with then 
 combinations with the alkalies, which form the triple com- 
 pounds Called NEUTRAL SALTS. 
 
 The class of acids is characterised by very distinct proper- 
 ties. They all change blue vegetable infusions to a red colour ; 
 they are all more or less sour to th j taste ; and have a general 
 tendency to combine with the earths, alkalies, and metallic 
 oxyds. 
 
 You have, I believe, a clear idea of the nomenclature 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 oxydation, that is, the quanti- 
 ty of oxygen it contains, by the termination of that name in ous 
 oric; thus sulphureous 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 
 greatest quantity of oxygen. 
 
 Mrs. B. A still greater latitude may, in many cases, be al- 
 lowed to the proportions of oxygen that can be combined with 
 acidificiable cadicals ; for several of these radicals are suscepti- 
 ble of uniting with a quantity of oxygen so small as to be insuf- 
 ficient to give them the properties of acids : in these cases, 
 therefore, they are converted into oxyds. Such is sulphur, 
 which by exposure to the atmosphere with a degree of heat in- 
 adequate to produce inflammation, absorbs a small proportion of 
 oxygen, which colours it red or brewni This, therefore, is the 
 first degree of oxygenation of sulphur ; the 2d converts it into 
 s'ti -ihnrous acid; the 3d into the sulphuric acid ; and 4ihly, if 
 found capable of combining with a still larger proportion 
 of - .vygeti, it would then be termed super-oxygenated sulphur" 
 acid. 
 
ACIDS. 197 
 
 Emily. Are these various degrees of oxygenation common 
 to all the acids ? 
 
 Mrs. B. No 5 they vary much in this respect : some are sus- 
 ; piible of only one degree of oxygenation; others, of two, or 
 .hive; there are but very few that will admit of more. 
 
 Caroline. The modern nomenclature must be of immense ad- 
 vantage in pointing out so easily the nature of the acids, and 
 their various degrees of oxygenation. 
 
 Mrs. B. Till lately many of the acids had not been decom- 
 posed ; but analogy afforded so strong a proof of their com- 
 pound nature, that I never could reconcile myself to classing 
 diem with the simple bodies, though this division has been 
 adopted by several chemical writers. At present there are on- 
 ly the muriatic and the fluoric acids, which have not had their 
 bases distinctly separated. 
 
 Caroline. We have heard of a great variety of acids 5 pray 
 how many are there in all ? 
 
 Mrs. B. I believe there are reckoned at present thirty-four, 
 and their number is constantly increasing, as the science im- 
 proves; but the most important, and those to which we shall 
 almost entirely confine our attention, are but few. I shall, how- 
 ever, give you a general view of the whole ; and then we shall 
 more particularly examine those that are the most essential. 
 
 This class of bodies was formerly divided into mineral, ve- 
 getable, and animal acids, according to the substances from 
 which they were commonly obtained. 
 
 Caroline. That, I should think, must have been an excellent 
 arrangement ; why was it altered ? 
 
 Mrs. B. Because in many cases it produced confusion. In 
 which class, for instance, would you place carbonic acid ? 
 
 Caroline. Now I see the difficulty. I should be at a loss 
 where to place it, as you have told us that it exists in the ani- 
 mal, 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 stones, and 
 likewise in some plants. 
 
 Mrs. /;. You see, therefore, the propriety of changing this 
 mode of classifica ion. These objections do not exist in the 
 present nomenclature ; for the composition and nature of each 
 individual acid is in some degree pointed out, 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 
 three heads : 
 
 Firs>t, Acids of known or supposed simple bases, which .are 
 18* 
 
193 
 
 ACIDS. 
 
 formed by the union of these bases with oxygen. They 
 the following : 
 
 The Sulphuric 
 Carbonic 
 Nttric 
 Phosphoric 
 Arsenical 
 Tungstenic 
 Molybdenic 
 Boracic 
 Fluoric 
 Muriatic 
 
 Acids, of known and simple bas<$. 
 
 This class comprehends the most anciently known and most 
 important acids. The sulphuric, nitric, and nyjriatic were for- 
 merly, and are still frequently, called mineral acids. 
 
 2dly, Acids that have double or binary radicals, and which 
 eonsequently consist of triple combinations. These are the 
 vegetable acids, whose common radical is a compound of hy- 
 drogen and carbon. 
 
 Caroline. But if the basis of all the vegetable acids be the 
 same, it should form but one acid ; it mav indeed combine with 
 different proportions of oxygen, but the nature of the acid must 
 be the same. 
 
 JvJrs. Ll. The only difference that exists in the basis of veget- 
 able acids, is the various proportions of* hydrogen and carbon 
 from which they are severally composed. But this is enough to 
 produce a number of acids apparently very dissimilar. That 
 the.y do not, however, differ essentially, is proved by their sus- 
 ceptibility of being converted into each other, by the addition 
 or subtraction of a portion of hydrogen or of carbon. The 
 sanies of these acids are, 
 
 The Acetic 
 Oxalic 
 Tartarous 
 Citric 
 
 Acids, of double bases, being of vegeta- 
 J\ucous bleorgin. 
 
 Benzoic 
 Sue time 
 Camphoric 
 Suberic 
 
ACIOS. 199 
 
 The 3d class of acids consists of those which have triple rad- 
 icals, and are therefore ot a still more compound nature. Tlfts 
 class comprehends the animal acids, which are, 
 
 The Lactic 7 
 Prussi-c 
 Formic 
 Bombic 
 Sebacic 
 Zoonic 
 Lithic 
 
 > Acids, of triple bases, or animal acids. 
 
 I have given you this summary account or enumeration of 
 the acids, as you may find it more satisfactory to have at once 
 an outline or a general notion of the extent of the subject ;. but 
 we shall now confine ourselves to the first class, which requires 
 our more immediate attention; and defer the few 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 capable of 
 being decomposed by combustible bodies, to which they yield 
 their oxygen. 11', for instance, 1 pour a drop of sulphuric acid 
 on this piece of iron, it will produce 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 oxy- 
 gen by which it was acidified on the metal. And again, if we 
 pour someacid on a compound combustible 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 decomposi- 
 tion. 
 
 Emily. It has changed the colour of the wood to black. How 
 is that ? 
 
 J\- : 'rs. tt. The oxygen deposited by the acid has burnt it ; 
 you know that wood in burning becomes black before it is re- 
 duced to ashes. Whether it derives the oxygen which burns 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 becomes 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 wuy wood turns black when burnt by the 
 application of an acid ? 
 
 Caroline. First, tell me what are the ingredients of wood ? 
 
00' ACIDS. 
 
 Mrs. B. Hydrogen and carbon are the chief constitutes 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 carbon of the wood, remaining alone, appears of its 
 usual black colour. 
 
 Mrs. B. Very well indeed, my dear ; that is certainly the 
 most plausible explanation. 
 
 Caroline. Would not this be a good method of making char- 
 coal ? 
 
 Mrs. 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 
 acid of fruits, do not produce this effect on wood ? 
 
 Mrs. H. They are vegetabe acids, whose bases are composed 
 of hydrogen and carbon ; the oxygen, therefore, will not be dis- 
 posed to quit this radical, where it is already united with hydro- 
 gen. The strongest of these may, perhaps, yield a little of 
 their oxygen to the wood, and produce a stain upon it ; but the 
 carbon will not be sufficiently uncovered to assume its black 
 colour. Indeed, the several mineral acids themselves possess 
 chis power of charring wood in very different degrees. 
 
 Emily. Cannot vegetable acids be decomposed, by any com- 
 bustibles ? 
 
 Mrs. B. N-9 ; because their radical is composed of two sub- 
 stances which have a greater attraction for oxygen than any 
 known body. 
 
 Caroline. And are those strong acids, which burn and de- 
 compose wood, capable of producing similar effects on the 
 skin and flesh of animals ? 
 
 , \lrs. B. Yes ; all the mineral acids, and one of them more 
 especially, possess powerful caustic qualities. They actually 
 corrode and destroy the skin and flesh ; but they do not produce 
 upon these exactly the same alteration they do on wood, proba- 
 bly because there is a great proportion of nitrogen and other 
 substances in animal matter, which prevents the separation of 
 carbon from being so conspicuous. 
 
5>F SULPHURIC AND SULPHUREOUS ACIDS. 20i 
 
 CONVERSATION XVII. 
 
 Of THE SULPHURIC AND PHOSPHORIC ACIDS; Oil THE 
 COMBINATION OF OXYGEN VVI TH SULPHUR AND PHOS- 
 PHORUS ; AND OF THE SULPHA FS AND PHOSPH \ TS. 
 
 Mrs. B. IN addition to the general survey which we have 
 takep of acids, I think you will find it interesting to examine 
 individually a tew of the most important of them, and like- 
 wise some of their principal combination with the alkalies, al- 
 kaline earths, and metals. The first of the acids, in point of 
 importance, is the SULPHURIC, formerly 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 ? 
 
 Mrs. B. Vitrol is the common name for sulphat of iron, a 
 salt which is formed by the combination of sulphuric acid and 
 iron; the sulphuric acid was formerly obtained by distillation 
 from this salt, and it very naturally received its name from the 
 substance which afforded it. 
 
 Caroline. But it is still usually called oil of vitirol ? 
 
 Mrs. B. Yes ; a sufficient length of time has not yet elap- 
 sed, since the invention of the new nomenclature, for it to be 
 generally disseminated ; but, as it is adopted by all scientific 
 chemists, there is. every reason to suppose that it will gradu- 
 ally beco.ne universal. When I received this bottle from the 
 chemists, oil of vitriol was inscribed on the label ; but, as 1 
 knew you were very punctilious in regard to the nomenclature, 
 I changed it, and substituted the words sulphuric acid. 
 
 Emily. This acid has neither colour nor smell, but it ap- 
 pears much thicker than water. 
 
 Mrs. B. It is nearly 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 hydrogen or carbon, which 
 are the essential constituents of oil. 
 
 Mrs. B. Certainly ; and therefore it would be the more ab- 
 surd to retain a name which owed its origin to such a mistaken 
 analogy. 
 
 Sulphuric acid, in its purest state, would probably be a con- 
 crete substance, but its attraction for water is such, that it is im- 
 possible to obtain that acid perfectly free from it j it is, there- 
 
202 OP THE SULPHURIC 
 
 fore, always seen in a liquid form, such as you here find it, 
 One of the rrnst striking properties of sulphuric acid is that ot 
 evolving a considerable quantity of heat when mixed with wa- 
 ter; this I have already shown you. 
 
 Emily. Yes, I recollect it ; but what was the degree of heat 
 produced by that mixture ? 
 
 Mrs. B. The thermometer may be raised by it to 300 de- 
 grees, which is considerably above the temperature of boiling 
 water. 
 
 Caroline. Then water might be made to boil in that mix- 
 ture? 
 
 Mrs. B. Nothing more easy, provided that you employ suf- 
 ficient quantities of acid and of water, and in the due propor- 
 tions. The greatest heat is produced by a mixture of one part 
 of water to four of the acid : we shall make a mixture of these 
 proportions, and immerse in it this thin glass tube, which is full 
 of water. 
 
 Caroline. The vessel feels extremely hot, but the water does 
 not boil yet. 
 
 Mrs. B. You must allow some time for the heat to penetrate 
 the tube, and raise the temperature of the water to the boiling 
 point 
 
 Caroline. Now it boils and with increasing violence. 
 
 Mrs. B. But it will not continue boiling long ; for the mix- 
 ture 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 particles is effected, the mixture will 
 gradually cool, and the water return to its former temperature. 
 
 You have seen the manner in which sulphuric acid decompo- 
 ses all combustible substances, whether animal, vegetable, or 
 mineral, and burns them by means of its oxygen ? 
 
 Caroline. I have very unintentionally repeated the experi- 
 ment 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. 
 
 Mrs. B. No, certainly ; for before you can put it into water, 
 the spot will become a hole, as the acid has literally burnr the 
 muslin. 
 
 Caroline. So it has indeed ! Well, I will fasten the stopper, 
 and put the bottle away, for it is a dangerous substance, Oh, 
 now I have done worse still, for I have spilt some on v hand ! 
 
 Mrs. B. It is then burned, as well as your gown, tor you 
 know thelt oxygen destroys animal as well as vegetable matters; 
 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. 
 
AND SULPHUREOUS ACIDS. 203 
 
 Caroline. It feels extremely hot, I assure you. 
 
 JV/rs. B. You have now learned, by experience, how cau- 
 tiously this acid must be used. You will soon become acquain- 
 ted with another acid, the nitric, which, though it produces less 
 heat on the skin, destroys it still quicker, and makes upon it an 
 indelible stain. You should never handle any substances of 
 this kind, without 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 de- 
 stroy its strength and purity. 
 
 Emily. Pray, how can sulphuric acid be extracted from sul- 
 phat of iron by distillation ? 
 
 Mrs. B. The process of distillation, you know, consists in 
 separating substances from one another by means of their dif- 
 ferent degrees of volatility, and by the introduction of a new 
 chemical agent, caloric. Thus, if sulphat of iron be exposed 
 in a retort to a proper degree of heat, it will be decomposed, 
 and the sulphuric acid will be volatilised. 
 
 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 acid ? 
 
 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 the 
 way of experiment,) but in heating it together with another 
 substance, nitre, which yields oxygen in sufficient abundance to 
 render the combustion in common air rapid and complete. 
 
 Caroline. This substance, then, answers the same purpose 
 as oxygen gas ? 
 
 Jtirs. B. Exactly. In manufactures the combustion is per- 
 formed in a leaden chamber, with water at the bottom, to re- 
 ceive the vapour and assist its condensation. The combustion 
 is, however, never so perfect but that a quantity of sulphure- 
 ous acid is formed at the same time ; for you recollect ihat the 
 sulphureous acid according to the chemical nomenclature, dif- 
 fers from the sulphuric only by containing less oxygen. 
 
 From its own powerful properties, and from the various com- 
 binations into which it enters, sulphuric acid is of great impor- 
 tance in many of the arts. 
 
 It is used also in medicine in a state of great dilution; for 
 were it taken internally, in a concentrated state, it would prove 
 
 : son. 
 o,,, ., t .,oii would bum the throat and stomach. 
 
204 OF THE SULPURIC AND SULPHUREOUS ACIDS. 
 
 Mrs. B. Can you think of any thing that would prove aii 
 antidote to this poison ? 
 
 Caroline. A large draught of water to dilute it. 
 
 Mrs. B. That would certainly weaken the caustic power o? 
 the acid, but it would increase the hrat to an intolerable degree. 
 Do you recollect nothing that wpuld destroy its deleterious prop- 
 erties more effectually ? 
 
 Emily. An alkali might, by combining with it ; but, then, a 
 pure alkali is itfelf a poison, on account of its causticity. 
 
 Mrs. B. There is no n ecessity that the alkali should be cans- 
 tic. Soap, in which it is combined with oil ; or magnesia, ei- 
 ther in the 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 sulphureows 
 acid, which we have found to be the product of sulphur slowly 
 and imperfectly burnt. This acid is distingusshed by its pun- 
 gent smell, and its gaseous foim. 
 
 Caroline. Its aeriform state is, I suppose, owing to the smal- 
 ler proportion of oxygen, which renders it lighter than sulphu- 
 nc acid ? 
 
 Mrs. B. Probably ; for by adding oxygen to the weaker ac- 
 id, it may be converted into the stronger kind. But this 
 change of state may also be connected with a change of affiiii- 
 ty with regard to caloric. 
 
 Emily. And may sulphureous acid be obtained from sulphu- 
 ric acid by a diminution of oxygen ? 
 
 Mrs. B. Yes; it can be done by bringing any combustible 
 substance in contact with the acid. This decomposition 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 sulphureous, and flies off in its gaseous 
 form. 
 
 Caroline. And cannot the sulphureous acid itself be decom- 
 posed and reduced to sulphur ? 
 
 Mrs. B. Yes ; if this gas be heated in contact with charcoal, 
 the oxygen of the gas will combine with it, and the pure sui-. 
 phur is regenerated. 
 
 Sulphureous acid is readily absorbed by water ; and in this 
 liquid state it is found particularly useful in bleaching linen and 
 woollen cloths, arid is much used in manufactures for those pur- 
 poses, J can show you its effect in destroying colours, by ta 
 
OP THE SULPHATS. 205 
 
 king out vegetable stains I think I see a spot on your gown, 
 Emily, on which we may try the experiment. 
 
 Emihf. 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 produced on that of Caroline 
 
 J.r*. b. There is no such danger from the sulphureous; but 
 the experiment must be made with great caution, for during the 
 formation of sulphureous acid by combustion, there is always 
 some sulphuric produced. 
 
 Caroline. But where is your sulphureous acid ? 
 
 Mrs. B. We may easily prepare some ourselves, simply by 
 burning a match ; we must first wet the stain with water, and 
 now hold it in this way, at a little distance, over the lighted 
 match : the vapour that arises from it is sulphureous acid, and 
 the stain, you see, gradually disappears. 
 
 Emily. I have frequently taken out stains by this means, 
 without understanding the nature of the process. But why is 
 it necessary to wet the stain before it is exposed to the acid 
 fumes ? 
 
 Mrs. B. The moisture attracts and absorbs the sulphureous 
 acid $ and it serves likewise to dilut? any particles of sulphu- 
 ric 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 ex- 
 posure to the atmosphere, without any elevation of tempera- 
 ture : 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 say a few 
 words of its principal combinations. It unites with all the al- 
 kalies, alkaline earths and metals, to form compound salts. 
 
 Caroline. Pray, give me leave to interrupt you for a mo- 
 ment : you have never mentioned any other salts than the 
 compound or neutral salts ; is there no other kind ? 
 
 Mrs. B. The term salt has been used, from time immemo- 
 rial, as a kind of general name for any substance that has sa- 
 vour, odour, is soluble in water, and crystallisable, whether it 
 be of an acid, an alkaline, or compound nature; but the com- 
 pound salts alone retain that appellation in modern chemistry. 
 
 The most important of the salts, formed by the combinations 
 of the sulphuric acid, are, first, sulphat of potash, formerly 
 called sal polycrest : 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 the immediate combination of sut 
 
 19 
 
206 OP THE SULPHATS- 
 
 phuric acid and potash. This salt is easily soluble in boiling 
 water. Solubility is, indeed, a property common to all salts ; 
 and they always produce cold in melting. 
 
 Emily. That must be owing to the caloric which they ab- 
 sorb in passing fiom a solid to a fluid form. 
 
 Airs. B. That is, certainly, the most probable explanation. 
 
 Sulphat of soda, commonly called Glauber's salt, is another 
 medicinal salt, which is still more bitter than the preceding. 
 We must prepare some of these compounds, that you may ob- 
 serve the phenomena which take place during their formation. 
 We need only pour some sulphuric acid over the soda which I 
 have put into this glass. 
 
 Caroline. What an amazing heat is disengaged ! I thought 
 you said that cold was produced by the melting of salts ? 
 
 Mrs. B. But you must observe that we are now making, not 
 melting' a salt. Heat is disengaged during the formation of 
 compound salts, and a faint light is also emitted, which may 
 sometimes be perceived in the dark. 
 
 Emily. And is this heat and light produced by the union of 
 the two opposite electricities of the alkali and the acid ? 
 
 Mrs. B. No doubt it is, if that theory be true. 
 
 Caroline. The union of an acid a;id an alkali is then an ac- 
 tual combustion ? 
 
 Mrs. B. Not precisely, though there is certainly much anal- 
 ogy in these processes. 
 
 Caroline, Will this sulphat of soda become solid ? 
 
 Mrs. B. We have not, I suppose, mixed the acid and the al- 
 kali in the exact proportions that are required for the formation 
 of the salt, otherwise the mixture would have been almost im- 
 mediately changed to a solid 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 to evaporate the 
 water, during which operation the salt would gradually crystal- 
 lise. 
 
 Caroline. But of what use is the addition of water, if it is 
 afterwards to be evaporated ? 
 
 Mrs. b. When suspended in water, the acid and the alkali 
 :ire more at liberty to act on each other, their union is more 
 complete, and the salt assumes the regular form of crystals du- 
 ring 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 effloresces? 
 I do not recollect your having mentioned it before. 
 
 Mrs. />. A salt is said to effloresce when it loses its water of 
 crystallisation on being exposed to the atmosphere, and is thus 
 
jf THE 
 
 gradually converted iuto a dry pow:ler : 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 their surface of 
 its lustre, by absorbing its water of crystallisation. Salts are, 
 ai general, either efflorescent or'deliquescent ; this latter prop- 
 erty is precisely the reverse of the former ; that is to say, de- 
 liquescent salts absorb water from the atmosphere, and are 
 snoistened and gradually melted by it. Muriat of lirne is an 
 instance of great deliquescence. 
 
 Emily. But are there no salts that have the same degiee of 
 attraction for water as the atmosphere, and that will conse- 
 quently 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 gypsum, or plaster 
 of Parts. 
 
 Sulphat of magnesia, commonly called Epsom salt, is ano- 
 ther very bitter medicine, which is obtained from sea-water and 
 from several springs, or may be prepared by the direct combi- 
 nation of its ingredients. 
 
 We have formerly mentioned sulphat of alumine as consti- 
 tuting the common alum ; it is found in nature chiefly in the 
 neighbourhood of volcanoes, and is particularly useful in the 
 arts, from its strong astringent qualities. It is chiefly employed 
 by dyers and calico-printers, to fix colours ; and is used also in 
 the manufacture of some kinds of leather. 
 
 Sulphuric acid combines also with the metals. 
 
 Caroline. One of these combinations, Sulphat of iron, we 
 are already w< j ll acquainted with. 
 
 Mrs. 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 affords a very 
 valuable tonic : it is of this salt that most of those preparations 
 called steel medicines are composed. 
 
 Caroline. But does any carbon enter into these compositions 
 to form steei ? 
 
 Mrs. B. Not an atom : they are, therefore, very improperly 
 called steel : but it is the vulgar appellation; and medical meft 
 themselves often comply with the general custom. 
 
 Sulphat of iron may be prepared, as you have seen, by dis- 
 solving iron in sulphuric acid ; but it is generally obtained 
 Jro.m the natural production called Pyrites, which being a sul- 
 
208 
 
 OP THE SULFHATS. 
 
 phuret of iron, requires only exposure to the atmosphere to be 
 oxydaied, in order to form the salt ; this, therefore, is much the 
 most easy way of procuring it on a large scale. 
 
 Emily. I a.n surprised to find that both acids and compound 
 salts are generally obiai iied from their various combinations, 
 ^rather than from ihe immediate union of their ingredients. 
 
 Mrs. B. Were the simple bodies always at hand, their com- 
 binations would natur-dlly be the most convenient method of 
 forming compounds; but you must consider that, in most in- 
 stances, ihere is great difficulty and expense in obtaining the 
 simple ingredients from their combinations; it is, therefore of- 
 ten more expedient to procure compounds from the decomposi- 
 tion of other compounds. But, to return to the sulphat of iron. 
 There is a certain vegetable acid called Gallic add, which 
 has the remarkable property of precipitating this salt black I 
 shall pour a few drops of the gallic acid into this solution of sul- 
 phat 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 colour 
 is owing to the formation of gallar of iron, which being insolu- 
 ble, renviins suspended in the fluid. 
 
 This arid has also the property of altering the colour of iron 
 in its metallic state. You may frequently see its effect on the 
 blade of a kniie, that has been used to cut certain kinds of 
 fruits. 
 
 Caroline. True; and that is, perhaps, the reason that a sil- 
 ver knife is preferred to cut fruits; the gallic acid, I suppose, 
 does not act upon silver. Is this acid found in all fruits ? 
 
 Mrs. B. It is contained, more or less, in the rind of cnost 
 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 same time blackened. But the 
 vegetable substance in which the gallic acid most abounds is 
 nutgall, a kind of excrescence that grows on oaks, and from 
 which the acid is commonly obtained for its various purposes. 
 
 M-'s. '3. W*i n;nv come to the PHOSPHORIC ami PHOSPHOROUS 
 ACIDS. In treating of phosphorus, you have seen how these 
 acids may be obtained from it by combustion ? 
 
 Emily YXs ; 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. 
 
 Mrs. You are right, my dear ; the phosphoric acid, for 
 general purposes, is extracted from bones, in which it is contain 
 
OF THE NITRIC AND NITROUS ACIDS. 209 
 
 e<j in the state of phosphat of lime ; from this salt the phos- 
 phoric acid is separated by means of the sulphuric, which com- 
 bines with the lime* In its pure state, phosphoric acid is either 
 liquid or solid, according to its degree of concentration. 
 
 Among the salts formed by this acid, phosphat of lime is 
 the only one that affords much interest ; and this, we have al- 
 ready observed, constitutes the basis of all bones. It is also 
 found in very small quantities in some vegetables. 
 
 CONVERSATION XVIII. 
 
 OF THE NITRIC AND CARBONIC ACIDS ; OR THE COM- 
 BINATIONS OF OXYGEN WITH NITKOGEN AND CAR- 
 BON; AND OF THE Nl FilATS AND CARBONA PS. 
 
 Mrs. B. I AM almost afraid of introducing the subject of the 
 NITRIC ACID, as I am sure that I shall be blamed by Caroline 
 for not having made her acquainted with it before. 
 
 Caroline. Why so, Mrs. B. ? 
 
 Mrs. B. Because you have long known its radical, which is 
 nitrogen or azote; and in treating of that element, I did not ev- 
 en hint that it was the basis of an acid. 
 
 Caroline. And what could be your reason for not mention- 
 nig 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 may recollect that ni- 
 trogen was one of the first simple bodies which we examined i 
 you were then ignorant of 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 at- 
 tempted to explain the nature and' formation of acids. 
 
 Caroline. I wonder, however, that it never occurred to us to 
 enquire whether nitrogen could be acidified ; for, as we knew 
 it was classed among the combustible bodies, it was natural to 
 suppose that it might produce an acid. 
 
 Mrs. B. That is not a necessary consequence : for it might 
 combine with oxygen only in the degree requisite to form an 
 oxyd. But you will find that nitrogen is susceptible of various 
 degrees of oxygenation, some of which convert it merely into 
 an oxyd, and others give it all the acid properties. 
 
 The acids, resulting from the combination of oxygen and ni- 
 19* 
 
210 
 
 OF THE MTfilL 
 
 trogen, are called the NITROUS and NITRIC acids. We will be 
 gin with the NITRIC, in which nitrogen is in the highest state of 
 OK.ypnation. This acid naturally exists in the form of gas ; 
 b.u is so very soluble in water, and has so great an affinity for it' 
 that one grain 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 ! 
 
 Mrs. Ji. 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 exact- 
 ly 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 charcoal* you see it inflames it immedi- 
 ately ; it would do the same with oil of tupentine, phosphorus, 
 and several other very combustible bodies. This shows you 
 how easily this acid is decomposed by combustible bodies, since 
 these effects must depend upon the absorption of its oxygen. 
 
 JNitric acid has been used in the arts from time immemori- 
 al, but it is only within these twenty-five years that its chemical 
 nature has been ascertained. The celebrated Mr. Cavendish dis- 
 covered that it consisted of about 10 parts of nitrogen and 25 
 of oxygen.t These principles, in the gaseous state, combine at 
 a high temperature ; and this may be effected by repeatedly 
 passing the electrical spark through a mixture of the two gases. 
 
 Emily. The nitrogen and oxygen gases, of which the atmos- 
 phere is composed, do not combine, I suppose, because their 
 temperature is not sufficiently elevated ? 
 
 Caroline. But in a thunder-storm, when the lightning re- 
 peatedly passes through them, may it not produce nitric acid ? 
 W 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 
 
 * To inflame charcoal, a stronger acid than that sold at the shops is 
 necessary. The experiment, with ol. turpentine and phosphorus, suc- 
 ceeds, if about a sixth part ofsuiph. acid is added to the nitric acid. 
 The experiment with the turpentine requires caution. The vial con- 
 taining the acid must be tied to a stick, a yard or two long, the opera- 
 tor pouring it into a small quantity of the turpentine standing at a 
 distance. C. 
 
 t The proportion stated by Sir H. Davy, in his Chemical Research- 
 es, is as i to 2,389. 
 
AND NITROUS ACIDS. 211 
 
 eau effect but a very small portion of the atmosphere, and 
 though it were occasionally to produce a little nitric acid, yet 
 this never could happen to such an extent as to be perceivable. 
 
 Emily. But how could the nitric acid be known, and used, 
 before the method of combining its constituents was discovered ? 
 
 ^V/r. B. Before that period the nitric acid was obtained, and 
 it is indeed still extracted, for the common purposes of art, from 
 tke compound salt which it forms with potash, commonly call- 
 ed nitre. 
 
 Caroline. Why is it so called ? 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 especially those 
 which are yet in common use ; otherwise, when you meet with 
 them, you would not be able to understand their meaning. 
 
 Emily. And how is the acid obtained from this salt ? 
 
 Mrs. B. By the intervention of sulphuric acid, which com- 
 bines with the potash, and sets the nitric acid at liberty. This 
 I can easily show you, by mixing some nitrat of potash and sul- 
 phuric acid in this retort, and heating it over a lamp ; the nitric 
 acid will come over in the form of vapour, which we shall col- 
 lect in a glass bell. This acid, diluted in water, is commonly 
 called aquafortiSj if Caroline will allow me to mention that 
 name. 
 
 Caroline. I have often heard that aqua fortis will dissolve al- 
 most all metals ; it is no doubt because it yields its oxygen so 
 easily. 
 
 Mrs* B. Yes ; and from this powerful solvent property, it 
 derived the name of aqua fortis, or strong water. Do you not 
 recollect that we oxydated, and afterwards dissolved, some cop- 
 per 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 decomposed and 
 converted into nitrogen and oxygen ? 
 
 Emily. That cannot be the case, Caroline ; since the acid 
 can be decomposed only by the combination of its constituents 
 ivith other bodies. 
 
 . Wrs. B. True ; but caloric is sufficient for this purpose. By 
 making the acid pass through a red hot porcelain tube, it is de- 
 composed ; the nitrogen and oxygen regain the caloric which 
 they had lost in combining, and are thus both restored to their 
 gaseoHS state, 
 
212 -OS 1 THE NITRIC 
 
 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 ox- 
 ygen 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, ^.nd 
 thus be converted into nitrous acid. Of this acid there are va- 
 rious degrees, according to the proportions of oxygen which it 
 contains ; the strongest, and that into which the nitric is first 
 converted., is of a yellow colour, as you see in this bottle. 
 
 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 es- 
 caping. 
 
 Here is another bottle of nitrous acid, which, you see, is of an 
 orange red ; this acid is weaker, the nitrogen being combined 
 with a smaller quantity of oxygen ; and with a still less propor- 
 tion 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 inflammable 
 substances than the nitric. 
 
 Emily. \ am surprised at that, as it contains less oxygen. 
 
 Mr*. B. But, on the other hand, it parts with its oxygen 
 much more readily : you may recollect that we once inflamed 
 oil with this acid. 
 
 The next combinations of nitrogen and oxygen form only 
 oxyds of nitrogen, the first of which is commonly called nitrous 
 air ; or more properly nitric oxydgas.* This may be obtain- 
 ed from nitric acid, by exposing the latter to the action of met- 
 als, as in dissolving them it does not yield the whole of its oxy- 
 gen, but retains a portion of this principle sufficient to convert 
 it into this peculiar gas, a specimen of which I have prepared, 
 and preserved within this inverted glass bell. 
 
 Emily. It is a perfectly invisible elastic fluid. 
 
 Mrs. B. Yes; and it may be kept any length of time in this 
 manner over water, as it is not, like the nitric and nitrous acids, 
 absorbable by it. It is rather heavier than atmospherical air, 
 and is incapable of supporting either combustion or respiration, 
 
 * To procure nitrous air put. into a retort some filings, or shavings of 
 copper, on which pour nitric acid, diluted with four or five parts of 
 water ; then apply the heat of a lamp, and receive the gas ia the usu- 
 al way, over water, C, 
 
AND NITROUS AClDb. 2lo 
 
 t 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 ! that is the more extraordinary, as the gas 
 within the glass is perfectly invisible. 
 
 Mrs. B. It would give me much pleasure if you could make 
 out the reason of this curious change without requiring any fur- 
 ther explanation. 
 
 Caroline. It seems, by the colour and smell, as if it were con- 
 verted into nitrous acid gas ; yet that cannot be, unless it com- 
 bines with more oxygen ; and how can it obtain oxygen the 
 very instant it escapes from the glass ? 
 
 Emily. From the atmosphere, no doubt. Is it not so, Mrs* 
 B.r 
 
 Mrs. B. You have guessed it 5 as soon as it comes in contact 
 with the atmosphere, it absorbs from it the additional quantity 
 of oxygen necessary to convert it into nitrous acid gas. And, 
 if I now remove the bottle entirely from the water, so as to 
 bring at once the whole of the gas into contact with the atmos- 
 phere, this conversion will appear still more striking 
 
 Emily. Look, Caroline, the whole capacity of the bottle is 
 instantly tinged of an orange colour ! 
 
 Mrs. B. Thus, you see, it is the most easy process imagina- 
 ble to convert nitrous oxyd gas into nitrous acid gas. The 
 property of attracting oxygen from the atmosphere, 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 tube, which is closed at 
 one end, (PLATE X. fig. 2.) 1 first fill it with water, and then 
 introduce a certain measure of nitrous gas, which, not being ab- 
 sorbable by water, passes through it, and occupies the upper 
 part of the tube. I must now add rather above two-thirds of 
 oxygen gas, which will just be sufficient to convert the nitrous 
 oxyd gas into nitrous acid gas. 
 
 Caroline. So it has ! I saw it turn of an orange colour ; but 
 it immediately afterwards disappeared entirely, and the water, 
 you see, has risen, and almost filled the tube. 
 
 Mrs. B. That is because the acid gas is absorbable by wa- 
 ter, and in proportion as the gas impregnates the water, the lat- 
 ter rises in the tube. When the oxygen gas is very pure, and 
 the required proportion of nitrous oxyd gas very exact, the 
 whole is absorbed by the water; but if any other gas be mixed 
 with the oxygen, instead of combining with the nitrous oxygen, 
 it will remain and occupy the upper part of the tube 5 or if thr 
 
214 OP THE NITRIC 
 
 gases be not in the due proportion, there will be a residue o* 
 that which predominates. Before we leave this subject, I must 
 not forget to remark that nitrous acid may be formed by dissol- 
 ving nitrous oxyd gas in nitric acid. This solution may be ef- 
 fected simply by making bubbles of nitrous 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 nitrous acid. 
 
 '/rs. S3. You have stated the fact with great precision. 
 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 men- 
 tion another curious modification of oxygenated nitrogen, whHi 
 has been distinguished by the name of gaseous oxyd of nitro- 
 gen. It is but lately that this sjas has been m finitely examin- 
 ed, and its properties have been investigated ''' iiy by Sir H. 
 Davy. It has obtained also the narii^ of ."M^ aas, 
 
 from the very singular property which that : > v n lias ijs- 
 covered in it, of elevating the animal spirits, w : .aled into 
 
 the lungs, to a degree sometimes resembling delirium or into AH 
 cation. 
 
 Caroline. Is it respirable, then ? 
 
 Mrs. B. It can scarcely be called respirtMp, RS it would not 
 support life for any length of time; but it m..'\ be hrf-u^ <! for 
 a few moments without any other effects, than th^smjuhr ex- 
 hilaration of spirits I have just mentioned. It rjff^is dlff-rent 
 people, however, in a very different manner. Some be.\, -re 
 violent, even outrageous; others experience a languor, atten-.led 
 with faintness ; but most a^ree in opinion, th.it the sensations it 
 excites are extremely pleasant. 
 
 Caroline. I think I should like to try it how do you breathe 
 it? 
 
 Mrs. B. By collecting the gas in a bladder, to which a short 
 tube with a stop-cock is adapted; this is applied to the month 
 with one hand, whilst the nostrils are kept closed \vith tbeotijt-r, 
 that the common air may have no access. You then altermire- 
 ly inspire, and expire the gas, till you perceive its effects. I'iit 
 I cannot consent to your making the experiment; for i!>e 
 nerves are sometimes unpleasantly affected by it, and I wn 'id 
 not run any risk of that kind. 
 
 Emily. I should like, at least, to see somebody breathe it 5 
 but pray by what means is this curious gas obtained ? 
 
AND NITROUS ACID!), 215 
 
 Mrs. H It is procured from nitrut of ammonia,* an artifi- 
 cial 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 extricated. 
 
 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 need not be preser- 
 ved, as it consists of little more than the common air that was 
 in th*> 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 proceed ? There 
 is no water in nitrat of ammonia? 
 
 Mrs. B. You must recollect that there is in every salt a quan- 
 tity of water of crystallisation, which may be evaporated by 
 heat alone. But, besides this, ^water is actually generated in 
 this experiment, as you will see presently. First tell me, what 
 are the constituent parts of nitrat of ammonia ? 
 
 Emily. Ammonia, and nitric acid ; this salt, therefore, con- 
 tains 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 decom- 
 
 * To make nitrate of ammonia, take some nitric acid, or aquafor- 
 tis dilute it with four, or five parts of water ; put it into a shallow 
 earthen dish, and throw in pieces of carbonate of ammonia, until the 
 effervescence ceases. Evaporate about one third of the liquor by a 
 gentle heat, and set it away to crystallize. The crystals are long stri- 
 ated prisms. To procure the nitrous oxide, or exhilarating gas, and 
 to try its effects by respiration, the following simple apparatus may be 
 used, where a better is not at hand. Put some nitrate of ammonia 
 into an oil flask, having first fitted to it a cork, and glass tube, bent 
 so as to go under the receiver in the water bath. Then apply the gen- 
 tle heat of a lamp. 
 
 For a receiver, fill a large jug with water, and invert it in the water 
 bath : have fitted to the jug a cork, having two holes made 
 through it with a burning iron ; into one of these holes put a glass tube 
 open at both ends, and nearly long enough to reach the bottom of the 
 jug. Provide a large bladder furnished with a short tube tied to it. 
 When the jug is nearly filled with the gas, remove, and set it upright 
 by passing the hand under its mouth then put in the cork and tube, 
 the other opening in the cork being closed. When you wish to breathe 
 the gas, take the stopper out of the cork, and pass in the tube attach- 
 ed to the bladder. Then by means of a small tunnel, pour water into 
 the jug through the long tube, until! itdrivs out gas enough to fill the 
 bladder. Mrs. B. describes the manner of oreathing it. 
 
 Caution. Let the gas stand an hour or two over water before it is 
 breathed. C. . 
 
OF THE NITRATS. 
 
 posed ; the hydrogen quits the nitrogen to combine with soni' 
 of the oxygen of the nitric acid, and forms with it the waters 
 vapour which is now coming over. When that is effected. 
 what will you expect to find ? 
 
 Emily. Nitrous acid instead of nitric acid, and nitrogen in- 
 stead of ammonia. 
 
 Mrs. B. Exactly so ; and the nitrous acid and nitrogen com- 
 bine, and form the gaseous oxyd of nitrogen, in which the pro- 
 portion of oxygen is 37 parts to 63 of nitrogen. 
 
 You may have observed, that for a little while no bubbles oi 
 air have come over, and we have perceived only a stream of 
 vapour condensing as it issued into the water. Now bubbles 
 of air again make their appearance, and I imagine that by this 
 time all the watery vapour is come away, and that we may be- 
 gin to collect the gas. We may try whether it is pure, by fill- 
 ing a phial with it, and plunging a taper into it yes, it will do 
 now, for the taper burns brighter than in the common air, and 
 with a greenish flame. 
 
 Caroline. But how is that ? I thought no gas would support 
 combustion but oxygen or chlorine. 
 
 Mrs. B. Or any gas that contains oxygen, and is ready to 
 yield it, which is the case with this in a considerable degree: 
 it is not, therefore, surprising that it should accelerate the com- 
 bustion of the taper. 
 
 You see that the gas is now produced in great abundance: 
 we shall collect a large quantity of it, and I dare say that we 
 shall find some of the family who will be curious to make the 
 experiment of respiring it. Whilst this process is going on, 
 we may take a general survey of the most important combina- 
 tions of the nitric and nitrous acids with the alkalies. 
 
 The first of these is nitrat of potash commonly called nitre 
 or saltpetre. 
 
 Caroline. Is not that the salt with which gunpowder is made r 
 
 Mrs B. Yes. Gunpowder is a mixture of five parts of ni- 
 tre 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 detonation of 
 gunpowder when set fire to ? 
 
 Mrs. B. Detonation may proceed from two causes ; the sud- 
 den formation or destruction of an elastic fluid. In the first 
 case, when either a solid or liquid is instantaneously 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. 
 
OF THE N I Tit AT 8. l 
 
 Caroline. That I comprehend very well ; but how can a 
 similar effect be produced by the destruction of a gas ? 
 
 Mrs.- B. A gas can be destroyed only by condensing it to u 
 liquid or solid state ; when this takes place suddenly, the gas, 
 in assuming a new and more con pact form, produces a vacuum, 
 into which the surrounding air rush-s with great impetuosity; 
 and it is by that rapid and violent motion that the sound is pro- 
 duced. In all detonations, therefore, gases are either suddenly 
 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 gases in its detonation ; but how, I cannot tell. 
 
 Mrs* 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 gases, the sud- 
 den expansion of which gives rise to the detonation. 
 
 Caroline. And in what instance does the destruction or con- 
 densation of gases produce detonation ? 
 
 Mrs. B. I can give you one with which you are well ac- 
 quainted 5 the sudden combination of the oxygen and hydrogen 
 gases. 
 
 'Caroline. True ; I recollect perfectly that hydrogen de- 
 tonates with oxygen when the two gases are converted into 
 water. 
 
 Mrs. B. But let us return to the nitrat of potash. This salt 
 is decomposed when exposed to heat, and mixed with any com- 
 bustible body, such as caibon, sulphur, or metals, these substan- 
 ces oxydating rapidly at the expense of the nitrat. I must show 
 you an instance of this. I expose to the fire some of the salt in 
 a small iron ladle, and, when it is sufficiently heated, add to it 
 some powdered charcoal ; this will 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 detonations, which, to 
 gether with the emission of flame, is called deflagration. 
 
 Nitrat of ammonia we have already noticed, on account of 
 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 of- 
 ten used by surgeons. We have said so much on a former oc- 
 casion, on the mode in which caustics act on animal matter, 
 ihat I shall not detain you any longer on this subject, 
 20 
 
218 CARBONIC ACID. 
 
 We now come to the CARBONIC ACID, which we have airea* 
 dy had many opportunities of noticing. You recollect that this 
 acid may be formed by the combustion of carbon, whether in 
 its imperfect state of charcoal, or in its purest form of diamond. 
 And it is not necessary, for this purpose, to burn the carbon in 
 oxygen gas, as we did in the preceding lecture ; for you need 
 only light a piece of charcoal and suspend it under a 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 oxygen gas. 
 
 Caroline. But how can you separate the carbonic acid, ob- 
 tained in this manner, from the air with which it is mixed ? 
 
 Mrs. ft. The readiest mode is to introduce under the receiver 
 a quantity of caustic lime, or caustic alkali, 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 dimin- 
 ished by a quantity equal to that of the carbonic acid which was 
 mixed with it. 
 
 Emily. Pray is there no method of obtaining pure carbon 
 from carbonic acid ? 
 
 Mrs. B. For a long time it was supposed that carbonic acid 
 was not decompoundable; but Mr. Tennant discovered, a few 
 years ago, that this acid may be decomposed by burning phos- 
 phorus in a closed vessel with carbonat of soda or carbonat of 
 lime: the phosphorus absorbs the oxygen from the carbonat, 
 whilst the carbon is separated in the form of a black powder. 
 This decomposition, however, is not effected simply by the at- 
 traction of the phosphorus for oxygen, since it is weaker than 
 that of charcoal ; but the attraction of the alkali or lime for the 
 phosphoric acid, unites its power at the same time. 
 
 Caroline. Cannot we aiake that experiment ? 
 
 Mrs. /->. Not easily ; it requires being performed with ex- 
 treme nicety, in order to obtain any sensible quantity of carbon, 
 and the experiment is much too delicate for me to attempt it. 
 But there can be no doubt of the accuracy of Mr. Tenmint's re- 
 sults ; and all chemists now agree, that one hundred parts of 
 carbonic acid gas consists of about twenty-eight parts of carbon, 
 to seventy-two of oxygen gas. But if you recollect, we decom- 
 posed carbonic acid gas the other day by burning potassium 
 in it. 
 
 Caroline. True, so we did ; and found the carbon precipita- 
 ted on the regenerated potash. 
 
 Mrs. B. Carbonic acid gas is found very abundantly in tia- 
 ture 5 it is supposed to form about one thousandth part of the 
 
CARBONIC ACID. 21 
 
 atmosphere, and is constantly produced by the respiration of 
 animals ; it exists in a great variety of combinations, and is ex- 
 haled from many natural decompositions. 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 
 of the cruel experiments made on the poor dogs, to gratify the 
 curiosity of strangers. But 1 understood that the vapour exha- 
 led by this cave was called Jixed air. 
 
 Mrs. B. That is the name by which carbonic acid was known 
 before its chemical composition was discovered. 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 ex- 
 tinguishes 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 
 the light as it were by enchantment, as the gas is invisible. I 
 never should have imagined that gas could have been poured 
 like a liquid. 
 
 Mrs. tt. It can be done with carbonic acid only, as no other 
 :^as is sufficiently heavy to be susceptible of being poured out in 
 she atmospherical air without mixing with it. 
 
 Emily. Pray by what means did you obtain this gas ? 
 
 Mrs. 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 carbonats. 
 Combined with lime, this acid forms chalk, which may '>e con- 
 sidered as the basis of all kinds of marbles, and calcareous 
 stones. From these substances carbonic acid is easily separa- 
 ted, as it adheres so slightly to its combinations, that the carbo- 
 nats are all decomposable by any of the other acids. I can easi- 
 iy show you how I obtained this gas ; I poured some diluted 
 sulphuric acid over pulverised marble in this bottle (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 perceive 
 
 Emily. Yes, it does; there is a great fermentation in the glass 
 vessel. What singular commotion is excited by the sulphuric 
 acid taking possession of the lime, and driving out the carbonic 
 acid ! 
 
 * Merely pouring it over a candle, will not extinguish it. Put ft 
 short piece of candl -, or taper, into the bottom of a deep tumbler, arid 
 then pour in the gas and the flame goes out as quick!/ as though you 
 poured in water. C. 
 
*0 GARBOJSIC AC11>. 
 
 Caroline. But did the carbonic acid exist in a gaseous stait 
 in the marble ? 
 
 Mrs. B. Certainly not ; the acid, when in a state of combi- 
 nation, is capable of existing in a solid form. 
 
 Caroline. Whence, then, does it obtain the caloric necessary 
 to convert it into gas ? 
 
 ,'Vfrs. B. It may be supplied in this case from the mixture of 
 sulphuric acid and water, which produces and evolution of heat, 
 even greater than is required for the purpose; since, as you 
 may perceive by touching the glass vessel, a considerable quan- 
 tity 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 th disengagement of carbonic acid gas, which 
 do not, like the sulphuric, produce heat on being mixed with 
 water. Carbonic acid may likewise 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 the burning of wood and coals should 
 exist also in such bodies as marble, and chalk, which are in- 
 combustible substances. 
 
 Jtor*. B. I will not answer that objection, Caroline, because 
 I think I can put you in a way of doing it yourself. Is carbo- 
 nic acid combustible ? 
 
 Caroline. Why, no because it is a body which has been al- 
 ready burnt ;* it is carbon only, and not the acid, that is com- 
 bustible. 
 
 Mrs. B. Well, and what inference do you draw from this ? 
 
 Caroline. That carbonic acid cannot render the bodies with 
 which it is united combustible ; but that simple carbon does, 
 and that it is in this elementary state that it exists in wood, 
 coals, and a great variety of other combustible bodies. Indeed, 
 Mrs. B., you are very ungenerous; you are not satisfied with 
 convincing me that my objections are frivolous, but you ob'ige 
 me to prove them so myself. 
 
 Mrs. B. You must confess, however, that I make ample 
 amends for the detection of error, when I enable you to dis- 
 cover the truth. You understand, now, I hope, that carbonic 
 acid is equally produced by the decomposition of chalk, or by 
 
 * Not burnt in the common acceptation of the word. The carbon 
 is already united to oxygen : and therefore has no affinity for it. IP 
 the artificial production of carbonic acid, the carbon is burnt f. 
 
CA&BONIC ACID. 221 
 
 f.he combustion of charcoal. These processes are certainly of 
 a very different nature; in the first case the acid is already for- 
 med, and requires nothing more than heat to restore it to its gas- 
 eous state , whilst, in the latter, the acid is actually made by 
 the process of combustion. 
 
 Caroline. I understand it now perfectly. But I have just 
 been thinking of another difficulty, which, I hope, you will ex- 
 cuse my not being able to remove myself. How does the irn 
 mense quantity of calcareous earth, which is spread all over the 
 globe, obtain the carbonic acid with which it is combined ? 
 
 Mrs. B. The question is, indeed, not very easy to answer; 
 but I conceive that the general carbonisation of calcareous 
 matter may have been the effect of a general combustion,* oc- 
 casioned by some revolution of our globe, and producing an 
 immense supply of carbonic acid, with which the calcareous 
 matter became impregnated'; or that this may have been effect- 
 ed by a gradual absorption of carbonic acid from the atmos- 
 phere But this would lead us to discussions which we cannot 
 indulge in, without deviating too much from our subject. 
 
 Emily. How does it happen that we do not perceive the per- 
 nicious effects of the carbonic acid which is floating in the at- 
 mosphere ? 
 
 ,'V/rs. B. Because of the state of very great dilution in which 
 it exists there. Hut can you tell me, family, what are the sour- 
 ces which keep the atmosphere constantly supplied with this 
 acid ? 
 
 Emily. I suppose the combustion of wood, coals, and other, 
 substances, that contain carbon. 
 
 J\lrs. B. And also the breath of animals. 
 
 Caroline. The breath of animals ! I thought you said that 
 diis gas was not at all respirable, but on the contrary, extreme- 
 ly poisonous. 
 
 rfirs. ti. So it is ; but although animals cannot breathe in 
 carbonic acid gas, yet, in the process of respiration, 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 
 certain 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 ? 
 
 * This idea is at random. We cannot account for the origin of car- 
 bonic acid in its native, state any better than we can for oxygen. It 
 catm-.t '>e the product of combustion, since it existed before the growth 
 f combustible materials. C, 
 
 20* 
 
CARBONIC ACll?- 
 
 Mrs. B. The manner in which this gas destroys life, seem* 
 to be merely by preventing the access of respirable air ; tor 
 carbonic acid gas, unless very much diluted with common air- 
 does not penetrate into the lungs, as the windpipe actually con- 
 tracts and refuses it admittance. But we must dismiss this sub- 
 ject at present, as we shall have an opportunity of treating of 
 respiration much more fully, when we come to the chemical 
 functions of animals. 
 
 Emily. Is carbonic acid as destructive to the life of vegeta- 
 bles as it is to that of animals ? 
 
 Airs. B. If a vegetable be completely immersed in it, I be- 
 lieve it generally proves fatal to it ; but mixed in certain pro- 
 portions with atmospherical air, it is, on the contrary, very fa- 
 vourable to vegetation. 
 
 You remember, I suppose, our mentioning the mineral wa- 
 ters, both natural and artificial, which contain carbonic acid 
 gas? 
 
 Caroline. You mean the Seltzer water ? 
 
 Mrs. B. That is one of those which are the most used ; 
 there are, however, a variety of others into which carbonic acid 
 enters as an ingredient : all these waters are usually distinguish- 
 ed by the name of acidulous or gaseous mineral waters. 
 
 The class of salts called carbonats is the most numerous in 
 nature ; we must pass over them in a very cursory manner, as 
 the subject is far too extensive for us to enter on it in detail. 
 The state of carbonat is the natural 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 almost always found comb necl 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 marbles, chalks, shells, calca- 
 reous spars, and lime-stones of every description, are neutral 
 salts, in which lime, iheir common basis, has lost all its charac- 
 teristic properties. 
 
 Emily. But if all these various substances are formed by the 
 union of lime with carbonic acid, whence arises their diversity 
 of form and appearance ? 
 
 >\:rs. B. Both from the different proportions of their compo- 
 nent parts, and from a variety of foreign ingredients which may 
 be occasionally blended with them : the veins and colours of 
 marbles, for instance, proceed from a mixture of metallic sub- 
 stances ; silex and alumine also frequently enter into these com- 
 binations. The various carbonats, therefore, which J have 
 
BORACIC ACID, 
 
 enumerated, cannot be considered as pure unadultered neutral 
 salts, although they certainly belong to that class of bodies. 
 
 CONVERSATION XIX. 
 
 ON THE BORACIC, FLUORIC, MURIATIC, AND OXYGEN- 
 ATED MURIATIC ACIDS; AND ON MU11IA TS ON IO- 
 DINE AND IODIC ACID. 
 
 Mrs. B. WE now come to the three remaining acids with 
 simple bases, the compound nature of which, though long sus- 
 pected, has been but recently proved. The chief of these is 
 the muriatic; but I shall first describe the two others, as their 
 bases have been obtained more distinctly than that of the muri- 
 atic acid. 
 
 You may recollect I mentioned the BORACIC ACID. This is 
 found very sparingly in some parts of Europe, but for the use 
 of manufactures we have always received it from the remote 
 country of Thibet, where it is found in some lakes, combined 
 with soda. It is easily separated from the soda by sulphuric 
 acid, and appears in the form of shining scales, as you see 
 here. 
 
 Caroline. I am glad to meet with an acid which we need 
 not be afraid to touch; for I perceive, from your keeping it in 
 a piece of paper, that it is more innocent than our late acquaint- 
 ance, the sulphuric and nitric acids. 
 
 Airs, /n Certainly; but being more inert, you will not find 
 its properties so interesting. However its decomposition, and 
 the brilliant spectacle it affurds when its basis again unites with 
 oxygen, atones for its want of other striking qualities. 
 
 Sir H. Davy succeeded in decomposing the boracic acid, 
 (which had till then, been considered as undecornpoimdable,) 
 by various methods. On exposing this acid to the Voltaic bat- 
 tery, the positive wire gave out oxygen, and on the negative 
 wire was deposited a black substance, in appearance resemb- 
 ling charcoal. This was the basis of the acid, which Sir H. 
 Davy has called Boracium, or Boron. 
 
 The same substance was obtained in more considerable 
 quantities, by exposing the acid to a great heat in an iron gun- 
 barrel. 
 
 A third method of decomposing the boracic acid consisted in 
 burning potassium in contact with it in vacuo. The potassium 
 attracts the oxygen from the acid, and leaves its basis in a sep- 
 arate state. 
 
\ 
 
 524 FLUORIC ACID. 
 
 The F^cora position of this acid I shall show you, by burning 
 some of its basis, which you see here, in a retort full of oxygen 
 gas. The heat of a candle is all that is required for this com- 
 bustion. 
 
 Emily. The light is astonishingly brilliant, and what beauti- 
 ful sparks it throws out ! 
 
 Mrs. B. The result of this combustion is the boracic acid, 
 the nature of which, you see, is proved both by analytic and 
 synthetic means. Its basis has not, it is true, a metallic ap- 
 pearance; but it makes very hard alloys with other metals. 
 
 Emily. But pray, Mrs. B., for what purpose is the boracic 
 acid used in manufactures? 
 
 Mrs. B. Its principal use is in conjunction with soda, that is, 
 in the state of borat of soda, which in the arts is commonly 
 called borax. This salt has a peculiar power of dissolving 
 metallic oxyds, and of promoting the fusion of substances capa- 
 ble of being melted ; it is accordingly employed in various me- 
 tallic arts; it is used, for example, to remove the oxyd from the 
 surface of metals, and is often employed in the assaying of me- 
 tallic ores. 
 
 Let us now proceed to the FLUORIC ACID. This acid is ob- 
 tained from a substance which is found frequently in mines, and 
 particularly in those of Derbyshire, called Jluor, a name which 
 it acquired -fcom the circumstance of its being used to render 
 the ores of metals more fluid when heated. 
 
 Caroline. Pray is not this the Derbyshire spar of which so 
 many ornaments are made? 
 
 Mrs. R. The same; but though it has long been employed 
 for a variety of purposes, its nature was unknown vmt.il Scheele, 
 the great Swedish chemist, discovered that it consisted of lime 
 united with a peculiar acid, which obtained the name of fluo- 
 ric acid. It is easily separated from the lime by the sulphuric 
 acid, and unless condensed in water, ascends in the form of gas. 
 A very peculiar property of this acid is its union with siliceous 
 earths, which I have already mentioned. If the distillation of 
 this acid is performed in glass vessels, they are corroded, and 
 the siliceous part of the glass comes over, united with the gas; 
 if water is then admitted, part of the silex is deposited, as you 
 may observe in this jar. 
 
 Caroline. I see white flakes forming on the surface of the 
 water ; is that silex ? 
 
 Mrs. B. Yes it is. This power of corroding glass has been 
 used for engraving, or rather etching, upon it. The jrlass is 
 first covered with a coat of wax, through which the fi: urvs to 
 be engraved are to be scratched with a pin ; then pouring the 
 
MURIATIC ACID. 
 
 fluoric acid over the wax, it corrodes the glass where the 
 scratches have been made. 
 
 Caroline. I should like to have a bottle of this acid, to make 
 engravings.* 
 
 Mrs. B. But you could not have it in a glass bottle, for in 
 that case the acid would be saturated with silex, and incapable 
 of executing an engraving ; the same thing would happen were 
 the acid kept in vessels of porcehun or earthen-ware 5 this acid 
 must therefore be both prepared and preserved in vessels of 
 silver. 
 
 If it be distilled from fluor spar and vitriolic acid, in silver 
 or leaden vessels, the receiver being kept very cold during the 
 distillation, it assumes the form of a dense fluid, and in that 
 state is the most intensely corrosive substance known. This 
 seems to be the aeid combined with a little water. It may be 
 called hydro fluoric add; and Sir H. Davy has been led, from 
 some late experiments on the subject, to consider pure fluoric 
 acid as a compound of a certain unknown principle, which he 
 calls fluorine, with hydrogen. 
 
 Sir H. Davy has also attempted to decompose the fluoric acid 
 by burning potassium in contact with it ; but he has not yet 
 been able by this or any other method, to obtain its basis in a 
 distinct separate state. 
 
 We shall conclude our account of the acids with that of the 
 MURIATIC ACID, which is perhaps the most curious and inter- 
 esting of all of them. It is found in nature combined with so- 
 da, 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 common tem- 
 perature of the atmosphere ; but it has a remarkably strong at- 
 traction for water, and assumes the form of a whitish cloud 
 whenever it meets any moisture to combine with. This acid is 
 remarkable for its peculiar and very pungent smell, and pos- 
 
 * A bottle of fluoric acid is not easily obtained. To make etchings 
 on glass, first cover the glass with a thin coat of bees wax. This is 
 done by warming it over a lamp, and passing the wax over the surface. 
 Then make the drawing by cutting through the wax quite down to the 
 glasa. To do the etching in the small way, take- a lead, or tin cup, 
 and on the bottom, place about a table spoonful of pulverised fluor 
 spar, and on this pour sulphuric acid enough to moisten it place the 
 glass on the cup as a cover, with the side to he etched downward- 
 then set the cup in warm water, or warm the bottom over a lamp, 
 taking care not to melt the wix. In 15 or 20 minutes or more, the 
 etching will be done. In this way, drawings are easily and beautiful 
 ! j made on glass , C , 
 
226 MURIATIC ACID, 
 
 sesses, 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 liquefied ? 
 
 J\lrs. B. By impregnating water with it ; its strong attractiou 
 for water makes it very easy to obtain it in a liquid form. Now, 
 if I open the phial, you may observe a kind of vapour rising 
 from it, which is muriatic acid gas, of itself invisible, but made 
 apparent by combining with the moisture of the atmosphere. 
 
 Emily. Have you not any of the pure muriatic acid gas ? 
 
 Mrs. B. This jar is full of that acid in its gaseous state it 
 is inverted over mercury instead of water, because, being ab- 
 sorbable by water, this gas cannot be confined by it. I shall 
 now raise the jar a little on one side, and sufier 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 mois- 
 ture of the atmosphere, that it is converted into this dewy va 
 pour. 
 
 Mrs. B. Certainly ; and for the same reason, that is tosay^ 
 its extreme eagerness to unite with water, this gas will cause 
 snow to melt as rapidly as an intense fire. 
 
 This acid proved much more refractory when Sir H. Davy 
 attempted to decompose it, than the other two undecompound- 
 ed acids. It is singular that potassium will burn in muriatic 
 acid, and be converted into potash, without decomposing the 
 acid, and the result of this combustion is a muriat of potash; 
 for the potash, as soon as it is regenerated, combines with the 
 muriatic acid. 
 
 Caroline. But how can the potash be regenerated, if the 
 muriatic acid does not oxydate the potassium ? 
 
 Mrs. B. The potassium, in this process, obtains oxygen 
 from the moisture with which the muriatic acid is always com- 
 bined, and accordingly hydrogen, resulting from the decompo- 
 sition of the moisture, is invariably evolved. 
 
 Emily. But why not make these experiments with dry mu- 
 riatic acid ? 
 
 Mrs. B. Dry acids cannot be acted on by the Voltaic batte- 
 ry, because acids are non-conductors of electricity, unless mois- 
 tened. In the course of a number of experiments which Sir 
 H. Davy made upon acids in a state of dryness, he observed 
 that the presence of water appeared always necessary to devel- 
 ope the acid properties, so that acids are not even capable of 
 reddening vegetable blues if they have been carefully deprived 
 of moisture. This remarkable circumstance led him to suspect, 
 that water, instead of oxygen, may be the acidifying principle ; 
 
OXY-MURIATIC ACID. 227 
 
 but this he threw out rather as a conjecture than as an establish- 
 ed point. 
 
 Sir H. Davy obtained very curious results from burning po- 
 tassium in a mixture of phosphorus and muriatic acid, and also 
 of sulphur and muriatic acid ; the latter detonates with great 
 violence. All his experiments, however, failed in presenting 
 to *is view the basis of the muriatic acid, of which he was in 
 search ; and he was at last induced to form an opinion respect- 
 ing the nature of this acid, which I shall presently explain. 
 
 Emily. Is this acid susceptible of different degrees of oxy- 
 genation ? 
 
 Mrs. B. Yes, for though we cannot deoxygenate this acid, 
 yet v/e may add oxygen to it. 
 
 Caroline. Why then, is not the least degree of oxygenation 
 of the acid called the muriatous, and the higher degree the 
 muriatic acid ? 
 
 Mrs. B. Because, instead of becoming, like other acids, more 
 dense, and more acid by an addition of oxygen, 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 oxyge- 
 nated, or oxy muriatic acid. This likewise exists in a gaseous 
 form, at the temperature of the atmosphere ; it is also suscepti- 
 ble of being absorbed by water, and can be congealed, or solid- 
 ified, by a certain degree of cold. 
 
 Emily. And how do you obtain the oxy-muriatic acid ? 
 
 Wr. B. In various ways ; but it may be most conveniently 
 obtained by distilling liquid muriatic acid over oxyd of manga- 
 nese, which supplies the acid with the additional oxygen. One 
 part of the acid being put into a retort, with two 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 have collected sooie in this jar * 
 
 Caroline. It is not invisible, like the generality of gases 5 for 
 it is of a yellowish colour. 
 
 Mrs. B. The muriatic acid extinguishes flame, whilst, on the 
 contrary, the oxymuriatic makes the flame larger, and gives it a 
 dark red colour. Can you account tor this difference in the 
 two acids ? 
 
 * Breathing only a tew bubbles of this gas is attended with bad, 
 sometimes with d m^erous ( o.is.-quaioes. ; iic j-oung chemist, there- 
 fore had better not undertake to make it. C. 
 
228 OXY-MUR1AT1C ACID. 
 
 Emily. Yes, I think so ; the muriatic acid will not suppi) 
 the flame with the oxygen necessary for its support ; but when 
 this acid is further oxygenated, it will part with its additional 
 quantity of oxygen, and in this way support combustion. 
 
 Mrs. B. That is exactly the case ; indeed the oxygen 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 actual- 
 ly inflames, without any previous increase of temperature. 
 
 Caroline. That is extraordinary, indeed ! I hope you mean 
 to indulge us with some of these experiments ? 
 
 Mrs. 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 smothered in a thick vapour. 
 , Caroline. What a disagreeable smell ! 
 
 Mrs. LJ. We shall try the same experiment with phosphorus 
 in another jar of this acid. You had better keep your hand- 
 kerchief to your nose when I open it now let us drop into \\ 
 this little piece of phosphorus 
 
 Caroline. It burns really ; and almost as brilliantly as in ox- 
 ygen gas ! But, what is most extraordinary, these combustions 
 take place without the metal or phosphorus being previously 
 lighted, or even in the least heated. 
 
 Mrs. 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 extraordina- 
 ry indeed to see bodies, and metals in particular, melted down 
 and inflamed, by a gas without any increase of temperature, ei- 
 ther of the gas, or of the combustible. The phenomenon, how- 
 ever, 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 ? 
 
 Mrs. B. Because, in the first place, it is a composition of 
 metals (consisting chiefly of copper) which burns readily; and 
 I use a thin metallic leaf in preference to a lump of metal, be- 
 cause it offers to the action of the gas but a small quantity of 
 matter under a large surface. Filings, or shavings, would an- 
 swer the purpose nearly as well ; but a lump of metal, hough 
 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 
 
OXY-MURIATIC ACID. 229 
 
 regta, 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 acid and nitric acid. But 
 in fact, the result of this mixture is the formation of oxy-rnuriatic 
 acid, as the muriatic acid oxygenates itself at the expense of the 
 nitric; this mixture, therefore, though it bears the name of ni- 
 tre-muriatic acid, acts on gold merely in virtue of the oxy-muri- 
 atic 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 show you the combustion 
 of all these bodies. 
 
 Caroline. There are several jars of the gas yet remaining. 
 
 Mrs. B. We must reserve these for future experiments. The 
 oxy-muriatic acid, does not, like other acids, redden the blue 
 vegetable colours ; but it totally destroys all colour, and turns 
 vegetables perfectly white. Let us collect some vegetable sub- 
 stances to put into this glass, which is full of gas. 
 
 Emily. Here is a sprig of myrtle 
 
 Caroline. And here some coloured paper 
 
 Mrs. B. We shall also put in this piece of scarlet riband, and 
 a rose 
 
 Emily. Their colours begin to fade immediately ! But how 
 does the gas produce this effect? 
 
 Mrs. B. The oxygen combines with the colouring 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 capable of reflecting them all, which, 
 you know, will make them appear white. Old prints may be 
 cleansed by this acid, for the paper will be whitened without 
 injury to the impression, as printers ink is made of materials 
 (oil and lamp black) which are not acted upon by acids. 
 
 This property of the oxy-muriatic acid has lately been em- 
 ployed in manufactures in a variety of bleaching 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 ef- 
 fects; for, in a gaseous state, it would destroy the texture as 
 well as the colour of the substance submitted to its action. 
 
 Caroline. Look at the things which we put into the gas > 
 they have now entirely lost their colour ! 
 
 Mrs. B. The effect of the acid is^lmost completed ; and if 
 we were to examine the quantity that remains, we should line! 
 it to consist chiefly of muriatic acid. 
 
 21 
 
2^0 OXY-MURIATIC AI1>. 
 
 The oxy-muriatic acid has been used to purify the air in fever 
 hospitals and prisons, as it burns and destroys putrid effluvia of 
 every kind. The infection of the small-pox is likewise destroy- 
 ed by this gas, and matter that has been submitted to its influ- 
 ence will no longer generate that disorder. 
 
 Caroline. Indeed, I think the remedy must be nearly as bad 
 as the disease ; the oxy-muriatic acid has such a dreadfully suf- 
 focating smell. 
 
 Mrs. B. It js certainly extremely offensive : but by keeping 
 the mouth shut, and wotting the nostrils with liquid tmmotiia, 
 in order to neutralise the vapour as it reaches the nose, its prej- 
 udicial effects may be in some degree prevented. At any rate, 
 however, this mode of disinfection can hardly be used in places 
 that are inhabited. And as the vapour of nitric acid, which is 
 ssarcely less efficacious for this purpose, is not at all prejudi- 
 cial, it is usually preferred on such occasions. 
 
 Caroline. You have not told us yet what is Sir H. Davy's 
 new opinion respecting the nature of muriatic acid, to which 
 you alluded a few minutes ago? 
 
 Mrs. B. True; I avoided noticing it then, because you 
 could not have understood it without some previous knowledge 
 of the oxy-muriatic acid, which I have but just introduced to 
 your acquaintance. 
 
 Sir H. Davy's idea is that muriatic acid, instead of being a 
 compound, consisting of an unknown basis and oxygen, is form- 
 ed by the union of oxy-muriatic gas with hydrogen? 
 
 Emily. Have you not told us just now that oxy-muriati\ 
 gas was itself a compound of muriatic acid and oxygen ? 
 
 Mrs. B. Yes; but according to Sir H. Davy's hypothesis, 
 ox v muriatic gas is considered as a simple body, which con- 
 tains no oxygen as a substance of its own kind, which has i> 
 great analogy to oxygen in most of its properties, though in 
 others it differs entirely from it. According to this view of the 
 subject, the name of oxy-muriatic acid can no longer be prop- 
 er, and therefore Sir H. Davy has adopted that of chlorine > or 
 chlorine gas, a name which is simply expressive of its greenish 
 colour; and in compliance with that philosopher's throry, we 
 Irave placed chlorine in our table among the simple bodies. 
 
 Caroline. But what was Sir H. Davy's reason for adopting 
 an opinion so contrary to that which had hitherto prevailed? 
 
 Mrs. B. There are many circumstances which are favoura- 
 ble to the new docttine; but the clearest and simplest fact in 
 its support is, that if hydrogen gas and oxy-muriatic gas be 
 
OXY-MURIATIC ACID. 
 
 331 
 
 mixed together, t)oth these gases disappear, and muriatic acid 
 nis is formed. 
 
 Emily. That seems to be a complete proof; is it not consid- 
 ered as perfectly conclusive ? 
 
 Mrs. B. Not so decisive as it appears at first sight ; because 
 it is argued by those who still incline to the old doctrine, that 
 muriatic acid gas, however dry it may be, always contains a 
 certain quantity of water, which is supposed essential to its for- 
 mation. So that, in the experiment just mentioned, this water 
 is supplied by the union of the hydrogen gas with the oxygen 
 of the oxy-muriatic acid ; and therefore the mixture resolves 
 itself into the base of muriatic acid and water, that is, muriatic 
 acid gas. 
 
 Caroline. I think the old theory must be the true one ; for 
 otherwise how could you explain the formation of oxy-muriatic 
 gas, from a mixture of muriatic acid and oxyd of manganese? 
 
 Mrs. B. Very easily ; you need only suppose that in this 
 process the muriatic acid is decomposed ; its hydrogen unites 
 with the oxygen of the manganese to form water, and the chlo- 
 rine appears in its separate state. 
 
 Emily. But how can you explain the various combustions 
 which take place in oxy-muriatic gas, if you consider it as con- 
 taining no oxygen ? 
 
 Mrs. B. We need only suppose that combustion is the result 
 of intense chemical action ;* so that chlorine, like oxygen, in 
 Combining with bodies, forms compounds which have less ca- 
 pacity for caloric than their constituent principles, and, there- 
 fore, caloric is evolved at the moment of their combination. 
 
 Emily. If, then, we may explain every thing by either the- 
 ory, to which of the two shall we give the preference ? 
 
 Mr&. B. It will, perhaps, be better to wait for more positive 
 .proofs, if such can be obtained, before we decide positively up- 
 on the subject. The new doctrine has certainly gained ground 
 very rapidly, and may be considered as nearly established ; 
 but several competent judges still refuse their assent to it, and 
 until that theory is very generally adopted, it may be as well 
 for us still occasionally to use the language to which chemists 
 have long been accustomed. But let us proceed to the exami- 
 nation of salts formed by muriatic acid. 
 
 * " Intense chemical action," neither explains the process, nor in~ 
 <!eed conveys to the mind any definite idea. The views of Sir H 
 Davy on the composition of chlorine, ore combatted by many of thC" 
 :^rst chemists in England, as well as in this country. The inquisitive 
 reader may become acquainted with the grounds of dispute on both 
 sides by referring to Cooper's edition of Thomson's chemistry. C. 
 
232 MURIATS. 
 
 Among the compound salts formed by muriatic acid, the an* 
 riat of sodri, or common salt, is the most 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 assists 
 the process of digestion. 
 
 Sea- water is the great source from which muriat of soda is 
 extracted by evaporation. But it is also found in large solid 
 masses in the bowels of the earth, in England, and in many oth- 
 er parts of the world. 
 
 Emily. I thought that salts, when solid, were always in the 
 state of crystals ; but the common taole-salt is in the form of 
 a coarse white powder. 
 
 Mrs. H. Crystallisation depends, as you may recollect, on 
 the slow and regular reunion of particles dissolved in a fluid ; 
 common sea-salt is only in a state of imperfect crystallisation, 
 because the process by which it is prepared is not favourable 
 to the formation of regular crystals. But if you dissolve it, and 
 afterwards evaporate the water slowly, you will obtain a regu- 
 lar crystallisation. 
 
 Muriat of ammonia is another combination of this acid, 
 which we have already mentioned as the principal source from 
 which ammonia is derived. 
 
 I can at once show you the formation of this salt by the im- 
 mediate combination of muriatic acid with ammonia. These 
 two glass jars contain, the one muriatic acid gas, the other am- 
 moniacal gas, both of which are perfectly invisible now, if I 
 mix them together, you see they immediately form an opaque 
 white cloud, like smoke. If a thermometer was placed in tha 
 jar in which these gases are mixed, you would perceive that 
 some heat is at the same time produced. 
 
 Emily. The effects of chemical combinations, are, indeed., 
 wonderful ! How extraordinary it is that two invisible bodies 
 should become visible by their union ! 
 
 Mrs. B. This strikes you with astonishment, because it is a. 
 phenomena which nature seldom exhibits to our view ; but the 
 most common of her operations are as wonderful, and it is their 
 frequency only that prevents our regarding them with equal ad- 
 miration. What would be more surprising, for instance, than 
 combustion, were it not rendered so familiar by custom ? 
 
 * According to Sir H- Davy's views of the nature of the muriatic 
 and oxy-muriatic acids, dry muriat of soda is a compound of sodium 
 and chlorine, for it may be formed by the direct combination of oxy- 
 muriatic gas and sodium. In his opinion, therefore, what we common- 
 ly call muriat of soda contains neither soda nor muriatic acid- 
 
OXY-MUKIA.TS. -ffSB 
 
 . That is true. But pray, Mrs. B., is this white cloud 
 tiie salt that produces ammonia? How different it is from the 
 solid muriut of ammonia which you once showed us! 
 
 Mrs. B. It is the same substance which first appears in the 
 state of vapour, but will soon befeondensed by cooling against 
 the sides of the jar, in the form of very minute crystals. 
 
 \Ve may now proceed to the oxy-muriats. In this class of 
 salts the oxy-muriat of potash* is the most worthy of our atten- 
 tion, for its striking properties. The acid, in this state of com- 
 bination, contains a still greater proportion of oxygen mar? 
 when alone. 
 
 Caroline. But how can the oxy-muriatic acid acquire an in- 
 crease of oxygen by combining with potash? 
 
 Mrs. B. It does not really acquire an additional quantity of 
 oxygen, but it loses some of the muriatic acid, which produces 
 the same effect, as the acid which remains is proportionably su- 
 per-oxygenated .t 
 
 If this salt be mixed, and merely rubbed together with sul- 
 phur, phosphorus, charcoal, or indeed any other combustibles 
 it explodes strongly. 
 
 Caroline. Like gun-powder, I suppose, it is suddenly con- 
 verted into elastic fluids? 
 
 Mrs. B. Yes; but with this remarkable difference, that no 
 increase of temperature, any further than is produced by gentle 
 friction, is required in Ithis instance. Can you tell me what 
 gases are generated by the detonation of this salt with charcoal r 
 
 Emily. Let me consider The oxy-muriatic acid parts 
 
 with its excess of oxygen to the charcoal, by which means it is 
 converted into muriatic acid gas; whilst the charcoal, being 
 burnt by the oxygen, is changed to carbonic acid gas What 
 becomes of the potash I cannot tell. 
 
 Mrs. B. That is a fixed product which remains in the ves- 
 sel. 
 
 Caroline. But since the potash does not enter into the new 
 combinations, I do not understand of what use it is in this ope- 
 ration. Would not the oxy- muriatic acid and the charcoal pro- 
 duce the same effect without it ? 
 
 Mrs. B. No ; because there would not be that very great 
 concentration of oxygen which the combination with the pot* 
 ash produces, as I have just explained. 
 
 * Oxy-muriat of potash is prepared by passing chlorine through aso- 
 lution of potash in water. Fhe process is long and diiTieult. C % . 
 
 t According to Sir H. Davy's r^v views, just explained, oxy-muri- 
 at of potash is a compound of chlorine with oxjrd of potassium. 
 
 21* 
 
234 OX 
 
 I mean to show you this experiment, but I would advise you 
 not to repeat it alone ; for if care be not taken to mix only ve- 
 ry small quantities at a time, the detonation 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 pro- 
 duced by so small a quantity of matter ? 
 
 ' Jurs. B. You must consider that an extremely small quanti- 
 ty of solid substance may produce a very great volume of gases 5 
 and it is the sudden evolution of these which occasions the 
 sound. 
 
 Emily. Would not oxy-muriat of potash make a stronger 
 gun-powder than nitrat of potash? 
 
 Mrs. 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 
 sommon gun-powder is quite sufficiently destructive. 
 
 Mrs. B. I can show you a very curious experiment with this 
 salt ; but it must again be on condition that you will never at- 
 tempt to repeat it by yourselves. I throw a small piece of 
 phosphorus into this glass of water; 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 at the bot- 
 tom of the glass) a small quantity of jgulphuric 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 out under 
 water, and rising through it ! Pray, how is this accounted 
 for? 
 
 Mrs. 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 combining with the 
 potash, so as to liberate the oxymuriatic acid gas by which the 
 phosphorus is set on fire ? 
 
 Mrs. B., Very well, Emily ; andavith a little more reflection 
 you would have discovered another concurring circumstance,, 
 which is, that an increase of temperature is produced by the 
 mixture of the sulphuric acid and water, which assists in pro- 
 moting the combustion of the phosphorus. 
 
 I must, before we part, introduce to yo 1 r acquaintance the 
 newly-discovered substance IODTNE, which you may recollect 
 
OXY-MUHIATS. 235 
 
 we placed next to oxygen and chlorine in our table of simple 
 bodies. 
 
 Caroline. Is, this also a body capable of maintaining com- 
 bustion like oxygen and chlorine ? 
 
 Airs, B. It is ; and although it does not so generally disen- 
 gage light and heat from inflammable bodies, as oxygen and 
 chlorine do, yet it is capable of combining with most of them ; 
 and sometimes, as in the instance of potassium and phospho- 
 rus, the combination is attended with an actual appearance of 
 light and heat. 
 
 Caroline. But what sort of a substance is iodine : what is its 
 form, and colmir ? 
 
 Mrs. B. It is a very singular body, in many respects. At 
 the ordinary temperature of the atmosphere, it commonly ap- 
 pears in the form of blueish black crystalline scales, such as you 
 see in this tube. 
 
 Caroline. They shine like black lead, and some of the scales 
 have the shape of lozenges. 
 
 Mrs. B. That is actually the form which the crystals* of io- 
 dine often assumes. But if we heat them gently, by holding 
 the tube over the flame of a candle, see what a change takes 
 place in them. 
 
 Carc'line. How curious ! They seem to melt, and the tube 
 immediately fills with a beautiful violet vapour. But look, 
 Mrs. B., the same scales are now appearing at the other end of 
 the tube. * ^ 
 
 Mrs. B. This is in fact a sublimation of iodine, from one 
 part of the tube to another ; but with this remarkable peculiar- 
 ity, that, while in the gaseous state, iodine assumes that bright 
 violet colour, which, as you may already perceive, it loses as 
 the tube cools, and the substance resumes its usual solid form. 
 - lt is from the violet colour of the gas that iodine has ob- 
 tained its name. 
 
 Caroline. But how is this curious substance obtained ? 
 
 Mrs. B. It is found in the ley of ashes of sea- weeds, after 
 the soda has been separated by crystallisation ; and it is disen- 
 gaged by means of sulphuric acid, which expels it from the al- 
 kaline ley in the form of a violet gas, which may be collected 
 and condensed in the way you have just seen. This interesting 
 discovery was made in the year 1812, by M. Courtois, a man- 
 ufacturer of saltpetre at Paris. 
 
 Caroline. And pray, Mrs. B., what is the proof of iodine be- 
 ing a simple body ? 
 
 Mrs. B. It is considered as a simple body, both because it 
 is not capable of being resolved into other ingredients 5 and be- 
 
236 
 
 COMPOSITION 
 
 cause it is itself capable of combining with other bodies, in a 
 manner analogous to oxygen and chlorine. The most curious 
 of these combinations is that which it forms with hydrogen jjas ; 
 the result of which is a peculiar gaseous acid. 
 
 Caroline. Just as chlorine *nd hydrogen gas form muriatic 
 acid ? In this respect chlorine and iodine seem to bear a strong 
 analogy to each other. 
 
 Mrs. B. That is indeed the case ; so that if the theory of 
 the constitution of either of these two bodies be true, it must be 
 true also in regard to the other ; if erroneous in the one, the 
 theory must fall in both. 
 
 But it is now time to conclude ; we have exsfmined such of 
 the acids and salts as 1 conceived would appear to you most 
 interesting. I shall not enter into any particulars respecting 
 the metallic acids, as they offer nothing sufficiently striking for 
 our present purpose. 
 
 CONVERSATION XX. 
 
 ON THE NATURE AND COMPOSITION OF VEGETABLE 
 
 Mrs. B. WE have hitherto treated only of the simplest com- 
 binations of elements, such as alkalies, earths, acids, compound 
 salts, ston<^s, *&e. ; 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 ORGANISED BODIES, which \vill furnish 
 us with a new source of instruction and amusement. 
 
 Emily. By organised bodies, I suppose, you mean the veget- 
 able and animal creation ? I have, however, but a very vague 
 idea of the word organisation, and I have often wished to know 
 more precisely what it means. 
 
 Mrs. B. Organised bodies are such as are endowed by na- 
 ture with various parts, peculiarly constructed and adapted to 
 perform certain functions connected with life. Thus you may 
 observe, that mineral compounds are formed by the simple ef- 
 fect of mechanical or chemical attraction, and may appear to 
 some to be in a great measure the productions of chance ; 
 whilst organised bodies bear the most striking and impressive 
 marks of design, and are eminently distinguished by that un- 
 known principle, called life, from which the various organs dev 
 rive the power of exercising their respective functions. 
 
 Caroline. But in what manner does life enable these organs 
 to perform their several functions ? 
 
* 
 
 OF VEGETABLES. 23? 
 
 Mrs, B. That is a mystery, which, I fear, is enveloped in 
 such profound darkness that there is very littje hope of our ev- 
 er being able to unfold it. We must content ourselves with ex- 
 amining 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 cleat idea of 
 life. 
 
 Mrs. B. Pray let me hear how you would define it ? 
 
 Caroline. It is perhaps more easy to conceive than to ex- 
 press let me consider Is not life the power which enables 
 both the animal and the vegetable creation to perform the vari- 
 ous functions which nature has assigned to them ? 
 
 Mrs. B. I have nothing to object to your definition ; but you 
 will allow me to observe, that you have only mentioned the ef- 
 fects 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 attempting to form an idea of its 
 real nature. 
 
 We shall begin with examining its effects in the vegetable 
 world, which constitutes the simplest class of organised bodies ; 
 these we shall find distinguished from the mineral creation, not 
 only by their more complicated nature, but by the power which 
 they possess within themselves, of forming new chemical ar- 
 rangements of their constituent parts, by means of appropriate 
 organ's. Thus, though all vegetables are ultimately composed 
 of hydrogen, carbon, 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 imme*- 
 diate materials. 
 
 These are : 
 
 Sap, Resins, 
 
 Mucilage, Gum Resins, 
 
 Sugar, Balsams, 
 
 Fecula, Caoutchouc, 
 
 Gluten, Extractive colouring Matter, 
 
 Fixed Oil, Tannin, 
 
 Volatile Oil, Woody Fibre, 
 
 Camphor, Vegetable Acids, fyc, 
 
338 COMPOSITION 
 
 Caroline. What a long list of names ! I did not suppose that 
 a vegetable was composed of half so many ingredients. 
 
 Mrs. B. You must not imagine that every one of these mate- 
 rials is formed in each individual plant. I only mean to say, 
 that they are all derived exclusively from the vegetable king- 
 dom. 
 
 Emily. But does each particular part of the plant, such as 
 ihe root, the bark, the stem, the seeds, the leaves, consist of one 
 or these ingredients only, or of several of them combined to- 
 gether ? 
 
 Airs. B. I believe there is no part of a plant which can be 
 said to consist solely of any one particular ingredient ; a cer- 
 tain number of vegetable materials must always be combined 
 for the formation of any particular part, (of a seed for instance,) 
 and these combinations are carried on by sets of vessels, or mi- 
 nute organs, which select from other parts, and bring together, 
 the several principles required for the developement and growth 
 of those particular parts which they are intended to form and to 
 maintain. 
 
 Emily. And are not these combinations always regulated by 
 the laws of chemical attraction ? 
 
 Mrs. B. No doubt ; the organs of plants cannot force princi- 
 ples to combine that have no attraction for each other ; nor 
 can they compel superior attractions to yield to those of inferi- 
 or power ; they probably act rather mechanically, by bringing 
 into contact such principles, and in such proportions, as will, 
 by their chemical combination, form the various vegetable pro- 
 ducts. 
 
 Caroline. We may then consider each of these organs as a 
 curiously constructed apparatus, adapted for the performance of 
 a variety of chemical processes. 
 
 Mrs. B. Exactly so. As long as the plant lives and thrives, 
 the carbon, hydrogen, and oxygen, (the chief constituents of its 
 immediate materials,) are so balanced and connected together, 
 that they are not susceptible of entering into other combinations ; 
 but no sooner does death take place, than this state of equilibri- 
 um is destroyed, and new combinations produced. 
 
 Emily. But why should death destroy it ; for these princi- 
 ples 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 vegetable, as well 
 as in the animal kingdom, it is by the principle of life that the 
 organs are enabled to act ; when deprived of that agent or sti- 
 mulus, their power ceases, and an order of attractions succeeds 
 
OF VEGKTABLBb. 
 
 similar to that which would take place in mineral or unorgan- 
 ised matter. 
 
 Emily. It is this new order of attractions, I suppose, that 
 destroys the organisation of the plant alter death ; for if the 
 same combinations still continued to prevail, the plant would 
 always remain in the state in which it died ? 
 
 Mrs. B. Arid that, you know, is never' the case; plants may 
 be partially preserved for some time after 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 Pro- 
 vidence, by which dead plants are rendered n't to enrich the 
 soil, and become subservient to the nourishment of living veget- 
 ables. 
 
 Caroline. But we are talking of the dissolution of plants, 
 before we have examined them in their living state. 
 
 Mrs. B> That is true, my dear. But I wished to give you a 
 general idea of the nature of vegetation, before we entered into 
 particulars. Besides, it is not so irrelevant as you suppose to 
 talk of vegetables in their dead state, since we cannot analyze 
 them without destroying 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 decomposition. 
 There are two kinds of analysis of which vegetables are sus- 
 ceptible ; first, that which separates them into their immediate 
 materials, such as sap, resin, mucilage. &c. ; secondly, that 
 which decomposes them into their primitive elements, as car- 
 bon, 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 r 
 
 Mrs. B. That, my dear, is rather the department of the bo- 
 tanist ; we shall consider these different parts of plants only, 
 as the organs by which the various secretions or separations are 
 performed ; but we must first examine the nature of these se- 
 cretions. 
 
 The sap is the principal material of vegetables, since it con- 
 tains the ingredients that nourish every part of the plant. The 
 basis of this juice, which the roots suck up from the soil, is wa- 
 ter ; this holds in solution the various other ingredients requir- 
 ed by the several parts of the plant, which are gradually secre- 
 ted from the sap by the different organs appropriated to that 
 purpose, as it passes them in circulating through the plant. 
 
 .\lucus, 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. 
 
240 COMPOSITION 
 
 Caroline. Is that the gum so frequently used instead of paste 
 or glue ? 
 
 J^trs B. It is; almost all fruit-trees yield some sort of gum, 
 but that most commonly used in the arts is obtained from a spe- 
 cies of acacia-tree in Arabia, and is called gum arable ; it 
 forms 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 gu;n was eatable. 
 
 Mrs. B. There is an account of a whole ship's company be- 
 ing saved from starving by feeding on the cargo, which was 
 gum Senegal. I should not, however, imagine, that it would 
 be either a pleasant or a particularly eligible diet to those who 
 have not, from their birth, been accustomed to it. It is, how- 
 ever, frequently taken medicinally, and considered as very 
 nourishing. Several kinds of vegetable acids may be obtain- 
 ed, by particular processes, from gum or mucilage, the princi- 
 pal 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; this saccharine 
 matter is to be met with in every vegetable, but abounds most 
 in roots, fruits, and particularly in the sugar-cane. 
 
 Emily. If all vegetables contain sugar, why is it extracted 
 exclusively from the sugar-cane ? 
 
 Mrs. b. Because it is both most abundant in that plant, and 
 most easily obtained from it. Besides, the sugars produced by 
 other vegetables differ a little in their nature. 
 
 During the late troubles in the West-Indies, when Europe 
 was but imperfectly supplied with sugar, several attempts were 
 made to extract it from other vegetables^ and very good sugar 
 was obtained from parsnips and from carrots; but the process 
 was too expensive to carry this enterprise to any extent. 
 
 Caroline. I should think that sugar might be more easily ob- 
 tained from sweet fruits, such as figs, dates, &c. 
 
 j\irs. B. Probably ; but it would be still more expensive, 
 from the high price of those fruits. 
 
 Emily. Fray, in what manner is sugar obtained from the su- 
 gar-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 to the surface. The 
 clarified liquor is let off below and evaporated to a very small 
 quantity, after which it is suffered to crystallize by standing in 
 a vessel, the bottom of which is perforated with holes, that are 
 imperfectly stopped, in order that the syrup may drain off, 
 
OP VEGETABLES. 241 
 
 The sugar obtained by this process is a coarse brown powder, 
 commonly called raw or moist sugar; it undergoes another op- 
 eration to be refined and converted into loaf sugar. For this 
 purpose it is dissolved in water, and afterwards purified by an 
 animal fluid called albumen. White of eggs chiefly consist of 
 this fluid, which is also one of the constituent parts of blood ; 
 and consequently eggs, or bullocks' blood, are commonly used 
 for this purpose. 
 
 The albuminous fluid being diffused through the syrup, com- 
 bines with all the solid impurities contained in it, and rises with 
 them to the surface, where it forms a thick scum ; the clear li- 
 quor is then again evaporated to a proper consistence, and 
 poured into moulds, in which, by a confused crystallisation, it 
 forms loaf-sugar. But an additional process is required to whi- 
 ten it; to 'his 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, combines with and 
 carries off 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. I have heard of some improvements by the late Mr. 
 Howard, in the process of refining sugar. Pray what are 
 they? 
 
 Airs. B. It would be much too long to give you an account 
 of the process in detail. But the principal improvement relates 
 to the mode of evaporating the syrup, in order to bring it to the 
 consistency of sugar. Instead of boiling the syrup in a large 
 copper, over a strong fire, Mr. Howard carries off the water by 
 means of a large air-pump, in a way similar to that used in Mr. 
 Leslie's experiment for freezing water by evaporation; that is, 
 the syrup being exposed to a vacuum, the water evaporates 
 quickly, with no greater heat than that of a little steam, which 
 is introduced round the boiler. The air-pump is of course of 
 large dimensions, and is worked by a steam engine. A great 
 saving is thus obtained, and a striking instance afforded of the 
 power of science in suggesting useful economical improvements. 
 
 Emily. And pray how is sugar-candy and barley-sugar pre- 
 pared ? 
 
 Mrs. 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 decomposition of sugar afford many ve- 
 
 22 
 
242 COMPOSITION 
 
 ry interesting particulars, which we shall fully examine, after 
 having gone through the other materials of vegetables. We 
 sha'l find that there is reason to suppose that sugar is not, like 
 the other materials, secreted from the sap by appropriate or- 
 gans; but that it is formed by a peculiar process with which 
 you are not yet acquainted. 
 
 Caroline. Pray, is not honey of the same nature as sugar ? 
 
 Mrs. B. Honey is a mixture of saccharine matter and gum. 
 
 Emily. I thought that honey was in some measure an ani- 
 mal swbstance, as it is prepared by the bees. 
 
 Mrs. B. It is rather collected by them from flowers, and con- 
 veyed to their store-houses, the hives. It is the wax only that 
 undergoes a real alteration in the body of the bee, and is thence 
 converted into an animal substance.* 
 
 Manna is another kind of sugar, which is united with a nau- 
 seous extractive matter, to which it owes its peculiar taste and 
 colour. It exudes like gum from various trees in hot climates, 
 some of which have their leaves glazed by it. 
 
 The next of the vegetable materials is fecula ; this is the 
 general name given to the farinaceous substance contained in 
 all seeds, and in some roots, as the potatoe, parsnip, &c. It 
 is intended by nature for the first aliment of the young vegeta- 
 ble; but that of one particular grain is become a favourite and 
 most common food of a large part of mankind. 
 
 Emily. You allude, I suppose, to bread, which is made of 
 wheat-flour ? 
 
 Mrs. 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 sup- 
 posed to be owing to the viscous qualities of this substance, that 
 wheat-flour forms a much better paste than any other. 
 
 Emily. Gluten, by your description, must be very likegum ? 
 
 Mrs. B. In their sticky nature they certainly have some re- 
 semblance ; but gluten is essentially different from gum in oth- 
 er points, and especially in its being insoluble in water, whilst 
 gum, you know, is extremely soluble. 
 
 The oils contained in vegetables all consist of hydrogen and 
 carbon in various proportions. They are of two kinds, fixed 
 and vo/afe7e,'both of which we formerly mentioned. Do you- 
 
 * It was the opinion of Huher, that the bees prepared (he wax from 
 honey and sugar, There is, however, found on the leaves of some 
 plants a substance, having all the properties of wax ; and that bees- 
 wax itself is not an animal substance, is clear from ite analysis. C, 
 
OP VEGETABLES. 243 
 
 remember in what the difference between fixed and volatile oil 
 consists? 
 
 Emily. If I recollect rightly, the former are decomposed by 
 heat, whilst the latter are merely volatilised by it. 
 
 Airs. B. Very well. Fixed oil is contained only in the 
 seeds of plants, excepting in the olive, in which it is produced 
 in, and expressed from, the fruit. We have already observed 
 that seeds contain also fecula; these two substances, united 
 with a little mucilage, form the white substance contained in 
 the seeds or kernels of plants, and is destined for the nourish- 
 ment of the young plant, to which the seed gives birth. The 
 milk of almonds, which is expressed from the seed of that name, 
 is composed of these three substances. 
 
 Emily. Pray, of what nature is the linseed oil which is used 
 in painting ? ^ 
 
 Mrs. B. It is a fixed on, obtained from the seed of flax. 
 Nut oil, which is frequently us&l for the same purpose, is ex- 
 pressed from walnuts. 
 
 Olive oil is that whichjs best adapted to culinary purposes. 
 
 Caroline. And what are the oils used for burning ? 
 
 Mrs. B. Animal oils most commonly; but the preference 
 *iven to them is owing to their being less expensive; for vege- 
 table 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 rea- 
 son that lamps so frequently require trimming ? 
 
 *M?% B. This sometimes proceeds from the construction of 
 the lamp, which may not be sufficiently favourable to a per- 
 fect combustion ; but there is certainly a defect in the nature of 
 oil itself, which renders it necessary for the best-constructed 
 lamps to be occasionally 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, gathers round 
 the wick, and thus impedes its combustion, and consequently 
 dims the light. 
 
 Caroline. But will not oils burn without a wick ? 
 
 Mrs. B. Not unless their temperature be elevated to five or 
 six hundred degrees ; the wick answers this purpose, as I think 
 I once before explained to you. The oil rises between the fi- 
 bres of the cotton by capillary attraction, and the heat of the 
 burning wick volatilises it, and brings it successively to the tem- 
 perature at which it is combustible. 
 
 Emily. I suppose the explanation which you have given with 
 regard to the necessity of trimming lamps, applies also to cart" 
 dies, which so often require 
 
-44 COMPOSITION 
 
 Mrs. /?. I believe it does ; at least, in some degree. But 
 besides the circumstance just explained, the common sort of 
 oils are not very highly combustible, so that the heat produced 
 by a candle, which is a coarse kind of animal oil, being insuffi- 
 cient to volatilise them completely, a quantity of soot is gradu- 
 ally deposited on the wick, which dims the light, and retards 
 the combustion. 
 
 Caroline. Wax candles then contain no incombustible mat- 
 ter, since they do not require snuffing ? 
 
 Mrs. B. Wax is a much better combustible than tallow, but 
 still not perfectly so, since it likewise contains 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 gooa combustibles, I wonder that 
 they should require so great an elevation of temperature before 
 they begin to burn ? 
 
 Mrs. B. Though fixed oils will not enter into actual combus- 
 tion below the temperature of about four hundred degrees,* yet 
 they will slowly absorb oxygen at the common temperature of 
 the atmosphere. Hence arises a variety of changes in oils 
 which modify their properties and uses in the arts. 
 
 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 of certain vegetables, even du- 
 ring their life. But it happens in many instances that the oil 
 does not retain all the oxygen which it attracts, but that part of 
 it combines with, or burns, the hydrogen of the oil, thus form* 
 ing a quantity of water, which gradually goes off by evapora- 
 tion. In this case the alteration of the oil consists not only in 
 the addition of a certain quantity of oxygen, but in the diminu- 
 tion of the hydrogen. These oils are distinguished by the name 
 of drying oils. Linseed, poppy, and nut-oils, are of this de- 
 scription. 
 
 Emily. I am well acquainted with drying oils, as I continu- 
 ally use them in painting. But I do not understand why the 
 acquisition of oxygen on one hand, and a loss of hydrogen on 
 the other, should render them drying ? 
 
 Mrs. B. This, I conceive, may arise from two reasons ; ei- 
 
 * This statement is too low. None of the fixed oils boil at a les? 
 temperature than 600 degrees, nor will they burn until converted into 
 vapour; consequently they cannot burn at a lower temperature than 
 600. C. 
 
OF VEGfcTABLfiSc 245 
 
 ther from the oxygen which is added being less favourable to 
 the state of fluidity than the hydrogen, which is subtracted ; or 
 from this additional quantity of oxygen giving rise to new com- 
 binations, in consequence of which the most fluid parts of the. 
 oil are liberated and volatilised. 
 
 For the purpose of painting, the drying quality of oil is fur- 
 ther increased by adding a quantity of oxyd of lead to it, by 
 which means it is more rapidly oxygenated. 
 
 The rancidity of oil is likewise owing to tlieir oxygenation, 
 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 consequence ; for 
 there are innumerable varieties of compound bodies which we 
 can decompose, although we are unable to reunite their ingredi- 
 ents. This, however, is not the case with oU, as it has very 
 lately been discovered, that it is possible to form oil, by a pe* 
 culiar 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 excepting 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 ? 
 
 Mrs. B. Certainly ; but this oil is often most abundant in the 
 rind of fruits, as in oranges, lemons, &c. from which it may be 
 extracted by the slightest pressure ; it is found also in the leaves 
 -of plants, and even iri the wood. 
 
 Caroline. Is it not very plentiful in the leaves of mint, and 
 of thyme, and all the sweet-smelling herbs? 
 
 Mrs. R. 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 existence in 
 wood. In short, all vegetable oilours or perfumes are produced 
 by the evaporation of particles of these volatile oils. 
 
 * Hydro-carbonate, ia also called olejlant or oil making gas, on ac- 
 count if the supposed property here mentioned. But later experi- 
 ments have shown that th>^ substance it forms with chlorine, is not aa 
 oil, out a kind of ether, foeuce it is now known *||der the name of cMo- 
 fic ether. IA 
 
 22* 
 
246 
 
 Emjfy. They are, I suppose, very light, and of very thin con- 
 sistence, 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. J 
 order to be prepared for perfumes, or essences, tiiese oils are 
 first properly purified, and then either distilled with spirit of 
 Wine, as is the case with lavender water, or simply mixed with 
 a large proportion of water, as is often done with regard to pep- 
 permint. Frequently, also, these odoriferous waters are prepar- 
 ed merely by soaking the plants in water, and distilling. The 
 water then comes over impregnated with the volatile oil. 
 
 Caroline. Such waters are frequently used to take spots of 
 grease out of cloth, or silk ; how do they produce that effect ? 
 
 Mrs. B. By combining with the substance that forms these 
 stains; for volatile oils, and likewise the spirit in which they 
 are distilled, will dissolve wax. tallow, spermaceti, and resins ; 
 if, therefore, the spot proceeds from any of these substances, it 
 will remove it. Insects of every kind have a great aversion to 
 perfumes, so that volatile oils are employed with success in mu- 
 seums for the preservation of stuffed birds and other species of 
 
 Caroline. Pray does not the powerful smell of camphor pro- 
 >ceed from a volatile oil ? 
 
 Mrs. 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 in the Indian isles, from the stem 
 and roots of which it is extracted.* Small quantities have also 
 been distilled from thyme, sage, and other aromatic plants; and 
 it is deposited in pretty large quantities by some volatile oils af- 
 ter long standing. It is extremely volatile and inflammable. 
 It is insoluble in water, but is soluble in oils, in which state, as 
 well as in 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 surface of a 
 bason of pure water, it will immediately begin to move round 
 and round with great rapidity ; but if you pour into the basin a 
 single drop of any odoriferous fluid, it will instantly put a stop 
 to this motion. You can at any time try this very simple ex* 
 
 * Camphor comesjJiiefly from Japan. It is obtained' by distilling 
 the wood of the laums camphara, or camphor tree, with water, iu 
 large iron pots, with earthen caps stuffed with straw. The camphor 
 sublimes and concretes upon the straw. C. 
 
OP VEGETABLES. 24? 
 
 pei'miem ; but you must not expect that I shall be able to ac- 
 count for this phenomenon, as nothing satisfactory has yet been 
 idvanced for its explanation. 
 
 Caroline. It is very singular indeed; and I will certainly 
 try the experiment. Pray what are resins, which you just now 
 mentioned ? 
 
 Mrs. B. They are volatile oils, that have been acted on, and 
 peculiarly modified, by oxygen. 
 
 Caroline. They are, therefore, oxygenated volatile oils? 
 
 Mrs. B. Not exactly ; for the process does not appear to 
 consist so much in the oxygenation of the oil, as in the combus- 
 tion of a portion of its hydrogen, and a small portion of its car- 
 bon. 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, similar to 
 that for preparing drying oils ? 
 
 Mrs. B. Yes; and it is by this operation that both of them 
 acquire a greater degree of consistence. Pitch, tar, and tur- 
 pentine, are the most common resins; they exude from the pine 
 and fir trees. Copal, mastic, and frankincense, are also of this 
 class of vegetable substances. 
 
 Emily. Is it of these resins that the mastic and copal varnish- 
 es, so much used in painting, are made ? 
 
 Mrs. B. Yes. Dissolved either in oil, or in alcohol, resins 
 form varnishes. From these solutions they may be precipita- 
 ted by water, in which they are insoluble. This I can easily 
 show you. If you will pour some water into this glass of mas- 
 tic varnish, it will combine with the alcohol in which the resin 
 is dissolved, and the latter will be precipitated in the form of a 
 white cloud 
 
 l-'.mily. It is so. And yet how is it that pictures or draw- 
 ings, varnished with this solution, may safely be washed with 
 water ? 
 
 Mrs. 13, As the varnish dries, the alcohol evaporates, and 
 the dry varnish or resin whjplPremains, not being soluble in wa- 
 ter, will not be acted on b/it* 
 
 There is a class of compound resins called gum resins, 
 which are precisely what their name denotes, that is to say, re- 
 sins combined with mucilage. Myrrh and assafcetida are of 
 this description. 
 
 Caroline. Is it possible that a substance of so disagreeable a 
 smell as assafcetida can be formed from a volatile oil ? 
 
 Mrs. B. The odour of volatile oils is by no means always 
 
248 COMPOSITION 
 
 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 consist of resin- 
 ous juices combined with a peculiar acid, called the benzoic ac- 
 id. 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 are the balsams of Peru, Tolu, &c. 
 
 We shall now take leave of the oils and their various modi- 
 fications, and proceed to the next vegetable substance, which is 
 caoutchouc. This is a white milky glutinous fluid, which ac- 
 quires consistence, and blackens in drying, in which state it 
 forms the substance with which you are so well acquainted, un- 
 der 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 ? 
 
 Mrs. B. It is obtained from two or three different species of 
 trees, in the East-Indies, and South-America, by making inci- 
 sions in the stem. The juice is collected as it trickles from 
 these incisions, and moulds of clay, in the form of little bottles 
 of gum-elastic, are dipped into it. A layer ,of this juice ad- 
 heres to the clay and dries on it : and several layers are suc- 
 cessively 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 countries 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 their being water- 
 proof. 
 
 The substance which comes next in our enumeration of the 
 immediate ingredients of vegetables, is extractive matter. This 
 is a term, which, in a general sense, may be applied to any sub- 
 stance extracted from vegetables; but it is more particularly 
 understood to relate to the extractive colouring matter of plants. 
 A s^reat variety of colours are prepared from the vegetable 
 kingdom, both for the purposes qfcg:>aiuting and of dying ; all 
 the colours called lakes are of th^Wescription ; but they are 
 less durable than mineral colours, for, by long exposure to the 
 atmosphere, they either darken or turn yellow. 
 
 Emily. I know that in painting, the lakes are reckoned far 
 
 * This is an erroneous idea. Balsams are original and peculiar sub- 
 stances, and consist chiefly of resinous matter in a s.-mifluid state. 
 The benzoic acid is most probably formed during the process by which 
 it is obtained. C 
 
OlT VEGETABLES. 24$ 
 
 less durable colours than the ochres ; but what is the reason of 
 it? 
 
 Airs. B. The change which takes place in vegetable colours 
 is owing chiefly to the oxygen of the atmosphere slowly burn- 
 ing their hydrogen, and leaving, in some measure, the blackness 
 of the carbon exposed. Such changes cannot take place in 
 ochre, 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 dye than linen and 
 cotton. 
 
 Caroline, Dying, then, is quite a chemical process ? 
 
 Mrs. B. Undoubtedly. The condition required to form a 
 good dye is, that the colouring matter should be precipitated, 
 or fixed, on the substance to be dyed, and should form a com- 
 pound not soluble in the liquids to which it will probably be 
 exposed. Thus, for instance, 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 woollens and 
 silks should withstand the action of grease and acids, to which 
 they may accidentally be exposed. 
 
 Caroline. But if linen and cotton have not a sufficient affini 
 ty for colouring matter, how are they made to resist the action 
 of washing, which they always do when they are well printed ? 
 
 Mrs. B. When the substance to be dyed has either no affin- 
 ity 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 com- 
 bine and adhere together. 
 
 Caroline. And what are the substances"that perform the of- 
 fice of thus reconciling the two adverse parties ? 
 
 Mrs. B. The most common mordant is sulphat of alumine, or 
 alum. Oxyds of tin and iron, in the state of compound salts, 
 are likewise used for that purpose. 
 
 Tannin is another vegetable ingredient of great importance 
 in the arts. It is obtained chiefly from the bark of trees ; but 
 it is found also in nut-galls, and in some other vegetables. 
 
 Emily. Is that the substance commonly called tan, which is 
 used in hot houses ? 
 
 Mrs. B. Tan is the prepared bark in which the peculiar sub- 
 stance, tannin, is contained.. But the use of tan in hot-houses 
 
250 COMPOSITION 
 
 is of much less importance than in the operation of tannmg,by 
 which the skin is converted into leather. 
 
 Emily. Pray, how is this operation performed ? 
 
 Mrs. B. Various methods are employed for this purpose., 
 which all consist in exposing skin to the action of tannin, or of 
 substances containing this principle, in sufficient quantities, and 
 disposed to yield it to the skin. The most usual way is to in- 
 fuse coarsely powdered oak bark in water, and to keep the skin 
 immersed in this infusion for a certain length of time. During 
 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 extracted from bark,) instead of em- 
 ploying the bark itself. But this quick mode of preparation 
 does not appear to make equally good leather. 
 
 Tannin 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 precipitated by a solution of isinglass, or 
 glue, with which it strongly unites arid forms an insoluble com- 
 pound. Hence its valuable property of combining with skin, 
 (which consists chiefly of glue,) and of enabling it to resist the 
 action of the water. 
 
 Emily. Might we not see that effort by pouring a little melt- 
 ed isinglass into a glass of wine, which you say contains tan- 
 nin ? 
 
 Mrs. B. Yes. I have prepared a solution of isinglass for 
 that very purpose. Do you observe the thick muddy precipi- 
 tate ? That is the tannin combined with the isinglass. 
 
 Caroline. This precipitate must then be of the same nature 
 as leather ? 
 
 Mrs. B It is composed of the same ingredients ; but the 
 organisation and texture of the skin being wanting, it has neither 
 the consistence nor the tenacity of leather. 
 
 Caroline. One mi^ht 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 ? 
 
 Airs. B. It is not impossible but that the coats of their stom- 
 achs may be, in some measure, tanned, or hardened by th; con- 
 stant use of this liquor ; but you must remember that where a 
 number of other chemical agents are concerned, and, above 
 all, where life exists, no certain chemical inference can be 
 drawn. 
 
OF VEGETABLES. 251 
 
 I must not dismiss this subject, without mentioning a recent 
 discovery of Mr. Hatchett, which relates to it. This gentle- 
 man found that a substance very similar to tannin, possessing all 
 its leading properties, and actually capable of tanning leather, 
 may be produced by exposing carbon, or any substance con- 
 taining carbonaceous matter, whether vegetable, animal, or mi- 
 neral, to the action of nitric acid.* 
 
 Caroline. And is not this discovery very likely to be of use 
 to manufactures ? 
 
 Mrs. B. That is very doubtful, because tannin, thus artifi- 
 cially prepared, must probably always 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 chemis- 
 try being able to imitate the proximate principles of organised 
 Bodies. 
 
 The last of the vegetable materials is woody fibre ; it is the 
 hardest part of plants. The chief source from which this sub- 
 stance is derived is wood, but it is also 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 car- 
 bon, united with a small proportion of salts, and the other con- 
 stituents common to all vegetables. 
 
 Emily. It is of 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 evaporable parts. 
 
 Before we take leave of the vegetable materials, it will be 
 proper, at least, to enumerate the several vegetable acids which 
 we either have had, or may have occasion to mention. I be- 
 lieve I formerly told you that their basis, or radical, was uni- 
 formly composed of hydrogen and carbon, and that their dif- 
 ference consisted only in the various proportions of cfxygen 
 which they contained. 
 
 The following are the names of the vegetable acids : 
 The mucous acid, obtained from gum or mucilage; 
 Suberic - - from cork ; 
 
 * To make artificial tannin, Mr Hatchett used 100 grains of char- 
 coal with 500 of nitric acid, diluted with twice its weight of water, 
 This mixture was heated and then suffered to digest for two days ; 
 more acid was then added, and the digestion continued untill the char- 
 coal was dissolved. The solution being evaporated to dry ness, 
 leaves a dark brown mass. This is the tannin in question, Its taste is 
 bitter and highly astringent. C, 
 
252 COMPOSITION 
 
 Camphoric - - from camphor ; 
 Benzoic - from balsams ; 
 
 Gallic - from galls, bark, &c. 
 
 Malic - from ripe fruits , 
 
 Citric - from lemon juice 5 
 
 Oxalic - from sorrelj 
 
 Succinic - - from amber ; 
 Tartarous - - from tartrit of potash ; 
 Acetic - from vinegar. 
 
 They are all decomposable by heat, soluble in water, and 
 turn vegetable blue colours red. The succinic, the tartaroits, 
 and the acetous acids, are the products of the decomposition 
 of vegetables, we shall, therefore, reserve 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 other acids may be converted 
 into the oxalic by an addition of oxygen, the oxalic itself is not 
 susceptible of a further degree of oxygenation ; nor can it be 
 made, by any chemical processes, to return to a state of lower 
 acidification.* 
 
 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 ? 
 
 Mrs. B. Yes. Though it is usually extracted from galls, on 
 account of its being most abundant in that vegetable substance, 
 it may also be obtained from a great variety of plants. It con- 
 stitutes what is called the astringent principle of vegetables ; 
 it is generally combined with tannin, and you will find that an 
 infusion of tea, coffee, bark, red wine, or any vegetable sub- 
 stance that confains the astrinuent principle, will make a black 
 precipitate with a solution of sulphat of iron. 
 
 Caroline. But pray what are galls ? 
 
 Mrs. B. They are excrescences which grow on the bark of 
 
 * Oxalic acid may be formed artificially. Put one ounce of white 
 sugar, powdered, into a retort, and pour on three ounces of nitric acid. 
 When the solution is over, make the liquor boil, and when it acquires 
 a reddish-brown colour, add three ounces more of nitric acid. Con- 
 tinue the boiling untill the fumes cease, and the colour of the liquor 
 vanishes. Then let the liquor be poured into a wide vessel, and on 
 white, slender crystals will be formed, These are oxalic acid. 
 
 C. 
 
OF VEGETABLES, 253 
 
 young oaks, ami are occasioned by an insect which wounds the 
 bark of trees, and lays its eggs in the aperture. The lacerated 
 vessels of the tree then discharge their contents, and form an 
 excrescence, which affords a defensive covering for these eggs. 
 The insect, when come to life, first feeds on this excrescence, 
 and some time afterwards eats its way out, as it appears from a 
 hole which is formed in all gall-nuts that no longer contain an 
 insect. It is in hot climates only Wiat strongly astringent gall- 
 nuts are found ; those which ,are used for the purpose of ma- 
 king ink are brought from Aleppo. 
 
 Emily. But are not the oak-apples, which grow on the leaves 
 of the oak in this country, of a similar nature ? 
 
 Mrs. B. Yes ; only they are an inferior species of galls, 
 containing less of the astringent principle, and therefore less 
 applicable to useful purposes. 
 
 Caroline. A re the vegetable acids never found but in their 
 pure uncombined state? 
 
 Mrs. B. By no means ; on the contrary, they are frequently 
 met with in the state of compound salts; these, however, are in 
 general not fully saturated with the salifiable bases, so that 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? 
 
 j\lrs. B. No $ that salt consists of the oxalic acid, combined 
 with a little potash. It is found in that state in sorrel. 
 
 Caroline. And pray how does it take out ink-spots ? 
 
 Mrs. B. By uniting with the iron, and rendering it soluble 
 in water. 
 
 Besides the vegetable materials which we have enumerated, 
 a variety of other substances, common to tiie three kingdoms^ 
 are found in vegetables, such as potash, which was formerly 
 supposed to belong exclusively to plants, *and was, in conse- 
 quence, called the vegetable alkali. 
 
 Sulphur, phosphorus, earths, and a variety of metallic oxyds, 
 are also found in vegetables, but only in small quantities. And 
 we meet sometimes with neutral salts, formed by the combina- 
 tion of these ingredients. 
 
 23 
 
254 DECOMPOSITION 
 
 CONVERSATION XXL 
 
 ON THE DECOMPOSITION OF VEGETABLES. 
 
 Caroline. THE account which you have given us, Mrs. B. 5 
 of the materials of vegetables, is, doubtless, very instructive but 
 ft does not completely satisfjlmy curiosity. I wish to know how 
 plants obtain the principles from which their various materials 
 are formed ; by what means these are converted into vegetable 
 matter, and how they are connected with the life of the plant ? 
 
 Mrs. 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 notions. Still I hope 
 that I shall be able, in some measure, to satisfy your curiosity. 
 But, in order to render the subject more intelligible, I must first 
 make you acquainted with the various changes which vegeta- 
 bles undergo, when the vital power no longer enables them to 
 resist the common laws of chemical attraction. 
 
 The composition of vegetables being more complicated than 
 that of minerals, the former more readily undergo chemical 
 changes than the latter : for the greater the variety of attrac- 
 tions, the more easily is the equilibrium destroyed, and a new 
 order of combinations introduced. 
 
 Emily. I am surprised that vegetables should be so easily- 
 susceptible of decomposition ; for the preservation of the veg- 
 *etable kingdom is certainly far more important than that of 
 minerals. 
 
 Mrs. B. You must consider, on the other hand, how much 
 more easily the former is renewed than the latter. The de- 
 composition of the vegetable takes place only after the death or" 
 the plant, which, in the common course of nature, happens 
 when it has yielded fruit and seeds to propagate its species. If. 
 instead of thus finishing its career, each plant was to retain its 
 form and vegetable state,. it would become an useless burden to 
 the eartli and its inhabitants. When vegetables, therefore, 
 cease to be productive, they cease to live, and nature then be- 
 gins her process of decomposition, in order to resolve them in- 
 to their chemical constituents, hydrogen, carbon, and oxygen ; 
 those simple and primitive ingredients, which she keeps in store 
 for all her combinations. 
 
 Emily. But since no system of combination can be destroy- 
 ed, except by the establishment of another order of attractions, 
 how can the decomposition of vegetables reduce them to their 
 simple elements ? 
 
OP VEGETABLES. 253 
 
 Mrs. B. It is a very long process, during which a variety of 
 new combinations are successively established and successively 
 destroyed; but, in each of these changes, the ingredients of 
 vegetable matter tend to unite in a more simple order of com- 
 pounds, till they are at length brought to their elementary state, 
 or at least, to their most simple order of combinations. Thus 
 j'ou will fintl that vegetables are in the end almost entirely re- 
 duced to water and carbonic acid; the hydrogen and carbon 
 dividing the oxygen between them, so as to form with it these 
 two substances. But the variety of intermediate combinations 
 that take place during the several stages of the decomposition of 
 vegetables, present us with a new set of compounds, well wor- 
 thy of our examination. 
 
 Caroline. How is it possible that vegetables, while putrefy- 
 ing, should produce any thing worthy of observation ? 
 
 Mrs. B. They are susceptible of undergoing certain changes 
 before they arrive at the state of putrefaction, which is the final 
 term of decomposition; and of these changes we avail ourselves 
 for particular and important purposes. But, in order to make 
 you understand this subject, which is of considerable import- 
 ance, 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 or- 
 der of particles, and the combination of another. This is call- 
 ed FERMENTATION. There are several periods at which this 
 process stops, so that a state of rest appears to be restored, and 
 the new order of compounds 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 fermentations, then, appear to be only the suc- 
 cessive steps by which a vegetable descends to its final dissolu* 
 tion. 
 
 Mrs. B. Precisely so. Your definition is perfectly correct. 
 
 Caroline. And how many fermentations, or new arrange- 
 ments, does a vegetable undergo before it is reduced to its sim- 
 ple ingredients? 
 
 Mrs. 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 matter stops and chan- 
 ges its course. But every kind of vegetable matter is not equal- 
 ly susceptible of undergoing all these fermentations. 
 
 There are likewise several circumstances required to pro- 
 
256 DECOMPOSITION 
 
 duce fermentation. Water and a certain degree of heat ait 
 both essential to this process, in order lo separate the particles, 
 and thus weaken their force of cohesion, that the new chemic- 
 al affinities may be brought into action. 
 
 Caroline. In frozen climates, then, how can the spontaneous 
 decomposition of vegetables take place? 
 
 Ms. B. It certainly cannot; and, accordingly, we find 
 scarcely any vestiges of vegetation where a constant frost pre- 
 vails. 
 
 Caroline. One would imagine that, on the contrary, such 
 spots would be covered with vegetables; for, since they cannot 
 be decomposed, their number must always increase. 
 
 Mrs. B. But, my dear, heat and water are quite as essential 
 to the formation of vegetables, as they are to their decomposi- 
 tion. Besides, it is from the dead vegetables, reduced to their 
 elementary principles, that the rising generation is supplied 
 with sustenance. No young plant, therefore, can grow unless 
 its predecessors contribute both to its formation and support j 
 and these not oaly furnish the seed from which the new plant 
 springs, but likewise the food by which it is nourished. 
 
 Caroline. Under the torrid zone, therefore, where water is 
 never frozen, and the heat is very great, both the processes of 
 vegetation and of fermentation must, I suppose, be extremely 
 rapid ? 
 
 Mrs. B. Not so much as you imagine : for in such climates 
 great part of the water which is required for these processes is 
 in an aeriform state, which is scarcely more conducive either to 
 the growth or formation of vegetables than that of ice. In 
 those latitudes, therefore, it is only in low damp situations, shel- 
 tered 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 enoughrfo produce 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 autumnal rains (which are very violent in such 
 climates,) that spontaneous fermentation can take place. 
 
 The several fermentations derive their names from theii 
 principal products. The first is called the saccharine ferment - 
 ation, because its product is sugar. 
 
 Caroline. But sugar, you have told us, is found in all vegeta- 
 bles ; it cannot, therefore, be the product of their decomposi- 
 tion. 
 
 Mrs. B. It is true that this fermentation is not cofined to the 
 decomposition of vegetables, as it continually takes place during 
 their life; and, indeed, this circumstance has, till lately, pre~ 
 
OP VEGETABLES. 257 
 
 vented it from being considered 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 vegetable 
 matter is so evidently a new compound, proceeding from the 
 destruction of the previous order of combinations, und essential 
 to the subsequent fermentations, that it is now, I believe, gene- 
 rally esteemed the first step, or necessary preliminary, to de- 
 composition, if not an actual commencement of that process. 
 
 Caroline. I recollect your hinting to us that sugar was suppo- 
 sed not to be secreted from the sap, in the same manner as mu- 
 cilage, fecula, o9, and the other ingredients of vegetables. 
 
 Mrs. 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 they have been gathered. Life, 
 therefore, is not essential to the formation of sugar, whilst on 
 the contrary, mucilage, fecula, and the other vegetable materials 
 that are secreted from the sap by appropriate organs, whose 
 powers immediately depend on the vital principle, cannot bo 
 produced but during the existence of that principle. 
 
 Emily. The ripening of Uiuits is, then, their first step to de- 
 struction, as well as their tast Cowards perfection ? 
 
 Mrs. B. Exactly. A process analogous to the saccharine 
 fermentation takes place also during the cooking of certain ve- 
 getables. This is the case with parsnips, carrots, potatoes, &c. 
 in which sweetness is developed by heat and moisture ; and we 
 know that if we carry the process a little farther, a more com- 
 plete decomposition would ensue. The 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. The materials of the seed 
 must be decomposed, and the seed disorganized, before a plant 
 can sprout from it. Seeds, besides the embrio plant, contain 
 (as we have already observed) fecula, oil, and a little mucilage. 
 These substances are destined for the nourishment of the future 
 plant ; but they undergo some change before they can be fit for 
 this function. The seeds, when buried in the earth, with a cer- 
 tain 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 
 substance of the seed is thus softened, sweetened, and converted 
 into a sort of white milky pulp, fit for the nourishment of the 
 embrio plant. 
 
 23* 
 
258 DECOMPOSITION 
 
 The saccharine fermentation of seeds is artificially produced, 
 for the purpose of making malt) by the following process *-<- A 
 quantity of barley is first soaked in water for two or three days : 
 the water being afterwards drained off, the grain heats sponta- 
 neously, swells, bursts, sweetens, shows a disposition to germin- 
 ate, and actually sprouts to the length of an inch, when the pro- 
 cess is stopped by putting it into a kiln, where it is well dried 
 at a gentle heat. In this state it is crisp and friable, and con- 
 stitutes the substance called malt, which is the principal ingredi- 
 ent of beer. 
 
 Emily. But I hope you will tell us how malt is made into 
 beer? 
 
 Mrs. B. Certainly ; but I must first explain to you the na- 
 ture of the second fermentation, which is essential to that ope- 
 ration. This is called the vinous fermentation, because its pro- 
 duct is wine. 
 
 Etnily. How very different the decomposition of vegetables 
 is from what I had imagined ! The pioducts of their disorgani- 
 sation appear almost superior to those which they yield during 
 their state of life and perfection. 
 
 Mrs. B. And do you not, at tht s^me time, admire the beau- 
 tiful economy of Niture, which, whether she creates, or wheth- 
 F er she destroys, directs all her operations to some useful snti 
 benevolent purpose ? It appears that the saccharine fermenta- 
 tisn is extremely favourable, if not absolutely essential, as a 
 previous step, to the vinous fermentation ; so that if sugar be 
 not developed 'luring the life of the plant, the saccharine fer- 
 mentation must be artificially produced before the vinous fer- 
 mentation can take place. This is the case with barley, which 
 does not yield any sugar until it is made into malt 5 and it 
 is in that state only that it is susceptible of undergoing the vi- 
 nous fermentation by which it is converted into beer. 
 
 Caroline. But if the product of the vinous fermentation is 
 always wine, beer cannot have undergone that process, for beer 
 is certainly not wine. 
 
 Mrs. B. Chemically speaking, beer may be considered as 
 the wine of grain. For it is the product of the fermentation of 
 malt, just as wine is that of the fermentation of grapes, or other 
 'fruits. 
 
 The consequence of the vinous fermentation is the decompo- 
 sition of the saccharine matter, and the formation of a spiritu- 
 ous liquor from the constituents of the sugar. But, in order to 
 promote this fermentation, net only water and a certain degree 
 of htat are necessary, but also some other vegetable ingredients, 
 besides the sugar, as fecula, mucilage, acids, salts, extractive 
 
 
Of VEGETABLES. 259 
 
 matter, &c. all of which seem to contribute to this process ; and 
 give to the liquor its peculiar taste. 
 
 Emily. It is, perhaps, for this reason that wine is notjobtain- 
 ed from the fermentation of pure sugar ; but that fruits are cho- 
 sen for that purpose, as they contain not only sugar, but like- 
 wise the other vegetable ingredients which promote the vinous 
 fermentation, and give the peculiar flavour. 
 
 Airs. b. Certainly. And you must observe also, that the re- 
 lative quantity of sugar is not the only circumstance to be con- 
 sidered 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 yi*!ds the most considerable propor- 
 tion of wine, but that it likewise affords it of the most grateful 
 flavour. 
 
 Emily. I have seen a vintage in Switzerland, and I do not 
 recollect that heat was applied, or water added, to produce the 
 fermentation of the grapes. 
 
 Mrs. />'. The common temperature of the atmosphere 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 sup- 
 ply of water, there is no occasion for any addition of it. But 
 when fermentation is produced in dry mSlt, a quantity of water 
 must necessarily be added. 
 
 Emily. But what are precisely the changes that happen du- 
 ring the vinous fermentation ? 
 
 Mrs. B. The sugar is decomposed, and its constituents are 
 recombined 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 gas, which escapes during 
 the fermentation. Wine, therefore, as 1 before observed, in a 
 general point of view, may be considered as a liquid of which 
 alcohol constitutes the essential part. And the varieties of 
 strength and flavour of the different kinds of wine are to be at* 
 tributed to the different qualti^es of the fruits from which they 
 are obtained, independently of the sugar. 
 
 Caroline. lam astonished to' hear that so powerful a liquid 
 as spirit of wine should be obtained from so mild a substance 
 as sugar. 
 
 Airs. B. Can you tell me in what the principal difference 
 consists between alcohol and sugar ? 
 
 Caroline. Let me reflect .... Sugar consists of carbon, hy- 
 drogen, and oxygen. If carbonic acid be subtracted from it ? 
 
260 DECOMPOSITION 
 
 during the formation of alcohol, the latter will contain less car- 
 bon and oxygen than sugar does ; therefore hydrogen must be 
 the prevailing principle of alcohol. 
 
 Mrs. B. It is exactly so. And this very large proportion of 
 hydrogen accounts for the lightness and .combustible property of 
 alcohol, and of spirits in general, all of which consist of alcohol 
 variously modified. 
 
 Emily. And can sugar be recomposed from the combination 
 of alcohol and carbonic acrd ? 
 
 Mrs. B. Chemists have never been able to succeed in effect- 
 ing this ; but from analogy, I should suppose such a recompo- 
 sition possible. Let us now observe more particularly the phe- 
 nomena that take place during the vinous fermentaiion. At the 
 commencement of this process, heat is evolved; and the liquor 
 swells considerably Iron) -the formation of the carbonic acid, 
 which is disengaged in such prodigious quantities as would be 
 fatal to any person who should unawares inspire it ; an acci- 
 dent which lias sometimes happened. If the fermentation be 
 stopped by putting the liquor into barrels, before the whole of 
 the carbonic acid is evolved, the wine is brisk, like Champagne, 
 from the carbonic acid imprisoned in it, and it tastes sweet, like 
 cyder, from the sugar not being completely decomposed. 
 
 Emily. But I do not understand why heat should be evolved 
 during this operation. For, as there is a considerable forma- 
 tion of gas, in which Ti proportionable quantity of heat must 
 become insensible, I should have imagined that cold, rather 
 than heat, would have been produced. 
 
 Mrs. 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 atten- 
 ding it, a quantity of chemical heat may be disengaged, suffi- 
 cient both to develope the gas, and to effect an increase of tem- 
 perature. 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, trans- 
 parent, spiritous liquor, called wine. 
 
 Emily. How much I regret not having been acquainted with 
 the nature of the vinous fermentation, when I had an opportu- 
 nity of seeing the process ! 
 
 Mrs. B. You have an easy method of satisfying yourself in 
 that respect by observing the process of brewing, which, in eve- 
 ry essential circumstance, is similar to that of making wine, 
 and is really a very curious chemical operation. 
 
 Although we cannot actually make wine at this moment, it 
 will be easy to show you the mode of analyzing it This is 
 
OP VEGETABLES. 2()1 
 
 done by distillation. When wine of any kind is submitted to 
 this operation, it is found to contain brandy, water, tartar, ex- 
 tractive colouring matter, and some vegetable acids. I have 
 put a little port wine into this alembic of glass (PLATE XIV. 
 fig. 1.,) and on placing the lamp under it, you will soon see the 
 spirit and water successively come over 
 
 Emily. But you do not mention alcohol amongst the pro* 
 ducts of the distillation of wine ; and yet that is its most es- 
 sential 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 ; it tastes 
 like strong brandy, but it is without colour, whilst brandy is 
 of a deep yellow. 
 
 Mrs. B. It is not so naturally ; in its pure state brandy is 
 colourless, and it obtains the yellow tint you observe, by ex- 
 tracting the colouring matter from the new oaken casks in which 
 it is kept. But if it does not acquire the usual tinge in this 
 way, it is the custom to colour the brandy used in this country 
 artificially, with a little burnt sugar, in order to give it the ap- 
 pearance of having been long kept. 
 
 Caroline. And is rum also distilled from wine ? 
 
 Mrs. B. By no means ; it is distilled from the sugar-cane, a 
 plant which contains so great a quantity of sugar, that it yields 
 more alcohol than almost any other vegetable. After the juice 
 of the cane has been pressed out for making sugar, what still 
 remains in the bruised cane is extracted by water, and this wa- 
 tery solution of sugar is fermented, and produces rum. 
 
 The spirituous liquor called arack is in a similar manner dis* 
 tilled from the product of the vinous fermentation of rice. 
 
 Emily. But rice has no sweetness ; does it contain any su- 
 gar ? 
 
 Airs. B. Like barley and most other seeds, it is insipid until 
 it has undergone the saccharine fermentation ; and this, you 
 must recollect, is always a previous step to the vinous fermenta- 
 tion 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 fermentation. 
 
 Mrs. B. Beer is not precisely the product of the vinous fer- 
 mentation of malt. For hops are a necessary ingredient for the 
 formation of that liquor ; whilst brandy is distilled from pure 
 
262 DECOMPOSITION 
 
 fermented malt. But brandy might, no doubt, be distilled from 
 beer as well as from any other liquor that has undergone the 
 vinous fermentation ; for since the basis of brandy is alcohol, it 
 may be obtained from any liquid that contains that spirituous 
 substance. 
 
 Emily. And pray, from what vegetable is the favourite spi- 
 rit of the lower orders of the people, gin, extracted ? 
 
 Mrs. B. The spirit (which is the same in alt fermented li- 
 quors) may be obtained from any kind of grain ; but the pe- 
 culiar flavour which distinguishes gin is that of juniper berries, 
 which are distilled together with the grain 
 
 I think the brandy contained in the wine we are distilling 
 must, by this time, be all come over. Yes taste the liquid 
 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 se- 
 ?ond product of wine, and comes over after all the spirit, which 
 is the lightest part, is distilled. The tartar and extractive col- 
 ouring 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 similar 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 fermentation. During this 
 operation it is precipitated, and deposils itself on the internal 
 surface of the cask in which the wine is contained. It is much 
 used in medicine, and in various arts, particularly dying, under 
 the name of cream of tartar, and it is 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 dregs ; it is perfectly 
 colourless. 
 
 Mrs. B. Because it consists of the pure salts only, in its crys- 
 tallised form ; whilst in the instance before us it is mixed with 
 the deep-coloured extractive matter, and other foreign ingredi- 
 ents. 
 
 Emily. Pray cannot we now obtain pure alcohol from the 
 brandy which we have distilled ? 
 
 Mrt. B. We might ; but the process would be tedious ; for 
 
 in order to obtain alcohol perfectly free from water, it is neces- 
 
 ,sary to distil, or, as the distillers call it, rectify it several times. 
 
 You must therefore allow me to produce a bottle of alcohol that 
 
 has been thus purified. This is a very important ingredient. 
 
OE VEGETABLES. l'0o 
 
 which has many striking properties, besides its forming the ba- 
 sis of all spirituous liquors. 
 
 Emily. It is alcohol, I suppose, that produces intoxication ? 
 
 Mrs. B. Certainly ; but the stimulus and momentary energy 
 it gives to the system, and the intoxication it occasions when 
 taken in excess, are circumstances not yet accounted for. 
 
 Caroline. I'thought that it produced these effects by increas- 
 ing the rapidity of the circulation of the blood ; for drinking 
 wine or spirits, I have heard, always quickens 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 vi- 
 gour, and propels the blood with accelerated quickness, After 
 such a strong excitation, the frame naturally suffers a propor- 
 tional degree of depression, so that a state of debility and lan- 
 guor is the invariable consequence of intoxication. Cut though 
 these circumstances are well ascertained, they aie far from ex- 
 plaining why alcohol should produce such effects. 
 
 Emily. Liquers are the only kind of spirits which I think 
 pleasant. Pray of what do they consist ? 
 
 Mrs. B. They are composed of alcohol, sweetened with sy- 
 rup, and flavoured with volatile oil. 
 
 The different kinds of odoriferous spirituous waters are like- 
 wise solutions of volatile oil in alcohol, as lavender water, eau 
 de Cologne, &c. 
 
 The chemical properties of alcohol are important and nume- 
 rous. It is one of the 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. 
 
 Mrs. B. 1 am happy to find that you recollect these circum- 
 stances so well. The same experinKMt affords also an instance 
 of another property of alcohol, its tendency to unite with wa- 
 ter; for the resin is precipitated in consequence of losing the al- 
 cohol, which abandons it from its preference for water. It is 
 attended also, as you may recollect, with the same peculiar cir- 
 cumstance of a disengagement of heat and consequent diminu- 
 tion of bulk, which we have supposed to be produced by a me- 
 chanical 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 th^ 
 extensive class of elixirs, tinctures, quintessences, &c, 
 
264 DECOMPOSITION 
 
 Emily. I suppose that alcohol must be highly combustible, 
 since it contains so large a proportion of hydrogen ? 
 
 Mrs. B. Extremely so ; and it will burn at a very moderate 
 temperature. 
 
 Caroline. I have often seen both brandy and spirit of wine 
 burnt; they produce a great deal of flame, but not a propor- 
 tional quantity of heat, and no smoke whatever. ' 
 
 Mrs. ti. The last circumstance arises from their combus- 
 tion being complete; and the disproportion between the flame 
 and heat shows you that these are by no means synonymous. 
 
 The great quantity of flame proceeds from the combustion of 
 the hydrogen to which you know, that manner of burning is pe- 
 culiar. Have you not remarked also that brandy and alcohol 
 will burn without a wick? They take fire at so low a tempe- 
 rature, that this assistance is not required to concentrate the 
 heat and volatilise the fluid. 
 
 Caroline. 1 have sometimes seen brandy burnt by merely 
 heating it in a spoon. 
 
 Mrs. B. The rapidity of the combustion of alcohol may, 
 however, be prodigiously increased by first volatilising it. An 
 ingenious instrument has been constructed on this principle to 
 answer the purpose of a blow-pipe, which may be used for 
 melting glass, or other chemical purposes. It consists of a 
 small metallic vessel (PLATE XIII. fig. 2.) of a spherical shape, 
 which contains the alcohol, and is heated by the lamp beneath 
 it; as soon as the alcohol is volatilised, 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 
 show 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? 
 
 Mrs. B. Yes ; because in tbis way the combustion goes on 
 much quicker, and, of course, the heat is proportionally increa- 
 sed. Observe its effect on this small glass tube, the middle of 
 which 1 present to the extremity of the flame, where the heat 
 is gieatest. 
 
 * A spirit lamp, which answers very well for bending small glass 
 tubes, may be constructd by almost any one. Take a lo vial with 
 a wide mouth, fit a coric to it and pierce tne cork to admit a piece of 
 glass tube, the bore of which is about the size o( a large gooscquill. 
 Let the tube lise an inch or two above the cork pass some cotton 
 wick through the tube then fill the vial with alcohol and put the cork 
 and tube in their places. The lamp is then ready. C. 
 
OF VEGETABLES. 
 
 Caroline. The glass, in that spot, is become red hot, and 
 bends from its own weight. 
 
 ./WAV. B. 1 have not drawn it asunder, and am going to blow 
 a ball at one of the heated ends : but I must previously close it 
 up, and flatten it with this little metallic 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 biowed too hard ; for the ball suddenly dilated 
 to a great size, and then burst in pieces. > 
 
 Mrs. B. You will be more expert another time; but I must 
 caution you, should you ever use this blow-pipe, to be very 
 careful that the combustion of the alcohol 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 ves- 
 sel bursting, as it is provided with a safety tube, which affords 
 an additional vent for the vapour of alcohol when required. 
 
 The products of the combustion of alcohol consist in a great 
 proportion of water, and a small quantity of carbonic acid. 
 There is no smoke or fixed remains whatever. How do you 
 account for that, Emily ? 
 
 Emily. I suppose that the oxygen which the alcohol absorbs 
 in burning, converts its hydrogen into water and its carbon h> 
 to carbonic acid gas, and thus it is completely consumed. 
 
 J\1rs. B. Very well. Ether, the lightest of all fluids, and 
 with which you are well acquainted, is obtained from alcoholj 
 of which it forms the lightest and most volatile part. 
 
 Emily. Eether, thn, is to alcohol, what alcohol is to brandy r 
 
 Mrs. B. No : there is an essential difference. In order to 
 obtain alcohol from brandy, you need only deprive the latter 
 of its water ; but for the formation of ether, the alcohol must 
 be decomposed, and one of its constituents partly subtracted 
 I leave you to guess which of them it is 
 
 Emily. It cannot be hydrogen, as ether is more volatile 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 
 i\ proportion of that principle; it is, therefore, most probably, 
 carbon, a diminution of which would not fail to render the new 
 compound more volatile. 
 
 Mrs. B. You are perfectly right. The formation of ether 
 consists simply L. subtracting from the alcohol a certain pro- 
 portion of carbon ; this is effected by the action q^the sul- 
 phuric, nitric, or muriatic acids, on a!r?hol. The acid and 
 carbon remain at the bottom of the vessel, whilst the decarbor 
 
 24 
 
266 DECOMPOSITION 
 
 nised alcohol flies off in the form of a condensable vapour, 
 which is ether. 
 
 Ether is the most inflammable 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 volatilised, which takes fire, and gradually increases 
 the violence of the combustion. 
 
 Sir Humphry Davy hr.s lately discovered a very singular 
 fact respecting the vapour of ether. If a few drops of ether 
 be poured into a wine-glass, and a fine platina wire, heated al- 
 most to redness, be held suspended in the glasj, close to the 
 surface of the ether, the wire soon becomes intensely red-hot, 
 and remains so for any length of time. We may easily try 
 the experiment 
 
 Caroline. How very curious ! The wire is almost white 
 hot, and a pungent smell rises from the glass. Pray how u; 
 this accounted for ? 
 
 Jl/rs. B. This is owing to a very peculiar property of the 
 vapour of ether, and indeed of many other combustible gaseous 
 bodies. At a certain temperature lower than that of ignition, 
 these vapours undergo a slow and imperfect combustion, which 
 does not give rise, in any sensible degree, to the phenomena of 
 light and flame, and yet extricates a quantity of caloric sufficient 
 to react upon the wire and make it red-hot, and the wire in its 
 turn keeps up the effect as Jong as the emission of vapour con- 
 tinues. 
 
 This singular effect, which is also produced by alcohol, may 
 be rendered more striking, and kvpt up for an indefinite length 
 of time, by rolling a few coils of platina wire, of the diameter of 
 from about 1-COth to l-70th of an inch, round the wick of a 
 spirit-lamp. If this lamp be lighted for a moment, and blown 
 out again, the wire, after ceasing for an instant to be luminous, 
 becomes red- hod again, though the lamp is extinguished, and 
 remains glowing vividly, till the whole of the spirit contained in 
 the lamp has been evaporated and consumed in this peculiar 
 maffher. 
 
 Caroline. That is extremely curious. But why should not 
 an iroti or silver wire produce the same effect ? 
 
 Mrs. B. Because either iron or silver, being much better 
 conductors of heat than platina, the heafis carried off too fast 
 by those metals to allow the accumulation of caloric necessary 
 to produce the effect in question. 
 
 Ether is so light that it evaporates at the common tempera- 
 ture of the atmosphere; it is therefore necessary to keep it con- 
 
OF VEGETABLES. 26f 
 
 fined by a well ground glass stopper. No degree of cold known 
 has ever frozen it.* 
 
 Caroline. Is it not often taken medicinally ? 
 
 Mrs. B. Yes ; it is one of the most effectual antispasmodic 
 medicines, and the quickness of its effects, as such, probably de- 
 pends on its being instantly converted into vapour by the heat 
 of the stomach, through the interventiou 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, 
 ft produces effects similar to those of intoxication. 
 
 We may now take our leave of the vinous fermentation, of 
 which I hope, you have acquired 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 a few words, as 
 it consists in the conversion of sugar and fermentable bodies in- 
 to alcohol and carbonic acid, which give rise both to the forma- 
 tion of wine, and of all kinds of spirituous liquors. 
 
 Mrs. B. We shall now proceed to the acetous fermentation^ 
 which is thus called, because it converts wine into vinegar, 
 by the formation of the acetous acid, which is the basis or rad- 
 ical of vinegar. 
 
 Caroline. But is not the acidifying principle of the acetous 
 acid the same as that of all other acids, oxygen? 
 
 Mrs. B. Certainly ; and on that account the contact 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. 
 
 Emily. But pray, Mrs. B., is not the acetous acid frequently 
 formed without this fermentation taking place ? Is it not, for in- 
 stance, contained in acid fruits/and in every substance that be- 
 comes sour ? 
 
 <\jrs. B. No, not in fruits; you confound it with the citric, 
 the malic, the oxalic, and other vegetable acids, to which living 
 vegetables owe theiu acidity. But whenever a vege able sub- 
 stance turns sour, after it has ceased to live, the acetous acid is 
 developed by means of the acetous fermentation, in which the 
 substance advances a step towards its final decomposition. 
 
 Amongst the various instances of acetous fermentation, that 
 of bread is usually classed. 
 
 Caroline. But the fermentation of bread is produced by yeast ; 
 how does that effect it ? 
 
 * Ether freezes, and shoots into crystals at 46 below the zero of 
 Fftbrenhei! ' ' 
 
DECOMPOSITION 
 
 Mrs. B. It is found by experience that any substance that 
 lias already undergone a fermentation, will readily excite it in 
 one that is susceptible of that process. If, for instance, yon 
 mix a little vinegar with wine, that is intended to be acidified, 
 it will absorb oxygen more rapidly, and the process be com- 
 pleted 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 con verted into beer, as well as that of paste which is to be 
 made into bread. 
 
 Caroline. But if bread undergoes the acetous fermentation, 
 why is it not sour ? 
 
 S.lrs. B. It acquires a certain savour which corrects the hea- 
 vy insipidity of flour, and may b* reckoned a first degree of 
 acidification ; or if the process were carried further, the bread 
 would become decidedly acid. 
 
 There are, however, some chemists who do not consider the 
 fermentation of bread as being of the acetous kind, but suppose 
 that it is a process of fermentation peculiar to that substance. 
 
 Tbe putrid fermentation is the final operation of Nature, and 
 her last step towards reducing organised bodies to their simplest 
 combinations. All vegetables spontaneously undergo this fer- 
 mentation after death, provided there be a sufficient degree of 
 heat and moisture, 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 fermentation 
 previous to this last ; or do they immediately suffer the putrid 
 fermentation ? 
 
 Mrs. B. That depends on a variety of circumstances, such as 
 the degrees of temperature and of moisture, the nature of the 
 plant itself, &c. But if you were carefully to follow and exa- 
 mine 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 un- 
 dergone the saccharine fermentation), previous to the total dis- 
 organisation and separation of the parts. 
 
 Emily. I have sometimes remarked a kind of spirituous taste 
 in fruits that were over ripe, especially oranges; and this was 
 just before they became rotten. 
 
 Airs. B. It was then the vinous fermentation which had suc- 
 ceeded the saccharine, and had you followed up these changes 
 attentively, you would probably have found the spiritous taste 
 followed by acidity, previous to the fruit passing to the state of 
 putrefaction. 
 
OP VEGlU'ABLES. 269 
 
 When the leaves fall from the trees in autumn, they do not 
 Jf there is no great moisture in the atmosphere) immediately 
 undergo a decomposition, but are first dried and withered ; as 
 soon, however, as the rain sets in, fermentation commences, 
 their gaseous products are imperceptibly evolved into the at- 
 mosphere, and their fixed remains mixed with their kindred 
 earth. 
 
 Wood, when exposed to moisture, also undergoes the putrid 
 fermentation and becomes rotten. 
 
 Emily. 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 essential to the putrid fermenta- 
 tion ? 
 
 Sifrs. B. True ; but it must not be in such a proportion 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 called dry rot, howev- 
 er, is not I believe a true process of putrefaction. It is suppo- 
 sed to depend on a peculiar kind of vegetation, which, by feed- 
 ing on the wood, gradually destroys it. 
 
 Straw and all other kinds of vegetable matter undergo th 
 putird fermentation more rapidly when mixed with animal mat- 
 ter. Much heat is evolved during this process, and a variety 
 of volatile products are disengaged, as carbonic acid arid hy- 
 drogen gas, the latter of which is frequently either sulphurated 
 or phosphorated. When nil these gases have been evolved, 
 the fixed products, consisting of carbon, 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 preserved from 
 decomposition by petrification ? I have seen very curious spe- 
 cimens of petrified vegetables, in which state they perfectly 
 preserve their form and organisation, 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 the history of mineral and veg- 
 etable 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 
 *o a substance in appearance resembling stone. 
 
 Mrs. B. It is not so, however, with the substances that are 
 called petrified vegetables ; for these are really stone, and gea~ 
 24* 
 
erally of the hardest kind, consisting chiefly of silex.* Tilt 
 case is this ; when a vegetable is buried under water, or in wet 
 earth, it is slowly and gradually decomposed. As each suc- 
 cessive particle of the vegetable is destroyed, its place is sup- 
 plied by a particle of siliceous earth, conveyed thither by the 
 water. In the course of time the vegetable is entirely destroy- 
 ed, but the silex has completely replaced it, having assumod its 
 form and apparent texture, as if the vegetable itself were chan- 
 ged to stone. 
 
 Caroline. That is very curious ! and I suppose that petrifi- 
 ed animal substances are of the same nature ? 
 
 J\irs. Bf Precisely. It is equally impossible for either ani- 
 mal or vegetable substances to be converted into stone. They 
 may be reduced, as we find they are, by decomposition, to their 
 constituent elements, but cannot be changed to elements, which 
 dt5 not enter into their composition. 
 
 There are, however, circumstances which frequently pre- 
 vent the regular and final decomposition of vegetables; as, 
 for instance, when they are buried either in the sea, or in the 
 earth, where they cannot undergo the putrid fermenation for 
 want of air. In these cases they are subject to a peculiar 
 change, by which they are converted into a new class of com- 
 pounds, called bitumens. 
 
 Caroline. These are substances I never heard of before. 
 
 Jk/rs. l>. You will find, however, that some of them are very 
 familiar to vou. Bitumens are vegetables so far decompo* 
 sed as to retain no organic appearance ; but their origin is 
 easily detected by their oily nature, their combustibility, the pro- 
 ducts of their analysis, and the impression of the forms oi 
 leaves, grains, fibres of wood, and even of animals, which thev 
 frequently bear. 
 
 They are sometimes of an oily liquid consistence, as the sub- 
 stance called naptha,* in which we preserved potassium ; it is 
 a fine transparent colourless fluid, that issues out of clays in 
 some parts of Persia. But more frequently bitumens are solid, 
 as osphaltum, a smooth, hard, brittle substance, which easily 
 melts, and forms, in its liquid state, a beautiful dark brown col- 
 our for oil painting. Jet, which is of a still harder texture, is 
 a peculiar bitumen, susceptible of so fine a polish, that it is 
 used for many ornamental purposes. 
 
 * Petrifactions arc of two Kinds, viz. silecious, when flinty particles 
 take the place of the original substance, and calcareous where the sub- 
 stance appears to be channel to li an -stone. The first kind give , fire 
 steel, antrHhe other effervesces with acids. C, 
 
OF VEGETABLES. 27i 
 
 Coal is also a bituminous substance, to the composition of 
 which both the mineral and animal kingdoms seem to concur. 
 This most useful mineral appears to consist chiefly of vegetable 
 matter, mixed with the remains of marine animals and marine 
 salts, and occasionally containing a quantity of sulphuret of 
 iron, commonly called pyrites. 
 
 Emily. It is, I suppose, the earthy, the metallic, and the sa- 
 line parts of coals, that compose the cinders or fixed products 
 of their combustion ; whilst the hydrogen and carbon, which 
 they derive from vegetables, constitute their volatile products. 
 
 Caroline. Pray is not co/te, (which 1 have heard is? much 
 used in some manufactures,) also a bituminous substance? 
 
 Mrs. B. No ; it is a kind of fuel artificially prepared from 
 coals. It consists of coals reduced to a substance analogous to 
 charcoal, by the evaporation of their bituminous parts. Coke, 
 therefore, is composed of carbon, with some earthy and saline 
 ingredients. 
 
 occm, or yellow amber, is a bitumen which the ancients 
 called elect rum, from whence the word electricity is derived, as 
 that substance is peculiarly, and was once supposed to be ex- 
 clusively, electric. It is found either deeply buried in the bow- 
 els of the 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 shows it to consist of an oil and an acid. The oil is 
 called oil of amber, the acid the siiccinic. 
 
 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 de- 
 composed by being exposed to moisture under ground, 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 th roots of plants are still dis- 
 cernible, and it equally answers the purpose of fuel. It is the 
 combustible used by the poor in heathy countries, which supply* 
 it abundantly. 
 
 * Naptha appears to be the only fluid in which oxygen does not ex- 
 ist ; hence its property of preserving potassium which has so strong 
 an affinity for oxygen as to absorb it from all other fluids. It howev- 
 er loses this property by exposure to the atmosphere, probably be- 
 cause it absorbs a small quantity of air, or moisture. It is again re- 
 stored by distillation. C, 
 
VEGfiTATIO'N. 
 
 It is too late this morning to enter upon the history of vegeta- 
 tion. We shall reserve this subject, therefore, for our next in- 
 terview, when I expect that it will furnish us with ample 
 for another conversation. 
 
 CONVERSATION XXII. 
 
 'HISTORY OF VEGETATION. 
 
 Mrs. B. THE VEGETABLE KINGDOM may be considered as 
 the link which unites the mineral and animal creation into one 
 common chain of beings : for it is through the means of vegeta- 
 tion alone that mineral substances are introduced into the ani- 
 mal system, since, generally speaking, it is from vegetables that 
 all animals ultimately- derive their sustenance. 
 
 Caroline. I do not understand that ; the human species sub- 
 sists as much on animal as on vegetable food, and there are 
 some carnivorous animals that will eat only 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 meat that we eat 
 is formed from the herbs of the field, and the prey of can 
 rous aiiKnals proceeds, either directly or indirectly, from the 
 same source. It is, therefore, through this channel that the 
 simple elements become a part of the animal frame. We should 
 in vain attempt to derive nourishment from carbon, 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 vegeta- 
 ble creation does not exhibit more wisdom in that admirable 
 system of organisation, by which it is enabled to answer its 
 'own immediate ends of preservation, nutrition, and propagation^ 
 than in its grand'and ultimate object of forming those arrange- 
 ments and combinations of principles, which are so well adapted 
 for the nourishment of animals. 
 
 Emily. But I am very curious to know whence vegetables 
 obtain their principles which form their immediate materials? 
 
 Mrs. 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 
 
VEGETATION. 
 
 what little I know on this subject, I will endeavour to explain 
 to you. 
 
 The soil, which, at first view, appears to be the aliment of 
 vegetables, is found, on a closer investigation, to be little more 
 than the channel through which they receive their nourish- 
 ment ; so that it is very possible to rear plants without any 
 earth or soil.* 
 
 * The opinion that water is the only food of plants, was adopted by 
 the learned on this subject in the 17th century; and many experi- 
 ments were made which seemed to prove that this was the truth. 
 Among others was a famous one by Van Helmout, which for a long 
 time was supposed to have established the point beyond all doubt. 
 He planted a willow which weighed five pounds,; in an earthern vessel 
 containing 200 Ibs of dried earth. This vessel was sunk into the 
 ground, and the tree was watered., sometimes with distilled, and some- 
 times with rain water. 
 
 At the end of five years the willow weighed 169 Ibs ; and on weigh- 
 ing the soil, dried as before, it was found to have lost only two oun- 
 ces. Thus the willow had gained 164 Ibs, and yet its food had been 
 only water. The induction from this experiment was obvious. Plants 
 live on pure water. This therefore was the general opinion, uutill 
 the progress of chemistry detected its fallacy. Bergman, in 1773 
 showed by some experiments that the water, which Van Helmout had 
 used contained as much earth as could exist in the tree at the end oi 
 the five years ; a pound of water containing about a grain of earth, 
 So that this experiment by no means proved that the willow lived on 
 water alone. Since this time a great variety of exp'-riments have 
 been made for the purpose of deciding what was the food of plants. 
 la the course of these, it has been found, that although seeds do vege- 
 tat&in pure distilled water, yet the plant is weakly, and finally dies 
 before the fruit is matured. 
 
 It id pretty certain then that earth is absolutely necessary to the 
 growth of plants, and that a part of their food is taken from the soil. 
 Indeed, the well known fact that a soil is worn out by a long succes- 
 sion of crops, and finally becomes sterile, unltss manured, is good proof 
 that plants do absorb something from it. 
 
 Saussure has shown that this is the fact, and also that the earth, 
 which is always found in plants, is of the same kind, as that on which 
 they grow. Thus trees growing in a granitic soil contain a large pro- 
 portion of silica, while those growing in a calcarious soil, contain lit" 
 tie silica, but a great proportion 'of calcareous earth. 
 
 In addition to what plants absorb from the ground, there is no doubt 
 but they obtain a part of their nourishment fiom water and air. 
 Some experiments made at Berlin, show that wheat, barley, &c. con- 
 tain a quantity of earth, though fed only on distilled water. 
 
 From the air plants absorb carbonic acid gas. The carbon they 
 retain, which forms the greatest part of their bulk. The oxygen is 
 omitted, and goes to purify the atmosphere. 
 
 Thus it is seen that plants obtain their food from the earth, from wa- 
 *er. and from the air C. 
 
274 VEGETATiON. 
 
 Caroline. Of that we have an instance in the hyacinth, and 
 other bulbous roots, which will grow and blossom beautifully in 
 glasses of water. But I confess I should think it would be dif- 
 ficult to rear trees in a similar manner. 
 
 Mrs. 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 im- 
 portant part which the earthy portion of the soil performs in 
 the process of vegetation ; for we can discover, by analysis, 
 but an extremely small proportion of earth in vegetable com- 
 pounds. 
 
 Caroline. But if earths do not afford nourishment, why is it 
 necessary to be so attentive to the preparation of the soil ? 
 
 Mrs. B. In order to impart it those qualities which render it 
 a proper vehicle for the food of the plant. Water is the chief 
 nourishment of vegetables 5 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 abound too much 
 with clay, the water will lodge in such quantities as to threaten 
 a decomposition of the roots. Calcareous soils are, upon the 
 whole, the most favourable to the growth of plants : soils are, 
 therefore, usually improved by chalk, which, you may recol- 
 lect, is a carbonat of lime. Different vegetables, however, re- 
 quire 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 fine sand than in a stiff clay ; 
 and a light ferruginous soil is best suited to fruit-trees. 
 
 Caroline. But pray what is the use of manuring the soil ? 
 
 Mrs. B. Manure consists of all kinds of substances, whether 
 of vegetable or animal origin, which have undergone the putrid 
 fermentation, and are consequently decomposed, or nearly so, 
 into their elementary principles. And it is requisite that these 
 vegetable matters should be in a state of decay, or approaching 
 decotn posit ion. The addition of calcareous earth, in the state 
 of chalk or lime, is beneficial to such soils, as it accelerates the 
 dissolution of vegetable bodies. 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 vegetables 
 with the principles which enter their composition. For ma- 
 nures not only contain carbon, hydrogen, and oxygen, -but by 
 their decomposition supply the soil with these principles in their 
 elementary form.* 
 
 * Rut what is the use of all this, if " water is the chief nourishment 
 of vegetables .-"' C. 
 
VEGETATION. 27& 
 
 Mrs. B. Undoubtedly; and it ts for this reason that the fin- 
 est crops are produced in fields that were formerly covered with 
 woods, because their- soil is composed of a rich mould, a kind ot 
 vegetable earth which abounds in those principles. 
 
 Emily. This accounts for the plentifulness of the crops pro- 
 Juced 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 appear much more 
 natural that the decomposed elements of vegetables should be 
 the most appropriate to the formation of new vegetables? 
 
 Mrs. l>. The addition of a much greater proportion of nitro- 
 gen, which constitutes the chief difference between animal and 
 vegetable matter, renders the composition of the former more 
 complicated, and consequently more favourable to decomposi- 
 tion. The use of animal substances is chiefly to give the first 
 impulse tMhe 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 tiie putrid fermentation that will not 
 make good manure. The heat produced by the fermentation 
 of manure is another circumstance which is extremely favour- 
 able to vegetation; yet this heat would be too great if the ma- 
 nure was laid on the ground during the height of fermentation j 
 it is used in this state only for hot-beds to produce melons, cu- 
 cumbers, and such vegetables as require a very high tempera- 
 ture. 
 
 Caroline. A difficulty has just occurred to me which I do 
 not know how to remove. Since all organised bodies are, in 
 the common course of nature, ultimately reduced to their ele- 
 mentary state, they must necessarily in that state enrich the soil ? 
 and afford food for vegetation. How is it, then, that agriculture, 
 which cannot increase the quantity of those elements that are 
 required to manure the earth, can increase its produce so won- 
 dei fully as is found to be the case in all cultivated countries ? 
 
 Mrs. B. It is by suffering none of these decaying bodies to 
 be dissipated, but in applying them duly to the soil. It is by a 
 judicious preparation of the soil, which consists in fitting it ei- 
 ther for the general purposes of vegetation, or for that of the 
 particular seed which is to be sown. Thus, if the soil be too 
 wet, it may be drained ; if too loose and sandy, it may be ren- 
 dered more consistent and retentive of water by the addition of 
 clay or loam ; it may be enriched by chalk, or any kind of cal- 
 careous earth. On soils thus improved, manures will act with 
 double efficacy, and if attention be paid to spread them on the 
 
'i VEGETATION. 
 
 ground at a proper season of the year, to mix them with the sew 
 So that they may be generally diffused through it, to destroy 
 the weeds which might appropriate these nutritive principles to 
 their own use, to remove the stones which would impede the 
 growth of the plant, &c. we may obtain a produce an hundred 
 fold more abundant than the earth would spontaneously supply. 
 Emily. We have a very striking instance of this in the scan- 
 ty produce of uncultivated commons, compared to the rich crops 
 of meadows which are occasionally manured. 
 
 Caroline. But, Mrs. B., though experience daily proves the 
 advantage of cultivation, there is still a difficulty which I can- 
 not get over. A certan 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 animal 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. 
 
 Mrs. B. Your reasoning is very plausible ; but experience 
 every where contradicts the inference you would draw from it ; 
 for we find that the animal and vegetable kingdoms, instead of 
 thriving, as you would suppose, at each other's expense, al- 
 ways increase and multiply together. For you should recollect 
 tl*it animals can derive the elements of which they are formed 
 only through the medium of vegetables. And you must allow 
 that your conclusion would be valid only if every particle of the 
 several principles that could possibly be spared from other pur- 
 poses were employed in the animal and vegetable creations. 
 Now we have reason to believe that a much greater proportion 
 of these principles than is required for such pusposes remains 
 either in an elementary state, or engaged in a less useful mode 
 of combination in the mineral kingdom. Possessed of such im- 
 mense resources as the atmosphere and the waters afford IKS, for 
 oxygen, hydrogen, and carbon, so far from being in danger of 
 working up all our simple materials, we cannot suppose that we 
 shall ever bring agriculture to such a degree of perfection as to 
 require the whole of what these resources could supply. 
 
 Nature, however, in thus furnishing us with an inexhaustible 
 stock of raw materials, leaves it in some measure to tlie ingenu- 
 ity of man to appropriate them to its own purposes. But like 
 a kind parent, she stimulates him to exertion, by setting the 
 example and pointing out the way. For it is on the operations 
 of nature that all the improvements of art are founded. The 
 art of agriculture consists, therefore, in discovering the readiest 
 method of obtaining the several principles, either from their 
 
VEGETATION* 277 
 
 rand sources, air and water, or from the decomposition of or- 
 ganised bodies; and in appropriating them in the best mannep 
 to the purposes of vegetation. 
 
 Emily. But, among the sources of nutritive principles, I am 
 surprised th^tyou do not mention the earth itself, as it contains 
 abundance of coals, which are chiefly composed of carbon. 
 
 Mrs. B. Though coals abound in carbon, they cannot, on 
 account of their hardness and impermeable texture, be imme- 
 diately subservient to the purposes of vegetation. 
 
 Emily. No ; but by their combustion carbonic acid is pro- 
 duced ; and this entering into various combinations on the sur- 
 face of the earth, may, perhaps, assist in promoting vegetation. 
 
 Mrs. B. Probably it may in some degree 5 but at any rate 
 the quantity of nourishment which vegetables derive from that 
 source can be but very trifling, and must entirely depend on lo- 
 cal circumstances. 
 
 Caroline. Perhaps the smoky atmosphere of London is the 
 cause of vegetation being so forward and so rich in its vicinity ? 
 
 Mrs. B. I rather believe that this circumstance proceeds 
 from the very ample supply of manure, assisted, perhaps, by 
 the warmth and shelter which the town affords. Far from at- 
 tributing any good to the smoky atmosphere of London, I con- 
 fess I like to anticipate the time when we shall have made such 
 progress in the art of managing combustion, that every particle 
 of carbon will be consumed, and the smoke destroyed at the 
 moment of its production. We may then expect to have the 
 satisfaction of seeing the atmosphere of London as clear as that 
 of the country. But to return to our subject : I hope that you 
 are now convinced that we shall not easily experience a defi- 
 ciency of nutritive elements to fertilize the earth, and that, pro- 
 vided we are but industrious in applying them to the best ad- 
 vantage by improving the art of agriculture, no limits can be 
 assigned to the fruits th*at we may expect to reap from our la- 
 bours. 
 
 Caroline. Yes ; I am perfectly satisfied in that respect, and 
 I can assure you that I feel already much more interested in the 
 progress and improvement of agriculture. 
 
 Emily. I have frequently thought that the culture of the land 
 was not considered as a concern of sufficient importance. Man. 
 ufactures always take the lead ; and health and innocence a-e 
 frequently sacrificed to the prospect of a more profitable em- 
 ployment. It has often grieved me to see the poor manufartu* 
 rers crowded together in close rooms, and confined for the wh./e 
 day to the most uniform and sedentary employment, instead of 
 
 25 
 
278 
 
 VEGETATION. 
 
 being engaged in that innocent and salutary kind of labour, 
 which Nature seems to have assigned to man for the immedi- 
 ate acquirement of comfort, and for the preservation of his 
 existence. I am sure that you agree with me in thinking so, 
 
 Mrs. B. I am entirely of your opinion, my dear, in regard 
 to the importance of agriculture; but as the conveniences of 
 life, which we are all enjoying, are not derived merely from the 
 soil, 1 am far from wishing to depreciate manufactures. Be- 
 sides, as the labour of one man is sufficient to produce food for 
 several, 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 accommodations for the 
 necessaries of life. Thus the carpenter 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 accommo- 
 dation which the artificer prepares. Such are the happy ef- 
 fects 'which naturally result from civilized society. It would 
 be wiser, therefore, to endeavour to improve the situation of 
 those who are engaged in manufactures, than to indulge in vain 
 declamations on the hardships to which they are too frequently 
 exposed. 
 
 But we must not yet take our leave of the subject of agricul- 
 ture ; we have prepared the soil, it remains for us now to sow 
 the seed. In this operation we must be careful not to bury it 
 too deep in the ground, as the access of air is absolutely neces- 
 sary to its germination ; the earth must, therefore, lie loose and 
 light over it, in order that the air may penetrate. Hence the 
 use of ploughing and digging, harrowing and raking, &c. A 
 certain 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 you have enumerated all the requisites of fer- 
 mentation. 
 
 Mrs. B. Do you forget, my dear, that the young plant de- 
 rives its existence from the destruction of the seed, and that it 
 is actually by the saccharine fermentation that the latter is de- 
 composed ? 
 
 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 fermen- 
 tation within it ? 
 

VEGETATION. 279 
 
 Mrs. B. Certainly. But, in order to understand the nature 
 of germination, you should be acquainted with the different 
 parts of which the seed is composed. The external covering 
 or envelope contains, beside the .gerrn of the future plant, the 
 substance which is to constitute ks first nourishment ; this sub- 
 stance, which is called the parenchyma, consists of fecula, mu- 
 cilage, and oil, as we formerly observed. 
 
 The seed is generally divided into two compartments, called 
 lobes or cotyledons, as is exemplified by this bean (PLATE XV. 
 fig. 1.) the dark-coloured kind of string which divides the 
 lobes is called the radicle, as it forms the root of the plant, and 
 it is from a contiguous substance, called plumula, which is in- 
 closed within the lobes, that the stem arises. The figure and 
 size of the seed depend very much upon the cotyledons ; these 
 vary in number in different seeds ; some have only one, as 
 wheat, oats, bailey, and all the grasses ; some have three, oth- 
 ers six. But most seeds, as for instance, all the varieties of 
 beans, have two cotyledons. When the seed is buried in the 
 earth, at any temperature above 40 degrees, it imbibes water, 
 which softens and swells the lobes ; it then absorbs oxygen, 
 which combines with some of its carbon, and is returned in the 
 form of carbonic acid. This loss of carbon increases the com- 
 parative proportion of hydrogen and oxygen in the seed, and 
 excites the saccharine fermentation, by which the parenchyma- 
 tous matter is converted into a kind of sweet emulsion. In 
 this form it is carried into the radicle by vessels appropriated 
 to that purpose ; and in the mean time, the fermentation hav- 
 ing caused the seed to burst, the cotyledons are rent asunder, 
 die radicle strikes into the ground and becomes the root of the 
 plant, and hence the fermented liquid is conveyed to the plu- 
 mula, whose vessels have been previously distended by the heat 
 of the fermentation. The plumula being thus swelled, as it 
 vere, by the emulative fluid, raises itself and springs up to the 
 surface of the earth, bearing with it the cotyledons, which, as 
 soon as they come in contact with the air, spread themselves, 
 :tnd are transformed into leaves. If we go into the garden, we 
 shall probably find some seeds in the state which I have de- 
 scribed 
 
 Emily. Here are some lupines that are just making their ap- 
 pearance above ground. 
 
 Mrs. B. We shall 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 radi- 
 cle striking downwards ? (PLATE XV. fig. 2.) In this thfi 
 
280 VEGETATION. 
 
 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 seeds leaves. 
 (PLATE XV. fig. 3.) 
 
 Caroline. These leaves are very thick and clumsy; and un- 
 like the other leaves, which I perceive are just beginning to ap- 
 pear, 
 
 Mrs. JBf. It is because they retain the remains of the paren- 
 chyma, with which they still continue to nourish 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 XIV. fig. 4.,) the radicle 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 5 the function of 
 the original 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 supply with aliment the or- 
 ganised being which they produce; and as soon as this has at- 
 Cained sufficient strength to procure its own nourishment, the 
 egg-shell breaks, whilst in the plant the seed-leaves fall off. 
 
 Mrs. B. There is certainly some resemblance between these 
 processes ; and when you become acquainted with animal chem- 
 istry, you will frequently be struck with its analogy to that of 
 the vegetable kingdom. 
 
 As soon as the young plant feeds from the soil, it requires 
 the assistance of leaves, which are the organs by which it 
 throws off its super-abundant 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 cal- 
 culated for carrying it on in sufficient quantities. This trans- 
 pired fluid consists of little more than water. The sap, by this 
 process, is converted into a liquid of greater consistence, 
 which is fit to be assimilated to its several parts. 
 
 Emily. Vegetation, then, must be essentially injured by de- 
 stroying the leaves of the plant? 
 
 Mrs. B. Undoubtedly; it not only diminishes the transpira- 
 tion, but also the absorption by the roots; for the quantity of 
 sap absorbed is always in proportion to the quantity of fluid 
 thrown off by transpiration. You see, therefore, the necessity 
 that a young plant should unfold its leaves as soon as it begins 
 to derive its nourishment from the soil ; and, accordingly, yon 
 
 
VEGETATION. 281 
 
 will And 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 described. 
 
 But I should inform you that this function of transpiration 
 seems to be confined to the upper surface of the leaves, whilst, 
 on the contrary, the lower surface, which is more rough and 
 uneven, and furnished with a kind of hair or down, is destined 
 to absorb moisture, or such other ingredients as the plant de- 
 rives from the atmosphere. 
 
 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 wake 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 ? 
 
 Mrs. B. That does not appear to be the case ; for in a 
 course of curious experiments, made by Mr. Senebier of Gene- 
 va, on plants which he reared by lamp-light, he found that the 
 flowers closed their petals whenever the lamps were extin- 
 guished. 
 
 Emily. But pray why is air essential to vegetation, plants do 
 not breathe it like animals? 
 
 Mrs. B. At least not in the same manner ; but they certain- 
 ly derive some principles from the atmosphere, and yield others 
 to it. Indeed it is chiefly owing to the action of the atmosphere 
 and the vegetable kingdom on each other, that the air contin- 
 ues always fit for respiration, But you will understand this 
 better when I have explained the effect of water on plants. 
 
 I have said that water forms the chief nourishment of plants ; 
 it is the basis not only of the sap, but of all the vegetable juices. 
 Water is the vehicle which carries into the plant the various 
 salts and other ingredients required for the formation and sup- 
 port of the vegetable system. Nor is this all; part of the wa- 
 ter itself is decomposed by the organs of the plant ; the hydro- 
 gen becomes a constituent part of oil, of extract, of colouring 
 matter, &c. whilst a portion of the oxygen enters into the for- 
 mation of mucilage, of fecula, of sugar, and of vegetable acids. 
 But the greater part of the oxygen, proceeding from the decom- 
 position of the water, is converted into a gaseous state by the 
 
 25* 
 
282 VEGETATION. 
 
 caloric disengaged from the hydrogen during its condensation 
 in the formation of the vegetable materials. In this state 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 not only a means of supplying it 
 with its chief ingredient, hydrogen, but at the same time of re- 
 plenishing the atmosphere with oxygen, a principle which re- 
 quires continual renovation, to make up for the great consump- 
 tion of it occasioned by the numerous oxygenations, combus- 
 tions, and respirations, that are constantly taking place on the 
 surface of the globe.* 
 
 Emily. What a striking instance of the harmony of nature. 
 
 Mrs. B. And how admirable the design of Providence, who 
 makes every different part of the creation thus contribute to the 
 support and renovation of each other! 
 
 But the intercourse of the vegetable and animal kingdoms 
 through the medium of the atmosphere extends still further. 
 Animals, in breathing, not only consume the oxygen of the air, 
 but load it with carbonic acid, which, if accumulated in the at- 
 mosphere, would, in a short time, render it totally unfit for res- 
 piration. Here the vegetable kingdom again interferes ; it at- 
 tracts and decomposes the carbonic acid, retains the carbon for 
 its own purposes, and returns the oxygen for ours.t 
 
 Caroline. How interesting this is ! I do not know a more 
 
 * The foregoing paragraph might mislead the student. Indeed it 
 seems to have been written without regard to proper authorities. For 
 instance, there is no proof that water is decomposed by the organs of 
 plants ; nor is it in the least degree probable that the oxygen emitted 
 by them owes its gaseous state, to the caloric set free by the condensa- 
 tion of hydrogen. Authors on this subject agree that the thickest veil 
 covers the processes by which the sap is converted into the several 
 parts of the plant. But it has been demonstrated, that most, if not all 
 the oxygen emitted by the leaves, is obtained by the decomposition of 
 air, instead of water, as here stated. If leaves are exposed to the rays 
 ef the sun, while under commm water, they emit oxygen. But if the 
 water is first deprived of its air, by an air pump, or by boiling, not 
 particle of oxygen is emitted. Now atmospheric air, always contains 
 a quantity of carbonic acid gas, and experiments show, that plants 
 give out oxygen in some proportion to the quantity of this gas contain- 
 ed in the waler. The fact then seems to be, that plants absorb car- 
 bonic acid, that this is decomposed by some unknown process ; the 
 plant retaining the carbon while the oxygen is given out. C. 
 
 t It is a curious fact, demonstrated by experiments, that the leaves 
 *f plants perform different offices at different periods of the 24 hours. 
 During the day they give oat water, absorb carbonic acid, and emit 
 oxygen gas ; but during the night they absorb water, and oxygen gas. 
 and give out carbonic acid. C 
 
VEGETATION. 283 
 
 beautiful illustration of the wisdom which is displayed in the 
 laws of nature. 
 
 Mrs. B. Faint and imperfect as are the ideas which our lim- 
 ited 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 comprehen- 
 sion, and it is no doubt among the wise dispensations of Provi- 
 dence, 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 en- 
 deavour to connect them into harmonious systems ; and, in a 
 word, to trace in the chain of beings, the kindred ties and be- 
 nevolent design which unites its various links, and secures its 
 preservation. 
 
 Caroline. But of what nature are the 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 functions, generally elude 
 our examination ; but we may consider them as so many ves- 
 sels or apparatus appropriated 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 oth- 
 er vegetable materials, in the organised arrangement of plants, 
 in which they form the bark, the wood, the leaves, flowers, and 
 seeds. 
 
 The bark is composed of the epidermis, the parenchyma, 
 and the cortical layers. 
 
 The epidermis is the external covering of the plant. It is a 
 thin transparent membrane, consisting of a number of slender 
 fibres, crossing each other, and forming a kind of net-work. 
 When of a white glossy nature, as in several species of trees, in 
 the stems of corn and of seeds, it is composed of a thin coating 
 of siliceous earth, which accounts for the strength and hardness 
 f those long and slender stems. Sir H. Davy was led to the 
 discovery of the siliceous nature of the epidermis of such plants, 
 by observing the singular phenomenon of sparks of fire emitted 
 by the collision of ratan canes with which two boys were fight- 
 ing in a dark room. On analysing the epidermis of the cane ? 
 he found it to be almost entirely siliceous.* 
 
 * In the scouring rash, (Equiselwn hyemale) the siliceous epider- 
 mis is still jpaore obvious. If drawn across a piece of soft metal, a^ 
 
284 VEGETATION. 
 
 Caroline. With iron then, a cane, I suppose, will strike fire 
 very easily ? 
 
 Mrs. B. I understand that it will. In ever-greens the epi- 
 dermis is mostly resinous, and in some few plants is formed of 
 wax. The re:in, from its want of affinity for water, tends to 
 preserve the plant from the destructive effects of violent rains, 
 severe climates, or inclement seasons, to which this species of 
 vegetables is peculiarly exposed. 
 
 Emily. Resin must preserve wood just like a varnish, as it 
 is the essential ingredient of varnishes ? 
 
 Mrs. B. Yes; and by this means it prevents likewise all un- 
 necessary expenditure of moisture. 
 
 The parenchyma is immediately beneath the epidermis ; it 
 is that green rind which appears when you strip a branch of 
 any tree or shrub of its external coat of bark. The parenchy- 
 ma 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 composed 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 descends after being elabo- 
 rated in the leaves. The cortical layers are annually renewed, 
 the old bark being converted into wood. 
 
 Emily. But through what vessels does the sap ascend?' 
 
 Mrs. B. That function is performed by the tubes of the al- 
 burnum, or wood, which is immediately beneath the cortical 
 layers. The wood is composed of woody fibre, mucilage, and 
 resin. The fibres are 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 in- 
 to wood. The oldest, amh^onsequently 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, there- 
 fore, spread into the leaves, and there communicate 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 parenchy- 
 
 silver or copper, i* ij^uts it likfc a file It even makes an impression oh 
 the hardest steeL C-. 
 
VEGETATION. %W 
 
 ina, since neither the ascending nor descending sap passes 
 through them ? 
 
 Mrs. B. They are supposed to perform the important func- 
 tion of secreting from the sap the peculiar juices from which the 
 plant more immediately derives its nourishment. These juic- 
 es 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 different parts 
 of the same individual plant : they are sometimes saccharine, 
 as in the sugar-cane, sometimes resinous, as in firs and ever- 
 greens, 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 incisions in the bark that pitch, 
 tar, and turpentine* are obtained from fir-trees. The durabili- 
 ty of this species of woed is chiefly owing to the resinous nature 
 of its peculiar juices. The volatile oils have, in a great meas- 
 ure the same preservative 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 
 human species have delight in them. They scarcely ever at- 
 tack any odoriferous parts of plants, and it is not uncommon 
 to see every leaf of a tree destroyed by a blight, whilst the blos- 
 soms remain untouched. Cedar, sandal, and all aromatic 
 woods, are on this account of great durability. 
 
 Emily. But the wood of the oak, which is so much esteem- 
 ed for its durability, has, I believe, no smell. Does it derive 
 this quality from its hardness alone ? 
 
 Airs. B. Not entirely ; for the chesnut, though considerably 
 harder and firmer than the oak, is not so lasting. The dura- 
 bility of the oak is, I believe, rn a great measure owing to its 
 having very little heart-wood, the alburnum preserving its vital 
 functions longer than in other trees. 
 
 Caroline. If incisions are made into the alburnum and cor- 
 
 * Turpentine is obtained as described in the te&t. But tar and 
 pitch are obtained by a very different method. A conical cavity is 
 dug in the earth, at the bottom d which is placed a reservoir. Over 
 this is piled billets of fir- wood, forming a large pile. The pile is cov- 
 ered with turf to smother the fire, which is kindled at the top. As the 
 wood is heated, and gradually converted into charcoal, the tar is dri- 
 ven out, and runs into the cavity, and finally into the reservoir. Tar 
 is a mixture of resin, empyreumatis oil, charcoal, and acetic acid. 
 The colour is derived from the charcoal. Pitch is made by boiling 
 tar, b^ which Its more volatile parts are driven off. C. 
 
VEGETATION. 
 
 deal layers, may not the ascending and descending sap be pro- 
 cured in the same manner as the peculiar juice is from the ves- 
 sels of the parenchyma ? 
 
 Mrs. B. Yes; but in order to obtain specimens of these flu- 
 ids, in any quantity, the experiment must be 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 the bark the sap 
 will flow much more plentifully than from the wood, as the as- 
 cending sap is much more liquid, more abundant, and more rap- 
 id 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, contains a much greater proportion of sol- 
 id matter, which retards its motion. It does not appear that 
 there is any excess of descending sap, as none ever exudes from 
 the roots of plants ; this process, therefore, seems to be carri- 
 ed on only in proportion to the wants of the plant, and the sap 
 descends no further, and in no greater quantity, than is requi- 
 red 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 jtfcwer, or blossom, 
 which produces thefruits and seed. These may be considered 
 as the ultimate purpose of nature in the vegetable creation. 
 From fruits and seeds animals derive both a plentiful source of 
 immediate nourishment, and an ample provision for the repro- 
 duction 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 fu- 
 ture vegetation. 
 
 These are the principal organs of vegetation, by means of 
 which the several chemical processes which are carried on du- 
 ring the life of the plant are performed. 
 
 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 vegetable matter ? 
 
 Mrs. B. By chemical processes, no doubt ; but the appara- 
 tus in which they are performed is so extremely minute as to 
 elude our examination. We can form an opinion, therefore, 
 only by the result of these operations. The sap is evidently 
 composed of water, absorbed by the roots, and holding in so- 
 lution the various principles which it derives from the soil. 
 From the roots the sap ascends through the tubes of the albur- 
 num into the stem, and thence branches out to every extremity 
 
VEGETATION. 287 
 
 of the plant. Together with the sap circulates a certain quan- 
 tity of carbonic acui, which is gradually disengaged from the 
 former hy the internal heat of the plant. 
 
 Caroline. What ? have vegetables a peculiar heat, analo- 
 gous to animal heat ? 
 
 Airs. B. It is a circumstance that has long been suspected ; 
 but late experiments have decided beyond a doubt, that vegeta- 
 ble heat is considerably above that of unorganised matter in 
 winter, and below it in summer. The wood of a tree is about 
 sixty degrees, when the thermometer is seventy or eighty de- 
 grees. And the bark, though so much exposed, is seldom be- 
 low forty 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 roots, it deposits in the 
 several sets of vessels with which it communicates, the materi- 
 als on which the growth and nourishment of each plant de- 
 pends. It is thus that the various peculiar juices, saccharine, 
 oily, mucous, acid, and colouring, are formed ; as also the 
 inoie solid parts, fecula, woody fibre, tannin, resins, concrete 
 salts : in a word, all the immediate materials of vegetables, as 
 well as the organised 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 partic- 
 ular nourishment. 
 
 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 ? 
 
 Airs. B Heat is such an important chemical agenr, 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 operation, it has been supposed that the 
 warmth of the spring dilates the vessels of plants, and produ- 
 ces 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 process goes on till the plant 
 blossoms and bears fruit, which terminates its summer career : 
 but when the cold weather sets in, the fibres and vessels con- 
 tract, 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 
 
288 COMPOSITION 
 
 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 the winter. 
 
 Caroline. Yet, in evergreens, vegetation must continue 
 throughout the year. 
 
 Mrs. B. Yes; but in winter it goes on in a very imperfect 
 manner, compared to the vegetation of spring and summer. 
 
 We have dwelt much longer on the history of vegetable 
 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 ac- 
 count of the fermentations for the conclusion ; for the decom- 
 position of vegetables naturally follows their death, and can 
 hardly, it seems, be introduced with so much propriety at any 
 other period. 
 
 J\lrs. B. It is difficult to determine at what (point precisely 
 k 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 di- 
 vide it. Had I begun with the germination of the seed, which, 
 at first view, seems to be the most proper arrangement, I could 
 not have explained the nature and fermentation of the seed, or 
 have described the changes which nvanure must undergo, in or- 
 der to yield the vegetable elements. To understand the nature 
 of germination, it is necessary, I think, previously to decom- 
 pose the parent plant, in order to become acquainted with the 
 materials required for that purpose. I hope, therefore, that, 
 upon second consideration, you will find that the order which 1 
 have adopted, though apparently less correct, is in fact the 
 best calculated for the elucidation of the subject. 
 
 CONVERSATION XXIII. 
 
 ON THE COMPOSITION OF ANIMALS. 
 
 Mrs. B. WE are now come to the last branch of chemistry, 
 which comprehends the most complicated order of compound 
 beings. This is the animal creation, the history of which can- 
 not but excite the highest degree of curiosity 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 nour- 
 ishment from vegetables, the chemistry of this order of beings 
 
OF ANIMALS. 289 
 
 must consist merely in the conversion of vegetable into animal 
 matter. 
 
 Mrs. B. Very true ; but the manner in which this is effect- 
 ed is, in a great measure, concealed from our observation. This 
 process is called animalisation, and is performed by peculiar 
 organs. The difference of the animal and vegetable kingdoms 
 does not however depend merely on a different arrangement o/ 
 combinations. A new principle abounds in the animal king- 
 dom, which is but rarely and in very small quantities found in 
 vegetables ; this is nitrogen. There is likewise in animal sub- 
 stances 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 fundamen- 
 tal principles ; oxygen, hydrogen, carbon, and nitrogen ? 
 
 Mrs. B. Yes ; and these form the immediate materials of an- 
 imals, which are gelatin^ albumen^ andj?6He.* 
 
 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 organisation. 
 
 Mrs. B. Their organisation is certainly more perfect and in- 
 tricate, and the ingredients that occasionally enter into their 
 composition are more numerous. But notwithstanding the 
 wonderful variety observable in the texture of the animal or- 
 gans, we find that the original compounds, from which all the 
 varieties of animal matter are derived, may be reduced to the 
 three heads just mentioned. Animal substances being the most 
 complicated of all natural compounds, are most easily suscept- 
 ible of decomposition, RS the scale of attractions increases m 
 proportion to the number of constituent principles. Theii 
 analysis is, however, both difficult and imperfect ; for as they 
 cannot be examined in their living state, and are liable to alter- 
 ation immediately after .death, it is probable that, when submt- 
 ted to the investigation of a chemist, they are always more 01 
 less altered in their combinations and properties, from what they 
 were, whilst they made part of the living animal. 
 
 Entity. The mere diminution of temperature, which they ex- 
 perience by the privation of animal heat, must, I should sup- 
 pose, be sufficient to derange the order of attractions that exist- 
 ed during life. 
 
 * These are the principal ingredients oi the soft parts. But in ad- 
 dition to these, animal substances contain, c-dGiiri'ii.:' matter of bluod, 
 mucous, sulphur, phosphorus, earths, alkalies, o<7s, adds, restw, arid 
 several others, -which it is unnecessary 4o specifv, (; 
 
 26 
 
29CT COMPOSITION 
 
 Mrs. B. That fs one of the causes, no doubt : but there arc 
 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, albumen, and 
 iibrine, form the basis of all the various parts of the animal 
 system ; either solid, as the skin, flesh, nerves, membranes, 
 cartilages, and bones ; or fluid, as blood, chyle, milk, mucus, 
 the gastric and pancreatic juices, bile, perspiration, saliva, 
 tears, &c. 
 
 Caroline. Is it not surprising that so great a variety of sub- 
 stances, and so different in their nature, should yet all arise from 
 so few materials, and from the same original elements ? 
 
 Mrs. B. The difference in the nature of various bodies de- 
 pends, as I have often observed to you, rather on their state of 
 combination, than on the materials of which they are compo- 
 sed. Thus, in considering the chemical nature of the creation 
 in a general point of view, we observe that it is throughout 
 composed of a very small number of elements. But when we 
 divide it into 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 and ani- 
 mal kingdoms, the attractions are peculiarly and regularly pro- 
 duced by appropriate organs, whose action depends on the vi- 
 tal principle. And we may further observe, that by means ot 
 certain spontaneous changes and decompositions, the elements 
 of one kind of matter become subservient to the reproduction 
 of another ; so that the three kingdoms are intimately connect- 
 ed, and constantly contributing to the preservation of each oth- 
 er. 
 
 Emily. There is, however, one very considerable class of 
 elements, which seems to be confined to the mineral kingdom : 
 I mean metals. 
 
 Mrs. A.'. Not entirely ; they are found,, though in very mi- 
 nute quantities, both in the vegetable and animal kingdoms. A 
 small portion of earths and sulphur enters also into the com- 
 position of organised bodies. Phosphorus, however, is almost 
 entirety confined to the animal kingdom ; and nitrogen, bn* 
 with few exceptions, is extremely scarce in vegetables. 
 
 Let us now proceed to examine the nature of the three prin- 
 cipal materials' of the animal system. 
 
 Gelatine, or jelly, is the chief ingredient of skin, and of all 
 the membranous parts oi ".animals. It may be obtained from 
 
?JF ANIMALS. 
 
 these substances, by means of boiling water under the forms of 
 ^iue, size, isinglass, and transparent jelly. 
 
 Caroline. Bu{ these are of a very different nature ; they can- 
 not therefore be all pure gelatine. 
 
 Mrs. B. Not entirely, but y^ery nearly so. Glue* is extract- 
 id from the skin of animals. Size is obtained either from skin 
 in its natural state, or from leather. Isinglass is gelatine pro- 
 cured 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 dissolving the isinglass in boiling water, and allowing 
 the solution to congeal. 
 
 Emily. The wine, lemon, and spices, are, I suppose, added 
 only to flavour the jelly ? 
 
 Mrs. B. Exactly so. 
 
 Caroline. But jelly is often made of hartshorn shavings, and 
 of calves' feet; do these substances contain gelatine ? 
 
 Mrs. B. Yes. Gelatine may be obtained from almost any 
 animal substance, as it enters more or less into the composition 
 of all of them. The process for obtaining it is extremely sim- 
 ple, as it consists merely in boiling the substance which con- 
 tains it, with water. The gelatine dissolves in water, and may 
 be attained of any degree of consistence or strength, by evapo- 
 rating this solution. Bones in particular produce it very plen- 
 tifully, as they consist of phosphat of lime combined or cement- 
 ed 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 ex- 
 tracted by the water. It is of hartshorn shavings that the jel- 
 lies for invalids are usually made, as they are of very easy di- 
 gestion. 
 
 Caroline, ft 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 gela- 
 tine 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 ammonia, or what is commonly called hartshorn, 
 the bones must be distilled, by which means the gelatine is de- 
 
 * Bones, muscles, tendons, ligaments, membranes, and skins, all of 
 them yield glue. But the best is made irom the skins of oh! animals. 
 
 G. \ 
 
292 COMPOSITION 
 
 composed^ and hydrogen and nitrogen combined in the form o 
 ammonia. So that the first operation is a mere separation OF 
 ingredients, whilst the second requires a chemical decomposi- 
 tion. 
 
 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 rendered 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 common 
 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 harts- 
 horn shavings ? 
 
 Mrs. B. There is a prejudice among the poor against a spe- 
 cies. of food that is usually thrown to the dogs ; and as we can- 
 not expect them to enter into chemical considerations, it is in 
 some degree excusable. Besides it requires a prodigious quan- 
 tity of fuel to dissolve bones and obtain the gelatine from them. 
 
 The solution of bones in water is greatly promoted by an ac- 
 cumulation of heat. This may be effected by means of an ex- 
 tremely strong metallic vessel,, called Papui's digester, in 
 which the bones and water are enclosed, without any possibili- 
 ty 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 low- 
 er classes. 
 
 Caroline. And why should not a manufacture be established 
 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 shavings? 
 
 Mrs. B. They could not be collected clean for such a pur- 
 pose, but'they are not lost, as they are used for making harts- 
 horn and sal ammoniac; and. such is the superior science and 
 industry of this country, that we now send sal ammoniac to the 
 Levant, though it originally came to us from Egypt. 
 
 Emily. When jelly is made of isinglass, does it leave no se- 
 diment ? 
 
 Mrs. B. No ; nor does it so much require clarifying, as it 
 consists almost entirely of pure gelatine, and any foreign matter 
 that is mixed with it, is thrown off during the boiling in UK 
 form of scum. These are processes which you may see per 
 
OP ANIMALS. 293 
 
 formed in great perfection in the culinary laboratory, by that 
 very able and most useful chemist the cook. 
 
 Caroline. To what an immense variety' of purposes chemis- 
 try is subservient ! 
 
 Emily. It appears, in that respect, to have an advantage over 
 most other arts and sciences ; for these, very often, have a ten- 
 dency to confine the imagination to their own particular object, 
 whilst the pursuit of chemistry is so extensive and diversified, 
 that it inspires a general curiosity, and a desire of enquiring in- 
 to the nature of every object. 
 
 Caroline. I suppose that soup is likewise composed of gela- 
 tine ; for, when cold, it often assumes the consistence of jelly ? 
 
 Mrs. B. Not entirely ; for though soups generally contain a 
 quantity of gelatine> the most essential ingredient is a mucous 
 or extractive matter, a peculiar animal substance, very soluble 
 in water, which has a s f rong taste, and is more nourishing than 
 gelatine. The various kinds of portable soup consist of this ex- 
 tractive matter in a dry state, which, in order to be made into 
 soup, requires only to be dissolved in water. 
 
 Gelatine, in its solid" state, is a semiductile transparent sub- 
 stance, 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 opera- 
 tion 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. pure gelatine ; as it is not designed for 
 eating, it is prepared without attending to the state of the ingre- 
 dients, which are more or less contaminated by particles that 
 have become putrid. 
 
 Gelatine may be precipitated from its solution in water by 
 alcohol We shall try this experiment with a glass of warm 
 jelly. You see that the gelatine 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 ? 
 
 Mrs. 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. 
 
 Mrs. B. True ; but you must observe that leather can be 
 26* 
 
294 COMPOSITION 
 
 produced only by gelatine in a membranous state; for though 
 pure gelatine and tannin will produce 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 albumen ,* 
 this, although constituting a part of most of the animal com- 
 pounds, is frequently found insulated in the animal system j 
 the white of egg, for instance, consists almost entirely of albu- 
 men ; the substance that composes the nerves, the serum, or 
 white part of the blood, and the curds of milk, are little else 
 than albumen variously modified. 
 
 In its most simple state, albumen appears in the form of a 
 transparent viscous fluid, possessed of no distinct taste or smell ; 
 it coagulates at the low temperature of 165 degrees, and, when 
 once solidified, it will never return to its fluid state. 
 
 Sulphuric acid and alcohol are each of them capable of coag- 
 ulating albumen in the same manner as heat, as I am going to 
 show you. 
 
 Emily. Exactly so. Pray, Mrs. B., what kind of action is 
 there between albumen and silver ? I have sometimes observ- 
 ed, that if the spoon with which I eat an egg happens to be 
 wetted, it becomes tarnished. 
 
 Mrs. B. It is because the white of egg (and, indeed, albu- 
 men in general) contains a little sulphur, which, at the tempe- 
 rature of an egg just boiled, will decompose the drop of water 
 that wets the spoon, and produce sulphurated hydrogen gas ? 
 which has the property of tarnishing silver. 
 
 We may now proceed tojibrine. This is an insipid and in- 
 odorous substance, having somewhat the appearance of fine* 
 white threads adhering together 5 it is the essential constituent 
 of muscles or flesh, in which it is mixed witSi and softened by 
 gelatine. It is insoluble both in water and alcohol, but sulphu- 
 ric acid converts it into a substance very analogous to gelatine. 
 
 These are the essential and general ingredients of animal 
 matter; but there are other substances, which, though not pe- 
 culiar to the animal system, usually enter into its composition,, 
 such as oils, acids, salts, &c. 
 
 Animal oz7is the chief constituent of fat; it is contained 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 vegeta- 
 ble oils? 
 
 Mrs. B. Not the same, but very analogous. The chief dif- 
 ference is that animal oil contains nitrogen, a principle which 
 
OF ANIMALS. ^95 
 
 seldom enters into the composition of vegetable 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 ob- 
 tained. 
 
 The animal acids have triple bases of hydrogen, carbon, and 
 nitrogen. Some of them are found native in animal matter; 
 others are produced during its decomposition. 
 
 Those that we find ready formed are : 
 
 The bombic acid, which is obtained from silk-worms. 
 
 the formic acid, from ants. 
 
 The latic acid, from the whey of milk. 
 
 The sebacic, from oil or fat. 
 
 Those produced during the decomposition of a;.imal sub- 
 stances by heat, are the prussic and zoonic acids. This last 
 is produced by the roasting of meat, and gives it a brisk fla- 
 vour. 
 
 Caroline. The class of animal acids is not very extensive? 
 
 Mrs. B. No; nor are they, generally speaking, of great im- 
 portance. The prussic acid* is, I think, the only one suffi- 
 ciently interesting to require any further comment. It can be 
 formed by an artificial process without the presence of any ani- 
 mal matter; and it may likewise be obtained from a variety, of 
 vegetables, particularly those of the narcotic kind, such as pop- 
 pies, laurel, &c. 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 uprussiat of 
 potash. From this state of combination 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 bloed, 
 how can the alkali attract it from thence? 
 
 * Prussir. acid can be obtained from Piussian blue (prussiate of 
 iron) by the following' process. Take 4 ounce? ofprussian blue, pul- 
 verize it finely, and mix with it 2 1-2 ounces of red oxide of mercury 
 (red precipitate /) boil the mixture with li* ounces of water in a glass 
 vessel, frequently stiring it with a stick. Filter the solution, which is 
 a prussiate of mercury, and is formed by the transfer of the prussic 
 acid, from the iron to the mercury. Put this solution into a retort, and 
 add to it two ounces of clean iron filings and six drachms of sulphuric 
 acid, and distil off two and a half ounces of prussic acid. This pro- 
 cess requires a good apparatus, and ought not to be undertaken by 
 any one who has not a knowledge of practical chemistry The fumes 
 during the distilation ought carefully to be avoided as poisonous. 
 Prussic acid has of late been much used in medicine, as a remedy in 
 consumption, hooping cough. &c. C, 
 
 
296 COMPOSITION 
 
 Mrs. B, It is the tripple basis 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 form- 
 ed, and it afterwards combines with the potash. 
 
 Emily. Now I comprehend it. But how can the prussic 
 acid be artificially made? 
 
 Mrs. B. By passing ammoniacal gas over red-hot charcoal ; 
 and hence we learn that the constituents of this acid are hydro- 
 gen, nitrogen, and carbon. 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 oxy- 
 gen being the principle of acidity. 
 
 Mrs. B. The colouring matter of prussian blue is called an 
 acid, because it unites with alkalies and metals, and not from 
 any other characteristic properties of acids; perhaps the name 
 is not strictly appropriate. But this circu instance, together 
 with some others of the same kind, has induced several chem- 
 ists to think that oxygen may not be the exclusive generator of 
 acids. Sir II. Davy, I have already informed you, was led by 
 his experiments on dry acids to suspect that water might be es- 
 sential to acidity. And it is the opinion of some chemists that 
 acidity may possibly depend rather on the arrangement than 
 on the presence of any particular principles. But we have not 
 yet done with the prussic acid,^ It has a strong affinity for 
 metallic oxyds, and precipitates the solutions of iron in acids 
 of a blue colour. This is the prussian blue, or prussiat 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 rs not reckoned a permanent oil- 
 colour. 
 
 Mrs. B. That defect arises, I believe, in general, from its be- 
 ing badly prepared, which is the case when 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 be- 
 ing exposed to the air, as I can immediately show you. 
 
 Caroline. It already begins to assume a pale blue colour. 
 But how does the air produce this change ? 
 
 Mrs. B. By oxydating the iron more perfectly. If we pour 
 some nitrous acid on it, the prussian blue colour will be imme- 
 diately produced, as the acid will yield its oxygen to the pre- 
 cipitate and fully saturate it with this principle, as you shall sex' 
 
OF ANIMALS. 297 
 
 Caroline. It is very cniious to see a colour change so instan- 
 taneously. 
 
 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, fand in a 
 short time is no longer in harmony with the other colours of the 
 painting. 
 
 Caroline. But it can never become darker, by exposure to 
 the atmosphere, than the true prussian blue, in which the oxyd 
 is perfectly saturated ? 
 
 Mrs. B. Certainly not. But in painting, the artist not reck- 
 oning upon partial alterations in his colours, gives his blue tints 
 that particular shade which harmonises with the rest of the pic- 
 ture. 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 cochineal, 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 ? 
 
 Mrs. B. It is a carbonaceous substance obtained by the com- 
 bustion of ivory. A more common species of black is obtain- 
 ed from the burning of bone. 
 
 Caroline. But during the combustion of ivory or bone, the 
 carbon, I should have imagined, must be converted into carbo- 
 nic acid gas, instead of this black substance ? 
 
 Mrs. B. In this, as in most combustions, a considerable part 
 of the carbon is simply volatilised by the heat, and again ob- 
 tained concrete on cooling. This colour, therefore, may bo 
 called the soot produced by the burning of ivory or bone. 
 
 CONVERSATION XXIV. 
 
 ON THE ANIMAL, ECONOMY. 
 
 Mrs. B. WE have now acquired some idea of the various 
 .materials which 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 as from animal 
 substances, it will be necessary to have some previous know- 
 
 *' Carmine is obtained by precipitating the colouring matter from 
 t+n infusion of <he insect by means of a solution of tin, C, 
 
298 ON THE 'ANIMAL ECONOMY. 
 
 ledge of the nature and functions of these organs, without which 
 it is impossible to form any distinct idea of the process of ani- 
 malisation and nutrition. 
 
 Caroline. I do not exactly understand the meaning of the 
 word animalisation ? 
 
 Mrs. B. Animalisation 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 render- 
 ed subservient to the purposes of nourishing and maintaining 
 the animal system. 
 
 Emily. This, I am sure, must be the most interesting of all 
 the branches of chemistry ! 
 
 Caroline. So I think ; particularly as I expect that we shall 
 hear something of the nature of respiration, and of the circula- 
 tion of the blood ? 
 
 Jllrs. B. These functions undoubtedly occupy a most impor- 
 tant place in the history of the animal economy. But I must 
 previously give you a very short account of the principal or- 
 gans by which the various operations of the animal sy steurare 
 performed. These are: 
 
 The Bonea, 
 Muscles, 
 Blood vessels, 
 Lympat/tic vessels. 
 Glands, and 
 Nerves. 
 
 The bones are the most solid part of the animal frame, and 
 in a great measure determines its form and dimensions. You 
 recalled, I suppose, what are the ingredients which enter into 
 their composition ? 
 
 Caroline. Yes ; phosphat of lime, cemented by gelatine. 
 
 Mrs. n. During the earliest period of animal life, they con- 
 sist almost entirely of gelatinous membrane having the form of 
 the bones, but of a loose sponzy 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 hardness and durability. Infants first receive it 
 from their mother's milk, and afterwards derive it from all ani- 
 mal and from most vegetable food, especially farinaceous sub- 
 stances, such as wheat-flour, which contain it in sensible quan- 
 tities. A portion of the phosphat, after the bones of the infant 
 have been sufficiently expanded and solidified, is deposited in 
 the teeth, which consist at first only of a gelatinous membran^ 
 
ON THE ANIMAL ECONOMY. -99 
 
 or case, fitted for the reception of this salt ; and which, after 
 acquiring hardness within the gum, gradually protrude from it. 
 
 Caroline. How very curious this is ; and how ingeniously 
 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 ! 
 
 Mrs. B. In quadrupeds the phosphats of lime is deposited 
 likewise in their horns, and the hair or wool with which they 
 are generally clothed. 
 
 In birds 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 solidity, the phosphat 
 of lime which is taken with the food is seldom assimilated, ex- 
 cepting when the female nourishes her young 5 it is then all se- 
 creted into the milk, as a provision for the tender benes 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 nourishment which is no 
 longer necessary to mother. Nature is, indeed, an admirable 
 economist ! 
 
 Caroline. Pray, Mrs. B., does not the disease in the bones 
 of children, called the rickets, proceed from a deficiency of 
 phosphat of lime ? 
 
 Mrs. B. I have heard that this disease may arise from two 
 causes 5 it is sometimes occasioned by the growth of the mus- 
 cles being too rapid in proportion to that of the bones. In this 
 case the weight of the flesh is greater than the bones can sup- 
 port, and presses 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 supposed to be an imperfect digestion 
 and assimilation of food, attended with an access of acid, which 
 counteracts the formation of phosphat of lime. In both in- 
 stances, 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 avoiding all food that is apt to 
 turn acid on the stomach, and to 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 
 digestion 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 proportions. 
 
 Caroline. I have often heard the rickets attributed to bad 
 
360 ON THE ANIMAL ECONOMY. 
 
 nursing, but I never could have guessed what connection there 
 was between exercise and the formation of the bones. 
 
 Mrs. B. Exercise is generally beneficial to all the animal 
 functions. If man is destined to labour for his subsistence, the 
 bread which he earns is scarcely more essential to his health 
 and preservation, than the exertions by which he obtains it. 
 Those whom the gifts of fortune have placed above the necessi- 
 ty 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 expe- 
 rience 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 daily 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, instead of pleasure, occasions painful sensations. So 
 that fatigue, no doubt, was intended to moderate our bodily ex- 
 ertions, 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 
 elasticity, the bones to slid<; easily over one another, so that 
 the joints may perform their office without difficulty or detri- 
 ment 
 
 Over the bones the muscles are placed j }hey consist of bun- 
 dles of fibres which terminate in a kind of string, or ligament, 
 by which they are fastened to the bones. The muscles are the 
 organs of motion ; by their power of dilatation and contrac- 
 tion,, they |5ut into action the bones, which act as levers, in all 
 the motions of the body, and form the solid support of its va- 
 rious parts. The muscles are of various degrees of strength or 
 consistence in different species of animals. The mammiferous 
 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 solidity in the 
 muscles of these several species of animals proceed, I imagine, 
 from the different nature of the food on which they subsist ? 
 
 Mrs. B. No ; that is not supposed to be the case : for the hu- 
 man species, who are of the mammiferous tribe, live on 
 
ON THE ANIMAL ECONOMW oOI 
 
 more substantial food than birds, and yet the latter exceed them 
 in muscular strength. We shall hereafter attempt to account 
 for this difference ; but 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 innumerable. The most considera- 
 ble of them are those through which the blood circulates, which 
 are of two kinds : the arteries, which convey it from the heart 
 to the extremities 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 different fluids into the 
 blood; they- arc generally called the absorbent or lymphatic 
 vessels : but it is to a portion of them only that the function oX 
 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 supposed to consist 
 of matter that has been previously animalised, and which, after 
 answering the purpose for which it was intended, must, in reg- 
 ular 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. 
 
 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 become useless. 
 
 Another set of absorbent vessels pump up the chyle from the 
 stomach and intestines, and convey it, after many circumvolu 
 tions, into the great vein near the heart.* 
 
 Emily. Pray what is chyle ? 
 
 Mrs. B. It is the substance into which food is converted by 
 digestion. 
 
 Caroline. One set of the absorbent vessels, then, is employ- 
 ed in bringing away the old materials which are no longer fit 
 
 * This is a mistake. The chyle is conveyed into the trunk of the 
 absorbent system, called by anatomists the thoracic duct. This runs 
 in a serpentine direction along the internal side of the back bone up 
 to the Kubclavian rein, which lies under the collarbone Into this 
 vein the chyle is discharged and mixes with the blood, and before it 
 reaches the heart it is converted into blood itself. C, 
 
 27 
 
302 ON THE ANIMAL ECONOMY. 
 
 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 
 tbe composition of the blood ? 
 
 Mrs. ti. You must observe that there is also a great variety 
 of substances to be secreted from it. We may compare the 
 blood to a general receptacle or storehouse for all kinds oi com- 
 modities, which are afterwards fashioned, arranged, and dispo- 
 sed of as circumstancs require. 
 
 There is another set of asorbent vessels in females which is 
 destined to secrete milk for the nourishment of the young. 
 
 Emily. Pray is not milk very analogous in its composition 
 to blood ; for, since the nursling derives its nourishment from 
 that source only, it must contain every principle which the ani- 
 mal system requires ? 
 
 Mrs. B. Very true. Milk is found, by its analysis, to con- 
 tain the principal materials of animal matter, albumen, oil, and 
 phospkat of lime ; so that the suckling has but little trouble 
 to digest and assimilate this nourishment. But we shall exa- 
 mine the composition of milk more fully afterwards. 
 
 In many parts of the body numbeis of small vessels are col- 
 lected 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 separate certain matters from the blood. 
 
 The secretions are not only mechanical, but chemical sepa- 
 rations from the blood ; 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 an- 
 imal fluids, as bile, tears, saliva, &c. ; and those which pro- 
 duce the general materials of the animal system, for tiie pur- 
 pose of recruiting and nourishing the several organs of tlu 
 body ; such as albumen, gelatine, and fibrine ; the latter may 
 be distinguished by the name of nutritive secretions. 
 
 Caroline. I am quite astonished to hear that all the seen - 
 tions should be derived from the blood. 
 
 Emily. I thought that the bile was produced by the liver ': 
 
 Mrs. B. So it is ; but the liver is nothing more tlv.n a ven, 
 large gland, \vhich secretes the bile from the blood. 
 
 The last of the animal organs which we have mentioned are 
 the nerves ; these are the vehicles of sensation, every other part 
 of the body being, of itself, totally insensible, 
 
 Caroline. They must then be spread through every part of 
 the frame, for we are every where susceptible of feeling. 
 
 Emily. Excepting the nails and the hair. 
 
ON THE ANIMAL EGONOMV. 303 
 
 Mrs. .B. And those are almost the only parts in which nerves 
 cannot be discovered. The common source of all the nerves is 
 the brain ; thence they decend, some of them through different 
 apertures in the skull, but the greatest part through the back 
 bone, and extend themselves by innumerable ramifications 
 throughout the whole body. They spread themselves over the 
 muscles, penetrate the glands, wind round the vascular system, 
 and even pierce into the interior of the bones. It is most pro- 
 bably through them that the communication is carried on be- 
 tween the mind and the other parts of the body; but in what 
 manner they are acted on by the mind, and made to re-act on 
 the body, is still a profound secret. Many hypotheses have 
 been formed on this very obscure subject, but they are all equaU 
 ly improbable, and it would be useless for us to waste our time 
 in conjectures on an enquiry, which, in all probability, is be- 
 yoiad the reach of human capacity. 
 
 Caroline. Cut you have not mentioned those particular 
 nerves that form the senses of hearing, seeing, smelling, and 
 tasting ? 
 
 Airs. B. They are considered as being of the same nature as 
 those which are dispersed over every part of the body, and con- 
 stitute the general sense of feeling. The different sensations 
 which they produce arise from their peculiar situation and con- 
 nection with the several organs of taste, smell, and hearing. 
 
 Emily. But these senses appear totally different fiom that of 
 i eel ing ? 
 
 Mrs. B. They are all of them sensations, but variously mod* 
 ified 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 odorifer- 
 ous 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 contact with 
 the nerves of the tongue. 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 ur> 
 on the optic nerve. These various senses, therefore, are ef- 
 fected 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 easily sepa- 
 rated and perfectly distinct, are loosely connected together by 
 a kind of spongy substance, in texture somewhat resembling 
 net-work, called the cellular membrane ; and the whole is cov- 
 ered by the skin. 
 
 The..?&/, as well as tlje bark of vegetables, is formed of 
 
304 ON THE ANIMAL ECONOMY. 
 
 three coats. The external one is called the cuticle or epider- 
 mis; the second, which is called the mucous membrane, is of a 
 thin soft texture, and consists of a mucous substance, which in 
 negroes is black, and is the cause of their skin appearing ot 
 that colour. 
 
 Caroline. Is then the external skin of negroes white like 
 ,ours ? 
 
 Mrs. IB. Yes ; but as the cuticle is transparent, as well as 
 porous, the blackness of the mucous membrane is visible through 
 if. The extremities of the nerves are spread over this skin, so 
 that the sensation of feeling is transmitted through the cuticle. 
 The internal covering of the muscles, which is properly the 
 skin, is the thickest, the toughest, and most resisting of the 
 whole ; it is this membrane* which 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, consists almost 
 exclusively of gelatine 5 and is capable of being converted into 
 ijrlue, size, or jelly. 
 
 The cavities betwen the muscles and the skin are usually fil- 
 led with fat, which lodges in the cells of the membranous net 
 before mentioned, and gives to the external form (especially in 
 the human figure) that roundness, smoothness, and softness, so 
 essential to beauty. 
 
 Emily. And the skin itself is, I think, a very ornamental 
 part of the human frame, both from the fineness of its texture, 
 and the variety and delicacy of its tints. 
 
 Mrs. B. This variety and harmonious gradation of colours, 
 proceed, not so much from the skin itself, as from the internal 
 organs which transmit their several colours through it, these be- 
 ing only softened and blended by the colour of the skin, which 
 is uniformly of a yellowish white. 
 
 Thus modified, 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 parts, the skin exhibits 
 the bloom of the rose, whilst where it is more opaque its own 
 colour predominates ; and at the joints, where the bones are 
 most prominent, their whiteness is often discernible. In 
 a word, every part of the human frame seems to contribute to 
 its external grace ; and this not merely by producing a pleas- 
 ing variety of tints, but by a peculiar kind of beauty which be- 
 longs to each individual part. Thus it is to the solidity and ar- 
 rangement of the bones that the human figure owes the grandeur 
 of its stature, and its firm and dignified deportment. The mus- 
 cles delineate the form, and stamp it with energy and grace. 
 
ON ANIMALISATION. 305 
 
 and the soft substance which is spread over them smooths their 
 nijitredness, and gives to the contours the gentle undulations of 
 the line of beauty. Every organ of sense is a peculiar and sep- 
 arate ornament; and the skin, which polishes the surface, and 
 gives it that charm of colouring so inimitable by art, finally con- 
 spires to render the whole the fairest work of the creation. 
 
 ]>ut now that we have seen in what manner the animal 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 maintafned. 
 
 This will lead us to a more particular explanation of the in- 
 ternal organs : here we shall not meet with so much apparent 
 beaut}', because these parts were not intended by nature to be 
 exhibited to view ; but the beauty of design, in the internal or- 
 ganisation of the animal frame, is, if possible, stiil mote remark- 
 able than that of the external parts. 
 
 We shall defer this subject till our next interview. 
 
 CONVERSATION XXV. 
 
 ON ANIMALISATION. NUTRITION. AND 
 RESPIRATION. 
 
 JV/Yf. B. WE have now learnt of what materials the animal 
 system is composed, and have formed some idea of the nature 
 of its organisation. In order to complete the subject, it re- 
 mains for us to examine in what manner it is nourished and 
 supported. 
 
 Vegetables, we have observed, obtain their nourishment 
 from various substances, either in their elementary state, or in a 
 very simple state of combination j as carbon, water, and salts, 
 which they pump up from the soil ; and carbonic acid and ox- 
 ygen, which they absorb from the atmosphere. 
 
 Animals, on the contrary, feed on substances of the most 
 complicated kind ; for they derive their sustenance, 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 its refinements. 
 
 Emily. Nor is this all ;. for our delicacies are collected from 
 27* 
 
306 ON NUTRITION. 
 
 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 con- 
 stitute the nourishment of animals, do not, I suppose, enter in- 
 to their system in their actual state of combination ? 
 
 Mrs. B. So far from it, that they not only undergo a new ar- 
 rangement of their parts, but a selection is made of such as are 
 most proper for the nourishment of the body, and those only 
 enter into the system, and are animalised. 
 
 Emily. And by what organs is this process performed ? 
 
 *t;rs. ij. Chiefly by the stomach, which is the organ of di- 
 gestion, and the prime regulator of the animal frame. 
 
 Digestion is the first step toward nutrition. It consists in 
 reducing into one homogeneous mass the various substances 
 that are taken as nourishment; it is performed by first chewing 
 and mixing the solid aliment with the saliva, which reduces in 
 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 appropri- 
 ate glands) is so powerful a solvent that scarcely any substan- 
 ces will resist its action. 
 
 Emily. The coats of the stomach, however, cannot be at- 
 tacked by it, otherwise we should be in danger of having them 
 destroyed when the stomach was empty. 
 
 . 'rs B. They are probably not subject to its action ; as long, 
 at least, as lift continues. But it appears, that when the gastric 
 juice has no foreign substance to act upon, it is capable of oc- 
 casioning a degree of irritation in the coats ot the stomach, 
 which produces the sensation of hunger. The gastric juice, 
 together with the heat and muscular action of the stomach, 
 converts the aliment into an 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 opera- 
 tion of other causes hitherto unknown, the chyme is changed 
 into chyle, a much thinner substance, somewhat resembling 
 milk, which is pumped by immense numbers of small absor- 
 bent vessels spread over the internal surface of the intestines. 
 These, after many 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, enters into the 
 circulation. 
 
 Carolina. But I do not yet clearly understand how the blood, 
 
ON RESPIRATION. 
 
 thus formed, nourishes the body and supplies all the secretions ? 
 Mrs. />'. 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 forming the chief ingredient of 
 blood ; but this fluid is not perfect until it has passed through 
 the lungs, and undergone (together with the blood that has 
 already circulated) certain necessary changes that are effected 
 
 by RESPIRATION. 
 
 Caroline. I am very glad that you are going to explain the 
 nature of respiration : I have often longed to understand it, for 
 though we talk incessantly of breathing, I never knew pre- 
 cisely what purpose it answered. 
 
 Mrs* B. 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 in alternate- 
 ly inspiring air into the lungs, and expiring it from them. 
 
 Mrs. :t. Your answer will do very well as a general defini- 
 tion. But, in order to form a tolerably clear notion of the va- 
 rious phenomena of respiration, there are many circumstances 
 to be taken into consideration. 
 
 In the first place, there are two things to be distinguished in 
 respiration, the mechanical and the chemical part of the pro- 
 cess. 
 
 The mechanism of breathing depends on the alternate ex- 
 pansions 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 forced out again. 
 
 Caroline. I thought that it was the lungs that contracted and 
 expanded in breathing? 
 
 Mrs. B. They do likewise ; but their action is only the con- 
 sequence of that of the chest. The lungs, together with the 
 heart and largest blood vessels, in a manner fill up the cavity of 
 the chest ; they could not, therefore, dilate if the chest did not 
 previously expand : and, on the other hand, when the chests 
 contracts, it compresses the lungs and forces the air out of them. 
 
 Caraline. The lungs, then, are like bellows, and the chest 
 is the power that works them. 
 
 Mrs. B. Precisely so. Here is a curious little figure (PLATE 
 XV. fig. 5.,) which will assist me in explaining the mechanism 
 of breathing, 
 
308 OX RESPIRATION. 
 
 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 vvhch communicates with the 
 mouth of the figure this represents the lungs contained with- 
 in the chest; the other bladder, which you see is tied loose, 
 represents a muscular membrane, called the ctidpkragtn, which 
 separates the chest from the lower part of the body. By the 
 hest, therefore, I mean that large cavity in the upper part of 
 the body contained within the ribs, the neckj and the dia- 
 phragm ; this membrane is muscular, and capable of contrac- 
 tion and dilatation. The contraction may be imitated by draw- 
 ing the bladder tight over the bottom 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 k 7i. By letting the bladder loose again, we imitate the 
 dilatation of the diaphragm, and the cavity 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. 
 
 Mrs. B. It illustrates tolerably well the action of the lungs 
 and diaphragm ; but those are not the only powers concerned 
 in the enlargement or diminution of the cavity of the chest; the 
 ribs are also possessed of a muscular motion for the same pur- 
 pose; they are alternately drawn in, edgeways, to assist the 
 contraction, and stretched out, like the hoops of a barrel, to 
 contribute 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. 
 
 Mrs. 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 the chest ; and the air rush- 
 ing into, and being expelled from the lungs, are only consequen- 
 ces of those actions. 
 
 Caroline. I confess that I thought the act of breathing be- 
 gan by opening the mouth for the air to rush in, and that it was 
 the air alone, which, by alternately rushing in and out, occa- 
 sioned the dilatations and contractions of the lungs and chest. 
 Mrs. 8, 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 dila- 
 ted, and the ribs expanded. But you will not be able to keep 
 them long in that situation. Your lungs and chest are already 
 
ON RESPIRATION. 
 
 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 respiration ; 
 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 understand by the circulation of the 
 blood ? 
 
 Caroline. I am delighted that you come to that subject, for 
 it is one that has long excited my curiosity. But I cannot con- 
 ceive how it is connected with respiration. The idea I have of 
 the circulation is, that the blood runs from the heart through tlie 
 veins all over the body, and back again to the heart ? 
 
 Mrs. B. I could hardly have expected a better definition 
 from you; it is, however, not quite correct, for you do not dis- 
 tinguish the arteries from the veins, which, as we have already 
 observed, are two distinct sets of vessels, each having its own 
 peculiar functions. The arteries convey the blood from the 
 heart to the extremities of the body $ and the veins bring it 
 back into 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 the heart, which may be considered as a common 
 centre to both sets of vessels. The heart is a kind of strong 
 elastic bag, or muscular cavity, which possesses a power of di- 
 lating and contracting itself, for the purposes of alternately re- 
 ceiving and expelling the blood, in order to carry on the pro- 
 cess of circulation. 
 
 Emily. Why are the arteries in this drawing painted red, 
 and the veins purple ? 
 
 Mrs. B. It is to point out the difference of the colour of the 
 blood in these two sets of vessels. 
 
 Caroline. Bat if it is the same blood which flows from the 
 arteries into the veins, how can its colour be changed? 
 
 Mrs. B. Thus change arises from various circumstances. In 
 the first place, during its passage through the arteries, the blood 
 undergoes a considerable alteration, some of its constituent 
 parts being gradually separated from it for the purposes ef 
 nourishing the body, and of supplying the various secretions. 
 In consequence of this, the florid arterial colour of the blood 
 changes by degrees to a deep purple, which is its constant col- 
 our in the veins. On the other hand, the blood is recruited 
 during its return through the veins by the fresh chyle, or im- 
 perfect blood, which has been produced by food ; and it re- 
 
310 ON RESPIRATION. 
 
 ceives also lymph from the absorbent vessels, as we have be- 
 fore mentioned. After having undergone these several chang- 
 es, the blood returns to the heart in a state very different from 
 that in which it left it. It is loaded with a greater proportion 
 of hydrogen and carbon, and is no longer fit for the nourish- 
 ment of the body, or other purposes of circulation. 
 
 Emily. And in this state does it mix in. the heart with the 
 pure florid blood which runs into the arteries ? 
 
 Mrs. B. No. The heart is divided into two cavities or corn- 
 partitions, called the right and left ventricles. The left ven- 
 tricle is the receptacle 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. I own that I always thought the same blood circu- 
 lated again and again through the body, without undergoing 
 any change. 
 
 Mrs. B. Yet you must have supposed that the blood circu- 
 lated 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 con- 
 veys nourishment to every part of the body, and supplies the 
 various secretions, you must be sensible that it cannot constant- 
 ly answer these objects without being proportionally renovated 
 and purified. 
 
 Emily. But does not the chyle answer this purpose ? 
 
 J\1rs. B. Only in part. It renovates the nutritive principles 
 of the blood, but does not relieve it from the superabundance of 
 water and carbon with which it is encumbered. 
 
 Emily. How, then, is this effected ? 
 
 j\Jrs. B. By RESPIRATION- This is one of the grand myste- 
 ries which modern chemistry has disclosed. When the venous 
 blood enters the right 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 cir- 
 culates 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 ac- 
 
 *Xot in actual contact. In this case it i obvious there would be 
 
 nothing to confine the blood and prevent its flowing out. The air cells 
 
 inarated from the blood vessels by an extremely thin membrane. 
 
 C, 
 
ON RESPIRATION* 311 
 
 curate judgment oi'it from the changes which it effects, not on- 
 ly in the blood, but also on the air expired. 
 
 The air, alter passing through the lungs, is found to contain 
 all the nitrogen inspired, but to have lost part of its oxygen, and 
 to have acquired a portion of watery vapour and of carbonic 
 acid gas. Hence it is inferred, that when the air comes in con- 
 tact with the venous blood in the lungs, the oxygen attracts 
 from it the superabundant quantity of carbon with which it has 
 impregnated itself during the circulation, and converts it into 
 carbonic acid. This gaseous acid, together with the redundant 
 moisture from the lungs,* being then expired, the blood is re- 
 stored 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 to me 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 beauti- 
 ful discoveries ? 
 
 Mrs. B. Priestley and Crawford, in this country, and La- 
 voisier, in France, are the principal inventors of the theory of 
 respiration. Of late years the subject has been farther illustra- 
 ted and simplified by the accurate experiments of Messrs Al- 
 len and Pepys. But the still more important and more admira- 
 ble discovery of the circulation of the blood was made long be- 
 fore by our immortal countryman, Harvey. 
 
 Emily. Indeed I never heard any thing that delighted 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 un- 
 dergo 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 
 collected 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 extremities of these little ramifications the blood is 
 transmitted to the veins, which bring it back to the heart and 
 lungs, to go round again and again in the manner we have 
 just described. You see, therefore, that the blood actually un- 
 dergoes two circulations ; the one, through the lungs, by which 
 
 * The quantity of moisture discharged by the lungs in 24 hours, may 
 be computed at eight or nine ounces, 
 
31:2 ON RESPIRATION. 
 
 it is converted into pure arterial blood ; the other, or general 
 circulation, by which nourishment is conveyed to every part of 
 the body : and ihese are both equally indispensible to the sup- 
 port of anim-il life. 
 
 Emily. But whence proceeds the carbon with which the 
 blood is impregnated when it comes into the lungs ? 
 
 Mrs. />'. Carbon exists in a greater proportion in blood than 
 in organised animal matter. The blood, therefore, after sup- 
 plying its various secretions, becomes loaded with an excess of 
 carbon, which is carried off by respiration ; and the formation 
 of new chyle from the food affords a constant supply of carbo- 
 naceous matter. 
 
 Caroline. I wonder what quantity of carbon may be expel- 
 led from the blood by respiration in the course of 24 hours? 
 
 Mrs. B. It appears by the experiments of Messrs. Allen and 
 Pepys that about 40,000 cubic inches of carbonic acid gas are 
 emitted from the lungs of a healthy person, daily; which is 
 equivalent to eleven ounces of solid carbon every 24 hours. 
 
 Emily. What an immense quantity ! And pray how much 
 of carbonic acid gas do we expel from our lungs at each expira- 
 tion ? 
 
 Mrs. B. The quantity of air which we take into our lungs 
 at each inspiration, is about 40 cubic inches, Which contain a 
 little less than 10 cubic inches of oxygen ; and of those 10 inch- 
 es, one-eighth is converted into carbonic acid gas on passing 
 once through the lungs,* a change which is sufficient to prevent 
 air which has only been breathed once from suffering a taper 
 to burn in it. 
 
 Caroline. Pray, how does the air come in contact with the 
 blood in the lungs ? 
 
 Mrs. B. I cannot answer this question without entering into 
 an explanation of the nature and structure of the lungs. You 
 recollect that the venous blood, on being expelled from the right 
 ventricle, enters the lungs to go through what we may call the 
 lesser circulation ; the large trunk or vessel that conveys it 
 branches out, at its entrance into the lungs, into an infinite 
 number of very fine ramifications. The windpipe, which con- 
 veys the air from the mouth into the lungs, likewise spreads 
 out into a corresponding number of air vessels, which follow 
 the same course as the blood vessels, forming millions of very 
 minute air-cells. These two sets of vessels are so interwoven 
 as to form a sort of net-work, connected into a kind of spongy 
 
 * The bulk of carbonic acid gas formed by respiration, is exactly 
 t)ie same a<= that of the oxygen gas which disappear?. 
 
ON RESPIRATION. &L3 
 
 mass, in which every particle of blood must necessarily come 
 in contact with a particle of air. 
 
 Caroline. But since the blood and the air are contained in 
 different vessels, how can they come into contact ? 
 
 J\>]rs. ft. They acton each other through the membrane which 
 forms the coats of these vessels ; for although this membrane 
 prevents the blood and the air from mixing together in the 
 lungs, yet it is no impediment to their 'chemical action on each 
 other.* 
 
 Emily. Are the lungs composed entirely of blood vessels and 
 air vessels? 
 
 J\lrs. B. I believe they are, with the addition only of nerves 
 and of a small quantity of the cellular substance beforemention- 
 ed, which connects the whole into an uniform mass. 
 
 Emily. Pray, why are the lungs always spoken of in the plu- 
 ral number ? Are there more than one ? 
 
 'Mrs.B. Yes; for though they form but one organ, they 
 really consist of two compartments called lobes, which are en- 
 closed 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 consequence of which, if one of the lobes be 
 wounded, the other performs the whole process of respiration 
 till the first is healed. 
 
 The blood, thus completed, by the process of respiration, 
 forms the most complex of all animal compounds, since it con- 
 tains not only the numerous materials necessary to form the va- 
 rious secretions, as saliva, tears, &c. but likewise all those that 
 are required to nourish the several parts of the body, as the 
 muscles, bones, nerves, glands, &c.t 
 
 * It is not absolutely certain that the change which the blood under- 
 goes in the lungs is entirely owing to the loss of carbon ; since experi- 
 ments show that any animal substance, even the hand, when confined 
 in a portion of atmospheric air, lessens the quantity of oxygen, and 
 produces a corresponding quantity of carbonic acid. It is possible, 
 then, that the carbon produced by respiration, may be owing merely 
 to the contact between the air and the lungs. C. 
 
 t The process of secretion does not consist merely in the separation 
 of certain materials from the blood by tne secreting organ ; but in ma- 
 ny instances, entirely new products are formed, no traces of which 
 have been detected in the blood. For instance the solid matter of the 
 bones is derived from the blood, yet not a particle ofphosphat of lime, 
 (a substance composing the basis of bone,) is found in it. It appears, 
 then, that the glands which are the organs of secretion, have the power 
 of producing from the ultimate atoms of the blood, the variety of pro- 
 peculiar to each. Thus the glands situated about the eyes ?r- 
 28 
 
314 ON RESPIRATION. 
 
 Emily. There seems to be a singular analogy between the 
 blood -of animals and the sap of vegetables ; for each of these 
 fluids contains the several materials destined for the nutrition of 
 the numerous class of bodies to which they respectively belong. 
 
 Mrs. B. Nor is the production of these fluids in the animal 
 and vegetable systems entirely different ; for the absorbent ves- 
 sels, which pump up the chyle from the stomach and intestines, 
 may be compared to the absorbents of the roots of plants, which 
 suck up the nourishment from the soil. And the analogy be- 
 tween the sap and the blood may be still further traced, if we 
 follow the latter in the course of its circulation; for, in the liv- 
 ing 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 do these organs derive their respective 
 powers ? 
 
 Mrs. B. From a peculiar organisation, the secret of which 
 no one has yet been able to unfold. But it must be ultimately 
 by means of the vital principle that both their mechanical and 
 chemical powers are brought into action. 
 
 I cannot dismiss the subject of circulation without mention- 
 ing perspiration, a secretion which is immediately connected 
 with it, and acts a most important part in the animal economy. 
 
 Caroline. Is not this secretion likewise made by appropriate 
 glands ? 
 
 J\Jrs. B. No; it is performed by the extremities of the arte- 
 ries, which penetrate through the skin and terminate under 
 the cuticle, through the pores of which the perspiration issues. 
 When this fluid is not secreted in excess, it is insensible, be- 
 cause 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 parts, and both exude from the surface by the ex- 
 tremities 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 of the 
 plants, the resemblance between the animal and vegetable cir- 
 culation is become still more obvious. The latter, however, is 
 
 Crete the tears, a saline, pellucid fluid ; while the liver secretes, from 
 the same source the bile, a greenish, opake, bitter and extremely nau- 
 seous substance. It is most probable that we shall ever remain in pro- 
 found ignorance, of any mode of imitating these operations. C. 
 
ON ANIMAL HEAT. 315 
 
 far from being complete, since, as we observed before, it con- 
 sists only in u rising and descending of the sap, whilst in ani- 
 mals the blood actually circulates through every part of the 
 system. 
 
 We have now, I think, traced the process of nutrition, from 
 the introduction of the food into the stomach to its finalty beco- 
 ming a constituent part of the animal frame. This will, there- 
 fore, be a fit period to conclude our present conversation. 
 
 What further remarks we have to make on the animal econ- 
 omy shall be reserved for our next interview. 
 
 CONVERSATION XXVI. 
 
 ON ANIMAL HEAT; AND ON VARIOUS ANIMAL PRO- 
 DUCTS. 
 
 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 carbon, producing carbonic acid gas. 
 
 Airs. B. I am much pleased that this idea has occurred to 
 you : these two processes appear so very analogous, that it has 
 been supposed that a kind of combustion actually takes place 
 in the lungs; not of the blood, but of the superfluous carbon 
 which the oxygen attracts from it. 
 
 Caroline. A combustion in our lungs ! that is a curious idea 
 indeed! But, Mrs. B., how can you call the action of the ah 
 on the blood in the lungs combustion, when neither light nor 
 heat nre produced by it? 
 
 Emily. I was going to make the same objection. Yet I do 
 not conceive how the oxygen can combine with the carbon, and 
 produce carbonic acid, without disengaging heat ? 
 
 Mrs. B. The fact is, that heat is disengaged.* Whether 
 any light be evolved, I cannot pretend to determine ; but that 
 heat is produced in considerable and very sensible quantities is 
 certain, and this is the principal, if not the only source of ANI- 
 MAL HEAT. 
 
 * It has been calculated that the heat produced by respiration in li! 
 hours, in the lungs of a healthy person, is such as would aielt about 100 
 pounds of ice. 
 
>10 ON ANIMAL HEAT. 
 
 Emily. How wonderful! that the very process which puri- 
 ties and elaborates the blood, should afford an inexhaustable 
 supply of internal heat ? 
 
 Mrs. B. This is the theory of animal heat in its original sim- 
 plicity, such nearly as it was first proposed by Black and La- 
 voisier. It was equally clear and ingenious ; and was at first 
 generally adopted. But it was objected, on second considera- 
 tion., that if the whole of the animal heat was evolved in the 
 lungs, it would necessarily be much less in the extremities ef 
 the body than immediately at its source ; which is not found 
 to be the case. This objection, however, which was by no 
 means frivolous, is now satisfactorily removed by the following 
 consideration : Venous blood has been found by experiment to 
 have less capacity for heat than arterial blood ; whence it fol- 
 lows that the blood, in gradually passing from the arterial to 
 the venus state, during the circulation, parts with a portion of 
 caloric, by means of which heat is diffused through every part 
 of the body.* 
 
 * This is substantially Dr. Crawford's theory of animal heat ; and 
 that it is a most beautiful and ingenions one, cannot be denied. Sub- 
 sequent experiments have however proved its fallacy. Dr. John Da- 
 vy has shown that the difference of capacity lor heat between the two 
 kinds of blood is much less than was supposed by Dr. Crawford the 
 capacity of arterial being only one per cent, above that of venous 
 blood. Now it is obvious, that this minute difference cannot account 
 for animal temperature ; nor is it certain that even this small quantity 
 of heat is givfen out to the system. Another objection is the result of 
 an experiment of Mr. Brodie. This indeed seems to settle the ques- 
 tion that animal heat does not depend on any change which the blood 
 undergoes in the lungs. He found that on keeping up an artificial 
 respiration in the lungs of a decapitated animal, the blood was changed 
 from black to red, and carbonic acid was given out as usual ; but that 
 the animal grew cold faster than another dead one, where such artifi- 
 cial respiration was not kept up. 
 
 This, it is obvious, would be the case unless heat was caused by 
 respiration, as the air forced into the lungs would tend to cool the ani- 
 mal. 
 
 Prof. Cooper of Philadelphia proposes another theory. < I see no 
 material difficulty, 1 ' says he, "' in accounting for the production of 
 animal heat from the doctrine of latent heat. The fluids of the body 
 are incessantly employed to renew the,-s.olids : when a fluid is convert- 
 ed into a solid, heat or caloric is precipitated. This takes place eve- 
 ry moment very gradually in every part of the system." 
 " We are ignorant of the train of arguments by which the learned Pro- 
 ;.' supports this theory. But, if on the one hand, the conversion of 
 a fluid into a solid produces heat, so it is equally well proved, that 
 the conversion of a solid into a fluid produces cold. No-.v the solid 
 parts of the. body after being deposited from the fluids, arc again con- 
 yrr*ed into fluid* bv tlu; nh a orbrni, Thi* theory then, accb 
 
ON ANIMAL HEAT. 3 if 
 
 More and more admirable ! 
 
 Caroline. The cause of animal heat was always a perfect 
 mystery to me, and I am delighted with its explanation. -But 
 pray, Mrs. B., can you tell me what is the reason of the in- 
 crese of heat that takes place in a fever ? 
 
 Emily. Is it not because we then breathe quicker, and there- 
 fore more heat is disengaged in the system ? 
 
 Mrs. B. That may be one reason: but I should think that 
 the principal cause of the heat experienced in fevers, is, that 
 there is no vent for the caloric which is generated in the body. 
 One of the most considerable secretions is the iiisensib]e per- 
 spiration ; this is constantly 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 caloric in 
 the body occasions those burning sensations which are so pain- 
 ful. 
 
 Emily. This is, no doubt, the reason why the perspiration 
 which often succeeds the hot stage of a fever affords so m-ch 
 relief. If I had known this theory of animal heat when 1 had 
 a fever last summer, I think I should have found some amuse- 
 ment in watching the chemical 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 so as you think; for the more exer- 
 cise you take, the more the body is stimulated, anil requires re-, 
 cruiting. For this purpose the circulation of the mood is quick- 
 ened, the breath proportionably accelerated, and consequently 
 'i greater quantity of caloric evolved. 
 
 Caroline. True ; after running very fast, I gasp for breath, 
 
 for the production of heat only when the deposition is greater than the 
 absorption, as during the growth of the system. 
 
 From some experiments, made by \]r. Brodie and Dr. Philip, they 
 have been induced to believe that animal temperature depends on the 
 influence of the nerves 
 
 In regard to this tiieory it may be observed, that in some instances 
 where the nervous influence seems to be suspended, the heat of the 
 part remains much the same as in health. 
 
 This subject has excited the attention of the learned and curious ia 
 all ages, and a great variety of theories have been offered to account 
 for it. We have seen none, however, to which insuperable objections 
 rnuy not be brought. We must therefore, at present, be contented 
 v/ith attributing the production of anirn\l warmth to the energies of 
 the vital principle; leaving it to future generations to determine and 
 feline its immediate cause. CX 
 
 28* 
 
318 ON ANIMAL Hi 
 
 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. 
 
 Mrs. B. Not if the person is in a good state of health ; for 
 the additional caloric is then carried off by the perspiration 
 which succeeds. 
 
 Emily. What admirable resources nature has provided for 
 us ! By the production of animal heat she has enabled us to 
 keep up the temperature of our bodies above that of inani- 
 mate objects ; and whenever this source becomes too abundant, 
 the excess is carried off by perspiration. 
 
 Mrs. 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 nearly 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. 
 
 Mrs. B. Yes, I do ; at least if you speak of the tempera- 
 ture of the blood, and the internal parts of the body ; for those 
 which are immediately in contact with the atmosphere, such as 
 the hands and face, will occasionally get warmer, or colder, than 
 the internal or more sheltered parts. If you put the bulb of a 
 thermometer in your mouth, which is the best way of ascer- 
 taining the real temperature of your body, you will scarcely 
 perceive 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 I am shivering with cold ? 
 
 Mrs. B. When a person in health feels very hot, whether 
 from internal heat, from violent exercise, or from the tempera- 
 ture of the atmosphere, his body is certainly a little warmer 
 than when he feels very cold : but this difference is much smal- 
 ler than our sensations would make us believe; and the natur- 
 al standard is soon restored by rest and by perspiration. It is 
 chiefly the external parts that are warmer, and I am sure that 
 you will be surprised to hear that the internal temperature of 
 the body scarcely ever descends below ninety-five or ninety-six 
 degrees, and seldom attains one hundred and four or one hun- 
 dred and five degrees, even in the most violent fevers. 
 
 Emily. The greater quantity of caloric, therefore, that we 
 receive from the atmosphere in summer, cannot raise the tem- 
 perature of our bodies beyond certain limits, as it does that of 
 inanimate bodies, because an excess of caloric is carried off by 
 perspiration. 
 
ON ANIMAL liEA-i. 3I<J 
 
 Caroline. But the temperature of the atmosphere, and con- 
 sequently that of inanimate bodies, is surely never so high as 
 that of animal heat ? 
 
 Mrs. B. I beg your pardon. In the East and West Indies, 
 and sometimes in the southern parts of Europe, the atmosphere 
 is frequently above ninety-eight degrees, which is the common 
 temperature of animal heat. Indeed, even in this country, it oc- 
 casionally 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 oth- 
 er gentlemen, made several very curious experiments. He re- 
 mained for some time in an oven heated to a temperature not 
 much inferior to that of boiling water, without suffering any 
 other inconvenience than a profuse perspiration, which he sup- 
 ported by drinking plentifully. 
 
 Emily. He could scarcely consider the perspiration as an in- 
 convenience, since it saved him from being baked by giving vent 
 to the excess of caloric. 
 
 Caroline. 1 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 are quite mistaken. When- 
 ever 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 perspiration, and it is in this way 
 that it affords relief. It is on that account also that we are apt 
 to catch cold, when in a state of profuse perspiration. It is for 
 the same reason that tea is often refreshing in summer, though 
 it appears to heat you at the moment you drink it. 
 
 Emily. And in winter, on the contrary, tea is pleasant on 
 account of its heat. 
 
 A'lrs. B. \ es $ 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, unless after dancing, or 
 any other violent exercise. 
 
 Caroline. What is the reason that it is dangerous to eat ice 
 after dancing, or to drink any thing cold when one is very hot ? 
 
 Mrs. B. Because the loss of heat arising from the perspira- 
 tion, conjointly with the chill occasioned by the cold draught, 
 produce more cold than can be borne with safety, unless you 
 continue to use the same exercise after drinking that you did be- 
 fore 5 for the heat occasioned by the exercise will counteract* 
 the effects of the cold drink, and the danger will be removed. 
 You may, however, contrary to the common notion, consider 
 it as a rule, that cold liquids may, at all times, be drunk with 
 
320 ON ANIMAL HEAT. 
 
 perfett safety, however hot you may feel,* provided you are 
 not at the moment in a state of great perspiration, and on condi- 
 tion that you keep yourself in gentle exercise afterwards. 
 
 Emily. But since we are furnished with such resources 
 against the extremes of heat or cold, I should have thought that 
 all climates would have been equally wholesome. 
 
 Mrs. B. That is true, in a certain degree, with regard to 
 those who have been accustomed to them from birth ; for we 
 find that the natives of those climates, which we consider as 
 most deleterious, are as healthy as ourselves; and if such cli- 
 mates are unwholesome to those who are habituated to a more 
 moderate temperature, it is because the animal economy does 
 not easily accustom itself to considerable changes. 
 
 Caroline. But pray, Mrs. B., if the circulation preserves the 
 body of an uniforn temperature, how does it happen that ani- 
 mals are sometimes frozen ? 
 
 J\-lrs. B. Because, if more heat be carried off by the atmos- 
 phere than the circulation can supply, the cold will finally pre- 
 vail, the heart will cease to beat, and the animal will be frozen. 
 And, likewise, if the body remained long exposed to a degree 
 of heat, greater than the perspiration could carry of, it would 
 at last lose the power of resisting its destructive influence. 
 
 Caroline. Fish. 1 suppose, have no animal heat, but only 
 partake of the temperature of the water in which they live ?t 
 
 Emily. And their coldness, no doubt, proceeds from their 
 not breathing ? 
 
 .Mrs. B. All kinds of fish breathe more or less, though in a 
 much .smaller degree than )and animals. Nor are they entire- 
 ly destitute of animal heat, though, for the same reason, they 
 are much colder than other creatures. They have compara- 
 tively but a very small quantity of blood, therefore but very lit- 
 tle oxygen is required, and a proportionally small quantity of 
 animal heat is generated. 
 
 Caroline. But how can fish breathe under water ? 
 
 Mrs. B. They breathe by means of the air which is dissolved 
 in the water, and if you put them into water deprived of air 
 by boiling, they are soon suffocated. 
 
 * The c immou notion on this subject is certainly the most safe. A 
 person heated, and almost exhausted by exercise on a hot day, ought 
 never to drink any cold liquid, except in very small quantities at a 
 time. Not a summer passes but we hear of deaths by drinking cold 
 water after violent exercise. C. 
 
 t Animals belonging to tlia order Cetcc of Naturalists, though they in- 
 habit the soa, breathe atmospheric air, and have hot, red blood, Thi? 
 order includes the ivhales, dolphins, nanoals, &c. C, 
 
N ANIMAL HEAT. 321 
 
 If a fish is confined in a vessel of water closed from the air, 
 it soon dies ; and any fish put in afterwards would be killed im- 
 mediately, as all the air had been previously consumed. 
 
 Caroline. Are there any species of animals that breathe more 
 than we do ? 
 
 Mrs. B. Yes ; birds, of all animals, breathe the greatest 
 quantity of air in proportion to their size ; and it is to this 
 h at they are supposed to owe the peculiar firmness and 
 strength of their muscles, by which they are enabled to support 
 the violent exertion of flying. 
 
 This difference between birds and fish, which may be con- 
 sidered as the two extremes of the scale of muscular strength, 
 is well worth observing. Birds residing constantly in the at- 
 mosphere, surrounded by oxygen, and respiring it in greater 
 proportions 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 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 5 the 
 quantity of hydrogen and carbon, that is in consequence accu- 
 mulated in their bodies,, fomrcthe oil which is so strongly char- 
 acteristic of that species of animals, and which relaxes and 
 softens the small quantity of fibrine which their muscles con- 
 tain. 
 
 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 fly, it is but feebly, and only to a short distance. 
 Their flesh, too, partakes of the oily nature, and even in taste 
 sometimes resembles that of fish. This is the case not only 
 with the various kinds of water fowls, but with all other am- 
 phibious animals, as the otter, the crocodile, the lizard, &c. 
 
 Caroline. Arid what is the reason that reptiles are so defi- 
 cient in muscular strength ? 
 
 JWrs. B. It is because they usually live under ground, and 
 seldom come into the atmosphere. Tbey have imperfect, and 
 sometimes no discernible organs of respiration ; they partake, 
 therefore, of the soft oily nature offish ; 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 
 water.* Whilst, on the contrary, the insect tribe, that are so 
 
 * Amphibious animals have the Denver of ?'i?pe:r 1 in; 3 r respiration for 
 
322 ON ANIMAL PRODUCTS. 
 
 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. 
 
 I have now given you a short account of the principal 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 applications of chemistry, these appear to me the most 
 curious and most interesting. 
 
 Caroline. But, Mrs. B., I must remind you that you promi- 
 sed to give us some account of the nature of milk. 
 
 Mrs. B. True. There are several other animal produc- 
 tions that deserve likewise to be mentioned. We shall begin 
 with milk, which is certainly the most important and the most 
 interesting of all the animal secretions. 
 
 Milk, like all other animal substances, ultimately yields by- 
 analysis oxygen, hydrogen, carbon, and nitrogen. These are 
 combined in it under the forms of albumen, gelatine, oil, and 
 water. But milk contains, besides a considerable portion of 
 phosphat of lime, the purposes of which I have already point- 
 ed out. 
 
 Caroline. Yes ; it is this salt which serves to nourish 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, with- 
 out any chemical assistance, may be decomposed into three 
 parts, cream, curds and whey. These constituents of milk 
 have but a very slight affinity for each other, and you find ac- 
 cordingly that cream separates from milk by mere standing. 
 It consists chiefly of oil, which being lighter than the other 
 parts of the milk, gradually rises to the surface. It is of this, 
 you know, that butter is made, which is nothing more than ox- 
 ygenated cream. 
 
 Caroline. Butter, then, is somewhat analogous to the waxy 
 .substance formed by the oxygenation of vegetable oils. 
 
 -Mrs. B. Very much so. 
 
 Emily. But is the cream oxygenated by churning ? 
 
 Mrs. B. Its oxygenation commences previous to churning, 
 merely by standing exposed to the atmosphere, from which it 
 absorbs oxygen. The process is afterwards completed by 
 
 a considerable timo. It is in consequence of this, that they are enabled 
 to live under water. (J. 
 
ON ANIMAL PRODUCTS. 3%3 
 
 churning ; the violent motion which this operation occasions 
 brings every particle of creani 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 creani into two substances, but- 
 ter and butter-milk. 
 
 Mrs. B. That is to say, in proportion as the oily particles of 
 the cream become oxygenated, they separate 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, 01 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 properties 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 from cream alone. In this 
 case, therefore, the butter-milk is deprived of the creamed milk, 
 which contains both the curd and whey. Besides, in conse- 
 quence of the milk remaining exposed to the atmosphere du- 
 ring 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 acidified by 
 oxygenation ? 
 
 .Mrs. B. Animal oil is not so easily acidified as the 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. Butter, however^ is susceptible of be- 
 coming acid by an excess of oxygen ; it is then said to be ran- 
 cid, and produces the sebacic acid, the same as that 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 ? 
 
 Mrs. B. This idea has been suggested by Sir H. Davy, who 
 supposes, that if rancid butter were well washed in an alkaline 
 solution, the alkali would separate the acid from the butter. 
 
 Caroline. You said just now that creamed milk consisted of 
 curd and whey. Pray how are these separated ? 
 
 Mrs. B. They may be separated by standing for a certain 
 length of time exposed to the atmosphere ; but this decompo- 
 sition may be almost instantaneously effected by the chemical 
 agency of a variety of substances. Alkalies, rennet,* and in- 
 
 * Rennet is the name given to a watery infusion of the coats of thf 
 
324 OK ANIMAL PRODUCTS. 
 
 deed almost all animals substances, decompose milk by combi 
 ning with the curds. 
 
 Acids and spirituous liquors, on the other hand, produce ;i 
 decomposition by combining with the whey. In order, there- 
 fore, 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 spiritous liquors. 
 
 Emily. This is a very useful piece of information ; for I 
 tind white-wine whey, which I sometimes take when I have a 
 cold, extremely heating; now, if the whey were separated by 
 means of an alkali instead of wine, it would not produce that 
 effect. 
 
 Mrs. B. Perhaps not. But I would strenuously advise you 
 not to place too much reliance on your slight chemical knowl- 
 edge in medical matters. I do not know why whey is not sep- 
 arated from curd by rennet, or by an alkali, for the purpose 
 which you mention ; but I strongly suspect that there must be 
 some good reason why the preparation by means of wine is 
 generally preferred. 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, being re- 
 markable light of digestion. But its effect, taken medicinally, 
 is chiefly, I believe, to excite perspiration, by being drunk warm 
 on going to bed. 
 
 From whey a substance may be obtained in crystals by evap- 
 oration, called sugar of milk. This substance is sweet to the 
 taste, and in its composition is so analogous to common 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 tri- 
 fling, that it can hardly answer that purpose. I have heard of 
 only one instance of its being used for the production of a spir- 
 ituous liquor, and this is by the Tartan Arabs ; their abund- 
 ance of horses, as well as their scarcity of fruits, has introduced 
 the fermentation of mares' milk, by which they produce a li- 
 quor called koumiss. Whey is likewise susceptible of being 
 acidified by combining with oxygen from the atmosphere. It 
 
 stomach of a sucking calf. Its remarkable efficacy in promoting co- 
 agulation is supposed to depend on the gastric juice with which it is 
 Jmprejrnated. 
 
N ANIMAL PRODUCTS. 
 
 then produces the lactic aoid, which you may recollect is class- 
 ed with 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 whey 
 by rennet, and yet this you have just told us is not the method 
 of obtaining pure curds ? 
 
 Mrs. B. Nor are pure curds so well adapted for the forma- 
 tion of cheese. For the nature and flavour of the cheese de- 
 pend, in a great measure, upon the cream or oily matter which 
 is left in the curds ; so that if every particle of cream be remov- 
 ed from the curds, the cheese is scarcely eatable. Rich chees- 
 es, 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 interesting 
 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. 
 
 Mrs B. There is however, a very essential difference. The 
 young animal is formed, as well as nourished, by the contents 
 of the egg-shell ; whilst milk serves as nutriment to the suck- 
 ling, 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 mentioned. 
 
 Spermaceti is of this class; it is a kind of oily substance ob- 
 tained from the head of the whale, which, however, must un- 
 dergo a certain preparation before it is in a fit state to be made 
 into candles. It is not much more combustible than tallow, but 
 it is pleasanter to burn, as it is less fusible and less greasy. 
 
 Ambergris is another peculiar substance derived from a spe- 
 cies of whale. It is, however, seldom obtained from the ani- 
 mal itself, but is generally found floating on the surface of the 
 sea. 
 
 Wax, you know, is a concrete oil, the peculiar product of the 
 bee, part of the constituents of which may probably be derived 
 from flowers, but so prepared by the organs of the bee, arid so 
 mixed with its own substance, as to be decidedly an. animal pro- 
 duct. Bees' wax is naturally of a yellow colour, but it is bleach- 
 ed by long exposure to the atmosphere, or may be instantane- 
 ously whitened by the oxy-muriatic acid. The combustion & 
 20 
 
326 ON ANIMAL PRODUCTS. 
 
 wax is far more perfect than that of tallow, and consequently 
 produces a greater quantity of light and heat. 
 
 Lac is a substance very similar to wax in the manner of its 
 formation ; it is the product of an insect, which collects its in- 
 gredients from flowers, apparently for the purpose of protecting 
 its eggs from injury. It is formed into cells, fabricated with as 
 much skill as those of the honey-comb, but differently arrang- 
 ed. The principal use of lac is in the manufacture of sealing- 
 wax, and in making varnishes and lacquers. 
 
 Musk, civet, and castor, are other particular productions, 
 from different species of quadrupeds. The two first are very 
 powerful perfumes : the latter has a nauseous smell and taste, 
 and is only used medicinally. 
 
 Caroline. Is it from this substance that castor oil is obtain- 
 ed ? 
 
 Mrs. B. No. Far from it, for castor oil is a vegetable oil, 
 expressed from the seeds of a particular plant ; and has not the 
 least resemblance to the medicinal substance 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; whilst in the insect it 
 is a fluid, which is coagulated, apparently by uniting with oxy- 
 gen, as soon as it comes in contact with the air. The moth of 
 the silk-worm ejects a liquor which appears to contain a pecu- 
 liar acid, called bombic, the properties of which are but very 
 little known. 
 
 Emily. Before we conclude the subject of the animal econo- 
 my, shall we not learn by what steps dead animals return to 
 their elementary state ? 
 
 Mrs. B. Animal matter, although the most complicated of 
 all natural substances, returns to its elementary state by one 
 single spontaneous process, the putrid fermentation. By this, 
 the albume^ fibrine, &c. are slowly reduced to the state of ox- 
 vgen, hydrogen, nitrogen, and carbon; and thus the circle of 
 changes through which these principles have passed is finally 
 completed. They first quitted their elementary form, or their 
 combination with unorganised matter, to enter into the vegeta- 
 ble system. Hence they were transmitted to the animal king- 
 dom ; and from this they return again to their primitive simpli- 
 city, soon to re-enter the sphere of organised existence. 
 
 When all the circumstances necessary to produce fermenta- 
 tion 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 dare say that 
 
ON ANIMAL PRODUCTS. 32? 
 
 Caroline, who is so fond of analogies, will consider this as a 
 kind of animal bitumen. 
 
 Caroline. And why should I not, since the processes which 
 produce these substances are so similar ? 
 
 Mrs. B. There is, however, one considerable difference ; the 
 state of bitumen seems permanent, whilst that of animal-sub- 
 stances, thus imperfectly decomposed, is only transient ; and 
 unless precautions be taken to preserve them in that state, a to- 
 tal dissolution infallibly ensues. This circumstance, of the oc- 
 casional conversion of animal matter into a kind of sperma- 
 ceti, is of late discovery. A manufacture has in consequence 
 been established near Bristol, in which, by exposing the carca- 
 ses of horses and other animals for a length of time under wa- 
 ter, the muscular parts are converted into this spermaceti-like 
 substance. The bones afterwards undergo a different process 
 to produce hartshorn, or more properly, ammonia, and phos- 
 phorus ; and the skin is prepared for leather. 
 
 Thus art contrives to enlarge the sphere of useful purposes, 
 for which the elements were intended by nature ; and the pro- 
 ductions of the several kingdoms are frequently arrested in. 
 their course, and variously modified, by human skill, which 
 compels them to contribute, under new forms, to the necessi- 
 ties or luxuries of man. 
 
 But all that we enjoy, whether produced by the spontaneous 
 operations of nature, or the ingenious efforts of art, proceed 
 alike from the goodness of Providence. To GOD alone man 
 owes the admirable faculties which enable him to improve and 
 modify the productions of nature, no less than those produc- 
 tions themselves. In contemplating the works of the creation, 
 or studying the inventions of art ; let us, therefore, never foi- 
 get the Divine Source from which they proceed ; and thus 
 every acquisition of knowledge will prove a lesson of piety 
 and virtue. 
 
DESCRIPTION OP TH 
 
 DESCRIPTION OF THE APHLOGISTIC, OR FLAMt.- 
 LESS LAMP. 
 
 BV DR. J. L. COMSTOCK, OP HARTFORD. 
 
 IN the construction of this Lamp, the object is to keep a coil 
 of wire in a state of ignition, without either flame or smoke. 
 
 The principle on which it is constructed, I believe, was first 
 discovered by Sir H. Davy. He found that on heating the end 
 of a piece ofptatina wire red hot, and instantly holding it near 
 the surface of some ether 9 placed in a wine glass, the wine was 
 kept at a red heat as long as the experiment was continued. 
 
 Whether Sir Humphrey pursued the subject any further, I 
 am not informed. It is most probable however that he did not, 
 as it is stated in a London paper of the last year, that Prof. Ure 
 of Glasgow had determined the circumstances which modify 
 the performance of the lamp, and that one constructed by him 
 was in full operation in that city (London) and had excited 
 much public curiosity. This notice contained some directions, 
 concerning the size of the wire, to be used, and the manner of 
 coiling it. I have however seen no description of this lamp 
 which would enable one readily to construct it. The following 
 may therefore interest such readers, as have seen an account of 
 so curious a discovery. 
 
 The principle on which the aphlogistic lamp is constructed 
 involves two conditions, which are absolutely requisite, viz. 
 that we make use of a combustible substance which evaporates 
 at a low degree of heat, and a metal which is a bad conductor 
 of caloric. For the combustible, alcohol seems best suited to 
 this purpose. Sulphuric ether, aside from its high price, and 
 disagreeable smell, I have sometimes found to fail ; the igni- 
 tion ceasing without any obvious cause. 
 
 In regard to the metal, gold and silver, both fail in conse- 
 quence of the rapidity with which they conduct caloric. Silver, 
 toy, would soon be destroyed by the intense heat. Iron, al- 
 though so bad a conductor, as to remain ignited for a time, soon 
 fails, being converted into red oxide. Platina seems to be the 
 only metal adapted to our purpose, being a slow conductor of 
 caloric, and not easily oxidated at the highest temperatures. 
 
 This is to be drawn into wire of 56-100 or 60-100 of an 
 inch in diameter, being about the size of card, or brass wire, 
 No. 26. Experience has shown that this size succeeds better 
 than any other. If larger, the heat is carried off too fast, and 
 the ignition ceases. 4f much finer, it does not retain sufficient 
 
APHLOGISTIC LAMP. 329 
 
 heat at the lower part of the coil to keep up the evaporation of 
 the alcohol from the wick. 
 
 The coiling of the wire, and the adjustment of the wick, are 
 the most difficult parts of the construction. 
 
 The coil A. fig. 1. (frontispiece) is made by winding the wire 
 round a piece of wood, cut of the proper size, and shape. The 
 size is determined by the bore of the glass tube, allowing for the 
 diameter of the wire. The shape is plane cylindrical in that 
 part which enters the tube ; and slightly conical where it pro- 
 jects above the tube, as seen in the figure. (I believe this is 
 the best shape, though I have succeeded as well when the coil 
 was of the same shape throughout.) 
 
 In winding the coil, it is best that the turns of the wire should 
 come in contact. Afterwards it is to be gently extended, so as 
 to leave the turns as nearly as possible to each other, without 
 touching. 
 
 The diameter of the coil is about one-sixth of an inch where 
 it enters the tube. Its length half an inch, or a little less, con- 
 taining from twenty to thirty turns of the wire. The projection 
 above the tube is about one half of the length. 
 
 B. Fig. 1. is a glass tube, containing a cotton wick, which by 
 capillary attraction carries the alcohol up to the platina coil. 
 The length of this is arbitrary, being from one to three or four 
 inches. The bore is about the sixth of an inch, so as barely to 
 admit the coil. The wick, consisting of eight or ten threads, 
 is first drawn through the tube, and then introduced about half 
 wa> into the coil, so as to come even with the top of the tube. 
 This requires very nice adjustment. If the wick is too high, the 
 wire is rapidly cooled by the alcohol, and' ignition ceases in a 
 few moments. If too low, the evaporation by the heat of the 
 wire is insufficient. If, however, the other parts are well con- 
 structed, a few trials will ensure success. 
 
 Fig. 2. shows the lamp complete. The body of it is a low 
 vial, or inkstand, capable of holding about two ounces of alco- 
 hol. It is stopped accurately with a cork, which is covered, for 
 ornament, with tin foil. The aperture for admitting the tube 
 and wick, is make with a hot iron. 
 
 D. is a small tube through which the alcohol is poured. A 
 dropping tube is convenient for this purpose, but a small funnel 
 is easily made by cutting off an inch of the neck of a broken re- 
 tort, into which is pushed a cork, and through this a small 
 quill. Another orifice still, for letting off the air, as the alco- 
 hol goes in, may be made through the cork. The orifices, of 
 course, are to be stopped, to prevent evaporation, after the lamp 
 is charged. 
 
 29* 
 
330 DESCRIPTION, &C. 
 
 When the lamp is completed and charged, the alcohol is in- 
 flamed by holding the coil in the blaze of a candle. After let- 
 ting it burn fora few minutes, the flame is blown out, when, if 
 every thing is properly adjusted, the wire will continue red hot 
 until the alcohol is exhausted. 
 
 The explanation why the ignition of the wire is permanent, 
 seems to be sufficiently simple. Alcohol, when in the state oi 
 vapour, combines with oxygen with great facility. The tem- 
 perature of the wire is first raised by the flame of the candle to 
 about 600 degrees', Fahrenheit. This degree of heat is such as 
 to effect the combustion of the alcohol with the oxygen of the 
 atmosphere. When this is once effected, the caloric extricated 
 by the combustion of the alcohol, is sufficient to keep the coil 
 at a red heat, which again is the temperature at which the alco- 
 hol is combustible, so that one portion of alcohol by the absorp- 
 tion of oxygen, and the consequent extrication of heat, lavs the 
 foundation for the combustion of another portion : and as the 
 alcohol rises in a constant stream, so the effect is constant. 
 The stream of vapour is much increased by the heat of the low- 
 er part of the coil, where it embraces the wick, and the tem- 
 perature of the alcohol is increased before it reaches the part of 
 the coil where combustion is effected. Sometimes the last, or 
 upper turn of the wire only is kept red hot. 
 
 This lamp, though one of the most curious inventions of the 
 age, is not merely a curiosity. The facility and certainty with 
 which, by means of a match, a light may be obtained from it, 
 constitutes its utility. The proper matches for this purpose are 
 prepared by dipping the common brimstone matches into a 
 paste made by mixing two parts of white sugar with one part of 
 chlorate (oxymuriat) of potash. The red French matches are 
 ofthis kind, and answer the purpose completely. 
 
 In cases where, a light might be wanted, but a constant one 
 would be offensive, this lamp might be a great convenience ; a 
 light being immediately obtained by merely touching a match 
 to the platina coil, and then to the wick of the candle. Physi- 
 cians or others who are liable to be called up in the night would 
 also find it convenient. 
 
 The aphlogistic lamp, with the proper matches may be ob- 
 tained at Mr. Charles Hosmer's Variety Store in this city. 
 
QUESTIONS FOR EXERCISE. 
 
 CONVERSATION I. 
 
 WHAT is the object of Chemistry ? 
 What is an elementary substance ? 
 What is decomposition ? 
 
 What is the difference between decomposition and division? 
 What is a compound body ? 
 What is the number of elementary substances ? 
 What is the difference between attraction of cohesion, and at- 
 traction of composition ? 
 How can a compound body be decomposed ? 
 What are the names and number of the simple bodies ? 
 
 CONVERSATION II. 
 
 Is there an inseparable connection between light and heat ? 
 How can they be separated ? 
 
 To what is the phosphorescence of dead animal matter owing ? 
 
 How do you distinguish heat and light from each other ? 
 
 What is free caloric? 
 
 Wiiat is combined or latent caloric ? 
 
 What is the difference between heat and caloric ? 
 
 What is the most remarkable effect of free caloric on bodies ? 
 
 Does heat expand all bodies in the same degree? 
 
 What is the temperature of boiling water ? 
 
 Why cannot water be heated above a certain degree in the open 
 air? 
 
 Why was the freezing point of Fahrenheit marked 32 ? 
 
 Why do air thermometers indicate smaller changes of tempera- 
 ture than others ? 
 
 Can you name any substance, or any known condition of a sub- 
 stance in which caloric is absent ? 
 
 What is cold ? 
 
 Why does a metallic mirror feel cold when placed before the 
 fire? 
 
 What kind of a surface radiates most heat ? 
 
 Why do metallic coffee pots retain the heat of the coffee longer 
 than earthen ones ? 
 
 What becomes of the caloric radiated by a hot body ? 
 
332 QUESTIONS. 
 
 What is the difference between the radiation and reflection of 
 caloric ? 
 
 CONVERSATION III. 
 
 Why do some substances feel hotter, or colder,, than others, at 
 the same temperature ? 
 
 Do fluids conduct caloric downwards ? 
 
 How are fluids heated when placed over a fire ? 
 
 Why does water first freeze at the surface ? 
 
 Why does not the surface of the sea freeze ? 
 
 Why does a fire heat glass, when the sun does not ? 
 
 Why, in the summer, is it particularly hot in cloudy, or foggy 
 weather? 
 
 Why is the wind cooling to our bodies ? 
 
 Does water boil from the top, or bottom of the vessel ? 
 
 What are the principle solvent fluids ? 
 
 What is the difference between solution and mixture ? 
 
 Is a fluid increased in bulk by the solution of a solid 1 
 
 When is a solvent saturated? 
 
 What is evaporation ? 
 
 When does the air contain most moisture ? in winter or sum- 
 mer ? 
 
 How do you account for the formation of dew ? 
 
 Why is a glass of cold water covered with moisture in hot 
 weather ? 
 
 Why does the evaporation of ether freeze water ? 
 
 How does ignition differ from combustion ? 
 
 CONVERSATION IV. 
 
 What is understood by capacity for caloric ? 
 Have all bodies of the same weight the same capacity for ca- 
 loric ? 
 
 How is the capacity of bodies for heat ascertained ? 
 What is latent caloric ? 
 
 How does latent caloric differ from specific caloric ? 
 Why does not the thermometer rise in a warm room, when its 
 . bulb is in a piece of ice ? 
 How much latent heat does water contain ? 
 Is the real zero known to exist ? 
 How can ice be made in the summer ? 
 Why does the slaking of lime produce heat ? 
 
QUESTIONS. 
 
 CONVERSATION V. 
 
 What kind of body is electricity ? 
 
 How many metals are required to produce the galvanic action ? 
 
 Can galvanism be produced without water ? 
 
 How many kinds of electricity are there ? 
 
 What were the ideas of Dr. Franklin on this subject ? 
 
 What is said to produce the heat of the electric fluid ? 
 
 What is the difference between electricity and galvanism 9 
 
 What difference does it make in the action of the galvanic bat- 
 tery, whether you increase the number of plates, or enlarge 
 their dimensions ? 
 
 CONVERSATION VI. 
 
 Of what is the atmosphere composed ? 
 
 What is a gas ? 
 
 To what do the gases owe their elasticity ? 
 
 What proportions of oxygen and nitrogen constitute common 
 air ? 
 
 When a substance burns, what does it absorb ? 
 
 Why is it necessary to heat a combustible substance to make 
 it burn ? 
 
 Why does a candle confined in a small portion of air soon go 
 out ? 
 
 How does oxygenatien differ from combustion ? 
 
 Why is there no smoke when the fire burns best ? 
 
 Do the constituents of the atmosphere exist in a state of chem- 
 ical combination ? 
 
 CONVERSATION VII. 
 
 What does the word hydrogen signify ? 
 
 How does hydrogen produce water ? 
 
 Of what is water composed ? 
 
 What are the means of decomposing water ? 
 
 What the results of galvanic action upon water? 
 
 How much ! ghter is hydrogen than common air? 
 
 Will oxygen and^.yuiugeii combine in any other proportion 
 
 than that which forms wate; 1 ? 
 In the burning of a candle, why is there a little space of wick, 
 
 left between the tallow and ti;? oe ? 
 What is the gas called which is used in lighting streets ? 
 How is this gas procured ? 
 
334 QUESTIONS. 
 
 Describe the miner's lamp. 
 What is the use of this lamp ? 
 
 CONVERSATION VIII. 
 
 Where is sulphur obtained J 
 
 How does brimstone differ from ihejlowers of sulphur ? 
 
 What is sublimation ? 
 
 When sulphur is burned/Vhat is the product ? 
 
 From whence is phosphorus obtained ? 
 
 What is the result of its combustion ! 
 
 How are the phosphorus and phosphoric acid formed ? 
 
 Does phosphoric combine with hydrogen ? 
 
 What are the singular properties of phosphuret of lime ? 
 
 CONVERSATION IX. 
 
 What is carbon 7 
 
 Under what form does crystallised charcoal appear ? 
 
 Why does charcoal burn without a blaze ? 
 
 What becomes of carbon during its combustion ? 
 
 Is it possible to burn a diamond ? 
 
 What is the product of its combustion ? 
 
 Does carbon unite with more than one proportion of oxygen '.' 
 
 Is it safe to breathe carbonic acid ? 
 
 Why does a small quantity of water increase the flame of a 
 fire ? 
 
 What is the composition of black lead? 
 
 How may the adulteration of volatile oil be detected ? 
 
 What are the products of a burning candle or lamp ? 
 
 How does carbon restore oxydated substances to their combus- 
 tible state ? 
 
 CONVERSATION X. 
 
 How many metals are there ? 
 
 Name them. 
 
 Where are the metals found r 
 
 How are they refined ? 
 
 Are all the metals combustible r 
 
 What are oxides ? 
 
 What use is made of metallic oxides ? 
 
 How is the most intense heat produced ? 
 
 Do the metals oxydate on being exposed to the air ? 
 
 When a metal dissolves in an acid, what causes the heat ? 
 
QUESTIONS. 335 
 
 What state must a metal be in before it can be dissolved by an 
 acid ? 
 
 What is crystallization ? 
 
 Do any of the metals combine with so much oxygen as to be- 
 come acids ? 
 
 At what degree of cold does mercury become solid ? 
 
 From whence do the metallic oxides derive their poisonous 
 qualities ? 
 
 What peculiarities have the new metals, discovered by Sir H. 
 Davy ? 
 
 CONVERSATION XIII. 
 
 What is the attraction of composition ? 
 
 What is the kind of attraction which brings acids and alkalies 
 to unite '? 
 
 What are the seven laws of chemical attraction ? 
 
 What are the salijiable bases ? 
 
 What are the salifiable principles ? 
 
 How do salts ending in ate differ from those ending in ite? 
 
 How do acids ending in ic differ from those ending in ous? 
 
 How are chemical compositions, and decompositions effected ? 
 
 What is meant by quiescent, and diveilant forces ? 
 
 When acids and alkalies unite in several proportions, what rela- 
 tion do these proportions bear to each other ? 
 
 When a salt is decomposed by galvanism, at which pole does 
 the acid appear ? 
 
 CONVERSATION XIV. 
 
 What are the alkalies ? 
 What is their composition ? 
 What are the general properties of the alkalies ? 
 On what does the causticity of the alkalies depend 9 
 To what colour do the alkalies change the vegetable blues ? 
 From whence is potash obtained ? 
 What is the chemical name of potash? 
 What is its composition ? 
 
 Why is heat disengaged when water is poured on caustic pot- 
 ash ? 
 
 What is the result when potash is melted with silex ? 
 What is the chemical name of salt petre ? 
 What is its composition ? 
 From whence does soda derive its name -? 
 How is it obtained ? 
 
336 QUESTIONS. 
 
 How does soda differ from potash? 
 
 Why is the volatile alkali called ammonia ? 
 
 From what is it extracted ? 
 
 By what means can ammonia be separated from the 
 
 acid? 
 
 Under what form does it appear when pure ? 
 What is the composition of ammonia ? 
 How can anmiouiacal gas be retained for experiments without a 
 
 mercurial bath f 
 How do you account for the production of cold, when ice is 
 
 melted with amraoniacal gas ? 
 What is the substance used in smelling bottles, called harts 
 
 horn ? 
 
 What is formed when ammonia unites with oil ? 
 From what class of substances can ammonia be extracted ? 
 
 CONVERSATION XV. 
 
 What is the number of earths, and what their names ? 
 
 Why are they incombustible ? 
 
 W licit costly substances do the earths compose ? 
 
 Witti what are the gems coloured ? 
 
 Which a iv the alkaline earths ? 
 
 Wiiat substances contain silica in the greatest abundance ? 
 
 Wilit is the composition of Derbyshire spar? 
 
 What are the important uses of silex ? 
 
 From whence does alumine derive its name ? 
 
 From what substance is this earth obtained ? 
 
 In what kind of soil does it occur most abundantly ? 
 
 Is it useful in the arts, or otherwise, and for what purposes ' 
 
 Name the alkaline earths. 
 
 Of what use is barytes ? 
 
 Has it any remarkable properties ? 
 
 In what respect does caustic lime differ from lime-stone ? 
 
 What is the process of making quick-lime? 
 
 What effect does the air produce on quick-lime ? 
 
 What effect has water on it ? 
 
 What is the cause of the heat, when lime is sprinkled with 
 
 water ' 
 
 Does it dissolve in water, and in what proportion ? 
 What is the process of making lime-water ? 
 For what has lime a remarkable affinity ? 
 Why does lime-water turn white on breathing into U ? 
 Of what use is lime in the arts ? 
 Of what use is it in agriculture ? 
 
QUESTIONS. 337 
 
 What are the principal uses of magnesia ? 
 
 Does it attract water ? 
 
 In what state is it used in medicine ? 
 
 What does it form when combined with sulphuric acid'.' 
 
 Is strontion of any use ? 
 
 What are its peculiarities ? 
 
 CONVERSATION XVI. 
 
 What is an acid ? 
 
 What are the general properties of tire acids ? 
 
 What is meant by the radical of an aci J ? 
 
 What substance unites to the radical to form an acid ? 
 
 How does the language of chemistry distinguish the stronger 
 
 from the weaker acid ? 
 
 What term is used to denote the first degree of oxygenation ? 
 When a radical unites with another proportion of oxygen alter 
 
 that denoted by zc, what term is used ? 
 Vre all the acids capable of equal degrees of oxygenation ? 
 What is the number of acids ? 
 Plow many kinds of acids are there ? 
 Name the acids which are known to have simple bases. 
 Which are called mineral acids ? 
 
 Of what are the radicals of the vegetable acids composed ? 
 Why do these acids differ, when composed of the same radicals '{ 
 What are the names of the vegetable acids ? 
 Name the acids with triple radicals. 
 
 What is their composition, and from whence are they obtained ? 
 By what means can the acids of simple radicals be decomposed r 
 Why does sulphuric acid change the colour of wood to black ? 
 Why do not the vegetable acids produce the same effect ? 
 What is the reason fche vegetable acids are not decomposed by 
 
 combustibles ? 
 Do the mineral acids have the same effect upon the skin thai: 
 
 they do on wood ? If they do not what is the reason ? 
 
 CONVERSATION XVII 
 
 What is the chemical name of oil of vitriol?. 
 What is the colour and smell of sulph. acid ? 
 What is its specific gravity ? 
 What is the consequence of mixing it with water .' 
 What is the process for obtaining snip, acid ? 
 What the best antidote, when a quantity is swallowed? 
 How can the sulphuric acid be changed to the sulphuro?/s ^ 
 
 30 
 
338 
 
 What use is ma3e of sulphurous acid ? 
 
 What is the easiest process for making this acid 1 
 
 Define what the term salt means.' 
 
 What is the chemical name and composition of Glaubers salt? 
 
 How can sulphate of soda be formed ? 
 
 What qualities in the salts are denoted by the terms efflorescent 
 
 and deliquescent? 
 
 From whence comes sulph. ofalumine? 
 What are its principal uses ? 
 
 How is sulphate of iron manufactured in the large way r 
 What substance strikes a black colour with sulph. of iron ? 
 Why does the cutting of an apple turn the blade of the knife 
 
 black ? 
 Where is phosphate of lime chiefly found ? 
 
 CONVERSATION XVIII. 
 
 What acids are formed by the combination of nitrogen and ox- 
 ygen ? 
 
 What acid contains the greatest proportion of oxygen ? 
 
 Explain the reason why nitric acid inflames charcoal, ol. tur- 
 pentine, &c. 
 
 How is nitric acid obtained, and from what substance ? 
 
 How can nitric, be converted in nitrows, acid ; and what is the 
 cause of the change 1 
 
 Why does nitric acid act with peculiar energy on combustibles 1 
 
 How can nitrous air be procured from nitric acid, and what is 
 the principle ? 
 
 How is nitrous air converted into nitrons acid gas ? 
 
 On what principle can nitrous air be applied to test the purity 
 of the atmosphere ? What is the process ? 
 
 How is the exhilarating gas procured ? 
 
 Describe the process of making nitrate of ammonia. 
 
 What caution is necessary before it is breathed ? 
 
 When do chemical decompositions and combinations take place 
 during the formation of this gas from nitrate of ammonia ? 
 
 Why is nitrate of potash used in making gun powder, rather 
 than any other salt ? 
 
 What causes the detonation when gun powder is fired ? 
 
 What gas is formed when charcoal is burned in oxygen gas ? 
 
 By what method can charcoal be procured from carbonic acid ? 
 
 What portion of the atmosphere is formed of this gas? 
 
 By what means is this gas procured for experiment ? 
 
 From whence came the immense quantity of carbonic acid con- 
 tained in limestone rocks ? 
 
QUESTIONS. 
 
 In what manner does this gas destroy life? 
 
 W.iat effect does it have on vegetation ? 
 
 Wnat are the waters called which contain this gas ? 
 
 What are the salts called which are partly composed of this 
 
 gas / 
 How extensive is this class of salts, and under what forms do 
 
 they chiefly occur in nature ? 
 
 CONVERSATION XIX. 
 
 What is the basis of boracic acid ? 
 
 What is the composition of borax ? 
 
 What are its uses ? 
 
 From whence \sfluoric acid obtained ? 
 
 What are its peculiar properties ? 
 
 Describe the method of etching on glass. 
 
 With what is muriatic acid chiefly found combined ? 
 
 What is the natural state in which this exists ? 
 
 How can this gas be confined without a mercurial bath ? 
 
 What is the basis of muriatic acid ? 
 
 Is this acid capable of combining with different proportions of 
 
 oxygen 1 
 Why is not the least degree of oxygenation called the muriat- 
 
 ou.s acid ? 
 
 How is oxy-muriatic acid obtained ? 
 Explain the reason why metals inflame in this gas. 
 Why does a mixture of nitric, and muriatic acids dissolve gold, 
 
 when neither of them will do it alone ? 
 Why does oxy-muriatic acid turn the colour of vegetables 
 
 white 1 
 
 Of what use is this acid in the arts ? 
 Why is oxy-muriatic acid lately called chlorine ? 
 What are the reasons for supposing that chlorine is a simple 
 
 substance ? 
 
 What are the reasons for supposing that it is not a simple sub- 
 stance ? 
 
 From whence, and by what process is muriate of soda obtained ? 
 What two gases, when mixed form muriate of ammonia? De*- 
 
 scribe the experiment. 
 
 What are the peculiar properties of oxy-muriate of potash ? 
 Why does it explode on being rubbed with charcoal, sulphur, &c. 
 What gases are generated at the moment of explosion with 
 
 charcoal ? Explain the changes which take place, and thfc 
 
 cause of the detonation. 
 
aUESTlONS. 
 
 How can phosphorus be set on fire at the bottom of a vessel oi 
 
 water ? and how do you account for it ? 
 What are the peculiarities ofiddinc ? 
 How can you show the violet coloured gas ? 
 From whence is iodine obtained ? 
 "Why is it considered a simple body ? 
 
 CONVERSATION XX. 
 
 What are organised bodies, and how do they difter from inor- 
 ganic matter ? 
 
 Define what life is. 
 
 What constitutes the simplest class of organised bodies ? 
 
 Of what are vegetables chiefly composed ? 
 
 What are the materials of vegetables ? 
 
 Is any part of a plant composed of a single ingredient ? 
 
 Why do vegetables decompose, when the principle of life is ex- 
 tinguished ? 
 
 Vegetables are susceptible of two kinds of analysis, what is the 
 object of each ? 
 
 What is mucilage, and what are its uses ? 
 
 Can gum be used as food ? 
 
 What proportion of vegetables contain sugar? 
 
 In what manner is sugar obtained from the sugar cane ? 
 
 How does honey differ from sugar ? 
 
 What hfecula ? 
 
 What is gluten ? 
 
 How many kinds of vegetable oils are there ? 
 
 From what part of plants are fixed oils obtained r 
 
 What are the principal drying oils ? 
 
 On what does this quality depend ? 
 
 Why do painters ald oxyd of lead to their oils ? 
 
 To what is the rancidity of oil owing r 
 
 Is there any known method of making oil by combining itfe 
 principles ? 
 
 How do volatile differ horn fixed oils ? 
 
 How are volatile oils obtained ? 
 
 When they are adulterated with fixed oils how can the fraud be 
 detected ? 
 
 From whence does camphor come, and from what is it ex- 
 tracted ? 
 
 What is the method of obtaining it ? 
 
 Is camphor contained in other plants r 
 
 What are resins ? 
 
 How are varnishes prepared r 
 
What are gum-resins ? 
 
 What are balsams ? 
 
 Give some account of caoutchouc or gum-elastic 
 
 What is extractive matter ? 
 
 What is the condition required to form a good dye ? 
 
 Explain the nature and uses of mordants. 
 
 What substances are commonly used as mordants ? 
 
 What is tannin ? 
 
 How is artificial tannin made ? 
 
 What is woody fibre ? 
 
 Of what is it chiefly composed ? 
 
 What are the names of the vegetable acids ? 
 
 What is the composition of the bases of these acids ? 
 
 What is the gallic acid ? 
 
 What are galls, and how are they formed ? 
 
 How does the oxalic acid remove ink spots ? 
 
 CONVERSATION XXI. 
 
 What are the elements into which vegetables are reduced by 
 
 natural decomposition ? 
 What is the process called which disunites and decomposes the 
 
 elements of vegetables ? 
 How many kinds of fermentation are there ? 
 What circumstances are necessary to induce this process ? 
 Give some account of the saccharine fermentation. 
 What is the process of making malt ? 
 What changes do the ingredients of the barley undergo to form 
 
 malt ? 
 
 What is the second fermentation called ? 
 Why does barley resist the vinous fermentation until it has 
 
 gone through the saccharine? 
 What changes take place among the ingredients present, during 
 
 the vinous fermentation ? 
 
 What is the principal difference between alcohol and sugar ^ 
 When wine is distilled, what is the product ? 
 How does sugar differ from starch? 
 What difference is there between gin and brandy ? 
 What is the origin of cream of tartar ? 
 On what does the intoxicating quality of liquors depend? 
 What is the composition of alcohol? 
 Describe the spirit lamp. 
 How is ether obtained ? 
 How does it differ from alcohol ? 
 What is the effect of the acetous fermentation r* 
 
 30* 
 
342 QUESTIONS. 
 
 What is the reason that wine, or cider, when corked tight doe: 
 
 not turn to vinegar ? 
 What kind of fermentation is excited by the yeast to make 
 
 bread ? 
 What is the final operation of nature to reduce vegetables to 
 
 their elements ? 
 
 How are petrifactions formed ? 
 What are bitumens, and how are they formed 1 
 Why does naptha preserve potassium ? 
 What is asphaltum ? 
 
 What is coal, and what are its ingredients ? 
 How does coke differ from coal ? 
 What is amber, and where is it found ? 
 
 CONVERSATION XXII. 
 
 From whence do all animals ultimately derive their sustenance? 
 
 From whence do plants derive their food ? 
 
 W'ill plants live on pure water? 
 
 Why do animal substances make the best manure"? 
 
 What part of the seed are the cotyledons ? 
 
 What is the radicle ? What is the plumule'? 
 
 What purpose do each of these answer during germination ? 
 
 What office do the leaves of plants perform during their growth ? 
 
 What different functions do the two sides of the leaves per- 
 form ? 
 
 What is essential to the developement of the colours of plants? 
 
 Why is air necessary to the growth of plants ? 
 
 In what way does animal and vegetable life mutually support 
 each other? 
 
 Through what vessels does the sap of plants ascend ? 
 
 What is the distinction between aburnum, and heart-wood? 
 
 How is pitch, tar, and turpentine obtained ? 
 
 Why do vegetables grow, only during the warm season ? 
 
 CONVERSATION XXIII. 
 
 What are the fundamental principles of animal compounds ? 
 V* hat are the immediate materials of animal compounds ? 
 What is gelatine 1 What use is made of it in the arts, or in 
 
 medicine ? 
 
 From what substance is gelatine extracted ? 
 By what means may it be extracted from bones ? 
 Of what is soup composed ? 
 How does glue differ from gelatine ? 
 
. aUESTIONS. 343 
 
 What is albumen ? 
 
 Why is silver tarnished by the white of an egg P 
 
 What is fibrine ? 
 
 How may it be procured ? 
 
 In what respect does the composition of animal oil, differ from 
 
 the oil of vegetables l . 
 What are the bases of the animal acids ? 
 What are the names of those which are found ready formed in 
 
 animal substances 1 
 
 What animal acids are produced by decomposition ? 
 By what means is the prussic acid procured ? 
 Does this acid exist ready formed in blood ? 
 By what chemical combinations is it produced 1 
 How is it, that this colourless acid is the colouring matter of 
 
 prussian blue ? 
 
 What is carmine ? How is it prepared ?. 
 W T hat is ivory black 1 
 
 CONVERSATION XXIV. 
 
 What is animalisation? 
 
 What is nutrition ? 
 
 What are the principal organs by which the operations of the 
 
 animal system is performed ? 
 What are the ingredients of the bones ? 
 From whence do infants obtain phosphat of lime ? 
 How are the teeth formed ? 
 Under what circumstance is the phosphate of lime assimilated 
 
 in adult animals? 
 
 What causes the disease in infants, called the rickets ? 
 How are the bones connected together ? 
 What are the uses of the cartilages ? 
 What are the muscles ? 
 
 Where are they situated, and what are their uses ? 
 What part in the circulation of the blood does the arteries per 
 
 form ? 
 
 What part do the veins perform ? 
 What is the nature of the lympht 
 W hat is chyle ? 
 What is its use ? 
 
 What is the composition of milk ? 
 What functions do the glands perform ? 
 Does the blood contain all the substances found in the products 
 
 of secretion 1 
 What offices do the nerves perform ? 
 
344 QUESTIONS. 
 
 What is the source of the nervous system ? 
 
 What parts of the animal system are without nerves ?" 
 
 How is it that the nerves convey different sensations, when 
 
 they all have a common source? 
 Of how many coats is the skin comprised r 
 What are they called ? 
 Where is the colour of the skin situated ? 
 What difference in colour is there between the cuticle of a 
 
 white man, and a black one? 
 
 CONVERSATION XXV. 
 
 What is digestion ? 
 
 Where is it performed ? 
 
 What is the solvent of the food in the stomach ? 
 
 Are the coats of the stomach liable to be destroyed by the 
 
 gastric juice ? 
 
 What produces the sensation of hunger ? 
 What is the aliment called after it has been acted on by the 
 
 gastric juice ? 
 
 What changes does the chyme undergo before it is absorbed ? 
 By what system of vessels is the chyle taken up ? 
 How does it obtain admittance into circulation ? 
 In what does respiration consist ? 
 What constitutes the mechanical part of this process 1 
 By what means is the ch$si expanded so as to admit air into 
 
 the lungs ? 
 
 How many times does a person breathe in a minute ? 
 Describe the circulation of the blood. 
 How does arterial blood differ from venous 1 
 How do you account for the difference of colour between them ? 
 What are the two cavities of the heart called ? 
 Which cavity receives the arterial, and which the venous blood ? 
 W'hat change does the blood undergo in its passage through 
 
 the lungs t 
 
 What effect does respiration have on the air we breathe? 
 The blood undergoes two circulations ; what is the difference 
 
 between them ? 
 What is the quantity of carbon expelled from the lungs of a 
 
 person in 24 hours ? 
 
 What quantity of air do we take into our lungs at each inspira- 
 tion ' 
 Is it absolutely certain that the carbon emitted by respiration 
 
 comes from the blood 
 Are all the products of secretion contained in the blood P 
 
QUESTIONS. 345 
 
 If not, how is it most probable that these new substances are 
 
 formed ? 
 By what system of vessels is the perspiration secreted ? 
 
 CONVERSATION XXVI. 
 
 What analogy is there between the effects of respiration, and 
 thjjse of combustion ? 
 
 What is the principal source of animal heat ? 
 
 What are the objections to Black's theory of animal heat ? 
 
 How are these objections obviated ? 
 
 What objections can be brought against Dr. Crawford's theory*? 
 
 What does Mr. Brodie's experiment prove ? 
 
 What are the objections to Dr. Cooper's theory ? 
 
 W 7 hat are the objections against Dr. Philip's theory ? 
 
 Why is the heat increased duripg a fever ? 
 
 Why does not violent exercise greatly increase the temperature 
 of the body 1 
 
 On what principle is it that the temperature of the body remains 
 the same in winter as in summer ? 
 
 Is the temperature of a living animal raised by being exposed 
 to a heat, greater than that of its own body ? 
 
 How* is it proved that fish cannot live without air? 
 
 What effect does the respiration of a large or small quantity 
 of air have on the muscular powers of animals ? 
 
 Why are amphibious animals enabled to remain a long time 
 under water 1 
 
 What is composition of milk? 
 
 What are the ingredients in milk? 
 
 What does cream absorb from the atmosphere to turn it into 
 butter? 
 
 Why does the butter-milk become sour when the butter separa- 
 ted from it is sweet ? 
 
 What causes butter to become rancid ? 
 
 What does rennet contain which causes the coagulation of milk? 
 
 What is spermaceti ? 
 
 What is ambergris'? 
 
 By what process does dead animal matter return to its elemen- 
 tary state ? 
 
A VOCABULARY 
 
 OF 
 
 CHEMICAL TERMS. 
 
 A. 
 
 Acetates. Compounds formed by the combination of a base 
 with acetic acid. 
 
 Adds. Compounds formed by the combination of oxygen 
 with certain elementary bodies forming in general a class ot 
 substances, which are sour to the taste, and which unite with 
 alkalies, and metallic oxides to form salts. 
 
 Acidules. Substances formed by the natural combination of 
 some acids with a quantity of potash. The oxalic and tar- 
 taric acids are examples. 
 
 Aeriform fluids. Elastic fluids. Atmospheric air, and the 
 gases are of this kind. Their aeiform state is owing to the 
 caloric with which their bases are combined. 
 
 Affinity, chemical. A term used to express that peculiar pro- 
 pensity which substances of different kinds have to unite with 
 each other, as acids and alkalies, &c. 
 
 of aggregation. That force is so called by which sub- 
 stances of the same kind tend to unite, without changing their 
 qualities. 
 
 of composition. That force by which substances of 
 different kinds combine, and form a third, which differs from 
 either of the two first, before the combination. Thus muri- 
 atic acid and soda form common salt. 
 
 Albumen. Coagulable lymph. It is contained in animal sub- 
 stances, as the serum of the blood. The white of eggs is al- 
 bumen. 
 
 Alcohol. Rectified spirit of wine. It is always the same, from 
 whatever kind of spirit it is distilled. 
 
 Alkalies. Peculiar substances which have a caustic burning 
 taste, and a strong tendency to combination, particularly 
 with acids, and witjh water. 
 
A VOCABULARY OF CHEMICAL TERMS. 347 
 
 Alloys. A combination of any two metals, except mercury. 
 
 Brass is an alloy of copper and zinc. 
 Amalgam. A mixture of mercury with any other metal. 
 Analysis. Separation of the constituent parts of compounds, 
 
 for the purpose of detecting their composition. This is done 
 
 by reagents. 
 Annealing. Rendering substances tough, which before were 
 
 brittle. The metals are annealed by heating them red hot, 
 
 and then cooling them gradually. 
 Arscniates. Salts} formed by the combination of a base with 
 
 the arsenic acid. 
 
 Azote. This name is given by the French chemists to nitro- 
 gen, which see. 
 
 B. 
 
 Balsams. Resinous, semi-fluid substances, which are obtained 
 
 from certain trees by making incisions. 
 Barometer. An instrument which indicates the variations of 
 
 the pressure of the atmosphere, as thermometers do of heat 
 
 and cold. 
 Base. A term used by chemists to denote the substance to 
 
 which an acid is united to form a salt. Thus soda is the 
 
 base of common salt. 
 Benzoates. Salts formed by the union of the benzoic acid with 
 
 a base. 
 Blow-Pipe. An instrument to increase and direct the flame of 
 
 a lamp for the analysis of minerals, and for other chemical 
 
 purposes. 
 Borates. Salts formed by the combination of any base with 
 
 the acid of borax. 
 
 c. 
 
 Calcareous. A chemical term formerly applied to describe* 
 chalk, marble, and all other combinations of lime with car- 
 bonic acid. 
 
 Calcination. The application of heat to saline, metallic, or 
 other substances ; so regulated as to deprive them of mois- 
 ture, &c. and yet preserve them in a pulverulent form. 
 
 Caloric. The chemical term for the matter of heat. 
 
 free. Is caloric in a separate state, or, if attached to- 
 other substances, not chemically united with them. 
 
 latent. Is the term made use of to express that por- 
 
348 A VOCABULARY 
 
 tion of caloric which is chemically united to any substance,, 
 so as to become <\.part of the said substance. 
 
 Calorimeter. An instrument for ascertaining the quantity of 
 caloric disengaged from any substance that may be the ob- 
 ject of experiment. 
 
 Calx. An old term made use of to describe a metallic oxide. 
 
 Camphor atas. Salts formed by the combination of any base 
 with the camphoric acid. 
 
 Capillary. A term usually applied to the rise of the sap in 
 vegetables, or the rise of any fluid in very small tubes ; owing 
 to a peculiar kind of attraction, called capillary attraction. 
 
 Carbon. The basis of charcoal. 
 
 Carbonates. Salts formed by the combination of any base with 
 carbonic acid. 
 
 Carburets. Compound substances, of which carbon forms om 
 of the constituent parts. Thus plumbago, which is compo- 
 sed of carbon and iron, is called carburet of iron. 
 
 Causticity. That quality in certain substances by which 
 they burn or corrode animal bodies to which they are appli- 
 ed. It is best explained by the doctrine of chemical affinity. 
 
 Chalybeate. A term descriptive of those mineral waters which 
 are impregnated with iron. 
 
 CharcoaL Wood burnt in close vessels : it is an oxide of 
 carbon, and generally contains a small portion of salts and 
 earth. Its carbonaceous matter may be converted by com- 
 bustion into carbonic acid gas. 
 
 Chlorine. A name lately given to the substance usually called 
 oxymuriatic acid. Its compounds are called by the name of 
 their bases with the ending of anc. As phosphorane, sul- 
 phurane, &c. 
 
 Chromates. Salts formed by the combination of any bas* 
 with the chromic acid. 
 
 Citrates. Salts formed by the combination of any base with 
 citric acid. 
 
 Coal. A term applied to the residuum of any dry distillation 
 of animal or vegetable matters. 
 
 Cohesion. A force inherent in all the particles of all substan- 
 ces, excepting light and caloric, which prevents bodies from 
 falling in pieces. 
 
 Columbates. Salts formed by the combination of any base with 
 the columbic acid. 
 
 Combination. A term expressive of a true chemical union of 
 two or more substances ; in^opposition to mere mechan- 
 ical mixture. 
 
 Combustibles. Certain substances which are capable of con? 
 
OP CHEMICAL TERMS. 
 
 tuning more or less rapidly with oxygen. They are divided 
 by chemists into simple and compound combustibles. 
 
 (Combustion The act of absorption of oxygen by combustible 
 bodies from atmospheric or vital air. The word decombus- 
 tion is sometimes used by the French writers to signify the 
 opposite operation. 
 
 Crucibles. Vessels of indispensable use in chemistry in the 
 various operations of fusion by heat. They are made of ba- 
 ked earth, or metal, in the form of an inverted cone. 
 
 Crystallization. An operation of nature, in which various 
 earths, salts, and metallic substances, pass from a fluid to a 
 solid state, assuming certain determinate geometrical figures. 
 
 -' water of. That portion which is combined with 
 
 salts in the act of crystallizing, and becomes a component part 
 of the said saline substances. 
 
 Cupel. A vessel made of calcined bones, mixed with a small 
 proportion of clay and water. It is used whenever gold and 
 silver are refined by melting them with lead. The process- 
 is called cupellation. 
 
 D. 
 
 Decomposition. The separation of the constituent principles 
 of compound bodies by chemical means. 
 
 Deflagration. The vivid combustion that is produced whene- 
 ver nitre, mixed with an inflammable substance, is exposed 
 to a red heat. It may be attributed to the extrication of ox- 
 ygen from the nitre, and its being transferred to the inflam- 
 mable body ; as any of the nitrates or oxygenized muriates 
 will produce the same effect. 
 
 Deliquescence of solid saline bodies, signifies their becoming 
 moist, or liquid, by means of water which they absorb from 
 the atmosphere in consequence of their great attraction for 
 that fluid. 
 
 Deoxidize (formerly deoxidate.) To deprive a body of oxygen. 
 
 Deoxidizement. A term made use of to express that operation 
 by which one substance deprives another substance of its 
 oxygen. It is called unburning a body by the French chem- 
 ists. 
 
 Detonation. An explosion with noise. It is most commonly 
 applied to the explosion of nitre when thrown upon heated 
 charcoal. 
 
 Digestion. The effect produced by the continued soaking of 
 a solid substance in a liquid, with the application of heat 
 3* 
 
A VOCABULARY 
 
 Papirfs. An apparatus for reducing animal or vt- 
 getable substances to a pulp or jelly expeditiously. 
 
 Distillation A process for separating the volatile parts of a 
 substance from the more fixed, and preserving them both in 
 a state of separation. 
 
 Ductility. A quality of certain bodies, in consequence of which 
 they may be drawn out to a certain length without fracture. 
 
 'Didcification. The combination of mineral acids with alcohol. 
 Thus we have dulcified spirit of nitre, dulcified spirit of vit- 
 riol, &c. 
 
 E. 
 
 EdulcQration. Expressive of the purification of a substance by 
 washing with water. 
 
 Effervescence. An intestine motion which takes place in cer- 
 tain bodies, occasioned by the sudden escape of a gaseous 
 substance. 
 
 Efflorescence. A term commonly applied to those saline crys- 
 tals which become pulverulent on exposure to the air, in con- 
 sequence of the loss of a part of the water of crystallization. 
 
 Elasticity. A. force in bodies, by which they endeavour to re- 
 store themselves to the posture from whence they were dis- 
 placed by an external force. 
 
 Elastic fluids. A name sometimes given to vapours and gas- 
 es. Vapour is called an clastic fluid ; gas, a permanently 
 elastic fluid. 
 
 Elective Attractions. A term used by Bergman and others to 
 designate what we now express by the words chemical affin- 
 itij^ When chemists first observed the power which one 
 compound substance has to decompose another, it was ima- 
 gined that the minute particles of some bodies had a prefer- 
 nce for some other particular bodies 5 hence this property of 
 matter acquired the term elective attraction. 
 
 Elements. The simple, constituent parts of bodies which are 
 incapable of decomposition ; they are frequently called prin- 
 ciples. 
 
 Empyreuma. A peculiar and indescribably disagreeable smell, 
 arising from the burning of animal and vegetable matter in 
 close vessels. 
 
 Ethers. Volatile liquids formed by the distillation of some of 
 the acids with alcohol. 
 
 Evaporation. The converson of fluids into vapour by heat. 
 This appears to be nothing more than a gradual solution of 
 
OP CHEMISAL TERMS. 331 
 
 the aqueous particles in atmospheric air, owing to the chem- 
 ical attraction of the latter for water. 
 
 Eudiometer. An instrument invented by L)r. Priestley for de- 
 termining the purity of any given portion of atmospheric air. 
 The science of investigating the different kinds of gases i 
 called eudiometry. 
 
 F. 
 
 Fermentation. A peculiar spontaneous motion, which takes 
 place in all vegetable matter when exposed for a certain time 
 to a proper degree of temperature. 
 
 Fibrine. That white fibrous substance which is left after free- 
 ly washing the coagulum of the blood, and which chiefly 
 composes the muscular fibre. 
 
 Flowers. In chemical language, are solid dry substances re- 
 duced to a powder by sublimation. Thus we have flowers 
 of arsenic, of sal ammoniac, of sulphur, &c. which are arsenic, 
 sal ammoniac, and sulphur unaltered except in appearance. 
 
 Fluatcs. Salts formed by the combination of any base with 
 fluoric acid. 
 
 Fluidity. A term applied to all liquid substances. Solids are 
 converted to fluids by combining with a certain portion of 
 caloric. 
 
 Flux. A substance which is mixed with metallic ore, or other 
 bodies to promote their fusion ; as an alkali is mixed with si- 
 lex, in order to form glass. 
 
 Fulmination. Thundering or explosion with noise. We have 
 fulminating silver, fulminating gold, and other fulminating 
 powders, which explode with a loud report by friction, or 
 when slightly heated. 
 
 Fusion. The state of ai)ody which was solid in the tempera- 
 ture of the atmosphere, and is now rendered fluid by the ar- 
 tificial application of heat. 
 
 G. 
 
 Gallates. Salts formed by the combination of any base with 
 gallic acid. 
 
 Ghlvanism. A new science which oflfers a variety of phenome- 
 na, resulting from different conductors of electricity placed in 
 different circumstances of contact ; particularly the nerve* of 
 the animal body. 
 
 Gas. All solid substances, when converted into permanently 
 elastic fluids by caloric, are called gases, 
 
A VOCABULARY 
 
 Having the nature and properties oi gas. 
 
 Gasometer. A name given to a variety of utensils and appara- 
 tus contrived to measure, collect, preserve, or mix the differ- 
 ent gases. An apparatus of this kind is also used for the 
 purposes of administering pneumatic medicines. 
 
 Gelatine. A chemical term for animal gelly. It exists partic- 
 ularly in the tendons and the skin of animals. 
 
 Gluten, A vegetable substance somewhat similar to animal 
 gelatine. It is the gluten in wheat flour which gives it the 
 property of making good bread, and adhesive paste. Other 
 grain contains a much less quantity of this nutritious sub- 
 stance. 
 
 Grain. The smallest weight made use of by chemical writers. 
 Twenty grains make a scruple ; 3 scruples a drachm ; 8 
 drachms, or 480 grains, make an ounce ; 12 ounces, or 5760 
 grains, a pound troy. The avoirdupois pound contains 7009 
 grains. 
 
 Granulation. The operation of pouring a melted metal into 
 water, in order to divide it into small particles for chemical 
 purposes. Tin is thus granulated by the dyers before it is 
 dissolved in the proper acid. 
 
 Gravity, specific. This differs from absolute gravity in as 
 much as it is the weight of a given measure of any solid or 
 fluid body, compared with the same measure of distilled wa- 
 ter. It is generally expressed by decimals. 
 
 Gums. Mucilaginous exudations from certain trees. Gum 
 consists of lime, carbon, oxygen, hydrogen, and nitrogen with 
 a little phosphoric acid. 
 
 H. 
 
 Heat, mutter of. See Caloric. 
 
 Hermetically. A term applied to the closing of the orifice of a 
 glass tube, so as to render it air-tight. Hermes, or Mercury, 
 was formerly supposed to have been the inventor of chemis- 
 try : hence a tube which was closed for chemical purposes, 
 was said to be Hermetically or chemically sealed. It is usu- 
 ally done by melting the end of the tube by means of a blow- 
 pipe. 
 
 Hydrogen. A simple substance; one of the constituent parts 
 of water. 
 
 gas. Solid hydrogen united with a large portion of 
 
 caloric. It is the lightest of all the known gases. Hence 
 t is used to inflate balloons. It was formerly called inflam- 
 mable air. 
 
OP CHEMICAL TERMS. 
 
 353 
 
 Hydro-Carbonates. Combinations of carbon with hydrogen 
 are described by this term. Hydro-carbonate gas is procur- 
 ed from moistened charcoal by distillation. 
 
 Hydrogenized sulphurets. Certain bases combined with sul- 
 phuretted hydrogen. 
 
 Hydro-Oxides. Metallic oxides combined with water. 
 
 Hydrometers. Instruments for ascertaining the specific gravi- 
 ty of spiritous liquors or other fluids. 
 
 Hygrometers Instruments for ascertainiug the degree of mois- 
 ture in atmospheric air. 
 
 Hyperoxygenized. A term applied to substances which are 
 combined with the largest possible quantity of oxygen. We 
 have muriatic acid, oxygenized muriatic acid, and hyperoxy- 
 genized muriatic acid. The latter can be exhibited only in 
 combination. 
 
 I. 
 
 Inflammation. A phenomenon which takes place on mixing 
 certain substances. The mixture of oil of turpentine with 
 strong nitrous acid is an instance of this peculiar chemical ef- 
 fect. 
 
 Infusion. A simple operation to procure the salts, juices, and 
 other virtues of vegetables by means of water. 
 
 Intermediates. A term made use of when speaking of chemic- 
 al affinity. Oil, for example, has no affinity for water unless 
 it be previously combined with an alkali; it then becomes 
 soap, and the alkali is said to be the intermedium which oc- 
 casions the union. 
 
 K. 
 
 Kali. A genus of marine plants which is burnt to procure min- 
 eral alkali by afterwards lixiviating the ashes. 
 
 L. 
 
 Laboratory. A room fitted up with apparatus for the per- 
 formance of chemical operations 
 
 Lactates. Salts formed by the combination of any base with 
 lactic acid. 
 
 Lakes. Certain colours made by combining the colouring mat- 
 ter of cochineal, or of certain vegetables, with pure alumine, 
 or with oxide of tin, zinc, &c. 
 
 Lamp, Argand's. A kind of lamp much used for chemical ex- 
 
 31* 
 
3 A VOCABULAR\ 
 
 periments. It is made on the principle of a wind furnace , 
 and thus produces a great degree of light and heat withou 1 
 smoke. 
 
 Lens. A glass, convex on both sides, for concentrating the 
 rays of the sun. It is employed by chemists in fusing re- 
 fractory substances which cannot be operated upon by an or- 
 dinary degree of heat- 
 
 Levigation. The grinding down of hard substances to an im- 
 palpable powder on a stone with a muller, or in a mill adapt- 
 ed to the purpose. 
 
 Litharge. An oxide of lead which appears in a state of vitri- 
 fication. It is formed in the process of separating silver 
 from lead. 
 
 Lixiviation. The solution of an alkali or a salt in water, or in 
 some other fluid, in order to form a lixivium. 
 
 Lixivium. A fluid impregnated with an alkali or with a salt. 
 
 Lute. A composition for closing the junctures of chemical ves- 
 sels to prevent the escape of gas or vapour in distillation. 
 
 M. 
 
 Maceration. The steeping of a solid body in a fluid in order 
 to soften it, without impregnating the fluid. 
 
 Malates. Salts formed by the combination of any base with 
 malic acid. 
 
 Malleability. That property of meta's which gives them the 
 capacity of being extended and flattened by hammering. Il 
 is probably occasioned by latent caloric. 
 
 Massicot. A name given to the yellow oxide of lead, as minium 
 is applied to the red oxide. 
 
 Matrass. Another name for a bolt-head. 
 
 Menstruum. The fluid in which a solid body is dissolved. 
 Thus water is a menstruum for salts, gums, &c. and spirit oi 
 wine for resins. 
 
 Metallic Oxides. Metals combined with oxygen. By this 
 process they are generally reduced to a pulverulent form ; 
 are changed from combustible to incombustible substances ; 
 and receive the property of being soluble in acids. 
 
 Mineral. Any natural substance of a metallic, earthy, or sa- 
 line nature, whether simple or compound, is deemed a mine- 
 ral. 
 
 Mineralizers. Those substances which are combined with 
 metals in their ores; such are sulphur, arsenic, oxygen, car- 
 bonic acid, &c. 
 
 Mineralogy. The science of fossils and minerals- 
 
OF CHEMICAL TERMS. 355 
 
 Mineral Waters. Waters which hold some metal, earth, or 
 salt, in solution. They are frequently termed Medicinal 
 Waters. 
 
 Molybdatcs. Salts formed by the combination of any base 
 with the molybdic acid. 
 
 Mordants. Substances which have a chemical affinity for par- 
 ticular colours ; they are employed by dyers as a bond to 
 unite the colour with the cloth intended to be dyed. Alum 
 is of this class. 
 
 Mucilage. A glutinous matter obtained from vegetables, trans- 
 parent and tasteless, soluble in water, but not in spirit of 
 wine. It chiefly consists of carbon and hydrogen, with a 
 little oxygen. 
 
 Wucitcs. Salts formed by the combination of any base with 
 the raucous acid. 
 
 Mitjlc. A semi-cylindrical utensil, resembling the tilt of a 
 boat, made of baked clay ; its use is that of a cover to cu- 
 pels in the assay furnace, to prevent the charcoal from fall- 
 ing upon the metal, or whatever is the subject of experiment. 
 
 Muriates. Salts formed by the combination of any base with 
 muriatic acid. 
 
 Natron. One of the names for mineral alkali, or soda. 
 
 'Neutralize. When two or more substances mutually disguise 
 each other's properties, they are said to neutralize one anoth- 
 er. 
 
 ~^etttr;t1 Salt. A substance formed by the union of an acid 
 with an alkali, an earth, or a metallic oxide, in such propor- 
 tions as to saturate both the base and the acid. 
 
 Nitrates. Salts formed by the combination of any base with 
 nitric acid. 
 
 Nitrogen. A simple substance, by the French chemists called 
 azote. It enters into a variety of compounds, and forms 
 more than three parts in four of atmospheric air. 
 
 O. 
 
 Ochres. Various combinations of the earths with oxide, or 
 carbonate, of iron. 
 
 Ores. Metallic earths, which frequently contain several extra- 
 neous matters ; such as sulphur, arsenic, &c. 
 
 Oxalatcs. Salts formed by the combination of any base with 
 oxalic acid. 
 
356 A VOCABULARY 
 
 Oxide. Any substance combined with oxygen, in a proper* 
 tion not sufficient to produce acidity. 
 
 Oxidize. To combine oxygen with a body without producing 
 acidity. 
 
 Oxidizemmt. The operation by which any substance is com- 
 bined with oxygen, in a degree not sufficient to produce acidity. 
 
 Oxygen. A simple substance composing the greatest part of 
 water, and part of atmospheric air. 
 
 gas. Oxygen converted to a gaseous state by calo- 
 ric. It is also called vital air. It forms nearly one-fourth 
 of atmospheric air. 
 
 Oxygenize. To acidify a substance by oxygen. Synonymous 
 with Oxygenate 5 but the former is the better term. 
 
 Oxygenizeme.nt. The production of acidity by oxygen. 
 
 P. 
 
 Pellicle. A thin skin which forms on the surface of saline so- 
 lutions and other liquors, when boiled down to a certain 
 strength. 
 
 Phlogiston. An old chemical name for an imaginary sub- 
 stance, supposed to be a combination of fire with some other 
 matter, and a constituent part of all inflanmiabJe bodies, and 
 of many other substances. 
 
 Phosphates. Salts formed by the combination of any base 
 with phosphoric acid. 
 
 Phosphites. Salts formed by the combination of any base 
 with phosphorous acid. 
 
 Phosphurets. Substances formed by an union with phospho- 
 rus. Thus we have phosphuret of lime, phosphuretted hy- 
 drogen, &c. 
 
 Plumbago. Carburet of iron, or the black lead of commerce. 
 
 Pneumatic. Any thing relating to the airs and g'ases. 
 
 trough. A vessel filled in part with water 
 
 or mercury, for the purpose of collecting gases, so that they 
 may be readily removed from one vessel to anoiiit r. 
 
 Precipitate. Any matter which, having been dissolved in a 
 fluid, falls J;o the bottom of the vessel on the addition of some 
 other substance capable of producing a decomposition of the 
 compound, in consequence of its attraction either for the 
 menstruum or for the matter which was before held in solu- 
 tion. 
 
 Precipitation. That chemical process by which bodies dissol- 
 ved, mixed, or suspended in a fluid, are separated from that 
 fluid, and made to gravitate to the bottom of the vessel. 
 
OF CHEMICAL TERMS. 357 
 
 Prussiates. Salts formed by the combination of any base with 
 prussic acid. 
 
 rut refaction. The last fermentative process of nature, fry 
 which organized bodies are decomposed so as to separate 
 their principles, for the purpose of reuniting them by future 
 attractions, in the production of new compositions. 
 
 Pyrites. An abundant mineral found on the English coasts, 
 and elsewhere. Some are sulphurets of iron, and others 
 sulphurets of copper, with a portion of alum me and silex. 
 The former are worked for the sake of the sulphur, and the 
 latter for sulphur and copper. They are also called Mar- 
 casites and Fire-stone. 
 
 martial. That species of pyrites which contains 
 
 iron for its basis. See a full accouut of these minerals in 
 HenckePs Pyritologia. 
 
 Pyrometer. An instrument invented by Mr. Wedgwood for 
 ascertaining the degrees of heat in furnaces and intense fires. 
 See Philosophical transactions, vol. Ixii. and Ixiv. and Chem- 
 ical Catech. 
 
 Pyrophori. Compound substances which heat of themselves, 
 and take fire on the admission of atmospheric air. See an 
 account of a variety of experiments with these composi- 
 tions in Wiegleb's Chemistry, quarto, page 622, &c. 
 
 Q. 
 
 Quartz. A name given to a variety of siliceous earths, mixed 
 with a small portion of lime or alumine. Mr. Kirwan con- 
 fines the term to the purer kind of siiex. Rock crystal and 
 the amethyst are species of quartz. 
 
 R. 
 
 Radicals. A. chemical term for the Elements of bodies; 
 which see. 
 
 compound. When the base of an acid is composed 
 
 of two or more substances, it is said that the acid is formed 
 of a compound radical. The sulphuric acid is formed with 
 a simple radical; but the vegetable acids, which have radicals 
 composed of hydrogen, and carbon, are said to be acids with 
 compound radicals. 
 
 Reagents. Substances which are added to mineral waters or 
 other liquids as tests to discover their nature and composition. 
 
 Realgar, lied sulphurretted oxide of arsenic. 
 
 Receivers. Globular glass vessels adapted to retorts for the 
 
358 A VOCABULARY 
 
 purpose of preserving and condensing the volatile matte t 
 raised in distillation. 
 
 Rectification, is nothing more than the re-distilling a liquid to 
 render it more pure, or more concentrated, by abstracting a 
 part of it only. 
 
 Reduction. The restoration of metallic oxides to their origi- 
 nal state of metals ; which is usually effected by mean.* of 
 charcoal and fluxes. 
 
 Refining. The process of separating the perfect metals from 
 other metallic substances, by what is called cupellation. 
 
 Refrigeratory. A contrivance of any kind, which, by con- 
 taining cold water, answers the purpose of condensing the va- 
 pour or gas that arises in distillation. A worm-tub is a re- 
 frigeratory. 
 
 Regulus. In its chemical acceptation, signifies a pure metallic 
 substance, freed from all extraneous matters. 
 
 Repulsion. A principle whereby the particles of bodies are 
 prevented from coming into actual contact. It is thought to 
 be owing to caloric, which has been called the repulsive 
 power. 
 
 Resins. Vegetable juices concreted by evaporation either spon- 
 taneously or by fire. Their character is solubility in alcohol, 
 and not in water. It seems that they owe their solidity chief- 
 ly to their union with oxygen. 
 
 Retort. A vessel in the shape of a pear, with its neck bent 
 downwards, used in distillation; the extremity of which neck 
 fits into that of another bottle called a receiver. 
 Rock-crystal. Crystallized silex. 
 
 S, 
 
 Saccholates. Salts formed by the combination of any base 
 with saccholactic acid. 
 
 Salifiable bases. All the metals, alkalies, and earths, which 
 are capable of combining \,ith acids, and forming salts, are 
 called salifiable bases. 
 
 Saline. Partaking of the properties of a salt. 
 
 Salts neutral. A class of substances formed by the combina- 
 tion to saturation of an acid with an alkali, an earth, or oth- 
 r salifiable base. 
 
 triple. Salts formed by the combination of an acid 
 
 with two bases or radicals. The tartrate of soda and potass 
 (Rochelle salt) is an instance of this kind of combination. 
 
 Saponaceous. A term applied to any substance which is of 
 the nature or appearance of soap. 
 
OF CHEMICAL TERMS. 339 
 
 Saturation. The act of impregnating a fluid with another 
 substance, till no more can be received or imbibed. A fluid 
 which holds as much of any substance as it can dissolve, is 
 said to be saturated with that substance. A solid may in the 
 same way be saturated with a iluid. 
 
 Sebates. Salts formed by the combination of any base with 
 sebacic acid. 
 
 Semi-Metal. A name formerly given to those metals which, 
 if exposed to the fire, are neither malleable, ductile, nor fix- 
 ed. It is a term not used by modern chemists. 
 
 Siliceous Earths. A term used to describe a variety of natu- 
 ral substances which are composed chiefly of silexj as 
 quartz, flint, sand, &c. 
 
 Simple Substances. Synonymous with Elements; which see. 
 
 Smelting. The operation of fusing ores for the purpose of 
 separating the metals they contain, from the sulphur and ar- 
 senic with which they are mineralized, and also from other 
 heterogeneous matter. 
 
 Solution. The perfect union of a solid substance with a fluid. 
 Salts dissolved in water are proper examples of solution. 
 
 Spars. A name formerly given to various crystallized stones ; 
 such as the fluor spar, the adamantine spar, &c. These 
 natural substances are now distinguished by names which de- 
 note the nature of each. 
 
 Stalactites. Certain concretions of calcareous earth found sus- 
 pended like icicles in caverns. They are formed by the 
 oozing of water, through the crevices, charged with this 
 kind of earth. 
 
 Steatites. A kind of stone composed of silex, iron, and mag- 
 nesia. Also called French chalk, Spanish chalk, and soap- 
 rock. 
 
 Sub-Salts. Salts with less acid than is sufficient to neutralize 
 their radicals. 
 
 Suberates. Salts formed by the combination of any base with 
 the suberic acid. 
 
 Sublimation. A process whereby certain volatile substances 
 are raised by heat, and again condensed by cold into a solid 
 form. Flowers of sulphur are made in this way. The soot 
 of our common fires is a familiar instance of this process. 
 
 Succinates. Salts formed by the combination of any base with 
 the succinic acid. 
 
 Sulphates. Salts formed by the combination of any base with 
 the sulphuric acid. 
 
 Sulphites. Salts formed by the combination of any base witk 
 the sulphurous acid. 
 
360 A VOCABULARl 
 
 Sulphures, or Sulphurcfs. Combinations of alkalies, or n. 
 with ^alphur. 
 
 Sulphuretted. A substance is said to be sulphuretted \vliei 
 it is combined with sulphur. Thus we may say Sulphuret- 
 ted hydrogen, &c. 
 
 Super Salts. Salts with an excess of acid, as the superior- 
 trate of potass. 
 
 Synthesis. When a body is examined by dividing it into its 
 component parts, it is called analysis; but when we at- 
 tempt to prove the nature of a substance by the union of its 
 principles, the operation is called synthesis. 
 
 T. 
 
 Tartrates. Salts formed by the combination of any bast- 
 with the acid of tartar. 
 
 Temperature. The absolute quantity of free caloric which is 
 attached to any body occasions the ^degree of temperature- 
 of that body. 
 
 Test. That part of a cupel which is impregnated with litharge 
 in the operation of refining lead. It is also the name of 
 whatever is employed in chemical experiments to detect the 
 several ingredients of any composition. 
 
 Test-Papers. Papers impregnated with certain chemical re- 
 agents ; such as litmus, turmeric, radish, &c. They are 
 used to dip into fluids to ascertain by a change of colours the 
 presence of acids and alkalies. 
 
 Thermometer. An instrument to show the relative heat of bo- 
 dies. Fahrenheit's thermometer is that chiefly used in Eng- 
 land. Other thermometers are used in different parts of Eu- 
 rope. 
 
 Tinrtfires. Solutions of substances in spirituous menstrua. 
 
 Trituration. A chemical operation whereby substances are 
 united by friction. Amalgams are made by this method. 
 
 Tubulated. Retorts which have a hole at the top for inserting 
 the materials to be operated upon without taking them out of 
 the sand heat, are called tubulated retorts. 
 
 Tungstates. Salts formed by the combination of any base with 
 tungstic acid. 
 
 V, 
 
 Vacuum. A space unoccupied by matter. The term is gen 
 erally applied to the exhaustion of atmospheric air by chem- 
 ical or philosophical means. 
 
OF CHEMICAL TERMS. 30! 
 
 Vapour. This term is used by chemists to Denote such exhala- 
 tions only as can be condensed and rendered liquid again at 
 the ordinary atmospheric temperature, in opposition to those 
 which are permanently elastic. 
 
 Vital Air. Oxygen gas. The empyreal or fire-air of Scheele, 
 and the dephlogisticated air of Priestly. 
 
 Vitrification. When certain mixtures of solid substances, such 
 as silex and an alkali, are exposed to an intense heat, so as 
 to be fused, and become glass, they are then said to be vitri- 
 fied, or to have undergone vitrification. 
 
 Vitriols. A class of substances, either earthy or metallic, which 
 are comUned with the vitriolic acid. Thus there is vitriol 
 of lime, vitriol of iron, vitriol of copper, &c. These salts 
 are now called Sulphates, because the acid which forms them 
 is called sulphuric acid. 
 
 Vitriolated Tartar. The old name for sulphate of potass. 
 
 Volatile Alkali. Another name for ammonia. 
 
 Volatile Salts. The commercial name for carbonate of ammo, 
 nia. 
 
 Volatility. A property of some bodies which disposes them 
 to assume the gaseous state. This property seems to be ow- 
 ing to their affinity for caloric. 
 
 Volume. A term made use of by modern chemists to express 
 the space occupied by gaseous or other bodies. 
 
 u. 
 
 Union chemical. When a mere mixture of two or more sub- 
 stances is made, they are said to be mechanically united ; but 
 when each or either substance forms a component part o! 
 the product, the substances have formed a chemical union. 
 
 W. 
 
 JVater. The most common of -all fluids, composed of 85 parts 
 of oxygen and 15 of hydrogen. 
 
 mineral. Waters which are impregnated with mineral 
 
 and other substances are known by this appellation. These 
 minerals are generally held in solution by carbonic, sulphur- 
 ic, or muriatic acid. 
 
 Way, dry. A term used by chemical writers when treating of 
 analysis or decomposition. By decomposing in the dry way, 
 is meant, by the agency of fire. 
 
 Way humid. A term used in the same manner as the forego 
 
 32 
 
^2 A VOCABULARY OF CHEMICAL' TERMS. 
 
 ing, but expressive of decomposition in a fluid state, or by 
 
 means of water, and chemical re-agents, or tests. 
 Welding Heat. That degree of heat in which two pieces of 
 
 iron or of platina may be united by hammering. 
 Wolfram. An ore of tungsten containing also manganese and 
 
 iron. 
 Worm-Tub. A chemical vessel with a pewter worm fixed in 
 
 the inside, and in the intermediate space filled with water. 
 
 Its use is to cool liquors during distillation. 
 Woulfe's apparatus. A contrivance for distilling the mineral 
 
 acids and other gaseous substances with little loss ; being a 
 
 train of receivers with safety-pipes, and connected together 
 
 by tubes. 
 
 Z. 
 
 Zafre. An oxide of cobalt, mixed with a portion of siliceous 
 matter. It is imported in this state from Saxony. 
 
 Zero. The point from which the scale of a thermometer is 
 graduated. Thus Celsius's and Reaumur's thermometers 
 have their zero at the freezing point, while the thermometer 
 of Fahrenheit has its zero at that point at which it stands 
 when immersed in a mixture of snow and common salt. 
 
LIST OF EXPERIMENTS. 
 
 IN making up the following list of experiments I have 
 careful in general to select such as can be made with safety to 
 the young student ; where this is not the case the caution is 
 mentioned. Most of them require but very simple apparatus. 
 Where any experiment illustrates the text, a reference is made 
 to the page. Some of them are original, others are borrowed, 
 I have not however deemed it necessary to cite authors. 
 
 1. To show that heat is not absorbed, but reflected by pol- 
 ished metallic surfaces, hold a common new tin-pan before the 
 fire. The pan will remain cold. See p. 29- 
 
 2. To show the power of a black surface to absorb caloric, 
 smoke, or paint black a spot of the size of a dollar on the bot- 
 tom of the tin-pan; and, hold it towards the fire. On touching 
 this spot, it will be found hot, while the parts around it remain 
 cold. See p. 31. 
 
 3. To make the upper part of a vessel of water boil, while 
 there is a cake of ice at the bottom. Into a glass tube put wa- 
 ter enough to occupy two inches. Freeze this, so as not to 
 burst the tube, with a freezing mixture, or by exposure to cold 
 in winter. Then fill the tube nearly full of water, and wind 
 a flannel clotl^everal times around the part containing the ice, 
 so that the heat of the hand will not melt it. Then hold the 
 tube in an oblique direction over a lamp, so as to heat the wa- 
 ter an inch or two above the ice. The. water will soon begin 
 to boil, and by raising the tube a little at a time, it will boil al- 
 most to the surface of the ice, without melting it. See p. 39. 
 
 4. To show that some of the metals conduct caloric better 
 than others, procure wires of the same size and length, of gold, 
 silver, copper, iron, zinc, tin, &c. The wires maybe 12 or 
 14 inches long. Coat one end of each with bees- wax, and put 
 the other ends into a vessel of hot water. The wax will melt 
 first on the metal which is the best conductor, and the compar- 
 ative conducting powers are calculated by the difference of tinve 
 between the melting of the wax on each. See p. 35. 
 
 5. The conducting powers of different substances in regard 
 to caloric, may be much more sensibly elucidated, by touching in 
 cold weather, a metal with one hand, and a piece of cork, wood, 
 or cloth with the other. Here the sensation of cold, to the 
 hand which touches the metal, is owing to the power which all 
 
364 EXPERIMENTS, 
 
 metals have of conducting off heat, more rapidly thauaiiy oth- 
 er class of substances. See p. 37. 
 
 6. To show that evaporation carries off caloric, moisten tbr 
 bulb of a thermometer tube with ether, by means of a hair pen- 
 cil. The mercury immediately begins to fail, and if the pro- 
 cess be continued, may be brought down to the freezing point, 
 even in warm weather. Whenever a fluid substance is con- 
 verted into vapour, it absorbs a quantity of caloric. In the 
 present case, the ether takes from the bulb of the thermometer, 
 the caloric necessary to give it the elastic form. Therefore, 
 every new application of the ether carries off successive por- 
 tions of heat, and the mercury continues to sink, until the bulb 
 becomes so cold, as to absorb caloric from the surrounding 
 air, faster than it is carried off by the evaporation. This is 
 the reason why the mercury cannot be depressed below a cer- 
 tain point by evaporation. The ether, although it assumes the 
 elastic form, does not receive the caloric necessary for this pur- 
 pose from the thermometer, but from the surrounding air. 
 See p. 53. 
 
 7- To demonstrate that fluids boil at comparatively small de- 
 grees of heat, when the pressure of the atmosphere is taken off, 
 about half fill with water a small retort, or Florence flask (com- 
 mon oil flask,) and let it boil over a lamp. When the upper 
 part is filled with steam, take it from the lamp, and instantly 
 cork it air tight. If now it is put into cold water, it begins to 
 boil violently. If taken out of the water, it stops boiling, and 
 this may be done many times. This curious method of mak- 
 ing water boil by the application of cold, is easily accounted 
 for. When the flask is put into cold water, the steam with 
 which it was filled, is condensed and returns again to water 
 This leaves a vacuum* in which water is converted into steam,, 
 or boils, at a much lower temperature than in the open air. 
 See p. 55. 
 
 8. If the above experiment is made by means of a small re- 
 tort, a very curious circumstance may be observed : When the 
 water is cold, and consequently nearly a perfect vacuum is 
 formed, if the retort is shaken, there is produced a sharp rattling 
 noise, as though it contained shot, instead of water, so that one 
 would suppose by the noise that the retort would be broken in- 
 to a thousand parts at every motion. This is owing to the 
 weight with which the water falls upon the glass, when there is 
 no air to impede its motion. 
 
 9. Into a thin glass vessel, pour an ounce or two of water, 
 and then pour in two drams of sulphuric acid; the glass will 
 instantly become too hot to be held in the hand. This expert- 
 
EXPERIMENTS. 365 
 
 ment elucidates the doctrine of latent heat. On mixing these 
 two fluids, a chemical combination takes place between their 
 particles, in consequence of which caloric is extricated, at the 
 same time their bulk is diminished. This also illustrates Dr. 
 Black's law. that when substances pass from a rarer to a denser 
 state, caloric is given out. If one measure of sulphuric acid, 
 and one of water, be mixed together, the mixture will not again 
 till the measure twice. See p. 69. 
 
 10. To procure nitrogen, take a bell glass, or large tumbler, 
 and invert it over a short taper, set in a shallow dish of water. 
 The taper burns until it absorbs all the oxygen contained in the 
 air under the bell glass. What remains is nitrogen. If now 
 a lighted taper be put under the bell glass, it will be instantly 
 extinguished, showing the absolute necessity of oxygen for the 
 support of combustion. See p. 85, 89. 
 
 11. The formation of water by the burning of hydrogen 
 may be shown thus : Take a Florence lias k and pour into it 
 half a pint of water, then put in about an ounce of granulated 
 zinc, or the same quantity of iron filings, and then pour in halt 
 an ounce by measure of sulphuric acid. Have ready a cork, 
 pierced with a burning iron, and the stem of a tobacco pipe 
 passed through the. aperture. After putting in the acid, put 
 the cork in its place, and fix the flask upright by setting it in a 
 bowl, surrounded by a cloth, to make it stand up and prevent 
 its breaking. As the hydrogen is formed, it issues through the 
 stem of the tobacco pipe, at the end of which it is to be fixed. 
 If now a glass tube two or three feet long and an inch or two 
 wide be passed on to the stem so as to include the flame within 
 its bore, the tube, in a few moments will be covered on tae in- 
 side with moisture. See p. 106. 
 
 If the orifice of the tube is quite small at the end where the 
 gas is fired, the above experiment serves to protiuce the musical 
 tones. See p. 108. 
 
 12. An exhibition of gas light may be made as follows : In- 
 to the bowl of a common tobacco pipe put a piece of mineral, or 
 what is called sea-coal, and cover the coal closely with clay. 
 When the clay is dry, place the bowl in the fire and heat it 
 slowly. In a few minutes the gas, called carburetted hydrogen 
 will issue from the end of the pipe stem ; set fire to it with a 
 candle, and it will burn with a beautiful bright flame. This is 
 gas with which the streets, factories &c. are lighted in many 01 
 the European cities. 
 
 In the absence of mineral coal, a walnut, small piece of pine 
 knot, or butternut meat &c. may take the place of the coal 
 See p. 114. 
 
 32* 
 
EXPERIMENTS. 
 
 13. The following gives an example of the manner in which 
 sulphuric acid is formed. 
 
 Mix with a small quantity of the flowers of sulphur, about 
 one fifth part of finely pulverized nitre. Make a stand by hol- 
 lowing with a hammer a large button, and attaching wire to the 
 eye, for feet, so that the button will be two inches high; or by 
 any other means, place the sulphur and nitre about this heighth 
 in a shallow dish, containing an inch or two of water. Set fire 
 to the mixture with a hot iron, and immediately invert over it 
 a bell glass, or large tumbler. The sulphur, as it burns, ab- 
 sorbs oxygen from the air contained under the bell glass, in a 
 proportion which would constitute sulphuroi/s acid. At the 
 same time the heat which this process occasions, compels the 
 nitre to give out another proportion of oxygen, which is absor- 
 bed by the sulphurous acid, and this additional quantity of ox- 
 ygen, constitutes sulphuric acid. See p. 121. 
 
 14. Take three parts of nitre, two of potash and one of sul- 
 phur, and mix them intimately, by rubbing in a mortar. This 
 compound is called fulminating powder. On placing a little 
 of it on a shovel over a hot fire, it explodes with great vio- 
 lence, and with a peculiarly stunning report. 
 
 15. The combustion of phosphuretted hydrogen in oxygen 
 gas, affords one of the most striking, and beautiful, among 
 chemical experiments. It is done as follows: Take some 
 phosphuret of lime, wrap it in a paper and push it under a ves- 
 sel, as a wide mouthed vial, filled with water, and inverted on 
 the shelf of theVater bath. As soon as the water penetrates 
 through the paper so as to wet the phosphuret of lime, bubbles 
 of phosphuretted hydrogen, begin to rise up through the water. 
 While this is going on, fill a strong glass vessel, as a tumbler, 
 or a piece of thick glass tube stopped at one end, with oxygen 
 gas. Invert this also on the shelf of the water bath. When 
 the phosphuretted hydrogen is collected, take the vessel con- 
 taining it in one hand, and that containing the oxygen in the 
 other ; bring the mouth of the former, by sinking it deeper in the 
 water, under the edge of the latter vessel, then by carefully de- 
 pressing the bottom of the vessel containing the phosphoretted 
 hydrogen, let up a bubble at a Vime into the oxygen gas. If 
 this experiment is made in a darkened room, the Bashes of light 
 appear astonishingly vivid and beautifuh See p. 126. 
 
 16. Take six or eight grains of oxy-muriat e of potash, put it 
 into a mortar and drop in with it about a grain of solid phospho- 
 rus, cut into two or three parts; then rub them together with 
 the pestle. Very violent detonations are produced by these 
 small quantities. It is best, therefore, not to use more than is 
 
EXPERIMENT?, 367 
 
 jiere mentioned at a time. The hand holding the pestle ought 
 always to be protected with a glove or handkerchief. 
 
 17. To make liquid phosphorus, take an ounce vial and half 
 fill it with olive oil, and put into the oil a piece of phosphorus of 
 the size of a pea ; gradually heat the bottom of the vial, until 
 the phosphorus is melted, taking care to keep the thumb on the 
 mouth ; then cork it air tight. If this vial is first shaken, and 
 then the cork be taken out, it becomes luminous, first near the 
 mouth, and gradually down to the oil, at the bottom. The light 
 which a bottle prepared in this way gives, particularly if warm- 
 ed, by holding it in the hand, is sufficient to tell the hour of 
 night by a watch. This luminous appearance, when the cork 
 is removed, is owing to the union of the oxygen of the atmos- 
 phere with the phosphorus. It is a slow combustion, attended 
 with light, and most probably with some heat. 
 
 18. If drawings be made on silk with a solution of nitrate of 
 silver, and the silk first moistened, is exposed to a stream of hy- 
 drogen gas, or in any other way exposed to the action of this gas, 
 the metal is instantly revived, and the silk is covered with fig- 
 ures of silver. See p. 147. 
 
 iy. If a few drops of a solution of nitrate of silver in water, 
 be placed on a bright surface of copper, the silver is revived, 
 and gives the copper a brilliant white coat of that metal. This 
 is- explained on the principle of affinity. The copper has a 
 stronger attraction for the acid which composes a part of the 
 nitrate of silver, than the silver itself has. Therefore it attracts 
 the acid from the silver, in consequence of which this is receiv- 
 ed, and at the same time precipitated on the copper. See p. 
 147. 
 
 20. Take a little of the.white arsenic of the shops, and mix 
 it with some fineU ground charcoal; put the mixture into a 
 small glass tube closed at one end, and expose the part where 
 the mixture is to a moderate degree of heat gradually raised 
 the arsenic will be received, and will attach itself to the upper 
 part of the tube, giving it a brilliant metallic coat like quick 
 silver. The arsenic may be preserved in this state by stopping 
 up the tube. See p. 149- 
 
 21. Dissolve a teaspoonfull of sugar of lead in a quart of 
 rain water. Put this into a decanter, or white glass bottle, and 
 suspend in it by means of a string a piece of zinc. The zinc 
 decomposes the acetate of lead by depriving it of its oxygen ; 
 the consequence is that the lead is precipitated in the metallic 
 state on, and around the zinc, and forms a brilliant tree of me- 
 tal 
 
 22. Pour a solution of nitrate of silver into a glass vessel 
 
368 EXPERIMENTS. 
 
 and immerse a few slips of copper in it. In a short time a 
 portion of copper will be dissolved, and all the silver precipi- 
 tated in a metallic forai. If the solution which now contains 
 copper be decanted into another glass, and pieces of iron ad- 
 ded to it, this metal will then be dissolved, and the copper pre- 
 cipitated, yielding a striking instance of peculiar affinities. 
 See p. 170. 
 
 23. Ivory may be coated with silver by the following pro- 
 cess. Make a strong solution of nitrate of silver in pure wa- 
 ter; into this immerse a piece of ivory until it turns yellow ; 
 then take it out and immediately plunge it into a vessel of dis- 
 tilled water exposed to the direct rays of the sun until it turns 
 black. On rubbing it gently -it will appear covered with a 
 brilliant coat of silver, resembling a bar of that metal. This 
 curious effect is owing to the solar light which decomposes the 
 nitrate silver by taking the oxygen from it, which flies off in 
 the form of oxygen gas. 
 
 24. Through a vessel of lime water, recently made, pass 
 bubbles of carbonic acid gas by means of a bladder and tube, 
 the lime water instantly becomes white and turbid, and finally 
 deposits a quantity of carbonate of lime in the form of pow- 
 dered chalk. If now the water be evaporated a white powder 
 remains which effervesces with acids. If this powder is put 
 into a retort, and sulphuric acid diluted with water is poured 
 upon it, the beak of the retort being under a vessel tilled with 
 water, the carbonic acid is again obtained, and the salt remain- 
 ing in the retort will be sulphate of lime, or gypsum. 
 
 25. Mix one part of nitric acid with 5 or 6 parts of water in 
 a vial ; into this put some copper filings, and in a few moments 
 pour off the liquid ; it will be colourless. If now there be ad- 
 ded some liquid ammonia, another colourless fluid, the mixture 
 becomes of an intense and beautiful blue. Hence ammonia is 
 a most delicate test for the presence of copper, with which it 
 strikes a deep blue colour. See p. 180. 
 
 26. Put into a vial of pure water a few drops of tire tincture 
 of nut galls, made by steeping the galls hi water; into another 
 vial of pure water put a grain or two of the sulphate of iron. If 
 these colourless fluids are mixed, they instantly become black, 
 Tincture of galls is a most delicate test for the presence of iron, 
 with which it strikes a black. These two substances form the 
 basis of ink. See p. 180. 
 
 27. Take two small glass jars, or tumblers, and fill one with 
 carbonic acid gas 7 and the other with oxygen gas. Have them 
 set upright with a cover on each. If a lighted taper be plunged 
 into the vessel containing the carbonic acid ? it is extinguished 
 
EXPERIMENTS. 
 
 instantly; but if it is immediately plunged into the other jar 
 containing the oxygen, it is as instantly lighted with a sort of 
 explosion. See p. 2l9 
 
 28. Put eight or ten grains of oozy-muriate of potash into a 
 teacup, and then pour in two or three drams of alcohol If now 
 about two drams of sulphuric acid is added, the mixture begins 
 to dart forth little balls of blue fire, and in a minute or two. the 
 whole bursts into flame. The alcohol is inflamed by the clo- 
 rine which is set free from the salt, in consequence of the com- 
 bination which takes place between the potash and sulphuric 
 acid. See p. 233. 
 
 29. Into a glass tube half an inch or an inch wide, two or 
 three inches long, with a bulb at the end, put a grain or two 
 of iodine. Warm the tube, (but not at that part where the 
 iodine is,) and immediately cork it tight; the tube remains co- 
 lourless, there being only a few little specks here and there. If 
 at any time the tube be warmed at that part where the; iodine is, 
 it is instantly filled with a gas of a most beautiful violet colour. 
 If care is taken to keep the tube well closed, so that the iodine 
 does not escape, when it takes the form of gas, this effect will 
 always be produced whenever the tube is warmed. A tube 
 with two bulbs, like what is called a pulse glass , containing the 
 iodine hermetically sealed, would be better. , Such a little ap- 
 paratus would be quite a curiosity to those who know nothing 
 of the nature of iodine. See p. 235. 
 
 30. Write on paper with a solution of the nitrat of silver, 
 taking care not to have it so strong as to destroy the paper. 
 So long as it is kept in the dark, or if the paper be closely fol- 
 ded, the writing remains invisible; but on exposure to the rays 
 of the sun the characters turn yellow, and finally black, so that 
 they are perfectly legible. 
 
 Mr. Accum says, that this change of colour is owing to the 
 partial reduction of the oxide of silver from the light expelling 
 a portion of its oxyeen ; the oxide therefore approaches to the 
 metallic state; for when the blackness is examined with a deep, 
 or powerful magnifier, the particles of metal may be distinctly 
 seen . 
 
 3t. Write on paper with a dilute solution of common sugar 
 of lead ; the writing will remain invisible. But on moistening 
 the lines with a pencil, or leather dipped in water impregnated 
 with sulphuretted hydrogen, the metal is rev : ved, and the let- 
 ters appear in metallic brilliancy. 
 
 The author above cited, says, that in this instance, the hy- 
 drogen of the sulphuretted hydrogen gas, abstracts the oxygen 
 from the oxide of lead, and causes it to re-approach to the me- 
 
3/0 EXPERIMENTS. 
 
 tallic state ; at the same time, the sulphur of the sulphuretted 
 hydrogen gas combines with the metal thus regenerated, and 
 converts it into a sulphuret, which exhibits the metallic colour. 
 
 32. Write on paper with a solution of the sulphate of cop- 
 per. If this is strong, the writing will be of a faint green col- 
 our ; if weak the characters are invisible. On holding the pa- 
 per over a vessel containing some liquid ammonia, or if it be 
 exposed to the action of this gas in any other way, the writing 
 assumes a beautiful blue colour. On exposing the paper to the 
 sun the colour disappears, because the ammonia evaporates. 
 
 33. Put a small piece of phosphorus into a crucible, cover 
 it closely with common chalk, so as to fill the crucible. Let 
 another crucible be inverted upon it, and both subjected to the 
 fire. When the whole has become perfectly red-hot, remove 
 them from the fire, and when cold, the carbonic acid of the 
 chalk will have been decomposed, and the Black Charcoal, the 
 basis of the acid, may be easily perceived amongst the mate- 
 rials. 
 
 34. Into a large glass jar, inverted upon a flat brick tile, 
 and containing near its top a branch of fresh rosemary, or any 
 other such shrub, moistened with water, introduce a flat thick 
 piece of heated iron, on which place some gimi benzoin in gross 
 powder. The benzoic acid, in consequence of the heat, will 
 be separated, and ascend in white fumes, which will at length 
 condense, and form a most beautiful appearance upon the leaves 
 of the vegetable. This will serve as an example of Sublima- 
 tion. 
 
 35. Mix a little acetate of lead with an equal portion of 
 sulphate of zinc, both in fine powder ; stir them together with 
 a piece of glass or wood, and no chemical change will be per- 
 .eeptible : but if they be rubbed together in a mortar, the two 
 solids will operate on each other ; an intimate union will take 
 place, arid a fluid will be produced. If alum or Glauber salt 
 be used instead of sulphate of zinc, the experiment will be 
 equally successful. 
 
 3& [f the leaves of a phnt, fresh gathered, be placed in the 
 sun, very pure oxygen gas may be collected. 
 
 37. Put a little fresh calcined magnesia in a tea-cup upon 
 the hearth, and suddenly pour over it as much concentrated sul- 
 phuric acid as will cover the magnesia. In an instant sparks 
 will be thrown out, and the mixture will be completely ignited. 
 
 38. If a few pounds of a mixture of iron filings and sulphur 
 be made in paste with water, and buried in the ground for a 
 few hours, the water will be decomposed with so much rapidi- 
 ty, that combustion and flame will be the consequence. 
 
EXPERIMENTS. SfJ 
 
 39. For want of a proper g!ass vessel, a table spoonful oi 
 ether maybe put into a moistened bladder, and the neck of the 
 bladder closely tied. If hot water be then poured upon it, the 
 ether will expand, and the bladder become inflated. 
 
 40. Procure a phial with a glass stopper accurately ground 
 [nto it ; introduce a few copper filings, then entirely fill it with 
 liquid ammonia, and stop the phial so as to exclude all atmos- 
 pheric air. If left in this state, no solution of the copper will 
 be effected. But if the bottle be afterwards left open for some 
 time, and then stopped, the metal will dissolve, and the solu- 
 tion will be colourless. Let the stopper be now taken out, and 
 the fluid will become blue, beginning at the surface, and spread- 
 ing gradually through the whole. If this blue solution has not 
 been too long exposed to the air, and fresh copper filings be put 
 in, again stopping the bottle, the fluid will once more be depri- 
 ved of its colour, which it will recover only by the re-admis- 
 sion of air. These effects may thus be repeatedly produced. 
 
 41. If a spoonful of good alcohol and a little boracic acid 
 be stirred together in a tea-cup, and than set on fire, they will 
 produce a very beautiful green flame. 
 
 42. Alloy a piece of silver with a portion of lead, place the 
 alloy upon a piece of charcoal, attach a blow-pipe to a gasome- 
 ter charged with oxygen gas, light the charcoal first with a bit 
 of paper, and keep up the heat by pressing upon the machine. 
 When the metals get into complete fusion, the lead will begin to 
 burn, and very soon will be all dissipated in a white smoke, 
 leaving the silver in a state of .purity. This experiment is de- 
 signed to show the fixity of the noble metals. . 
 
 43. Burn a piece of iron wire in a deflagrating jar of oxygen 
 gas, and suffer it to burn till it goes out of itself. If a lighted 
 wax taper be now let down into the gas, this will burn in it for 
 some time, and then become extinguished. If ignited sulphur 
 be now introduced, this will also burn for a limited time. Last- 
 ly, introduce a morsel of phosphorus, and combustion will also 
 follow in like manner. These experiments show the relative 
 combustibility of different substances. 
 
 44. Drop a piece of phosphorus about the size of a pea into 
 a tumbler of hot water, aad from a bladder, furnished with a stop 
 cock, force a stream of oxygen gas directly upon it. This will 
 afford the most brilliant combustion under water that can be 
 imagined. 
 
 45. Take ai amalgam of lead and mercury, and another 
 amalgam of bismuth, let these two solid amalgams be mixed by 
 triture, and they will instantly become fluid. 
 
 46. Into distilled water drop a little spirituous solution of 
 
372 EXPERIMENTS. 
 
 soap, no chemical effect will be perceived ; but if some ot 
 the same solution be added to hard-water, a milkiness will im- 
 mediately be produced, moie or less, according to the degree oi 
 its impurity. This is a good method of ascertaining the purity 
 of spring water. 
 
 47. To silver copper, or brass. Clean the article intended 
 to be silvered, by means of dilute nitric acid, or by scouring it 
 with a mixture of common salt and alum. When it is perfectly 
 bright, moisten a little of the powder, known in commerce by 
 the name of silvering" powder , with water, and rub it for some 
 time on the perfectly clean surface of copper, or brass, which 
 will become covered with a coat of metallic silver. It may af- 
 terwards be polished with soft leather. 
 
 The silvering powder is prepared in the following manner : 
 Dissolve some silver in nitric acid, and put pieces of copper into 
 the solution ; this will throw down the silver in a state of metal- 
 lic powder. Take fifteen or twenty grains of this powder, and 
 mix with it two drachms of acidulous tartarite of potash, the 
 same quantity of common salt, and half a drachm of alum. 
 Another method : Precipitate silver from its solution in nitric 
 acid by copper, as before ; to half an ounce of this silver, add 
 common salt and muriate of ammoniac, of each two ounces, and 
 one drachm of corrosive sublimate 5 rub them together, and 
 make them into a paste with water. With this, copper uten- 
 sils intended to be silvered, that have been previously boiled 
 with acidulous tartarite of potash and alum, are to be rubbed 5 
 after which they are to be made red-hot, and polished. 
 
 48. To prove that the air of the atmosphere always con- 
 tains carbonic acid. This may be shewn by simply pouring 
 any quantity of barytic water, or lime water, repeatedly from 
 one vessel into another. The barytic water, when deprived of 
 the contact of air, is perfectly transparent ; but it instantly be- 
 comes milky, and a white precipitate, which is carbonate of ba- 
 rvtes, is deposited, when brought into contact with it for a few 
 minutes only. 
 
 The quantity of carbonic acid contained in the atmosphere, 
 seldom varies, except in the immediate vicinity of places where 
 respiration and combustion are going on in the large way, aiul 
 is about one hundredth part 
 
.Absorbent vessels, 301 
 Absorption of caloric, 35 
 Acetic acid, 198, 252 
 
 Acetous fermentation, 267 
 
 acid, 252 
 
 Acidulous gaseous mineral wa- 
 ters, 222 
 
 salts, 253 
 
 Aoids, 196 
 
 Aeriform, 19 
 
 Affinity, 10, 165 
 
 Agate, 188 
 
 Agriculture, 274 
 
 Air, 84 
 
 Air pump, 53 
 
 Albumen, 194 
 
 Alburnum, 2C6 
 
 Alchemists, 2 
 
 Alcohol, or spirit of wine, 259 
 
 Alembic, 118, 261 
 
 Alkalies, 173 
 
 Alkaline earths, 174, 188 
 
 Alloys, 155 
 
 Alum, or sulphat of alumine, 190, 
 207 
 
 Alumine, 185, 190 
 
 Alumium, 8 
 
 Amalgam, 156, 182 
 
 Ambergris, 325 
 
 Amethyst, 191 
 Amianthus, 195 
 
 Ammonia, or volatile alkali, 163, 
 174, 181 
 
 Ammoniacal gas, 181 how obtain- 
 ed, 183 
 
 Ammonium, 7 
 Amphibious animals, 321 
 Analysis, 130 
 of vegetables, 254 
 
 Animals, 288 
 
 33 
 
 Animal acids, 199, 295 
 
 economy, 297 
 
 colours, 297 
 
 heat, 315 
 
 oil, 243, 294 
 
 Animalization, 140, 289, 29$ 
 Antidotes, 193 
 Antimony, 8 
 Aphlogistic lamp, 328 
 Aqua fortis, 21 1 
 
 regia, 153 
 
 Arrack, 261 
 Argand's Lamp, 96 
 Arsenic, 8, 153, 156 
 Arteries, 301, 309J 
 Arterial blood, 309, 312 
 Asphaltum, 270 
 Assafcetida, 247 
 Assimilation, 299 
 Astringent principle, 252 
 Atmosphere, 49, 84, 97 
 Atmospherical air, 85 
 Attraction of aggregation, or co- 
 hesion, 9, 168 
 
 Attraction of composition, 11,165 
 Azot, or nitrogen, 209 
 Azotic gas, 84 
 
 B 
 
 Balsams, 148 
 
 Balloons, 112 
 
 Bark, 283 
 
 Barytes, 191 
 
 Bases of acids, 120, 198 
 
 gases, 85 
 
 salts, 167 
 
 Beer, 258 ' 
 
 Benzole acid, 198, 252 
 Bile, 306 
 Birds, 301, 321 
 Bismuth , 6 
 
374 
 
 INDEX.. 
 
 Bitumens, 270, S27 
 Black lead, or plumbago, 1 37 
 Bleachir/g, 204 
 Blow pipe, 132, 146 
 
 Hare's 147 
 
 Blood, 311,313 
 
 Blood vessels, 289, 311, 
 
 Boiling water, 55 
 
 Bombic acid, 295, 326 
 
 Bones, 298 
 
 Boracic acid, 164, 223 
 
 Boracium, 8, 223 
 
 Borat of soda, 224 
 
 Brandy, 261 
 
 Brass, 155 
 
 Bread, 268 
 
 Bricks, 191 
 
 Brittle metals, 8 
 
 Bronze, 155 
 
 Butter, 322 
 
 Buttermilk, 323 
 
 c. 
 
 Calcareous earths, 191 
 
 , stones, 219 
 
 Calcium, 7 
 Caloric, 17 
 
 , absorption of, 35 
 
 , conductors of, 36 
 
 , combined, 57 
 
 , expansive power of, 18, 20 
 
 , equilibrium of, 26 
 
 , reflexion of, 33 
 
 ' , radiation of, 27, 31 
 
 , solvent power of, 46 
 
 , capacity for, 59 
 
 Calorimeter, 72 
 Caloriuuoter, 83 
 Calx, 91 
 Camphor, 246 
 Camphoric acid, 198 
 Caoutchouc, 248 
 Carbonats, 176, 222 
 Carbonat of ammonia, 184 
 
 barytes, 192 
 
 lead, 144 
 
 lime, 193 
 
 magnesia, 195 
 
 potash, 176 
 
 Carbonated hydrogen gas, 136 
 
 Carbon, 128 
 
 Carbonic acid, 131, 21tt 
 
 Carburet of iron, 135 
 
 Carmine, 297 
 
 Cartilage, 300 
 
 Castor, 326 
 
 Cellular membrane, 303 
 
 Caustics, 157 
 
 Chalk, 193, 222 
 
 Charcoal 129 
 
 Cheese, 325 
 
 Chemical attraction, 9, 166 
 
 Chemistry, 2 
 
 Chest, 307 
 
 China, 190 
 
 Chlorine, 230 
 
 Chrome, 8, 15.3 
 
 Chyle, 301 
 
 Chyme, 306 
 
 Citric acid, 198, 252 
 
 Circulation of the blood, 30S 
 
 Civet, 326 
 
 Clay, 191 
 
 Coke, 271 
 
 Coal, 271 
 
 Cobalt, 8, 159 
 
 Cochineal, 297 
 
 Cold, 26 
 
 from evaporation, 50, 53, 54 
 
 Colours, change of, 180 
 
 Columbium, 8, 153 
 
 Combined caloric, 57 
 
 Combustion, 88 
 
 , volatile, products of, 
 
 96 
 
 , fixed products of, 96 
 
 , of alcohol, 264 t , 
 
 , of boracium, 224 
 
 , by oxy muriatic acid 
 
 or chlorine, 228 
 
 , of carbon, 131, 218 
 
 , of coals, 109, 137 
 
 -, of charcoal by nitrk 
 
 acid, 210 
 
 -, of candles, 140 
 -, of diamonds, 13 
 -, of ether, 266 
 
 208 
 
 , of hydrogen, 99, 106 
 
 -, of iron, 94 
 
 , of metals, 145 
 
 , of oils, 139 
 
 , of oil of turpentine br 
 
 nitrous acid. 167, 210 
 
 . of phosphorus, 12-3 
 
 ^ of sulphur^ 1 19 
 
Combustion of potassium, 162 
 
 , of candles, 108 
 
 -Compound bodies, 5, 173 
 
 or neutral salts, 175 
 
 Conductors of heat, 38, 39 
 
 - : , , solids^ 36 
 
 , fluids, 39 
 
 , , Count Rumford's 
 
 theory, 39 
 
 Constituent parts, 5 
 
 Copper, 8, 158 
 
 Copal, 247 
 
 Cortical layers, 283 
 
 Cotyledons, or lobes, 279 
 
 Cream, 322 
 
 Cream of tartar, or tartrit of pot- 
 ash, 353, 262 
 
 Cryophurus, 72 
 
 Crystallisation, 152 
 
 Cucurbit, 117 
 
 Culinary heat, 42 
 
 Curd, 322 
 
 Cuticle, or epidermis, 304 
 
 D 
 
 Decomposition, 4 
 
 of atmospherical 
 
 air, 85, 89 
 of water by the 
 
 Voltaic battery, 101 
 
 of salts by the Vol- 
 
 taic battery, 172 
 
 of water by metals, 
 
 103 
 
 136 
 
 by carbon, 
 
 224 
 
 - of vegetables, 254 
 
 - of potash, 164 
 
 - of soda, 163 4 
 
 - of ammonia, 163 
 
 - of animals, 327 
 
 - of the boracic acid, 
 
 - of the fluoric acid, 
 olgbe muriatic acid, 
 
 226 
 
 Deflagration, 217 
 Definite proportions, 171 
 Deliquescence, 207 
 Detonation, 217 
 Dew, 50 
 
 Diamond, 129 
 Diaphragm, 308 
 Digestion, 306 
 Dissolution of metal*, 150 
 Distillation, 117, 203, 261 
 
 of red wine, 261 
 
 Divellent forces, 170 
 Division, 4 
 Drying oils, 244 
 Dyeing, 249 
 
 E 
 
 Earths, 185 
 
 Earthen-ware, 191 
 
 Effervescence, 135 
 
 Efflorescence, 206 
 
 Elastic fluids, 19, 85 
 
 Electricity, 13, 74, 79, 1U 
 
 Electric machine, 78 
 
 Elective attractions, 168 
 
 Elementary bodies, 7 
 
 Elixirs, tinctures, or quintesceii' 
 
 ces, 263 
 Enamel, 191 
 Epidermis of vegetables, 28 3 
 
 of animals, 304 
 Epsom salts, 195 
 .Equilibrium of caloric, 26 
 Essences, 245 
 
 Essential or volatile oils, 245 
 Ether, 265 
 Evaporation, 49 
 Evergreens, 288 
 Eudiometer, 125 
 Expansion of caloric, 18 
 Extractive colouring matter, 24.8 
 Exhilarating gas, 215 
 
 Falling stones, 154 
 Fat, 323 
 Feathers, 299 
 Fecuia. 242 
 Fermentation, 255 
 Fibrine, 294 
 Fire, 4, 14 
 Fish, 320 
 
 Fixed air, or carbonic acid, 131, 
 219 
 
 alkalies, 174 
 
 oils, 139, 243 
 
376 
 
 JtNDEX 
 
 Fixed products of combustion, 96 
 
 Flame, 110 
 
 Flint, 188, 191 
 
 Flower or blossom, 286 
 
 Fluoric acid, 187, 224 
 
 Fluorium, or Fluorine, 225 
 
 Food of plants, 273 
 
 Formic acid, 295 
 
 Fossil wood, 271 
 
 Frankincense, 247 
 
 Free or radiant caloric, or heat of 
 
 temperature, 27 
 Freezing mixtures, 67 
 
 by evaporation, 53. 72. &c. 
 Frost, 50 
 Frostbearer, 72 
 Fruit, 257, 286 
 Fuller's earth, 190 
 Furnace, 142 
 
 Galls, 252 
 
 Gallat of iron, 208 
 
 Gallic acid, 208, 252 
 
 Galvanism, 75 
 
 Gas, 84 
 
 Gaslights, 110 
 
 Gaseous oxyd of carbon, 134 
 
 nitrogen, 214 
 Gastric juice, 306 
 Gelatine, or jelly, 292 
 Germination, 279 
 Gin, 262 
 Glands, 298, 302 
 Glass, 178 
 Glauber's salts, or sulphat of soda, 
 
 177 
 
 Glazing 191 
 Glucium, 7 
 Glue, 291 
 Gluten, 242 
 Gold, 8, 153 
 Gum, 240 
 
 arabic, 240 
 
 elastic, or caoutchouc, 248 
 
 resins, 247 
 Gunpowder, 216 
 Gypsum, or plaister of Paris, or 
 sulphat of lime, 207 
 
 Hall, Sir James, $7 
 
 H arrogate water, 122 
 
 Hartshorn, 174, 183 
 
 Heart, 311 
 
 Heat, 14, 18 
 
 latent, 55, 62 
 of capacity, 58 
 of temperature, 17 
 
 Honey, 242 
 
 Horns, 291 
 
 Hydro carbonat, 110, 137 
 
 Hydrogen, 98 
 
 gas, 99 
 
 I and J. 
 
 Jasper, 188 
 
 Ice, 66 
 
 Jelly, 291, 304 
 
 Jet, 270 
 
 Ignes fatui, 126 
 
 Ignition, 56 
 
 Imponderable agents, 6 
 
 Inflammable air, 99 
 
 Ink, 208 
 
 Ink spots, 253 
 
 Integrant parts, 5 
 
 Iodine, 7, 235 
 
 Iridium, 156 
 
 Iron, 148 
 
 Isinglass, 291 
 
 Ivory black a 297 
 
 K 
 
 Kali, 180 
 Koumiss, 324 
 
 H 
 
 Hair, 302 
 
 Lac, 326 
 
 Lactic acid, 295, 325 
 Lakes, colours, 248 
 Lamp without flame, 338 
 Latent heat, 55 
 Lavender water, 263 
 Lead, 144, 149 * 
 Leather, 250, 283 
 Leaves, 281 
 Life, 236 
 Ligaments, 300 
 Light, 14, 281 
 Lightning, 210 
 
INbEX. 
 
 Lime, 192 
 
 water, 193 
 Limestone, 192 
 Linseed oil, 243 
 Liqueurs, 263 
 Liver, 302 
 Lobes, 279, 313 
 Lunar caustic, or nitrat of silver, 
 
 157, 217 
 
 Lungs, 310, 312 
 Lymph, 301 
 Lymphatic vessels, 301 
 
 M 
 
 Magnesia, 195 
 
 Magniuni, 7 
 
 Malic acid, 198, 252 
 
 Malt, 258 
 
 Malleable metals, 8 
 
 Manganese, 8 
 
 Manna, 242 
 
 Manure, 274 
 
 Marble, 222 
 
 Marine acid, or muriatic acid, 225 
 
 Mastic, 247, 305 
 
 Materials of animals, 289 
 
 of vegetables, 237 
 
 Mercury, 8, 155 
 
 new mode of freezing, 
 53, 156 
 
 Metallic acids, 153 
 oxyds, 143 
 
 Metals, 140 
 
 Meteoric stones, 154 
 
 Mica, 195 
 
 Milk, 302, 322 
 
 Minerals, 142 
 
 Mineral waters, 134, 198 
 
 acids, 198 
 Miner's lamp, 115 
 Mixture. 47 
 Molybdena, 8, 153 
 Mordant, 249 
 Mortar, 195 
 Mucilage, 209 
 Mucous^ acid, 240, 198 
 
 membran e, 304 
 
 Muriatic 'acid, or marine acid, 225 
 Muriats, 232 
 
 Muriat of ammonia, 181, 232 
 lime, 67 
 
 Muriat of soda, or common salt, 
 225, 232 
 
 potash, 2.26 
 Muriatium, 8 
 
 Muscles of animals, 298, 300 
 Musk, 326 
 Myrrh, 247 
 
 N 
 
 Naptha, 160, 270 
 Negative electricity, 13, 74, 79 
 Nerves, 302 
 
 Neutral, or compound salts, 196 
 Nickel, 7, 154 
 
 Nitre, or nitrat of potash, or salt- 
 petre, 211, 216 
 Nitric acid, 209 
 Nitrogen, or azot, 48 
 
 gas, 90 
 Nitro muriatic acid, or aqua re- 
 
 gia, 153, 229, 
 Nitrous acid gas, 213 
 
 air, or nitric oxyd gas. 
 212 
 
 Nitrats, 215 
 Nitrat of copper, 167 
 
 ammonia, 215, 217 
 potash, or nitre, or salt- 
 petre, 180, 211, 217 
 
 silver, or lunar caustic, 
 217 
 Nomenclature of acids, 120, 196 
 
 compound salts. 
 166 
 
 Nut-galls, 208 
 Nut-oil, 244 
 Nutrition of plants, 274 
 of animals, 298 
 
 Oils, 138. 243 
 Oil of amber, 271 
 
 vitriol, or sulphuric acid, 20 1 \ 
 Olifiant gas, 24t> 
 Olive oil., 243 
 Ores, 142 
 
 Organized bodies, 236 
 Organs of animals, 303 
 vegetables, 288 
 
 33* 
 
378 
 
 INfcEX, 
 
 Osmium, 8, 158 
 Oxalic acid, 252, 198 
 Oxyds, 150 
 Oxyd of manganese, 145 
 
 iron/91 
 
 lead, 144 
 
 sulphur, 206 
 Qxydation, or oxygeuation, 150, 
 
 196 
 Oxygen, 7, 84, 119 
 
 gas, or vital air, 84 
 Qxy -muriatic acid, 153, 227 
 Oxy-muriats, 233 
 Qxy-muriat of potash, 233 
 
 Palladium, 153 
 Papin's digester, 292 
 Parenchyma, 279, 283 
 Particles, 9 
 'Pearl-ash, 176 
 Peat, 271 
 
 Peculiar juice of plants, 283 
 Perfect metals, 8 
 Perfumes, 245 
 Perspiration, 314 
 Petrifaction, 270 
 Pewter, 155 
 Pharmacy, 2 
 Phosphat of lime, 209 
 Phosphorated hydrogen gas. 126 
 Phosphorescence, 16 
 Phosphoric acid, 208 
 Phosphorous acid, 208 
 Phosphorus, 123 
 Phosphoret of lime, 126 
 
 sulphur, 127 
 Pitch, 283 
 Plaister, 195 
 Platina, 8, 147 
 Plating, 155 
 Plumbago, 139 
 Plumula, 279 
 Porcelain, 191 
 
 Positive electricity, 13, 74, 79, &c. 
 Potassium, 8, 160, 162 
 Pottery 190 
 Potash, 160 
 Precipitate, 12 
 
 Pressure of the atmosphere, 55, 56 
 prussiat of iron, or Prussian blue, 
 295 
 
 Prussiat of potash, 295 
 Prussic acid, 295 
 Putrid fermentation, 268, 326 
 Pyrites, 155, 207 
 Pyrometer, 20, 25 
 
 Q 
 
 Quicklime, 192 
 Quiescent forces, 170 
 
 R 
 
 Radiation of caloric, 28 
 
 Prevost's theory, 27, 
 
 Pictet's explana- 
 tions, 28 
 
 Leslie's illustrations, 
 31 
 
 Radicals, 196, 199 
 
 Radicle, or root, 279 
 
 Rain, 50 
 
 Rancidity, 245 
 
 Rectification, 262 
 
 Reflexion of caloric, 28, 31 
 
 Reptiles, 321 
 
 Resins, 246 
 
 Respiration, 307 
 
 Reviving of inetals, 147 
 
 Rickets, 299 
 
 Rhodium, 153 
 
 Roasting metals, 142 
 
 Rock crystal, 188 
 
 Ruby, 187 
 
 Rum, 261 
 
 Rust, 143, 148 
 
 Saccharine fermentation, 256 
 
 Sal ammoniac, or muriat of ainfliQ- 
 nia, 181 
 
 polychrest, or sulphat of pot- 
 ash, 205 
 
 volatile, or carbonat of am> 
 monia, 184 
 
 Salifiable bases, 167 
 
 Salifying principles, 167 
 
 Saltpetre, or nitre, or nitrat ol 
 potash, 180, 211, 217 
 
INDEX. 
 
 379 
 
 Salt, 150, 205 
 
 Sand, 189 
 
 Sandstone, 189 
 
 Sap of plants, 239, 257, 286 
 
 Sapphire, 187 
 
 Saturation, 48 
 
 Seas, temperature of, 41 
 
 Sebacic acid, 245, 195 
 
 Secretions, 313 
 
 Seeds of plants, 257, 286 
 
 Seltzer water, 134, 194 
 
 Senses, 303 
 
 Silex, or silica, 185, 188 
 
 Silicium, 8 
 
 Silk, 326 
 
 Silver, 145 
 
 Simple bodies, 5 
 
 Size, 291 
 
 Skin, 290 
 
 Slaking of lime, 192, 303 
 
 Slate, 190 
 
 Smelting metals, 142 
 
 Smoke, 96 
 
 Soap, 176 
 
 Soda, 163, 180 
 
 water, 136 
 Sodium, 163 
 Soils, 273 
 Soldering, 155 
 Solubility, 205 
 Solution, 46 
 
 by the air, 47 
 of potash, 178 
 Specific heat, 59 
 Spermaceti, 325, 327 
 Spirits, 260 
 Spirit lamp, 264 
 Steam, 57, 65 
 Steel, 138 
 Stomach, 306 
 Stones, 186 
 Stucco, 195 
 Strontites, 195 
 Strontium, 8 
 Suberic acid, 252, 198 
 Sublimation, 117 
 Succin, or yellow amber, 271 
 Succinic acid, 252, 271 
 Sugar, 240, 256 
 
 of milk, 324 
 Sulphats, 197 
 
 Super-oxygenated sulphuric acid, 
 196 
 
 Sulphat of alumine, or alum, 190 
 barytes, 192 
 iron, 207 
 
 lime, or gypsum or 
 plaister of Paris, 207 
 
 magnesia, or Epsom 
 salt, 195, 207 
 
 potash, or sal poly- 
 chrest, 205 
 
 soda,orGlauber's salts, 
 177,, 206 
 Sulphur, 117 
 
 flowers of, 117 
 
 Sulphurated hydrogen gas, 122 
 Sulphurets, 155 
 Sulphurous acid, 203 
 Sulphuric acid, 201 
 Sympathetic ink, 159 
 /Synthesis, 130 
 
 T 
 
 Tan, 249 
 
 Tannin, 251 
 
 Tar, 283 
 
 Tartarous acid, 252 
 
 Tartrit of potash, 253 
 
 Teeth, 298 
 
 Tellurium, 8 
 
 Temperature, 17 
 
 Thaw, 73 
 
 Thermometers, 21 
 
 Fahrenheit, 21 
 Reaumur's, 22 
 Centrigrade, 22 
 air, 22 
 
 differential, 23 
 construction of, 23 
 
 Thoracic duct, 301 
 
 Thunder, 113 
 
 Tin, 145, 159 
 
 Titanium, 156 
 
 Turf, 271 
 
 Turpentine, 167, 283 
 
 Transpiration of plants, 280 
 
 Tungsten, 8, 153 
 
 Vapour, 57, 65, 266 
 Vaporisation, 49 
 Varnishes, 247 
 Vegetables, 236, 272 
 Vegetable acid, 188, 252 
 
380 
 
 INDEX- 
 
 Vegetable colour?, 248 
 heat, 2:37 
 oils, 244 
 Veins, 304, 309 
 Venous blood, 309, 312 
 Ventricles, 310 
 Verdigris, 158 
 Vessels, 301 
 Vinegar. 267 
 Vinous fermentation, 258 
 Vital air, or oxygen gas, 84 
 Vitriol, or sulphatof iron, 201 
 Volatile oils, 139,242, 245 
 
 products of combustion. 
 254 
 
 alkali, 174, 181 
 
 Voltaic battery, 142, 146, 160, 
 172 
 
 Uranium, 8 
 
 u 
 
 w 
 
 Water, 99, 107 
 
 decomposition by carbon, 
 136 
 
 Water, decomposition of, by elec- 
 tricity, 107, &c. 
 
 condensation of, 41 
 
 of the sea, 41 
 
 boiling, 45, 55 
 
 solution by, 47 
 
 of crystallisation, 152 
 Wax, 244, 325 
 Whey, 322 
 Wine, 258 
 Wood, 200 
 
 Woody fibre, 251, SJ84 
 Wool, 299 
 
 Yeast, 267 
 Yttria, 185 
 Yttrium, 7 
 
 Zinc, 8 
 -Zicornia, 185 
 Zoonic acid, 295 
 
TABLE OF THE EFFECTS OF 
 
 Fahrenheit. 
 
 55 
 
 46 
 
 39 
 
 36 
 
 22 
 
 11 
 
 7 
 
 20 
 
 25 
 
 28 
 30 
 32 
 
 36 
 46 
 
 $4 
 
 40 
 
 82 
 97 
 90 
 104 
 109 
 112 
 127 
 149 
 145 
 155 
 212 
 
 1. FREEZING POINTS OP LIQUIDS. 
 
 Strongest nitric acid freezes (Cavendis.1)) 
 
 Ether and liquid ammonia 
 
 Mercury 
 
 Sulphuric acid (Thompson) 
 
 Acetous acid 
 
 2 Alcohol, 1 water 
 
 Brandy 
 
 Strongest sulphuric acid (Cavendish) 
 
 Oil of turpentine (Macquer) 
 
 Strong wines 
 
 Fluoric acid 
 
 Oils bergamot and cinnamon 
 
 Human blood 
 
 Vinegar 
 
 Milk 
 
 Oxymuriatic acid 
 
 Water 
 
 Olive oil 
 
 Sulphuric acid, specific gravity 1JTS (Keir) 
 
 Oil of anniseeds, 50 (Thompson} 
 
 2. MELTING POINTS OP SOLIDS. 
 
 Equal parts of sulphur and phosphorus 
 
 Adipocire of muscle 
 
 Lard (Nicholson) 
 
 Phosphorus 
 
 Resin of bile 
 
 Myrtle wax (Cadet) 
 
 Spermaceti (Bostock) 
 
 Tallow (Nicholson) 92 (Thompson) 
 
 Bees' wox 
 
 Ambergris (La grange) 
 
 Bleached wax (Nicholson) 
 
 Bismuth 5 parts, tin 3, lead 2 
 
382 
 
 TABLE OF THE 
 
 Fahren. 
 
 Wedg. 
 
 234 
 
 
 235 
 
 
 383 
 
 
 303 
 
 
 -334 
 
 
 442 
 
 
 460 
 
 
 476 
 
 
 612 
 
 
 680 
 
 
 809 
 
 
 3809 
 
 21 
 
 4587 
 
 27 
 
 4717 
 
 22 
 
 5237 
 
 32 
 
 17977 
 
 130 
 
 20577 
 
 150 
 
 21097 
 
 154 
 
 21637 
 
 158 
 
 21877 
 
 160 
 
 23177 
 
 4-170 
 
 140 
 
 
 145 
 
 
 170 
 
 
 176 
 
 
 212 
 
 
 219 
 
 
 230 
 
 
 242 
 
 
 248 
 
 
 283 
 
 
 540 
 
 
 554 
 
 
 560 
 
 
 570 
 
 
 590 
 
 
 600 
 
 
 660 
 
 
 Sulphur (Hope) 212 (Fourc.) 185 (Kirw.) 
 Adipocire of biliary calculi (Fourcroy) 
 Tin and bismuth, equal parts 
 Camphor 
 
 Tin 3, lead 2, or tin 2, bismuth 1 
 Tin (Chrichton) 413 (Irvine) 
 Tin 1, lead 4 
 Bismuth (Irvine) 
 
 Lead (Crichton) 594 (Iry.) 540 (Newton) 
 Zinc 
 
 Antimony 
 Brass 
 Copper 
 Silver 
 Gold 
 Cobalt 
 Nickel 
 Soft nails 
 Iron 
 
 Manganese 
 
 Platinum, tungsten, molybdena, uranium, ti- 
 tanium, &c. 
 
 3. SOLIDS AND LIQUIDS VOLATILIZE. 
 
 Ether boils 
 Liquid ammonia boils 
 Camphor sublimes (Venturi) 
 Sulphur evaporates (Kirwan) 
 Alcohol boils, 174 (Black) 
 Water and essential oils boil 
 Phosphoius distils (Pelletier) 
 Muriate of lime boils (Dalton) 
 Nitrous acid boils 
 Nitric acid boils 
 White arsenic sublimes 
 Metallic arsenic sublimes 
 Phosphorus boils 
 
 Oil of turpentine boils, about 212 (Dalton) 
 Sulphur boils 
 
 Sulphuric acid boils (Dalton) 546 (Black) 
 Linseed oil botls, sulphur sublimes (Davy) 
 Mercury boils (Dalton) 644 (Secondat) 600 
 (Black) 672 (Irvine) 
 
EFFECTS OF HEAT. 
 
 383 
 
 4. MISCELLANEOUS EFFECTS OF HEAT. 
 
 Wedg. 
 
 1 
 
 f- 2 
 
 6 
 
 14 
 
 40 
 
 57 
 
 70 
 
 86 
 
 94 
 
 102 
 
 105 
 
 H2 
 
 114 
 
 121 
 
 124 
 
 125 
 
 150 
 
 185 
 
 Greatest cold produced by Mr. Walker 
 
 Natural cold produced at Hudson's Bay 
 
 Observed on the surface of the snow at Glas- 
 gow, 1780 
 
 At Glasgow, 1780 
 
 Equal parts, snow and satt 
 
 Phosphorus burns slowly 
 
 Vinous fermentation begins 
 
 to 135 Animal putrefaction 
 
 to 80 Summer heat in this climate 
 
 Vinous fermentation rapid, acetous begins 
 
 Phosphorus burns in Oxygen, 104 (Gottling) 
 
 Acetification ceases 
 
 to 100 Animal temperature 
 
 Feverish heat 
 
 Phosphorus burns vividly (Fourcroy) 148 
 (Thomson) 
 
 Albumen coagulates, 156 (Black) 
 
 Sulphur burns slowly 
 
 Lowest heat of ignition of iron in the dark 
 
 Hydrogen burns, 1000 (Thomson) 
 
 Charcoal burns (Thomson) 
 
 Iron red in twilight 
 
 Iron red in day light 
 
 Azotic gas burns 
 
 Enamel colours burned 
 
 Diamond burns (M'Kenzie) 30 W. = 5000 
 F (Morveau) 
 
 Delft ware fired 
 
 Working heat of plate glass 
 
 Flint glass furnace 
 
 Cream-coloured ware fired 
 
 Worcester china vitrified 
 
 Stone ware fired 
 
 Chelsea china fired 
 
 Derby china fired 
 
 Flint glass furnace greatest heat 
 
 Bow china vitrified 
 
 Plate glass greatest heat 
 
 Smith's forge 
 
 Hessian crucible fused 
 
 Greatest heat observed 
 
Y6 36017 
 
 M289981 
 
 THE UNIVERSITY OF CALIFORNIA UBRARY