A History of science v. 5

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Chapter II Beginnings Op Modern Chemistry

Chemistry at the beginning of the eighteenth century, p. 11 — Stephen Hales and the study of gases, p. 11 — Black's studies of carbon dioxide, p. 12 — Black's studies continued by Cavendish, p. 13 — His discovery that water was formed by the combination of hydrogen and oxygen, p. 14 — His discovery of nitrous acid, p. 15 — The work of Joseph Priestley, p. 18 — His discovery of oxy- i^ gen, p. 19 — His refiisal to reject the phlogiston theory, p. 22 — The work of Scheele, p. 23 — His independent discovery of oxygen, p. 24 — His important discovery of chlorine, p. 25 — Lavoisier and the foimdation of modem chemistry, p. 28.

Chapter III Chemistry Since Dalton

John Dalton and the atomic theory, p. 38 — Berthollet's refusal to accept it, p. 40 — The theory that chemical elements combine in definite proportions championed by Proust, p. 41 — Berzelius's ac-

• • •

m ceptance of Dalton's theory, p. 41 — The law of Avogadro, p. 43 — Amadeo Avogadro names the compotind atoms "molecules," p. 44 — Berzelius's studies of ** equivalents," p. 44 — The establishment of the laws of the specific heat of atoms, and of isomorphism, p. 45 — Experiments of Davy in decomposing substances with electricity, p. 46 — His famous Bakerian lecture of 1806, p. 48 — The theory of binary composition of chemical compounds, p. 53 — Urea synthesized in the laboratory by W6hler, and organic chemistry established, p. 54 — Liebig's and Wohler's studies of compound radicals, p. 55 — Revival of Avogadro's law by Gerhardt, p. 57 — Investigations of the "valency" of different atoms, p. 57 — Ste.- Claire Deville's investigations of "dissociation," p. 61 — Isomerism proved by Liebig and Wohler, p. 62 — William Prout's studies of atomic weights, p. 66 — Revival of Prout's alleged law by Dumas, p. 67 — Mendeldeff's "periodic law," p. 68 — The spectroscope perfected by Kirchhoff and Bunsen, p. 69 — Daguerre discovers practical photography, p. 70 — Draper's application of photography to spectroscopy, p. 70 — Observations of the sun and stars by the spectroscope and photographic plate, p. 71 — Sir Norman Lockyer's deductions from these observations, p. 71.

Chapter IV Anatomy And Physiology In The Biohtbbnth Cbntury

Albert von Haller, p. 73 — His doctrine of irritability, p. 74 — Battista Morgagni and morbid anatomy, p. 76 — The work of William Hunter, p. 76 — John Hunter, p. 78 — His study of lymphatics, p. 79 — His discovery of the collateral circulation of the blood, p. 81 — His operation for aneurism, p. 84 — Lazzaro Spallanzani and the study of spontaneous generation, p. 86 — His chemical theory of digestion, p. 88 — Hunter's studies of digestion, p. 90 — The discovery of the function of respiration, p. 92 — Erasmus Darwin on vegetable respiration, p. 94— -Closing epoch of the eighteenth century, p. 99.

Chapter V Ninbtbbnth-century Anatomy And Physiology

Cuvier's "law of co-ordination," p. 102 — Bichat's studies of the "animal systems" and "organic systems" of vertebrates, p. 107 — His division of anatomical structures into sets of "tissues," p. 108 — Attempts to improve the compound microscope, p. 109 — WoUaston's improvement by making use of plano-convex lenses, p. no — Sir John Herschel's improvement, p. 1 1 1 — Lister's experiments with

iv lenses, p. 112 — His paper before the Royal Society detailing his theories and experiments, p. 113 — Amici's improved compound microscope, p. 113 — The rise of histology, p. 114 — The question of the shape of the red coqjuscles settled by Lister, p. 114 — Robert Brown's discovery of the nuclei of plant cells, p. 115 — Schwann's researches on animal cells, p. 118 — Schwann's famous -cell theory, p. 119 — Studies in embryology by Von Baer, Miiller, and Carpenter, p. 122 — Von Mohl's investigation of the cell contents, p. 123 — The studies of protoplasm by De Bary and Max Schultze,p. 125 — Von Mohl's discovery of the formation of cells by division of pre-existing cells, p. 126 — Virchow's demonstration of ttle correctness of Von Mohl's theory of cell formation, p. 127 — The discovery of hydrochloric acid in the gastric juice by Prout, p. 129 — Discovery of glands in the mucous membrane of the stomach and intestines, p. 130 — Discovery of the function of the various glands and organs that act. in the process of digestion, p. 130 — Liebig's demonstration that the activities of life are the product of energy due to destructive processes occurring in the ultimate cells, p. 131 — Exhaustive studies of the function of the red corpuscles, p. 135 — Claude Bernard's studies of the ductless glands, p. 137.

Chapter VI Thboribs Op Organic Evolution

Goethe's studies of the metamorphosis of plants, p. 140 — His doctrine that all parts of the flower are modified or metamorphosed leaves, p. 142 — Extension of the doctrine of metamorphosis to the animal kingdom by Goethe and Oken, p. 146 — Erasmus Darwin and his Botanic Garden, p. 147 — His suspicion that different species are modifications of one parent stock, p. 148 — The work of Jean Baptiste de Lamarck, p. 150 — His conception of the transmutation of species, p. 152 — Cuvier's opposition to the transmutation doctrine, p. 153 — The term "biology" coined independently by Treviranus and Lamarck, p. 160 — The doctrine of transmutation championed by Etienne Geoffroy Saint- Hilaire, p. 160 — Robert Chambers and his Vestiges of the Natural History of Creation, p. 162 — Darwin begins his work on the doctrine of evolution, p. 166 — His studies of variation in different species of domestic animals, p. 168 — The years spent in gathering his facts, p. 170 — The work of Alfred Russel Wallace, p. 172 — The joint papers of Darwin and Wallace before the Linnaean Society, in 1858, p. 173 — Darwin's Origin of S pedes ^ p. 173 — Its effect upon the scientific world, p. 175 — Huxley's estimate of Darwin's accomplishment, p. 178 — The disputed question of "spontaneous" variations, p. 178 — Weismann's objections to the

V

Lamarcldan conception, p. 178 — Pouchefs belief in spontaneous generation, p. 180 — Pasteur's refutation of. the doctrine, p. 180.

Chapter VII

The fame of Hermann Boerhaave as a physician, p. 181 — His classification of the different branches of medicine, p. 183 — Animists, vitalists, and organidsts, p. 184 — The "Brunonian system," p. 187 — The system of Hahnemann, p. 188 — Jenner and vaccination, p. 190 — His famous paper on vaccination, p. 194 — Reception of the discovery of vaccination in Europe, p. ig6.

Chapter VIII Ninbtbbnth-c

Corvisart lays the foundation of physical diagnosis, p. 300 — La^- nec's invention of the stethoscope, p. aoi — Piorry's introduction of ipediate percussion, p. 103 — The work of Hali, Magendie, and Louis in overthrowing "depletive methods" of treatment, p, 103 — Renucci's demonstration that the itch mite is tfae cause of the disease, and the impetus given to the study of parasitic diseases, p. 206— Owen's discovery of the Trichina spiralis, p. 207 — Schoenlein's discovery of the cause of favus, p. 108 — Dr. Horace Wells's euperiment in painless dentistry by means of nitrous oxide, p. 313 — Morton's discovery of ether anaesthesia, p. 314 — His demonstration at the Boston Hospital, October 16, 1846, p. 314 — The claims of Jackson and Long as to priority of the discovery, p. 315 — Simpson's discovery that chloroform produces aniesthesia, p. 317 — Pasteur's studies of fermentation, p. 317 — The studies of micro-organisms by L^tour and Schwann, p. 318 — Liebig's opposition to the theory that micro-organisms are responsible for fermentation and putrefaction, p. 119— Pasteur proves that micro-organisms cause decay of organic tissues, p. aao^Devaine's discovery that anthrax is caused by bacteria, p. 337 — Koch's corroboration of Devaine's discovery, p, aaS — Pasteur's experiments settle forever the question of bacilli as the cause of anthrax, p. 318 — Lister's discovery of antisepsis, p. 339 — Pasteur's experiments with chicken cholera, p. 332 — His attenuation of the microbe of anthrax, p, 333 — His public demonstration of the protection afforded domestic animals by inoculation of this "virus," p. 138 — His inoculations to prevent hydrophobia, p. 240 — Behring's discovery of tetanus and diphtheria antitoxine, p. 241 — The paper of Dr. Roux read before the Congress of Hygeine at Buda-Pesth, p. 342 — ^The establishment of serum-therapy, p. 243.

Chapter IX

Reforms in methods of caring for the insane begim by Rtish, Tuke, and Pinel, p. 246 — Pinel's liberation of the inmates at the Bicdtre and the Salp^tridre, p. 246 — The studies in psychology by Dr. Franz Joseph Gall, p. 247 — Desmoulins' discovery that the brain atrophies in old age, p. 248 — Sir Charles Bell's discovery of motor and sensory nerves, p. 250 — Marshall Hall's observations of reflex action, p. 251 — Studies of the nerve tracts by Schwann, Remak, and others, p. 258 — Claude Bernard's demonstration that the sympathetic nerves regulate the blood supply of any part, p. 260 — His further discovery of inhibitory nerves, leading finally to complete understanding of superior and subordinate nerve centres, p. 261 — Helmholtz's measurement of the speed of nervous impulses, p. 262 — Gustav Fechner's Psycho physik, and the beginnings of physiological psychology, p. 263 — Weber's experiments on nerve stimuli, p. 264 — Fechner verifies Weber's fundamental law of psychophysics, p. 265 — Wundt's studies of sensation, apperception, and volition, p. 267 — Establishment of the laboratory of Physiological Psychology at Leipzig, p. 269 — The work of Dr. James Braid on the phenomenon of hypnotism, p. 269 — The subject revived by Charcot and Heidenhain, p. 269 — Flourens' studies of brain physiology, p. 270 — His discovery of the "vital knot," p. 270 — Hughlings- Jackson's studies of "brain centres," p. 272 — Broca's localization of the centre for speech, p. 272 — Localization of motor centres by Ferrier and Munck, p. 274 — Method of cutting thin sections of tissues for microscopical examination, by Rolando, p. 277 — Studies of the ganglion cells, p. 279 — Waller and the study of "trophic centres," p. 279 — The histological scheme of Gerlach, p. 281 — Golgi's discovery of the process of staining nerve cells, and its application in tracing nerve filaments, p. 282 — Cajal's demonstration of independent nerve filaments, p. 283 — The importance of this discovery in explaining thought-mechanism, p. 285.

CHAPTER X THE NEW SCIENCE OP ORIENTAL ARCHiGOLOGY

How the "riddle of the Sphinx" was read, p. 287 — The Rosetta Stone in the British Museiun, p. 289 — Decipherment of the Rosetta

Vll

Stone by Young and ChampoUion, p, igo — The "Cedar of Lebanon," p. 191 — The restoration of Assyrian sculptures, p. agj — The great library of Asurbanipal, p. 294 — How the records were read, p. 397 — The work of Sir Henry Rawlinson, p. 199.

APPENDIX 303

ILLUSTRATIONS

LAVOISIER IN HIS LABORATORY FrotUispi0C9

JOSEPH PRIESTLEY Facmgp. 20

JOHN DALTON " 40

JOHN W. DRAPER " 70

JOHN HUNTER " 84

II Sir Joseph Lister Iio

THBODOR SCHWANN '* I20

KARL ERNST VON BABR " 122

MAX SCHULTZB " 1 26

JEAN BAPTISTE DE LAMARCK " 1 52

ETIENNE GEOFFROY SAINT-HILAIRB " 160

CHARLES ROBERT DARWIN " 166

ALFRED RUSSEL WALLACE " 1 72

THOMAS HENRY HUXLEY ** 1 76

EDWARD JENNER " I92

LAENNEC, INVENTOR OP THE STETHOSCOPE, AT THE

NECKER HOSPITAL, PARIS ** 202

WILLIAM T. G. MORTON " 214

CRAWFORD W. LONG " 2l6

LOUIS PASTEUR " 232

PINEL AT LA SALPBTRI^RB, IN 1 795* RBLBASXNO THE

INSANE FROM THEIR MANACLES " 246

GUSTAV THEODOR PECHNBR " 264

JEAN MARTIN CHARCOT " 268

PAUL BROCA ** 272

THB ROSBTTA STONB " 288

ix

BOOK IV

MODERN DEVELOPMENT OF THE CHEMICAL AND BIOLOGICAL SCIENCES

AS regards chronology, the epoch covered in the i\ present volume is identical with that viewed in the preceding one. But now as regards subject matter we pass on to those diverse phases of the physical world which are the field of the chemist, and to those yet more intricate processes which have to do with living organisms. So radical are the changes here that we seem to be entering new worlds; and yet, here as before, there are intimations of the new discoveries away back in the Greek days. The solution of the problem of respiration will remind us that Anaxagoras half guessed the secret ; and in those diversified studies which tell us of the Daltonian atom in its wonderful transmutations, we shall be reminded again of the Clazomenian philosopher and his successor Democritus. Yet we should press the analogy much too far were we to intimate that the Greek of the elder day or any

HARVARD COLLEGE LIBRARY

■5'J.cyi

HARVARD COLLEGE LIBRARY struments are required to make these shavings whose curls are in no wise uniform, but seemingly casual ; and what is more remarkable, bodies that before seemed unelastic, as beams and blocks, will afford them." •

Although this explanation of the composition of the air is most crude, it had the effect of directing attention to the fact that the atmosphere is not " mere nothingness," but a "something" with a definite composition, and this served as a good foundation for future investigations. To be sure. Boyle was neither the first nor the only chemist who had suspected that the air was a mixture of gases, and not a simple one, and that only certain of these gases take part in the process of calcination. Jean Rey, a French physician, and John Mayow, an Englishman, had preformed experiments which showed conclusively that the air was not a simple substance ; but Boyle's work was better known, and in its effect probably more important. But with all Boyle's explanations of the composition of air, he still believed that there was an inexplicable something, a "vital substance," which he was unable to fathom, and which later became the basis of Stahl's phlogiston theory. Commenting on this mysterious substance, Boyle says: "The difficulty we find in keeping flame and fire ahve, though but for a little time, without air, renders it suspicious that there be dispersed through the rest of the atmosphere some odd substance, either of a solar, astral, or other foreign nature; on account of which the air is so necessary to the substance of flame!" It was this idea that attracted the attention of George Ernst Stahl (1660-1734), a professor of medicine in the 6

PHLOGISTON THEORY IN CHEMISTRY

University of Halle, who later founded his new theory upon it. Stahl's theory was a development of an earlier chemist, Johann Joachim Becker (163 5-1 682), in whose footsteps he followed and whose experiments he carried further.

In many experiments Stahl had been struck with the fact that certain substances, while diflfering widely from one another in many respects, were aUke in combustibility. From this he argued that all combustible substances must contain a common principle, and this principle he named phlogiston. This phlogiston he believed to be intimately associated in combination with other substances in nature, and in that condition not perceivable by the senses ; but it was supposed to escape as a substance burned, and become apparent to the senses as fire or flame. In other words, phlogiston was something imprisoned in a combustible structure (itself forming part of the structure), and only liberated when this structure was destroyed. Fire, or flame, was free phlogiston, while the imprisoned phlogiston was called combined phlogiston, or combined fire. The peculiar quality of this strange substance was that it disliked freedom and was always striving to conceal itself in some combustible substance. Boyle's tentative suggestion that heat was simply motion was apparently not accepted by Stahl, or perhaps it was unknown to him.

According to the phlogistic theory, the part remaining after a substance was burned was simply the original substance deprived of phlogiston. To restore the original combustible substance, it was necessary to heat the residue of the combustion with something

TOL. IT.— a y that btimed easily, so that the freed phlogiston might again combine with the ashes. This was explained by the supposition that the more combustible a substance was the more phlogiston it contained, and since free phlogiston sought always to combine with some suitable substance, it was only necessary to mix the phlogisticating agents, such as charcoal, phosphorus, oils, fats, etc., with the ashes of the original substance, and heat the mixture, the phlogiston thus freed uniting at once with the ashes. This theory fitted very nicely as applied to the calcined lead revivified by the grains of wheat, although with some other products of calcination it did not seem to apply at all.

It will be seen from this that the phlogistic theory was a step towards chemistry and away from alchemy. It led away from the idea of a ''spirit" in metals that could not be seen, felt, or appreciated by any of the senses, and substituted for it a principle which, although a falsely conceived one, was still much more tangible than the ** spirit," since it could be seen and felt as free phlogiston and weighed and measured as combined phlogiston. The definiteness of the statement that a metal, for example, was composed of phlogiston and an elaucfU was much less enigmatic, i»\'en if wrong, than the statement of the alchemist that '* metals are produced by the spiritual action of the tha*e imneiples, salt, mercur>', sulphur" — ^particularly when it is explained that salt, mercury, and sulphur were really not what their names implied, and that theiv was no universiiUy accepted belief as to what they rt^ully were.

The meUils, which are now regarded as elementary

PHLOGISTON THEORY IN CHEMISTRY

bodies, were considered compounds by the phlogistians, and they believed that the calcining of a metal was a process of simplification. They noted, however, that the remains of calcination weighed more than the original product, and the natural inference from this would be that the metal must have taken in some substance rather than have given off anything. But the phlogistians had not learned the all-important significance of weights, and their explanation of variation in weight was either that such gain or loss was an unimportant "accident" at best, or that phlogiston, being light, tended to lighten any substance containing it, so that driving it out of the metal by calcination naturally left the residue heavier. At first the phlogiston theory seemed to explain in an indisputable way all the known chemical phenomena. Gradually, however, as experiments multiplied, it became evident that the plain theory as stated by Stahl and his followers failed to explain satisfactorily certain laboratory reactions. To meet these new conditions, certain modifications were introduced from time to time, giving the theory a flexibility that would allow it to cover all cases. But as the number of inexplicable experiments continued to increase, and new modifications to the theory became necessary, it was found that some of these modifications were directly contradictory to others, and thus the simple theory became too cumbersome from the number of its modifications. Its supporters disagreed among themselves, first as to the explanation of certain phenomena that did not seem to accord with the phlogistic theory, and a little later as to the theory itself. But as yet there 9 was no satisfactory substitute for this theory, which, even if unsatisfactory, seemed better than anything that had gone before or could be suggested.

But the good effects of the era of experimental research, to which the theory of Stahl had given such an impetus, were showing in the attitude of the experimenters. The works of some of the older writers, such as Boyle and Hooke, were again sought out in their dusty comers and consulted, and their surmises as to the possible mixture of various gases in the air were more carefully considered. Still the phlogiston theory was firmly grounded in the minds of the philosophers, who can hardly be censured for adhering to it, at least until some satisfactory substitute was offered. The foundation for such a theory was finally laid, as we shall see presently, by the work of Black, Priestley, Cavendish, and Lavoisier, in the eighteenth century, but the phlogiston theory cannot be said to have finally succumbed until the opening years of the nineteenth century.

II

THE BEGINNINGS OF MODERN CHEMISTRY

THE "pneumatic" CHEMISTS

MODERN chemistry may be said to have its begimiing with the work of Stephen Hales (1677- 1761), who early in the eighteenth century began his important study of the elasticity of air. Departing from the point of view of most of the scientists of the time, he considered air to be " a fine elastic fluid, with particles of very different nature floating in if ; and he showed that these " particles " could be separated. He pointed out, also, that various gases, or "airs,*' as he called them, were contained in many solid substances. The importance of his work, however, lies in the fact that his general studies were along lines leading away from the accepted doctrines of the time, and that they gave the impetus to the investigation of the properties of gases by such chemists as Black, Priestley, Cavendish, and Lavoisier, whose specific discoveries are the fotmdation-stones of modem chemistry.

JOSEPH BLACK

The careful studies of Hales were continued by his younger confrere. Dr. Joseph Black (i 728-1 799), whose experiments in the weights of gases and other chemicals were first steps in quantitative chemistry. But

II even more important than his discoveries of chemical properties in general was his discovery of the properties of carbonic-acid gas.

Black had been educated for the medical profession in the University of Glasgow, being a friend and pupil of the famous Dr. William Cullen. But his liking was for the chemical laboratory rather than for the practice of medicine. Within three years after completing his medical course, and when only tr^^enty-three years of age, he made the discovery of the properties of carbonic acid, which he called by the name of " fixed air." After discovering this gas. Black made a long series of experiments, by which he was able to show how widely it was distributed throughout nature. Thus, in 1757, he discovered that the bubbles given off in the process of brewing, where there was vegetable fermentation, were composed of it. To prove this, he collated the contents of these bubbles in a bottle containing lime-water. When this bottle was shaken violently, so that the lime-water and the carbonic acid became thoroughly mixed, an insoluble white powder was precipitated from the solution, the carbonic acid having combined chemically with the lime to form the insoluble calcium carbonate, or chalk. This experiment suggested another. Fixing a piece of burning charcoal in the end of a bellows, he arranged a tube so that the gas coming from the charcoal would pass through the lime-water, and, as in the case of the bubbles from the brewer's vat, he found that the white precipitate was thrown down; in short, that carbonic acid was given off in combustion. Shortly after, Black discovered that by blowing through a glass tube inserted into lime-water, chalk was precipitated, thus proving that carbonic acid was being constantly thrown off in respiration.

The effect of Black's discoveries was revolutionary, and the attitude of mind of the chemists towards gases, or " airs,'' was changed from that time forward. Most of the chemists, however, attempted to harmonize the new facts with the older theories — to explain all the phenomena on the basis of the phlogiston theory, which was still dominant. But while many of Black's discoveries could not be made to harmonize with that theory, they did not directly overthrow it. It required the additional discoveries of some of Black's fellow-scientists to complete its downfall, as we shall see.

HENRY CAVENDISH

This work of Black's was followed by the equally important work of his former pupil, Henry Cavendish (1731-1810), whose discovery of the composition of many substances, notably of nitric acid and of water, was of great importance, adding another link to the important chain of evidence against the phlogiston theory. Cavendish is one of the most eccentric figures in the history of science, being widely known in his own time for his immense wealth and brilliant intellect, and also for his peculiarities and his morbid sensibility, which made him dread society, and probably did much in determining his career. Fortunately for him, and incidentally for the cause of science, he was able to pursue laboratory investigations without being obliged to mingle with his dreaded fellow-mortals, his every want being provided for by the inmiense fortune inherited from his father and an uncle.

When a young man, as a pupil of Dr. Black, he had become imbued with the enthusiasm of his teacher, continuing Black's investigations as to the properties of carbonic-acid gas when free and in combination. One of his first investigations was reported in 1766, when he communicated to the Royal Society his experiments for ascertaining the properties of carbonic-acid and hydrogen gas, in which he first showed the possibility of weighing permanently elastic fluids, although Torricelli had before this shown the relative weights of a column of air and a column of mercury. Other important experiments were continued by Cavendish, and in 1784 he announced his discovery of the composition of water, thus robbing it of its time-honored position as an " element." But his claim to priority in this discovery was at once disputed by his fellow-countryman James Watt and by the Frenchman Lavoisier. Lavoisier's claim was soon disallowed even by his own countrymen, but for many years a bitter controversy was carried on by the partisans of Watt and Cavendish. The two principals, however, seem never to have entered into this controversy with anything like the same ardor as some of their successors, as they remained on the best of terms.* It is certain, at any rate, that Cavendish announced his discovery officially before Watt claimed that the announcement had been previously made by him, " and, whether right or wrong, the honor of scientific discoveries seems to be accorded naturally to the man who first publishes a demonstration of his discovery." Englishmen very generally admit the justness of Cav- ^idish's claim, although the French scientist Arago, after reviewing the evidence carefully in 1833, decided in favor of Watt.

It appears that something like a year before Cavendish made known his complete demonstration of the composition of water, Watt communicated to the Royal Society a suggestion that water was composed of "dephlogisticated air (oxygen) and phlogiston (hydrogen) deprived of part of its latent heat." Cavendish knew of the suggestion, but in his experiments refuted the idea that the hydrogen lost any of its latent heat. Furthermore, Watt merely suggested the possible composition without proving it, although his idea was practically correct, if we can rightly interpret the vagaries of the nomenclature then in use. But had Watt taken the steps to demonstrate his theory, the great "Water Controversy" would have been avoided.

Cavendish's report of his discover}' to the Royal Society covers something like forty pages of printed matter. In this he shows how, by passing an electric spark through a closed jar containing a mixture of hydrogen gas and oxygen, water is invariably formed, apparently by the tmion of the two gases. The experiment was first tried with hydrogen and common air, the oxygen of the air tmiting with the hydrogen to form water, leaving the nitrogen of the air still to be accounted for. With pure oxygen and hydrogen, however, Cavendish fotmd that pure water was formed, leaving slight traces of any other substance which might not be interpreted as being chemical impurities. There was only one possible explanation of this phenomenon — that hydrogen and oxygen, when combined, fonn water.

IS

" By experiments with the globe it appeared," wrote Cavendish, "that when inflammable and common air are exploded in a proper proportion, almost all the inflammable air, and near one-fifth the common air, lose their elasticity and are condensed into dew. And by this experiment it appears that this dew is plain water, and consequently that almost all the inflammable air is turned into pure water.

" In order to examine the natm« of the matter condensed on firing a mixture of dephlogisticated and inflammable air, I took a glass globe, holding 8800 grain measures, furnished with a brass cock and an apparatus tor firing by electricity. This globe was well exhausted by an air-pump, and then filled with a mixture of inflammable and dephlogisticated air by shutting the cock, fastening the bent glass tube into its mouth, and letting up the end of it into a glass jar inverted into water and containing a mixture of 19,500 grain measures of dephlogisticated air, and 37,000 of inflammable air; so that, upon opening the cock, some of this mixed air rushed through the bent tube and filled the globe. The cock was then shut and the included air fired by electricity, by means of which almost all of it lost its elasticity (was condensed into water vapors). The cock was then ^ain opened so as to let in more of the same air to supply the place of that destroyed by the explosion, which was again fired, and the operation continued till almost the whole of the mixture was let into the globe and exploded. By this means, though the globe held not more than a sixth part of the mixture, almost the whole of it was exploded therein without any fresh exhaustion of the globe." 16