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GAY-LUSSAC, JOSEPH Louis (1778-1850), one of the most distinguished of modern physicists and chemists, was born at St Leonard, in the department of Haute Vienne, on the 6th of December 1778. His father, Antoine Gay, who was procureur du roi and judge at Pont-de-Noblac, had added to the common family name the distinctive title Lussac, from a small property he had in the neighbourhood of St Leonard. The family consisted of two sons, of whom Joseph Louis was the elder, and three daughters. Intended for the bar, young Gay-Lussac prosecuted his early studies in Latin. and other elementary subjects at home, under the superintendence of the Abbe Bourdeix and other masters, until 1794, when he was sent to Paris, where he worked very hard for three years preparing for admission to the Ecole Polytechnique. After a brilliant examination he was received into this institution on December 27, 1797, whence on the 22d of November 1800 he was transferred to the school Des Ponts et Chaussees. Shortly afterwards he was assigned to Berthollet, whohad returned from Napoleon's Egyptian expedition, and who was desirous of having an able student from the Ecole Polytechnique to aid him in his researches. The results expected by the author of the Statigue Cleineique were not verified by his assistant's experiments, which seem to have been recorded without any consideration of the theorizer's feelings. It was on this occasion, according to Arago, that Berthollet, at first nettled to find that his ideas were not confirmed, delivered himself as follows : "Young man, it is your destiny to make discoveries. You shall be henceforth my companion. I wish - it is a title of which I am sure I shall have cause some day to be proud - I wish to be your father in science."
Gay-Lussac accordingly entered on a long series of researches upon certain physical phenomena, which though of constant recurrence in experimental inquiries, had up to this time been very imperfectly examined. In his first memoir (Ann. de Chortle, t. xliii., 1802) he shows that different gases are dilated in the same proportion when heated from 0° to 80° (116aumur). He does not seem to have been aware of Dalton's experiments on this subject, which were indeed very far from being accurate ; but he states in a footnote that " le cit. Charles' avait remarque depuis 15 ans la meme propriete dans ces gaz ; mais, n'ayant jamais publie ses resultats, c'est par le plus grand hasard que je les ai connus." In return for his having thus rescued from oblivion the remark which his fellow-citizen, probably wisely, did not think worth recording, some recent authors have changed the title of the law from that of Gay-Lussac to that of Charles. The investigations recorded in this memoir were followed by experiments on the improvements of thermometers and barometers, on the tension of vapours, their mixture with gases, and the determination of their density, evaporation, hygrometry, and capillarity. In course of these researches, which engaged him for a couple of years, he acquired not only dexterity in manipulation and the contrivance of experiments, but a great deal of valuable knowledge of physics. During the interval, in the year 1802, he had been nominated Fourcroy's demonstrator at the Ecole Polytechnique, and as he had in this capacity to .lecture frequently for the professor, he was beginning to acquire reputation as a teacher and expounder of chemistry and physics, by the clearness, precision, and care which his lectures evinced. In 1803-4 certain results respecting terrestrial magnetism had been obtained during two balloon ascents, which appeared of so much interest that the French Academy was desirous of having them repeated. Through Berthollet and Chaptal the balloon which had been used in Egypt was obtained, and fitted up with various instruments; who made their first ascent from the garden of the Conservatoire des Arts et Metiers, on August 24, 1804. In this ascent an altitude of 4000 metres was attained, but unexpected difficulties were encountered, and the results were not decisive. Not satisfied with the expedition, Gay-Lussac got a larger balloon provided with every requisite, and made an ascent by himself on September 16 of the same year. On this occasion the balloon rose to a height of 7016 metres, an altitude greater than any which had been formerly reached, and surpassed only by a few later ascents. At this great elevation of nearly 23,000 feet, and with the thermometer at 9° C. below freezing, Gay-Lussac remained for a considerable time making observations on temperature, on the moisture of the air, on magnetism, and other points. He observed particularly that he had considerable difficulty in breathing, that his pulse was quickened, and that by the absence of moisture in the air his mouth and throat became so parched that it was painful to swallow even a piece of bread. The experiments on magnetism for which the ascent was primarily made were imperfect, but they led him to the conclusion that the magnetic effect at all attainable elevations above the earth's surface remains constant.I Having collected samples of air at different elevations he, on his return to Paris, proceeded to analyse them ; and in conjunction 'with Alexander von Humboldt, whom he had associated with himself in this investigation, he published several papers on endiometric analysis and related topics. The memoir, which was read to the Institute on October 1, 1804, contained the germ of what was afterwards Gay-Lussac's most important generalization. The authors observed that when oxygen and hydrogen combine together by volume, it is in the proportion of one volume of the former to two volumes of the latter. Prior to this the numerous experiments on the volume composition of water had always brought out various complicated ratios, though approaching the simple one more or less closely. It was not, however, till 1808, that Gay-Lussac announced the law of combination by volume in its general form. Shortly after these investigations were completed, Gay-Lussac got leave of absence to accompany Von Humboldt on a scientific journey to Switzerland, Italy, and Germany. Provided with physical and meteorological instruments, they left Paris March 12, 1805, and travelled by Lyons, Chambery, and Mont Cenis to Genoa, and thence to Rome, where they arrived on July 5. After a short stay at Rome in the residence of William von Humboldt, during which Gay-Lussac made a few chemical analyses, they departed for Naples in company with Leopold von Buch, afterwards so eminent as a geologist. During this visit Gay-Lussac had the opportunity of study. ing on the spot volcanic eruptions and earthquakes. Vesuvius, which was in violent action, he ascended six times. After this the party went back to Rome, and then started for Florence on September 17, 1805. A few days having been spent there, they went on to Bologna and thence to Milan, which they reached on October 1, and there they had the pleasure of meeting Volta. The party crossed the St C-otthard on October 14-15, in the midst of a storm which prevented their seeing anything, and after some delay reached Gottingen, where they were received with much attention by Blumenbach, the famous naturalist. On November 16 they arrived at Berlin, where the winter and the following spring were spent. In this way Gay-Lussac became acquainted with the best society in Berlin, and was especially intimate with Klaproth and Erman. In spring he hurriedly returned to Paris. The death of an Academician had left a vacant place, and he was hopeful that he might be elected to fill it. Arago remarks that it is curious that Gay-Lussac should have found it necessary to be on the spot to ensure success. What he had already done for science might have been considered sufficient, apart from personal considerations, but there were prejudices which might have acted unfavourably, if he had not been present to meet them. These were, however, successfully overcome, and he entered the Academy in 1806. In the following year was inaugurated the Societe d'Arcueil, a small group of scientific men who used to assmble at Berthollet's house. •ay-Lussac was an original member of this society, which is of interest chiefly on account of its having been the means of publishing some papers which have since proved of great historical interest. The results of his magnetic observations made along with Humboldt were published in vol. i. of its Ittemoires (1807); and vol. ii. (1809) contains the important memoir on gaseous combination, in which he pointed out that, when gases combine with one another by volume or by measure, they do so in the very simplest proportions, 1 to 1, 1 to 2, 2 to 3, and so on, and that the volume of the product in the gaseous state bears a very simple ratio to that of the constituents. This law, which, along with Humboldt, he had shown to be true of water, he extended to several other gases, and he even deduced from the vapour density of compounds that of certain elements, more particularly, carbon, mercury, and iodine, which had not been ascertained by direct experiment.
It would take too much apace to give in detail the criticism which the enunciation of the principle evoked, more particularly from Dalton, who would not accept GayLussac's position, and affirmed his belief that " gases do not unite in equal or exact measures in any one instance ; when they appear to do so, it is owing to the inaccuracy of our experiments."2 There was at that time the difficulty that the specific gravity of gases and vapours had been imperfectly determined, and the necessary consequence of GayLussac's law, that the specific gravity and combining weight of elements should be expressed by the same number, could not be experimentally confirmed. Moreover, Dalton rested combination on atomic and not on combining weights, and the numbers he employed were in almost every instance very different from those which more accurate analysis has since determined. But the imperfect character of the then available data, and the amount of seemingly adverse experimental evidence, only throw a stronger light on the genius of 'Gay-Lussac in divining a law which, as science has progressed, has been duly confirmed, and which not only forms the most important control of the combining weight of chemical substances, but, when i'iterpreted by the kinetic theory of gases, shows that the physical molecules (that is to say, the portions of the substance which are not broken up into smaller parts during the motion which we call heat) exist in equal numbers in equal volumes of different gases at the same temperature and pressure. This law, which has as high a claim as the other to bear the name of Gay-Lussac, is also sometimes deprived of that honour, and called the law of Avogadro, who, long afterwards, by his more extended researches, caused the importance of the law to be recognized by chemists.
The next events +n Gay-Lussac's scientific career are connected with what may be called his rivalry with Davy, who in matter of age (b. December 17, 1778) was almost exactly his contemporary. In 1808 when Davy, having isolated potassium and sodium, was awarded Napoleon's prize for the most important discovery in voltaic electricity, the emperor is said to have asked how it was that these discoveries were made abroad and French prizes were carried away. Having been informed that there was no battery of power equal to that used by Davy, he caused a very large one to be made, and presented it to the Ecole Polytechnique. While waiting for it, Gay-Lussac and Thenard succeeded in preparing potassium by a direct chemical, action, in which fused potash was brought in contact with red-hot iron. This method enabled chemists to prepare the alkali metals in quantity, ana Gay-Lussac and Thenard availed themselves of it to examine the properties of potassium very completely, and , not only so, but also to use it as a means of decomposing other substances. It was in this way that they separated boron from boracic acid, an element which was also prepared by Davy with the same materials. It is worth notice that Davy admitted the advantage of the method of Gay-Lussac and Thenard, though he seems to have subsequently regarded their appropriation of the newly-discovered metal as not altogether warranted.1 The researches with the great batterrafter it was made did not come up to their expectations ; the power fell far short of what had been anticipated, and they confined themselves rather to an examination of the phenomena presented by the apparatus itself, than to using it as an engine for effecting important decompositions.
In 1809 was published the second investigation parallel to one by Davy, namely, upon hydrochloric (or, as it was then called, muriatic) acid, and chlorine, then called oxymuriatic acid. This memoir was read to the Institute, and was also published in the second volume of the Memoires d'Arczreil. Gay-Lussac and Thenard describe a crowd of reactions they had tried for determining the characters of these bodies. They pointed out differences between the mnriatic and other acids, and indicated that the anomalies which it presented were explicable either on the hypothesis of water being an essential constituent of the acid, or on that of the oxymuriatic acid being a simple gas. At the end of their memoir, however, they decided in favour of oxymuriatic acid being compound, although they had failed to get oxygen from it by heating it with carbon. The explanation of this decision seems to be that, while they themselves were influenced to some extent by Lavoisier's oxygen theory of acids, some of the other members of the Arcueil Society, such as Laplace and Berthollet, were keen Lavoisierians, and were prepared to oppose any criticism which might lead to a modification of the great Frenchman's opinion on so vital a point. To admit the existence of an acid without oxygen might have led to a loss of the whole scientific position which France had gained by Lavoisier's defeat of phlogiston. Davy, who was not under the same influence, declared, as the result of his inquiries, that oxymuriatic acid gas was simple, and that therefore there may be acids without oxgyen. Sometime after, Gay-Lussac the only way of determining the composition of organic substances was to explode them with oxygen, and as this method was practicable only in the case of bodies which were gaseous, or could be readily volatilized, the great majority of fixed organic substances still remained unexamined. Gay-Lussac and Thenard introduced the plan of adding some oxidizing agent to the substance and burning it in a tube. They used chlorate of potassium, and the products of combustion were collected over mercury. The results obtained were in some cases very accurate, but the process was difficult of execution, and it is singular that the authors should have preferred it to combustion with oxide of copper, which they also tried. In 1815, however, Gay-Lussac employed the latter agent for the examination of cyanogen, and the other method was abandoned. The final improvements were made some years later by Liebig, when working in Gay-Lussac's laboratory. By their original method Gay-Lussac and Thenard determinedthe composition of -fifteen organic substances, including sugar, starch, gum, wax, oil, various woods, resin ; mucic, oxalic, tartaric, citric, and acetic acids ; and albumen, fibrin, gelatin, and casein. Gay-Lussac succeeded also, in 1811, in obtaining pure hydrocyanic acid. He described its physical properties, but did not announce anything about its composition till 1815, when he published his celebrated memoir in which he described cyanogen as a compound radical, prussic acid as a compound of this radical with hydrogen alone, and the prussiates as compounds of the radical with metals. He also showed how to prepare free cyanogen, and explained Berthollet's oxyprussic acid to be really chloride of cyanogen. The proof that prussic acid contains hydrogen and no oxygen was a most important support to the hydrogen acid theory, while the isolation of the radical cyanogen was of equal importance for the subsequent epoch of compound radicals in organic chemistry.
In 1813-14 Gay-Lussac published his memoirs on iodine. This was the third investigation which involved a rivalry with Davy, and it was also that about which there was most feeling. Courtois had discovered the substance in 1811, and had given some of it for examination to Clement-Dosormes. He had only published a brief notice of it when Davy arrived in Paris, having obtained express permission of Napoleon to pass through France on his way to Italy. Davy got a few fragments of this curious substance, and after a brief examination with a very limited portable laboratory which he had with him, perceived its analogy to chlorine, and drew the conclusion that it must be a simple body of similar character. Gay-Lussac, it is said, having heard of Davy-'s making experiments with it, went off to Courtois, got a specimen, and proceeded to examine it. He also saw its likeness to chlorine, but his previous decision respecting that body hampered him, and it was with some hesitation that he ultimately acknowledged its elemental character. Whether or not Gay-Lussac was actuated by the motive ascribed to him by Arago - that it would be a reflexion on French science were the settlement of the characters of this substance to be left to a foreigner visiting Paris - it is not necessary to enquire; but Davy seems to have felt that Gay-Lussac was competing, and not altogether fairly, with him. In a letter to Clement he gives a brief account of his work, and lays claim to the first revelation of the elemental character of iodine, and again in a subsequent letter to his brother, which contains a short review of the Parisian chemists and their reception of him, the only complaint he makes is that Gay-Lussac had played him a trick in trying to appropriate the discovery of the character of iodine and of hydriodic acid. Quite apart, however, from this claim on Gay-Lussac's part, the memoirs remain models of investigation and description. Davy quite freely admitted that full light might be expected on the subject from its having been taken in hand by so able and accurate a chemist as Gay-Lussac.
The year 1815 saw the completion of the research on cyanogen already referred to, and with it concludes the period of Gay-Lussac's most important discoveries. Having now attained a leading if not the foremost place among the scientific men in the French capital, his advice was often required on important questions. His attention was thus turned in part from purely scientific subjects to points of practical interest. In these new fields, however, he displayed the same powers which he had exercised so sedulously in the pursuit of scientific truth; in fact he was now to introduce and establish scientific accuracy where there had been previously only practical approximations. The most important of these later discoveries were the method of estimating the amount of real alkali in potash and soda by the volume of standard acid required for neutralization ; the method of estimating the amount of available chlorine in bleaching powder by a solution of arsenious acid ; directions for the use of the centesimal alcoholometer, published in 1824, and specially commended by the commission of the Institute appointed to report on it, as displaying all the accuracy and exhaustive treatment of the author ; and lastly, the perfecting of the method of assaying silver by a standard solution of common salt, a volume on which was published in 1833. This last has superseded the old method of assaying silver by cupellation, as being more rapid, more accurate, and easier of execution; and indeed all these processes are so complete and satisfactory, and are besides so identified with their author's name, that his reputation is secured by them, quite independently of his earlier work. In what has been said above, only the more important of Gay-Lussac's discoveries have been alluded to. To enter into an account, however brief, of all his labours, would occupy more space tkan can be allowed here. Indeed the list of his papers in the Royal Society's catalogue amounts to 148, besides those of which he was joint-author with Von Humboldt, Thenard, Welter, and Liebig ; and they embrace every department of the science as cultivated fifty years ago. Among his later researches may be mentioned those on fermentation, and those executed by Liebig in conjunction with him, after the young German chemist had gained the coveted admission to Gay-Lussac's private laboratory during the years 182324. The latter include improvements on organic analysis, and the examination of fulminic acid. Gay-Lussac continued his work, and published the results in the Annales de Chinzie, of which he had been joint-editor for some thirty years, up till almost his death, which took place at Paris on May 9, 1850.
Some of the appointments he held have been already referred to. After having acted as Fourcroy's demonstrator, he was made professor of chemistry at the Ecole Polytechnique. From 1808 to 1832 he was professor of physics at the Sorbonne, and he only resigned that office when he was made professor of chemistry at the Jardin des Plantes. Besides being on the commission of arts and manufactures, and the " administration " of gunpowder and nitre, he was appointed assayer for the mint in 1829. In 1831 he was elected to the chamber of deputies as member for Haute Vienne, and finally, in 1839, entered the chamber of peers.
Gay-Lussac's scientific work is remarkable not only for its range but for its intrinsic worth, its accuracy of detail, its experimental ingenuity, its descriptive clearness, and the soundness of its inferences. He did not hesitate to criticize his own results, and replace them by others more accurate either of his own or of another's discovery ; he improved and invented physical and chemical apparatus : the barometer, thermometer, cathetometer, alcoholometer, and the burette, which still bears his name, all bear witness to his ingenuity and practical skill. He devised new analytical methods ; he discovered new substances, such as fluoride of boron, and iodic, hydrosulphocyanic, dithionic, and hyposulphurous acids ; he enlarged and corrected the knowledge of those already discovered ; he examined the physical conditions of chemical action ; he searched into the causes of chemical combination and chemical change. That he had the power of grasping the law underlying a few facts is nowhere more evident than in the memoir on gaseous combination, his most important contribution to science. That he missed the opportunity of assigning the chief limit to Lavoisier's hypothesis, must be ascribed partly at least to the influence of others. Authority decided it, perhaps against his secret convictions.
From Arago's and other notices one gathers that Gay-Lussac was reticent, patient, persevering, accurate to punctiliousness, perhaps a little cold and reserved, and not unaware of his great ability. But he was also bold and energetic, not only in his work, but equally so in defence and support of his friends. His earliest childish adventures, as told by Arago, herald the fearless aeronaut and undaunted investigator of volcanic eruptions. The endurance he exhibited under the laboratory accidents which befell him shows the power of will with which he could face the prospect of becoming blind and useless for the prosecution of the science which was his very life, and of which he is one of the most distinguished ornaments. It was only at the very end, when the disease from which he suffered left him no hope, that he complained with some bitterness of the hardship of leaving this world when so many discoveries were making, and when so many more were likely to be made.
The more important of Gay-Lussac's papers are scattered through journals difficult of access. The most complete list of them is contained in the Royal Society's catalogue of scientific papers ; lists are also given at the end of Hocfer's article in the Biographic Generale, and in Poggendorff's Blographisch-literarisches Handworterbuch,, Leipsic, 1863. Accounts of various portions of GayLussac's discoveries and views will be found in such works as Thomson's History of Chemistry, vol. ii., London, 1830 ; Kopp's Gcschichte der Chemie, Brunswick, 1843-47; Kopp's Entwickcl• sing der Chemie, Munich, 1871 ; Dumas, Lecons sur la Philosophle Chimique, Paris, 1837, and reprinted Paris, 1878 ; Ladenburg, Vortrage fiber die .12,i dwickelungsgeschiehte der Chemic, Brunswick, 1869 ; Forbes, A Review of the Progress of Mathematical aril Physical Science in more recent times, Edinburgh, 1858. The chief authorities for the life of Gay-Lussac are Arago (lEus-res, Paris, 1855, t. iii.); Biot (Abstracts, Royal Society, vol. v., 1843-50, p. 1013); P. A. Cap (Le Museum d'Histoire Naturelle, Paris, 1854, pt. 1, p. 137). (J. F.)