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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. Vhile waiting for it, Gay—Lussae and Thénard 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, and Gay—Lussae and Thénard 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—Lussae and Thénard, though he seems to have subsequently re- garded their appropriation of the newly—discovered metal as not altpgether warranted.‘ The researches with the great battery“after it was made did not come up to their expecta- tions ; 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 oxymuriatie acid. This memoir was read to the Institute, and was also published in the second volume of the Jlfémoires d’Arcuez'l. Gay—Lussae and Thénard describe a crowd of reactions they had tried for determining the characters of these bodies. They pointed out differences between the muriatic 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 ex- planation 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 Berthollct, were keen Lavoisierians, and were prepared to oppose any criticism which might learl 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 oxy- muriatic acid gas was simple, and that therefore there may be acids without oxgyen. Sometime after, Gay-Lussac and Thénard agreed with this view, which they could do with less hesitation, as they had themselves indicated it in their own memoir. Among the investigations which Gay-Lussac under- took with Thénard in the years 1810-1811, and which ultimately yielded most valuable results, must be men- tioned those upon organic chemistry, and especially upon the analysis of fixed organic compounds. Before this time 1 Gay—Lussae and Thénard made no claim, of co11rse, to the dis- covery of potassium and sodium, though several important discoveries followed from their experiments. Thus, in addition to boron, they got also the fluoride of boron; and by the rapid combustion of the alkali metals in dry oxygen they got their peroxides, by means of which Thénard subsequently prepared the peroxide of hydrogen. At first, however, they seem to have thought that the alkali metals contained hydrogen, and it was not for a couple of years that they accepted Davy's view of their simplicity. Indeed, about this time there appears to have been considerable uncertainty about the elemental character of the metals, it being thought that they contained hydrogen, an idea which, on account of its retrograde nature, was criticized by Davy as a kinl of phlogistic revival. m GrAY—LUSSAC 123 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 unex- amined. Gay-Lussac and Thénard 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 methodGay-Lussac and Thénard determinedthe composition of ‘fifteen organic substances, including sugar, starch, gum, wax, oil, various woods, resin 3 mucic, oxalic, tartaric, citric, and acetic acids; and albumen, fibrin, gelatin, and casein. Gay—Lussae 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 1 813-14 Gay—Lussae 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 Clément-Désormes. 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—Lussae 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- Lussae was competing, and not altogether fairly, with him. In a letter to Clément he gives a brief account of his work, and lays claim to the first revelation of the elemental char- acter 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—Lussae 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 inves- tigation and description. Davy quite freely admitted that

full light might be expected on the subject from its