GAY-LUSSAC 185 



posts and professorships of chemistry and physics, and also 

 other pubhc offices, which brought him great pubhc recogni- 

 tion. He died at the age of seventy-two, in Paris. 



Best known of his work is the law named after him, which 

 states the equal expansion by heat of all gases, and which he 

 discovered simultaneously with Dalton, by performing ex- 

 periments, just as the latter did, for the first time in a proper 

 manner, with a number of the different kinds of gas then 

 known. The fact that the co-efficient of expansion measured 

 by him, as also by Dalton, turned out a little too large (as we 

 know to-day), was obviously caused by the property of glass 

 vessels, then still unknown, of holding water condensed on 

 their surfaces with great tenacity, and it does not in the least 

 diminish the value of the discovery of this peculiarity re- 

 garding the gaseous state, namely that all kinds of matter 

 show the same behaviour without distinction. 



Gay-Lussac's work, performed partly in collaboration with 

 Humboldt, also related to gases, being an investigation of the 

 relationship by volume in which gases enter into chemical 

 combination with one another. He first, in 1795, investi- 

 gated the combination of hydrogen and oxygen to form 

 water, in the manner discovered twenty-four years previously 

 by Cavendish, who was then still alive, and whose data as 

 regards volume already showed at least approximately the 

 ratio 2 : i for the two gaseous components.^ Gay-Lussac 

 and Humboldt found that when they allowed the two gases, 

 mixed in correct proportions, to explode by electric spark in 

 Volta's 'eudiometer,' that this simple relationship holds with 

 striking accuracy. After this, Gay-Lussac alone investi- 

 gated, in 1808, a very considerable number of further pro- 

 cesses of gaseous combination, such as the union of 

 hydrochloric acid gas and ammonia gas, of carbon dioxide 



1 Even Volta already had stated that hydrogen and oxygen give the best 

 explosive mixture when mixed in this proportion; only no one knew pre- 

 viously to Cavendish's work that the result of the explosion was water. 



