550 JEAN-BAPTISTE-ANDR^ DUMAS. 



although ho spoke with the highest praise of his experimental skill. 

 At that time Dumas showed no signs of impaii-ed strengtii. But 

 durinfT the following year his health began to fail, and he died on the 

 11th of April, at Cannes, where he had sought a retreat from the 

 severity of the winter climate of Paris. 



Dumas was one of the few men whose greatness cannot be estimated 

 from a single point of view. lie was not only eminent as an investiga- 

 tor of nature, but even more eminent as a teacher and an administrator. 

 Beginning the study of chemistry at the culmination of the epoch of 

 the Lavoisierian system, and regarding, as he always did, tlie author 

 of that system with the greatest admiration, he nevertheless was the 

 first to discover the weak point in its armor and inflict the wound 

 which led to its overthrow. Without attempting to detail Dumas's 

 numerous contributions to chemical knowledge, we will here only refer 

 to three important investigations, which produced a marked influence 

 in the progress of chemical science. 



While still in Geneva, Dumas, as has been said, made numerous 

 determinations of the densities of allied substances, with a view to dis- 

 covering the relations of what he called their molecular or atomic 

 volumes ; and it is no wonder to us that the problem proved too 

 complex to be solved at that time. After his removal to Paris he 

 took up the much simpler problem which the relations of the mo- 

 lecular volumes of aeriform substances present, and his paper " On 

 Some Points of the Atomic Theory," which was published in the 

 Annales de Chlmie et de Physique for 182G, had an important influ- 

 ence in developing our modern chemical philosophy. Gay-Lussac had 

 previously observed, not only that the relative weights of the several 

 factors and products concerned in a chemical process bear to each 

 other definite proportions, but also that, when the materials are aeri- 

 form, the relative volumes preserve an equally definite and still simpler 

 ratio. Moreover, on the physical side, Avogadro, and afterwards 

 Ampere, had conceived the theory, that in the state of gas all mole- 

 cules must have the same volume. It was Dumas who first saw 

 that these principles furnished an important means of verifying the 

 molecular and atomic weights. 



" I am engaged," he writes, " in a series of experiments intended to 

 fix the atomic weights of a considerable number of bodies, by determin- 

 ing their density in the state of gas or vapor. There remains in this 

 case but one hypothesis to be made, which is accepted by all phj'sicists. 

 It consists in supposing that, in all elastic fluids observed under the 

 same conditions, the molecules are placed at equal distances, i. e. 



