WORK OF VAN T HOFF — BRUNI. 775 



light in 1884. This book was filled with the spirit which henceforth 

 was to inspire all the productions of van't Hoff. 



The author attempted in it to apply, so far as possible, mathe- 

 matical methods, and, above all, the principles of thermodynamics, 

 to the study of chemical phenomena. The idea in itself was not new : 

 20 years before that Clausius had pointed out the possible application 

 of these principles, especially of the second, but he had given no 

 concrete examples of it. It is true there was also in existence the 

 work of Willard Gibbs, but it was still lying like a. colossal block of 

 granite buried in the proceedings of an obscure American academy, 

 ignored by scientists, certainly by all chemists. The only attempts 

 of any importance at its application were those of Horstmann and 

 Peslin and Moutier to the phenomena of dissociation. 



The work of van't Hotf was much more considerable and sys- 

 tematic, and since the author, like a true chemist, carries abreast 

 theoretical study and experimental verification, this work exercised 

 a preponderant influence by making known to chemists the methods 

 and principles of this new branch of science. 



He studied principally the velocity of reactions, selecting the most 

 varied types of changes, reducing to order their laws, and seeking to 

 discover in what measure the methods of chemical kinetics are ap- 

 plicable to the determination of the order of the reactions. He 

 invented the most ingenious methods to discover general laws when 

 the latter are concealed by disturbing secondary reactions, which he 

 eliminated in both experiment and calculation. He finally studied 

 the variations which the velocity of reaction undergoes under the 

 influence of the temperature. 



From there he passes to the consideration of chemical equilibrium, 

 viewed as the result of two inverse processes, and concerns himself 

 first of all with homogeneous equilibriums in gases or solutions. He 

 gives special attention to heterogeneous equilibriums and more espe- 

 cially to those which he calls condensed systems — that is, systems in 

 which no bodies of variable composition, such as gases or solutions, 

 intervene. He recognizes that in these cases, instead of having a 

 continual displacement of the equilibrium, one has a transition tem- 

 perature such that one of the systems is stable above this point, the 

 other below. The transition temperature had been Imown for a long 

 time in the polymorphic modifications of one and the same substance, 

 as in those of rhombic and monoclinic sulphur; but the author 

 generalizes this concept, and shows that one can extend it to the 

 reciprocal transformation of chemical isomers, to the dehydration of 

 hydrated salts, to the formation of decomposition of double salts, etc. 



Discussing, then, the displacement of equilibrium which is pro- 

 duced by variations of temperature, he announces for the first time 



