782 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1913. 



of coarse dispersions into true solutions in the strictest sense, and 

 have given for the first time a plausible demonstration of the real 

 existence of molecules, and thence of the kinetic nature of gaseous 

 and osmotic pressures. 



But let us return to our subject. In 1890 van't Hoff published a 

 very interesting extension of his theory. He showed that it can be 

 applied equally to the solid homogeneous mixtures of the nature of 

 isomorphous mixed crystals, and founded thus the theory of solid 

 solutions to the development of which the writer can congratulate 

 himself on having contributed. 



In the further development of the theory of solutions by experi- 

 mental studies, van't Hoff took no more part, confining himself to 

 making it public with the aid of recapitulations and explanatory arti- 

 cles and of conferences. He did not, however, abandon experimental 

 work, which he followed with untiring assiduity, though he reserved 

 this side of his activity for the other group of questions treated in 

 his " Etudes de dynamique chimique," for heterogeneous equilibri- 

 ums and condensed systems. 



This domain had already been treated, particularly as to the phe- 

 nomena of dissociation, by a brilliant French school which began 

 with St. Claire Deville and ended with Le Chatelier, and another 

 Dutch school, headed by Bakhuis Eoozeboom, starting with only 

 slightly different ideas, began to work in the same direction. 



Van't Hoff and his pupils busied themselves first of all with the 

 conditions of formation and of decomposition of double salts in 

 aqueous solutions by devoting their attention on the one hand to 

 compounds such as Astrakanite and Carnallite, which are minerals 

 found in nature, and on the other hand to the racemates, thus again 

 studj^ing stereochemical questions. The results have been collected 

 in a little book entitled " Vorlesungen iiber Bildung und Spaltung 

 der Doppelsalze," published in 1897, one of the least Imown books of 

 our scientist, because of the nature of the subject, which, although of 

 great importance, is of such an abstruse character that it can be 

 treated only in a somewhat dry fashion. 



This group of works covers the decade fi'om 1886 to 1895, the 

 second period of van't Hoff's stay in Amsterdam. 



We now come to the Berlin period of his activity, devoted entirely 

 to the application of principles and methods previously discovered, 

 to the investigation of the conditions of formation of oceanic de- 

 posits and particularly of the famous deposits of Stassfurt. In this 

 work, which was the first, and remains the greatest, attempt to apply 

 physical chemistry to the problems of geolog}^ and to transform the 

 latter, so far as possible, into an experimental science, he had 

 Wilhelm Meyerhoffer as a constant collaborator for 10 years, until 

 his untimely death, in 1906, at the early age of 42 years. 



