WORK OF VAn't HOFF — BKUiTI. 787 



of the three fundamental publications which bear on these contained 

 all the essential parts of the respective theory not only in germ but 

 sufficiently developed and demonstrated. 



This creator of theories, this man who gave science so many new 

 ideas, was nevertheless a stranger to all metaphysics, to every exag- 

 geration; he was not one of those who, into whatever domain they 

 enter, wish at any price to create a general system which embraces 

 all the universe, which shall comprise all important and unimportant 

 facts, existing and not existing. Though a generalizing and syn- 

 thetic mind, he was never abstract nor schematic. We see this also 

 in the lectures in which the theories are almost always set forth, not 

 in an abstract fashion, but resting upon concrete examples. 



This tendency of his mind explains his attitude with regard to the 

 theory of phases, and this point is one of the most curious in the 

 scientific life of van't Hoff. It is Imown that the phase rule is con- 

 tained in the great work of Willard Gibbs, published between 1874 

 and 1878 in the Proceedings of the Connecticut Academy; but it re- 

 mained unknown for about 10 years, until van der Waals mentioned 

 its importance in a private conversation with Bakhuis Eoozeboom, 

 who had already commenced his researches on heterogeneous equi- 

 librium. Eoozeboom for the first time adopted the phase rule for 

 the classification of heterogeneous equilibriums in 1887, three years 

 after the publication of " Etudes de dynamique chimique.'- Now, in 

 the part relating to heterogeneous equilibriums, to condensed sys- 

 tems, to double salts, etc., the studies of van't Hofi" have already pene- 

 trated from one end to the other of the understanding of the theory 

 of phases ; they are the theory of phases in action, and he laclis only 

 the definite schemes, for Gibb's phase rule is, at bottom, nothing else. 



It is psychologically comprehensible that van't Hoff had conceived 

 a certain aversion for this theory, an aversion which he never gave 

 up; he spoke of it reluctantly, and never used it in his treatises. It 

 was only in 1902 that he decided to present to the Chemical Society 

 of Berlin a recapitulatory address on this subject, an address in 

 which, besides a clear and objective statement of the theory and of 

 its applications, are found these phrases, which translate his thought 

 or rather his sentiment: "It is regrettable that, whatever may be 

 the importance of the phase rule, the appreciation of its value has 

 been somewhat exaggerated. Many things are attributed to it which 

 are not due to its application. The great importance of the phase 

 rule rests less in the value which it may have as a guide in research 

 than in the pedagogic value which it presents whenever it is a ques- 

 tion of treating and classifying the phenomena of equilibrium," 



Now, this does not seem to me quite exact, and I may say that that 

 is the only point in which I find that van't Hoff is a little lacking in 

 justice and yields unconsciously to a weakness. That the theory of 



