142 DISCUSSION OF EVIDENCE. 



amounts of acetic acid were also determined. By comparing the three 

 sets of results, from Raoult's law we could calculate the composition 

 of the hydrates formed by the sulphuric acid, if any were formed. 



We added large amounts of water relative to the sulphuric acid, 

 but could obtain no evidence of any hydrate of sulphuric acid more 

 complex than H 2 S04,2H 2 O, which is the well-known compound H 6 S0 6 . 

 We did not obtain the slightest evidence of the existence of any of the 

 more complex hydrates which Mendeleeff, from his work, had supposed 

 to exist. I was, therefore, at that time, thoroughly convinced of the 

 untenability of the Mendeleeff theory of hydrates, and, indeed, of any 

 theory of hydration. I regarded the ions in solution as having an 

 existence not only independent of one another, but also independent 

 of the molecules of the solvent. In a word, I was at that time firmly 

 convinced that no theory of hydration was necessary to explain the 

 facts that were then known. This seemed to be the view which was 

 held at that time also by most of those who founded the new school 

 of chemistry. 



A comparatively few years later, my cooperators, Ota 1 and Knight, 2 

 brought to light certain facts which could not be explained in terms of 

 any relation that was then known. They found that certain double 

 salts, such as double chlorides, nitrates, sulphates, cyanides, etc., pro- 

 duced abnormally great lowering of the freezing-point of water when 

 the solutions were concentrated. What was more perplexing was the 

 fact that the molecular depression of the freezing-point increased with 

 the concentration beyond a certain definite concentration. 



Similar results were found for a fairly large number of salts by Jones 

 and Chambers, 3 and by Chambers and Frazer working with Jones. 4 

 The salts studied by these workers were those that are known to be 

 very hydroscopic, to have great power of combining with water. The 

 question arose, what did these results mean? At that time I was 

 antagonistic to any hydrate theory. My experience in the laboratory 

 of Arrhenius had produced that state of mind; yet I was unable to 

 explain our results in terms of any other assumption than that a part 

 of the water present was combined with the dissolved substance, and 

 was therefore removed from playing the role of solvent. I ventured 

 this suggestion, for want of any better in 1900. 5 



The suggestion of hydration in aqueous solution would explain the 

 results that had been obtained. If a part of the water present was 

 combined with the dissolved substance, there would be less water act- 

 ing as solvent ; and since freezing-point lowering is proportional to the 

 ratio between the number of molecules of the solvent and of the dis- 

 solved substance, the less solvent present the greater the lowering of 

 its freezing-point. It is one thing to make a suggestion which accounts 

 for the known facts; it is a very different matter to show that this is 



1 Amer. Chem. Journ., 22, 5 (1899). 3 Ibid., 23, 89 (1900). *IbM., 23, 103 (1900). 



z IUd., 110 (1899). *Ibid., 512 (1900). 



