CHAPTER VII. 



DISCUSSION OF EVIDENCE ON THE SOLVATE THEORY OF SOLUTION 



OBTAINED IN THE LABORATORIES OF THE JOHNS 



HOPKINS UNIVERSITY. 1 



About fifteen years ago the work which led to the present theory of 

 solution was begun in this laboratory. From a very simple begin- 

 ning, which did not have for its object the study of the nature of 

 solution in general, the work has widened in a fairly large number of 

 directions. There have already been published by my co-workers 

 and myself about eighty papers dealing with one or another phase 

 of the problem. These are fairly widely scattered through chemical 

 and physical literature, having been published in American, German, 

 French, and English scientific journals. In addition, the Carnegie 

 Institution of Washington, which has so generously supported the 

 work, and without which it would have been impossible to have car- 

 ried out many of the investigations, has published nine monographs 

 of researches bearing directly and indirectly on the question of the 

 nature of solution. 



Taking all of these facts into account, it has seemed desirable to 

 discuss here, as briefly as possible, the more important lines of evidence 

 which have been brought out, bearing on the nature of that condition 

 of matter which gives rise to the sciences of chemistry, geology, and 

 to a large part of biology. 



EARLIER WORK. 



In the summer of 1893 I went to Stockholm to work with Svante 

 Arrhenius. He suggested that we carry out a research on the question 

 as to whether sulphuric acid forms a few definite hydrates when in the 

 presence of water, as the theory of Mendeleeff maintained. According 

 to this theory, some of these hydrates were very complex, one of 

 them containing as much as 100 molecules of water to 1 molecule of 

 sulphuric acid. Mendeleeff arrived at this conclusion chiefly from a 

 study of the specific gravities of aqueous solutions of sulphuric acid of 

 different concentrations. The specific-gravity curves showed certain 

 discontinuities or breaks, which Mendeleeff interpreted to mean the 

 existence of definite chemical compounds or hydrates. 



At the suggestion of Arrhenius, I studied the problem in the following 

 way. Acetic acid was used as the solvent. The freezing-point lowerings 

 of the acid produced by adding different known amounts of water were 

 determined. The freezing-point lowerings produced by adding known 

 amounts of sulphuric acid to pure acetic acid were measured. The 

 freezing-point lowerings produced by adding, simultaneously, known 

 amounts of sulphuric acid and known amounts of water to known 



'See paper in Journ. Franklin Institute, Nov. and Dec. 1913. 



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