PREFACE. 



This investigation is the outcome of an observation made in this labora- 

 tory in connection with an entirely different line of work. A Japanese, 

 Ota, was working on the condition of certain double salts in the presence 

 of water, to ascertain whether they existed as such, to any appreciable 

 extent, or were broken down by the solvent into the constituent molecules. 

 As soon as he began to work with concentrated solutions, he found that 

 these solutions froze abnormally low ; the molecular lowering passing through 

 a well-defined minimum with change in concentration. Similar results were 

 obtained a little later by Dr. Knight, also working in this laboratory. 



There was nothing in the theory of solutions then in vogue to account 

 for such results the molecular lowering should decrease continually from 

 the most dilute to the most concentrated solution. This was obviously a 

 remarkable phenomenon, especially if it should be shown to manifest itself 

 in the case of any large number of substances. 



With the aid of three Grants generously awarded by the Carnegie Insti- 

 tution of Washington, this investigation has been extended step by step 

 to about one hundred substances; including typical acids, bases, salts, 

 and neutral organic compounds. The result has been to show that this is 

 a general property of solutions, manifesting itself to a greater or less extent 

 for nearly all of the substances studied. 



Having established the general fact, it remained to ascertain its meaning. 

 A possible explanation that occurred to me early in the investigation 

 was that in solution a part of the solvent is combined with the dissolved sub- 

 stance, and no longer plays the role of solvent, at least as far as the freezing- 

 point method is concerned. As the concentration of the solution increased, 

 more and more of the solvent would be held in combination by the dissolved 

 substance. This suggestion would account for the experimentally estab- 

 lished facts. It, however, remained to show that it was true. 



No less than four distinct lines of evidence have been furnished experi- 

 mentally, all of which point to the correctness of this theory. Perhaps the 

 most important of these, and the most general, is the relation between 

 lowering of freezing-point and water of crystallization. This relation is 

 so unmistakable, and bears so directly on the problem, as we shall see, 

 that it is difficult to lay too much stress upon it. 



The relation between amount of water of crystallization and temperature 

 is also very significant in the present connection, as well as the evidence 

 from the study of the absorption spectra. 



i 



