JACQUES LOEB 383 



transformed into a salt with monovalent anion or cation, all those 

 properties which depend upon the number of gelatin molecules in 

 solution increase with the proportion of gelatin salt formed, the 

 maximum being reached when all the insoluble gelatin is trans- 

 formed into soluble gelatin salt. This explains the paralleHsm 

 between the curves for the bromine number of gelatin treated with 

 HBr and the curves for the osmotic pressure of the solution. 

 These molecular data must explain also the paralleHsm between the 

 curves for viscosity and swelling with that of the bromine number. 

 The view taken in this paper that the osmotic pressure of protein 

 solutions obeys the laws of classical physical chemistry is shared by 

 one of the greatest authorities in this field, namely Sorensen.^ 

 Sorensen worked on egg albumin of a well defined composition 

 which necessitated the investigation of the osmotic pressure of 

 gelatin in the presence of ammonium sulfate. In spite of the great 

 theoretical and experimental difficulties, which only a master like 

 Sorensen could succeed in overcoming, he arrived at constant values 

 for the osmotic pressure and the molecular weight of egg albumin. 

 He states: 



"The properties of colloidal solutions can be most efficiently inquired into by 

 application, as far as possible, of the same views and methods as those generally 

 applied to true solutions. . . . ^^ 



"Colloidal chemistry in the shape which has been given it by its energetic 

 champion Wo. Ostwald offers, no doubt, to protein study a system organized with 

 great talent, but exact experimental investigation has not been able to keep up 

 with the systematic treatment, and therefore the value of the contents does not 

 always correspond with the perfection of the system itself. Thus I disagree with 

 Ostwald, who . . . warns us against a comparison of the circumstances in col- 

 loidal and real solutions. In the case of albumin solutions, and doubtless also 

 several other typical emulsoid systems, such a comparison between the proper- 

 ties of the colloidal solution and those of a real solution is of the greatest sig- 

 nificance for the right understanding of the character of the colloidal solution. 

 Indeed, I think it is even possible to go one step further and to say that the study 

 of real solutions may derive considerable advantage from the results which an 

 exact research of well-defined protein solutions can give, the colloidal character 

 of these permitting the use of research-methods — I refer especially to the use of 



^ Sorensen, S. P. L., Compt. rend. trav. Lab. Carlsherg, 1911 , xii. 

 ^^ Sorensen, Compt. rend. trav. Lab. Carlsberg, 1917, xii, 369. 



