254 CHEMISTRY OF THE PROTEIDS CHAP. 



THE GENERAL PHYSICAL PROPERTIES OF ALBUMINS (ACCORDING TO 



THE AUTHOR) 



The question of the physical state of albumins is so important 

 from the biological and chemical points of view that the author has 

 thought it best to give his own views in a connected manner, although 

 he has dealt with them more fully (up to the year (1901-2) in his 

 Physiological Histology. In the following account cognisance is, how- 

 eveiytaken of papers bearing on the colloidal nature of substances which 

 have been published in the last three years. 



For purposes of discussion it is necessary to have a clear under- 

 standing as to the meaning of ' solution,' ' electrolyte,' ' hydrolyte,' 

 and * colloid,' and therefore these terms are denned in the first 

 instance. 



SOLUTION. A substance, on coming into contact with a fluid, is 

 said to pass into solution when its molecules separate from one 

 another and, diffusing into the fluid, mix with the molecules of the 

 latter. The resulting mixture, consisting of the molecules of the 

 solvent and the solute, 1 may form so homogeneous a system as not to 

 interfere in any way with the transmission of light, or, to use a 

 technical term, the mixture may be 'optically void,' i.e. contain no 

 visible particles. On the other hand, the solute may consist of 

 particles of such size as to interfere more or less with the transmission 

 of light, when we speak of 'colloidal' solutions (see below) or of 

 suspensions. All solutions are therefore mixtures. 



A substance in solution, as van 't Hoff has shown, is in every way 

 comparable to a gas. There is, however, one difference, for in the 

 case of an ordinary gas the amount contained in the fluid is propor- 

 tional to the amount of the same gas outside the fluid, or, in other 

 words, the gaseous tension in the fluid is proportional to the partial 

 pressure exerted by the gas outside the fluid. In the case of dissolved 

 solids, however, the solid cannot leave the fluid, because the very fact 

 of a substance dissolving at all depends on definite electro-chemical 

 interactions between the solvent and the substance dissolving, as has 

 been shown by Briihl. 2 According to this observer, the power of 

 acting as a solvent depends on the latter possessing some atom which 

 is potentially plurivalent ; for example, oxygen in water is divalent, 

 but capable of becoming tetravalent ; 7 , the nitrogen of ammonia is 

 trivalent, but with a tendency to become pentavalent, and so on. To 

 this must be added the conception that the body passing into solution 



1 A solute is any substance which has passed into solution. 

 2 J. W. Briihl, Zeitsch. f. physik. Chem. 1O. 1 (1899). 



