322 PHYSICAL PROPERTIES 



ate which is neutral to phenolphthalein the added alkah does not 

 remain unneutrahzed, as Sackur assumes, but, on the contrary, 

 is partially bound by the casein until 180xl0~^ equivalents are 

 combined with every gram of casein. But we have also seen 

 (Chap. IX) that each successive equivalent of combined alkah 

 splits another — NHOC— bond in the casein molecule and con- 

 sequently gives rise to another pair of ions. With increasing 

 content of combined base, therefore, the caseinate, apart from 

 slight modifications of its degree of dissociation, yields a corre- 

 sponding proportion of ions. The fact that the viscosity of 

 caseinate solutions markedly increases with alkalinity is therefore 

 in strong support of Sackur's thesis that the viscosity of these 

 solutions is primarily attributable to protein ions, although not 

 for the reasons which he advances. The fact that the increase in 

 viscosity with increasing alkalinity attains a maximum at just 

 about the same time that the combining capacity of the casein 

 attains a maximum (Cf. above table and the tables and diagram 

 in Chap. IX) lends very striking support to this hypothesis. 



The view that the viscosity of protein solutions is in a remark- 

 ably high degree dependent upon the protein ions which they 

 contain has also been advanced, with substantial experimental 

 support, by W. B. Hardy (41) and by Bottazzi (14). The latter 

 observer has shown that the viscosity of protein solutions is at a 

 minimum when ionic protein is absent, when the protein is un- 

 combined with base or acid, and that on adding either acids or 

 bases to this solution the viscosity increases. 



Now a very little consideration suffices to show that the viscosity 

 of protein solutions is of a different type from the viscosity, for 

 example, of solutions of sugar or glycerol in water. Apart from 

 the extraordinary magnitude of A, alluded to above, the type of 

 viscosity exhibited by solutions of proteins differs from the vis- 

 cousness of a glycerol-water mixture in that it affords no hindrance, 

 or very slight hindrance, to the motion of ions and of crystalloid 

 molecules. The properties of agar are, in this respect, very similar 

 to those of protein. Thus Graham (35) showed that the velocity 

 with which crystalloids diffuse through gelatin jellies is remarkably 

 near to that with which they diffuse through water, and Voigt- 

 lander (126) has confirmed this result for agar jellies. Similar 

 results have been obtained by Hiif ner (47) . According to Bechhold 

 and Ziegler (6) the rate of diffusion of (at any rate concentrated) 



