324 PHYSICAL PROPERTIES 



alcohol- or glycerol-water mixtures exhibit. Thus we have seen, 

 in Chapter XI, that the mobilities of caseinate ions in alcohol- 

 water mixtures are almost exactly in inverse proportion to the 

 viscosity of the solvent, and this despite the fact that the viscosity 

 of the solvent, measured by the time which it takes to run through 

 a capillary tube, is so profoundly influenced by the introduction of 

 the caseinate itself as to be in many cases, doubled in magnitude. 

 Solutions of KCl in alcohol-water mixtures are, comparatively 

 speaking, unaltered in their viscousness by the KCl, yet the 

 dependence of the conductivities of solutions of potassium casein- 

 ate upon the percentage (between and 60 per cent) of alcohol 

 which they contain obeys exactly the same law as that which 

 applies to the conductivity of KCl solutions in alcohol-water 

 mixtures, a law which implicitly involves the conclusion that the 

 total effect is due solely to the alteration in the mobilities of the 

 ions attributable to the viscousness of the solvent. To make 

 the matter clear by reference to a numerical example: Referring to 

 the tables in Chapter XI we see that the viscosity of N/10 KOH 

 (dilute alkali) is doubled by the introduction of 3.125 per cent of 

 casein; halving the concentration of the solution, according to 

 Sackur's results cited above, must more than halve the effect of the 

 caseinate upon its viscousness; yet the mobilities of the caseinate 

 ions are unaltered by this. The viscosity of the solvent can be 

 also doubled by the introduction of 40 per cent alcohol and this, 

 on the contrary, halves the mobility of the caseinate ions. The 

 alcohol considerably modifies the degree to which the caseinate 

 alters the viscousness of the solvent, yet this fact does not at all 

 disturb the regularity of the relation between the viscosity of the 

 solvent and the mobility of the caseinate ions which are dissolved 

 therein. In estimating the influence of viscosity upon the mobilities 

 of caseinate ions we can entirely disregard that portion of the viscosity 

 of the solution which, although comparable in magnitude with the 

 viscosity of the solvent, is attributable to the caseinate itself. 



Bearing in mind the possibility, which was indicated in the 

 previous chapter, that protein solutions may contain a pre- 

 formed molecular structure analogous to that of the jellies or 

 coagula which they can form, we are strongly impelled towards 

 the belief that the type of viscosity which solutions of proteins 

 exhibit may in some manner owe its existence to this structure, 

 and not to the type of internal friction which hinders molecular 



