268 ELECTROCHEMISTRY 



to 60 per cent alcohol and rapidly decreases between 60 and 

 75 per cent alcohol, is especially confirmatory of this view. 



It will be noted that the viscosity of the solvent is notably 

 increased by the addition of the concentrations of casein em- 

 ployed, and this effect, of course, must vary very considerably 

 with the dilution; yet the Ostwald law holds good, and despite the 

 fact that the dissolved substance itself very materially affects the 

 viscosity of the solutions, it is the viscosity of the solvent alone which 

 determines the mobility of the protein ions. We can only conclude 

 from this that that portion of the viscosity of the solution which 

 is attributable to the caseinate itself does not in any appreciable 

 degree interfere with the mobility of the protein ions. The signif- 

 icance of this fact will be more fully discussed in Chap. XIII. 



6. The Molecular Condition of Potassium Caseinate in 75 

 Per Cent Alcohol. We have seen that the behavior, optical,* 

 and electrical, of potassium caseinate dissolved in alcohol-water 

 mixtures, undergoes an abrupt change in passing from 60 to 

 75 per cent alcohol-content. The degree of dissociation, which 

 is but little affected by lower concentrations of alcohol, under- 

 goes a profound diminution in 75 per cent alcohol, and the 

 opacity of the solution undergoes a concurrent increase. The 

 phenomena suggest the possibility that this concentration of 

 alcohol leads not only to the formation of anhydrides of the 

 protein and therefore, as explained in Chaps. I and VI, to a dimi- 

 nution of the degree of dissociation, but also to a polymerization 

 of the protein, as outlined in equations (i) to (iv) in Chap. VI. 

 This polymerization might, very conceivably, be accompanied 

 by an increase in the weight of casein involved in the transport 

 of one atomic charge. Accordingly, experiments were under- 

 taken with a view to ascertaining the effect of increasing alcohol- 

 content of the solvent upon the electrochemical equivalent of 

 casein. 



The experiments were carried out in the manner described 

 in Chap. VIII, upon solutions containing 50 and 75 per cent of 

 alcohol, made up in the manner described above. The altera- 

 tions in the percentage casein-content of the solutions due to 

 deposition of the casein upon the anode, was estimated from the 



* Not only is the opalescence of the solution greatly increased but also the 

 change in the refractive index of the solvent due to the introduction of one 

 gram of casein per 100 c.c. is considerably diminished (Cf. Chap. XIV). 



