REFRACTIVE INDICES 



361 



employed and represents the change in the refractive index of the 

 solvent which is brought about by dissolving one gram of the 

 protein in 100 cc. 

 The following results are illustrative : * 



TABLE III 

 Solvent 0.10 A/" NaOH 



In the first column of the table is given the amount of casein in 

 grams which was dissolved in 100 cc. of the solution. In the 

 second column is given the refractive index of the solution meas- 

 ured at 20° C. In the third is given the value of the constant a 

 calculated from the above formula for the given value of the 

 constant ui (i.e., the refractive index of the solvent, previously 

 determined at the same temperature). 



The equation n — rii = a X c also holds good for solutions of 

 ovomucoid in water (44), of paranuclein in N/10 KOH (45), of 

 potassium serum globulinate (46), of potassium caseinate in 

 alcohol-water mixtures (47), of gliadin in various solvents (54) and 

 of edestin in aqueous solvents (56), 



The change in the refractive indices of aqueous solvents which 

 is brought about by a given percentage of casein is independent of 

 the nature of the acid or base with which the casein is combined. 

 This is shown by the fact that this change is the same whether the 

 casein be dissolved in dilute KOH, NaOH, LiOH, NH4OH, 

 Sr(0H)2, Ba(0H)2, Ca(0H)2 or HCl solutions. Also, between 

 0.01 N and 0.1 N it is independent of the concentration of alkali 



* In all of these determinations a Pulfrich refractometer was employed, 

 reading the angle of total reflection accurately to within 1', and a sodium flame 

 was employed as the source of light. 



