82 THEORY OF COLLOIDAL BEHAVIOR 



gelatin, and that it is not true that chlorides, bromides, and 

 nitrates have "hydrating" and acetates, tartrates, citrates, and 

 phosphates " dehydrating " effects. If the pH of the gelatin is 

 taken into consideration, it is found that for the same pH the 

 effect on swelling is the same for Cl, NO 3 , trichloracetate, tartrate, 

 succinate, oxalate, citrate, and phosphate, while the swelling is 

 considerably less for S(>4. This is exactly what we should expect 

 according to the valency rule on the basis of the combining 

 ratios of different acids with gelatin, since the weak dibasic and 

 tribasic acids combine with gelatin in molecular proportions 

 while the strong dibasic acid H 2 SO 4 combines with gelatin in 

 equivalent proportions. In the case of the weak dibasic acids 

 the anion in combination with gelatin is monovalent and in 

 the case of the strong H 2 SO4 it is bivalent. Hence, it is only 

 the valency and not the nature of the ion in combination with 

 gelatin which affects the degree of swelling. 



(C) VISCOSITY 



The valency rule which permits us to predict the relative 

 osmotic pressure of solutions of protein holds also in the case 

 of viscosity of gelatin and casein solutions. 



We will begin with experiments on the influence of gelatin 

 on the viscosity of water. 1 A 4 per cent stock solution of 

 isoelectric gelatin was prepared, and some of the stock solution 

 was heated to 45 and made up to a 1.6 per cent solution in 

 quantity sufficient for a day's experiments. This 1.6 per cent 

 solution was kept during the day at 24C. To 50 c.c. of this 

 solution was added the desired acid or alkali in sufficient quantity 

 and then the volume raised to 100 c.c. by the addition of enough 

 distilled water. The 0.8 per cent solution was then rapidly 

 brought to a temperature of 45, kept there for 1 minute and was 

 then rapidly cooled to 24C. The solution was stirred constantly 

 during the heating and cooling. The viscosity was measured 

 immediately after the solution was cooled to 24C. The measure- 

 ments were all made at 24C. by using the time of outflow 

 through a viscometer. The time of outflow of distilled water 

 through the Ostwald viscometer used was exactly 1 minute at 



1 LOEB, J., J. Gen. Physiol, vol. 3, p. 85, 1920-21. 



