206 SOLUTION AND PRECIPITATION OF PROTEINS 



prevails over the velocity of formation, the viscosity of the gelatin 

 solution will diminish on standing. All agencies which accelerate 

 the rate of solution of solid gelatin should counteract the aggregate 

 formation and the rise of viscosity of a gelatin solution on standing; 

 while all agencies which diminish the rate of solution of solid gelatin 

 should increase the rise of viscosity of the gelatin solution on standing. 



We have seen that powdered isoelectric gelatin is dissolved the 

 more rapidly, the more HCl we add, and that there is no maximum 

 followed by a drop when a certain hydrogen ion concentration is ex- 

 ceeded. Hence we should expect that the lower the pH of a gelatin 

 solution containing the same concentration of originally isoelectric 

 gelatin, the smaller the increase of the viscosity of the solution on 

 standing. In a preceding paper we have already given curves show- 

 ing that this is the case and that there is no Donnan effect noticeable 

 in this case.^^ 



We have seen in Fig. 5 that Na2S04 commences to diminish 

 noticeably the rate of solution of solid gelatin chloride as soon as the 

 concentration of Na2S04 exceeds m/64, while CaCla commences to 

 have the opposite effect as soon as the concentration of CaCl2 

 exceeds m/4. 



We prepared gelatin chloride solutions of pH 3.4 containing 1 gm. of 

 originally isoelectric gelatin in 100 cc. solution. The solutions were 

 made up in various concentrations of Na2S04 and CaCU. The solu- 

 tions were rapidly heated to 45°, rapidly cooled to 20°C., and kept 

 at this temperature for 1 hour. The time of outflow of the solution 

 through a viscometer was measured immediately and in intervals 

 of 5 or 10 minutes. The time of outflow of water through the vis- 

 cometer at 20° was 61 seconds. 



The viscosity of a gelatin chloride solution of pH 3.4 rises gradually 

 but very slowly (uppermost curve in Fig. 7) and the rate of increase 

 of viscosity on standing is not materially altered in m/512 Na2S04 

 and only little in m/128 Na2S04. In m/32 Na2S04 the viscosity 

 increases more rapidly on standing, in m/8 Na2S04 still more 

 rapidly, and in m/2 Na2S04 very sharply. This is exactly what 

 we should expect since the Na2S04 causes a diminution of the 

 rate of solution of gelatin chloride as soon as the concentration of 



1^ Loeb, J., /. Gen. Physiol, 1921-22, iv, 97. 



