278 COLLOIDS AND ELECTROLYTES 



Fig. 2 shows the influence of the concentration of NaOK upon the 

 initial rate of diffusion of water into the solutions of Na gelatinate. 

 The ordinates represent the height to which the liquid had risen in 

 the manometer 30 minutes after commencement of the experiment. 

 The abscissas are again the logarithms of the concentration of the 

 NaOH and the pH is that found after 30 minutes. The reader will 

 notice that the critical points in this curve coincide with the critical 

 points in Fig. 1. The curve rises steeply until pH = 8.4 when the 

 maximum is reached, and falls equally steeply until a pH = 12.2 is 

 reached. We have given the reason for this coincidence of the critical 

 points in the curves of Figs. 1 and 2 in a preceding paper.^ 



The question arises, what causes the drop of the two curves when 

 the pH exceeds 8.4? This drop seems to be the same as the drop in 

 the initial rate of diffusion of water into a solution of Na2S04 which 

 occurs when the concentration exceeds m/256. When we separate 

 metal gelatinates from distilled water by a collodion membrane, 

 water diffuses into the gelatin solution as if its particles were positively 

 charged; being attracted by the gelatin anion and repelled by the 

 metal ion. Metal gelatinates behave therefore towards the electri- 

 fication and rate of diffusion of water through collodion membranes 

 like neutral or alkaline solutions of Na2S04 or Na4Fe(CN)6. The 

 analogy can be carried further, since the addition of httle salt depresses 

 both the rate at which water will diffuse into the gelatin solution 

 through the membrane as well as the permanent osmotic pressure of 

 the solution. 



Fig. 3 shows the rapid fall in the permanent osmotic pressure of a 

 1 per cent solution of Na gelatinate with a pH of about 8.4 to which 

 various concentrations of a salt, KCl, K2SO4, K3 citrate, and CaCl2, 

 are added. The amounts of salts contained in 100 cc. of gelatin 

 solution were 0, 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, and 25.6 cc. of m/4. 

 These solutions were put into the collodion bags described, and the 

 collodion bags were put into beakers containing the same salt in the 

 same concentration which had been added to the gelatin solution. 

 Fig. 3 gives the rise in the manometer after 30 minutes and Fig. 4 

 the osmotic pressure after 6 hours. Tha curves show the rapid drop 



» Loeb, J., J. Gen. Physiol., 1919-20, ii, 87. 



