JACQUES LOEB AND ROBERT F. LOEB 



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The ordinates are the average diameters of the particles after 1 and 

 24 hours respectively. The abscissas are the concentrations of NaCl. 

 The depressing effect is similar to that found in the case of the swelling 

 of a jelly of gelatin. After 24 hours the particles had dissolved in 

 the NaCl solutions of a concentration of below m/256, but not in 

 concentrations of NaCl higher than m/256. 



That the solution of casein chloride is thus regulated to a large 

 extent by the Donnan effect was ascertained also by measurements 

 of the quantity of casein chloride dissolved at 20°C. at various pH of 

 the solution. 1 gm. of isoelectric powdered casein was put into 100 

 cc. of solutions of HCl of dififerent concentration and kept in these 

 solutions in one case for 1 hour, in a second case for 22 hours. The 

 mass was then poured into graduated cylinders and the undissolved 

 part was allowed to settle to the bottom for 2 and for 6 hours respec- 



TABLE I. 

 Amount of Casein Dissolved at 20° C in HCl of Different pH. 



tively at 20°C. The supernatant liquid was removed and the sediment 

 dried over night in an oven at about 100°C. Table I gives the result. 

 The dry weight of 1 gm. of isoelectric casein was found to be 0.870 gm. 

 and this weight diminished by the dr}^ weight of the sediment was 

 the amount dissolved. Table I shows that, the rate of solution in- 

 creases with diminishing pH from 4.4 to 2.18 where the solubility of 

 casein chloride is a maximum ; with a further decline in pH the solu- 

 bility diminishes again. This is in agreement with the Donnan effect. 

 In a similar way the depressing effect of NaCl on the rate of solu- 

 tion of casein chloride was ascertained. Solutions of 12.5 cc. of 0.1 N 

 HCl in 100 cc. and containing 1 gm. of powdered, originally isoelectric 

 casein were prepared in 0, m/2048, m/1024, to m/4 NaCl. The pH of 

 a solution of 1 gm. casein in 100 cc. containing 12.5 cc. of O.l N HCl 

 was 2.12 and this pH was the same in all solutions made up in NaCl. 



