568 AMPHOTERIC COLLOIDS. V 



sodium gelatinate molecules yielding eight charges and eight ions. 

 This would produce equality of charges and a ratio of osmotic pres- 

 sures of 3:8. The same assumption appHed to gelatin bromide and 

 gelatin sulfate would demand that gelatin4 (804)2 dissociate into three 

 particles, two negative SO4 ions and one aggregate (gelatin4) with four 

 positive charges; while in the case of gelatin bromide the same num- 

 ber of charges would be carried by eight separate ions, four Br and 

 four separate positive gelatin ions. This would again produce 

 equality in the number of charges and a ratio of 3 : 8 in the number 

 of particles. 



When pH becomes less than 3.3 the values for osmotic pressure 

 drop again. This drop which had been noticed by previous investi- 

 gators, especially by Pauli, is ascribed by the latter to a diminution 

 in the degree of electrolytic dissociation of the gelatin salt. This 

 assumption meets, however, with a difficulty in the fact that the 

 conductivity of the gelatin salts does not show this drop but con- 

 tinues to rise steeply for values of pH less than 3.3. 



Antagonism between HBr and H2SO4. 



The real crux between the colloidal and the chemical conception 

 seems to lie in the question of the justification of the assumption of 

 "hydratation" as the cause of osmotic pressure of protein solutions. 

 The writer does not question the possible correctness of the idea 

 that ions are in general surrounded by a jacket of water molecules; 

 he only doubts the correctness of the idea that this possible hydra- 

 tation of the protein ion is the cause of the osmotic pressure, the 

 swelling, and the other physical properties of proteins as Pauli, 

 Michaelis, and others assume. The following experiment seems to be 

 a further proof against this apphcation of the hydratation hypothesis. 

 We had seen that a 1 per cent solution of both gelatin bromide and 

 gelatin sulfate reaches the maximal osmotic pressure at a pH of 

 about 3.5 and that for this pH the same amount of gelatin is com- 

 bined with equivalent amounts of Br and SO4, namely 0.1 gm. of 

 gelatin binding about 3.6 cc. of 0.01 n Br or SO4. Both solutions 

 have the same conductivity, namely about 9.7. In order to produce 

 gelatin bromide or gelatin sulfate of a pH of about 3.4 it is necessary 



