580 AMPHOTERIC COLLOIDS. V 



and gelatin bromide being about 3 : 8. The same ratio had been 

 found for the ratio of maximal osmotic pressures of calcium and 

 sodium gelatinate. 



3. The curves representing the influence of other dibasic and tri- 

 basic acids, viz. oxalic, tartaric, succinic, citric, and phosphoric, 

 upon gelatin are almost identical with those representing the effect 

 of monobasic acids. 



4. The facts mentioned under (2) and (3) permit us to decide 

 between a purely chemical and a colloidal explanation of the influ- 

 ence of acids on the physical properties of gelatin. In the former 

 case we should be able to prove, first, that twice as many molecules 

 of HBr as of H2SO4 combine with a given mass of gelatin; and, 

 second, that the same number of molecules of phosphoric, citric, 

 oxaHc, tartaric, and succinic acids as of HNO3 or HCl combine with 

 the same mass of gelatin. It is shown in the present paper that this 

 is actually the case. 



5. It is shown that gelatin sulfate and gelatin bromide solutions of 

 the same pH have practically the same conductivity. This disproves 

 the assumption of colloid chemists that the difference in the effect 

 of bromides and sulfates on the physical properties of gelatin is due 



_ to a different ionizing and hydratating effect of the two acids upon 

 the protein molecule. 



