570 AMPHOTERIC COLLOIDS. V 



same, while the osmotic pressure should vary according to the relative 

 proportion of HBr and H2SO4 used. HCl was used in this experi- 

 ment instead of HBr since we had found that HCl and HBr act 

 quahtatively and quantitatively alike on the physical properties of 

 gelatin. The mixtures in which the 15 cc. of 0.01 n acid were pre- 

 pared were made up as .follows: 15 cc. 0.01 N HCl + cc. 0.01 N 

 H2SO4; 14 cc. 0.01 N HCl + 1 cc. 0.01 N H2SO4; 13 cc. 0.01 n HCl + 2 

 cc. 0.01 N H0SO4, etc., and finally cc. 0.01 N HCl + 15 cc. 0.01 N 

 H2SO4. Table III gives the numerical values for the pH, the cor- 

 rected titration number, the conductivity, and the osmotic pressure 

 of each gelatin solution. While the titration number (Row 2) and 

 the values for conductivity (Row 3) are everywhere practically iden- 

 tical, the osmotic pressures vary from 300 to 128. Fig. 4 gives the 

 graphical expression of the result. 



It is obvious that the values for osmotic pressure are not the alge- 

 braic mean between the values for pure HCl and pure H2SO4. The 

 curve is convex towards the axis of abscissae, thus showing that the 

 depressing effect of SO4 increases more rapidly than the quantity of 

 SO4 added. This is characteristic for a true antagonistic salt effect. 



The main result is unequivocal; namely, that the differences in the 

 osmotic pressures are not due to differences in ionization and hydra- 

 tation of protein ions as the colloid chemists assume, since the 

 conductivities remain constant while the osmotic pressures vary 

 considerably. 



What is true for the relative influence of the two acids on osmotic 

 pressure is also true for their relative influence on swelling, and 

 viscosity of gelatin as is shown in Figs. 5 and 6. 



Proof that Dibasic and Trihasic Acids {with the Exception of H-iSOi) 

 Behave Practically like Monobasic Acids toward Gelatin. 



Of the other dibasic and tribasic acids which the writer has thus 

 far investigated, namely oxalic, tartaric, succinic, citric, and phos- 

 phoric acid, none shows the valency influence. We are able to give 

 the explanation for this peculiar behavior by proving that all these 

 acids react with gelatin practically as if they were monobasic acids. 



