572 



AMPHOTERIC COLLOIDS. V 



We repeated the experiments represented in Tables I and II with 

 a number of other acids, the method of adding acid to gelatin being 

 the same in all cases, though the quantity of acid needed to produce 



275 



250 



225 



200 



175 



150 



125 



100 



10 



9 



6 



4 



cc.0.01 N HGl 15 14 13 IZ II 10 9 8 7 6 5 4 3 Z I 

 CC.0.01 N HiS04 1 Z 3 4 5 6 7 8 9 « 11 iZ 13 14 15 

 pH 3.4 3.35 34 335 3.35 34 3.35 34 3.4 335 335 3.35 3.35 3.35 3.35 335 



Fig. 4. Effect of mixtures of HCl and H2SO4 upon conductivity and osmotic 

 pressure of gelatin. Abscissae represent mixtures of the two acids; ordinates of 

 lower curve, amount of acid in combination with 0.1 gm. of gelatin. The curve 

 is a straight line, proving that equivalent amounts of H2SO4 and HCl are bound 

 by 0.1 gm. of gelatin. Ordinates of middle curve, corrected conductivities of 

 gelatm treated with different proportions of a mixture of the two acids. The 

 curve is also practically a straight line. Upper curve, osmotic pressure curve, 

 showing that the osmotic 'pressure is the greater the greater the proportion of 

 HCl is in the mixture. The curve is convex to the axis of abscissas, which is char- 

 acteristic for antagonism. Notice identity of conductivities and the difference 

 in osmotic pressure, contradicting the hydratation theory of colloid chemists. 



the same pH was different for different acids. In the case of phos- 

 phoric acid we determined directly (with the uranylacetate method) 

 the PO4 in combination with 10 cc. of a 1 per cent gelatin solution 



