i* 



m 



a 

 ^li 



iU 



"2* 





Si 





pii 3.6 as 4.1 4.3 ^;6 47 5.0 



Fig. I. 



f M^ M M HM_M3«_f13nM__M>«_>;;_M_0 



C!TC JSea a « 52 64 128 M C* lO* « 'Q*" ?>4 *» »« 



p^ itt ■5i :j i9 4 4J 46 47 50 iJ S' i:^ i: M 



GeUtin treated wuh different concentrationa of HNOj. from M/8 to 

 M/8192. washed, and then treated with the same concentration of AgNGj (u/16), 

 and then washed again. Abscissa show concentrations ol acid used. The final 

 pH of the gelatin solution is found under the figure lor the concentration of 

 acid used- 



The ordinales ol the lower curve give the values lor the silver found in com- 

 bination with the gelatin. The curve shows that at the isoelectric point (pH = 

 4.7) and on the acid side of the isoelectric point, the gelatin was practically free 

 from silver. On the more alkaline side the amount of silver found in combination 

 with the gelatin increased with the pH. This proves that gelatin can combine 

 with a cation only on the alkaline side from the isoelectric point, and this is corrob- 

 orated by the fact that on the alkaline side from the isoelectric point only was the 

 gelatin darkened by light- The ordinates of the upper curve are the valoes for the 

 swelling of the same gelatin. On the alkaline side from the isoelectric point, 

 where the gelatin had combined with silver, the curve for swelling runs parallel 

 to the curve for silver gelatinale formed. It was, therefore, the ^relative mass of 

 silver gebtinatr lormrd which determined the physical properties of gelatin. 



Fig, 2. 



Influence of HCI HNO3. lUPO*, HiSO*. trichloracetic, and oxalic 

 ■cids on the swelling of gelatin Abscissae are the pH, ordinates the volume ol 

 gelatin. .The curves for all the acids are practically identical except that (or 

 HtSOi which is about one-half a* high as the cur/eri for the other acids. 



Fig. 3. 



U" 



