CORRECTNESS OF THE CHEMICAL VIEWPOINT 31 



quently treated for 1 hour with the same concentration of AgNO 3 , 

 e.g., M/64 AgNO 3 , and then washed. In this case, the exposure 

 to light showed us that silver gelatinate existed only on the alka- 

 line side of the isoelectric point, since only on that side did the 

 gelatin turn black. When we now add enough alkali to the 

 gelatin solutions with a pH of 4.6 or less to bring their pH to 4.8 

 or above, they will not turn black when exposed to light. This 

 shows that the gelatin of pH below 4.6 did not contain any 

 demonstrable quantity of silver. 1 It was conceivable that such 

 gelatin of pH below 4.6 contained Ag in a non-ionogenic form. If 

 this were the case, this fact should have betrayed itself in a 

 blackening upon the addition of enough alkali to bring the pH 

 above 4.7. 



When we bring powdered gelatin of pH>4.7, which has been 

 treated with M/64 AgNO 3 and washed, to a pH of 4.7, or below, 

 the silver which was in combination with the gelatin can be 

 removed by washing with cold water, and such gelatin will not 

 turn black when subsequently exposed to light, provided the 

 washing had been adequate. 



When we include that part of the gelatin molecule which 

 cannot react with other electrolytes in brackets, while the part 

 of the molecule which is capable of reacting with other electro- 

 lytes is kept outside the brackets, we can symbolize our results 

 in the following way : 



Isoelectric gelatin is entirely inside the brackets since at the 

 isoelectric point gelatin can combine neither with anions nor with 

 cations, 



-NH 2 1 



COOHj 



On the alkaline side from the isoelectric point practically only 

 COOH groups of the molecule are capable of reacting with 

 other compounds and we represent the protein molecule on this 

 side in the following form: 



1 This dogmatic presentation of our results is only approximately correct, 

 since a trace of anion should also combine, theoretically at least, on the 

 alkaline side of the isoelectric point; and a trace of cation on the acid side, 

 at least near the isoelectric point. As a matter of fact, however, this cannot 

 be demonstrated, though the theory of amphoteric electrolytes demands 

 that this should be so. 



