JACQUES LOEB . 59 



that both ions of a neutral salt influence a protein simultaneously. 

 The writer has shown in previous publications that these statements 

 are contrary to fact and based on erroneous methods of work. Our 

 present paper shows that these claims of colloid chemists are also 

 theoretically impossible. 



6. In addition to other physical properties the conductivity of 

 gelatin previously treated with acids has been investigated and 

 plotted, and it was found that this conductivity is a minimum in the 

 region of the isoelectric point, thus confirming the conclusion that 

 gelatin can apparently not exist in ionized condition at that point. 

 The conductivity rises on either side of the isoelectric point, but not 

 symmetrically for reasons given in the paper. It is shown that the 

 curves for osmotic pressure, viscosity, swelling, and alcohol number 

 run parallel to the curve of the conductivity of gelatin when the 

 gelatin has been treated with acid, supporting the view that these 

 physical properties are in this case mainly or exclusively a function of 

 the degree of ionization of the gelatin or gelatin salt formed. It is 

 pointed out, however, that certain constitutional factors, e.g. the 

 valency of the ion in combination with the gelatin, may alter the 

 physical properties of the gelatin (osmotic pressure, etc.) without 

 apparently altering its conductivity. This point is still under investi- 

 gation and will be further discussed in a following publication. 



7. It is shown that the isoelectric point of an amphoteric electro- 

 lyte is not only a point where the physical properties of an am- 

 pholyte experience a sharp drop and become a minimum, but that 

 it is also a turning point for the mode of chemical reactions of the 

 ampholyte. It may turn out that this chemical influence of the 

 isoelectric point upon hfe phenomena overshadows its physical 

 influence. 



8. These experiments suggest that the theory of amphoteric colloids 

 is in its general features identical with the theory of inorganic 

 hydroxides {e.g. aluminum hydroxide) , whose behavior is adequately 

 understood on the basis of the laws of general chemistry. 



Addendum. Since this paper went to print the writer has been 

 able to show by volumetric analysis that the view expressed in 

 this paper is correct; namely, that on the alkaline side from the 

 isoelectric point gelatin combines with the cation of a neutral salt ^ 



