JACQUES LOEB 485 



gelatinate proves that the difference in the influence oi the valency of 

 the cation upon the physical properties of gelatin cannot be ascribed 

 to a difference in the degree of ionization of the two types of salts, 

 but is due to some other as yet unknown factor. It seems possible 

 to explain all the phenomena on the basis of the tentative assumption 

 that gelatin salts with a bivalent cation dissociate into cations and 

 aggregates of four, or six, or eight gelatin ions, each individual gelatin 

 ion of the aggregate retaining its original negative charge, while the 

 anions of salts of sodium gelatinate consist of only one gelatin ion 

 each. The quantitative data suggest that the number of gelatin 

 anions contained in each aggregate is of a stoichiometrical order, being 

 a simple multiple of the number representing the valency of the 

 poljrvralent metal ion. 



//. Amount of Alkali Combining with Gelatin. 



We used powdered Cooper's non-bleached gelatin which is impure, 

 having a pH of about 7.0 and consisting to a large extent of calcium 

 gelatinate. It is necessary to purify this gelatin before using it by 

 bringing it to the isoelectric point pH = 4.7. ^ This is done by putting 

 1 gm. of gelatin for | hour into 100 cc. of 3 m/1024 HCl or m/128 acetic 

 acid, then putting the gelatin on a filter, allowing the excess of solu- 

 tion to drain off, and washing the gelatin two or three times with 25 

 cc. of distilled water at 5°C. If we wish to transform the pure isoelec- 

 tric gelatin into a metal gelatinate we treat it subsequently with the 

 hydroxide of the metal — e.g. NaOH, Ca(0H)2, etc. — -with which we 

 wish the gelatin to combine. 



We always used finely powdered gelatin rendered isoelectric in the 

 manner described. When we intended to prepare sodium gelatinate we 

 treated different doses of isoelectric gelatin of 1 gm. each with 75 or 

 100 cc. of a NaOH solution varying from m/4 to m/8192 NaOH, after- 



^ Isoelectric gelatin does not react with neutral salts like NaCl but will react 

 with NaOH, since in this latter case the pH is raised beyond that of the isoelectric 

 point. Common Cooper's gelatin, with a pH = 7.0, consisting of gelatin salts, 

 especially Ca gelatinate, will be influenced in the same way by a treatment with 

 NaOH as with NkCl, since in both cases a replacement of Ca by Na will occur. 

 This is supported by the writer's previously published papers. 



