The Influence of Neutral Salts, Bases, and Acids on the Precipitability of Gelatin by Alcohol

It has been shown in the previous publications’ that the eriect of neutral salts on gelatin is repressed in the presence of the salt and that we can study such effects with any profit only when the excess of salt is washed away after it has had a chance to act on the protein. Such gelatin reveals qualities which are masked in the presence of the salt and which allow us to gain a clear insight into the effect of the salt. The first striking result was: that contrary to the current belief the cation of the salt was found to be the active ion, while the anion did apparently not act at all. All salts with univalent cation and bivalent anion (type Na&304 or KS oxalate) had exactly the same effect as all the salts of the type NaCl or NH&l (univalent cation and univalent anion) when the cation concentration was the same in solutions of both salts. While’the salts with univalent cation caused an additional swelling and an increase in viscosity of the gelatin after the salt was washed away, the salts with bivalent cation caused little or no such additional swelling and no or only a slight increase in viscosity. This difference in the effect of univalent and bivalent cations, as well as the repressing effect of the presence of t.he salt, was explained on the assumption that the neutral salts form with gelatin metal gelatinates which dissociate electrolytically into a negative gelatin ion and a positive cation (that of the salt used), while the anion either does not combine at all with th.e gelatin