The Isoelectric Point of Gelatin and Its Rela- Tion to the Minimum Physical Properties of Gelatin

In a preliminary statement the writer (1) presented the proposition that the minimum physical properties of gelatin (conductivity, osmotic pressure, viscosity, maximum opacity) which are usually thought to define its isoelectric point are propert’ies of pure gelatin, and that pure gelatin is not isoelectric; that pure gelatin from lime-conditioned stock is a weak acid which in an electrical field migrates to the anode; that the reactions necessary to bring pure gelatin to its isoelectric point are such as to indicate that isoelectric gelatin is an ionized salt of gelatin in which the positive and negative charges on the gelatin radical exactly balance each other (external rather than internal compensation of the charges on the gelatin molecule being assumed). In the present paper, experimental data and references are given in support of these assumptions. Pure gelatin from lime-conditioned stock may be assumed to have the formula XEgt” (where X represents the main gelatin radical and the other groups are representative of the acid and basic groups) and should accordingly furnish the ions (X$$L)&. Since, however, this type of gelatin acts as a weak acid, the number of ionized groups furnishing Hf ions would be greater and the ionized molecule may be represented by (X$y-)H’. The addition of a strong acid (HCl) to such gelatin will partly suppress its ionization as an acid and react with some of the NH2 groups to form a hydrochloride of gelatin, X$&f& which as a salt of gelatin would dissociate to form the more highly ionized