260 ION SERIES AND PROTEINS. II 



We should expect that when the hydrogen ion concentration of a 

 gelatin chloride solution becomes very high its solubility in an alcohol- 

 water mixture will be diminished again. This is indeed the case, and 

 happens when in 100 cc. of 2 per cent solution of isoelectric gelatin 

 are contained 30 or 40 cc. of m/1 HCl. When to 5 cc. of such a solu- 

 tion are added 25 or 20 cc. of 95 per cent alcohol, the turbidity occurs 

 again. When 100 cc. of the solution contain 50 cc. of m/1 HCl only 

 14.7 cc. of 95 per cent alcohol are required. 



The same result was obtained with Na gelatinate which can also be 

 precipitated again by alcohol when its pH exceeds 12 or 13. 



The fact that the gelatin-acid salts (with the exception of gelatin 

 sulfate) become completely soluble in alcohol when the pH reaches 

 the low value of 4.4 is not easy to harmonize with the hypothesis of 

 Pauli that this is due to the ionization of the gelatin, since the relative 

 amount of ionized gelatin is exceedingly small at pH 4.4. 



The experiments on the relative solubility of different gelatin salts 

 therefore show the same influence of the valency of the ion in combi- 

 nation with gelatin as was shown in regard to the other physical prop- 

 erties of proteins. 



///. Conductivity and Ionization of Gelatin Solutions. 



The influence of ions on the conductivity of protein solutions should 

 run parallel to the influence on swelling, viscosity, and osmotic pres- 

 sure, if it be true that these properties depend on the concentration of 

 the protein ions in the solution. According to this theory, first pro- 

 posed by Laqueur and Sackur^ and elaborated by Pauli, ^ the values for 

 the physical properties of proteins are a minimum at the isoelectric 

 point for the reason that the ionization of the protein molecules is a 

 minimum at that point. When we add acid, e.g. HCl, protein chlor- 

 ide is formed which is highly ionized and the increase in the viscosity, 

 swelling, and osmotic pressure with the increase of acid is explained 

 by the ionization theory on the assumption of an increase in the 

 concentration of the protein ions in the solution. When, however, 

 too much acid is added, i.e. as soon as the pH of the gelatin solution 



® Laqueur, E., and Sackur, O., Beitr. cheni. Physiol, u. Path., 1903, iii, 193. 

 ' Pauli, W., Kolloidchemie der Eiweisskorper, pt. 1, Dresden and Leipsic, 1920. 



