258 



ION SERIES AND PROTEINS, II 



opacity of the mixture it was necessary to dip the test-tube in ice 

 water during the process of mixing and keep the gelatin solution 

 approximately at 10°C. 



When we prepare gelatin chloride by adding small quantities of 

 HCl to isoelectric gelatin we need the more alcohol the lower the pH 

 and very soon a limit is reached when the addition of 25 cc. or more 

 alcohol no longer brings about any precipitate or even cloudiness. 

 Thus 10 cc. of isoelectric gelatin required 2 cc. of 95 per cent alcohol 

 to bring about that high degree of opacity at which the test letters were 

 no longer legible. When the pH of the gelatin was lowered to 4.55 



TABLE IV. 



by the addition of HCl, 5.5 cc. of alcohol were required for the same 

 degree of opacity. When the pH of the 1 per cent gelatin chloride 

 solution was only a trifle lower, namely 4.50, the addition of 25 cc. 

 of alcohol or more did not suffice for bringing about the degree of 

 opacity required for our test; only a lower degree of turbidity resulted. 

 A gelatin chloride solution of pH 4.45 remained perfectly clear (with 

 a bluish tint) regardless of how much alcohol was added. We may 

 say that gelatin chloride becomes soluble in an alcohol-water mixture 

 containing more than 75 per cent alcohol as soon as its pH is < 4.45. 

 It seemed of interest to compare the relative solubility of other 

 gelatin-acid salts with that of gelatin chloride. Table IV gives the 



