254 



ION SERIES AND PROTEINS, II 



the measurement of pH in this case due to the adhesion of some of 

 the original acid on the outside of the granules. This error was 

 partly compensated by the addition of distilled water of pH of about 

 5.6 in making up the 1 per cent solution of gelatin. On the whole the 



85 



80 



75 



•S 70 

 Id 



'S 65 

 ^ 60 

 8 55 



o 



CO 



B 

 § 



50 



o 



^ 45 



40 

 35 

 30 



^ 25 



■■§ 



i5 20 



Ok) 



jr: 15 



10 



pH 1 



6 



Fig. 2. Influence of citric, tartaric, and acetic acids on swelling of gelatin. 

 The curves for citric and tartaric acids are practically identical with those for 

 HCl and HNO3 in Fig. 1. That for acetic acid is a little higher owing probably 

 to some specific and secondary effect of this acid. 



probable error was +0.1 or +0.2; i.e., the real pH was 0.1 or at the 

 utmost 0.2 greater than in our abscissae. The most important fact is, 

 however, that the curves for the influence of HCl, HNO3, trichlor- 

 acetic, oxalic, phosphoric, citric, and tartaric acids are practically 



