106 



THEORY OF COLLOIDAL BEHAVIOR 



and Na acetate on the swelling of gelatin chloride of pH 3.3 

 (the curve for Na 2 S04 is added for comparison), and Table VII 

 gives the variation of the pH of the gelatin caused by the addition 

 of these salts. Our theory demands that all these salts (except 

 Na 2 SO 4 ) should depress the swelling of gelatin chloride of pH 

 3.3 to the same amount, and that deviations from this rule 



TABLE VII. CHANGES IN pH OF 0.8 PER CENT GELATIN CHLORIDE OF 

 pH = 3.3 UPON ADDITION OF VARIOUS CONCENTRATIONS OF SALTS 



must find their explanation in variations of pH caused by the 

 addition of salt. Table VII shows that the variations in pH are 

 small for NaCl, NaCNS, and NaH 2 PO 4 and hence, the curves 

 for the depressing effect of these three salts upon the swelling of 

 gelatin are almost identical, as the valency rule demands. Mono- 

 sodium citrate and tartrate have a greater depressing effect on 

 the hydrogen ion concentration and Na acetate has a still greater 

 depressing effect than these two salts. This explains the appar- 

 ent deviation of the curves for these three salts from the valency 

 rule. 



A. D. Hirschfelder 1 has published a paper on the effects of 

 different salts on the swelling of fibrin in HC1 in which he showed 

 that the effect of citrates, acetates, and phosphates on swelling 

 was the same as that of chlorides, bromides, and nitrates if the 

 hydrogen ion concentration was kept constant; only the sulphates 

 had a greater depressing effect. The influence of salts on the 



1 Hirschfelder, A. D., J. Am. Med. Ass., vol. 67, p. 1891, 1916. 



