THE VALENCY RULE AND THE HOFMEISTER SERIES 79 



ing in acid. The abscissae are the pH found in the gelatin after 

 equilibrium was established. The ordinates represent the figures 

 for the volume of the granules of about 0.8 gm. of gelatin in 

 different acids. It is obvious that in all cases the volume (or 

 swelling) is a minimum at the isoelectric point pH = 4.7, that it 

 rises with diminishing pH until the maximum is reached at a pH 

 of about 3.2 or a little less, and that the curve drops steeply with 



6 



FIG. 19. Influence of HC1, HNO 3 , H 3 P04, H 2 SO 4 , trichloracetic, and oxalic 

 acids on the swelling of gelatin. Abscissae are the pH, ordinates the volume of 

 gelatin. The curves for all the acids are practically identical except that for 

 HaSCh which is about one-half as high as the curves for the other acids. 



a further diminution of pH (i.e., a further increase of hydrogen 

 ion concentration) . The main fact is, however, that the curves 

 for the influence of HC1, HNO 3 , trichloracecic, oxalic, phos- 

 phoric, citric, and tartaric acids are practically identical, proving 

 that only the valency and not the nature of the anion of the 

 acid used influences the swelling of gelatin; since the anion of 

 weak dibasic or tribasic organic acids combining with the gelatin 

 is always monovalent. 



