THE VALENCY RULE AND THE HOFMEISTER SERIES 81 



physical modification of the gelatin (e.g., diminution of cohesion 

 between the particles of gelatin). 



Figure 21 gives the curves for the action of alkalies on swelling. 

 The curves for Li, Na, K, and NH4 gelatinate of the same pH 

 are practically the same, except that the values for NH 4 OH are 

 irregular for pH above 8.5, possibly on account of the fact that 

 the concentration of NH 4 OH required to bring gelatin to such pH 



5 6 7 8 9 10 11 12 



FIG. 21. Curves for the effect of different bases on swelling. Those for 

 LiOH, NaOH, KOH, and NH 4 OH are practically identical and about twice as 

 high as those for Ca(OH) 2 and Ba(OH) 2 . 



is rather high. The main fact is that the ratio of the maximal 

 swelling of gelatin salts with bivalent cation, like Ca or Ba, is 

 considerably less than that of gelatin salts with monovalent 

 cation, like Na, K, or NEU. 1 This agrees with the results of the 

 titration experiments which show that Ca(OH) 2 and Ba(OH)2 

 combine with gelatin in equivalent proportions and that, hence, 

 the cation in combination with the gelatin is, in this case, bivalent. 



It should be pointed out that the maximal swelling of gelatin 

 in alkalies was less than that in acids. This was not observed in 

 the osmotic pressure curves. It is probably due to differences of 

 cohesion of the ions of the gel in the two cases. 



The results show clearly that the Hofmeister series is not the 

 correct expression of the relative effect of ions on the swelling of 



1 LOEB, J., /. Gen. PhysioL, vol. 3, p. 247, 1920-21. 



