CONSISTENCY OF COLLOIDS 69 



When such heterogeneous substances as gelatin, fibrin, etc., behave 

 similarly under the influence of electrolytes, we may assume that the 

 same cause determines the behavior, and this cause must be sought 

 in the chemical nature of these substances. Apparently these sub- 

 stances are amphoteric, i.e., at the same time weak acids and weak 

 bases, forming under the influence of acids and bases, more or less 

 ionized salts. lonization causes an hydration, i.e., an imbibition of 

 water which is evidenced in the case of these gels by their capacity 

 to swell, and in the case of dissolved albumins, by an increase of the 

 internal friction. We should therefore not expect to see these phe- 

 nomena in the case of gels of entirely different chemical properties, 

 silicic acid gel, for example. 



Neutral salts, to a certain extent, favor the imbibition of water and 

 indeed the swelling is greater in such dilute salt solutions than it is 

 in pure water. At a certain concentration (for NaCl, 13.8 per cent) 

 the amount of fluid taken up reaches a maximum and then falls 

 again. The anions are primarily active in favoring swelling, whereas 

 the cations have a lesser influence and, in favoring swelling, 



CNS > I > Br > N0 3 > C1O 3 > Cl; 

 whereas in favoring shrinking, 



SC>4 > tartrate > citrate > acetate. 



Although a dry jelly removes more water from a salt solution than 

 it does salt so that the concentration of the solution is increased, a 

 swollen jelly takes up more salt than it does water, thus diminishing 

 the concentration of the solution. The swelling in acid or alkaline 

 solution is always much decreased by the presence of neutral salts, 

 and anions are much more active than cations. In producing this 

 decrease 



citrate > tartrate > phosphate (?) > S0 4 > acetate > I > CNS 



> N0 3 > Br >C1; 

 Fe > Cu > Sr > Ba > Ca > Mg > NH 4 > Na > K. 



Though, e.g., 0.78 gin. gelatin in 100 cc. of 0.05 nHCl swelled up to 



14.61 gm., the swelling reached only 2.84 gm. in the presence of -~- 



& 



potassium citrate and about 7 gm. in the presence of -~- KC1. 



Antagonistic Effects. In addition to the antagonistic action of neu- 

 tral salts on the swelling due to H and OH ions, there is also an 

 antagonism to monovalent cations by polyvalent cations. 



