216 ANIMAL PROTEINS 



but decreases more slowly. With common salt there is a 

 slight swelling followed by contraction. Caustic soda gives 

 a rapid increase in volume at first, afterwards much less so, 

 and finally yields an exceedingly slow decrease. The corre- 

 spondence of these facts with the type-curves inevitably 

 suggests that the phenomenon of swelling might be accounted 

 for, in part at least, along these lines. 



Of course it is not likely that the simple figures selected 

 for the illustration of the argument are either relatively or 

 absolutely correct. Thus we know that the adsorption 

 curve for hydrions and hydroxylions are not likely to be 

 quite identical, as assumed above. As gelatin is primarily 

 slightly positive, it is probable that the values of a and of n 

 for hydrion adsorption will be relatively slightly greater. 

 The relative values supposed, however, are near enough to 

 illustrate the contention that the type of the maximum 

 volume curve can be explained on this assumption of different 

 adsorption isotherms for each of the ions. 



If the remarks on the compression of the continuous 

 phase be recalled, it will be obvious that in the present para- 

 graphs we have been giving the question of equilibrium - 

 volume a rather one-sided consideration. The volume of the 

 gel when equilibrium is established may be determined in 

 type by the nett charge adsorbed by the disperse phase, but 

 it will be modified also by the lyotrope influence of the 

 particular substance on the continuous phase. When 

 gelatine swells in solutions the influences on both phases are 

 always in operation, and either upon occasion may become 

 predominant. In the case of neutral organic substances, 

 such as cane-sugar, the lyotrope influence is the determining 

 factor. In the case of neutral salts the predominant influence 

 is decided by the place occupied by the salts in the lyotrope 

 series. If at either end of the series the lyotrope influence is 

 uppermost and the effect of ionic adsorptions is practically 

 swamped. Thus sodium sulphate and sodium iodide hinder 

 and promote imbibition respectively as could be expected 

 from their strong lyotrope power. On the other hand, 

 in the case of sodium chloride, which has comparatively 



