57 



That the quantity a, defined as the free space within the unswoUen 

 jelly, has a measurable value for gelatin is suggested by the fact that 

 the volume of the swollen jeUy is sUghtly less than the sum of the 

 volumes of the gelatin and absorbed water before swelling. But the 

 values for V are generally so much greater than the total volume of 

 the gelatin before swelling that any error due to neglecting a would 

 be insignificant. Appreciable errors might have resulted from the 

 assumption of total ionization of the electrolyte, were it not for the 

 fact that the rates of change of the slopes of the curves are greatest 

 for concentrations of HCl less than 0-01 N. 



In order to apply the theory to weak acids, it is necessary to 

 include the equation which defines the ionization constant of the 

 acid. Procter and Wilson have derived equations which explain 

 the action of salt in repressing the swelling of gelatin in acid solutions ; 

 for these and others dealing with poly basic acids, reference should 

 be made to the original papers. At the moment of WTiting no evidence 

 incompatible with the theory has been discovered. E. A. and H. T. 

 Graham stated that the theory would not account for the repression 

 of swelling by sugars, but Wilson pointed out that the difference in 

 molal fugacity of the sugar in the two phases due to the differences 

 in ion concentrations is sufficient to account for the repressing action 

 of sugar. 



The possibilities of gain to pure science fully justify the undertaking 

 of the enormous amount of work stiU to be done on the theoretical 

 side of imbibition and the problem appears to lie as much in the 

 field of the mathematician as in that of the chemist. 



Recent Publications on Imbibition of Gels. 

 {See also bibliography at end of Part II.) 



Aeisz, L. ' The Sol and Gel State of Gelatin Solutions.' I. Gelatinising. 

 II. Swelling. ' Koll. Beihefte,' 7, 1 (1915). Size of gelatin particles and 

 attractions between them probably decrease during swelling. SwelUng 

 and solution are considered two stages of the same process, indefinite swelling 

 amounting to solution. 



Bennett, H. G. 'The Swelling of Gelatin.' 'J. Soc. Leather Trades Chem.', 

 2, 40 (1918). Polemical. 



Fischer, Martin H. Edema and Nephritis. (J. Wiley & Sons, 1915.) On 

 Hydration and "Solution" in Gelatin. 'Science,' 42, 223 (1915). A 

 warning against the general adoption of the view that the " solution " of a 

 protein represents but the extreine of that which in a lesser degree is called 

 swelling. Hydration or swelling is to be regarded as a change through which 

 the protein enters into physicochemical combination with water ; ' ' solution ' ' 

 as one which can be most easily understood as the expression of an increase 

 in the degree of dispersion of the colloid. 



Fischer, M. H. and Sykes, A. ' The influence of Non-electrolytes on the 

 Swelling of Protein.' ' Kolloid-Z.' 14, 215. Non-electrolytes decrease the 

 degree of swelling of protein the more so the greater the concentration. The 

 conclusion is drawn that the phenomenon is one of adsorption rather than 

 osmosis. 



' The Non-acid and Non-alkaline Hydration of Proteins.' ' KoUoid-Z.' 

 16, 129 (1915). In the swelling of gelatin by urea, there are two changes, 

 one towards increasing hydration, the other towards increasing degree of 

 dispersion. 



FiscECER, M. H. and Hooker, M.O. ' On the Swelling of Gelatin in Polybasic 

 Acids and their Salts.' 'J. Am. Chem. Soc' 40, 272 (1918). 



