PROPERTIES OF GELATINE AND GLUE 215 



therms be plotted as usual we get the fairly typical curves 

 shown in Fig. i. 



Now in practice there are always two of these ions, each 

 giving its own specific effect in opposite senses, and the 



difference (a } n^ a^) represents the nett charge adsorbed. 

 Hence we have the following combinations : 



Inorganic acid loc 3 ^ 6c^ 



Organic acid 



Alkali 



Inorganic salt 7^* 6c* 



If we plot these values of nett adsorption against the 

 concentration we obtain the curves shown in Fig. 2. 



MtoA. 



c 



FIG. 2. 



On the assumption that the nett charge adsorbed is the 

 dominant factor in determining the maximum swelling at 

 equilibrium, one must therefore regard the curves of Fig. 2 

 as representing the changes in volume of the swollen gel as 

 the concentration is increased. Now in type these curves 

 correspond to those obtained by experiment from hydro- 

 chloric acid, acetic acid, caustic soda, and common salt. 

 The maximum swelling with hydrochloric acid increases 

 rapidly with the concentration at first and then rapidly 

 decreases, though not at such a great rate. The swelling 

 with acetic acid increases less rapidly and to a less maximum, 



