Clear 

 M M M 



Slight Precipitate Clear 

 turbidity 

 MMMMMMMH 



AlCUonc. M M M 



4 8 16 32 64 128 256 512 1024 2048 40S6 8192 " 



pH 45 46 4.6 4.6 4.6 47 47 48 5.0 5.3 6.1 65 71 



Fig. 14. Impure gelatin (chiefly calcium gelatinate) treated with different con- 

 centrations of an acid salt with trivalent cation, namely, AICI3. As long as pH 

 < 4.7 no aluminium gelatinate is formed and the gelatin exists in the form of gelatin 

 chloride which gives a clear solution. At the isoelectric region pH = 4.7 gelatin 

 is insoluble and all the curves show the low level characteristic of gelatin at the 

 isoelectric point. When pH > 4.7 gelatin exists as Al gelatinate. As long as the 

 concentration of AICI3 used was high enough to transform all the original calcium 

 gelatinate into aluminium gelatinate, m/512 to m/1024, all the gelatin was trans- 

 formed into the insoluble aluminium gelatinate which formed a precipitate as in 

 the case of cerium gelatinate. When the concentration of the AICI3 solution used 

 was less than m/1024 not all the calcium gelatinate was transformed into 

 aluminium gelatinate and the solution became gradually clear again. 



502 



