JACQUES LOEB 503 



AICI3 forms acid solutions and it seemed of interest to study the 

 effect of a treatment of gelatin with AICI3. We know now that for 

 pH <4.7 gelatin treated with AICI3 must form gelatin chloride and 

 cannot be affected by the aluminium. The same is true also for pH 

 = 4.7, where gelatin exists as sparingly soluble pure gelatin. For 

 pH > 4.7 aluminium gelatinate can be formed which should be in- 

 soluble. If, however, the concentration of AICI3, becomes too low, less 

 and finally practically no aluminium gelatinate should be formed . These 

 predictions were all fulfilled as the complicated curves in Fig. 14 show. 

 1 gm. of Cooper's powdered gelatin {i.e. chiefly Ca gelatinate) was put 

 for 1 hour at 20° into a series of beakers, each containing 100 cc. of a 

 solution of AICI3 varying in concentration from m/4 to m/8192. 

 The gelatin was then freed from the excess of salt solution by washing 

 as described before. In Fig. 14 the abscissae are the logarithms of the 

 concentration of the AICI3 solution used and the final pH of the washed 

 gelatin is found under each concentration. For pH <4.7 no effect 

 of aluminium is noticeable; the curves are typical gelatin chloride 

 curves. For pH = 4.7 we find a region where gelatin behaves like 

 isoelectric gelatin. For pH = 4.8 and 5.0 we have a precipitate forma- 

 tion due to the formation of aluminium gelatinate. When the con- 

 centration of AICI3 solution used is less than m/1024 the solution be- 

 comes clear again and the curves rise with increasing dilution of the 

 AICI3 solution used. In other words, for pH >4.7 the curves for 

 aluminium gelatinate and cerium gelatinate run parallel as our theory 

 demands.^*' 



This curve suggests incidentally why in the writer's former experi- 

 ments on Fundulus eggs the antagonistic influence of AICI3 to the toxic 

 action of a sodium chloride solution was so restricted. On the acid side 

 of the isoelectric point of amphoteric colloids AICI3 cannot act on the 

 colloid, and on the basic side the concentration of Al is too low. It is 

 the writer's intention to repeat these experiments with Ce2Cl6or LaCls, 

 the solutions of which are less acid. 



^° One wonders what interpretation such a curve as that for AICI3 would have 

 found on the part of the colloid chemists who have persistently ignored not only 

 the hydrogen ion concentration of their protein solutions but who have also over- 

 looked the chemical significance of the isoelectric point. 



