ALUMINIUM HYDROXIDE BY ELECTEOLYTES. 



27 



with most organic substances which form real (not colloidal) 

 solutions and do not undergo electrolytic dissociation. 



Mannite solution, to which boric acid had been added, was 

 also found quite inactive, although it formed complex acids of con- 

 siderable strength.^ Boric acid itself exerts no coagulative action. 



Crum observed the coagulating action of some decoctions of 

 certain dye-stuffs. The solutions of many colouring matters are 

 colloidal, and when the suspended particles have negative electric 

 charge, this is to be expected, particularly according to the 

 observations of Biltz." We made observations on the solutions 

 of helianthin, fuchsin, and eosin, and also on that of tannin ; 

 and found their coagulative power very strong as shown in the 

 following table. 



TABLE 15. 



It is known that eosin has cathodic cataphoresis and the same 

 is probably the case with other substances in the table. 



It was also observed that the colloidal solution of aluminium 



1. Magnanini: Zeits. für physik. Chem., 6, (1890), 58. 



2. Berichte d. deutschen chemischen Gesellschaft, 37, (1904), lll.*^ 



