48 



weakly ionized HgCl, has accordingly the siriallest discharging 

 power. 



5. In conclusion we wish to draw attention to a consequence of 

 the stated electro-viscous character of part' of the viscosity- in the 

 rnbbersol. It has often been tried to compare the quality of different 

 samples of rubber by measuring the viscosity of benzene solutions 

 of the same concentration. Tiie ciioice of thi.s property for a com- 

 parison is not unlogical, a.s in the tirst instance the viscosity may 

 be considered as a measure for the solvation, and tiiis can be taken 

 into account as a real colloid cliaracteristic. PCxperience now actually 

 teaches that there exists a certain correlation between the viscosity 

 of the sol and the mechanic properties which determine the quality ; 

 it is, however, no more than a vague correlation. It has, however, 

 appeared above, that part of the viscosity is not in connection wilh 

 the solvation, but is of electric origin, and has, therefore, a perfectly 

 casual character, dependent on the soluble components which accom- 

 pany the rubber and which have no influence on (he mechanic 

 properties in these minimum concentrations. If it is, therefore, desired 

 to detect a functional relation between viscosity and the pi-operties 

 of the quality o'f the rubber, it will be necessary to eliminate before- 

 hand the electro viscous effect by judicious addition of the electrolyte. 



We consider tiie knowledge of these electro-viscous phenomena 

 of importance from the standpoint of pure colloid chemistry, because 

 they open a way to the study of the electric relations in non- 

 aqueous sols. 



Utrecht, VAN 't HoFF-laboratory, 1922. 



