﻿Electrolytes on Colloidal Solutions. 

 3. Results. 



475 



The solutions used were prepared in pure water by Bredig's * 

 electrical method, and the velocities were measured as already- 

 described in a former paper by the writer f. Large quantities 

 of very pure solution were quite easily prepared by the use 

 of a motor to carry on the sparking between the metal 

 electrodes underneath the surface of the pure water. The 

 water used had a specific conductivity of 3 x 10 — 6 at 18° C. 



In each case (silver and gold solutions) the velocity was 

 measured for the pure solution ; varying quantities of 

 aluminium sulphate were then added to fresh samples of the 

 stock colloidal solution and the velocity again measured. 

 Aluminium sulphate was used because the metal ions being 

 trivalent have a large coagulative power; if these ions in pro- 

 ducing coagulation do diminish the charge on the particles, a 

 very small addition of aluminium ions should have a perceptible 

 effect on the velocity of the particles, while at the same time 

 the specific conductivity, and consequently the current 



N 



through the colloid, is small. 



1000 



aluminium sulphate 



(pure, from Kahlbaum) was added drop by drop to some 

 40 c.cs. of the colloidal solution, the whole well mixed and 

 the velocity measured ; each experiment was completed in 

 the course of two hours after adding the electrolyte. In 

 Tables I. and II. the velocities corresponding to the various 

 weights of aluminium per 100 c.cs. of colloidal solution are 

 given : a gradual decrease in the velocity and final reversal 

 of direction is shown in each case. The positive sign in the 

 velocity column indicates motion of the particles toward 

 the anode. 



Table I. — Silver Solution. 

 Amount of silver per 100 c.cs. = 6'5 mgs. 



No. 



1 

 Grnis. of Al. per Spec. Conductivity 

 100 c.cs. ofSolutiouatlS J C. 



Velocity at 

 18° C. 



1 







14 x 10 -6 



31 xlO -6 

 30-3 *10~ 6 



+224x10-° 

 + 7-2 xl0~ 5 

 - 59 xlO -5 

 -13-SxlO - 



2 



3 



3SxlO~ 6 297 X10 -6 

 77xl0 — 6 *>S-r>ylO~ 6 



4 









* Loc. cit. 



t Phil. Mag. [6] vol. xi. April 1900. 



