104 



THE ROYAL SOCIETY OF CANADA 



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Figure 1 



In Fig. 1 is represented the U tube used by the writer some years 

 ago in determining the mobility of colloidal particles in an electrical 

 field. The method is as follows i^ 



The colloidal solution to be tried is poured into the funnel so as 

 to fill the funnel and small tube to the tap, which is closed; water 

 having a specific conductivity equal to that of the colloid is then 

 poured into the U tube so as to fill it to a height of about 3 cms. The 

 whole tube then is placed in a large glass water bath so as to be almost 

 submerged; this water should be kept at a constant temperature 

 during the course of any experiment. At the end of a few minutes the 

 tap (T) is opened very slightly and the colloidal solution allowed to 

 force the water gently up the limbs of the tube to any required height. 

 If carefully manipulated the surface of separation between the clear 

 water and the solution is very distinct and will remain so for hours. 

 Two electrodes are attached to the terminals of a set of storage cells of 

 constant voltage, and when the current is completed, the surface of 

 separation in one limb will at once begin to rise gradually, while that 



1 Physical Properties of Colloidal Solutions. (Burton), p. 131-2. Phil. Mag., 

 6, 11, 1906, p. 436. 



