[burton] COLLODIAL PARTICLES 107 



The radius of these particles as determined at the time by the counting 

 method was 1-7X10"^ cm. The closeness of the agreement of these 

 two determinations is an indication that careful observation of this 

 settling would give an extremely serviceable method of determining 

 the size of colloidal particles much below the microscopic size. It 

 should be noted that there was no particular incentive to record 

 exactly the portion of the colloidal surfaces in the U tube at the end 

 of the first 10 minutes run, as this reading was used merely as a check 

 as to whether or not the apparatus was working normally. 



Experiments are now being carried out by Mr. W. W. E. Ross, 

 under direction of the writer, to determine the settling very exactly. 

 By the application of ultramicroscopic illumination of single particles 

 in a slowly alternating electric field acting in a vertical direction, 

 it is hoped that the settling will be observed over a very much more 

 extended interval of time and that an exceedingly exact method of 

 weighing these particles will be developed. In addition, this method 

 should prove useful in determining the effect of the addition of various 

 electrolytes on the size of colloidal particles, and thereby shed a great 

 deal of light on the incipient processes of coagulation. 



Department of Physics, 

 University of Toronto. 

 March 7th, 1919. 



