﻿the Kinetics of the Process of Coagulation. 309 



to show the validity of the fundamental equations of 

 Smoluchowski. The fact that the curves showing the 

 change in viscosity with time are dissimilar shows that 

 these assumptions are not justified, and Smoluchowski 

 thinks that " T " is dependent on the magnitude of the 

 aggregates. 



Since as yet it is not possible to express physical pro- 

 perties — e. [/., the viscosity or the absorption of light — in 

 terms of definite functions of the number and size of 

 particles, a quantitative comparison of different sols is 

 not possible by indirect methods. We have, therefore, to 

 restrict ourselves to the same sol. 



Experiments icitJi Gold Sols. — An examination of the 

 changes in the colour of gold sols on the addition of an 

 electrolyte showed (Mukherjee and Papaconstantinou, Trans. 

 Chetn. Soc. vol. cxvii. p. 1563 (1920)) that the variation in 

 the absorption of light of gold sols affords an easy and 

 accurate method suitable for this purpose. The gold sols 

 prepared by the nucleus method of Zsigmondy conform 

 very nearly to the requirements of equations (1) to (3) 

 in so far as the particles are fairly uniform in size. It 

 would be very convenient to work with a sol with re- 

 producible properties, as data obtained on different dates 

 with different preparations could be rigorously compared. 



It was found that a sol on standing for some time under- 

 goes somewhat irregular changes, which may in part be due 

 to dust particles getting in accidentally. In spite of all 

 precautions, one cannot be sure that there is no such variation 

 in a particular sample. This variation is not wholly due to 

 the fungus that grows in these sols. For this reason it is 

 necessary to vary one factor only at a time and compare 

 its effects. 



The comparison was therefore restricted to the same sol 

 so long as it showed no variation in its properties. 



The Constancy of^T" in Equations (1) to (3) during 

 the Process of Coalescence. 



According to the simple assumptions of Smoluchowski, 

 the progress of coalescence should be uniformly the same 

 for various electrolytes and for their different concentrations. 

 The constancy of u T " implies that if we assume a series of 

 consecutive stages of coalescence of a sol — under a definite 

 set of conditions, namely a definite electrolyte concentration 



