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XXVI IT. An Experimental Test of Sm oluc ho iv ski's Theory of 

 the Kinetics of the Process of Coagulation. By Jnanendra 

 Nath Mukherjee, D.Sc, Professor of Physical Chemistry, 

 University of Calcutta, and B. Constantine Papacon- 

 STANTINOU, D.Sc, Assistant Professor of Chemistry, Uni- 

 versity of Athens *. 



A short account of the Theory. 



IN some experiments on the degree of dispersion of 

 colloidal arsenious sulphide on the rate of coagulation, 

 it has been shown (J. Amer. (Jhem. Soc. vol. xxxvii. p. 2026, 

 1915 : and Sen, Trans. (Jhem. Soc. vol. cxv. pp. 467-8, 

 1919) that the finer sol is less stable. In 1915 one of 

 us pointed out the obvious connexion with the increased 

 facilities of coalescence. The smaller particles have a 

 more vigorous Brownian movement due to the smaller 

 frictional resistance of the medium. This would be clear 

 from the well-known equation of Einstein. The diminution 

 in the mean distance between the particles also increases 

 the rate of collisions. It w r as stated that the adsorption 

 theory does not take these factors into consideration. 

 Recently Smoluchow T ski (Zeit. Phys. Chem. vol. xcii. 

 p. 129, 1917) has been able to formulate the progress 

 of the coalescence with time. His attention was drawn 

 to the subject by Zsigmondy. Bredig (Anorganische 

 Fermente, 1901, p. 15) suggested as the cause of coalescence 

 an increase in surface tension with a decrease in the 

 electric density on the particles. Zsigmondy (Zeitsch. 

 Physikal. Chem. vol. xcii. p. 500, 1918) modified this idea 

 in the sense that there is an attraction, between the particles 

 which increases with decrease in the electric charge. As 

 a result of this attraction he assumes that when one particle 

 comes within a certain distance of another, the two coalesce. 

 This distance is taken as a measure of the force of attraction 

 and is called the radius of the sphere of action. It has 

 been shown by Zsigmondy that the time required for a 

 definite colour-change in a gold sol gradually decreases 

 with rise in electrolyte concentration till it reaches a 

 minimum t, which does not change any further with higher 



* Communicated by Prof. F. G. Donnan, F.R.S. 



t Similar minimum times have been observed with cupric sulphide 

 and mercuric sulphide sols by the writers. A copper sulphide sol gave 

 two minutes as the time necessary for the appearance of visible clots 

 when the concentration of the precipitating electrolyte (barium chloride; 

 was varied from N/300 to N/20. At dilutions higher than N/300 the 

 time was observed to increase as usual (Mukherjee and Sen, loc. cit.). 



Phil. Mag. S. 6. Vol. 44. No. 260. Aug. 1922. X 



