﻿Particles upon the Adsorption of Electrolytes. 403 



of mastic were completely coagulated with a concentration of 

 3*0 millemols. of HC1, and redispersed in an equal quantity 

 of water. It appears below as solution B. It is to be 

 expected that Fr. II. will contain particles of an average size 

 greater than those in Fr. VI. and both will contain particles 

 of more uniform size than those in solution B. 



The solutions after dispersion were kept in dialysers of 

 parchment paper until the dialysate was uncontaminated 

 with HC1. They were then placed in perfectly clean vessels 

 of resistance glass fitted with a siphon, and a soda-lime tube 

 attached to the air-inlet. The siphon pipes were closed by 

 short pieces of rubber tubing and pinch cocks. 



Basis of Comparison. 



Any method of comparison between two or more solutions 

 based upon the total masses of the disperse phase in unit 

 volume is useless when applied to data due to adsorption. It 

 is possible to take as a basis the number of particles in unit 

 volume, or, what is probably more characteristic and capable 

 of giving more directly comparable results, the total inter- 

 facial surface in unit volume. The former may in most cases 

 be ascertained by a direct count under the ultramicroscope. 

 To evaluate the latter it is necessary, beyond this, to know 

 the total mass of the disperse phase, which can be effected by 

 weighing after evaporation to dryness, or by the methods of 

 volumetric analysis. In addition it demands a knowledge of 

 the density of the disperse phase, or of the specific gravity 

 of the solution and of the dispersion medium. 



Perrin in his researches upon Brownian movement 

 obtained the density of the mastic with which he was working 

 by evaporating- a portion of his suspension to dryness and 

 estimating the density of the solid mastic. This value 

 (1'064) he found to agree admirably with the density as 

 determined from specific gravity measurements. It seems 

 uncertain, however, as Burton * has pointed out, whether it 

 is justifiable to assume that the density of the particles in the 

 ordinary colloidal solution of gum mastic is the same as that 

 of the solid substances. Perrin, as a matter of fact, used a 

 suspension of mastic which had been obtained by centrifnging 

 the larger particles from a solution of mastic and rejecting 

 the remainder. In the case of the present solution, it 

 seemed desirable to determine the density of the particles 

 directly, with a pvknometer. 



* Burton, ' Physical Properties of Colloidal Solutions,' 2nd Edition, 

 p. 125. 



1 D 2 



