﻿Particles upon the Adsorption of Electrolytes. 405 



in the field of view. One hundred counts were taken at half- 

 minute intervals, and the average number deduced from this. 

 A few of the {(articles, especially in the case of Fr. II., 

 tended to adhere to the walls of the cell, and to prevent 

 any error due to this, the field of view was shifted five 

 times during- each count. 



The results obtained were as follows : — 



Solution. Dilution. 



Soln.B.. x72G 



Fr. II. . . x 396 



Fr.VL.J X396 



I 



Ob- 

 ject iA-e. 



'4 mm. f.l. 



Eye- 

 piece. 



jDiam. of 



, Field of 



vieAV. 



X 12 -30 mm. 

 X 12 -30 „ 

 Xl8 I -20 „ 



Volume of Field ^ '% 



of view. t-, ,'. , 



Particles, 



14'1 X 10 - 5 mm. 

 14-lxlO- 5 „ 

 6-28 X 10 - 5 „ 



4-1 

 30 

 4-0 



Density of the Particles. 



The density of the solutions was determined with an 

 accurate pyknometer in a thermostat at 17*2° C. The 

 weighings agreed to *0002 gm. Fr. VI. was too dilute to 

 give accurate results. The specific gravity of each solution 

 rose slightly during dialysis, owing probably to the removal 

 of adsorbed or dissolved alcohol. This rise continued for 

 about five days. The weighings were made at the end of 

 ten days. The dialysis was then continued in more efficient 

 dialysers made by Soxhlet thimbles impregnated with 

 collodion, but the specific gravity remained constant. As a 

 mean of four weighings for each solution, the following 

 values for the density of the particles were obtained : — 



Soln. 3. = 1-195. 

 Fr. II. =1-186. 



As a mean the density of the mastic was taken to be 1*190. 

 This value is considerably higher than the density of the 

 mastic in bulk, owing possibly to changes occurring either 

 on dispersion, or coagulation. Perrin * states that he 

 observed the density of his carefully washed granules 

 apparently to rise in salt solutions, and this may account in 

 part for the difference. 



Size of Particles. 



From these three sets of data — the number of particles in 



unit volume, the total mass of mastic in unit volume, and the 



density of the particles— it is possible to calculate the mean 



* Perrin, Ann. C'him. Phys. xviii. p. 5 (1909). 



