﻿406 Mr. H. D. Murray on Influence of Size of Colloid 



radius r of the particles in each liquid. 01' these three 

 measurements that of the density seemed possibly least 

 accurate, but, as it occurs in each calculation, the relative 

 sizes remain unchanged. 



Solution. 



Soln.B. 

 Fr. II.. 



Fr. VI. 



No. of 

 Particles 

 in mm. 3 



(=»). 



211x10 s 



84-2 xlO 5 

 252 x10 s 



1 



Total Massi 



of Particles 



in 10 c.c. 



•0046 gm. 

 •0034 ,. 



•0017 „ 



1 



Mean volume 



of one 



particle. 



1-83X10- 2 



3-40x10-2 



•57x10-2 



J" 3 



Radius 

 (=r). 



r 2 X»XlO -3 . 



•164 p 

 •201 p 

 ■111 JU 



564 

 340 

 307 



r 2 xn is a measure of the interfacial surface in unit 

 volume. 



Borjeson * has successfully combined the principle of 

 gilding metal particles with observation of the rate of sedi- 

 mentation of the particles so gilded, to measure the size of 

 the original particles. He failed to obtain successful results 

 with gelatine and gum arabic sols. An attempt to apply 

 this method to the mastic solutions as a check on the results 

 obtained also met with failure. It appears therefore unsuit- 

 able for organic colloids. 



Rate of Coagulation. 



It has been customary to fix an arbitrary time during 

 which the colloid solution is allowed to stand after the 

 addition of the electrolyte and before the amount of 

 coagulation is measured. Burton f allowed the solutions 

 which he examined to stand ten hours ; and again J the more 

 dilute solutions which he examined were left for "some days." 

 Weiser and Nicholas § allowed the solutions under examina- 

 tion to stand for twenty-four hours. 



In some preliminary experiments the writer found that 

 abnormal results were obtained with a dilute solution owing 

 to the fact that the time elapsing before examination was too 

 short to permit of coagulation with the minimal quantity of 

 electrolyte. This led to an examination of the actual rate of 

 coagulation. Two solutions were employed, one being ten 

 times more dilute than the other. The results w ere as 

 follows : — 



* Borjeson, Koll. Zeit. xxvii. p. 18 (1920). 



t Burton and Maclimes, Jour. Phys. Chem. xxv. p. 517 (1921). 

 X Burton & Bishop, Jour. Phys. Chem. xxiv. p. 703 (1920). 

 § Weiser and Nicholas, Jour. Phys. Chem. xxv. p. 742 (1921). 



