﻿472 Mr. E. F. Burton on the Action of 



Since the thiu ring had the same cross-section as the rods, 

 we may assume that its magnetic hardness was equal to theirs- 

 The experiments here described amply confirm Mr. Peirce's 

 results, and show that large cast iron magnets can be made 

 cheaply and easily ; we hope that this short paper will draw 

 the attention of our instrument makers to the matter. In 

 conclusion I would express my thanks to Dr. H. C. H. 

 Carpenter for his kind help in the chilling of the specimens. 



LI. The Action of Electrolytes on Colloidal Solutions. 

 By E. F. Bueton, B.A. [Emmanuel College, Cambridge),, 

 1851 Exhibition Science Scholar of the University of 

 Toronto, Research Exhibitioner of Emmanuel College*. 



1. Introduction. 



THE study of the coagulative action of comparatively 

 small quantities of electrolytic solutions on irreversible 

 colloidal solutions, besides being of intrinsic interest, has 

 thrown most important light on the mechanism of such 

 solutions ; the suggested theories as to the forces which keep 

 the minute particles in suspension in the liquid media rest 

 to a great extent on the behaviour of these particles on the 

 addition of electrolytes. 



The importance of the phenomenon was first emphasized 

 by the quantitative experiments of Linder and Picton f; they 

 determined the coagulative power of different'salt-solutions on 

 a colloidal solution of arsenious sulphide, and discovered that 

 this property depended directly upon the valency of the 

 metal of the salt. They found that equivalent solutions 

 containing monovalent, divalent, and trivalent metallic ions 

 possess coagulative powers in the ratio of 1 : 35 : 1023. 

 Additional work along the same line has shown that the 

 valency of the metallic ion is important only in the case in 

 which the colloidal particles are negatively charged. In 

 fine, the coagulative power of any electrolytic solution on 

 any colloidal solution depends on the valency of the ion 

 which bears the charge opposite in sign to that on the 

 colloidal particle. 



The next fundamentally important step was made by the 

 researches of Hardy J. Working with egg albumen, he 

 found that the direction in which its particles move in an 



* Communicated by Professor J. J. Thomson, F.R.S. 

 t Journ. of Chem. Soc, vol. Ixvii, p. 63. 



X Proc. Roy. Soc. vol. Ixvi. p. 110: Jour, of Phys. vol. xxix. p. 26 

 (1903). 



