486 Transactions. —Chemistry. 



This tlieory lias been combated by eminent scientists, as will shortly 

 appear ; but wlietlier it be true or not, it is certain that the mode of action 

 of such salts is quite different to that by which alum is always supposed to 

 operate, although they have been, for want of due consideration, undis- 

 tinguished from each other. It is, moreover, certain that clay, so coagu- 

 lated, is de-hydrated, and the knowledge of the two cognate facts — - 

 simultaneous coagulation and dehydration of clay under such circumstances 

 — is, as will shortly be seen, one step towards the solution of the question 

 before us (the cause of the persistent suspension of clay in certain water), 

 as it is thereby shown that clay must be hydrated to an extent at about its 

 maximum in order to manifest this ^Jroperty. 



Induced by a knowledge of thjs fact, I ventured (in the communication 

 referred to) in explanation of this persistent suspension, the opinion that 

 clay can hydrate to an indefinite extent, so that it can even take up in a 

 combined form the whole of the water in which it may be diffused, making 

 a kind of jelly with it, very weak but still having enough consistence to 

 retain in a comparatively fixed state the clay particles of which it is in part 

 composed. But having lately taken careful cognizance of the remarkable 

 fact that particles of clay when persistently in suspension are as persistently 

 in motion (describing the so-named Browinian movements), I have now 

 perceived that hydration of clay never does occur to this extent ; these 

 movements of such particles proving the presence of free water in their 

 neighbourhood, which, of course, is against the theory of indefinite hydra- 

 tion, and so left the question as to this persistent suspension of clay still to 

 me unsolved. 



Upon casting about in our scientific works and periodicals for a solution 

 of this phenomenon, I came across various theories professing to account for 

 it. Notably, one by Prof. Jevons, ascribing it to electricity ; one by Dr, 

 Hunt, ascribing it to the viscidity or cohesiveness of pure water ; and 

 another by Mr. Dancer, who attributes it to the effect of heat unevenly 

 distributed. Upon mature deliberation I concluded that each of these 

 theories is as unsound as the one which I had discarded, and it then 

 occurred to me that in the action of Osomose we have the solution sought 

 for, i.e., the cause of the persistent suspension of clay, and after a careful 

 consideration of this view of the case, I am so impressed with the idea of 

 its accuracy that I now venture to submit it for your criticism. 



In order to present this view to you in as favourable and clear a light as 

 possible, I will first briefly state the princij)les of Osomose. 



Any colloid (that is, a substance which cannot be crystallized, and 

 which, though insoluble in water, is capable of largely combining with 

 it) has the property of allowing water to pass through it, and crystalloids 



