486 Transactions.—Chemistry. 
This theory has been combated by eminent scientists, as will shortly 
appear ; but whether 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 property. 
Induced by a knowledge of this 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 principles 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 
aa 
