184 
PROFESSOR GRAHAM ON OSMOTIC FORCE. 
clay. A plate of Caen stone, which is an impure limestone, was greatly more active 
with a solution of carbonate of potash than a plate of pure white marble was. The 
effect of impurities in making limestone suitable for osmose did not escape the ob- 
servation of Dutrochet ; it was referred by him to the attraction of alumina for 
water. Mere capillarity, therefore, is insufficient to produce the liquid movement, 
while the vis motrix appears to be some form of chemical action. 
For the proper appreciation of a chemical theory of the osmotic force, I would now 
invite attention to a purely speculative subject, namely, the molecular constitution 
of water and saline solutions. Allowing that water, in the state of vapour, is correctly 
represented as a compound of one equivalent of oxygen and one of hydrogen, it may 
still be true that the molecule of liquid water is a varying aggregate of many such 
molecules, or is n times HO. But if so much is conceded, a new and peculiar 
grouping of the atoms of oxygen and hydrogen becomes not only possible but pro- 
bable. Instead of arranging them in a series of pairs of H+O, H+O in our com- 
pound molecule, we may give a binary form to that molecule in which a single atom 
of oxygen is the negative or chlorous member, and the whole other atoms united 
together form a positive or basylous radical. In this radical we have a certain mul- 
tiple of HO with one H in excess, the last condition being most usual in compound 
radicals, such as methyl, ethyl, benzoyl, &c., which have all a single unbalanced 
equivalent of hydrogen ; H„ O n — (H w+1 O m ) +0. 
Further, this new oxide should be more easily decomposed than oxide of hydrogen, 
HO. The basicity of the radical (H m+1 O m ) depends upon the disproportion of the 
equivalents of oxygen and hydrogen in its constitution, there being one of hydro- 
gen in excess. Now that disproportion becomes less as we ascend, as in 3H+ 20, 
llH + 100, 101H + 100O; and the more feeble the basyl-atom, it may be supposed 
to retain less forcibly its fellow oxygen-atom or other negative element with which it 
is combined. When water, therefore, has to undergo decomposition in a voltaic 
circle, it will naturally assume the molecular arrangement supposed, as being the 
binary form which is most easily divisible into a positive and negative element, or 
that in which water is most easily decomposed. 
This molecular view has been brought forward at present principally for the aid 
which it gives in conceiving what is known as electrical endosmose. 
This interesting phenomenon, first well developed by our colleague Mr. Porrett, 
has very lately been defined with great clearness by M. Wiedemann*. The water 
which accumulates at the negative pole (or follows the hydrogen), in the electrolysis 
of the pure liquid, is found to be exactly proportional to the amount of circulating 
affinity ; that is, with every equivalent of hydrogen that is discharged at the negative 
pole the same quantity of water arrives there, and will force its way through a 
porous diaphragm to reach that destination. The reason now suggested is, that the 
travelling basylous atom in the voltaic decomposition is not hydrogen simply, but 
* Wiedemann, Poggendorff’s Annalen, vol. ixxxvii. p. 321. 
