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PROFESSOR GRAHAM ON THE DIFFUSION OF LIQUIDS. 
1. I would place first the method of observing liquid diffusion. This method, 
although simple, appears to admit of sufficient exactness. It enables us to make a 
new class of observations which can be expressed in numbers, and of which a vast 
variety of substances may be the object, in fact everything soluble. Diffusion is also 
a property of a fundamental character, upon which other properties depend, like the 
volatility of substances ; while the number of substances which are soluble and there- 
fore diffusible, appears to be much greater than the number of volatile bodies. 
2. The novel scale of Solution Densities, which are suggested by the different dif- 
fusibilities of salts, and to which alone, guided by the analogy of gaseous diffusion, 
we can refer these diffusibilities. Liquid diffusion thus supplies the densities of anew 
kind of molecules, but nothing more respecting them. 
The fact that the relations in diffusion of different substances refer to equal 
weights of those substances, and not to their atomic weights or equivalents, is one 
which reaches to the very basis of molecular chemistry. The relation most frequently 
possessed is that of equality, the relation of all others most easily observed. In liquid 
diffusion we appear to deal no longer with chemical equivalents or the Daltonian atoms, 
but with masses even more simply related to each other in weight. Founding still 
upon the chemical atoms, we may suppose that they can group together in such 
numbers as to form new and larger molecules of equal weight for different sub- 
stances, or if not of equal weight, of weights which appear to have a simple relation 
to each other. It is this new class of molecules which appear to play a part in solu- 
bility and liquid diffusion, and not the atoms of chemical combination. 
3. The formation of classes of equi-diffusive substances. These classes are evi- 
dently often more comprehensive than the isornorphous groups, although I have 
reason to imagine that they sometimes divide such groups; that while the diffusion 
of salts of baryta and strontia, for instance, is similar, the diffusion of salts of lead 
may be different. 
4. The separation of the whole salts (apparently) of potash and of soda into two 
divisions, the sulphate and nitrate groups, which must have a chemical significancy. 
The same division of the salts in question has been made by M. Gerhardt, on the 
ground that the nitrate class is monobasic and the sulphate class bibasic. 
5. The application of liquid diffusion to the separation of mixed salts, in natural 
and in artificial operations. 
6. The application of liquid diffusion to produce chemical decompositions. 
7. The assistance which a knowledge of liquid diffusion will afford in the investi- 
gation of endosmose. When the diffusibility of the salts in a liquid is known, the 
compound effect presented in an endosmotic experiment may be analysed, and the 
true share of the membrane in the result be ascertained. 
But on the mere threshold of so wide a subject as liquid diffusion, I must postpone 
speculation to the determination of new facts and the enlargement of my data, of the 
present incompleteness of which I am fully sensible. 
