348 Prof. Graham on the Diffusion of Liquids, 



salt which deviates most considerably is sulphate of soda, 

 which for the 1 per cent, solution is 6' 55, or 95*9. A low 

 temperature, however, must be unfavourable to diffusion ex- 

 periments, from increasing the tendency of salts to crystallize. 



In conclusion, I may sum up the results of most interest 

 which this inquiry respecting liquid diffusion has hitherto fur- 

 nished. 



1. I would place first the method of observing liquid dif- 

 fusion. 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 every- 

 thing soluble. Diffusion is also a property of a fundamental 

 character, upon which other properties depend, like the vola- 

 tility of substances ; while the number of substances which 

 are soluble and therefore diffusible, appears to be much greater 

 than the number of volatile bodies. 



2. The novel scale of Solution Densities, which are sug- 

 gested by the different diffusibilities of salts, and to which 

 alone, guided by the analogy of gaseous diffusion, we can refer 

 these diffusibilities. Liquid diffusion thus supplies the den- 

 sities of a new kind of molecules, but nothing more respecting 

 them. 



The fact that the relations in diffusion of different sub- 

 stances 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 

 substances, 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 solubility and 

 liquid diffusion, and not the atoms of chemical combination. 



3. The formation of classes of equi-diffusive substances. 

 These classes are evidently often more comprehensive than 

 the isomorphous groups, although I have reason to imagine 

 that they sometimes divide such groups; that while the dif- 

 fusion 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 



