248 ANNUAL OF SCIENTIFIC DISCOVERY. 



poisoned by any substance capable of bein<* dialysed, might be made 

 to act as their own dialysers, by simply tying the openings so as to 

 securely enclose their contents, and then plunging them into a ves- 

 sel of water for some hours, when the crystalline poison, such as 

 arsenic or strychnine, would dialyse out, and could be readily de- 

 tected in the external fluid. 



DYALYSIS. 



The application of the researches of Prof. Graham (see Annual Sci. 

 Dis. 1862, p. 197), respecting the diffusion of liquids to the purposes 

 of practical chemistry and the arts of civilization, offers one of the 

 most interesting examples of the eventual tendency of even the most 

 abstract scientific investigations to become practical, and so to aid in 

 promoting the comfort and welfare of mankind. It is almost impossible 

 to imagine a subject offering apparently less practical advantages than 

 docs the admixture of two liquids with each other, and yet from the 

 rigorous and scientific investigation of the phenomena of their mutual 

 diffusion, and the laws which regulate its operation, has sprung a new 

 method of analysis, which promises to revolutionize a very large num- 

 ber of chemical operations, and to introduce new methods of manu- 

 facture into the arts that will entirely subvert many existing processes. 



The subject is so interesting and so novel in its practical bearings, 

 that it is desirable to trace its gradual development from an abstract 

 scientific truth to its present useful applications. 



Mr. Graham's first experiments on the diffusion of liquids were 

 made by means of what he terms pliial diffusion, and they were per- 

 formed as follows : Solutions of different salts, whose diffusive powers 

 were to be examined, were prepared of equal strength, and phials of 

 exactly the same size and shape were filled with these solutions, and 

 then placed separately under the surface of water contained in much 

 larger vessels, the mouths of the phials being left open. Under these 

 circumstances it was found that a certain proportion of the heavy 

 solution contained in the phial rose in opposition to the attraction of 

 gravitation, and mingled with the water by which the phi.il was sur- 

 rounded. In the case of colored solutions, this diffusion v. r as visible 

 to the eye, and in others it was capable of being proved by analysis. 

 It was found, however, that the solutions of different bodies diffused 

 themselves with very different degrees of velocity. Thus common 

 salt diffused with twice the rapidity of Epsom salts or sugar. These, 

 again, are doubly as diffusive as a solution of gum; and albumen, or 

 white of egg, in its turn, does not possess -f of the diffusive power of 

 gum, nor scarcely more than ^ of that of common salt. 



These experiments were varied in different modes, by allowing 

 the diffusion to take place under slightly varying conditions, but 

 the same general results were obtained. The laws deduced from these 

 phenomena are, that crystalline bodies such as salt, sugar, niter, 

 etc., are much more readily diffusible than those that are amorphous, 

 such as gum, gelatin, albumen, solution of starch, or any substances 

 that enter into combination with water in the same manner as the first- 

 named bodies. 



Hence, with reference to this subject, Mr. Graham arranges sub- 

 stances into two groups : those crystalline in character and readily 



