372 Mr. T. Graham on Liquid Diffusion applied to Analysis. 



gramme of hydrate of soda was added (one-tenth of the weight 

 of the albumen), and the liquid was placed upon parchment- 

 paper. No albumen could be discovered in the diffusate of 

 several days, but it gave '069 gramme of carbonate of soda, 

 equivalent to *053 gramme of hydrate of soda — that is, the whole 

 soda originally added to the albumen. The separation of the 

 soda from the albumen may possibly have been aided by the 

 presence of carbonic acid in the water ; but certainly the entire 

 separation of the alkali from albumen by diffusion through 

 a colloidal film is a remarkable fact. Hydrate of potash was 

 found to diffuse away from albumen in the same manner. 



A solution of Emulsineis precipitated by albuminic and gum- 

 mic acids, but not by un purified albumen or gum-arabic. The 

 precipitates are white and opake, pulverulent, and not gelatinous. 

 They are soluble in acetic acid. 



A thin stratum of pure albumen coagulated by heat appears 

 to intercept completely the passage of liquid albumen of the egg. 

 Forty grammes of undiluted egg-albumen, representing 5 - 6 

 grammes of dry albumen, were placed on a dialyser of the small 

 size, composed of two sheets of calico well-impregnated with 

 albumen and coagulated by heat of steam, as in the albumen- 

 ized osmometer*. After twelve days the volume of liquid within 

 the instrument had increased to 117 grammes by osmose, while 

 a diffusate had passed through the dialyser of 0*243 gramme, or 

 4*34 per cent, of the original dry albumen. This diffusate con- 

 sisted of salts chiefly, with some organic matter, but no portion 

 of the latter was coagulable by heat. 



Neither gelatinous starch, animal gelatine dissolved in water, 

 nor extract of flesh appears to be capable of diffusing through a 

 colloid septum in a sensible degree, although salts and other 

 crystallizahle substances, which are mixed with the former, dif- 

 fuse through the septum readily, and may thus be separated 

 from the former substances. 



6. Separation of Arsenious Acid from Colloidal Liquids. 



Dialysis may be advantageously applied to the separation of 

 arsenious acid and metallic salts from organic solutions in medico- 

 legal inquiries. The process has the advantage of introducing 

 no metallic substance or chemical reagent of any kind into the 

 organic fluid. The arrangement for operating is also of the 

 simplest nature. 



The organic fluid is placed, to the depth of half an inch, on a 

 dialyser formed of a hoop of gutta percha 10 or 12 inches in dia- 

 meter, covered with parchment-paper (fig. 1, page 208). The 



* Philosophical Transactions, 1854,, p. 189. 



