]ME. T. GEAHAM ON LIQUID DIEFUSION APPLIED TO ANALYSIS. 
217 
able process of M. Wuetz is so slow, that several clays are required to produce a sensible 
result. Thus the diffusate from a solution of 2 grammes of albumen in 50 grammes of 
water was 0-052 gramme m eleven days, which gives 0-005 gramme in a single day. 
Albumen, then, appears to be about 2^ times less dialysable than gum, and 1000 times 
less so than chloride of sodium. 
Even combination with an alkali does not appear to enable albumen to pass through 
the colloid septum. To half a gramme of pure albuminic acid dissolved in 50 grammes 
of water, -05 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 hychate 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 certeinly the entire separa- 
tion 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 Emulsin is precipitated by albuminic and gummic acids, but not by 
unpurified albumen or gum-arabic. The precipitates are white and opaque, 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 albumenized osmometer*. After twelve days the volume of 
liquid within the instrument had increased to 117 grammes by osmose, while a diffu- 
sate had passed through the dialyser of 0-243 gramme, or 4*34 per cent, of the original 
diy albumen. This diffusate consisted 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 crystallizable substances, which are mixed with the former, diffuse 
tlirough the septum readily, and may thus be separated from the former substances. 
6. Sejparation of Arsenious Acid from Colloidal Liquids. 
Dialysis may be advantageously applied to the separation of arsenious acid and metal- 
lic 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 diameter, covered with parchment-paper (fig. 1, 
page 186). The dialyser is then floated in a basin containing a volume of water about 
* Philosophical Transactions, 1851, p. 189. 
2 H 
MDCCCLXI. 
