^IR. T. GEAHAII ON LIQUID DIFFUSION APPLIED TO ANALYSIS. 
219 
5. A quantity of white of egg, amounting to 50 grammes, to which 0-01 gramme 
of arsenious acid in solution had been added, was coagulated by heat. The solid mass 
was then cut up into small pieces and placed on the dialyser, mixed with 50 grammes 
of water; after the usual period of twenty-four hours, the diffusate gave O'Ol gramme 
of tersulphide of arsenic, equivalent to O' 00 8 gramme arsenious acid. Here, of the 
mass upon the dialyser, the arsenious acid formed only i o.ooo dth part, yet four-fifths 
of it are recovered. 
6. One hundred grammes of milk, charged with lo.ooo ^^^^ of arsenious acid (O'Ol 
gramme), and forming a stratum on the dialyser of 10 millimetres, gave a diffusate 
which yielded O'OlO tersulphide of arsenic, equivalent to O' 00 8 gramme of arsenious 
acid. The outer hquid was colourless, and gave no indication of casein, but it contained 
of course the salts and the sugar of the milk. 
7. The same experiment was repeated with sized writing-paper, as the septum, applied 
to the same bulb. The result was a slight increase in the quantity of arsenious acid 
recovered. 
It appears, then, that arsenious acid separates on the dialyser from gum, from gela- 
tine, albumen, fluid or coagulated, and from casein, and is obtained in a solution fit for 
the application of reagents. 
8. Half a litre of dark-coloured porter, with 0'05 gramme of arsenious acid added 
(ToroWo^ffli of arsenious acid) was placed on a hoop dialyser, 8 inches in diameter, 
and the whole floated in an earthenware basin containing 2 or 3 litres of water. After 
twenty-four hours the latter fluid had acquired a slight tinge of yellow. It yielded, 
when concentrated and precipitated by sulphuretted hydrogen, upwards of one-half of 
the original arsenious acid in a fit state for examination. 
0. In a similar experiment on 200 grammes of defib rinated blood charged with 
jo^dth part of arsenious acid (0'05 gramme), and placed in a similar dialyser to the 
last for twenty-four hours, the diffusate of arsenious acid was recovered with the same 
facility, and appeared to be equally considerable. 
10. Animal intestines, charged with the usual minute proportion of arsenious acid, 
were cut into small pieces and digested in water, about 32° C., for twenty-four hours. 
Tlie whole was then thrown upon a dialyser for an equal time. Arsenious acid diffused 
out so free from colloidal matter that the action of reagents was not interfered with. A 
high temperature in digesting the intestines is quite unnecessary, and appeared indeed 
to increase the difficulty of diffusing out the arsenious acid afterwards. 
The tartrate of i^otash and antwiony, mixed in the small proportion of rorWo^^h, 
with defibrinated blood and with milk, was separated by dialysis quite as effectually as 
arsenious acid above. 
Strychnine also was separated from organic fluids in the same manner, a small addi- 
tion of hydrochloric acid being first made to the fluid on the dialyser. 
Dialysis then appears of general application in the preparation of a liquid for exami- 
nation by chemical tests, whether the poison looked for be mineral or organic. All 
2 H 2 
