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ME. T. GEAHAM ON LIQUID DIPFUSION APPLIED TO ANALYSIS. 
It may perhaps be allowed to me to apply the convenient term dialysis to the method 
of separation by diffusion through a septum of gelatinous matter. The most suitable of 
all substances for the dialytic septum appears to be the commercial material known as 
vegetable parchment or parchment-paper, which was first produced by M. Gaij^e, and is 
now successfully manufactured by Messrs. De la E-ue. This is unsized paper, altered 
by a short immersion in sulphuric acid, or in chloride of zinc, as proposed by ISIr. T. 
Taylor. Paper so metamorphosed acquires considerable tenacity, as is well known ; 
and when wetted it expands and becomes translucent, evidently admitting of hydration. 
A slip of 25 inches in length was elongated 1 inch in pure water, and 1’2 inch in water 
containing one per cent, of carbonate of potash. In the wetted state parchment-paper 
can easily be applied to a light hoop of wood, or better, to a hoop made of sheet gutta 
percha, 2 inches in depth and 8 or 10 inches in diameter, 
so as to form a vessel like a sieve in form (fig. I). The disc 
of parchment-paper used should exceed in diameter the 
hoop to be covered by 3 or 4 inches, so as to rise well round 
the hoop. It may be bound to the hoop by string, or by 
an elastic band, but should not be firmly secured. The 
parchment-paper must not be porous. Its soundness will 
be ascertained by sponging the upper surface with pure 
water, and then observing that no wet spots show them- 
selves on the opposite side. Such defects may be remedied 
by applying liquid albumen,* and then coagulating the same 
by heat. Mr. De la Rue recommends the use of albumen in cementing parchment- 
paper, which thus may be formed into cells and bags very useful in dialytic experiments. 
The mixed fluid to be dialysed is poured into the hoop upon the surface of the parch- 
ment-paper to a small depth only, such as half an inch. The vessel described [dialyser) 
is then floated in a basin containing a considerable volume of water, in order to induce 
the egress of the diffusive constituents of the mixture. Half a litre of urine, dialysed 
for twenty-four hours, gave its crystalloidal constituents to the external water. The 
latter, evaporated by a water-bath, yielded a white saline mass. From this mass urea 
was extracted by alcohol in so pure a condition as to appear in crystalline tufts upon 
the evaporation of the alcohol. 
I. Jar-diffusion. 
The mode of diffusing more lately followed, which I have already alluded to as jar- 
diffusion, is extremely simple, and gives results of more precision than could possibly be 
anticipated. The salt is allowed to rise from below into a cylindrical column of water, 
and after a fixed time, the proportion of salt which has risen to various heights in the 
column is observed. The water was contained in a plain cylindrical glass jar, of about 
152 millimetres (6 inches) in height and 87 millimetres (3-45 inches) in width. In 
operating, seven-tenths of a litre of water were first placed in the jar, and then one-tenth 
Eig. 1. — Hoop Dialyser. 
