8 
ORIGINAL COMMUNICATIONS. 
Water displaces alcohol, and vice versa. In displacing one 
liquid by another, the interposition of a small quantity of the 
former is recommended, before the substitution of that by 
which you would displace it. In fibrous vegetable substances, 
or such as have been too coarsely bruised, the liquid runs off too 
fast. In this case the aperture of the funnel should be closed 
by a cork, and the drained liquid returned to the funnel : suf- 
fer it to remain for sometime, until all the finer parts subside, 
then remove the cork, and if it still flows rapidly, or has a 
turbid appearance, pass again, and repeat until regular and 
limpid. 
The operation of continued displacement at first imposed 
upon me the necessity of watching it to keep up a supply of 
liquid, by adding from time to time new portions. But by 
resorting to the process of Hauy, jr., in simple filtration, this 
trouble is saved me, and my presence not even required, 
while the displacement goes on in a very uniform manner. 
It is by the superposition of an inverted bottle or matrass, 
filled with the same liquid as that with which you are con- 
ducting your operation, and with its mouth below the surface 
of the liquid in the funnel. As a drop escapes from the bot- 
tom of the funnel, a bubble of air which is seen to rise 
through the liquid, announces that a corresponding drop has 
filled up the vacuum. Previous maceration is deemed super- 
fluous. 
If the matter is much pressed, less liquid is absorbed ; the 
running is slower, and greater time is required. 
You can operate by heat or cold as may be necessary, but 
heat retards the filtering from its action upon the farinaceous 
matters of the vegetable substance, causing a diminution of the 
interstices by the swelling of the mass. 
An excellent evidence of the advantage of displacement 
adduced by Messrs. Boullay, is that of the cold water wash- 
ings of herbs. We are all aware of the difficulty of filter- 
ing decoctions and infusions, and their oft-turbid appearance, 
especially that of bark, which when filtered, speedily resumes 
its opacity. Messrs. B. say that cold water displacement 
