538 
PHARMACEUTICAL MEETING. 
placement of the tincture be effected with spirit, this will be left in the marc, 
and can only be recovered either by subsequent displacement with water, or 
partially by expression. In either case, the spirit so recovered will be more 
or less impure, and will not readily admit of purification, or of any useful 
application in its unpurified state. It is to avoid this loss or inconvenience 
that many operators, after percolating with the quantity of spirit required for 
the production of the tincture, instead of displacing what is left in the perco¬ 
lator with a further portion of spirit, substitute water at once as the displacing 
liquid; but the almost inevitable effect of this practice is to cause the intro¬ 
duction of variable quantities of water into the tinctures, and in other respects 
to alter and deteriorate the products. 
It is easy to show by experiment that water placed over spirit falls through 
the latter, and in doing so rapidly mixes with it. Thus, if two glass bulbs, 
connected by a slender tube, be filled, one with pure water and the' other 
with coloured spirit, and placed so that the spirit is above the water, they will 
remain unmixed for a great length of time; but if the apparatus be reversed, 
so that the water is placed above the spirit, complete admixture takes place in 
a few minutes. 
Now, in attempting to displace a spirituous tincture with water, a column 
of the latter is placed over the tincture, and although the very rapid admixture 
of the two is counteracted by the minuteness of the channels through which 
they have to flow, yet admixture does take place, the spirit passing upwards 
while the water passes down ; and the extent to which this occurs will depend 
upon the length of time during which this part of the process is in operation, 
and the condition of the ingredients through which the liquids have to pass. 
It is now admitted by the most able advocates of the process, that one and 
the same liquid should be used for percolation and displacement, until the 
whole of the product intended for use as tincture has been collected, and that 
water can only be used safely and properly for recovering the impure spirit 
left in the percolator after the production and separation of the tincture has 
been completed. In accordance with this view, it will be found that in the 
preparation of those tinctures for which percolation is ordered in the United 
States Pharmacopoeia, the spirituous menstruum is directed to be usedthrough- 
out the process, and no reference is made to the recovery of the spirit left in 
the apparatus when the operation is completed. Buignet, to whom I have 
already alluded, also takes the same view, and directs the spirit to be used 
from first to last. In countries where spirit is cheap, the loss that is thus 
entailed may be of little importance, but such is not the case in this country; 
and if displacement of the tincture with water be not considered admissible, 
as it certainly cannot be, this will materially modify the opinion that many 
have formed with reference to the economy of the process of percolation. 
No better case could be taken for illustrating the process throughout, for 
showing how a vegetable powder may be exhausted with the minimum quantity 
of liquid, and the extent to which the solution so formed may be separated 
from the solid mass by displacement, than is afforded in the preparation of—• 
Essence of Ginger. This may be very readily economically and successfully 
produced by treating finely-powdered ginger with rectified spirit in a perco¬ 
lator. The ginger cannot be too finel} 7- powdered, yet it does not require ad¬ 
mixture w ith sand or any other substance. It may be tightly compressed in 
the percolator, and yet it will not unduly impede the percolation. It easily 
yields its soluble matter to spirit, and may be exhausted with about its own 
weight of this liquid; yet, in its exhaustion by spirit, there is not such a dimi¬ 
nution effected in the volume of the powder, and consequent contraction of 
the solid mass, as to interfere with the efficiency of the percolation. The con¬ 
ditions are thus in every respect favourable to the success of the operation. 
