546 
PHARMACEUTICAL MEETING. 
1st 3 oz. had sp. gr. of. 927*2 
of 8th 40 oz. „ . 926*8 
Finished Tincture .... mean 947 
Pressings of residue, 70 fl. oz. . . .. 926 
The state of disintegration of the ingredients to be operated upon, and the 
quantity of moisture to be employed in the first wetting of them, were matters 
for grave consideration; they had to be modified according to circumstances. 
Theoretically, the finer the state of division the better; but practically, this will 
not answer. In small quantities some substances may be finely divided, but 
on a large scale it would be impracticable,—in the first place, from the impos¬ 
sibility of working a large quantity of fine powder, and secondly, the expense of 
time and labour required would be a complete bar to its adoption. A sieve 
twenty wires to the inch is fine enough for most things, and some substances to 
be operated upon with water only may be very much coarser. The quantity 
of fluid to be employed must vary according to the nature of the ingredients 
whether they are of a hard or soft texture, and whether spirit or water, or a 
mixture of both, is to be the medium. One great impediment to successful 
operation is the presence of multitudes of air-bubbles dispersed through the 
matter operated upon, giving rise to channels through which the fluid will 
pass rather than uniformly through the whole mass. These arise from various 
■causes, which experience only will teach ; but there is one source of difficulty 
on this point which appears to have been entirely overlooked by most ope¬ 
rators, or at least not referred to in print, namely, the intercellular air-spaces 
of many vegetable substances. It is a great mistake with such substances to 
at once wet them with a quantity of fluid, which would convert them into a 
kind of pudding or mud, especially if they contain much mucilaginous mat¬ 
ter. The exhausting of such a substance with a moderate amount of fluid, 
especially if it be water, is almost impracticable, in consequence of the water 
surrounding the air-spaces and rendering the escape of the confined air almost 
an impossibility; but the method recommended in the Edinburgh Pharma¬ 
copoeia is founded on sound philosophical principles, and obviates the difficulty, 
so that even rhubarb, a most troublesome substance, can be managed by it. 
It recommends the substance to be wetted with half its weight of the liquid. 
Why should this small quantity, which leaves the substance in a merely damp 
mealy condition, be better than the larger quantity, which appears to wet it 
so much more completely ? Tie apprehended it was this,—that the smaller 
quantity being sufficient to damp the substance and cause the cells filled with 
dry matter to swell out, by so doing caused the expulsion of the air from the 
empty cells and intercellular spaces, and thus removed one great obstacle to 
the satisfactory extraction of the soluble matter. But, as before observed, it 
is not every substance that can be so treated; others require a much larger 
quantity of fluid to begin with, and it is singular that too much or too little 
fluid used in the first wetting will lead to an equally unsatisfactory result in 
the non-exhaustion of the substance with a reasonable amount of fluid. As a 
general rule, he had found that substances were not exhausted with less than 
four times their weight of fluid; there were exceptions—some might be ex¬ 
hausted with less than four, and some required five or six times their weight, 
but much depended upon the state of disintegration and the skill of the ope¬ 
rator ; hence the extraction of a small quantity of tincture from a large quan¬ 
tity of dry substance was a very difficult operation even in the hands of the 
most experienced, and for this reason he regretted to see such conditions re¬ 
quired in the new Pharmacopoeia. When a large quantity was to be obtained 
from a small quantity of matter, the case was very different; but even then, on 
