443 
ON PERCOLATION. 
4 
disintegration, and to have these carefully packed in the apparatus ; but neither 
of these conditions were provided for in the Pharmacopoeia process. He looked 
upon the process as a compromise between maceration and percolation, in 
which neither process was fully carried out. 
Dr. Redwood agreed with the previous speaker, that the process of the 
British Pharmacopoeia could not be correctly designated percolation. It 
appeared to be the result of a compromise, but he considered it a compromise 
in which displacement rather than percolation was appended to macera¬ 
tion. The terms displacement and percolation were both applied to the 
process, which had been so much extolled for several years past as a pharma¬ 
ceutical process, and these terms were frequently looked upon as synonymous, 
but, in fact, although both equally applicable to that process when properly 
conducted, they did not both signify the same thing. Percolation signified the 
passing of each drop of the liquid from particle to particle through a compact 
mass of solid ingredients, until the drop became thus fully charged with solu¬ 
ble matter, and the solid substances by contact with a great number of suc¬ 
cessive drops of liquid were exhausted of the matter soluble in such liquid. 
The object of percolation was therefore that of exhausting the solid ingredients 
with a comparatively small quantity of liquid, but as much of this liquid is in 
that part of the process left in the solid mass, this has to be removed by con¬ 
tinued percolation, and this constitutes displacement. Now in the Pharma¬ 
copoeia process the exhaustion of the solid ingredients is effected by macera¬ 
tion, and the last part of the process is for the displacement or recovery of the 
solution held by absorption in the solid substance. He looked upon the process 
therefore, as a combination of maceration and displacement. In saying this, 
however, he did not mean to disparage the process of the Pharmacopoeia. On 
the contrary, he was disposed to think that in its general characters it was 
likely to prove a good and suitable process for general adoption by chemists' 
and druggists. It was necessary to bear in mind that the Pharmacopoeia con¬ 
tained the instructions to be followed by all who were engaged, including the 
least experienced and skilled, in the preparation of medicines. The Pharma¬ 
copoeia processes should therefore, as far as possible, be such as could be ap¬ 
plied by operators of various amounts of skill and experience, and yet pro¬ 
duce good and uniform results. It must be admitted that the process of per¬ 
colation afforded an excellent method of preparing many tinctures, but it must 
also be admitted that it required in the operator a greater amount of skill and 
experience than the process of maceration required, and more than would be 
generally found among the fifteen or sixteen thousand chemists and druggists, 
including assistants and apprentices, throughout the country. He (Dr. Red¬ 
wood) had been struck with an observation made by a speaker (Mr. Burden) 
at a previous meeting, to the effect that “ he liked the process of percolation, 
but he liked to perform it himself.” It was, in fact, a process which answered 
very well in many cases when performed by those who made it their study 
and practised it con amove, but it was hardly suitable as a general process, at 
any rate in the present state of pharmaceutical knowledge. Even among 
those who professed to understand the process, he believed errors were often 
committed, especially in the part relating to displacement. Some operators 
undertook to make a tincture by percolation, and to recover the whole of the 
product by displacing the tincture with water. This he considered to be 
practically impossible, and the attempt to effect it often caused greater discre¬ 
pancies in tinctures thus made than in those made by the old process of ma¬ 
ceration. 
The President said he was sorry that time did not admit of their prolong¬ 
ing the discussion on this interesting and important subject. He was sorry 
also that so powerful an opponent of the general adoption of the process of 
