ON DRUG-GRINDING. 
The druggist effects the pulverization of drugs by tritura- 
tion, with a pestle and mortar, usually made of marble. 
Sometimes he uses the porphyry slab and muller, but this 
method of operating is of rare occurrence. There are also 
a few cases in which the substance to be powdered is mere- 
ly rubbed over the surface of a sieve. 
The drug-grinder also reduces drugs to powder by tri/ura- 
tion, and this, indeed, is the principal mode of operating 
adopted at the drug-mills. But the apparatus employed by 
the drug-grinder for powdering'by trituration, differs greatly 
from that used for a similar purpose by the druggist. The 
triturating implement of the drug-grinder, is usually called 
the drug-mill 3 when used for other purposes, it is sometimes 
distinguished as the pugging-mill. It consists of two stone 
cylinders, (a a) commonly called the runners, four or five 
feet in diameter, and 12 or 15 inches in thickness, which are 
trundled round a central beam workingon aspindle. This mill 
is a most efficient instrument for effecting the comminution of 
drugs. The runners, which are made of granite or other 
hard stone, and usually weigh a ton or more, break down 
or tear asunder the hardest and toughest substances. The 
disintegration is effected partly by weight of the stone, and 
partly by the grinding or triturating action produced incon- 
sequence of the outer and inner edges of the revolving cy- 
linder, which are both equal, being made to perform une- 
qual circuits in the same time. Thus, if either of the cy- 
linders were simply trundled without control, it would pro- 
ceed in a straight line, but being made to describe a circle 
immediately around the central beam, the outer edge of the 
cylinder has to travel through a longer path than that as- 
signed to the inner edge, so that every advance onwards, by 
which the weight or pressure is imposed upon a new sur- 
face, is accompanied by a lateral friction caused by the un- 
equal progression of the two edges of the cylinder. 
A drug-grinding room usually contains a pair of stones 
(a a), a set of five or six stampers such as b b, and a sifting 
apparatus (c). 
