ON DRUG-GRINDING. 
29 
lours of some powders, and that oil is also added in some 
cases, during the process of comminution, with a similar 
object. These additions are made in such small quantities, 
that they probably would not occasion any appreciable dif- 
ference in the action of the medicines, but the fact that any 
such means are adopted establishes the necessity for some 
better criteria of quality than the mere appearances. 
There is yet another source of disparity in the quality 
and strength of powdered drugs, which consists in a con- 
ventional practice of the trade with reference to the allow- 
ance made for loss of product during the process of grind- 
ing. 
It has already been stated that the loss of weight which 
drugs undergo in grinding, is occasioned by the evaporation 
of water and other volatile constituents in the drying-room, 
and by the waste from dissipation in the form of dust, and 
from adhesion to the apparatus, in the grinding-room. It 
must be obvious that the amount of loss thus sustained will 
not be uniform; it will vary according to the nature of the 
substance under operation, and even with substances of the 
same nature, the loss will depend upon the quantity ope- 
rated upon at a time, and their state of dryness when sent to 
the mill. Some drugs are frequently met with in commerce 
in a perfectly moist state, such as opium, aloes, scammony, 
and jalap. The loss of weight in drying these drugs, must 
of course be considerably greater than that which occurs 
with other less moist specimens, or with substances, such as 
rhubarb, ipecacuanha, or bark, which are never met within 
a moist state. Now, there is in this variable condition of 
drugs as to dryness, a source from which disagreement 
might arise between the druggist and the drug-grinder, which 
probably led to the adoption of a practice in the trade of 
making a uniform allowance for loss of weight in grinding, 
whatever the nature or quality of the drug might be. 
The rule adopted among the London drug-grinders, has 
been to have allowed to them four pounds on every hundred* 
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