220 MOHR AND REDWOOD'S PRACTICAL PHARMACY. 
rally assume a pilular consistence when mixed with an 
equal weight of carbonate of magnesia, and this is the best 
method of solidifying it, when the pills are required for im- 
mediate use. If the balsam should contain an unusually 
Jarge proportion of essential oil, it may require more of the 
excipient, or it may be found convenient to dissolve a little 
white wax in the balsam previously to the addition of the 
magnesia. Sometimes the balsam is solidified by the addi- 
tion of white wax alone. When sufficient time can be taken 
for the purpose, a very small quantity of calcined magnesia 
may be made to solidify balsam of copaiba or any of the 
fluid turpentines. One part of recently calcined magnesia, 
added to sixteen parts of balsam of copaiba, or true Venice 
turpentine, and allowed to stand for a week or two, will 
become solid and fit to form into pills. The mixture should 
be exposed to a gentle heat for about an hour, and should 
subsequently be stirred from time to time until it becomes 
solid. In this case, as in that previously alluded to, it must 
be observed that some specimens of copaiba, which are 
very rich in volatile oil, do not completely solidify without 
the addition of wax or of a portion of turpentine, such as 
Bordeaux turpentine. The peculiar action of the magnesia 
consists in the formation of a soap with the acid resins of 
the copaiba or turpentine, and this soap absorbs the volatile 
oil, which is the other constituent of the oleo-resin. Quick 
lime might be substituted for magnesia, and in some cases 
has been found to answer better. 
" Certain volatile oils, without any other active ingre- 
dients, are sometimes prescribed in the form of pill. Thus, 
oil of pimento , cloves, peppermint, &c, have been ordered 
to the extent of three or four drops in each pill, the selec- 
tion of an appropriate excipient being left to the dispenser. 
The best excipients to use in such cases are soap and mag- 
nesia. 
" Calomel will form the type of a class of powders requir- 
ing an excipient which possesses and can impart adhesive- 
