PHARMACY. 



artificial warmth, less than 100 Fahren- 

 heit, and well exposed to a current of 

 air. When perfectly dry and friable, they 

 have little smell; but after being 1 kept 

 some time, they attract moisture from the 

 air, and regain their proper odour. 



The boxes and drawers in which vege- 

 table mutters are kept, should not impart 

 to them any smell or taste; and more cer- 

 tainly to avoid this, they should be lined 

 with paper. Such as are volatile, of a 

 delicate texture, or subject to suffer from 

 insects, must be kept in well covered 

 glasses. Fruits and oily seeds, which are 

 apt to become rancid, must be kept in a 

 cool and dry, but by no means in a warm 

 or moist place. 



Oily seeds, odorous plants, and those 

 containing 1 volatile principles, must be 

 collected fresh every year. Others, whose 

 properties are more permanent, and not 

 subject to decay, will keep for several 

 years. Vegetables collected in a moist and 

 rainy season are in general more watery 

 and apt to spoil. In a dry season, on the 

 contrary, they contain more oily and re- 

 sinous particles, and preserve much bet- 

 ter, 



Mechanical Operations. 



These consist of the mode of deter- 

 mining the weight, or measure of bodies; 

 their division into minute particles; their 

 separation of part from part, or of the 

 useful from the useless; the modes of 

 intermixing them. 



Weights and Measures. The quantities 

 of substances employed as medicines are 

 determined with the greatest accuracy 

 bv weighing. The scales should balance 

 with the utmost precision, and turn with 

 the utmost facility. Balances should lie 

 defended as much ns possible from acid 

 and other corrosive vapours, and not be 

 unnecessarily suspended, as their delicacy 

 of decision is hereby much impaired; and 

 to guard against this last evil in another 

 way, they should never be over-loaded. 



The want of .an uniformity of weights 

 and measures, which is felt in every coun- 

 try, and in every branch of trade and 

 commerce, is of peculiar inconvenience 

 in pharmacy. All our college pharmaco- 

 poeias command the use of troy weight; 

 yet the wholesale druggists in every in- 

 stance, excepting where a very small 

 portion of an article is bought by grains, 

 scruples, or drachms, sell by avoirdupoise 

 weight; and there is reason to fear that, 

 both amongst apothecaries and druggists, 

 jflost of the pharmaceutic compositions 



are prepared by this last division ; in con- 

 sequence of which it is impossible tor the 

 physician to know the exact strength of 

 the dose he prescribes; and if lie do, he 

 cannot often obtain it in the proper pro- 

 portions of its respective mgiv 

 The difficulty is still increased by a pro- 

 miscuous use of weights and measures, in 

 determining the quantities of fluids; on 

 which account, though the London col- 

 lege still authorises both for distinct pur- 

 poses, the colleges of Edinburgh and 

 Dublin have rejected measures altogether. 



For measuring fluids, the graduated 

 glass measures are always to be preferred: 

 they should be of different sixes, accord- 

 ing to the quantities they are intended to 

 measure. Elastic fluids are also measured 

 in glass tubes, graduated by inches and 

 their decimals. 



Specific gravity is the weight of a de- 

 terminate bulk of any body. For a stand- 

 ard of comparison distilled water has been 

 assumed as unity. The specific gravity 

 of solids is ascertained by comparing the 

 weight of the body in the air with its 

 weight when suspended in water. The 

 quotient obtained by dividing its weight 

 in air, by the difference between its 

 weight in air and its weight in water, is 

 its specific gravity. The specific gravity 

 of fluids may be ascertained by compar- 

 ing the loss of weight of a solid body, 

 such as a piece of crystal, when immersed 

 in distilled water, with its loss when im- 

 mersed in the fluid we wish to examine; 

 by dividing its loss of weight in the fluid 

 by its loss of weight in the water, the 

 quotient is the specific gravity of the 

 fluid; or a small phial, containing a known 

 weight of distilled water, may be filled 

 with the fluid to be examined and weigh- 

 ed, and by dividing the weight of the 

 fluid by the weight of the water, the 

 specific gravity is ascertained. 



Although these are the only general 

 principles by which specific gravities are 

 ascertained, yet as the result is always 

 influenced by the state of the thermo- 

 meter and barometer at the time of the 

 experiments, and as the manipulation is 

 a work of great nicety, various ingenious 

 instrument's have bee'n contrived to ren- 

 der the process and calculation easy. Of 

 all these, the gravimeter of Morvcau 

 seems to deserve the preference. 



It would be of material consequence to 

 science and the arts, if specific gravities 

 were always indicated by the numerical 

 term expressing their relation to the 

 specific gravity of distilled water. This, 

 however, is unfortunately not the case, 



