~ 
_ Puarmacy is the. art of preserving, preparing, and compound-_ 
ing medicines. a 
The Preservation of medicines is its least extensive part. mi 
cludes principally the general rules for collecting plants at ain 
seasons, or in particular states of maturity, and those by which they 
are dried or preserved from the injuries they would sustain by expo-. 
sure to light, air, and moisture. It comprehends, in like manner, 
rules for the collection and preservation of animal and mineral sub- 
stances, : ‘ 
That part of pharmacy termed the PREPARATION of medicines; in- 
cludes a variety of important operations. : 
The virtues of those remedies which are derived from.the 
kingdom, generally depend on one or other of the proxim: 
ples of each substance, ‘on its gum, its resin, essential oil, or som 
other. These different principles are dissolved by different agents, 
by water alcohol, &c-; and. as they are often, as they exist in the 
entire vegetable, mixed with much inert matter, it is of advantage to 
extract the active principle by means of its proper solvent, and to 
exhibit it in its pure and concentrated state. Hence have arisen the 
various pharmaceutic preparations of infusions, decoctions, tinctures, 
extracts, &c. these being all processes by which the active matter 
of any substance is separated from the inert matter with which it is 
naturally mixed, and differing only from each other in the solvent 
employed, or in the form to which the solution is reduced. © 
Sometimes, also, the principles of these substances are extracted _ 
by other means, as when an unctuous oil is obtained by expression, 
_ or an essential oil by the application of heat. ‘Phis oil may also”  . 
combined with water or alcohol, and thus distilled waters or spirits _ 
~ By such processes, we extract only a principle previously existing -_ 
in any particular substance; we form no new remedy, but merely 
obtain the same virtue in a different form. In other cases, pharmacy 
produces remedies altogether new. These are always.the result of 
chemical action ; they are either compounds, produced by the com-. 
bination of two or more chemical agents, or they are the products of 
chemical decomposition. In this manner.are obtained:the various 
saline and metallic preparations. ‘These preparations too, are often — 
dissolved in various fluids, in order that they may be conveniently 
exhibited ; processes analogous to the infusions or tinetures of vege- 
table substances. 
