PHARMACY. 
with specimens of known quality, that we 
can judge of the goodness either of the 
drugs themselves, or of their oils. 
Most of the volatile oils indeed are too 
hot and pungent to be tasted with safety ; 
and the smell of the subject is so much con- 
centrated in them, that a small variation in 
this respect is not easily distinguished ; but 
we can readily dilute them to any assign- 
able degree. A drop of the oil may be 
dissolved in spirit of wine, or received on a 
bit of sugar, and dissolved by that interme- 
dium in water. The quantity of liquor 
which it thus impregnates with its flavour, 
or the degree of flavour which it communi- 
cates to a certain determinate quantity, will 
be the measure of the degree of goodness of 
the oil. 
Medical use. Volatile oils, medicinally 
considered, agree in the general qualities of 
pungency and heat; in particular virtues 
they differ as much as the subjects from 
which they are obtained, the oil being the 
direct principle in which the virtues, or at 
least a considerable part of the virtues, of 
the several subjects reside. Thus the car- 
minative virtue of the warm seeds, the diu- 
retic of juniper berries, the emmeuagogue 
of savin, the nervine of rosemary, the sto- 
machic of mint, the antiscorbutic of scurVy- 
grass, the cordial of gromatics, &c. are sup- 
posed to be concentrated hi their oils. 
There is another remarkable difference 
in volatile oils, the foundation of which is 
less obvious, that of the degree of their 
pungency and heat. These are by no means 
in proportion, as might be expected, to 
those of the subject they were drawn from. 
The oil of cinnamon, for instance, is exces- 
sively pungent and fiery; in its undiluted 
state it is almost caustic ; whereas cloves, a 
spice which in substance is far more pun- 
gent than the other, yields an oil which is 
far less so. This difference seems to depend 
partly upon the quantity of oil afforded, 
cinnamon yielding much less than cloves, and 
consequently having its active matter concen- 
trated into a smaller volume ; partly, upon 
a difference in the nature of the active parts 
themselves : for though volatile oils contain 
always the specific odour and flavour of their 
subjects, whether grateful or ungrateful, 
they do not always contain the whole pun- 
gency; this resides frequently in a more 
fixed matter, and does not rise with the 
oil. After the distillation of cloves, pepper, 
and some other spices, a part of their pun- 
gency is found to remain behind : a simple 
iHicture of them in rectified spirit of wine 
is even more pungent than their pure essen- 
tial oils. 
The more grateful oils are frequently 
made use of for reconciling to the stomach 
medicines of themselves disgustful. It has 
been customary to employ them as correc- 
tors for the resinous purgatives; an use 
which they do not seem to be well adapted 
to. All the service they can here be of is 
to make the resin sit more easily at first on 
the stomach : far from abating the irritating 
quality upon which the violence of its ope- 
ration depends, these pungent oils super- 
add a fresh stimulus. 
Volatile oils are never given alone, on 
account of their extreme heat and pun- 
gency ; w'hich in some is so great, that a 
single drop let fall upon the tongue pro- 
duces a gangrenous eschar. They are readily 
imbibed by pure dry sugar, and in this form 
may be conveniently exhibited. Ground 
with eight or ten times their weight of sugar 
they become soluble in aqueous liquors, and 
thus may be diluted to any assigned degree. 
Mucilages also render them miscible with 
water into an uniform milky liquor. They 
dissolve likewise in spirit of wine ; the more 
fragrant in an equal weight, and almost all 
of them in less than four times their own 
quantity. These solutions may be either 
taken on sugar, or mixed with syrups, or the 
like. On mixing them with water the 
liquor grows milky, and the oil separates. 
The more pungent oils are employed ex- 
ternally against paralytic complaints, numb- 
ness, pains, and aches, cold tumours, and in 
other cases where particular parts require 
to be heated or stimulated. The tooth-ach 
is sometimes relieved by a drop of these al- 
most caustic oils, received on cotton, and 
cautiously introduced into the hollow tooth. 
Among the volatile oils ought also to be 
enumerated theempyreumatic oils ; for these 
also are volatile, but have a character pecu- 
liar to themselves. The simple volatile oils 
exist ready formed in the aromatic sub- 
stances from which they are obtained, and 
are only separated from the fixed principles 
by the action of a heat not exceeding that 
of boiling water. The empyreumatic, on 
the contrary, are always formed by the ac- 
tion of a degree of heat considerably higher 
than that of boiling water, and are the pro- 
duct of decomposition, and a new arrange- 
ment of the elementai-y principles of sub- 
stances, containing at least oxygen, hydro- 
gen, and carbon. Their production is there- 
fore always attended with the formation of 
other new products. Iii their chemical 
