PHARMACY. 
of the butter-tree of Africa, to the fluidity 
of olive oil. 
Fixed oils are either, 1. Fat, easily con- 
gealed, and not inflamniable by nitric acid, 
oil of olives, almonds, rapeseed, and ben. 
i!. Drying, not congealable, inflammable by 
jiitric acid, oil of linseed, nut, and poppy. 
;3. Concrete oils, palm oil, &c. 
Fixed oil is separated from fruits and 
seeds which contain it, either by expression 
or decoction. Heat, by rendering the oil 
more limpid, increases very much the quan- 
tity obtained by expression ; but as it 
renders it less bland, and more apt to be- 
come rancid, heat is not used in the prepa- 
ration of oils which are to be employed in 
medicine. When obtained by expression, 
oils often contain a mixture of mucilage, 
starch, and colouring matter ; but part of 
these sejrarate in course of time, and fall to 
the bottom. When oils become rancid, 
they are no longer fit for internal use, but 
are then said to etfect the killing of quick- 
silver, as it is called, more quickly. Decoc- 
tion is principally used for the extraction 
of the viscid and consistent oils, which are 
melted out by the heat of the boiling water, 
anil rise to its surface. 
Tliose who prepare large quantities of the 
oil of almonds, blanch them, by steeping 
them in very hot water, which causes their 
epidermis to swell, and separate easily. 
After tliey peel them, they dry them in a 
stove, then grind them in a mill like a 
coffee mill, and lastly, express the oil from 
the paste inclosed in a hempen bag. By 
blanching the almonds, the paste which re- 
mains within the bag is sold with greater 
•advantage to tlie perfumers, and Uie oil ob- 
tained is perfectly colourless. But tlie 
heat employed disposes the oil to become 
rancid, and the colour the oil acquires from 
the epidermis does not injure its qualities. 
For pharmaceutical use, therefore, the oil 
should not be expressed from blanched al- 
monds, but merely rubbed in a piece of 
coarse linen, to separate the brown powder 
adhering to the ^idermis, as much as pos- 
sible. Sixteen ounces of sweet almonds 
commonly give five ounces and a half of oil. 
Bitter almonds afford the same proportions, 
but tlie oil has a pleasant bitter taste. 
In this manner are to be expressed, 
Oleum amygdalae, almond oil, from the 
kernel. 
Oleum iini, linseed oil, from the bruised 
seeds. 
Oleum ricini, castor oil, from the seeds 
previously decorticated. 
Oleum sinapeos, oil of mustard, from tlid 
bruised seeds. 
Clae-s VII. Distillates, DiSTiLLEU 
Waters. 
Substances which differ in volatility, may 
be separated from each other by applying a 
degree of heat capable of converting tlie 
most volatile into vapour, and by again con- 
densing this vapour in a proper apparatus. 
Water is converted into vapour at 212'’, and 
may be separated by distillation from the 
earthy and saline matters which it always 
contains in a natural state. But, it is evi- 
dent, that if any substances which are as vo- 
latile as water, be exposed to the same de- 
gree of heat, either by immersing them in 
boiling water, or exposing them to tlie 
action of its steam, they will rise with it in 
distillation. In this way the camplior and 
volatile oils of vegetable substances are se- 
parated from the more fixed principles j 
and as water is capable of dissolving a cer- 
tain quantity of these volatile substances, it 
may be impregnated with a great variety of 
flavours by distilling it from different aro- 
matic substances. If the subject of our 
distillation contain more volatile oil than the 
w-ater employed is capable of dissolving, it 
will render the water milky, and afterwards 
separate from it. It is in this way that es- 
sential oils are obtained. 
Essential oils are obtained only from odo- 
riferous substances ; but not equally fi om 
all of this class, nor in quantity proportional 
to their degree of odour. Some, which, if 
we were to reason from analogy, should 
seem very well fitted for this process, yield 
extremely little oil, and others none at all. 
Roses and chamomile flowers, whose strong 
and lasting smell promises abundance, are 
found to contain but a small quantify of 
oil ; the violet and jessamine flower, which 
perfume the air with their odour, lose their 
smell upon the gentlest coction, and do not 
afford any oil, on being distilled, unless im- 
mense quantities are submitted to the ope- 
ration at once ; while savin, whose dis- 
agreeable scent extends to no great dis- 
tance, gives out the largest proportion of oil 
ofalmost any vegetable known. 
Nor are the same plants equally fit for 
this operation, when produced in different 
soils or seasons, or at different times of tlieir 
growth. Some yield more oil, if gathered 
when the flowers begin to fall off, than at any 
other time. Of this we have examples in 
lavendar and rue ; others, as sage, afford 
the largest quantity when young, before 
