C H E M 
tort, with the pneumatic apparatus, the produdts are 
water, oil, and ammoniac; the coal contains a good 
deal of fixed alkali. Lime-water, and all the earthy 
and metallic falts, decompofe foap. Alcohol difiblves it 
alio with the afiiltance of a little heat, and forms ejjence of 
foap, which is to be fweetened with a volatile oil. 
A foap is prepared with ammoniac, known by the name 
of volatile liniment, or animal foap. Mix oil of fweet al¬ 
monds with one-fourth of its weight of ammoniac, in a 
wide-necked bottle, (haking it till the iubllances are per¬ 
fectly united. 
Oil combines with fugar, forming a kind of foap, mix¬ 
ing eafily with water, and kept in ful'penfion. The tri¬ 
turation of almonds with fugar and water makes almotid- 
milk, orgeat, and other emullions. 
VOLATILE OILS. 
Volatile or eflential oils differ from fixed oils by the 
following characters : Their fmell is llrong and aromatic; 
their volatility is fuch, that they rife with the heat of 
boiling water ; and their tafte is very acrid. They are 
-likewile much more combuftible than the fixed oils. Thefe 
oils thicken into refills by contadl with oxygen, congeal 
in a great degree of cold, and furnifli little laline cryltals 
of a camphorated fmell ; they combine more difficultly 
with alkalis. 
Thefe oils are the lefs plentiful, not being fo generally 
diftributed through the vegetable fyltem ; they exift only 
in the fweet-fmelling plants, fometimes in the leaves, at 
other times in the roots, the flowers, or the outer rind of 
the fruit, and fometimes, though rarely* in the whole 
fubftance of the plant. Some are concrete, others always 
liquid; they vary alfo in colour. 
The following are the parts of vegetables in which vo¬ 
latile oils are contained : In iris, difitamnum, kidney- 
wort, See. the root. Sandal, faflafras, rhodium, &c. the 
ftem. Cinnamon, caflia lignea, winteranus, &c. the bark. 
Peppermint, rofemary, thyme, balm, wormwood, &c. 
the leaves. Rofes, lavender, cloves, &c. the calyces of 
the flowers. Camomile and orange-flowers, the petals. 
Pepper, cubebs, juniper-berries, See. th e fruits. Nutmeg, 
anife, fennel, and molt umbelliferous plants, in the feeds. 
The concrete oils are thofe from rofes, parfley, elecam¬ 
pane, kidney-wort, and ftar-wort. 
The following are the diltinCtions of volatile oils with 
refpeCt to colour, r. Yellow, as from lavender. 2. Brown, 
from cinnamon and cloves. 3. Blue, from camomile. 
4. Sea-green, from St. John’s wort. 5. Green, as from 
parfley. Heavy oils, finking in water, are thole of iafla- 
firas and cloves. 
The volatile oils, which are drawn out by expreffion, 
are thole contained in viiible cells, as in lemons, oranges, 
cedra, and bergamot; by merely prefling the rind o'f the 
fruit, the oii runs out. Or they may be grated, by which 
means, the rind being torn, the oil drops into the veil'd 
beneath. Having thus rai'ped a certain quantity of fruit, 
colled the rind, which will be like a pulp; prefs this be¬ 
tween two plates of glafs to extract the volatile oil. This 
oil depolits the impurities it carried along with it, and 
clarifies, if left to itfelf at relt. 
By diftiilation, the molt ufual and the belt method is 
to take the plant in the time of its greatell Itrength, and 
when its odour is the ltrongeft, and to choofe luch part 
of the plant as exhales the llrongell fmell. Put it into 
the cucurbit of an alembic without a balnaeum marise 5 
add water enough to l'oak the plant fufficiently, and to 
keep it from touching the bottom of the cucurbit. A 
peculiar kind of receiver is to be adapted, called the Flo¬ 
rentine receiver. This vefiel lets out the excels of water 
by an opening on its belly lomewhat below the neck, by 
which means the oil is collected in the neck, and cannot 
efcape. Urge the fire fuddenly to the heat necelfary to 
make the water boil. The water in this dillillation rifes 
much loaded with the fmell of the plant, and carries with 
it all its volatile oil. This water, when at the tempera- 
I S T R Y. 335 
ture of 8o°, is clear and tranfparenf j but, at a few de¬ 
grees below, the diifolved volatile oil begins to leparate, 
rendering it turbid and fomewhat milky ; the water then 
retains no more than is neceflary to give it the aromatic 
odour which conftitutes diftilled venter, water charged vuith 
refiifedfpirit ; the reft of theoiifloats on the furfape of the 
water, or finks to the bottom, according to the fpecific 
gravity of the oil. Continue the diftiilation till the water 
begins to lock clear, oblerving to add water from time to 
time, that the plant may always be covered. 
There is ftill another mode of extracting volatile oils, 
which is called diftiilation per defeenfum, and was per¬ 
formed by applying the fire over the plant 5 it was more 
particularly uled in extracting oil of cloves; but this 
kind of diftiilation, as w r e have already remarked, in 
p. 192, is now entirely difufed. 
Volatile oils lofe their fmell by heat; as they are very 
volatile, fire alone does not decompofe them. When 
heated in dole veflels, a large quantity of hydrogen is 
dilengaged. When heated with contact of air, they quick¬ 
ly take fire, and emit a very thick fume, which becomes 
condenfed into a fine and light coaly matter: they leave 
very little fixed coal after their inflammation; becaufe 
they are fo volatile, that the coaly matter is formed in 
the part which is volatilized. By expofure to the air 
they become thick, and in procefs of time aflame the 
character of refin. Needle-formed cryftals aredepofited j 
but thefe have not, as fome have pretended, properties an¬ 
alogous to camphor ; thefe concretions feem to approach 
to the nature of refins, and to contain an acid fait fimilar 
in its properties to the flowers of benzoin. Deyeux and 
Vauquelin difeovered the properties of the benzoin acid, 
in the concretions depofited in the water of canella, fo 
early as the year 1792. 
Volatile oil, by being long kept in a bottle, will be 
partly decompofed ; water will be collected at the bottom 
of the bottle ; large cryftals alfo are formed, which ap¬ 
pear to be oxalic acid; laftly, a part of the oil remains 
undecompofed. Prouft feems to have been among the 
firft who examined accurately the cryftalline ramifica¬ 
tions which fometimes form in eflential oils. By evapo¬ 
rating thefe oils in the open air, at a temperature vary¬ 
ing from—6° to +10 of Reaumur, he obtained cryftals, 
which he conceived to be camphor. 
In every eflential oil, according to Prouft, there are 
two fubftances which have a tendency to combine with 
oxygen ; one, the radical of a refill, the other the radical 
of an acid. The relinous radical feems to have the 
ftrongeft affinity ; the acid bafe operates only through 
along period of time. Thefe oils cannot be often ex- 
pofed to the air, nor diftilled repeatedly, without'exhi- 
biting fome mark of acidity. Prouft attributes the con- 
verfion of thele fubftances into refins to the abforption 
of atmofpherical oxgen. An. de Chem. tom. iv. p. 179. 
Margueron remarks, that fome of the volatile oils af- 
fume the concrete ftate in a temperature about 8° above 
the freezing point of water; while others, again, retain 
their fluidity far below that point. This chenuft oblerved 
carefully the phenomena which take place, by expofing 
thefe oils in (mall flalks to a temperature ol n° below 
freezing. In the upper and internal part of the flalks, 
ramifications were to be perceived, fimilar to thofe which 
are formed on the glafs panes of windows during an in- 
tenfe froft. The oil of bergamotte, during its expofure 
to this cold, exhibited in its fubftance a quantity of linall 
elliptic laminae; that of citrons had depolited linall cryf¬ 
tals ; the oil of oranges was the leaft fluid; and that of 
canella alba was partly congealed. By expofing thefe 
oils for two hours to an artificial cold of—21°, iome of 
the corks were driven out of the flalks by the formation 
and fudden expanfion of an elaftic fluid, and the upper- 
part of the flalks were at the fame time covered with nu¬ 
merous faline, cryftallized, dendritual, ramifications. 
The inferior furface of the flalk, containing the volatile 
oil of peppermint, was covered with fmall needles, which 
were 
