C H E M I 
cryftalHzc, but it affords a cruft by evaporation that is 
deliquescent. Lime and alkalis decorapofe this fait, and 
precipitate the iron of a green i(h blue colour, which foon 
becomes yellow. From thefe experiments Difpan con¬ 
cludes that the'ciceric acid is of a peculiar nature, diffe¬ 
rent from all other vegetable acids ; but it teems to be 
(till undetermined whether the acid liquor exuding from 
the pea vetches contains two different acids, or if the ci- 
ceric is a modification of the oxalic acid. 
Of FIXED OILS. 
Oil was long regarded as a fimple fubftance ; but it is 
now demonftrated, by the ufeful experiments of Lavoilier, 
tharit is a fubftance effentially compofed of carbon and 
hydrogen, differing only from the firft products of vege¬ 
tation by a greater proportion of hydrogen, and a more 
intimate combination. Oil in vegetables is an inflam¬ 
mable body, which is fufficient to diftinguifh it from the 
preceding fubftances. It is infoluble in water, which 
is a fecond diitindiioh. Oil gives out much water in 
burning, and fome carbonic acid; more water is formed 
than there was originally of oil: this exhibits a third 
diitinguifhing mark. Thus it is manifeft that oil is com- 
pofed of carbon, hydrogen, and a fmall quantity of 
oxygen. 
Oils are diftinguiflied in general into two cla'fles : The 
firft are called fat oils, fweet oils, J expreffed oils, and by 
chemifts fixed oils. The fecond were formerly called ef- 
fential oils, and are now named volatile oils. Ail the fixed 
oils have a mild infipid tafte; they ftick to the tides of 
veffels, which has occafioned them to be called fat oils. 
They are not emitted from the furface oi vegetables, but 
are contained in the kernels, the pippins, and emulfive 
feeds. They are extracted by breaking the cellules in 
which they are enclofed; th.it is to fay, by pounding and 
preffure. It is obfervable, that feeds with a Angle cotyle¬ 
don or lobe, do not contain oil, but much fecula ; but 
the two-lobed, &c. contain oil; and in general ail feeds 
which make an emuHion with water. 
There are three genera of fixed oils. i. Pure fixed oils, 
fat, congealing, which do not take fire with nitric acid. 
Such are the oil of olives, of fweet almonds, and of a 
kind of cabbage called cole, (generally named rape-oil,) 
and of the ben-nut from Egypt and Arabia.' The mode 
of extracting oil of almonds, may ferve as an example 
for the reft. Take the fweet almonds, new and well 
dried in the air ; rub them in a' clean rough cloth, to 
carry off that reddifh-yellow powder which lies on their 
furface; bruife them in a marble mortar, or crulh them 
between millftones, to reduce them to a pulp ; fliape this 
pulp into a flattened ball or cake, which wrap as tight 
as poftible in a piece of ticking ; then put it in the prefs. 
Fourcroy direfts it to be preffed in lacks piade of ruffes. 
The oil paffes through the iriterfticesof the cloth, by ex- 
preffion, into a veflfel beneath. The parenchyma remains 
on the cloth ; this is called the mace, and is fometimes 
rnoiftened with water, and preffed again p but this pro¬ 
duces an oil lefs pure, which depofits a fediment: the firft 
is called -virgin oil. 2. Drying oils, which do not congeal, 
'are afted upon by nitric acid, and become dry by expo- 
fiure to the air. Such are, the oil of linfeed, of nuts, of 
pinks, &c. 3. Concrete oils and vegetable butters. The 
diftinflive character of thefe is to become folid as foon 
as extradfed, Lefs oxygen is required for the combuftion 
of concrete oils than others, becaufe they have more in 
their compofition. This Berthollet has proved very 
clearly. He boiled fome oil of the firft and fecond kind 
upon copper, and compared it wfith the third fort. The 
copper in the iaft operation was oxydated green, but no 
oxyd was formed with the two firft genera of oiis. 
Oils of this nature are, butter of cocoa, of the croton 
febiferum, wax of Louifiana, and of the gall in China. 
For an example, we (hall give the mode of extracting the 
butter of cocoa. Several methods are in uie for this pur- 
pofe; but the two following are moil deferving of at- 
Vol. IV. No. 200. 
S T R y. 333 
tention. 1. Machy’s procefs, from the Journal de Phnr- 
macie, p. 56. Fourfpeciesof cocoaarediftinguiflied, the 
large and fmall Caracca, the Berbice, and that of the 
iflands. The latter is ufed in this procefs: let it be as 
frefh as poftible; rub it in a rough cloth to cleanfe the 
furface; bruife it, both bark and leeds, ar.d put it into 
a hair-cloth; fpread the powder or dull upon another 
hair-cloth fomewhat finer. Place it over the fire in an open 
vefiel containinga little water; over the hair-cloth lay the 
ticking which is to be ufed in exprefling the butter, and 
fome linen rags, to confine the vapours of the water 
when it begins to boil : thele vapours uniformly pene¬ 
trate the powdered cocoa; then put the plates of the 
prefs into boiling water; makeup the cakes in the ticking; 
then take out the prefling-plates and dry them; put the 
cakes of cocoa between the plates, and let the prefs to 
work; the butter runs immediately. Sixteen parts of 
cocoa yield five or fix parts of butter. 
2. Jofle’s method, as defciibed by La Grange. Dry 
the cocoa (lightly by the fire, and pick it very clean ; 
pound it in a mill, and afterwards on a ilone. When, 
brought to a pafte, heat it gently, and mix three 
parts of boiling water with fixteen of the pafte. Tire 
mixture then takes a firmer confidence; wrap it ,in 
ticking, and put it in the p,refs between two vyarin 
plates of iron. The product, this way, is (even or 
eight parts in fixteen, if the preffure has been even 
and ftrong. But, as this mode of expreflion draws out 
fome of the colouring matter, it requires purifying. 
For this purpofe, Jofle provided a tin funnel, lbldered into 
a copper vefiel forming a fand-bath ; this vefiel, has a hole 
in the bottom to let through the tube of the funnel, 
which is lengthened fo as to go into the neck of a bottle. 
Place this apparatus in a furnace, put a filtreof blotting - 
paper into the funnel, and pour on the butter of cocoa 
which is to be purified; then put water into the copper 
vefiel, and keep it hot enough to prefefive the butter in a 
fluid (late, lb as to pats eafily through the (litre. Twelve 
or thirteen pounds of butter of cocoa may thus be puri¬ 
fied in about three hours time. 
In examining the chemical qualities of fixed oils, we 
(hall choofp,, as an example, the oil of olives, for the pro¬ 
perties of all the others are nearly the fame. By dilfillation 
in a retort, with the pneumatic apparatus, it affords an 
acid phlegm of a penetrating fined, a light oil, a denfer 
oil, and a large quantity of hydrogen gas mixed with 
carbonic acid. The quantity of refidual coal is not 
abundant, and contains no alkali. By re-diftilling thefe, 
(ebacic acid, and an oil which becomes lighter each time, 
are obtained. This. is. known by the name of pbilofopbical 
oil ; the alchemifts prepared it by diltilling, for feveral 
fucceffive times, a fixed oil, with which they had impreg¬ 
nated a brick. It is not exa&iy known bow far this de- 
compofition may be. carried, though it is faid that fixed 
oil may tins way be reduced into the difengaged inflam¬ 
mable principle, water, acid, air, and earth. It may 
be deprived of its colouring matter by diftillation over 
fand or clay. Expofed to the air, it eafily combines with 
oxygen ; it is changed, becomes thicker, and rancid. 
To prove this, by way of experiment, put water in a 
veffcl, and cover the furface with oil. If oii be put into 
a bottle, and oxygen gas be introduced, the effeCl is 
quicker ; the oxygen is prefently ablorbed. 
When the combination of pure air is favoured by the 
volatilizing of the oil, then there is an inflammation or 
combuftion. To make this combination a6t, the oil 
mult be volatilized by the application of fome hot lub- 
ftance; the flame thus produced is capable of fuftaining 
"the degree of volatility and of maintaining combuftion; 
and, if a current of air be kept up in the middle of the 
wick and the flame, the great quantity of oxygen occa- 
fions a more rapid combuftion, and a (Longer heat j 
lienee the light is brighter, and there is no longer any 
fmoke, for the finoke is burnt and deftroyed by the great 
heat. This is the principle of Argand's lamp. 
Oils 
