varied chemical composition—some containing
only carbon and hydrogen, as the oil of turpentine;
others adding oxygen, as the oil of cloves;
and others containing sulphur, as the oil of
garlic. But our present flasks are all filled with
the fixed or fatty oils: the volatile or essential
must wait their turn.

By the discoveries of Chevreul, "the father
of the fatty acids," as he is called, the fixed oils
are known now to have three invariable
constituents, oleine, margarine, and stearine—all
compounds of glycerine with fatty acid—and it is
according to the greater or less proportion of
one or the other that fat is more or less fusible
or solid. Thus, oleine is liquid at any ordinary
temperature, but margarine is solid up to
116 deg. Fahrenheit, and stearine up to 130 deg.
Fahrenheit. An experiment on these two
substances may be made by those fond of chemistry
and not afraid of evil smells or dirty fingers.
Melt some solid mutton fat in a glass flask, and
shake it with several times its weight of ether.
When cool the stearine falls in beautiful soft
crystals, leaving the margarine and oleine in
solution. Press out the soft mass of stearine in
a cloth, and evaporate the liquid remaining:
you will then get margarine and oleine together,
if you press them out through folds of blotting-
paper. The residue, dissolved afresh in ether,
gives pure margarine; very like stearine, only
melting at a lower point. Oleine is difficult to
get pure. The best way is to freeze olive oil,
when the margarine crystallises and sinks, and
the oleine is left floating at the top, and can be
skimmed off. The importance of all these
discoveries, and which of the animal fats and
vegetable oils have more or less of these compounds,
can hardly be over-estimated, when we see their
practical results in the beautiful candles which
are sold now at half the original cost, and more
than twice the light-giving power, of the ancient
wax and muttons; and in the pure and bright
burning oils—so pure and colourless that they
reveal the secret of straw-coloured gloves, and
do not let them pass for white.

There is scarcely a portion of the animal
body that has not fat mixed with it, either in
separate masses, or indistinguishably; as in the
bones and fibrous parts of the body to be got
at only by certain processes; but not many
plants yield oil. The richest are the
cruciferous tribe, including the seeds of radish,
mustard, rocket, camellina (gold of pleasure),
garden cresses, and rape, in the three varieties
of Brassica napus et campestris, the common
rape; Brassica præcox, summer rape; and
Brassica campestris oleifera, or colza. But
these are not all good for food or light;
some of them being of the kind called
"drying oils," as we shall see presently. The
quantity of oil to be got from plants and
seeds varies, not only in different species of the
same thing, but according to climate and
culture; still, for broad measurement, it may be
said that nuts yield half their weight of oil;
Brassica oleracea et campestris, one-third; the
variety called colza, in France, two-fifths;
hempseed, one-fourth; and linseed from one-
fourth to one-fifth. The grasses and pea tribe
(gramineæ et leguminosæ) rarely give a trace
of oil; only one of the former—the roots of
the Cyprus grass, which is not a true grass by
the way—and two of the latter; both foreign.
One is called the oil of Behen, from the seeds
of a plant (Moringa aptera) growing wild in
Arabia and Syria but cultivated in the West
Indies, and chiefly used in perfumery, "to
dissolve out the odoriferous principle of the
flowers," being absolutely pure, mild to the taste,
inodorous, becoming slowly rancid, and free from
all acid: the other is ground-nut oil, from the
Arachis hypogæa, a native of America. The
properties of ground-nut oil were tested by a kind
of accident in Europe. A large cargo of nuts
had arrived at Bremen, and found no purchasers
in their natural state, as good for luncheon or
dessert; so the importers expressed the oil,
and then found market enough. Where the
ground-nut grows, that is, in tropical climates,
the inhabitants eat the seeds raw, which then
have a slight resemblance to haricot beans, or
make them into a kind of paste-like chocolate.
They are very pleasant when properly roasted,
which is rather hard to get done down stairs;
and have the further quality of being wholesome
and nutritious. The potato tribe, Solanaceæ,
give us henbane-seed oil, tobacco-seed oil, and
oil of deadly nightshade; while the Rosaceæ,
which term includes the peach, cherry, plum,
almond, and the seeds of the apple, are among
the most valuable of all. But the king of the
oil-yielding trees is the Olive; that dusky,
dusty-looking, shadeless, narrow-leaved, humbug
of a tree, which disappoints every one so bitterly
at first sight, and for which Europe is indebted
to the Greeks of past times, who introduced it
from Syria, where the Hebrews had long known
its virtues.

The salad oil of commerce and our summer
dinners, is said to be got from Nice and Genoa;
we call it Florence oil, in a grand kind of
generalising way; but excepting the coarse
shipments from Galllpoli, good chiefly for machinery,
we get but comparatively little Italian oil at all,
and very seldom good olive oil unadulterated,
even from Aix and Montpellier, whence our
chief supplies come. Poppy oil, ground-nut oil,
and oil of sesamum, adulterate our table oil;
colza oil adulterates the second running of olive
oil, for the manufacturers; and colza oil itself
is adulterated with various cheaper oils, but
principally with whale oil. All of which may
be discovered by various chemical tests, by
which the oil changes colour according to the
kinds employed; but by ways and appearances
too long to give here.

The olive harvest at Aix is an important
circumstance in the local life; on the good or ill
result of which depends the well-being or misery of
many hundreds of people. When gathered, the
fruit is heaped up in barns and cellars for a few
days, to allow just the beginning of fermentation
to set in; only the beginning; for, if suffered
to ferment throughout the mass as it lies