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Page 95
* * * * *
ON THE NATURAL FATS.
BY DR. CHARLES L�WIG.
The fats which exist in nature can be divided into the general and the
special; the former exist in almost all plants and parts of plants; the
latter includes only some vegetable substances, as _laurostearine_,
_myristicine_, and _palmatine_. The consistence of fats of the general
kind depend upon the proportions of margarine, stearine, and oleine
contained in them. The former preponderate in the solid fats (butter,
lard, and tallow); and the latter in the fluid ones or oils. According
as an oil contains oleic acid or olinic acid, it is termed a fatty or
drying oil. To the class of fatty oils belong olive, almond, hazel-nut,
beech, rape oils, &c.; to that of drying oils, linseed, nut, hemp,
poppy, grape-seed, oils, &c.; which are used for varnishes.
In the vegetable kingdom the fats are chiefly in the seeds and in their
coverings, seldom in the perispemium (poppy), and in the fleshy
substance surrounding the seed (olive). The fat in the seed is mostly
enclosed in cells with a proteine compound. In the animal kingdom
certain parts of the body are quite filled with fat-cells, particularly
under the skin (_Paniculus adiposus_), in the cavities of the abdomen,
in the so-called _omentum_, in the kidneys and the tubulated canals of
the bones. Fat is also enclosed in cells (fatty globules) in milk.
It is established, without a doubt, that a greater portion of the fat
which exists in the animal kingdom originates from the vegetable
kingdom, for it is introduced into the body cotemporaneously with the
proteine compounds of that kingdom. A portion of the fat as well as wax
is formed in the animal organismus, as shown by a number of
observations, and in most cases it is unquestionable that the
non-nitrogenous nutriments, as starch, serve for the formation of fat by
a process of deoxidation; nevertheless, the formation of fat in the
animal body appears only to take place when the substances containing
starch enter the body simultaneously with fat.
If the fat existing in the animal body is contained in cellular tissue,
its separation may be simply effected by placing the incised tissue in
hot water. The cells burst and the fat collects itself on the surface of
the water. If vegetable substances contain fat in large quantity, as,
for example, seeds, it may be obtained by expression. The dried seeds
are bruised and expressed between either cold or hot metallic plates.
Olives are laid in heaps before expression; when they begin to ferment,
they can be completely expressed. If animal and vegetable substances
contain only a little fat, it must be extracted by ether.
In the pure condition the fats are mostly odorless and tasteless; when
they possess an odor, it arises mostly from the presence of small
quantities of volatile fatty acids, as butyric acid, capric acid, &c.;
which becomes free through the decomposition of their oxide of glycyl
combinations. This ensues by the presence of water and air through a
kind of fermentation, and as it appears, by the presence of a
nitrogenous substance. The fats are insoluble in water, and, with the
exception of castor oil, are taken up by cold alcohol in very small
quantities, however, more in proportion as they contain oleine. In
boiling alcohol they are dissolved, but are, for the most part, again
separated on cooling, particularly those rich in stearine. All fats are
taken up by ether but those containing stearine in the smallest
quantity.
Their specific gravities fluctuate between .91 and .93. When heated,
fats assume a dark color, and boil between 482� and 572� Fahr., but the
boiling-point continuously rises, while an uninterrupted decomposition
proceeds. From oxide of glycyl ensues acroline; oleic acid affords a
fatty acid, and among the decomposition products of fats containing
stearine and margarine are found pure margaric acid, and, at the same
time, some hydro-carbons are formed. When exposed quickly to a high
temperature, fats are completely decomposed. (Oil gas.) In closed
vessels the pure fats undergo no change, but, placed in thin layers in
the air, the fats containing oleine and oline rapidly absorb oxygen
under the strong evolution of heat, which will inflame porous bodies, as
cotton wool. The purer the fats are the more quickly their oxidation
results. When the fats contain slimy materials, these latter can be
destroyed with a little oxide of lead and water. (Preparation for the
application of varnishes.) The action of nitric acid, nitrous acid,
chlorine, sulphuric acid, &c., on fats is the same as that of these
bodies on the fatty acids. The fatty oils dissolve sulphur in the heat
which is again partly precipitated on cooling. When sulphur is heated
with fatty oils, namely, with linseed oil, it dissolves by degrees, and
a thick dark mass is formed, the so-called balsam of sulphur. By raising
the heat, a violent reaction ensues under the evolution of sulphuretted
hydrogen, and, at the same time, an oil resembling oil of garlic
volatilizes. This oil begins to boil at 160� Fahr., but its
boiling-point rises continually.
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