interest to agriculturists; the
_volatile oils_ being those which confer on certain plants their
fragrant odour. There are a great variety of vegetable oils, but
the proximate constituents of most of them are chiefly _stearin_,
_margarin_, _olein_, and _palmitin_.

_Stearin_ is a white crystalline substance, sparingly soluble in alcohol
and ether, but insoluble in water. There are two or three modifications
of this substance, but they do not essentially differ from each other.
The melting point varies from 130 deg. to 160 deg. Fahr. Stearin is the most
abundant of the fats.

_Margarin_ presents the appearance of pearly scales. It is the solid fat
present in olive oil, and it is also met with in a great variety of fats
and oils. It melts at 116 deg. Fahr.

_Olein_ is the fluid constituent of oils and fatty substances. It
resists an extreme degree of cold, without solidifying. There are
several modifications of this body--the olein of olive oil being
somewhat different from that of castor oil; the olein of linseed is
sometimes termed _linolien_.

_Palmitin._--This fat occurs in many plants, but as it makes up the
great bulk of palm oil, it has been termed palmitin. It is white, and
may be obtained in feathery-like masses. Its melting point varies from
114 deg. to 145 deg., there being, according to Duffy, three modifications of
this substance.

The fats and oils are lighter than water. They contain far more carbon
and hydrogen, and less oxygen, than are found in the sugars and
starches. They all consist of acids (stearic, palmitic, &c.) united with
glycerine. On being boiled with potash or soda, the latter take the
place of the glycerine, which is set free, and a _soap_ is produced.
The fatty acids strongly resemble the fats. In nutritive power, one part
of fat is equal to 2-1/2 parts of starch or sugar.

The Albuminous substances contain, in addition to the elements found
in starch, nitrogen, sulphur, and phosphorus. _Albumen_, _fibrin_, and
_legumin_ constitute the three important members of the "Nitrogenous"
constituents of plants.

_Albumen_ is an uncrystallizable substance. It is soluble in water,
unless when heated to 140 deg. Fahr., at which temperature it coagulates,
_i.e._, becomes solid and insoluble. The _gluten_ of wheat is composed
chiefly of albumen, and of bodies closely allied to that substance.

_Fibrin_, when dried, is a hard, horny, yellow, solid body. It contains
a little more oxygen than is