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° to 145°, 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 2½ 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 found in albumen. This substance is best known as a constituent of animals, and it does not appear to be abundant in plants. The portion of the gluten of wheat-flour, which is insoluble in boiling alcohol, is considered by Liebig and Dumas to be coagulated fibrin.
In the seeds of leguminous and a few other kinds of plants large quantities of a substance termed legumin are found. It resembles the casein, or cheesy ingredient of milk; indeed, some chemists consider it to be identical in composition with that substance. When pure, it is pearly white, insoluble in boiling water, but soluble in cold water and in vinegar. The saline matters found in plants are always associated with the albuminous bodies; the latter, therefore, form the bones as well as the muscles of animals.
A great many substances are found in plants, such as wax, mannite, "extractive matter," citric, malic, and other acids, of the nutritive value of which very little is known. The substances described in this section constitute, however, at least 95 per cent. of the weight of the vegetable matters used as food by live stock.