Important: Safety Warning
This page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
Oils and Fats
Fats are merely solid or semi-fluid oils. The fixed oils and fats form a well-defined group of organic compounds, which are abundantly obtained from the animal and vegetable kingdoms. They are not so heavy as water, their specific gravity ranging from 0.91 to 0.94. They differ very much in their degrees of solidity, and do not consist of any single substance in a state of purity, being principally mixtures in varying proportions of four different but closely-allied bodies, viz.: stearine (or suet); palmitine (so called from olive-oil, being very abundant in the latter); margarine (from a pearl, owing to its pearly lustre); and oleine. The three first are solid at common temperatures, while the fourth remains liquid. Fat is softer and its melting-point lower in proportion to the quantity of oleine it contains. Fats are all soluble in ether, oil of turpentine, benzol, and to a certain extent in alcohol, but not in water. The most solid fats are readily reducible, and become reduced to a fluid or oily state at a temperature lower than that of the boiling-point of water. When the fats or oils are boiled with an alkali they undergo the remarkable change called saponification. The fat by this process is decomposed into a fatty acid and glycerine, the acid combining with the alkali to form soap, and the glycerine passes into solution. Chevreul discovered that the fats and oils consisted of several proximate principles, known as stearine, margarine, and oleine, which are each capable of being separated into an acid and a base, the base being the same in all, and known as glycerine.
Oleine is that portion of oil which, as before said, causes its fluidity. Stearine gives to certain fats and oils the opposite quality of solidity, as in candles, etc. Margarine resembles stearine in its property of hardness; it exists in human fat, butter, olive-oil, etc.
The fixed oils are of two classes--the drying oils, or those which harden on exposure to the air; and the unctuous oils, or those which remain soft and greasy under the same exposure. The hardening of the oils is due to the absorption of oxygen.
The most important of the drying oils is linseed, which is obtained by subjecting flaxseeds to pressure. Next in importance as a drying oil for paints is hemp-seed, poppy, and walnut. The most important non-drying oils are olive-oil, almond-oil, and colza-oil, which are extensively used in making soap, candles, and illuminating oils. Castor-oil is a connecting link to these two classes of oils, being gradually hardened by long exposure to the atmosphere.
The drying property of oils is much increased by heating them with about .05 of their weight of litharge, which becomes dissolved by the oil. Linseed-oil thus treated is known as boiled oil. See LITHARGE.