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Adhesives, Paints, and Varnishes: Oils

Oils. - Oils exist ready made in nature, and may be divided into fixed oils, which are either of animal or vegetable origin, and essential or volatile oils, which are principally vegetable products. Fixed oils are mostly liquid at ordinary temperatures, smooth to the touch, and on paper make a permanent greasy stain. Many of them have neither taste nor odor. They are not, as a rule, soluble in water, and are only slightly soluble in alcohol, but may be readily dissolved in ether. The chief characteristic of the fixed oils is their ability to unite with alkalies to form soap, setting free glycerin.

The volatile oils are not capable of saponification.

Fixed Vegetable Oils. - The fixed vegetable oils, including certain butterlike fats, as palm oil, cocoa oil, and the like, are usually found in plants: in the seeds, as linseed oil; in the pulp about the seeds, as olive oil, and more rarely in roots, as in the earth almond. They are procured by grinding and pressing the oil-producing parts, and are usually found associated with more or less gum and other impurities.

The fixed vegetable oils are of two sorts: the drying oils, as linseed oil, which oxidize when exposed to the air, and are transformed into a hard, resinous varnish; and the fatty or nondrying oils, as olive oil, which become rancid and thicken when exposed to the air, but do not dry up.

To Purify Vegetable Oils. To purify crude vegetable oils, pour the oil in a lead-lined vat and add 2 or 3 per cent of concentrated sulphuric acid. Stir until the mixture takes on a greenish tint. Let stand 24 hours, add about 2 per cent its volume of water, hot but not boiling, and stir vigorously until the mixture takes on a milky color. Then let stand in a warm place for a few days to settle, and pour off the clear liquor through cheese cloth or filter paper.

To Prepare Drying Oils. - To improve the quality of drying oils, boil them with oxide of lead, binoxide of manganese, and borate or acetate of manganese. But this process gives the oil a high color. Hence, to make drying oils for colorless varnishes, prepare oleate of lead by adding oleic acid to oxide of lead or litharge, and add this to the oil when cold.

Or prepare a solution of sulphate of manganese, and add borax dissolved in water as long as a precipitate forms. Let this settle, turn off the liquor, wash the precipitate, and let it dry. This is manganese borate.

Add 2 per cent of this substance to the oldest linseed oil obtainable, and mix with gentle heat in a double boiler. Stir constantly, lifting the oil and letting it run back into the boiler, to expose it as much as possible to the air. This gives a quick-drying oil of very high color.

A class of substances called dryers are added in painting to hasten the oxidation of the drying oils, but the rapidity of this process depends greatly upon atmospheric conditions, temperature, and the like. Fixed Animal Oils. These are compounds of glycerin with various fatty acids. They are very similar to the nondrying vegetable oils. Many of the animal oils have a peculiar ADHESIVES, PAINTS, AND VARNISHES odor, which in some of the fish oils is very offensive. Sperm oil is found in the head of the sperm whale mixed with spermaceti. This is the most valuable of the animal oils and also the highest in price.

Whale or train oil is found in the blubber of the right whale, the blackfish, and other species of whale. Various other marine animals produce oils having the same general characteristics, as the seal, shark, and sea calf. The menhadens are also used in large quantities for their oil.