This section is from the book "A Practical Treatise On Friction, Lubrication, Fats And Oils", by Emil F. Dieterichs. Also available from Amazon: A practical treatise on friction, lubrication, fats and oils.
Lard is the prepared fat of the hog. The fat freed from membranous matter is cut up into small pieces and boiled with water. It is then carefully separated from the water and melted over a slow fire. Lard is a soft, white, unctuous fat, with a faint odor, is free from rancidity and has a bland taste and a neutral reaction. Its specific gravity is about 0.938, or about 20° to 21° by Baume's hydrometer. Lard is entirely soluble in ether, in benzine, and in disulphide of carbon. It melts at or near 95° F., and when melted it readily unites with oils, wax or resins. Like most animal fats, it consists of stearin, palmitin and olein. Olein, the liquid principle of lard, can be readily separated from the stearin it contains by subjecting it, at a cold temperature, to strong pressure, when the liquid olein is pressed out, leaving the solid stearin, which is principally used in the manufacture of stearin candles. Exposed long to the air, lard and lard oil will absorb oxygen and become rancid. Lard oil as obtained from lard is a colorless or pale yellowish oily liquid ; it becomes opaque at or below the temperature of 32° F. It has a slightly fatty odor and a bland taste. Its specific gravity is from 0.900 to 0.920, or from 22° to 24° by Baume's hydrometer. It contains varying proportions of stearin, and is much adulterated with cottonseed oil and refined petroleum neutral oils. Lard oil is sold in the market as "Extra Winter Strained" lard oil when obtained by pressure at a cold temperature; as "No. 1" when pressed at a warmer temperature; and as "No.2" when obtained from impurer lard, and by the rendering process. The better qualities are often used to adulterate olive oil.
Tallow is obtained from the fat of sheep and oxen. It is prepared by cutting the fat into pieces, melting it at moderate heat and straining through coarse cloth. It is sometimes previously purified by boiling with a little water. Mutton fat is of a firmer consistency, and fuses at a higher temperature than fat from other animals. Tallow is very white, sometimes brittle; it is inodorous, has a bland taste, and is insoluble in water. It consists of about seventy per cent of stearin and pal-mitin and thirty per cent of olein. It gradually dissolves in two parts of benzine, from which it slowly separates in a crystalline form on standing. It melts between 113° and 122° F. and congeals between 98° and 104° F. Its specific gravity lies between 0.937 and 0.952 or 18° to 20° by Baume's hydrometer.
Tallow oil, i. e. the percentage of liquid olein in tallow, is obtained by melting the tallow and keeping it in a warm room at a temperature of about 80° to 90° F. for some hours; the stearin which the tallow contains crystallizes in a granular form, and in this state it is placed in canvas or hair-cloth bags and subjected to hydraulic pressure. The olein is thus separated from the stearin. It still contains stearin in various proportions, and the oil is of more or less fluidity, and for that reason its specific gravity varies from 0.911 to 0.915, or from 23° to 24° by Baume's hydrometer.
Tallow oil is of an almost white color when cold, or, at the most, of a faint yellow tint. It has a slight odor of animal fat. Varying with its quality, it has a flash point of from 475° to 500° F.
Neatsfoot oil is obtained from the feet of cows, sheep and horses. The hoofs are trimmed and boiled in water, when the oil collects on the surface and is skimmed off, and is further purified by repeated boiling with water. Neatsfoot oil appears either as a turbid or a limpid liquid of a yellow-brownish color, has a pleasant odor and a sweet taste, and has little tendency to become rancid; it becomes solid in cold weather from deposition of stearin, has a specific gravity of about 0.912 or 23° Baume at 60° F., and solidifies at. about 32° to 33° F.
Bone fat, bone grease or marrow tallow comes from the shank bones of cows, bullocks and horses. They are either boiled in water, and the rising oil is skimmed off, or they are subjected to steam heat of from 50 to 60 pounds pressure in digesters for from half an hour to an hour. At the end of the operation the fat is drawn off.
Horse tallow, or fat obtained from the rendering of dead horses, is much like the tallow obtained from cows and sheep, and under pressure furnishes an oil which is known in the market as horse tallow oil, and is often sold under the name of "Neatsfoot Oil." It has at 60° F. a specific gravity of 0.915 to 0.980, or 22° Baume.
The oil known as elain or red oil gets its name from the dark reddish color it derives from its contact with the hot iron press plates and the high temperature to which it is subjected in its production by the saponification process with lime or sulphuric acid, or by high steam pressure or by distillation, whereby the fat is decomposed into oleic acid, stearic acid and glycerin. The fatty acids are allowed to solidfy, and are pressed between hot iron plates, whereby the Red Oil (liquid olein or elain) is separated from the solid stearin. The latter is used in the manufacture of the well-known "Adamantine Candles," and the red oil in the manufacture of soaps and in the compounding of lubricating oils and lubricating for carding wool. By the saponification of solid fats by the lime, sulphuric acid or steam process, the fatty acids are set free from their combination with glycerin, and are allowed to solidify, and are pressed. According to the temperature, more or less stearin and palmitic acids go into the product, and can be separated by distillation. The oil is often semi-solid, resembling tallow grease; the distilled varieties are light brown to deep red; specific gravity at 60° F. is from .899 to .909, or 24° to 25° Baume.