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.
The next question arises: What are oils and what is fatty matter? What are the characteristics, and from what sources of nature do they come, and how are they obtained?
Oils are liquid and semi-solid substances, derived from the animal and the vegetable kingdoms. They are unctuous to the touch, are insoluble in water, and possess the power of supporting combustion with flame. They are obtained from the roots, seeds, fruits and flowers of plants and trees, and from the fat of animals, by extraction, by pressure, by rendering, by boiling with water, or by distillation. They are also obtained from the mineral kingdom, from shale, and out of receptacles in the bowels of the earth.
Oils are divided into two classes: They are either oxyhydro-carbons, that is, compounds of oxygen, hydrogen and carbon, and are known as "fixed oils," or they are hydro-carbons, composed of hydrogen and carbon only, and are known as volatile or essential oils. The "fixed oils' do not sensibly evaporate at ordinary temperature. They stain paper permanently and render it translucent. They do not distil or evaporate at the temperature of boiling water, and they have only a faint odor, like that of the substance from which they have been extracted. The volatile or essential oils evaporate freely. They have a caustic, acrid taste and an aromatic odor, and when distilled with water they pass over at 212° F.
All of the "fixed oils" have an attraction more or less powerful for oxygen. Exposed to the atmosphere, some of them become hard and resinous, and they are called "drying oils;" others thicken only slightly and become sour and rancid, and they are known as non-drying or "fatty oils." The fatty oils in general use for lubricating and in the manufacture of Lubricating Oils are:
For lubricating purposes these oils, vegetable as well as animal, are largely compounded with mineral oils of all grades and colors and in endless proportions.
Drying Oils, more or less, are: Linseed Oil, Nut Oil, Poppy Oil, Hempseed Oil, Castor Oil, Cottonseed Oil and Rosin Oil. Some of them are used in the manufacture of greases for lubricating purposes, but all of them are unfit for lubricating machinery on account of their resinous nature.
The volatile or essential oils are: The Oils of Amber, Bergamot, Cloves, Lemon, Rose, Orange Flower and many others, all derived from the vegetable kingdom. They are usually more limpid and less unctuous than the fatty oils, with which they mix in all proportions. They are more or less soluble in alcohol and ether, and are sparingly soluble in water, to which, however, they impart their peculiar flavor. Nearly all the volatile oils resist saponification, and do not combine with the alkaline bases to form soapy compounds. They are not used for lubricating purposes.
The mineral Oils and the Petroleum Oils are Hydro-carbons, and belong to the class of volatile and essential oils. They have little affinity for oxygen or moisture. They will not saponify, and they do not ferment or become rancid. The Mineral Oils are derived from bituminous coal and shale by distillation, and have been almost entirely superseded by the Petroleum Oils since the utilization of the latter.
The Mineral Oils obtained by distillation of coal tar, which is the product of the dry destructive distillation of coal at gas works, are chiefly used for dissolving rubber, in the manufacture of the beautiful aniline colors, and in making printing inks, varnishes and paints.
The Petroleum Oils have been placed by nature within easy reach of mankind, and have been of great use for lighting, heating and lubricating purposes. In their natural state they are found in all forms of consistency, from a solid to a thin oily liquid, and from the darkest to the lightest shades of color. This peculiar product of nature is composed of an endless series of Hydro-carbon compounds, from a light, incondensible gas, to a solid body. They are similar in characteristics to the Mineral Oils obtained from coal tar and from shale, but differ materially in their chemical composition.