Before man discovered that nature had stored a tremendous supply of mineral oil in the earth he was obliged to hunt broadcast for fats and waxes to supply him with artificial light.  He also was obliged to endure unpleasant odors from the crude fuels and in early experiments with fats and waxes the odor was carefully noted as an important factor.  Tallow was a by-product of the kitchen or of the butcher.  Stearine, a constituent of tallow, is a compound of glyceryl and stearic acid.  It is obtained by breaking up chemically the glycerides of animal fats and separating the fatty acids from glycerin.  Fats are glycerides; that is, combinations of oleic, palmetic, and stearic acids.  Inasmuch as the former is liquid at ordinary temperatures and the others are solid, it follows that the consistency or solidity of fats depend upon the relative proportions of the three constituents.  The sperm-whale, which lives in the warmer parts of all the oceans, has been hunted relentlessly for fuels for artificial lighting.  In its head cavities sperm-oil in liquid form is found with the white waxy substance known as spermaceti.  Colza-oil is yielded by rape-seed and olive-oil is extracted from ripe olives.  The waxes are combinations of allied acids with bases somewhat related to glycerin but of complex composition.  Fats and waxes are more or less related, but to distinguish them carefully would lead far afield into the complexities of organic chemistry.  All these animal and vegetable products which were used as fuels for light-sources are rich in carbon, which accounts for the light-value of their flames.  The brightness of such a flame is due to incandescent carbon particles, but this phase of light-production is discussed in another chapter.  These oils, fats, and waxes are composed by weight of about 75 to 80 per cent. carbon; 10 to 15 per cent. hydrogen; and 5 to 10 per cent. oxygen.

Until the middle of the eighteenth century the oil-lamps were shallow vessels filled with animal or vegetable oil and from these reservoirs short wicks projected.  The flame was feeble and smoky and the odors were sometimes very repugnant.  Viewing such light-sources from the present age in which light is plentiful, convenient, and free from the great disadvantages of these early oil-lamps, it is difficult to imagine the possibility of the present civilization emerging from that period without being accompanied by progress in light-production.  The improvements made in the eighteenth century paved the way for greater progress in the following century.  This is the case throughout the ages, but there are special reasons for the tremendous impetus which light-production has experienced in the past half-century.  These are the acquirement of scientific knowledge from systematic research and the application of this knowledge by organized development.