lamp and
the candle were the mainstays of artificial lighting throughout many
centuries. The fats and waxes which these light-sources burned were many
but in the later centuries they were chiefly tallow, sperm-oil,
spermaceti, lard-oil, olive-oil, colza-oil, bees-wax and vegetable
waxes. Those fuels which are not liquid are melted to liquid form by the
heat of the flame before they are actually consumed. The candle is of
the latter type and despite its present lowly place and its primitive
character, it is really an ingenious device. Its fuel remains
conveniently solid so that it is readily shipped and stored; there is
nothing to spill or to break beyond easy repair; but when it is lighted
the heat of its flame melts the solid fuel and thus it becomes an
"oil-lamp." Animal and vegetable oils were mainly used until the middle
of the nineteenth century, when petroleum was produced in sufficient
quantities to introduce mineral oils. This marked the beginning of an
era of developments in oil-lamps, but these were generally the natural
offspring of early developments by Ami Argand.

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 distingu