The Romance of Modern Chemistry

FATS AND OILS however diverse their origin. A fat or fatty oil is a substance analogous to a salt, which, as already shown, is a neutral compound produced by the combination of an acid and a base. The constituent of the fats and oils which corresponds to the base of a salt is glycerine, while the acid is very often stearic, oleic, or palmitic acid. The compound formed by the union of glycerine and one of these “ fatty ” acids is termed a “ glyceride,” and the commonly occurring fats and oils are to be looked on as mixtures of different glycerides. That fats and oils are obtained from an extraordinary variety of sources is shown by the fact that hogs1 kidneys, cotton seed, milk, hazel nuts, cod livers, and cows’ feet, are among the raw materials requisitioned for the purpose. Fats and oils of a vegetable origin are obtained mostly from fruits, which in some cases contain a high pro- portion of fatty material. The fruits of the olive tree contain about half their weight of oil, used, for instance, in packing sardines, while in the seed of the flax plant there is 30 to 35 per cent, of oil, familiar to every one as linseed oiL A vegetable oil is extracted from the seed in one of two ways. The seed is either crushed under pressure, so that the oil is squeezed out, or it is heated with some volatile liquid such as petroleum or carbon disulphide, which dissolves out the oil and can afterwards be boiled away. When the first method is employed the expressed oil is collected in suitable vessels, and the compressed residue, still containing a small proportion of oil, is sold as oil- cake for feeding cattle. This way of utilising the residue is obviously an economical one, for the unextracted oil is ultimately recovered from the cow or bullock in the form of butter, tallow, or neat’s-foot oil. 238