FATS. In chemistry, this class of sub stances was originally understood to include all those compounds of carbon, hydrogen and oxygen which leave a permanent, translucent grease-spot upon paper. In more recent times, however, it has been the custom to include only such bodies of this sort as admit of saponifica tion. They are odorless, colorless, tasteless, white or yellowish, insoluble in water, but soluble in ether, chloroform and benzol. Our knowledge of the constitution of the fats is due in large measure to the labors of the French chemist Chevreul, who showed that they are mostly composed of glycerin, in combina tion with certain organic acids, known as the fatty acids (q.v.), prominent among which are oleic, stearic and palmitic acids. Fats may be extracted from animal tissues simply by heat, a temperature of 212° F. being generally suffi cient. From seeds and other vegetable sub stances in which they occur they are commonly extracted by heating the ground-up tissues and subjecting them to heavy pressure. As obtained by these methods, the fats often retain frag ments of the original tissues in which they occur, as well as certain nitrogenous substances that come away with them. The nitrogenous matters may be removed by shaking the fluid fat (or oil) with sulphuric acid, and the fat may be separated from the fragments of tissue by dissolving in ether, carbon disulphid, ben zene or light petroleum and subsequently filter ing the solution and recovering the fat by the evaporation of the solvent. The membranous particles that come away with the animal fats may also be removed by treating the fats with very dilute hydrochloric acid, which dissolves the membranous matter while leaving the fat unaltered.
The fats are decomposed when heated to F., by the separation of their glycerin from the fatty acids with which it is combined. They may also be decomposed by saponification. —that is, by boiling them with aqueous solu tions of the alkalis,— the decomposition, in this case, being due to the replacement of the com bined glycerin by the alkali. The glycerin is thereby set free and the resulting compounds of the alkali with the organic acids of the fats are known as soaps, (See SOAP). The ran cidity that develops in fats when they are kept for some time is due to the formation or libera tion of certain volatile fatty acids and it may be removed by boiling the fat with water (in which case the objectionable acids are volatil ized), or by treating it with an aqueous solu tion of sodium carbonate (in which case the volatile acids are neutralized by the alkali, with the formation of their unobjectionable sodium salts).
As has been noted above, stearic, oleic and palmitic acids are the commonest of the .acids that occur in fats. Their compounds (or ((esters))) with glycerin are known, respectively, as stearins, olems and palmitins and are mark edly similar in their general properties. The nature of these compounds may be sufficiently illustrated by stearin as an example. The formula of stearic acid is H.CA-1,00, and that of glycerin is GI-14(OH)s. If the two are heated together, they may combine in the following manner : GH.(OH).