O LEIN , or the Glyceride of oleic acid , is the liquid principle of oils, and is unknown in the native state. It is convertible by saponification into glycerin and oleic acid. This substance should not be confused with the stearin used in the making of stearin candles, which consists mainly of free stearic and palmitic acids, to which some wax is added to prevent crystallization. The remaining fluid is then known in commerce as lard oil . Lard contains from 32 to 40 per cent of solid constituents.
Margarin is a mixture of stearin and palmitin.
By incorporating with lard, while hot, a small amount of benzoin or benzoic acid, and stirring until cold, rancidity is prevented. Poplar buds, various balsams, and some volatile oils have the same effect. Pure benzoic acid should not be used, but rather the ordinary acid prepared from the gum, which still retains balsamic qualities. Adulterations and Tests. Again, for the purpose of yielding a whiter lard and to render the incorporation of water with it less difficult, salt of tartar is added to it by dishonest dealers.