Animal oil in a concrete state, deposited in minute cells in various parts of the bodies of animals. The colour is white or yellowish; it is insipid, inodorous, insoluble in water and in alcohol, but it combines with alkalies and forms soap. It absorbs oxygen by exposure to the air, and becomes rancid, forming a peculiar acid, called the sebacic. It is decomposed by heat, producing the sebacic acid, an empyreumatic oil, and carbonated hydrogen, leaving a residuum of charcoal. Fat is oxidated by the acids, and it oxidates several of the metals, when they are combined with it in the form of an ointment. Some interesting information on the nature and properties of fat, and the mode of separating its constituent properties, will be found under the head Candle. See also Soap.

Fat is also a name given to a measure of capacity, differing in different commodities. Thus, a fat of isinglass contains 3 to 4 cwt.; a fat of unbound books is four bales; a fat of wire 20 to 25 cwt.; a fat of yarn 220 bundles.