SEBACIC acid, the acid of fat. The penetrating fumes which are exhaled from melted tallow, and which affect the eyes, the nostrils, and even the lung!, had been long ago observed. Little at tention, however, was paid to their nature and properties. in 1754, appeared a dis sertation by M. Seguer, on the acid of animal fat, which contained a number of well conducted experiments. Crell en deavoured to improve the process for the separation and ,purification of this acid, and to ascertain the properties of its com binations. These were published in the Philosophical Transactions for the years 1780 and 1782 But it appears, that the acid obtained by those who first treated of the subject was either the acetic acid, or some acid different from the sebacic, the properties of which are quite distinct from those which had been formerly de scribed. The process by which Thenard obtained the sebacic acid is the following. He distilled a quantity of hog's lard, and washed the product several times with hot water. He then dropped into it ace tate of lead ; there was formed a flaky precipitate, which was collected and dried put into a retort with sulphuric acid and heated. The liquor in the re
ceiver had no acid character ; but there appeared in the retort a melted matter analogous to fat This is carefully sepa rated, and after being washed, is boiled with water. By the action of heat the whole is dissolved by the water, and when it cools, crystals in the shape of needles are deposited. These are the sebacic acid, which has the following pro perties. It has no smell, a slight acid taste, and reddens strongly the tincture of turnsole. When heated it melts like tal low. It is much more soluble in warm than in cold water. Alcohol dissolves it in large quantities. Boiling water satu rated with this acid forms a solid mass on cooling. It crystallizes in small needles, but with certain precautions may be ob tained in the form of long, large, and very brilliant plates. It precipitates the acetate and nitrate of mercury and lead, and nitrate of silver ; it neutralizes the al kalies, and forms with them soluble salts.