The discovery of naphthalene in coal tar was made simultaneously by Garden and Brande in 1819, and its composition was determined by Faraday in 1826 and later by Laurent in 1832. Naphthalene is almost invariably a constituent of the products obtained when organic matter is heated to comparatively high temperatures. For example, it is formed in small quantities when acetylene, alcohol, acetic acid, benzene, or toluene are heated to high temperatures. Together with certain aromatic hydrocarbons it is formed in the cracking of petroleum and in the hydrogenation of petroleum fractions. Naphthalene is a constituent of the principal varieties of tar produced from coal in the manufacture of gas and coke under ordinary conditions, but not of low-temperature tar. It is present in coal gas although its presence must be kept as low as possible to avoid blocking service pipes in cold weather. The proportion in gas tar varies with the kinds of coal used and is greater the higher the temperature used during carbonization; it usually amounts to 4 to 6 percent but is sometimes as much as 10 percent. In tars obtained from byproduct coke ovens the proportion of naphthalene and other aromatic hydrocarbons depends on the type of oven used. Byproduct coke-oven tar averages 10 to 11 percent naphthalene; blast-furnace tar contains only very small amounts. Processes to synthesize naphthalene were described as early as 1873 by Aronheim, in 1876 by Wroden and Znatowicz, and in 1884 by Baeyer and Perkin. English Patent No. 26,061 of 1898 claims that it may be obtained by heating barium carbide with barium hydroxide to a high temperature. None of these processes has become of commercial importance. Recovery of naphthalene. Naphthalene is recovered in the distillation of coal tar, in the fraction boiling at 180° to 250° C., in the creosote oil fraction boiling at 240° to 270° C. and most abundantly in the carbolate or middle oil fraction boiling at 200° to 250° C. When these fractions are allowed to cool most of the naphthalene crystallizes out and is separated by draining and hot-pressing. This crude material is partially purified by washing with hot caustic soda solution to remove tar acids and then with mineral acid to remove basic substances. Refined naphthalene is obtained by subliming, or preferably by distilling the crude product. Description and uses. The Tariff Act of 1930 defines crude naphthalene as naphthalene solidifying under 79° C. after the removal of all water present; and refined naphthalene as that having a solidifying point at or above 79° C. after the removal of all water present.