Naphthalene is a hydrocarbon formed by heating many organic substances, and is on this account present in coal-tar, in which it was first discovered in 1819. From this source it may be obtained by allowing the portions of the tar which boil at from 180° to 200° C. to crystallise. After purification it is obtained as a white flaky solid, with a peculiar aromatic odour. It melts at 98°, and boils at 218° C, but sublimes readily at lower temperatures. It forms very many important compounds - the naphthalene derivatives, many of which are employed in the manufacture of various dyes. It is employed in the albo-carbon gas-burners, and is also used as an insecticide and preservative.