a hydrocarbon found in the pitchy residue obtained in the distillation of peat-tar and of petroleum. This is distilled to dryness and the distillate repeatedly recrystallized from cymene. It may be synthetically prepared by the action of anhydrous aluminium chloride on a mixture of naphthalene and ethylene dibromide (R. Lespieau, Bull. soc. chim., 1891, (3), 6, p. 238), or by distilling a-dinaphthostilbene (T. Hirn, Ber., 18 99, 3 2, p. 334 1). It crystallizes in large colourless plates which possess a blue fluorescence. It is soluble in concentrated sulphuric acid with a green colour. Chromic acid in glacial acetic acid solution oxidizes it to picene-quinone, picene-quinone carboxylic acid, and finally to phthalic acid. When heated with hydriodic acid and phosphorus it forms hydrides of composition H and H (see E. Bamberger and F. D. Chattaway, Ann., 18 95, 284, P. 61).