n. A white crystalline substance, C6H4(OH)2; orthodihydroxybenzene. It occurs in the urine of horses as pyrocatechol-sulphuric acid, and also in human urine and in some plants. It is made by fusing phenol, bromphenol, etc., with caustic potash and by the dry distillation of catechin and many tannins; it melts at 104° C. Also called pyrocatechin, pyrocatechinol, oxyphenic acid; and catechol.