Sal Ammoniac consists of chloride of ammonium NH4Cl, a white solid which may be artificially prepared by the direct union of hydrochloric acid and ammonia, dense white fumes resulting from the combination of the two colourless gases. It has been known from early times. It was imported first from Asia, afterwards from Egypt, where it was prepared from camel's dung, and later it was manufactured by the distillation of horns, hoofs, etc. At the present time it is almost entirely obtained as a bye-product in the manufacture of coal-gas. The gas liquor, as it is called, contains large quantities of ammoniacal salts; it is heated with lime and the ammonia expelled and received in dilute hydrochloric acid. From the solution so formed the sal ammoniac is obtained pure by recrystallisation and sublimation. It forms colourless crystals of the regular system, frequently forming arborescent aggregations. As obtained by sublimation it is usnally a tough fibrous mass. It is easily soluble in water, the solution possessing a sharp taste. It is used to a slight extent in medicine, and very largely in the dyeing industry, besides which it finds frequent application in the chemical laboratory.