AMMONIAC, a concrete, gummy, resinous juice brought from the East Indies, usually in large masses, composed of little lumps or tears, of a milky colour, but soon changing, upon being exposed to the air, to a yellowish hue. We now know that the plant which affords this juice is Dorema ammoniacum. It is one of the Umbelliferæ (Pent. digyn.), and grows on an arid soil in the province of Irak in Persia, 42 miles from Ispahan. It grows also near Herat in Khorassan, and on the north-western slopes of the Himalayas. The plant is said also to grow in Nubia, Abyssinia, and the interior parts of Egypt. It is brought to the western parts of Europe from Egypt, and to England from the Red Sea, by ships trading to the east. Such tears as are large, dry, free from little stones, seeds, or other impurities, should be picked out, and preferred for internal use; the coarser kind is purified by softening it in hot water and colature, and then carefully inspissating it; unless this be skilfully done, the gum will lose a considerable portion of its more volatile parts. There is often vended in the shops, under the name of strained gum-ammoniacum, a composition of ingredients much inferior in virtue. Ammoniac has a nauseous, sweet taste, followed by a bitter one; and a peculiar smell, somewhat like that of galbanum, but
more grateful; it softens in the mouth, and grows of a whiter colour when chewed. Thrown upon live coals, it burns away in flame. It is partially soluble in water and in vinegar, with which it assumes the appearance of milk; but the resinous part, amounting to about one-half, subsides on standing. It is of considerable use in the Materia Medica as an antispasmodic.