Gum. Called also armoniacum, but improperly; hammoniaci lachryma, assac, azac: and in English, gum ammoniac.

It is a concrete gummi-resinous juice, produced in the East Indies, and brought in masses from Ammonia, consisting of little lumps, which inwardly are very white, but outwardly yellowish or brownish; its whitest parts become yellow on being exposed to the air. From what plant it is obtained we know not; but, according to Dioscorides, it is from a shrub called argasyllis. It has been supposed with great probability to be an exudation from a species of ferula; another species of which produces asafœtida. It hath a strong smell, somewhat like that of galbanum, but not so disagreeable; a nauseous sweetish taste mixed with a bitterness.

Such pieces as are white, clear, dry, and large, should be preferred for internal use.

Thrown on live coals, it burns away in flames; it is soluble both in water and vinegar into a kind of milk; but the resinous part, which is nearly one half of the whole, subsides on standing: spirit of wine dissolves near one half of it, taking up all its active parts.

Dr. Dedier says, that Ammoniacum 445 i. of this gum, afforded by distillation of phlegm 3 vi. volatile spirit ij. a volatile fetid oil vi. But other skilful chemists have failed to obtain any oil from it by this process. Water is very slightly impregnated with it by distillation.

This drug has been esteemed a deobstruent, and an useful medicine in hysteric complaints; but modern practice confines its internal use to its expectorant powers in asthma, and difficult breathing: it gently moves the belly, and externally applied with squills, it has been recommended for resolving indurated tumours. See Ammoniaci emplastrum cum hydrargyro.

The dose may be from gr. x. to 3 ss. three times a day, dissolved in water, when it is called lac ammoniaci; or in pills, which is the most agreeable form.

It is adulterated with common resin, and the method of purifying it is, by softening it in a bladder, which is immersed in boiling water; and straining it while fluid: but for inward use, the best is the largest and most unadulterated pieces.