Ammonium compounds are divisible into two classes. In the first class the ammonium is combined with a strong acid such as hydrochloric or sulphuric. These form stable, neutral salts which act largely by their salt action. In the second class, the ammonium is combined with a weak acid radical such as hydroxyl or the radical of carbonates. These compounds are unstable decomposing readily with liberation of ammonia. Such compounds produce reflex effects by the irritating action of the ammonia evolved. All ammonium compounds used in medicine are soluble in water and the carbonate and hydroxid have a strong alkaline reaction.

Action and Uses: Ammonium salts, when injected into the circulation, stimulate the central nervous system, but they are so rapidly excreted or converted into urea that they cannot produce systemic action when taken by mouth, even though they are absorbed very readily. Their effects are, therefore, entirely local. Ammonium acetate was believed to be diaphoretic, but probably has little value.

The neutral salts are rather irritant and thus cause a mild stimulation of the mucous membanes, explaining the use of ammonium chlorid as an expectorant. With ammonium carbonate, this effect is reinforced by its alkaline reaction, through which it liquefies and dissolves mucus.

Ammonia (NH3)

A gas which is very soluble in alcohol and water with formation to some extent of NH4OH. Water of ammonia and the several preparations containing it are strongly alkaline.

Incompatibilities: It is incompatible with acids, neutralizing them and forming the salts of ammonium. It is also incompatible with the soluble salts of many metals because it precipitates from these solutions the hydroxid of the metals. Thus ammonia water with solution of ferric chlorid produces an insoluble precipitate of ferric hydroxid. Solutions of ammonia are also incompatible with the salts of alkaloids from which they liberate the alkaloid. Thus ammonia water added to a solution of strychnin sulphate produces a precipitate of the insoluble alkaloid strychnin.

Actions and Uses : Ammonia internally in the form of water of ammonia or of aromatic spirit of ammonia is stimulant, because the ammonia escaping irritates the mucous membranes of the nose and of the stomach and causes a reflex increase in the force of the heart and in the blood-pressure. Little, if any, of the gas is absorbed by the respiratory tract.

Externally, ammonia is used as a counterirritant. It reddens the skin but does not blister, unless applied in concentrated solution.