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ELEMENTS OF MATERIA MEDICA.

Properties. —It has a yellow colour. Its most remarkable property isthat of dissolving gold and platinum, metals that are insoluble in eithernitric or hydrochloric acid separately. It should be kept in a cooldark place ; for heat rapidly expels the chlorine, while light enables it todecompose the water and to form hydrochloric acid.

Characteristics.- —It is recognised by its colour, by its power ofdissolving gold, by its precipitating a solution of nitrate of silver; theprecipitate being insoluble in nitric acid, but soluble in ammonia ; bythe production of two salts, a chloride and a nitrate, when an alkali isadded to it; and by the evolution of binoxide of nitrogen on the additionof copper turnings (see Nitric Acid ).

Physiological Effects. —It is a powerfully corrosive poison, actingin a similar manner to nitric acid.

Uses. —It has been employed internally in the same cases as nitricacid, more especially syphilis, diseases of the liver, and some of theexanthemata. Externally it has been used as a bath, either local orgeneral, in syphilis and hepatic affections. In India the whole body (thehead excepted) is immersed, but in this country pediluvia only areusually employed, or the body is merely sponged with it. The nitro-muriatic bath is prepared in wooden tubs, by adding this acid to water,until the latter becomes as acid to the taste as vinegar (from 4\ to 6 fluid-ounces of the acid to about 3 gallons of water in a deep narrow tub). Thepatient should remain in the bath from 10 to 30 or 40 minutes. Itexcites tingling and prickling of the skin, and is said to affect the gumsand salivary glands, causing plentiful ptyalism ; indeed, we are told thatwithout the latter effect, every trial is to be regarded as inconclusive.In the passage of biliary calculi this bath is said to be remarkablyeffective.

Administration. —When taken internally the dose is three or fourdrops properly diluted and carefully increased.

Antidote. —Poisoning by this acid is to be treated in the same way asthat by sulphuric acid.

Ammo'nia. — Ammo'nia or Ammoni'acal Gas.

History and Synonymes. —Dr. Black, in 1756, first pointed out thedistinction between ammonia and its carbonate; and Dr. Prestley {OnAir, vol. ii. p. 369, 1790) first procured ammonia in a gaseous form. Hecalled it alkaline air. It is sometimes termed volatile alkali, and occa-sionally azoturetted hydrogen.

Natural History . —Ammonia, free or combined, exists in both king-doms of nature-

{a.) In the inorganized kingdom. —Hydrochlorate and sulphate ofammonia are met with native usually in the neighbourhood of volcanoes.Aluminous sulphate of ammonia (or ammonia-alum) occurs in Bohemia .Dr. Marcet detected the hydrochlorate in sea water. This salt has alsobeen recognized in mineral waters (Gairdner, On Mineral Springs, p. 15).Ammonia exists in many of the native oxides of iron, and in some chaly-beate waters [Diet, des Drogues, t. i. p. 293).

(b.) In the organized kingdom. —Ammonia is found in vegetables, insmall quantities only. In the free state, it is said to exist in severalplants, as Chenopodium vulvaria, Sorbus auevparia {Diet , des Drag.,