A powerful alkali, sometimes called the volatile. In its pure state it is a gas transparent and colourless, and possessing all the mechanical properties of ordinary atmospheric air. Its smell is pungent and suffocating, and it3 taste extremely caustic. It extinguishes combustion, and immediately destroys animal life. One hundred cubic inches weigh 18.16 grs. Its spec, grav. is 0.5954. If the gas is passed through an ignited porcelain tube, containing iron, it is decomposed, and its volume doubled; it is then found to consist of 11/2 volume of hydrogen, and 1/2 volume nitrogen, which are condensed into the bulk of one volume as ammoniacal gas. It is rapidly absorbed by cold water, which, when impregnated with gas, is called liquid ammonia, or spirits of hartshorn. At a temperature of 50, water absorbs about 670 times its volume of the gas, and its spec. grav. is reduced to 0.875. This liquid, by heating, parts with the ammoniacal gas, hence it is called the volatile alkali. The manufacture of liquid ammonia is a very important one.

As this alkali is very extensively employed in medicine, chemistry, and the arts, we shall, therefore, briefly describe the process.

Into a retort connected with a series of Woolfe's bottles, put two parts of slaked lime, mixed with one part of muriate of ammonia (sal ammoniac). The Woolfe's bottles must be filled with pure water, and if they are surrounded by cold water, frequently renewed; if by ice, a more highly saturated liquid will be obtained. The muriate of ammonia is decomposed by the lime, and the ammonia passes into the water in the bottles in the state of gas, where it is immediately absorbed. The addition of hot water, and application of moderate heat, ensure complete decomposition of the salt. The liquid ammonia may be obtained by a more direct process, but not so economically. The following mode is recommended by Mr. R. Phillips, as being superior to that recommended in the London Pharmacopoeia. Pour half a pint of water on 9 oz. of well burnt lime, and when it has remained in a close vessel an hour, add 12 oz. of sal ammoniac, and 31/2 pints of boiling water. Filter the solution when cool, and distil from it 20 fluid oz. This will have a spec. grav. of 0.954, which is as strong as it can be conveniently kept. The spec. grav. of liquid ammonia is a sure test of its strength. That above-mentioned will contain about 11 per cent, of ammonia.

If the spec. grav. be .850, the liquid will contain about 35 per cent.; intermediate densities indicate intermediate proportions of ammonia. The muriate of ammonia, or sal ammoniac, from which the above-described liquid is obtained, was formerly brought from Egypt almost exclusively. In the neighbourhood of the temple of Jupiter Amnion, were many inns for the accommodation of pilgrims and their camels. From the sublimed dung of these animals the salt was obtained, and its name was derived from the locality of its manufacture. In modern times, ammonia has been procured by the dry distillation of bones, horns, and other animal matters; and, more recently, from the waste liquor of the gas works, which contains large quantities of impure ammoniacal salts. The muriate of ammonia is employed in chemical analysis, in dyeing, and in tinning or soldering. It is the most delicate test for the presence of platinum, and is generally used by the chemist to precipitate that metal from its combinations in solution. There are many other valuable salts of ammonia, the most important of which are the nitrate and carbonate. The nitrate, when heated to 400° Fahr, is decomposed, and yields the nitrous oxide, or laughing gas, in abundance.

It is also used in the preparation of frigorific mixtures: if mixed with an equal weight of water, the thermometer sinks above 30° Fahr. The carbonate is a useful chemical agent, and is used in medicine as a stimulant. This substance is the common smelling-salts of the shops. All the salts of ammonia are decomposed at a red heat. Chlorine decomposes liquid ammonia, or the gas, with great energy. If a bottle containing chlorine gas be brought in contact with the surface of liquid ammonia, the hydrogen of the latter substance combines with the chlorine, forming muriatic acid, which unites with another portion of ammonia, and nitrogen is left in the bottle. If this experiment be formed in a dark room, a flash of light will be seen at the moment of combination. If the mouth of a bottle containing chlorine gas be brought in contact with the mouth of another containing ammoniacal gas they combine with explosive violence, a flash and report accompany the action, and the bottles are sometimes broken.