Ammonia, HARTSHORN, or the VOLATILE ALKALI, was one of the few substances known to the chemistry of the ancients; being referred to by Pliny under the name of rechement odour, which he evolved by mixing lime with nitrum (probably sal ammoniac). It derives its name ammonia from its being obtained from sal ammoniac, which was first procured by heating camels' dung in Libya, near the temple of Jupiter Ammon. The atmosphere contains a minute quantity of ammonia, amounting to 210 to 247 parts in 10,000,000,000 parts of air, which is equal to 1 volume of ammonia in 28,000,000 of air. It is likewise present in rain-water in variable proportion. The supply of ammonia to the atmosphere is due to its evolution during the putrefaction of animal and vegetable substances, during the vinous fermentation, and the combustion of coal. It is likewise present in respired air, and is therefore a product of the daily wear and tear of the animal system. The principal source of ammonia at the present time is the destructive distillation of coal, as in gas-making. Blast-furnaces and paraffin works also produce large quantities. The materials which pass over from the retort are partly uncon- densable and truly gaseous, and these are carried to our gas-jets, and burned; but in other parts they are condensable, and are received during the purification of the gas, as a mixed tarry and watery liquid. On allowing this liquid to settle, the watery portion, containing ammonia, can be separated, and, hydrochloric acid being added to it, there is formed a compound of ammonia and hydrochloric acid, called chloride of ammonium, which can be obtained dry, by evaporating the solution down in shallow vessels. Pure ammonia is manufactured from this impure chloride of ammonium by mixing it with its own weight of slaked lime in a retort, and applying a gentle heat, when the ammonia as a gas passes over, and is received in a vessel containing water. The solubility of ammonia in water is very great, 1 volume of water at . (.) dissolving 1050 volumes of ammoniacal gas.
The liquor ammoniæ of the chemists, or hartshorn of the shops, contains about 32 per cent. by weight of the gas, and it is lighter than water, its density being .891. The solution of ammonia in water is transparent, colourless and strongly alkaline. In taste it is acrid caustic, and in odour very pungent. Applied to the skin in a concentrated form, it blisters. Exposed to the air, the ammonia escapes, and the solution thus gets weaker, and reduced to . (.), it freezes. As generally obtained, even in the gaseous condition, it is in combination with water, and may be represented by the formula or . Dry ammonia can be procured by passing the vapour of ammonia, as ordinarily obtained, over fused chloride of calcium, when the water is abstracted, and true gaseous ammonia is left, having the composition of one atom of nitrogen and three of hydrogen, . Gaseous ammonia can be liquefied under pressure and cold, and then yields a colourless, clear, mobile liquid, with the characteristic odour and other properties of ammonia much intensified. Ammonia combines with acids to form a class of salts which are of considerable importance. Thus, the crystallised sulphate of ammonia, , is very extensively used as a top-dressing by farmers, and is also mixed with manures where an increase of ammoniacal matter is desirable. The chloride of ammonium is also employed in agriculture; likewise largely by the Russian peasantry, in place of common salt, as a condiment for food. See MINDERERUS SPIRIT.
In medicine, the gaseous ammonia has been rarely used. The solution of ammonia is employed as a means of rousing the respiratory and vascular systems; and of the speedy alleviation of spasm. It is also used as a local irritant and antacid. It is serviceable in dyspeptic complaints with preternatural acidity of stomach and flatulence; to produce local irritation or destruction of certain parts, and to render comparatively harmless the bites of poisonous animals, such as serpents and insects.
Ammonium is the term applied to the group of atoms represented by the formula . As this group enters into the composition of many salts, exactly in the same way that potassium, sodium, and other metals do, the term hypothetical metal has been applied to it, although no one has ever succeeded in isolating it. Ammonium may be prepared by acting on an amalgam of sodium and mercury with a solution of chloride of ammonium. A portion of mercury is slightly heated in a porcelain vessel, and pieces of sodium introduced, when the sodium and mercury combine, and form an amalgam of sodium and mercury, which is a semi-solid substance, and scarcely occupies more space than the bulk of the mercury employed. If this be introduced into a vessel containing a strong or saturated solution of chloride of ammonium, , the chlorine combines with the sodium, Na, of the amalgam, forming chloride of sodium, , and the ammonium unites with the mercury, forming the amalgam of ammonium and mercury. As the change referred to proceeds, the amalgam increases in size many times, and forms a spongy mass of the consistence of butter, which rises through the saline solution and floats on the surface. The amalgam of ammonium and mercury very readily decomposes, and hence the difficulty of determining its exact composition.