A simple or undecomposed gaseous substance, was first distinguished by Dr. Rutherford, in 1772. It is sometimes called azote, from its inability to support animal life; but it is commonly designated nitrogen, from its being an essential ingredient in nitric acid. It constitutes four-fifths of the volume of the atmosphere, and may therefore be procured by abstracting the oxygen from atmospheric air. It may be conveniently prepared by burning a piece of phosphorus in a jar full of air, inverted over water. The phosphorus, on account of its strong affinity for oxygen, will abstract it from the mixture, and the vessel will become filled with a white cloud, which is the pyrophos-phoric acid. In about half an hour this will subside, and the residual gas is nitrogen, contaminated with a little carbonic acid and vapour of phosphorus, both of which may be removed by agitating them with a solution of pure potash. A solution of protosulphate of iron, charged with binoxide of nitrogen, will separate the oxygen from common air in a few minutes. A stick of phosphorus placed in it will accomplish the same in twenty-four hours. Nitrogen gas may also be obtained by exposing a mixture of fresh muscle and nitric acid to a moderate temperature.

Effervescence occurs, and a large quantity of nitrogen, mingled with carbonic acid, is evolved, the latter of which may be removed by agitation with lime water. Nitrogen, when pure, is a colourless gas, devoid of either smell or taste; it does not burn, and extinguishes all burning bodies immersed in it; it does not change the blue colour of vegetables; no animal can live in it, yet it exerts no injurious influence on the lungs or other parts of the animal system, the privation of oxygen being the sole cause of death. Water, when deprived of air by boiling, takes up about one and a half per cent. of it. Its specific gravity is .9722; and therefore 100 cubic inches, at a mean temperature and pressure, will weigh 30.15 grains. In the combination of nitrogen with oxygen in the atmosphere, it seems merely to moderate or dilute the oxygen, so as to render its action less energetic. Considerable doubts have existed as to its simple nature, in consequence of experiments made with the galvanic battery. When ammonia (which is a compound of nitrogen and hydrogen) is submitted, in conjunction with mercury, to the action of galvanism, an amalgam is formed, which is considered to arise from some metallic base in the hydrogen or nitrogen; but as the idea of a metadic base to hydrogen seems precluded by reason of its extreme lightness, it has been inferred that it must form a constituent of the nitrogen.

This supposition, however, seems incapable of proof, as the constituents of the amalgam separate, and are resolved into ammonia, hydrogen, and mercury, as soon as the galvanic influence is withdrawn. Nitrogen unites with several substances in different proportions, forming a variety of compounds, distinguished by striking peculiarities. With oxygen are formed the nitrous and nitric oxide, and the hypo-nitrous, nitrous, and nitric acid. With chlorine and iodine it forms the chloride and iodide of nitrogen, and with hydrogen it forms ammonia. Our limits will permit us to give but a brief account of these. The nitrous oxide, or protoxide of nitrogen, was discovered by Dr. Priestley in 1772, who called it dephlogisticated nitrous air. The best mode of procuring it is by means of nitrate of ammonia. When this salt is exposed to a temperature of 400° or 500° Fahr. it liquefies, and bubbles of gas begin to escape, and in a short time a brisk effervescence ensues, which continues till all the salt disappears. The nitrate of ammonia should be contained in a glass retort, and the heat of a lamp applied, so as to maintain a moderately rapid evolution of gas. In accurate experiments the gas must be received over mercury; but for ordinary purposes it may be received over water.

It has a sweet taste, and a faint, agreeable odour, and is absorbed by its own volume of recently-boiled water. Most substances burn in it with far greater energy than in the atmosphere; but the most remarkable of its properties is its effect when respired. A few deep inspirations are followed by the most agreeable feelings of excitement, similar to the early stages of intoxication. This is shewn by a strong propensity to laughter, by a rapid flow of vivid ideas, and an unusual disposition to muscular exertion. These feelings soon, however, subside, and the person recovers his ordinary state without experiencing that languor which is the usual result of excitement by spirituous liquors. It varies somewhat in its effects on different individuals, and sometimes produces disagreeable symptoms. The specific gravity of this gas is 1.5277; and 100 cubic inches weigh 47.377 grains. The binoxide of nitrogen, or nitric oxide, is best obtained by the action of nitric acid of specific gravity 1.2 on metallic copper. Brisk effervescence ensues, and the gas may be collected over water or mercury. The nitric oxide is a colourless gas; but when mixed with oxygen or atmospheric air, dense suffocating, orange-coloured vapour of nitrous acid is produced.

Few inflammable substances burn in it; charcoal and phosphorous, however, when in vivid combustion, burn in it with increased brilliancy. It is sparingly absorbed by water, does not redden vegetable blues, and is quite irrespirable. 100 cubic inches weigh 32.3 grains, and its specific gravity is 1.0416. The hypo-nitrous acid has not hitherto been obtained in a free state, but combined with potash. Pure nitrous acid is formed by the mixture of binoxide of nitrogen with oxygen gas, out of contact with either water or mercury. When condensed in water, it forms the liquid nitrous acid.