(excepting atmospheric air) might be included under it; for even oxygen itself will not indefinitely support life: moreover, nitrogen, as it exists in the atmosphere, mixed with oxygen, appears to be absolutely essential to animal life; for no other gas can be substituted for it. If we consider the term nitrogen as merely implying that it is a component of nitric acid, it is explicit and unobjectionable. We, therefore, adopt it in preference to that of azote.-Brande.

Whether nitrogen is or is not a simple body has been much discussed among eminent chemists, without any conclusive result. In Silliman's American Journal for 1829, we read of a discovery of nitrogen gas issuing in almost a pure state from the earth, through three springs, in Hoosick, New York. According to Trousset, the gas emitted by the skin is pure nitrogen; and Mr. Faraday has proved that if sea-sand, after ignition, be handled, it will yield an azotic impregnation from the skin, which the sand itself would not do.

Professor Emmett recommends the preparation of nitrogen by dipping zinc into fused nitrate of ammonia: it is instantly oxidized and dissolved, and nitrogen and ammoniacal gases are evolved. Every grain of the metal furnishes nearly a cubic inch of the gas; while the ammonia, which also escapes, becomes wholly condensed, as soon as it enters into the water of the pneumatic cistern.

Why is there so much nitrogen in atmospheric air, seeing that it is injurious to animal life?

Because it dilutes and modifies the oxygen of the atmosphere, so as to prevent too rapid combustion, and stimulating respiration. Dr. Lambe observes, that" if the proportions of oxygen and nitrogen were reversed in atmospheric air, the air taken in by respiration would be more stimulant, the circulation would become accelerated, and all the secretions would be increased; the tone of the vessels, thus stimulated to increased action, would be destroyed by over excitement, and, if

the supply from the stomach were not equal to the consumption, the body must inevitably waste and decay. Why is nitrous oxide popularly called “laughinggas?

Because it produces a certain degree of pleasurable excitement, often accompanied by laughter, in those who inhale it. It was discovered by Dr. Priestley, in 1772, but was first accurately investigated by Sir Humphry Davy, in 1779. The best mode of procuring it is to expose nitrate of ammonia to the flame of an argand lamp, in a glass retort. When the temperature reaches 400° Fahrenheit, a whitish cloud will begin to project itself into the neck of the retort, accompanied by the copious evolution of gas, which must be collected over mercury for accurate researches, but for common experiments may be received over water.

In Sir Humphry Davy's volume of Researches, concerning nitrous oxide, are many interesting details of its effects when respired. Sir Humphry describes those upon himself thus:-"Having previously closed my nostrils and exhausted my lungs, I breathed four quarts of nitrous oxide from and into a silk bag. The first feelings were similar to giddiness; but in less than half a minute, the respiration being continued, they diminished gradually, and were succeeded by a sensation analogous to gentle pressure on all the muscles, attended by an highly pleasurable thrilling, particularly in the chest and the extremities. The objects around me became dazzling, and my hearing more acute. Towards the last inspiration the thrilling increased, and at last an irresistible propensity to action was indulged in. I recollect but indistinctly what followed: I know that my motions were various and violent. These effects very soon ceased after respiration. In ten minutes I had recovered my natural state of mind. The thrilling in the extremities continued longer than the other sensations. Almost every one who has breathed this gas, has observed the same things. On

some few, indeed, it has no effect whatever, and on others the effects are always painful." The experiment cannot be made with impunity, especially by those who are liable to a determination of blood to the head. Why is nitric acid so called?

Because it is usually obtained by distilling purified nitre with sulphuric acid; this, however, is only sufficiently pure for ordinary purposes.

Nitric acid stains the greater number of animal substances of a yellow colour, and is hence used in producing yellow patterns upon coloured or woollen goods; it is used in fumigations, to destroy contagious and infectious matter, more especially in inhabited apartments, where chlorine would prove injurious. For this purpose, nitrate of potassa (nitre) and sulphuric acid are mixed in a saucer, and the evolution of the acid vapour aided by a gentle heat. In pharmacy, and a variety of other processes, it is susceptible of interesting applications: it is used for etching on copper, and as a solvent for tin,* in the preparation of valuable mordants, used by dyers and calico printers. It is an important agent in metallurgy, and especially in the art of assaying.-Brande.

For the purposes of the arts, it is commonly used in a diluted state, and contaminated with the sulphuric and muriatic acids, by the name of aqua fortis. A compound, made by mixing two parts of the nitric acid with one of muriatic, known formerly by the name of aqua regia, and now by that of nitro-muriatic acid, has the property of dissolving gold and platina.

Why is oxalic acid also called acid of sugar ?

Because it is most commonly procured by the action of nitric acid on sugar.

* In a recent German Journal, M. Mitscherlich mentions that iron, tin, and several other metals, may be put into, and even boiled in nitric acid, of 1.522 specific gravity, without the least effect; whilst zinc is immediately oxidized and dissolved.

AMMONIA.

Why is ammonia also called volatile alkali ? Because it converts most vegetable blues to green, and the yellows to red-properties which belong to the alkalies. The change of colour thus effected by ammonia is, however, distinguished from that produced by the fixed alkalies, by the return of the original tint, when the ammonia flies off by exposure. It saturates the acids, and produces an important class of ammoniacal salts, which are recognized by the evolution of ammonia, when they are triturated with potassa, soda, or lime.-Brande.

Why is sal ammoniac so called?

Because it was first made in the neighbourhood of the temple of Jupiter Ammon. According to Pliny, there were large inns in the vicinity of this famous temple, where the pilgrims, who came to worship, lodged; and who usually travelled on camels. The proprietors of these stables had some contrivance for preparing aud concentrating the urine of these beasts, and the salts which it produced were afterwards sublimed in glass vessels for sale. Another account is, that ammoniacal salt was abundantly obtained from the blood of the victims who were slaughtered in honour of the god.

Why should liquid ammonia be kept in well-stopped bottles?

Because it loses ammonia, and absorbs carbonic acid, when exposed to the air.

Why is ammonia generally used in a liquid state? Because, being next to hydrogen and carburetted hydrogen, the lightest of all the gaseous bodies, it has a great affinity for water. Now, though water is incapable of dissolving either hydrogen or nitrogen, yet when these are united in ammonia, their nature is so changed, that they become very soluble in water; that

fluid having the power of taking up and condensing nearly 670 times its own bulk of ammoniacal gas; and when thus saturated, the solution is lighter than an equal volume of water, in the proportion of 875 to 1000. Why is ammonia important in dyeing?

Because of its extensive use in making archil. A Florentine merchant, about the year 1300, having accidentally observed that stale urine, which always contains ammonia, imparted a very fine colour to a certain species of moss, &c., made experiments, and thus learned to prepare archil.-Berthollet.

A recent French Journal states, that aqua ammonia will give to new brandy all the qualities of that of the oldest date. Five or six drops of the ammonia are to be poured into each bottle of brandy, and shaken well, that it may combine with the acid, on which the taste and other qualities of the new liquor depend.

Why is ammonia so abundantly found in nature? Because all putrifying animal and vegetable substances furnish it, in proportion to the quantity of nitrogen which they contain. It is, however, now generally procured by dry distillation of bones, horns, &c. Besides various uses in the arts, in chemical researches, and in medicine, ammonia combines with carbonic acid, and forms the article known as volatile salts, which are likewise obtained from coal soot, and from the waste liquor collected in the manufactories of coal gas. It has also an useful domestic application in aiding the lightness of bread; which is explained by its great volatility, and the heat of baking. Another and more extensively useful combination of ammonia, is with muriatic acid, forming muriate of ammonia, or sal ammoniac, originally fabricated in Egypt, from the soot of the dung of camels, burnt as fuel. It is now made in Europe, and is used by dyers to prevent tin from precipitating; in tinning metals, to cleanse the surface, and prevent them oxidizing by heat; and in