505. Nitrogen, or azote, is a substance diffused through nature, and particularly in animal bodies.

Nitrogen is not to be found in a solid or liquid state; but combined with caloric, it forms azotic gas, or mephitic air, in which no animal can breathe, or any combustible burn.

Seventy-eight parts combined with 22 of oxygen, form 100 parts of atmospheric air. In a higher degree of oxygenation when an actual combination between it and oxygen is effected, it produces nitrous gas; and in a still higher, nitric acid.

Obs. 1.-As oxygen is absorbed during burning or breathing, and as soon as the 22 parts, or nearly, of oxygen are absorbed, the remainder is nitrogen, and be

comes mephitic or deadly, being incapable of sustaining life or flame.

2. As the constitution of the atmosphere constantly remains the same, it is evident there must be some process in nature, by which a fresh quantity of oxygen is produced equal to that consumed. One principal means of the reproduction of oxygen appears in the process of vegetation; healthy plants exposed in the sun-shine to air, containing small quantities of carbonic acid gas, destroy that elastic fluid, and evolve oxygen gas; so that the two great classes of organized beings are dependent upon each other. Carbonic acid gas, which is formed in many processes of combustion, as well as in respiration, if not removed from air, by its excess, would be deleterious to animals; but it is the healthy food of vegetables; and these vegetables produce oxygen, so necessary to the existence of animals. This part of the œconomy of nature is therefore preserved, by the very functions to which it is subservient; and the order displayed in the arrangement, demonstrates the intelligence by which it was designed.

506. Oxygen, Nitrogen, (or azote,) Hydrogen and perhaps Caloric and Light, may therefore be considered as the active and universal elements of nature.

They constitute the bulk, basis, or substance of atmospheric air, water, vegetables, and animals; and it is suspected, that gold, other metals, and all other bodies and powers of nature, will, in due time, be proved to arise out of their combinations in various proportions.

We say, for the present, call them agents of Nature; and the other simple substances may be called patients.

Obs-Chlorine, or Oxymuriatic Gas, which Sir H. Davy assimilates to oxygen, as an elementary substance, is of a yellowish green colour; and it is this property

which suggested its name. Its odour is extremely disagreeable. It is not capable of being respired, and even when mixed in very small quantities with common air, renders the air extremely pernicious to the lungs. When an inflamed taper is introduced into a phial filled with it, the light continues, but of a dull red colour, and a dark carbonaceous smoke arises from the flame.

Many of the metals introduced into it in thin filaments, or leaves, or powder, take fire, and burn spontaneously at common temperatures: such, are copper, tin, arsenic, zinc, antimony, and the alkaline metals.

Phosphorus burns in it spontaneously, with a pale white light, producing a white volatile powder.

Sulphur melted or sublimed in it does not burn; but forms with it a volatile red liquor. Chlorine has never been found pure in nature; but exists in many compounds; particularly in common salt, as it may be produced from that substance.

507. Before we proceed further, we request that it may be remembered.

1. That all fluids are combinations of heat or motion, with some other substances;

2. That combustion arises from the action of heat on the parts of the combustible body; and that the process called burning, is nothing more than the oxygen of the atmosphere uniting with certain parts of the body;

3. That oxygen seems to be the acidifying principle; and that all acids are combinations of ogen with other substances;

4. And that all compounded salts are combinations of an acid with some other substance.

508. Acids therefore are formed from oxygenous combinations; and salts from acid combinations. Weak acids are indicated by the termination ous,

as sulphurous, &c.; and strong ones by ie, as sulphuric, &c.

But in forming salts from acids, if those acids ending in ous are used, the salt is terminated by ite, as sulphite, &c.; but if from the strong acid ending in ic, the salt ends with at; as sulphat, &c.

When there is an excess of acid, the preposition super is added; and when an excess of the base, then sub is prefixed.

509. The other substances which have not yet been decompounded, and therefore called elementary, are, Carbon, Sulphur, Phosphorus, and two or three others, which, combined with oxygen, form acids.

There are also nine earthy substances, as lime, magnesia, silex or fiint, alumine or clay, and five others, which, combined with acids, form numerous salts.

All pure metals have, hitherto, been deemed simple substances; as platina, gold, silver, iron, &c. They are nearly forty in number.

510. Carbon, or diamond, or pure charcoal, is that hard substance which is diffused through all animal and vegetable bodies. It may be obtained by exposing them to a red heat, which drives off all their aqueous and foreign combinations.

Carbon combined with oxygen, of course forms an acid, called carbonic acid, which exists in large quantities in chalk, lime-stone, &c.

Carbonic acid cannot be obtained in a liquid form; but its purest state is that of gas.

The carbonic acid gas (i. e. a gas raised by applying heat to a combination of oxygen and carbon) is the choke damp of mines.

Combined with hydrogen, it forms fixed and volatile oils; and with other bodies, what are called carbonats and carburets.

511. Sulphur, or brimstone, found near volcanoes, in coal-mines, &c., has a great tendency to combination.

United with metals, it forms pyrites; as iron or martial pyrites, copper-pyrites, &c.

The modern name of its combinations with earths, metals, &c., is sulphuret; as sulphuret of iron, sulphuret of magnesia, &c.

Combined with oxygen, it forms sulphurous and sulphuric acid.

512. Phosphorous is a simple substance, found in a state of combination with the bones of animals, from which it is extracted.

Its tendency to unite with oxygen is so great, that it always burns in the open air; and bursts into flame, at a degree of heat a little above that of the human body.

Its combinations with earths and metals are called phosphurets.

Obs. Many amusing experiments may be performed with it; but great care should be taken, and a basin of water kept at hand, for it will kindle into an unextinguishable flame even by friction.

513. Chemists, by separating earths from fo reign matters, and from each other, have discovered nine primitive earths, which are not soluble in water or in flame: the principal are,

1. Lime, or calcareous earth, is obtained by applying heat to chalk, marble, lime-stone, &c., by which carbonic acid gas and water are expelled, and the lime left as a product.