Acted upon, or combined with caloric, it becomes oxygen gas; which forms 28 parts of 100 of atmospheric air; and further condensed, it forms 85 of every 100 parts of water.

Obs.---Oxygen gas is distinguished from all other gaseous matter by several important properties. Inflammable substances burn in it under the same circumstances as in common air, but with infinitely greater vividness. If a taper, the flame of which has been extinguished, the wick only remaining ignited, be plunged into a bottle filled with it, the flame will be instantly rekindled, and will be very brilliant, and accompanied by a crackling noise. If a steel wire, or thin file, having a sharp point, armed with a bit of wood in inflammation, be introduced into a jar filled with the gas, the steel will take fire, and its combustion will continue producing a most brilliant phænomenon. Oxygen gas is respirable; a small ani. mal, confined in a jar filled with this gas, lives four or five times as long as within an equal quantity of common air ;---hence, it has been called vital air.

510. During the burning of any combustible body, the oxygen leaves the atmospheric air, and combines with the calx or residuum, adding to its weight, and forming what is called an oxyde.

This process is called oxygination; and if oxygen be combined with sulphur, phosphorus, carbon, or any other substance in various degrees, it will produce acids of strength proportioned to the degree of oxygenation; which are distinguished by the terminations ous and ic; as, 1. Oxide of sulphur; | 1, Oxide of phosphorus ; 2. Sulphurous acid; 2. Phosphorous acid; 3. Sulphuric acid. 3. Phosphoric acid.

Combined with metals in various degrees, oxygen produces oxides of different colours; as grey oxyde of lead, red oxyde of lead, &c.

511. Hydrogen is one of the most abundant

principles in nature; and 15 parts of it combined with 85 of oxygen, form water.

It is only to be met with in the gaseous form; and then it is 12 times lighter than atmospheric air; and is employed to fill balloons.

It is also inflammable, and is the gas called the fire-damp, so often fatal to miners; it is the chief constituent of oils, fats, spirits, ether, &c. It is always produced from water.

Obs.---The process for filling balloons, is, by mixing five parts of water with one of sulphuric acid; and, by pouring the mixture on iron filings; the light gas, by the decomposition of the water, will rise into the balloon; and the balloon, being 12 times lighter than the atmospheric air, will rise through it.

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 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 becomes 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 o ranized beings are dependent upon each other. Carboc 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.

513. 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 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 may, 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 com pounds; particularly in common salt, as it may be produced from that substance.

514. 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 oxygen with other substances;

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

515. Acids therefore are formed from oxygenous combinations; and salts from acid combinations. Weak acids are indicated by the termination ous, as suphurous, &c.; and strong ones by ic, as sulphuric, &c.

But in forming salts from acids, if those acids ending in ous are used, the acid 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.

516. The other substances which have not 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 carthy substances, as lime, magnesia, silex or flint, 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.

517. 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.