sive matters are formed from tasteless substances; colours are fixed upon stuffs; or changed; or made to disappear; and the productions of the mineral, vegetable, and animal kingdoms, are converted into new forms, and made subservient to the purposes of civilized life. To trace, in detail, these diversified and complicated phenomena, to arrange them, and deduce general laws from their analogies, is the business of Chemistry.

500. It is, now, found, that the AIR which we breathe is composed of a mixture of two distinct elements; one called nitrogen or Azote; the other Oxygen; and both are kept in their gazeous state by Heat, called Caloric, and that WATER is a mixture of Oxygen with Hydrogen;-that EARTH is a mixture of many substances; and that FIRE is composed of Heat (or Caloric,) and Light, united to a combustible substance.

Obs.-The forms of matter, are well arranged into four distinct classes, by SIR H. DAVY. The first class consists of solids; which compose the great, known, part of the globe. Solid bodies, when in small masses, retain whatever mechanical form is given to them; their parts are separated with difficulty, and cannot readily be made to unite after separation; some solid bodies yield to pressure, and do not recover their former figure, when the compressing force is removed, and they are called non-elastic solids; others, that regain this form, are called elastic bodies. Solids differ in degrees of hardness; in colour; in degrees of opacity or transpa rency; in density, or in the weight afforded by equal volumes; and when their forms are regular or crystallized, in the nature of these forms.

The second class consists of fluids; of which there are much fewer varieties. Fluids when in small masses, assume the spherical form; their parts possess freedom of motion; they differ in degrees of density and tenacity; in colour and degrees of opacity or transparency. They are usually regarded as incompressible; at least a very

great mechanical force is required, to make them oc cupy a space perceptibly smaller.

Elastic fluids or gases, the third class, exist free in the atmosphere; but they may be confined by solids, or by solids and fluids, and their properties examined. Their parts are highly moveable; they are compressible and expansible; and their volumes are inversely, as the weights compressing them. All known elastic fluids are transparent, and present only two or three varieties of colour; they differ materially in density.

Besides these forms of matter, which are easily submitted to experiment, and the parts of which may be considered as in a state of apparent rest, there are other forms of matter which are known to us only in their states of motion when acting upon our organs of sense, or upon other matter, and which are not susceptible of being confined. They have been sometimes called ethereal substances, which appears a more unexceptionable name than imponderable substances. It cannot be doubted that there is matter in motion in the space, between the sun, the stars and our globe; though it is a subject of discussion, whether successions of particles be emitted from these heavenly bodies; or motions communicated by them, to particles in their vicinity, and transmitted by successive impulses to other particles. Ethereal matter differs, either in its nature, or in its affections by motion; for it produces different effects ;radient heat, and different kinds of light.

501. CALORIC is a mere name of that element or property, which, combined with various bodies, produces the sensation of heat while it is passing from one body to another.

According to its quantity in different bodies, it renders them fluid; or converts them into gas, or air.

Ice is water deprived of its caloric: when the caloric returns, the ice is again converted into

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water; and a further addition converts the water into steam, or aqueous gas.

It has been called sensible caloric, when it gives the sensation of heat; and combined caloric, when it is supposed to form an insensible part of the substance of bodies.

Obs. 1.-By mixing sulphuric acid with water, caloric is given out or disengaged, and the mixture becomes heated: and by mixing snow and nitre, the combination absorbs caloric from surrounding bodies by which they become evolved.

2.-Different bodies change their states at very different temperatures. Thus mercury, which is a solid at about 40 below Fahrenheit, boils at about 660; sulphur, which becomes fluid at 218°, boils at 570°; either boils at 98°. The temperatures, at which the common metals become gaseous, are generally very high, and most of them incapable of being produced by common means. Iron, manganese, platina, and some other metals, which can scarcely be fused in the best furnaces, are readily melted by electricity; and by the Voltaic apparatıls, a degree of heat is attained, in which platina not only fuses with readiness, but seems even to evaporate.

3. When solids are converted into fluids, or fluids into gases, there is always a loss of heat of temperature; and vice versa: when gases are converted into fluids, or fluids into solids, there is an increase of heat of temperature; and in this case, it is said, that latent heat is absorbed, or is given out.

4.-Sir Richard Phillips has published a new Theory of Heat and Light in the Monthly Magazine, No. 239. He considers both, as the effect of motion;-heat, as the motion or vibration of the parts of solid and non-elastic bodies, and light, as the effect of the vibrations of the elastic medium which fills the universe; and the expansion of which same medium, produces also the phenomena of gravitation. The change of the phenomena

of Heat, into the phenomena of Light, he ascribes to the action and re-action which take place in the elastic medium, during the decomposition which attends combustion when heat becomes light; or, in other words, when the motion of solids is transferred to ethereals.

502. OXYGEN is an element or simple substance diffused generally through nature; and its different combinations (for, like caloric, it does exist by itself;) are essential to animal life and combustion.

Some chemists consider oxygen as the basis or substratum of all nature.

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 instantly be 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 phenomenon. Oxygen gas is respirable; a small animal, 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.

503. During the burning of any combustible body, the oxygen leaves the atmospheric air and combining with the calx or residuum of said.

body, adds to its weight, and forms what is called an oxyde.

This process is called oxygenation; and if the 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.

504. 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 bal loon; and the balloon, being 12 times lighter than the atmospheric air, will rise through it.