Simple Bodies. Oxygen is one of the most important of the elementary bodies. In a simple state, it is obtained only in the form of gas. It is an exceedingly abundant body; the air of the atmosphere contains One-fifth, and water is resolveable into a mixed gas, one-third of which, by bulk, is oxygen, and the remainder hydrogen. It also exists in most natural products - animal, vegetable, and mineral. Oxygen gas is, like common air, colourless, invisible, tasteless, inodorous, and elastic. But it is heavier than common air, in the proportion of 11 1/2 to 10. It is a powerful supporter of combustion ; that is to say, when any inflamed body, as a lighted candle, is put into it, it burns very vigorously - much more so than when in common air; indeed, it is owing to the oxygen it contains that common air supports combustion at all. Its presence is also necessary for the continuance of animal life. We cannot breathe air which has been deprived of its oxygen.

Hydrogen is known only in the state of gas, and is sometimes called inflammable air. It is the lightest of all bodies that can be weighed. It is one of the ingredients which form water - from which it can be easily procured. Hydrogen gas, when pure, possesses all the mechanical properties of common air. It does not support combustio , though it is itself one of the most combustible of all bodies; for if a lighted candle be put into a vessel containing hydrogen, the candle will be instantly extinguished, while the gas itself will be inflamed. It is not fit for respiration, for animals which breathe it die almost instantaneously. If pure oxygen and hydrogen be mixed together, and the mixture set fire to, it explodes with great violence, and forms water. Hence we see the origin of the term hydrogen, which literally signifies the water- former. Hydrogen gas is, on account of its greater levity, employed to fill balloons.

Nitrogen, called also Azote, is a gaseous body, rather lighter than common air; of which it forms four-fifth parts, the remaining one-fifth, being oxygen. It has neither colour, smell, nor taste. It does not support combustion, nor is it combustible itself, for if a lighted candle be put into a vessel containing nitrogen, it is instantly extinguished, and the gas itself does not take fire, as is the case with hydrogen. Nitrogen is fatal also to animal life ; any animal put into it dies in a very short time.

Carbon. When wood is heated to a certain degree in the open air, it takes fire, and forms, whilst burning, water and carbonic acid gas, till the whole of it is consumed. A small portion of ashes is the sole residue. But if the wood be heated to redness in close vessels, so that the atmospheric air cannot have free access to it, a large quantity of gaseous and other volatile matters is expelled, and a black, hard, porous substance is left, called charcoal.

Charcoal may be procured from other sources. When the volatile matters are driven off from coal, as in the process for making coal gas, a peculiar kind of charcoal, called coke, remains in the retort. Most animal and vegetable substances yield it, when ignited in close vessels. Thus a very pure charcoal may be procured from starch or sugar, and from the oil of turpentine or Spirit of wine, by passing their vapour through tubes heated to redness. When bones are made red-hot in a covered crucible, a black mass remains, which consists of charcoal mixed with the earthy matters of the bone. It is called ivory-black, or animal charcoal.

Carbon is the name given to the pure inflammable part of charcoal, of which substance the diamond is only a variety in a pure crystallized state; for pure charcoal and diamond, when treated in the same manner, produce precisely the same results. Carbon is insoluble in water, and infusible by the most intense heat, provided air be excluded. Animal and vegetable oils are composed almost entirely of carbon and hydrogen. The same may be observed of gum, sugar, and starch. These bodies, however, contain oxygen.

Charcoal absorbs the odoriferous and colouring principles of most animal and vegetable substances. When coloured infusions of this kind are digested with a due quantity of charcoal, a solution is obtained, which is nearly if not quite colourless. Tainted flesh may be rendered sweet and eatable by this means, and foul water may be purified by filtering through charcoal.

Sulphur occurs as a mineral production in some parts of the earth, particularly in the neighbourhood of volcanoes, as in Italy and Sicily. It is commonly found in a massive state; but is sometimes met with in a crystallized form. It is procured abundantly in combination with several metals, such as silver, copper, antimony, lead, and iron. It is obtained in large quantities by exposing the common iron pyrites to a red-heat in close vessels.

Sulphur is well known under the name of brimstone. It is a brittle solid body, of a greenish-yellow colour, emits a peculiar odour when rubbed, and has little taste. It is insoluble in water; but, if poured into it when liquified, it retains its softness, and is in this state employed for taking impressions from seals and medals.

Phosphorus was discovered about the year 1669, by Brandt, an alchemist of Hamburgh. It is a semi-transparent yellowish matter, of the consistence of wax. It is procured, in general, by the decomposition of bones. It is exceedingly inflammable. Exposed to the air at common temperatures, it undergoes a slow combustion; it emits a dense white smoke, which has the smell of garlic, appears luminous in the dark, and is gradually consumed. On this account, phosphorus should always be kept under water. On account of its very combustible nature, it requires to be handled with great caution; gentle pressure between the fingers is sufficient to kindle it. It burns rapidly, emitting a splendid white light, and causing an intense heat.

Chlorine was discovered in 1770. It is a substance of much importance, being, in combination with other substances, extensively used in the arts. Chlorine is a yellowish-green coloured gas, which has an astringent taste, and a disagreeable odour. It is one of the most suffocating of the gases, exciting great irritability in the windpipe, even when considerably diluted with air. When strongly and suddenly compressed, it emits both heat and light - a character which it possesses in common with oxygen gas. Under considerable pressure it assumes the form of a limpid liquor of a bright yellow colour. Chlorine is a supporter of combustion. If a lighted taper be plunged into chlorine gas, it burns with a small red flame and emits a large quantity of smoke. Phosphorus takes tire in it spontaneously. Se-vera ]of the metals, such as tin, copper, arsenic, antimony, and zinc, when introduced into chlorine in the state of powder, or in fine leaves, are suddenly inflamed. Chlorine, though formerly called an acid, possesses no acid properties. It has not a sour taste, nor does it redden the blue colour of plants, which nearly all acids do. One of the most important properties of chlorine is its bleaching power. All animal and vegetable colours are speedily removed by chlorine; and when the colour is once discharged, it can never be restored. Chlorine, however, cannot bleach unless water be present. Chlorine is useful also for the purposes of fumigation, and is used to purify the air in fever hospitals The infection of the small-pox is also destroyed by this gas, and matter that has been submitted to its influence will no longer generate that disease.

Iodine is a substance much resembling chlorine in some of its properties. It may be procured by drying and powdering common sea-weed, and heating it with sulphuric acid and peroxide of manganese: a violet coloured vapour rises, which, if received in a cool vessel, will condense on its sides, and will form scaly crystals of a somewhat metallic lustre. These crystals are the substance : from the violet colour of its vapour it is called iodine. It has the property of forming a beautiful blue colour, when mixed with a little powdered starch, diffused through cold water; hence iodine and starch are used as tests of the presence of each other. Iodine stains the fingers yellow, but not permanently. Like chlorine, it destroys vegetable colours, though not so powerfully. Iodine is used in medicine: in small doses it increases the appetite; but in large doses, or continued too long, it produces remarkable emaciation.

To these simple non-metallic bodies we might add bromine, selenium, boron, fluorine (the base of fluor spar), and silicon (the base of flint). But as they are of less importance, and as the nature of some of them is still a subject of dispute with chemists, we shall omit the consideration of them for the present.