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tutes a part of a great number of inflammable substances, such as oils, resins, gums, sugar, &c. Hydrogen gas is formed by the combination of hydrogen and caloric. It is the lightest of all substances that have weight; and this property renders its use to be preferred for filling balloons. When burnt alone, it has a bluish flame; but in a state of combustion with oxygen, it produces more heat than any other known agent, Notwithstanding it possesses, in itself, the property of being inflammable, the flame of a lighted taper is extinguished when plunged into a vessel that contains it. But if it is mixed with an equal portion of atmospheric air, or half the quantity of oxygen gas, it will suddenly burn; and by the application of the flame of a candle to the mixture, it will violently explode. Though noxious in its effects upon animals, it is not instantaneously so; and, on the contrary, it is favourable to vegetable life. This gas has never been obtained in such a form as to be visible in a separate state; and it was formerly denominated inflammable air.

Hydrogen is the most inflammable of the gases, and as it combines with a greater proportion of oxygen than any other, it yields more heat by combustion. The greatest degree of heat yet known is produced by its mixture with oxygen gas; and its powerful action on various substances, when used with the blow-pipe, has been remarkably proved by Dr. E. D. Clarke. Hydrogen is also one of the elements

of which water is composed. When about 88 parts of oxygen are united to about 12 parts of hydrogen, by combustion, a great deal of heat is given out, and the two bodies combine and form water. Hydrogen gas is about one fourteenth of the weight of atmospheric air, and the space it occupies in the form of gas is about 1500 times greater than when it is combined with oxygen in the form of water. The time when, or the person by whom, this gas was discovered, has not been ascertained; but Mr. Cavendish appears to have been the first who minutely examined its properties, in 1766.

NITROGEN. This element, like the last, has been obtained only in a state of combination: it is one of the component parts, and constitutes the greatest portion, of atmospheric air. Nitrogen gas is not inflammable; and is not capable of supporting combustion. Plants vegetate and grow freely in it, although it is fatal to animal life. When mixed with oxygen gas, in a certain proportion, it has the property of rendering the oxygen fit for respiration, and forms a considerable part of all animal substances. This gas has also had the name of azote, or azotic gas.

So great is the power of nitrogen gas to extinguish flame, that if phosphorus, even in a state of great inflammation, be plunged into it, the flame is instantly destroyed. It constitutes about four-fifths of the common atmospheric air. It seems to have been discovered both by Dr. Priestley and Dr. Rutherford, in 1772.

It

NITROUS GAS. This is also called nitrous oxide, and is invisible and rather heavier than atmospheric air; but, when it comes into contact with that or any other kind of air containing oxygen, it assumes a beautiful orange colour. suffocates animals that breathe it, yet phosphorus and some other substances burn in it with great brilliancy. If sulphur, feebly inflamed, be introduced into it, the gas extinguishes it immediately; but if the flame of the sulphur be very active, it burns vividly, producing a beautiful rose colour. Charcoal made red-hot and plunged into it burns more brilliantly than in atmospheric air. When hydrogen gas is mixed with nitrous gas, on the application of a lighted taper a loud detonation is produced.

This gas was discovered by Dr. Priestley, who denominated it dephlogisticated nitrous air; and it was the occasion of his inventing his Eudiometer, which is an instrument employed in ascertaining the purity of any precise portion of the atmospheric air. When this gas is mixed with atmospheric air over water, the bulk of the mixture rapidly diminishes by the nitrous gas combining with the oxygen contained in the air, and the water absorbs the nitric acid thus formed: the diminution of the bulk of the mixture, being in proportion to the quantity of oxygen, of course indicates the measure of oxygen which the portion of air experimented upon may contain, and thus its purity is

determined. This mode of operating upon different kinds of gases is called Eudiometry.

CARBON. This is classed with the simple combustible bodies, and it has not yet been obtained in a separate state, unless the diamond be admitted as coming under this description. Its combinations and uses are numerous and important. The principal component parts of all bituminous substances, and nearly the whole of the solid particles of vegetables, consist of carbon. Its union with iron also forms steel and plumbago. Charcoal is that combination of it which is most familiar to us, and possesses a great variety of useful and interesting properties. Among others, it forms a very essential ingredient of gunpowder; it preserves animal substances from putrefaction; and, even after they have been slightly tainted, restores them to sweetness.

The sagacity of Sir Isaac Newton led him to conjecture that the diamond was a combustible body, from its possessing the power of refracting light: but M. Guyton (de Morveau) was the first who proved it to contain carbon; and from his and M. Lavoisier's experiments it has been concluded that the diamond is the only pure form of carbon. Mr. Tennant also proved its similarity to carbon by effecting its combustion in a crucible of gold. Not only coal, but the greater proportion of wax, as well as animal fat and oils, consist of different proportions of carbon and

hydrogen. Wax and spermaceti are purer compounds than tallow; and oil is the tallow or fat reduced to a fluid state by the addition of caloric.

CARBURETTED HYDROGEN GAS.

This gas

consists of carbon dissolved, or united with hydrogen by means of caloric; and it is denominated light or heavy, according to the proportions of carbon and hydrogen which form its composition. Thus the gas which possesses the greatest portion of hydrogen is designated light; but if the carbon be the greatest, the gas is then called heavy. Pit-coal produces it abundantly; and it has also been named heavy inflammable air. Among miners it is denominated the fire-damp; and it has frequently been the cause of very serious and distressing accidents in coal pits.

An admirable and striking instance of the benefits which science has conferred upon mankind by the practical application of its principles, is displayed in the invention of the safety lamp by Sir Humphrey Davy. By his familiar elucidation of the causes of the dangers to which miners are exposed from the fire-damp, he has furnished them with an instrument that may enable them to avoid its effects, and to prevent such calamitous accidents as have heretofore too often attended their operations. It requires that they should only exercise a due degree of attention and care in the use of it.-See Sir H. Davy on the Safety Lamp, 1825.

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