machine which will make 19 millions of pins in a week. Brunel's block-machine will make 1420 blocks in a day; and his saw-mill at Chatham, with the assistance of 10 or 12 persons, will perform the labour of 50 saw-pits: it takes the timber from the vessels, and delivers the sawn

planks to the stacks. At Weovil, near Portsmouth, eight men and two boys will manufacture in one hour and a half, by means of machinery, ninety hundred-weight of biscuits. The advantage obtained by spinning, weaving, &c., are equally wonderful and effective.

GASEOUS BODIES.

Nature of Gaseous Bodies-Component parts of Atmospheric Air-OxygenNitrogen and Carbonic Acid Gas-Peculiar properties of each-How obtained for experiment, &c.-Component parts of Water-Oxygen and Hy drogen - Properties of Hydrogen, &c. &c.-Carburetted Hydrogen-Sulphuretted Hydrogen-Phosphuretted Hydrogen-Chlorine-Nitrous Oxide, or Laughing Gas-Their properties-How obtained for experiment, &c.

A GASEOUS body is an elastic, transparent, and permanently aeriform fluid. All gases are said, chemically, to be a compound of solid matter and caloric, the caloric by its repulsive action separating the particles of the solid, and giving it a gaseous form. The difference between gas, and vapour or steam, consists in the former constantly retaining its aeriform state, while the latter will return to a fluid or solid state when the caloric is abstracted. The affinity between the caloric and the base of the gas is so intense, as to resist any means of separating them, and the gas is consequently rendered perfectly aeriform.* As the kinds of gases are so numerous it is intended here to notice the most important of this class of bodies, of which those that enter into the composition of atmospheric air and water claim the chief consideration.

The atmosphere, as has been already observed,† is a mixture of three gases, oxygen, nitrogen, and carbonic acid gas.

This is to be understood in a general sense, as most of the gases have been condensed to a liquid state.

See article Pneumatics.

Oxygen takes its name from a Greek word, and literally means a generator of acidity, from the fact of acids being generally a combination of oxygen with a base. Oxygen gas is an invisible fluid, without taste or colour, and capable of expansion and compression, similar to atmospheric air. It is a supporter of life and light; for it has been found by experiment, that an animal will die and light will become extinguished when the atmosphere is deprived of its oxygen; even fruit will not ripen in an atmosphere deprived of oxygen. In the process of respiration the oxygen, as it passes through the lungs, combines with the blood, which it changes from a purple to a red colour, and renders it a stimulus to the action of the heart and arteries, and is the cause of animal heat. Oxygen combines with all combustible bodies, disengaging at the same time its caloric, and producing a strong light and flame. It also combines with metals, which act of combination is called oxidizement; the oxide, therefore, or rust of any metal, is the metal combined with oxygen, and it may be observed that the greatest number, if not all such combinations, with the exception of the oxide of iron, are highly poisonous. The specific gravity of oxygen is somewhat greater than that of atmospheric air.

Oxygen may be obtained for experiment in many ways; the more general way is from the black oxide of manganese. The manganese is powdered coarsely, and put into an iron or stone retort, and heated to redness, when the gas will come off, and may be collected over water in a gasometer or other receiver. If the manganese be mixed with sulphuric acid until it becomes a thin paste, the heat of a lamp will be sufficient to disengage it. It may be also obtained in a very pure state from the chlorate of potash. Vegetables are found to give out oxygen gas in the day-timè, undoubtedly a design of Providence to renovate the atmosphere, and form a supply for that fixed by respiration and combustion. Oxygen never exists in a separate state, it is always in a gaseous form, or in combination with other substances.

Nitrogen gas, or Azote, will neither support flame nor animal life. It has neither taste nor smell, and its specific gravity is somewhat less than that of atmospheric air. It

may be obtained from atmospheric air, by abstracting its oxygen, which may be effected by burning phosphorus in a jar, inverted over water; the oxygen will unite with the phosphorus and form phosphoric acid, while the nitrogen will remain. If an equal quantity of iron filings and sulphur be made into a paste with water, and put into a vessel over water, as on the stand of a pneumatic trough, and a jar of common air be inverted over it, in a day or two the mixture will have imbibed the oxygen, which may be seen by the water rising in the jar, when the remainder will be nitrogen. It may be also obtained from the lean of meat, particularly beef, by pouring over it, in a retort, very diluted nitric acid; the heat of a lamp will disengage the gas, which may be collected over water. Nitrogen, like oxygen, is never in a separate state, but always in combination it combines with hydrogen, and forms ammonia; it combines with oxygen in various proportions and forms different acids, as nitric acid, &c.; it also enters into several other combinations.

Carbonic acid gas, similar to nitrogen, will neither support life nor flame; if attempted to be but slightly breathed, it produces so violent a constriction of the glottis as to threaten suffocation; it is called chokedamp by miners, who are frequently suffocated by it. Its specific gravity is considerably greater than that of atmospheric air, it consequently occupies the lower part of caverns and mines. The Grotto del Cano, a cavern in the kingdom of Naples, has been celebrated for ages for a stratum of this gas covering its bottom; so that if a dog, or any animal which holds its head down, enters the cavern, it becomes suffocated, while a man will not feel it. In consequence of its weight it may be poured out of one vessel into another; so that if a taper be placed at the bottom of a deep vessel, and a small quantity of this gas be poured upon it, it will become extinguished, although from the transparency of the gas the eye will not perceive it. This gas is given out in large quantities during the process of fermentation; the bubbles which are thrown up from beer recently brewed contain this gas. In several instances, men that have been employed to clean out large vats in

breweries, when emptied of their contents, have been suffocated, by entering them without having taken the proper precaution, through the deleterious property of this gas. It is usual to let down a candle, when, if the candle burns, it is considered respirable; the same precaution is generally taken before descending a well, which, if carried through a chalky soil, is very likely to be charged with carbonic acid gas. Champagne and cider owe their sparkling qualities to this gas, and so do all fermented liquors. Bottled porter contains it in large quantities. Water contains a small quantity of it naturally, but by means of a forcing pump it may be made to absorb two or three times its bulk. Soda-water is water impregnated with it, and that very grateful beverage, ginger-beer, is indebted to it for its briskness and pleasant taste. Carbonic acid gas is considered to possess much utility in promoting vegetation. It is probably decomposed by the organs of plants, and its base furnishes the carbon which they retain

while they give out the oxygen. Carbonic acid gas

abounds in the mineral world: chalk, or carbonate of lime, marble, spars, and other calcareous substances, contain nearly one-half of their weight of it. It may be extricated from either of these bodies by heat, heat being the grand antagonist to affinities of all kinds. In the process of making lime, for instance, the carbonic acid gas is driven off from the limestone (carbonate of lime) in the kiln, leaving the lime uncombined. Carbonic acid gas may be obtained for experiment by putting a little chalk or marble, powdered, into a gas retort, and pouring over it a little muriatic acid, diluted with four or five times its bulk of water. Or it may be obtained simply from carbonate of ammonia, by the heat of a lamp; in the latter instance, the carbonate of ammonia becomes decomposed, the water imbibes the ammonia,* and allows the carbonic acid gas to escape.

*This is called the Volatile alkali, and exists, when uncombined, in a state of gas. Ammoniacal gas is of a very volatile nature, has an extremely pungent smell, and will neither support life nor flame. When combined with water, for which it has a great affinity, it forms

It may be observed that while oxygen is in many instances so beneficial to the lungs and revivifying, and in combination is so injurious to the stomach and system; carbonic acid gas produces death, if attempted to be breathed, while some of its compounds, as the carbonates of potash, of magnesia, of ammonia, &c., are occasionally most beneficial to the system.

This gas very strongly resists putrefaction, so that meat. has been kept in it for years without becoming even tainted.

Water is a compound of Oxygen and Hydrogen, consisting of about 85 parts by weight of the former, and 15 of the latter, or of about one part by measure of the former, and two parts of the latter.

Hydrogen, like oxygen, takes its name from a Greek word, and implies a generator of water; it is only known in a gaseous form, that is, with caloric, or in combination with other bodies. Hydrogen, when in an aerial state, or hydrogen gas, is the lightest of all known substances, being fourteen times lighter than common air. From its extreme buoyancy, aeronauts formerly used it to fill their balloons; but from the facility with which coal-gas is obtained, the latter is now generally used, though not so buoyant.

Hydrogen gas will not support life, as animals when obliged to breathe in it die almost instantaneously; neither will it support flame, as a burning body is instantly extinguished when immersed in it, but when in contact with atmospheric air or oxygen, it is highly inflammable. A

liquid ammonia, and in this state it is used in our manufactories, and in medicine. Animal and vegetable substances in a state of putrefaction give out this gas; it may be procured by the distillation of bones, but it is now obtained from the gas-works. Ammonia forms various combinations; it combines with muriatic acid gas, and forms muriate of ammonia or sal ammoniac, a substance much employed by dyers, braziers, and others, as well as in medicine. It was from this substance-sal ammoniac--being dug out of the earth near the temple of Jupiter Ammon that it received its name.

* Charcoal, also, which has carbon for its base, is noted for its antiseptive properties. For this reason vessels are charred which are intended to contain water in sea voyages. Meat, also, slightly tainted, may by the application of charcoal be almost instantly made sweet.

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