result was of a sap green colour, but still elastic. Two pints of the gas with a pint of hydrogen was of a light yellow green, without any fluid, and highly destructive of colours.

This gas acts powerfully on various combustible bodies. If four parts of it, and three of hydrogen, be put into a bottle closely stopped, inverted, with its mouth under water, and the stopple be taken out in this situation after they bave thus stood twenty-four hours, nearly the whole of the gas will have disappeared, and the remainder will be absorbed by the water. The hydrogen may be combined at once with the oxygen of this gas by the electric spark, which causes them to detonate. Phosphorus takes fire spon taneously in oxygenized muriatic acid gas; so do perfectly dry powdered charcoal of beech wood, and almost all the metals in fine filings, or very thin leaves. About a cubic inch of the gas is sufficient for a grain of metal; the bottom of the vessel should have a little sand on it, to prevent it from cracking; and the temperature should not be less than 70°. If a drachm of good ether be thrown into a three pint vessel filled with this gas, and the mouth covered with a piece of paper, a circulating white vapour will arise in a few seconds, which will soon be followed by an explosion with flame.

For the rest of its properties, see MuRIATIC OXYGENIZED ACID, NITRIC ACID GAS, and NITRIC acid.

We

GAS, nitric oxide, or NITROUS GAS. owe our first knowledge of this elastic fluid to Dr. Priestley, who called it nitrous air. It may be formed by passing ammoniacal gas through the black oxide of manganese, heated red hot in an earthen tube; but it is most easily obtained by abtracting a portion of its oxygen from nitric acid. For this purpose fine copper wire, or copper filings, may be put into a retort, with an equal weight of nitric acid, diluted with four or five parts of water, and moderate heat applied; or diluted only with an equal quantity of water, and no heat employed. After the atmospheric air is expelled from the retort, the gas that comes over may be received in the pneumatic apparatus. Other metals might be employed for the same purpose, but mercury and copper appear to afford it in the greatest purity; and the latter is perhaps preferable, because the process goes on more regularly with it.

This gas is colourless, and somewhat heavier than atmospheric air. It is extremely deleterious, killing even insects very quickly, and destroying plants. Wa

ter deprived of air absorbs about oneninth of its bulk of this gas, without acquiring any taste from it; and a boiling heat expels it again unchanged. If the water contains air, the gas is partly decomposed, and the absorption, though in reality greater, is apparently less, from the nitrogen evolved. Water impregnated with earthy salts, does not absorb so much; a solution of green sulphate, or green muriate of iron, however, absorbs it rapidly, and becomes dark brown, and almost opaque. When this is effected over mercury, the gas may be expelled unchanged by a moderate heat, or by placing the solution in a vacuum, though perhaps not the whole of it. Solutions of nitrate of iron, the sulphates of tin, and of zinc, and muriate of zinc, likewise absorb it.

Nitrous gas has no acid properties. It does not redden vegetable colours, but impairs them. It extinguishes the flame of a candle, or burning sulphur, and the phosphoric light of animal substances: but lighted charcoal continues to burn in it; lighted phosphorus burns in it with great splendour, though, if not previously kindled, it may be melted or sublimed in it, without taking fire; and Homberg's pyrophorus kindles in it spontaneously. Its most important property is its affinity for oxygen gas, on account of which it was employed by Dr. Priestley, as it still is by many, to ascertain the quantity contained in atmospheric air. See EUDIOMETER.

When mixed with oxygen gas, red fumes arise, heat is evolved, and the two gases, if in due proportion and both pure, disappear, being converted into nitric

acid.

This gas is soluble in nitric aaid, and alters its properties in some measure, without, however, converting it into an acid, in a distinct state of oxygenation, as some had supposed.

GAS, nitrous oxide. This is the gaseous oxide of nitrogen, or of azote of some; a compound of nitrogen with a still less proportion of oxygen than the preceding gas.

It is not to be obtained certainly, with any purity, but by the decomposition of nitrate of ammonia. For this purpose, nitric acid, diluted with five or six parts of water, may be saturated with carbonate of ammonia, and the solution be evaporated by a very gentle heat, adding occasionally a little of the carbonate, to supply what is carried off. The nitrate crystallizes in a fibrous mass, unless the evaporation has been carried so far as to

leave it dry and compact. The latter at a heat between 275° and 300° sublimes without being decomposed; at 320° it becomes fluid, and is partly decomposed, partly sublimed: between 340° and 480° it is decomposed rapidly. The fibrous is not decomposed below 400°, but a heat above 450° decomposes it; at 600° a luminous appearance is produced in the retort, and nitric oxide, nitrous oxide, and nitrogen, mixed in various proportions, are evolved; at 700° or 800° an explosion takes place. It is best to perform the operation over an Argand's lamp, as the heat may thus be brought to the requisite degree speedily, and kept from going too far. It should be received over water,

and suffered to stand an hour in contact with it, to free it from any nitrate of ammonia that may have been sublimed, as well as from any acid suspended in it. Dr. Pfaff recommends mixing very pure sand with the nitrate, to prevent the hazard of explosion; and observes, that it is particularly requisite it should not be contaminated with muriatic acid. One pound of the compact nitrate, yields 4.25 cubic feet of gas, and a pound of the fibrous nearly five cubic feet.

The most singular property of this gas is its action on the animal system. Dr. Priestley had found that it was fatal to animals confined in it. Mr. Davy first ventured to respire it, which he did to considerable extent. When breathed alone for a minute or two, and some have gone so far as four or five minutes, it generally produces a pleasant thrilling, particularly in the chest and extremities, frequently with an inclination to laugh, and sometimes an irresistible propensity to gesticulation and muscular exertion. The mind meanwhile is often totally abstracted from all surrounding objects. Sometimes its effects are not entirely dissipated for some hours; and it is remarkable, that, however strong they may have been, no sense of debility or langour is in duced after they have subsided. On a few individuals, however, its effects have been unpleasant and depressing; in some it has produced convulsions, and other nervous symptoms; and on some it has had no sensible effect. Indeed, not only different persons, but the same individual, will be variously affected by it, perhaps, at different times. Similar effects have been produced on those who have tried it abroad.

In debility, arising from residence in a hot climate, and intense application to

business, this gas has proved a complete remedy. It has given voluntary power over palsied parts while inhaled, and the subsequent application of other remedies has effected a cure. Dr. Pfaff his suggested its use in melancholia: but in some cases of this disease it has done no good, and in one harm.

GAS, nitrogen or azotic. Under the article ATMOSPHERE it has been observed, that about three fourths of our atmosphere consist of gas, unfit to maintain combustion, or support life. It is called nitrogen or azotic gas, and is a little lighter than atmospheric air. It is incapable of supporting life, or combustion, yet a small portion is absorbed in respiration. It is not inflammable, though it unites with oxygen in different proportions, forming nitrous oxide, when the oxygen is only .37, nitric oxide when it is .56, and nitric acid when .705. It is one of the most general elements of animal substances. With hydrogen it forms ammonia; and Fourcroy suggested, that it might possibly be the alkaligenating principle, though he confesses there are no facts in support of this conjecture; the name of alkaligen, therefore, which has been proposed for it, is certainly inadmissible. It dissolves small portions of phosphorus, sulphur, and carbon.

GAS, oxygen. This gas was obtained by Dr. Priestley in 1774, from red oxide of mercury exposed to a burning lens, who observed its distinguishing properties of rendering combustion more vivid, and eminently supporting life. Scheele obtained it in different modes in 1775; and in the same year Lavoisier, who had begun, as he says, to suspect the absorption of atmospheric air, or, of a portion of it, in the calcination of metals, expelled it from the red oxide of mercury heated in a retort. Priestley called it dephlogisticated air; Scheele, from its peculiar property, fire air, a name before given it by Mayow, or empyreal air.

Oxygen gas forms about a fourth of our atmosphere, and its base is very abundant in nature. Water contains .85 of it, and it exists in most vegetable and animal products, acids, salts, and oxides.

This gas may be obtained from nitrate of potash, exposed to a red heat in a coated glass or earthen retort, or in a gun barrel, from a pound of which about 1200 cubic inches may be obtained; but this is liable, particularly towards the end

of the process, to a mixture of nitrogen. It may also be expelled from the red ox de of mercury, or that of lead; and still better from the black oxide of manganese, heated red hot in a gun barrel, or exposed to a gentler heat in a retort, with half its weight, or somewhat more, of strong sulphuric acid. To obtain it of the greatest purity, however, the hyperoxymuriate of potash is preferable to any other substance, rejecting the portions that first come over, as being debased with the atmospheric air in the retort. Growing vegetables, exposed to the solar light, give out oxygen gas; so do leaves laid on water in similar situations, the green matter that forms in water, and some other substances.

Oxygen gas has neither smell nor taste. It is a little heavier than atmospheric air; under great pressure, water may be made to take up about half its bulk. It is essential to the support of life; an animal will live in it a considerable time longer than in atmospheric air; but its respiration becomes hurried and laborious before the whole is consumed, and it dies; though a fresh animal of the same kind can still sustain life for a certain time in the residuary air.

Combustion is powerfully supported by Oxygen gas; any inflammable substance, previously kindled, and introduced into it, burns rapidly and vividly. If an iron or copper wire be introduced into a bot tle of oxygen gas, with a bit of lighted touch-wood or charcoal at the end, it will burn with a bright light, and throw out a number of sparks. The bottom of the bottle should be covered with sand, that these sparks may not crack it. Mr. Accum says a thick piece of iron or steel, as a file, if made very sharp at the point where it is first kindled, will burn in this gas. If the wire, coiled up in a spiral like a corkscrew, as it usually is in this experiment, be moved with a jerk the instant a melted globule is about to fall, so as to throw it against the sides of the glass, it will melt its way through in an instant, or if the jerk be less violent, lodge itself in the substance of the glass. If it be performed in a bell-glass set in a plate filled with water, the globules will frequently fuse the vitreous glazing of the plate, and unite with it, so as not to be separable without detaching the glaze, though it has passed through perhaps two inches of water.

As oxygen gas appears to be a very

powerful stimulus to the animal economy, it has been applied medicinally; and is reported to have been of great service in many cases of debility, palsy, nervous affections, scrofula, rickets, and even hydrocephalus

GAS, sulphurous acid. When sulphur is burnt slowly, as gas arises, of a suffo cating pungent smell, consisting of sulphur combined with oxygen in less proportion than is requisite to form sulphuric acid. This was known to the earlier modern chemists, and Stahl examined some of its combinations; Priestley showed it was permanently elastic; Berthollet pointed out its difference from the sulphuric acid; and Fourcroy and Vauquelin completed its examination.

In the mode above mentioned, it is very difficult so to regulate the combustion as to obtain it free from sulphuric acid, which is formed when the sulphur burns with a certain degree of rapidity; so that it is commonly made by subtracting oxygen from sulphuric acid by some other inflammable substance. The metals answer the purpose, but such as do not decompose water should be employed, otherwise more or less hydrogen will be evolved. Tin or quicksilver answers best, one part of which may be put into a retort, with two of concentrated sulphuric acid, and heat applied. It should be received over mercury, as water absorbs it, taking up thirty-three times its bulk.

This gas is above twice as heavy as atmospheric air: it kills animals very speedily, and extinguishes burning bodies. From this latter property it has been recommended, when a chimney is on fire, to throw a spoonful or two of flowers of sulphur into the grate. It whitens and gives lustre to silk, and is useful in bleaching woollens. Fresh prepared muriate of tin decomposes it, sulphur being deposited, and the muriate oxygenized. Mr. Northmore has condensed it by pressure: and Monge did the same, with the addition of artificial cold. According to Dr. Thompson, it consists of sulphur sixty-eight parts, oxygen thirty-two.

One hundred grains of water take up 5 grains of this gas, or 25 parts by measure; or, according to Dr. Thomson, 8.2 grains, equal to 33 times its volume. The solution has a pungent disagreeable odour, and an acid taste. It reddens some of the vegetable colours, such as that of litmus, or red cabbage; there are others,

however, the colour of which it destroys, as that of the red rose. The effect of the gas upon these colours is similar.

The saturated solution allows the gas to escape at a very moderate heat, and by boiling, the greater part is expelled, though the liquor remains acid, apparently from the presence of sulphuric acid. It is singular that it is not expelled by freezing, but still remains combined with the ice, and renders it so heavy that it sinks in water. This act shows that that this has, comparatively with others, little tendency to pass into the aeriform state. The freezing of the solution takes place at a few degrees below 32.

When two parts of the gas are mix. ed with one part of oxygen gas, if the mixture is kept over mercury, they do not act on each other. But if a small portion of water is introduced, they gradually combine and form sulphuric acid, a fact explained by Mr. Murray, on the supposition that the water exerts a strong disposing affinity to this acid, or, to speak more intelligibly, according to the explanation of disposing affinity given under our article CHEMISTRY, the water attracts the sulphurous gas, and, by depriving it of its state of elastic fluidity, renders it capable of more readily uniting

with the oxygen, which is also effected by a like action of the water; and as these combine into sulphuric acid, which is more soluble than the sulphurous, the process is still more facilitated, and goes on progressively until the effect is completed. By passing s mixture of oxygen gas and sulphurous acid gas through a tube heated to redness, they instantly combine, and sulphuric acid is formed.

This acid combines with facility with the alkalies, forming salts denominated sulphites, which differ considerably from the salts formed by the sulphuric acid. Their taste is sulphurous; they are decomposed by a high temperature, their acid being either expelled, or a portion of sulphur being driven off, in which case they become sulphates; they are also decomposed by the greater part of the acids, and then the sulphurous acid is disengaged with effervescence. The alkaline sulphites are more soluble than the sulphates in water, the earthy sul. phates less so. All these salts are converted into sulphates by exposure to the atmospheric air, or by the action of any snbstance capable of affording them oxygen. They suffer this change, for example, by deflagration with nitre. See SULPHUROUS ACID.