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The light evolved appeared to be in proportion to the oxygen consumed, so that the first four in the list yielded very little; but the last much exceeded all the rest. Its detonation with oxygen gas too is more violent than that of any other inflammable gas .03 of a cubic inch, with 17 of oxygen gas, being sufficient to burst a strong glass tube.

About the year 1792, Mr. Murdoch made various experiments on the gas from coal, peat, and other substances, as a substitute for lamps and candles, both as fixed and as moveable lights, and in 1793 he applied it to the purpose of lighting the extensive manufactory at Soho. Light was procured by the same means several years ago at the ovens in Shropshire, for preparing coke and tar, on Lord Dundonald's plan. And six or seven years since a projector at Paris lighted up his house and gardens, and proposed to light the streets of the city in a similar way.

The varieties above enumerated differ in specific gravity, the olefiant gas being the heaviest, and that from charcoal the lightest. They differ likewise in the quantity absorbed by water, which takes up one-eighth its bulk of olefiant gas, onesixty-fourth of that from stagnant pools,

and still less of the others.

GAs, phosphuretted hydrogen. This may be procured by boiling in a retort a little phosphorus, with a solution of pure pot

ash. The phosphorus should be first melted under water in the retort, which is to be emptied when the phosphorus has congealed, and then filled with the alkaline solution. Of this a sufficient portion is to be displaced by hydrogen gas. Or one part of phosphorus, cut into very small pieces, and two of finely granulated zinc, may be put into ten parts of water, and six parts of concentrated sulphuric acid added; the gas is disengaged in small bubbles, which cover the whole surface of the fluid, and take fire on reaching the air, so as to form by their succession a well of fire.

If two parts of phosphuret of lime, broken into pieces the size of a pea, and one of hyperoxymuriate of potash be put into an ale glass, or a Florence flask, the ves sel be filled with water, and six or eight parts of concentrated sulphuric acid be poured in through a long-necked funnel reaching to the bottom, as soon as decomposition commences, flashes of fire will dart from the surface, and the bottom of the vessel will be illumined with a beautiful green light.

When phosphuretted hydrogen gas is suffered to escape into the air, as it is sues from the retort it takes fire, and a dense white smoke arises, in the form of a horizontal ring, enlarging its diameter as it ascends. It detonates when mixed suddenly with oxygen, oxygenized muriatic acid, or nitrous oxide gas. By standing it loses its property of spontaneous ascension, the phosphorus being deposited on the inner surface of the vessel containing it.

Phosphuretted hydrogen gas may be dissolved in about four times its bulk of distilled water, at 44° Fahrenheit, and imparts to it a bitter taste, and strong unpleasant smell. This solution speedily converts the oxides of lead and mercury,

and nitrate of silver, into phosphurets of those metals. Nitrates of lead, mercury, and arsenic, and sulphates of copper and iron, are acted upon by it more or less slowly; but some of the posphurets then formed are changed, by standing some time, into phosphates.

The ignis fatuus, or jack with a lantern, is supposed to be produced by this gas, arising from the putrefaction of animal substances in swampy places.

GAS, sulphuretted hydrogen. This gas, formerly termed hepatic air, may be obtained, by adding dilute muriatic acid to a solution of sulphuret of potash or of soda, which evolves it with violent efferves cence; or by pouring diluted sulphuric or muriatic acid on sulphuret of iron. Sul

phur and iron mixed together with a little water, likewise afford it by distillation. Sulphuretted hydrogen is particularly characterized by its offensive smell, resembling that of rotten eggs. Like the other compounds of hydrogen, it detonates if mixed with oxygen or atmospheric air, and then fired, and burns silently, if inflamed as it comes in contact with them from a small aperture. If three parts of it be mingled with two of nitrous gas, the mixture burns with a yellowish green flame.

This gas is decomposed by oxymuriatic acid gas, by sulphurous acid gas, or by being kept mixed with atmospheric air, and its sulphur is precipitated. If passed through ignited charcoal, it is converted into carburetted hydrogen gas. It precipitates all metallic solutions, except those of iron, nickel, cobalt, manganese, titanium, and molybdana. It tarnishes silver, mercury, and other polished metals, and immediately blackens white paint.

This gas is absorbed by water, which at 55° takes up .86 of its bulk, and at 85° only .78. The solution exposed to the air becomes covered with a pellicle of sulphur; and deposits sulphur even in well corked bottles. A few drops of nitric or nitrous acid likewise precipitate the sulphur.

It is remarkable that sulphuretted hy drogen, which contains no oxygen, consisting, according to Thenard, of 29 by. drogen, and 71 sulphur, should possess the properties of an acid, reddening litmus paper, and uniting with the alkalies and all the earths, except alumina and zircon. These compounds are soluble, and most of them are susceptible of crystallization. They are at first colourless, but by exposure to the air become green, or of a greenish yellow, and deposit sulphur. At length, however, the solution again becomes colourless, and the base is found ultimately converted into a sulphate. Acids disengage their sulphuretted hy drogen gas. Vauquelin, having lixiviated a considerable quantity of soda manufactured in France, found, after some weeks, a white transparent salt, crystallized in tetrahedral prisms, terminated by quadrangular or octangular pyramids. Its taste was acrid and intolerably bitter, and it had a slight hepatic smell. It did not precipitate any of the earthy salts, except those of alumina, zircon and yttria. Some of the German chemists have classed it as an acid, by the name of the hydrothian. The waters called sulphurous, or hepatic, as those of Harrowgate, are solutions of this gas. They are recommended

as alteratives in cutaneous affections, against worms, in gout and jaundice, and as deobstruents; but they are said to have been very injurious in dropsy.

GAS, muriatic acid. Muriatic acid exists in a separate state only in the form of gas, but its attraction for water is so strong, that it can be received and confined only over mercury. According to Kirwan, water absorbs rather more than 420 times its bulk, and is augmented by it about one third: in Dr. Thomson's experiments it took up 515 times its bulk at 60° Fahrenheit. It liquifies ice very rapidly, and the temperature is lowered. It has a pungent smell, is fatal to animals, and extinguishes flame, first imparting to it a greenish tinge. Its bulk is increased by a succession of electric shocks, which Mr. Henry has shewn to arise from the decomposition of water, of which he infers, from his experiments, 60 grains hold 1.4 in solutions. On its coming into contact with atmospheric air, a white cloud is produced. Brisson gives its specific gravity, atmospheric air being 1000, at 1430, Henry at 1780, Kirwan at 1929. For its other properties, see MURIATIC ACID.

Gas, oxygenized muriatic acid. This gas, which is a compound of the preceding with oxygen, presents another anomaly in the theory of acidification; it was observed that sulphuretted hydrogen resembles an acid in many of its properties, though it contains no oxygen; and we here find the radical of an acid, which, with a certain proportion of oxygen, ranks among the most powerful, so much weakened in its properties, as even to be denied by some a place among the acids.

This gas is not invisible, as it has a greenish yellow colour. It has a pungent, suffocating smell, and is very injurious to the lungs; it extinguishes burning bodies; a temperature of 40° Fahrenheit reduces it to a liquid form. Mr. Northmore condensed nearly two pints in a receiver of the capacity of 24′ inches, in which state it was a yellow fluid, so extremely volatile, as to evaporate the instant the screw of the receiver was opened. A pint of this gas being injected upon halfa pint of oxygen, the result was a thicker substance, that did not evaporate so soon, and left a yellowish mass behind. Nitrogen in the same proportion gave a still thicker substance, and of a deeper yellow. In both these experiments much of the grease of the machine was carried down. Into a receiver, of three inches capacity, a pint of carbonic acid gas was pumped, and then rather more than a pint of oxygenized muriatic acid gas: the

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 have 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 spontaneously 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 OXIGENIZED ACID, NITRIC ACID GAS, and NITRIC acid.

GAS, nitric oxide, or NITROUS GAS. We 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 putinto 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 impregnat ed 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, ređ 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

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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 induced 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 has 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 observ

ed, 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 bottle 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 econgmy, 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 sufiocating 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 sul phuric acid; and Foureroy 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 oxy gen from sulphuric acid by some other inflammable substance. The metals an swer 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,

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