both prosperous and adverse adventures, that having stoutly vanquished thy enemies both of body and soul, thou mayest not only receive the praise of this transient combat, but be crowned with the palm of eternal victory."

Then the knight elected kisses the Sovereign's hand, thanks his Majesty for the great honour done him, rises up, and salutes all the companions severally, who return their congratulations.

GAS. This term was first applied by Van Helmont, to denote the permanently elastic exhalations afforded in chemical processes. Dr. Priestley, whose extensive and successful researches into this department of natural philosophy in the space of a few years produced a revolution in the science of chemistry, used the word air as the generic term for permanently elastic fluids. Other chemical writers of great reputation have thought fit to revive Van Helmont's term, and confine the word air to the atmospheric fluid. As this has been found convenient, to prevent confusion of ideas, it is now generally adopted; the gases which are not fully treated under the articles of their respective bases, will properly find a place here.

GAS, ammoniacal. See AMMONIA.

GAS, carbonic acid. This is the first of the elastic fluids that appears to have been distinguished from common air, though its nature was not properly understood till it was investigated by Dr. Black. Its deadly properties, as it is met with in subterranean cavities, particularly the celebrated Grotto del Cano near Naples, occasioned it to be distinguished by the name of spiritus lethalis. Van Helmont first gave the name of gas, from a German word equivalent to our spirit, to this vapour produced from burning charcoal. He likewise called it spiritus sylvestris, and when arising from fermented liquors spiritus vinosus. From its existing in the inelastic state, in water, it was called fixed air, a name which Black and others long retained; Bewley termed it mephitic air, from its great abundance in nature combined with lime in the form of chalk, and it has been named the cretaceous and the calcareous acid, subsequent to the discovery of its acid nature. But carbonic acid has superseded all those, since it appears to have been ascertained, that its radical is carbon. Of this, or rather of charcoal, according to the experiments of Lavoisier, it contains twenty eight parts by weight, to seventy-two of exygen. Guyton Morveau considers it as

composed of 17.88 pure carbon, and 82.12 of oxygen.

Carbonic acid gas exceeds every other in specific gravity, except the sulphurous. Hence the vapour in the Grotto del Cano, rises but a little above the surface; and the choak damp of miners, which is this gas, lies on the ground. Thus, too, when it is emitted from a fermenting liquor, it first fills the empty portion of the vat, displacing the lighter atmospheric air; and then flows over the sides, almost as water would do. For the same reason, if a bottle filled with it be inverted over the flame of a candle at some distance, it will descend, and extinguish it. According to the experiments of Mr. Cavendish, one part of this, mixed with nine of atmospheric air, renders it incapable of supporting combustion.

From the powerful attraction of carbon for oxygen, the base of this gas is not easily decomposed; but Mr. Tennant effected it by introducing phosphorous into a coated glass tube, closed at one end, and over this powdered marble. A very small aperture only being left in the other end of the tube, and a red heat applied for some minutes, phosphate of lime and charcoal were found in the tube. Dr. Pearson did the same with phosphorus and carbonate of soda.

The carbonic acid gas, is likewise decomposed in part by hydrogen gas, assisted by electricity. In a glass tube eight lines in diameter, De Saussure exposed a column of four inches in height, of carbonic acid gas, and three inches of hydrogen gas, over mercury, to the action of the electric fluid circulating between iron conductors, for twelve hours. The gases were at first condensed very rapidly, but by degrees more and more slowly, till in this period they were reduced to four inches. Of this, one inch was absorbed by potash, being carbonic acid gas, and the other three were nearly pure carbonic oxide, the hydrogen having formed water with the oxygen, abstracted from the carbonic acid. The mercury and the conductors were but very little oxyded. De Saussure had previously found, that carbonic acid, and hydrogen gases standing together over mercury, for the space of a twelvemonth had decreased in volume.

GAS, carbonic oxide. This gas was first made known, by Mr. Cruickshank. Dr. Priestley had observed, that, when scales of iron mixed with charcoal, or with carbonate of barytes, were exposed to a strong heat, large quantities of a combustible gas were extricated, which he supposed to be heavy

inflammable air, or carburetted hydrogen. He considered this as a strong argument against the modern theory of the formation of water; as, from the dryness of the ingredients, which were previously exposed to a red heat, and mixed and experimented upon immediately, and the quantity evolved, it could not be accounted for upon the supposition of the decomposition of water. This objection was successfully combated by Mr, Cruickshank showing that the air did not contain hydrogen, but was an oxide of carbon. It is equally procured from the oxides of other metals, and charcoal; but in proportion to the facility with which these give up their oxygen, the carbon is more or less saturated with it; so that the product is a mixture of carbonic acid gas, and carbonic oxide, the proportion of the former decreasing as the process is continued.

The carbonic oxide gas, freed from carbonic acid by washing with lime-water, is very little lighter than atmospheric air. It does not explode, when fired in atmospheric air, but burns with a blue lambent flame: with oxygen gas it detonates. It is noxious to animals. Water absorbs about a fifth only of its bulk. It is not absorbed by the pure alkalies, and does not precipitate lime-water. If it be mixed with hydrogen gas, and passed through an ignited glass tube, its oxygen unites with the hydrogen to form water, and charcoal is deposited. De Saussure, jun. however ascribes this appearance of carbonaceous matter lining the tube, to the action of the hydrogen on the lead in the glass, as he produced it by hydrogen alone with a glass tube; and could not by hydrogen and carbonic oxide in a tube of porcelain. The purest oxide of carbon is obtained, by passing the carbonic acid gas through red hot charcoal.

GAS, hydrogen. This is generally obtained from the reverse of the process for the decomposition of water. Iron moistened with water becomes oxided, by decomposing the water; but this process is very slow. If the vapour of water be passed through a tube containing iron wire kept at a red heat, the decomposition will go on with much more celerity. But the readiest method is to employ an acid, as the sulphuric, diluted with five or six times its weight of water, poured on iron filings or turnings, or on zinc in small pieces. Zinc affords it the purest, as that from iron is apt to be contaminated with carbon. Muriatic acid diluted with twice or thrice its weight of

water, may be employed, but it is less œconomical.

Hydrogen gas is the lightest of all ponderable substances, particularly if received over quicksilver, and freed from any humidity which it may contain by exposure to any substance that attracts water strongly. When perfectly dry it is free from smell, but when it contains moisture it is slightly fœtid. Though highly inflammable, it extin guishes burning bodies if completely enveloped in it without the contact of oxygen. It is incapable of supporting life, but does not appear to possess any directly noxious quality, as it may be breathed for several respirations, or even nearly a minute. Fired, in combination with oxygen, it explodes very loudly; but if kindled as it escapes from the extremity of a capillary tube into the atmosphere, it burns calmly, with a white flame, the colour of which, however, may be varied by different substances dissolved in the gas. It is thus the philosophical fireworks without smoke or smell are formed. If a tube of glass, metal, or any elastic material be held over a jet of inflamed hydrogen gas, musical tones will be produced, varying in depth and strength, according to the length, diameter, and material of the tube. A glass jar has a similar effect, but it must not be too wide, or so narrow as to extinguish the flame. Dr. Higgins first discovered this property.

A very high temperature is generally considered as necessary to produce the combination of hydrogen and oxygen. Biot compressed the two gases together in the syringe of an air-gun; they took fire, exploded violently, and burst the syringe; but here the temperature was sufficiently increased by the pressure. A gentleman of Orkney, however, introduced nearly equal quantities of the two gases into a glass jar over mercury, which stood in a room without fire, and with little light, from the beginning of January to the end of May, when he found, that of twelve cubic inches, three and a half had disappeared. The residuum was still a mixture of the two gases.

The chief practical application of hydrogen gas is for the filling air-balloons.

GAS, hydrogen arseniated. Scheele, dissolving tin in arsenic aeid, observed the extrication of an inflammable gas, holding arsenic in solution. Proust afterwards obtained it by digesting arsenious acid and zinc in diluted sulphuric acid. It may be

procured likewise by treating arsenious acid, or arsenic and iron filings, or arsenic and tin filings with muriatic acid; but still better by treating four parts of granulated zinc and one of arsenic, with sulphuric acid diluted with twice its weight of water.

This gas is insoluble in water; does not render lime water turbid, mixed with atmospheric air no diminution of bulk ensues, but the mixture, when fixed, detonates loudly, and deposits metallic arsenic; it has an alliaceous smell; it extinguishes burning bodies, and is fatal to animals; it is decomposed by oxygenated muriatic acid gas. If a lighted taper be immersed in a phial of this gas, it is instantly extinguished; but the gas burns at the mouth of the phial with a lambent white flame, which diffuses white fumes of arsenious acid. If it be inflamed in a phial with a small orifice, the flame gradually descends to the bottom of the phial, which becomes coated with crystallized metallic arsenic. Two parts of this gas, with one of oxygen, will explode loudly, and the products are water and arsenious acid; soap bubbles made with a mixture of these gases, explode with a blueish white flame. Equal parts of the gases explode with a much more vivid flame, but less noise. A stream of this gas, burned in a large receiver filled with oxygen, emits a blue flame of uncommon splendour. According to Tromsdorff's calculation, a cubic inch of the gas contains about a quarter of a grain of the arsenic. Its specific gravity is rather more than half that of atmospheric air.

GAS, carburetted hydrogen. There are several varieties of this gas, the hydrogen holding different proportions of carbon in solution, according to the process by which it is obtained.

The gas of stagnant water, which may be procured by stirring the mud at the bottom with a stick, and collecting the gas, as it rises in bubbles, in an inverted bottle, is this compound, as is also the fire damp of coal mines. The vapour of water passed through a tube containing ignited charcoal, consists of this gas and carbonic acid, which may be separated by agitating the mixture with lime diffused in water. The vapour of ether, or of alcohol, passed through a red hot tube of porcelain, coated` with clay, affords the same products. If three parts of concentrated sulphuric acid, and one of alcohol, be distilled in a glass retort with a gentle heat, a carburetted hydrogen comes over. This is distinguished by the name of

olefiant gas, from its property of forming an oil on coming into contact with oxygenated mauriatic acid gas. If five measures be mixed with six of the oxygenated muriatic gas, as rapid a diminution takes place as when nitrous and oxygen gases are added to each other, and a thin film of oil forms on the surface of the water.

Mr. Henry examined these and some other varieties, as well as pure hydrogen, with a particular view to the light they were capable of affording, and the following are his tabulated results:

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 oneeighth its bulk of olefiant gas, one-sixty

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 potash. The phosphorus should be first melted under water in the retort, which is to be emptied when the phosphorous 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 vessel 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 issues from the retort it takes fire, and a dense white smoke rises 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 phosphurets 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 ob

tained by adding dilute muriatic acid to a solution of sulphuret of potash or of soda, which evolves it with violent effervescence; or by pouring diluted sulphuric or muriatic acid on sulphuret of iron. Sulphur and iron mixed together with a little water likewise afford it by distillation.

Sulphuretted hydrogen is particularly characterised 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 into 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, nicke!, cobalt, manganese, titanium, and molybdæna. 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 hydrogen, which contains no oxygen, consisting, according to Thenard, of 29 hydrogen, 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 desit sulphur. At length, however, the solution again becomes colourless, and the base is found ultimately converted into a sul phate. Acids disengage their sulphuretted hydrogen gas. Vauquelin, having lixiviated a considerable quantity of soda manufac tured 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