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 car bonate of barytes, were exposed to a strong heat, large quantities of a combus tible gas were extricated, which he sup posed to be heavy inflammable air, or carburetted hydrogen. He considered this as a strong argument against the mo dern 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 wa ter. This objection was successfully com bated by Mr. Cruickshank, showing that the air did not contain hydrogen, but was an oxide of carbon. It is equally pro cured 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 satu. rated with it ; so that the product is a mixture of carbonic acid gas and car bonic oxide, the proportion of the for mer decreasing as the process is conti nued.
The carbonic oxide gas, freed from carbonic acid by washing with lime-wa ter, 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 deto nates. 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. Hit be mixed with hydrogen gas, and passed through an ignited glasstube, 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 ob tained from the reverse of the process for the decomposition of water. Iron moistened with water becomes oxyded, by decomposing the water ; but this pro cess is very slow. If the vapour of water be passed through a tube, containing iron wire, kept at a red heat, the decomposi tion 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 contaminat ed with carbon. Muriatic acid, diluted with twice or thrice its weight of water, may be employed, but it is less econo mical Hydrogen gas is the lightest of all pon derable substances, particularly if receiv ed over quicksilver, and freed from any humidity which it may contain, by expo sure to any substance that attracts water strongly. When perfectly dry, it is free
from smell, but when it contains moisture, it is slightly foetid. Though highly in flammable, it extinguishes burning,bodies, if completely enveloped in it without the contact of oxygen. It is incapable of sup porting life, but does not appear to pos sess any directly noxious quality, as it may be breathed for several respirations, or even nearly a minute. Fired, in com bination 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 flame, the colour of which, however, may be varied by different substances dissolv ed 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, he held over a jet of in flamed hydrogen gas, musical nines will be produced, varying in depth and strength, according to the length, diame ter, 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. Blot 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, introduc • ed nearly equal quantities ofthe 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 by drogen gas is for the filling air-balloons.
GAS, hydrogen arsenicated. Scheele, dis solving tin in arsenic acid, 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 arse. nious acid, or arsenic and iron fillings, 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.