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 proper ties 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 absorp tion 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 dephlogis ticated 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 man ganese, 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 hyper oxymuriate 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 nortaste. It is a little heavier than atmospheric air; under great pressure.water may be made to take up about half its bulk. It A essen tial to the support of life ; an animal will live in it a considerable time longer than in atmospheric air; but its respiration be comes 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 resi duary 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 econo my, it has been applied medicinally ; and is reported to have been of great sery cc in many cases of debility, palsy, nervous affections, scrofula, rickets, and even hy drocephalus.
Gas, sulphurous acid. When sulphur is burnt slowly, as gas arises, of a suffo cating pungent smell, consisting of sul phur combined with oxygen in less pro portion than is requisite to form sulphuric acid.' This was known to the earlier mo dern 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 Fourcroy and Vauquelin completed its examination. . is In the mode above mentioned, it 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 de compose 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 re tort, with two of concentrated sulphuric acid, and heat applied. It should be re ceived over mercury, as water absorbs it taking up thirty-three times its bulk.