[80] Watts.
Prop. Oxygen gas is colourless, tasteless, inodorous, and incombustible; the sp. gr. is 1·057 (Dumas; 1·1026—Berzelius & Dulong; 1·111—Thomson); 100 cubic inches at 60° Fahr., and 36 inches of the barometer, weigh 34·29 gr. (Dumas; 34·109 gr.—Berz.; 34·6 gr.—Brande; 33·85 gr.—Ure). Its density to that of atmospheric air is, therefore, as about 11 to 10. It is a powerful supporter of combustion, and its presence is essential to the existence of both animal and vegetable life. It forms 21% (20·81%) by volume, and 23% by weight, of the atmosphere. (M. Dumas.) Water dissolves about 5 per cent. by volume of oxygen, and by pressure a much larger quantity, forming oxygenated water (AQUA OXYGENII). Oxygen has recently been liquified.
Tests. 1. It is distinguished from other gases by yielding nothing but pure water when mixed with twice its volume of hydrogen and exploded, or when a jet of hydrogen is burnt in it.—2. A recently extinguished taper, with the wick still red hot, instantly inflames when plunged into this gas.—3. A small spiral piece of iron wire ignited at the point, and suddenly plunged into a jar of oxygen, burns with great brilliancy and rapidity. Charcoal does the same.
Estim. The estimation of the quantity of oxygen in an organic compound has already been described. For determining the quantity present in atmospheric air, and other like gaseous mixtures, Dobereiner has proposed the use of pyrogallic acid. The air under examination (freed from moisture) is measured into an accurately graduated tube over mercury, capable of holding about 30 cubic centimètres, and which it should 2⁄3rds fill. A solution formed of 1 part of dry hydrate of potassium and 2 parts of water, and in volume about 1⁄35th that of the air, is next introduced by means of a pipette with a curved point, and is gently agitated therewith in the gas for a short time; the decrease of volume gives the proportion of carbonic anhydride present. A solution of pyrogallic acid (1 gramme in 5 or 6 centimètres of water), equal in volume to one half that of the solution of potassa already used, is then introduced by means of another pipette, and the mixed liquids are cautiously shaken together over the inner surface of the tube. When absorption ceases (which it does in a few minutes), the quantity of residual gas (nitrogen) is read off from the graduations; the difference in volume before and after the introduction of the pyrogallic acid indicates the proportion of oxygen. This is a mere modification
of Prof. Liebig’s method. 1 gramme of pyrogallic acid in combination with hydrate of potassium is capable of absorbing about 189 cubic centimètres of oxygen. (Dobereiner.) Other methods employed for the analysis of air, depending on the increase or loss of weight when the air is passed over finely divided copper heated to redness, the loss of volume when the air is exploded in a eudiometer with half its bulk of hydrogen, or when a stick of phosphorus is left in it for some hours, are well known, and described at length in every elementary work on chemical analysis. The last method, although less accurate than the others, has the advantage of extreme simplicity.
Uses. Oxygen has been employed to increase the illuminative and heating power of lamps, and to render vitiated air respirable, &c.; and when largely diluted with atmospheric air, or condensed in water, as a remedial agent in asphyxia arising from the inhalation of carbonic acid and carbonic oxide.
Dr Ringer says that if oxygen be administered as a gaseous bath for an hour or two at a time, and the bath repeated six or eight times a day, it is of great service in senile gangrene.
Concluding Remarks. Oxygen gas may be collected in the usual way, either over water, mercury, or in bags; or, on the large scale, in gasometers. The purity of the products of the several processes given above depends on the substances from which the gas is obtained being themselves pure. For particular experiments the first portion of gas should be allowed to escape, or be received apart, as with this, as with the other gases, it is contaminated with the atmospheric air of the apparatus. The gas procured from manganese or nitre may be purified by passing it through milk of lime or a solution of caustic potash; it will still, however, retain some traces of nitrogen. M. Limousin[81] has devised an apparatus for the preparation of oxygen by the attendants of hospitals, which obviates the risk of bursting of the retorts, attending its preparation by the old method. The apparatus consists of two cast-iron hemispheres, whose edges, which are well polished and about two centimètres thick, can be fitted hermetically upon each other, and fastened by three screws. The mixture of chlorate of potash and peroxide of manganese is placed in the lower hemisphere, which rests upon a tripod; the upper hemisphere, from which projects an iron tube, is now screwed on, and the iron tube connected with india-rubber and glass tubing with a Wolf’s wash-bottle, from which the gas after being washed passes through a second glass tube, and is thus ready for use. It may be conducted into an air-tight bag, in which it will keep for several weeks. Such a bag when supplied with a tube and stop-cock will afford a ready means for inhalations. Oxygen in a condensed or compressed
state is prepared by Mr Orchard, High Street, Kensington. See Organic substances, Ozone, Gases, Liquefaction of, &c.
[81] ‘Pharm. Centralhalle,’ xiv, 318.