Oxidation occurs in various ways. Besides those already mentioned, all verdigris produced on copper, all decays of whatever kind, disintegration, and respiration, are the effects of oxygen. The following experiment for the extraction of oxygen directly from the air was made by M. Boussingault, who passed the gas upon a substance at a certain temperature, and released it at a higher. The illustration on page 351 will show the way in which the experiment was performed.
Boussingault permitted a thin stream of water to flow into a large empty flask, and by this water the air was gradually driven out into a flask containing chloride of calcium and sulphuric acid, which effectually dried it. This dry air then passed into a large tube inside the reverberatory furnace, in which tube were pieces of caustic baryta. Heated to a dull redness this absorbs oxygen, and when the heat is increased to a bright red the superabundant gas is given off. Thus the oxygen was permitted to pass from the furnace-tube into the receiving glass, and so pure oxygen was obtained from the air which had been in the glass bottle at first (fig. 338).
Fig. 336.—Phosphorus burning in oxygen.
HYDROGEN—SYMBOL H; ATOMIC WEIGHT 1.
Hydrogen is abundant in nature, but never free. United with oxygen it forms water, hence its name, “water-former.” It is to Parcelcus that its discovery is due, for he found that oil of vitriol in contact with iron disengaged a gas which was a constituent of water. This gas was subsequently found to be inflammable, but it is to Cavendish that the real explanation of hydrogen is owing. He explained his views in 1766.
Hydrogen is obtained in the manner illustrated in the cut, by means of a furnace, as in fig. 339, or by the bottle method, as per fig. 340. The first method is less convenient than the second. A gun-barrel or fire-proof tube is passed through the furnace, and filled with iron nails or filings; a delivery tube is at the farther end, and a flask of water boiling at the other. The oxygen combines with the iron in the tube, and the hydrogen passes over. The second method is easily arranged. A flask, as in the cut, is provided, and in it some zinc shavings are put. Diluted sulphuric acid is then poured upon the metal. Sulphate of zinc is formed in the flask, and the hydrogen passes off.
Hydrogen being the lightest of all known bodies, its weight is put as 1, and thus we are relatively with it enabled to write down the weights of all the other elements. Hydrogen is fourteen-and-a-half times lighter than atmospheric air, and would do admirably for the inflation of balloons were it not so expensive to procure in such large quantities as would be necessary. Ordinary coal gas, however, contains a great deal of hydrogen, and answers the same purpose.
