. The principles of chemistry . mists still employ this methodwhen it is required to ignitea mixture of oxygen wit]i a combustible gas in a closed vessel. For thispurpose, especially since Bunsens time,^^ an eudiometer is consists of a thick glass tube graduated along its length in milli-metres (for indicating the height of the mercury column), and calibratedfor a definite volume (weight of mercury). Two platinum wires are 29 bis ii^ , instead of a spark a fine wire may be taken, and an electric currentpassed through it to bring it to a state of incandescence; in this case the
. The principles of chemistry . mists still employ this methodwhen it is required to ignitea mixture of oxygen wit]i a combustible gas in a closed vessel. For thispurpose, especially since Bunsens time,^^ an eudiometer is consists of a thick glass tube graduated along its length in milli-metres (for indicating the height of the mercury column), and calibratedfor a definite volume (weight of mercury). Two platinum wires are 29 bis ii^ , instead of a spark a fine wire may be taken, and an electric currentpassed through it to bring it to a state of incandescence; in this case there will be nosparks, but the gases will inflame if the wire be fine enough to become red hot by thepassage of the current. 50 Now, a great many other different forms of apparatus, sometimes designed forspecial purposes, are employed in the laboratory for the investigation of gases. Detaileddescriptions of the methods of gas analysis, and of the apparatus employed, must belooked for in works on analytical and applied Fia. 31.—Cavendishs apiiaratus for exploding detonatinggas. Tlie bell jar standing in the bath is filled with amixture of two volumes of hydiogen and one volume ofoxygen, and the thick glass vessel A is then screwedonto it. The air is first pumped out of this vessel, sothat when the stopcock c is opened, it becomes filledwith detonating gas. The stopcock is then re-closed,and the explosion produced by means of a spark fi-oma Leyden jar. After the explosion has taken place thestopcock is again opened, and the water rises into thevessel A. OXYGEN AND ITS SALINE COMBINATIONS 169 fused into the upper closed end of the tube, as shown in fig. 32.^^ Bythe aid of the eudiometer we may not only determine the volumetriccomposition of water,•^- and the quantitative contents of oxygen in 5 They must be sealed into the tube in such a manner as to leave no aper-ture between them and the glass. In order to test this, the eudiometer is filledwith mercury, and its o
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