1868.] and Carbonic Oxide in Oxygen under great pressure, 421 



I have recently extended these experiments to the combustion of jets of 

 hydrogen and carbonic oxide in oxygen under a pressure gradually in- 

 creasing to twenty atmospheres. These experiments were conducted in a 

 strong iron vessel, furnished with a thick plate of glass of sufficient size to 

 permit of the optical examination of the flame. The results are so re- 

 markable that, although still far from being complete, I venture to com- 

 municate them to the Rcyal Society before the close of the Session. The 

 appearance of a jet of hydrogen burning in oxygen under the ordinary 

 atmospheric pressure is too well known to need description. On in- 

 creasing the pressure to two atmospheres, the previously feeble luminosity 

 is very visibly augmicnted, whilst at ten atmospheres' pressure the light 

 emitted by a jet about 1 inch long is amply sufficient to enable the 

 observer to read a newspaper at a distance of 2 feet from the flame, and 

 this without any reflecting surface behind the flame. Examined by the 

 spectroscope, the spectrura of tins flame is bright and perfectly continuous 

 from red to violet. 



With a higher initial luminosity, the flame of carbonic oxide in oxygen 

 becomes much more luminous at a pressure of ten atmospheres than a 

 flame of hydrogen of the same size and burning under the same pressure. 

 The spectrum of carbonic oxide burning in air is well known to be con- 

 tinuous ; burnt in oxygen under a pressure of fourteen atmospheres, the 

 spectrum of the flame is very brilliant, and perfectly continuous. 



If it be true that dense gases emit more light than rare ones when 

 ignited, the passage of the electric spark through different gases ought to 

 produce an amount of light varying with the density of the gas ; and this 

 is in fact the case, for electric sparks passed as nearly as possible under 

 similar conditions through hydrogen, oxygen, chlorine, and sulphurous 

 anhydride emit light the intensity of which is very slight in the case of 

 hydrogen, considerable in that of oxygen, and very great in the case of 

 chlorine and sulphurous anhydride. When liquefied sulphurous anhy- 

 dride is sealed up in a strong tube furnished with platinum wires, and the 

 temperature then allowed to rise until the internal pressure amounts to 

 three or four atmospheres, the passage of induction-sparks through the 

 enclosed gas is attended with very brilliant flashes of hght. Further, if a, 

 stream of induction-sparks be passed through air confined in a glass tube 

 connected with a condensing syringe, and the pressure of the air be gradu- 

 ally augmented to two or three atmospheres, a very marked increase in the 

 luminosity of the sparks is observed, whilst on allowing the condensed air 

 to escape, the same phenomena are observed in the reverse order. 



The electric arc from fifty cells of Grove's battery is incomparably more 

 brilliant when mercury vapour, instead of atmospheric air, is interposed 

 in the path of the discharge between the carbon points. The gases and 

 vapours just mentioned have the following relative densities : — 



Hydrogen 1*0 



Air 14-5 



Oxygen . , . . , , 16-0 



2 p 2 



