1891.] Influence of Pressure on the Spectra of Flames. 221 



edges to begin with, it is extremely difficult to judge whether there 

 is any expansion. At all events, we may say that there is no 

 expansion produced by pressure at all comparable with that produced 

 in a flame at ordinary pressure by increasing the quantity of sodium 

 in the flame. We noticed, however, that the presence of sodium, 

 which produces a feeble continuous spectrum in a flame at an 

 ordinary pressure, seemed to increase the continuous spectrum of the 

 flame under pressure, especially in the orange and green. 



Oxy-hydrogen Jet in Carbonic Acid Gas. 



For this experiment a two-branched tube (the upper one in the 

 figure) was used. The jet of mixed oxygen and hydrogen was first 

 lighted and introduced into the experimental cylinder while the 

 latter was full of air and the stopcock s open. The air was then 

 replaced by CO., entering by the tube c. The effect of this was at 

 once to brighten the flame and change its colour from yellow to blue. 

 Seen in the spectroscope, the change consisted in an increase of 

 continuous spectrum, especially towards the more refrangible end. 

 When the stopcock s was closed so that the pressure rose in the 

 experimental cylinder, the flame increased in brightness, but there 

 was no other change in the spectrum. It remained continuous with 

 no bright or dark lines, or bands, except the D lines of sodium. It 

 resembled an ordinary flame of CO. The jet would not burn in C0 2 

 unless there was some excess of oxygen, and even with an excess of 

 oxygen we could not get it to continue to burn in CO 2 at a pressura 

 higher than 2 atmospheres. 



Ethylene in Oxygen. 



A jet of ethyl ene burning in oxygen gave, when the flame was 

 small, the usual candle-flame spectrum, together with a band in the 

 indigo (X 431) shading towards the violet ; but as the pressure was 

 increased the continuous spectrum brightened and completely over- 

 powered the bands, and at the same time the absorption spectrum of 

 N0 2 appeared. We carried the pressure up to 33 atmospheres, and 

 at that pressure the flame seemed to give nothing but a continuous 

 3ctrum, intersected by the absorption bands of NO 2 . In our tube, 

 flame was viewed almost directly end on, and it is possible that if 

 re had seen the flame sideways, we might have detected the hydro- 

 irbon flame spectrum near the nozzle. At the high pressure much 

 separated. We tried burning a mixture of ethylene and oxygen, 

 le mixed jet burnt well in air and, when the supply of oxygen was 

 ifficient, gave the hydrocai'bon flame spectrum. In the experi- 

 ital tube in oxygen, the jet burnt well at the atmospheric pressure, 



