1891.] Influence of Pressure on the Spectra of Flames, 217 



The application of (46) gives 



and Ft*) = {1+/O/:})} 2 .............. (49). 



We see then that the modulus of (43) will be a minimum^ when 



(50) ' 



and in taking the square root the ambiguity must be so determined as 

 to make the real part of a positive. 



Equation (50) coincides with that obtained by MIN Heaviside for 

 the case where all the quantities axe real. 



II. " On the Influence of' Pressure on the- Spectra of Flames." 

 By G. D. LIVEING, M.A., F.R.S., Professor of Chemistry, 

 and J. DEWAR, M.A., F.R.S., Jacksonian Professor, 

 University of Cambridge.. Received January 22> 1891. 



"We have already described (' Phil. Trans.,*" A, 1888) the remarkable 

 pectrum of the oxy -hydrogen flame burning at the ordinary atmo- 

 iheric pressure. Recently we have examined the spectrum of the 

 me flame at various pressures : hydrogen burning in excess of 

 xygen up to a pressure of 40 atmospheres, said oxygen in excess of 

 hydrogen up to a pressure of 25 atmospheres, also that of the mixed 

 gases burning in. carbonic acid gas. 



The apparatus employed was an adaptation of one of the tubes 

 id in oar experiments on the absorption spectra of compressed 

 .ses ('Phil. Mag.,' September, 1888, and 'Roy. Soc. Proc.,' vol. 46, 

 p. 2:22). It consisted of a steel cylinder, about 50 mm. in internal 

 diameter and 225 mm. long, fitted at one end with a quartz stopper, 

 in the annexed figure, and with a jet, &,. for burning the gas, 

 pted by a properly fitting union joint to the opposite end. There 

 ere two tubes, c and d, connected to the cylinder at the sides, of 

 hich one, e, served for the introduction of gas, while the other, d, 

 fitted with a stopcock and was used to draw off the water formed, 

 to reduce the pressure of the gas in the cylinder if that was 

 ired. The flame was observed, nearly end on, through the quartz 

 pper. The whole apparatus was kept cool by a stream of cold 

 ter running on to a sponge cloth wrapped round the cylinder. In 

 course of the tube conveying gas to the jet b was interposed a 

 all cylinder, e, in which sodium was placed, and by heating this, 

 e gas entering could be charged with sodium vapour. 



Q 2 



