2-22 



Profs. G. D. Liveing and J. Dewar. [Feb. 19, 



but we failed to get it to continue burning when the pressure was 

 increased. The shaded band, commencing with a sharply-defined 

 edge about \ 431, seems to be independent of the pressure, and has 

 been before observed in a gas flame (Huggins, 'Roy. Soc. Proc.,' 

 vol. 30, p. 580). In fact, the only effect of pressure in this, as in the 

 former cases, seemed to be the increase of the continuous spectrum. 



Cyanogen and Oxygen. 



As we could not obtain cyanogen at such pressures as we had used 

 in the case of the other gases, we were obliged to content ourselves 

 with exploding mixtures of cyanogen and oxygen in an iron bottle, 

 fitted with a quartz stopper like that of the experimental tube above 

 described. The bottle, having been exhausted by an air-pump, was 

 filled with the mixture of gases, and exploded by an electric spark. 

 With less than 3 vols. of oxygen to 1 vol. of cyanogen, there was 

 always a considerable deposit of carbon, which covered the quartz and 

 impeded vision ; but, with 3 vols. of oxygen to 1 of cyanogen, the 

 carbon was all burnt. Notwithstanding the brilliant banded spectrum 

 of a flame of cyanogen in oxygen at ordinary pressure, nothing but a 

 continuous spectrum could be seen in the flash of the exploded gases, 

 except the ubiquitous D lines of sodium. The continuous spectrum 

 was bright. Photographs showed a continuous spectrum with lines 

 of iron, calcium, potassium, and sodium, but no cyanogen or carbon 

 bands, or carbon lines. When a little hydrogen was added to the 

 mixture of gases, no trace of the hydrogen red or green line could be 

 detected in the spectrum of the exploding gas. 



In every case, the prominent feature of the light emitted by 

 flames at high pressure appears to be a strong continuous spectrum. 

 There is not the slightest indication that this continuous spectrum is 

 produced by the widening of the lines, or obliteration of the 

 equalities, of the discontinuous spectra produced by the same 

 at lower pressures. On the contrary, it seems to be developed inde- 

 pendently. This is, on the whole, quite in accordance with what 

 would be expected, considering that under pressure the molecules of 

 the gases have much less freedom, encounters amongst them are 

 much more frequent, and they have much less chance of vibrating 

 independently, and of taking up exclusively, or chiefly, the funda- 

 mental rates of vibration which are natural to them when free. 

 Their condition, during a large part of any given time, approximates 

 to that of the molecules of a liquid, and their spectra approximate to 

 that of a liquid to at least a like extent. On the other hand, the 

 higher temperature which, in many flames, attends an increased 

 pressure ought to give some intensity to the special radiation which 

 the molecules emit during their time of free motion ; and this we have 



