1880.] On the Spectra of the Compounds of Carbon, fyc. 497 



band in the solar spectrum, which has been designated by the letter P ; 

 and near this, on the more refrangible side, a much fainter diffuse band, 

 which also seems to coincide with a part of the solar spectrum sensibly 

 less luminous than the parts on either side of it. This spectrum is 

 remarkably persistent at all temperatures of the flame. Watts found 

 that it did not disappear when the flame was cooled down as much as 

 possible by diluting the cyanogen with carbonic acid ; and we have 

 found that it retains its characters when the cyanogen is burnt in 

 nitric oxide. The flame in the last case must be one of the hottest 

 known, from the large amount of heat evolved in the decomposition of 

 cyanogen and nitric oxide, namely, 74,500 and 43,300 units per molecule 

 respectively. There is in the case of cyanogen, as in the case of so many 

 other substances, a difference in the relative intensities of the different 

 parts of the spectrum of the flame at different temperatures, but no 

 other change of character ; and we are unable to confirm the observa- 

 tion of Watts, that cyanogen burning in oxygen gives only the bands 

 which we assign to hydrocarbons. It is true, that in the upper part 

 of the flame where much or all of the cyanogen is oxidised or decom- 

 posed the spectrum is continuous, but at the base of the flame where it 

 is issuing from the nozzle we have always seen the nitrocarbon bands, 

 both when the cyanogen is burning in oxygen and when it is burning 

 in nitric oxide. y .. .... 



On the theory that these groups are the product of an exceptional 

 temperature in the case of the cyanogen flame, it is inconceivable that 

 they could disappear by combustion in oxygen, instead of in ordinary 

 air. Our observations accord with the statement of Morren, Pliicker, 

 Hittorf, and Thai en, that a cyanogen flame, fed with oxygen, when it is 

 intensely luminous, still yields these peculiar groups. We have found 

 these peculiar groupings in the flame when it had a current of oxygen 

 in the middle, and was likewise surrounded outside with oxygen. 

 There is nothing remarkable in observing only a continuous spectrum 

 from any hydrocarbon or nitrocarbon by using excess of oxygen, as we 

 know from Frankland's experiments that carbonic acid and water 

 vapour at the high temperature of flame under compression gives a 

 continuous spectrum. In fact, this is what we should anticipate, pro- 

 vided intermediate, and not the final, compounds are the active sources 

 of the banded spectrum. 



Each of the five sets of bands shown in the diagram is attended on 

 its more refrangible side by a series of rhythmical lines extending to a 

 considerable distance, not shown in the diagram, but easily seen in the 

 photographs. 



Coal gas burning in oxygen gives no bands above that near Gr within 

 the range of the diagram, fig. 1, nor are the visible cyanogen 

 bands seen in the flames of many organic compounds containing com- 

 bined nitrogen ; but beyond this our photographs show a spectrum 



