680 Professor Deivar [June 10, 



flame was cooled by diluting tlie 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, 41,000 and 43,300 units respec- 

 tively. 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 at different temperatures, but no other change 

 of character. 



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

 exceptional temperature in the case of the cyanogen flame, it is incon- 

 ceivable that they could disappear by combustion in oxygen, instead of 

 in ordinary air. Our observations accord with the statement of 

 Morren, Pliicker, Hittorf, and Thalen, 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 sur- 

 rounded outside with oxygen. There is nothing remarkable in the 

 fact that only a continuous spectrum is seen to proceed from any 

 hydrocarbon or nitrocarbon burning in excess of oxygen, as we 

 know from Frankland's experiments that carbonic acid and water 

 vapour at the high temperature of flame under compression give in 

 the visible portion a continuous spectrum. In fact, this is what we 

 should anticipate, provided 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 ex- 

 tending 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 G 

 within the range of the diagram, Fig. 2 ; but beyond this our photo- 

 graphs show a spectrum of a character quite different from that at the 

 less refrangible end. The most remarkable part of this spectrum is a 

 long series of closely set strong lines, filling the region between the 

 solar lines R and S, and ending abruptly with two strong lines a 

 little beyond S. These are lines of various intensities, not regularly 

 arranged so as to give shaded bands like those in the less refrangible 

 part of the spectrum. Beyond these lines there is another large 

 group of lines, not so strong or so closely set, but sharp and well 

 defined. This peculiar part of the spectrum is really due to the 

 vapour of water, and shall bo discussed in the sequel. 



SparJc Discharge in various Gases. 

 Mr. Lockycr's experiments on the spectrum of carbon compounds 

 arc directly opposed to the results given above, as will be understood 

 by the following extract from one of his papers on the subject : * — 



* ' Troc. Roy. Soc' vol. xxx. p. 33G. 



