Dr. W. M. Watts on the Spectra of Carbon. 257 



of the gas, the carbonic anhydride is decomposed and the new 

 carbon-spectrum becomes visible. 



If we attempt to define the conditions under which these dif- 

 ferent forms of the carbon-spectrum are produced, we are met 

 by very considerable difficulties. The knowledge we possess of 

 the temperature of gases ignited by the electric discharge is so 

 small, that we cannot with any certainty compare the spectra 

 produced in this way with those obtained from the flames of car- 

 bon-compounds. Indeed it seems by no means certain that 

 we are right in attributing the differences obtained in electric 

 spectra simply to the different temperature to which the gas is 

 heated. 



In comparing the spectra of fig. 1, we notice that the changes 

 take place at the ends of the spectra, the central groups 7, 8, e 

 remain substantially the same. If we pass from the spectrum 

 of the olefiant-gas flame to that of the cyanogen-flame, we find 

 the change at the blue end of the spectrum consisting in the dis- 

 appearance of the group / and its replacement by the groups f 

 and 6. The group / is not absolutely proved to belong to car- 

 bon (that is, it may be caused by carbonic oxide or carbonic 

 anhydride) ; but the groups f and 6, since they are common to 

 carbonic oxide, cyanogen, and naphthalin, must be due to car- 

 bon, and their presence may with much probability be attributed 

 to the higher temperature of the cyanogen-flame. 



The temperatures of flames, calculated on the assumption that 

 the total heat of combustion is expended, in heating up the pro- 

 ducts of combustion, have been shown by Deville to be immensely 

 too high. Thus, for example, the temperature of the oxyhy drogen- 

 flame, which calculation fixes at 6880° C, is determined experi- 

 mentally by Deville* to be not higher than 2500° C, and by 

 Bunsen not higher than 2800° C. The following are the cal- 

 culated temperatures of some flames, with which are compared 

 the recent experimental results of Bunsen f: — 



Hydrogen in air . . 

 Hydrogen in oxygen . 

 Carbonic oxide in air . 

 Carbonic oxide in oxygen 

 Cyanogen in air . . 

 Cyanogen in oxygen . 

 Olefiant gas in air 

 defiant gas in oxygen 



Calculated. Experimental. 



2738 C. 2024 C. 



6880 2844 



, 2996 1997 



7067 3033 



3519 3297 

 , 10557 

 , 2619 

 , 8626 



* Legons sur la Dissociation, p. 281. 

 t Pogg. Ann. vol. cxxxi. p. 161. 



