220 On the Spectrum of Cyanogen produced by Spark Discharge. 



the fact that the spark does not show the- cyanogen bands when 

 cyanides are submitted to its action. In this case it is possible that 

 the temperature is too high, and that the cyanogen is decomposed, 

 possibly by oxidation, for there can be no doubt that such condensed 

 sparks are at a higher temperature than that of the arc. We know, 

 too, that several metals are oxidised when volatilised in the spark, if 

 not entirely at least partially.* But by using gold electrodes with 

 the cyanides we do not obtain even a carbon spectrum. 



Here again, possibly, the carbon is oxidised, and we know that 

 carbon dioxide in carbonates yields no spectrum of carbon, nor any 

 lines peculiar to carbon dioxide. 



I have sought in every direction for a reasonable explanation of 

 that which, up to the present, has proved inexplicable, in order that 

 by working on some hypothesis one might devise a means of putting 

 the matter to experimental proof. This has now been accomplished 

 in the following manner. 



An almost saturated solution of pure crystallised potassium 

 cyanide was put into a tube fitted with graphite electrodes in the 

 manner described in a previous communication.f 



The apparatus was fitted into a horizontal wooden tube with a 

 window of quartz at one end, and carbon dioxide was passed into the 

 tube until filled. The spark was then passed for five minutes, and 

 again for ten minutes, a photograph being taken of the two spectra. 

 The instrument used gave a dispersion equal to four quartz prisms. 

 A glass tube with a similar window of quartz was fitted with gold 

 electrodes and filled with cyanogen gas, and another spectrum was 

 photographed. A fourth spectrum was then obtained by passing 

 cyanogen into the wooden tube containing the graphite electrodes ; 

 after the carbon dioxide had been expelled by air and replaced by 

 cyanogen, the Ll'tube was filled up with the solution of potassium 

 cyanide. In all four cases the principal group of the cyanogen 

 bands was obtained, but it was not very strong. A flame of cyano- 

 gen was then photographed with exposures varying from one to two, 

 five, and ten minutes. A beautiful series of spectra was obtained, 

 and the lines belonging to the edges of bands constituting the prin- 

 cipal group were found to coincide exactly with those photographed 

 from the potassium cyanide solution when the spark was passed in an 

 atmosphere of carbon dioxide and in cyanogen, also when the spark 

 was passed between gold electrodes in cyanogen. These appear to 

 be the bands referred to by Eder and Valenta, which were described 

 as carbon lands% when graphite electrodes were used with the spark 



* ' Boy. Soc. Proc.,' TO!. 49, p. 448, " On the Physical Characters of the Lines in 

 the Spark Spectra of the Elements." 

 f ' Phil. Trans.,' vol. 175, p. 49, 1884. 

 J Hartley and Adeny, ' Phil. Trans.,' vol. 175, p. 63, Part I, 1884. 



