1880.] Compounds of Carbon with Hydrogen and Nitrogen. 157 



fied, by comparison with, the spark in a vacuum tube, with the C line 

 of hydrogen. The F line, identified in like manner, was also seen as 

 a faint diffuse band. This last line was in general overpowered by the 

 continuous spectrum, but was regularly seen, when, from some varia- 

 tion in the discharge, the continuous spectrum became less brilliant. 

 This was the first occasion on which we had seen the hydrogen lines 

 in the arc at all, though Secchi (" Compt. Rend.," 1873) states that 

 he had seen them by the use of moist carbon poles. We tried to 

 repeat his experiment, without success. The hydrocarbon bands in the 

 green and blue were at intervals well seen. Those in the yellow and 

 orange were, owing doubtless to the smaller dispersion of the light in 

 that region, overpowered by the continuous spectrum. Whereas when 

 air and carbonic acid gas were used, the inside of the globe was 

 quickly covered with dust from the disintegrated poles, scarcely any, 

 if any, such dust was thrown off when the arc was passed in hydro- 

 gen. 



Spectrum of the Arc in Nitrogen. 



Nitrogen was next substituted for the hydrogen . A longer arc 

 would now pass, the seven blue, the violet and ultra-violet bands all 

 came out well, at intervals brilliantly. The green and blue hydro- 

 carbon bands were also well developed. 



Spectrum of the Arc in Chlorine. 



On filling the globe with chlorine and keeping a current of that 

 gas passing through it, the arc would not pass through a greater dis- 

 tance than about 2 millims. No metallic lines were visible. At first 

 the violet bands, as well as the green and blue hydrocarbon bands, 

 were visible, but gradually when the current of chlorine had been 

 passing for some minutes, there was nothing to be seen but a con- 

 tinuous spectrum with the green and blue hydrocarbon bands. 

 Neither of these bands were strong, and at intervals the blue bands 

 disappeared altogether. 



Spectrum of the Arc in Carbonic Oxide. 



When the globe, previously full of air, was filled with carbonic 

 oxide and a current of that gas passed through it, the arc would not 

 pass through any greater space than in chlorine. There was much 

 continuous spectrum ; the yellow, green, and blue hydrocarbon bands 

 were well seen, some of the seven blue bands were just discernible, the 

 violet had nearly, and the ultra-violet quite, gone from sight. No 

 trace of the carbonic oxide bands, as seen in the spark discharge in 

 that gas, was visible. This is the more remarkable since under 

 similar circumstances two of the characteristic lines of hydrogen were 

 seen. 



