1881.] on the Oriijhi and Identity of Spectra. G83 



pumped out. AMicu tlie air had again been pretty completely 

 exhausted, the nitrocarbon bands were no longer visible, but gradu- 

 ally reai>peared again as air leaked through the crack. Another 

 tube, containing a mixture of naphthaline and benzol, showed no trace 

 of the nitrocarbon bands. 



The observation of the nitrocarbon bands in the spectrum of the 

 spark in naphthaline was one of the reasons which led Watts at one 

 time to ascribe these bands to free carbon. 



In our first experiments with carbonic oxide the gas was made by 

 the action of sulphuric acid on dried formiate of sodium. 



At first the six violet cyanogen bands were well seen, and the 

 seven blue bauds faintly ; but gradually, as the air became more 

 completely expelled, the blue bands disappeared entirely, and then 

 the violet bands so far died out that it was only by manipulating the 

 coil that they could be made visible, and then only very ftiintly. A 

 bubble of air about ^l^ part of the volume of gas in the generating 

 flask and tube, was now introduced, when almost immediately the 

 bands reappeared brightly. As the stream of gas continued, they 

 again gradually died away until they were represented only by a 

 faint haze. It was subsequently found that each introduction of fresh 

 acid into the flask was attended with a marked increase in the bright- 

 ness of the nitrocarbon bands, which died away again when the 

 current of gas was continued without fresh introduction of acid. On 

 testing the acid it was found to contain, as is frequently the case 

 with sulphuric acid, a very small quantity of the oxides of nitrogen. 

 The difficulty of getting all the air expelled from the apparatus 

 and reagents led us to adoj)t another method of making carbonic 

 oxide. Carbonic oxide was generated by heating in a tube of hard 

 glass in a combustion furnace a mixture of pure dry potassium 

 oxalate with one quarter of its weight of quicklime, the mixture 

 having been previously heated for some time to expel traces of 

 ammonia. No trace whatever of the nitrocarbon bauds could be 

 detected in this carbonic oxide, however the spark might be varied. 

 The pressure of the gas was reduced to 1 inch of mercury, while 

 the spectrum was observed from time to time. Still no trace of 

 the nitrocarbon bands could be detected. More of the oxalate was 

 heated, and the observations repeated again and again, always with 

 the same result. Carbonic oxide, therefore, if quite free from 

 nitrogen, docs not give, at the atmospheric or any less pressure, 

 the nitrocarbon spectrum. 



On passing the spark between carbon poles in nitrogen, the nitro- 

 carbon bands are plainly seen ; and remain visible through great 

 variations in the character of the spark. Photograjihs taken, with 

 and without the use of the condenser, showed the violet and ultra- 

 violet nitrocarbon bands, including those near N and P. If the 

 nitrogen was swept out by a current of carbonic acid gas, on passing 

 the spark the nitrocarbon bands could no longer be detected, and 

 photographs showed no trace of any of the ultra-violet bands. 



