502 



Profs. Liveing and Dewar. 



[June 10, 



centims., so that vapour of carbon tetrachloride when mixed with 

 part of its volume of nitrogen, gives under the action of the electric 

 spark the nitrocarbon bands distinctly. Other similar experiments 

 confirmed this result. It is worthy of remark that the nitrocarbon 

 bands were not seen instantaneously on the admission of nitrogen into 

 the tube, but were gradually developed, as if it was necessary that a 

 certain quantity of nitrocarbon compound should be formed under the 

 influence of the electric discharge and accumulated before its spectrum 

 became visible. 



Spark Discharge in other Compounds of Carbon. 



Some carbon bisulphide was introduced into another tube, which 

 was drawn out to a long narrow neck, and the carbon bisulphide 

 boiled out in an oil-bath at 200° C, and the tube sealed off. In the 

 spectrum of the spark taken in this tube no nitrocarbon bands, 

 either blue or violet, could be detected however the discharge was 

 varied. 



A similar tube, containing benzol and similarly treated, showed no> 

 trace of the nitrocarbon bands. 



Another tube, containing naphthaline, previously well washed with 

 dilute sulphuric acid, dried and resublimed, was attached to the 

 Sprengel pump, and treated as the tubes with tetrachloride had been. 

 The spark in this tube likewise showed no nitrocarbon bands. After 

 a time the tube cracked, and then the nitrocarbon bands made their 

 appearance, and on setting the pump going a good deal of gas was 

 pumped out. When the air had again been pretty completely 

 exhausted, the nitrocarbon bands no longer showed, but gradually 

 reappeared 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 carbon only. Naphthaline is not well 

 adapted to be the subject of a test experiment in this case, for, from 

 its mode of preparation, it is liable to be contaminated with nitro- 

 genous bases ; and the tension of its vapour at ordinary temperatures 

 is so small that, unless the supply is kept up by heating the tube, the 

 spark soon so far decomposes it that the spectrum is reduced to that 

 of hydrogen only. It appears, however, from our experiments, that if 

 the naphthaline is sufficiently purified and freed from air it does not 

 furnish the nitrocarbon spectrum. 



As Watts laid much stress on the occurrence of the nitrocarbon 

 bands in the spectrum of the spark taken in carbonic oxide at atmo- 

 spheric pressure, though they do not appear in carbonic oxide at 

 reduced pressures, as a proof that these bands were due to carbon only,. 



