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Profs. G. D. Liveing and J. Dewar. [Dec. 21, 



oxide spectrum, and at the same time to bring out strongly the lines 

 of oxygen and carbon ; at a certain stage of the exhaustion, when the 

 flame spectrum is very weak without the jar, the effect of the jar is to 

 bring it out again but without sensibly enfeebling the carbonic oxide 

 spectrum, and without bringing out the carbon lines. At a still 

 higher stage of exhaustion, when the carbonic oxide spectrum alone is 

 seen without the jar, the flame spectrum is sometimes, not always, 

 brought out by putting on the jar, though the carbon lines again 

 show well. At this stage, at which the flame spectrum is not seen at 

 all, the distance between the striae in the wide part of the tube is con- 

 siderable, and much metal is thrown off the electrodes, which are 

 rapidly heated by the discharge. Some of these tubes were filled 

 with carbonic oxide made by heating a mixture of potassium oxalate 

 and lime contained in a prolongation of the tube containing the 

 phosphoric anhydride. Others were filled from a mixture of sodium 

 oxalate and sulphuric acid heated in a flask sealed to a long tube 

 which had the middle part filled with quicklime and the two ends 

 filled with phosphoric anhydride ; and after all the air was expelled and 

 the flask had been sealed off, the quicklime was heated to absorb the 

 carbonic acid. These tubes showed no trace of the cyanogen flutings 

 at any stage of exhaustion, either to the eye or in photographs of the 

 spectrum. Nevertheless, in the earlier stages of exhaustion, some of 

 such tubes do show, when the jar is used, a group of three lines in 

 the indigo which is seen in the flame of cyanogen, and has formerly 

 been described by us as part of the spectrum of cyanogen. We must 

 now, however, retract the opinion that this group is due to cyanogen. 

 We have before noted ("Proc. Roy. Soc," vol. 34, pp. 125, 127) that 

 these three lines are seen under many different circumstances when 

 the cyanogen flutings are absent, and as the flutings also are fre- 

 quently seen without the three lines, it seems that the three lines 

 belong to some other spectrum than the flutings, and as we have 

 now found them where nitrogen has been carefully excluded, we are 

 forced to attribute them either to carbon or some compound other 

 than cyanogen. 



In one case a very little copper-nitride was introduced into one 

 end of the drying tube, and after the whole had been filled with gas 

 and the generating flask sealed off, the nitride was heated so as to mix 

 a small quantity of nitrogen with the carbonic oxide. In the spectrum 

 of this tube the cyanogen flutings were not visible to the eye, but the 

 ultra-violet set between K and L came out plainly in the photo- 

 graphs. No hydrogen line could be detected in it. This is remarkable, 

 because Berthelot did not find that cyanogen is generated by electric 

 sparks in a mixture of nitrogen and carbonic oxide unless hydrogen 

 be also present. It would, however, be rash to assume that no trace 

 of hydrogen was present because the lines of hydrogen were not 



