1882.] On the Origin of the Hydrocarbon Flame Spectrum, 423 



turn connected by fusion to the (Sprengel) pump. To dry the gas it 

 is not enough to pass it through such a tube or even a much longer 

 one full of phosphoric anhydride ; it has to be left in contact with the 

 anhydride for several hours, and to get the adhering film of mois- 

 ture out of the tube it has to be heated after exhaustion, while con- 

 nected as above described with the drying tubes, up to the point at 

 which the glass begins to soften, and kept at near this temperature for 

 some time. To get most of the gases out of the electrodes the tube 

 must be exhausted and sparks passed through it for some time before 

 it is finally filled with the gas to be observed. Even when these pre- 

 cautions have been taken, the lines of hydrogen can often be detected 

 in tubes filled with gases which should contain no hydrogen. The 

 general result of our observations on the spectra observed in tubes 

 so prepared is that the channelled spectrum of the flame of hydro- 

 carbons is not necessarily connected with the presence of hydrogen ;* 

 it does not come and go according as hydrogen is or is not present 

 along with carbon in the way that the channelled spectrum of cyanogen 

 comes and goes according as nitrogen is present or absent. Our 

 observations confirm those of Wesendonck on this point. 



A tube filled with hydrogen containing a small percentage of 

 cyanogen and exhausted, was found to give plainly the seven channel- 

 lings in the blue and six channellings in the indigo characteristic of 

 cyanogen, and the hydrogen lines of course strongly, but no more 

 than a trace of the brightest green line of the spectrum of the flame 

 of hydrocarbons. The use of a Leyden jar brought out no more. 

 Continued sparking made no sensible difference, the cyanogen spec- 

 trum remained, the green line did not alter : and no other line of the 

 spectrum of the hydrocarbon flame appeared. 



Tubes filled with carbonic oxide exhibit in general at different 

 stages of exhaustion the following phenomena. When the exhaustion 

 is commencing and the spark will just pass, the spectrum of the dis- 

 charge in the capillary tube is usually that of the flame of hydro- 

 carbons and nothing else. As the exhaustion proceeds the spectrnm 

 of carbonic oxide makes its appearance superposed on the former, 

 and gradually increases in brilliance until it overpowers and at 

 last, at a somewhat high degree of exhaustion, entirely supersedes 

 the flame spectrum. This is when no jar is used. In the earlier 

 stages of exhaustion the effect of the jar is to increase the relative 

 brilliance of the flame spectrum and diminish that of the carbonic 



* This statement may have to he qualified if the spectrum described as the second 

 spectrum of hydrogen by Plucker and Hittorf and by Wullner, and recently f urther 

 investigated by Hasselberg ("Mem. Imp. Acad, Sc., St. Petersburg," xxx, No. 7), be 

 the most persistent spectrum of hydrogen at low pressures ; because the statement 

 in the text is based on the supposition that hydrogen could be detected with cer- 

 tainty by the " C " or " F " line. (Jan. 26, 1883.) 



2 f 2 



