the Spectrum of Cyanogen. 389 



on the tube M, while C is the bulb in which the gas was 

 frozen. The gasholder B was provided with a three-way 

 stopcock D, one arm of which was connected to the cyanogen- 

 supply apparatus, and the other to one end of the vacuum- 

 tube E. The other end of the vacuum-tube was connected 

 to the pump through the tap F, and the cyanogen supply 

 apparatus was also connected to the pump through the tap Gr. 



On account of the very rapid deposition of paracyanogen on 

 the walls of the vacuum-tube when the discharge is passed 

 through cyanogen, it was found impossible to examine the 

 spectrum of the discharge in the usual way, as the brown 

 deposit became rapidly quite opaque. It was necessary there- 

 fore to observe the discharge " end on," and the tube was 

 arranged as shown in the diagram. The electrode I was 

 made in the shape of a hollow cylinder of sheet-aluminium, 

 which fitted tightly into the tube and enabled the spectrum 

 of the negative glow to be examined if desired. Connexion 

 was made with I by a platinum wire sealed in at L. The 

 other electrode was of aluminium wire of the usual design, 

 and was sealed in at H. Connexion was made with a 

 mercury-pump through the tube K, and in this way both 

 parts or the apparatus could be separately exhausted. 



The first stage of course was to prepare the pure cyanogen, 

 which was carried out as follows : — The gasholder B was 

 nearly emptied of mercury, which was run into the reservoir 

 and the iiuliarubber tube tightly clipped. The three-way 

 tap D was turned so as to connect the gasholder with the 

 cyanogen apparatus, and the whole was exhausted as far as 

 possible through the tap G. In this way all the condensed 



Phil. Meg. S. 6. Vol. 2. No. 10. Oct. 1901. 2 D 



