MancJicstcr Memoirs, Vol. xliv. {igoo), No. 115. 15 



taking place between carbon poles in the presence of a 

 large excess of air. 



In this case the conditions of high temperature obtain 

 in an excessive degree. Whether nitrogen oxides would 

 be produced by the combustion of the cyanogen, or by 

 direct oxidation of the nitrogen itself under these condi- 

 tions, formed an interesting question. To study this, the 

 apparatus used in the former experiments was employed. 

 Carbon electrodes, about 20 mm. in diameter, were substi- 

 tuted for the platinum-iridium terminals. A current of 

 15 amperes at about 100 volts was used to generate the 

 arc. The air was drawn through the apparatus in the 

 usual way. After operating for six hours, it was found 

 that only o'424grm. of nitric acid had been formed. 



The loss suffered by the platinum-iridium electrodes 

 due to the passage of the electric discharge is very slight. 

 A pair was weighed, and, after being in operation for 80 

 hours, lost only O'OI grm. in weight. The platinum- 

 iridium settled in the exit-tube from the combustion- 

 chamber, and formed a kind of mirror. 



A curious phenomenon is observed when the electrodes 

 are made red hot. They may be drawn out to the 

 maximum distance apart, when sometimes a bluish glow 

 is seen, somewhat resembling the brush discharge from an 

 electrical machine. Then, all at once there is a click, and 

 the flame is established. The initial striking distance in 

 this case may have been only about 2 mm., and the 

 maximum from 25 to 40 mm. 



J. J. Thomson has proved that gases become electrified 

 in the neighbourhood of glowing metals, the ions so pro- 

 duced being able to discharge insulated condensers. In 

 this case we may look upon the electrodes as condensers, 

 and the breaking down of the air-insulation as being due 

 to the discharge taking place through the electrified gas. 



