1896.] Argon and Helium submitted to Electric Discharge. 261 



5. Cyanogen, prepared by heating mercuric cyanide. During the 



passage of the spark, decomposition occurred, and the tube 

 was covered with a thin film of a brownish deposit. The 

 results may have been vitiated by this, but the difference in 

 behaviour is still very striking. 



The band was broad and continuous at 23 mm. 



On increasing pressure, sparking occurred at 24 „ 



6. Nitrogen. — The nitrogen was made from air by withdrawing 



oxygen with phosphorus ; it therefore contained argon. The 

 transition with nitrogen was very difficult to observe. The 

 band was always ill-defined. The results are probably little 

 to be trusted. 



Sparks 59 mm. 



No sparks ; ill-defined " fluffy " band. ... 31 „ 

 Sparks beginning ; band still visible. ... 34 „ 



It may be taken that the point looked for lies between 31 and 

 34 mm., say 33 mm. 



7. Carbon Monoxide. — Prepared from formic acid treated with 



sulphuric acid. The transition was very clear. 



Continuous band, somewhat "fluffy ". . . . 49 mm. 

 Sparks beginning at ... ; 50 ,, 



8. Helium. — Free from hydrogen and nitrogen. Showed pure 



spectrum. Gas extracted from broggerite. 



Continuous band 766 mm. 



Sparks seen intermittently 1310 ,, 



Sparks ceased and band reappeared . . 1270 „ 



These results are summed up in the following table : — 



Pressure of 

 changes of character 

 Gas. of discharge. 



Air 73 or 74 mm. 



Hydrogen 42 or 43 ,, 



Oxygen 81 „ 



Carbon dioxide 92 or 94 „ 



Cyanogen 23 ,, 



Nitrogen 33 „ 



Carbon monoxide 49 „ 



Helium 1270 



These phenomena are, without doubt, very complex ; but one fact 

 is unmistakable : that helium presents a behaviour very different 



