Disappearance of Gas in the Electric Discharge. 603 



be well to consider first carbon monoxide in the absence of 

 phosphorus, for bore the most definite and illuminating 

 results have been obtained. 



The carbon monoxide was prepared from sulphuric and 

 formic acids and stored over water ; it probably, therefore, 

 contained a trace of air, but other likely impurities would 

 be removed by the liquid-air trap Tj. When the apparatus 

 was arranged as in fig. 1, it was found that practically no 

 change of pressure occurred when the filament was heated 

 to 2000° K. so long as V was less than V^. But as soon as 

 Vg was exceeded and the glow appeared, the pressure began 

 to decrease, it' it lay initially between 0*1 and O'OOl mm., 

 and the gas disappeared. A large number of observations 

 were taken on the relation between the rate of decrease of 

 pressure and the values of V and i ; but, for a reason which 

 will appear presently, it is not proposed at present to 

 consider them in detail. In general, it may be said that the 

 rate of decrease increased, as might be expected, when i 

 was increased, either by increasing V or by increasing the 

 temperature and thermionic emission of the filament. 

 Further, an increase in V in general increased the rate of 

 disappearance even if i was unchanged, though there were 

 some exceptions to this rule ; sometimes there was an 

 optimum value of V at which the rate of decrease was a 

 maximum. With the very crude spectroscopic arrangements 

 employed, no lines except those of the ordinary carbon 

 monoxide spectrum could be detected. 



The disappearance of gas continued in all cases until the 

 pressure became so low that the potential applied could no 

 longer maintain the discharge. V did not usually exceed 

 300 volts, and with this potential the glow ceased at about 

 0*0008 mm. If the potential were maintained after this 

 limit was reached, a further slight decrease to 0*0006 mm. 

 occurred, the ultimate limit depending on the potential ; the 

 lowest limit was reached when V was about 200 volts, 

 slightly higher limiting pressures being reached with either 

 higher or lower potentials. Since some of the gas which 

 disappears is undoubtedly contained on the walls of the 

 lamp, it is thought that this limiting pressure represents a 

 balance between the disappearance of gas and its evolution 

 from the walls by the action of the discharge. 



By admitting fresh gas to replace that which had dis- 

 appeared, the process could be continued apparently without 

 end and without any marked change in the rate of dis- 

 appearance. A slight wastage of the filament occurred and 

 the walls became slightlv blackened, but no simple relation 



2K2 



