Absorption of Gas in a Crookes Tube, 



507 



a pressure of 1 mm., the mass of air which was absorbed 

 increased as the pressure was diminished down to about 

 •5 mm., when the rate of absorption gradually decreased. 

 This presence of a maximum effect was, however, proved to 

 be due to the electrodes not being clear of gas, and this being- 

 given off masked the effect it was desired to measure. The 

 later experiments always showed that the lower the pressure 

 the quicker the rate at which gas was absorbed, the current 

 every case. 



Fiar. 3. 



being the same in 



70 









\ 

















60 









\ 























\ 

















€0 

 40 









\ 























\ 







































30 















































20 

 10 

 





































































eo 



40' 



60 



80 100 120 



Pressure 



180 ZOO 220 



Fig. 3 shows the effect of a constant current at different 

 pressures. The abscissae are pressures ; the ordinates are 

 proportional to the mass of gas absorbed in thirty minutes 

 when the mean pressure has a value given by the corre- 

 sponding abscissa. 



3. A cylindrical tube of soda-glass provided with aluminium- 

 wire electrodes was first used. From an extensive series of 

 readings, the rate at which it ran down * was determined for 

 pressures varying from 1 mm. downwards. In doing this a 

 considerable quantity of gas was caused to disappear. The 

 tube was then strongly heated for several hours by a Bunsen 

 burner : only a very small fraction of the gas reappeared. 

 (This was found to be the case afterwards when a still stronger 

 heating was applied to the broken tube enclosed in combustion- 

 tubing.) If this was again absorbed by means of the current 

 and the heating again performed, still less came off; and by 

 repeating this several times scarcely any could be driven off 

 at last, but on admitting fresh gas it was found that the 



* I have used the term " running do wu " to denote the lessening of the 

 pressure due to the continued passage of the discharge. 



2 Li 2 



