﻿by Elements in the Electric Discharge- Tube. 219 



Observations were then taken of the changes in pressure 

 due to the disappearance o£ the hydrogen when an electric 

 discharge passed through the gas. The results obtained are 

 shown in the accompanying table. 



The accelerating potential was 94 volts, obtained by using 

 small accumulators. The current through the tube was kept 

 constant, and was 546 micro-amps. 



Each set of readings corresponds to an electric discharge 

 for ten minutes, except in the cases of sulphur, phosphorus, 

 and iodine, where the observations were taken at intervals 

 of two minutes — i. <?., with sodium the pressure changed 

 from 743 xlO" 3 mm. of Hg. to 336 x 10" 3 mm. of Hg. in 

 ten minutes, while with sulphur the pressure was lowered 

 from 740 xlO" 3 mm. of Hg. to 329 x lO" 3 mm. of Hg. in 

 two minutes. 



The amount of hydrogen which would be liberated from 

 a water voltameter in 10 mins. by the same current is 

 39 x 10~ 3 c.c. at atmospheric pressure. 



As the gas may disappear into the walls of the anode 

 even in the absence of any substance on the anode, and 

 as the glowing filament may affect the rate of disappearance, 

 preliminary observations were always made when an electric 

 discharge passed through the tube without the substance 

 present on the anode. The volume of gas which disappeared 

 owing to these two effects was always very small compared 

 with that which was absorbed when the element under test 

 was on the anode. 



3. Experimental Results. 



After each element had been tested, the tube was heated 

 to 300° C, and the volume of gas reliberated was calculated 

 from the observed change of pressure. The amount thus 

 recovered varied considerably, but was always less than that 

 which had disappeared. This evolved gas was again absorbed 

 when a discharge was passed, and it is evidently hydrogen 

 in the same condition as it was before disappearance. 



If, after the gas had disappeared, a fresh amount of 

 hydrogen was admitted, the volume which disappeared on 

 discharge was reduced. For example, with sodium and the 

 gas pressure at 743 X 10" 3 mm. of Hg., the vacuum was 

 reduced to 96xl0" 3 mm. Hg. before the action ceased. 

 Admitting a further supply of gas to the tube, the pressure 

 fell from 743 xlO" 3 mm. Hg. to 233 xlO" 3 mm. Hg. 

 Repeating the process again, the pressure fell from 

 743 xlO" 3 mm. Hg. to 436 x 10" 3 mm. Hg., and then the 



