Disappearance of Gas in the Electric Discharge. 921 



passes. Again, the substitution of a filament of half the 

 length, designed for half the voltage, produced no change in 

 P, nor did the use of a separate anode and cathode similar to 

 the arrangement shown in fig. 1 of (I.). If electrodes of area 

 comparable with that of the glass walls were used, such as 

 those of a thermionic valve, changes in P undoubtedly 

 occurred ; but they are .to be attributed rather to changes in 

 the form of: the vessel than to changes in the nature of the 

 discharge. In discussing the other factors, factor (5) may 

 be left out of account. 



It should be mentioned that experiments made on different 

 batches of lamps, in all respects apparently the same, never 

 agreed so perfectly in the determination of P as those made 

 on a single batch. This variation is unexplained. 



Factor (7), the temperature of the vessel, does not appear 

 to be important, at any rate if the variation of the tempera- 

 ture is confined between 0° and 30° ; but no systematic 

 observations on this matter have been undertaken. It is 

 possible, but not probable, that some part of the unexplained 

 variations are due to a secondary influence of temperature. 

 Factor (6), the form of the vessel, undoubtedly has some 

 effect ; it appears generally that the amount of gas that can 

 be absorbed by a given amount of phosphorus increases 

 somewhat with the area of the walls exposed to the action 

 of the discharge. If the vessel in which the discharge takes 

 place is merely connected by a narrow tube with another 

 vessel, the weight of gas that can be absorbed with a given 

 weight of phosphorus is unchanged ; but if the same electrode 

 system (e. g. the lamp filament) is placed in a larger bulb of 

 approximately the same shape, the weight absorbed with a 

 given weight of phosphorus is increased. But again no 

 systematic measurements have been undertaken. 



6. There remains the important question whether P is 

 really an adequate measure of the amount of gas that can be 

 absorbed. It will be so only if the amount absorbed is 

 independent of the starting pressures; or, in other words, if , 

 starting from a pressure P +p, the final pressure reached is 

 always p, whether ^? is (as in the method described) or is 

 comparable with P. The experiments that have been made 

 indicate that the amount absorbed is so independent of the 

 starting pressure within wide limits. They were made by 

 the use of the Pirani gauge. Table I. gives two typical 

 series of results made in vessels of different volumes with 

 different amounts of phosphorus. The first column gives the 

 starting pressure P + p, the second the final pressure p, the 



