178 



Dr. Karl Przibram on the 



between 100 and 600 mm. of CO2 the potential-difference 

 seems nearly independent of the composition of the mixture 

 and then drops down to 3()00 volt in pure OO2. There is no 

 alteration in the luminosity, which, in this case, remains a 

 mere star at the point, somewhat brighter than when the 

 point is positive. 



These facts having been established for CO2, a number of 

 other gases were tested and in most cases the same results 

 were obtained. The lowering of the potential-difference for 

 the positive point-discharge and the appearance of a long 

 brush was observed in mixtures of 



CO2, CI2, CO, NH3, H2S with air, and of CO2 with Hg. 



All these gases gave about the same drop of potential of 

 200 to 300 volts. The effect could not be observed in mixtures 

 of N2 with H2, and of CI2 with OO2. 



The figures show the curves giving the connexion between 

 the potential-difference, in units of 100 volts, and the partial 



pressure of the mixture, in cms. of mercury. 



Fig. 1 



for a 



+3600 V. 

 H. 



-2600 Y. 



+4500 V. 

 Air. 



-3700 v. 



Fig. 2. 



Fio-. 1. 



mixture of air and COq. Fig. 2 for hydrogen and nitrogen 

 and CO2 respectively. 



In all cases the light from the brush was too weak to allow 

 spectroscopical analysis. But if the gas admitted was CO, 

 the colour appeared decidedly different to the naked eye, 

 the brush having a greenish tint, whilst it was more violet in 

 all other cases. 



A number of organic vapours were tried next. Air which 

 had been standing over the liquid concerned, so as to get 

 saturated, was blown in varying quantities into the vessel. 



