866 Trof. E. Wiedemann on the Behaviour of Gases 





Air. 





Hydrogen. 



p 



+ 



- 



P 



+ 



- 



680 



1-15 



1-02 



680 



1-03 



0-90 



360 



080 



0-55 



350 



0-56 



0-58 



14-9 



0-40 



— 



126 



0-27 



0-25 



32-4 



016 



0-18 



34-6 



Oil 



o-io 



11 



006 



0066 



11-7 



0-055 



0-06 J" 



3-7 



0056 



0-065 



39 



0-060 



0-06 



0-4 



0-065 



0-081 



1-5 



0-063 



0-062 



X 



1-25 



1-01 



01 



0-26 



0-33 









X 



0-85 



0-50 



The numbers shoiv that, as the pressure diminishes, the quan- 

 tities of heat evolved diminish to a minimum and then rise again. 

 With hydrogen the heating is generally less than with air. 



Hydrogen and air show with alteration of pressure the same 

 change in the number of discharges. In general this was 

 less in air than in hydrogen, and larger when the positive 

 electrode was put to earth than when the negative electrode 

 was so connected. 



For example, hydrogen gave for the number of discharges : — 



p = 660, 45; p = 365, 75; p = 126, 180; p=®,h& 



At pressures from 90 millims. to ^ millim. the discharges were 

 not to be separated, since a sufficient velocity of rotation could 

 not be given to the mirror. Below the pressure of ■§• millim. the 

 apparently continuous band of light resolved itself into sepa- 

 rate luminous strips, the beginning and end of which were 

 especially bright; but these strips also were resolved into 

 single discharges as the exhaustion was continued. 



The number of discharges increases therefore as the pressure 

 diminishes, and then decreases again. 



The measurement of the number of discharges is ren- 

 dered very difficult at medium pressures by the extremely 

 feeble intensity of the light, especially when the negative 

 electrode is insulated. The colour of the conical discharge 

 radiating from the positive electrode is greenish-white in hy- 

 drogen at a pressure of 365 millims.; a red spot appears at the 

 positive electrode^ at the point of the cone. When the exhaus- 

 tion was carried far, the dark space round the negative electrode 

 expanded as far as the positive pole, which it intersected in a 

 circle. No positive discharge issued from within this space, 

 which remained perfectly dark. 



An increase in the number of discharges corresponds to a 

 decrease in the quantity of electricity in each discharge, and 

 consequently to a decrease in the potential before each dis- 

 charge, if the electrodes remain of the same shape ; but inas- 



