630 Relation between P. D. and Spark-length. 



Table X. — Platinum in H and C0 2 . 



Hydrogen. 



Carbon dioxide. 



Distance, 

 X. 



Potential, 

 volts. 



Distance, 

 X. 



Potential, 

 volts. 



15 



2 



25 



2-5 



3 



4 



6 

 10 

 125 

 15 

 29 

 37-5 

 50 



175 



242 

 275 

 275 

 280 

 285 

 285 

 285 

 285 

 285 

 290 

 320 

 365 



1-2 



2 



2-7 



34 



3-7 



5 



75 

 10 

 12-5 

 15 

 25 

 375 



140 

 255 

 320 

 390 

 420 

 420 

 420 

 420 

 420 

 430 

 465 

 515 



hydrogen, 10*3 mm. at 1 mm. distance and 280 volts, and 

 for C0 2 , 5'03 mm. at the same distance and 420 volts, the 

 calculations can be made for the distances at which the curves 

 should rise above the minimum potential abscissae. These 

 calculations give 28 X for hydrogen and 12*5 X for C0 2 , which 

 agree almost exactly with the experimental values obtained 

 (see fig. 9). 



(4) The lag which is characteristic of the discharge at 

 higher potentials disappears entirely for distances below the 

 elbow. 



Y. Summary. 



(1) With one spherical and one plane electrode, at constant 

 pressure the spark-potential is directly proportional to the 

 distances between the electrodes, until the potential reaches 

 the minimum value for the gas. 



(2) In any gas the potential of discharge reaches its mini- 

 mum value for the gas at distances which are inversely 

 proportional to the pressures existing between the electrodes. 



(3) For the same electrodes the discharge in air at distances 

 from zero to about Sjul is wholly independent of the pressure 

 or of the nature of the gas between the electrodes. 



(4) For the same electrodes the distances at which the curves 

 assume a horizontal slope are proportional to the minimum 

 spark-potential of the gas between the electrodes. 



(5) When a discharge of electricity occurs between two 



