Electric Discharge in rarefied Hgdroqen and Oxygen. 30f> 



3 x 10 9 



AQ x ions, e being the electrostatic charge on each. 



If then we divide the number of molecules of hydrogen and 

 oxygen which disappeared by the number of ions which 

 readied each electrode and observe that Ng = l*22xl0 10 

 (Townsend, Phil. Trans. 1899), white in the present research 



A jo 

 S = 810 c.c, we get the number 1*5^4. . But 3 molecules 



of hydrogen and oxygen go to form 2 molecules of water. 

 Therefore a,, 



U - d AQ* 



That being so, if Ave find the slope (increase of ordinate 

 per centimetre-increase of abscissa) of one of the curves of 

 fig. 2, and multiply it by 3, we obtain the number of mole- 

 cules of water which result from the motion of a negative 

 ion through a centimetre of the positive column corresponding- 

 to the curve in question. Let iv denote this number of 

 molecules; then iv depends both on the pressure p of the 

 gas (namely that marked on the curve) and on the electric 

 force Y within the positive column. In fact w is the chemical 

 effect of the motion of a negative ion under the force Y 

 through hydrogen and oxygen at the pressure p. 



The fact that the chemical action per coulomb is for large 

 distances between the electrodes so much greater when the pres- 

 sure is very low than when the pressure is much higher, is now 

 easily explained by the hypothesis here adopted, namely, that 

 the ions dissociate into uncharged atoms those molecules which 

 they strike under favourable conditions and with sufficient 

 velocity, thus setting the atoms free to recombine into water. 

 At the higher pressures the free paths of the ions are smaller 

 than at the lower pressures. Now an ion acquires its 

 velocity of impact by moving freely under the electric force 

 between successive impacts. Hence at the lower pressures 

 an ion has greater velocities of impact, unless the electric 

 force is reduced in the same proportion with the pressure. 

 But in the positive column diminution of force does not 

 keep pace with diminution of pressure. Accordingly, though 

 at the lower pressures the number of the impacts made by an 

 ion in moving through a centimetre is smaller than at a 

 higher, yet the velocities of impact are greater. Hence it 

 follows that more molecules may be dissociated per centi- 

 metre in the positive column at a lower than at a higher 

 pressure, the fewness of the impacts at the dower pressure 

 Phil Mag. S. 6. Vol. 13. No. 75. March 1907. Z 



