304 Rev. P. J. Kirkby: Chemical Effects of the 



by the curves in each figure corresponding to the pressures 

 2*1, 1*05 mms.; the pair of curves corresponding to each of 

 these pressures begin their approximately uniform upward 

 slope when the distance between the electrodes exceeds about 

 the same value. If the chemical combination is the result 

 of, and is proportional to, the number of molecules dissociated 

 by the collision of the ions, the proportion contributed to the 

 whole observed chemical reaction by each strip of the dis- 

 charge must depend upon the electric force within that strip. 

 That being so, we could only account completely for the 

 forms of the curves of fig. 2, just as we could only account 

 for the forms of the curves of fig. 3, by a complete knowledge 

 of the distribution of force in the neighbourhood of the 

 cathode. But the portions of the curves of both figures, 

 where their slope is practically constant, are explained on the 

 same lines. When the distance between the electrodes is 

 great enough, any further separation of them, the current 

 and pressure constant, merely extends the positive column 

 without altering its character. That being so, the final and 

 nearly uniform slope of the curves of fig. 2 gives the chemical 

 action per coulomb that takes place in a centimetre of the 

 positive column. Now this chemical action cannot be due 

 to the positive ions which are generated by collision within 

 the positive column : if it were, the slope of the curves 

 (fig. 2) would not become constant, but would become 

 proportional to the length of the positive column, and the 

 chemical action to the square of its length. Hence unless 

 positive ions are generated near the anode in large numbers, 

 the chemical action within the positive column must be 

 attributed exclusively to the negative ions ; and then it is 

 easy to calculate the number of molecules of water which 

 result from the motion of a negative ion through a centi- 

 metre of the positive column. 



In the first place, let W denote, as in my previous papers, 

 the number of molecules of water, whose formation is the 

 effect of the motion to the electrodes of each pair of ions ; 

 then it is very easy to show that, with the present apparatus, 



W = 3 -rye almost exactly. 



For let N be the number of molecules in a c.c. of gas 

 under normal temperature and pressure, then in a vessel of 

 capacity S a fall of pressure Ap means the disappearance of 



7«n — molecules, while AQ coulombs is carried by 





