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



AQ = the quantity o£ electricity measured in coulombs 

 which passed, namely, the product of the mean 

 current and its duration. 

 X = the mean potential-difference of the electrodes 



during the discharge. 

 D = the distance in centimetres between the parallel 

 plate electrodes. 

 The mean current used throughout was approximately 

 constant and '00275 ampere. 



The capacity * of the apparatus where Ap was observed 

 was 840 c.c. 



These tables show that when the distance D between the 

 electrodes is large, the weight of water formed per coulomb 

 passed through the gas is greater for the lower pressures 

 than for the higher. Thus the amount of the chemical 

 reaction is by no means proportional to the concentration of 

 the gases. On the contrary, the amount of the reaction per 

 coulomb is absolutely increased, and very substantially in- 

 creased, by diminishing the pressure down to about 1*4 mm. 

 provided that the distance between the electrodes exceeds a 

 certain value. When the pressure falls below 1*4 mm., the 

 reaction per coulomb becomes less. The greatest effects 

 were observed at 1*4 rams, pressure. 



The tables are illustrated by the curves now given (p. 298). 



The abscissas in these curves are the distances between 



the electrodes measured in centimetres. The ordinates are 



the values of -r^, and therefore measure the chemical 

 AQ' 



reaction per coulomb passed through the mixed gases. 



Each curve is determined by one of the tables and so 



corresponds to a definite mean pressure, which is marked 



upon it. But, to avoid confusion, only four of the tables are 



represented. With a battery whose voltage was less than 



2000 it was not found possible to extend the curve for the 



pressure 9 '3 rams., even with the help of an induction-coil 



in starting the discharge, because the current did not at 



once assume its steady value, and so accurate measures both 



of AQ and of X were out of the question. It will be seen 



A» 

 that j^£r is always roughly the same when D is very small. 



For a given pressure -r-4- rises in a well-marked way up to 

 a certain point, while the distance D between the electrodes 



increases to about 2 cms. After that, the rise in -—£- is very 



AQ 



* This was measured by comparing it with the capacity of a glass 

 bulb through an obvious application of Boyle's Law. 



