The Effect of the Electric Discharge on Water Vapour. 153 
(15) DiSCHAEGE PASSED THROUGH H^O UNDER 17 MM. (SATURATION) 
Pressure (Trap being open, and Mercury at b just wet.) 
Times. 
12.5 
12.6 
12.10 
12.24 
1.27 
1.37 
noon. 
Pressure. 
0-000 mm. 
0-002 
0-081 
0-40 
0-98 
0-98 
Temperature. 
19-80° C. 
19-80 
19-85 
19-80 
19-80 
19-80 
Curve 21 ((Q shows how the maximum pressure due to electrolytic gas 
produced by the passage of the discharge varied with the pressure under 
which the water vapour was admitted into the apparatus. Up to that 
critical value of the pressure under which the vapour was admitted, at 
which the passage of the discharge brought about the disappearance of the 
coloration, the maximum pressure due to gas increased with increasing 
pressure under which vapour was admitted. At the critical value referred 
to there was a turning-point, and the pressure due to gas fell slightly for 
a certain range of water-vapour pressures, till a second critical value of the 
latter quantity was reached. Beyond this point the maximum pressure 
due to electrolytic gas increased rapidly and linearly with the pressure 
under which vapour was admitted, till this quantity reached the value of 
" saturation pressure." 
Curves 21 (a) (b) (c) (e) show how^ the maximum pressure due to 
electrolytic gas varied with the pressure under which water vapour was 
admitted for temperatures of 15^ C, J 5-6° C, 18*7° C, and 23° C. respec- 
tively. Their general nature is similar to that for 19*8° C, except in the 
case of 21(rt), in which the portion of the curve between the two critical 
points is horizontal. 
The gradients of the curves near the origin increase with increase of 
temperature. The gradients of the curves beyond the second critical point 
appear to be independent of the temperature. 
The maximum pressure of gas formed by the passage of the discharge 
through vapour under saturation pressure diminished as the value of the 
saturation pressure increased, and appeared to do so according to a well- 
defined law. This variation was investigated. The discharge was passed 
through vapour under saturation pressure at other temperatures on several 
occasions. The final pressures of gas formed in various instances are 
shown in 21. From the results obtained it seems that the pressure of gas 
produced was almost independent of the value of the saturation pressure. 
