The Effect of the Electric Discharge on Water Vapotir. 143 
collected. About 3 cc. were collected over mercury and found to be 
inflammable. 
These results seem to point to a reduction of the water vapour, 
probably by aluminium-mercury-couple, formed from the aluminium in 
the presence of mercury, or perhaps even of mercury vapour, hydrogen 
being liberated and the aluminium being converted into the hydrate 
AIO3H3. This reduction, however, apparently cannot take place unless 
the discharge has passed at least once through the tube ; but once it has 
been brought about, it increases rapidly in magnitude. 
Experiments were made which showed that the presence of aluminium 
in contact with mercury vapour was solely responsible for the supposed 
reduction effect on the water vapour, but that the passage of a discharge 
at least once was always necessary before the effect occurred. Water 
vapour suffered no reduction if admitted into a new tube. A point of 
some interest noted in the course of these experiments was that the 
aluminium in the tube need not necessarily form one of the electrodes ; 
indeed it might even be quite removed from the direct path of the 
discharge. 
Elimination of the Becluction Effect. — With a view to eliminating the 
reduction effect, a discharge tube containing no aluminium, about 13 cm. 
long, with two platinum wire electrodes, was fitted. 
Vapour under its saturation pressure was allowed to stand in the 
apparatus on three successive occasions, and any reduction effect found to 
be totally absent. 
On passing the discharge through vapour under 0*9 mm. pressure, the 
tube being free of any platinum-black, the McLeod gauge indicated a small 
increase in pressure from 0-015 mm. to 0*017 mm. (Curve 1.) 
On repeating the experiment the results were as follows : — 
11.27 A.M. Same Quantity H2O admitted, and Discharge passed 
CONTINUOUSLY. 
Initial pressure : 0*000 mm. 
Time. 
Pressure as per Gauge. 
11.32 a.m. 
0-047 mm. 
11.39 
11.46 
11-54 
0-030 
0-020 
0-021 
(Curve 2.) 
10 
