HYDROGEN AND OXYGEN IN CONTACT WITH HOT SURFACES. 
33 
The apparatus was then cooled and thoroughly exhausted at the ordinary 
temperature. It was again heated to redness, when about 5 cub. centims. of hydrogen 
were extracted. Experiments on the absorption of oxygen at red heat gave entirely 
negative results. 
Summarising now the above results, it is evident that (1) with normal electrolytic 
gas the rate of combination is proportional to the pressure of the dry gas, (2) when 
an excess of either of the reacting gases is present, the rate is determined mainly by 
the partial pressure of the hydrogen, and (3) the catalysing power of the material is, 
on the one hand, greatly stimulated by hydrogen, but, on the other hand, diminished 
by oxygen. These considerations, together with the fact that the material occludes 
hydrogen but not oxygen at red beat, show that its catalytic action must be referred 
to its power of occluding hydrogen. 
Part III. —Experiments with Silver. 
In selecting silver as the first metallic surface for investigation, we had in view two 
considerations, namely (l) the instability of its oxides above 350°, # and (2) its 
relationship to sodium and copper, which suggest the possibility of its forming a 
hydride at high temperatures, f For most of the experiments, the metal was 
employed in the form of a gauze of 23 strands per centimetre, each strand having a 
diameter of 0T8 millim. a final series of experiments was, however, made with foil 
prepared from “assay” silver. 
First Series with Silver Gauze at 400°. 
Throughout the first series of six experiments, the temperature of the combustion 
tube was 400°, and the rate of circulation 1 in 60 minutes. The weight of silver 
gauze employed was 62 grammes, and the area exposed to the reacting gases would be 
about 430 sq. centims. 
At the outset of the series, successive charges of normal electrolytic gas were 
continuously circulated over the heated gauze for 12 hours, its catalysing power 
gradually increased, by about 30 per cent., up to a steady maximum, which was 
considered to represent the “normal” condition. The rate of combination was then 
determined as follows :— 
* According to Carnelly and Walker (‘Trans. Chem. Soc.,’ 1888, vol. 53, p. 79), the decomposition 
of Ag 2 0, which is rapid between 270° and 300°, is quite complete between 300° and 430°. 
f The recent experiments of Leduc (‘Comp. Rend.,’ 1902, vol. 135, p. 1332, and 1903, vol. 136, 
p. 1254) have shown that copper forms a stable hydride at temperatures below red heat, where the tension of 
dissociation only becomes appreciable at temperatures when the metal rapidly absorbs oxygen from the air. 
| The gauze, which was kindly supplied by Messrs. Johnson and Matthey, was made of the purest 
obtainable wire. We made a careful chemical analysis of about 10 grammes of the gauze, but were unable 
to detect the presence of any impurity. Both copper and bismuth were specially tested for. 
YOL. CCYI.-—A. 
E 
