HYDROGEN AND OXYGEN IN CONTACT WITH HOT SURFACES. 
55 
At the conclusion of VIII., the residual gas was as rapidly as possible pumped out 
of the apparatus, and the rate for normal electrolytic gas immediately afterwards 
determined (Experiment IX.). The “hydrogenised” surface was now much more 
than normally active, and the values for “ k” remained nearly constant throughout. 
This shows that after a certain degree of “ hydrogenation ” of the surface, the rate of 
combination is practically proportional to the pressure of the dry gas. 
Experiment IX.* 
June 15, 1905. 
Normal electrolytic gas over “ hydrogenised” surface. 
t . . . . 
0 
1 2 
3 
4 
5 hours. 
p . . . 
505-6 
363-7 257-6 
179-3 
122-1 
78 - 2 millims. 
h . . . 
— 
0-1430 0-1464 
0-1501 
0-1543 
0-1621 
In the final experiment of the series, a mixture corresponding to H 2 + 30 2 was 
employed. I he excess of oxygen, however, almost prevented any combination, the 
pressure in the apparatus only falling from 504'8 to 503'0 millims. during the first 
hour (/'| j = 0'0042). This result, taken in conjunction with the results of the three 
preceding experiments, proves that the catalytic process depends in no way upon 
occluded oxygen, or superficial oxidation of the metal, but rather upon an association 
of the surface with hydrogen. A microscopic examination of the gauze at the 
conclusion of the above series of experiments revealed nothing indicative of any 
chemical action on the metal ( e.g ., hydride formation). There had been no pitting of 
the surface, as in the case of silver, nor were the mechanical properties of the metal 
at all impaired. 
Summarising the results obtained with the four metals examined, we find a 
substantial agreement in respect of four important particulars, namely, (I) that the 
catalytic action is m each case primarily due to an association of the surface with 
hydrogen in the case of silver probably to the formation of an unstable hydride, in 
the other three cases to an occlusion of the gas; (2) that with normal electrolytic gas 
the rate of combination is proportional to the pressure of the gas; (3) that whereas 
the activity of a surface may always be stimulated by previous exposure to hydrogen 
at modelately high temperatures, oxygen per se has no such accelerating influence, 
but rather, owing to its “ dehydrogenising” action, the reverse; (4) that when an 
excess of either gas is present, the rate of combination is nearly proportional to the 
It was at the conclusion of this experiment that the apparatus was continuously exhausted at 220 J 
foi tlnee days in order to as far as possible “ dehydrogenise” the gauze in preparation for Experiment VI. 
(June IS, 1905). Ihe result of this operation was to greatly reduce the activity of the surface (vide 
Experiment VI.), where h = O'0122 for the first hour. 
