59 
HYDROGEN AND OXYGEN IN CONTACT WITH HOT SURFACES. 
11 millims. only. These results were fully confirmed in the 3rd group of experiments 
at 200° in which a new surface of the freshly calcined material was used. 
3 rd Group. 
The rate of combination for normal electrolytic gas over the new surface at 200° 
corresponded to the disappearance of 27 -4 per cent, of the original gas during the 
first hour (k, = 0*140). The ratio H 2 /0 2 for the residual gas at the end of three 
hours was 2 - 0 exactly. 
On circulating pure hydrogen over the surface at 200° the pressure fell from 449-5 
to 420-4 millims., or by 6*5 per cent, only, during the first hour. After the surface 
had been reduced at 300° by several successive full charges of hydrogen, oxygen was 
finally circulated over it at 200°. The pressure now fell from 486’9 to 460‘5 millims., 
or by 5*4 per cent, only, during the first hour. 
B. Experiments with Nickel Oxide. 
For these experiments, the combustion tube of the apparatus was packed with 
porous lumps of grey oxide of nickel containing 99 per cent, of NiO. After some 
preliminary trials a temperature of 160° was selected as fulfilling the condition that 
the gases would combine with fair velocity without the surface itself undergoing any 
permanent reduction or oxidation. In all the five experiments of this series the rate 
of circulation was 1 in 35 minutes. 
Experiment I, with normal electrolytic gas, gives the “ normal” value of “ k” for 
the series, and also proves that the rate of combination was proportional to the 
pressure of the dry gas. In Experiment II, an original mixture H 2 + 20, was 
employed; from the values “ k R ” it will be seen that the surface was no more than 
normally active, and that the rate of combination was determined by the partial 
pressure of the hydrogen throughout. Experiment III., which gives the rate for 
normal electrolytic gas after the residual oxygen from II. had been circulated over the 
surface at 200° for 48 hours, proves that its catalysing power had remained unaltered. 
Proof that the catalytic process had not involved any permanent reduction or 
oxidation of the surface was afforded by the analysis of samples of the gas shut off at 
regular intervals during the course of Experiments I. and II. The ratios H 2 /0„ for 
the samples in I. varied between 2-05 and 2*10 only, whilst for the samples obtained 
in III. they were all 2'00 exactly. The falls in pressure obtained during the first 
hour m these two experiments corresponded with the disappearance of 20-4 and 20-7 
per cent, respectively of the original gas. Moreover, the values of “ k-^ ” in Experi¬ 
ment II. show that the excess of oxygen had no accelerating effect on the rate of 
disappearance of the hydrogen (exactly 20 per cent, of it disappeared during the first 
hour). 
