HYDROGEN AND OXYGEN IN CONTACT WITH HOT SURFACES. 
21 
The catalysing power of the surface was, therefore, greatly stimulated by previous 
exposure to hydrogen at 430°, the stimulus being the more marked and enduring the 
longer the surface had been subjected to the action of the gas. Moreover, the great 
contrast between the rates observed, according as the surface had been previously 
treated with hydrogen or oxygen, is very striking. The stimulus imparted by the 
40 hours’ preliminary treatment with hydrogen in Experiment XV. gradually wore 
away when successive charges of electrolytic gas were circulated over the surface, 
until finally it was restored to its normal condition. 
In the next three experiments (XVI. to XVIII. inclusive), the stimulating influence 
of hydrogen was very marked. In Experiment XVI., after a preliminary treatment 
of the surface with oxygen at 430° for 48 hours, the rate of combination observed 
was almost exactly normal (compare Experiment XII.). In Experiment XVIII., the 
usual procedure was somewhat modified in that after the 24 hours’ preliminary 
treatment with hydrogen the apparatus was continuously exhausted for 18 hours, 
the combustion tube being kept at 430° the whole time. It is evident from the 
results that the imparted “ stimulus” survived this long exhaustion. 
Experiment XVI. 
May 12 to 14, 1904. 
Preliminary treatment with oxy¬ 
gen at 430° for 48 hours. 
Rate of circulation = 1 in 35 
minutes. T = 430°. 
Experiment XVII. 
May 16 to 19, 1904. 
Preliminary treatment with hy¬ 
drogen at 430 for 72 hours. 
Rate of circulation = 1 in 35 
minutes. T = 430°. 
Experiment XVIII. 
May 30 to 31, 1904. 
Preliminary treatment with hy¬ 
drogen at 430° for 24 hours. 
Rate of circulation = 1 in 35 
minutes. T = 430°. 
t. 
P. 
t. 
P. 
h. 
t. 
P. 
h. 
hours. 
0 
2 
4 
6 
8 
millims. 
412-7 
347-5 
289-5 
244-0 
208-7 
0-0373 
0•0385 
0-0380 
0-0370 
hours. 
0 
2 
4 
6 
8 
millims. 
405-2 
304-3 
225-4 
175-8 
138-0 
0-0622 
0-0637 
0-0604 
0-0585 
hours. 
0 
2 
4 
millims. 
298-8 
233-8 
181-3 
0-0543 
0-0542 
The ratio hydrogen/oxygen in the gas withdrawn from the apparatus at the end of 
Experiment XVII. was 2T38, a circumstance which certainly indicates some occlusion 
of hydrogen in the pores of the porcelain during the long preliminary treatment. 
The stimulus caused by the hydrogen in this experiment gradually wore away as 
successive charges of electrolytic gas were circulated over the surface during the next 
18 hours, until finally it was restored to its normal condition. 
At Red Heat. 
Whilst the preceding experiments leave no room for doubt but that the catalytic 
action of porcelain is connected with a preliminary change in which the hydrogen is 
