OCCLUSION OF OXYGEN AND HYDROGEN BY PLATINUM BLACK. 
143 
A still being kept hot, the tube B was similarly exhausted at a red heat, and the gas 
collected separately. 
The composition of the gases obtained in this way is shown by the following- 
analysis — 
Gas from tube adjacent to pump. 
Gas from tube B, adjacent to burette. 
COo 
1'91 cub. centims. = lO'O vols. 
1-14 cub. centims. — 8-8 vols. 
0 ., 
2-94 „ „ =23-7 „ 
0-00 „ „ = 00 „ 
H, 
0'40 ,, ,, = 3-2 ,, 
7 36 ,, „ = 56 0 „ 
Total . . 
6-2.5 „ „ =42-4 „ 
8-50 „ ~ „ = 65-4 „ 
These results confirm our previous statement that when a limited quantity of 
hydrogen is admitted to platinum black containing oxygen, it simply removes the 
oxygen, as water, from that portion of the platinum black with which it first co-mes 
into contact, and then takes its place ; for it will be seen from the above Table that 
the platinum black in the tube adjacent to the burette contained an excess of hydrogen 
associated with it, whilst the portion next the pump contained an excess of oxygen. 
Precisely the same thing, but only in reversed order, takes place when oxygen is 
admitted to platinum black charged with hydrogen, as an experiment performed in 
the converse way clearly showed. 
These results show that, in the case of the fii'st experiment which led to tlieir l)eing 
performed, we may have a given quantity of platinum blamk containing both, what we 
may be permitted provisionally to call, p/atdnnri oxygen and hydrogen, but 
they give us no trustworthy indication of how much of each is present; for, it is 
more than likely that on heating, some of the oxygen from the platinum ox^^gen 
combines with some of the hydrogen from the platinum hydrogen forming water ; 
and that the free gases finally obtained are only the portions which from accidental 
circumstances escape the catalytic action of the platinum. 
The quantities of platinum oxygen and platinum hydrogen existing in the same 
sample are thus probably greater than the above experiments seem to indicate. 
V. The Heat of Occlusion of Oxygen hy Platinum Black. 
Having failed in the preparation of a sample of platinum black which would 
occlude oxygen directly at 0° C., and so enable us to determine directly the heat of 
occlusion of oxygen, our only alternative was to remove as much of the oxygen as 
possible by charging with hydrogen and then to make allowance for the heat due to 
the formation of water in subsequent^ charging with oxygen. 
All the experiments made in the preceding section go to show that if a portion of 
