OCCLUSION OF OXYGEN AND HYDROGEN BY PLATINUM BLACK. 
been previously removed from the platinum before starting. This experiment is, 
perhaps, not quite conclusive, but we think, from the general behaviour of platinum 
black, that it had already, from the very beginning, absorbed or occluded its quantum 
of water, and that this is not affected by placing the platinum in a vacuum, or by 
condensing more dew on its surface. 
This assumption was confirmed by surrounding the bulb of a Beckmann thermo¬ 
meter in an ordinary calorimeter with 5 grams of platinum black, dried at 100 G. 
When the temperature had become steady, the platinum black was moistened with 
water at the same temperature, injected from the outer bath of the cal or line tei, but 
no definite rise or fall of temperature could be detected. 
After charging up fully with oxygen, in Operation 20, the experimental tube 
was removed from the calorimeter, the platinum black tiansfeiied to a haid-glass 
tube, exhausted at the ordinary temperature, and then heated to redness in vacuo. 
21-67 cub. centims. = 0-03098 gram of oxygen were pumped off at a red heat, and 
this represents the amount of oxygen which was actually occluded in Opeiations 25 
and 26. 
So far we have not been able to obtain any very definite direct value for rlie heat 
of occlusion of oxygen, except that in Operations 5, 10, and 23 we found approximate 
values, viz., 10-0, 14-4, and IDS K per gram of oxygen occluded. 
With the data which we possess, however, and knowing that during the last process 
of charging with oxygen 21-67 cub. centims. of oxygen were occluded, we can calcu¬ 
late the heat of occlusion indirectly. 
(l.) In Experiment VII., lO'SO cub. centims. of oxygen were used, and of this 
21-67 were actually occluded, whilst the remainder, 10-13 cub. centims., must have 
been burnt to water. Now, on combustion, 19-13 cub. centims. = 0 02735 gram 
oxygen should jiroduce - —- = 1-1695 K. But, during the combustion, 
2 X 19-13 = 38-26 cub. centims. = 0-003443 gram of hydrogen must have been 
removed from the platinum black, and since 69 K are absorbed on the removal of 
1 gram of hydrogen, the removal of 0-003443 gram should absorb 0-003443 X 69 
= 0-2376 K. 
If, therefore, the heat of formation of water minus the heat absorbed on the 
removal of the hydrogen, i.e., 1-L695 — 0--2376 = 0-9319 K, represents all the heat 
clianges which take place, with the exception of the heat evolved or absorbed on the 
occlusion of 0-03098 gram of oxygen, then the difference between the actual heat 
developed, viz., 1-2763 K and 0-9319 K, i.e,, -j- 0-3444 K, represents the heat evolved 
on the occlusion of 0-03098 gram of oxygen, or 11-1 K are evolved per gram of oxygen 
occluded. 
This number is in good agreement with those indicated by the preceding nioie 
direct measurements. 
