OCCLUSION OF OXYGEN AND HYDROGEN BY PLATINUM BLACK. 
147 
The net result of these five operations is to fix the upper limit of the heat of occlu¬ 
sion of oxygen at 10 K per gram. From the fact that in Operation 4 some oxygen 
was extracted from the tube, we may suppose that at this stage most, if not all, the 
hydrogen had been removed as water, and that the number 15’8 is obtained because 
the effect due to true occlusion preponderates over that due to the formation of 
water. From the smallness of the quantity of oxygen occluded in Operation 5, no 
great reliance can be placed on the value 10 K, taken singly, but in all probability 
we are dealing in this case with true occlusion. 
In Operation 6, 47‘59 cub. centims. of hydrogen were admitted to the experimental 
tube still in the calorimeter, the heat evolved per gram of hydrogen absorbed being 
203'1 K. This number has an asterisk attached to it to signify that the results 
may be calculated in another way, namely, 47'59 cub. centims. = 0'00428 gram of 
hydrogen were absorbed, the heat evolved being 0’8698 K. Now, one gram of 
hydrogen on being burnt to water evolves 342 K, hence, if we assume that the whole 
of the 47‘59 cub. centims. of hydrogen were oxidised to water, the heat evolved 
should be 342 X 0'00428 = 1’4645 K. If the difierence, viz., 1'4G45 — 0’8698 
= 0'5947 K, represents the heat absorbed on removing 23'8 cub. centims. of oxygen 
from the platinum black, then the heat absorbed on the removal of one gram of 
oxygen will be 0'5947 -f 23'8 X 0‘00143 — — 16’8 K. This number approaches 
those obtained in Operations 1-4, but, of course, has the negative sign. The assumj)- 
tlon on which this number is calculated, viz., that the ivhole of the hydrogen added 
went to form water, cannot be justified, and hence this number cannot be regarded as 
the true amount of heat absorbed per gram of oxygen removed. 
The 47‘59 cub. centims. of hydroge]i added in Operation 6 were less than what is 
theoretically required for the complete removal of the oxygen contained in the 
platinum black, and, consequently, before Operation 7 was started, the platinum black 
was in pretty much the same condition as before the first operation, except that in 
all probability it contained a larger proportion of platinum hydrogen, since it had not 
been shaken up or exhausted at 184° C. This possibly explains why the values of 
the heat evolved per gram of oxygen absorbed in Operations 7, 8, and 9 are higher 
than in the corresponding Operations 1, 2, 3, and 4. 
In Operation 10 the platinum black was fully charged up. If this had been done 
in two stages, say, by adding 6 cub. centims. and then 1’64 cub. centims., the value 
for the last would probably have been much less than 14'4 K. The falling off in 
Experiment III. is otherwise very siniilar to that in Experiment I. 
In the fourth experiment hydrogen was added in successive stages. During Opera¬ 
tion 14, 10T4 cub. centims. of hydrogen were admitted, and on making connexion 
with the pump it was found that the vacuum was far from complete. Since the 
pressure within the apparatus was not known, it was impossible to estimate how 
much hydrogen was really absorbed, and how much was simply filling the experi¬ 
mental tube. About 8 cub. centims. altogether were pumped off. In Operation 15 
U 2 
