OCCLUSION OF OXYGEX AXD HYDROGEN BY PLATINUM BLACK. 
153 
Julius Thomsen. We were never able to obtain the platinons hydrate perfectly free 
from chlorine in this way, and we were surprised to find that after drying at 100 ° G. 
it always contained more than the theoretical amount of oxygen, and that the oxygen 
appeared to increase with the time taken in drying. On heating at higher tempera¬ 
tures in a current of dry air, still further (quantities of oxygen were absorbed, but 
between 237° and 360° oxygen is again lost, reminding one of the behaviour of 
qdatinum black which begins to give off its oxygen at about 360° under ordinary 
atmospheric qiressure. 
Platinous hydrate apqiears to lose the bulk of its water at about 200°-250° C., and 
the oxide PtO so formed, begins to give off its oxygen very slowl}^ at 380° in vacuo. 
At 444° a large fraction of the oxygen may lie slowly pumqjed off^ as the following 
talile shows, but for its complete removal ignition at a red heat is necessary. 
First three hours at 444° 
Second day ,, ,, 
Third 
Fourth „ 
Fifth „ „ 
Sixth ,, ,, 
Exhausted at 460° 
,, „ a red heat 
8'50 cub. centims. extracted. 
15-45 
2-50 
J5 
5 > 
5? 
5 J 
3 3 
/•} 
1-39 
33 
1-02 
33 
3 5 
33 
35 
3.’ 
0-63 
4-56 
6-68 
33 
33 
33 
40-73 
A previous analysis of the same sample showed that 41*01 cub. centims. should 
have been obtained. 
Platinum black and platinous oxide in general appear to behave in pretty much 
the same way, except that when heated in vacuo the oxygen comes oft the oxide 
qiroper more slowly and at a slightly higher temperature. 
Although some important evidence might lead us to supqiose that the absorption of 
oxygen by platinum black is simjDly due to the superficial oxidation of the finely 
divided metal, the question cannot yet be regarded as definitely settled. 
What is either a very curious coincidence or the best argument in favour of the 
view that the occlusion of oxygen is simply suqDerficial oxidation is to be found in 
Thomsen’s'" determination of the heat of formation of qilatinous hydrate. 
According to Thomsen the reaction 
Pt + 0 + H 3 O = Pt(0H)2 + 179 K 
takes place with the evolution of 179 K for 16 grams of oxygen, whilst we found 
that the occlusion of the same quantity of oxygen by platinum black was accompanied 
by the evolution of 176 K, the water which is a necessary factor in the above reaction 
being always present in platinum black. 
* J. Tuomsen, ‘ Thcrmochcmisclie Uutcrsucliaugcu,’ Vol. 3, page 429. 
VOL. CXC.—A. 
X 
