138 
DRS. L. MONI), W. RAMSAY, AYD J. SHIELDS OX THE 
III. On some Attempts to remove the Oxygen from Platinum Blach without des¬ 
troying its Occlusive Power [Occlusion SO. 2 , CO, NH 3 , &c.). 
As far as we know the thermal change which takes place when oxygen is occluded 
by platinum black has never been measured. In 1883 the attempts which Bes- 
THELOT made in this dmection proved fruitless. We have already pointed out that 
platinum black, as usually prepared, invariably contains oxygen which cannot be 
removed by heating in vacuo without destroying the black and converting it into 
sponge, and consequently we tried a large number of experiments, having for their 
idtimate object the removal of the oxygen from platinum black, or, in other words, 
the preparation of a samiDle which per se at 0 ° C. would occlude oxygen directly. 
All our attempts to prepare such a specimen have hitherto been unsuccessful, but 
some of them which are interesting in themselves may be briefly recorded here. 
Sulphur dioxide. —One of the first of these was to treat platinum black with 
sulphur dioxide, in the hope that the sulphur trioxide formed, along with an}" 
occluded sulphur dioxide, might be completely extracted in vacuo at a temperature 
v.diich would not impair the absorptive power of the platinum black for oxygen. 
It was found, however, that although practically all the oxygen was removed 
as SOg in this way, the platinum black itself vras charged with 84'2 volumes of 
sulphur dioxide. Of this occluded sulphur dioxide, which for the purpose we had in 
view was quite as objectionable as oxygen, only about one-fifch, or 15 volumes, could 
be removed in vacuo at the ordinary temperature ; wdiilst for its complete removal 
ignition at a red heat, and consequently the conversion of the bla-ck into sponge, was 
necessary. 
From the fact that the platinum black originally contained about 79 m volumes 
of oxygeip and that 84‘2 volumes of SO^ were subsequently occluded, it may be 
inferred that platinum black occludes approximately the same number of volumes 
of both gases. 
Carhon monoxide.~As "we already know from former experiments, carbon dioxide 
may be readily removed from platinum black at temperatures which do not seriously 
affect its absorptive power. Attempts were therefore made to convert the oxygen 
contained in platinum black into carbon dioxide by the admission of carbon monoxide. 
Experiments showed that the bulk of the oxygen could be easily removed in this 
w’ay, but on exhausting the tube it was found that carbon monoxide was itself 
occluded by the platinum black, and could only be removed by heating to redness in 
a vacuum. 
In two experiments a sample of platinum black wdrich contained initially about 
90 volumes of oxygen wms found to have occluded 95‘7 and 93'5 volumes respectively 
of carbon monoxide. 
Formic acid. —The method we have generally adopted for the preparation of 
platinum black has been by the reduction of sodium platinichloiide by sodium 
