occlusions' of oxygen and hydrogen by platinum BIjACK. 
139 
formate, and it might be expected that the oxygen contained in platinum black could 
be removed by treatment with formic acid. 
In the first of Wo experiments which were performed, the details of which need 
not be given, the platinum black was treated with the vapour of formic acid ; whilst 
in the second, it was warmed with a dilute solution of formic acid in the experimental 
tube. In the latter case the excess of water and formic acid was evaporated off in 
vacuo, suitable absorbing agents having been introduced between the pump and 
experimental tube, and the residual substance dried at 100° C. in vacuo before 
exhausting at a higher temperature. 
On gradually heating the platinum black obtained after treatment with (A), the 
vapour of formic acid, and (B), an aqueous solution of formic acid, gas was con¬ 
tinuously given off in vacuo until a dull red heat had been maintained for some time. 
In both cases the gas pumped off was found to be a mixture of carbon monoxide and 
hydrogen, as shown in the following table. 
CO 
A. 
Platinum black 
treated witli the vapour 
of formic acid. 
B. 
Platinum black 
treated with dilute aqueous 
formic acid. 
^'ols. 
88-3 
■ 21-0 
vols. 
86-8 
38-4 
Total. 
115-8 
125-2 
Hitherto we were inclined to ascribe the presence of oxygen in platinum black to 
the fact that it w^as washed and dried at 100° in the presence of air, since platinum 
black, when heated in an atmosphere of oxygen, absorbs this gas until the tempera¬ 
ture reaches 360°-380° C. If freshly reduced platinum black contains either or both 
of these gases occluded in it, then it is easy to account for the presence of oxygen in 
the substance we actually obtain ; for, on coming into contact with the air, both of 
these substances would be immediately burnt out and oxygen would take their place. 
As a last resource for the preparation of pure platinum l)lack, free from oxygen, 
we originally intended, if all else failed, to attempt to wash and dry it out of contact 
with the air; but these experiments show that even if wm did succeed in keeping out 
oxygen, we might, it is true, obtain platinum black free from oxygen, but it would 
on the other hand be equally valueless for our purpose, since it would in all probability 
contain carbon monoxide and hydrogen. 
Methyl alcohol, ammonia, &c .—Platinum black submitted to the action of the vapour 
of methyl alcohol, and then subjected to a preliminary exhaustion at 100° C,, was 
found on heating to a red heat in vacuo to give off 101 volumes of a gas consisting 
of 11 volujnes of carbon dioxide and 90 volumes not absorbed by alkaline pyro- 
T 2 
