140 
DRS. L. MOND, W. RAMSAY, AND J. SHIELDS ON THE 
gallate. On ti'ansfeiTing the latter to the eudiometer and exploding with oxygen, it 
was found to be composed chiefly of hydrogen, together with a small quantity of some 
hydrocarbon which was not further investigated. 
On several occasions we have obtained specimens of platinum black of low 
absorptive jDower, which may readily be distinguished by the fact that they have 
a grey appearance instead of the usual dead black. (Platinum black of this 
description is apparently formed by the reduction of solutions Avhich are acid instead 
of neutral or slightly alkaline.) 
A quantity of this greyish platinum l^lack from a preparation which on ignition 
in a vacuum gave off only 21 volumes of oxygen was treated with ammonia gas." 
After exhausting at the ordinary temperature, 24’8 volumes of gas were extracted 
on ignition and were found to consist of CO 3 4‘2 volumes, O 3 O'O volumes, 
H 3 15'6 volumes, and N 3 5'0 volumes. 
The total gas extracted, viz., 24‘8 volumes, is sufficiently close to 21 volumes, the 
amount of oxygen originally contained in another sample of the same preparation, to 
warrant the inference previously drawn with regard to sulphur dioxide, and confirmed 
in the case of carbon monoxide, hydrogen, methyl alcohol and formic acid, that, when 
these reducing substances act on platinum black the oxygen is removed but its 
place IS taken by nearly the same number of volumes of the reducing substance or its 
products of decomposition. In former experiments, this number always approximated 
to 100 volumes, since the platinum black investigated contained nearly 100 volumes 
of oxygen. Furthermore, the removal of the reducing substance or its products 
from the platinum black seems to be just as difficult to accomjalish as the removal of 
the oxygen itself 
An attempt to remove the oxygen by treating with hydrogen peroxide also proved 
unsuccessful. 
When a platinum wire serves as the cathode in a vacuum tube through which an 
electric discharge is sent, the platinum volatilises, or gets thrown off, and forms 
a mirror on the walls of the tube. It was thought that by making a mass of platinum 
black the cathode in such a tube, the oxygen might be removed. On trying the 
experiment, however, only a very few bubbles of gas were extracted, and these Avere 
obviously due to the heating efiect alone, and not to any mysterious action during 
the passage of the current. 
In most of these experiments the reducing substance was employed in excess, but 
* The ammouia gas employed in this experiment was obtained by admitting strong aqueous ammonia 
at tbe bottom of a small flask, provided with a side tube dipping into mercury, nearly filled with chips 
of caustic potash, so that the gaseous ammonia given off might be dried as it ascended. When potash is 
dissolved in water, heat is evolved, and when ammonia is libei'ated from an aqueous solution, heat is 
absorbed, and the latter effect seems to be greater than the former, for, on admitting ammonia, the 
flask became veiy cold, and it was only necessary to warm it gently with the hand to obtain a steady 
stream of the gas. 
