180 Proceedings of Royal Society of Edinburgh. [sess. 
oxygen from the palladium black was readily taken up. A hissing 
noise then occurred, and the palladium disappeared in the mercury. 
Apparently the function of the hydrogen was simply to clean the 
layer of oxide off the surface of the palladium black, which was then 
able to dissolve easily in the mercury. An attempt was therefore 
made to make a liquid palladium-hydrogen amalgam, hut this was 
unsuccessful. Although electrolytic hydrogen was liberated for a 
considerable time on the surface of the amalgam, none was absorbed. 
In another experiment a quantity of palladium black was fully 
charged with hydrogen by direct exposure to the gas, and this, 
always kept in an atmosphere of hydrogen, was gradually tipped 
over into mercury contained in a bent branch of the tube. In 
order to prevent overheating, this mercury was kept cold in a bath 
of water, but the bulk of the occluded hydrogen was liberated 
immediately and the rest on standing over night. It thus seems 
impossible to prepare a palladium-hydrogen amalgam. Some of 
the solid palladium amalgam obtained by squeezing the excess of 
mercury through wash leather had the approximate composition 
MHg 5 . 
A pair of the above electrodes of known weight which had been 
subjected to as nearly as possible the same treatment, was then 
placed in dilute sulphuric acid (n, and in some cases O’ln — H 2 S0 4 
was used). The cell was then connected by means of a capillary 
syphon tube with a second cell, containing a platinum electrode. 
The function of' the divided cell was simply to separate the elec- 
trode at which oxygen was evolved from the cell proper; and care 
was taken to prevent, as far as possible, the access of air to the 
hydrogenised palladium electrodes, or to the electrolyte containing 
them. 
In series with the charging current was placed a hydrogen 
voltameter, so that the amount of hydrogen introduced into the 
palladium electrodes could be read off directly. Of course the 
charging had to take place so slowly that the whole of the 
hydrogen was absorbed by the palladium. 
In order to determine the electromotive force of the cell, or the 
potential of either of the electrodes against a normal electrode — 
viz., zinc in zinc sulphate solution — a modification of Poggendorfffs 
compensation method was adopted, with a capillary electrometer 
