130 
DRS. L. MOXD, W. RAMSAY, AND J. SHIELDS ON THE 
During our attempts to solve tlie problem whether the occlusion of gases by metals 
is a chemical or pliysical phenomenon, we have investigated the thermal changes 
which take place on the occlusion of hydrogen and oxygen by platinum black. 
Independent of the object for which the investigation was undertaken, the results we 
have obtained, which we now beg to lay before the Society, are of interest in 
connection with many electrical experiments where platinum or platinised electrodes 
are employed. The present communication also contains an account of the behaviour 
of several other gases towards platinum black, together with some speculations 
regarding the occlusion of oxygen. 
IL The Heat of Occlusion of Hydrogen hy Platinum BlacJc. 
In attempting to determine the heat evolved on the occlusion of hydrogen by 
platinum black several courses were open to us. The first of these, namely, the 
preparation of pure platinum black, and the subsequent treatment of this with 
hydrogen in the calorimeter, had to be abandoned, as we have up to the present been 
unable to obtain this substance free from occluded gases. 
A second conceivable method would be to treat platinum black as we find it, that 
is to say, platinum black containing oxygen, small quantities of carbon dioxide, and 
usually traces of other substances,* with hydrogen, and to make a correction for the 
heat evolved due to the formation of water. This method, however, has two dis¬ 
advantages ; firstly, the correction for the heat evolved on the formation of water is 
much greater than the constant to be measured, and secondly, it is very difficult to 
estimate exactly the quantity of oxygen in the sample experimented upon. Any 
attempts to remove the oxygen by heating m vacuo resulted in the formation of 
platinum sponge, which occludes relatively only small quantities of hydrogen. 
As will be seen in Section III., chemical methods for removing the oxygen without 
introducing other deleterious substances also jjroved unsuccessful, and hence we were 
reduced to the third alternative. This consisted in fully charging up the platinum 
black with hydrogen at atmospheric pressure, removing as much as possible of the 
hydrogen by means of the pump, at as high a temperature as the platinum black 
could safely stand (184° C.) without being converted into sponge, and finally charging 
up fully again with hydrogen in the calorimeter. In this way the hydrogen converts 
all the oxygen initially present in the platinum black into water (the bulk of which is 
subsequently removed), and also exerts its full influence on oxides of nitrogen or other 
impurities before the heat evolved on the true occlusion of hydrogen is measured in 
the calorimeter. 
It seems to us that the only objection which can be raised to this method of 
* The cliief of these are oxides of nitrogen, derived from nitroso componnds formed on the solution of 
platinum in arina regia, and 'which cannot bo destroyed even on repeatedly evaporating the solution 
sirccessively with water and hydrochloric acid. 
