Occlusion of Oxygen and Hydrogen by Platinum Black. 51 



found that 68*8 K (6880 ^-calories) were evolved per gram of 

 hydrogen occluded. It is shown that the arguments put forward by 

 Berthelot in favour of the existence of the compounds Pfc 30 H 2 and 

 Pt 30 H 3 are not justified. According to Favre there is a difference 

 between the behaviour of palladium and platinum to hydrogen, inas- 

 much as when hydrogen is admitted fractionally, in small portions at 

 a time, the heat evolved in the former case is constant, whilst in the 

 latter it becomes less and less. This difference is apparent only and 

 not real, and is due to the presence of oxygen in the platinum black. 



In order to determine the heat of occlusion of oxygen in platinum 

 black, a great many experiments were made to try to remove the 

 oxygen, which is always present, without destroying the occlusive 

 property of the platinum, and so obtain platinum black which would 

 per se occlude oxygen directly at the temperature of the calorimeter, 

 and thus eliminate all corrections for the simultaneous occurrence of 

 other reactions. Several reducing agents were employed, including 

 sulphur dioxide, carbon monoxide, ammonia, methyl alcohol, and 

 formic acid in the state of vapour and in dilute solution, and it was 

 found that, although the oxygen was removed, the reducing sub- 

 stance or its products of decomposition were occluded by the plati- 

 num black, and were just as difficult to remove as the oxygen itself ; 

 and, further, the volume of gas given off, derived from the reducing 

 agent or its decomposition products, was approximately equal to the 

 volume of oxygen originally contained in the platinum black. In 

 most cases this was about 100 volumes. 



An extended series of experiments is described showing how 

 platinum oxygen and platinum hydrogen can exist in the presence of 

 each other. If the quantity of hydrogen which is theoretically 

 necessary to remove all the oxygen in the form of water be admitted 

 to platinum black, then, instead of removing all the oxygen first with 

 formation of water, the hydrogen only removes the oxygen from the 

 platinum black with which it first comes into contact, and imme- 

 diately takes its place. 



The heat of occlusion of oxygen in platinum black was finally 

 measured both directly and indirectly in the following ways. Plati- 

 num black fully charged with hydrogen was exhausted at 184° C. to 

 remove as much of this gas as possible. The experimental tube was 

 then placed in the calorimeter, and oxygen was added in small quan- 

 tities at a time. From the experiments on the co-existence of platinum 

 oxygen with platinum hydrogen, the heat evolved during this process 

 was known to be partially due to the formation of water and partially 

 to the occlusion of oxygen. The vacuum in the apparatus remained 

 perfect up to a certain point, when the presence of a slight excess of 

 oxygen caused the pressure to increase. On now admitting oxygen 

 up to full atmospheric pressure, a further small quantity of oxygen was 



E 2 



