1895.] Occlusion of Oxygen, fyc., by Platinum Black. 243 



gen absorbed by platinum is very largely influenced by slight traces 

 of impurity, probably grease or other matter which forms a skin over 

 the platinum. 



Platinum black in vacuo absorbs a certain quantity of hydrogen. 

 On increasing the pressure of the hydrogen up to about 200 300 

 mm. a further quantity is absorbed, but after this pressure is almost 

 without effect. By increasing the pressure from one atmosphere up 

 to four and a half atmospheres, only one additional volume of hydro- 

 gen was absorbed. On placing platinum black charged with oxygen 

 in an atmosphere of oxygen, and increasing the pressure to the same 

 extent eight and a half additional volumes were however absorbed. 



Platinum black charged with hydrogen and placed in an atmosphere 

 of hydrogen kept approximately at atmospheric pressure, and plati- 

 num black charged with oxygen and confined in an atmosphere of 

 oxygen, behave quite differently when heated. In the former case 

 hydrogen is immediately expelled on raising the temperature, whilst in 

 the latter case oxygen is steadily absorbed until a temperature of 

 about 360 C. (the temperature of maximum absorption) is reached, 

 when on further heating oxygen begins to come off again. 



Incidentally it was noticed that mercury begins to combine with 

 oxygen at 237 C., and that a mixture of platinum black and phos- 

 phorus pentoxide absorbs oxygen at a high temperature probably with 

 the formation of a phosphate or pyrophosphate. 



In the discussion of the results special reference is made to the 

 work of Berliner and Berthelot, and it is pointed out that there is not 

 sufficient evidence for the existence of such chemical compounds as 

 PtaoHs and PtaoH-j. Moreover, the authors are of opinion that the 

 heats of combination of hydrogen and platinum as determined by 

 Berthelot and Favre are valueless, and that the heat which they 

 measured is due for the most part if not entirely to the formation of 

 water by the oxygen always contained in platinum black. It has yet 

 to be proved that the absorption of hydrogen by pure platinum black is 

 attended by the evolution of heat, and as regards the formation of 

 supposed true chemical compounds, solid solutions, or alloys, the 

 authors prefer to wait until sufficient data have been accumulated for 

 an adequate enquiry, before coming to any definite conclusion. 



