152 
DRS. L. HON'D, W. RAHSA.Y, AND J. SHIELDS ON THE 
that the dilRculties in deciding the corresponding cpiestion for the less well-defined 
product obtained by charging platinum black with hydrogen can not easily be sur¬ 
mounted. As far as we can see at present, the only solution to the problem is to be 
got by a more minute study of the physical properties of the substance. 
It must be admitted that the inference which we have drawn, viz., that any given 
sample of platinum black occludes approximately the same volume of the difierent 
gases, seems to point to the conclusion that we are dealing with some phenomenon 
which is conditioned by the extent of the surface of tlie platinum black, as otherwise 
it is not Cjuite clear why hydrogen, oxygen, carbon monoxide, and sulphur dioxide 
should all be absorbed in equal volumes. On the other hand, we have to deal with 
the equally significant fa,ct that neither nitrogen nor carbon dioxide are absorbed 
except in comparatively small quantity. If, however, we confine our attention to 
the occlusion of oxygen by platinum black, the balance of the evidence which we can 
bring forward at the present time seems to indicate the formation of a definite 
compound or oxide. 
If, in the first place, the occlusion of oxygen were merely the physical condensation 
of ox 3 ^gen in the capillary pores of the platinum black, we should expect that raising 
the temperature w^ould either have very little effect or would simply re-evaporate the 
condensed oxygen, whilst, as a matter of fact, rise of temperature is accompanied by 
increased absorption up to the temperature of about 360°-380° C., when the oxygen 
is again given off. 
This behaviour seems to militate against the view that we are dealing with physical 
condensation or liquefaction in the pores. Solid solution however is not excluded ; 
but if it be remembered that platinum black absorbs about 100 volumes of oxygen, 
whilst there is no authenticated case on record in which platinum in the concrete 
form has been known to absorb more than a few volumes at the outside, it would 
follow that, if we were really dealing with solid solution, platinum in all its forms 
should absorb approximately the same quantity of oxj’gen, although we would be 
quite prepared to find a different rate of absorption in the different forms. 
If we admit the possibility that the different varieties of platinum may be allotropic 
modifications, then the above arguments would not necessarily hold good, as may 
readily be seen by a comparison of the properties of red and yellow phosphorus. 
Carbon bisulphide may be regarded as being soluble in the yellow variety, but 
insoluble in the red, since it is purely a conventional matter which we call the 
solvent and which the dissolved substance. 
In connexion with the view that the absorption of oxygen by platinum black may 
simply be due to superficial oxidation, we made a few experiments with the object of 
comparing the general behaviour of platinum black charged with oxj^gen with the 
lowest oxide of platinum. Several samples of platinous hydrate Pt(OH)o were pre¬ 
pared by boiling a dilute solution of potassium platinochloride KaPtCl^, with the 
theoretical cjuantity of caustic potash according to the method recommended by 
