2S6 



Mr. J. H. T. Roberts on the 



the phenomenon of the disintegration of the platinum strip to 

 be mistaken for one of simple volatilization *. 



The constant- volume gas-chamber used for the following 

 experiments is shown in fig. 5. It consists simply of the 



Fig. 5. 



cylindrical glass bulb containing the glowing wire, with 

 connecting tubes for the withdrawal and admission of gas, 

 the shape of the tubes being such that the bulb can be 

 immersed in running water in a trough. The pressure at 

 constant volume is read in the usual way by means of the 

 sliding mercury reservoir. 



The behaviour which would be expected from the above 

 considerations as to the nature of the oxide was exactly what 

 was observed. Before the water-cooling arrangement was 

 employed, the small glass vessel used to get exceedingly hot 

 and the weight of oxygen lost was always too small for a 

 simple atomic relation. Many precautions were taken to 

 try to improve the relation between the weights of oxygen 

 and platinum, but it will be interesting to mention the 

 precautions which most readily suggest themselves, as the 

 most important precaution (that of water-cooling the small 

 glass vessel) was stumbled upon in endeavouring to eliminate 

 an error which seemed negligible. Conditions (other than 



* Crookes, loc. cit. 



