Disintegration of Metals at High Temperatures. 293 



Discussion of Results. 



By the delicate test of the expansion apparatus it is found 

 that platinum begins to disintegrate at so low a temperature 

 as 500° C. (just below the dullest red heat), but in such 

 infinitesimal quantities that no loss of weight would be 

 detected even after days of heating. The disintegration 

 does not begin to come within range of the balance until 

 1900° C. or 1100° C. The fact that the second set of nuclei, 

 -even in the region of 500° C, are so persistent, and that they 

 do not change in size or character, together with the fact 

 that they are produced in pure oxygen, no matter how long 

 the heating has been continued; and are not produced in the 

 absence of oxygen, either in nitrogen, hydrogen, or in a 

 Tacuum, shows that they are not likely to be either particles 

 of the metal brought off by the escaping gas or traces of 

 compounds of different gases. 



The fact that the rate of loss of weight of the platinum 

 wire is roughly proportional to the oxygen pressure points 

 to the formation of an endothermic oxide. The experiments 

 in the constant-volume gas-chamber in which the ratio of 

 the loss of platinum to the los"s of oxygen was determined, 

 gave results which approximated in the case of air to 2Pt : O 

 and in the case of oxygen to Pt : 20. It does not seem 

 probable that this large amount of oxygen is simply 

 adsorbed ; it must be combined chemically, at any rate for 

 the most part. During the cooling of the oxide after its 

 formation at the hot wire, some decomposition takes place, 

 and the amount of this decomposition will be greater the 

 lower the oxygen pressure. If we assume that the quantity 

 of oxygen adsorbed by the deposit is small, the composition 

 of the oxide in the experiments in oxygen must be either 

 Pt0 2 or some higher oxide. If this oxide is also present in 

 the deposit obtained in air, there must be a considerable 

 amount of platinum mixed with it, this platinum being the 

 result of dissociation of the oxide during cooling. 



According to the observations of Nahrwold, Stewart, and 

 Holborn and Austin, the rate of disintegration of the 

 platinum metals (excluding palladium) diminishes with 

 the pressure of the surrounding oxygen ; this is in 

 accordance with the oxidation theory. Palladium, however, 

 us has been shown in the course of this paper, volatilizes; 

 it oxidizes if there be any oxygen present : this agrees with 

 the observations of Stewart, and Holborn and Austin, that 

 the rate of disintegration of palladium is practically in- 

 dependent of the nature, but increases with diminution of 

 the pressure, of surrounding gas. 



