the Platinum Metals in Different Gases. 389 
being calculated from the empirical formula 
t=1:157 S—67°2. 
It was found that the disintegration increased very rapidly 
with increasing temperature, iridium showing a loss of weight 
of 11:8 mg. in an hour at 1210°C., 72 mg. at 1670°, and 
277 mg. at 2130°. At 1670° platinum and rhodium showed 
about the same loss in weight, while iridium lost approxi- 
mately ten times as much. The pure metals showed no 
decrease in disintegration during the longest heating (3 
hours), the loss appearing to be proportional to the time. 
Changes were observed, however, in the cases of the plati- 
num-iridium alloys, undoubtedly due to the changes in the 
composition at the surface on account of the more rapid 
disintegration of the iridium. Silver and gold heated to 100° 
below their melting-points showed no certain loss in weight. 
We have now extended this work to cover the disintegration 
in different gases. 
Observations on the disintegration of glowing metals in 
different gases thus far have been confined to platinum and 
palladium. LElsterand Geitel *, and Nahrwold + found, con- 
trary to Berliner {, that platinum showed very little dis- 
integration in hydrogen. Stewart § investigated platinum 
and palladium, and observed that both metals showed little or 
no disintegration in nitrogen ; that in hydrogen, platinum 
showed no loss in weight and palladium much less than in 
air. He made no observations with oxygen, but cites an 
observation by Kaufmann to the effect that in oxygen the 
disintegration of platinum is six times as great as in air. 
According to Stewart, the disintegration of platinum in air 
decreases with decreasing pressure, while in the case of 
palladium it increases. Emich || has studied the action of 
hot platinum in air and in nitric oxide, and has shown that 
oxygen is taken up by the platinum from the air and from 
the decomposed nitric oxide. 
In the present work the same methods were followed as in 
the former, except that now it was necessary to decrease the 
width of the metal strips in order to bring them to the 
required temperature witha smaller current. These narrower 
_ strips, especially in the cases of the very hard rhodium and 
iridium, were very difficult to produce of uniform width and 
* J. Elster and H. Geitel, Wied. Ann. xxxi. p. 126 (1887). 
+ R. Nahrwold, 7b. xxxv. p. 116 (1888). 
{ A. Berliner, 2b. xxxili. p. 291 (1888). 
§ W. Stewart, 7. lxvi. p. 88 (1898); Phil. Mag. [5] xlviii. p. 481 
(1899). 
|| F. Emich, Sitz.-Ber. der Wiener Akademie, ci. [2b], p. 88 (1892). 
