1149 



Silver. 



The precipitates of silver are even less stable than those of gold. 



Example: In a lamp, immersed in liqnid air, the snblimation 

 was continued nntil the colour of the precipitate was blue-violet 

 and the resistance 1000 Ohm. It was not constant, however, but 

 fell slowly ; after 1 hour 835, after 7 hrs 768, after 14 hrs 758 Ohm. 

 Heated to roomtemperature it first fell to 161 Ohm, but then rose 

 again and after two days it had become oo. ^) Once more we now 

 sublimated al roomtemperature till the resistance was 14.800 and 

 did not appreciably' alter in a period of two hours. Covered with a 

 sublimate of CaK, it fell to about 11.000 Ohm, to rise again after 

 one day to 15.880. By spreadiiig with Canadabalsam it became 

 13.520, after two hours 20.620, then rose owing to special 

 circumstances') to 120.000 and after 24 hours to 159.000. The 

 vacuum was now interrupted and air was admitted into the lamp. 

 The resistance rose somewhat, to 165.000, then it rose slowly, so 

 that after 3 hours it was 185.000 and after five days 335.000 Ohm. 



The conclusion to be drawn from this measurement is firstly that 

 the layers of silver are ver}' unstable and secondly that by applying 

 a protection of CaF',, and of Canadabalsam they are not materially 

 influenced, whereas these layers make a very good protection against 

 the influence of the air, at least in the beginning. 



Platinum. 



Thin layers of this metal are much more stable than those of 

 Au and Ag. 



A precipitate formed at a temperature of liquid air had a resistance 

 of 872.5 Ohm, 2 hrs later 875.7 Ohm. Continually keeping it at 

 about —185°, CaF, was now sublimated over the metal ; resistance 

 876.6. Hence it remains constant. 



By heating at roomtemperature the lesistance first decreased to 

 673 and then to a limit value of =t: 384 Ohm. Then after thawing 

 we brought from a side-tube that had all the time been kept at 

 — 183°, Canadabalsam on the precipitate. The resistance remained 

 386 Ohm and after 24 hi-s it still had the same value. With breaking 

 of the vacuum and with the entrance of air the resistance suddenly 

 decreased to 360, and then continued constant. 



This lowering may be attributed to the fact, that |)art of the 



') The colour of the silver-sublimate appeared to have become much lighter. 

 2) Probably because in the same room TESLA-discharges were efïected ; of. among 

 others of J. Clay. (These Proceedings 14 (1911) 126). 



