1150 



metal had not been covered with Canadabalsam and that in that 

 place the moist air may have influenced. 



Tungsten. 



This metal gives the most constant layers. A precipitate formed 

 at the temperature of liquid air and kept at it, had a resistance of 

 5330 Ohm, which decreased after some hours to 5310, but then 

 remained constant for 10 hrs. 



Brought to roomtemperature, the resistance fell to 300 Ohm, again 

 in liquid air 3618; at roomtemperature 2662, after 24 hrs 2627. 

 The resistance-changes caused by modifications of temperature, are 

 here too non reversible, but the deviations are not nearly so great 

 as with the former metals. 



After applying a layer CaF,, 2110 Ohm (constant). 



After covering with Canadabalsam 2282. 



After breaking the vacuum and entrance of air 2297, 24 hrs 

 later 3100, 120 hrs later 12.000 Ohm. 



Practically the metal is altogether protected from the influence of 

 the air by the two protecting layers CaF, and Canadabalsam, at 

 least in the initial stage. In the long run the resistance rises again, 

 probably owing to oxidation. ') 



On the whole the resistance-measurements show, that a layer 

 CaF, and Canadabalsam do not alter the underlying metal, and 

 that they give a very good protection against the atmospheric 

 influence. With our ultra-microscopic observations we must have 

 seen the unaltered form of the metal-layer that had been sublimated 

 at roomtemperature. 



The precipitates formed at a temperature of liquid air, when 

 heated at roomtemperature, indicate a non-reversible change of 

 resistance, which is considerable, especially with Ag and Au. 



Though many causes for this change may be supposed, it does 

 not seem unlikely that it must be attributed to a change in the 

 finer structure of the precipitate, so that we observe in the ultra- 

 microscope at room-temperature a different formation than the one 

 formed originally at about — 180°. 



Summary and Discussion of the Results Obtained. 



A. Structure of the precipitates. 



On comparing the various elements we investigated, we are struck 



1) We may remark in passing, that also in the case when tlie wall of the bulb 

 is immersed in liquid air, the tungsten being deposited on the silver-electrodes during 

 the evaporation of the tungstenwire, forms with the silver a bronze brown product, 

 an indication for the formation of an alloy. 



