1148 



same we were assisted by Mr. Oosterhuis, to whom we herewith 

 tender our thanks. 



To the inside of the c^'lindrical glass-balloon in which later on the 

 filament was to glow, two or more silverelectrodes were tixed. This 

 was effected bj' first silvering the whole wall and then removing 

 part of the silver with nitric acid. The wall was then carefully 

 cleansed, the support with the evaporation-filament was inserted, the 

 balloon was evacuated and the filament was brought to a state of 

 incandescence. 



Gold. 



By evaporation in vacuo we obtained a sublimate the resistance 

 of which was 119 Ohm. This layer proved not to be quite constant. 

 The resistance decreased slowly in vacuo, more rapidly with access 

 of air and by contact with glycerine and water as the following 

 numbers will indicate: 



in vacuo air admitted 



time 0,5 24 48 h. 3 6 24 48 h. 



resistance J 19 112 99 95 Ohm. 99 83 80 74,5 72,4 Ohm. 



glycerine admitted water added 



time 24 72 h. 24 h. 



resistance 71,8 66,4 64,7 Ohm. 60,6 58,0 Ohm. 



By covering with CaF, and Canadabalsam the layer of gold 

 becomes very constant against the infiuence of the air, as the 

 following experiment will be seen to bear out. 



A steel-blue gold precipitate, formed while the whole lamp was 

 immersed in liquid air, at roomtemperature obtained a resistance 

 which w^as first 250, after H hr. 211, after 24 hrs. 194 Ohm. 



After covering with CaF, W = 181 Ohm. 



After covering with Canadabalsam 187, two days later 189 i2. 



After entrance of air 185, 186,5 and finally 187 Ohm. By all these 

 operations the resistance does not materially alter. 



When a precipitate has been formed at a temperature of liquid 

 air and is then brought at room-temperature, a marked non-reversible 

 decrease of the resistance sets in. With the lamp as described above 

 it decreased from 2000 to 250 Ohm. With another lamp which had 

 been kept immersed in liquid air for 24 hrs and in this situation 

 had a constant resistance of 40.000 Ohm, it decreased by heating 

 to room-temperature to 6400, to increase once more, when in liquid 

 air to 6800. After heating to room-temperature the resistance was 

 very unstable, first 5800, later on 12.000 Ohm and the next day ao . 



