Disintegration of Metals at High Temperatures. 281 

 Nuclei in Pure Oxygen. 



Tests were made upon hydrogen-free wires, and it was 

 found that the minimum temperature at which the second 

 nuclei began to be produced was not altered, but that the 

 nuclei produced at that temperature were more numerous in 

 the oxygen than in the air. 



Nuclei in Pure Electrolytic Hydrogen. 



At a bright yellow heat a small shower was obtained in 

 hydrogen, doubtless formed upon nuclei of the first set pro- 

 duced by the absorbed hydrogen. Before the introduction 

 of the hydrogen, the wire had been hydrogen-free, according 

 to the vacuum test. 



Nuclei in Nitrogen. 



If the nuclei depend upon hydrogen and oxygen re- 

 spectively, no nuclei should be obtained when a hydrogen- 

 free wire is heated in pure nitrogen. In view of the 

 delicacy of the expansion method of detecting particles, it is 

 essential that the nitrogen be absolutely free from hydrogen 

 and oxygen. For the tests in nitrogen a special form of 

 nuclei-chamber was employed, containing two platinum 

 wires, which were hydrogen-free according to the vacuum 

 test, and could be heated independently. Atmospheric air 

 was introduced into the apparatus through KOH, P 2 5 , and 

 cotton- wool and glycerine tubes ; by means of mercury 

 reservoirs it was then passed to and fro through a tube of 

 palladium asbestos, prepared according to the method of 

 Winkler *, and the oxygen was finally combusted by bringing 

 dry phosphorus, floating on the surface of the mercury, 

 sufficiently near to one of the platinum wires, which was 

 heated, to cause it to ignite. After the combustion was 

 complete, the second wire was heated for a few minutes, and 

 the whole apparatus was left until all nuclei must have 

 disappeared • the second wire was then heated to a white 

 heat, and the expansion test made, expansion 1*188 ; a few 

 drops only were seen. Considering the delicacy of the 

 expansion method, this may be regarded as a zero effect; 

 it is probable that the wire was not absolutely hydrogen- 

 free, and that in a vacuum the very few nuclei were produced 

 at the beginning of the heating and were lost before the end 

 of the heating ; whereas when surrounded by a gas, as in the 

 nitrogen tests, they would be much more likely to be caught. 



* Technical Gas Analysis. 

 Phil. Mag. S. 6. Vol. 25. No. 146. Feb. 1913. U 



