Disintegration of Metals at High Temperatures, 279 



they rapidly increase in size with iucrease o£ pressure, until 

 at 2*5 cm. pressure they are caught with expansions of 1*016. 



Fig-. 4. 



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(.160 



1.120 



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1.040 



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A 





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set 



Before discussiug the nature of these nuclei, let us con- 

 sider the effect of heating the wire in the highest vacuum, as 

 it was in this way that the existence of two different sets of 

 nuclei was first detected. We have seen that the first set of • 

 nuclei are got rid of after prolonged experimenting, while 

 the second set are never got rid of in air. The experiments 

 upon the heating of a wire in a vacuum were conducted as 

 follows : — The chamber C was pumped out to a high vacuum 

 by means of a Gaede pump ; B was closed and the wire was 

 heated. The heating current was then shut off, and the 

 moment the wire lost its colour B was reversed, with the 

 result that C was instantly filled with nuclei-free air at 

 atmospheric pressure. 



For simplicity we will anticipate the results by assuming 

 that the platinum wire has been well soaked in hydrogen. 

 On heating in a vacuum, large nuclei caught by expansions 

 of 1'027 are produced at very low temperatures ; in some 

 cases nuclei were detected after the wire had been raised to 

 a temperature between 150° C. and 200° C. After one or 

 two heatings at any temperature, no more nuclei are obtained 

 for that temperature, but nuclei will be given for a higher 



