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XX. 



AN EXPEEIMENT ON THE POSSIBLE EFFECT OF HIGH 

 PRESSUEE ON THE RADIO-ACTIVITY OF RADIUM. 



By W. E. WILSON, D.Sc, F.R.S. 



[Eead, February 16 ; Eeceived for Publication, February 19 ; Published, 

 March 9, 1904.] 



If the phenomenon of radio-activity is due to chemical changes in 

 such substances as radium, it seems to me to be worth trying if 

 high pressure would in any way reduce the rate of change which is 

 supposed to be taking place in them. We know that pressure 

 modifies, and in some cases arrests, chemical change of the nature of 

 dissociation ; and if we found that the changes taking place in the 

 salts of radium were affected by this means, it would go a long 

 way to explain why radium, as now obtained from pitchblende, is 

 radio-active at all. Rutherford estimates the life of radium as 

 about one million years ; but pitchblende, from which it is extracted, 

 is found in some of the older geological rocks which must be of far 

 greater antiquity than this, and therefore the question arises, Why 

 is the radio-activity not over long ago ? One possible explanation 

 seems to be that the pitchblende when bound up with the pressure 

 of the superincumbent rocks was not radio-active, and that it was 

 only when the pitchblende was quarried and relieved from its 

 rocky prison that it became radio-active. 



A small annular brass cell was made to hold five millegrams of 

 radium bromide. The radium salt was embedded in a drop of 

 Canada balsam, along with a small piece of paper coated with 

 barium platino-cyanide. The cell was then covered on both sides 

 with mica attached to the brass by Canada balsam. The balsam 

 was in a thick viscous condition, capable of transmitting the 

 pressure to the enclosed radium salt, while at the same time 

 protecting the salt from the action of water. The cell was then 

 fixed inside against a strong window of quartz in a gun-metal 



