

1905.] the Beta and Gamma Rays of Radium. 509 



crystalline phase. The reality of this change was further confirmed 

 by finding that the phosphorescent quality, which had fallen to 2/100 

 in the amorphous state, had been restored by the heating to 33/100. 



13. The analogy between the changes in colour and phosphorescent 



quality brought about by the transformation C - A and the 



corresponding changes which result from the action of the ft rays is 

 thus shown to be very close ; it remained to be seen if the analogy 

 also held good in the reverse transformation by heat. 



14. Crystals which had been reddened by the ft rays were lightly 

 crushed and quickly heated to 110 in a .capillary tube with an open 

 end. The colour of the salt became 1 much paler and its phosphorescent 

 quality was considerably increased. As the temperature necessary to 

 bring about the transformation was also high enough to drive off some 

 of the water of crystallisation, a fresh portion of lightly crushed red 

 crystals was packed tightly into a capillary tube which was sealed off 

 as close to the surface of the salt as possible. The tube was heated to 

 120, when the transformation into the yellow salt took place quite 

 sharply, beginning simultaneously at the middle and at one end of 

 the tube and quickly spreading all over, the brown colour giving place 

 to bright yellow. The transformation was carried out at 120, so that 

 no water in the liquid state can have taken part in it. After cooling, 

 some minute drops of condensed water were visible on the inner 

 surface of the tube. Necessarily, a corresponding portion of the salt 

 must have parted with some of its water of crystallisation, but this 

 did not affect the transformation of the remaining part. The phosphor- 

 escent quality was raised from the 8/100 of the red crystals to 33/100. 



15. Even in the sealed tube, however, the conditions for the trans- 

 formation A > C are distinctly unfavourable to anything like a 



perfect conversion or the production of a uniformly crystalline material, 

 therefore, the very definite results obtained, namely, the partial 

 restoration both of colour and phosphorescence, are strongly confirma- 

 tory of the phase view of the change brought about by the /? rays. 



16. The retention by the reddened crystals of their crystalline form 

 and transparence points to a persistence of a proportion of the crystal- 

 line phase side by side with the amorphous. Having regard to my 

 earlier observations on phase transformation in overstrained crystals, 

 this persistence of the C phase is quite to be expected. In the case of 

 gold it was shown that even after severe and repeated beating of the 

 metal in the form of the thinnest foil the crystalline structure could not 

 be completely obliterated.* More recent observations on the flow of 

 crystalline salts, which have not yet been published, fully confirm this 

 point. These still further confirm the explanation of this fact offered 

 in my former papers, namely, that the amorphous phase which is 

 formed at all the moving surfaces of the crystalline units acts as an 



* ' Phil. Mag.,' vol. 8, p. 263. 



