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1904.] Radium Emanations on Diamond. 49 



The radium emanations have therefore a double action on the 

 diamond. The /3-rays (electrons) effect a superficial darkening, con- 

 verting the surface into graphite in a manner similar to, but less 

 strongly than, the more intense electrons in the cathode stream. But 

 the alteration of the body colour of the stone by emanations which are 

 bstructed by the thinnest film of solid matter, even by a piece of thin 

 paper, is not so easy to understand. A superficial action might be 

 expected, but not one penetrating through the whole thickness of the 

 diamond. I believe the alteration of colour is a secondary effect ; in 

 presence of radium the diamond is extremely phosphorescent, and it 



ntinues to shine during the whole time of the experiment. This 

 constant state of vibration in which the diamond was kept for many 

 weeks may have caused an internal change revealing itself in a change 

 of colour. Indeed, it is not difficult to suppose that a chemical as well 

 as a physical action may result. If the yellow colour is due to iron in 

 the ferric state a reduction to the ferrous state would quite account for 

 the change of colour to a pale blue-green. 



This alteration of colour may be of commercial importance. If "off 

 olour " stones can be lightened their value will increase, while if the 



olonged action of radium is to communicate to them a decided colour 



ey would be worth much more as " fancy " stones. 



[Added June 16, 1904. After the 10 days' heating in the above acid 

 :ture the two diamonds were put together in a glass tube and carried 

 ibout for 25 days, sometimes loose and sometimes in the tube. They 

 len were laid near together on a sensitive film in total darkness for 24 

 lours. On developing, diamond B had impressed a strong image on 

 film, but only a very faint mark could be seen where the other 

 lond had been. Probably this slight action was due to a little 

 radio-activity induced in A during its 25 days' proximity to B. 



The experiment was then repeated for confirmation, allowing the 

 diamonds to remain on the sensitive surface for only 5 hours. On 

 development, a good image of diamond B was seen, but not so black 

 as in the former case. 



The fact that diamond B was strongly radio-active after it had been 

 away from radium for 35 days, for 10 of which it was being heated in 

 a mixture powerful enough to dissolve off its outer skin of graphite, 

 seems to me proof that radio-activity is by no means a simple 

 phenomenon. It not merely consists in the adhesion of electrons or 

 emanations, given off by radium, to the surface of an adjacent body, 

 but the property is one involving deep-seated layers below the surface, 

 and like the alteration of tint is probably closely connected with the 

 intense phosphorescence the stone had been experiencing during its 

 78 days' burial in radium bromide.] 



VOL, LXXIV. 



