To Newbery — Lupton, Radio-activity and Coloration of Minerals. 



from Canada, a very hard phosphorite from France, and a mixed 

 apatite and phosphorite from Aqua del Todo Ano, Spain. This 

 last specimen contained zones of a beautiful mauve apatite separated 

 and surrounded by a white flaky phosphorite, and provided the 

 most brilliant example of thermo-luminescence observed throughout 

 this work. 



All the specimens used approached the colourless state on 

 heating. The Canadian specimens became pale brown and very 

 pale blue respectively on heating small pieces on a platinum wire 

 before a good blow-pipe, while the mauve Spanish variety became 

 pure white on warming in a soft glass tube. The green Canadian 

 variety was also rendered white by long heating, but the brown 

 specimen still retained much of its colour. All the apatite specimens 

 gave a feeble phosphorescence on heating strongly in a hard glass 

 tube. The French phosphorite decrepitated but gave no visible 

 light. The Spanish phosphorite on gentle warming appears to take 

 fire and a beautiful golden yellow glow is emitted, so brilliant that 

 a fragment the size of a small pea allowed the time to be easily seen 

 on a small watch held a foot away. This glow only lasts for about 

 thirty seconds to one minute and then disappears, after which, 

 further heating has no effect. 



No colour change was produced by the action of radium on any 

 of the original untreated specimens, but the thermo-luminescence 

 was increased in all cases. 



The green Canadian apatite, which had been turned white and 

 semi-transparent by strong heating, was coloured a fairly strong 

 brown by two days' exposure to 50 mg. of radium. When this 

 brown substance was gently heated in a soft glass tube a brilliant 

 violet light was emitted many times stronger than that obtained 

 with the unheated specimen. . The brown colour faded rapidly in 

 daylight. 



The brown Canadian apatite behaved similarly to the green 

 variety, although the colour change on treatment with radium was 

 hardly visible. 



The French phosphorite after treatment with radium was 

 unaltered in appearance, but the thermo-luminescence was strong, 

 and violet in colour. 



The Spanish phosphorite, after heating until all the glow had 

 disappeared, was treated with 25 mg. of radium for six days. No 

 change in external appearance was produced, but on heating it was 

 found that the power of emitting the beautiful yellow light had 

 been restored, and was greater and more lasting than that of the 

 original specimen. 



The finest display of this yellow light was however obtained 

 when a large fragment of the original material was brought under 

 the action of the cathode rays. In this case there is no disappear- 

 ance of the glow with time ; it continues with undiminished brilliancy 

 as long as the rays fall on the substance. Also, a specimen which 

 had been deprived of its thermo-luminescence by strong heating 

 regained this property with increased brilliancy in the cathode rays. 



