48 Sir W. Crookes. On the Action of [June 9, 



quite free from moisture. The action on the black layer is very slow. 

 There is produced graphitic oxide, which at an increased temperature 

 yields pyrographitic acid, easily destroyed by nitric acid. Hence 

 the variety of carbon which coated the diamond was graphite. 

 The transformation of diamond into graphite requires the high tempera- 

 ture of the electric arc. The higher the temperature to which graphite 

 is raised the greater is its resistance to oxidation. M. Moissan concludes 

 that the temperature reached by the surface of the diamond in my radiant 

 matter tubes is probably about 3600. 



The /3-rays from radium having like properties to the cathode stream 

 in a radiant matter tube, it was of interest to ascertain if they would 

 exert a like difference on diamond. Two Bingara diamonds, A and B T 

 weighing respectively O960 and 1-020 grains, were selected as near as 

 the eye could judge of the same size and colour very pale yellow, 

 technically known as "off colour." Diamond A was put in a drawer 

 far removed from radium or any radio-active body. Diamond B was- 

 kept close to a quartz tube containing about 15 milligrammes of pure' 

 radium bromide sealed in vacuo. It phosphoresced brightly and con- 

 tinued to glow the whole time of the experiment. 



After a fortnight the two diamonds were put side by side and com- 

 pared. I could see no appreciable diiference in colour between them. 

 Diamond B was now replaced close to the quartz tube of radium, and 

 they were kept in contact for six weeks. At the end of that time 

 examination again showed scarcely any difference between the two. 

 The one which had been near the radium might be a little the darker 

 of the two, but the difference was too slight to enable me to speak 

 positively. 



Diamond B was now put inside a tube with radium bromide, the 

 salt touching it on all sides, as it was thought possible that a screen of 

 quartz might interfere with the passage of emanations which would act 

 on the diamond. The comparison diamond was kept removed from 

 the emanations as before. The experiment was continued for 78 days, 

 when the two diamonds were again examined. There was now a 

 decided difference in colour between them; diamond A was of its- 

 original pale yellow "off colour," and diamond B was of a darker 

 appearance and of a bluish-green tint, with no yellow colour apparent. 



It thus appears that the property which radium emanations possess 

 of darkening transparent bodies which they impinge upon a property 

 very marked in the case of glass, and less with quartz also holds 

 good in the case of diamond. 



Diamond B was now heated to 50 C. in a mixture of strongest 

 nitric acid and potassium chlorate for 10 days, the mixture being 

 renewed each day. At the end of this time the diamond had lost its 

 dull surface colour, and was as bright and transparent as the other 

 stone, but its tint had changed from yellow to a pale blue-green. 



