388 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On the Action of Radium Emanations on Diamond. — 

 Having previously shown that diamonds, when exposed to the 

 impact of radiant matter in a high vacuum, become blackened 

 from a superficial coating of graphite, Sir William Ckookes has 

 recently experimented upon the action of the rays from radium 

 upon these gems. Two diamonds having the same pale yellow 

 color were selected, and one of them was kept for a fortnight 

 close to a quartz tube containing 15 mg. of radium bromide sealed 

 in vacuo. Comparison of the exposed diamond with the one not 

 exposed showed no appreciable difference in color, and the same 

 result was obtained after six weeks of exposure. The diamond 

 phosphoresced brightly and continued to glow during the whole 

 period of the experiment. The previously exposed diamond 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. After a continuation of this exposure for seventy- 

 eight days, the diamond had a darker appearance than the one 

 reserved for comparison, and it showed a bluish green tint with 

 no apparent yellow color. It thus appears that radium emana- 

 tions, which darken glass in a marked manner, and quartz to a 

 slighter extent, are also capable of darkening the diamond. The 

 exposed diamond was now treated for ten days with mixtures of 

 the strongest nitric acid and potassium chlorate, for the purpose 

 of testing for a superficial formation of graphite. It was evident 

 that graphite had been present, for the diamond lost its dull sur- 

 face color and was as bright and transparent as the other stone, 

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



The conclusion is reached that the radium emanations have a 

 double action on the diamond. The /3-rays (electrons) exert a 

 superficial darkening, converting the surface into graphite in a 

 manner similar to, but less strongly than, the more intense elec- 

 trons in the cathode stream. But the alteration of the body color 

 of the stone by emanations which are obstructed by the thinnest 

 film of solid matter, even by a piece of thin paper, is not so easy 

 to understand. It is believed that the alteration of color is a 

 secondary effect, connected with the extremely phosphorescent 

 state of the diamond during its exposure. It is not difficult to 

 suppose that a chemical as well as a physical action may result. 

 If the yellow color is due to iron in the ferric state, a reduction 

 to the ferrous state would account for the change of color to a 

 pale blue-green. This alteration of color may be of commercial 

 importance in treating " off color" stones. 



After the exposed diamond had been treated for ten days with 

 the acid mixture, it was carried about with its unexposed com- 



