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



The following substances were experimented with : — 

 Elements. — Diamond, native sulphur. 

 Halides. — Fluor-spar, cryolite, rock salt, sylvine and artificial 



potassium bromide and iodide. 

 Oxides. — Quartz (including rose quartz, amethyst and cairn- 

 gorm), ruby. 

 Sulphates. — Selenite, anhydrite, celestine, barytes, anglesite. 

 Phosphates. — Apatite, phosphorite. 

 Silicates. — Tourmaline, topaz, zircon, beryl, kunzite. 

 Carbonates. — Calcite, strontianite. 

 Other Substances. — Glass, bakelite. 

 Exposure to radium was made in most cases by placing a glass 

 tube containing the radium salt directly on or very near to the 

 specimen under observation. In this way only ft and y rays 

 actually reached the crystal and of these only the y rays would 

 penetrate to any appreciable depth. This method of treatment 

 is implied throughout the present work unless the contrary is 

 directly stated. In many cases it was easy to distinguish the 

 separate effects of the two types of rays, but in case of doubt, y rays 

 alone could be obtained by interposing a thin sheet of lead, or fi 

 rays alone by the use of a cathode-ray tube. 



In a few cases the specimen was exposed to the direct influence 

 of the emanation by putting it into a tube containing the active gas 

 over mercury. In this case a, /3 and y rays would act simultaneously. 

 Diamond. — This was a small pale yellow crystal from New 

 South Wales kindly lent to us by Prof. Boyd Dawkins. No change 

 of colour and no luminescence was observed on heating to redness 

 in a soft glass tube. 



When exposed to radium the specimen glowed with a bright 

 blue light, while an imitation diamond placed alongside it was quite 

 inactive. 



Exposure to 4 mg. of radium for twenty days had very little 

 visible effect upon this crystal. The colour appeared very slightly 

 deeper, but was restored to its original condition without lumines- 

 cence on gentle heating. 



Exposure to 20 millicuries of emanation decaying over a period 

 of seven days in contact with the crystal produced a more marked 

 darkening of the yellow colour. 



Crookes, by embedding a Bingara yellow diamond in radium 

 bromide for seventy-eight days obtained a bluish-green colour. 



Sulphur. — A clear crystal of native sulphur from Vesuvius 

 was exposed for twenty days to 50 mg. of radium. No change of 

 any kind could be detected and no luminescence was produced. 

 Doelter states that sulphur is slightly changed in colour. 



Fluor-spar. — Owing to their wonderful range of colour and the 

 remarkable thermo-luminescence of many specimens, the fluor-spars 

 are undoubtedly the most interesting minerals dealt with in this 

 work. In fact, a comparison of the very similar behaviour on heating 

 of purple fluor and of glass which had been turned purple by radium 

 was the initial observation which led to this research. 



