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



colouring matter had been driven off by heat, it is inconceivable 

 that it should be brought back by radium treatment. 



Barnes and Holroyd claim to have synthesised pure fluor-spar 

 in crystals which showed all the known natural colours — green, yellow, 

 rose, purple, etc. They therefore conclude that the colour is an 

 optical phenomenon dependent upon the crystallisation and physical 

 state of the substance. 



The essentiaUy weak point in Barnes' and Holroyd's theory is 

 their statement that their " synthesised " fluor-spar was pure. It 

 was made from calcium carbonate (presumably precipitated chalk, 

 which usually contains traces of chloride, sulphate, sodium, water, 

 etc.), and hydrofluoric acid. The latter, being always prepared 

 from native fluor-spar, would contain most of the volatile impurities 

 in the original fluor, together with other impurities picked up from 

 the sulphuric acid used, the rubber bottle in which it was kept, etc. 

 Finally the whole was heated in a steel tube to bright redness. Since 

 the steel may contain carbon, hydrogen, sulphur, phosphorus, 

 manganese, silicon, etc., in addition to iron, all of which may easily 

 contaminate the fluor-spar, it is evident that the supposition that 

 this fluor-spar was chemically pure is unjustifiable. 



Strutt found that phosphatic nodules (coprolites) and phos- 

 phatised bones of all geological ages possess marked radio-activity, 

 sometimes fifty times as great as that of the surrounding rock. He 

 detected helium in these minerals even when they were not of more 

 than Pleiocene age. He also detected and measured the quantity 

 of helium in zircons, and from his results was able to calculate the 

 minimum age of the rocks in which these were found. 



Glew exposed kunzite, a pink transparent variety of spodumene, 

 to the y rays from radium for some days and found that the colour 

 changed to green. On warming the crystal thus treated, a brilliant 

 orange-coloured light was evolved for some minutes and the green 

 colour was removed. He suggests that dissociation occurred under 

 the action of the y rays and that the subsequent heating gave the 

 dissociated ions room to turn round and recombine with evolution 

 of energy in the form of light. 



Goldstein carried out a very interesting and extended investiga- 

 tion of the effects of cathode rays on certain colourless salts. Since 

 cathode rays in a vacuum tube are of the same nature as the /5 rays 

 from radium, it is quite possible that the effects obtained by Goldstein 

 in a few seconds may be similar to those produced naturally in radio- 

 active rocks in the course of centuries. Sodium chloride was coloured 

 deep yellow ; potassium chloride, violet ; potassuim bromide, deep 

 blue and sodium fluoride a fine red by a few seconds' exposure to 

 cathode rays. 



These colours are only produced on the surfaces exposed to the 

 direct rays and are sensitive to light and heat in very different 

 degrees. Some of the bodies thus treated emit a phosphorescent 

 light when warmed. If salts such as sodium chloride are exposed 

 to the cathode rays for considerable periods until they become quite 

 hot, the colours produced are not discharged by light or gentle 



