DISCOVERY AND PROPERTIES OF RADIUM 145 



found to produce a sore on the body if carried in the pocket. 

 It is this caustic effect of the radiations from radium which is 

 being used experimentally for medical purposes on cancers and 

 other malignant growths in the human tissues. 



A specimen of radium then looks like a few grains of common 

 salt, which, however, is slightly luminous, and therefore visible 

 in the dark. But one of its most striking properties is the power 

 it possesses of exciting phosphorescence in other substances 

 brought near it. Thus all diamonds gives out light of various 

 tints and intensity in the presence of radium, and a certain variety 

 of blende (native zinc sulphide) lights up brilliantly. On 

 examining the light given forth by the zinc sulphide by means 

 of a magnifying glass it was observed to be due to brilliant 

 separate flashes which are more numerous as the radium is 

 nearer to the screen and so less numerous as it is further away, 

 that the sparks, which appear like stars on a black sky, may be 

 counted. 



This effect was discovered by Sir William Crookes, who has 

 arranged a simple apparatus called the spinthariscope (Gr. 

 <T7riv9apls, a spark) for observing it. This consists of a tube 

 about two inches long, having a zinc sulphide screen at one end 

 with a small surface coated with a radium salt near it. At the 

 other end is a low-power lens through which the sparks can be 

 seen. 



Contact with a radium salt is followed in some cases with 

 remarkable changes of colour. Sir William Crookes possesses a 

 diamond which, having been embedded in radium bromide for 

 some months, has assumed an olive-green colour though un- 

 changed in other respects. This colour is persistent, and cannot 

 be removed by boiling the stone in acids or other chemical 

 agents. The glass tubes in which radium salts have been kept 

 always become discoloured, generally assuming pretty rapidly 

 a purplish tint. Sir William Crookes has also shown recently 

 that the diamond may acquire and retain indefinitely the 

 property of radio-activity. In the Philosophical Transactions 

 of the Royal Society for 1914 he thus describes a case : " A 

 large brilliant-cut diamond of pure water assumed a fine green 

 colour after having been kept for sixteen months (from May, 

 1904, to September, 1905) in a bottle and covered with powdered 

 radium bromide. At the end of that time it was highly radio- 

 active. This diamond has been carried about in my pocket, oi! 



