POPULAR SCIENCE 57 



ceived from their experiments that the natural activity of the 

 uranium compounds was largely due to the presence of a trace 

 of some other substance. They set to work on a large quantity 

 — more than a ton — of uranium residues ; and, by an almost 

 endless series of precipitations and crystallisations, they finally 

 succeeded in isolating a few milligrams of a salt of a new element 

 of intense activity. In short, they had discovered radium. 



A ton of material contains roughly a thousand million 

 milligrams ; and the laborious work entailed will stand 

 for all time as a monument to the skill and patience which 

 the Curies brought to bear upon a problem calling for the 

 highest technical skill. Since then, radium has been obtained 

 as a shining white metal ; but the name in its everyday use 

 always implies the salts of radium. These are white powders 

 which, in the dark, can be seen to phosphoresce somewhat like 

 a glow-worm. 



A Methuselah among Metals 



Radium is the most amazing and revolutionary substance 

 ever known to man. Unceasingly it gives out heat, light, 

 electricity, and X rays, all of which is effected entirely at the 

 expense of the energy within the atom. And the atom of 

 radium is unstable. So that, though transmutation — the dream 

 of the alchemist — has in the discovery of radium become a 

 reality, it is limited by this restriction, that the change is uncon- 

 trollable by man. We cannot alter by one iota the rate at 

 which radium disintegrates ; we have as yet found no means of 

 controlling the stupendous forces within the atom. 



We now know radium to be one of a number of unstable 

 intermediate products constituting a family-tree, whose original 

 ancestor is uranium and the last surviving member lead. The 

 lives of these various radioactive elements range from a fraction 

 of a second to several million years. Radium itself is the most 

 energetic member of the family and possesses a long life. Two 

 thousand years pass before its activity sinks to half value. 



During the process of disintegration, it emits three different 

 types of rays together with a heavy gas, or " emanation," itself 

 radioactive. These rays are to be regarded as the outward and 

 visible signs of the breaking up of the various atoms. The 

 existence of the rays can be most readily demonstrated by their 



