POPULAR SCIENCE 59 



radium workers, such protection is unnecessary, as the rays 

 pass through the body without any ill effect. In respect of the 

 human body, it is only against the alpha and beta rays that 

 one must and fortunately can guard. 



A Costly Commodity 



The distribution of radium in the earth's crust is universal ; 

 but it no more pays to extract radium from low-grade ores than 

 it does, for example, to separate from the sea-water the gold 

 which we know is contained in it in appreciable amounts. The 

 labour of extraction goes up enormously as the concentration 

 falls. Sir Ernest Rutherford has calculated that the total 

 amount of radium in the earth's crust is of the order of 500 tons ; 

 but the majority of this is so diffusely distributed as to be in- 

 separable by any known process. 



It is upon uranium ores that the world depends for its supply 

 of the precious metal ; and, as the proportion of radium to 

 uranium is always about one in three millions, it is sufficient for 

 the radium prospector to establish the presence of uranium. 

 At present radium is derived from the richer ores of uranium, 

 such as the pitchblende found in Australia and in Cornwall.. In 

 Colorado the mineral carnotite is being successfully worked, 

 while Portugal has sent us considerable quantities of radium 

 extracted from the mineral autunite. The first consignment 

 of radium from Australia came over quite recently. It is inter- 

 esting, finally, in this regard, to note that the lava from 

 Vesuvius is steadily growing more radioactive with each 

 eruption. 



It is believed, however, that not much more than one 

 ounce of radium has yet been, separated. It will therefore be 

 recognised that it is by far the most costly substance ever yet 

 sold in commerce. Its price indeed has been steadily 

 advancing in consequence of the great demand, and has now 

 reached a figure in the neighbourhood of £20 a milligram, 

 which is at the rate of £600,000 a n ounce ! Such a high-priced 

 commodity is naturally liable to many commercial abuses, and 

 a prospective purchaser of radium should emphatically insist 

 on its previous standardisation by the National Physical Labora- 

 tory at Teddington. The British Radium Standard (which 

 may be found described in Kaye's X Rays, published by Messrs. 



