REPORT OF THE DIRECTOR I917 201 



in recent ye*ars, especially for military purposes, that it now con- 

 sumes more radium than is used in medicine. Radium salts are 

 more or less luminous when seen in a darkened room, and this 

 quality is often increased by the admixture of certain other materials, 

 notably zinc sulphide. Hence their value in luminous paints. 

 Radium salts also cause certain minerals to fluoresce, notably the 

 zinc minerals willemite and sphalerite. In Germany, where radium 

 during the war has become scarce on account of the shortage of the 

 ores from which it is extracted, radium salts are said to be pre- 

 served for medical purposes, and mesothorium and other radio- 

 active substances are said to be used in making luminous paints. 



USES OF URANIUM 



Uranium is a heavy white metal, which slowly tarnishes on expos- 

 ure to the air. The chief use of uranium today is as a source of 

 radium. For many years before the discovery of radium, however, 

 uranium compounds were used in a small way in coloring glass and 

 porcelain, in photography, in reagents for chemical analysis, in 

 mordants for dyeing and for other small purposes. The use of 

 uranium metal in small quantities in steel manufacture has been 

 tried with some degree of success. 



ORES OF RADIUM AND URANIUM 



General statement. The principal uranium minerals at present 

 known in nature, which are therefore the principal sources of both 

 uranium and radium, are carnotite and uraninite, with the impure 

 amorphous form of uraninite known as pitchblende. Torbernite, 

 autunite and some of the rarer uranium minerals have produced a 

 little radium and uranium. 



Carnotite and uraninite or pitchblende as mined for ores are 

 generally more or less mixed with other materials and are rarely 

 found pure. The uranium in the ores is usually stated commer- 

 cially for convenience in the form of the uranium oxides represented 

 by the formula UO2 + 2UO3, briefly expressed as U 3 8 . Most car- 

 notite ore varies from 1 per cent to 3 per cent of U 3 8 ; a 5 to 10 

 per cent ore is considered high grade; a 20 to 40 per cent ore is 

 remarkably rich. Uraninite and pitchblende ordinarily contain 

 more uranium than carnotite contains, and even in the impure 

 forms in which they are mined as ores, they often show this greater 

 uranium contents. The ordinary uraninite and pitchblende ores 

 carry from 2 to 3 per cent to 8 or 10 per cent U 3 8 , and a 20 per 



