MANUFACTURE OF RADIUM MATIGNON 231 



The transformation into the chlorides is best made through the help 

 of the carbonates which are finally dissolved in a hydrobromic acid 

 solution. 



In the first series of fractionations all the enriched portions are 

 collected as soon as they have reached a quota of 0.05 per cent of 

 radium. The initial solution of chlorides contained only 0.0001 per 

 cent; accordingl}^, this enrichment is in the ratio to the first .state as 

 125 to 1. This fir.st fractionation takes place in enameled vats, 60 in 

 number, the size of which decreases from the first for the entrance of 

 the material to the last for the enriched crystals. 



The work is now continued in the laboratory. Each batch for 

 further purification contains some 2 to 3 grams of radium in a 

 mixture of some 5 to 6 kilos of the mixed chlorides. 



During the process of concentration the lead is eliminated from 

 time to time by the passage of a current of hydrogen sulphide. All 

 the operations require the use of very pure distilled water, for the 

 least trace of sulphuric acid, not even detectable with barium chloride, 

 will precipitate the radium as a sulphate less soluble than that of 

 barium. Generally a little barium chloride is added to the water to 

 be distilled to remove the least trace of sulphuric acid. 



At the works at Oolen the last fractionation is reached when the 

 radium bromide has l)ecome 95 to 96 per cent pure; that is the market- 

 able form of radium. 



The crystals thus obtained hold two molecules of water and must be 

 dried to preclude an explosive decomposition of the water. An abso- 

 lute dessication is obtained b}^ heating the salt up to fusion. It then 

 appears as a whitish mass very luminous in the dark. It is preserved 

 in glass tubes, sealed by melting the glass. 



We have noted the important part played during the course of 

 treatment by measures of radioactivity. To avoid the disturbing 

 action of any secondary or parasitic radioactivity the measuring 

 laboratory is situated about a kilometer (0.6 mile) distant from the 

 works. 



When the y-rays alone are desired, the sulphate of radium is pref- 

 erably used; its greater insolubility giving better guaranty against 

 loss. But if the emanation is desired, a soluble form is necessary, so 

 that it may be easily removed from the emanation. 



The following table gives the amount of radium in the principal 

 forms found on the market : 



Per cent 



RaCh 76.3 



RaBr^ 58.6 



RaBr2.2H20 53.(5 



RaS04 70. 2 



