226 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1925 



The insoluble sulphates are first purified and enriched by chang- 

 ing them in an autoclave under pressure into alkaline carbonates; 

 next they are chano^ed into chlorides by solution of these carbonates 

 in hydrochloric acid. These operations are repeated a second time 

 after which the carbonates are rich enough to be passed into the 

 crystallization laboratory. At the time of the solution of the 

 carbonates in hydrocliloric acid, a radiferous silica is ahvays precip- 

 itated Avhich is given a special treatment for its radium. The car- 

 bonates are finally transformed into chlorides. These chlorides, es- 

 sentially a mixtuie of the chlorides of barium and radium, are sub- 

 mitted to fractional cr3'stallization. 



When a certain richness in radium is reached, it is best to trans- 

 form the chlorides into bromides; the product undergoes an in- 

 crease in richness. ]\Ioreover, commercially radium is used as the 

 bromide. 



The initial hj^drochloric liquid containing the vanadium is treated 

 to recover the vanadium. The solution is neutralized by sodium car- 

 bonate, then carried to the boiling point, in order to carry the 

 vanadium into a precipitate of vanadic acid containing iron, uranium, 

 etc. All the vanadium is never precipitated. The addition of soda 

 to the liquid just separated from the vanadium precipitates the 

 uranium as the insoluble uranate of sodium, carrying down with 

 the precipitate the greater part of the remaining vanadium. In 

 the United States they go no farther than this first precipitation 

 which gives the oxide of vanadium, since the demand for vanadium 

 is very small. 



We will now consider some of the details in the separation of 

 barium and radium. It depends upon the difference in solubility 

 of the tAvo chlorides or the tAvo bromides, those of radium being the 

 less soluble. The operations commence with the chlorides and are 

 finished with the bromides Avhen the concentration of the radium 

 has reached a minimum of 20 milligrams of radium per kilogram 

 of the salt. 



The ratio between the concentration in the crystals separated to 

 that of the initial crystals is called the factor of crystallization. The 

 concentration of radium is generally defined by the number of milli- 

 grams of radium contained in a gram or a kilogram of the anhydrous 

 crystal. 



In the case of the chlorides, the factor of crystallization is 1.6, when 

 the crystals separated represent 50 per cent of the total Aveight 

 treated. AVith the bromides the factor is raised to 2.2 with a separa- 

 tion of crystals amounting to 42 per cent of the total. 



The following sketch (Barker) shows very clearly the march of 

 crystallization occuring with the chlorides, dividing at each crystal- 

 lization a half of the salt into two equal parts. At the start a kilo- 



