276 Bolt-wood — Radio-activity of Uranium Minerals. 



the activity of uranium taken as a standard. In my earlier 

 work* I had found that very satisfactory results could be 

 obtained when the uranium was separated and weighed as the 

 phosphate, but in the present instance it was considered 

 preferable to weigh the separated uranium in the form of 

 uranoso-uranic oxide (U 3 O g ) and to employ as a standard of 

 radio-activity a specimen of the same oxide prepared in an 

 identical manner from a very pure sample of uranium nitrate. 

 The method used for separating the uranium from the min- 

 erals was a slight modification of the method described by 















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Hillebrand.f One gram of the finely powdered mineral was 

 decomposed with dilute nitric acid and the solution was evapo- 

 rated to dryness. The residue was moistened with a little 

 dilute nitric acid, digested with a few cubic centimeters of 

 water and the resulting solution was filtered to remove insolu- 

 ble matter. After further dilution the solution was treated 

 with an excess of hydrogen sulphide and the precipitate of 

 sulphides was filtered off.;}; The filtrate was then evaporated 

 to dryness and the residue was heated for some time at 110° to 

 insure complete drying. The dry residue was thoroughly 

 extracted with pure, dry ether which removed nearly all of the 

 uranium salt present. The material insoluble in ether was dis- 

 solved in dilute nitric acid, and to this solution an excess of 



*Phil. Mag., ix, 603, 1905. 



f Bulletin U. S. Geological Survey, No. 78, p. 46, 1891. 



% It was found that when the precipitation was conducted in a very dilute 

 nitric acid solution the precipitate could be filtered off and completely 

 washed without the slightest difficulty. When a dilute hydrochloric acid, 

 solution was used the precipitated sulphides could not be satisfactorily 

 removed as they ran through the finest filter paper with great readiness. 



