346 Mr. F. Soddy and Miss Ruth Pirret on the 



points out, it is more difficult to explain why a mineral 

 should possess a greater than normal ratio of radium to 

 uranium than the reverse. But the results with this mineral 

 are not yet decisive. However, the results with autunite are 

 of interest in connexion with the subject discussed in the 

 preceding paper, so that it seems advisable to give an account 

 of what has so far been done. The thorianite solution for 

 the radium estimations was made by dissolving sixty milli- 

 grams of the powdered mineral in nitric acid, which had 

 been distilled over barium chloride, diluting without filtering 

 to a known weight and sealing up a known fraction, deter- 

 mined by weighing. The specimen of thorianite used left 

 about 3*5 per cent, of residue insoluble in nitric acid. 

 Previous experiments had shown that this residue, when 

 examined in an electroscope, was practically free from radio- 

 active matter. No /9-activity whatever could be detected in 

 the insoluble residues from 16 grams of the thorianite, used 

 in the analyses, which had been sealed up in test-tubes for 

 four months. Therefore neither uranium nor radium could 

 have been present in appreciable amount. 



The autunite employed was of Portuguese origin and 

 consisted of beautiful crystals of the pure mineral in a 

 clayey matrix. Twenty grains were used, and the whole of 

 the autunite, consisting of about 40 per cent, of ihe total 

 mineral, was dissolved out in hydrochloric acid. The residue 

 was sealed up in a test-tube. After a month no /3-activity 

 whatever could be detected from the tube, showing that the 

 whole of the uranium and radium had been dissolved. In 

 the hydrochloric acid solution the uranium was estimated 

 in one part and the radium in another. 



Estimation of Uranium in Thorianite. — The method mainly 

 employed was based upon the one described by Boltwood 

 (Am. J. Sci. 1908, xxv. p. 261)), and used by him in esti- 

 mating the amount of uranium in many minerals (including 

 thorianite) containing uranium and thorium. We found 

 however that, as described, it was impracticable for the 

 following reason. The solution of the mineral in nitric 

 acid after removal of the lead with sulphuretted hydrogen 

 is evaporated to dryness at 110°. In Boltwood's description 

 the uranium is mainly removed from the dry residue by 

 extraction with pure dry ether. The part insoluble in ether 

 is then dissolved in dilute nitric acid, treated with oxalic 

 acid to remove thorium and other rare earths. After removal 

 of oxalic acid by ignition the dissolved residue is treated 

 with ammonium carbonate and sulphide to remove iron &c. 

 and the uranium, recovered from the filtrate by boiling, is 



