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



specimen of Joachimsthal pitcli blende containing a much 

 larger proportion of uranium. " G.E.A.P." was a German 

 East-African pitchblende. The autunites were all specimens 

 of Portuguese autunite. A specimen of the new mineral 

 pilbarite was obtained from Mr. Simpson of the West 

 Australian Government Survey. It is described in the 

 'Australian Mining Standard/ 7/9/10 (Chem. News, 1910, 

 cii. p. 283). 



Method of Estimation of Radium. — The radium was esti- 

 mated in the solution of the mineral by the emanation 

 method. The apparatus used was at first (series A) that 

 described by one of us (Phil. Mag, 1909 [6] xviii. p. 846). 

 Later a new apparatus was employed with a microscope of 

 about four times less magnifying power. With this instrument, 

 the leaf was charged positively instead of negatively, and 

 was not kept charged during the period of three hours pre- 

 ceding the measurements (series B and C). A period of 

 about three months elapsed between series B and C. In all 

 twenty-seven radium preparations were used including the 

 six old pitchblende standards already described (loc. cit.), 

 representing twelve different minerals. These were pre- 

 pared by dissolving quantities of minerals which could be 

 accurately weighed, and taking a known fraction by weight 

 of the solution. 



Table II. shows the results. Column (1) gives the desig- 

 nation of the preparation, those bracketed being of the same 

 specimen of the same mineral. Column (2) gives the number 

 of milligrams of uranium in the preparation. Columns 

 3, 4, 5 give the number of divisions of leak of the electro- 

 scope-leaf per minute in the three respective sets of 

 observations, and 6, 7 ', 8 the same per milligram of uranium 

 present. 



The old standards I. to VI. had existed for nearly four 

 years, and comparing the results in Table II. with the deter- 

 minations previously published (loc. cit.) made at the time of 

 preparation, the variations among the standards are rather 

 larger than they were initially, but do not show any certain 

 influence of age. " R I " and " R II }) were made up on 

 June 16, 1910, from a solution of radium bromide obtained 

 from Professor Rutherford, and described by him as con- 

 taining 1570 xlO -12 gram of radium. The Rutherford- 

 Bolt wood ratio is assumed in stating the quantity of 

 uranium in these (3*4 xlO -7 gram of radium per gram of 

 uranium). 



