Ratio between Uranium and Radium in Minerals. 657 



Dealing first with the pitchblendes, the mean results for 

 the old standards are : — 



A 13-83, B 13-74, C 1397, 



which gives a mean result for this mineral of 13*85. The 

 mean of the three determinations for the mineral " J. P. A " 

 and " J. P. B " is 13*77. So that from these two results the 

 mean value 13*8 may be taken with considerable confidence 

 as representing Joachimsthal pitchblende. The specimen 

 P I, giving a mean result of 12*72, must be rejected, for, 

 as will be seen from Table I., its uranium analysis is far 

 from satisfactory. Indeed this mineral proved most trouble- 

 some to analyse, the uranium content being low and the 

 proportion of foreign constituents high. The mean of the 

 four determinations with Rutherford's radium standard 

 is 14*9 ; so that, if this is taken as the primary standard, 

 the ratio of radium to uranium in Joachimsthal pitchblende 

 is 3*15(xl0 -7 ). The original value given by Rutherford 

 and Boltwoodwas 3*8, which was lowered subsequently to 3*4 

 owing to an error in the uranium analysis (Boltwood, Am. 

 Journ. Sci. 1911, xxv. p. 296). The radium solution pro- 

 vided by Professor Rutherford was part of the original 

 employed by these investigators ; so that, assuming the 

 solution has not changed since its preparation, our results 

 indicate that the corrected value is still somewhat high. The 

 value we have arrived at, 3*15(x 10~ 7 ), is in good agreement 

 with the following results of Mile. Gleditsch, obtained with 

 Mme. Curie's standards of radium (Mme. Curie, Radioactivite\ 

 ii. p. 441): — St. Joachimsthal pitchblende 3*21, Norwegian 

 Cleveite 3*23, Broggerite 3*22, Portuguese chalcolite 3*24. 



Dealing now with the thorianites, the Table shows that 

 although the first specimen investigated, "Thl," as recorded 

 in the last paper, gives an undoubtedly higher value than 

 Joachimsthal pitchblende, it is alone of those examined in 

 this respect. Five different uranium analyses and six esti- 

 mations of the radium in three solutions of this mineral give 

 the mean result 14" 6, which is about 6 per cent, higher than 

 that for Joachimsthal pitchblende. Even if the highest 

 uranium result and the lowest radium result are compared, 

 the value arrived at would still be as high as the mean for 

 Joachimsthal pitchblende . But the other thorianites examined 

 give an entirely different result. The mean five determi- 

 nations on the three minerals is 13*47. Omitting " Th E," 

 for which only one determination has so far been done, the 

 mean is 13*55. Hence the later results have not confirmed 



