358 Relative Activities of Radio-Products of Thorium. 



activities are recorded in column five of Table V. In column 

 four are given the calculated activities of the two groups of 

 products ; for ThX + Em -f A the calculated activity is taken 

 as the sum of the values of KR 2 / 3 for the three products. 

 For Ci+C 3 the sum of the values of KR 2 '' 3 would be 2'96 

 while the actual value is 1*54. The explanation of the 

 apparent discrepancy is found in the fact, established by the 

 work of Marsden and Barratt * and of Barratt f, that Ci and 

 C 2 together give per second the same number of alpha 

 particles as the equilibrium amounts of each of the preceding 

 substances, Oi giving 65 per cent, and C 2 85 per cent, of the 

 total. If we add together these fractions of the respective 

 values of KR 2 - 3 for C 1 and C 2 we get 1*56, which is almost 

 identical with the experimental value 1*54. 



In the last column of Table V. are given the theoretical 

 activities, calculated on the basis of the value under KR 2 ' 3 , 

 excepting that for the activity of the components of C, KR 2 :: 

 is taken as 1*56. The theoretical activity as calculated for 

 thorium is 11*4 per cent, of the total activity of the series. 

 Now Ashman J has found 11 per cent, for this activity. The 

 agreement is excellent, but the experimental result is pro- 

 bably not wholly trustworthy because of the probable 

 presence of some ionium in the thorium : since Boltwood § 

 lias found that all the ionium in a mineral remains with the 

 thorium. Ashman/s thorite contained some uranium and 

 must therefore have contained some ionium. However, we 

 may expect that the activity of thorium will actually have 

 just about the value Ashman found. The close agreement 

 between the activities actually observed, as represented by 

 the ratios x and y, and those calculated from the ranges, give 

 farther experimental evidence of the validity of the ex- 

 pression I = KR 23 ; they also lead us to believe that the 

 uncertainty which up to the present time has existed in 

 regard to the thorium series has at last been removed. 



Summary \ 



1. Numerous chemical reactions of the radioactive pro- 

 ducts of thorium were studied. It was found that each 

 product has its own characteristic chemical properties. From 

 a knowledge of these properties, methods were worked out 

 for the separations of the various products from inactive 



* Loo. cit. 



t Le Radium, ix. p. 81 (1912). 



t Am. Jour. Sci. [4] xxvii. p. 65 (1909). 



$ Am. Jour. Sci. [4] xxv. p. 292 (190S). 



