of the Radio-active Elements. 



85 



which would be formed according to this hypothesis, and to 

 compare this amount with the amount actually present in the 

 minerals. 



Calculations and comparisons of this sort have been made 

 for a number of minerals and the results are given in the fol- 

 lowing table (Table IV). 



Table IV. 



Per cent 



Per cent Helium 



No. Mineral Lead present 



1. Uraninite, Glastonbury, Conn., 2-9 0-34 



2. Uraninite, Branchville, Conn., 4-0 0*39 



3. Uraninite, Elvestad, Nor., 9-3 0-18 



4. Uraninite, North Carolina, 3*9 0-05 



5. Uraninite, Skaartorp, Nor., 8 - 8 0-15 



6. Uraninite, Huggenaskilen, Nor., 8*8 0-15 



7. Uraninite, Annerod, Nor., 8*4 0-17 



8. Uraninite, Elvestad, Nor., 8-0 0-15 



9. Uraninite, Llano Co., Tex., 9-4 0*08 



10. Uraninite, Colorado, 0-6 0-02 



11. Uraninite, Arendal, Nor., 10-2 0-16 



12. Thorianite, Ceylon, (2*6) 0-16 



13. Aeschynite, Hitteroe, Nor., (1-2) 0*02 



14. Samarskite, North Carolina, (0'42) 0-03 



15. Gadolinite (?), Ytterby, Sweden, (0-25) 004 



16. Cyrtolite, Texas, (0-53) 0-02 



17. Euxenite, Arendal, Nor. (0-41) 0-013 



18. Uraninite, Canada, 10-5 0*12 



19. Thorianite, Ceylon, 2-40 0-19* 



20. Thorianite, Ceylon, 2-25 0-15 



Nos. 1 to 11 and No. 18 are from analyses by Hillebrand, 

 Nos. 12 to IT from determinations by Strutt (the per cent of 

 lead being calculated from the ratios in Table I), No. 19 from 

 the analysis of Dunstan and Blake, and No. 20 from that of 

 Biichner. In the last column under the heading R is given 

 the ratio of the amount of helium actually present to the 

 amount formed according to the -hypothesis multiplied by 100, 

 or in other words, the percentage of the total helium formed 

 which has been retained by the mineral. 



It will be noted that the values obtained in this manner for 



R are very reasonable numbers and are not unlike what might 



be expected from general considerations. This relation is the 



more evident when the density of the minerals is also exam- 



* In the analysis of Dunstan and Blake an error is made in calculating the 

 per cent of helium in this mineral, which is given as 0"39 per cent of helium. 

 It is stated that the mineral contained 10"5 CC of helium per gram which is 

 equal to 049 per cent of helium. 



Per cent 

 Helium 

 calcu- 

 lated 



0-43 

 0*60 

 1-40 

 0-58 

 1-32 



•32 



'26 



■21 



•40 

 0-10 

 1-53 

 0-40 

 0-18 

 0-06 

 0-04 

 0-08 

 0-06 

 1:6 

 0-36 

 0-34 



E 

 79 

 65 

 18 



9 

 11 

 11 

 13 

 12 



6 

 20 

 10 

 40 

 11 

 50 

 100 

 25 

 20 



8 

 53 

 44 



