44 Radioactivity of Rocks of the Transandine Tunnel. 



No. 



1. 



2. 



3.' 



4. 



5. 



6. 



7. 



8. 



9. 

 10. 

 11. 

 12. 

 13. 

 14. 

 15. 

 16. 

 17. 

 18. 

 19. 



Description. 



Trachyte 



Tuff 



Tuff 



Felspathic Tuff 



Tuff 



Tuff 



Audesitic Tuff 



Oligoclase Trachyte 



Trachyte 



Trachyte 



Andesite 



Trachyte 



Tuff 



Sanidine-Oligoclase-Trachyte 



Tuff 



Tuff 



Felspathic Tuff 



Sanidine-Oligoclase-Trachyte 

 Tuff 





2-425 

 2-425 

 2-500 

 2-650 

 2-650 

 2 725 

 2-850 

 2-890 

 3-125 

 3-158 

 3-200 

 3-360 

 3-466 

 3-540 

 3545 

 4 209 

 4-409 

 3(509 

 4-709 



Mean 



o g 



I % 



•32 



•80 



•40 



114 



1-40 



1-26 



•90 



•35 



•77 



•57 



•52 



•64 



111 



107 



•68 



•93 



133 



•33 



•58 



© 5 

 X M 



H So 



•39 

 ■43 

 

 ■05 



•58 

 •31 

 •51 

 •41 

 •27 

 •84 

 •71 

 •85 

 111 

 •55 

 •30 

 •83 



79 



•56 



State of 

 Solution 



It may be noted that the mean ratio borne by the thorium 

 content of these rocks to the radium content, viz. *71 x 10 7 , 

 bears an approximation to that obtained by Professor Joly 

 in a paper on " The Radioactivity of certain Lavas " (Phil. 

 Mag. October, 1909), where the proportion of thorium to 

 radium found was *65 X 10 7 . 



The striking feature of these results is their poorness in 

 radioactive matter. This may possibly be referred to the 

 alterations undergone by the rocks, which may have been 

 attended by the removal of all that part of the radium 

 which was soluble in percolating waters. In no case was 

 any trace of radium, and in few cases was any thorium 

 discovered in the alkaline solutions. 



The quantities of radioactive matter observed would give 

 rise to very small heating effects. Taking the mean radium 

 content for the rocks in the neighbourhood of the tunnel as 

 •79 X 10~ 12 gram per gram, and the thorium content as 

 •52 X 10~ 5 gram per gram, we find for the radium the rate 

 of evolution of heat as 20P6 x '79 x 10" 12 = 1*6 x J 0" 10 calorie 

 per gram per hour ; and for the thorium — allowing that the 

 heat produced per hour per gram of elemental thorium in 



