Amount of Thorium in Sedimentary Rocks. 125 



\nt*= A.uRKp where X m is the wave-length for which e has 

 its maximum value, gives with the expression found for S¥ 



16<7ra' 



c^: 



(4-965\ m )' 





Consequently the number of elements of disturbance per c.c. 

 can be calculated from \ m without knowing the density of the 

 energy. Since \ m t-=0'294:, we get approximately 



Thus at 2000° on the absolute scale there are 1 56 x 10 11 

 elements per c. c. in full radiation according to the theory 

 considered here. 



Montreal, April 13, 1910. 



^ -- — 



X. The Amount of Thorium in Sedimentary Rocks. — 

 I. Calcareous and Dolomitic Rocks. By J. Joly, F.R.S.* 



THE systematic determination of the amount of thorium 

 in sedimentary rocks does not seem to have been 

 hitherto attempted. Using a method already fully described 

 by me (Phil. Mag., May and July 1909) I have recentlv 

 measured the thorium content of calcareous and dolomitic 

 rooks from various parts of the world and of various geolo- 

 gical ages. The results are given below. 



In all cases, the rock after being brought to a coarse powder 

 was treated with 100 ccs. of HC1 diluted to a bulk of 200 ccs. 

 with distilled water. A test applied to 500 ccs. of the acid 

 used showed no trace of thorium. After the first violent 

 effervescence had ceased, the whole was heated for a couple 

 o£ hours on the water-bath. The undissolved part was then 

 filtered off, dried, and fused with about twice its weight of 

 the usual fusion-inixture of the carbonates of sodium and 

 potassium. The melt was then leached with water and 

 acidified with sufficient acid rapidly stirred up with it. In 

 most cases a clear or almost clear solution resulted, which 

 could be added to the solution containing the soluble part of 

 the rock. In a few cases, where the insoluble residue, 

 obtained after treating the rock with HC1, was large, the 



* Communicated by the Author. 



