Amount of Thorium in Sedimentary Bocks. 353 



wave-length of maximum radiation at temperature T, and 

 which is by Wien's displacement-law a universal constant, 

 suffices and is required, in conjunction with the other re- 

 cognized universal constants of nature, to establish an absolute 

 system of fundamental units of mass, length, and time ; its 

 dimensions are therefore not expressible in terms of those of 

 other universal constants, and it must have an independent 

 existence of its own. 



Cambridge, July 4, 1910. 



XXXIII. The Amount of Thorium in Sedimentary Rocks. 

 II. Arenaceous and Argillaceous Rocks. By J. Joly, 

 F.R.S.* 



IN this paper the results of thorium measurements applied 

 to detrital sedimentary rocks are given. The method 

 used has been described in previous papers (Phil. Mag. May 

 and July 1909). The rock is ground to a fine powder and 

 passed through a sieve of 100 mesh to the inch. It is then 

 mixed with from 2-J- to 3^ times its weight of mixed car- 

 bonates (thorium-free) and fused in a closed platinum 

 crucible till effervescence ceases. The melt is thrown while 

 fluid into a platinum dish, and what remains in the crucible 

 chilled and broken out. The fragments are then ground 

 to a coarse powder in a mortar and leached in hot water 

 over the water-bath. After standing all night the cold 

 supernatant liquid is removed by decantation. The residue 

 is ground to a paste in the mortar ; about 100 c.c. of water 

 added, and finally 80 to 100 c.c. of strong HC1 (thorium-free) 

 rapidly stirred in. The final solution is seldom quite limpid. 

 I have not found, however, that the presence of a small 

 amount of precipitate interferes with the liberation of the 

 emanation. Known quantities of a thorite solution added to 

 such rock solutions, or mixed with the rock-po^ der before its 

 decomposition in the crucible, produce the sr.me effect upon 

 the electroscope, sensibly, as do limpid aqueous solutions 

 containing the same quantity of thorium. 



The alkaline solution, which is poured off the insoluble 

 part of the melt, contains very little thorium ; in most cases 

 none that can be detected with certainty under the con- 

 ditions of the experiment, whether the solution is acidified 

 or not. The examination of the alkaline solutions has, 

 therefore, not been carried out in every case. The investi- 

 gation is tedious and generally indecisive,, many hours of 



* Communicated bv the Author. 



