760 Prof. J. Joly on the Distribution of Thorium 



[In all experiments on absorption, both the normal absorp- 

 tion of " soft " rays and the special absorption connected with 

 the emission of secondary rays, and on secondary rays, both 

 as regards intensity and character, nickel behaves as a normal 

 element of atomic weight about 61'3.] 



George Holt Physics Laboratory, 

 Liverpool. 



LXX. On the Distribution of Thorium in the Eartlis Surface 

 Materials. By J. Jolt, F.R.S.* 



X) ECENT observations have shown that the emanation of 

 XVi thorium exists in the atmosphere to an extent which 

 is difficult to account for unless a very considerable quantity 

 of the element thorium is distributed in the surface rocks 

 and soils. Thus Bumstead (Am. Journ. Sc. July 1904) and 

 Dadourian (Am. Journ. Sc. Jan. 1905) in New Haven, Conn., 

 Blanc (Phil. Mag. March 1907) at Pome, and Wilson (Phil. 

 Mag, Feb. 1909) at Manchester, have found that of the total 

 active deposit gathered upon a negatively charged wire 

 exposed for many hours to the air, a considerable part — it 

 may be even a major part — exhibits the properties of the 

 active deposit derived from the emanation of thorium. 

 Blanc estimates that at Pome from 50 to 70 per cent, of the 

 whole activity is due to thorium ; and Wilson infers from 

 his observations at Manchester that there must be about seven 

 times as much thorium as uranium in the surface soils. On 

 the other hand, Gockel (Le Radium, Jan. 1909) finds that at 

 Zermatt the emanation of thorium is almost entirely absent. 

 It is a question of much importance to geological science 

 to decide how far these observations refer to purely local 

 conditions, or whether they indicate a general prevalence of 

 thorium in rocks. 



Method of Measurement. 



The material under investigation is brought into solution 

 by the aid of reagents (e. g. hydrochloric acid and the car- 

 bonates of soda and potassium) which are themselves shown 

 to be free from thorium by the method to be now described* 

 The solution is boiled in a flask (see figure, p. 761) to which 

 the steam is returned by an attached condenser. A prelimi- 

 nary boiling, lasting from 20 to 30 minutes, is required to 

 completely expel any accumulated emanation of radium. 

 A small quantity of powdered talc must always be put into 

 the solution in order to secure uniformity of ebullition. 



* Communicated by the Author. 



