present in Rocks in the Neighbourhood of Montreal. 237 



rocks have to be examined, the extraction of the emanation 

 by heating may serve as a valuable preliminary test, and 

 furnish an indication of the amount of material which should 

 be reduced to a state of solution, in order to obtain an 

 accurate determination with the least expenditure of time and 

 chemicals. 



Some tests were also made of the effect of adding a little 

 sulphuric acid to the solution of Tinguaite. The radium was 

 then probably precipitated, for the emanation was not freed 

 by boiling. In one experiment the amount obtained was 

 only one-fifth of that measured previous to the addition of 

 the sulphuric acid. 



A special experiment was made with Tinguaite. which was 

 finely powdered and the soluble portion was leached out 

 with water. When tested, the insoluble gave about eight 

 times as much emanation as the soluble. The addition of 

 HC1 made no change in the ratio nor in the total amount 

 obtained. In the case of clay, Strutt found that the total 

 emanation could not be obtained until HC1 was added. The 

 ratio of the emanation derived from the acid and alkaline 

 solutions, as found by Strutt for various substances, is about 

 the same as that found by us in Tinguaite. 



In a previous paper published in this Magazine (Sept. 1906) 

 an account was given of an attempt to measure the amount 

 of radium in the earth from the penetrating radiation due to 

 it. The result found was 10" 5 x 10 — 12 gram of radium per 

 gram of rock, and it depended upon Cooke's value of the 

 penetration radiation measured on the College campus at 

 Montreal. The subsoil consists of Saxicava sand and Leda 

 clay ; and it is clear that the value found by the penetrating 

 radiation method, although of the right order, is too large, 

 unless there is a large quantity of radiothorium in the ground. 

 Or a partial explanation may be found in the value of the 

 coefficient of absorption of the y rays by rocks. Wigger 

 has found that the value of \ for the most penetrating- 

 rays is considerably less than that assumed in the paper in 

 question. 



We are indebted to Professor Rutherford for his interest 

 and advice in this work, and to Professor Adams and 

 Mr. Bancroft for their assistauce in matters geological. 



McGill University, Montreal, 

 Mav 1907. 



