140 . Prof. J. JoJy on a Method of Investigating the 



the suggestion to Prof. E. Werner) stirred into the charge 

 in the form of powder, confers an intensity of effervescence 

 upon it in no way inferior to that obtaining in the case of an 

 acid rock. 



In order to investigate the capabilities of this new method 

 I took certain rocks which had recently been dealt with in 

 my laboratory under circumstances in every way favourable 

 to the solution method ; no pains having been spared to 

 obtain limpid solutions, and, finally, to effectively boil off the 

 emanation. I refer to the rocks which entered into Mr. 

 Fletcher's experiments on the granites of Leinster, and into 

 his measurements of the radium in rocks of the Andes 

 tunnel*. The first serving as typical acid rocks, the latter 

 as representing intermediate or basic rocks. 



Before proceeding to these measurements it is evidently 

 necessary to determine the calibration constant of the electro- 

 scope by means of furnace experiments. 



The electroscope used for the purpose had previously been 

 frequently calibrated by the solution method ; uraninite of 

 Joachimsthal having 64 per cent, of uranium being used. 

 The calibrating solution in these tests was a highly dilute 

 aqueous solution of the uraninite, containing some three or 

 four milligrams of the ore and about 30 or 40 c.c. of redis- 

 tilled HC1 in 600 c.c. of distilled water. Such experiments 

 gave for the constant of the electroscope values generally 

 varying closely about 0' 62 X 10~ 12 gram. That is to say, a 

 gain of one scale-division per hour corresponds to this amount 

 of radium. It was also found that equally low constants were 

 not obtained when the solution of uraninite was put into ordi- 

 nary rock solutions or into sea water. The calibration constant 

 then rose to 0*8 xlO -12 , or occasionally somewhat higher. 

 This indicates the retention of some of the added emanation. 

 The absolute values of these figures were found to be 

 justified when the electroscope was finally tested by a 

 standard solution of radium which Professor Rutherford 

 kindly sent me. 



In finding the calibration constant of this electroscope by 

 a furnace experiment some of the same uraninite used in the 

 preparation of the solution referred to above was mixed in 

 the form of powder with an ordinary rock charge, and the 

 experiment proceeded with in the usual manner. Subse- 

 quently a precisely similar charge, save that the uraninite 

 was omitted, was dealt with in the furnace. The effect on 



* A. Fletcher, Phil. Mag. July 1910, and Jan. 1911. 



