38 Mr, A. L. Fletcher on the Radioactivity of 



the leaf, consequent upon the rapid introduction of the 

 emanation, from an aqueous solution containing 1 m.g. 

 uraninite. Subsequently the calibration was effected under 

 conditions more nearly approximating to those obtaining 

 when a rock or low radium content is being examined. To 

 this end a quantity of radium was used, more nearly com- 

 parable with the amount found in the solutions examined, 

 and one of the electroscopes was calibrated from an alkaline 

 rock solution, whose radium content had been previously 

 determined ; the other similarly from an acid solution. 



The following results will show that the calibration of 

 the electroscopes under the new conditions resulted in a 

 marked modification in the constant. The following is a 

 list of the calibrations. 



Electroscope A. 



(1) Standardized from 1 m.g. uraninite (from a standard 

 solution of a uraninite containing 64 per cent, uranium, made 

 by dissolving the mineral in HNG 3 , and diluting to a strength 

 of 1 m.g. in 1 c.c.) in about 500 c.c. distilled water ; enclosed 

 for 19 hours 25 minutes, involving the accumulation of 

 14 per cent, of the equilibrium amount of the emanation. 



The transference was through a capillary tube and occupied 

 about ten minutes. 



Gain = 60 scale-divisions per hour. 



From this C = 0-52xl0" 12 , 



where C represents the quantity of radium in grams re- 

 sponsible for a gain of one scale-division per hour. 



(2) An earlier experiment of the same character gave 



G= 0-51 xlO- 12 . 



In these experiments the emanation in the electroscope 

 would be equivalent to an amount in equilibrium with 

 31*2 x 10 -12 gram of radium, i. e. a quantity almost four 

 times in excess of the average measured in the experiments, 

 in which the gain was seldom over 20 scale-divisions per 

 hour. 



(3) Standardized with *4 m.g. uraninite in 600 c.c. distilled 

 water. Closed 20 hours, i. e. 14'4 per cent, emanation col- 

 lected. Boiled 36 minutes with talc, using slow admission 

 to electroscope. Emanation present in electroscope equivalent 

 to- 12*5 X 10" 12 gram radium in solution. 



Gain = 24*5 scale-divisions per hour. 

 Hence C = -51xl0r M . 



