102 THE ROYAL SOCIETY OF CANADA 



operation. In some laboratories^ the emanation from the standard 

 solution is introduced by drawing into the electroscope a current of 

 air which is allowed to bubble through the solution. This method 

 has certain disadvantages which need not be considered here. Another 

 method of calibrating an electroscope in terms of radium has been 

 suggested ^ which consists in collecting the total amount of radium 

 emanation in equilibrium with the radium contained in a known 

 weight of suitable uranium mineral whose uranium content is known. 

 This may be accomplished in two ways. Either the mineral is dis- 

 solved under suitable conditions and the emanation set free is collected, 

 or^ a solution of the mineral is prepared, sealed up, and allowed to 

 stand until the equilibrium amount of emanation has accumulated. 

 In the former case it is only necessary to determine the proportion 

 of emanation^ which spontaneously escapes from the powdered mineral 

 used as a specimen, thus involving two determinations, with the 

 consequent possibility of considerable error. The second method is 

 open to objection since there is* usually a lack of assurance that the 

 radium salts remain in solution, an essential requirement if the results 

 are to be trustworthy. Either of these methods is inconvenient and 

 somewhat troublesome, especially in the hands of those who are not 

 particularly experienced. 



In any series of experiments involving the frequent determination 

 of radium it is important to calibrate the electroscope from time to 

 time as its sensibility is subject to occasional and unavoidable varia- 

 tions. For calibration the use of a specimen of primary uranium 

 mineral in which the proportion of uranium present is determined by 

 analysis has the additional drawback that the accurate quantitative 

 determination of uranium is, from the analytical standpoint, a some- 

 what difficult operation. The use of such a mineral involves also, as 

 has already been mentioned, the determination of the "emanating 

 power" of the mineral and the assumption that this emanating power 

 is a constant under the general conditions of experiment. It has been 

 observed ^ by a number of experimenters that solid substances con- 



^ This method is used in the laboratory of Madame Curie. 



5 Boltwood. B. B., Am. Jour. Sc. 18, 381, 1904; Phil. Mag. 9, 599, 1905. 



« Heimann und Marckwald, Phys. Zeit. 14, 303, 1913. 



7 Boltwood, B. B., Phil. Mag. 9, 599, 1905. 



8 Boltwood, B. B., Am. Jour. Sc. XXV, 294, Ap. 1908, also Phil. Mag. 9, 599, '05. 

 Dorn, Abh. der Naturforsch, Ges. fur Halle -a-s, 1900. 



Rutherford, Phys. Zeit. 2, 249, 1901. 



P. Curie, Theses presentee a la Faculté des Sciences de Paris, 1903, p. 1-9. 



Strutt, Proc. Roy, Soc. LXXHI, 191, 1904. 



Kolowrat, Le Radium, 4, 317, 1907; 6. 321, 1909; 7, 266, 1910. 



