THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXX. — On the Radio-activity of Uranium Minerals ; 

 by Bertram B. Boltwood. 



[Contributions from the Sloane Physical Laboratory of Yale University.] 



A comparison of the radio-activity of uranium minerals 

 with the radio-activity of freshly prepared uranium com- 

 pounds and metallic uranium was first made by Madame 

 Curie* and is of interest chiefly because it was one of the 

 first steps which led to the discovery of polonium and radium. 

 Further, and much more elaborate, experiments of a similar 

 character have been carried out by McCoy, who has published 

 a number of important papers on the subject. In McCoy's 

 first paperf it is stated that the uranium minerals (free from 

 thorium) have an activity which is 5 - 7 times as great as that 

 of the uranium which is contained in them. In a subsequent 

 paper the value of the ratio was found to be 4*15, ^ and in a 

 recently published paper§ the value is given as 4 - 54. These 

 differences in the value for the ratio are due to the introduc- 

 tion of certain modifications in the methods of analysis, meas- 

 urement and calculation which were employed. 



A knowledge. of the exact value of this ratio is highly desir- 

 able and its determination is by no means a simple matter. 

 It is also equally important that we should know what part of 

 the total activity of a uranium mineral is due to each of the 

 separate radio-elements or products which are contained in it. 

 It was particularly with a view to obtaining light on the latter 

 question, namely, the relative proportion of the total activity 

 of uranium minerals due to each separate active constituent, 



*S. Curie, C. E., exxvi, 1101, 1898. 



+ Ber. d. chem. Ges., xxxvii, 2641, 1904. 



JPhil. Mag., xi, 176, 1906. 



g McCoy and Eoss, Jotir. Am. Chem. Soc, xxvii, 1698, 1907. 



Am. Jour. Sci. — Fourth Series, Vol. XXV, No. 148. — April, 1908. 

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