THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XXXVI. — The Radio- Activity of the Salts of 

 Radium •* by Bertram B. Boltwood. 



The relation between the a-ray activity of a salt of radium 

 from ' which all the emanation and the corresponding active 

 disintegration products have been removed and the a-ray 

 activity of the same salt when the total, equilibrium quantity 

 of emanation and active products are present, does not appear 

 to have been previously determined with any great degree of 

 accuracy. According to Mine. Curie, f the maximum activity 

 attained by solid salts of radium after several months is five to 

 six times that which they possess when first separated from a 

 solution. It is stated elsewhere in the same work (p. 116) that 

 when a sample of radium-barium chloride was heated to a red 

 heat, the final, maximum activity was about 1*5 times greater 

 than that attained by the same salt in the normal, crystalline 

 condition, while, in the case of a similar preparation which 

 had been heated to fusion for several hours, the final activity 

 attained a value over twice as great as that ultimately reached 

 by the salt in the form separated from solution. For radium- 

 barium chloride which had been heated to a cherry-red heat 

 for several hours, the activity of the salt immediately after 

 heating was found to be only 16*2 per cent of the activity of 

 the same salt when tested fifty-seven days later (p. 117). 



Rutherford and Soddyij: have also determined the rise in 

 activity of a solid radium salt in the form of a thin film 



* The general results and conclusions reached in this paper were presented 

 at a meeting of the American Physical Society held in New York City on 

 February 24, 1906. 



f Untersuchung iiber die Eadioaktiven Substanzen. Uebersetzt von W. 

 Kaufmann. Braunschweig, 1904, p. 32. 



JFhil. Mag. (6), v, 445, 1903. 



Am. Jour. Sci. — Fourth Series, Yol. XXI, No. 126.— June, 1906. 

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