THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XIV. — On the Ratio of Radium to Uranium in some 

 Minerals ; by Bertram B. Boltwood. 



The experiments which will be described in this paper were 

 undertaken with the object of determining the relative propor- 

 tions of radium and uranium present in certain mineral sub- 

 stances.* 



The method which has been used for the quantitative estima- 

 tion of the radium depends upon the electrical measurement 

 of the radium emanation which is given off when a known 

 quantity of the mineral is dissolved or decomposed by suitable 

 chemical reagents and this solution is allowed to stand for 

 several days in direct communication with a closed glass vessel. 

 Another plan which has also been tried is to decompose the 

 mineral completely in an open vessel and to heat the solution 

 to boiling in order to expel all of the accumulated emanation. 

 The solution was then sealed up in a closed glass vessel and the 

 emanation allowed to accumulate for a given period, at the end 

 of which it was removed and measuredf. 



The testing of the emanation was carried out in an air-tight 

 electroscope (fig. 1) similar in principle and design to that 

 described by C. T. R. Wilson. It consisted of a rectangular 

 brass case A, 15 cm high, 10 cm wide and 4-5 cm deep. The 



*A preliminary notice in which some of the results were given has already 

 appeared in the Engineering and Mining Journal, lxxvii, p. 756, and in the 

 London Nature, lxx, p. 80. 



fin a paper by Strutt (Proc. Eoyal Soc, lxxiii) some measurements of the 

 amounts of radium emanation given off by certain minerals on heating are 

 described. Some experiments which I have made show that samarskite, on 

 heating to low redness, gives off only 10 per cent, and on heating to bright 

 redness only 20 per cent, of the emanation set free when this mineral is com- 

 pletely decomposed with hot sulphuric acid. 



Am. Jour. Sci. — Fourth Series, Vol. XVIII, No. 104. — August, 1904. 



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