THE TERRESTRIAL DISTRIBUTION OF RADIUM 13 



the earth contained 4*6 x io _u grams of radium, the heat so 

 produced would be equivalent to that brought to the earth's 

 surface by conduction and lost by radiation into space. 



In the following year Rutherford's suggestion was quanti- 

 tatively put to the test by Professor Strutt, who devised a 

 method for determining minute quantities of radium, and applied 



M.s\ m 



PT^ ; ' , '" ; >,"" " T - Tj 



f 



Apparatus for the estimation of Radium. 



The rock is brought into solution by fusion, treatment with water (alkaline solution) and treatment of the 

 resione with acid (acid solution). Each solution is stored up for a few weeks in a closed flask until 

 the equilibrium amount of emanation has accumulated. To estimate the radium in one of the solu- 

 tions the flask A containing; it is attached to the water condenser B. Emanation is expelled by vigorous 

 boiling, the steam condensing in B and falling back into A. At the end of an hour the cooling water is 

 run out of B and the steam then drives the emanation into c, after which the connection at D is closed. 

 Meanwhile the electroscope F has been exhausted and the air of the gasholder c, charged with 

 emanation, is passed into the electroscope through the tap at E. A measurement of the rate of 

 fall of the leaf then suffices to determine the amount of radium emanation present. 



it successfully to a large number of representative rocks. 1 The 

 apparatus employed is figured in the adjoining illustration, to 



1 See R. J. Strutt, Proc. Roy. Soc, A., vol. lxxvii. p. 475, 1906, and A. Holmes, 

 The Age of the Earth, London, 1913, p. 105. 



