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LII. The Radium Content of the Books of the Loetschberg 

 Tunnel. Bij J. H. J. Poole, B.A.I* 



HT^HIS series of results was obtained some years ago, but 

 X its publication has been delayed owing to circumstancs 

 arising out of the war. The fusion method of determining 

 the radium content was employed in all cases. This method 

 has been fully described by Prof. Joly in previous papers f, 

 but perhaps a brief recapitulation of the process employed is 

 desirable. 



The rock to be dealt with is first pulverized till it passes 

 through a. sieve of about 25 mesh to the centimetre. Six 

 grammes ofthe powdered rockare weighed out and 18 grammes 

 of an equal mixture of potassium and sodium carbonate are 

 added. In the cnse of calcareous rocks about one gramme 

 each of borax and boracic acid is also used in order to increase 

 the evolution of C0 ;; . The resulting mixture is heated in a 

 platinum boat in an electric tube furnace to about 1100° C, 

 at which temperature the rock is completely decomposed. 

 A large amount of C0 2 is evolved during this process, which 

 is led through a soda-lime tube, where it is absorbed ; and 

 the residual gases (for the most part air driven out from the 

 furnace by thermal expansion) are stored in a strong rubber 

 bladder. When the rock is completely decomposed (an hour 

 is usually amply sufficient for this purpose), an exhausted 

 electroscope is attached to the apparatus, and all the gases 

 are swept into the electroscope, the arrangement being such 

 that the gas in the rubber bladder is carried through the 

 furnace and soda-lime tubes again before reaching the elec- 

 troscope, thus ensuring a thorough wash-out of the system. 

 Any excess of air necessary to fill the electroscope is drawn 

 in through a mercury trap at the far end (from the electro- 

 scope) of the tube furnace ; this air also serving to ensure 

 that the last traces of emanation are carried into the electro- 

 scope. All the air used, both for filling the electroscope and 

 also for supplying the mercury trap connected to the furnace, 

 was drawn in from outside the laboratory, as it was found 

 that the natural leak of the electroscope did not vary so much 

 from day to day when filled with air thus obtained. 



The electroscope used was one which had previously been 

 standardized by Prof. Joly. Its constant, when working 

 in conjunction with the electric furnace, was 0'75 scale- 

 division per hour per billionth of a gramme of radium, and 

 this constant was accordingly used. No direct sunlight 

 was allowed to enter the room in which the electroscope was 



* Communicated bv Prof. J. Jolv, F.R.S. 

 f Joly, Phil. Mag. July 1911 and Oct. 1912. 



