56 Messrs. J. H. L. Johnstone and B. B. Boltwoo'd on the 



The specific activity of the uraninite was determined by 

 the measurement of four films weighing from approximately 

 2 to 6 milligrams. The results are given in Table II. 



Table II. 



Film Weight Activity in divisions per 



Number. gram. minute per gram. 



27 0-00387 2627 



28 0-00240 2655 



29 0-00588 2627 



30 0-00170 2600 



These results give the mean value for the specific activity 

 of the uraninite as 2624 divisions per minute per gram. 



As already stated, the mineral contained 0"019 gram of 

 thorium oxide (and other thorium products in equilibrium 

 with this) per gram of mineral. The above value for the 

 specific activity of the mineral includes the increment due to 

 the thorium products which must be eliminated. To accom- 

 plish this measurements were made of a series of films pre- 

 pared from a specimen of thorite containing 52 per cent, of 

 thorium oxide and 0"37 per cent, of uranium. The results 

 are tabulated in Table III. 





Table III. 





Film 



Number. 



Weight 

 gram. 



Activity per gram in 

 divisions per minute. 



39 



00056 



511 



40 



0-0076 



515 



42 



0-00776 



514 



Av. 513 



The activity of the uranium and its radioactive products 



contained in the thorite will closely equal 



9A9A 

 ( . "--. X 0'0037-=13*3 divisions per minute. 



Correcting the specific activity of the thorite by this number 

 and dividing the remainder by 0'52 (the weight of thorium 

 oxide per gram) we obtain 960 divisions per minute as the 

 activity of one gram of thorium in equilibrium with its pro- 

 ducts. We may now correct the value found for the activity 

 of the uraninite by an amount equal to the activity of 

 the thorium components (960 x 0*019), and obtain the value 



