Boltwood — Radio-activity of Uranium Minerals. 295 



of uranium and its products less 54 per cent of the equilibrium 

 amount of radium emanation, radium A, radium B and radium 

 C. The difference between the initial and final activities, 

 namely, 4*72 less 3"51, equals 1*21 xU; and this value can be 

 considered as equivalent to 54 per cent of emanation and prod- 

 ucts. This corresponds to a value of 2 - 24xU for the relative 

 activity of the total amounts of radium emanation, A, B and 

 C, a number which is in good agreement with the value 2*09 XU 

 found by the more direct method (p. 283). 



The indications that none of the polonium was volatilized 

 in heating the mineral as described were somewhat unexpected, 

 as this active product is quite readily driven off by similarly 

 heating more concentrated preparations. A further quantity 

 of the mineral was therefore heated in a porcelain crucible over 

 the blast-lamp. The activity of the ignited material was only 

 about 2*0 times the activity of the uranium present. After 

 about thirty days the activity of the uranium and the uranium 

 products was equal to about 3 - 8xU, and this value increased 

 during a further period of about 12 months to 3*95 XtJ. It 

 is probable, therefore, that at the higher temperature a large 

 part of the polonium as well as portions of the other more 

 permanent products were removed. In the case of another 

 portion of the mineral heated to an equally high temperature 

 in an atmosphere of pure oxygen the activity of uranium and 

 its products was reduced to 3*17 XU and the corresponding 

 value four months later was 4'41xU. 



It was noted in general that the emanating power of a 

 mineral was greatly reduced by heating. A sample of carnotite 

 which lost 12 per cent of its radium emanation in the natural 

 state lost only 1*4 per cent after it had been heated to a very 

 low red heat. 



Activity of Old Radium. — Rutherford has shown that 

 polonium is a disintegration product of radium. As he has 

 pointed out,* it is to be expected that old preparations of radium 

 will contain appreciable amounts of polonium, the actual 

 amount depending on the age of the radium salt and the rates 

 of disintegration of the products. The standard solution of 

 radium bromide prepared by Rutherford, Eve and Boltwoodf 

 was made from pure radium which is now at least four years 

 old. A portion (10 cc ) of this solution containing 1-57X10 -8 

 gram of radium was recently evaporated to dryness in a shal- 

 low platinum tray and the activity of the radium free from 

 emanation and immediate products was determined in the 

 electroscope. The activity of the uranium with which 

 l # 57xl0~ 8 gram of radium would be in radio-active equili- 

 brium was then calculated. It was found that the activity of 



*Phil. Mag., x, 290, 1905. f This Journal, xxii, pp. 1 to 7, 1906. 



