294 Bolticood — Radio-activity of Uranium Minerals. 



very uncertain and often incomplete. In the course of some 

 further experiments, which will be described in a later paper, 

 where larger quantities of minerals were used, the data obtained 

 on the chemical behavior of actinium indicated that the 

 quantitative separation of this radio-element and its subsequent 

 complete recovery are matters of considerable difficulty. The 

 investigations of other experimenters have been directed 

 chiefly toward determining its qualitative characteristics, so 

 that the information to be found in the literature is of but 

 little assistance. 



Other Experiments. 



Activity of Heated Minerals. — That a greater or less pro- 

 portion of the radium emanation contained in minerals can be 

 expelled by heating has been observed by Strutt.* About one 

 gram of the uraniuite No. 4 (Table IV) in the form of- fine 

 powder was placed in a porcelain crucible, which was enclosed 

 in a covered platinum crucible and heated to bright redness 

 for about ten minutes over a Bunsen burner. The loss in 

 weight of the mineral was determined (3*21 per cent) and a 

 film was prepared from the heated material. About three 

 hours after heating, the activity of this film was measured and 

 at the same time the proportion of the total amount of radium 

 emanation present was determined in a duplicate sample of the 

 ignited mineral. It was found that the ignited mineral 

 contained 46 per cent of its equilibrium amount of radium 

 emanation. After correcting for the activity of the thorium 

 products present, the activity of the uranium and its productsf in 

 the film was found to be equal to 3*51 times the activity of the 

 uranium only. 



A few days later (3 days 19 hours after the first measure- 

 ment) the activity of the mineral in the film was again 

 measured, and the activity of the uranium and its products 

 was found to have risen to 4*08 X IT. When a further j>eriod 

 of 26 days from the start had elapsed the corresponding 

 activity was 4'75xU. Four months later the activity -was 

 4 - 72xtT, and the same value was found when the film was 

 measured about IT months from the time of heating. It was 

 found that after it had been heated, the mineral retained over 

 99 percent of the total radium emanation subsequently formed. 



It is apparent that the final activity reached by the ignited 

 mineral was the same as that found for a natural mineral con- 

 taining equilibrium amounts of all the products. This indicates 

 that the amount of polonium expelled by the heating was 

 inappreciable and allows the activity (3*51x11) found for the 

 freshly ignited material to be taken as a measure of the activity 



*Proc. Roy Soc, lxxiii, 191, 1904. 



f By "uranium and its products" is nieant the uranium and all other 

 active substances except thorium products contained in the mineral. 



