364 



PKOCEEDINGS OP SECTION B. 



One hundred c.c. of water was then put in, and the rate of leak deter- 

 mined. The activity calcuhxted from this rate of leak was subtracted 

 from the total activity. The remainder was the activity of the thorium 

 emanation present. 



Solutions. 



The solutions were obtained thus : Acid soluble minerals dissolved 

 as in anal5'ses, and made up to lOOc.c. with water. Monazites decom- 

 posed with H2SO4 and evaporated dry ; 10c. c. H2SO4 was added, and 

 the sulphates dissolved in 120c.c. ice-cold water. The monozites were 

 all pure, and ^ave only minute residues. The clear solutions could 

 be boiled down quite safely to lOOc.c, getting rid of any radium emana- 

 tion in the process. Aeschynite and pyrochlore were fused with acid 

 potassium fluoride, and then decomposed with concentrated HaSO^ ; dis- 

 solved in about 90c. c. ice-cold water ; filtered off the residue, which was 

 inactive ; made up to lOOc.c. The thorianite blanks were made up with 

 the same amount of acid as the minerals. 



Radium emanation was removed where possible by prolonged boil- 

 ing. The aeschvnite and pyrochlore solutions were not boiled, the 

 emanation being got rid of by drawing a rapid air current through them 

 for several hours in a separate apparatus. 



Actinium emanation jjractically completely decays before reaching 

 the testing cylinder. 



Table of Results. 



Column I. gives the mineral ; column II. the percentage of ThO;j 

 present in it. Column III. is the amount of the mineral taken for 

 radio-active measurement, and column IV. gives the amount of Th02 

 present in that amount of mineral. In column V. the corrected activity 

 {i.e., total activity less the excited activity on the negative electrode) is 

 tabulated. The activity of thorianite is arbitrarily taken as 100. 

 corrected activity 



The ratio 



mass of Th02 

 minations, is shown in column VI. 



-, as calculated from the two series of deter- 



Tahle of Results. 



VII. Remarks.- 



-(o) Rather small lor accuracy. (6) Slight activity, probably from Ac. 

 (c) Tested mineral — inactive. 



