H. M. Dadourian — Radio-activity of Thorium. 429 



solutions were found to be 10*9 and 5'4 respectively. These 

 results show that, everything' else being the same, the amount 

 of emanation obtained is strictly proportional to the concen- 

 tration of the solution, as would be expected on theoretical 

 grounds. 



The substances tested, chosen on account of their easy solu- 

 bility, and the results obtained are given in the following 

 table : 







No. of 



Percent- 



No. of 







Substance. 





grams in 



age of 



grams of 



Observed 



Specific 







solution. 



Th0 2 . 



Th0 2 . 



activity. 



activity. 



I. 





II. 



in. 



IV. 



v. 



VI. 



Thorite 





2-00 



51-7 



1-034 



j 25-7 

 ( 26-3 



\ 24-8 

 | 25-4 



Thorianite 





1-29 



76-5 



0-987 



j 21-2 



( 25-2 



j 21-5 

 I 25-5 



Thor. nitrate 



'(I)- 



.. 2-20 



45-6 



1-003 



10-7 



10-7 



« u 



(2)- 



._ 2-15 



46-6 



1-002 



12-5 



12-5 



ec a 



(3)*. 1-00 



38-0 



0-38 



4-3 



11-3 



a a 



(4)- 



._ 0-77 



48-9 



0-376 



8-3 



22-1 



a a 



(5). 



.. 2-U7 



48'3 



1-00 



22-0 



22-0 



Column I. The thorite was dissolved in dilute hydrochloric 

 acid. The solution was evaporated to dryness, to render the 

 silica insoluble, the silica filtered off and the filtrate diluted in 

 50 co of distilled water. The thorianite was dissolved in con- 

 centrated nitric acid, the solution diluted and a slight residue 

 of insoluble material filtered off. The solution was then 

 evaporated to remove the excess of nitric acid and the remain- 

 der diluted to 50 cc with distilled water. The thorium nitrates 

 number (1) and number (2) were prepared by the Welsbach 

 Light Co., from .North Carolina and Brazilian monazites 

 respectively. Thorium nitrate number (3) was bought from 

 Eimer & Amend about three years ago. Thorium nitrates 

 number (4)f and number (5)f were prepared from North 

 Carolina monazite and from thorianite respectively, by Dr. 

 B. B. Boltwood, to whom the writer is indebted for the 

 minerals and salts tested in these experiments, as well as for 

 their chemical analyses. 



Column II gives the number of grams of the substances in 

 the solutions, column III the percentage of thorium oxide in 

 each substance. 



In column IY the number of grams of thorium oxide 

 present in the solutions is given. It is obtained by multiply- 

 ing the numbers of column II by those of column III. 



*The percentage of Th0 2 of this salt was not known, therefore it was 

 calculated from the formula Th(N0 3 ) 4 + 12H 2 0. This gives the minimum 

 percentage, hence the calculated specific activity is maximum. 



f The process of preparation of these salts is given in a paper by Dr. B. 

 B. Boltwood, in this number of the Journal. 



