H. M. Dadoiwitm — Radio-activity of Thorittm. 427 



Art. XXXVIII. — The Radio-activity of Thorium •* by 

 H. M. Dadoukian. 



It has been shown by O. Halm f that it is possible to sepa- 

 rate from thorianite minute quantities of a radio-active sub- 

 stance which is far more active than what is known as thorium. 

 The fact that this substance gives off the same emanation as 

 thorium has led him to suggest that the activity of thorium 

 may be due to the presence in thorium of this substance, which 

 he has named radio-thorium. He has further made the natural 

 supposition that radio-thorium is a disintegration product of 

 thorium. But so far as the writer knows, radio-thorium has 

 not yet been separated from any source except thorianite and 

 no quantitative determi- 



nations 

 between 

 thorium 

 activity 

 so that 



of the relation 

 the amount of 

 and its radio- 

 has been made, 

 the interesting 



c 



B 



A 



suggestions mentioned 

 above cannot be regarded 

 as fully confirmed. 



The following experi- 

 ments were undertaken in 

 order to determine the 

 quantitative relation be- 

 tween the thorium activ- 

 ity of various minerals 

 and separated salts, and 

 their content of thorium. 



The method used is 

 based upon the measure- 

 ment of the excited activ- 

 ity obtained by exposing 



a negatively charged body to the emanations evolved by the 

 substance to be tested. The adjoining figure is a sketch of 

 the charging vessels used in these experiments. Each mineral 

 or salt to be tested was dissolved and the solution poured into 

 a flat-bottomed glass dish, A, of 9"5 cms diameter and 4 cms 

 depth. This was placed in a tin vessel, C, of 15 cms diameter 

 and 18 cms height, which had a movable cover and could be made 

 air-tight. The body upon which the active deposit was to be 

 obtained was a circular copper plate, BB, of H cms diameter, 



*Eead before the American Physical Society, Feb. 24, 1906. 

 f Chemical News, April 28 and Dec. 21, 1905, Jahrbtich fur Radioactivitat 

 und Electronik, 1905. 



