H. 31. Dadourian — Radio-activity of Thorium. 431 



According to this hypothesis radio-thorium is a disintegra- 

 tion product of thorium and the producer of thorium X. 

 Thorium emanation being a radio-active product of thorium X, 

 the amount given off by a substance is proportional to the 

 quantity of thorium X present. For a substance in which 

 thorium X and radio-thorium are in radio-active equilibrium, 

 the quantity of thorium emanation given off will be propor- 

 tional to the amount of both thorium X and radio-thorium 

 but not necessarily to that of thorium present in the substance. 

 If, however, all three, thorium, radio-thorium and thorium X, 

 are in radio-active equilibrium, the proportionality will hold for 

 each of them. All of the substances tested were in radio-active 

 equilibrium as regards thorium X. Therefore the quantity of 

 thorium emanation evolved by any of them should be propor- 

 tional to the amount of radio-thorium only or to the amount of 

 both radio-thorium and thorium present, according as the latter 

 were or were not in radio-active equilibrium in the substance. 



The experimental results given in the above tables follow as 

 natural consequences of this hypothesis. Thus the amount of 

 thorium emanation evolved by the solutions of the minerals 

 should be proportional to their content of thorium as v^ell as 

 radio-thorium, as these are, in all probability, in radio-active 

 equilibrium in the minerals. In other words, the specific 

 thorium activity of the minerals should be the same. This 

 was shown to be the case for the minerals tested, and thorium 

 nitrate number (5), which was prepared from thorianite. 



On the other hand, this hypothesis leads to the conclusion 

 that the low specific thorium activity of the commercially pre- 

 pared salts is due to the loss of part of the radio-thorium in 

 the process of chemical preparation. Therefore, if thorium 

 nitrate salts are prepared from minerals without losing any 

 radio-thorium, their specific thorium activity should be the 

 same as those of the minerals. In order to test this, thorium 

 nitrate number (4) was prepared from 10 grains of North 

 Carolina monazite. The specific thorium activity of this salt 

 was found to be 22*1. This is about the same as the specific 

 thorium activities of thorium nitrate number (5) and the min- 

 erals thorite and thorianite. But thorium nitrate number (1), 

 which was prepared from the same mineral (North Carolina 

 monazite), had a specific thorium activity of only 10'T.* The 

 only rational explanation of this great difference in the activity 

 of thorium obtained from the same mineral but by two dif- 

 ferent analytical methods, is the one just given. 



Thus thorium and radio-thorium were in radio-active equi- 

 librium in the specimens of North Carolina monazite from 



* Dr. B. B. Boltwood tested these substances by a method described in a 

 paper in this number of the Journal and arrived at similar results. 



