the Cause and Nature of Radioactivity. 575 



studied by heating about equal quantities in a platinum 

 crucible over an ordinary Bunsen burner for different 

 periods. 



Heated 10 minutes. Emanating power =61 per cent. 

 „ 1 hour. ,, „ =59 „ 



24 hours. „ „ = 42 „ 



It thus appears that there is a large and practically sudden 

 decrease of emanating power for each temperature above a 

 red heat, followed by a very gradual decrease with time 

 when the temperature is maintained ; thus, five minutes on 

 the blowpipe, whilst much more effective than the same time 

 at the temperature of the Bunsen burner, produced rather 

 less effect than 24 hours at the latter temperature. 



Effect of Moisture. — The next point to be examined was 

 whether the loss of emanating power could be attributed to 

 the loss of water and desiccation of the thoria by ignition. 

 A sample of de-emanated thoria (retaining about 14 per cent.) 

 was placed in the middle of a Jena glass tube, one end of 

 which was closed and contained water, the other end being- 

 drawn out to a jet. This was supported in a powerful tube- 

 furnace in a sloping position, and the part containing the 

 thoria heated to the highest possible temperature, while a 

 slow current of steam from the water at the end was passed 

 over it, escaping by the jet. When all the water was evapor- 

 ated, the jet was drawn off and the tube allowed to cool in 

 an atmosphere of steam free from air. The thoria, on testing, 

 was found to have been lowered in emanating power to about 

 7 per cent. The- further heating had thus reduced the ema- 

 nating power without the steam having at all regenerated it. 



In the next experiment, the reverse was tried. Two exactly 

 parallel processes were carried out for ordinary thoria pos- 

 sessing the normal amount of emanating power. In the first, 

 it was heated in a porcelain tube in the tube-furnace for 

 three hours, while about 500 c.c. of water were distilled over 

 it from a retort. In the second, another quantity of thoria 

 was heated in exactly the same way for the same time, only 

 a current of well-dried air was substituted for the steam. 

 The result was conclusive: each sample had had its emanating 

 power reduced to exactly the same amount, that is, about 

 50 per cent, of the original. 



These experiments prove that water-vapour exerts no 

 influence either in de-emanating thoria or in effecting a 

 recovery of its lost emanating power. 



The Regeneration of the Emanating Power by Chemical 

 Processes. — The task of subjecting de-emanated thoria to a 



