576 Prof. E. Rutherford and Mr. F. Soddy on 



series of chemical changes to see if it would recover its lost 

 emanating power was then undertaken. 



It may first be mentioned that thoria which has been 

 subjected to ignition has changed very materially in chemical 

 and physical properties. The pure white colour changes at 

 temperatures corresponding to the first stages of de-emanation 

 to a light brown, and after subjection to the very highest 

 temperature to a pure pink. At the same time the solubility 

 of the substance in sulphuric acid is greatly diminished. 

 A part always obstinately refuses to dissolve, even after long 

 and repeated boiling with the concentrated acid, although 

 this part is diminished on each successive treatment, and 

 appears to be in no way different from the rest of the 

 substance. No difference, however, occurs in the readiness 

 with which chlorine attacks it when intimately mixed with 

 carbon. The formation of the chloride by this method is the 

 easiest way of dissolving ignited thoria. 



Preliminary experiments went to show that emanating 

 power is a quantity which varies, not only with the nature 

 o£ the chemical compound but also for the same compound 

 very materially with its previous history. Thus the cxide 

 from the oxalate does not possess as a rule so great an 

 emanating power as that used for comparison. The following 

 two exactly parallel experiments were therefore made, the 

 one with the ordinary, and the other with de-emanated thoria 

 possessing 9 to 10 per cent, of the emanating power of the first. 

 Each was converted to chloride in the ordinary way, by mixing 

 with sugar solution, carbonising, and igniting the mixture 

 of oxide and carbon so obtained in a current of dry chlorine. 

 Each sample was then treated with water, the thorium 

 precipitated as hydroxide with ammonia, and the hydroxides 

 washed and dried at 110°. The result was conclusive, for 

 each sample showed the same emanating pov~er. For the 

 first few days after preparation this value increased rapidly, 

 but after having been kept a fortnight both specimens showed 

 about 260 per cent, of the emanating power of the thoria 

 used as a comparison sample. 



Thus the process of de-emanating thoria by ignition does 

 not irretrievably destroy the emanating power, for after 

 solution and reprecipitation no difference whatever exists in 

 the emanating power between ordinary and de-emanated 

 thoria. A fair conclusion from these experiments is that the 

 cause of the emanating power is not removed by ignition, but 

 only rendered for the time being inoperative. 



