574 Prof. E. Kutherford and Mr. F. Soddy on 



This Las been found almost completely to stop the straight 

 line radiation, whilst allowing the emanation to pass through 

 "unimpeded. The current is now measured when a steady 

 state has been reached, due to the accumulation o£ the ema- 

 nation. This takes some time, and draughts of air must be 

 guarded against. For this reason, it is less convenient than 

 that first described, but the results obtained by the two 

 methods are almost exactly the same. Thus a sample of " de- 

 emanated" thoria, which gave 12 per cent, of the emanating 

 power of the comparison sample by the first method, gave 

 13 per cent, by the second method, whilst a sample of oxide 

 prepared from thorium oxalate gave 37 per cent, and 39 per 

 cent, by the two methods respectively. This close agreement 

 in the values by methods so completely different in character 

 is a proof that the indications of the methods are worthy of a 

 great degree of confidence. 



III. The De-emanation of Thoria and the Regeneration 

 of the Emanating Power. 



The emanating power of thoria, as has been stated, is 

 destroyed to a large extent by intense ignition. A closer 

 study of this is the first step in the investigation of the phe- 

 nomenon. Previous experiments had not succeeded in com- 

 pletely de-emanating thoria, although a reduction to about 

 15 per cent, of its original value had been accomplished. A 

 sample of this preparation which had been kept for two 

 years had not altered from this value. An experiment was 

 performed in which thoria was heated for one hour by means 

 of a powerful gasoline furnace to the highest temperature 

 which could be safely employed with platinum vessels. The 

 temperature was such that the fireclay walls fused, and the 

 pipeclay of a triangle showed signs of having been softened. 

 It was found that the sample retained about 8 per cent, of its 

 original emanating power. In another experiment, a small 

 platinum crucible filled with thoria was heated for half-an- 

 hour in a small furnace by a large blowpipe and powerful 

 pair of bellows. Some asbestos-wool had completely fused 

 on the outside of the crucible, and the temperature was pro- 

 bably but little lower than in the previous experiment. This 

 sample also retained about 8 per cent, of its emanating power. 

 No further attempt has yet been made to completely destroy 

 the emanating power. 



A small quantity of thoria heated in a platinum crucible in 

 the open over an ordinary- sized blowpipe and bellows for 

 five minutes retained about 45 per cent, of its emanating 

 power. The effect of time as well as of temperature was 



