452 Prof. Rutherford and Mr. Soddy on the 



An experiment gave as the value of the emanating-power 

 of solid radium chloride in a dry atmosphere less than half 

 per cent, of the emanating-power of the solution; or to express 

 the result in another way, the amount that escapes per second 

 is less than 10~ 8 of that occluded in the compound. Moisture, 

 however, increases it many times. 



Exactly the same consideration applies to the case of 

 thorium. If the manufacture of the thorium emanation pro- 

 ceeds under all circumstances at the same rate, the solution of 

 a solid non-emanating thorium compound should also be 

 accompanied by a " rush " of emanation at first greater 

 than the amount obtained subsequently. But here the very 

 rapid rate of decay of the emanation will make the effect less 

 marked. For the case of the thorium emanation 



q A 



It has been shown that thorium nitrate in the solid state 

 only possesses 2W0 part of the emanating-power of the same 

 compound in solution. A quantity of finely powdered thorium 

 nitrate was dropped into a Drechsel bottle containing hot 

 water and the emanation immediately swept out into the 

 testing vessel by a rapid current of air. 



The ionization current in the vessel rose to a maximum, 

 and then fell again immediately to a steady value, showing 

 that the amount of emanation released when the nitrate dis- 

 solves is greater than the subsequent amount produced by 

 the solution. The rapid rate of decay renders a quantitative 

 comparison difficult. By slightly altering the arrangement 

 of the experiment, however, a definite proof was obtained that 

 the rate of production of emanation is the same in the solid 

 compound as in the solution. After dropping in the nitrate,, 

 a rapid air-stream was blown through the solution for 

 25 seconds into the testing vessel. The air-stream was 

 stopped and the ionization current in the testing vessel im- 

 mediately measured. The solution was then allowed to stand 

 for 10 minutes undisturbed, in which time the accumulation 

 of the emanation in the Drechsel bottle again attains a 

 practical maximum and again represents the steady state. 

 The air-stream was then blown through as before for 25 

 seconds, stopped, and the ionization current again taken. 

 In both cases the electrometer recorded a deflexion of 100 

 divisions in 6' 8 seconds. By blowing the air continuously 

 through the solution the deflexion observed when a steady 

 state was reached was 100 divisions in 12'6 seconds, or 

 about one-half of that observed after the first " rush." 



