450 Prof. Rutherford and Mr. Socldy on the 



generally that the emanating-powers of both radium and 

 thorium are at a practical maximum in solution. 



The question arises as to what the variations in ernanating- 

 power (i. e. the amount of emanation produced per gramme 

 per second) are due. It was pointed out in the case of thorium 

 that they can be interpreted in two ways. Either an alte- 

 ration in the velocity of the reaction producing the emanation 

 occurs, or the same amount is produced in all cases but the 

 time taken for the emanation to escape from the compound is 

 different under different circumstances. This question, which 

 is of comparatively secondary importance in the case of 

 thorium, becomes of paramount importance in the case of 

 radium. For since the radium emanation loses its activity 

 only after a period of several weeks, the view that the 

 emanation is being continually produced at a constant rate 

 necessitates the conclusion that there must exist in a solid 

 non-emanating radium compound a large amount of emanation 

 stored up or " occluded " in the compound. This will be 

 given up when the substance is dissolved, so that there should 

 occur a sudden "rush" of emanation from the solution very 

 much greater than the amount subsequently produced. 

 Assuming that in a solid radium salt no emanation escapes, 

 and that in the same salt when dissolved the emanation 

 escapes as fast as it is formed, it is easy to calculate the ratio 

 of the amount given off on the solution in the first " rush" to 

 the amount given off in any subsequent period. 



Let q = the number of particles of emanation produced 

 per second by a given amount of radium. 

 N =the number of particles stored up in the same 

 quantity in the solid state. 



N represents the equilibrium state when the rate of pro- 

 duction of fresh particles of emanation is balanced by the 

 rate of change of those already present. If the process of 

 production were stopped, the number N* left after the time t 

 would be given by 



where X is the constant of decay of the activity of the 

 emanation. The rate of change 



at 

 At the equilibrium point therefore 



^=^=463,000, 

 q \ 



substituting the value of X found in § 2. 



