598 Profs. B. B. Boltwood and E. Rutherford 



on 



The results obtained in both determinations were as 

 follows : — 



First determination. — Period of accumulation 83 days. 



Volume of Helium at 0° and 760 mm. pressure. 



First measurement of series 9*08 cubic millimetres. 



Second „ ,, 6*79 „ „ 



Third „ „ 6*59 „ „ 



Fourth „ „ 6'54 „ „ 



Fifth „ „ 6-60 „ 



Average of third, fourth, and fifth 6'5S „ ,, 



Second determination. — Period of accumulation 132 days. 



Volume of Helium at 0°and 760 mm. pressure. 



First measurement of series 1032 cubic millimetres. 



Second „ „ 10*37 „ „ 



Third „ „ 10-45 „ 



Average of all 10*38 cubic millimetres. 



Calculation of Rate of Production of Helium. 



If x is the volume of helium produced per day by the 

 amount of radium (element) present in the salt, and y is the 

 volume of helium produced per day by the emanation and 

 the two a-ray products, (radium A and radium C) in equi- 

 librium with the radium ; then when the three latter products 

 are present in equilibrium amounts y = 3%, or, in other words, 

 the amount of helium produced by the three a products will 

 be three times that produced by the radium itself. 



At the beginning of each period of accumulation, however, 

 all emanation had been removed from the radium salt. The 

 amount of helium produced during a subsequent period of 

 T days would therefore be equal to 



T* +y[ o T (l-ir»>ft = Tx+ (t - C.*)y = T*+(t - £)& 



where X is the constant of change of the radium emanation, 

 the unit of time being taken as the day ; for a value of T 

 greater than 40 days, e~ A * is very nearly 1. 



If Q is the total quantity of helium produced in the time T, 

 and the value 3# is substituted for y in the above expression, 

 we obtain 



q = [t +3 (t-9>. 



