Production of Helium by Radium. 603 



second by one gram of radium has been found by Rutherford 

 and Geiger to be equal to 3*4 x 10 10 . The amount of polonium 

 present in the preparation was therefore equal to the amount 

 in equilibrium with 4*1 milligrams of radium. 



The amount of helium produced by the polonium should 



be proportional to -(l — e~ xt ), where X is the disintegration 

 A, 



constant of polonium and t is the time in days. The value 

 given by this expression is 98 ; i. e, the amount of helium 

 produced in 128 days is 96 times the amount produced per 

 day by the quantity of polonium present at the start. The 

 total amount of helium formed would therefore be 0*0041 x 

 0-107 x 96 = 0*042 cub. mm. 



The amount of helium found was therefore only about 

 1/4 of the amount to be expected from the theory, but the 

 discrepancy was probably due to the fact that a very large 

 proportion of the a particles emitted by the polonium were 

 embedded in the metallic copper. When the copper wns 

 heated only a portion of the helium formed from the a parti- 

 cles was set free. The experiment was therefore of value 

 only in qualitatively showing the production of helium by 

 polonium. 



Production of Helium in Radium D. 



Although radium D has been found to emit no a particles, 

 when a specimen of this material is allowed to stand for 

 some time radium E and radium F (polonium), will be 

 formed from it, and the a. particles from the latter may be 

 expected to produce helium. The lead sulphate separated 

 from the polonium solution (p. 602), and containing the 

 radium D (radio-leadj from the original radium solution, 

 was sealed up in an exhausted, hard glass tube for about 

 110 days. The lead sulphate was then heated and the gases 

 were pumped out of the tube. The residual gas not absorbed 

 by cooled charcoal gave a good spectrum of helium, but its 

 volume was not determined. 



Summary of Results. 



The rate of production of helium by a radium salt has 

 been accurately measured and has been found to be equal to 

 approximately 0*107 cubic millimetre of helium per day 

 per gram of radium (element), which is equivalent to 

 156 cubic millimetres of helium per year per gram of radium 

 in equilibrium with its first disintegration products, the 

 emanation, radium A, and radium C. 



The rate of production, 1-58 cubic millimetres of helium 



