1904.] 



On the Production of Helium from Radium. 



357 



bourhood of 160, not more than one atom of emanation can be 

 produced from one atom of radium. To determine the ratio between 

 the quantity of emanation and the quantity of radium producing it, 

 it is necessary to know the volume that would be occupied by the 

 radium in the form of monatomic gas. This is for 1 gramme of 

 radium (2 x 1 1*2)/225 = 0*1 litre - 10 5 cub. mm. One gramme of radium 

 produces 3 x 10 -6 cub. mm. of emanation per second, and if one atom 

 of radium produces one atom of emanation, then A, the proportion of 

 the radium changing per second, is 3 x 10 _n . The proportion changing 

 per year is 9*5xl0~ 4 ; thus slightly less than one-thousandth part 

 changes per year. The average life of the radium atom is 

 l/X = 3-3 x 10 10 seconds = 1050 years. 



In the second experiment, the emanation was accumulated 

 6 days, and measured 0*0254 cub. mm. In this case, 



Q.t = 0-674 Q x = 312,060 Q , 



and Q = 0'81 x 10~ 7 cub. mm. ; A = 2'4 x 10 -11 , and 1/A = 1250 years. 

 The mean of the two experiments, therefore, gives for 1 gramme of 

 radium (element) Q = 2*85 x 10~ 6 cub. mm. ; =1*3 cub. mm., 

 * = 2-85 x 10~ n , and 1/A = 1150 years. 



Rutherford and Barnes* have shown that 75 per cent, of the total 

 heat-evolution of radium which has reached its equilibrium state is 

 derived from the emanation and its subsequent products of change. 

 Since 1 gramme of radium evolves 100 calories per hour (Curie), 

 1*3 cub. mm. of emanation emit 75 calories per hour. The total 

 quantity of heat H emitted during the complete change is given by 

 multiplying h the emission per second, by the average life of the 

 emanation in seconds, thus giving H = A/A. = 9,646 calories. 

 One c.c. of emanation would therefore emit 7*4 x 10 6 calories 

 during its complete change. A cubic centimetre of hydrogen and oxygen 

 in the proportion required to form water evolve 2*04 calories on 

 explosion, or a quantity 3,600,000 times less than is emitted by an 

 equal volume of the radium emanation. If the density of the emana- 

 tion is assumed to be 100, the ratio of the energies emitted by equal 

 weights of emanation and of water is 216,000 to 1. 



The total quantity of energy evolved during the change of 1 gramme 

 of radium is given by multiplying the energy emission per second by 

 the average life of the radium atom in seconds, and is 10 9 calories. 

 The energy evolved in the formation of 1 gramme of water is 

 3'8 x 10 3 calories ; hence the ratio is again about 250,000 to 1. 



The volume of Q x , the equilibrium quantity of emanation produced 

 by 1 gramme of radium, was theoretically calculated by Eutherfordf 

 from the energy emitted by radium per second, and the energy of 



* ' Phil. Mag.,' 1904, 6, vol. 7, p. 202. 

 f ' Nature,' August 20, 1903. 

 VOL. LXXIII. 2 C 



