Heating Effect of Radium and its Emanation. 329 



for complete absorption of a particles is 118 gram calories 

 per hour, and for the emanation 94*5 gram calories per hour. 



These results are expressed in terms of the Rutherford 

 standard, for the value ne depends on this standard. Cor- 

 recting in terms of the Vienna standard, the corresponding 

 heating effects are 124 and 100 gram calories per hour. 



We have seen (§ 2) that the heating effect of one curie 

 of emanation on the Vienna standard is 103*5 gram calories 

 per hour Since under the experimental conditions probably 

 5 per cent, of this is due to the /3 rays, it is seen that the 

 calculated and measured values for one curie of emanation are 

 in good agreement. 



St. Meyer and Hess found that the heating effect of one 

 gram of radium in terms of the Vienna standard was 132*3 

 gram calories per hour. This includes the heating effect of 

 the /3 rays and 15 per cent, of the y rays. This is in ex- 

 cellent accord with the value deduced from the observed 

 heating effect of the emanation. The heating effect of one 

 curie of emanation surrounded by 1*2 mm. of lead was 

 105*5 gram calories per hour. The heating effect due to 

 a particles and recoil atoms is probably about 98*5 gram 

 calories. The theoretical rates of the heating effects for 

 radium in equilibrium compared with its emanation is 1*255. 

 The heating effect of one gram of radium surrounded by 

 1*2 mm. of lead thus comes out to be 123*6 + 7 = 130*6 gram 

 calories per hour. Allowing a small correction for the extra 

 absorption of 7 rays in the Vienna experiments, this value is 

 in close accord with that found by Meyer and Hess. 



Too much stress should not be laid on the agreement of 

 the calculated value of the heating effect of radium with that 

 deduced experimentally, for the data used in the calculations 

 are not fixed with the accuracy required. For example, the 



calculation depends on the accuracy of the values and n.e. 



The former was determined by measuring the electrostatic 



deflexion of the a rays. A combination of the value so 



m xi 

 found with the value — found bv deflexion of the same 



e 



rays in a magnetic field gave a value e/m = 5'01 x 10 3 . There 

 is now no doubt that the a. particle is a helium atom carrying 

 two charges, and the value of e/m should be 4*84 x 10 3 . 



Taking the value — =4*06 xlO 5 found by Rutherford for 

 the a particle from radium C as correct, and assuming 



<?/m=4*84xl0 3 , the value -5- =3*99 x 10 14 instead of the 



ze 



value 4*21 xlO 14 used in the calculation. Taking the new 



Phil. Mag. S. 6. Vol. 25. Tso. 146. Feb. 1913. Z 



