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XXXIV. Heating Effect of Radium and its Emanation. By 

 Prof. E. Rutherford^ F.R.S., and H. Robinson, M.Sc, 

 Demonstrator and Assistant Lecturer in the University of 

 Manchester *, 



SINCE the initial discovery of" the rapid and continuous 

 emission of heat from radium by P. Curie and Laborde 

 in 1903, a number of investigations have been made by 

 various methods to determine with accuracy the rate of 

 emission of heat. Among the more important of these may 

 be mentioned the determination of Curie and Dewar f by 

 means of a liquid air and liquid hydrogen calorimeter ; of 

 Angstrom J; and of Schweidler and Hess § by balancing the 

 (heating effect of radium against that due to an electric 

 current ; and of Callendar|| by a special balance method. 

 It is difficult to compare the actual values found on account 

 of the uncertainty as to the relative purity of the radium prepa- 

 rations employed by the different experimenters. The most 

 definite value is that recently obtained by Meyer and Hess ^f 

 using part of the material purified by Honigschmid in his 

 determination of the atomic weight of radium. As a result 

 of a series of: measurements, they found that 1 gram of 

 radium in equilibrium with its short-lived products produces 

 'heat at the rate of 132*3 gram calories per hour. 



Rutherford and Barnes ** in 1904 made an analysis of the 

 •distribution of the heat emission between radium and its 

 ^products. They showed that less than one quarter of the 

 heat emission of radium in radioactive equilibrium was due 

 to radium itself. The emanation and its products, radium A, 

 !B, and C, supplied more than three quarters of the total. 

 The heating effect of the emanation was shown to decay 

 'exponentially with the same period as its activity, while the 

 heating effect of the active deposit after removal of the 

 emanation was found to decrease very approximately at 

 the same rate as its activity measured by the a rays. The 

 results showed clearly that the heat emission of radium was a 



* Communicated by the Authors. This paper was read before the 

 KK. Akad. d. Wissenschaft. in Wien, July 4, 1912, and published in the 

 Wien. Ber. October 1912. 



f Curie and Dewar, Mme. Curie, JRecherches sur les substances radio- 

 actives, p. 100, 2me Edition, Paris, 1904. 



% Angstrom, Ark.f. Mat. Astr. ochFysik, i. p. 532 (1904); ii. No. 12 

 .(1905) ; Phys. Zeit. vi. p. 685 (1905). 



§ Schweidler and Hess, Wiener Berichte, 117, p. 879 (1908). 

 Jj Callendar, Phys. Soc. Proc. xxiii. p. 1 (1910). 

 5[ Meyer and Hess, Wiener Berichte, 121, p. 603, March 1912. 

 ** Rutherford and Barnes, Phil. Mag. vii. p. 202 (1904). 



