| \ rr [ 202 ] 
a XIX. ace g Effect of the Radium Emanation *. By 
EK. Ruruerrorp, F.R.S., and H. T. Barnus, D.Sc., Pro- 
Jessors of Physics, McGill Univer sity, Montreal ¢. 
P. CURIE and Labordef first observed the rapid rate 
of heat emission of radium, and deduced that 1 gram of 
radium emitted heat at the rate of about 100 gram-calories 
per hour. In a later paper P. Curie§ found that the rate 
of emission of heat depended upon the age of the radium 
preparation. The heating effect for freshly prepared radium 
compound was small at first, but gradually increased to a 
maximum after a month’s interval, and remained constant 
over a further interval of two months. 
The present experiments were undertaken with the view 
of seeing how the heat emission of radium is connected with 
its radioactivity. It has been shown by Rutherford and 
Soddy || that the radiation emitted from a radium compound 
in a state of radioactive equilibrium may be divided into three 
parts :-— 
(1) Anon-separable radiation consisting entirely of a rays 
— ee mee about 25 per cent. of the total radiation. 
(2) The radiation from the emanation occluded in the 
radian also consisting entirely of @ rays. 
(3) The excited radiation produced by the emanation in 
_ the mass of the radium, and consisting of a, 8, and ¥ rays. 
(2) and (3) together constitute about 75 per cent. of the 
total radiation. 
Some experiments have been recently made to find how 
much of the activity of radium is supplied directly by the 
emanation occluded in it. The saturation-current, between 
parallel plates, due to a radium preparation spread uniformly 
over a platinum plate, was determined by means of an elec- 
trometer. The platinum plate was then heated rapidly to a 
temperature sufficient to completely drive off the emanation 
and the saturation-current due to the radium immediately 
measured. There was a decrease observed corresponding to 
18 per cent. of the total. The gradual decay of the excited 
activity left behind in the radium after the removal of the 
emanation is shown graphically in fig. 5, curve A (p. 213). 
We may thus conclude that the emanation supplies 
* A short account of the preliminary résults was published in ‘Nature’ 
(Oct. 29, p. 622, 1903). Read before the American Physical Society, 
St. Louis, Dec. 29, 1903. 
+ Communicated by the Authors. 
t Comptes Rendus, cxxxvi. p. 673 (1903). 
§ Société de Physique, 1903. 
|| Phil. Mag. April 1905. 

