Sy FR eaece 
re 



158 _ RATE OF EMISSION OF ENERGY [CH. 
Number of Emission of energy Bhs f ; 
a particles in form of a rays SSD Cece 
per sec. per hour Leah 
Uranium ... 70000 | 35x 10~5 gram-cal. ‘3 gram-cal. 
Thorium ... 70000 3°5 x 10-4 Bs : 5 | 
Radium... 104 | 80 5 4:4 x 10° gram-cal. 





The rate of emission of energy in the form of @ and y¥ rays 1s 
probably about 1 per cent. of the above values. For a thin layer 
of a radio-element the amount of energy radiated into the air in 
the form of rays is for most cases about 10 per cent. of the above 
values. 
105. Heat emission of radium. P. Curie and Laborde! 
first drew attention to the striking result that a radium compound 
kept itself continuously at a temperature several degrees higher 
than that of the surrounding atmosphere. Thus the energy 
emitted from radium can be demonstrated by its direct heating 
effect as well as by photographic and electric means. Curie 
and Laborde determined the rate of the emission of heat in 
two different ways. In one method the difference of tempera- 
ture was observed by means of an iron-constantin thermo-couple 
between a tube containing one gram of radiferous chloride 
of barium, of activity about 1/6 of pure radium, and an ex- 
actly similar tube contaiming one gram of pure barium chloride. 
The difference of temperature observed was 15°C. In order to 
measure the rate of emission of heat, a coil of wire of known 
resistance was placed in the pure barium chloride, and the strength 
of the electric current required in order to raise the barium to the 
same temperature as the radiferous barium was observed. In the 
other method, the active barium, enclosed in a glass tube, was 
placed inside a Bunsen calorimeter. Before the radium was intro- 
duced, it was observed that the level of the mercury in the stem 
remained steady. As soon as the radium, which had previously 
been cooled in melting ice, was placed in the calorimeter, the 
mercury column began to move at a regular rate. If the radium 
tube was removed, the movement of the mercury ceased. It was 
1 C. R, 136, p. 673, 1903. 
