Vit] RADIO-ACTIVE EMANATIONS 215 
The writer! showed that the emanating power of ordinary thoria 
was increased three to four times by heating the substance to a dull 
red heat in a platinum tube. If the temperature was kept con- 
stant, the emanation continued to escape at the increased rate, 
but returned to its original value on cooling. If, however, the 
compound was heated to a white heat, the emanating power was 
greatly reduced, and it returned on cooling to about 10°/, of the 
original value. Such a compound is said to be “de-emanated.” 
The emanating power of radium compounds varies in a still more 
striking manner with rise of temperature. The rate of escape 
of the emanation is momentarily increased even 10,000 times by 
heating to a dull red heat. This effect does not continue, for the 
large escape of the emanation by heating is in reality due to the 
release of the emanation stored up im the radium compound. Like 
thoria, when the compound has once been heated to a very high 
temperature, it loses its emanating power and does not regain it. 
A further examination of the effect of temperature was made 
by Rutherford and Soddy?. The emanating power of thoria decreases 
very rapidly with lowering of temperature, and at the temperature 
of solid carbonic acid it is only about 10°/, of its ordinary value. 
It rapidly returns to its origimal value when the cooling agent is 
removed. 
Increase of temperature from 80° C. to a dull red heat of plati- 
num thus increases the emanating power about 40 times, and the 
effects can be repeated again and again, with the same compound, 
provided the temperature is not raised to the temperature at which 
de-emanation begins. De-emanation sets in above a red heat, and 
the emanating power is then permanently diminished, but even 
long continued heating at a white heat never entirely destroys the 
emanating power, 
142. Regeneration of emanating power. An interesting 
question arises whether the de-emanation of thorium and radium is 
due to a removal or alteration of the substance which produces the 
emanation, or whether intense ignition merely changes the rate 
of escape of the emanation from the solid into the surrounding 
atmosphere. 
1 Phys. Zeit. 2, p. 429, 1901. 2 Phil, Mag. Nov. 1902. 
