PRESENT PROBLEMS OF RADIOACTIVITY 169 



independently of the substance in which they are produced. Experi- 

 ments of this character would be difficult, but would throw light on 

 the important question of the division of the energy radiated between 

 the expelled a ray particle and the system from which it arises. 



The enormous evolution of energy by the radioactive substances 

 is very well illustrated by the case of the radium emanation. The 

 emanation released from 1 gram of radium in radioactive equilibrium 

 emits during its changes an amount of energy corresponding to about 

 10,000 gram-calories. Now Ramsay and Soddy have shown that the 

 volume of this emanation is about 1 cubic millimeter at standard 

 pressure and temperature. One cubic millimeter of the emanation 

 and its product thus emits about 10 7 gram-calories. Since 1 centimeter 

 of hydrogen, in uniting with the proportion of oxygen required to form 

 water, emits 3.1 gram-calories, it is seen that the emanation emits 

 about 3 million times as much energy as an equal volume of hydrogen. 



It can readily be calculated, on the assumption that the atom of 

 the emanation has a mass 100 times that of hydrogen, that 1 pound 

 of the emanation some time after removal could emit energy at the 

 rate of about 8000 horse-power. This would fall off in a geometrical 

 progression with the time, but, on an average, the amount of energy 

 emitted during its life corresponds to 50,000 horse-power days. Since 

 the radium is being continuously transformed into emanation, and 

 three quarters of the total heat emission is due to the emanation and 

 its products, a simple calculation shows that 1 gram of radium must 

 emit during its life about 10 9 gram-calories. As we have seen, the 

 heat emission of radium is about equally divided between the radium 

 itself and the three other a ray products which come from it. 



The heat emitted from each of the other radioactive substances 

 while their activity lasts, should be of the same order of magnitude, 

 but in the case of uranium and thorium the present rate of heat emis- 

 sion would probably continue, on an average, for a period of about 

 1000 million years. 



VI. Source of the Energy emitted by the Radioactive Bodies 



There has been considerable difference of opinion in regard to the 

 fundamental question of the origin of the energy spontaneously emit- 

 ted from the radioactive bodies. Some have considered that the 

 atoms of the radio-elements act as transformers of borrowed energy. 

 The atoms are supposed to be able, in some way, to abstract energy 

 from the surrounding medium and to emit it again in the form of the 

 characteristic radiations observed. Another theory, which has found 

 favor with a number of physicists, supposes that the energy is de- 

 rived from the radio-atoms themselves and is released in consequence 

 of their disintegration. The latter theory involves the conception 



