INTRA-ATOMIC ENERGY. 173 



It is necessary to analyze out this remarkable fact. We 

 know that the radio-activity of a mass of radium compound 

 is complex and consists of the united activities of the ra- 

 dium itself and its disintegration products, the emanation, 

 the emanation X and the two or three active bodies into 

 which the emanation X successively breaks down. It has 

 been determined that the heat emission is due almost en- 

 tirely to the alpha-rays, the positively electrified particles 

 of atomic dimensions. In a mass of radium nearly all the 

 alpha-rays emitted from it are absorbed in the radium it- 

 self. The radium is thus subjected to an intense bombard- 

 ment by the alpha particles projected from its own mass. 

 It is little wonder, under the circumstances, that the ra- 

 dium is heated. The energy of the alpha particles is im- 

 mense. These particles, small as they are, are 2,000 times 

 the mass of a corpuscle and travel with a velocity 40,000 

 times that of the swiftest rifle bullet. If an alpha par- 

 ticle were the size of a cannon ball the heat generated by 

 its impact on the target would be many times more than 

 sufficient not only to melt it but to dissipate it into vapour. 

 But the alpha particles are projected not only from radium 

 itself but from all its disintegration products; and we dis- 

 cover that the heat emission is distributed thus: 



Radium freed from active products. . . 25 per-cent. 



Emanation and successive active products. 75 " 

 Seventy five calories, then, of the heat emitted from a gram 

 of radium are due to the emanation stored therein. But 

 the volume of the emanation is infinitesimally small. From 

 one gram of radium compound the volume of the emana- 

 tion evolved would not amount to more than 1 .3 of a cubic 

 millimetre. This needle point of gas evolves enough heat 

 per hour to raise the temperature of 75 grams of water one 

 degree. If it were possible to obtain one cubic centimetre 



