1904.] The Succession of Changes in Radio-active Bodies. 495 



After the three rapid changes have taken place in emanation X of 

 radium, there remains another product, which loses its activity 

 extremely slowly. Mme Curie showed that a body, which had been 

 exposed for some time in the presence of the radium emanation, 

 always manifested a residual activity which did not appreciably 

 diminish in the course of 6 months. A similar result has been 

 obtained by Giesel. Some experiments are described, in which the 

 matter of slow decay, deposited on the walls of a glass tube containing 

 the emanation, was dissolved in acid. The active matter was found to 

 emit both a, and /? rays, and the latter were present in unusually large 

 proportion. The activity measured by the /? rays diminished in the 

 course of 3 months, while the activity measured by the a rays was 

 unaltered. The active matter was complex, for a part which gave out 

 only a rays was removed by placing a bismuth plate in the solution. 

 The radio-active matter deposited on the bismuth is closely allied in 

 chemical and radio-active properties to the active constituent contained 

 in the radio-tellurium of Marckwald. The evidence, as a whole, is 

 strongly in support of the view that the active substance present in 

 radio-tellurium is a disintegration product of the radium atom. Since 

 the radium emanation is known to exist in the atmosphere, the active 

 matter of slow dissipation produced from the emanation must be 

 deposited on the surface of all bodies exposed to the open air. The 

 radio-activity observed in ordinary materials is thus probably, in part, 

 due to a thin surface film of radio-active matter deposited from the 

 atmosphere. 



A review is given of methods of calculation of the magnitude of the 

 changes occurring in the radio-elements. It is shown that the amount 

 of energy liberated in each radio-active change, which is accompanied 

 by the emission of a particles, is about 100,000 times as great as the 

 energy liberated by the union of hydrogen and oxygen to form an 

 equal weight of water. This energy is, for the most part, carried 

 off in the form of kinetic energy by the a particles. 



A description is given of some experiments to see if the a rays 

 carried a positive charge of electricity, with the view of experimentally 

 determining the number of cc particles projected from one gramme of 

 radium per second. Not the slightest evidence was obtained that the 

 a rays carried a charge at all, although it should readily have been 

 detected. Since there is no doubt that the a rays are deflected in 

 magnetic and electric fields as if they carried a positive charge, it 

 seems probable that the a particles must in some way gain a positive 

 charge after their expulsion from the atom. 



Since on the disintegration theory, the average life of a given quan- 

 tity of radium cannot be more than a few thousand years, it is neces- 

 sary to suppose that radium is being continuously produced in the earth. 

 The simplest hypothesis to make is that radium is a disintegration 



