PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 373 



radioactivity. If these changes are atomic in character it neces- 

 sarily follows that the atom, at least the atoms of a radio-active 

 element, can not be regarded as made up of indivisible particles. 

 The conception of the atom which seems to be most in accord 

 with modern researches, regards it as made up of a positively 

 charged mass constituting by far the greater portion of the entire 

 mass of the atom, and a limited number of negatively charged 

 particles called electrons, each of which has a mass approximately 

 1-1800 of the mass of the hydrogen atom. These electrons when 

 expelled, constitute the beta rays to which reference has been 

 made. 



Having this conception of the atom before us and recalling 

 that radioactive elements are constantly giving off the alpha, 

 beta and gamma rays referred to above, let us try to get a mental 

 picture of the changes, taking place in the disintegration of a 

 radioacti\e element. 



The atoms of all radio-active elements possess a certain 

 degree of instability. As a result of the unstable character the 

 atom disintegrates forming a new atom. This new atom may 

 likewise be unstable and so in turn it disintegrates ; and the proc- 

 ess goes on until a final stable product is reached. The disin- 

 tegration of the atom may consist either in the expulsion of one 

 or more alpha particles or one or more beta particles, or both 

 kinds of particles may be expelled. If the change consists simply 

 in the expulsion of an alpha particle (which particle has an 

 atomic mass of 4 and a doul)le charge of positive electricity) 

 then, the change would be accompanied not only by a decrease 

 of 4 units in the atomic weight but by a change of 2 in valence ; 

 for according to our modern conception, the valence of an ele- 

 ment is simply a measure of the number of units of electric 

 charge it possesses, a uni\alent element having a unit charge, a 

 divalent element having a two unit charge and so on. On the 

 other hand if the change consists simply in the expulsion of a 

 beta ray with its unit negative charge, then the change would be 

 accompanied by a decrease in the mass of the atom equal to about 

 1-1800 the mass of the hydrogen atom and by a change of one in 

 valence. It thus becomes possible in a general way to predict 



