492 POPULAR SCIENCE MONTHLY. 



conclusion that such substances are continually projecting particles 

 with enormous velocities, for if these particles are projected from all 

 the molecules of the active substance, it would be expected that the 

 temperature of the mass of the substance would rise under this un- 

 ceasing internal bombardment. But whence comes this energy which 

 is represented in the projected particles, and of which this heat and 

 light are the ultimate manifestation? 



Radio-activity a Manifestation of Subatomic Energy. 



The answer to this last question has not yet been fully given. This 

 much, however, can be said, that, thanks to the splendid work of Ruther- 

 ford and Soddy, of McGill University, of Sir William Crookes, of the 

 Curies and Becquerel in Paris, and of one or two German physicists, a 

 fairly satisfactory answer is at least in sight. Whatever be the cause of 

 this ceaseless emission of particles by radio-active substances, it is cer- 

 tain that it is not due to any ordinary chemical reactions, such as those 

 with which we have heretofore been familiar ; for Madame Curie showed, 

 when she originally discovered the activity of thorium, that the activity 

 of all the active substances is proportional simply to the amount of the 

 active element present and has nothing whatever to do with the nature 

 of the chemical compound in which that element is found. Thus, 

 thorium may be changed from a nitrate to a chloride, or from a chloride 

 to a sulphide, or it may undergo any sort of a chemical change, without 

 any change whatever being noticeable in its activity. Furthermore, 

 radio-activity has been found to be absolutely independent of all 

 changes in physical as well as chemical condition. A radio-active 

 substance may be subjected to the lowest temperatures known, or to the 

 highest temperature obtainable, without showing in either case any 

 alteration whatever in the amount of its activity. Eadio-activity seems 

 therefore to be as unalterable a property of the atom of the radio-active 

 substances as is weight itself. It is certainly something which is en- 

 tirely beyond the range of ordinary molecular forces. This is strong 

 evidence in favor of the view that radio-active change, i. e., the change, 

 whatever it be, which is responsible for the expulsion of the alpha and 

 teta particles, involves a change in the nature of the atom itself. This 

 is the first time in the history of science that any subatomic store of 

 energy has been tapped by man, although, as stated above, the possi- 

 bility of breaking up the atom was first proved by the study of cathode 

 rays. 



The Production of Uranium X. 



The view that radio-activity consists in some change going on in 

 the nature of the atom has received powerful support from a series of 

 discoveries which were started in 1900 by an experiment performed" 

 by Sir William Crookes. He found that if uranium nitrate were pre- 

 cipitated by ammonium carbonate and then enough of the ammonium 



