198 . RADIUM. 



when contained in a mixture of inactive substance in the proportion 

 of 1 to 10(»,0(iO,(MiO. 



liadiuni is a higher honiologue of barium in the series of alkaline 

 earth metals. Its atomic weight has been determined by Madame 

 Curie to be 226. 



While thus a near neighbor to barium, it is not found, even as a 

 trace, in the ordinar}- mineral sources of Itarium, and only accompanies 

 it in the uranium ores, which fact is of great theoretical importance. 



X. 



Radium therefore gives us an example of a t)ody which, while 

 remaining in the same state, evolves continuously a considera))le 

 amount of energy. This fact is apparently in contradiction to the 

 fundamental principles of energetics, and various hypotheses have 

 been put forward to avoid this contradiction. 



Among these hypotheses we may consider two which were made at 

 the beginning of tne studies of radio-activity." 



In the tirst hypothesis it is assumed that radium is an element in 

 process of evolution. It nuist then be admitted that the evolution is 

 extremely slow, so that no appreciable change of state is discernable 

 in the course of several 3'ears, for the energy which is disengaged 

 in the course of a year corresponds with an insignificant transforma- 

 tion of matter. It would appear natural to suppose that the quantity 

 of energy put in play in the transformation of atoms is considera])le. 



The second hypothesis assumes the existence in space of radiations 

 still unknown and inaccessible to our senses. Radium might be 

 assumed to be capable of absorbing the energy of these hypothetical 

 rays and transforming it into radio-active energy. 



The two hypotheses which we have mentioned seem not incompatible. 



Since the deliver}' of this lecture there was made (June 1!>, l!»0o) a 

 discovery of great importance 1)}' Messrs. Ramsay and Soddy. They 

 found that the emanation of radium as it disappears gives place to the 

 production of helium gas, whose presence can be recognized by spec- 

 trum analysis. It seems, then, that we are here brought face to face 

 for the first time with the formation of an element. It is possible 

 that radium is an unstable chemical element, and that helium is pro- 

 duced as one of the products of its disaggregation. 



« Mme. Curie, Revue general des Sciences, Jan. 30, 1899. 



