The Evolution of the Sciences 



presence of mercury; it soon decomposes into 

 ammonia NH 3 and hydrogen. To reconstitute 

 the compound NH 4 Cl it is necessary to follow a 

 much longer course; first the chlorine must be 

 combined with the hydrogen and then the 

 ammonia subjected to the action of hydrochloric 

 acid; we are perfectly able to carry out these 

 transformations, but as yet we have not been able 

 to produce similar changes with radium and the 

 products of its decomposition." 



No agent capable of modifying the evolution 

 of radium is known ; it is, however, probable that 

 such agents exist. The radio-active substances 

 have lain buried in the depths of the earth for 

 thousands of centuries, and had their trans- 

 mutation been taking place at the rate observed 

 by Ramsay they would have long ago disappeared 

 completely. It is therefore reasonable to infer 

 the existence of some retarding action, or even 

 of a process of retrogression still unknown to us. 



Helium is not the only product of the disin- 

 tegration of radio-active bodies ; an extraordinary 

 quantity of energy is liberated at the same time 



of which nothing in any known chemical re- 



78 



