lo SODDY, Evolution of Matter by Radio-active Elements. 



acetylene, fulminate of mercury, etc. The difference 

 appears when we consider the whole mass of the substance 

 instead of the individual particle. For the case of an 

 explosive compound, the disruption of a single particle 

 causes the surrounding particles to disrupt, and the whole 

 compound explodes in an excessively short space of time. 

 In the case of a radio-active element, a fixed and small 

 proportion of the total disintegrates in the unit of time,; 

 without affecting the rate of disintegration of the remainder. 

 This disintegration process proceeds according to this law 

 for each type of unstable atom known. The rate, or pro- 

 portion of the total breaking up in the unit of time, varies 

 enormously in the different types, but is for any one type 

 fixed and independent of the most powerful chemical and 

 physical agencies to which the substance may be subjected- 

 If, however, the disintegrating atom passed from its initial 

 to its final state in one change, as in the analogous molecular 

 cases considered, it would have been difficult to have 

 obtained much knowledge of the process. Fortunately 

 this is not the case. The thorium atom passes to its final 

 state after at least five separate and successive disintegra- 

 tions, each of which, considered by itself, is suddenly and 

 explosively consummated so far as the individual atom is 

 concerned, by the radial expulsion of fragments in the 

 form of a particles. In the case of radium the number 

 of disintegrations suffered by each atom is probably 

 similar to the case considered, while in the case of uranium 

 only two stages are at present known. 



The complete series of changes of the disintegrating 

 atom therefore takes a considerable time for completion. 

 In consequence there exist a certain number of short- 

 lived transition-forms of matter intermediate between the 

 initial and the final atoms which result from the process. 

 The term " Metabolon " has been proposed by Professor 



