586 Prof. Rutherford and Mr. Soddy 



radio-elements will be augmented in the future, and that 

 considerably more than the three at present recognized exist 

 in minute quantity. In the first stage of the search for such 

 elements a purely chemical examination is of little service. 

 The main criteria are the permanence of the radiations, their 

 distinctive character, and the existence or absence of dis- 

 tinctive emanations or other disintegration products. 



§ 6. The Relation of Radioactive Change to Chemical Change. 



The law of radioactive change, that the rate of change is 

 proportional to the quantity of changing substance, is also 

 the law of monomolecular chemical reaction. Radioactive 

 change, therefore, must be of such a kind as to involve 

 one system only, for if it were anything of the nature of a 

 combination, where the mutual action of two systems was 

 involved, the rate of change would be dependent on the 

 concentration, and the law would involve a volume-factor. 

 This is not the case. Since radioactivity is a specific 

 property of the element, the changing system must be the 

 chemical atom, and since only one system is involved in the 

 production of a new system and, in addition, heavy charged 

 particles, in radioactive change the chemical atom must 

 surfer disintegration. 



The radio-elements possess of all elements the heaviest 

 atomic weight. This is indeed their sole common chemical 

 characteristic. The disintegration of the atom and the 

 expulsion of heavy charged particles of the same order of 

 mass as the hydrogen atom leaves behind a new system 

 lighter than before, and possessing chemical and physical 

 properties quite different from those of the original element. 

 The disintegration process, once started, proceeds from stage 

 to stage with definite measurable velocities in each case. 

 At each stage one or more a. " rays " are projected, until 

 the last stages are reached, when the {3 " ray " or electron is 

 expelled. It seems advisable to possess a special name for 

 these now numerous atom-fragments, or new atoms, which 

 result from the original atom after the ray has been expelled, 

 and which remain in existence only a limited time, continuallv 

 undergoing further change. Their instability is their chief 

 characteristic. On the one hand, it prevents the quantity 

 accumulating, and in consequence it is hardly likely that 

 they can ever be investigated by the ordinary methods. On 

 the other, the instability and consequent ray-expulsion 

 furnishes the means whereby they can be investigated. We 

 would therefore suggest the term metabolon for this purpose. 



