SCCCKSSION OK CII.\M;I> i\ I;M'|OACTIVK MODIKS. 



outlying revolving electrons, oomprinog the radio-atom, la{>ses into a position which 

 results in a slow loss of energy from the atom in the form of radiation. In conse- 

 quence of this loss of energy, the atom becomes unstable, and ultimately an a particle 

 flies off with its great orbital velocity, but the atom still retains the disturbing cause. 

 The residue, in consequence, again becomes unstable and ejects another a particle, 

 and the process goes on from stage to stage, until finally the ft particle is violently 

 ejected from the system. 



Following the general point of view suggested by Sir OLIVER LODGE in a recent 

 letter to ' Nature,' it may be jK>ssible that, as a result of continuous radiation, the 

 velocity of the ft particle in its orbit has steadily increased, until finally in the last 

 stage a sudden lapse into a new state of the atom occurs, in which not only does an 

 a. particle escape, but also the ft particle. When the ft particle is removed from it, 

 the residual atom adjusts itself again into a position of more permanent equilibrium. 



The experimental evidence as a whole points strongly to the conclusion that the 

 change in which the ft rays appear is far more disruptive in character than any of the 

 preceding ones ; for not only is the ft particle thrown off with nearly the velocity of 

 light, but the a particle, ejected at the same time, has greater penetrating power 

 :md probably greater kinetic energy than in any of the other changes. 



In addition, there is at present some evidence that this final change is of such a 

 violent character that the atom is in some cases disrupted into several fragments, and 

 that, in addition to the a and ft particles, two or more atoms are produced, each of 

 which has some distinctive physical and chemical properties, and also a distinctive 

 rate of decay. If the greater proportion of the matter resulting from the disintegra- 

 tion is of one kind, it would lie difficult to detect the presence of a small quantity of 

 rapidly changing matter from observations of the curves of decay ; but if the products 

 have distinctive electrochemical behaviour, a partial separation, in some cases, should 

 be effected by electrolysis. The electrolytic method is a very powerful means of 

 separating active products which may be present in small quantity compared with 

 the other radioactive products. It has already been mentioned (section 13) that the 

 results of PEOHAM and VON LERCH, obtained by electrolysis of thorium solutions, may 

 be in part explained on the supposition that thorium A and thorium B have dis- 

 tinctive electrochemical behaviour. PEORAM, however, in addition, observed the 

 presence of a product which lost half of its activity in about 6 minutes. This active 

 product was obtained by electrolysing a solution of pure thorium salt, to which a 

 small quantity of copper nitrate was added. The copper deposit was found to be 

 radioactive to a slight extent, and the activity decayed to half value in about 

 6 minutes. 



The presence of such radioactive products, which do not come under the main 

 scheme of changes, indicates that at some stage of the disintegration more than one 

 radioactive substance results. In the violent disintegration which occurs in radium C 

 and thorium B, such a result is to be expected ; for it is not improbable that there 



vol.. CCIV. A. 2 E 



