116 Excited Radioactivity and its Transmission. 



There is thus evidence of four distinct changes in each of 

 which the matter produced has distinct chemical properties. 

 For example , Th.X is soluble in ammonia, while thorium and 

 products of the later changes are not. The emanation is not 

 soluble in hydrochloric or sulphuric acid, unlike the matter 

 responsible for excited radioactivity. There is strong evidence 

 also that the chemical changes in the matter responsible for 

 excited radioactivity are complex in character. It has been 

 shown that the excited radiation in a body increases after 

 removal w^hen the body is exposed for a short time in the 

 presence of the emanation. This effect is analogous to the 

 increase of radioactivity of Th.X for the first day after sepa- 

 ration, which has been shown to be due to the excited activity 

 produced in the matter constituting the Th.X. 



"In order to account for the increase in radiating power 

 after removal, one must suppose that the matter which is 

 deposited from the thorium emanation gradually undergoes 

 a chemical change. The transformed matter undergoes a 

 secondary change, the time-rate of wmich is slower than the 

 primary, but which gives rise to greater radioactivity. From 

 data of § 5 half the matter has undergone change about 1 hour 

 after deposit, while in the secondary change the corresponding- 

 time is about 11 hours. 



Summary of Results. 



(1) Excited radioactivity produced by thorium and radium 

 compounds is due to the deposit of radioactive matter, which 

 is derived from the emanation given out by these bodies. 



(2) Excited radioactivity is transmitted by positively 

 charged carriers, produced from the emanation, which travel 

 in an electric field with about the same velocity as the positive 

 ions produced in air by Rontgen rays. This velocity (about 

 1*3 cm. per sec. for 1 volt per cm.) is about the same for the 

 carriers of thorium and radium excited activity. 



(3) These positively charged carriers are due to the ex- 

 pulsion of a negatively charged body from the molecule of 

 the emanation. 



(4) Evidence is adduced for t;he view that the easily 

 absorbed and apparently nondeviable rays of radioactive 

 substance are due to the expulsion of charged bodies at a 

 high velocity. The rays are thus analogous to the Canal 

 Strahlen of Goldstein, which Wien has shown to be positively 

 charged bodies projected at a great speed. 



In the case of the emanations the expelled particles are for 

 the most part negative in sign. 



(5) In the case of radium about 5 per cent, of the carriers 



