CHAPTER VIII. 

 EMANATION X AND THE BIRTH OF HELIUM. 



In addition to the power of giving off the alpha-rays or 

 positive ions possessed by the emanation, it has the ad- 

 ditional very remarkable property of exciting activity in 

 any substance with which it comes in contact. This is the 

 induced radio-activity discovered by Curie. This activity 

 of surrounding objects not otherwise radio-active is due to 

 the fact that the emanation hi decaying breaks down into 

 a third invisible and unweighable radio-active body which 

 deposits itself upon neighbouring bodies and which, appar- 

 ently, is in the nature of a solid. Surrounding objects thus 

 become radio-active. This " excited " activity, since it is 

 evolved from and results in the decay of the emanation has 

 been called emanation X. The emanation X has definite 

 chemical properties for it can be dissolved in some acids 

 and not in others. If the acid in which the emanation X 

 is dissolved be evaporated it is left behind on the dish and 

 its radio-activity is unimpaired. It has recently been dis- 

 covered that this emanation X may be volatilized at a 

 white heat and re-deposited on cold bodies in the neighbour- 

 hood, making them radio-active. It is not the emanation 

 for the rate of decay of its activity is markedly different 

 from the rate of decay of the emanation. It is a second 

 form of active matter generated from radium via the ema- 

 nation. It is this form of matter that gives rise to the beta- 

 and, gamma-rays which are emitted from the solid radium 

 compound and which we failed to find either in the emana- 

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