170 SUMMARY OF ELECTRON THEORY [CH.XVIII. 



weight must change, presumably by an amount 

 appropriate to the loss of an atom of helium. It 

 will be observed that the gamma or Rontgen rays 

 always accompany the emission of a beta particle or 

 electron, and never appear otherwise ; also that it is 

 only in some of the changes that electrons are thrown 

 off. It will be understood that the so-called " emana- 

 tions" are all of the nature of gas, while the other 

 products are like a solid deposit or coating. These 

 active deposits, or " excited activities," can be sub- 

 jected to ordinary chemical tests : some of them are 

 soluble in acids, some in ammonia ; some of them 

 are volatile at a high temperature, some are not 

 readily volatile. The following table contains the 

 principal features of the transformations of the more 

 remarkable radio-active substances ; for more details 

 Rutherford's book must be referred to. The product 

 here called Radium F appears to be the same as that 

 called by other observers Radio-tellurium, or by its 

 original discoverer, Mme. Curie, Polonium : 



