Wells & Foote — One Hundred Years of Chemistry. 285 



In 1898 Ramsay and Travers, by the nse of ingenious 

 methods of fractional distillation and absorption by char- 

 coal, obtained three other much rarer inactive gases 

 from the atmosphere which they called neon, krypton and 

 xenon. 



The inactive gases are all colorless, and as they form 

 no chemical compounds they are characterized by their 

 densities, which give their atomic weights, by their boil- 

 ing points, and by their characteristic Geissler-tube spec- 

 tra. 



The gaseous radium emanation, or niton, belongs also 

 to the inactive group, and it was also collected and 

 studied by Ramsay who was compelled to work with only 

 0-0001 cc. of it, as the volume obtained by heating radium 

 salts is very small. It is an evanescent element, disap- 

 pearing within a few days on account of radioactive dis- 

 integration. Meanwhile it glows brilliantly when lique- 

 fied and cooled to the temperature of liquid air. It has 

 an atomic weight of 222, four units below that of radium, 

 and the difference is considered as due to the loss by 

 radium of an atom of helium in passing into the 

 emanation. 



The Radioactive Elements. — The discovery of radium 

 in 1898 by Madame Curie, and the study of that and other 

 radioactive elements has produced a profound effect 

 upon chemical theory. It was found that the two ele- 

 ments of the highest atomic weights, uranium and 

 thorium, are always spontaneously decomposing into 

 other elements at a fixed rate of speed which can be con- 

 trolled by no artificial means, and that the elements 

 resulting from these- decompositions likewise undergo 

 spontaneous changes into still other elements at greatly 

 varying rates of speed, forming in each case a remark- 

 able series of temporary elements. These transforma- 

 tions are accompanied by the emission at enormous 

 velocities of three kinds of rays, one variety of which has 

 been shown to consist of helium atoms. The greater 

 number of the elements formed in these transformations 

 have not as yet been obtained in a pure condition, and 

 they are known only in connection with their radio- 

 activity, volatility, etc. ; but radium and niton, two of 

 these products, have been obtained in a pure condition, 

 so that their atomic weights and their places in the 

 periodic system have been fixed. 



