424 



SCIENCE 



[N. S. Vol. XL VI. No. 1192 



babilite bien superieure a eelle du. plus 

 grand nombre des faits historiques sur 

 lesquels on ne se permet aucune doute. 



THE ATOMS AEE INTKA-ATOMIC HELIUM-HY- 

 DROGEN COMPOUNDS 



The atoms of radioactive substances are 

 known to sboot off alpha particles with 



trates the change which occurs in this 

 process. Any special element, such as 

 radium (which is an extremely active solid, 

 with a valence of 2, and belonging there- 

 fore to group 2) has its valence reduced by 

 two when the atom ejects an alpha par- 

 ticle (which carries two positive charges), 

 and in this case changes into the inactive 



Fig 1. Teansfoemations op the Radioactive Elements. The a and /3 changes of the radio-ao- 

 tive elements. Note that the atoms of even atomic number are more numerous than those of odd atomic 

 number. Thus there are 32 of the former class to 11 of the latter. 



speeds as high as 20,000 miles per second. 

 These alpha particles carry two positive 

 charges, have an atomic weight of 4.0, and 

 when they are collected and take up nega- 

 tive electrons, give ordinary helium. They 

 may be thought of as the nuclei of helium 

 atoms, and seem to be shot out from the 

 nucleiis of the more complex atom such as 

 that of radium or thorium. Fig. 1 illus- 



gas, radium emanation or niton. The alpha 

 particle has a weight of 4, and niton has 

 an atomic weight which is 222, or four less 

 than that of radium (226). That this is a 

 general rule was discovered by Soddy, and 

 it was verified later by Fajans, Russell, von 

 Hevesy and Fleck. 



Let us picture the changes which occur 

 during the long chain of processes which 



