850 
Isotopy. 
I  Am.  Jour.  Pharm. 
X     December,  1920. 
research  nor  an  extensive  discussion  of  the  present  day  views,  but 
the  following  summary  will  suffice  for  an  introduction  to  the  special 
subject  of  this  address. 
The  Electron. — All  atoms  contain  a  common  constituent,  the 
electron,  the  discovery  of  which  resulted  especially  from  studies 
made  with  the  Crookes  tube.  Differing  completely  from  light,  the 
cathode  rays  are  made  up  of  distinct  corpuscles  of  extremely  minute 
mass — about  i  / 1700  that  of  the  atom  of  hydrogen — which  corpuscles 
are  negatively  charged,  and  have  a  high  velocity,  approximating 
50,000  kilometers  per  second.  The  velocity  is  dependent  on  the 
electric  potential  influencing  them,  but  the  charge  and  mass  are 
always  the  same  whatever  may  be  the  circumstances  of  their  libera- 
tion.   The  electron,  therefore,  is  a  universal  constituent  of  matter. 
The  Positive  Nucleus. — To  compensate  for  the  negative  charges 
of  the  electron,  the  neutral  atom  should  contain  a  positively  charged 
mass,  which  Rutherford  considers  as  reduced  to  a  very  small  central 
nucleus,  about  0.0001  of  the  diameter  of  the  whole  atom.  Around 
this  positive  nucleus,  in  which  is  concentrated  the  individuality 
of  the  atom  and  almost  its  whole  mass,  the  'electrons  circulate  in 
number  about  equal  to  half  the  atomic  weight.  Helium  (at.  wt.  4) 
has  two  electrons;  carbon  (at.  wt.  12)  has  six,  and  so  on,  but  hydrogen 
does  not  follow  the  rule  as  it  has  one  electron  and  a  positive  nucleus. 
Moreover,  though  all  electrons  are  identical  among  themselves, 
they  probably  do  not  have  exactly  the  same  value  as  constituent 
particles,  for  it  seems  illogical  to  suppose  the  same  origin  for  the 
electrons  that  are  emitted  in  such  peculiar  transformations  as  those 
of  the  radioactive  substances  (beta-rays),  as  the  electrons  that  are 
concerned  in  the  simple  change  of  valency  when  ferrous  salts  are 
converted  into  ferric.  In  the  former  instance,  the  electrons  probably 
come  from  a  deeper  and  more  essential  part  of  the  atom  than  do 
those  in  the  latter. 
It  can  also  be  assumed  that  the  electrons  are  arranged  in  several 
concentric  groups  and  be  in  close  contact  with  the  positive  nucleus. 
One  of  the  results  of  this  structure  of  the  atom  is  the  possibility 
of  transformation  of  one  type  of  atom  into  another,  in  other  words,  the 
creation  of  one  element  from  another.  This  has  been,  as  is  well 
known,  the  dream  of  ages.  It  has  now  been  shown  to  be  possible, 
not  along  the  lines  in  which  the  search  has  been  made,  namely,  the 
conversion  of  the  baser  metals  into  gold,  but  in  the  conversion,  for 
instance,  of  uranium  into  helium.    It  has  been  found  that  uranium 
