Am.  Jour.  Pharni. 
April,  1909. 
A  Piece  of  Pitchblende. 
173 
this  manner  the  heavy  radio-active  atoms  are  gradually  "  degraded  " 
into  other  atoms  of  smaller  weight,  but  of  greater  stability.  The  rays, 
then,  which  are  peculiar  to  the  radio-active  substances,  are  simply 
the  emission  of  particles  resulting  from  the  continuous  disruption 
of  their  atoms. 
In  the  light  of  our  present  knowledge  it  appears  that  the  known 
radio-active  substances,  with  the  exception  of  thorium,  are  de- 
rived from  uranium,  and  represent  successive  stages  in  a  series  of 
transformations,  and  perhaps  ramifications  of  this  series.  These 
relations  are  shown  in  this  pedigree:  uranium,  uranium  X,  ionium, 
radium,  radium  emanation,  radium  A,  B,  C,3  D,  Ei,  E2,  and  F, 
which  latter  is  identical  with  polonium  or  radio-tellurium.  Actinium 
is  regarded  as  belonging  to  a  branch  of  this  series,  while  other  radio- 
active substances  are  the  descendants  of  thorium.  There  can  be  no 
doubt  that  even  the  youngest  known  members  of  these  series  undergo 
further  transformations,  and  not  a  little  evidence  has  been  gathered 
to  indicate  that  other  elements  also  undergo  a  "  rayless  "  disintegra- 
tion into  elements  of  smaller  atomic  weight.  At  present,  however, 
the  connections  which  may  exist  among  the  non-radio-active  elements 
are  largely  conjectural,  and  the  observations  of  some  of  the  most 
distinguished  workers  in  this  field  are  in  many  respects  contradictory. 
This  much,  however,  is  certain,  that  the  radio-active  changes 
are  not  chemical  changes  in  the  accepted  sense  of  the  term.  They 
must  be  regarded  as  a  spontaneous  disintegration  of  elementary 
atoms,  and  cannot,  therefore,  be  recognized  by  strictly  chemical 
methods.  Their  discovery  has  given  us  a  new  chemistry  which  does 
not  limit  the  changes  in  matter  to  rearrangements  of  the  Daltonian 
atoms,  but  penetrates  to  the  still  smaller  units,  or  corpuscles,  of 
which  they  are  made  up,  and  to  those  marvellous  forces  which  are 
liberated  in  their  disintegration. 
In  conclusion  let  us  cast  another  glance  at  our  black  and  shape- 
less piece  of  pitchblende,  and  recall  the  interesting  and  dramatic  part 
this  mineral  has  played  in  the  history  of  physical  science.  Its  chem- 
ical investigation  during  the  past  120  years  has  not  only  brought  to 
light  a  large  number  of  the  most  interesting  elementary  substances, 
but  has  also  furnished  science  with  a  novel  and  most  powerful  weapon 
for  attacking  such  fundamental  problems  as  those  of  the  constitution 
3  Radium  A,  B  and  C  constitute  the  quickly  decaying  "  active  deposit " 
which  radium  produces  on  bodies  placed  near  it. 
