172 
A  Piece  of  Pitchblende. 
Am.  Jour.  Phann. 
April,  1909. 
as  active  as  radium,  and  the  heat  liberated  in  its  disintegration, 
according  to  Ramsay,  is  about  3,000,000  times  as  great  as  that 
resulting  from  the  explosion  of  a  like  volume  of  oxyhydrogen  gas. 
The  only  product  of  the  disintegration  of  radium  emanation  which 
has  been  definitely  identified  is  helium,  the  gas  which  exists  in  so 
many  of  the  uranium  and  thorium  minerals.  The  production  of 
helium  from  radium  was  first  observed  by  Ramsay  and  Soddy  in 
1903  and  has  since  been  abundantly  confirmed  by  others.  It  is  the 
first  instance  of  the  transformation  of  one  well-defined  element  into 
another.  The  announcement  created  a  sensation  in  the  scientific 
world,  for  it  broke  down  one  of  the  most  cherished  doctrines  of 
chemistry,  that  of  the  immutability  of  the  atoms,  and  thus  seemed 
to  shake  the  very  foundations  of  the  atomic  theory. 
During  the  past  five  years  there  has  been  accumulated  a  vast 
amount  of  experimental  evidence  to  elucidate  the  true  nature  of  the 
radio-active  changes,  and  it  is  to  Professor  Rutherford  that  we  owe 
not  only  a  masterful  and  complete  account  of  what  has  been  accom- 
plished, but  also  the  one  consistent  generalization  that  explains  the 
facts.  As  my  time  is  nearly  up,  I  must  pass  over  the  experimental 
results  from  which  the  theory  derives  its  support,  and  I  shall  only 
briefly  indicate  the  main  features  of  Rutherford's  hypothesis.  It 
proceeds  from  the  bold  and  novel  assumption  that  the  atoms  of  the 
radio-active  elements  are  in  a  state  of  continuous  disintegration,  and 
that  these  smallest  units  which  enter  into  chemical  changes,  in  the 
accepted  sense  of  this  term,  are  really  made  up  of  great  numbers  of 
still  smaller  particles,  carrying  negative  electrical  charges.  Just 
how  these  electrons,  as  they  are  called,  are  disposed  within  the 
chemical  atoms  has  taxed  and  is  still  taxing  the  ingenuity  of  the 
foremost  physicists  of  our  time,  but  a  fairly  satisfactory  conception 
has  been  developed  by  such  men  as  Lord  Kelvin,  J.  J.  Thomson, 
Lorentz,  and  others.  According  to  the  electronic  hypothesis  the 
integral  parts  of  the  complex  little  structures  or  atoms  are  in  a  state 
of  incessant  and  rapid  motion;  they  rotate  about  a  common  centre, 
and  it  is  this  oscillation  which  supplies  the  energy  which  the  atoms 
are  capable  of  yielding  up.  The  atom  as  whole  is  supposed  to  be 
positively  charged,  while  the  moving  electrons  carry  negative 
charges.  A  definite  number  of  the  radio-active  atoms  undergo 
spontaneous  disintegration  in  a  unit  of  time,  one  or  several  of  the 
electrons  being  expelled,  while  the  remaining  ones  form  a  new  con- 
figuration, which  in  turn  suffers  analogous  radio-active  changes.  In 
