802 
Dr.  0.  Halm  on  .some  Properties  of 
The  simplest  explanation  of  the  results  is  that  we  have  a  new 
thorium-product  which  is  transformed  very  rapidly  compared 
with  thorium  B. 
Fiff.  2. 
I  2  3  4-  5 
/ON /  ZA  T I  QN . 
From  a  study  of  the  ionization  curves  alone,  it  is  not 
possible  to  decide  whether  this  new  product  comes  between 
thorium  A  and  B  or  after  thorium  B.  This  point  was  settled 
by  another  experiment  as  follows.  The  active  deposit  was 
dissolved  from  a  copper  wire,  and  in  the  acid  solution  was 
placed  a  little  nickel  plate.  Von  Lerch*  has  shown  that  by 
this  method  thorium  B  is  separated  from  thorium  A,  and  that 
the  nickel  loses  its  activity  exponentially  with  a  period  of  one 
hour,  i.  e.  according  to  the  period  of  thorium  B.  The 
ionization-distance  curve  was  taken  with  this  nickel  plate 
as  a  source  of  rays.  The  curve  showed  again  the  two 
characteristic  portions, indicating  two  different  a  ray  products. 
Such  a  result  shows  that  the  new  product  always  accompanies 
thorium  B.  The  fact  that  the  active  nickel  plate  loses  its 
activity  according  to  an  exponential  law  shows  that  the  new 
*    Wiener  Ber.  March  1905. 
