Some  Properties  of  the  a  Rays  from  Radiothorium.     793 
If  all  salts  give  positive  and  negative  ions  having  the  same 
velocities  in  a  flame,  this  can  be  explained  by  supposing  that  a 
salt  molecule  emits  a  corpuscle  which  is  the  negative  ion, 
and  that  the  positively  charged  salt  molecule  forms  an 
aggregate  of  molecules  whose  size  depends  only  on  the 
charge,  and  so  is  the  same  for  all  salts.  This  view  is 
consistent  with  the  fact  that  the  velocity  of  the  positive  ions 
is  only  about  60  cms.  per  sec.  while  that  of  the  negative  ions 
is  1000  cms.  per  sec.  According  to  Prof.  Moreau's  results, 
the  positive  and  negative  ions  ought  to  have  nearly  equal 
velocities,  for  the  atomic  weight  of  the  metals  is  comparable 
with  the  molecular  weight  of  the  acid  radicals. 
The  experiments  done  by  the  writer  in  1899  showed  that 
lithium  (Li  =  7)  salts  give  ions  having  the  same  velocities 
as  the  ions  from  caesium  (Cs  =  133)  salts  ;  which  proves 
clearly  that  the  velocity  of  the  negative  ions  does  not  vary 
inversely  as  the  square  root  of  the  atomic  weight  of  the 
metal — a  conclusion  which  Prof.  Moreau  has  drawn  from 
experiments  on  potassium  (K  =  39)  and  sodium  (Na  =  23) 
salts. 
It  has  been  shown  by  Prof.  Lenard  that  the  salt  vapour 
emitting  light  in  flames  moves  in  a  strong  electric  field  as 
though  it  were  positively  charged.  I  have  verified  this 
result,  which  clearly  proves  that  the  metal  goes  to  form  the 
positive  ions,  for  the  light  is  undoubtedly  emitted  by  the 
metal  atoms  and  not  by  the  acid  radical  of  the  salts. 
I  think  therefore  that  the  view  that  all  alkali  salts  in 
flames  give  ions  having  nearly  the  same  velocities  is  really 
supported  by  Prof.  Moreau's  observations  as  well  as  by  those 
of  Dr.  Marx  and  the  writer. 
LXXIV.    On  some  Properties  of  the  a.  Rays  from 
Radiotliorium.  (I.)     By  0.  Hahn,  Ph.D.* 
IN  a  previous  paper  f,  I  have  given  an  account  of  the 
methods  of  separation  and  the  radioactive  properties  of 
a  very  active  substance,  called  radiothorium,  which  was 
prepared  from  the  Ceylon  mineral  thorianite.  It  was  shown 
that  radiotliorium  was  probably  a  slowly  changing  product 
of  thorium — the  latter  is  then  supposed  to  be  inactive — which 
lies  between  thorium  and  thorinm-X. 
Radiothorium  possesses  in  an  intense  degree  all  the  radio- 
active properties  of  thorium,  for  it  gives  rise  to  thorium-X, 
*  Communicated  by  Prof.  E.  Rutherford,  F.R.S. 
f  Proc.  Roy.  Soc.  March  1905 ;  Jalirbuch.  d.  liadiaktiuitlit,  II.  3. 1905. 
Phil.  Maq.  S.  6.  Vol.  .11.  Na.  66,  June  .1906.  3  F 
