﻿The 
  Deposit 
  upon 
  the 
  Poles 
  of 
  Metallic 
  Arcs. 
  333 
  

  

  must 
  further 
  be 
  supposed 
  that 
  the 
  thorium 
  or 
  product 
  which 
  

   grows 
  this 
  body 
  remains 
  with 
  the 
  uranium 
  after 
  the 
  uranium 
  

   has 
  been 
  freed 
  from 
  uranium 
  X. 
  

  

  Had 
  Fleck 
  published 
  the 
  absorption 
  and 
  decay 
  curves, 
  not 
  

   only 
  for 
  pure 
  uranium 
  X, 
  but 
  also 
  for 
  uranium 
  X 
  separated 
  

   from 
  uranium 
  known 
  to 
  contain 
  thorium, 
  then 
  comparison 
  of 
  

   these 
  curves 
  with 
  those 
  published 
  in 
  my 
  paper 
  would 
  settle 
  

   this 
  point. 
  Until 
  this 
  is 
  done, 
  however, 
  my 
  results 
  cannot 
  be 
  

   ■held 
  to 
  be 
  disproved. 
  The 
  fact 
  that 
  he 
  did 
  not 
  succeed 
  in 
  

   separating 
  uranium 
  Y 
  in 
  the 
  material 
  he 
  used 
  does 
  not 
  

   necessarily 
  prove 
  it 
  does 
  not 
  exist, 
  for 
  he 
  did 
  not 
  use 
  exactly 
  

   the 
  method 
  employed 
  by 
  me. 
  Its 
  separation, 
  as 
  I 
  said 
  in 
  my 
  

   paper, 
  is 
  a 
  matter 
  of 
  some 
  difficulty. 
  

  

  Since 
  he 
  has 
  been 
  unable 
  to 
  find 
  any 
  trace 
  of 
  uranium 
  Y 
  in 
  

   the 
  uranium 
  he 
  used, 
  and 
  as 
  L 
  feel 
  confident 
  that 
  my 
  uranium 
  

   was 
  free 
  from 
  thorium 
  and 
  its 
  products, 
  it 
  is 
  obvious 
  that 
  

   repetition 
  of 
  the 
  work 
  is 
  necessary 
  to 
  decide 
  which 
  of 
  us 
  is 
  

   right. 
  I 
  am 
  unable 
  to 
  do 
  this 
  with 
  advantage 
  until 
  more 
  

   precise 
  information 
  is 
  available 
  as 
  to 
  the 
  exact 
  methods 
  of 
  

   purifi 
  cation 
  of 
  the 
  uranium 
  salts 
  employed 
  by 
  Fleck. 
  

  

  G. 
  N. 
  Antoxoff. 
  

  

  "Chemical 
  Laboratory 
  of 
  the 
  Academy 
  of 
  Sciences, 
  

   St. 
  Petersburg. 
  

   June 
  1913. 
  

  

  XXI. 
  The 
  Deposit 
  upon 
  the 
  Poles 
  of 
  Metallic 
  Arcs. 
  By 
  

   W. 
  G. 
  Duffield, 
  D.Sc, 
  Professor 
  of 
  Physics, 
  University 
  

   College, 
  Reading*. 
  

  

  [Plates 
  IX. 
  & 
  X.] 
  

  

  DURING 
  some 
  experiments 
  upon 
  the 
  spectrum 
  emitted 
  

   by 
  an 
  iron 
  arc 
  burning 
  in 
  air, 
  it 
  was 
  frequently 
  ob- 
  

   served 
  that 
  one 
  or 
  other 
  of 
  the 
  poles 
  was 
  covered 
  with 
  a 
  

   brownish 
  deposit 
  after 
  the 
  arc 
  had 
  been 
  burning 
  for 
  some 
  

   time. 
  This 
  deposit 
  was 
  remarkable 
  for 
  its 
  organic 
  appearance, 
  

   resembling 
  on 
  different 
  occasions 
  a 
  delicate 
  coral 
  formation, 
  

   a 
  tree-like 
  growth 
  and 
  a 
  feathery 
  structure 
  ; 
  sometimes 
  it 
  

   formed 
  an 
  even 
  powder 
  spread 
  over 
  the 
  upper 
  pole. 
  Of 
  

   other 
  metals 
  which 
  have 
  been 
  similarly 
  examined 
  copper 
  has 
  

   proved 
  the 
  most 
  interesting, 
  the 
  growths 
  upon 
  poles 
  of 
  this 
  

   metal 
  being 
  confined 
  to 
  one 
  type, 
  and 
  since 
  there 
  is 
  some 
  

   evidence 
  that 
  from 
  a 
  corresponding 
  type 
  in 
  the 
  iron 
  arc 
  the 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  