﻿Deposit 
  upon 
  the 
  Poles 
  of 
  Metallic 
  Arcs. 
  339 
  

  

  An 
  arc 
  between 
  carbon 
  and 
  iron 
  poles 
  was 
  investigated, 
  

   but 
  no 
  growths 
  were 
  produced 
  because 
  the 
  arc 
  covered 
  a 
  

   larger 
  area 
  and 
  must 
  have 
  destroyed 
  any 
  incipient 
  growth 
  ; 
  

   moreover, 
  the 
  carbon 
  acted 
  as 
  a 
  reducing 
  agent 
  upon 
  the 
  

   oxide, 
  the 
  iron 
  remaining 
  bright 
  and 
  metallic, 
  even 
  in 
  those 
  

   regions 
  from 
  which 
  the 
  arc 
  had 
  actually 
  sprung. 
  

  

  Effect 
  of 
  cooling. 
  — 
  That 
  the 
  condensation 
  of 
  the 
  vapour 
  

   into 
  the 
  forms 
  described 
  was 
  not 
  occasioned 
  by 
  cooling 
  alone 
  

   was 
  shown 
  by 
  introducing 
  cool 
  objects 
  insulated 
  and 
  without 
  

   charge 
  into 
  it, 
  a 
  meagre 
  powdery 
  deposit 
  was 
  obtained 
  in 
  

   such 
  cases. 
  

  

  Introduction 
  of 
  different 
  metals. 
  — 
  The 
  effect 
  of 
  introducing 
  

   charged 
  electrodes 
  of 
  different 
  metals 
  above 
  a 
  copper 
  arc 
  

   was 
  also 
  investigated, 
  but 
  no 
  differences 
  in 
  the 
  nature 
  of 
  

   the 
  growths 
  were 
  discovered, 
  — 
  this 
  precludes 
  the 
  growths 
  

   being 
  derived 
  from 
  the 
  metal 
  of 
  the 
  pole 
  upon 
  which 
  they 
  

   form, 
  a 
  process 
  which 
  was 
  suggested 
  by 
  the 
  resemblance 
  of 
  

   these 
  forms 
  to 
  organic 
  growths. 
  Further 
  proof 
  of 
  this 
  con- 
  

   clusion 
  is 
  furnished 
  by 
  experiments 
  upon 
  arcs 
  in 
  which 
  the 
  

   electrodes 
  were 
  of 
  different 
  met:ils. 
  

  

  Rotation 
  of 
  the 
  growths. 
  — 
  The 
  growths 
  were 
  frequently 
  

   observed 
  to 
  rotate, 
  the 
  whole 
  mass 
  of 
  foliage 
  turning 
  round 
  

   about 
  the 
  main 
  trunk 
  or 
  the 
  laterals 
  revolving 
  round 
  a 
  

   branch. 
  This 
  may 
  be 
  due 
  to 
  chance 
  convection 
  currents 
  or 
  

   may 
  be 
  connected 
  with 
  the 
  rotation 
  observed 
  by 
  Trotter 
  *, 
  

   though 
  slower 
  than 
  the 
  rate 
  he 
  found. 
  The 
  direction 
  of 
  

   rotation 
  of 
  the 
  deposit 
  was 
  not 
  constant 
  but 
  more 
  frequently 
  

   in 
  the 
  direction 
  in 
  which 
  it 
  would 
  be 
  necessary 
  to 
  turn 
  a 
  

   right-handed 
  screw 
  advancing 
  from 
  the 
  negative 
  towards 
  the 
  

   positive 
  pole. 
  

  

  Discussion 
  of 
  the 
  Phenomenon. 
  

  

  From 
  the 
  foregoing 
  description 
  of 
  the 
  metallic 
  growths 
  

   their 
  outstanding 
  features 
  are 
  seen 
  to 
  be 
  (1) 
  their 
  preference 
  

   for 
  the 
  cathode, 
  (2) 
  their 
  formation 
  upon 
  a 
  third 
  electrode 
  

   if 
  its 
  potential 
  be 
  sufficiently 
  high, 
  and 
  especially 
  if 
  it 
  be 
  

   negatively 
  charged, 
  (3) 
  their 
  preference 
  for 
  a 
  pointed 
  

   electrode, 
  (4) 
  their 
  derivation 
  from 
  the 
  material 
  of 
  either 
  

   the 
  anode 
  or 
  cathode 
  but 
  chiefly 
  from 
  the 
  latter, 
  (5) 
  their 
  

   organic 
  form, 
  which 
  is 
  different 
  for 
  different 
  metals, 
  (6) 
  the 
  

   rapidity 
  of 
  their 
  development 
  as 
  they 
  approach 
  the 
  anode 
  

   and 
  when 
  an 
  outburst 
  of 
  vapour 
  occurs. 
  

  

  * 
  ' 
  The 
  Electrician/ 
  vol. 
  xxxiii. 
  p. 
  297 
  (1894). 
  

  

  