﻿170 
  

  

  Mr. 
  W. 
  H. 
  Johnson 
  on 
  the 
  Action 
  of 
  [Jan. 
  14, 
  

  

  produced 
  by 
  immersion 
  in 
  acid 
  is 
  greater 
  and 
  more 
  rapid 
  than 
  with 
  the 
  

   same 
  steel 
  in 
  a 
  soft 
  state. 
  

  

  Suspecting 
  that 
  the 
  absence 
  of 
  frothing 
  on 
  the 
  surface 
  of 
  steel 
  after 
  

   immersion 
  in 
  acid 
  might 
  arise 
  from 
  the 
  bubbles 
  of 
  gas 
  given 
  off 
  being 
  

   so 
  small 
  as 
  to 
  be 
  invisible 
  to 
  the 
  naked 
  eye, 
  I 
  examined 
  the 
  moistened 
  

   fracture 
  of 
  a 
  piece 
  of 
  steel 
  under 
  a 
  microscope 
  with 
  a 
  power 
  of 
  250 
  dia- 
  

   meters. 
  My 
  expectations 
  were 
  fulfilled, 
  for 
  numbers 
  of 
  minute 
  bubbles 
  

   were 
  seen 
  to 
  rise 
  from 
  parts 
  of 
  the 
  moistened 
  fracture. 
  It 
  appears 
  that 
  

   the 
  fibrous 
  and 
  open 
  structure 
  of 
  iron 
  allows 
  any 
  gas 
  which 
  has 
  been 
  

   occluded 
  in 
  its 
  substance 
  to 
  pass 
  more 
  easily 
  to 
  the 
  surface 
  of 
  the 
  fracture 
  

   than 
  will 
  the 
  close, 
  unfibrous, 
  homogeneous 
  structure 
  of 
  steel 
  ; 
  conse- 
  

   quently 
  the 
  evolution 
  of 
  gas 
  will 
  not 
  be 
  so 
  rapid 
  with 
  steel 
  as 
  with 
  iron. 
  

   Moreover 
  the 
  fracture 
  of 
  steel 
  presents 
  an 
  almost 
  infinite 
  number 
  of 
  small 
  

   points, 
  all 
  favourable 
  to 
  the 
  rapid 
  evolution 
  of 
  small 
  bubbles 
  invisible 
  to 
  

   the 
  naked 
  eye. 
  Iron 
  wire, 
  on 
  the 
  other 
  hand, 
  breaks 
  with 
  a 
  fibrous 
  

   mossy 
  fracture, 
  which 
  will 
  retain 
  the 
  small 
  bubbles 
  until 
  they 
  have 
  grown 
  

   sufficiently 
  large 
  to 
  be 
  visible 
  to 
  the 
  naked 
  eye. 
  Hence 
  the 
  frothing 
  in 
  

   iron 
  and 
  its 
  absence 
  in 
  steel. 
  

  

  The 
  following 
  experiments 
  were 
  made 
  to 
  ascertain 
  if 
  there 
  was 
  any 
  

   appreciable 
  increase 
  in 
  weight 
  in 
  iron 
  which 
  frothed 
  over 
  the 
  same 
  iron 
  

   when 
  in 
  its 
  usual 
  state. 
  The 
  pieces 
  of 
  iron 
  and 
  steel 
  wire, 
  after 
  immer- 
  

   sion 
  in 
  acid, 
  were 
  well 
  washed 
  in 
  cold 
  water, 
  and 
  when 
  dry 
  weighed, 
  this 
  

   being 
  the 
  weight 
  when 
  the 
  metal 
  contained 
  the 
  gas. 
  Subsequently 
  they 
  

   were 
  heated 
  several 
  hours 
  in 
  an 
  oven 
  to 
  restore 
  them 
  as 
  far 
  as 
  possible, 
  

   and 
  again 
  weighed. 
  The 
  result 
  of 
  the 
  last 
  weighing, 
  in 
  every 
  instance, 
  

   must 
  always 
  have 
  been 
  a 
  little 
  too 
  large, 
  as 
  it 
  was 
  found 
  impossible 
  to 
  

   prevent 
  a 
  thin 
  film 
  of 
  rust 
  forming 
  on 
  the 
  surface 
  of 
  the 
  metal 
  when 
  being 
  

   heated 
  in 
  the 
  oven. 
  Notwithstanding 
  this, 
  the 
  results 
  showed 
  in 
  every 
  

   case 
  a 
  gain 
  in 
  weight 
  after 
  immersion 
  in 
  acid. 
  After 
  five 
  hours' 
  immer- 
  

   sion 
  in 
  acid 
  the 
  average 
  gain 
  in 
  weight 
  for 
  mild 
  steel, 
  charcoal-iron, 
  and 
  

   common 
  iron 
  was 
  in 
  

  

  Hydrochloric 
  acid 
  *028 
  per 
  cent. 
  

  

  Sulphuric 
  acid 
  -036 
  „ 
  

  

  The 
  steel 
  gained 
  considerably 
  the 
  most 
  — 
  a 
  result 
  well 
  worthy 
  of 
  notice 
  ; 
  

   for 
  we 
  shall 
  see 
  that 
  the 
  tensile 
  strain 
  and 
  elasticity 
  of 
  steel 
  are 
  far 
  more 
  

   affected 
  by 
  the 
  presence 
  of 
  absorbed 
  hydrogen 
  than 
  iron 
  under 
  like 
  con- 
  

   ditions 
  — 
  probably 
  in 
  part 
  because 
  more 
  gas 
  is 
  occluded 
  by 
  steel 
  than 
  iron 
  

   (a 
  conclusion 
  which 
  the 
  greater 
  increase 
  in 
  weight 
  of 
  steel, 
  in 
  compari- 
  

   son 
  with 
  iron, 
  bears 
  out), 
  and 
  in 
  part 
  owing 
  to 
  the 
  different 
  molecular 
  

   structure 
  of 
  steel. 
  

  

  I 
  hope 
  at 
  some 
  future 
  time 
  to 
  ascertain, 
  if 
  possible, 
  if 
  this 
  gain 
  in 
  

   weight 
  is 
  entirely 
  due 
  to 
  occluded 
  hydrogen, 
  or 
  whether 
  also 
  to 
  absorp- 
  

   tion 
  of 
  acid 
  to 
  a 
  greater 
  or 
  less 
  extent. 
  

  

  Having 
  examined 
  in 
  detail 
  some 
  of 
  the 
  effects 
  of 
  immersion 
  in 
  acid 
  

  

  