﻿1875.] 
  Hydrogen 
  and 
  Acids 
  on 
  Iron 
  and 
  Steel. 
  169 
  

  

  copious 
  bubbles 
  of 
  gas 
  beiug 
  given 
  off 
  from 
  the 
  whole 
  surface 
  of 
  the 
  

   fracture 
  for 
  30 
  to 
  40 
  seconds, 
  or 
  even 
  longer, 
  making 
  the 
  water 
  on 
  the 
  

   fractured 
  surface 
  appear 
  to 
  boil 
  violently. 
  This 
  frothing 
  is 
  increased 
  by 
  

   any 
  thing 
  that 
  augments 
  the 
  heat 
  produced 
  by 
  fracture 
  ; 
  in 
  fact 
  it 
  is 
  

   necessary 
  that 
  the 
  fracture 
  be 
  more 
  or 
  les's 
  warm 
  to 
  cause 
  the 
  escape 
  of 
  

   bubbles 
  ; 
  for 
  if 
  the 
  wire 
  be 
  nicked 
  and 
  broken 
  short 
  without 
  generating 
  

   any 
  heat, 
  few 
  or 
  no 
  bubbles 
  will 
  be 
  seen. 
  By 
  further 
  experiment 
  I 
  found 
  

   that 
  other 
  acids, 
  such 
  as 
  acetic, 
  had 
  the 
  same 
  effect 
  on 
  iron 
  as 
  those 
  first 
  

   used 
  ; 
  and 
  it 
  became 
  evident 
  that 
  any 
  acid 
  which 
  liberates 
  hydrogen 
  by 
  

   its 
  action 
  on 
  iron 
  is 
  able 
  to 
  produce 
  them. 
  Nitric 
  acid, 
  which 
  under 
  

   usual 
  conditions 
  does 
  not 
  liberate 
  hydrogen 
  by 
  its 
  action 
  on 
  iron, 
  is, 
  how- 
  

   ever, 
  without 
  effect. 
  The 
  frothing, 
  the 
  diminution 
  of 
  toughness, 
  and 
  all 
  

   other 
  changes 
  caused 
  by 
  immersion 
  in 
  acid 
  are, 
  as 
  a 
  rule, 
  only 
  temporary 
  ; 
  

   for 
  after 
  an 
  exposure 
  to 
  a 
  temperature 
  of 
  about 
  16° 
  C. 
  for 
  three 
  days, 
  or 
  

   of 
  200° 
  C. 
  for 
  half 
  a 
  day, 
  the 
  wire 
  will 
  be 
  found 
  to 
  have 
  regained 
  its 
  ori- 
  

   ginal 
  toughness, 
  and 
  no 
  bubbles, 
  or 
  any 
  sign 
  of 
  evolution 
  of 
  gas, 
  will 
  be 
  

   seen, 
  as 
  before, 
  on 
  moistening 
  the 
  fracture. 
  The 
  bubbles 
  also 
  cease 
  to 
  be 
  

   visible 
  long 
  before 
  the 
  wire 
  has 
  recovered 
  its 
  original 
  toughness 
  or 
  elas- 
  

   ticity. 
  Immersion 
  in 
  water, 
  particularly 
  if 
  warm, 
  hastens 
  the 
  restoration 
  

   of 
  toughness, 
  and 
  numerous 
  bubbles 
  may 
  be 
  seen 
  to 
  arise 
  from 
  the 
  iron 
  

   when 
  first 
  immersed. 
  If 
  a 
  little 
  caustic 
  soda, 
  or 
  other 
  alkali, 
  be 
  added 
  to 
  

   the 
  water 
  in 
  which 
  the 
  iron 
  is 
  laid, 
  its 
  recovery 
  is 
  still 
  further 
  hastened, 
  

   as 
  it 
  neutralizes 
  a 
  film 
  of 
  acid 
  which 
  seems 
  to 
  adhere 
  to 
  the 
  surface 
  of 
  all 
  

   iron 
  which 
  has 
  been 
  attacked 
  by 
  acid. 
  

  

  It 
  seems 
  at 
  first 
  remarkable 
  that 
  steel 
  does 
  not 
  froth 
  when 
  fractured 
  

   after 
  immersion 
  in 
  acid, 
  under 
  the 
  same 
  conditions 
  as 
  will 
  produce 
  a 
  vio- 
  

   lent 
  evolution 
  of 
  gas 
  with 
  iron 
  ; 
  and 
  yet 
  the 
  action 
  of 
  acids 
  on 
  steel 
  is 
  

   more 
  rapid, 
  more 
  marked, 
  and 
  more 
  permanent 
  than 
  on 
  iron. 
  The 
  decrease 
  

   in 
  toughness 
  is 
  such 
  that 
  a 
  piece 
  of 
  steel 
  which, 
  previous 
  to 
  immersion 
  

   in 
  hydrochloric 
  or 
  sulphuric 
  acid, 
  would 
  stand 
  bending 
  on 
  itself 
  and 
  back 
  

   two 
  or 
  three 
  times, 
  will 
  break 
  short 
  off 
  like 
  a 
  pipe-stem 
  when 
  bent. 
  So 
  

   great 
  is 
  the 
  influence 
  of 
  acid, 
  in 
  fact, 
  that 
  10 
  minutes' 
  immersion 
  in 
  dilute 
  

   sulphuric 
  acid 
  will 
  sometimes 
  cause 
  a 
  coil 
  of 
  highly 
  carbonized 
  tem- 
  

   pered 
  cast-steel 
  wire 
  to 
  break 
  of 
  itself 
  into 
  several 
  pieces 
  while 
  in 
  the 
  

   liquid. 
  

  

  The 
  amount 
  of 
  carbon 
  in 
  the 
  steel 
  appears, 
  moreover, 
  to 
  be 
  connected 
  

   with 
  the 
  action 
  of 
  acid 
  ; 
  for 
  in 
  mild 
  Bessemer 
  steels, 
  containing 
  about 
  

   0*20 
  to 
  0*25 
  per 
  cent, 
  of 
  carbon, 
  the 
  change 
  is 
  a 
  very 
  little 
  more 
  marked 
  

   than 
  in 
  iron, 
  even 
  frothing 
  being 
  apparent 
  after 
  prolonged 
  immersion. 
  

   With 
  an 
  increased 
  percentage 
  of 
  carbon 
  the 
  action, 
  however, 
  is 
  more 
  

   marked 
  and 
  of 
  longer 
  duration. 
  Half 
  an 
  hour's 
  immersion 
  in 
  hydro- 
  

   chloric 
  acid 
  will 
  make 
  a 
  piece 
  of 
  steel 
  containing, 
  say, 
  0'60 
  per 
  cent, 
  

   of 
  carbon 
  break 
  with 
  a 
  much 
  darker-coloured 
  fracture, 
  and 
  render 
  it 
  so 
  

   brittle 
  that 
  no 
  amount 
  of 
  exposure 
  to 
  the 
  air 
  or 
  heat 
  will 
  ever 
  completely 
  

   restore 
  it. 
  On 
  hardened 
  and 
  tempered 
  steel 
  the 
  decrease 
  in 
  toughness 
  

  

  p 
  2 
  

  

  