﻿1875.] 
  

  

  Hydrogen 
  and 
  Acids 
  on 
  Iron 
  and 
  Steel. 
  

  

  171 
  

  

  upon 
  iron 
  and 
  steel, 
  we 
  will 
  now 
  more 
  closely 
  consider 
  them 
  with 
  the 
  

   object 
  of 
  discovering 
  the 
  cause. 
  

  

  It 
  might 
  at 
  first 
  sight 
  be 
  thought 
  that 
  the 
  frothing 
  could 
  be 
  explained 
  

   on 
  the 
  supposition 
  that 
  by 
  the 
  action 
  of 
  acid, 
  iron 
  is 
  thrown 
  into 
  what 
  

   may 
  be 
  called 
  the 
  " 
  active 
  state," 
  in 
  opposition 
  to 
  the 
  so-called 
  passive 
  

   state 
  caused 
  by 
  nitric 
  acid, 
  and 
  that 
  in 
  this 
  " 
  active 
  state 
  " 
  it 
  is 
  able 
  to 
  

   decompose 
  water 
  at 
  the 
  ordinary 
  temperature, 
  forming 
  oxide 
  of 
  iron 
  and 
  

   bubbles 
  of 
  free 
  hydrogen. 
  The 
  facts, 
  however, 
  do 
  not 
  bear 
  out 
  this 
  

   theory, 
  as 
  the 
  bubbles 
  are 
  still 
  seen 
  if 
  oil 
  be 
  employed 
  instead 
  of 
  water 
  ; 
  

   and 
  no 
  matter 
  how 
  numerous 
  the 
  bubbles, 
  the 
  closest 
  examination 
  fails 
  

   to 
  show 
  any 
  formation 
  of 
  oxide. 
  Again, 
  the 
  frothing 
  is 
  greater 
  from 
  the 
  

   long 
  end 
  than 
  from 
  the 
  short 
  end 
  of 
  the 
  piece 
  of 
  wire, 
  whereas, 
  if 
  due 
  to 
  

   oxidation, 
  it 
  should 
  be 
  the 
  same 
  at 
  both 
  ends. 
  

  

  Now 
  the 
  following 
  facts 
  make 
  it 
  certain 
  that 
  hydrogen 
  is 
  either 
  the 
  sole 
  

   cause 
  of 
  the 
  changes 
  produced 
  in 
  iron 
  by 
  some 
  acids, 
  or 
  is 
  inseparably 
  

   connected 
  therewith 
  : 
  — 
  

  

  1st. 
  Only 
  those 
  acids 
  which 
  evolve 
  hydrogen 
  by 
  their 
  action 
  on 
  iron 
  

   produce 
  any 
  change 
  in 
  iron 
  and 
  steel, 
  nitric 
  acid 
  (which 
  does 
  not 
  

   liberate 
  hydrogen 
  except 
  under 
  particular 
  conditions) 
  having 
  no 
  effect. 
  

  

  2nd. 
  It 
  is 
  difficult 
  to 
  collect 
  the 
  bubbles 
  which 
  form 
  the 
  froth 
  on 
  the 
  

   moistened 
  fracture 
  of 
  a 
  piece 
  of 
  iron 
  in 
  sufficient 
  quantity 
  for 
  analysis 
  ; 
  

   but 
  by 
  putting 
  a 
  coil 
  of 
  wire, 
  previously 
  steeped 
  in 
  acid, 
  into 
  hot 
  water 
  

   under 
  a 
  bell-jar, 
  the 
  bubbles 
  of 
  gas 
  evolved 
  by 
  the 
  iron 
  may 
  be 
  collected, 
  

   and 
  will 
  be 
  found 
  to 
  burn 
  with 
  the 
  characteristic 
  flame 
  of 
  hydrogen. 
  

  

  Hence 
  it 
  is 
  probable 
  that 
  iron 
  and 
  steel, 
  when 
  placed 
  in 
  hydrochloric, 
  

   sulphuric, 
  or 
  other, 
  acid, 
  absorb 
  some 
  of 
  the 
  nascent 
  hydrogen 
  generated 
  

   by 
  the 
  action 
  of 
  the 
  acid, 
  thus 
  forming 
  what, 
  for 
  lack 
  of 
  a 
  better 
  term, 
  

   may 
  be 
  called 
  an 
  alloy* 
  of 
  iron 
  and 
  hydrogen. 
  This 
  alloy 
  may 
  be 
  com- 
  

   pared 
  to 
  that 
  formed 
  when 
  zinc 
  is 
  amalgamated 
  with 
  mercury 
  ; 
  and 
  just 
  

   as 
  in 
  process 
  of 
  time 
  the 
  mercury 
  disconnects 
  itself 
  from 
  the 
  zinc, 
  

   appearing 
  in 
  globules 
  on 
  its 
  surface, 
  so 
  hydrogen 
  gradually 
  disengages 
  

   itself 
  from 
  the 
  iron 
  — 
  a 
  movement 
  which 
  is 
  greatly 
  facilitated 
  by 
  heat, 
  as 
  

   is 
  natural 
  to 
  expect. 
  

  

  The 
  analogy 
  may 
  be 
  carried 
  still 
  further 
  ; 
  for 
  as 
  amalgamated 
  zinc 
  is 
  

   made 
  brittle 
  in 
  consequence 
  of 
  the 
  pores 
  or 
  interstices 
  between 
  the 
  mole- 
  

   cules 
  of 
  the 
  metal 
  being 
  filled 
  up 
  by 
  mercury, 
  motion 
  of 
  one 
  molecule 
  over 
  

   another 
  being 
  then 
  impeded, 
  so 
  in 
  like 
  manner 
  iron 
  becomes 
  brittle 
  when 
  

   its 
  pores 
  are 
  filled 
  up 
  by 
  condensed 
  hydrogen 
  gas 
  ; 
  and 
  naturally, 
  when 
  

   the 
  hydrogen 
  or 
  mercury 
  is 
  driven 
  out 
  of 
  the 
  molecular 
  interspaces, 
  

   movement 
  of 
  the 
  molecules 
  on 
  one 
  another 
  is 
  less 
  impeded, 
  and 
  hence 
  the 
  

   former 
  toughness 
  or 
  elasticity 
  is 
  restored. 
  

  

  Nor 
  is 
  amalgamated 
  zinc 
  the 
  only 
  analogous 
  case 
  ; 
  for 
  the 
  following 
  

   remarkable 
  experiment 
  lends* 
  further 
  probability 
  to 
  the 
  theory, 
  by 
  show- 
  

   ing 
  how 
  rapidly 
  the 
  absorption 
  of 
  zinc 
  by 
  iron 
  may 
  take 
  place, 
  attended 
  

   * 
  By 
  the 
  term 
  alloy 
  I 
  mean 
  a 
  solution 
  of 
  one 
  metal 
  in 
  another. 
  

  

  