﻿178 
  

  

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

  

  the 
  tensile 
  strain 
  rises, 
  till 
  eventually 
  it 
  exceeds 
  the 
  original 
  strain 
  before 
  

   immersion 
  in 
  acid. 
  

  

  2. 
  A 
  most 
  unexpected 
  change 
  in 
  the 
  elasticity 
  of 
  steel, 
  the 
  elasticity 
  

   of 
  the 
  wire 
  being 
  considerably 
  increased 
  by 
  the 
  occlusion 
  of 
  hydrogen 
  ; 
  

   but 
  when 
  a 
  portion 
  of 
  this 
  hydrogen 
  is 
  expelled 
  by 
  heat, 
  the 
  elasticity, 
  as 
  

   measured 
  by 
  elongation 
  at 
  the 
  moment 
  of 
  fracture, 
  falls 
  remarkably, 
  as 
  

   much 
  as 
  4*7 
  per 
  cent, 
  in 
  annealed 
  and 
  0*64 
  per 
  cent, 
  in 
  bright 
  steel. 
  

   "When 
  the 
  hydrogen 
  is 
  completely 
  expelled, 
  the 
  elasticity, 
  however, 
  rises, 
  

   being 
  then 
  greater 
  than 
  before 
  immersion 
  in 
  acid. 
  

  

  The 
  following 
  experiments 
  on 
  hardened 
  and 
  tempered 
  cast-steel 
  wire 
  

   containing 
  about 
  three 
  times 
  as 
  much 
  carbon 
  as 
  the 
  mild 
  steel, 
  show 
  an 
  

   extraordinary 
  diminution 
  in 
  the 
  tensile 
  strain 
  when 
  containing 
  occluded 
  

   hydrogen 
  ; 
  this, 
  however, 
  is 
  regained 
  or 
  even 
  surpassed 
  when 
  the 
  hydro- 
  

   gen 
  is 
  expelled 
  by 
  heat. 
  

  

  

  Break- 
  

  

  Mean 
  error 
  

  

  

  Mean 
  error 
  

  

  Number 
  of 
  

  

  

  ing- 
  

  

  in 
  breaking- 
  

  

  Elongation. 
  

  

  in 
  

  

  experiments 
  

  

  for 
  each 
  

   result 
  given. 
  

  

  

  strain. 
  

  

  strain. 
  

  

  

  elongation. 
  

  

  

  

  per 
  cent. 
  

  

  per 
  cent. 
  

  

  per 
  cent. 
  

  

  

  Steel 
  before 
  immersion 
  1 
  

  

  123-79 
  

  

  ±2-7 
  

  

  2-16 
  

  

  ±0-27 
  

  

  6 
  

  

  Steel 
  immersed 
  in 
  1 
  

   H 
  2 
  SO 
  4 
  12 
  hours,.. 
  J 
  

  

  100 
  

  

  ±4-9 
  

  

  1-916 
  

  

  ±0-416 
  

  

  6 
  

  

  Steel, 
  H 
  expelled 
  by 
  1 
  

  

  

  

  

  

  

  beating 
  10 
  days 
  to 
  > 
  

  

  12253 
  

  

  ±609 
  

  

  2-66 
  

  

  ±0-55 
  

  

  6 
  

  

  from 
  100° 
  to 
  200°... 
  J 
  

  

  

  

  

  

  

  Steel 
  before 
  immersion 
  1 
  

   inH 
  2 
  S0 
  4 
  J 
  

  

  100-27 
  

  

  ±1-28 
  

  

  3-75 
  

  

  ±0-25 
  

  

  2 
  

  

  Steel 
  after 
  immersion 
  | 
  

   inH 
  2 
  S0 
  4 
  1 
  hour 
  ... 
  / 
  

  

  100 
  

  

  ±2-19 
  

  

  3-75 
  

  

  ±0-25 
  

  

  2 
  

  

  Steel 
  heated 
  24 
  hours 
  1 
  

  

  

  

  

  

  

  to 
  100°-200°, 
  to 
  ex- 
  \ 
  

  

  105-49 
  

  

  ±2-9 
  

  

  2-75 
  

  

  ±0-25 
  

  

  2 
  

  

  pel 
  H 
  J 
  

  

  

  

  

  

  

  The 
  change 
  produced 
  by 
  occluded 
  hydrogen 
  must 
  have 
  an 
  important 
  

   influence 
  on 
  the 
  stability 
  of 
  all 
  iron 
  and 
  steel 
  structures 
  ; 
  for 
  as 
  the 
  

   rusting 
  of 
  iron 
  is 
  mainly 
  attributable 
  to 
  the 
  action 
  of 
  the 
  carbonic 
  acid 
  in 
  

   the 
  air, 
  it 
  is 
  probable 
  that 
  the 
  hydrogen 
  liberated 
  when 
  the 
  acid 
  attacks 
  

   the 
  metal 
  is 
  occluded 
  by 
  the 
  iron 
  or 
  steel, 
  with 
  consequent 
  diminution 
  

   of 
  tensile 
  strength 
  and 
  elasticity. 
  In 
  some 
  cases, 
  where. 
  rust 
  has 
  spread 
  

   very 
  rapidly, 
  the 
  writer 
  has 
  noticed 
  a 
  decided 
  diminution 
  of 
  toughness 
  ; 
  

   but, 
  as 
  a 
  rule, 
  it 
  is 
  difficult 
  to 
  detect 
  any 
  change, 
  as 
  probably 
  the 
  hydrogen 
  

   is 
  present 
  in 
  very 
  small 
  quantity 
  ; 
  also 
  when 
  it 
  has 
  reached 
  a 
  certain 
  per- 
  

   centage 
  its 
  tendency 
  to 
  escape 
  from 
  the 
  metal 
  will 
  balance 
  the 
  force 
  of 
  

   occlusion. 
  

  

  Electric 
  Conductivity. 
  

   Several 
  experiments 
  have 
  been 
  made 
  to 
  ascertain 
  if 
  there 
  is 
  any 
  altera- 
  

   tion 
  in 
  the 
  electric 
  conductivity 
  of 
  iron 
  wire 
  when 
  containing 
  hydrogen. 
  

  

  