﻿176 
  

  

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

  

  rature 
  of 
  the 
  pieces 
  tested 
  will 
  alter 
  the 
  result 
  considerably. 
  In 
  order 
  

   also 
  to 
  obviate, 
  as 
  far 
  as 
  possible, 
  errors 
  arising 
  from 
  the 
  irregularity 
  and 
  

   absence 
  of 
  perfect 
  homogeneousness 
  of 
  structure, 
  even 
  in 
  the 
  most 
  care- 
  

   fully 
  prepared 
  iron 
  and 
  steel, 
  the 
  number 
  of 
  tests 
  has 
  been 
  multiplied 
  as 
  

   much 
  as 
  possible 
  and 
  the 
  mean 
  only 
  given.] 
  

  

  The 
  mode 
  of 
  experiment 
  was 
  as 
  follows 
  : 
  — 
  After 
  immersion 
  in 
  acid, 
  the 
  

   pieces 
  were 
  wiped 
  and 
  then 
  tested, 
  this 
  giving 
  the 
  tensile 
  strain 
  and 
  

   elasticity 
  when 
  containing 
  occluded 
  hydrogen 
  ; 
  subsequently 
  they 
  were 
  

   heated 
  on 
  hot 
  plates 
  or 
  in 
  ovens, 
  as 
  the 
  most 
  ready 
  method 
  of 
  expel- 
  

   ling 
  the 
  hydrogen, 
  to 
  a 
  temperature 
  considerably 
  below 
  that 
  required 
  

   to 
  anneal 
  them 
  ; 
  and 
  when 
  cold, 
  the 
  breaking-strain 
  &c. 
  of 
  the 
  iron, 
  

   which 
  had 
  now 
  recovered 
  its 
  natural 
  state, 
  was 
  again 
  ascertained 
  by 
  

   testing. 
  

  

  It 
  might 
  be 
  thought 
  that 
  tests 
  of 
  iron 
  in 
  its 
  natural 
  state 
  could 
  be 
  best 
  

   made 
  by 
  experimenting 
  on 
  it 
  before 
  immersion 
  in 
  acid. 
  Besults 
  so 
  ob- 
  

   tained 
  cannot, 
  however, 
  be 
  fairly 
  compared 
  with 
  tests 
  of 
  the 
  same 
  piece 
  

   made 
  after 
  immersion 
  in 
  acid, 
  as 
  the 
  action 
  of 
  the 
  acid 
  somewhat 
  reduces 
  

   the 
  diameter 
  of 
  the 
  iron. 
  

  

  The 
  following 
  results 
  are 
  the 
  means 
  of 
  30 
  tests 
  made 
  on 
  annealed 
  and 
  

   bright 
  iron 
  wire 
  respectively 
  — 
  first, 
  after 
  being 
  one 
  hour 
  in 
  hydrochloric 
  

   acid, 
  and, 
  secondly, 
  after 
  being 
  heated 
  12 
  to 
  48 
  hours 
  to 
  drive 
  off 
  the 
  

   hydrogen. 
  

  

  

  Break- 
  

   ing- 
  

   strain. 
  

  

  Mean 
  error 
  

   in 
  breaking- 
  

   strain. 
  

  

  Elongation. 
  

  

  Mean 
  error 
  

   in 
  

  

  elongation. 
  

  

  Number 
  of 
  

   experiments 
  

   of 
  which 
  each 
  

   result 
  is 
  mean. 
  

  

  Annealed 
  iron 
  wire 
  \ 
  

   when 
  containing 
  H. 
  . 
  . 
  J 
  

   Annealed 
  iron 
  wire, 
  \ 
  

  

  Bright 
  iron 
  wire 
  when 
  1 
  

  

  Bright 
  iron 
  wire, 
  H 
  ] 
  

  

  100 
  

  

  100-487 
  

   100 
  

  

  100274 
  

  

  per 
  cent. 
  

   ±1-16 
  

  

  ±1-37 
  

  

  ±2-57 
  

  

  ± 
  -47 
  

  

  per 
  cent. 
  

  

  20- 
  5 
  

  

  21- 
  3 
  

   2 
  

  

  2-83 
  

  

  per 
  cent. 
  

   ±1-12 
  

  

  ±1-71 
  

  

  ±0-66 
  

  

  ±0-64 
  

  

  12 
  

   12 
  

  

  3 
  

   3 
  

  

  Thus 
  the 
  tensile 
  strain 
  of 
  annealed 
  iron 
  wire 
  appears 
  to 
  be 
  affected 
  to 
  

   twice 
  the 
  extent 
  that 
  bright 
  wire 
  is 
  by 
  immersion 
  in 
  acid 
  for 
  same 
  length 
  

   of 
  time. 
  The 
  reverse 
  is 
  the 
  effect 
  on 
  the 
  elongation. 
  

  

  Longer 
  immersion 
  in 
  acid 
  causes 
  the 
  iron 
  to 
  take 
  up 
  more 
  hydrogen, 
  

   and 
  makes 
  the 
  change 
  much 
  greater, 
  as 
  the 
  following 
  experiments 
  show. 
  

   Denoting 
  by 
  100 
  the 
  breaking-strain 
  of 
  bright 
  charcoal-iron 
  wire 
  after 
  

   12 
  hours' 
  immersion 
  in 
  very 
  dilute 
  sulphuric 
  or 
  hydrochloric 
  acid, 
  and 
  

   subsequent 
  5 
  hours' 
  exposure 
  in 
  air 
  at 
  a 
  temperature 
  of 
  12°, 
  during 
  which 
  

   time 
  some 
  of 
  the 
  occluded 
  hydrogen 
  must 
  have 
  escaped, 
  then 
  the 
  break- 
  

  

  