﻿DEC. 
  4, 
  1922 
  PROCEEDINGS 
  : 
  PHILOSOPHICAL 
  SOCIETY 
  461 
  

  

  By 
  invitation 
  Mr. 
  Raymond 
  Davis 
  presented 
  a 
  paper 
  on 
  "deciphering 
  of 
  

   charred 
  paper 
  records" 
  which 
  was 
  illustrated 
  by 
  lantern 
  slides. 
  After 
  the 
  

   presentation 
  of 
  the 
  paper 
  the 
  author 
  answered 
  numerous 
  questions 
  by 
  Messrs. 
  

   White, 
  Crittenden, 
  Heyl, 
  and 
  others. 
  

  

  Author's 
  Abstract: 
  The 
  bureau 
  of 
  Standards 
  was 
  recently 
  called 
  upon 
  to 
  

   find 
  a 
  method 
  for 
  deciphering 
  the 
  written 
  and 
  printed 
  matter 
  contained 
  on 
  

   charred 
  paper. 
  

  

  The 
  charred 
  papers 
  submitted 
  apparently 
  had 
  been 
  subjected 
  to 
  heat 
  in 
  a 
  

   closed 
  vessel, 
  such 
  as 
  a 
  safe, 
  — 
  the 
  paper 
  having 
  been 
  converted 
  into 
  black 
  

   sheets 
  of 
  carbon 
  and 
  not 
  to 
  ashes 
  as 
  would 
  have 
  been 
  the 
  case 
  had 
  they 
  been 
  

   burned 
  in 
  an 
  open 
  container. 
  

  

  With 
  casual 
  observation 
  no 
  traces 
  of 
  writing 
  are 
  visible, 
  but 
  under 
  certain 
  

   critical 
  conditions 
  of 
  lighting 
  very 
  faint 
  traces 
  of 
  markings 
  can 
  be 
  seen. 
  These 
  

   traces 
  are 
  not 
  sufficiently 
  clear 
  to 
  permit 
  deciphering. 
  

  

  In 
  some 
  preliminary 
  trials 
  made 
  on 
  paper 
  charred 
  for 
  the 
  purpose, 
  con- 
  

   version 
  of 
  the 
  iron 
  salts 
  contained 
  in 
  the 
  ink 
  into 
  colored 
  salts 
  was 
  tried. 
  

   These 
  were 
  unsuccessful. 
  

  

  It 
  is 
  known 
  that 
  the 
  photographic 
  plate, 
  besides 
  being 
  sensitive 
  to 
  light, 
  

   is 
  also 
  sensitive 
  to 
  certain 
  gases 
  and 
  vapors. 
  Some 
  of 
  these 
  have 
  the 
  property 
  

   of 
  fogging 
  or 
  rendering 
  developable 
  such 
  portions 
  of 
  the 
  plate 
  as 
  are 
  exposed 
  

   to 
  their 
  actions. 
  Certain 
  other 
  gases 
  or 
  vapors 
  have 
  the 
  contrary 
  property, 
  

   that 
  is, 
  they 
  partially 
  or 
  completely 
  desensitize 
  the 
  plate. 
  

  

  For 
  the 
  first 
  trial 
  a 
  sheet 
  of 
  the 
  carbonized 
  paper 
  was 
  placed 
  between 
  the 
  

   two 
  "fast" 
  photographic 
  plates 
  and 
  kept 
  in 
  the 
  dark 
  for 
  two 
  weeks. 
  On 
  

   development 
  in 
  the 
  usual 
  manner 
  a 
  very 
  perfect 
  copy 
  of 
  both 
  the 
  writing 
  and 
  

   the 
  printing 
  was 
  obtained. 
  It 
  appears 
  that 
  the 
  carbonized 
  paper 
  contains 
  

   gases 
  that 
  fog 
  the 
  photographic 
  plate. 
  Where 
  the 
  ink 
  is 
  present, 
  little 
  or 
  no 
  

   effect 
  takes 
  place. 
  Apparently 
  the 
  ink 
  acts 
  as 
  a 
  screen, 
  hindering 
  the 
  escape 
  

   of 
  the 
  gas. 
  

  

  It 
  is 
  interesting 
  to 
  note 
  that 
  the 
  writing 
  on 
  both 
  sides 
  of 
  the 
  charred 
  paper 
  

   appears, 
  that 
  from 
  the 
  back 
  being 
  fainter 
  than 
  that 
  from 
  the 
  face. 
  Appar- 
  

   ently 
  the 
  ink 
  penetrates 
  the 
  paper 
  sufficiently 
  so 
  that 
  its 
  residue 
  reduces 
  the 
  

   amount 
  of 
  gas 
  escaping 
  from 
  beneath. 
  

  

  No 
  attempt 
  was 
  made 
  to 
  determine 
  the 
  nature 
  of 
  the 
  active 
  material 
  con- 
  

   tained 
  in 
  the 
  charred 
  paper. 
  It 
  is 
  quite 
  likely 
  that 
  it 
  contains 
  products 
  

   similar 
  to 
  those 
  obtained 
  by 
  the 
  destructive 
  distillation 
  of 
  wood. 
  

  

  Further 
  tests 
  showed 
  that 
  photographic 
  plates 
  of 
  sensitiveness 
  usually 
  termed 
  

   fast 
  or 
  medium 
  are 
  best 
  adapted 
  for 
  this 
  purpose. 
  However, 
  the 
  sensitiveness 
  

   to 
  light 
  is 
  no 
  definite 
  indication 
  of 
  the 
  sensitiveness 
  to 
  the 
  charred 
  paper. 
  

   For 
  example 
  Seed 
  30 
  and 
  Seed 
  26 
  X 
  are 
  of 
  equal 
  sensitiveness 
  to 
  the 
  charred 
  

   paper, 
  the 
  former 
  is 
  considerably 
  faster 
  to 
  light 
  than 
  the 
  latter. 
  Very 
  good 
  

   copies 
  can 
  be 
  obtained 
  with 
  either 
  of 
  these 
  plates 
  after 
  a 
  weeks 
  time 
  in 
  con- 
  

   tact 
  with 
  charred 
  paper. 
  Very 
  slow 
  plates 
  such 
  as 
  ''Process'' 
  are 
  not 
  suitable 
  

   as 
  exposure 
  of 
  32 
  days 
  shows 
  only 
  faint 
  action. 
  Photographic 
  printing 
  and 
  

   enlarging 
  papers 
  are 
  very 
  insensitive 
  to 
  the 
  charred 
  paper. 
  

  

  Results 
  obtained 
  by 
  the 
  use 
  of 
  photographic 
  films 
  were 
  very 
  surprising, 
  

   as 
  shown 
  by 
  the 
  two 
  types 
  of 
  emulsions 
  selected 
  for 
  the 
  test, 
  namely 
  : 
  East- 
  

   man 
  "Portrait 
  Film" 
  and 
  Eastman 
  "Super 
  Speed 
  Portrait 
  Film." 
  

  

  The 
  Portrait 
  Film 
  showed 
  no 
  effect 
  in 
  32 
  days. 
  The 
  Super 
  Speed 
  Portrait 
  

   showed 
  very 
  slight 
  but 
  interesting 
  effect 
  with 
  a 
  16 
  day 
  exposure 
  and 
  only 
  a 
  

   little 
  better 
  at 
  32 
  days. 
  This 
  was 
  just 
  the 
  reverse 
  of 
  that 
  with 
  the 
  plates, 
  

  

  