﻿ACADEMY 
  OF 
  SCIENCES. 
  201 
  

  

  the 
  pitch 
  pass 
  ofif 
  into 
  the 
  atmosphere. 
  The 
  opening 
  for 
  access 
  into 
  the 
  pit 
  is 
  

   closed 
  by 
  an 
  iron 
  door. 
  

  

  The 
  tar 
  we 
  use 
  is 
  made 
  at 
  the 
  gas 
  works 
  in 
  this 
  city. 
  We 
  use 
  stills 
  of 
  1,200 
  

   to 
  1,800 
  gallons 
  capacity. 
  In 
  the 
  progress 
  of 
  our 
  work 
  the 
  still 
  containing 
  the 
  

   coal 
  tar 
  is 
  run 
  until 
  the 
  thermometer 
  on 
  the 
  top 
  near 
  the 
  man-plate 
  indicates 
  a 
  

   heat 
  420° 
  Fahrenheit, 
  when 
  we 
  cease 
  firing. 
  The 
  still 
  and 
  contents 
  are 
  then 
  

   allowed 
  to 
  stand 
  and 
  cool, 
  until 
  the 
  same 
  thermometer 
  indicates 
  a 
  heat 
  of 
  200° 
  

   to 
  212° 
  Fahrenheit. 
  At 
  this 
  heat 
  the 
  liquid 
  pitch 
  is 
  allowed 
  to 
  run 
  from 
  the 
  

   still 
  into 
  the 
  pitch 
  pit. 
  As 
  it 
  cools 
  it 
  becomes 
  solid. 
  From 
  the 
  time 
  the 
  ther- 
  

   mometer 
  in 
  the 
  still 
  indicates 
  a 
  heat 
  of 
  420° 
  Fahrenheit, 
  until 
  and 
  after 
  the 
  

   time 
  of 
  letting 
  out 
  the 
  pitch, 
  the 
  cocks 
  remain 
  open 
  in 
  the 
  vapor 
  pipe 
  con- 
  

   necting 
  the 
  still 
  with 
  the 
  wood-preserving 
  tank. 
  

  

  Until 
  April, 
  1872, 
  this 
  letting 
  out 
  of 
  the 
  hot 
  pitch 
  was 
  attended 
  with 
  danger 
  

   of 
  fire, 
  because 
  of 
  the 
  tendency 
  of 
  its 
  vapors 
  to 
  spontaneous 
  combustion. 
  If 
  

   running 
  the 
  still 
  daily, 
  such 
  accidents 
  would 
  occur 
  three 
  or 
  four 
  times 
  a 
  year. 
  

   The 
  vapors 
  from 
  the 
  pitch 
  in 
  the 
  pit, 
  as 
  they 
  passed 
  out 
  of 
  the 
  ventilating 
  

   chimney, 
  were 
  yellow, 
  being 
  the 
  vapors 
  of 
  the 
  napthalin 
  oil 
  contained 
  in 
  the 
  

   coal 
  tar. 
  The 
  combustion 
  would 
  take 
  place 
  after 
  the 
  pitch 
  had 
  been 
  running 
  

   freely 
  from 
  the 
  still 
  for 
  some 
  minutes. 
  It 
  was 
  always 
  accompanied 
  by 
  an 
  ex- 
  

   plosion, 
  loud 
  enough 
  to 
  be 
  heard 
  across 
  the 
  street, 
  and 
  powerful 
  enough 
  to 
  force 
  

   away 
  the 
  wooden 
  braces 
  placed 
  against 
  the 
  iron 
  door. 
  Pieces 
  of 
  timbering 
  in 
  

   the 
  pitch 
  pit 
  would 
  take 
  fire, 
  and 
  burn 
  until 
  extinguished. 
  

  

  From 
  the 
  time 
  the 
  fire 
  is 
  extinguished 
  under 
  the 
  stills, 
  to 
  the 
  time 
  of 
  letting 
  

   out 
  the 
  pitch, 
  there 
  is 
  always 
  an 
  interval 
  of 
  fourteen 
  hours. 
  The 
  furnace 
  of 
  

   the 
  still 
  is 
  always 
  closed 
  with 
  an 
  iron 
  door, 
  and 
  clayed 
  up. 
  There 
  is 
  a 
  strong 
  

   draft 
  up 
  the 
  chimney 
  of 
  the 
  still. 
  

  

  The 
  top 
  of 
  the 
  ventilating 
  chimney 
  of 
  the 
  pitch 
  pit 
  is 
  as 
  high 
  as 
  that 
  of 
  the 
  

   fire 
  chimney 
  to 
  the 
  still, 
  and 
  there 
  is 
  always 
  a 
  strong 
  draft 
  up 
  this 
  chimney 
  

   through 
  the 
  cracks 
  between 
  the 
  iron 
  door 
  and 
  the 
  brick 
  work 
  of 
  the 
  pitch 
  pit. 
  

   A 
  person 
  standing 
  at 
  the 
  iron 
  door 
  would 
  not 
  smell 
  any 
  of 
  the 
  vapor 
  of 
  the 
  

   pitch. 
  The 
  distance 
  from 
  the 
  outlet 
  of 
  the 
  pitch 
  pipe 
  of 
  the 
  still 
  to 
  the 
  fur- 
  

   nace 
  door 
  of 
  the 
  still, 
  is 
  not 
  less 
  than 
  twenty-two 
  feet. 
  At 
  the 
  time 
  of 
  our 
  last 
  

   explosion, 
  the 
  furnace 
  of 
  the 
  still 
  had 
  been 
  carefully 
  examined 
  before 
  the 
  pitch 
  

   was 
  let 
  out. 
  No 
  remains 
  of 
  fire 
  were 
  found 
  there, 
  nor 
  was 
  there 
  any 
  other 
  fire 
  

   in 
  the 
  building. 
  The 
  hour 
  was 
  10 
  a. 
  m., 
  Sunday 
  morning 
  — 
  the 
  works 
  not 
  in 
  

   operation. 
  

  

  This 
  property 
  of 
  heated 
  hydro-carbon 
  vapors 
  to 
  spontaneously 
  ignite 
  after 
  

   absorbing 
  a 
  certain 
  quantity 
  of 
  atmospheric 
  air, 
  is 
  not 
  laid 
  down 
  in 
  any 
  work 
  to 
  

   which 
  I 
  have 
  had 
  access. 
  A 
  number 
  of 
  scientific 
  gentlemen 
  to 
  whom 
  I 
  have 
  

   mentioned 
  the 
  above 
  facts, 
  were 
  as 
  ignorant 
  as 
  myself 
  of 
  their 
  having 
  that 
  

   property. 
  The 
  remedy 
  I 
  have 
  devised, 
  after 
  experience, 
  is 
  simple 
  and 
  com- 
  

   plete. 
  It 
  is 
  the 
  introduction 
  of 
  a 
  small 
  quantity 
  of 
  water 
  into 
  the 
  pitch 
  pit 
  

   while 
  the 
  pitch 
  is 
  running 
  from 
  the 
  still. 
  The 
  hot 
  pitch 
  vaporizes 
  the 
  water, 
  

   the 
  yellow 
  vapor 
  from 
  the 
  chimney 
  is 
  turned 
  to 
  white 
  vapor, 
  and 
  the 
  desired 
  

   safety 
  is 
  obtained. 
  Too 
  much 
  water 
  must 
  not 
  be 
  put 
  into 
  the 
  pit 
  at 
  one 
  time, 
  

   or 
  the 
  pitch 
  will 
  boil 
  over; 
  not 
  a 
  dangerous 
  but 
  a 
  troublesome 
  result. 
  

  

  