'^Sptember^Yj'm}    Methyl  Alcokol  and  Ethyl  Alcohol.  633 
In  from  one  to  two  hours  after  the  wood  is  placed  in  the  ovens, 
water  distillation  takes  place,  and  this  distillate  has  an  acid  content 
of  about  2  per  cent.  The  next  to  issue  from  the  wood  is  called 
"green  gas,"  and  this  comes  freely  for  about  five  to  six  hours.  At 
about  300°  Fahrenheit  the  endothermic  reaction  begins,  but  it 
is  more  decided  at  the  maximum  temperature,  which  is  about  680° 
Fahrenheit,  and  at  this  latter  point  great  care  must  be  exercised 
that  the  liquor  is  not  "burned;"  that  is,  the  temperature  must  not 
be  permitted  to  rise  higher,  otherwise  there  will  be  an  undue  forma- 
tion of  condensation  products.  After  the  wood  has  been  in  the 
heating  process  for  about  six  hours,  the  temperature  attains  an 
average  of  about  450  °  Fahrenheit.  About  the  sixth  hour  pyroligneous 
acid  begins  to  flow  from  the  condensers  and  continues  up  to  about 
the  eighteenth  hour.  The  color  of  this  acid  determines  whether 
too  much  heat  is  being  maintained  and  whether  the  wood  fibers  have 
been  broken  down  sufficiently.  At  the  latter  end  of  the  heating 
process  the  distillate  forms  a  considerable  portion  of  tar. 
Charcoal  Coolers. — The  cars,  now  containing  the  charcoal,  are  drawn 
out  of  the  ovens  and  into  the  first  coolers,  where  they  remain  for  a 
period  of  about  24  hours,  or  the  length  of  time  required  to  carbonize 
the  wood  in  the  ovens.  The  cars  are  then  moved  into  the  second 
coolers,  whore  they  remain  an  equal  length  of  time.  These  coolers 
are  similar  in  shape  to  the  ovens,  are  made  of  steel  and  are  equipped 
with  two  doors,  one  at  each  end,  so  that  the  cars  may  be  run  straight 
through.  The  coolers  are  placed  in  line  with  each  other  and  with 
the  ovens,  and  are  at  the  discharge  end  of  the  ovens.  Coolers  are 
not  so  heavy  in  construction  as  ovens,  because  their  purpose  is  to 
radiate  the  heat  from  the  charcoal  and  dispose  of  it  in  the  air.  A 
small  vent  is  provided  in  each  cooler  for  the  vapors  to  pass  out,  yet 
this  vent  is  not  large  enough  to  allow  much  oxygen  to  enter.  The 
function  of  the  coolers  is  to  prepare  the  charcoal  so  that  it  may  be 
exposed  to  the  air.  If  the  hot  charcoal  should  be  taken  out  of  the 
ovens  and  left  standing  in  the  air,  it  would  immediately  ignite  from 
spontaneous  combustion.  Therefore,  it  is  drawn  into  the  coolers, 
where  it  can  stand  without  being  exposed  to  the  air,  and  gradually 
its  heat  passes  off  through  the  steel  of  the  cooler. 
Charcoal  Sheds. — After  leaving  the  second  coolers,  the  cars  of 
charcoal  must  stand  in  the  open  air  under  shed  roofs  for  a  period 
of  48  hours.  This  is  a  requirement  of  the  government  to  insure 
that  there  is  no  danger  of  spontaneous  combustion.    After  that 
