634  Methyl  Alcohol  and  Ethyl  Alcohol.    { ^gp/ember^^gz": 
time,  it  may  be  loaded  in  freight  cars  for  shipment,  but  it  must  be 
left  standing  in  these  cars  for  at  least  twelve  hours  before  shipping. 
Before  such  precautions  were  taken,  many  fires  took  place  and  many 
railroad  cars  were  destroyed. 
"Raw"  Liquor. — The  vapor  which  issues  from  the  vapor  outlet 
nozzles  of  the  ovens  and  which  passes  off  from  the  wood  during  the 
process  of  carbonization  enters  tubular  condensers  and  is  converted 
into  a  liquid  called  pyroligenous  acid,  or  "raw  liquor."  This  does 
not  come  from  the  condensers  during  the  entire  period  of  carboniza- 
tion, but  only  from  about  the  sixth  to  eighth  hour  on  to  the  end 
of  the  run.  It  is  a  yellowish  green,  ill-smelling  liquor  during  most 
of  the  run,  and  towards  the  latter  part  its  color  changes  and  be- 
comes quite  dark.  This  acid  is  collected  from  the  condensers  by 
means  of  a  copper  branch  into  a  main  copper  pipe  line  which  passes 
through  the  middle  of  the  retort  setting  and  terminates  in  a  wooden 
sump  set  in  the  ground.  These  sumps  are  simply  for  the  purpose 
of  providing  a  reservoir  into  which  the  raw  liquor  may  be  run. 
Gas. — The  oven  vapor  is  not  all  condensable,  but  one  of  the 
products  of  distillation  is  wood  gas,  termed  by  the  manufacturers 
"non-condensable"  gas.  This  is  trapped  off  at  the  outlets  of  the 
condensers  and  used  for  fuel.  It  has  been  found  that  about  ii,ooo 
to  14,000  cubic  feet  of  this  non-condensable  gas  are  obtained  from 
each  cord  of  wood  distilled,  and  has  a  considerable  value.  It  is 
carried  from  the  condensers  in  copper  pipes  into  a  main  gas  line, 
and  there  are  also  copper  distributing  lines  to  convey  it  to  the  oven 
furnaces  and  to  the  boilers. 
The  raw  liquor  is  pumped  from  the  sumps  to  a  series  of  wooden 
settling  tanks.  The  pump  used  for  this  purpose  must  be  entirely 
of  brass,  or  brass  lined.  The  brass  construction  is  necessary  where 
the  liquor  comes  in  contact  with  the  metal,  as  the  liquor  is  acid  and 
therefore  the  metal  must  be  acid-resisting. 
Wooden  Settling  Tanks. — The  purpose  of  these  tanks  is  to  allow 
the  tar  in  suspension  in  the  raw  liquor  to  precipitate.  The  tanks 
are  so  connected  together  that  the  liquor  passes  from  one  to  the 
other  serially,  and  the  pipe  connections  between  them  are  at  vary- 
ing heights,  the  connection  to  the  first  tank  being  high  up,  and  the 
other  connections  being  made  gradually  lower  down,  until  the  con- 
nection in  the  last  settler  is  only  about  one-third  of  the  distance 
above  the  bottom.    The  first  settler  accumulates  the  most  tar 
