COLOKINa  MATTERS  FROM  COAL  TAR. 
45 
the  acid  principles  like  phenol,  creosote  and  rosolic  acid.  Vohl* 
has  already  proposed  to  extract  phenol  and  creosote  from  the 
alkaline  solution  by  supersaturating  it  with  the  acid  solution, 
decanting  the  oily  layer  which  separates,  and  rectifying  it  over 
a  naked  fire.  A  more  rational  process,  according  to  the  author, 
would  be  the  following  : — Collect  all  the  acid  and  alkaline 
liquors,  and  determine  how  much  of  the  acid  liquor  would  be 
sufficient  to  saturate  a  given  volume  of  the  alkaline.  This  being 
known,  mix  the  alkaline  solution  with  twice  the  quantity  of  acid 
liquor  necessary  to  saturate  it.  If  the  two  be  mixed  rapidly, 
sufficient  heat  will  be  developed  to  raise  the  mixture  almost  to 
the  boiling-point,  and  a  concentrated  solution  of  bisulphate  of 
soda  will  be  formed  which  retains  in  solution  the  bisulphates  of 
aniline  and  toluidine,  while  the  phenol  and  creosote  easily  sepa- 
rate in  form  of  a  brown  oil.  This  oil  may  be  separated  while 
the  mixture  is  still  warm,  and  rectified.  A  light  neutral  oil 
first  passes,  and  afterwards  the  phenol  and  creosote  distil  almost 
pure. 
The  solution  containing  the  acid  sulphates  of  soda  and  the 
organic  bases,  yields  on  cooling,  crystals  of  bisulphate  of  soda, 
which  may  be  collected  on  a  filter.  The  acid  liquor  not  used  to 
saturate  the  soda  solution  may  then  be  added  from  the  mother- 
liquor  from  the  crystals,  and  the  whole  heated  to  60^  or  80°  G. 
Chalk  or  milk  of  lime  is  then  added  to  partial  saturation,  the 
sulphate  of  lime  is  allowed  to  deposit,  and  the  liquor  is  concen- 
trated. Finally  the  concentrated  acid  sulphates  are  introduced 
into  an  iron  still,  and  an  excess  of  quick  lime  is  added.  Sul- 
phate of  lime  and  some  sulphate  of  soda  are  formed,  the  organic 
bases  are  set  at  liberty,  and  on  heating  they  pass  over  and  con- 
dense with  some  water.  If  the  quantity  of  water  be  sufficient 
to  hold  the  bases  in  solution,  the  distilled  aqueous  solution  must 
be  saturated  with  hydrochloric  acid  and  evaporated,  first  over  a 
naked  fire  and  then  over  a  water  bath,  almost  to  dryness.  The 
residue  placed  in  a  retort  is  mixed  with  an  excess  of  quick  lime 
and  distilled,  when  an  oily  liquid  is  obtained  which  consists 
principally  of  aniline,  toluidine  and  quinoline,  sufficiently  pure 
for  the  preparation  of  the  coloring  matters.     We  shall  now 
'^Journal  fur  Prakt.  Chem.  Bd.  Ixv.  s.  296. 
