MANUFACTURE  AND  PROPERTIES  OF  ANILINE  COLORS.  543 
which  furnishes  oils  containing  benzol  and  toluol  is  coal  tar,  which 
is  produced  in  making  coal  gas. 
In  the  distillation  of  these  tars  the  first  product  is  an  oil  lighter 
than  water,  commercially  called  "light  oil,"  and  containing — 
1st.  Neutral  liquid  hydrocarbides,  benzol,  toluol,  cumol,  &c, 
and  a  little  solid  hydrocarbide  naphthaline. 
2d.  Phenols,  bodies  holding  at  the  same  time  both  alcohols  and 
acids,  phenic  and  cresylic  acids. 
3d.  Very  small  quantities  of  alkaloids,  aniline,  picoline,  quino- 
line. 
To  extract  from  these  oils  the  principles  used  in  making  aniline 
colors,  it  is  first  necessary  to  separate  the  phenols  ;  this  result  is 
obtained  by  agitating  the  oils  with  small  quantities  of  caustic 
soda  at  40°  Baume,  or  even  more  concentrated.  If  we  separate 
the  watery  layer  containing  the  phenols  in  combination  with  soda, 
this  operation  twice  repeated  completely  frees  the  oils  from 
phenols. 
Sometimes,  before  this  operation,  the  alkaloids  are  removed 
from  the  oils  by  being  rapidly  agitated  with  a  small  proportion 
of  sulphuric  acid. 
These  washings  should  be  terminated  before  new  rectifications 
are  commenced,  for  the  naphthaline  separates  much  more  readily 
by  a  redistillation  when  neutral  oils  are  operated  upon. 
It  then  merely  remains  to  separate  the  benzol  and  toluol  from 
their  homologues,  the  other  liquid  hydrocarbides. 
We  generally  operate  by  fractional  distillation — that  is  to  say, 
by  collecting  all  that  is  distilled  between  80°  and  120°,  and  this 
portion  is  sold  under  the  name  of  benzol,  and  serves  in  the 
making  of  aniline. 
Benzol  is  usually  sold  with  a  standard  of  distillation  fixed  be- 
forehand, either  at  90  per  cent,  or  60  per  cent. — that  is  to  say, 
90  or  60  per  cent,  distilling  below  100°  C. 
During  the  last  few  years  benzol  at  90  per  cent,  has  been  most 
in  demand,  but  it  has  lately  been  found  that  aniline  made  with 
benzol  at  60°  gives  the  greatest  yield  of  coloring  matters. 
These  benzols  are  composed  almost  exclusively  of  two  bodies — 
benzine  and  toluol. 
Benzine,  C12H6,  distils  at  80°  ;  treated  by  nitric  acid  it  gives 
