PREPARATION  OF  ARTIFICIAL  COLORINa  MATTERS,  ETC.  135 
if  need  be,  until  a  heavy  oily  matter  (aniline)  deposits,  which 
must  be  separated  from  the  liquor  and  re-distilled  by  itself. 
The  aniline  is  thus  obtained  nearly  pure. 
Instead  of  using  an  alcoholic  solution  of  nitro-benzole,  and 
treating  it  successively  with  ammonia  and  sulphuretted  hydrogen 
the  alcoholic  solution  of  sulphide  of  ammonium  maybe  prepared 
beforehand,  and  the  nitro-benzole  poured  into  it.  A  part  is 
dissolved  immediately,  and  the  remainder  by  dryness  in  the 
course  of  the  operation.  It  is  sometimes  advantageous,  instead 
of  waiting  until  the  aniline  separates,  to  add  hydrochloric  acid 
to  the  liquor  in  the  retort  until  it  is  slightly  acid,  and  then  to 
distil  almost  to  dryness,  by  which  means  chloride  of  aniline  is 
obtained.  This  is  decomposed  by  an  excess  of  caustic  soda, 
and  the  aniline  set  at  liberty  is  distilled  oif. 
To  avoid  any  danger  from  the  bumping  a  tinned  copper  still 
must  be  used,  which  should  be  heated  by  steam  under  a  light 
pressure.  At  first  the  temperature  should  not  exceed  90^0. 
but  after  some  time  it  may  be  raised  to  100^  or  110*^. 
The  ammoniacal  alcohol  condensed  in  the  worm  may  be  re- 
saturated  with  the  sulphuretted  hydrogen,  and  used  over  again 
with  a  new  quantity  of  the  nitro-benzole. 
2.  Reduction  of  the  nitro-henzole  hy  nascent  hydrogen.  In 
preparing  aniline  by  this  process  the  nitro-benzole  and  zinc  are 
placed  in  a  vessel  and  dilute  sulphuric  or  hydrochloric  acid  is 
added  so  as  to  produce  the  disengagement  of  a  small  quantity 
of  hydrogen.  By  degrees  the  nitro-benzole  disappears  and 
aniline  is  formed,  which  remains  in  solution  in  hydrochloric  or 
sulphuric  acid.  To  isolate  it,  an  excess  of  caustic  soda  is 
added  and  the  mixture  is  distilled,  on  which  the  aniline  passes 
over  with  the  vapor  of  water. 
Bechamp  first  recommended  the  employment  of  acetic  acid 
and  iron  filings.  He  places  in  a  retort  one  part  of  nitro-benzole, 
one  and  a  half  parts  of  iron  filings,  and  one  part  of  concen- 
trated acetic  acid.  The  reaction  takes  place  without  the  appli- 
cation of  external  heat,  the  mixture  becoming  hot  by  itself, 
and  the  vapor  being  condensed  in  a  receiver,  which  must  be 
kept  well  cooled.  The  condensed  products  consist  of  aniline, 
acetate  of  aniline,  and  some  unchanged  nitro-benzole.  These 
are  allowed  to  cool  and  are  then  returned  to  the  retort  and 
