132    PEEPARATION  OF  ARTIFICIAL  COLORINa  MATTERS,  ETC. 
39  to  47  of  this  volume,  to  which  we  refer  the  reader,  and 
also  to  the  paper  by  Mr.  Mansfield,  in  the  Quarterly  Journal 
of  the  Chemical  Society^  i.  p.  244. 
Crude  naphtha,  or  the  benzole  of  commerce,  is  generally  a  yel- 
low or  brown  liquid,  having  a  density  varying  from  -09  to  -95 ; 
it  usually  contains,  besides  benzole,  some  of  the  homologues  of 
benzole,  toluol,  cumol,  and  cymol.  It  is  impossible  to  separate 
these  bodies  by  an  ordinary  process  of  rectification  ;  for  although 
the  boiling  point  of  toluol  is  108^  or  109^,  and  that  of  cumol 
143°  or  145*^,  their  vapors  are,  so  to  say,  dissolved  in  the  vapor 
of  benzole,  and  are  carried  over  and  condense  together.  Their 
presence,  however^,  need  not  interfere  with  the  preparation  of 
nitro-benzole  and  aniline. 
The  benzole  found  in  commerce  is  at  times  very  impure ;  some, 
indeed,  has  been  met  with  containing  but  a  trace  of  real  benzole. 
Such  an  article  is  generally  the  result  of  the  distillation  of  bitu- 
minous schists  or  asphaltum  ;  and,  besides  hydrocarbons  belong- 
ing to  another  series  than  that  of  benzole,  it  generally  contains 
a  small  amount  of  oxygenated  products,  and  consequently  can- 
not be  advantageously  used  in  the  preparation  of  aniline.  It  is 
therefore  important  to  be  able  readily  to  detect  benzole  in  a 
mixture  of  other  oils.  For  this  purpose  we  may  avail  ourselves 
of  the  facility  with  which  true  benzole  is  converted  into  nitro- 
benzole  and  then  into  aniline  by  the  action  of  nascent  hydro- 
gen. 
The  following  is  Hoffmann's  method  : — A  drop  of  benzole  is 
heated  in  a  small  test  tube,  with  fuming  nitric  acid,  to  convert 
it  into  nitro-benzole.  A  good  deal  of  water  is  then  added,  to 
precipitate  the  nitro-benzole  in  small  drops,  which  must  be  taken 
up  by  ether.  The  etherial  solution  is  then  poured  into  another 
small  tube,  and  equal  volumes  of  alcohol  and  dilute  hydrochloric 
acid  are  added;  a  few  fragments  of  granulated  zinc  are  then 
dropped  in.  In  about  five  minutes  sufficient  hydrogen  will  have 
been  disengaged  to  produce  aniline,  which  will  be  found  com- 
bined with  the  acid.  The  liquid  is  supersaturated  with  an  alkali 
and  shaken  with  ether,  which  dissolves  the  aniline  set  free.  A 
drop  of  this  etherial  solution  allowed  to  evaporate  on  a  watch 
glass,  and  mixed  after  the  evaporation  of  the  ether  with  a  drop 
of  a  solution  of  hypochlorite  of  lime,  will  show  the  violet  tints 
