428 
Alizarin. 
J  Am.  Jour.  Pharm  , 
\     Sept  .,  1876. 
the  still  is  raised  to  2io°C,  and  thereby  the  important  anthracen  is  obtained,  a  body 
which,  in  a  state  of  purity,  is  a  hydrocarbon,  has  the  chemical  formula  C14H10,  and 
furnishes  the  raw  material  for  the  preparation  of  alizarin.  According  to  the  quality  of 
the  coal  used  for  the  manufacture  of  illuminating  gas,  the  tar  contains  from  1  to  2  per 
cent,  of  pure  anthracene. 
The  important  invention  of  making  it  serviceable  for  the  production  of  alizarin, 
resulted  by  accidental  circumstances. 
In  1868,  Messrs.  Graebe  &  Liebermann,  of  Germany,  experimented  with  alizarin 
(CjjHgOJ,  contained  in,  and  centuries  since  extracted  from  madder,  with  the  view 
of  finding  improvements  for  its  use  in  printing  on  cotton,  when  they  obtained  a 
compound  having  the  chemical  composition  represented  by  C14H10.  Finding  this 
to  be  also  the  corrected  formula  of  anthracene  from  coal-tar,  they  promptly  went 
farther  on  with  the  right  inspiration — that  if  alizarin  from  madder  could  be  traced 
back  to  anthracene,  it  wanted  only  a  practical  way  for  introducing  four  atoms  of 
oxygen  into,  and  withdrawing  two  atoms  of  hydrogen  from,  the  coal-tar  anthra- 
cene, to  make  it  alizarin. 
This  correct  idea  was  their  invention.  But  as  is  often  the  case  with  such  im- 
portant revolutions,  brought  about  by  chemical  genius,  they  had  only  broken  the 
ice  without  opening  the  river  for  navigation.  The  processes  they  had  adopted 
turned  out  to  be  impractical  for  cheap  production  in  larger  quantities,  and  only  after 
experimenting  for  several  years  more  practical  processes  have  been  found  by  us  and 
others,  which  opened  the  way  for  the  immense  production  it  has  reached  already, 
and  affect  very  materially  the  cultivation  of  madder. 
The  crude  distillate  is  brought  into  the  market  in  a  concentration  of  generally 
25  to  30  per  cent,  of  pure  anthracene.  It  is  a  doughy,  pasty  mass,  which,  besides 
anthracene,  contains  also  lubricating  oils  of  high  boiling  points.  In  order  to  pre- 
pare this  crude  anthracene  for  use  at  the  factory,  or,  to  make  it  more  plain,  to  free 
it  from  a  part  of  the  homologous  admixtures  which  hinder  the  subsequent  process  of 
oxidation,  it  is,  after  previous  heating,  freed  first  from  part  of  its  oils  by  hydraulic 
pressure,  and  then  shows  40  to  50  per  cent,  of  pure  anthracene. 
Through  further  treatment,  either  by  means  of  solvents — for  instance,  naphtha, 
petroleum  ether,  etc. —  or  by  sublimation,  it  is  more  purified,  so  as  to  contain  from 
68  to  90  per  cent.  C14H10.  For  special  purposes  it  is  prepared  in  a  more  perfect 
state  by  crystallization  with  95  per  cent.  CUH10,  or  even  chemically  pure,  which,  by 
sublimation,  gives  beautiful  crystals. 
In  order  to  produce  alizarin  as  the  ultimate  product  from  anthracene,  different 
methods  may  be  adopted,  either  by  forming  bichlor- anthracene  C14H8C12,  or, 
bibrom-a?ithracene  C]4H8Br2,  or  by  oxidizing  anthracene  with  the  assistance  of  bichro- 
mate of  potassa  and  sulphuric  acid  into  anthraquinone,  which,  when  chemically 
pure,  has  the  formula  C14H802,  and  crystallizes  in  beautiful  needles. 
It  is,  of  course,  impossible  for  us  to  specify  the  many  different  methods  by  which 
the  point  aimed  at,  viz.,  alizarin,  can  be,  and  is,  reached  ;  but  we  give  the  following 
way,  tested  in  practice,  which  renders  it  possible  to  obtain  a  clear  insight  into  the 
successive  development  of  the  end  product. 
Both  bichloranthracene  and  bibromanthracene,  as  well  as  anthracene  chlorinated 
by  special  processes,  and  also  the  anthraquinone  form  when  heated  with  anhydrous 
