Alizarine  crystallizes  in  fine  red  prisms  or  needles,  which  melt  at
289°,  and  can  be  sublimed.  It  is  readily  soluble  in  alcohol  and  ether,
combines  with  a  violet  or  purple  color  with  alkalies,  and  forms  various
colored  insoluble  compounds  or  '* lakes"  with  metallic  oxides,  the  ones
of  chief  importance  being  those  of  aluminum  and  tin  (red),  the  iron
(violet-black),  and  the  lime  (reddish-blue).  The  finest  color  obtained
with  alizarine,  known  as  "Turkey  red,"  is  produced  by  mordanting
the  materials  with  acetate  of  alumina  and  treating  them  with  a  sulpho-
nated  castor  oil,  known  as  **  Turkey  red  oil, "  before  applying  the  alizarine.
646  ORGANIC  CHEMISTRY.
By  the  reduction  of  alizarine  with  ammonia  and  zinc-dust  is  foimed

yC(OH)^
desoxyalizarine,    C^H^'f  |         ^^C^HjCOH)^,    which,    under    the    name

^CH-

of  "  anthrarobin, "  has  been  used  in  medicine  as  a  non-poisonous  sub-
stitute for  chrysarobin  and  chrysophanic  acid.
Purpurine  (Trioxyanthraquinone),  C,4H5(OH)jO,. — ^This  dye  is  found
along  with  alizarine  in  madder-root,  and  is  also  prepared  artificially.
A  homologue  of  anthracene  is  also  found  in  coal-tar, — viz.,  Methyl-
atUhracene,  Cj^H^CCHj).  It  is  capable  of  analogous  reactions,  yielding
a  quinone  and  hydroxyl  derivatives  of  the  same.  The  name  of  one  of
the  latter  is  Chrysophanic  Acid  (Dioxy-methyl-anthraquinone),  Cj^H,-
(CH3)(OH)jO,.  It  is  found  in  certain  lichens,  in  yellow  dock  (Rutnex),
in  senna,  and  in  rhubarb.  It  crystallizes  in  golden-yellow  prisms  or
needles,  melting  at  102^,  and  soluble  in  alcohol,  ether,  or  benzene.
Alkalies  also  dissolve  it,  forming  dark-red  solutions.  When  distilled
over  zinc-dust  it  yields  methyl-anthracene.
