Am.jour.Pharm.j  The  Chemistry  of  Rhubarb.  619 
December,  1895. 
stance  and  the  chrysophan-hydro-anthron  prepared  in  a  different 
way  by  Liebermann ; 13  but  I  am  disposed  to  think  that  the  differ- 
ence is  due  to  some  accidental  circumstance. 
2.     EM  ODIN. 
This  substance  is  dissolved,  together  with  rhei'n,  by  the  solution 
of  potassium  carbonate,  with  which  the  pulverulent  residue  is  treated 
in  separating  chrysophanic  acid.  The  solution  acidified  with  hydro- 
chloric acid  was  shaken  with  ether,  and,  on  evaporating  the  ether, 
a  residue  was  left  consisting  essentially  of  emodin  and  rhei'n.  By 
treatment  with  boiling  toluene,  emodin  is  extracted  from  the  resi- 
due, and  most  of  it  is  deposited  again  as  the  solution  cools ;  on 
evaporating  the  toluene,  a  further  small  portion  of  emodin  is  obtain- 
able, which  may  be  conveniently  put  aside  for  further  treatment 
with  toluene.  The  crystals  first  deposited  were  then  dissolved  in 
hot  glacial  acetic  acid,  and  the  solution  mixed  with  boiling  water 
until  crystallization  commenced,  the  emodin  then  separated  in  well- 
defined,  orange-colored  prisms  containing  one  molecule  of  water, 
which  is  given  off  at  1200  C,  the  crystals  then  becoming  dull. 
Calculated  for 
C15H10Os  +  H2O.  Found. 
H20   6-25  6-30 
Calculated  for 
C15H10O5.  Found. 
Carbon   66-67  66*35 
Hydrogen   370  3-93 
Anhydrous  emodin  melts  about  2500  C.  It  dissolves  readily  in 
a  cold  water  solution  of  potassium  or  sodium  carbonate  with  purple- 
red  color ;  very  readily  in  caustic  potash  or  soda.  It  also  dissolves 
readily  in  ammonia  solution,  and,  on  addition  of  lead  acetate,  a 
flocculent,  amorphous,  purple- colored  precipitate  is  formed.  Emodin 
is  freely  soluble  in  alcohol,  especially  with  the  aid  of  heat,  and  the 
solution  has  an  acid  reaction.  When  treated  with  hydriodic  acid 
(1-7  sp.  gr.)  in  Zeisel's  apparatus,  there  is  not  any  formation  of 
methyl  iodide,  as  might  be  expected ;  but,  on  the  contrary,  emodin 
is  reduced  in  the  same  manner  as  chrysophanic  acid,  chrysophan- 
oxyhydro-anthron,  C15H1204,  being  produced.  On  recrystallizing 
this  product  from  hot  glacial  acetic  acid,  it  forms  pale  yellow  shin- 
uBerichtey  21,  436. 
