Am.  Tour,  Pharm.  \ 
December,  1895.  j 
The  Chemistry  of  Rhubarb. 
615 
THE  CHEMISTRY  OF  RHUBARB.  - 
By  Dr.  J.  Oswald  Hesse. 
Reprinted  from  the  Pharmaceutical  Journal,  October  19,  1895. 
According  to  the  investigations  of  Schlossberger  and  Dbpping,1 
rhubarb  contains,  in  addition  to  three  resins — aporetin,  phaeoretin 
and  erythroretin — as  an  essential  constituent,  chrysophanic  acid, 
which  was,  on  the  basis  of  its  properties  and  analysis,  declared  by 
them  to  be  identical  with  the  chrysophanic  acid  which  had  pre- 
viously been  obtained  by  Rochleder  and  Heldt  from  the  yellow 
lichen,  Physcia  parietinar  This  chrysophanic  acid  of  rhubarb  was 
subsequently  observed  by  Warren  de  la  Rue  and  Hugo  Miiller,  in  a 
sediment  from  rhubarb  tincture  which  had  been  kept  for  a  long 
time,  and  they  showed  how  this  substance  could  be  prepared  from 
rhubarb  by  means  of  benzene.3  They  adopted  the  name  of  chryso- 
phan,  as  the  substance  has  not  the  character  of  an  acid,  but  their 
proposal  has  not  been  generally  followed.  These  observers  also 
obtained  another  constituent  of  rhubarb,  viz:  emodin;  to  which 
they  gave  the  formula  C40H30O13,  representing  chrysophan  or  chry- 
sophanic acid  by  the  formula  C10H8O3,  which  had  been  adopted  by 
Rochleder  and  Heldt  for  the  chrysophanic  acid  of  Physcia. 
Meanwhile,  Gerhardt  had  suggested  that  the  formula  of  chryso- 
phanic acid  should  be  CuH10O4,  and  that  it  was  in  some  way  related 
to  alizarin.  At  the  instigation  of  Rochleder,  the  chrysophanic  acid 
of  rhubarb  was  then  further  investigated  by  Pilz,4  who  confirmed 
the  results  obtained  by  Schlossberger  and  Dbpping,  and  concluded 
that  the  formula  suggested  by  Gerhardt  was  incorrect.  In  a  sub- 
sequent investigation,  however,  Rochleder5  obtained  results  per- 
fectly in  accordance  with  Gerhardt's  formula,  and  he  explained  this 
difference  as  being  due  to  the  circumstance  that  the  substance  can- 
not be  dried  at  ioo°  C,  but  is  rendered  anhydrous  only  when 
heated  to  1 1 5  °  C.  in  a  current  of  carbonic  anhydride.  Still  later, 
this  formula  was  found  to  be  incorrect,  when  Liebermann  and  O. 
Fischer*5   showed  that  the  sublimed  substance  has  the  formula 
lAnnale?i  der  Chem.  Pharm.,  30,  213. 
-Ibid.,  48,  12. 
■'Chem.  Soc.  Quart.  Journ.,  10,  300. 
4 Chem.  Centralbl.,  1862,  p.  6. 
bBerichte,  2,  374. 
"Ibid.,  8,  1 102. 
