6i8 
The  Chemistry  of  Rhubarb. 
f  Am.  Jour.  Pharm. 
1  December,  1895. 
the  whole  of  the  active  constituent  of  the  drug,  and  consequently 
that  does  not  appear  to  be  of  the  nature  of  a  glucoside.  The  resin- 
ous character  of  this  substance,  however,  deterred  me  from  under- 
taking any  further  investigation  of  it,  and  I  proceeded  to  examine 
the  above-mentioned  crystalline  powder,  which  consisted  essentially 
of  chrysophanic  acid,  emodin,  and  a  new  substance,  rhei'n. 
I.  CHRYSOPHANIC  ACID. 
The  crystalline  residue  separated  from  the  extract  was  repeatedly 
treated  with  a  dilute  solution  of  potassium  carbonate  at  a  tempera- 
ture of  about  400  C,  in  a  vessel  from  which  air  was  ^excluded,  until 
a  solution  was  eventually  obtained  which  did  not  become  sensibly 
red-colored  within  twenty-four  hours.  The  undissolved  portion  of 
the  powder  was  then  dissolved  in  alcohol  or  glacial  acetic  acid  and 
recrystallized  until  the  melting  point  of  the  crystals  was  1780  C. 
Pure  chrysophanic  acid  does  not  dissolve  at  the  normal  tempera- 
ture in  a  water  solution  of  potassium  or  sodium  carbonate.  On 
boiling,  a  little  is  dissolved,  forming  a  red  solution,  from  which  the 
greater  part  of  the  chrysophanic  acid  is  again  deposited  on  cooling. 
But  the  solution  still  remains  colored  red,  probably  indicating  that 
some  part  of  the  chrysophanic  acid  has,  under  the  influence  of  expo- 
sure to  the  air,  been  converted  into  emodin,  the  substance  most  nearly 
related  to  it,  with  which  it  is  associated  in  rhubarb.  Chrysophanic 
acid  is  quite  insoluble  in  a  water  solution  of  potassium  or  sodium 
bicarbonate.  When  crystallized  from  alcohol  or  glacial  acetic  acid 
it  forms  golden-yellow  laminae,  resembling  moss  in  their  arrange- 
ment; these  crystals  melt  at  1780  C;  they  are  not  hygroscopic, 
neither  do  they  lose  water  when  heated  to  1 1 5 0  C,  or  at  higher 
temperatures.  The  composition  of  chrysophanic  acid  is  represented 
by  the  formula  C15H]0O4. 
Calculated.  Found. 
Carbon   70*86  70  81 
Hydrogen   3 '93  3  87 
When  chrysophanic  acid  is  treated  with  hydriodic  acid  (1-7  sp. 
gr.)  no  alkyl  iodide  is  formed,  but  the  substance  is  converted  by 
reduction  into  chrysophan-hydro-anthron,  C15H1203,  which  dissolves 
in  the  alkaline  liquid  with  a  wine-red  color,  but  apparently  is  not 
again  converted  into  chrysophanic  acid  on  shaking  the  solution 
with  air.    In  this  particular  there  is  a  difference  between  this  sub- 
