262  Active  Principle  of  Senna  Leaves.  {^'^'£y\m^'''^^ 
If  the  solution  of  the  acid  or  one  of  its  salts  be  boiled  for  a  few 
minutes  with  a  dilute  mineral  acid,  the  clear  solution  becomes  turbid 
and  throws  down  a  yellowish  brown  precipitate  mixed  with  black 
flecks  ;  these  latter  collect  themselves  into  a  black  mass,  and  finally 
form  the  only  decomposition  product  which  is  insoluble  in  water.  It 
is  the  cathartogenic  acid  of  Kubly  (also  purgative),  but  contains  other 
bodies  as  well.  In  the  filtered  solution  there  is  present  a  kind  of  glu- 
cose which  reduced  Fehling's  solution,  but  could  not  be  got  to  ferment 
with  yeast.  Boiling  with  caustic  potash  also  decomposes  cathartic 
acid,  but  the  products  were  not  investigated. 
The  yellowish  brown  precipitate  was  next  examined.  It  was  sepa- 
rated from  the  other  matters  present  by  agitation  with  ether,  which  dis- 
solves it,  the  yellow  ethereal  solution  being  then  poured  off.  On  evap- 
orating the  ether  a  light  orange  colored  resinous- looking  body  is  left  be- 
hind. It  is  insoluble  in  water,  but  was  purified  by  dissolving  it  in  a 
small  quantity  of  sodium  carbonate  solution  from  which  it  was  pre- 
cipitated by  the  addition  of  hydrochloric  acid,  the  precipitate  being 
collected  on  a  filter,  well  washed  with  water  and  finally  dissolved  in 
alcohol.  On  evaporating  the  alcohol,  a  dark  brown  amorphous  body 
is  obtained,  which  however  consists  of  various  constituents.  On 
treating  it  with  ether  a  portion  of  it  only  is  dissolved,  the  solution 
being  of  a  pure  yellow  color.  This  body  is  also  amorphous,  and 
on  the  addition  of  an  alkali  gives  a  bright  cherry-red  color,  being 
probably  the  substance  which  gives  this  reaction  in  the  urine.  It^ 
howev^er,  is  also  not  a  simple  substance,  as  it  undergoes  further 
changes  on  being  boiled  with  an  acid. 
Among  the  decomposition  products  of  cathartic  acid  is  also  found  a 
body  which  is  present  in  commercial  chrysarobin.  It  is  obtained  from 
chrysarobin  by  treating  the  latter  with  ether,  whereby  a  small  portion 
of  it  is  dissolved.  The  ethereal  solution  is  then  washed  with  very 
dilute  potassium  hydrate,  and  the  substance  obtained  by  allowing  it  to 
crystallize  out  from  a  hot  alcohol-chloroform  solution.  This  body 
is  almost  identical  with  chrysarobin,  but  differs  from  it  in  so  far  as 
that  when  dissolved  in  strong  caustic  potash  and  exposed  to  the  air  it 
is  not  oxidized  into  chrysophanic  acid,  and  in  fact  seems  to  undergo  no 
change  whatever. 
If  this  body  be  oxidized  by  boiling  it  with  Fehling's  solution,  and 
after  the  addition  of  HCl  the  whole  be  shaken  up  with  ether,  a  por- 
tion of  it  is  dissolved.    The  ethereal  solution  is  dichroous,  being  by 
