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ON  SOME  CONSTITUENTS  OF  EHUBABE. 
ON  SOME  CONSTITUENTS  OF  KHUB  ARB. 
By  Warren  de  la  Rue,  ph.d.?  p.  r.  s.,  treas.  c.  s.,  and  Hugo  Muller.  ph.b. 
I.-— Investigation  of  a  Deposit  found  in  Tineture  of  Rhubarb. 
It  has  been  often  observed,  that  when  freshly  prepared  tinc- 
ture of  rhubarb  is  left  to  itself  for  some  time,  it  becomes  turbid, 
and  deposits  a  dark-colored  precipitate,  which  cannot  be  redis- 
solved,  either  by  heating  the  tincture  or  by  diluting  it  with  fresh 
alcohol.  The  attention  of  the  Society  was  recently  called  to 
this  circumstance  by  Mr.  Whipple,  who  frequently  has  occasion 
to  prepare  the  tincture  of  rhubarb  on  a  large  scale  :  Mr.  Whipple, 
at  the  same  time,  gave  an  account  of  a  few  experiments  he  had 
made  with  the  precipitate,  and  stated  that  his  leisure  did  not 
permit  of  his  investigating  the  subject  further,  but  that  he  would 
furnish  material  to  any  member  who  might  feel  inclined  to  pur- 
sue the  inquiry.  As  it  appeared  to  be  very  probable,  that  the 
deposit  from  the  tinctura  rhei  contained  some  constituents  of  in- 
terest, we  availed  ourselves  of  Mr.  Whipple's  offer;  and  we  take 
this  opportunity  to  express  to  him  our  thanks  for  the  liberal 
supply  of  material  which  he  kindly  placed  at  our  disposal. 
The  deposit  from  rhubarb  tincture  is  of  a  dark  color,  and 
resinous  nature ;  it  resembles  logwood  extract  coarsely  powdered, 
and  has  in  a  slight  degree  the  characteristic  odor  of  rhubarb. 
When  heated  in  a  test-tube,  it  does  not  melt,  but  gives  off  yellow 
fumes,  which  condense  to  a  yellow  liquid,  a  black  residue  being 
left.  Heated  on  platinum  foil,  it  burns  without  melting,  leaving 
a  tolerably  large  quantity  of  ash,  which  consists  principally  of 
potash  and  lime.  Boiled  with  water,  it  imparts  a  yellowish  tint 
to  it,  but  an  almost  inappreciable  quantity  of  it  is  dissolved :  al- 
cohol, when  boiled  with  the  precipitate,  assumes  a  dark  yellow- 
brown  tint,  but  the  quantity  dissolved  is,  nevertheless  very 
small.  Similar  results  are  obtained  on  treating  the  precipitate 
with  ether,  chloroform,  and  glacial  acetic  acid.  Ammonia  and 
concentrated  sulphuric  acid  dissolve  the  greater  part,  but  not 
the  whole  of  the  substance ;  the  fixed  alkalies,  on  the  other  hand, 
when  aided  by  heat,  completely  dissolve  it,  with  the  exception  of 
a  slight  residue,  consisting  of  accidental  impurities  :  the  solution 
in  ammonia,  the  alkalies,  or  sulphuric  acid,  is  of  a  dark,  dingy 
purple  color. 
