120  Presence  of  Tannin  in  Gentian  Root.  {Am'J^7trm' 
brown  color  of  the  infusion  or  tincture  prepared  directly  from  unex- 
hausted root.  It  gives,  with  ferric  chloride,  a  deep  brown-green  color, 
and  also  a  precipitate,  if  sufficiently  concentrated  ;  on  diluting  it  with 
water,  the  mixture  turns  muddy  from  the  separation  of  resin  and  fat, 
its  color  becoming  of  a  dirty  green-brown  ;  if,  instead  of  water,  alcohol 
be  added  to  the  mixture,  a  perfect  solution  is  obtained,  having  a  brown 
color  with  a  greenish  tint.  The  tincture  prepared  from  the  nearly 
exhausted  root  is,  therefore,  likewise  free  from  tannin. 
In  order  to  further  elucidate  the  subject,  a  portion  of  the  tincture 
was  evaporated,  and  the  residue  washed  with  cold  water  to  remove  the 
remaining  bitter  principle,  gentiopicrin.  The  clear,  yellow  filtrate 
evidently  contains  gentianic  (gentisic)  acid  in  solution,  it  yields,  with 
ferric  chloride,  a  deep  brown  color,  without  any  percepible  green 
tint.  Dilution  of  the  mixture  with  water  revealed  the  absence  of  a 
precipitate. 
The  yellow  granular  mass  left,  after  washing  the  alcoholic  extract 
with  water,  was  washed  with  cold  ether  to  remove  adhering  resin  and 
fat  ;  on  evaporation  of  the  yellow  etherial  solution,  a  yellow  amorphous 
mass  was  left,  which,  dissolved  in  a  little  alcohol,  yields,  with  ferric 
chloride,  a  dark  brown-green  precipitate,  the  mixture  becoming  muddy 
on  the  addition  of  water,  but  perfectly  transparent  by  alcohol. 
The  portion  left  undissolved  by  ether,  consisting  of  nearly  pure 
gentianic  (gentisic)  acid,  was  recrystallized  by  hot  alcohol  ;  but  the 
quantity  operated  on  being  small,  the  acid  was  not  obtained  in  an 
absolutely  pure  state.  Its  alcoholic  solution  behaved  nearly  like  the 
solution  of  the  etherial  washings,  except  that  the  precipitate  of  the 
latter  with  ferric  chloride,  and  its  solution  in  alcohol,  was  of  a  more 
decided  green  color. 
If  it  is  remembered  that  gentianic  (gentisic)  acid  is  slightly  soluble 
in  water,  not  freely  in  ether,  but  readily  in  alcohol,  the  dark  coloration 
imparted  to  various  simple  preparations  of  gentian  by  ferric  salts  is 
easily  explained,  likewise  the  dark-colored  precipitate  occurring  by  the 
same  agent  with  fluid  extract  of  gentian  ;  and  if  it  is  remembered  that 
alcohol  takes  up  from  gentian  root  also  resin  and  fat,  which  are 
precipitated  on  the  addition  of  water,  the  occurrence  of  a  per- 
manent precipitate  in  the  presence  of  iron  apparently  remaining  on 
diluting  the  alcoholic  liquid  with  water,  will  likewise  become 
obvious. 
