^'&'S&m'}   Presence  of  Tannin  in  Gentian  Root.  119 
But  what  is  the  effect  of  ferric  salts  upon  gentian  ?  The  investiga- 
tions mentioned  above  have  thrown  considerable  light  on  this  point. 
Henry  already  noticed  the  dark  color  produced  by  ferric  chloride  with 
what  he  supposed  to  be  the  bitter  principle,  but  which  was  subsequently 
proven  to  be  merely  the  yellow  coloring  principle  contained  in  the  root. 
Baumert  says  that  the  concentrated  alcoholic  solution  of  pure  gentianic 
(gentisic)  acid  produces  with  ferric  chloride  a  red-brown  precipitate, 
and  Ludwig  found  that  the  aqueous  solution  of  the  extract  contains  a 
body 'which,  under  certain  circumstances,  imparts  a  dark-green  fluores- 
cence. In  these  observations  we  have  the  key  for  the  behavior  of 
ferric  salts  with  the  preparations  of  gentian,  which  I  shall  endeavor  to 
explain  with  the  following  experiments. 
Well-dried  and  bruised  gentian  root  was  nearly  exhausted  by  cold 
water,  first  by  percolation  and  subsequently  by  expression  after  mace- 
ration. The  first  portion  of  the  percolate  gelatinized  on  standing  a 
day  or  two,  in  consequence  of  the  separation  of  pectin  compounds. 
This  aqueous  infusion  is  not  disturbed  by  gelatin  solution,  a  pretty  sure 
evidence  of  the  total  absence  of  tannin  ;  in  the  course  of  a  few  hours, 
a  scant  light-colored  precipitate  made  its  appearance,  which,  after  having 
been  thoroughly  washed  with  water  is  merely  tinged  light-brown  by 
dilute  ferric  salts.  The  infusion,  however,  strikes  with  ferric  chloride 
a  dark  reddish-brown  color,  which  in  reflected  light  shows  a  deep 
greenish  tint ;  no  precipitate  takes  place,  as  the  liquid  remains  perfectly 
transparent  in  thin  layers,  although  a  concentrated  infusion  apparently 
becomes  opaque  on  the  addition  of  the  iron  salt,  but  after  water  is 
added  shows  not  the  slightest  sign  of  a  precipitate,  even  on  standing. 
If  the  infusion  has  been  previously  diluted  with  water,  the  addition  of 
ferric  chloride  will  scarcely  darken  it. 
Alcohol  added  to  the  cold  infusion  precipitates  pectin  compounds, 
albuminous  and  gummy  matter,  and  the  clear  liquid  behaves  exactly  as 
the  infusion  from  which  it  had  been  made.  The  infusion  preserved  by 
alcohol  was  treated  with  a  fragment  of  fresh  hide  for  24  hours  ;  the 
behavior  of  the  liquid  to  ferric  chloride  showed  no  difference.  The 
experiments  detailed  prove  conclusively  that  the  aqueous  infusion  of 
gentian  does  not  contain  any  tannin. 
Gentain  root,  previously  nearly  exhausted  with  water,  was  now 
macerated,  and  then  displaced  with  strong  alcohol.  The  tincture  thus 
obtained  is  of  a  bright  yellow  color,  quite  distinct  from  the  yellowish- 
