Am.  Jour.  Pharm. ) 
Dec,  1882.  j 
Estimation  of  Tannin. 
601 
being  to  ascertain  the  cause  of  this  discrepancy.  The  analyses  were 
-conducted  in  the  following  manner :  The  sokition  of  potassium  per- 
manganate contained  1  gram  per  liter,  1  cc.  equal  to  0*00135  g.  tannin. 
It  is  standardized  with  iron,  and  the  tannin  equivalent  calculated 
according  to  Neubauer's  estimations  (0*063  g.  oxalic  acid  =  0*04157' 
g.  tannin).  The  indigo  solution  is  prepared  so  that  20  cc.  require  18 
to  20  cc.  of  the  solution  of  potassium  permanganate.  In  titrating  the 
tannin  infusion  the  author  invariably  used  20  cc.  of  indigo  solution, 
the  advantage  being  that  the  liquid  to  be  titrated  gives  the  same 
yellow  color  in  each  case,  so  that  the  eye  gradually  becomes  accustomed 
to  it.  The  gelatin  solution  is  made  according  to  LowenthaFs  pre- 
scription, the  filtration,  however,  is  conducted  according  to  Kathreiner's 
method.  In  preparing  the  infusion  the  quantity  of  tannin  should  be 
regulated  so  that  10  cc.  of  the  solution  require  12  cc.  of  potassium 
permanganate.  Although  it  is  unnecessary  to  adhere  strictly  to  this 
strength,  it  is  important  to  consider  the  quantity  of  tannin  taken,  and 
not  to  use  too  small  a  quantity,  in  which  case  the  above-mentioned 
€rror  would  be  multiplied.  Again,  it  is  not  advisable  to  have  the 
infusion  in  too  concentrated  a  state,  as  the  oxidation-products  of  the 
organic  substances  affect  the  yellow  color  very  considerably  and  hinder 
the  recognition  of  the  end  reaction.  In  order  to  ascertain  whether 
the  extraction  has  been  complete  ferric  oxide  paper  is  used,  /.  e.,  strips 
of  filter-paper  are  steeped  in  a  solution  of  1  gram  ferric  chloride,  and 
1  gram  sodium  acetate  in  100  cc.  water,  and  dried  in  the  air.  This 
paper  gives  a  distinctly  visible  black  stain  with  a  solution  containing 
1  part  of  tannin  in  10,000  water.  With  a  smaller  quantity,  a  black 
ring  is  produced  round  the  drop  of  the  solution  poured  on  filter-paper. 
The  acidulated  water  used  contains  in  100  cc.  3*786  g.  H2SO4. 
The  analysis  is  made  as  follows  :  10  cc.  of  the  infusion  are  treated  in 
a  shallow  porcelain  basin  with  1  liter  of  water  and  20  cc.  indigo  solu- 
tion. Potassium  permanganate  is  then  added  slowly  drop  by  drop 
until  a  yellow  color  with  faint  reddish  tinge  is  produced.  To  deter- 
mine the  oxidizable  non-tannin  constituents  the  tannin  in  50  cc.  of 
tlie  infusion  is  precipitated  with  50  cc.  of  gelatin  solution  saturated 
with  salt,  and  25  cc.  acidulated  water.  After  shaking  u]^  and  allowing 
to  stand  for  some  time  the  mixture  is  filtered.  25  cc.  of  the  clear 
filtrate  (corresponding  to  10  cc.  infusion)  are  then  treated  with  1  liter 
^  According  to  Councler  and  8chroeder  the  correct  e(][uivalent  is  ()-03425 
to  0-03430  gm.—Berichte,  1882,  p.  1373. 
