1 20    New  Process  for  Estimating  Tannin  Volumetrically.  { Am^£cl\ 
Pharm. 
ON  A  NEW  PROCESS  FOR  ESTIMATING  TANNIN 
VOLUMETRICALLY. 
By  Joseph  W.  England,  Ph.  G. 
Many  processes  have  been  recommended  for  the  volumetric  esti- 
mation of  tannin,  but  the  greater  number  of  them  are  tedious  and 
difficult  to  cany  out  in  practice,  and  even  when  accomplished  yield 
results  far  from  satisfactory.  The  process  offered  by  E.  Durien 
(Annali  di  Chim.  Med.  Farm.,  Dec,  1885,  p.  350;  Jour.  Phar.  Chim.y 
1885,  xii,  p.  374),  is  very  easy  of  execution  and  is  based  upon  the 
following  reactions : — 
1.  That  the  addition  of  chloride  of  iron  solution  to  one  of  tannin 
forms  a  black  or  green  coloration  ;  and — 
2.  That  this  coloration  is  destroyed,  little  by  little,  and  then  com- 
pletely, on  the  addition  of  a  solution  of  chlorinated  lime. 
The  mode  of  operation,  with  the  results. obtained,  is  as  follows: — 
1.  Prepare  a  solution  of  calcium  hypochlorite  (10*  gm.)  in  distilled 
water  (200*  gm.)  and  filter.  2.  Make  a  second  solution  of  pure  tan- 
nin by  this  formula: — 
Tannin,  pure  ,   0*10  gm. 
Officinal  solution  of  ferric  chloride  1   15  drops. 
Acid  acetic,  concentrated  (glacial)     20  drops. 
Distilled  water   20-  c  c. 
This  solution  is  made  in  a  100  c  c.  glass  flask  and  serves  as  a  titrate 
to  the  first  solution.  With  a  Gay-Lussac  burette,  graduated  to  the 
One-tenth  of  a  c  c,  rapidly  add,  drop  by  drop,  the  hypochlorite, 
agitating  after  each  addition,  when  the  green  or  black  color  of  the 
liquid  will  gradually  grow  lighter  and  pass,  suddenly,  to  a  rose-brown, 
at  which  point  the  operation  must  be  arrested.  This  rose-brown 
color,  by  the  action  of  the  air,  passes  to  a  green,  but  there  is  no  need 
of  taking  into  calculation  this  secondary  reaction.  Working  in  this 
manner  it  will  be  found  that  14  c  c.  of  solution  of  hypochlorite  will 
be  required  to  destroy  the  inky  color  formed  from  0*10  gm.  of  pure 
tannin. 
To  fully  establish  the  accuracy  of  his  method,  Mr.  Durien  made 
various  mixtures  of  sugar  and  pure  tannin,  in  order  to  ascertain  what 
1  Chlorure  Ferrique  dissous,  French  Codex,  sp.  gr.  1*26 ;  containing  26  per 
cent.  Fe2  Cl6. 
