772 
Determination  of  Tannin. 
(  Am.  Jour.  Pharm. 
(       Nov.,  1921. 
liquor  being  allowed  to  run  through  the  open  cock  into  a  beaker  and 
returned  until  reasonably  clear.5  The  stopcock  is  then  closed  and  B 
is  half  filled  with  water  and  then  fitted  to  part  A  with 
stopcock  closed. 
The  remaining  part  of  the  washing  apparatus  is  a 
reservoir  of  water  set  high  enough  from  the  table 
to  exert  a  pressure  equal  to  a  column  of  about  4  ft.  of 
water  upon  the  glass  receptacle,  which  is  connected 
to  the  reservoir  by  means  of  a  rubber  tube  attached  to 
A.  The  stopcock  in  A  is  opened  wide,  and  the  rate  of 
flow  of  water  is  regulated  to  about  500  cc.  per  hr.  by 
means  of  the  stopcock  in  C,  which  is  connected  to  the 
drain.  Since  the  washing  is  usually  complete  in  about 
12  hrs.,  it  is  convenient  to  start  it  just  before  leaving 
the  laboratory  in  the  evening  so  that  it  will  be  complete 
at  the  start  of  the  next  day.  However,  washing  should 
not  be  stopped  until  the  wash  water  is  colorless  and 
does  not  darken  upon  the  addition  of  a  drop  of  ferric 
chloride. 
The  powder  is  then  washed  on  to  a  Biichner  funnel  and  freed 
from  as  much  water  as  possible  by  suction.  It  is  theii  allowed  to 
dry  in  the  air  over  night,  after  which  it  is  completely  dried  in  a 
vacuum  oven  for  2  hrs.,  desiccated  and  weighed.  It  is  returned  to 
the  oven  and  reweighed  as  a  check  against  insufficient  drying.  The 
increase  in  weight  of  the  dry  powder  represents  the  amount  of  tan- 
nin present  in  100  cc.  of  the  orignal  tan  liquor. 
We  have  found  it  very  convenient  to  have  rotating  boxes  capable 
of  holding  twelve  bottles  each  and  cylindrical  stands  equipped  with 
twelve  washing  devices  each.  Given  twelve  filtered  liquors  Monday 
morning,  the  powders  would  be  tanned  and  ready  for  washing  be- 
fore evening,  ready  for  drying  next  morning,  and  the  tannin  values 
available  before  noon  Wednesday.  With  one  such  outfit  an  analyst 
can  easily  complete  twelve  determinations  every  day  and  still  have 
time  for  other  work. 
5  This  liquor  must  always  be  tested  for  tannin  by  adding  one  drop  at  a 
time,  a  freshly  prepared  solution  of  10  g.  gelatin  and  100  g.  sodium  chloride 
per  liter.  A  precipitate  indicates  that  tannin  is  present^  in  which  case  the  de- 
termination must  be  repeated,  using  a  more  dilute  solution  of  the  tanning  ma- 
terial. 
