A.m.  Jour.  Pharm. 
Nov.,  1921. 
Determination  of  Tannin. 
771 
so  conducted  that  no  powder  was  lost,  making  the  determination 
direct  instead  of  by  difference  and  increasing  the  accuracy  for  un- 
skilled analysts.  The  new  washing  apparatus  not  only  makes  this 
possible,  but  reduces  the  amount  of  hide  powder  required  for  a 
determination  to  one-sixth. 
PRESENT  PROCEDURE. 
A  solution  of  the  tanning  material  is  prepared  of  such  strength 
that  2  g.  of  hide  powder  will  detannize  100  cc.  in  6  hrs.  of  shaking. 
With  a  little  experimenting,  safe  limits  are  easily  determined  for  all 
ordinary  materials  so  that  the  need  for  repetition  will  be  rare.  For 
the  extracts  used  in  this  work,  suitable  concentrations  in  grams  per 
liter  are  20  for  hemlock,  larch,  oak,  and  sumac,  16  for  gambier,  and 
7  for  solid  quebracho.  The  solution  must  be  freed  from  insoluble 
matter,  which  may  be  done  in  the  usual  manner  by  adding  kaolin, 
filtering  through  a  thin  paper,  returning  the  filtrate  to  the  paper  for 
an  hour  to  tan  it,  then  discarding  all  liquor  which  has  touched  the 
paper,  pouring  fresh  liquor  on  to  the  filter  and  collecting  when  the 
filtrate  comes  through  clear.  For  materials  which  filter  with  difficulty, 
time  can  be  saved  by  setting  up  several  filters  at  one  time.  Stand- 
ard hide  powder,4  or  its  equivalent,  is  extracted  with  chloroform  to 
remove  all  extractable  matter,  and  is  then  freed  from  solvent  and 
stored  ready  for  use.  This  treatment  is  chiefly  to  remove  fatty  mat- 
ters, and  it  may  be  found  convenient  to  treat  a  year's  supply  at 
once.  Two  grams  of  this  powder,  of  known  moisture  content,  are 
put  into  a  6-oz.,  wide-mouth  bottle,  100  cc.  of  tan  liquor  are  added, 
and  the  whole  is  put  into  a  rotating  box  and  shaken  for  6  hrs.  It  is 
advisable  to  keep  the  liquor  and  wash  water  cool  to  guard  against 
any  tendency  towards  decomposition  of  the  untanned  portion  of  the 
hide  powder.   This  matter  requires  attention  only  in  hot  weather. 
The  essential  part  of  the  washing  apparatus  is  shown  in  Fig.  1 
and  consists  of  three  glass  parts  fitting  tightly  into  one  another  by 
means  of  ground  joints.  A  small  piece  of  fine  filter  cloth  is  stretched 
tightly  over  the  bottom  outlet  of  part  B  and  is  firmly  secured  by 
winding  and  tying  strong  thread  around  the  groove.  Parts  B  and  C 
are  then  put  together  and  the  stopcock  is  opened.  The  tan  liquor  and 
hide  powder,  after  the  6-hr.  shaking,  are  washed  into  part  B,  the 
4  Prepared  by  the  Standard  Mfg.  Co.,  Ridgway,  Pa. 
