770 
Determination  of  Tannin. 
Am.  Jour.  Pharm. 
Nov.,  1921. 
and  abroad  are  greatly  in  error,  exceeding  200  per  cent,  in  some 
cases.  Changing  a  method  of  analysis  upon  which  millions  of  dol- 
lars of  tanning  materials  are  bought  and  sold  annually  is  admittedly 
a  serious  matter.  "Were  the  new  method  to  supplant  the  old  in  the 
sale  of  extracts,  drastic  price  changes  would  have  to  be  made  and 
many  extracts  would  no  longer  hold  their  present  relative  standings 
or  reputation  as  to  tanning  value.  Since  the  official  methods  have 
been  clearly  proved  unreliable,  it  would  seem  that  the  new  method 
must  now  be  tested  generally  to  determine  whether  or  not  it  will 
meet  all  the  conditions  that  ought  to  be  required  of  a  method  so  im- 
portant. Until  now  its  use  has  been  restricted  because  the  pro- 
cedure as  originally  described  was  both  cumbersome  and  time  con- 
suming, all  of  the  first  efforts  having  been  directed  exclusively  to  de- 
vising an  accurate  method.  But  the  procedure  has  since  been  de- 
veloped until  it  is  now  quite  as  simple  as  that  of  any  method  in 
general  use.  In  this  paper  we  describe  the  simplified  procedure,  and 
also  refute  the  objections  which  have  been  raised  against  the  new 
method. 
DEFINITION  OF  TANNIN. 
A  thorough  review  of  the  literature  shows  that  it  has  been  gen- 
erally agreed  to  class  as  tannin  that  portion  of  the  water-soluble 
matter  of  certain  vegetable  materials  which  will  precipitate  gelatin 
from  solution  and  which  will  form  compounds  with  hide  fiber  which 
are  resistant  to  washing.  Much  confusion  would  have  been  avoided 
in  discussion  by  making  it  clear  whether  the  criticism  was  directed 
against  the  definition  or  the  method. 
CHANGES  IN  PROCEDURE. 
In  the  method  as  orginally  described,  the  tanned  hide  powder 
had  to  be  washed  by  shaking  with  water  for  30  min.,  squeezing 
through  linen,  and  repeating  with  fresh  water  until  free  from  soluble 
matter,  which  usually  required  about  twelve  washings.  This  is  now 
accomplished  with  very  little  effort  in  a  washing  apparatus  to  be  de- 
scribed later.  The  washed  powder,  after  drving,  was  analyzed  for 
water,  ash,  fat,  and  hide  substance  (NX 5.62),  and  the  percentages 
of  these  subtracted  from  100  gave  the  per  cent,  of  tannin  in  the 
powder.  It  was  suggested  earlier  "that  this  figure  might  be  ob- 
tained simply  by  noting  the  increase  in  weight  of  the  dry  powder 
after  tanning  and  washing,  provided  the  washing  operation  was 
