776 
Determination  of  Tannin. 
Am.  Jour.  Pharm. 
Nov.,  1921. 
by  hide  substance,  they  had  occasion  to  use  very  strong  liquors. 
Hide  powder  was  treated  with  a  chrome  liquor  containing  14.75  &• 
of  chromic  oxide  per  liter,  but  after  48  hrs.  the  concentration  had 
risen  to  15.40  g.,  although  the  hide  powder  had  actually  removed 
chromium  from  solution.  This  would  correspond  to  a  negative 
value  for  tannin  by  the  A.  L.  C.  A.  method.  What  happened  was 
that  the  hide  powder  absorbed  a  solution  more  dilute  than  the  re- 
maining chrome  liquor  and  therefore  concentrated  the  liquor  more 
than  enough  to  offset  the  chromium  removed  by  combination  with 
the  hide  substance.  It  is  quite  clear  that  one  cannot  determine 
the  amount  of  matter  removed  from  solution  by  noting  the  decrease 
in  concentration  of  the  liquor  and  calculating  according  to  the  in- 
structions of  the  A.  L.  C.  A.  method. 
SYNTHETIC  TANNINS. 
A  representative  of  a  firm  manufacturing  synthetic  tanning 
materials  of  the  Neradol  type  informed  us  that  the  use  of  the 
official  method  on  their  product  meant  nothing  as  it  could  be  made 
to  give  any  results  desired.  He  was  anxious  to  learn  if  the  new 
method  would  indicate  the  per  cent,  of  matter  capable  of  forming 
a  stable  compound  with  hide  substance.  While  we  have  done  no 
work  with  syntans,  as  they  are  called,  it  is  obvious  that  they  differ 
from  ordinary  tan  liquors  in  that  they  usually  contain  a  large 
amount  of  free  sulfuric  acid.  In  using  the  new  method  on  such  ma- 
terials there  is  the  possibility  that  the  acid  might  cause  the  hide  sub- 
stance to  swell  considerably  during  washing.  This  would  slow  down 
the  washing  action  and  tend  to  favor  decomposition  of  hide  sub- 
stance, with  a  consequent  loss  in  accuracy  of  the  method.  It  seems 
possible  that  this  might  be  avoided  by  using  tap  water  saturated 
with  salt  for  the  first  washings,  until  all  sulfuric  acid  was  re- 
moved, and  then  completing  the  washing  with  distilled  water. 
SUMMARY. 
A  modification  of  the  authors'  new  method  of  tannin  analysis 
is  described  which  results  in  a  great  saving  of  time  and  labor,  and 
tends  towards  increased  accuracy. 
Objections  raised  against  the  new  method  are  refuted. 
It  is  shown  that  the  principle  underlying  the  present  official 
methods  is  unsound. 
A  suggestion  for  using  the  new  method  with  syntans  is  made. 
