Am,  Jour.  Pharm. ) 
July,  1885.  J 
Commercial  Tannin, 
347 
One  feature  in  the  table  will  strike  every  observer  as  being  quite 
peculiar,  if  not  altogether  anomalous.  If  we  take,  for  example,  No.  8, 
we  find  the  oxidizable  matter  other  than  tannin  to  be  38'3  per  cent., 
and  this  consumed  0*0555  gram  K2Mn208,  whereas  in  the  case  of  No. 
1  the  oxidizable  matter  is  6*2  per  cent.,  yet  it  consumed  0*0586  gram 
KgMuoOg.  I  fear  I  am  unable  to  suggest  a  reasonable  explanation  for 
these  apparent  discrepancies ;  but  it  might  be  possible  to  account  for 
them  by  supposing  that  we  were  estimating  oak-bark  tannin  or  mix- 
tures of  oak-bark  tannin  and  gall  tannin,  in  place  of  pure  gall  tannin. 
The  coefficients  assigned  by  Neubauer  and  Oser  to  oak-bark  tannin  are 
equivalent  to  0*759  K2Mn208  to  IJ  grams  tannin,  so  that  if  we  were 
prepared  to  assume  that  this  tannin  has  been  made  use  of,  we  would 
get  in  the  case  of  No.  3,  for  example,  81  in  place  of  54,  and  so  on. 
This  theory  is,  however,  opposed  by  two  considerations.  In  the  first 
place,  Gunther  allows  very  much  the  same  value  to  oak-bark  tannin 
as  to  gall  tannin,  the  figures  being  32  and  32*5  respectively  to  16  of 
oxygen  from  the  permanganate ;  and  in  the  second  place,  a  sample  of 
gall  tannin,  prepared  by  another  than  the  B.P.  process,  and  not  included 
in  the  table  because  not  strictly  a  commercial  tannin,  showed  much  the 
same  anomalous  result,  there  being  66  per  cent,  of  tannin  and  26  per 
cent,  of  oxidizable  matter  other  than  tannin,  the  latter  consuming  only 
0-055  gram  K2Mn208. 
Moisture. — It  was  found  to  be  impossible  to  take  the  moisture  by 
drying  in  the  usual  way,  as  in  no  case  could  constant  weighings  be 
obtained,  and  recourse  was  therefore  had  to  drying  in  vacuo  over 
sulphuric  acid.  According  to  Strecker,^  tannic  acid  heated  to  160°C. 
becomes  darker  in  color  from  incipient  decomposition.  Several  of  the 
samples  began  to  change  color  very  rapidly.  No.  7,  for  example,  being 
perceptibly  darker  after  being  kept  for  an  hour  at  about  110°  C,  w^hile 
No.  2  was  apparently  unaltered  at  the  expiry  of  two  and  a  half  hours, 
all  the  others  occupying  positions  between  these  two. 
Ash. — Authorities,  generally,  are  agreed  that  tannin  should  on 
incineration  be  free  from  ash,  and,  practically  speaking,  it  was  found 
that  all  the  samples  save  one  answered  to  tliis  requirement,  the  excep- 
tion. No.  7,  giving  as  much  as  0*4  per  cent.  This  relatively  large  pro- 
portion of  mineral  matter  doubtless  accounts  for  the  excess  in  weight 
of  this  sample  as  compared  with  those  in  which  the  tannic  acid  content 
is  very  similar. 
1  "  Gmelin,"  vol.  xv,  p.  458. 
