346 
Commercial  Tannin, 
J  Am.  Jour.  Pharm 
I       July, 1885. 
by  Sutton,  according  to  whom,  one  gram  of  pure  gallotannic  acid  re- 
quires for  oxidation  0*759  gram  KgMugOg.  It  is  somewhat  unfortunate 
that  authorities  are  not  agreed  as  to  tlie  value  to  be  assigned  to  the 
permanganate.  Dragendorff,  on  Gunther's  authority  states  that  "16 
parts  of  oxygen  from  the  permanganate  oxidize  32*5  parts  of  gallo- 
tannic acid/^  Even  if  we  assumed  that  the  K2Mn208  parted  with  all 
its  oxygen  for  this  purpose  we  would  still  find  that  0'759  gram  only 
represents  0*62  gram  acid,  in  other  words,  that  Gunther's  value  is,  at 
Ihe  very  utmost,  only  five-eighths  that  of  Neubauer's.  Too  much 
stress  need  not  be  laid  on  these  differences,  however,  as  the  method  of 
procedure  adopted  may  sufficiently  account  for  the  discrepancies,  and 
admitting  that  the  actual  value  of  the  permanganate  has  not  yet  been 
ascertained,  there  can  nevertheless  be  no  doubt  that  as  a  comparative 
test  for  the  same  class  of  tannins  Lowenthal's  process  is  unexception- 
able. 
Organic  flatter  other  than  Tannic  Acid. — The  percentage  of  oxidizable 
matter  other  than  tannic  acid  can  of  course  only  be  taken  by  difference, 
a  method  of  which  the  disadvantages  are  jjeculiarly  evident  in  the  case 
of  tannin.  The  application  of  Mr.  Young's  cyanide  of  potassium  test,^ 
assuming  it  to  be  correct,  showed  that  all  the  samples  contained  traces 
of  gallic  acid,  the  coloration  being  much  more  distinct  in  some  than  in 
others.  When  this  reagent  is  added  to  a  solution  of  tannin,  there  is 
thrown  down  a  precipitate  which  is  usually  at  once  redissolved.  The 
bulk  of  this  precipitate  seems  to  be  in  direct  ratio  to  the  purity  of  the 
tannin,  as  Nos.  1,  2,  and  5  gave  very  heavy  precipitates,  whereas  those 
in  3  and  4  were  scarcely  noticeable.  This  precipitate  was  immediately 
redissolved  in  every  case  with  exception  of  No.  8,  but  after  a  lapse  of 
twenty-four  hours  it  was  found  that  all  the  solutions  contained  a  more 
or  less  thick  layer  of  another  precipitate,  which  consisted  of  an  amor- 
phous white  powder.  This  was  smallest  in  No.  7,  and  gradually  in- 
creased in  the  following  order  :  2,  9,  5,  4,  3,  1,  6  and  8.  No  attempt 
was  made  to  estimate  these  precipitates,  as  it  was  found  that  an  insoluble 
preci[)itate  can,  under  certain  conditions,  at  once  be  produced  by  this 
same  reagent,  so  that  it  is  possible  that  we  have  here  another  method 
for  the  gravimetric  estimation  of  tannic  acid,  as  well  as  for  the  separa- 
tion of  that  acid  from  gallic  acid  ;  but  further  experiments  are  required 
to  elucidate  these  points. 
^  "Chemical  News,"  vol.  xlviii,  p.  31. 
