Am  jour  Pharm.)  Determination  of  Tannin.  77$ 
Imov.,  1921.       $  3  /  /  u 
Schell  is  right  in  insisting  that  these  nontannins  have  a  value 
which  should  be  recognized  in  judging  the  value  of  an  extract,  but 
the  values  should  be  recognized  also  of  those  substances  which  aid 
in  the  diffusion  of  the  tannins  into  the  hides  and  the  sugars  which 
form  the  necessary  acids.  Two  extracts  of  apparently  the  same  tan- 
nin content  may  have  very  different  properties.  The  tannin  content 
alone  is  no  sure  guide  to  the  value  of  an  extract;  much  importance 
is  attached  to  the  reputation  of  the  extract  manufacturer.  It  is  not 
improbable  that  it  will  eventually  be  found  preferable  to  sell  extracts 
on  a  basis  of  total  solid  matter,  leaving  the  extract  men  to  compete 
with  each  other  in  establishing  a  reputation  for  producing  extracts 
of  high  quality  and  constant  composition. 
In  speaking  of  hydroquinol-like  bodies,  Schell  implies.,  the  sug- 
gestion that  what  the  official  method  really  determines  is  the  sum  of 
these  and  the  true  tannins,  but  this  is  not  so.  Gallic  acid  belongs  to 
the  class  of  nontannins  capable  of  conversion  into  tannin,  but  when 
added  to  a  tan  liquor  only  a  variable  fraction  of  it  appears  as  tan- 
nin by  the  A".  L.  C.  A.  method,  which  makes  the  method  quite  un- 
reliable and  often  very  misleading.  This  is  strikingly  shown  with 
gambler  extract.  The  method  calls  for  12.5  g.  of  dry  hide  powder 
to  detannize  200  cc.  of  tan  liquor,  which  amount  was  assumed  to 
be  correct  because  the  nontannin  filtrate'  gave  no  test  with  the 
gelatin-salt  reagent.  Using  this  method  on  a  gambier  extract  we 
found  26  per  cent,  tannin.  But  we  then  reduced  the  amount  of  hide 
powder  to  1.5  g. ;  the  nontannin  filtrate  gave  a  negative  test  with 
the  gelatin-salt  reagent,  but  the  per  cent,  of  tannin  found  was  only 
13.  The  extract  is  listed  as  containing  26  per  cent,  tannin  simply 
because  a  group  of  men  were  more  favorably  disposed  to  make 
12.5  g.  of  hide  powder  official  than  some  other  amount.  This  is 
treated  more  fully  in  our  first  paper. 
The  A.  L.  C.  A.  method  is  based  upon  a  principle  often  em- 
ployed in  absorption  experiments.  It  falsely  assumes  that  the  de- 
crease in  concentration  of  a  tan  liquor  upon  shaking  with  hide 
powder  is  a  measure  of  the  tannin  content  and  that  the  solution 
absorbed  by  the  substance  of  the  hide  is  of  the  same  composition  as 
the  remaining  liquor.  Thomas  and  Kelly  10  have  shown  to  what 
ridiculous  conclusions  this  can  lead.  In  studying  the  effect  of  con- 
centration of  chrome  liquor  upon  the  adsorption  of  its  constituents 
Journ.  Ind.  and  Eng.  Chem.,  13  (1921),  31. 
