774 
Determination  of  Tannin. 
f  Am.  Jour.  Pharm. 
\       Nov.,  1921. 
Their  second  objection  was  that  the  detannized  liquor  and  wash 
waters  gave  a  test  for  tannin  when  concentrated  to7  small  bulk.  In 
an  earlier  paper  7  we  showed  that  certain  nontannins  are  converted 
into  tannin  when  their  solutions  are  evaporated  and  that  this  trans- 
formation can  be  followed  by  means  of  the  new  method,  but  not  by 
the  A.  L.  C.  A.  method. 
Their  third  objection  was  that  the  degree  of  subdivision  of 
standard  hide  powder  is  not  uniform,  that  the  finer  portions  become 
more  heavily  tanned  but  are  more  easily  lost  during  the  washing 
operation  or  in  later  handling,  thus  tending  to  give  low  results  for 
tannin  as  a  result  of  making  the  analyses  on  the  portions  of  powder 
less  heavily  tanned.  In  the  revised  procedure  no  loss  of  powder  dur- 
ing the  washing  is  possible,  and  all  of  the  powder  is  weighed  after 
drying.  It  is  worthy  of  note,  however,  that  the  results  we  obtained 
by  the  original  and  revised  procedures  are  practically  identical. 
Schell 8  has  raised  an  objection  to  the  method  that  involves  the 
definition  of  tannin.  Following  the  work  of  Meunier,6  he  conceives 
the  existence  of  two  kinds  of  tannin  which  may  be  likened  to  quin- 
one  and  hydroquinol.  Meunier  showed  that  quinone  has  tanning 
properties,  while  hydroquinol  apparently  has  none.  Given  plenty  of 
access  to  the  air,  however,  solutions  of  hydroquinol  become  capable 
of  tanning  because  of  oxidation.  According  to'  Schell,  the  new 
method  determines  only  the  quinone-like  tannin  and  fails  to  include 
hydroquinol-like  bodies. 
But  hydroquinol  admittedly  has  no  tanning  properties.  It  seems 
to  us  that  the  method  is  all  the  more  accurate  for  not  including  as 
tannin,  those  bodies  which  are  not  tannin,  although  convertible  by 
oxidation  or  otherwise  into  tannin.  The  existence  of  these  sub- 
stances in  tanning  materials  has  been  recognized  and  discussed  in  our 
last  paper,  in  which  it  was  shown  that  the  tannin  content  of  a  tan 
liquor  is  increased  by  boiling.  There  is  good  reason  to  believe  that 
the  new  method  can  be  developed  to  determine  the  amount  of  sub- 
stances convertible  into  tannin  as  well  as  of  actual  tannin.  This 
might  be  done  simply  by  analyzing  the  liquor  both  before  and  after 
some  special  treatment,  such  as  oxidation,  that  will  convert  into 
tannin  all  substances  capable  of  such  conversion.  However,  the 
data  available  to  us  indicate  that  only  a  fraction  of  these  substances 
really  appear  as  tannin  in  the  finished  leather. 
7  Joum.  Ind.  and  Eng.  Chem.,  12  (1920),  1149. 
8  Le  Cuir,  9  (1920),  491. 
0  Chimie  &  Industrie  1  (1918),  71. 
