Am.  Jour.  Pharm. 
Nov.,  1921. 
Determination  of  Tannin. 
773 
COMPARATIVE  ANALYSES. 
The  analyses  of  six  typical  extracts  given  in  Table  I  show  that 
there  is  practically  no  difference  in  results  obtained  by  the  original 
and  revised  procedures  of  the  new  method.  Analyses  by  the  official 
method  of  the  American  Leather  Chemists  Association,  widely  used 
in  this  country,  are  given  for  comparison. 
Table  I — Comparative  Analysis  of  Extracts  by  A.  L.  C.  A.  Method  and 
the  Original  and  Revised  Procedures  of  the  New  Method. 
,  A.  L..  C.  A.  Method  v      New  Method 
,  Tannin  , 
Original  Re- 
Procedure  vised 
Tannin      ( By  Proced- 
Non-      ( By  Dif-   Differ-  ure 
Extract  Water  Insoluble  tannin  ference)  ence)  (Direct) 
Gambier    48.84  7.58  1578  27.80  7.32  7-44 
Hemlock"   5176  7-32  I5-04  25.88  16.38  "16.39 
Larch    51.63  541  20.00  22.96  12.70  12.82 
Oak    53.51  2.55  18,35  25.59  11.63  H-42 
Quebracho    19.41  9-5o  6.86  64.23  44.33  44.03 
Sumac    49-44  2.86  22.56  25.14  i3-io  13,04 
DISCUSSION. 
A  common  objection  to  the  new  method  has  been  that  it  ap- 
peared inconceivable  that  leather  chemists  everywhere  should  have 
been  so  misguided  as  to  accept  as  official  a  method  liable  to  a  200 
per  cent,  error.  The  fallacy  in  the  argument  put  forward  lies  in  its 
assumption  that  leather  chemists  everywhere  have  found  the  official 
methods  to  be  borne  out  quantitatively  in  practice.  When  data  were 
called  for  to  prove  this  assumption,  apparently  none  were  available. 
On  the  contrary,  we  have  been  able  to  secure  data  from  both  upper 
and  sole  leather  yards  showing  that  the  amount  of  tannin  appearing 
in  the  finished  leather  is  very  much  less  than  entered  the  yards  ac- 
cording to  the  A.  L.  C.  A.  method;  and  that  the  apparent  loss  of 
tannin  corresponds  closely  to  the  difference  in  tannin  content  of  the 
extracts  as  determined  by  the  new  and  official  methods. 
After  some  experimenting  with  the  new  method,  Schultz  and 
Blackadder  0  raised  a  number  of  objections  to  it.  Their  first  was 
that  it  was  difficult  to  obtain  concordant  results,  which  they  explained 
as  being  due  in  part  to  the  fact  that  the  tannin  was  determined  by 
difference  and  was  subject  to  the  errors  involved  in  determining  the 
water,  ash,  fat,  and  hide  substance  in  the  tanned  powder.  This  ap- 
pears to  us  rather  a  matter  of  skill  in  manipulation,  but  in  any  event 
the  cause  has  vanished  with  the  revision  of  the  procedure. 
67.  Am.  Leather  Chem.  Assoc.,  15  (1920),  654. 
