AMseptURi,mT  }      Determining  Tanning  Materials.  427 
in  alcohol,  yielding  a  solution  of  a  very  fine  green  color. — Journ. 
Ohem.  Soe.,  1874,  July,  from  Chem.  Centr. 
COMPARATIVE   METHOD   OP  DETERMINING  TANNING  MA- 
TERIALS. 
By  E.  Schmidt. 
The  question  to  be  solved  is — Knowing  that  a  certain  weight,  P, 
of  pure  tannin  is  required  to  obtain  a  certain  result,  how  much  of 
another  tanning  body,  e.g.,  the  extract  of  a  wood,  is  required  to 
produce  the  same  result  ?  None  of  the  published  methods  for  the 
determination  of  tannin  is  sufficiently  precise,  easy,  and  rapid  for 
industrial  purposes.  The  author  proposes  a  modification  of  Pribram's 
method  with  sugar  of  ]ead. 
A.  Preparation  of  the  Test  Liquor. — 50  grms.  neutral  acetate  of 
lead  are  dissolved  in  400  grms.  of  alcohol  at  92  per  cent,  and  distilled 
water  is  added  so  as  to  make  up  1  litre. 
On  the  other  hand,  1  grm.  of  tannin  is  dissolved  in  40  grms.  of 
alcohol  at  the  same  strength,  and  the  solution  is  made  up  with  water 
to  the  bulk  of  100  c.c. 
This  being  done,  10  c.c.  of  the  tannin  solution  are  taken,  20  c.c.  of 
water  are  added,  and  heated  to  60°.  The  lead  liquor  is  then  run  into 
the  hot  solution  with  a  burette  graduated  to  tenths  of  a  c.c,  so  long 
as  a  precipitate  is  formed.  At  this  temperature,  and  with  these 
alcoholised  liquids,  the  precipitate  forms  and  settles  rapidly.  Iodide 
of  Potassium  may  be  used  as  an  indicator  to  show  excess  of  lead, 
proceeding  in  the  same  manner  as  is  done  with  ferrocyanide  in 
titrating  phosphates  with  nitrate  of  uranium.  If  we  suppose  that  to 
precipitate  10  c.c.  of  the  tannin  solution  28  degrees  of  the  lead 
liquor  have  been  required,  then  2*8  c.c.  of  the  latter  =  0*10  grm.  of 
tannin. 
B.  Preparation  of  the  Sample  to  be  Tested. — Suppose  that  chestnut- 
bark  is  to  be  examined.  It  is  coarsely  powdered,  and  10  grms.  are 
mixed  with  an  equal  volume  of  washed  sand,  and  exhausted  with 
water  at  50°  or  60°  C.  The  filtered  liquid  is  evaporated  to  dryness 
in  the  water  bath  in  a  tared  porcelain  capsule.  After  evaporation 
the  capsule  is  weighed,  which  shows  the  yield  of  the  bark  in  aqueous 
extract.  This  extract  is  taken  up  in  40  grms.  of  alcohol  at  92°,  and 
water  is  added  to  make  up  100  c.c.  This  liquid  is  filtered  if  needful. 
In  this  manner  the  resinous,  albumenoid,  pectic,  and  gummy  matters 
are  got  rid  off. 
