630  Extraction  of  Tanning  Materials.  {^e'cimbej?™' 
It  was  found  that  this  was  practically  sufficient  water  to  extract 
all  the  available  tannin  and  color,  very  small  additional  quantities 
being  obtained  when,  for  experiment,  a  second  litre  was  percolated 
at  the  same  temperature. 
The  solution  was  now  allowed  to  cool,  filtered,  analyzed,  and 
measured  in  a  half-inch  cell  by  Lovibond's  tintometer,  and  the 
results  calculated  for  a  half  per  cent,  solution  of  tanning  matter. 
The  total  colors  are  expressed  numerically  in  terms  of  standard 
glasses.  The  analyses  for  tannin  were  made  by  the  hide-powder 
filter  method. 
The  method  of  extraction  wyas  in  each  case  identical,  so  that  the 
results  obtained  may  be  compared  with  one  another,  while,  for  the 
sake  of  accuracy,  it  was  found  necessary  to  make  at  least  three 
extractions  at  each  temperature,  stating  our  results  as  the  mean  of 
the  three  analyses.  Our  first  experiments  were  made  with  a  some- 
what poor  sample  of  Belgian  oak  bark,  40  grammes  of  the  ground 
material  being  extracted  as  described  above,  at  each  of  the  ten 
temperatures  given  in  the  subjoined  table.  Besides  this,  the  follow- 
ing materials  were  estimated  by  working  on  decoctions  made  from 
12  grammes — myrabolans,  Smyrna  valonia  (beard),  and  Greek 
valonia  (cup  and  beard);  while  from  Natal  mimosa  (black  wattle), 
sumach,  quebracho  wood  and  mangrove  bark  (species  uncertain,  but 
thought  not  to  be  Rhizophora  mangle)  decoctions  were  prepared 
representing  20  grammes  of  the  material  in  the  litre. 
The  results  are  tabulated  in  percentage  of  the  highest  amount  of 
tanning  and  coloring  matter  obtained. 
Scanning  the  table,  it  will  be  seen  that  all  the  available  tannin 
cannot  be  extracted  by  cold  water.  In  the  case  of  oak  bark  a 
second  litre  was  extracted  at  150  and  also  at  500,  but  they  only 
resulted  in  getting  less  than  another  0-25  per  cent,  out  of  the  mate- 
rial, showing  that  the  extraction  had  been  thorough.  It  will  be 
noticed  that  38-1  per  cent.,  or  more  than  one-third  more  tannin,  is 
extracted  at  8o°-90°  than  in  the  cold,  but  that  the  proportion  of 
color  to  tannin  has  also  increased  35-8  per  cent.  It  may,  therefore, 
be  necessary,  where  color  is  a  primary  object,  to  continue  to  use 
cold  extraction  for  oak  bark,  but  it  is  well  to  realize  that  one-third 
of  the  tannin  is  then  wasted. 
With  myrabolans  the  best  results  as  regards  tanning  matter  are 
obtained  at  from  90°-iOOc,  whereas  the  maximum  color  is  got  by 
actual  boiling.    It  is  important  to  notice  that  the  color  is  very  little 
