ON  THE  PREPARATION  OF  GALLIC  ACID. 
33T 
as  possible,  stirred  up  with  water  into  a  thin  paste,  and  left 
standing  for  ten  days,  during  which  it  is  frequently  stirred,  and 
mixed  with  fresh  water  to  replace  that  which  is  absorbed.  To- 
wards the  end  so  much  water  is  added  that  after  it  has  quietly 
settled  there  may  be  three  inches  of  it  at  the  top  ;  the  supernatant 
fluid  is  decanted  and  preserved. 
The  paste  which  remains  is  put  into  a  wooden  vessel,  adapted 
for  extraction  by  displacement  by  water ;  everything  soluble  is 
then  extracted. 
The  whole  of  the  extracts  are  poured  together,  allowed  to 
settle  completely,  decanted  and  strained  into  large  stone-ware 
dishes,  which  are  placed  in  winter  in  the  neighborhood  of  a  warm 
chamber  stove,  but  in  summer  in  the  open  air,  lightly  covered. 
They  are  left  standing  until  all  the  gallic  acid  has  separated,  for 
which  purpose  from  three  to  four  months  are  required.  The 
mother-liquors  are  poured  off,  and  the  yellowish-red  gallic  acid, 
which  crystallizes  in  transparent  cubes,  is  washed  several  times 
with  distilled  water  and  dried.  From  the  above  quantity  2-t 
pounds  of  gallic  acid  are  usually  obtained. 
Before  this  acid  is  bleached,  it  must  first  of  all  be  freed  from 
the  flocculent  resinous  matters,  which  would  otherwise  stop  up 
the  filter.  The  acid  is  dissolved  in  boiling  distilled  water,  allowed 
to  settle  whilst  warm,  and  decanted  into  another  glask  flask  ; 
pure  animal  charcoal  is  then  added  to  it,  it  is  again  heated  and 
filtered  whilst  hot  through  white  filtering  paper.  The  filtrate 
is  heated  afresh,  poured  into  the  crystallizing  dish,  which  must 
previously  be  warmed,  and  left  to  stand  quietly  and  well  covered 
for  twenty-four  hours. 
The  crystalline  cake  when  taken  out  must  be  immediately 
wrapped  up  in  white  filtering  paper,  as  otherwise  the  moist  apices 
of  the  crystals  are  rendered  black  by  ferruginous  dust-particles 
floating  in  the  air  ;  subsequently  the  black  color  diffuses  itself  to 
the  bases  of  the  crystals,  which?  however,  produces  a  remarkably 
beautiful  appearance. 
Although  gallic  acid  is  but  little  employed  at  present,  except 
in  the  preparation  of  pyrogallic  acid  for  photography,  it  is  never- 
theless to  be  expected  that  it  will  one  day  find  frequent  employ- 
ment in  dyeing. — Chern.  Gaz.,  April  1,  1857,  from  jSitzungsber. 
der  Akad,  der  Wiss.  zu  Wien. 
22 
