154 
ON  DECOLORIZED  CHARCOALS. 
Aluminized  charcoal    ....    0.32  per  cent. 
Ivory  black  7.58   "  « 
Washed  ivory  black  ....  3.40  "  " 
It  is  evident,  therefore,  that  aluminized  charcoal  is  especially 
well  adapted  for  the  decolorizing  crude  tartaric  and  citric  acids, 
as  it  introduces  such  a  very  small  quantity  of  inorganic  matter 
into  the  mother  liquors.  And,  doubtless,  it  is  owing  to  their 
employing  washed  animal  charcoal,  and  sometimes  even  bone- 
black,  that  the  tartaric  acid  manufacturers  find  their  mother 
liquors  so  intractable  from  the  large  quantity  of  inorganic  salts 
they  contain. 
An  artificial  bone-black  may  likewise  be  produced  by  impreg- 
nating powdered  wood  charcoal  with  basic  phosphate  of  lime, 
dissolved  in  an  excess  of  hydrochloric  acid,  so  as  to  impregnate 
the  charcoal  with  seven  and  a  half  per  cent,  of  bone  earth 
instead  of  eighty  per  cent,  as  in  ordinary  animal  char- 
coal. It  is  manufactured  by  a  precisely  similar  process 
to  that  already  described,  the  acid  and  water  being  driven  off  by 
ignition  in  close  vessels.  It  decolorizes  very  well,  but  can  only 
be  employed  in  neutral  solutions.  It  is  evident  that  both  alumi- 
nized and  artificial  phosphate  of  lime  charcoals,  just  described, 
are  merely  mordaunted  charcoals,  which  decolorize  solely  by 
the  bases  or  mordaunts  which  they  contain. 
Besides  the  aluminized  charcoal,  I  have  also  prepared  an  addi- 
tional substitute  for  purified  animal  charcoal,  by  means  of  hydrate 
of  lime  and  a  mixture  of  coal-tar  pitch  ^and  coal-tar.  The  fol- 
lowing is  the  process  employed  for  this  purpose.  I  take  one 
pound  by  weight  of  coal-tar  pitch,  and  gently  heat  it  in  an  iron 
pot  till  it  melts.  I  then  add  two  pounds  of  fluid  coal-tar,  and 
mix  the  liquids.  Seven  pounds  of  hydrate  of  lime  in  very  fine 
powder  are  next  gradually  stirred  into  the  mass,  which  soon  be- 
comes thick  and  pasty.  It  is  then  gently  roasted,  the  stirring 
being  continued  during  the  whole  time  till  it  is  reduced  to  the 
state  of  a  very  fine  powder.  The  great  object  of  the  stirring 
and  roasting  being  to  incorporate  the  lime  with  the  vegetable 
matter  as  intimately  as  possible.  The  dark  brown  powder  ob- 
tained in  this  way  is  then  introduced  into  ordinary  covered  crucibles 
or  iron  retorts,  and  is  ignited,  until  the  whole  of  the  vegetable 
matter  is  entirely  carbonized.    The  mixture  when  cold  is  then 
