150    Action  of  Sulphuric  Acid  upon  Wood-Charcoal.  {^mS'.S? m' 
charcoal  originally  used.  This  acid  mixture  is  taken  up  in  water 
and  saturated  with  ammonia,  which  precipitates  the  oxides  of  iron 
and  manganese,  the  lime,  etc.,  in  the  state  of  basic  salts.  The  fil- 
trate, on  strong  concentration,  deposits  crystals  of  ammonium  mel- 
late,  which  are  obtained  perfectly  pure  on  three  or  four  recrystalli- 
zations  from  I  y2  parts  of  water.  The  yield  is  about  4  per  cent,  of 
the  weight  of  charcoal  originally  taken. 
This  ammonium  mellate  is  characterized  by  its  crystalline  form, 
which,  according  to  WyroubofT,  is  that  of  an  orthorhombic  prism, 
with  mm.  ==  1140  25',  a'  p  =  15  1°,  ef  p  ==■  160-5°  similar  to  that 
described  by  G.  Rose. 
The  determination  of  the  ammonia,  calculated  as  NH4,  gives 
17-39  Per  cent-  Theory  for  C6(C02)6(NH4)69H20,  requires  17-82 
per  cent. 
With  barium  chloride  it  gives  in  a  dilute  solution  a  white  amor- 
phous precipitate,  which  is  quickly  transformed  into  a  mass  of  fine 
characteristic  needles  which  after  desiccation  over  sulphuric  acid  cor- 
respond to  the  formula  C12012Ba36H20. 
I  have  found  that  this  ammonium  mellate  is  transformed  at 
160°  into  euchroic  acid,  which,  on  a  zinc  plate,  gives  the  fine  char- 
acteristic blue  color,  turning  crimson,  on  treatment  with  alkalis 
(Woehler). 
These  facts  prove  that  one  of  the  acids  produced  in  the  oxidation 
of  charcoal  by  means  of  sulphuric  acid  is  mellic  acid. 
(2)  I  have  not  found  a  simple  and  rapid  method  for  purifying  the 
salts  which  remain  in  the  brown  aqueous  solution  separated  from 
the  crude  mellate.  The  process  which  I  have  adopted  consists  in 
transforming  these  ammonium  salts  into  barium  salts,  in  dissolving 
the  latter  into  hydrochloric  acid,  then  in  fractionating  the  baryta. 
The  brown  substances  which  contaminate  these  products  are  thus 
entirely  removed. 
To  this  end  the  solution  of  the  ammonium  salts  is  evaporated  to 
dryness  in  presence  of  a  slight  excess  of  barium  hydroxide.  The 
basic  salts  obtained  are  then  dissolved  in  the  cold  in  HQ  diluted 
with  ten  parts  of  water.  To  this  liquid  is  added  a  hot  concentrated 
solution  of  baryta  until  the  formation  of  a  permanent  precipitate. 
After  this  the  precipitation  is  fractionated  by  adding  to  the  liquid 
a  solution  of  30  grms.  barium  hydroxide  per  kilo  of  charcoal  used. 
The  first  precipitate,  separated  the  next  day  from  the  supernatant 
