AmMi?ch,f894.rm  }  Action  of  Sulphuric  Acid  upon  Wood-Charcoal.  149 
upon  wood-charcoal  do  not  appear  to  have  been  hitherto  the  object 
of  any  study.1  . 
The  black,  viscid  and  non-crystalline  product  which  forms  the 
residue  of  this  operation  contains  several  interesting  substances, 
among  which  I  have  already  been  able  to  extract,  in  considerable 
quantities,  two  of  the  principal  benzene-carbonic  acids,  mellic  acid 
(pheno-hexamethyloic  acid)  and  benzene-pentacarbonic  acid  (pheno- 
pentamethyloic  acid).  Their  preparation  and  identification  form  the 
object  of  this  memoir. 
(1)  The  formation  of  these  acids  seems  to  me  principally  connected 
with  the  great  concentration  of  the  sulphuric  acid,  and  consequently 
with  the  temperature  of  the  reaction.  Hence  it  is  suitable  to  effect 
a  rapid  escape  of  the  gases  to  prevent,  as  far  as  possible,  the  reflux 
into  the  flask  of  the  water  produced  during  the  reaction. 
On  account  of  the  impurities  of  charcoal  (water,  ash,  etc.),  and 
to  avoid  the  destruction  of  the  products  first  formed,  by  a  large 
excess  of  sulphuric  acid,  I  used  in  my  first  experiments  only  1,400 
grms.  ordinary  acid  to  100  grms.  charcoal. 
A  thermometer  immersed  in  the  liquid  shows  that  the  reaction 
reaches  its  full  intensity  about  2800.  The  temperature  rises  to  3000 
only  at  the  end  of  the  operation.  The  flask  is  weighed  from  time 
to  time,  and  when  it  only  contains  from  90  to  IOO  grms.  of  matter, 
which  ensues  after  heating  for  about  six  hours,  the  process  is  ter- 
minated. It  is  difficult  to  exceed  these  limits  without  the  risk  of 
burning  the  product.  The  quantity  of  organic  matter  which  is 
carried  away  with  the  water  and  the  sulphuric  and  sulphurous  acids 
which  distil  over  is  unimportant.  When  cold  the  mass  is  taken  up 
with  water  which  becomes  charged  with  substances  of  a  deep  brown 
color,  and  leaves  a  black  insoluble  matter  undissolved,  in  which  no 
trace  of  the  original  charcoal  can  be  recognized.  This  product, 
which  is  soluble  in  alkalis  and  in  concentrated  sulphuric  acid,  will 
be  the  subject  of  future  study. 
The  sulphuric  acid  contained  in  the  liquid  is  eliminated  by  means 
of  barium  chloride,  avoiding  excess.  The  clear  decanted  liquid  is 
then  evaporated  to  dryness.  There  remains  a  brown  amorphous 
substance,  very  acid,  the  weight  of  which  is  about  one-fifth  of  the 
1  M.  Terreil  has  certainly  indicated  the  formation  of  a  small  quantity  of  an 
organic  acid  which  sublimes  during  the  preparation  of  sulphurous  acid  gas  by 
this  process  {Bull.  Soc.  Chimigue,  2d  Series,  Vol.  II,  p.  413). 
