558  NEW  PROCESS  FOR  PREPARING  FORMIC  ACID. 
according  to  Gay-Lussac's  experiments  ;  but  the  quantity  of  for- 
mic acid  thus  produced  is  always  very  small. 
Now,  I  have  observed  that  we  may  combine  with  the  elements 
of  water,  all  the  oxide  of  carbon  furnished  by  oxalic  acid, 
and  simply  transform  this  substance  into  carbonic  acid  and  for- 
mic acid. 
C4IP08=C204+04. 
It  is  sufficient  to  introduce  another  body  operating  by  action 
of  contact — glycerine.  I  have  already  noticed  this  fact,  and 
I  shall  now  deduce  from  it  a  new  process  for  preparing  formic 
acid. 
4,  I  operate  as  follows. 
Into  a  retort,  of  the  capacity  of  half  a  gallon,  I  introduce  1 
kilogramme  (about  two  pounds)  of  oxalic  acid,  I  kilogramme  of 
syrupy  glycerine,  and  from  100  to  200  grammes  of  water.  I 
adapt  a  receiver  and  I  heat  the  retort  very  gently  ;  the  tempera- 
ture should  scarcely  exceed  100°  C.  (212°  F.)  A  brisk  effer- 
vescence is  soon  set  up,  and  pure  carbonic  acid  is  disengaged. 
After  about  12  or  15  hours,  all  the  oxalic  acid  is  decomposed  ; 
half  of  its  carbon  and  oxygen  are  disengaged,  under  the  form  of 
carbonic  acid  gas  ;  a  small  quantity  .of  water,  charged  with  formic 
acid  distils  over,  and  there  remains  in  the  retort  the  glycerine 
holding  in  solution  almost  all  the  formic  acid.  This  acid  may 
be  extracted  directly,  by  means  of  carbonate  of  lead ;  but  the  fol- 
lowing method  is  far  preferable: — 
Pour  into  the  retort  a  pint  of  water  and  distil.  Replace  the  water 
which  distils  over,  and  continue  the  operation  until  six  or  seven 
quarts  of  distilled  liquor  has  been  collected.  At  this  moment 
almost  all  the  formic  acid  is  volatilised  with  the  water,  and  the 
glycerine  alone  remains  in  the  retort.  It  may  be  used  for  de- 
composing asecond  kilogramme  of  oxalic  acid,  a  third,  and  so  on. 
3  kilogrammes  of  ammoniacal  oxalic  acid,  C4H208-f  4HO, 
yielded,  by  this  process,  1«05  kilogrammes  of  formic  acid, 
C2H204. 
According  to  the  formula — 
C4H208,  4HO=C204+4HO+C2H204, 
3  kilogrammes  of  pure  oxalic  acid  should  furnish  1*09  kilo- 
grammes of  formic  acid. 
