NEW  PROCESS  FOR  PREPARING  FORMIC  ACID.  559 
The  difference  between  the  results  obtained  and  the  calculated 
result  is  as  small  as  possible  ;  moreover  it  may  be  explained  by 
the  impurities  which  commercial  oxalic  acid  contains.* 
5.  The  following  is  the  detail  of  the  foregoing  preparation  : — 
kilogrammes. 
Oxalic  acid        .  1 
Glycerine     .....  1 
We  operated  as  has  just  been  stated,  and  we  obtained  : — 
grms. 
1st.  2  litres  of  distilled  liquid  containing  — formic  acid  146 
2nd.  5-5  litres  "       «  "  "  176 
322 
The  glycerine  still  retained  some  formic  acid.  We  added 
to  the  retort  a  second  kilogramme  of  oxalic  acid.  We  ob- 
tained : 
grms. 
3rd.  1  litre  of  distilled  liquid  containing  .-—formic  acid  70 
4th.  4  litres  «       «         "  «  250 
320 
The  glycerine  still  retained  some  formic  acid.  We  added  a 
third  kilogramme  of  oxalic  acid.     We  obtained  : — 
grms. 
5th.  3  litres  of  distilled  liquid  containing: — formic  acid  180 
6th.  4-5  litres       «       "  "  "  229 
409 
To  sum  up  : — 3  kilogrammes  of  oxalic  acid  furnished  1.051 
kilogrammes  of  formic  acid. 
This  preparation  is  so  regular  that  it  may  be  executed  with- 
out any  difficulty,  with  any  quantity,  whatever,  of  oxalic  acid. 
It  does  not  require,  moreover,  much  watching. 
6.  The  only  essential  point,  is  not  to  hurry  the  decomposition 
of  the  oxalic  acid  by  the  glycerine.  Indeed,  if  we  operate  too 
rapidly,  if  the  temperature  of  the  mixture  rises  too  high,  the  dis- 
engagement of  carbonic  acid  is  at  first  accelerated ;  but  as  soon 
as  it  has  ceased,  the  temperature  of  the  mass  very  soon  reaches 
from  190°  to  200°  C.  (374°  to  392°E.),  and  a  new  gaseous  dis- 
*  100  parts  of  the  acid  employed  left  a  fixed  residue  equal  to  2-07  parts. 
