Oxamic  acid  is  certainly  a  very  remarkable  compound,  being
an  acid  amidide,  or  at  least  admitting  of  being  so  regarded,
C*  Os ,  N  Ha .  There  are  many  other  examples  of  acid  amidides,
and  we  shall  soon  come  to  one,  namely  euchronie  acid,  which
is  highly  analogous  to  oxamic  acid:  being  formed  by  the  action
of  heat  on  mellitate  of  ammonia,  along  with  a  neutral  amidide,


66  CAKBONIC   OXIDE    WITH   CHLORINE.
paramide,  similar  to  oxamide ;  and  as  oxamio  acid  yields  acid
oxalate,  so  euchronic  acid  yields  acid  mellitate  of  ammonia  when
long  boiled  with  water.  Cyanic  acid  may  also  be  considered  as,
in  some  sense,  an  acid  amidide  ;  for  C2  N  0,  H  0  =  Ca  62 ,  N  H  ;
and  C202,  N  H  +  2  H  0  =  N  Hs,  2  C  Oa;  or,  as  is  well  known,
cyanic  acid,  in  contact  with  water,  produces  bicarbonate  of
ammonia.
Oxamic  acid  may  further  be  viewed  as  a  coupled  oxalic  acid,
the  adjunct  in  which  is  oxamide ;  for  C*  Os  N  H2  is  equal  to
C2  Os  +  C2  02 ,  N  Ha .  Berzelius  adopts  this  view,  and  is,  generally
speaking,  favourable  to  the  idea  of  coupled  acids.
An  alcoholic  solution  of  oxalic  ether,  when  ammonia  is
cautiously  added  till  a  precipitate  of  oxamide  just  begins  to
appear,  yields  a  very  beautifully  crystallisable  compound,  long
known  as  oxamethan,  which  is  nothing  else  than  oxamate  of
oxide  of  ethyle  (see  salts  of  oxide  of  ethyle).  Its  composition
is  Cs  Hz  N  06=  (C*  Ho)  0  +  C*  Ha  N  Os:.  A  similar  com-
pound exists  with  oxide  of  methyle,  and  was  formerly  called
oxamethylan.
II.  CARBONIC  ACID.     C02=:22.
