The  last  two  compounds  are  isomeric,  the  only  difference  being
that  in  the  first  the  radical  ethyl  replaces  an  atom  of  hydrogen
of  the  amidogen,  while  in  the  second  it  replaces  the  alcoholic
hydrogen  of  the  lactic  acid.  That  there  is  a  real  difference
between  the  two  is  proved  by  the  following  reactions  :  —


ff)  Potassic  Ethyl-lactate.  ff

1  The  acid  has  not  been  isolated,  but  the  ammonic  salt  is  well  known.
§171.]  NITROGEN.  245


C2#,     N+  K-O-H  =  K,H=OfC3HtO  +         H>  N.  [165]

H  )  Potassic  Lactate.  ff  )

Ethylamine.
These  complex  amide  compounds  may  also  be  referred  to  a
system  of  mixed  types.  (Compare  30,  Part  I.)

169.  Imides.  —  If  from  an  acid  monamide  we  eliminate  a
molecule  of  water,  or  if  from  a  neutral  diamide  we  eliminate  a
molecule  of  ammonia  gas,  we  obtain  as  the  product  a  compound
which  may  be  regarded  as  formed  by  the  union  of  the  acid  rad-
ical with  the  compound  radical  HN.  Thus,


HN-  C3ff4  0.     [166]

Lact-imide.
HN-  04ff4  02.         [1  67]

Succin-amide.  Succin-imide.
Such  compounds  are  called  Imides,  and  they  always  act  as
monobasic  acids.
170.  Nitriles.  —  If  from  a  neutral  monamide  we  eliminate
a  molecule  of  water,  the  residue,  which  may  be  regarded  as  a
compound  of  nitrogen  with  a  trivalent  radical,  has  been  called
a  Nitrile.  Thus,

=  H,0  +  CifffN.  [168]

Acetonitrile.
=  HZ0  +  CA-=N.  [169]

Valeramide.  Valeronitrile.
These  compounds  are  weak  bases,  like  ammonia,  combining  di-
rectly with  acids  to  form  salts,  and  they  may  be  regarded  as  a
part  of  the  class  of  amines.
