NH4.O.CN

from The Collaborative International Dictionary of English v.0.48

Cyanate \Cy"a*nate\ (s?"?-n?t), n. [Cf. F. cuanate. See
   {Cyanic}.] (Chem.)
   A salt of cyanic acid.
   [1913 Webster]

   {Ammonium cyanate} (Chem.), a remarkable white crystalline
      substance, {NH4.O.CN}, which passes, on standing, to the
      organic compound, urea, {CO.(NH2)2}.
      [1913 Webster]