The Collaborative International Dictionary of English v.0.48:

ammoniac \am*mo"ni*ac\ ([a^]m*m[=o]"n[i^]*[a^]k), Ammoniacal
\Am`mo*ni"a*cal\ ([a^]m`m[-o]*n[imac]"[.a]*kal), a.
   Of, pertaining, or containing ammonia, or possessing its
   properties; as, an ammoniac salt; ammoniacal gas.
   [1913 Webster]

   Ammoniacal engine, an engine in which the vapor of ammonia
      is used as the motive force.

   Sal ammoniac [L. sal ammoniacus], the salt usually called
      chloride of ammonium, and formerly muriate of ammonia.
      [1913 Webster] Gum ammoniac

WordNet (r) 3.0 (2006):

ammoniacal
    adj 1: pertaining to or containing or similar to ammonia [syn:
           ammoniac, ammoniacal]