What is "mercurammonium"

Mercurammonium \Mer`cur*am*mo"ni*um\, n. [Mercuric + ammonium.] (Chem.) A radical regarded as derived from ammonium by the substitution of mercury for a portion of the hydrogen.

n. (context chemistry English) A radical regarded as derived from ammonium by the substitution of mercury for a portion of the hydrogen.