NH2HgCl

Precipitate Pre*cip"i*tate, n. [NL. praecipitatum: cf. F. pr['e]cipit['e].] (Chem.) An insoluble substance separated from a solution in a concrete state by the action of some reagent added to the solution, or of some force, such as heat or cold. The precipitate may fall to the bottom (whence the name), may be diffused through the solution, or may float at or near the surface. [1913 Webster]

2. atmospheric moisture condensed as rain or snow, etc.; same as {precipitation[5]}. [PJC]

{Red precipitate} (Old. Chem), mercuric oxide ({HgO}) a heavy red crystalline powder obtained by heating mercuric nitrate, or by heating mercury in the air. Prepared in the latter manner, it was the {precipitate per se} of the alchemists.

{White precipitate} (Old Chem.) (a) A heavy white amorphous powder ({NH2.HgCl}) obtained by adding ammonia to a solution of mercuric chloride or corrosive sublimate; -- formerly called also {infusible white precipitate}, and now {amido-mercuric chloride}. (b) A white crystalline substance obtained by adding a solution of corrosive sublimate to a solution of sal ammoniac (ammonium chloride); -- formerly called also {fusible white precipitate}. [1913 Webster]