Mercury(II) nitrate

Mercury(II) nitrate is an inorganic compound with the chemical formula Hg(NO3)2. It is the mercury(II) salt of nitric acid HNO3. It contains mercury(II) cations Hg(2+) and nitrate anions NO3−, and water of crystallization H2O in the case of a hydrous salt. Mercury(II) nitrate forms hydrates Hg(NO3)2*xH2O. Anhydrous and hydrous salts are colorless or white soluble crystalline solids that are occasionally used as a reagents. Mercury(II) nitrate is made by treating mercury with hot concentrated nitric acid. Neither anhydrous nor monohydrate has been confirmed by X-ray crystallography. The anhydrous material is more widely used.

Uses
Mercury(II) nitrate is used as an oxidizing agent in organic synthesis, as a nitrification agent, as an analytical reagent in laboratories, in the manufacture of felt, and in the manufacture of mercury fulminate. An alternative qualitative Zeisel test can be done with the use of mercury(II) nitrate instead of silver nitrate, leading to the formation of scarlet red mercury(II) iodide.

Health information
Mercury compounds are highly toxic. The use of this compound by hatters and the subsequent mercury poisoning of said hatters is a common theory of where the phrase "mad as a hatter" came from.