is a reagent
named after Julius Neßler
and is used to detect small amounts of ammonia
. It is a 0.09 mol/L solution of potassium tetraiodomercurate(II) (K2
]) in 2.5 mol/L potassium hydroxide. A yellow coloration indicates the presence of ammonia: at higher concentrations, a brown precipitate
may form. The sensitivity as a spot test
is about 0.3 μg NH3
in 2 μL.
- NH4+ + 2[HgI4]2− + 4OH− → HgO·Hg(NH2)I + 7I− + 3H2O
It is toxic if swallowed, inhaled or absorbed through the skin. It presents a neurological hazard and may act as a carcinogen
and be a reproductive hazard. It is corrosive
and causes burns.
Nessler's solution, mercuric potassium iodide, mercury(II) potassium iodide, Channing's solution, potassium mercuric iodide, potassium tetraiodomercurate(II)
Nessler's reagent is generally prepared from potassium iodide
and mercury(II) iodide
. Hot concentrated solution of mercury(II) chloride is added to concentrated solution of potassium iodide, until the precipitate of mercury(II) iodide
stops dissolving. The liquid is filtered, and potassium hydroxide
and a further bit of mercury(II) chloride solution are added. The resulting solution is then cooled and diluted to required concentration.