Historical reference: Do not rely on this information. It is very old. About this collection
Nessler's Reagent is prepared by dissolving mercuric iodide in a solution of potassium iodide, with the addition of caustic potash. An almost colourless liquid is so obtained which gives a yellow coloration, with faintest trace of ammonia or an ammoniacal compound. It is employed on this account for the estimation of ammonia in potable waters.