Mercuric potassium iodide (also known as potassium tetraiodo mercurate) is available as odorless yellow crystals. It is soluble in water and is highly toxic. It is used as mayers reagent to detect the presence of alkaloids in plant extracts. The formation of a yellow colored precipitate indicates the presence of alkaloids. An alkalic solution of mercury potassium iodide (called Nessler's reagent) is used in the detection of ammonia. The pale solution becomes yellowish in the presence of ammonia. At higher concentrations of ammonia, a dirty brown precipitate is obtained. Quantity Provided: 25 gm/Bottle Molecular Weight: 786.40 Molecular Formula: HgI4K2 CAS No: 7783-33-7