The Ricca Chemical Nessler's reagent (mercuric - potassium iodide TS) is composed of 83.91% water, 10.44% potassium hydroxide, 4.00% potassium iodide and 1.65% mercuric chloride. It is used in detecting ammonia and ammonium compounds. It can be stored at a temperature of 15 to 30 degree C. USP 25 formulation