What is nessler reagent?

Nessler's reagent is a chemical solution used to detect and quantify ammonia levels, particularly in water samples. It is composed of mercuric iodide dissolved in potassium iodide, resulting in a yellow-orange complex when ammonia is present. This color change allows for the estimation of ammonia concentration through spectrophotometric methods. The reagent is named after the German chemist Julius Nessler, who developed the test in the 19th century.