Trichloramine (NCl 3 ), also known as nitrogen chloride or trichloride, is a toxic, explosive, nasty-smelling oily liquid with a boiling point of 71 ºC. It is unstable in air and rapidly decomposes in water.

The earliest reported synthesis of NCl 3 (Pierre Louis Dulong, 1813) was the reaction of molecular chlorine or sodium hypochlorite with ammonium salts. It can also be prepared from ammonia and chlorine and by the electrolysis of aqueous ammonium chloride.

NCl 3 ’s primary commercial use was bleaching flour, but this use was banned in the United States in the late 1940s. It had been discovered in 1947 that eating bread made from NCl 3 -contaminated flour caused severe neurological disorders in humans and animals.

NCl 3 is most famous (or infamous) for being the product of the reaction of chlorine in swimming pools with urea in urine or sweat. It is much more responsible for pools’ “chlorine smell” than chlorine itself.

In an article on disinfection byproducts in swimming pools related to the Rio de Janeiro Olympic Games, Celia Henry Arnaud discusses NCl 3 in connection with professional swimmers’ habit of intentionally peeing in pools. NCl 3 can not only cause respiratory problems in swimmers, but it also can corrode metals in and around pools.

Mr. Phelps: Your mission, should you choose to accept it, is to discontinue this practice and urge other Olympians to do the same.