Chloropicrin Chloropicrin , also known as PS , is a chemical compound currently used as a broad - spectrum antimicrobial , fungicide , herbicide , insecticide , and nematicide . Its chemical structural formula is ClCNO . Discovery . Chloropicrin was first discovered in 1848 by a Scottish chemist John Stenhouse . He prepared it by the reaction of a chlorinating agent with picric acid : Because of the precursor he used , Stenhouse named the compound chloropicrin , although the two compounds are structurally dissimilar . Properties . Chloropicrin ’ s chemical formula is CClNO and its molecular weight is 164 . 38 grams / mole . Pure chloropicrin is a colorless liquid , with a boiling point of 112 °C . Chloropicrin is highly soluble in water with solubility of 2 , 000 milligrams per liter at 25 °C . It is volatile , with a vapor pressure of 23 . 2 millimeters of mercury ( mm Hg ) at 25 °C ; the corresponding Henry ’ s Law Constant is 0 . 00251 atmosphere - cubic meter per mole . The octanol - water partition coefficient ( K ) of chloropicrin is estimated to be 269 . Its soil adsorption coefficient ( K ; normalized to soil organic matter content ) is 25 cm / g . Use . In agriculture , chloropicrin is injected into soil prior to planting a crop in order to clean the soil of a broad spectrum of fungi , microbes , insects , and other harmful pests . It is commonly used as a stand alone treatment or in combination / co - formulation with methyl bromide and 1 , 3 - Dichloropropene . Safety . At the national level , chloropicrin is regulated by the United States Environmental Protection Agency as a restricted use pesticide . The EPA has approved chloropicrin as safe for use by farmers nationwide . The distribution and use of chloropicrin is available only to licensed professionals and specially certified growers who are trained in its proper and safe use . In the US , occupational exposure limits have been set at 0 . 1 ppm over an eight - hour time - weighted average . Agriculture . In 2008 the US EPA re - approved chloropicrin as safe for use in agricultural settings , stating that treatments " can provide benefits to both food consumers and growers . For consumers , it means more fresh fruits and vegetables can be cheaply produced domestically year - round because several severe pest problems can be efficiently controlled . " To ensure chloropicrin is used safely , the EPA requires a strict set of protections for handlers , workers , and persons living and working in and around farmland during treatments . EPA protections were increased in both 2011 and 2012 , reducing fumigant exposures and significantly improving safety . Protections include the training of certified applicators supervising pesticide application , the use of buffer zones , posting before and during pesticide application , fumigant management plans , and compliance assistance and assurance measures . High Concentrations . Unlike its use in agriculture , in unregulated settings chloropicrin can be harmful to humans . Chloropicrin can be absorbed systemically through inhalation , ingestion , and the skin . At high concentrations it is severely irritating to the lungs , eyes , and skin . In World War I German forces used concentrated chloropicrin against Allied forces as a tear gas . While not as lethal as other chemical weapons , it caused vomiting and forced Allied soldiers to remove their masks to vomit , exposing them to other , more toxic chemical gases used as weapons during the war . Preparation . Chloropicrin is manufactured by the reaction of nitromethane with sodium hypochlorite :