text: Hydrogen cyanide, discovered in the late 18th century, was used in the 1880s for the fumigation of citrus trees in California. Its use spread to other countries for the fumigation of silos, goods wagons, ships, and mills. Its light weight and rapid dispersal meant its application had to take place under tents or in enclosed areas. Research by Fritz Haber of the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry led to the founding in 1919 of Deutsche Gesellschaft für Schädlingsbekämpfung mbH (Degesch), a state-controlled consortium formed to investigate military use of the chemical. Chemists at Degesch added a cautionary eye irritant to a less volatile cyanide compound which reacted with water in the presence of heat to become hydrogen cyanide. The new product was marketed as the pesticide Zyklon (cyclone). As a similar formula had been used as a weapon by the Germans during World War I, Zyklon was soon banned.
  Deutsche Gold- und Silber-Scheideanstalt (German Gold and Silver Refinery; Degussa) became sole owners of Degesch in 1922. There, beginning in 1922, , Bruno Tesch, and others worked on packaging hydrogen cyanide in sealed canisters along with a cautionary eye irritant and adsorbent stabilizers such as diatomaceous earth. The new product was also labelled as Zyklon, but it became known as Zyklon B to distinguish it from the earlier version. Heerdt was named the inventor of Zyklon B in the Degesch patent application (number DE 438818) dated 20 June 1922. The Deutsches Patent- und Markenamt awarded the patent on 27 December 1926. Beginning in the 1920s, Zyklon B was used at U.S. Customs facilities along the Mexican border to fumigate the clothing of border crossers.