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Zyklon B (German pronunciation: [tsykloːn ˈbeː]; also spelled Cyclon B or Cyclone B) was the trade name of a cyanide-based pesticide invented in the early 1920s, and manufactured by German chemical conglomerate IG Farben. Zyklon B consisted of hydrogen cyanide (prussic acid), a stabilizer, a warning odorant (ethyl bromoacetate), and one of several adsorbents. Zyklon A was a previously produced liquid pesticide, which released hydrogen cyanide in a chemical reaction with water. After the invention of Zyklon B, Zyklon A production ceased.
The product is infamous for its use by Nazi Germany to murder an estimated 1.2 million people, including approximately 960,000 Jews, in gas chambers installed in several extermination camps during the Holocaust. One of the co-inventors of Zyklon B, chemist and businessman Bruno Tesch, was executed by the British in 1946 for his role in this operation.
Hydrogen cyanide is a poisonous gas that interferes with cellular respiration. Cyanide prevents the cell from producing ATP by binding to one of the proteins involved in the electron transport chain. This protein, cytochrome c oxidase, contains several subunits and has ligands containing iron groups. The cyanide component of Zyklon B can bind at one of these iron groups, heme a3, forming a more stabilized compound through metal-to-ligand pi bonding. As a result of this new iron-cyanide complex, the electrons which would situate themselves on the heme a3 group can no longer do so. Instead, because of the new bond formed between the iron and the cyanide, these electrons destabilize the compound (based on molecular orbital theory); thus, the heme group no longer accepts them. Consequently, electron transport is halted, and the cell can no longer produce the energy needed to synthesize ATP.
Even before any of the modern methods of mass-producing prussic acid were developed, suggestions were made that it could be used systematically to kill humans. A Berlin pharmacist is credited with the proposal to use rags with prussic acid placed on bayonets to combat the advancing Napoleonic army in 1813. During World War I, the French army reportedly – according to Fritz Haber, the German chemist who helped develop poisonous gas for German Army use (see below) – used 2000 tons of prussic acid as a poison gas agent in artillery ammunition.
Hydrocyanic acid was widely used for the fumigation of valuable tree crops. It was initially applied to citrus fruit in 1887 in California. Use spread to Spain and other countries using either liquid prussic acid, calcium cyanide, or sodium cyanide preparations. During World War I other HCN-based pest control applications were developed, and soon fumigation of ships, stores, factories, and even residential buildings with hydrocyanic acid gas became a popular method of combating insect and rodent pests in many countries. Thousands of ships, cereal mills, and other food processing factories were fumigated with hydrocyanic acid gas until the mid-1930s in Germany alone.
Degussa ("Deutsche Gold- und Silber-Scheideanstalt", German Gold and Silver Refinery) had a leading role in the German research on pest control with hydrocyanic acid gas from 1916/17 on. Degussa's expertise in handling HCN resulted from its use in the extraction of gold from gold ore. Initially, the so-called pot method was used to generate HCN gas by treating sodium cyanide or potassium cyanide with diluted sulfuric acid in a pot. Like the utilisation of highly concentrated liquid prussic acid, the pot method has disadvantages. For example, prussic acid is chemically stable only for a limited period of time. Highly explosive air-HCN mixtures form easily when applied.
In March 1919, Deutsche Gesellschaft für Schädlingsbekämpfung mbH (Degesch, lit. "German Limited Company for Pest Control") was founded by a consortium of German chemical companies including Degussa, and initially led by chemistry Nobel laureate Fritz Haber. Haber had World War I experience in the development of poison gas for the German chemical warfare program. At Degesch, Ferdinand Flury developed Zyklon A in 1920. Its development was a major advance over previous methods of delivering hydrocyanic acid for pest control because of its improved chemical stability and the presence of a warning odorant.
Walter Heerdt, Bruno Tesch and Gerhard Peters were all collaborators of Fritz Haber working at the Kaiser Wilhelm Institute for Physical Chemistry and Electrochemistry at Berlin-Dahlem. Out of this group of Haber assistants, Walter Heerdt was named the official inventor of Zyklon B in a Degesch patent application from 20 June 1922 (number DE 438818). The German Patent Office awarded the patent on 27 December 1926. The main invention in Zyklon B consisted of the absorption of liquid hydrocyanic acid into a highly porous adsorbent. Initially, heated diatomite (diatomaceous earth) was used as an adsorbent. Later, high-porosity gypsum pellets called Erco-dice (described by eyewitnesses as "crystals") as well as disks made from wood fibre were also used. The adsorbed hydrocyanic acid was very safe in handling and storage when placed in inexpensive airtight cans of various sizes. Gerhard Peters, manager of Degesch, cites M. Kaiser to the effect that
Today Zyklon-prussic-acid is known on all continents as the "means of choice" [...] not only for debugging and delousing but also, in general, for disinfesting large rooms. (Heute ist die Zyklon-Blausäure als "das Mittel der Wahl" [...] nicht nur zur Entwanzung und Entlausung, sondern ganz allgemein zur Entwesung großer Räume in allen Erdteilen bekannt.)
From 1929 onwards the United States used Zyklon B to disinfect the freight trains and clothes of Mexican immigrants entering the U.S. Farm Securities Administration photographer Marion Post Wolcott recorded the use of cyanide gas and Zyklon B by the Public Health Service at the New Orleans Quarantine Station during the 1930s.
In early 1942, Zyklon B had emerged as the preferred extermination tool of the Nazi regime for both the Auschwitz-Birkenau and Majdanek extermination camps during the Holocaust. The chemical claimed the lives of roughly 1.2 million people in these camps. Rudolf Höss, commandant of Auschwitz, said that the use of Zyklon-B came about on the initiative of one of his subordinates, Captain Karl Fritzsch, who used the substance to kill some Russian POWs in late August 1941. The experiment was repeated on more Russian POWs, with Höss watching, in September. The emergence of Zyklon-B as the preferred chemical was a multistranded process.
Degesch played a key role in the development (see above) and manufacturing of Zyklon B. Many German companies had stock in Degesch, but all eventually sold their shares to the chemical giant Degussa (now part of Evonik Industries) in the early 1920s.
Degesch's role at this point was limited to acquiring patents and intellectual property: it did not produce Zyklon B. The manufacture of Zyklon B was handled by Dessauer Werke für Zucker and Chemische Werke, which acquired the stabilizer from IG Farben, the warning agent from Schering AG and the prussic acid from Dessauer Schlempe and assembled them into the final product. Dessauer Schlempe extracted prussic acid from the waste products of the sugar beet refining process. Apart from Dessauer Werke, Zyklon B was also produced from 1935 by Kaliwerke AG in the Czech town of Kolín and in France.
Upon production, Zyklon B was sold by Degesch to Degussa. To cut costs, Degussa sold the marketing rights of Zyklon B to two intermediaries: the Heerdt and Linger GmbH (Heli) and Tesch & Stabenow (Tesch und Stabenow, Internationale Gesellschaft für Schädlingsbekämpfung m.b.H., or Testa) of Hamburg. Both suppliers split their territory along the Elbe river, with Heli handling the clients to the west and Testa those to the east.
Zyklon B is still in production in the Czech Republic in the factory Draslovka Kolín a.s. in the city of Kolín, under the tradename Uragan D2, and is sold for the purpose of eradicating insects and small animals. The Czech word uragan means "hurricane" or "cyclone" in English.
In addition to the production of Zyklon B without the warning odorant specifically for the purpose of mass killings of humans, it has been suggested that some Zyklon B may have lacked the odorant because of supply shortages.
Zyklon B was used during the Holocaust by Nazi Germany to murder prisoners in gas chambers installed in the extermination camps Auschwitz-Birkenau, and Majdanek, and Sachsenhausen; most of the victims were Jews and Poles. The chemicals used had been deliberately manufactured without its warning odorant.
On September 3, 1941, about 600 Soviet prisoners of war and 250 sick Polish POWs were gassed to death with Zyklon B in Auschwitz Camp I. This massacre came shortly after the first experiment with gas, in which about 25 Soviet prisoners were gassed to death in the basement of Block 11. The experiments lasted longer than 20 hours.
According to Rudolf Höss, the commandant of Auschwitz, Bunker 1 held 800 victims, and Bunker 2 held 1,200 victims. Once the gas chambers were full, their doors were closed tightly, and solid pellets of Zyklon B were dropped into the chambers through pipes in the side walls, thus releasing the cyanide gas immediately. Those victims inside the gas chambers usually died within 20 minutes. The speed of the deaths depended on how close the victim was standing to a poison gas vent, according to Höss, who estimated that about one third of the victims died practically immediately. Johann Kremer, an SS doctor who oversaw the gassings, testified: the "shouting and screaming of the victims could be heard through the opening and it was clear that they fought for their lives". If the gas chamber had been crowded, which they typically were, the corpses were found half-squatting, their skin discolored pink with red and green spots, with some found foaming at their mouths, or bleeding from their ears.
After World War II ended in 1945, the two directors of the Testa company, Bruno Tesch and Karl Weinbacher, were tried in a British military court, convicted of mass murder, and executed for their part in producing and distributing Zyklon B.
The continued use of the trade name Zyklon (the German word for "cyclone") has prompted angry reactions from Jewish groups. In 2002, both the Siemens and Umbro companies withdrew their attempts to use or trademark the word for their products.
Holocaust deniers claim that Zyklon B gas was not used in the gas chambers, relying for evidence on the low levels of residues of Prussian blue in samples of the gas chamber walls and ceilings found by Fred A. Leuchter, which Leuchter ascribed to the general delousing of the buildings. Leuchter's "negative control", a sample of gasket material taken from a different building in the camp, registered as having no such cyanide residue.
The manager of the chemical laboratory hired by Leuchter stated in an interview in the movie Mr. Death: The Rise and Fall of Fred A. Leuchter, Jr., that Leuchter's thick samples of brick would have diluted completely the cyanide residue, which formed only a very fine layer on the masonry walls and cannot penetrate deeper.
In 1994, the Institute for Forensic Research in Kraków re-examined this claim on the grounds that formation of Prussian blue by exposure of bricks to cyanide is not a highly probable reaction. Using more sophisticated microdiffusion techniques, they tested 22 samples from the gas chambers, delousing chambers (as positive controls), and living quarters (as negative controls), finding cyanide residue in both the delousing chambers and the ruins of the gas chambers but none in the ruins of the living quarters.
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