Lack of Prussian Blue Staining on the Walls of Gas Chambers


The Holocaust (which occurred during World War II, from 1939 to 1945) involved systematic murder and was the deadliest genocide in history. Nazi Germany erected concentration camps (also called “death camps”) that were equipped with gas chambers, at Auschwitz-Birkenau, Belzec, Chełmno, Majdanek, Sobibór, and Treblinka.

In this paper a detailed chemical approach has been applied to the investigation as to why no Prussian blue (Ferric ferrocyanide) stains are visually observed on the walls and ceiling of the homicidal gas chambers (such as in the concentration camps at Auschwitz-Birkenau). The chemical reaction of Zylon B (Hydrogen cyanide gas (HCN)) with iron oxide {Fe2O3· xH2O} to produce Fe4[Fe(CN)6] yH2O {Prussian blue (Ferric ferrocyanide)} is discussed in detail (see EQ 1). Chemical analyses from other researchers found in delousing and gas chambers in concentration camps are analysed for chemical validity, and chemical alternatives as to why Prussian blue is observed in delousing chambers and not observed in gas chambers are also introduced and discussed.

Zyklon B (pronouned Cyclone B, with the B standing for Blausäure – “Blue Acid”) is the trade name of a German cyanide-based pesticide invention, consisting of hydrogen cyanide gas (HCN)(also called prussic acid) and absorbents such as diatomaceous earth (consisting of amorphous silica (SiO2) and the remains of dead diatoms (microscopic single-celled algae) or gypsum (Ca(SO4)2. 2H2O). HCN is a colorless, extremely poisonous liquid that boils slightly above room temperature (25.6 °C or 78.1°F).1 HCN is a linear molecule, with a triple bond between carbon and nitrogen. HCN is a weak acid and it partially ionizes in water solution to give the cyanide anion, CN−.

Uses of Zyklon B included delousing clothing, disinfecting ships, warehouses, and trains. Zyklon B also was used by the Nazi’s in World War II (early in Ca. 1942, during the Holocaust) to murder millions of people in gas chambers (since HCN is a poisonous gas that interferes with cellular respiration) found in concentration camps at Auschwitz-Birkenau, Majdanek, and others. A total of 729 metric tons of Zyklon B was sold in Germany between 1942–44 and a quantity of 56 metric tons (about 8 per cent of domestic sales) were sold to concentration camps. Auschwitz received 23.8 tons, of which 6 tons were used for fumigation.

The iron compounds needed to form Prussian blue stains on walls and ceiling are an integral part of all building materials, such as: bricks, sand, clay, gravel and cement (such as Portland cement). These building materials found in German concentration camps contain a certain amount of rust (iron oxide {Fe2O3 xH20}, usually between 1 and 5 percent). Rust or iron oxide, is usually a red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable both visually and by spectroscopy, and form under different circumstances (see EQ 1).

Prussian blue (Ferric ferrocyanide) {the first modern synthetic pigment probably synthesized by the paint maker Diesbach in Berlin around the year 1700} is a dark blue pigment with the chemical formula Fe7(CN)18. yH2O (where y is 14-16 as determined by using X-ray crystallography and neutron crystallography). To better understand the binding situation in this complex compound the formula can also be written as Fe4[Fe(CN)6]3 · yH2O (see EQ 1). Prussian blue (Ferric Ferrocyanide) is long known as a stable compound. Prussian blue is characterized by two different oxidation states: Fe+2 (3 Fe atoms coordinated to CN) and Fe+3 (4 Fe atoms outside of the brackets) (see EQ 1). The interaction between these two different iron ions (Fe+2 and Fe+3) gives rise to the blue color for this compound (due to its charge-transfer complex properties).


It should be noted, that the equation above (EQ 1) for simplicity is balanced for atoms and charges {ie., Fe+2 (regarding the 3 Fe atoms coordinated to 6 CN- atoms), Fe+3 (regarding the 4 Fe atoms coordinated to 12 CN- atoms outside of the brackets)}. This reaction (EQ 1) is a the redox reaction of iron (III) oxide (Fe+3 from 3.5 Fe2O3 xH20) in the presence of water or air moisture. EQ 1 is balanced on the product side of the equation {Fe4[Fe(CN)6]3 · yH2O (Prussian blue) + zO2 (dioxygen gas), with y = 16 and z = 0.75} for charge where a quantity of 18 CN- atoms (18 e- or electrons) are balanced with 3 Fe+2 atoms {3 X +2 (from Fe inside of bracket) or 6 positive charges (6+) } and 4 Fe+3 atoms {4 X +3 (from Fe outside of bracket) or 12 positive charges (12+)}. Therefore, a total of 18 e-(from CN- atoms) are coordinated and balanced with a total of 18 positive charges (6+ + 12+ = 18+) (from the two different charged Fe atoms (Fe+2 and Fe+3) found for Prussian blue).

It should also be noted, the carbon (C) and nitrogen(N) from cyanide and Iron (Fe) atoms are balanced but the xH20 from 3.5 Fe2O3 xH20 (iron oxide), yH2O from Fe4[Fe(CN)6]3 · yH2O (Prussian blue) and zO2 (dioxygen gas) are not. This is because x, y and z could represent a fraction of a whole number such as; x could be 1, 1.5, 2, etc., y could be 14, 15.5, 16.0, etc. and z could be 0.5, 0.75, 1.0, etc. A possible solution however, could be x = 2, y= 16 and z = 0.75, which results in a balanced equation.

Figure 1 illustrates the blue staining (Prussian blue) on the walls and ceiling of a typical delousing chamber resulting from the reaction of iron oxide (Fe2O3· xH2O) and HCN gas (see EQ 1). Interestingly, only a few chemical analyses have been reported measuring the levels of cyanide found at concentration camps. Cyanide has been measured in the delousing and gas chambers (see Table 1).


On inspection of Table 1 both the Rudolf1 and Leuchter2 results are consistent with one another where; measurements of total cyanide in delousing chambers range from more than 1,000 mg/kg and measurements of total cyanide from gas chambers range between 0-8 mg/kg. The results from the Markiewicz, et al. study however, illustrates that the cyanide (without iron cyanide) from the delousing and gas chambers are similar with a value between 0-0.8 mg/kg. But this finding does not support the visual observations that Prussian blue stains are found on the walls and ceiling of delousing chambers (see Figure 1) and not on gas chamber walls and ceilings.

Upon further inspection of Table 1, if one concentrates on the results of Rudolf1 and Leuchter2 one sees that in order to kill humans as quickly as attested to by eye witnesses, HCN gas (Zylon B) used in the gas chambers would have to have had concentrations similar to those used for delousing procedures. It has been suggested (from the data in Table 1) that much less HCN gas would have been required to kill human in the gas chambers than to kill lice in the delousing chambers. But this argument does not make any scientific sense.

How does the results from Rudolf1 and Leuchter2 make scientific sense when numerous eye witnesses (for example, under oath in court proceedings) as well as Nazi perpetrators such as Rudolf Höss, commandant of Auschwitz state that gas chambers were used to kill prisoners. Rudolf Höss said that the idea to use Zyklon-B to kill prisoners was initiated by one of his subordinates, SS-Hauptsturmführer (captain) Karl Fritzsch. Fritzsch used Zylon B to kill Russian POWs in late August 1941 in the basement of Block 11 in the main Auschwitz camp.

After the War in 1945, the Krakow Institute for Forensic Research (Instytut Ekspertyz Sadowych) prepared a report on a forensic investigation of Auschwitz that was submitted in evidence in the 1946 Auschwitz trial in Krakow, Poland. The Krakow forensic investigators performed chemical analyses on hair (presumably cut from inmates) and hair clasps from bags found by the Soviets in Auschwitz. Results from both hair and clasps samples tested positive for cyanide. Additionally, zinc-plated metal covers (from gas chamber exhaust ducts) were also tested for cyanide and found to have a positive result (which can be presumed to be Zn(CN)2). It should be noted, that the exact quantitative measurements for cyanide found in the hair, hair clasps and zinc-plated covers (from gas chamber exhaust ducts) are not given.

Here, it is proposed that the zinc-plated metal covers from gas chamber exhaust ducts provides a possibe answer to why no Prussian blue staining is found on the walls and ceiling of the gas chambers in Auschwitz. Zinc Cyanide {with the chemical formula Zn(CN)2} is a white solid inorganic compound that is easily produced as compared to Prussian blue (which is a complex compound (Fe4[Fe(CN)6]3 ·yH2O ). The reaction of HCN gas (Zylon B) with Zinc (Zn) {found on the zinc-plated metal covers of gas chamber exhaust ducts} to produce Zn(CN)2 is presented in EQ 2.


It is proposed here, that EQ 2, the reaction to produce Zn(CN)2 (zinc cyanide) is more favorable than the reaction EQ 1 to produce Fe4[Fe(CN)6]3 · yH2O (Prussian blue). In other words, a competition between reactions (EQ 1 and EQ 2) exists and since EQ 2 results in Zn(CN)2 which is a simplier and easier reaction, this results in more Zn(CN)2 produced as compared to Fe4[Fe(CN)6]3 · yH2O (Prussian blue). This could explain the visual observations of the lack of Prussian blue staining on the walls and ceiling in the gas chambers and the chemical analyses reported by Rudolf1 and Leuchter2. Both Rudolf1 and Leuchter2 measured the total cyanide concentrations from wall samples and did not test zinc-plated covers from the exhaust ducts in the gas chambers. It is also proposed here, that the EQ 2 reaction prevents the formation of reaction EQ 1 (which would presumingly require more time to produce Prussian blue). EQ 2 and the formation of Zn(CN)2 is also supported by the results from the Krakow Institute for Forensic Research (Instytut Ekspertyz Sadowych in 1945) and their forensic investigation of Auschwitz where cyanide was detected.

Prussian Blue Staining on Walls of Typical Delousing Gas Chamber

Prussian Blue Staining on Walls of Typical Delousing Chamber (Credits: Dr. Brett I. Cohen)

A comprehensive chemical literature search for thermodynamic data for Prussian blue (Fe4[Fe(CN)6]3 · yH2O ) and zinc cyanide (Zn(CN)2) only yielded ΔHf {delta H (enthalpy) of formation} of zinc cyanide with a value of ΔHf = 22.9 kcal/mol at 298.15°K or 25°C with no thermodynamic data found for Prussian blue. ΔHf is the change in enthalpy when one mole of a substance (in this case Zn(CN)2 ) in the standard state (1 atm of pressure and 298.15°K) is formed from its pure elements {zinc (Zn), carbon (C) and nitrogen(N)} under the same conditions. This thermodynamic data (ΔHf )for Zn(CN)2 gives some insight to the formation and stability of Zn(CN)2.

In general, the more negative a ΔHf for a compound, the more stable it is, which results in easier formation of the compound from its original elements. Although the ΔHf for Zn(CN)2 is not negative, Zn(CN)is still considered a stable compound that is easy to produce from its original elements. Methane (with one carbon atom) is the most elementary, stable and easiest hydrocarbon to produce and has a ΔHf = -17.88 kcal/mol. In contrast, ethylene {with two carbon atoms and the next hydrocarbon from methane} has a ΔHf of 12.45 kcal/mol9 and this value for ΔHf is very similar to that Zn(CN)2. Ethylene is stable and this compound is easy to produce from its original elements.

Therefore, this paper proposes that the reason there is no Prussian blue (no blue staining) on the walls and ceilings of gas chambers (in the German concentration camps during World War II) was due to the competition reaction of the formation of zinc cyanide (EQ 2) as compared to Prussian blue (EQ 1).


About Author

Dr Brett I. Cohen holds a PhD in inorganic and bioinorganic chemistry from the State University of New York at Albany. He received his PhD in November 1987 for his thesis entitled “Chemical Model Systems for Dioxygen-Activating Copper Proteins” and was a postdoctoral fellow at Rutgers University in 1988–1989. His research at Rutgers was in the area of peptide synthesis utilising transition metal chemistry. After his postdoctoral fellowship, from 1989 to 2003 Dr Cohen was one of the owners of Essential Dental Systems (manufacturer of dental composites and dental materials) where he was Chief Executive Officer and Vice President of Dental Research. Dr Cohen has been awarded 16 US patents and has had over 100 papers published in peer-reviewed journals (such as Journal of the American Chemical Society, Inorganic Chemistry, Journal of Dental Research, Journal of Prosthetic Dentistry, Journal of Endodontics and Autism, etc.). These papers cover a variety of areas such as inorganic and bioinorganic chemistry, biomedicine, autism, physical chemistry, dentistry and more.

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