# Why the cyanide residue argument fails

A critical review of the chemical evidence at Auschwitz-Birkenau

**The absence of conspicuous Prussian blue does not establish that homicidal gassing never occurred.** Low cyanide readings and the absence of conspicuous Prussian blue do not establish that the Auschwitz gas chambers were never used for murder. That inference requires a reliable prediction of the residues that would have formed and survived in the particular materials tested. Comparing them with heavily stained delousing walls does not, by itself, supply that prediction.

The converse must also be kept clear: detecting cyanide cannot, on its own, identify a room’s purpose, determine when it was exposed, or count victims. Chemical results belong alongside the documentary, testimonial, and physical evidence. This revised edition distinguishes observations, calculations, and historical inferences throughout.

*Reviewed 1 October 2026. Revised from Cyanide_Residue_Argument_Rebuttal_2. See the [correction record](fact-check) and [additional arguments reviewed](additional-arguments).*

## 1. The argument in its strongest form

The argument developed by Fred Leuchter and Germar Rudolf is more substantial than “no blue colour, therefore no gas.” Its stronger version compares measured cyanide concentrations and the conditions thought to favour persistent iron-cyanide compounds. It proposes that repeated homicidal gassing should have produced residues comparable to those in delousing facilities, and that the observed difference is evidence against the historical account.

Rudolf’s 2020 presentation acknowledges that a lack of reliable residues is not conclusive by itself. He nevertheless argues that moisture, alkalinity, material structure, and repeated exposure favour substantial residue formation in the crematorium basements. The 2013 Rudolf–Kollerstrom paper also distinguishes visible colour from total cyanide: a material can contain appreciable cyanide without looking blue. A rebuttal must address this comparative prediction, rather than treating visible colour as the whole argument. [Rudolf, 2020, pp. 15–18](https://holocausthandbooks.com/wp-content/uploads/ChemistryAuschwitz-5th-Script-2020.10.20.pdf); [Rudolf and Kollerstrom, 2013](https://codoh.com/library/document/differential-exposure-of-brickwork-to-hydrogen/).

Nor is “Rudolf admits it is not rigorous proof” a complete answer. Historical arguments can be probabilistic. The question is how well the predicted residue levels are supported, how uncertain their inputs are, and how the prediction fares against the other evidence.

## 2. What should be conceded

Several common counterarguments are too simple:

- **Blue staining can result from HCN fumigation.** The Bavarian church case cited by Rudolf is relevant evidence of that possibility. It does not establish that every exposure, or every repeatedly exposed wall, must develop the same residue pattern.
- **Prussian blue can be very persistent.** Its absence should not be casually explained by saying that rain washed it all away. Persistence of a pigment and loss of more readily extractable cyanide are different questions.
- **A universal ten-micrometre penetration limit is not defensible.** Green himself questioned the general application of Roth’s estimate. Sampling depth still matters, but must be measured rather than assumed.
- **Minimum lethal concentration is not actual historical concentration.** The familiar humans-versus-lice comparison cannot establish how much HCN was present during a particular operation. Nominal loading, release from the carrier, and concentration over time are different quantities.
- **Total-cyanide measurements are relevant.** The Kraków assay was not a substitute for measuring every cyanide fraction. An ideal comparison would report complementary methods on matched samples.

These concessions remove weak rebuttals. They do not demonstrate the missing relationship between past use and surviving residues. [Green, 2001, pp. 14–16, 41–50](https://phdn.org/archives/holocaust-history.org/irving-david/rudolf/affweb.pdf); [church case reproduced by CODOH](https://codoh.com/library/document/wood-preservation-through-fumigation-with/).

## 3. What the Kraków study actually measured

Jan Markiewicz, Wojciech Gubała, and Jerzy Łabędź published their study in 1994. They deliberately used an assay that did not break down Prussian blue. The measured quantity is therefore best described operationally: **cyanide released under that assay’s conditions**. Calling it simply “free cyanide,” “water-soluble cyanide,” or all “non-iron cyanide” can imply a chemical specificity that the paper does not establish for every possible compound.

The paper reported a lower limit of determinability of **3–4 µg/kg**, triplicate analyses, repeated positive tests, calibration standards, and laboratory analysis by a group separate from the sampling team. These are useful controls; they are not independent replication by a second laboratory or a complete modern method-validation dossier. [1994 study, pp. 20–21](https://phdn.org/archives/holocaust-history.org/auschwitz/chemistry/iffr/report.shtml).

### The results, without selecting only the largest readings

The following summary was checked against Tables II–III of the scanned publication. Counts refer to physical samples; three repeat readings of one sample are not three independent samples. “Numeric positive” means at least one reported positive numerical result; the separate trace result is identified below.

| Location | Samples | Numeric positives | Range of numeric positive readings, µg/kg | Example triplicate, µg/kg |
| --- | --- | --- | --- | --- |
| Crematorium I | 7 | 4 | 26–292 | No. 20: 288 / 292 / 288 |
| Crematorium II | 7 | 6 | 8–640 | No. 25: 640 / 592 / 620 |
| Crematorium III | 7 | 7 | 8–68 | No. 32: 68 / 68 / 68 |
| Crematorium IV | 5 | 4 | 12–500 | No. 41: 500 / 496 / 496 |
| Crematorium V | 7 | 6 | 12–248 | No. 46: 244 / 248 / 232 |
| Block 11 cellars | 3 | 2 | 16–28 | No. 13: 28 / 24 / 24 |

Crematorium IV sample 42 was reported as **trace / 0 / 0**. Other samples also gave zero. The eight dwelling-control samples in Table I gave zero; two earlier screening controls did likewise. “Zero” here means no cyanide reported by this method, not proof of absolute chemical absence. The table caption describes the dwelling rooms as **probably fumigated once**; calling them demonstrably unexposed is incorrect. [Tables I–III, pp. 22–23; original scan](https://codoh.com/media/files/downloads/MarkiewiczEtAl1994-ocr.pdf).

**The defensible finding:** the study reported cyanide in samples from every crematorium building tested and from Block 11, with negative dwelling controls. It did not obtain a positive result from every piece sampled, nor establish a result for every individual room within each building.

### What those results do and do not show

The data contradict a blanket assertion that no cyanide was detected. Several readings are well above the study’s stated limit. For example, 640 µg/kg is 160–213 times 4–3 µg/kg. But the smallest numeric positives, 8 µg/kg, are only about two to three times that limit. Large multiples of the limit must not be applied to every positive.

The assay does **not** isolate historical exposure independently of chemistry. Its result still depends on what formed, persisted, and could be released during analysis. Negative controls strengthen the interpretation but do not rule out every matrix-specific interference or alternative source. They also do not reconstruct the walls’ original chemical loading.

The study supports contact with cyanide compounds in the sampled structures, interpreted in their historical setting. Residue alone cannot distinguish homicidal use from pest control. That distinction requires other evidence.

## 4. Why the delousing comparison is not a calibrated test

A valid comparison needs more than the same poison and the same general category of building material. It needs defensible information about exposure duration, concentration history, material composition, moisture, pH, maintenance, survival of original surfaces, and sampling depth. A large difference between samples is an observation; assigning it to one historical cause is a further inference.

**Exposure duration matters, but the often-cited totals are estimates.** Green illustrated the possible contrast with approximately 117 hours for one crematorium chamber and at least 7,200 hours for BW5a. These were reconstructions from assumed numbers and lengths of operations, not readings from surviving exposure logs. The ratio cannot be treated as a measured constant or extended to all buildings. It does illustrate why kilograms supplied to a camp are not equivalent to exposure at a particular wall. [Green, 2001, pp. 43–44](https://phdn.org/archives/holocaust-history.org/irving-david/rudolf/affweb.pdf).

**Repetition does not settle the issue by itself.** The number of operations, their duration, and the fate of absorbed cyanide between operations interact. A short exposure repeated many times cannot be equated with a long fumigation merely by counting events; neither can its cumulative effect be dismissed without modelling retention.

**Freshness, moisture, and alkalinity can favour uptake.** It is too strong to say that Rudolf’s own mechanism simply predicts the opposite of his conclusion. His later account allows prolonged retention in cement-rich material and delayed formation as conditions change. That is a real counterargument to a simplistic surface-only explanation. What is missing is a validated quantitative prediction of the residue distribution in these specific walls. [Rudolf, 2020, pp. 10–12](https://holocausthandbooks.com/wp-content/uploads/ChemistryAuschwitz-5th-Script-2020.10.20.pdf).

**The church analogy establishes possibility, not equivalence.** One fumigation can produce staining under favourable conditions. But a case report supplies neither a representative base rate for all fumigations nor a calibration for the Auschwitz materials. Differences cannot simply be declared to cancel each other without measurement. [Church report and Rudolf’s comparison](https://codoh.com/library/document/wood-preservation-through-fumigation-with/).

## 5. Cleaning, carbon dioxide, and pH: plausible effects, limited reconstruction

### Cleaning

Testimony about hosing does not establish a uniform wall-washing regime. Green’s footnote 55 actually brings together descriptions of washing the **floor**, washing **bodies**, damp floors, and Bennahmias’s account of hosing and whitewashing. Those are not interchangeable observations about every wall after every operation.

Cleaning could remove accessible precursor compounds. Green’s dilution estimates, however, were expressly approximate. They do not demonstrate a particular reduction throughout the wall’s pores. Whitewashing after every use should remain attributed to the specific account rather than presented as a universally documented practice. [Green, 2001, pp. 43–44, note 55](https://phdn.org/archives/holocaust-history.org/irving-david/rudolf/affweb.pdf).

### Carbon dioxide

The Kraków experiments show that changing conditions can change the measured retained cyanide. Their average losses after a month were 56% for the HCN series and 73% for the HCN-plus-CO₂ series; some individual materials behaved differently, including higher initial uptake by fresh plaster in the latter series. This was not a controlled reproduction of wartime chamber operation and does not establish a single universal CO₂ effect on pigment formation. [1994 study, Tables V–VI and discussion](https://phdn.org/archives/holocaust-history.org/auschwitz/chemistry/iffr/report.shtml).

There is also an arithmetic inconsistency in the paper. **3.5% of 15–20 litres is 0.525–0.700 litres, not 0.950 litres.** Using those stated inputs gives 2.625–3.500 m³ from 1,000 people over five minutes, or about 0.53–0.70% of a 500 m³ room, before considering other processes. This is a correction of the quoted arithmetic, not a physiological reconstruction. It is not necessary to rely on the paper’s overstated figure to recognise that exhaled CO₂ could affect local conditions.

### Cyanide-ion fraction

Using the pKₐ of 9.31 cited by Green and the ideal acid–base relation, the fraction present as CN⁻ is:

**fraction = 1 / (1 + 10^(pKₐ − pH)).**

| pH | Calculated CN⁻ fraction of HCN + CN⁻ |
| --- | --- |
| 6 | 0.049% |
| 7 | 0.487% |
| 10 | 83.0% |

Thus “about 1% at pH 6–7” is an inaccurate simplification. More importantly, a pH measured decades later does not establish wartime pore-water pH. These simple equilibrium calculations also do not include all reactions in a cementitious material. Green’s printed rearrangement on p. 49 contains a denominator error; the equation above follows directly from the acid-dissociation relation. [Green, 2001, pp. 49–50](https://phdn.org/archives/holocaust-history.org/irving-david/rudolf/affweb.pdf).

## 6. The proposed threshold explanation is not a settled reconstruction

Green used solution-chemistry work by Alich, Haworth, and Johnson to discuss a cyanide-dependent route to iron-blue formation. The cited concentration, about 3.3 × 10⁻⁴ mol/L in that discussion, should not be elevated into a universal on/off threshold for historic masonry. That extrapolation is not established.

The concentration, pH, iron availability, and reaction pathway matter; alternative pathways and changes during years of ageing cannot simply be excluded. The original Alich paper’s bibliographic record was located, but its full experimental text was not independently examined for this review. The numerical claim is therefore attributed to **Green’s interpretation**, not presented as an independently verified material constant. [Green, 2001, pp. 45–50](https://phdn.org/archives/holocaust-history.org/irving-david/rudolf/affweb.pdf); [Alich et al., 1967, DOI](https://doi.org/10.1016/0022-1902(67)80207-0).

Similarly, a ratio between an extractable-cyanide result from one investigation and a total-cyanide result from a different sample is not a measured chemical fraction of one wall specimen. Different laboratories, methods, dates, and sampling locations introduce additional uncertainty. Such proportions should not be treated as established conversion efficiencies.

The justified point is that residue formation need not be proportional to nominal gas use. The reviewed sources do not provide a validated prediction of the surviving residue distribution across these buildings. That is narrower than declaring that no experiment or model of any kind has ever been produced.

## 7. Replies to the most consequential objections

### “The Kraków method was rigged because it excluded the stable pigment.”

The exclusion is real and limits what the study can say about **total** cyanide. The paper’s speculative discussion of blue paint should not be repeated as an established explanation. Nevertheless, an explicitly selective assay can report meaningful results for what it measures. Method selection alone does not demonstrate fabricated readings. Complementary analysis would strengthen the evidence; it would not retrospectively make the published numbers all zero.

### “The positives were below the detection limit.”

Relative to the paper’s stated 3–4 µg/kg determinability limit, the positive numerical entries for the crematoria and Block 11 are above it. The one marginal crematorium entry is labelled trace. Whether the claimed sensitivity was adequately validated is a separate question; it cannot be answered merely by calling every sub-ppm result negligible. **1 mg/kg equals 1,000 µg/kg.** A limit expressed per litre of analytical solution cannot be compared directly with a result per kilogram of original solid without the preparation and recovery factors.

These objections appear in [the December 2024 forum thread](https://www.codohforum.com/viewtopic.php?t=122) and, in a different form, in [Rudolf and Kollerstrom’s discussion of analytical sensitivity](https://codoh.com/library/document/differential-exposure-of-brickwork-to-hydrogen/). The study reports a method-specific limit; independent validation of it remains a legitimate research question.

### “All residues could come from ordinary disinfestation.”

Residue chemistry alone cannot rule out non-homicidal exposure. The absence of the operational Birkenau crematoria during the mid-1942 camp fumigation undermines that particular blanket explanation; it does not exclude any later pest-control use. Nor do negative dwelling controls prove how every other room was treated. The broader alternative must be assessed against specific evidence for each building, rather than assumed from the general existence of lice. [Museum’s construction and use chronology](https://www.auschwitz.org/en/history/auschwitz-and-shoah/gas-chambers); [July 2025 forum discussion](https://www.codohforum.com/viewtopic.php?t=468).

### “Weathering cannot remove stable Prussian blue.”

An unsupported assertion that rain removed all existing pigment is inadequate. The opposite absolute, that weathering **cannot** affect its absence, is also too strong: destruction, erosion, or loss of a surface can remove pigment-bearing material. Chemical stability is not invulnerability of an entire structure. The published water-flushing experiment addressed the measured extractable fraction; it did not demonstrate the washout of a mature Prussian-blue deposit. Present-day residues are the product of both formation and survival.

### “Criticising Leuchter is irrelevant once Rudolf’s work exists.”

Correct as a methodological warning: objections to one investigator do not automatically refute another’s measurements. Each sampling scheme and analytical method must be assessed separately. Rudolf’s stronger argument still requires a justified comparison between the expected and observed residues. It does not become a validated reconstruction merely because it addresses some weaknesses of Leuchter’s work.

## 8. Conclusion and remaining limits

The rebuttal is strongest when it does not ask the chemistry to prove more than it can. The observed contrast between stained delousing walls and the sampled crematoria is real evidence to explain. It is not a calibrated test establishing that homicidal gassing could not have occurred. Conversely, the Kraków positives are evidence of cyanide in historically relevant structures, not a chemical identification of their purpose.

Uncertain formation rates, changing surface conditions, selective preservation, and incomplete sampling prevent a simple conversion from present residue to past use. The independent historical record must be considered alongside the chemistry. A challenge to one simplified explanation does not erase the documents, testimony, and physical findings; nor should those sources be used to pretend every proposed chemical explanation has been experimentally demonstrated.

Further useful research would include independently replicated analyses, documented sampling depths, matrix controls, complementary cyanide assays on matched specimens, and uncertainty estimates tied to particular materials. This review assesses published evidence and arguments; it does not report a new laboratory investigation.

## Sources and reading notes

- **Markiewicz, Gubała, and Łabędź (1994)**, “A Study of the Cyanide Compounds Content in the Walls of the Gas Chambers in the Former Auschwitz and Birkenau Concentration Camps,” *Z Zagadnień Nauk Sądowych* 30, 17–27. [Readable transcription](https://phdn.org/archives/holocaust-history.org/auschwitz/chemistry/iffr/report.shtml) and [scanned publication](https://codoh.com/media/files/downloads/MarkiewiczEtAl1994-ocr.pdf). Tables checked against the scan; the transcription duplicates sample number 17 where the scan has 16 and 17.
- **Richard J. Green (2001)**, expert report concerning Rudolf’s claims in the Irving appeal proceedings. [PDF](https://phdn.org/archives/holocaust-history.org/irving-david/rudolf/affweb.pdf). The exposure and dilution estimates are attributed to Green, not independently measured here.
- **Germar Rudolf (2020)**, *The Chemistry of Auschwitz*, fifth-edition presentation script. [PDF](https://holocausthandbooks.com/wp-content/uploads/ChemistryAuschwitz-5th-Script-2020.10.20.pdf). A source for the argument being assessed, not an independent validation of it.
- **Germar Rudolf and Nicholas Kollerstrom (2013)**, “Differential Exposure of Brickwork to Hydrogen Cyanide during World War Two.” [CODOH text](https://codoh.com/library/document/differential-exposure-of-brickwork-to-hydrogen/). Relevant to total cyanide, depth, and assay comparisons.
- **“Wood Preservation Through Fumigation With Hydrogen Cyanide.”** [CODOH reproduction and commentary](https://codoh.com/library/document/wood-preservation-through-fumigation-with/). Distinguish the reported church case from Rudolf’s appended historical inferences.
- **Alich, Haworth, and Johnson (1967)**, “Spectrophotometric studies of hexacyanoferrate(III) ion and its reaction with iron(III) in water and ethanol,” *Journal of Inorganic and Nuclear Chemistry* 29, 1637–1642. [DOI](https://doi.org/10.1016/0022-1902(67)80207-0). Full experimental text not independently reviewed.
- **CODOH forum:** [“The Prevarications of Markiewicz,” December 2024](https://www.codohforum.com/viewtopic.php?t=122) and [“Markiewicz Report in 1994,” July 2025](https://www.codohforum.com/viewtopic.php?t=468). Accessible opening pages reviewed; later pagination was not fully accessible. No claim of an exhaustive forum survey is made.