Zyklon B


i am a senior in high school and i have to do a massive project to graduate. i love the 40s and i enjoy learning more about the Holocaust and how a man would want to destroy a pouplution of millions just for his own hate. to my question now: i would like to know what is Zyklon-B made of. i am trying to find all of its properties and what its make up is. my Chemistry teacher does not know what it is made of. i need the information of its chemical make up and then she and i will look up the rest.

Richard J. Green answers:

Zyklon-B was hydrogen cyanide (HCN) impregnated in a porous solid support one of which was called Erco (a gypsum material), with a few other additives for stabilization and warning.

See the articles below for more information:




Rich Green

Another Question:

I'm Finnish historian and I'm preparing my dissertation about the World War I related issues. I'm studied in some extent war gasses. One of the bes source books, "The War Gases" by Mario Sartori (translated form the Second Enlarged Italian Edition by L. W. Marrison) Second edition. J.& A. Churchill 1940 knows the Zyklon A and Zyklon B.

What Dr. Sartori wrote about those gases when he dicussed halogenated esters of organic acids is worth of noting: "Because of its [methyl chloroformate] strongly irritant properties, it has been used in insecticidal preparations: 'Zyklon A," which is a mixture of 90% of methyl cyanoformate and 10% of methyl chloroformate, and 'Zyklon B,' a mixture of liquid hydrocyanic acid and irritant chlorinated and brominated compounds." (Sartori, War Gases. p. 104)

The source of Dr. Sartori was German "Frickhinger, Gase in der Schädlingsbekämpfung, Berlin 1933, 27.

It is possible that those irritant compounds were halogenated esters. If so, the use of Zyklon B against human beings would have added a horrible torture in the final agony of the victims. Some halogenated esters are insupportabale in concentrations as small as 50 mg in a cubic meter of air. Accounts concerning the dead of the victims of chambers support my suspect that the gas had much stronger irritant efect than pure hydrocyanic acid. The vapor pressure of hydrocyanic acid is weak. It takes relatively long time to form a lethal concentration. That fact made hydrocyanic acid unsuitable as war gas in the World War I. When used in the gas chabers with irritant compounds those irritant agencies presumably evaporate first and cause a horrible pain to the victims before the HCN killed them.

I haven't been able to find the Frickhingers book. I suppose that the details of those irritant compounds can be found there.

If my hypothesis is correct the use of Zyklon B in Holocaust was even more brutal crime than we have understood. Please tell me that I'm wrong.

Harry W. Mazal OBE answers:

Thank you for your very interesting query.

I am one of the persons in the Holocaust History Project that responds to questions like yours. It is possible that you will receive other answers from my colleagues. You will have seen the various articles on our web-page, particularly

Blausäure zur Schädlingsbekämpfung ,


Die Einsatzfähigkeit der Blausäure-Durchgasung bei tiefen Temperaturen


Nochmals: Die Einsatzfähigkeit der Blausäure-Durchgasung bei tiefen Temperaturen

If so, I would first refer you to:

AUSCHWITZ: Technique and Operation of the Gas Chambers
Jean Claude Pressac,
c. 1989, The Beate Klarsfeld Foundation (New York)
Library of Congress Catalogue Card No. 89-81305

Page 17:

KL Auschwitz was supplied with Zyclon-B mainly by a firm called TESTA, and abbreviation for the Tesch und Stabenow Internationale Gesellschaft fuer Scaedlingsbekaempfung / international pest control company domiciled at Messberghoff, Hamburg 1. This company had the monopoly for distributing Zyclon-B in the eastern territories of the Reich (in fact to the east of the Elbe). But the Auschwitz SS, having at the same time to combat epidemics and carry out the 'special treatment' of Jews sometimes turned directly to Degesch (located in 1939-45 at 43, Schauminkai or 9, Weissfrauenstrasse, Franfurt am Main, then at 70, Kaserstrasse, Friedberg/ Hessen) to obtain quantities sufficient for their needs. For this reason a five ton truck with a trailer ran back and forth between Auschwitz and the factory producing Zyclon-B, the DESSAUER WERKE fuer Zucker - und Chemische Industrie, AG, 40, Askanische Strasse, Dessau (about 50 kilometers north of Leipzig). The 'reserve stocks' of the PMO have cans of Zyclon-B from both sources: Testa and Degesch (Dessauer Werke). Zyclon-B without a warning agent (ohne Warnstoff) or without irritant (ohne Reizstoff) was delivered by the Dessauer Werke as from August 1942. This was because of a LACK of the warning agent generally used, a bromoacetic ester. The Degesch laboratory people, who had remained at Frankfurt, would have liked to replace it by a chlorinated carbon xide [? HWM] ester (methyl chloroformiate) with a suffocating effect, but the Friedberg management decided to produce Zyclon-B with no warning agent.

From the same book, page 201:

Letter addressed to the staff and SS of the camp by its Commandant, Rudolf Hoess:

"Auschwitz, 12 August 1942

Auschwitz Concentration Camp

Special Order

A case of indisposition with slight symptoms of poisoning by hydrocyanic acid gas which occurred today makes it necessary to warn all those participating in the gassings and all other SS members that in particular on opening rooms used for gassing SS not wearing masks must wait at least five hours and keep a distance of at least 15 metres from the chamber. In addition, particular attention should be paid to the wind direc- tion.

The gas being used at present contains less odorous warning agent and is therefore especially dangerous.

The SS garrison doctor declines all responsibility for any accident that should occur in the case when these directives have not been complied with by SS members.

Signed: Hoess
SS Lieutenant-Colonel and Commandant"

[Cc list deleted for brevity - HWM]

Pressac apparently believed that the warning agents were removed from the Zyklon-B because of a scarcity of the material. This does not make good sense to me as there were any number of other compounds that could have been used for that purpose. I believe that Hoess wished to spare his his S.S. staff the distress of seeing men, women and children suffer a horrible agony. Until Zyklon-B was obtained without the warning agent, the victims must have suffered greatly before succumbing to the hydrogen cyanide. The spectacle of victims dying a horrible death affected the S.S. guards. Without the agent, the victims would die quickly, suffer little, and not affect the minds of the S.S. guards.

There are other views. From:

The Crime and Punishment of I.G. Farben Joseph Borkin
c. 1978, The Free Press (New York)
ISBN 0-02-904630-0

Page 123

There was still another episode that gave the officials of Degesch more than a hint of the dread purpose to which their Zyklon B was being put by the S.S. When manufactured as a pesticide Zyklon B contained a special odor or indicator to warn human beings of its lethal presence. The inclusion of such a warning odor was required by German Law. When the S.S. demanded that the new large order of Zyklon B omit the indicator, no one familiar with the workings of the S.S. could have failed to realize the purpose behind the strange request. The Degesch executives at first were unwilling to comply. But compassion was not behind their refusal. What troubled them was the fact that the S.S. request endangered Degesch's monopoly position. The patent on Zyklon B had long ago expired. However Degesch retained its monopoly by a patent on the warning odor. To remove the indicator was bad business, opening up the possibility of unwelcome competition [FN50). The S.S. made short shrift of this objection and the company removed the warning odor. Now the doomed wouldn't even know it was Degesch's Zyklon B.

"[FN50] NI-1210, memorandum from Dr. Heinrich to Mr. Amend, dated June 21, 1944."

I hope that this information assists you in writing your dissertation. If you need more information please do not hesitate to ask us for assistance.

Yours sincerely,

Harry W. Mazal OBE

Response from questioner:

Dear Mr. Mazal

Thank you for your help. It seems propable to me that in the first phase of using gas chambers with original Zyklon B the gas contained ethyl bromoacetate. The limit of insupportability of this chemical is 40 mg per cubic meter of air and the concentration of 10 mg per cubic meter of air provokes irritation of eyes.

The physiology of this chemical was widely studied during and after the WWI, because it was used in gas shells. It was colorless and hard to detect. This type of chemicals were used, because they penetrated through gas masks and made the soldears to tear their gas masks off. In combination of more toxic war gases, like the phosgene, the irritants made the defence against gases harder.

It is easy to understand that SS preferred not to use original Zyklon B with irritants and warning agents.

I'm thankfull for your kind help. Here in Finland we don't have very detailed knowledge about the Holocaust. More detailed books are hard to find. It is not a part of our history because the Finns were not involved in it. Luckily this doesn't mean ignorance, and our schools teach the subject in a objective way. There have been no serious attempts of denying the Holocaust here. Thank's again. I wish you good luck.


I believe Rich Green forwarded my enquiry regarding the chronology of Zyklon B production to you a few weeks ago, and as I haven't heard anything yet I am contacting you to see if any progress has been made, or if it is worth posting the enquiry in full again.

Harry Mazal OBE responds:

I am one of the persons in the Holocaust History Project who responds to questions from our readers. I apologize for the slowness in my response but I have been extremely busy for the past few weeks.

The best source for obtaining information on Zyklon-B is in the United Kingdom. The Zykon-B Trial was held under the auspices of the British Military Court in Hamburg, much in the same way as the Belsen Trial, and over a dozen others:

Vol. I: The "Peleus" Trial*
Vol. II: The Belsen Trial*
Vol. III: The Gozawa Trial*
Vol. IV: The Hadamar Trial*
Vol. V: The Natzweiler Trial*
Vol. VI: Trial of von Falkenhorst*
Vol. VII: The Velpke Baby Home Trial*
Vol. VIII: The "Zyklon B" Trial
Vol. IX The Double Tenth Trial*
Vol. X: The Dulag Luft Trial*
Vol. XI: The Justice Trial
Vol. XII: Trial of Field Marshall Kesselring
Vol. XIII: The Stalag Luft Trial
Vol. XIV: The Trial of Arthur Grieser
Vol. XV: The Doctor's Trial

* Copies in my library.

Although I have sought to purchase the other books, and especially the Zyklon-B Trial, I have not had any success. I have been told that these books were contracted out (Zyklon-B to J. Harcourt Barrington) but never published.

This is most unfortunate because the trials were all extremely well documented and would have answered many of the questions which you (and many others) raise.

The original papers, documents in evidence, and interrogatories must be held by some branch of HM's Government. You might try to obtain this information from the British Library. If you do find it please share it with us!

I do have several volumes of the Law Reports of War Criminals: Selected and Prepared by the United Nations War Crimes Commission Volume 1 of which fortunately has a multi-page excerpt of the famous trial against Bruno Tesch, Karl Weinbacher, and Dr. Joachim Drosihn.

You may view this excerpt in its totality by visiting my personal web site:


and clicking on the Zyklon B Case link in "What's New on this Site."

Other books that might be of use to you are:

Nazi Mass Murder: A Documentary History of the Use of Poison Gas*
Edited by Eugen Kogon et al.
Translated by Mary Scott and Carolyn-Lloyd Morris
c. 1993, Yale University Press
ISBN 0-300-05441-6

I.G. Farben*
Richard Sasuly
c. 1947, Boni & Gaer (New York)

Josiah E. Dubois, Jr.
c. 1952, Beacon Press (Boston)
Library of Congress Catalog Card No. 52-7872

The Crime and Punishment of I. G. Farben
Joseph Borkin
c. 1978, The Free Press (New York)
ISBN 0-02-904630-0

and, of course, the voluminous and seminal:

Trials of War Criminals before the Nuernberg Military Tribunals under Control Council Law No. 10
Volume VII* & VIII*: "The Farben Case"
United States Government Printing Office
(1953), Washington D.C.

A large number of the documents offered in evidence and the testimonies of the witnesses refer to manufacturing processes including those for 'poison gas.'

Could you please explain more fully what you wish to do with this information?

I will continue to seek out more books on the subject. In the meantime these few recommendations ought to be of some assistance.

Yours sincerely,

Harry W. Mazal OBE


Dear Sir: My father survived the camps, his parents and sisters were not so lucky. I am writing about zyklon-B and dual-use precursors to chemical weapons. I would like to know (and obtain a reference) for whether the executives of Degesch or Tesch&Stabenow or IG Farben knew what their product was used for.

Gord McFee Responds:

I am one of the volunteers who answers these questions. Others of my colleagues may also answer.

The short answer to your question, at least according to the courts and the proof, is that that they knew what their product was intended for. According to remember.com,

Two German firms, Tesch/Stabenow and Degesch, produced Zyklon B gas after they acquired the patent from Farben. Tesch supplied two tons a month, and Degesch three quarters of a ton. The firms that produced the gas already had extensive experience in fumigation. "In short, this industry used very powerful gases to exterminate rodents and insects in enclosed spaces; that it should now have become involved in an operation to kill off Jews by the hundreds of thousands is not mere accident."(Hilberg, Commandant, 567) After the war the directors of the firms insisted that they had sold their products for fumigation purposes and did not know they were being used on humans. But the prosecutors found letters from Tesch not only offering to supply the gas crystals but also advising how to use the ventilating and heating equipment. Hoess testified that the Tesch directors could not help but know of the use for their product because they sold him enough to annihilate two million people. Two Tesch partners were sentenced to death in 1946 and hanged. The director of Degesch received five years in prison. (Feig)

My colleague Harry W Mazal, OBE has addressed this question in our question and answer service at:


and his personal site links to the Zyklon-B trial at:


See the verdict at:


In short, the firms knew what the Zyklon-B was being used for.

I hope this is helpful.


Best regards

Gord McFee


1. Zyklon-B works most effectively when it is heated or warmed up and spread out in a large area where air can reach it, which causes the release of the cyanide. How can Zyklon-B still work so quickly (with 20 minutes) on thousands of people when it is not heated up, and it is placed in the gas chambers via wire-mesh containors, which slows the amount of Zyklon-B to be released to a bare minimum in the gas chamber? Wouldn't this have taken longer than just 20 minutes to kill all the inhabitants?

Jamie McCarthy Responds:

Zyklon-B outgasses most quickly when it is warm, but it outgasses quickly enough when it is cold. The short answer to your question is "no," twenty minutes would have sufficed to kill everyone in the room even if it was quite cold. The "bare minimum" you refer to is deadly enough to kill a human being in a few breaths.

The long answer is explained in great detail in two essays by our member Dr. Richard Green (one of which I co-authored). Please see:



In particular, in that second essay, scroll down to the line of argumentation that begins "How fast could a lethal concentration be reached?" We address exactly this point.


2. The wire-mesh could be easily damaged when it is lowered into the chambers by the victims, but how come there is a lack of damage to these items? Had these itemes been damaged, withdrawing the Zyklon-B would be hazardous and slow as the chamber would not be ready until it would be fully ventilated and clean.

Jamie McCarthy Responds:

The thinner wire mesh baskets which held the HCN were lowered down within thicker wire mesh columns:


The columns or "wire pillars" (which provided no structural support for the room, only protection for the lowered basket) were described as having their outer layer of mesh made from 3 mm (1/8") diameter wire. It is unlikely that the victims inside could do much to damage even that outer layer.

Keep in mind that as soon as they realized poison was being lowered in, the people nearest to the wire columns died within a few seconds. Getting *to* the source of the poison, in order to futilely cause a little easily-repaired damage to a wire column, would surely not be the immediate objective of the rest of the people in the room.

It is easy for Holocaust-deniers to construct hypothetical scenarios, but one must take into account what people would actually do: crowded naked into a concrete basement, locked in and helpless, confused, yet led to believe that nothing would happen to them. When they realized the truth, they had moments to live. This is not a scenario which would produce even a minimally successful rebellion. The Nazis had made sure of that.


3. Why were the gas chambers kept to cool temperatures when Zyklon-B is better in warm areas?

Jamie McCarthy Responds:

What is "better" is irrelevant; as long as the killing operation proceeded well enough, it sufficed. Keep in mind that the difficult part of murdering 1000 people was not the gassing, which took roughly 20 minutes at most. It was the incineration of the corpses which followed which took hours. For detailed information on this, see:


"Optimizing" the killing operation by making the gassing a few minutes faster would have been a waste of time and resources. If it took 30 minutes instead of 20, nobody would have cared. It just would not have mattered.

But -- you can probably think of answers to this question if you phrase it differently. Why were the gas chambers underground, where it was cool? For one thing, that made it impossible for the victims to push down the walls or otherwise cause significant damage to the room. For another, it hid the operation more effectively from the sight and hearing of the rest of the camp. And from Allied overflights that might have been looking for evidence of mass murder, perhaps (that is just speculation).

Finally, your question supposes that the temperature was a problem in the summer, when underground was cooler. Please note that in the winter, the only time when Holocaust-deniers express concern about the ambient temperature and the outgassing rate of Zyklon-B, it was warmer underground.

So isn't underground exactly where such a room would have been constructed?


4. After the 20 minute period passed, what was done with the Zyklon-B that was not fully complete outgassing the cyanide? Was it reused? Was it buried? Has a dump with Zyklon-B been found in the death camps? Who had the job of carrying away the used Zyklon-B?

Jamie McCarthy Responds:

I would assume it was dumped on the ground and allowed to outgas, but nobody really knows. The SS men on the roof, still wearing gas masks, would probably have simply hauled up the baskets, dumped the still-potent Zyklon on the ground or into a bucket, and walked away.

A few hours later, when it was completely spent, it could have been dealt with. Perhaps after the cremation of the corpses was finished, or while it was still going on. The Zyklon could have been left where it was, ground to dust under someone's heel, shoveled into a pit or the ditch a few dozen yards away, or any number of other disposal methods. Most likely, it was just dumped into the ashes that remained of the victims, and however they were disposed of, the Zyklon was as well -- as farm fertilizer, or dumped into the nearby river.

Bone fragments of the victims of Auschwitz-Birkenau litter the ground in places. But no dump full of Zyklon has been found, that I know of. (Auschwitz was the only camp which used Zyklon in a large number of homicidal gassings.)


5. Why use Zyklon-B in such a primitive fashion in the gas chambers, when it was introduced more suitable for HCN in the delousing chambers?

Jamie McCarthy Responds:

I disagree that the gas chambers of Auschwitz-Birkenau were "primitive"; they are the most effective mass murder installations yet built by human beings. The gas chamber of Krema II is the single room on the planet where the most human beings have ever died. I am not sure what you think was "primitive" about the gassing operation and subsequent cremation. It seems to me quite the opposite, an assembly line of death. Was it primitive because it did not use lasers?

I am not entirely sure what you are getting at regarding the delousing chambers. The same poison was used (but obviously there was no need for the wire mesh pillars, the doors with peepholes protected by wire mesh, etc.)


6. Why use Zyklon-B in gas chambers instead of diesel exhaust chambers at Treblinka, which were supposedly more capable than Zyklon-B?

Jamie McCarthy Responds:

Zyklon was a better killer than engine exhaust, actually; it was probably a fair bit faster, and HCN is unquestionably a deadlier poison than anything in engine exhaust.

But again, I must question the relevancy of this question. The mass murder program in Nazi Germany evolved over time. Some methods of killing, at different times and places, were more capable than others. Since different methods were being tried, and different allocations of resources were more or less important at different places and stages of the war, it would not be at all surprising to find that, measured scientifically in retrospect, killing efficiency would go up and down.

But in this case, the engine-exhaust chambers of Belzec, Sobibor and Treblinka -- apparently some were diesel and some were not -- were followed the next year by the Zyklon chambers of Auschwitz, which were indeed more effective on a number of levels. If you find this surprising, I do not understand why.

And I repeat myself, but please note that questions about the "capability" of the poison gas are largely irrelevant, since the bottleneck of the operation was the disposal of the corpses.


I love the holocaust-history.org website. I also am not a Holocaust denier, I just do not have the sources or knowledge to reply to these denier questions.

Jamie McCarthy Responds:

Thank you. If you have followup questions, please feel free to write us again.

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