Formation and Stability of Iron Blue

Hundreds of thousands of people are claimed to have been killed in the alleged Auschwitz gas chambers by hydrogen cyanide in the form of the product Zyklon B . The question which now arises is the following could this poisonous gas leave chemical traces, which could perhaps be detected in these alleged chemical slaughterhouses  

If hydrogen cyanide (HCN), the reactive compound in Zyklon B, were only bound to the walls by adsorption (adhesion),313 there would not be any detectable residues today anymore, due to the volatility of hydrogen cyanide (boiling point 25.7°C) all the hydrogen cyanide involved would long since have evaporated. 

But if one assumes that the hydrogen cyanide, during fumigation, would combine with certain materials in the masonry to create other, considerably more stable compounds, then one might anticipate the possible existence of chemical residues even today. 

The reaction products of interest to us in this respect are the salts of hydrogen cyanide, called cyanides,314 in particular, the iron cyanide group, formed by a compound of iron and cyanide. Iron occurs universally in nature. It is iron which gives brick its red color, sand its ochre color, and clay its color ranging from yellowish to reddish-brown. More precisely, we are speaking of iron oxide, popularly known as rust . Basically, all walls consist of at least 1% rust, as a result of sand, gravel, clay, and cement, of which the wall is constructed. 

The iron cyanides have long been known for their extraordinary stability, one of them having achieved particular fame as one of the most commonly used blue pigments during the last three centuries  

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The. exceptionally high affinity of iron(II) for cyanide ion is reflected in the heat of formation - of the [Fe(CN)6] " anion (equation 31). The stability of this, the ferrocyanide ion, is illustrated by the nature and history of its iron(III) salt, Prussian blue, possibly the first isolated coordination complex, which is discussed in Section 44.1.5.2.4. 

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