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        INSTITUTE OF FORENSIC RESEARCH
        In the name of Prof. Dr. Jan Sehn, Krakow
        Division of Forensic Toxicology

                                Krakow, 24 Sept. 1990
                                Westerplatte 9 / Code 31-033
                                Tel. 505-44, 592-24, 287-50
                                Telex 0325213 eksad ...

      The hydrocyanic acid (HCN) that is released from the Zyklon B
      preparation is a liquid with a boiling point of about 27 degrees
      Celsius.  It has an acidic character, and therefore forms
      compounds with metallic salts, which are known as cyanides.  The
      salts of alkaline metals (such as sodium and potassium) are
      water soluble.

      Hydrocyanic acid is a very weak acid, and accordingly its salts
      dissolve easily in stronger acids.  Even carbonic acid, which is
      formed as a reaction of carbon dioxide with water, will dissolve
      ferro-cyanide.

      Stronger acids, such as sulfuric acids, easily dissolve the
      cyanides.  The compounds of cyanide ions with heavy metals are
      longer lasting.  This includes the already mentioned Prussian
      blue, although this will also slowly dissolve in an acidic
      environment.

      Therefore, one can hardly assume that traces of cyanic compounds
      could still be detected in construction materials (plaster,
      brick) after 45 years, after being subjected to the weather and
      the elements (rain, acid oxides, especially sulfuric and
      nitrogen oxides).  More reliable would be the analysis of wall
      plaster [samples] from closed rooms which were not subject to
      weather and the elements (including acid rain).

      The discovery of hydrocyanic acid compounds in samples of
      material which had been subject to the elements can only be
      accidental.
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