THE RUDOLF REPORT

GERMAR RUDOLF · THE RUDOLF REPORTincreased water accumulation in rust, too. The rust expands, so tospeak, and thus becomes more reactive towards competing ligands 345like cyanide. Freshly precipitated, extremely moist and non-homogenousiron hydroxide precipitations possess extreme reactivity, andtogether with hydrogen cyanide, as shown in chapter 6.5.2.2., theyform the pigment in visible quantities in minutes.For the formation of colloidally dispersible Iron Blue, the quickformation in aqueous solution with high concentrations of the agents isrequired (see chapter 6.4.2.), since this leads to heterogeneous crystallites(tiny crystals) with many inclusions (ions, solvent molecules) anda high degree of disorder. These crystallites have only a small tendencyto coagulate.The slow interface reaction on the phase-boundary layer liquidsolidwith quite low concentrations of the reacting agents will suppressthe formation of colloidally dispersible Iron Blue. The process describedhere, occurring in walls exposed to hydrogen cyanide, stronglyresembles the formation of monocrystals as described by Buser, 329since in this case also, one reagent (Fe 2+ ) had to be formed throughslow reduction by excess cyanide. Thus, except from the inhomogeneousmaterial, the conditions here under consideration are suitable for aslow crystal growth of insoluble Iron Blue without large amounts ofinclusions and formation of crystal defects.6.5.4. Temperature6.5.4.1. OverviewThe environmental temperature influences larger magnitudes inquite a different manner:A) Accumulation of hydrogen cyanide in the moisture of the masonry;B) Water content of the solid body;C) Velocity of reaction.A: Graph 2 shows the maximum solubility of HCN in water atvarious temperatures with a hydrogen cyanide content of 1 mol% in345 In complex chemistry, ligands refer to in most cases negatively charged particles (anions)surrounding in most cases a positively charged central particle (cation, in general a metal ion).In this case, the central atom iron (Fe 2+/3+ ) is surrounded by the ligand cyanide (CN – ).164