THE RUDOLF REPORT

6. FORMATION AND STABILITY OF IRON BLUEest here, this long-term test involved considerably more severe conditions,since in this case, the externally formed Iron Blue was only superficiallyadsorbed upon the aluminium sheets. The pigment neverthelessresisted extremely well.Another event proves the extraordinary long-term stability of IronBlue. For many decades at the end of the 19 th and the early decades ofthe 20 th century, Iron Blue was a by-product in the generation of citygas, because the hydrogen cyanide contained in coke gas had to beeliminated for security reasons by washing it with iron hydroxide priorto introduction into the city gas network. Iron Blue is the end productof this washing process. City gas works frequently disposed of thisproduct by distributing some of it over their factory terrain with theintend to kill weeds—in vain, though, since Iron Blue has no effect asan herbicide. Today, the grounds of former German city gas works stillcontain high quantities of Iron Blue, many decades after the workswere put out of operation. It was neither decomposed, nor dissolved orwashed away by rain water, since it is insoluble. In particular, terrainwith a high Iron Blue content is not considered polluted, since it isphysiologically unobjectionable due to its stability. 385In summary, it may be stated that Iron Blue having formed in theinterior of a wall as a component of the wall itself, possesses a longevitycomparable to the iron oxide from which it has formed. This means simplythat Iron Blue possesses a degree of stability which is comparable tothat of the masonry itself: the Iron Blue will remain contained in the wallfor as long as the wall itself remains in existence. 386Once perceptible quantities of cyanide have accumulated within awall, therefore, and once conditions permit the conversion of the cyanideinto Iron Blue, no perceptible reduction in the Iron Blue content can beanticipated, even after fifty years or more.A typical example of the manner in which the media deal with thesefacts is a press report issued by the German Press Agency (DeutschePresseagentur, dpa) on March 29, 1994, and which was then publishedin many German newspapers and even broadcast on radio. The report385 D. Maier, K. Czurda, G. Gudehus, Das Gas- und Wasserfach, in: Gas • Erdgas, 130 (1989),pp. 474-484.386 An interesting study has been conducted in this connection about the reduction of solublecomponents in concrete standing in water, providing support to the statements made here: noteven the concentration of alkali ions, which are the most soluble components of concrete, wasmassively reduced: H.A. El-Sayed, Cement and Concrete Research, 11 (1981), pp. 351-362.179