THE RUDOLF REPORT

GERMAR RUDOLF · THE RUDOLF REPORTFe 3+ can be quantitatively removed from sour wine with [Fe(CN) 6 ] 4- , ausual procedure to remove iron ions from wine. 371 Concentrated alkalicarbonate solutions will precipitate the Fe 2+ of Iron Blue as FeCO 3 , sothat they destroy the entire pigment by precipitating Fe 3+ as Fe(OH) 3(due to alkalinity) and the hexacyanoferrate(II) salt [Fe(CN) 6 ] 4- . 372 Calciumcarbonate solutions, however, would not be sufficient due to theirmarginal saturation solubility. Besides that, Kohn examined the supportiveeffect of most of the organic ligands to disperse Iron Blue. 373Thus, apart from OH – (alkaline medium), there are no other ligandsto be considered competing in the formation or dissolution of IronBlue in the cases here under consideration.6.6.4. Effects of Light6.6.4.1. OverviewIron Blue itself is generally considered a light-resistant pigment,which is only slowly decomposed by the effects of UV radiation. 374Thus, there are even patents utilizing Iron Blue as a UV-absorbingpigment, which is only meaningful with sufficient resistance to UVradiation. 375 Since the walls of interest to us here are protected fromUV radiation and because UV radiation can only exert a superficialeffect on the walls, while the Iron Blue would form and remain withinthe walls, a possible process of decomposition by UV radiation canhave no influence upon our investigation.6.6.4.2. ExcursusCertain wave lengths of ultraviolet radiation may set free CN – fromhexacyanoferrate(II) and -(III), the preliminary stages of Iron Blue. Asfar as hexacyanoferrate(III) is concerned, this leads to the formation of371 C. Lapp, C. Wehrer, P. Laugel, Analusis, 13 (4) (1985), pp. 185-190.372 G.-O. Müller, op. cit. (note 358).373 M. Kohn, Anal. Chim. Acta 3 (1949), pp. 558ff.; ibid., 5 (1951), pp. 525-528; ibid., 11 (1954),pp. 18-27.374 See also Winnacker-Küchler, Chemische Technologie, volume 2, Carl Hanser Verlag, Munich1982, p. 197; H. Ferch, H. Schäfer, op. cit. (note 333); Wilhelm Foerst (ed.), Ullmanns Encyklopädieder technischen Chemie, volume 13, Urban und Schwarzenberg, Munich 3 1962, p.794; ibid., volume 18, Verlag Chemie, Weinheim 1979, pp. 623ff.; H. Watanabe, J. Jap. Soc.Col. Mat., 34 (1961), pp. 5-8; L. Müller-Focken, Farbe und Lack, 84 (1987), pp. 489-492.375 H. Tada, M. Kunio, H. Kawahara, Jpn. Kokai Tokkyo Koho, 1990, 3 p. Source only availableas abstract.176