THE RUDOLF REPORT

6. FORMATION AND STABILITY OF IRON BLUEin the extremely voluminous precipitate. The resulting crystal is thereforevery faulty and more appropriately called a polymer. 330 By filtration,drying and intensive grinding, however, this very inhomogeneous,polluted Iron Blue can be transformed into a pigment which isonly hardly colloidal dispersible. 331 This ‘soluble’ Iron Blue is notsoluble in the original sense of the word, but can more easily be colloidallydispersed than the ‘insoluble’ Iron Blue, which is very importantfor its application as a pigment. 332,333However, these colloids are very instable and precipitate easilywhen salts are added. 334 According to Buser, 329 even in presence ofhigh concentrations of potassium ions, almost pure ‘insoluble’ IronBlue can be obtained, if the formation process is proceeding slowlyenough. In case of deeper interest about the structure one might consultthe following literature. 329,3356.5. Formation of Iron Blue6.5.1. OverviewWe are only concerned, in this connection, with how Iron Bluearises from hydrogen cyanide and iron compounds in building materials.In building materials, the iron is generally present in trivalent form(Fe 3+ ), in the form of ‘rust’.330 Originally, this term was used only in organic chemistry for chainlike connected, sometimesalso branched attachments of equal segments.331Dispersion (lat.: dispersere, distribute) are distribution of two different phases within eachother. They are called colloids (gr.: gluelike) if the particles are between 10 -8 and 10 -7 m small.Such a mixture in liquids scatters the light (Tyndall effect), is thus not clear. But due to electrostaticrepulsion (equally charged particles), colloids do not tend to coagulate and precipitate.Suspension: (lat.: to float) are coarsely dispersed system with particle sizes bigger than 10 -6 m.332 R.E. Kirk, D.F. Othmer, Encyclopedia of Chemical Technology, Vol. 13, 3. ed., Wiley &Sons, New York 1979, pp. 765-771; J.A. Sistino, in: Peter A. Lewis (ed.), Pigment Handbook,Vol. 1, Wiley and Sons, New York 1974, pp. 401-407; A.F. Holleman, N. Wiberg, Lehrbuchder Anorganischen Chemie, de Gruyter, Berlin 100 1985, p. 1143333 H. Ferch, H. Schäfer, Schriftenreihe Pigmente Nr. 77, Degussa AG, Frankfurt 1990.334 K.A. Hofmann, Anorganische Chemie, Vieweg, Braunschweig 21 1973, p. 677; B.N. Gosh,K.C. Ray, Trans. Far. Soc. 53 (1957), pp. 1659-1661; E.F. Zhel’vis, Y.M. Glazman, UkrainskiiKhim. Zh. 35 (1969), pp. 766ff.; East European Sci. Abs. 5 (1969), pp. 84f.335 M.B. Robin, Inorg. Chem. 1 (1962), pp. 337-342; Gmelins Handbuch der AnorganischenChemie, 59 (Fe), B4, Verlag Chemie, Weinheim 1932, pp. 670-732; R.E. Wilde, S.N. Ghosh,B.J. Marshall, Inorg. Chem. 9 (1970), pp. 2512-2516; R.S. Saxena, J. Ind. Chem. Soc. 28(1951), pp. 703-709; A.K. Bhattacharya, J. Ind. Chem. Soc. 28 (1951), pp. 221-224.159