THE RUDOLF REPORT

GERMAR RUDOLF · THE RUDOLF REPORTperature, and since, as a rule, the relative humidity of the air decreases,and since both lead to a drop in the water content, any increase in thetemperature has a cumulative effect. Drops in water content by a powerof ten at temperature increases of 10°C have been proven in the temperatureranges of 10-30°C under consideration (see chapter 6.7.).C: Only an acceleration in the slowest of the five steps describedin chapter 6.5.1. can be responsible for a change in the velocity of theentire reaction. In neutral or alkaline medium, this is the displacementof the oxygen or OH – -ion in rust by the cyanide ion (point c). Althoughthe iron(III)-cyanide [Fe(CN) 6 ] 3– itself is stable in a moderately alkalinemedium 350 —that is, the iron(III)-cyanide is more stable than therust—the displacement of the OH – -ions in rust is inhibited by the cyanide,since the rust is not dissolved in water. An increase in temperatureby 20°C usually doubles the velocity of reaction, if the other parametersremain unchanged.This is, however, not so in extreme cases, since, as shown above,the velocity of reaction is very strongly negatively influenced by themassively decreased water content at higher temperatures (see above):decreased mobility of the reaction partner, decreased reactivity of iron,increased evaporation of ad-/absorbed hydrogen cyanide etc. (seechapters 6.5.2. and 6.5.3.). A strong reduction in pigment formationmust therefore be expected at increased temperatures.A decisively higher water content of the solid material and theconsiderably better absorption and solubility properties of hydrogencyanide in water are the reasons for the tendency of solid materials toaccumulate more cyanides with lower temperatures. An increase in thereactivity of iron oxide (rust) in the solid body with relation to hydrogencyanide with a higher water content of the solid material at lowertemperatures must be anticipated, as well as with a general increase inthe reactivity of all agents. A cooler, and thus moister, solid material istherefore better suited to the formation of Iron Blue than a warm, drybody. 351350 See also J.C. Bailar’s remarks on the massive reduction force of Fe(CN)6] 3- in the alkalineenvironment, op. cit. (note 338).351 In the immediate vicinity and beyond the freezing point of water, however, the reactivitydrops of course.166