THE RUDOLF REPORT

8. EVALUATION OF CHEMICAL ANALYSESterial and its preparation. The hard, iron-poor interior plaster of limemortar adheres very poorly to the wall and is already falling off insome places. The contact between plaster and wall is so poor in places,that when one knocks on the wall, one hears that there is a hollowspace beneath. Such weak contact between wall and plaster, however,prevents moisture in the wall from diffusing through to the surfaceplaster and carrying soluble cyanide compounds (for example, iron(II)-cyanide) with it.Sample 19 was divided in two, since the upper layer of plaster inthis room is visibly different from the layer lying beneath: The first 4mm of plaster consists of a white, brittle, hard material (sand-poor limeplaster), while the layer underneath consists of an ochre-colored, sandrichlime plaster. The separation was not completely successful; partsof the sand-rich mortar remain in Sample 19a. The analysis for iron,which might possibly have been even lower in the presence of completeseparation, confirms the assumption that the upper layer is aniron-poor lime plaster. This explains the deficient formation of bluespots of pigment on the surface of the plaster in this room, since thereis too little iron available for the formation of pigment. Nevertheless,even the upper layer of plaster exhibits quite high cyanide values. Thisshows that the layer of plaster was not applied after termination of thedisinfestation actions.8.3.3.4. Samples 25-30: TestsFor an evaluation of the reactivity of hydrogen cyanide with buildingmaterials, a series of tests was undertaken; during the first series,only brick was fumigated with hydrogen cyanide, generated from adefined quantity of KCN+H 2 SO 4 in a gas-tight container. Over thecourse of the tests, it became apparent by means of sensitive differentialpressure measurements that only a part of the hydrogen cyanideadded to 16% sulfuric acid was released as gas. Hydrogen cyanide isso easily soluble, even in this acid, that only a portion of it is actuallyreleased into the gas room. The actual quantity of gas in the reactioncontainer therefore lay far below the mathematically calculated 3.7%by volume, while the pressure measurements consequently lay around2 % by volume.On the construction of a reaction container from a glass cylinder,sealed above and below by PVC plates with gas qualities and O-rings,265