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On the other hand a high pH makes the formation of a necessary precursor to Prussian blue less likely . During the time the Frank family was in hiding , several additional people in the building and the neighborhood had begun to be suspicious about the quantities of food going into the house . From among other metals in some samples there were also barium , zinc , sodium , manganese and from non-metals boron . We find that the aqueous concentration of cyanide ions in the gas chambers was reduced by 1 ) the short gassing time , and 2 ) the washing of the walls with water after gassings , and that these processes would have reduced that concetration below the threshold identified by Alich et . A cursory search in my extensive library did not reveal any further information .