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Wet with hose down.The tips resemble a mix of the technical and unfussy, calling pro chemicals such so hydrogen sulphide and ammonia, with directives to sponge down with fill with tears and dry taking part in the air.A not many other steps include wetting the paper with iron sulphate and a slight solution of potassium ferrocyanide, all of which, according to the provide evidence, collectively expose a host of other substances like iron and copper used to conceal characters, as follows enlightening the expressions and making the pages readable.The secret symbols keep a record instructs spies how to disguise their correspondence.The tips call in support of a nitrate and starch solution, which, according to the keep a record, may perhaps survive conceded in support of model wearing handkerchiefs or else starched collars.A tumbler of wet is boiled at once with a schedule spoon of starch, allow to cool, and add ten gramms sic of nitrite of juice, the advice say.