Feldmann, R.R.FeldmannHuettenhain, S.H.S.H.Huettenhain2022-03-082022-03-081990https://publica.fraunhofer.de/handle/publica/302321The invention relates to an indication device generating a dye to detect the presence of traces, in particular of toxic, low-valency sulphur compounds in a gas mixture, whereby the indication device comprises a neutral solid substrate (2) which is saturated with acid indicator and oxidizing agent. The visible side of the substrate (2) is coated with a transparent membrane (4) consisting of plastic foil, which has a specific permeability for organic and chemical molecules of the anticipated size and polarity. The oxidizing agent can only be applied in localized areas (6) of the substrate (2).de608570610620660patent1988-3826090