| http://www.w3.org/ns/prov#value | - Preferably the indicating element used in the detector of the present invention comprises an aqueous solution of a colorless compound which provides an alkaline solution, i.e. a base, a chromogenic pH-sensitive indicator and a hygroscopic, colorless, transparent, water-miscible liquid, and the sensitivity of the indicating element in each of said components is established by varying the concentrat
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