| http://www.w3.org/ns/prov#value | - The elements may for example be used in the form of easily obtainable salts of the corresponding acids, for example NH4 VO3 or Na2 Cr2 O7 .sup.. 2 H2 O. Tetravalent and/or pentavalent vanadium or hexavalent chrome are active also in the presence of impurities of dilute sulfuric acid which have a reducing effect, such as organic components.
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