| http://www.w3.org/ns/prov#value | - The reducing agent may include chelates formed of formic acid, citric acid, metasilicic acid, ethylenediaminetetraacetic acid, ethylenedinitrotetraacetic acid or a sodium salt or potassium salt of any of these and a heavy metal such as iron, copper or chromium; and ferrous sulfate or ferrous pyrophosphate.
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