| http://www.w3.org/ns/prov#value | - The concentration of iron ions in the water may be varied depending on conditions such as the kind and temperature of the water, the kind of the iron ions or the iron ion supply compound and the like, but generally the concentration is preferably 0.005 to 0.05 mg/liter, more preferably 0.01 to 0.03 mg/liter.
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