Two methods specified using potassium dichromate as titrant after reduction of the iron (III) by tin (II) chloride and titanium (III) chloride. Excess reductant oxidized by either dilute potassium dichromate or perchloric acid.Cross References:BS 1792BS 5660:Part 1BS 5660:Part 2BS 5661BS 7020:Part 1BS 7020:Part 2ISO 385-1ISO 648