<unk>  is a food additive with E number E381 used as an acidity regulator.[citation needed]  It is a green or reddish-brown powder which is very soluble in water.
The molecular formula of ammonium iron(III) citrate is variable. It can be prepared by adding Fe(OH)3 to an aqueous solution of citric acid and ammonia.  The brown form is approximately 9% NH3, 16.5–18.5% Fe, and 65% hydrated citric acid; the green form is approximately 7.5% NH3, 14.5–16% Fe, and 75% hydrated citric acid.  The green type is more readily reduced by light than the brown.
Other uses for<unk>  include water purification and printing (cyanotype). It is used as a reducing agent of metal salts of low activity like gold and silver and is also in a commonly used recipe with potassium ferricyanide to make cyanotype prints.<unk>  is also used in Kligler iron deeps to determine hydrogen sulfide production in microbial metabolism.<unk>  is present in Scottish carbonated soft drink Irn-Bru.
In medicine,<unk>  is used as a contrast medium.  It is also used as a hematinic.
Ammonium ferric citrate
Sodium aurothiomalate
Calcium arsenate
Sodium selenate
Ammonium hexachloroplatinate
Tetraferric tricitrate decahydrate
Pentetate Zinc Trisodium
Magnesium peroxide