What is the difference between potassium ferrocyanide and ferricyanide?

K₄[Fe(CN)₆] 

Potassium ferrocyanide (E536) is classified as a neutral salt and is becoming increasingly common in the diet by being added to iodised salt as an anti-caking agent.

Sodium, potassium and calcium ferrocyanides (E535, E536 and E538) are authorised as food additives in the European Union (EU) in accordance with Annex II to Regulation (EC) No 1333/2008 on food additives and specific purity criteria have been defined in the Commission Regulation (EU) No 231/20121.

Applications

Potassium ferrocyanide finds many niche applications in the industry. It and the related sodium salt are widely used as anticaking agents for both road salt and table salt. The potassium and sodium ferrocyanides are also used in the purification of tin and the separation of copper from molybdenum ores. Potassium ferrocyanide is used in the production of wine and citric acid.

It can also be used in animal feed.

In the laboratory, potassium ferrocyanide is used to determine the concentration of potassium permanganate, a compound often used in titrations based on redox reactions. Potassium ferrocyanide is used in a mixture with potassium ferricyanide and phosphate-buffered solution to provide a buffer for beta-galactosidase, which is used to cleave X-Gal, giving a bright blue visualization where an antibody (or other molecule), conjugated to Beta-gal, has bonded to its target. On reacting with Fe(3) it gives a Prussian blue colour. Thus it is used as an identifying reagent for iron in labs.

Potassium ferrocyanide can be used as a fertilizer for plants.

Prior to 1900 AD, before the invention of the Castner process, potassium ferrocyanide was the most important source of alkali metal cyanides. In this historical process, potassium cyanide was produced by decomposing potassium ferrocyanide.

Toxicity

Potassium ferrocyanide is nontoxic and is not decomposed to cyanide in the body.

Formula: K₄[Fe(CN)₆] · 3H₂O

Molecular Weight:  422.388 g/mol
Form: Light yellow, monoclinic crystalline granules
CAS Number: 14459-95-1
Density: 1.85 g/cm³
Synonyms:  (Yellow) Prussiate of Potash, Potassium hexacyanoferrate (II) trihydrate, Tetrapotassium ferrocyanide trihydrate, Ferrate hexacyano tetrapotassium trihydrate