Editing Potassium ferrocyanide (section)

==Synthesis==

In 1752, the French chemist [[Pierre Macquer|Pierre Joseph Macquer]] (1718–1784) first reported the preparation of Potassium hexacyanidoferrate(II), which he achieved by reacting [[Prussian blue]] (iron(III) ferrocyanide) with [[potassium hydroxide]].<ref>{{cite journal |last1=Macquer |title=Éxamen chymique de bleu de Prusse |journal=Histoire de l'Académie Royale des Sciences …, § Mémoires de l'Académie royale des Sciences |date=1752 |pages=60–77 |url=https://www.biodiversitylibrary.org/item/88112#page/250/mode/1up |trans-title=Chemical examination of Prussian blue |language=fr}} 
 From pp. 63-64:  ''"Après avoir essayé ainsi inutilement de décomposer le bleu de Prusse par les acides, … n'avoit plus qu'une couleur jaune un peu rousse."''  (After having tried so vainly to decompose Prussian blue by acids, I made recourse to alkalies.  I put a half ounce of this [Prussian] blue in a flask, and I poured on it ten ounces of a solution of nitre fixed by tartar [i.e., [[potassium nitrate]] (''nitre'') which is mixed with crude [[potassium bitartrate|cream of tartar]] and then ignited, producing potassium carbonate].  As soon as these two substances had been mixed together, I saw with astonishment that, without the aid of heat, the blue color had entirely disappeared; the powder [i.e., precipitate] at the bottom of the flask had only a rather gray color:  having put this vessel on a [[sand bath]] in order to heat the solution until it simmered, this gray color also disappeared entirely, and all that was contained in the flask, both the powder [i.e., precipitate] and the solution, had only a yellow color [that was] a little red.)</ref><ref>{{cite journal |last1=Munroe |first1=Charles E. |last2=Chatard |first2=Thomas M. |title=Manufactures: Chemicals and Allied Products |journal=Twelfth Census of the United States: Bulletins |date=1902 |issue=210 |pages=1–306 |url=https://books.google.com/books?id=8UIUAQAAMAAJ&pg=RA1-PA31}}; see p. 31.</ref>

===Modern production===
Potassium hexacyanidoferrate(II) is produced industrially from [[hydrogen cyanide]],  [[iron(II) chloride]], and [[calcium hydroxide]], the combination of which affords Ca<sub>2</sub>[Fe(CN)<sub>6</sub>]·11H<sub>2</sub>O.  This solution is then treated with potassium salts to precipitate the mixed calcium-potassium salt CaK<sub>2</sub>[Fe(CN)<sub>6</sub>], which in turn is treated with [[potassium carbonate]] to give the tetrapotassium salt.<ref name=Ullmann>{{ cite encyclopedia |author1=Gail, E. |author2=Gos, S. |author3=Kulzer, R. |author4=Lorösch, J. |author5=Rubo, A. |author6=Sauer, M. |author7=Kellens, R. |author8=Reddy, J. |author9=Steier, N. |author10=Hasenpusch, W. | title = Cyano Compounds, Inorganic | encyclopedia = Ullmann's Encyclopedia of Industrial Chemistry |date=October 2011 | publisher = Wiley-VCH | location = Weinheim | doi = 10.1002/14356007.a08_159.pub3 |isbn=978-3527306732 }}</ref>

===Historical production===
Historically, the compound was manufactured from nitrogenous organic material, iron filings, and potassium carbonate.<ref name=Wagner>{{cite book|last=Von Wagner|first=Rudolf|title=Manual of chemical technology|year=1897|publisher=D. Appleton & Co.|location=New York|page=474 & 477|url=https://archive.org/details/manualofchemical00wagnuoft}}</ref> Common [[nitrogen]] and [[carbon]] sources were [[torrefaction|torrified]] horn, leather scrap, [[offal]], or dried blood. It was also obtained commercially from gasworks spent oxide (purification of city gas from hydrogen cyanide).