The elements of materia medica and therapeutics: Ferri Ferro-sesquicyanidum. - Sesqui-ferrocyanide of iron, or Prussian Blue.

The elements of materia medica and therapeutics
by Jonathan Pereira, M.D. F.R.S. & L.S.
Fourth Edition, enlarged and improved, including notices of themost of the medicinal substances in use in the civilized world, and forming an Encyclopædia of Materia Medica.
Vol. I.
London: printed for Longman, Brown, Green, and Longmans, Paternoster Row.
1854.Formula 4Fe,3Cfy, or 7Fe,9Cy. Equivalent Weight 430.

History. — This compound was accidentally discovered at the commencement of the last century by Diesbach and Dippel. It was termed Prussian or Berlin blue (cæruleum borussicum seu berolinense). It is also termed ferroprussiate of iron.

Preparation. — It is sometimes prepared by mixing a solution of per sulphate or perchloride of iron with a solution of ferrocyanide of potassium.

In commerce it is procured by adding a mixture of two parts of alum and one of sulphate of iron to an impure solution of ferrocyanide of potassium (called blood-lye or lixivium sanguinis). A dingy green precipitate falls, which, by repeated washing with very dilute hydrochloric acid and exposure to the air, becomes gradually of a deep blue. It is then collected and drained on a cloth, and afterwards dried.

By the reaction of ferrocyanide of potassium on sulphate of the protoxide of iron, sulphate of potash is formed in solution, and a white precipitate subsides, which, by exposure to the air, becomes blue. Ferrocyanide of potassium, with sulphate of the sesquioxide of iron, forms sulphate of potash and ferrosesquicyanide of iron. Commercial Prussian blue contains alumina derived from the alum), and usually some sesquioxide of iron.

[Pure Prussian blue is obtained by adding a solution of ferrocyanide of potassium to a solution of persulphate of iron. The precipitate thus obtained should be thoroughly washed with water slightly acidulated with sulphuric acid, and subsequently with pure water. It should then be dried in a warm place.

In this reaction three equivalents of ferrocyanide of potassium 3(K₂FeCy₃) decompose two equivalents of persulphate of iron 2(Fe₂O₃,3SO₃), and the equation may be thus represented —
3K₂,FeCy₃ + 2Fe₂,3SO₃ - 6KO,SO₃ + 3Cy₃ + 2Fe₂ (Prussian blue) = 7Fe,9Cy (Prussian blue)

If the sesquichloride of iron be employed for the production of the precipitate, then the reaction will be as follows: — [---]

Properties. — Prussian blue occurs in masses of a rich dark blue colour. It is tasteless and inodorous. When broken or rubbed, it has a copper or bronze tint, somewhat like that of indigo, but which is distinguished from that of the latter by its being removed by rubbing with the nail. It is insoluble in water, alcohol, and the diluted mineral acids. Strong sulphuric acid forms with it a white pasty mass, from which water again separates Prussian blue. Both nitric acid and chlorine decompose it. Hydrochloric acid abstracts part of its iron.

Characteristics. — Its colour and copper tint above described form part of its characteristics. Boiled with water and binoxide of mercury it yields bicyanide of mercury. Boiled with solution of potash it forms ferrocyanide of potassium. Heated in a retort it yields water, hydrocyanate of ammonia, then carbonate of ammonia, and leaves a black, carbonaceous, and ferruginous mass.

The blue precipitate which falls when red prussiate of potash is added to a protosak of iron, is called Turhbull's Blue. It consists of 5 eq. iron and 6 eq. cyanogen; or 3 eq. protocyanide of iron and 2 eq. sesquicyanide of iron. Liebig calls it ferridcyanide of iron (6Cy+5Fe or 3Fe+(Cy_?Fe_?). It is distinguished from Prussian bine by the circomsttnK, that, when boiled in a solution of yellow prussiate of potash, it affords red prussiate of potash, which is dissolved, and a grey insoluble residue of ferrocyanide of iron and ferrocyanide of potassium.

Basic Prussian Blue, or the Basic Sesquiferrocyanide of Iron, is a compound of 1 met. Prussian blue and 2 equiv. sesquioxide of iron. It is soluble in water. It is formed by exposing ferrocyanide of potassium and iron (the bluish-white precipitate formed when yellow prussiate of potash is added to a protosalt of iron) to the air. Oxygen is absorbed, and two products are obtained, viz. basic Prussian blue and yellow prussiate of potash 2 eq. of ferrocyanide of potassium and iron (Fe₁₀Cy₁₂K), with 3 eq. of oxygen (O₃), yield 1 eq. yellow prussiate of potash (FeCy_?K_?), 1 eq. Prussian blue (Fe₇Cy_?), and 2 q. of sesquioxide of iron (Fe_?O_?).

Composition. — The following is the composition of pure and anhydrous Prussian blue: — [---]

Prussian blue contains the elements of water, of which it cannot be deprived without an alteration in the properties of the compound. This shows that it is rather a hydroferrocyanate of the peroxide of iron than a cyanide, as it is commonly described to be. Its formula in this state would be 2(Fe₂O₃) + 3(CfyH₂), i. e. 1 atom of anhydrous Prussian blue and 6 atom of water: —

[---]

According to Brande, the weight of iron in common Prussian blue is to that in the ferridcyanide (Turnbull's blue) as 14 to 15: —
6Cfy + 8Fe = Common Prussian Blue.
8Cfy + 9Fe = Prussian Blue from Ferridcyanide, — Ed.]

Purity. — Prussian blue of commerce usually contains alumina and sesquioxide of iron. These may be delected by boiling the suspected compound with diluted hydrochloric acid, which dissolves both the impurities. Caustic ammonia added to the filtered solution throws down the impurities; excess of the alkali will redissolve the alumina.

¹ Wibmer, Wirk. d. Arzneim. ii. 356.

² Handwört. d. prukt. Arzneim. ii. 557.

³ Treatise on the Usee of Prussian Bine in Intermitting and Remitting Fevers, Maryland, 1822.

⁴ New York Medical and Physiological Journal, 1823, quoted by Uichter, Ausf. Arzneim.

⁵ Mat. Med. i. 233.

⁶ Froriep'a Notizen, Bd. xvii. 340.

⁷ United States Dispensatory.Physiological Effects, a. On Animals. — Coullon gave it to dogs and sparrows without killing them; and Schubarth states that the only effect pro duced on a dog by two drachms was dejection.¹

b. On Man. — Ite effects on man are not very obvious. It is reputed alterative, tonic, and febrifuge. Sachs² calls it a resolvent tonic.

Uses. — It has been recommended by Dr. Zollickoffer³ as a more certain, prompt, and efficacious remedy for intermitting and remitting fevers than cinchona; and particularly adapted for children, on account of its insipidity and sinalluess of dose. It may be administered during the paroxysm as well as in the intermission, and does not disagree with the most irritable stomach. Hosack,⁴ Eberle,⁵ and others, have borne testimony to its good effects. Subsequently, Zollickoffer found it useful in dysentery. Kirkhoff⁶ used it for many years in epilepsy, with the best results, having cured some cases of several years' standiug. It has also been employed by Dr. Bridges, of Philadelphia,⁷ in a case of severe and protracted facial neuralgia, with very considerable relief. Lastly, it has been used in the form of ointment, as an application to foul ulcers.

In pharmacy it is employed in the manufacture of bicyanide of mercury.

Administration. — The dose of commercial Prussian blue is from four to six or more grains every four hours. The ointment above referred to may be prepared with a drachm of Prussian blue and an ounce of lard.