Blue, Prussian, 52 Boiling

Upon boiling the alkaline ferrous salt solution, some ferric ions are inevitably produced by the action of the air upon the addition of dilute siilphurio acid, thus dissolving the ferrous and ferric hydroxides, the ferrocyanides reacts with the ferric salt producing ferric ferrocyanide (Prussian blue) ... 

If sulphur is present, a black precipitate of ferrous sulphide is obtained when the ferrous sulphate crystals dissolve. Boil the mixture for about 30 seconds, and acidify with dilute sulphuric acid the ferrous sulphide dissolves and a precipitate of Prussian blue forms if nitrogen is present. 

Nitrogen. Treat one portion with 1-2 ml. of 5 per cent, sodium hydroxide solution and 0 1 g. of powdered ferrous sidphate. Boil for 1 minute and cool. Cautiously acidify with dilute sulphuric acid (carbon dioxide is evolved). A precipitate of Prussian blue indicates that nitrogen is present. 

Tabun may be detected by the air-flow method, by aspirating into ferrous sulphate solution to which a few drops of 10 per cent sodium hydroxide has been added. The mixture is then boiled and acidified with dilute sulphuric acid and filtered to observe the blue specks of Prussian blue on the filter paper. 

This acid was isolated by Winterl (1790), Buchholz (1798) and Rink (1804).4 Its potassium salt was first prepared by Porret in 1808 by boiling potassium sulphide solution with Prussian blue. The composition of the acid was first determined by Berzelius in 1820. The question of the formation of the acid in animals has been the subject of investigation by Dezani and others, but their results have led to the conclusion that the acid is not produced in the animal organism, but is purely exogenetic.6... 

Other Tests.—In some cases a small quantity of Prussian blue is added to black pigments and especially to soot black to correct any tendency to reddish brown. This may be detected by boiling the pigment with alkali and filtering, and treating the filtrate, after acidification, with ferric chloride, which gives a blue precipitate. 

A portion of the substance is boiled with sodium hydroxide solution, diluted and filtered, the filtrate being acidified and treated with ferric chloride a blue precipitate shows that the indigo contains Prussian blue. 

Cyanide ion, and hence nitrogen in the sample, may be detected by the Prussian Blue test. The filtered alkaline solution, resulting from the action of water upon the sodium fusion, is treated with iron(n) sulphate and thus forms sodium hexacyanoferrate(n). Upon boiling the alkaline iron(n) salt solution, some iron(m) ions are inevitably produced by the action of air upon addition of dilute sulphuric add, thus dissolving the iron(n) and (hi) hydroxides, the hexa-cyanoferrate(n) reacts with the iron(m) salt producing iron(m) hexacyano-ferrate(n), Prussian blue ... 

Potassium Cyanide Solutions. Wear breathing apparatus, eye protection, laboratory coat, and butyl rubber gloves. Instruct others to keep a safe distance. Cover the spill with a 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. Scoop the mixture into a container and transport to the fume hood. Slowly, and while stirring, add the slurry to a pail containing household bleach (about 70 mL/g of cyanide). Test the solution for the presence of cyanide using the Prussian blue test. To 1 mL of the solution, add 2 drops of a freshly prepared 5% aqueous ferrous sulfate solution. Boil the mixture for at least 60 seconds, cool to room temperature and add 2 drops of 1 % ferric chloride solution. Add 6 M hydrochloric acid (prepared by... 

Prussian blue test This is a delicate test and is carried out in the following manner. The solution of the cyanide is rendered strongly alkaline with sodium hydroxide solution, a few millilitres of a freshly prepared solution of iron(II) sulphate added (if only traces of cyanide are present, it is best to use a saturated (25 %) solution ofiron(II) sulphate) and the mixture boiled. Hexacyanoferrate(II) ions are thus formed. Upon acidifying with hydrochloric acid (in order to neutralize any free alkali which may be present), a clear solution is obtained, which gives a precipitate of Prussian blue upon the addition of a little iron(III) chloride solution. If only a little cyanide was used, or is present, in the solution to be tested, a green solution is obtained at first this deposits Prussian blue on standing. 

Barium ferrocyanide,1 Ba2Fe(CN)6.6H20, is readily prepared by boiling Prussian blue (see p. 225) with the requisite quantity of barium hydroxide solution. It also results when ferrous sulphate and barium cyanide solutions interact. 

Calcium ferrocyanide, Ca2Fe(CN)e.dH20 (where =11,5 or 12,6), may be obtained by boiling Prussian blue with the calculated quantity of milk of lime. It is also formed when hydrogen cyanide is passed into a suspension of lime and ferrous hydroxide in water. The salt crystallises m pale yellow triclinic prisms, which are more soluble in cold water than in hot. 

Upon prolonged exposure to light, a solution of potassium ferrocyanide deposits Prussian blue (see p. 225), whilst on continued boiling ammonia is evolved. WTith ferrous salts it yields an immediate white precipitate of ferrous potassium ferrocyanide, K2Fe[Fe(CN)6], which readily absorbs oxygen, becoming blue. The presence of dilute hydrochloric or sulphuric acid, or the employment of excess of the ferrous salt, accelerates the formation of the blue colour, and the reaction is exceedingly delicate.12... 

Sodium ferrocyanide, Na4Fe(CN)e.10H2O, may be prepared in an analogous manner to the potassium salt.7 It may also be prepared by boiling Prussian blue with aqueous solutions of sodium carbonate or hydroxide. 

Add a freshly prepared 10% solution of ferrous sulphate in freshly boiled and cooled water a precipitate of ferrous hydroxide is formed. Add sufficient dilute hydrochloric acid to dissolve the precipitate a blue colour (Prussian Blue) indicates the presence of cyanide. 

The test is done by boiling a portion of the alkaline solution from the solution fusion with iron(II) sulfate and then acidifying. Sodium cyanide reacts with iron(II) sulfate to produce ferrocyanide, which combines with iron(III) salts, inevitably formed by air oxidation in the alkaline solution, to give insoluble Prussian Blue, NaFe[Fe(CN)J. Iron(II) and iron(III) hydroxide precipitate along with the blue pigment but dissolve on acidification. 

Detection of cyanide ion and other tests for nitrogen. The cyanide is converted first to ferrocyanide ion by boiling with ferrous sulfate, then to ferric ferrocyanide, or Prussian blue, by addition of ferric chloride and addition of acid. The Prussian blue is detected by its blue color, which is intensified by addition of fluoride ion ... 

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