Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![FeOjEe^Oj [FCaO,], is black; it dissolves in hydrochloric acid to ferroiis and ferric chlorides, in aqua regia to ferric chloride. 2. The neutral anhydrous salts of ferric oxide are nearly white • the basic salts are yellow or reddish-brown. The colour of the solutions is brownish-yellow, and becomes reddish-yellow on heating. The soluble neutral salts redden litmus-paper, and the salts containing volatile acids are decomposed by heat. 3. Sulphuretted hydrogen in solutions made acid by the stronger acids produces a milky white turbidity, due to separated sulphur; the ferric salt being at the same time converted into a ferrous salt • FeP3,3S03 -I- HS = 2(FeOS03) + H0,S03 + ^ [Fe,(SO,)3 + H,S = 2FeSO, + H.SO, + S]. If solution of sulphuretted hydrogen is rapidly added to neutral solu- tions, a transient blackening of the liquid also occurs. Sulphuretted hydrogen throws down the greater part of the iron from solutions of neutral acetate of ferric oxide; but in the presence of a sufl&cient quantity of free acetic acid, sulphiir alone separates. When sul- phuretted hydrogen is passed into a solution of a ferric salt mixed with acetate of soda and acetic acid, scarcely anything but sulphur is thrown down in the cold, but on warming a part of the iron is precipitated. 4. Sulphide of ammonium precipitates from neutral, and sul- phuretted hydrogen from alkaline solutions, the whole of the metal as black hydrated ferrous sulphide or protosulphide of iron, FeS [FeS], mixed with sulphur, Fe^Cl, + SNH^S = 2FeS + 3NH CI + S [Fe,Cl6+3(NHJ,S = 2FeS + 6NH,CI + S]. In very dilute solutions, the re- agent produces only a blackish-green coloration. The minutely divided ferrous sulphide subsides in such cases only after long standing. Chloride of ammonium most materially promotes the precipitation. Ferrous sulphide, as already stated (§ 110, 5), is insoluble in alkalies and alkaline sulphides, but dissolves readily in hydrochloric and nitric acids. 5. Potassa, soda and ammonia produce bulky reddish-brown pre- cipitates of hydrated ferric oxide, Fe203,2HO [FejCOHy^ vrhich are insoluble in an excess of the precipitant as well as in salts of ammonia. Non-volatile organic acids and sugar, when present in suflB.cient quantity, entirely prevent the precipitation. 6. Ferrocyanide of potassium, even in highly dilute solutions, produces a deep blue precipitate of ferric ferrocyanide, or Prussian blue, Fe^Cfyj [Fe.lFeC^N^)^]: 2Fe,Cl3 + 3K,Cfy = Fe.Cfyg + 6KC1 [2Fe,OI„ + 3K4FeC,N3 = Fe,(FeCsN„), + 12KCI]. This precipitate is insoluble in hydrochloric acid, but is decomposed by potassa with separation of hydrated ferric oxide. 7. Ferricyanide of potassium deepens the colour of solutions of ferric salts to reddish-brown; but it does not produce a precipitate. 8. Sulphoeyanate of potassium imparts a most intense blood-red colour to acid ferric solutions; this is due to the formation of a soluble sulphoeyanate of iron. The colour does not disappear on the addition of a little alcohol and warming (difference from the analogous reaction of hyponiti-ic acid, § ] 58). Solutions of ferric salts, containing acetate of soda (which consequently are more or less red from ferric acetate), do not show the blood-red colour of the sulpho-](https://iiif.wellcomecollection.org/image/b21966953_0154.jp2/full/800%2C/0/default.jpg)
