i'roteearlesete of iron (FeO, CO,) occurs native. It is from this ore that most of the English iron is obtained. (lima, in NAT. Ilisr. Div.! It she) exists, dissolved by the aid of carbonic acid, in certain nature eaten' or ciudybeate springs. It may ho formed artificially by precipi tating a rot/salt of iron with an alkaline carbonate: at first it is white, but rapidly loses earbonie acid, absorbs oxygen from the air, becomes green, black, and finally red (peroxide of iron). This change may be considerably retarded by mixing It while moixt, with powdered white sugar, and rapidly drying over a water-bath; it then constitute. the cereeeate of vita sugar of the London Pharmacopeia.
l'hosphata of iron arc numerous, but ill defined. The principal are these:— 1. Phosphate of protoxido of iron.
2. Phosphate of peroxido of iron.
3. Pyrophosphate of peroxide of iron.
I. Thospkale of protoxide of iron, or protophosphate of iron (2FoO, 110.1•0„ or 2 re°, PO,)- This Is obtained as a white precipitate on adding ordinary tntseie phosphate of soda to protosulphnte of iron. It is insoluble hi water, but soluble in solution of phosphoric acid, and the latter liquid, when mixed with sugar, constitutes tho syrup (1 phew pAate (or toperphosphate) of iron used in medicine.
2. l'hoephate of pero.ride of iron, or perphosphate of iron (Fe,0,, PO 4Aq.), fella as a white precipitate on mixing solutions of a permit of iron and ordinary triLanic phosphate of soda. Unlike the proto phoephate, It does not absorb oxygen from the air, and, being of constant composition, is frequently used in quantitative analysis as a mesas of estimating phosphoric acid. It is Insoluble In acetic acid,but ..
.bible In solution of pera.cetate of iron.
71 I'yrohhoryphate of peroxide of iron (pyroplasephate of iron), ?APO, $ 9Aq.), a white powder produced by double decomposition of a perish of iron with dihrisio phosphate (or pyrophosphate) of soda. It is insoluble in eater or in dilute acids, but soluble in 'litanies pyro phosphates or citrate., such solutions yielding, when evaporated to a syrup and el/read over glans plates, beautiful transparent scalea of sllowlelegresn or rod colour. They are used In medicine under various names, the eitro-ammoniaeal-pyrophoephate of iron and soda being one of them.
Sulphates of iron are two :— 1. Protoeulphate of iron.
2. Pereulph.sto of iron.
1. Prorate/Plate of iron. Green vitriol. Copperas. (FeO, SO, + 7Aq.)
This salt Is largely produced in the manufacture of Atom. It is also formed in the process for precipitating copper from the solution of sulphate of copper obtained in certain nietallurgical operations with that metal. Old scrap iron is used for this purpose, and, replacing the copper in solution, is obtained as sulphate of iron on evaporating the liquor. Sulphate of iron may bo formed on the small scale by dissolving iron in dilute sulphuric acid. The following decomposition takes place :— Fe + 00, SO, = FrO, SO, + II Iron. Sulphuric acid. Sulphate of Ilydrogen.
trop.
On evaporating the solution the salt crystallise; out in beautiful bluish-green rhomboidal crystals. These, however, like all the proto salta of iron, must be exposed as little as possible to the air, for they quickly absorb oxygen, and a separation into basic and neutral persalts results, thus :— 4FeO; SO, + 0, = SO, + SSO, Protosulphate Oxygen. Subsulphate Persulphate of iron. of iron. of iron.
Subsulphates of other composition are also frequently produced.
Protosulphate of iron is insoluble in alcohol, soluble in twice its weight of cold water, but much more so in hot water. When heated it loses six equivalents of its water of crystallisation, at a red heat is decomposed into sulphurous and sulphuric acids, which escape, while peroxide of iron (colcothar) remains. It is largely used in black Desasu and in the manufacture of writing lee.
2. Pt-reap/tale of iron (Fe,0,, Five parts of crystals of proto sulphate are dissolved in water, one part of sulphuric acid added, and nitric acid poured into the hot solution till no more black colour is pro duced. Abundance of nitrous vapours are evolved, and the yellow solution, on evaporation to dryness, yields a buff-coloured mass of peraulphato of iron, having the above composition.
This salt occurs native. [Inom, Coquimbile, in NAT. MIST. DM] Potassio-sulphate of iron 3S0,+ KO, SO, + 24Aq.) is a double salt containing persulphate of iron and sulphate of potash. Correspond. ing salts with the other alkaline sulphates may also be formed. They all crystallise, and, being isomorphous with common alum, are frequently, though erroneously, called iron alums. They are formed by the spon taneous evaporation of mixed solutions of the salts, are to some extent used in medicine, but aro liable to decompose..