2. J'Aosphent of peroxide of iron, or perphosphate of iron + 4Aq.), falls I1A a white precipitate on mixing solutions of a permit of Iron and ordinary tritium phosphate of soda. Unlike the prob.) phozphaCe, It does not absorb oxygen from the air, and, being of constant composition, is frequently used in quantitative analysis as n loans of estimating phosphoric acid. It is insoluble in acetic acid,but voluble in solution of perseetato of iron.
X. Pyrophosphate of peroxide of iron (pyrophosphate of iron), (2Fe,0,, MP°, + 9Aq.), a white powder produced by double decomposition of a permit of iron with dibasic phosphate (or pyrophoepludo) of soda. It to inoahible in alter or in dilute acids, but soluble in alkaline pyro or citrates, such solution. yielding, when evaporatod to a syrup and sieved over glees plates, beautiful transparent scales of yallowish-grcan or rod colour. They are used in tuedicino under various names, the eitro-ammoniacolpyrophosphete of iron and soda being one of them.
Sulphates of iron are two :— 1. Protosulphate of iron.
2. Persulphate of iron.
1. Protosulphate of iron. Green vitriol. Copperas. (FeO, SO, + 7A9.) This salt is largely produced in the manufacture of ALCM. It is also formed in the process for precipitating copper from the solution of sulphate of copper obtained in certain metallurgical operations frith that metal. Ohl 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 be formed on the small scale by dissolving iron in dilute sulphuric acid. The following decomposition takes placo : Fe + II0, SO, = Fe0, SO, + II Iron. Sulphuric acid. Sulphate of Hydrogen.
Iron.
On evaporating the solution the salt crystallises out in beautiful bluish-green rhomboidal crystals. These, however, like all the proto salts of iron, must be exposed as little as possible to the sir, for they quickly absorb oxygen, and a separation into basic and neutral persalts results, thus :— 4Fe0; SO, + 0, = Fe,0,, SO, + Fe,0,, SSO, Protosulphatc Oxygen. Subsulphate of iron. of iron. of Iron.
Subsulphatee 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 equivalent§ 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 DYEING
and in the manufacture of writing fax.
2. Persulphate of iron 350,). Five parts of crystals of proto. sulphate aro 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 persulphato of iron, having the above composition.
This salt occurs native. [I no:e, Coquimbite, in NAT. Hist. Div.] Potassio-sulphate of iron (Fe,0„ 3S0,+ KO, SO, + 24Aq.) is a doublo 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, arc to sonic extent used in medicine, but aro liable to decompose..
The iodate, bromate, and pereldorate of iron are indefinite, maim portant salts.
of iron.—Tho protonitrate (FeO, NO,) is formed when cold nitric acid is saturated with protosulphide of iron : on evaporating tho solution in enema, the salt crystallises out in pale green crystals containing seven atoms of water. The cry stile are very deliquescent, and unstable. The pernitrate is produced when metallic iron is dissolved in strong nitric acid. It is very difficult to crystallise, the solution on evaporation depositing a basic salt. Solution of pernitrato of iron is used In dyeing.
Silicates of iron. Many of theso occur native. Clime, in NAT. HIST. Div.) Arsenita and arsenates of iron. In caeca of poisoning by arsenic, the beet antidote to adininister• is freshly precipitated peroxide of iron mixed with a little hydrate of magnesia. The efficiency of this anti dote depends upon the formation of perarsenito of iron, which is all insoluble compound ; that is, insoluble in water, but not altogether insoluble in the liquids of the stomach, which usually contain traces of hydrochloric, acetic, and lactic acids : the solution may, however, be prevented by mixing the oxide with magnesia, which neutralities throe acids in a fat more effectual manner than excess of peroxide of iron would do.