Tho iodate, bromate, and perellbyate of iron are indefinite, unim portant salts.
itralcs of iron.—The pi-do/a /rate (FeO, is formed when cold nitric acid is /saturated with protoeulphide of iron : on evaporating the solution in vacuo, the salt crystallises out in pale green crystals containing seven atoms of water. The crystals are very deliquescent, and unstable. The pernitrate is produced when metallic iron is dissolved in strong nitrio acid. It is very difficult to cryetalliee, the solution on evaporation depositing a basic salt. Solution of pernitmte of iron is used In dyeing.
Silieateo of iron. Many of these occur native. [hoe, in NAT. IIIST. DIV.) etrscnifes and arsenates of iron. In eases of poisoning by arsenic, the beat antidote to administer is freshly precipitated peroxide of iron mixed with n little hydrate of magnesia. The efficiency of this anti dote depends upon the formation of perarsenite of iron, which is an 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 adds : the solution may, however, be prevented by mixing the oxide with magnesia, which neutralises those acids in a far more effectual manner than excess of peroxide of iron would do.
Acetates of iron. [AeETATE.) Galatea and tannates of iron. [INK: 1Vritiny Ink.] Citrates of iron. A double citrate of iron and runmonia is obtained when freshly precipitated peroxide of iron is dissolved in citric acid and excess of ammonia added. The compound does not crystalline ; but when the solution is evaporated to the consistence of syrup and spread over glass plates it dries up and forms brilliant transparent scales of garnet-red colour.
Citrate of iron and quinine is a medicinal agent of some repute. It is prepared by dissolving together three parts of citrate of iron and one of citrato of quinine, and styling as just described. The citrate of iron is inndo by saturating citric acid with moist peroxide of iron, evapo rating and scaling ; and the citrate of quinine by double decomposition of ealphate of quinine and citrate of soda.
Tartrate of iron. A double compound of tartrate of iron and potash, of somewhat similar physical properties to the last preparations, but darker in colour, may be formed by dissolving moist, recently precipi tated peroxide of iron in a hot solution of bitartrate of potash. This compound is also used in medicine.
Alloys of iron are numerous, but only two are important, namely, those with tin and with zinc. The former will be found described under Tr:a (tin-plate); the latter is produced when sheets of iron, cleaned as perfectly as if required for tin-plate, are dipped into a bath of melted zinc, on the surface of which is a stratum of sal 'ammoniac.
The surface of the iron then becomes alloyed with zinc, and is thus preserved from oxidation by the air when employed in exposed situa tions. Moreover articles made of galvanised as this zinc plate is commonly called, are easily soldered together, wlich is not the case with sheet-iron alone.
Tests for iron. Solutions of the protosalts yield greenish or bluish white precipitates with the alkalies, or their carbonates; none with sulphuretted hydrogen; black with sulphide of ammonium ; dark blue with red prussiate of potash ; and light blue with the yellow prussiate of potash.
Solutions of the permits give red-brown precipitates with the alkalies or their carbonates ; are reduced to the state of protosalts by sulphu retted hydrogen, a light yellow precipitate of sulphur occurring at the same time ; are precipitated black by sulphide of ammonium ; dark blue by the yellow prussiate of potash, and not at all by the red prus siate of potash. Exceedingly small quantities of iron may also be detected in solution by the sulphocyanide of potassium, which gives a red liquid, and by tincture of galls which produces a black colour (ink).
In the quantitative estimation of iron the metal is always weighed in the form of peroxide. The definite state of the latter is ensured first by boiling the solution with nitric acid in order that the iron may be completely peroridised, and second by precipitating with ammonia, because any trace of the salts of that alkali may be readily expelled by igniting the well washed precipitate. The resulting red oxide of iron is pure sesquioxide (Fe, 0,), and contains, in one hundred parts, seventy of iron (Fe) and thirty of oxygen (0). • Ferrocyanogen (Fey or is a bibasic radical which has not been isolated, but which is assumed to exist in certain familiar chemical compounds. With two equivalents of hydrogen it forms FERROCYANIC ACID (H, Cfy), and with two of metal a class of salts called ferrocyanides, of which ferrocyanicle of potassium (K, Cfy) is a type.
Fcrrielcyanogen (Fcdy or Cfdy = is a similar radical, but tribasic. With three equivalents of hydrogen it forms FERRIDCYANIC ACID (H, Fcdy), and with three of metal, a class of salts called ferrid eye nides, of which ferridcyanide of potassium (K, Fcdy) is the type.
Prussian blue is a variable mixture of the ferro- and ferrid-cyanides of iron. [BLUE prussian blue.]