A ce t a tea of iron. [ACETATE.] Gal/ales and tannates of iron. [1:.t : Writiny Ink.] Citrates of iron. A double citrate of iron and ammonia is obtained when freshly precipitated protoxide of iron is dissolved in citric acid and excess of ammonia added. The compound does not crystalline ; hut when the solution is evaporated to the consistence of syrup and !spread over glass plates it dries up and forms brilliant transparent maim of garnet-red colour.
Citrate of iron and quinine is a medicinal agent of some repute. It is prepared by dissolving together threes parts of citrate of iron and one of citrate of quinine, and scaling as just described. The citrate of iron is made by saturating citric acid with moist peroxide of iron, evapo rating and scaling ; and the citrate of quinine by double decomposition of sulphate of quinine and citrate Of soda.
Tartrate of iron. A doublo 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 TIN (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 galeanised iron, as this zinc plate is commonly called, are easily soldered together, which is not the case with sheet-iron alone.
Testa for iron. Solutions of the protosalts yield greenish or blnish 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 peraalts 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 slate 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 guantitatire 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 peroxidised, 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 ono hundred parts, seventy of iron (Fe) and thirty of oxygen (0). • Ferroeyanoyen (Fey or Cfy=FeCy,) is a bibasie 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 (II, Cfy), and with two of metal a class of salts called ferrocyanides, of which ferroeyanide of potassium (K, Cfy) is a type.
FerritIcyanogen (Fcdy or Cfdy = Fe,Cy„) 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 cyanides, of which ferridcyanide of potassium (K, Fcdy) is the type.
Prussian blue is a variable mixture of the ferro- and ferrid-cyauides of iron. [BLUE prussian blue.]