[ALCM.) The I.AorpAides of iron are unimportant Iron and eldorine form two compounds :— I. Protoehloride of hoe Feel Perchloeide of iron . , .
1. Protochloride of iron in the anhydrous state (Feel) is obtained on posing dry hydrochloric acid gas over iron filings heated to redness, hydrogen is evolved, and the salt sublimes in white micaceous 'scales. In the hydrated coudition it may be prepared by dissolving iron in hydrochloric acid, and evaporating in VSCUO ; green crystals are then produced (Feel + 4 Aq.), which most be preserved in an atmosphere of hydrogen or of earboulo acid.
Other metals may be coated with iron by boiling them in a solution of protochloride of iron containing chloride of ammonium and of zinc.
2. Perchloride of iron (Fe,C1,) (sesqukhloride). Obtained in brown scales on passing excess of chlorine over iron heated to redness. It sublimes at a red heat, is 'soluble in alcohol or ether, and is very deliquescent. The hydrated perehloride is deposited in large red crystals on evaporating a solution of the hydrated peroxide in hydro chloric acid. They contain six equivalents of water of crystallisation. Solution of perchloride of iron has a great tendency to dissolvo per oxide, and on evaporation the solution yields a confusedly crystalline masa of uncertain composition. The following is a convenient method of preparing a definite solution of perchlorido of iron. Five parts of iron filings are dissolved in twenty parts of the common strong hydrochloric acid, the liquid filtered through asbestos, three additional parts of the acid then poured In, and the whole heated to ebullition; nitric acid is now gradually added till no more red fumes are evolved, when the iron will all be in the state of perchloride. If necessary, the solution may be evaporated to the crystallising point ; if carefully prepared it will contain no free acid.
Solution of perchlorido of iron mixed with alcohol forms the tincture of senniehloride of iron used in medicine.
Iron and iodine, • Iron and &routine, and • Iron and fluorine form oombinations corresponding to the two chi°.
rides. Tho only one of importance is the l'rotoiodide of iron (Fel). This salt is used in medicine, and is prepared by boiling iodine with excess of iron filings, or small nails, in water. On evaporation, the solution yields green crystals, containing Fel + 4Aq. Those crystals fuse on the application of a moderate heat, give off their water of crystallisation, and on cooling solidify into a steel-grey crystalline mass. In manipulating with iodide of iron, con tact of air should be avoided as much as possible, as no oxyiodide is very apt to form ; the operations should also be conducted in iron vessels, and when in solution a piece of iron wire should be immersed in the liquid.
Protoearbonate of iron (FeO, CO,) occurs native. It is from this ore that most of the English iron is obtained. [Noe, in NAT. HIST. DIV.] It also exists, dissolved by the aid of carbonic acid, In certain natural waters or cludybeste springs. It may be formed artificially by precipi tating a prutmalt of Iron with an alkaline carbonate: at first it is white, but rapidly Imes carbonic 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 moist with powdered white sugar, and rapidly drying over a water-bath ; it then constitute* tho carbonate of iron with moor of the London Pharmacorceia.
I'Aosphates of iron are numerous, but ill defined. The principal are them:— 1. Phosphate of protoxide of iron.
2. Phospluste of peroxide of iron.
3. Pyrophoephate of peroxide of iron.
1. Phosphate of iron, or protophosphote of iron (21'00, 110,1'0„ or 3Fe0,1'0,). This is obtained as a white precipitate on adding ordinary tribasic phosphate of Bode to protosulphate of iron. It is insoluble in water, but soluble in solution of phosphoric acid, and the latter liquid, when mixed with sugar, constitutes the syrup of phos (or mperpAospanta) of iron used in medicine.