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Peroxide of Iron
Peroxide, or ish-green color, and then a brownish-red, sesquioxide of iron, is a brownish-red powder, which is much brightened by exposure to a known as the red oxide or rust of iron; in its red heat, at the same time that its solubility hydrated form it is very soluble in acids, but in acids is considerably lessened. The salts of less so when anhydrous. The salts of peroxprotoxide of iron have a greenish color, but yield nearly colorless solutions, except when concentrated. The white hydrate is precipitated from solutions of the protosalts of iron by the pure alkalies. (Cooley.) 4152. Tests for Solutions of the Salts of Protoxide of Iron. When acidulated they are not precipitated by sulphuretted hydrogen; even neutral solutions with weak acids are incompletely precipitated; whilst alkaline solutions are precipitated of a black color.
Neutral solutions are precipitated black by hydrosulphuret of ammonia.
Ammonia and potassa give a greenish-white precipitate, gradually becoming green, and then brown in the air. The presence of ammoniacal salts interferes with these tests. Ferrocyanide of potassium (yellow prussiate of potash) gives a nearly white precipitate, becoming gradually blue in the air, and immediately so on the addition of a little weak nitric acid or chlorine water.
Ferridcyanide of potassium (red prussiate of potash, produces a rich deep blue precipitate, insoluble in muriatic acid. In highly dilute solutions the effect is only a deep bluish-green coloration. Aurochloride of sodium gives a purple precipitate; and phosphate of soda a bluc one. Cochineal freed from fat by ether, and then ide of iron have for the most part a reddishyellow color, and redden blue litmus paper. (Cooley.) 4157. Tests for the Solutions of the Salts of Peroxide of Iron. Sulphurctted hydrogen throws down a black precipitate from alkaline solutions.
Hydrosulphuret of ammonia does the same with neutral solutions; in very dilute solutions the precipitate is blackish-green; the precipitate in both cases being soluble in muriatic and acetic acids.
Ammonia and potassa produce bulky reddish-brown precipitates insoluble in excess of the precipitant.
Ferrocyanide of potassium (yellow prussiate of potash) gives a rich blue precipitate, insoluble in muriatic acid, and readily decomposed by potassa. Ferridcyanide of potassium (red prussiate of potash) deepens the color, but does not give a blue precipitate, as it does with the protoxide. (Sce No. 4152.) Sulphocyanide of potassium gives an intense ruby-red color to neutral or acid solutions; this is the most sensitive test known. Meconic acid and the meconiates also give a red color.
A tincture or infusion of galls strikes a black color; and phosphate of soda throws down a white precipitate. 4158. Το Obtain Pure Oxalate of evolved steam will exclude air from the vessel. Iron. Vogel recommends the precipitation The whole of the uncombined water may be of a solution of an ordinary protosulphate of known to be evaporated when vapor ceases iron by oxalic acid. The filtered solutions to condense on a piece of cold glass held over exclude all insoluble matter, and the precipi- the mouth of the flask; a piece of moistened tated oxalate needs but sufficient washing and starch paper occasionally applied in the same drying to obtain the oxalate of iron in a state way will indicate whether free iodine be of purity and of constant composition. This evolved; should such be the case, the heat salt gently heated, with exposure to the air, should be immediately lessened. When the takes fire, or may be kindled, and then con- evaporation is completed, the mouth of the tinues to burn until the whole becomes con- flask should be stopped up by laying a piece verted into impalpable peroxide of iron. This of sheet India-rubber on it, and over that a cheap, rapid, and perfect method of obtaining flat weight; the flask must be then removed, a perfect oxide of iron, free from all grit and and, when cold, broken to pieces, the iodide eminently fitted for all the finer polishing weighed, and put into dry and warm stoppered purposes, had led to the use of this article for wide-mouthed glass phials, which must be polishing the finest optical glasses. By heating immediately closed, tied over with bladder, the product to a higher temperature, a much and the stoppers dipped into melted wax. harder substance may be obtained, useful 4162. Ammonio Citrate of Iron. of Iron. rather for grinding than for polishing pur- Take 124 ounces carbonate of soda, and 12 poses. By adding salts of alumina, chro- ounces sulphate of iron; dissolve each sepamium and other similar salts to the iron solu- rately in 6 pints boiling distilled water. Mix tion, we may obtain in the final result-using the solutions while hot, and allow the precipsufficient heat-products nearly, if not quite, itate to subside. Decant the liquor, and, after equal to emery, and of extraordinary fine- washing the precipitate frequently with ness. water, drain it. Then add to it 6 ounces