4157. Tests for the Solutions of the Salts of Peroxide of Iron

4157.    Tests for the Solutions of the Salts of Peroxide of Iron. Sulphuretted 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; tho 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. (Sec 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. To Obtain Pure Oxalate of Iron

4158. To Obtain Pure Oxalate of Iron. Vogel recommends the precipitation of a solution of an ordinary protosulphate of iron by oxalic acid. The filtered solutions exclude all insoluble matter, and the precipitated oxalate needs but sufficient washing and drying to obtain the oxalate of iron in a state of purity and of constant composition. This salt gently heated, with exposure to the air, takes fire, or may bo kindled, and then continues to burn until the whole becomes converted into impalpable peroxide of iron. This cheap, rapid, and perfect method of obtaining a perfect oxide of iron, free from all grit and eminently fitted for all tho finer polishing purposes, had led to tho use of this article for polishing tho finest optical glasses. By heating tho product to a higher temperature, a much harder substance may be obtained, useful rather for grinding than for polishing purposes. By adding salts of alumina, chromium and other similar salts to the iron solution, wo may obtain in the final result - using sufficient heat - products nearly, if not quite, equal to emery, and of extraordinary fineness.

4159. Acetate of Iron

4159. Acetate of Iron. Dissolve 20 ounces sulphate of iron in 7 ounces strong sulphuric acid, and heat in a porcelain dish nearly to boiling. Then add gradually 10 ounces strong nitric acid; and, when action ceases, while still hot, add sufficient ammonia to precipitate all tho iron as sesquioxide. Collect this on a linen cloth, and wash with water until tho washings taste no longer saline. "While still moist, put tho sesquioxide into a bottle with sufficient strong acetic acid to dissolve it.

Twenty ounces of sulphate of iron contain 4 ounces iron; hence, if sufficient water bo added to make tho acetate up to CO ounces, tho solution of acetate of iron thus obtained will contain 8 per cent, of iron.