4152. Tests for Solutions of the Salts of Protoxide of Iron

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 arc precipitated black by hydrosulphuret of ammonia.

Ammonia and potassa give a greenish- white precipitate, gradually becoming green, and then brown in tho air. Tho 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 blue one.

Cochineal freed from fat by ether, and then digested in water (or very weak spirit), gives a solution which is colored violet by the protosalts of iron.

4153. Anhydrous Sesquioxide of Iron

4153.     Anhydrous Sesquioxide of Iron. A pure anhydrous sesquioxide is obtained, by precipitating a solution of sesqui-sulphate or sesquichloride of iron with ammonia in excess, and washing, drying, and igniting the resulting hydrated peroxide.

4154. Jewelers' Rouge

4154.     Jewelers' Rouge. The best jewelers' rouge is prepared by calcining the precipitated peroxide of iron (see No. 4153 (Anhydrous Sesquioxide of Iron)) until it becomes scarlet. The rust of iron contains some combined water, and is more soluble than the oxide prepared by calcination ; but it is less soluble than that recently precipitated from its solution in an acid. This is also called Colcothar, Crocus, or Crocus Martis.

4155. Hydrated Sesquioxide of Iron

4155.    Hydrated Sesquioxide of Iron. Take 4 ounces sulphate of iron; 31/2 fluid ounces oil of vitriol; water, 1 quart; mix, dissolve, and boil, then gradually add 9 fluid drachms nitric acid; stirring well and boiling for a minute or two after each addition, until the liquor yields a yellowish-brown precipitate with ammonia, when it must bo filtered and precipitated with 31/2 ounces strong liquor of ammonia, rapidly added and well mixed in; collect, wash well with water, drain on a calico filter, and dry at a heat not exceeding 180° Fahr. When intended as an antidote for arsenic it should not be dried, but kept in the moist or gelatinous state. It should be kept in a well-stoppered bottle filled with recently distilled or boiled water. This preparation is also called hydrated peroxide of iron.

4156. Peroxide of Iron

4156.    Peroxide of Iron. Peroxide, or Sesquioxide of iron, is a brownish-red powder, known as tho red oxide or rust of iron; in its hydrated form it is very soluble in acids, but less so when anhydrous. The salts of peroxide of iron have for the most part a reddish-yellow color, and redden blue litmus paper. (Cooley.)