Licence: Public Domain Mark
Credit: Qualitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![GEOUP IV. [§§ 105, 106. exhibits the same behaviour as tautalic acid ; from the solution of niobate of potassa, solution of soda precipitates an almost insoluble niobate of soda^ On boiling a solution of niobate of potassa with bicarbonate of potassa^. an almost insoluble acid niobate of potassa is thrown down. On fusing niobic acid with carbonate of soda aud boiling the melt with water, a» crystalline acid niobate of soda remains undissolved. Carbonic acid, when passed into solutions of niobate of soda, precipitates all the niobic acid as aa acid salt. Microcosmic salt dissolves niobic acid readily ; the bead held in the outer flame appears colourless as long as it is hot; in the inner flame it has a violet, blue, or brown colour, according to the quantity of the acid present, and acquires a red colour on the addition of ferrous sulphate. For the best methods of detecting the whole of the members of the third group in presence of each other, see Part II., Section III. § 105. Fourth Group. More common oxides:—Oxide of zinc, Protoxide of Man- ganese, Protoxide of ISTickel, Protoxide of Cobalt, Protoxide of Iron, Sesquioxide of Iron. Karer oxides:—Sesquioxide of Uranium, Protoxide of Thallium, Oxide of Indium, Oxide of Gallium, Oxides of Vanadium. ProjJerties of the group.—The solutions of the oxides of the- fourth group, if a strong free acid is present, are not precipitated by sulphuretted hydrogen; nor are neutral solutions, at least not com- pletely. Alkaline solutions, however, are completely precipitated by sulphuretted hydrogen; and so are other solutions if a sulphide of an alkali metal is used as the precipitant, instead of sulphuretted hydrogen.* The precipitated metallic sulphides corresponding vpith the several oxides are insoluble in water; some of them are readily soluble in dilute acids; others (sulphide of nickel and sulphide of cobalt) dissolve only with very great diJQ&culty in these menstrua. Some are insoluble in sulphides- of the alkali metals, others (nickel) are sparingly soluble in them under certain circumstances, whilst others again (vanadium) are completely soluble. The oxides of the fourth group accordingly diflTer from those of the first and second groups in this, that their solutions are precipi- tated by sulphide of ammonium, and from those of the third group inasmuch as the precipitates produced by sulphide of ammonium are sulphides, and not hydrated oxides, as is the case with alumina, ses- quioxide of chromium, &c. Special Keactions of the more common Oxides of the fourth group. § 106. a. Oxide of Zinc, ZnO [ZnO]. 1. Metallic zinc is bluish-white and very bright; when ex-posed to the air, a thin coating of basic carbonate of zinc forms on its. surface. It is of medium hardness, malleable at a temperature of * Vanadic acid behaves in a peculiar way with sulphide of ammonium: see- § 113, e. ,](https://iiif.wellcomecollection.org/image/b21966953_0142.jp2/full/800%2C/0/default.jpg)
