Manual of qualitative analysis / by Robert Galloway.

  • Galloway, Robert.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: Manual of qualitative analysis / by Robert Galloway. Source: Wellcome Collection.

    86/272 (page 68)
    MANGANESE by the blowpipe test. Treat the precipitate, whether manganese is present or not, with cold dilute hydro- chloric acid; the sulphides of nickel and cobalt will remain undissolved, whilst the sulphides of manganese and zine will dissolve ; boil the filtered hydrochloric acid solution, which may contain MANGANESE and zrNc, until all sulphide of hydrogen 1s expelled, then add a solution of one of the fixed alkalies in excess ; manganese * will be precipitated, whilst zine will remain in solution; filter if the alkali has produced any precipitate, and add to the filtrate or to the solution (when it does not require filtering) sulphide of hydrogen, when zinc, if present, will be precipitated. After having washed the black residue, examine it for nickel and cobalt in the following way :—Expose a small portion of the pre- eipitate on a bead of borax to the outer blowpipe flame, in the way directed in par. 180. A blue bead denotes the presence of cobalt; this is a safe and certain test for cobalt ; consequently, if a blue bead is not produced, cobalt is absent. Ifa yellow, and not a blue, bead has been formed, which becomes gray and dull in the inner flame, nickel is present. When cobalt is present, nickel is sought for in the followmg way:—The remainder of the precipitate is dissolved in nitro-hydrochloric acid, and the acid solution evaporated almost to dryness; a concentrated solution of cyanide of potassium is then added in excess, and the whole * It is almost impossible to prevent a minute quantity of the sul- phides of cobalt and nickel oxidizing, even if the precipitate is washed most carefully with water containing sulphide of ammonium; the oxidized portion of these two bodies will, therefore, be present in the hydrochloric acid solution, and consequently be precipitated by the fixed alkali; a precipitate may, therefore, be produced by the alkali,when no manganese is present. It will not be necessary to examine the pre- cipitate for nickel and cobalt, as sufficient will remain undissolved, unless the student has allowed the precipitate to remain on the filter for a great length of time. #5