A text-book of assaying

by C. Beringer; J. J. Beringer

VOLUMETRIC METHOD.

The solution containing the cadmium is concentrated by evaporation, and mixed with an excess of oxalic acid and alcohol. The precipitate is filtered, washed with alcohol, dissolved in hot hydrochloric acid, and titrated with permanganate of potassium.

FOOTNOTES:

[64] When chromium is present some of the iron may escape precipitation but it can be recovered from the solution by means of ammonic sulphide.

[65]

(1) 10FeSO₄ + 2KMnO₄ + 8H₂SO₄ = 5Fe₂(SO₄)₃ + 2MnSO₄ + K₂SO₄ + 8H₂O. (2) 6FeCl₂ + K₂Cr₂O₇ + 14HCl = 3Fe₂Cl₆ + Cr₂Cl₆ + 2KCl + 7H₂O.

[66]

(1) Fe₂Cl₆ + SnCl₂ = 2FeCl₂ + SnCl₄.
(2) Fe₂Cl₆ + SH₂ = 2FeCl₂ + 2HCl + S.
(3) Fe₂Cl₆ + Na₂SO₃ + H₂O = 2FeCl₂ + Na₂SO₄ + 2HCl.
(4) Fe₂Cl₆ + Zn = 2FeCl₂ + ZnCl₂.

[67] 20 grams of stannous chloride and 20 c.c. of dilute hydrochloric acid are diluted to one litre.

[68] The maximum reducing effect of zinc is obtained by exposing as large a surface as possible of the metal in a hot concentrated solution containing but little free acid (Thorpe).