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The determination of ferrous iron in resistant silicates

Published online by Cambridge University Press:  14 March 2018

Max H. Hey*
Affiliation:
Mineral Department, British Museum

Extract

The determination of ferrous iron in minerals, such as staurolite and kornerupine, which cannot be effectively dissolved by dilute sulphuric and hydrofluoric acids has been made possible on the macro-scale by the work of H. P. Rowledge; the mineral is fused with sodium fluoride and boric oxide at 900°C. in a sealed pyrex glass tube, the fusion cake dissolved in hot dilute sulphuric acid in a current of carbondioxide, and the solution titrated with potassium permanganate. We have met with no difficulty in applying the method on the macro-scale, but when only small amounts of a mineral are available several difficulties arise, and modifications become necessary.

The air present in the sealed tube of a Rowledge fusion, using the quantities and dimensions he specifies, is already sufficient to oxidize about 3 to 5 mg. of ferrous oxide. But when the weight of the sample is reduced to 10 mg., it is not possible to reduce the dead-space in the tube in proportion ; it can hardly be reduced below about ¼c .c. which is sufficient to oxidize 0·3 mg. or 3% FeO and is likely to be more effective in this direction than on the larger scale, since the surface of the fusion is proportionally greater.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1941

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References

page 116 note 1 Rowledge, H. P., Journ. Roy. Soc. Western Australia, 1934, vol. 20 (for 1933–1934), p. 165. [M.A. 6–191.]Google Scholar

page 117 note 1 Sarver, L. A., Journ Amer. Chem. Soc., 1927, vol. 49, p. 1472.CrossRefGoogle Scholar

page 117 note 2 Experiments have been commenced in this connexion.

page 118 note 1 0·18 g. KIO3 and 0·28 g. KI in 250 c.c. conc. HCl and 250 c.c. water; add a little CCl4, and if free iodine is present, add very dilute KIO3 drop by drop till it is removed ; if absent, add a few drops of dilute KI till it appears and then remove with KIO3; store in the dark; if iodine develops on standing, remove with KIO3.

page 118 note 1 Pratt, J. H., Amer. Journ. Sci., 1894, set. 3, vol. 48, p. 149.CrossRefGoogle Scholar