A method for removing and determining the free oxide in soil colloids
1935
Drosdoff, M. | Truog, E.
It was found that the free ferric oxide (hydrated and unhydrated) in soil colloids may be easily separated and determined if the suspension of the colloid is first treated for about 1/2 hour with H2S. The H2S quickly changes the free ferric oxide by surface action to iron sulfides which are easily soluble in dilute acid and may thus be extracted and determined. Combined or silicate iron is unaffected in the limited time required as are also other constituents and the base exchange capacity. It was found that the amount of free ferric oxide in a lateritic soil colloid was high; in colloids from several Wisconsin soils it was less than the combined or silicate iron; and in one soil colloid and two bentonite colloids it was absent, while the combined iron oxide ranged from 4.8 to 6.3%. Free colloidal iron oxide may be removed directly from a soil without previous separation of the colloid as a whole. This is useful in mechanical analysis including specific gravity separations, petrographic work, and phosphate fixation studies.
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