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Assay Lab Resources

A reactant or reagent is a substance consumed during a chemical reaction. The reaction process always results in the interconversion of chemical substances.

The dry reagents listed below are useful in determining the major elements present in a given specimen, and serve as aid in mineral identification.


The Chemistry of Gold Extraction

John Marsden

  DRY REAGENTS


Sodium carbonate:  Na2CO3; a.k.a. “soda”; used as a flux; facilitates and enhances the process of metal reduction when heating is performed on a charcoal block.

Sodium bicarbonate:  NaHCO3; a.k.a. “baking soda”; also used as a flux in the same situations as sodium carbonate

Sodium tetraborate:  Na2B4O7•10H2O; a.k.a. “borax”; used as a flux, like sodium carbonate, borax flux facilitates and enhances the process of reduction during fusion on a charcoal plate

Sodium metaphosphate:  NaPO3; a.k.a. “phosphorus salt” when in its hydrated and ammonium-bearing form; used as a flux; care must be taken not to spill the molten bead when it is first fused as it is considerably less viscous than the beads formed from other fluxes; when fused with silicate minerals, sodium metaphosphate always leaves a residue of undissolved silica

Potassium bisulphate:  KHSO4; used in several specialized fluxes; also used to precipitate iodine from iodide compounds and as a component of Von Kobell’s Flux which can be used to reduce certain metals (i.e. antimony, silver, bismuth, and lead) from their compounds; also used to liberate the halogen gases from halides when heated in a closed tube.

Von Kobell’s Flux:  a specialized flux consisting of a 1:2:1 mixture of potassium iodide, sulfur, and potassium bisulphate.

Turner’s Flux:  a specialized flux consisting of a 1:3 mixture of finely powdered fluorite and potassium bisulphate.

Tin foil.

Aluminum foil.

Zinc metal strips.

Potassium nitrate:   KNO3

Powdered galena:  PbS; used to distinguish chlorides, bromides, and iodides of silver; when mixed with a sample of either of the above and heated in a closed tube, a globule of lead halide is formed. If the globule is colorless when hot and white when cool, the sample is a chloride; if the globule is yellow when hot and white when cool, the sample is a bromide; if the globule is dark orange-red when hot and lemon yellow when cool, it’s an iodide.

Powdered gypsum:  occasionally used as a flux to help reduce certain metals (Li, Na, and K) from their silicate structures.

Powdered fluorite.