How to Measure for Gold

Fire assay is How to Measure for Gold and it has been practiced since ancient times and has proven to be very reliable in the determination of precious metal. References to fire assaying are found in the old testament of the Bible and artefacts in past civilizations’ ruins. Assaying began to appear in French and English literature in the 12th century and from there spread to the rest of Europe shortly after. The substances that can be fire assayed can be ores, metallic solutions and any material that are thought to be containing gold and silver. It uses scientific methodology and it is branch of analytical and inorganic chemistry.
 
Fire assay uses a combination of intense heat (1900 0F) that is produced by a furnace, dry reagents called fluxes, and bone ash containers called crucibles and cupels. One uses this combination to fuse the fluxing agents and to isolate the precious metals. The ability to fire assay a substance relies on a number of facts. First of all, the samples that contain gold and silver should be solubility in molten metallic lead and that gold and silver are insolubility in slag. Fire assay also relies on the difference in specific gravity between the two liquids, the molten lead and the slag. This difference in specific gravity separates the precious metal – bearing alloy from the slag. The precious metals can be isolate by a carefully controlled oxidizing fusion, in a porous container called a cupel. Lastly, fire assay is possible because of the solubility of silver in nitric acid and gold’s insolubility in nitric acid. One requires a certain proficiency in fire assay in order to produce reproducible results. One should assay known pulp standards and run duplicates of the samples to ensure results are correct.
 
The results are calculated and have a standard measurement unit. In fire assaying one deals with small amounts of gold in a large sample and therefore one uses the unit, an Assay ton for fire assay. The assay ton is a 29.166 grams. The assay – ton system is based on the number of Troy Ounces in a Short Ton. The standard units that are reported are grams/ton or oz/ton. One should have some familiarity of the units and the conversions.
 
Unit conversion factors table.
1 troy ounce = 31.10 grams
1 troy ounce = 1.0971 ounces avoirdupois (av.)
1 ounce (av) = 28.35 grams
1 pound (av) = 14.58 oz (troy)
1 pound (av) = 453.6 grams
1 pound (troy) = 12 oz (troy)
1 pound (troy) = 373.2 grams
1 pound (troy) = 13.17 oz. Av
1 long ton (2,240 lb. av.) = 32,666 oz. troy
1 short ton (2,000 lb. av.) = 29,166 oz. troy
1 metric ton (2,204.6 lb. av.) = 32,150 oz. troy
1 kg = 32.15 oz. troy
1 kg = 2.68 lb. troy
1 kg = 35.27 oz. av
1 kg = 2.20 lb. av
1 ppm = 1mg/kg
1ppb = .001 mg/kg