SILVER (Ag) - LEAD (Pb) TEST
By Delos Toole
Useful information to begin testing for silver-lead ores.
Silver should be of high grade, (quality), ore to achieve a good reaction in the test without all of the extra work involved to concentrate. The best procedure is to take a couple of pounds of ore sample and pulverize this into fine grains or powder, put this into a gold pan and concentrate to about a couple of tablespoons.....this is now ready for testing as a concentrate.
Silver (Ag) and Lead (Pb) are mostly associated together in the host rock and both of these are soluble in diluted Nitric Acid (HNO3); each of these can be precipitated by adding a Chloride, such as Hydrochloric Acid (HCl), Salt (NaCl), etc. The precipitate is then: Silver Chloride (AgCl) and/or Lead Chloride (PbCl). Silver Nitrate is a colorless crystalline salt (AgNO3) obtained by dissolving Silver in Nitric Acid, and evaporating.
Silver precipitates are sensitive to light and will turn dark on exposure to sunlight, whereas Lead precipitates will remain a white spectrum, usually crystalline resembling crystals:
Silver Chloride precipitates are soluble in Ammonia (NH3), but are not soluble in hot water:
Lead Chloride precipitates are soluble in hot water, but are not soluble in Ammonia:
Silver Chloride precipitates when dissolved in Ammonia most likely can be re-precipitated by adding a few drops, (with an eye dropper), of Nitric Acid:
Lead Chloride precipitates usually dissolves in hot water and can be re-precipitated by adding a few drops, (with an eyedropper), of Sulphuric Acid (H2SO4).
In testing for Silver (Ag) or for Lead (Pb) ores with diluted Nitric Acid, the diluted water being used must be free of Chlorine (Cl); otherwise the test will get a different reaction and will be misguiding. All water to be used for this testing must be first tested for Chlorine (Cl).
To test for Chlorine in the water, place 2cc of water in a clean test tube and add to this about 9 drops of pure concentrated Nitric Acid. Note; cc is the abbreviation for Cubic Centimeter and 20 drops from an eyedropper are equal to about 1cc. Heat this solution to a boiling point and then allow it to set until it has cooled; add to this about 2 drops of Silver Nitrate Solution. The results from this will be a curdy or milky color, proving that Chlorine is present in the water and cannot be used for further testing.
Should there be no Chlorine show up thru the Chlorine test, then, the water may be used in several degrees of testing as follows:
Testing to see if a mineral is a Chloride; Place a powdered suspected mineral the size of a green pea in a clean test tube and add 2cc of water known to be free of Chlorine, then, add 6 drops of pure concentrated Nitric Acid. Boil this solution, slightly, then let it set until cooled. After cooling, add a few drops of Silver Nitrate solution to the mixture. A milky color or curdy mass proves that Chlorine is present.
Silver (Ag) Test.
In diluted Nitric Acid, precipitated by a Chloride; use a powdered suspected mineral ore, (specimen), or concentrates, about the size of a navy bean and place this in a clean test tube, add to it 1cc Nitric Acid and 2cc of water (free of Chlorine). Boil this for a reasonable time until the Silver is dissolved. Use a filter, allow the solution to cool. Divide the filtered solution in half and place into two clean test tubes. To test tube no. 1 add a few drops of Hydrochloric Acid: if Silver or Lead is present, it will have a milky or opal appearance in color to it suggesting that a very low quality or grade of specimen is present. Should the solution appear to be a thick curdy mass in substance, then, it is of a high quality grade specimen.
Silver (Ag) will turn dark when exposed to sunlight.
Lead (Pb) precipitate will remain white in appearance.
Additional confirmation will be to let set until all of the precipitate has settled to the bottom of the test tube, then, poor off as much of the liquid solution as possible without disturbing or loosing the precipitate resting in the bottom of the test tube. Add to this 2cc of water, (no chlorine), and heat to a boiling point. The results from this test should be that the Lead Chloride in the precipitate will dissolve. Should there be Silver Chloride present, then, the precipitate will not dissolve. Should the Silver Chloride not have dissolved, then, confirm Silver with further testing by pouring off the water without disturbing the precipitate and add 1cc of strong Ammonia. Shake the test tube slightly. If the Silver precipitate dissolves, add 2cc of water, (no chlorine), and add to this 2 drops of Nitric Acid. The results are that Silver will be re-precipitated.
Testing with a spot test by using the test solution in tube no. 2 and place a piece of spot paper, (filtered paper squares), on a piece of glass. To the spot paper, (filtered paper squares), add 1 drop of the test solution, (tube no. 2), and add to this 1 drop of Hydrochloric Acid. Add 1 additional drop of the test solution. Should Silver be present, the spot paper will turn dark after setting for a few moments.
Should the water used for testing contain chlorine for diluting the acid, use powdered suspected mineral specimen or concentrates the size of a navy bean and place this in a clean test tube with 2cc of strong Nitric Acid. Boil this solution for a considerable time or until the Silver is dissolved. The results from this mixture is a white precipitate with Silver (Ag) or Lead (Pb) being present. Should Silver precipitate turn dark on exposure to sunlight, then, Silver is present; whereas Lead will remain white. End of test.
Delos Toole copyright 2000.
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