[Jewelry making - Article 00373] - Re: [Orchid] Argent I need your help.

[Alden & Glenda Blood]

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    Reading between the lines of your post of April 8, I gather you are
    quartering a gold alloy.  That is, you are either adding sufficient
    silver or copper to the alloy to reduce the quality to 6K or less,
    or the sample is already 6K or less.  At that quality a 1:1 by
    volume of conc. nitric acid : distilled water solution will react
    with the alloy dissolving the Ag, Cu, Zn, etc. and leave a very fine
    brown powder which is fairly pure gold.  Concentrated reagent or CP
    grade nitric acid is 68 - 70% (g/100 cc) acid with a density of 1.42
    g/cc.  Specific Gravity and density, for all practical purposes, are
    the same to the second decimal point.  Diluting with an equal volume
    of water would give 34 - 35% acid with a Sp. Gr. at 60 degrees F of
    1.21 which is equivalent to 24 degrees Baume (your "24 Bums"). 
    Please note that Baume should have an accent mark over the e. 

    If you checked the acid with the hydrometer immediately after
    diluting/mixing and obtained a reading of 24 degrees Baume, and then
    checked again  five minutes later and got 34 degrees, then you have
    an inexplicable situation.  A case of black magic or the first
    reading was in error.  If, however, you took the gravity reading
    about five minutes after making the solution and got 34 degrees
    instead of the expected 24 degrees, then the only answer is  that 50
    ml of water per 100 ml of conc. acid was added instead of 100 ml of
    water.  The only way to increase the acid concentration by 16% is to
    remove water by distillation.  There is the tacit assumption in all
    this that the conc. acid used was at full strength and was of normal
    purity. 

    The 7.4 pH of the water used indicates distilled water was not used,
    or the distilled water was contaminated, or the pH reading was not
    accurate.  If the pH of 7.4 is correct, the small amount of base
    present would decrease the amount of acid, not increase it.  It is
    necessary to use distilled water in the process to eliminate
    precipitation of AgCl which would contaminate the Au product.  The
    way to check the pH meter is to use standard reference buffer
    solutions on a regular basis.  This will assure you that the acidity
    measurements are correct and that the glass electrode is functioning
    properly.  I don't know what the ambient temperature is where you
    work, but it would be advisable to check the temperature
    compensation of the meter from time to time also. 

    If the situation you describe had happened to me, I would have
    titrated a sample against standard base to confirm the hydrometer
    reading.  You would then know that insufficient water was added. 

    I wish you good fortune in your future endeavors. 

Captain Blood
"Marlinespike Seamanship in Precious Metals"
mariner AT tgtel.com



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