[Jewelry making - Article 00281] - Re: [Orchid] Argent I need your help.

[Watchman]

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>      We prepare solution of Nitric Acid ( HNO3) 33% with concentration
>     of 24Bums( density = 1.2) whichused to paration silver(Ag) from
>     Gold(Au) as mention In ISO11426, Also we used water( PH=7.4) but
>     after 5minute -1 days we found the concentration of solution( HNO3)
>     higher than before around 34Bums( 46%) . 

    The only mechanism which would cause the solution to concentrate
    like this over a short period of time would be the evaporation of
    water by heat. I suspect that this may be due to the way you are
    preparing the solution and that you may be adding the concentrated
    acid to the water (you are doing it this way round aren't you??) too
    quickly. If you just dump the acid into the water quickly, this will
    cause the temperature of the water to rise, sometimes even to boiling
    point, and so the water will evaporate as it cools down. Try adding
    the acid very slowly and put it into a stoppered bottle until you
    need it. 

Best wishes,
Ian
Ian W. Wright
Sheffield, UK


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