[Jewelry making - Article 00984] - Re: [Orchid] Bad Pickle

[John Burgess]

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    G'day    Sparex is sold by jewellery supply people to use as a
    pickle to clean up sterling and carat gold after soldering or other
    heating.  It is supposed to be sodium bisulphate, but as I
    understand from many Orchidians it often seems to contain some brown
    scunge or other.  So let me tell you how sodium bisulphate is made . 

    It is a byproduct made during the production of hydrochloric acid.  
     That acid is made by heating common salt; sodium chloride, NaCl
    with concentrated sulphuric acid; H2SO4, which to give the proper
    name is dihydrogen sulphate  So the chloride part of the salt
    combines with the hydrogen of sulphuric acid, and the  poisonous gas
    hydrogen chloride is given off.    This gas is extremely soluble in
    water  and so dissolves up to a maximum strength of 35.5% 

    What is left in the reaction vessel is the combination of the
    sulphate part of the  sulphuric acid plus some hydrogen together
    with the sodium part of the sodium chloride  to make sodium
    bisulphate, or correctly, sodium hydrogen sulphate NaHSO4.  All the
    chemicals used are colourless. So is sodium bisulphate. Therefore 
    brown Sparex must contain impurities.   It is the hydrogen part of
    sodium bisulphate that dissolves copper oxides and silver sulphides
    to act as a pickle.  It will of course also dissolve the borax and
    borates from the soldering flux. 

    Finally, to those who don't like the thought of dumping used pickle
    into the sewage system, please remember that in England and in New
    Zealand (and other countries) a commercial product called Harpic is
    sold for cleaning and removing the incrustation of lime that may be
    found in baths, wash basins and toilet bowls.    And what is Harpic?
     Well, whisper it - mainly sodium bisulphate! Understand whatever you
    use. 

-- 
Cheers for now,
John Burgess;   johnb AT ts.co.nz of Mapua, Nelson NZ


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