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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 Mapua, Nelson NZ |
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