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
Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ