You are very correct, I did make a mistake in my use of words, I meant to say sodium metabisulfite, (and not sodium metabisulfate), the endings in these chemical names are important as they contain differing amounts of oxygen and so they can react differently in solution.
Thank you for catching my goof, this also shows me your paying close attention and learning, and if I were allowed to use the wrong name for a chemical, some new member could think that it would work, or that we use that chemical when we do not, and not know I used the wrong name for that chemical, with chemistry and mixing chemicals and metals, using the wrong chemicals or chemical name, could become dangerous, I will post a correction to the post above in red.
Phil,
I think dirty solutions can be hard to precipitate from, no matter what chemical used, take the case of tin in solution for example tin is involved in electronics from the solder, when in a solution dissolved with gold, tin will reduce the gold, forming colloids in solution, these gold metal particles will not settle but become charged particles, and repel each other they will not combine, to precipitate, but keep each other in solution, they also have been reduced to metal gold particles (by the reaction with tin), so they have already have gained back their missing electrons, so adding a copper buss bar will not cement them or reduce them to metals (they are already reduced), these gold particles are already reduced to metal so stannous chloride will not test for gold in this solution, they are already gold metal particles so a chemicals will not reduce them, so we are stuck here, we cannot tell there is gold in this solution and we cannot precipitate the gold unless we can break the colloid, (high heat and raising acid content can help some here).
