Refining gold with oxalic acid

[Helian]

I just dropped some gold with oxalic acid for the first time, so will share a few observations. After going through the usual steps to drive off nitric, I diluted my gold chloride solution to about 30:1. I then brought it and a saturated solution of oxalic acid in water to a boil. After adding the oxalic acid to the chloride solution, I let it boil for 10 minutes, then added another 25 ml of oxalic and boiled an additional two minutes. The gold came out exactly as described in the books, in fine particles and flakes, some of it adhering to the inside wall of the beaker making it look as if it had been plated. As I prefer decanting to filtering, I then let the beaker sit overnight. In the morning, a fine, faint blue precipitate had dropped out of solution, and was covering the gold. I suspect this was copper oxalate. In any case, the oxalates are soluble in nitric acid, so I washed the precipitate to make sure all the HCl was gone, then added dilute nitric. The pale blue precipitate, disappeared, leaving the gold. Apparently that's why the books occasionally have a caveat about eliminating copper before trying to refine with oxalic acid.