subsecret - 9-2-2015 at 15:29
After I had left my Rooto acid in a desiccator with some p-TsOH for a few weeks, it produced a very thin, white precipitate on the bottom of the
beaker. Before I poured the acid into the beaker, I had shaken the bottle it came in, just to see if something different would happen. The bottle had
been almost empty. After several weeks, I poured the spent acid into a waste container, and decided to add concentrated sodium sulfide to the
precipitate in the beaker, which was still moist with acid. An intense, black, and transient precipitate formed.
Many metals form black sulfides, but I suspect that it is lead contamination from the acid's former life as battery acid (?).