Paige said:
I boil my AR to get rid of nitric. Afraid I might be boiling off some gold????
If you are actually boiling, I'm afraid you are, indeed, losing gold.
The story is long, and hardly worth repeating, but the short version is that prior to my first fume hood, I ran from a bench in my garage, directly under a window in which I'd placed an exhaust fan. My travel trailer was parked a couple feet beyond the window, in direct line with the fan. (What the hell was I thinking?)
I was evaporating a solution one day and noticed that it was going a little too fast. A few days later, a large area, fan shaped, was covered in light purple dots. I had to rub the siding with compound to remove the stains.
When evaporating, keep watch on the cloud that leaves the dish. If it contains the slightest hint of color, you're losing gold. Insure that the temperature is always below the boiling point. Even when you add a button of gold to consume free nitric, if the button is actively dissolving, keep a watch glass over the beaker. You'll notice that gold chloride forms on the watch glass and drips back into the beaker. Once the action is subtle, you can remove the watch glass and begin the evaporation process, eliminating the final traces of nitric.
I just boil in a large beaker.
That should be adequate, especially if you add a button to help consume the free nitric. An evaporating dish is better if you rely on evaporation alone---it presents a larger surface area, therefore expels heat at a greater rate, and evaporates quicker.
Should I be using one of those flat bottom glassware things that narrows at the top and condensing my evaporate to save any gold going up in the boiling process?
An Erlenmeyer flask?
I don't see the need for one of those in any of the refining operations unless you're using one with a spigot and a Buchner funnel for vacuum filtration. Erlenmeyer flasks defeat the purpose you're trying to achieve.
Or just don't boil too rapidly?
Exactly!
As Harold_V has taught, I always check my solution by hanging a bracelet chain in the solution to make sure there is no more reaction.
I suggest you move to a piece (button) of pure gold. A chain, yellow gold, is capable of forming enough silver chloride on the surface to present a false indicator to you. It might show no action when there was still considerable nitric present, but isolated from the chain by the chloride film that forms.
My procedure was to use a button of relatively pure gold, gold that needed to be re-refined, anyway. I weighed it before adding it to the solution I intended to evaporate, then weighed it afterwards, so I knew how much gold I had added to the process. That was important for me because I ran my customer's gold on an individual batch basis, and had to know what belonged to me.
Harold
