anachronism said:
Regarding Ascorbic acid.
I use it for a number of reasons and in particular situations. Firstly it doesn't "gas off" Sulphur Dioxide making it more user friendly than SMB. Secondly it's fast and it's also really easy to see when your solution has given up all its gold by the colour change. It's also very good at taking out the last small piece of gold from a solution that you've already dropped with "green stuff" and instead of having to make up a new batch you can put a teaspoon of this in and leave it. You get no false positives from this like you can do with SMB.
It's also extremely good for small concentrated solutions where "green stuff" doesn't work so well without increasing the volume dramatically.
The only downside is that it does require more settling in some cases as the precipitant (especially on weak solutions) can be very fine indeed. That given I do tend to pour off the majority of the gold and clean it from my drops whilst leaving the small amount that requires settling to do its thing overnight so it doesn't make too much of a difference to me.
It's been discussed before on the forum about the selectivity of ascorbic acid. According to Lou, ascorbic acid will precipitate silver, palladium and copper from solutions, at least when boiling.
Any experience with that? Any problem with selectivity? Do you heat the solution when precipitating gold?
I did some digging on the forum (over 90 posts about ascorbic acid) and tried to put together a short article about ascorbic acid.
http://goldrefiningwiki.com/mediawiki/index.php/Ascorbic_acid
Göran