The reason citric acid is used for pickling in small workshops is because it is SAFE. Stick a bit of sugar in it and it could almost be classed as lemonade (before use of course). You can even use your bare hands to pick things out of it (but wash them afterwards because of the metals and crap contained within the solution).
The easy way to get your saturated mix is to use say half or a pint of warm water and gently add crystals whilst stirring continuously, until no further crystals will dissolve, you will soon see it, there will just be a few rotating in the bottom of the container. There is no benefit in putting extra in to try to increase the potency, the water can only support a certain amount in solution, and once that point is reached, that's it.
There is no need to discard it after use, just keep using it until it doesn't work any more. You usually get things like algae growing in it over time, but unless it is swimming about and has teeth, nothing to worry about. A spoonful of domestic bleach is supposed to stop the algae growing.
I used to do a fair amount of silver soldering, and a 1 pint batch in a Tupperware sealed container would easily last me six months. Once it is exhausted, just pour it down the drain.
It isn't as powerful as the usual Sulphuric acid mix or commercial pickling salts, but it is a lot safer, and besides, what is half an hour extra wait when you are having so much fun.
BTW, I have forgotten about bits and left them in there for weeks, and they never came to any harm, it seems that it cleans, forms it's own pure oxide coating and then stops eating away at anything. The bits will still solder up perfectly well.
John
