Regarding Chlorine , do not overuse bleach , if you work outside a plastic lid over your container CAN help you to minimize the escaping Cl2 in a given time: it's safer. The lid helps because inside the beaker pressure goes up (very little , no explosion) and this additional pressure change the gas-liquid phase equilibrium, in simple words : more Cl2 come back in the solution ( chlorine concentration has a distribution: more in the upper part of the liquid, less on the bottom) and if you are very patient and in time oscillate your beaker back and forth to swirl the liquid inside, you will be able to dissolve a little more gold. But all what I wrote above is more Easy to say that to do in practice. I do not suggest to follow my advice for your first try. A possibile setback, if you are not patient, is to bring up the lid too early: this change the gas liquid equilibrium in the opposite way. Only if you understand what I mean with this last sentence you can use a lid.
