>wish to know the very detail of preparing the mixture of oxalyic acid
I buy it at the local hardware stores as "wood bleach". I vaporize it and it requires no mixing at all.
The amount I use is about 1.5 grams for three medium boxes (or two deep boxes if you use deeps).
I have a simple "L" shaped evaporator made of brass pipe that has a cap on one end where I put in the oxalic and screw it on and the other end fits in a hole in an old shallow super. I put the super on top and the lid on top of that and use a propane torch to vaporize the oxalic acid. You can also buy an evaporator:http://members.shaw.ca/orioleln/Vaporizer.htm
DON'T BREATH IT THE VAPOR! That's the main precaution. I always have a smoker lit so I can see which way the smoke drifts and I make sure I'm standing up wind.
If you do inhale it it burns and makes you cough a lot. You probably won't make the same mistake again.