Concentrating Oxalic Acid by Evaporation I bought Oxalic Acid in an aqueous solution from a hardware store years ago. I need to turn it to powder form for easier storage and other things. 

Can I simply evaporate the solution? I seem to notice that evaporating it releases fumes that are similar when one is boiling Acetic Acid. Are there more Oxalic Acid being lost just as it is when boiling Acetic Acid (not distillation)
Depends on how hot the plate is I'd say. Oxalic acid is hygroscopic, so it will be hard to completely dry it by just subjecting it to heat as you might just cause it to break down.

There's a paper and procedure on Organic Synthesis on how to obtain the anhydrous form, so you should check that out to see if that meets your requirements.