Oxalic acid (C2H2O4) is a chemical compound used for cleaning, bleaching or restoring wood. The substance can kill people in high enough doses, with the median lethal dose being 71 mg/kg. Buying oxalic acid is a fairly simple process, provided you can find a retailer that sells the substance.
Determine Your Needs
Determine whether you require a pure oxalic acid or simply a product that contains oxalic acid, such as Savogran Wood Bleach. You can laboratory-grade oxalic acid with ease over the Internet (see the resources section). You also can find high-grade oxalic acid at many pharmacies. However, you can often buy it much more cheaply at gem stores or rock collector's shops. Many dealers will sell you oxalic acid for as little as $3 per pound or $2.50 per pound for five pounds. Check your local yellow pages for gem dealers or rock hunter's shops in your area.
It takes roughly a pound of acid to create a solution with five gallons of water, so plan accordingly.
You will want to dispose of this material safely. Once a batch of acid is fully used up, it generally turns an emerald green color. By adding lime (CaO) to the oxalic acid and water mixture, you can neutralize the acid, making it safe to throw away. Use a funnel to empty the waste into a milk jug, cap it, and put it out with your trash. It is not flammable and is not hazardous once neutralized.
Tips and Precautions
When buying oxalic acid in person, make sure to receive a detailed receipt that outlines what exactly the material is. Because it is a white powder, sometimes sold in unmarked bags, you don't want the police to think you are transporting cocaine if you happen to get pulled over. Your receipt should state what the oxalic is, where it was purchased, and what it is commonly used for. Chances are you won't need the receipt, but it is better to have it and not need it than to need it and be unable to produce it.
Remember that this acid is corrosive, and harmful if ingested, and can irritate both skin and eyes. If you plan to work with this material, make sure you have the number for poison control handy and access to an emergency eye wash station or other source of clean running water. You should always wear gloves and protective eyewear. Always work in a well-ventilated area.