Oxalic Acid: Sawdust Heated with Alkali Lye in Vacuum, Oxidised, Precipitated as Calcium Oxalate (Zacher)

Oxalic acid from wood, by Zacher's process (English Patent 2308, 1897) as Thorpe's Dictionary (1913) gives it: sawdust is dried under vacuum at about 70 °C, heated with hot caustic lye up to no more than 180 °C, and oxidised at the end. The product is dissolved, treated with lime to throw down calcium oxalate, and that is broken up with sulphuric acid; one recrystallisation gives good white oxalic acid. Hot lye and strong acid burn: goggles, gloves. The picture: our diagram.