Wood vinegar, or pyroligneous acid, is the fluid or sap derived from tree cells, which exhibits exceptional permeability and sterilizing properties. During experiments, it was confirmed that the great absorbing power of wood vinegar makes it fit to be used in physiotherapy, for minor pain relief and to decrease swelling in the body. Wood vinegar or pyroligneous acid has also traditionally been used as an insect repellant, deodorizer, antibacterial agent, sterilizer, alkaline bath and wash, and food additive.
Pyroligneous acid is obtained by the dry distillation of wood. This is a development of the traditional process of charcoal burning or the burning of wood in an airless condition reducing it to a charcoal rather than a carbon dioxide, water vapor and ash. In the process of wood distillation, a chamber of firebricks is substituted for the mound of earth, and a device is added to collect and cool the vapors released to condense them. The condensate consists of pyroligneous acid and a tarry residue, which will separate and settle upon cooling.