Pyroligneous Acid, or WOOD VINEGAR, a crude commercial form of Acetic Acid (q.v.). It is made by the destructive distillation of wood, and, besides acetic acid, contains tar, creosote, wood-naphtha, and other products, which have to be removed if it is required in a very pure state.
The best woods for the distiller are 'hard' woods, although all will yield it. Oak branches stripped of their bark are cut into short billets, which are placed in cast-iron retorts, and a sufficient heat applied to drive off the volatile constituents and carbonise the wood. This acid is of great use in the arts, especially in making the acetates used by dyers and calico-printers; and it is also, when very carefully purified and properly diluted with water, used extensively as a substitute for common vinegar in pickling, and even for table use. It is also used in the preservation of fish, giving them a 'smoked' flavour.