When wood is subjected to destructive distillation or is greatly heated in close vessels, an acid liquor oozes over with the tar and gaseous products. This acid liquor is the pyroligneous acid. It is really an impure vinegar, from which acetic acid can be obtained, and the method employed is as follows: The pyroligneous acid freed from the tar, naptha, &c., is saturated w'th chalk or powdered slacked lime, filtered, and evaporated in suitable vessels. By this means an impure acetate of lime is obtained. This is gently heated to destroy the oily matter without injuring the acid, and then mixed with sulphate of soda or salt cake as the manufacturers call it ; this affords a beautiful acetate of soda, in solution, which is then drawn off from the remaining sulphate of lime. The solution is heated, evaporated to dryness, re-dissolved and crystallized, and by these means the acetate of soda is procured in crystals. These crystals are then placed in a retort with oil of vitriol and heated, when acetic acid distils over, which being the active principle of vinegar, this useful acidifier can easily be made from it, and of the very best qnality. The charcoal which remains in the retort in which the wood is distilled is excellent, and is lal'gely used for the manufacture of gunpowder.
This article was originally published with the title "Pyroligneous Acid or Wood Vinegar" in Scientific American 13, 10, 73 (November 1857)