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Pyroligneous Acid

wood, acetic and temperature

PYROLIGNEOUS ACID, an impure, di lute form of acetic add obtained by the dry distillation of wood. The foliaceous trees, espe cially the beech,• or the oak and birch, which latter having been deprived of their bark are better adapted for its manufacture than the conifers. The dry distillation of wood is ac complished in iron airtight retorts, of which there are many styles; and in accordance with the temperatures employed varying products, yrhich are partly gaseous and partly liquid, are formed. The gases are consumed and the liquid component separates into two layers of which one is aqueous and dark brown, contain ing the wood vinegar, while the other is oily, almost black, containing wood tar. During dis tillation the first distillates, which contain very little acid, pass over at F. (79-113° C.) while at 288° F; (142° C.) the lighter oils pass. As soon as the water shows a sufficient content of acid the temperature is raised to 315° F. 157° C). Above that temperature the 'heavier oils distil over. The quantities received vary, as has been said, according to the temperature employed: in general about 35 per tent of pyre ligneous acid; 20 per cent of 'wood •tar and 33 per cent of charcoal are the products.

Pyroligneous acid, as it iu received from the still, is a reddish brown fluid having a rather dis agreeable, sour, smoky, empyretnnatic odor and taste. It is a very complex product, containing besides acetic acid, all the homologues of acetic acid from formic to caproic acid; methyl alco hol, acetone, mitacetone,.aldehyde, etc.

Commercial acetic acid is prepared chiefly from pyroligneous acid purified by distillation and strengthened by rectification, the acetic acid obtained by the oxidation of ethyl alcohol being of limited concentration and used prin cipally for table use, and.preserving food articles. The crude pyroligneous acid is used for the preservation of wood and ropes, for embalming, in veterinary surgery for many dis eases, and in some of the arts, as in calico printing.