PYROLIGNEOUS ACID. 291 



of wood is thirty-five gallons. Before the pyroligneous 

 acid begins to distil over, there comes a peculiar fluid 

 called pyroligneous ether, or pyro-acetic spirit, which 

 is used, when purified by a subsequent distillation 

 with lime and animal charcoal, for burning in spirit 

 lamps, for the solution of shell-lac, and indeed for 

 many purposes in which the use of alcohol was for- 

 merly required; but at present the greatest consump- 

 tion of this spirit is in dissolving caoutchouc. 



This impure acid is rectified by a second distilla- 

 tion, when from every hundred gallons twenty of a 

 viscid, tarry matter are collected. The fluid is now 

 become a transparent brown vinegar, having a con- 

 siderable empyreumatic smell, and a specific gravity 

 of 1 '01 3. Its acid powers are superior to those of 

 the best household vinegar in the proportion of 3:2. 

 This was formerly called acid spirit of wood, and 

 since pyroligneous acid. Fourcroy and Vauquelin 

 showed that this acid was merely the acetic conta- 

 minated with empyreumatic oil and bitumen. The 

 empyreumatic matter may be separated by satu- 

 rating the acid with quick-lime, then evaporating this 

 to dryness, and exposing it to gentle torrefaction. 

 The acetic acid combines in this process with the 

 lime, forming acetate of lime, while the separated 

 impurities have been driven off. If this acetate be 

 decomposed by sulphuric acid, a pure, perfectly 

 colourless, and grateful vinegar rises in distillation. 



It was discovered a few years ago that pyrolig- 

 neous acid, previously to being thus purified, has the 

 property of preventing the decomposition of animal 

 substances. " Putrefaction," it is said, " not only 

 stops, but retrogrades,'' on the application of this 

 acid. The effect has been ascribed in part to the 

 empyreumatic oil contained in the impure acid ; and 

 hence the agency of smoke has been accounted for 

 in the preservation of some kinds of^animal food. 



