MANUFACTURE OF WOOD-VINEGAR. 215 



CHAPTER XXI. 



MANUFACTURE OF WOOD-VINEGAR. 



AMONG the numerous organic substances which by distillation 

 in -closed vessels give rise to acid products, wood is employed in 

 the arts for the manufacture of acetic acid. "Wood-vinegar, or 

 acetic acid from wood, is also known when impure under the 

 name of pyroligneous acid. 



Wood essentially consists of woody fibre, small quantities of 

 salts and sap, and a variable quantity of hygroscopic water. 

 Woody fibre or cellulose constitutes about 96 per cent, of dry 

 wood, and is composed of C 6 H 10 O 5 ; in 100 parts, of carbon 

 44.45; hydrogen 6.17; oxygen 49.38. The vegetable sap con- 

 sists chiefly of water, but contains organic as well as inorganic 

 matters, partly in solution and partly suspended. The inorganic 

 constituents (the ash left after the incineration of the wood) arc 

 the same in all kinds of wood. The quantity of water contained 

 in wood is generally larger in soft than in hard woods. One 

 hundred parts of wood recently felled contain, according to 

 Schubler and Xeuffer, the following quantities of water : 



Beech .... 18.6 

 Birch . . . .30.8 

 Oak .... 34.7 



Oak (quercus pedunculata) 35.4 

 White fir 37.1 



Common fir . . .39.7 

 Red beech . . .39.7 

 Alder .... 41.6 

 Elm .... 44.5 



Red fir , 45.2 



The branches always contain more water than the trunk. 



Wood is called air-dry when its weight no longer changes at 

 an ordinary temperature ; in this state it contains still 1 7 to 20 

 per cent, of water. The latter can be expelled by continued 

 heating at 212 F., but wood thus dried re-absorbs about 20 per 

 cent, of water from the air. 



When felled nearly all kinds of wood are lighter than water ; 

 a few are, however, heavier, but these are the harder kinds in which 



