6 4 



BURNING OR OXIDATION 



plants, and may be prepared by burning bones and animal 

 refuse as in the case of wood. 



Destructive distillation. When wood is burned without 

 sufficient air, it is changed into soft brittle charcoal, a substance 



very different from wood 

 and only one fourth as 

 heavy. Because charcoal 

 is unlike wood and be- 

 cause it weighs less, wood 

 in turning to charcoal 

 must lose some of the 

 substances of which it is 

 composed. We can prove 

 this by putting dry wood 

 shavings in a strong test 

 tube connected with a 

 bottle of water as shown 

 in Figure 34. Heating the 

 tube gently and slowly 

 we notice that a change takes place in the wood, and if we bring 

 a lighted match to C while the wood is being heated, a small 

 flame appears. Evidently a combustible gas is given off from 

 the wood. It is not easy in the ordinary school laboratory to 

 determine the other substances given off from the wood, but 

 it has been done by experts, who have found wood alcohol, 

 wood tar, acetic acid, and other commercial substances. 



Wood heated without sufficient air is broken up into a num- 

 ber of simpler substances. The process by which complex 

 substances are thus broken up into simpler substances is called 

 destructive distillation. 



Most of the substances given off by wood burning without 

 air are valuable commercially. Wood alcohol serves as a fuel, 

 and is largely used to dissolve and thin varnishes, oils, and 



FIG. 34. Destructive distillation of wood. 



