CHAPTER VII 

 Carbon 



47. Occurrence. Carbon is found in the free state 

 only in limited amounts, but is present in nature mainly 

 in combination with other elements. With the mineral 

 elements and oxygen, it forms carbonates, such as calcium 

 carbonate or limestone. With hydrogen and oxygen, and a 

 few other elements, it forms a large number of compounds 

 of which plant and animal tissues are composed. All sub- 

 stances which char or blacken when burned contain this 

 element in combination. Diamonds, coal, and graphite 

 are forms of carbon in various degrees of purity. With 

 oxygen, it is present in the air in small amounts as carbon 

 dioxid. About half of the dry substance of wood and 

 animal tissue is carbon. It occurs in nature in a great 

 variety of forms. 



48. Preparation. In the form of charcoal, it can be 

 prepared from wood, by the application of heat in the ab- 

 sence of air or oxygen, when a change known as destruc- 

 tive distillation takes place. The hydrogen, oxygen, and 

 nitrogen are expelled, while the black mass of impure car- 

 bon and mineral matter is left. In the preparation of 

 charcoal, the wood is piled and burned in suitable pits, 

 which, after the combustion is well started, are covered 

 with turf to protect the burning mass from the air. Char- 

 coal can be produced on a small scale in the laboratory, 

 in the following manner : 



Experiment 4. Place two or three small pieces of wood in a 



