76 CHEMISTRY. 



CHAPTER VII. 



CARBON AND CARBONIC ANHYDRIDE. 



89. Abundance of Carbon. The two elements which we 

 have described to you in Chapters V. and VI. are gaseous. 

 Carbon, the element which we are now to consider, is a solid. 

 This is present almost every where. It forms nearly one half 

 of all the solid part of all vegetable and animal substances. 

 The different varieties of coal are nearly pure carbon. This 

 element is one of the ingredients of all limestones and mar- 

 bles. All shells are composed in part of it. It is present 

 every where in the air, united with oxygen to form a gas, 

 carbonic anhydride, which we shall speak of particularly in 

 the latter part of this chapter. 



90. Charcoal. One of the most common forms in which 

 we see carbon is charcoal. Before hard coal was introduced 

 into use it was the most common form ; and it is for this 

 reason that the word charcoal is often used as being syn- 

 onymous with carbon. Charcoal is ordinarily made from 

 wood ; or, to speak more correctly, it is obtained from wood, 

 for no new substance is formed, but there is merely a sep- 

 aration of the components of the wood. All the compo- 

 nents except the carbon are driven off, for the most part. 

 This is done by a smothered and imperfect combustion. 

 The wood is piled together and covered over with turf. It 

 is then set on fire from below, and suitable openings are 

 kept in the covering to allow the proper degree of combus- 

 tion. Figs. 17 and 18 (p. 77) illustrate the manner of piling 

 the wood and conducting the operation. Some of the car- 



