CHAPTER XIV 



THE CHEMISTRY OF COMMON INDUSTRIAL 

 SUBSTANCES 



172. Chemistry in Industry. There are certain chemical 

 changes, such as the burning of forms of carbon, explosions, 

 etc., that are very common in industrial life. Moreover, the 

 chemical composition of certain building materials, such as 

 concrete, is so important to industry that everyone should 

 understand the fundamental principles underlying their 

 manufacture. 



173. Forms of Carbon. When an element is found in 

 several forms which have essentially different properties, 

 it is said to be allotropic in character. Carbon is such an 

 element, the different forms or modifications of which are 

 the diamond, graphite, and pure amorphous carbon. 



The diamond is pure, crystalline carbon. It has a specific 

 gravity of 3.5 and is one of the hardest substances known. 

 On account of its hardness it is used to cut glass. The black, 

 impure variety, called carbonado, is set into the end of a 

 drill, called a diamond drill, which is used for boring holes 

 in hard substances. 



Graphite is a soft, lead-colored, shiny solid often called 

 "black lead" or plumbago because it was originally sup- 

 posed to contain lead. It is smooth and greasy to the touch 

 and is used in the form of flakes as a lubricant because it 



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