ECONOMY AND BURNING VALUE OF FUELS 177 



after drying, may take the place of coal or wood. It is be- 

 lieved by many scientists that petroleum and natural gas 

 are also formed through slow chemical changes from dead 

 bodies of plants and animals buried millions of years ago. 

 Great areas holding gas and oil have been discovered in 

 different parts of 

 the United States, 

 the largest produc- 

 tion coming from 

 Pennsylvania, West 

 Virginia, Indiana, 

 Texas, California, 

 Oklahoma, and Illi- 

 nois. Mexico has 

 fields of great value, 

 and oil is found in 

 paying quantities in 

 other parts of the 

 world, southern 

 Russia being one 

 of the richest 

 areas. 



Economy and burning value of different fuels. Wood 

 is used the world over, and is probably used now in more 

 homes than any other fuel. Hardwood, such as hickory, 

 oak, maple, or beech, burns longer and gives a steadier heat 

 than softwoods, such as poplar, hemlock, or pine, but soft- 

 woods give off heat more quickly. Coal is a much used 

 fuel in our eastern homes, soft coal being used more where 

 it is abundant. Soft coal is much dirtier, but somewhat 

 cheaper than hard coal, or anthracite. Coke, which is coal 

 from which certain gases have been removed, is valuable 



H.-WHIT. CIV. SCI. IN THE HOME 12 



In an oil region. 



