248 INDUSTRIAL PLANTS 



materials. With still further mastery over metals both wood 

 and stone have latel}' come to be replaced rather extensively 

 in building by iron and steel. Nevertheless, in spite of the 

 increased facilities for obtaining and working its various 

 rivals, wood is now being used more than ever. During the 

 past fifty years, in this country, each decade has shown a 

 large and steady increase in the amount of wood used pro- 

 portional to tlie poi)ulation. The reason for this must be 

 sought in the remarkalole advantages which wood possesses 

 over all other materials for a wide range of uses. 



The economic superiority of wood is well shown for ex- 

 ample, by comparing it with metals such as iron and steel. 

 (1) The supply of wood under proper forest management is 

 practically inexhaustible and very widespread, while mines 

 are not only exhaustible but strictly local. (2) Wood is 

 cheap, and metals are dear because of the much greater 

 labor required in metal-working. Even as lumber, after long- 

 distance transportation, wood rarely costs more than 50 cents 

 a cubic foot, the price of iron being from .?5 to -IflO; while the 

 much greater ease with which wood may be shaped, reshaped, 

 and combined in structures makes it much less expensive to 

 manufacture. Ci) Wood is stronger than is commonly sup- 

 posed. In tensile strength, /. c, r(>sistance to a pull length- 

 wise of the grain, a bar of hickory exceeds a similar bar of 

 iron or steel of the same weight. Similarly the resistance to 

 compression parallel to the grain (i c, against the ends of 

 a stick) is found to lie greater m a selected piece of hickory 

 or hard pine than in a rod of wrought iron of the same weight 

 and height. Though under certain conditions iron appears 

 to be much stiffer than wood, it is found that a ten-foot beam 

 of hard pine recjuires considerably more load to bend it by 

 one inch than a similar bar of injnof same weight and length. 

 (4) Wood endures a far greater distortion than metal with- 

 out losing its power to recover the original form. (5) Wood 

 does not rust or crystallize like metal, and, (G) as wood is a 

 poor conductf)r of heat it is not only |)leasanter to t(.)uch but 

 when used as the chief material oF dwellings and ships lias 

 none of tlie injurious efiects of iron and steel. (7) Wooden 

 beams though combustible, are often safer in case of hre than 



