248 INDUSTRIAL PLANTS 
materials. With still further mastery over metals both wood 
and stone have lately 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 the population. The reason for this must be 
sought in the remarkable 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 $10; while the 
much greater ease with which wood may be shaped, reshaped, 
and combined in structures makes it much less expensive to 
manufacture. (3) Wood is stronger than is commonly sup- 
posed. In tensile strength, 7. e., resistance 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 (% e., against the ends of 
a stick) is found to be greater in 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 requires considerably more load to bend it by 
one inch than a similar bar of iron of 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, (6) as wood is a © 
poor conductor of heat it is not only pleasanter to touch but 
when used as the chief material of dwellings and ships has 
none of the injurious effects of iron and steel. (7) Wooden 
beams though combustible, are often safer in case of fire than 
Tere 
