234 FIBST BOOK OF FOEESTBY 



Similarly, a select block of hickory or of longleaf pine 

 sustains a greater weight in compression endwise (parallel 

 to the grain of the wood) than a block of wrought iron 

 of the same height and weight, and nearly approaches 

 cast iron in this respect. 



6. Wood is light; iron and steel are heavy. The 

 average weight of all wood used in this country does not 

 exceed thirty-one pounds per cubic foot ; that of iron and 

 steel is from four hundred and thirty to four hundred 

 and fifty pounds per cubic foot. This quality affects ease 

 of handling and transportation ; it permits the floating of 

 most woods when green, and of all of them when dry. 



7. Wood is a poor conductor of heat and electricity. 

 Heated to one hundred and fifty degrees Fahrenheit, or 

 cooled below the freezing point of water, iron, steel, and 

 other metals are painful to the touch ; and even far within 

 these limits metals are objectionable on account of their 

 ready conductivity of heat. Wood, on the other hand, is 

 entirely inoffensive as long as its temperature remains 

 within the above limits. The objections to metal dwellings 

 on this account are experienced in heavy-armored ships, 

 which, in spite of the excellence of an ocean climate, are 

 notoriously uncomfortable. 



When exposed to heat, wood is ignited and destroyed 

 by fire. The inflammability and combustibility of wood 

 at high temperatures, though among its most valuable 

 properties, are, at times, a drawback which metals do not 



