PROPERTIES AND THEIR RELATION TO USES OF WOOD 163 



Hardwoods cannot be floated or driven on streams because of their 

 weight and the likelihood of sinking. Some of our heaviest hardwoods 

 are hickory, persimmon, white oak, hard maple, beech, ash, and elm. 

 Among the heaviest softwoods are longleaf pine, western larch, and 

 Douglas fir. The light-weight hardwoods include the cottonwoods, 

 aspen, yellow poplar, butternut, willow, chestnut and catalpa; light- 

 weight softwoods are redwood, the cedars, white pine, eastern hemlock 

 and the true firs. 



Strength, hardness, cleavability, flexibility and toughness * are im- 

 portant mechanical properties of wood. 



The chemical utilization of wood within recent years has empha- 

 sized the importance of the chemical properties of wood. Each species 

 varies both in its physical and in its chemical characteristics. The 

 field of chemical utilization has only begun as far as its ultimate 

 possibilities are concerned. When wood is dried in extreme tempera- 

 tures, it is found to contain about 99% organic matter and about 

 \% inorganic matter. The latter comprises the ash when wood is 

 burned. Wood is found to contain largely carbon and oxygen with a 

 small amount of hydrogen and very small quantities of nitrogen, po- 

 tassium, sodium, calcium, and magnesium. The wood fibers consist 

 of a skeleton of cellulose which includes varying amounts of lignin, 

 tannin, resins, and gums. Cellulose is readily converted into some of 

 the simpler sugars.f 



Durability is a very important quality of wood; it may be de- 

 scribed as the ability to resist decay. Durability is very important in 

 wood which is to be used for railroad cross ties, poles, posts, mine 

 timbers, piling, and foundations, which are susceptible to decay. 

 Durability is often the determining factor in the value of some species 

 that may be exposed to certain soil, weather, or moisture conditions 

 conducive to decay. It is the purpose of the preservative treatment 

 of wood to lengthen its life in service. Wood does not naturally 

 decay. Specimens have been taken from piling driven by Caesar in 

 crossing the Tiber River near Rome about 2000 years ago which are 

 still sound. All decay is caused by fungi or bacteria which live on the 

 constituents of the wood, causing dry rot, heart rot, and punk in 

 both living trees and lumber and wood materials manufactured from 

 trees. Fungi live and propagate when environmental factors such as 



* For further information on this subject see "The Mechanical Properties of 

 Wood" by George Garratt, John Wiley & Sons, New York, 1931. 



t For further information on chemical properties of wood see "The Chemistry 

 of Wood" by L. F. Hawley and L. E. Wise, Chemical Catalog Co., New York, 

 1926. 



