2 INTRODUCTION. 



tions as resins, coloring matter and water. The small proportion 

 of mineral in wood is evident as ash.* 



When heated, wood first gives off about one quarter of its 

 weight as water, after which the volatile, inflammable gases 

 separate from a solid base of carbon which itself finally con- 

 sumes with much heat but no flame and releases the residue 

 of ash. 



Wood is preferred because it is easily worked and light in 

 weight. In many positions it is as durable as iron. It is a 

 poor conductor of heat and electricity, and is stronger than is 

 generally supposed. The tensile strength of a bar of hickory 

 may exceed the tensile strength of a similar bar of wrought iron 

 of the same length and weight. f 



Wood is not homogeneous, like metal and most of the 

 stones, but is more complicated and so variable that several 

 portions of the same tree often exhibit widely different qualities. 



The consumption of wood has never decreased, although 

 metals and stones have been substituted for it in many posi- 

 tions. In England the per capita consumption more than 

 doubled in the fifty years preceding (1895) in spite of the fact 

 that nearly all of the wood used in that country had to be im- 

 ported. | The total yearly mill value of wood products in the 

 United States is now (1906) over nine times as great as its com- 

 bined product of gold and silver, or twice as great as the value 

 of its wheat crops. 



* Wood, timber and lumber may not mean the same. Properly speaking all 

 woody tissue is wood, but roots and branches contain much wood that is not 

 suitable for construction. Wood that is suitable although not necessarily ready 

 for construction is timber, and wood that is not only suitable but ready for con- 

 struction is lumber. 



The word timber may thus include living trees in the forest, as well as logs 

 and shaped pieces, whereas lumber refers only to boards, planks, beams and 

 other sawn pieces of limited sizes and then only in America. The term lumber, 

 which is not sharply definable, is seldom used abroad. 



t Roth, 1896 Yearbook, U. S. Dept. of Agriculture, p. 392. 



% U. S. Forestry Bulletin No. 10, p. 5. 



A conservative estimate places the yearly mill value of wood products at 

 $1,100,000,000. The spring and winter wheat crops of 1905 were together 

 valued at $5 18,372, 727. The production of gold and silver (1904) was valued 

 at $112,871.026. 



