WOOD IN GENERAL 249 



iron ones because the latter twist out of shape at high tem- 

 perature in a waj' to wreclv the entire structure. (8) Being 

 unaffected by wines or other weak acids, and imparting no 

 disagreeable flavor, certain woods may be used for caslvs 

 where metal would ])e ol)jectionable or even poisonous. 



(9) Woods have an organic beauty unrivaled by metals. 



(10) The peculiar elasticity of certain woods render them 

 incomparably superior to any metal as material for the res- 

 onant parts of violins and similar musical instruments. 



(11) Pieces of wood may be easilj' and strongly united simply 

 by glueing, while metals require the more difficult operation 

 of welding or soldering. As against wood it must be said 

 (1) that it cannot be melted and cast or rolled; thougli by 

 steaming, rods or sheets may be readih' bent into curves of 

 small radius; and when reduced to pulp, as we have seen, 

 it can be pressed into almost any shape. (2) It shrinks or 

 expands with variations of moisture, more than metals do 

 under ordinary variations of temperature. (3) It decays 

 unless proper precautions are taken to prevent, though muler 

 water wood lasts longer than steel or iron. (4) It is more 

 easily crushed than iron and therefore is not so well suited 

 for bearing the greatest weights or for resisting very heavy 

 blows. (5) Finally, the greater hardness of many metals 

 gives them obvious advantages over wood for sharp impli.'- 

 ments and a large variet}' of objects that have to stand severe 

 wear. A great deal is often gained by combining wood and 

 metal because the properties of one so largely complement 

 those of the other. 



A piece of wood consists essentially of a mass of extremely 

 slender fibers or fibrils, each comparable to a fibril of cotton, 

 but firmly cemented together. The valuable qualities of 

 woods, and their defects as well, depend in great measure 

 upon the character and arrangement of these fibrils and of 

 similar parts associated with them. Therefore some knowl- 

 edge of the structure of wood helps us to understand its prop- 

 erties and to tell one kind of wood from another; and thus 

 should lead us to a more intelligent, economical use of the 

 material. The fibrous nature of wood is clearly shown by 

 its sjDlintery fracture when broken across the grain and by 



