ECONOMIC WOODS OF THE UNITED STATES 67 



in wood, for incipient decay causes wood to become dull and 

 "dead." Sound wood in thin sections is translucent and exhibits 

 double refraction. The presence of rosin in wood increases its 

 translucency. 



References 



GAYER, K.: Schlich's Manual of Forestry, Vol. V (1908), pp. 47, 79. 

 EXNER, W. F.: Lorey's Handbuch der Forstwissenschaft, pp. 111-112. 

 NORD LINGER, H. : Die Technischen Eigenschaften der Holzer, pp. 46-51. 



SCENT OR ODOR 



Every wood when fresh possesses in some degree a characteristic 

 scent, though in a great many cases it is so weak or fleeting that 

 it escapes notice. Odor depends upon chemical compounds (e.g., 

 ethereal oils and tannin) which form no part of the wood itself. 

 Ordinarily it is more pronounced in heartwood than in sapwood. 

 It is also greater in wood in a green condition than when seasoned, 

 more evident on moist surfaces than on dry. Upon prolonged 

 exposure to air, or when submerged in water, wood gradually 

 loses its scent. In some cases the loss is complete throughout; 

 in others only the outer portions are affected. Woods deriving 

 their odors from the presence of ethereal oils, as is the case in 

 many cedars, apparently may be kept indefinitely and still emit 

 their characteristic odors when a fresh surface is exposed. 



Upon exposure to the air for a short time some green woods 

 (e.g., Quercus) acquire a disagreeable, soured odor, probably due 

 to the decomposition of certain organic compounds. Woods in 

 process of decay emit various odors, sometimes very disagreeable 

 (e.g., Populus), sometimes not unpleasant (e.g., Quercus), but 

 always different from the natural scent characteristic of the sound 

 wood. 



The fumes of burning wood are occasionally characteristic. 

 Resinous woods, as Pinus, give off an odor of tar. The woods of 

 Juniperus virginiana and Chamcecyparis lawsoniana burn with a 

 pungent, spicy scent, giving the latter a special value for match- 

 sticks. The woods of Cercidium and Parkinsonia give off very 

 penetrating, disagreeable fumes when burned, reducing materially 

 their desirability for fuel. 



The scent of certain woods renders them commercially valuable. 

 Cigars are believed to be considerably improved by being kept in 



