CHEMICAL PROPERTIES. 79 



heard distinctly at the other end. Dry wood conducts sound 

 hotter than wet wood. The conduction of sound is interrupted 

 or the sound deadened by decay in the centre of the tree, so 

 that the healthy or diseased condition of the wood of a felled 

 tree may he thus tested. 



(il) LI <jl it. 



Wood only in very thin sections is permeable by light; 

 then, like calc-spar, it exhibits double refraction. Wood 

 is very permeable by Roiitgen rays. 



C. CHEMICAL PROPERTIES OF WOOD. 



The ultimate analysis of woods varies within narrow limits; 

 ils organic substance when dry is composed of the following 

 elements: Carbon, SO, hydrogen, (>. oxygen, 1:>'7, nitrogen, O'JJ, 

 half its volume being carbon. 



The chief constituents of wood are cellulose (( ''J I m< V-,) 

 and lignin ((--,,-,1 I :{0 O 7 o). Cellulose is therefore a carbohydrate 

 resembling sugar in its composition. Lignin is the most 

 highly carbonised constituent of the cell-wall. Lignin is also 

 known as woody substance; as the lignifying substance of 

 cellulose; with other materials in paper-manufact lire, as 

 the encrusting substance. Lignin is not a homogeneous 

 substance, but according to Payen a mixture of four others 

 with different reactions to alcohol and ether. Pure cellulose is 

 dissolved entirely by concentrated sulphuric acid and converted 

 into dextrin and fermentable sugar. Treated with ammoniacal 

 oxide of copper, cellulose is dissolved completely, but can be 

 precipitated again by the addition of acids, saline and sugar solu- 

 tions and gums, as a whites structureless mass.' When cellu- 

 is treated with 11X() :! nitro-cellulose is obtained, a highly 

 explosive compound (gun-cotton, pyroxylin), very soluble in 

 alcohol or ether, and when the solvents arc; evaporated the 

 precipitate is eollodiuiii, colourless and without any structure. 



ANALYSIS i:v WKK;HT. 



< Y-lliilnsc. l.iiriiin. Mc;m i'or Wood. 



C 44-44 ;VJ-<;5 49'2 



H C.-17 5-25 6-1 



1<>-:I<J 42-10 44'7 



.1. Borsch, - Die Verwertung dea lM/::s. v ixi:t. 



