TECHNICAL QUALITIES OF THE TREES 103 



(a) So-called "solvents" of cellulose are:- 



1. Solution of chloride of zinc. 



2. Copper hydroxide dissolved in ammonia. 



These solvents, however, do not dissolve cellulose as such; they alter and transform it incidentally. 



(b) The PERCENTAGE OF CELLULOSE CONTAINED IN WOOD dried at 110 degrees centigrade is approxi- 

 mately 45 per cent. 



For example (after Dr. Councler, Z. f. F. & J. W., 1907, page 428):- 



1. Oak wood contains :- 



Cellulose 



Incrustating substances 

 Substances that can be withdrawn: — 



By alcohol -benzol ... 

 By water 



2. Pine wood contains: - 



Cellulose 



Incrustating substances 

 Substances that can be withdrawn :- 



By alcohol-benzol ... 

 By water 



100-00 7o 



II. Wood and bark contain on an average 45 per cent (weight) of water. Conifers contain less water 

 broad -leafed species. The percentage varies irregularly with the seasons and with the precipitations. 

 Substances found in the woody tissue are: — 



(a) In the sap and medulla :- Albumen, starch, sugar, oils; 



(b) In the cells and cell walls: — Tannin, rosin, and pigments. 



The specific gravity of pure wood fibre is r56. 



(C) OUTER QUALITIES, or qualities discernible by eye, touch or scent. 



I. Texture. The texture is fine or rough according to the ease with which the parts composing the 

 tissue can be distinguished. 



The texture is: — 



(a) Very fine in yew, box, holly, persimmon; 



(b) Fine in pear tree, hornbeam, black gum; 



(c) Pretty rough in spruce, fir, magnolia, cottonwoods; 



(d) Rough in cherry, sycamore, maple; 



(e) Very rough in oak, elm, locust, beech. 



II. Color. Color is an advantage in the furniture trade and a disadvantage in the manufacture of 

 paper. The heart of seasoned wood is always darker than the sapwood. 



Tropical species are particularly rich in color. 



Wood exposed to air changes its color more or less distinctly, in the course of weeks or years. 

 The heart of yellow poplar changes to a dark brown. Alder changes from white to red. Ash from white 

 to light violet. Mahogany from brown to black. 



III. Gloss. Gloss is due to evenness, number and size of medullary rays. 

 Shining species are maple, ash, elm, beech. 



Medium shining are oak, alder, hornbeam. 



Dull are peach, pear, conifers. 



Quarter sawing and planing increases the gloss. 



