30 TECHNICAL PROPEKTIKS OF WOOD. 



while the chemical tests are entirely misleading (the more so, the 

 larger the quantity of hydrogen contained in the wood is). In ac- 

 tual practice the relative value of the different woods depends to a 

 very great extent on the purpose for which the firewood is required, 

 and on how it is he used. Thus for warming purposes generally 

 we want a wood that does not burn too fast, but gives a steady 

 prolonged heat; but so much here depends on the draught that the 

 value of a given wood will be different according as it is to be 

 burnt in the open (as in a camp fire) or in a fireplace, or in a 

 stove. The difference is still greater for cooking purposes ; we 

 have every variety of chula, with chimneys and without chim- 

 neys, and dishes, some of which require a slow fire, others a quick 

 fire, and so on. The baker and brickmaker require wood that 

 gives out all its heat in as short a time as possible, so that for the 

 short time it lasts, the heat may be intense. For well-made lime- 

 kilns also quick-burning wood is necessary; for the very primitive 

 ones used by most of our Indian lime-burners the wood must 

 not reach full combustion too soon, nor must it burn too quickly, 

 although it must give out an intense heat. 



Section X. — Defects and Unsoundness. 



The difference between a defect and unsoundness is that the form- 

 er is purely a discontinuity of tissue, or abnormal development of 

 the fibres, which may interfere with the cutting up of the wood, or 

 at least unfit it for certain purposes, whereas the latter is always 

 some form or stage of decay. Nevertheless, as some defects are 

 often accompanied by decay, it is best to treat both under one and 

 the same head. It is not intended here to treat of the diseases of 

 trees, the discussion of which belongs to the province of botany, but 

 only to refer to them so far as they affect the technical value of wood. 

 Aeticle 1. Defects. 



The principal defects are — (1) shakes, (2) knottiness and exag- 

 gerated waviness of the fibre, (3) twisted fibre, (4) rindgalls, (5) 

 covered sections of pruned branches, (6) enclosed dead branches, 

 and {!) interior bark. 



1. Shakes. 



Shakes are separations of the wood fibres extending along the 

 entire or partial length of the trunk of a tree. According to their 

 position and the direction in which they run on a transverse section 

 they are either (A) Heart-shakes, or (B) Radial-shakes, or (C) 

 Cup-shakes. 



A. Heart-shakes. — A heart-shake is a crack, which, beginniui; at 

 the centre of the trunk, extends itself outwards both ways towards 



