SEASONING, SHRINKING AND EXPANSION, WARPING. 21 



air or from any liquid in contact with it. Hence the extremely- 

 important fact that the longer and more slowly a wood has been 

 seasoned, the more slowly does it absorb moisture. Hence also 

 the fact that oak cask staves cut in December, when seasoning is 

 slowest, allow only half a litre of wine to pass through in one year 

 and become evaporated, whereas similar staves cut from trees felled 

 in January allow a loss of eight litres in the same time. 



Change of volume of wood through loss or gain of moisture. — As 

 wood seasons it shrinks. Once seasoned, it swells or shrinks with 

 the varying quantity of moisture in its environment. The extent 

 to which this constant change of volume takes place depends on 

 the kind of wood and the accompanying circumstances. Thus — 



(a). It is greater, the larger the quantity of moisture con- 

 tained in the wood is : the wood of young parts, the sapwood, the 

 wood of the roots and of the crown shrink more than heartwood 

 and the older wood of the trunk. 



(h). It is slightest in the direction of the fibres, so slight 

 iudeed, that for all practical purposes it may be entirely left out of 

 account. It is much greater in the direction of the medullary 

 rays, in which it may reach 5 per cent, of the original dimension 

 of the wood. But it is greatest parallel to the concentric rings, 

 or which comes to the same thing, in a direction tangential to the 

 circumference, in which direction it may reach the high figure of 

 10 per cent. {Pinus longifolia) . Hence the best planks to use are 

 those sawn as nearly as possible parallel to a radius. 



(c). It is in direct proportion to the warmth and dryness of 

 the environment. Hence the necessity of using only thoroughly 

 seasoned wood for the furniture of dwelling rooms. 



(d). For one and the same species it is greatest in close-grained 

 heavy wood. On the other hand, when the species are different, 

 this rule does not always bold good, for there are numerous excep- 

 tions. It would be very important to ascertain by careful experi- 

 ments the amount of shrinkage and expansion of all our principal 

 woods under different conditions of the atmosphere. 



(e). Seasoned wood immersed in water swells up at once rapidly, 

 and in from 1 to 1^ months acquires the same or nearly the same 

 volume as it occupied before it was cut. After this there is no, or 

 hardly any, further increase of volume, but the wood continues to 

 absorb more water for the next one to three years, when every pore, 

 even those which contained a large proportion of air in the green 

 wood, will be found gorged with water and unable to take in more. 

 Warping. — If as the volume of a piece of wood changes with 

 loss or absorption of moisture, the shrinkage or expansion ia 



