10 TECHNICAL PROPERTIES OF WOOD. 



difference in the width of the concentric rings, while it may ac- 

 centuate the original greater weight of the heartwood, may also 

 turn the scale in favour of the sapwood. 



In all the foregoing remarks the quantity of water in the wood 

 has been left out of account. In practice we distinguish three 

 states of the wood after it has been felled — (1) when it has been 

 fresh-felled, (2) when it has undergone some degree of seasoning 

 before it is removed from the forest (we may use the \Grni forest- 

 seasoned in this case), and (3) when it has been completely seasoned, 

 that is to say, has lost all the water it can part with under shelter 

 in a dry atmosphere. Fresh-felled wood may for all practical 

 purposes be assumed to contain 45 per cent, of water, while in 

 completely seasoned wood the quantity of moisture varies from 15 

 to 20 per cent. The proportion of moisture in forest-seasoned 

 wood is, of course, a very variable quantity. 



According to Theodor Hartig's experiments the quantity of 

 water in any wood depends on the species to which it belongs. As 

 a rule, the conifers contain the largest quantity, and the hardest 

 woods the least. There are, of course, exceptions to the rule. Thus 

 alder, birch and poplar, all very soft woods, are amongst those 

 which contain least water ; while oak, sal and some other hard woods 

 contain it in abundance. In the case of woods that are naturally 

 impregnated with resins and oils, the difference between the green 

 and seasoned weights is inversely proportional to the quantity of 

 those substances in the wood. The more recently formed wood 

 in a healthy growing tree contains more water than the older por- 

 tions, and hence the sapwood and the wood in the crown are more 

 full of moistui e than the heartwood and the wood of the trunk re- 

 spectively. Hartig's experiments, already referred to, apparently 

 establish the remarkable fact that the quantity of moisture in the 

 soil has no inflaence whatsoever on the amount of moisture in the 

 wood of trees grown thereon; at any rate, there is no interdepen- 

 dence between them. Contrary to the general belief hitherto pre- 

 vailing, every one of the European trees, which, like alder, oak and 

 poplar, delight in wet and even watery soils, are conspicuous by 

 the small quantity of moisture in their wood. Further research is, 

 however, still necessary before any final conclusions can be drawn. 

 The wood of trees is more full of moisture during the season of 

 rest than during the season of vegetation. Hence the green 

 weight of wood depends also on the time of the _, ear at which it 

 is felled. But as the wood contains most reserve matter while the 

 trees are resting, even the dry weight of wood is dependent on the 

 season in which it is cut. 



