WEIGHT. 11 



It is obvious, as said before, that resin and oils impregnating 

 wood increase its dry weight. For this reason, in resiniferous 

 trees the wood in the interior of the stem is heavier than the out- 

 side layers ; and in conifers, the narrow-ringed wood of the branches, 

 and in pines and deodar, also the resin-gorged wood of the roots, 

 is heavier than the wood in other portions of the tree. In conifers 

 the outer zone of each ring is richest in resin, and hence the 

 broader-ringed a piece of conifer wood is, the smaller will, as a 

 rule, be the proportion of resin in it, and consequently the less its 

 weight. But besides resin and oils, wood may contain inorganic 

 salts, such as calcium carbonate, potash, magnesia, &c., silex, and 

 other substances, which add their own weight to that of the origi- 

 nal substance of the wood. Long immersion in water, and 

 especially floating, dissolves out these various substances and makes 

 the wood very appreciably lighter. 



In one and the same tree the weight of the wood is, as a rule, 

 more or less different, according as it is taken from the roots, or 

 from the lower or upper part of the stem, or from the centre of 

 the stem, or from near the bark or from the branches. In the stem 

 this difference is in a great measure due to a difference in the 

 width of the concentric layers of wood and in the relative width of 

 the inner and outer zones of those layers in its different portions. 

 The wood of the branches is generally heavier than that of the stem, 

 but in the case of small twigs there is, according to Nordlinger, very 

 little difference even from species to species in the green weight of 

 the wood, the figure for all species taken together ranging from 57 

 to 66 lbs. per solid cubic foot. The wood of the roots is the lightest 

 of all. But from this general rule must be excepted (i) that of the 

 crown of the roots, which is frequently remarkably heavy, and (ii) 

 that of conifers producing resin in abundance, the wood of the roots 

 of which sometimes weighs as much as 65 lbs. per cubic foot. 

 According to Nordlin<jer the weight of the wood is, in all species, 

 proportionate to the thickness of the roots from which it is taken. 

 Knotty growth, in whatever part of a tree it occurs, increases 

 the weight of the wood. The new growth of wood surrounding 

 or covering healthy wounds is also heavy. 



For convenience sake we may establish six classes or degrees as 

 follows in respect of weight : — 



I. Extremely/ heavy. — Average weigld of cubic foot = 70 lbs. and 



upwards. 

 HardwicMa linata, ebony, Pterocarpus santalinus, Mesua ferrea. 



II. Very heavy. — Average weight of cubic foot = over 60 and up 



to 70 lbs. 



