DURABILITY. 91 



[It may be noted here as a general rule that the more durable the 

 heartwood of any tree, the richer in reserve-material and consequently 

 the more perishable is its sapwood. — Tr.] 



Oakwood, highly resinous wood of larch aud Scotch pine, and 

 especially the wood of the different varieties of Finns Laticio, 

 are the most durable European kinds, provided all sapwood 

 has been removed. In the absence of the above-mentioned 

 timbers, and in urgent cases when the supply of building- 

 timber is restricted — circumstances which frequently occur in 

 the construction of works for timber-transport — spruce and 

 silver-fir wood may be used, but always at the cost of durability ; 

 these woods are only half as durable as that of larch, which is un- 

 doubtedly second only to expensive oak-timber for such purposes. 



The decay to which wood, subjected only to wind and weather, 

 is exposed, is, as a rule, much slower than when it is continually 

 kept wet. A number of timbers may be used where exposure 

 to atmospheric precipitations, sunshine and wind only is in- 

 volved. After oakwood, coniferous wood may be used for the 

 framework of buildings, for fences, gates, roof- and wall-shingles, 

 agricultural implements aud other purposes. 



(d) Timber used in the Ground. — When used in the ground, 

 wood decays rapidly, and so much the faster, the looser, damper, 

 and warmer the soil, and especially the greater the range of 

 dampness and dryness to which it is subject : thus, wood lasts 

 much longer in a compact, damp clay soil, which excludes the 

 air, than in loose, coarse sand or gravel, which is alternately wet 

 or dry. Timber rots more quickly in warm and only moderately 

 damp calcareous soil than in compact loam ; and most quickly 

 of all in soil rich in humus, or well manured. Wood is used in 

 the soil for railway-sleepers, house-, gate- or telegi-aph-posts, and 

 for various agricultural purposes, such as fences, hop-poles, vine- 

 props, bean-sticks, fruit-tree supports, &c. Water- conduits also 

 lie on the ground, but as they are frequently completely buried, 

 and usually contain running water, they are not so subject to 

 decay as wood used for the above purposes. Wood lying on the 

 ground may be even less durable than when in the ground, for 

 the alternatives of moisture and dryness to which it is then 

 exposed are greater than when it is partially buried. The same 



