92 TECHNICAL PKOPEUTIES OF WOOD. 



woods already considered as the most durable when exposed to 

 alternations of moisture and dryness are also the most durable 

 when partially in the ground, and to them the wood of the alder, 

 roblnia and sweet chestnut may be added. Split chestnut- 

 coppice wood, according to Forstmeister Kaysing, lasts fifteen 

 years in Alsace as vine-props, whilst barked oak-coppice vine- 

 props scared}' last two years. 



[It must liowevcr be remembered tliat peeled oak coppice-wood is 

 entirely sapwood, while sweet clicstnut lias only 2~i annual zones of 

 sapwood. 



Posts which arc placed in tlie ground usually decay most rapidly 

 near the surface of the soil. To protect tliem, their butt-ends should 

 be charred or tarred, or better still may rest on masonry-supports 

 and not reach the ground at all. White ants in India live close to 

 the surface of the soil, and bacteria which assist in the decomposition 

 of wood are also more numerous there than lower down, whilst the 

 air which is necessary for their growth and that of fungi is the more 

 excluded, the lower the depth at which any part of the post may be. 



At a certain height above the ground the action of the sun and 

 air in drying wood is also more eftectivc, and consequently wood- 

 destroying fungi do not thrive so well as between certain distances 

 above and below the surface of the ground. — Th.J 



Railway- sleepers which are half in and half out of the soil, are 

 very badly situated for durability, as they are exposed not only 

 to continual alternations of damp and drjmess according to the 

 state of the weather, but owing to the damp soil below them 

 and insolation of their upper surface, they crack and warp. The 

 durability of railway-sleepers is influenced by : — the consistency 

 and nature of the soil, the nature of the locality as regards free 

 currents of air or the reverse, whether the sleepers are on 

 cuttings or embankments, on cold or hot aspects, and whether 

 the railway-traffic over them is considerable or not. 



[In India, wherever the passing of trains is frequent and regular, 

 white ants are not to be feared for deodar sleei)ei-s, but they freely 

 destroy them in rarely used sidings or when stacked in depots. — Tu.] 



Sleepers usually commence decaying at the lop, and from 

 places Avhere bark or sapwood has not been removed. More 

 will be said about them further on. Wood used on the ground 



