508 AUXILIARY FOREST INDUSTRIES. 



starch by the new foliage, whilst freshly formed carbohy- 

 drates cannot descend the stem ; this is said to increase the 

 durability of the wood. The question whether wood felled in 

 summer or in winter is the more durable has been discussed 

 since the time of Pliny (cf. p. 102). Of much greater import- 

 ance, however, than the season of felling is the subsequent 

 treatment of the wood (during conversion, seasoning or trans- 

 port) and the kind of weather that prevails at the time of 

 felling. As regards the latter, autumn and winter are probably 

 the most favourable felling-periods. 



Every precaution taken to secure thorough desiccation and 

 to prevent the wood from again becoming wet (cf. p. 6) increase 

 its durability. Slow desiccation of coniferous wood must 

 increase its durability, as more rosin becomes injected naturally 

 into the heartwood and less of the volatile turpentine evapo- 

 rated. Councler considers that when wood is steeped in 

 running water or floated, its soluble contents are removed and 

 that this favours durability. This can be the case only when 

 the wood, after removal from the water, is dried thoroughly. 

 Steaming wood has a similar effect when it is dried after being 

 steamed. 



When wood is used under conditions unfavourable for its 

 durability, those species should be selected that are highest in 

 the scale of durability on page 100 of this book ; as the sap- 

 wood is not durable it should be removed always. The surface 

 of posts and piles in contact with the ground may be charred, 

 which should be done by applying a blast flame to it, as placing 

 the wood in an open fire cracks it and exposes it to the attacks 

 of insects and fungi, or to the inhibition of rain-water. The 

 tops of posts can be sheltered from rain by nailing on them 

 plates of copper or zinc, a measure that is also protective for 

 the wood-work at sea-ports against teredos, etc. 



Impregnating wood with antiseptic substances is to be 

 recommended. An extensive literature has appeared on this 

 subject owing to the great interest in railway and mining 

 works, street-paving, etc., and to the desire of forest-owners, 

 that woods which are naturally of slight durability only IIIMV 

 ohhiin ji better market. The next section will deal with this 

 subject as far as is necessary for Forest Utilisation. 



