FOREST UTILIZATION 63 



less than sap wood, and conifers warp 

 less than hardwoods. Boards obtained 

 from close to the slab warp worst of all. 

 Remedies against working are steaming; 

 varnishing; forming boards by gluing 

 fine veneers one upon another; allowing 

 framework of doors to be sufficiently 

 grooved for receiving the panels. 

 VII. Duration of wood. 



(a) Duration of wood depends on : 



1. The surrounding conditions; i. e., tropics 



or arid deserts : presence of insects 

 (ants and fungi) ; contact with clay, 

 limestone or sandy soil ; immersion in 

 water (toredo) ; exposure to atmos- 

 phere ; moisture conditions ; presence 

 of preserving matter (salt water, cop- 

 - . per mine water). 



2. The natural qualities of wood, especially 



the presence or absence of rosin, tannin 

 and other preservatives ; the specific 

 gravity ; the percentage of sapwood ; 

 the susceptibility to fungus and insect 

 diseases. Locust, red cedar, sequoia, 

 bald cypress, are less subject to such dis- 

 eases when dead than when alive. 



(b) Remedies against destruction are : Impregnation or 



painting ; charring the part imbedded in the soil ; 

 winter cutting; change of species when replac- 

 ing ties ; kiln drying and steaming and smoking ; 

 raising buildings high above ground. 



(c) Bulletin No. 10 gives the following data for the 



average "life" of ties : 



White and chestnut oak, 8 years 



Chestnut, 8 " 



Tamarack, 7 8 " 



Cherry and walnut, 7 " 



Elm, 6 7 " 



Longleaf pine, 6 " 



Hemlock, 4 6 " 



Spruce, 5 " 



Red and black oaks, 4 5 " 



Ash, beech, maple, 4 " 



Locust, cypress, 10 



Red cedar, 10 " 



Redwood, 12 * 



