FOREST UTILIZATION 63 



less than sapwood, 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, 67 



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 



