of strength. Sap should therefore be first 

 removed by seasoning; that is, either by 

 drying the wood in air at natural or higher 

 temperatures, or by first steaming the wood 

 under pressure so as to vaporize the sap, 

 and then removing the latter by means of 

 a vacuum. Thorough seasoning of large 

 timbers in dry air at ordinary temperatures 

 may require years; too rapid kiln-drying 

 cracks and weakens the wood. But it is 

 questionable whether steaming and vacuum 

 removes sap as thoroughly as do the slower 

 dry processes. Alternate exposure to water 

 and air is very destructive. It causes wet 

 rot. 



Sea worms, the limnoria terebrans, works 

 from near high water mark to a little below 

 the surface of mud bottom; the teredo navalis 

 within somewhat less limits. The teredo 

 is said to be rendered less active by the 

 presence of sewage in water. 



The best limber-preserving processes are 

 practically useless unless thoroughly well 

 done. If the gain in durability will not 

 warrant the expenditure of time and money 

 required for this, it is more economical to 

 use the wood in its natural state. The 

 woods best adapted to treatment are those 

 of an open or porous texture. They absorb 

 the oil, etc., better than the denser woods; 

 and their cheapness renders the use of the 

 treatment more economical. Most of the 

 processes in common use seem to render 

 wood less combustible. After treatment 

 by any process, the wood should be well 

 dried before using. Creosote oil, or dead 

 oil, is the best known preservative. Against 

 sea worms it is effective for 15 to 20 years. 

 The teredo is less active in the north than in 

 the south. 



-See paper by Dr. Hermann von Schrenk, 

 read before the American Railway Engi- 

 neering and Maintenance of Way Associa- 

 tion, March, 1901. 



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