58 TIMBER. 



by impregnating it with various salts or other chemicals, which prevent 

 the fungus from feeding on the wood. The wood is first steamed, to 

 open tlie pores and remove the hardened surface coating of sap and 

 dirt, and a liquid solution of the preservative material is then injected 

 with the assistance of heat and pressure. 



The most efficient fluids used on a large scale are bichloride of zinc 

 and creosote, or both combined. The " life" of railroad ties is thereby 

 increased to twice and three times its natural duration. 



