The Durability and Preservation of Woods 249 



made for it, except in the case of elm, of which the heart- 

 wood treats more readily than the sap. The more dis- 

 tinct the heartwood, the harder it is to treat. 



The deeper the penetration, the more efficient the treat- 

 ment. It is for this reason that open and closed tank 

 treating processes are preferred to the cheaper brush 

 methods. The better the wood is seasoned, the easier 

 the treatment and the deeper the penetration. An oily or 

 resinous solution is better than a solution of mineral salts. 

 The species without distinct heartwood treat as though 

 they were all sap. 



The process of treating the so-called inferior woods to 

 increase- their durability has been in use in Europe for 

 many years. The results of the treatment of European 

 woods by all the different processes under European condi- 

 tions of soil and atmosphere are fairly well known. The 

 factories which do the treating often guarantee their 

 products for a certain number of years. For example, 

 such companies in France guarantee their beech railroad 

 ties for fifteen years' service. It is an established and 

 thoroughly reliable industry. It has been put to every 

 test and found satisfactory. In the United States the 

 abundance of all kinds of wood prevented the use of pre- 

 servatives. Only the increasing scarcity of durable woods 

 and the higher price in consequence have made it possible. 

 The government and the railroads have been doing most 

 of the experimental work along this line. All the pro- 

 cesses known in Europe and some original ones have been 

 tried with varying results. Dozens of different methods 

 and impregnating materials are used. Many of these 

 require an expensive and complicated apparatus which 



