DURABILITY OF WOOD. 237 



Iron Railroad Ties. A few years ago it was thought 

 probable that iron railroad ties would come into general 

 use in Europe, owing to the scarcity of Oak ties. They 

 have, however, been found to give a very unyielding road 

 bed, and are not generally liked, and are seldom used 

 for more than a short distance at railroad stations. The 

 disposition now is to substitute impregnated Beech ties 

 for iron, and the successful impregnation of this wood, 

 causing it to become quite durable, has had a large effect in 

 doing away with iron ties. 



The Impregnation of Beech Wood for railway ties is a 

 large industry in Europe. Without impregnation Beech 

 is one of the least durable of woods, but by modern impreg- 

 nation methods it can be made to last at least fifteen years 

 in any soil, and it is customary for concerns engaged in 

 this business to warrant the durability of their impreg- 

 nated ties for twelve years. Pine and Oak ties are not 

 impregnated. 



The process commonly followed in many parts of Ger- 

 many is about as follows: A large boiler-tank is provided, 

 which is about six feet in diameter and forty to one hundred 

 feet long. This is made with heads that can be securely 

 and tightly bolted on. It also has a small track for the 

 cars which carry the ties. Before treatment, the ties are 

 mortised to receive the rail plates. After the tank is 

 filled with cars loaded with ties, the steam is turned on 

 for one to three hours, with a pressure of about twenty- 

 five pounds. This treatment softens the wood and dis- 

 solves the sap. The air is then pumped out of the tank, 

 which removes the sap from the ties and leaves a vacuum. 

 When this has been completed and the vacuum made, the 

 impregnating material is added under a pressure of about 

 120 pounds. This forces the impregnating material into 

 the cells of the wood. The preservative material used 

 is made up one-third of a three per cent, solution of chlo- 



