292 FOREST PRODUCTS 



nut and longleaf pine were practically the only species used and they gave 

 satisfaction until higher prices were demanded with the decreasing avail- 

 able supply. 



The life of untreated cross ties depends upon a" number of factors, 

 principal of which is the durability of the species involved. However, 

 the length of service is determined by the following factors aside from 

 natural durability: 



1. Size of tie, including both thickness and face. Small ties rot away 

 or shatter under heavy rolling stock much faster than larger ones. 



2. Amount of sap wood. Even the sap of white oak rots away much 

 faster than the heartwood. 



3. Degree of seasoning. It has already been explained that thor- 

 oughly seasoned ties are much more durable than those in a green or 

 partially seasoned state. 



4. Climatic conditions. It has been demonstrated that white oak 

 ties in a warm, humid climate will not last more than from five to six 

 years, whereas in a colder and dry climate they may last from eight to 

 twelve years. Ties resist decay in the climate of the West much better 

 than in the East. 



5. Condition of the road bed, such as character of the ballast, drainage 

 facilities, etc. 



6. Weight of rolling stock, frequency of trains, and whether on main 

 or branch lines, sidings, etc. 



7. Protection against mechanical wear. The use of tie plates, screw 

 spikes, dowels, etc., is of material assistance in adding to the length of 

 service of all forms of cross ties. 



It is obvious from the above, therefore, that it is impossible to fore- 

 cast the life of untreated ties in the track. The variation within the 

 individual species is very great, depending upon these factors. The 

 following is offered as a rough guide in estimating the life of the prin- 

 cipal species used for ties in the untreated condition. 1 



Species Length of Life in Years. 



Beech 2-4 



Birch, yellow or red 2-4 



Cedar, eastern red 12-15 



Cedar, northern white 10-15 



Chestnut 5- 8 



1 For further data see " Durability Records of Cross Ties," by C. P. Winslow and 

 C. H. Teesdale in Proceedings, American Wood Preservers' Association, 1916. 



