P.SM 



CTICAL ARBORICULTURE 293 



the demand is already greater than the supply, and make possible in Europe 

 the use of metal> which on American lines will long remain impracticable. 

 Dense population, greater support per mile of roads operated, low rates of 

 interest, and financiers who are satisfied with smaller dividends, place Euro- 

 pean roads on a different footing from those of the United States. Yet it has 

 not been decided in Europe that metal ties are profitable, nor how durable 

 and economical they may be as compared with ties of suitable wood. 



One railway in Mexico has part of its tracks tied with steel. Many of 

 these ties are cracking, while the fastenings are easily disarranged, being 

 secured with keys driven into raised projections which are punched through 

 the sheet of steel and bent upward to receive the rail flanges. 



The trains have a rigid motion, less pleasant to the traveler than those 

 of other roads which have elastic wooden ties. 



The life of wooden ties has been gradually shortened in the past two de- 

 cades because of the inferior wood used in their construction. 



Formerly none but the best heartwood of the trunks of large white oak 

 trees would be accepted. As timber became more valuable for lumbering, the 

 tops, small immature trees, and knotty portions were accepted by the inspec- 

 tors while competition became great among purchasers of various railways. 



Rock oak and various forms of the red and black oak families under 

 sundry names, were received in certain proportions, and many roads were 

 glad to secure chestnut, pine, redwood and many other kinds of timber grow- 

 ing in the vicinity of the lines. 



From nine years' duration as the best heart white oak, the average has 

 fallen to four or five years. 



This has led to the more extended use of treating plants, the inferior 

 woods thus being made available through antiseptic solution. 



The redwood of California is rapidly worn by the grinding motion of the 

 rails acting upon sand which finds its way between the tie and rail. The use 

 of tie plates but partly overcomes this rapid wear. 



Beech, which is totally worthless when placed in contact with moist soil, 

 is trebled in durability by the ordinary zinc chloride treatment. 



Red oak, good for only four years, may be extended to twelve by chem- 

 ical treatment. White pine and other woods may be made to last from ten to 

 fifteen years if the treatment is thorough. 



In Europe the creosote used "in preservation of timber is a product of 

 wood distillation. 



The great expense of this material has led to the use of coal tar products, 

 under the name of creosote, but it is much inferior. Both processes are too 

 expensive to justify their use in treating cross ties and a resort is had to a 

 by-product of the smelters, zinc chloride. 



(ilue and other substances are used by the various preserving plants to 

 fix the zinc in the pores of the wood, but in time it is liable to be redissolved 

 and washed out, leaving the wood subject to attack by the fungus which 

 causes decay. 



