PRACTICAL ARBORICULTURE 293 
the demand is already greater than the supply, and make possible in Europe 
the use of metals 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 satistied 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 zine 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 vears 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, zine chloride. 
Glue and other substances are used by the various preserving plants to 
fix the zine 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. 
