I 



PRACTICAL ARBORICULTURE 287 



ELASTICITY. 



Every railway frog in the world is a practical illustration of the neces- 

 sity for elasticity in rail connections with the bed-plate or sleepers. Here 

 rigidity is the positive rule. Steel rails are bolted to steel connections, and 

 these require frequent repairs and renewals. The same result must be 

 expected whenever this policy of rigidity governs cross-tie connections. The 

 safety of swiftly moving trains, especially under American railway conditions, 

 depends upon this element of elasticity which exists in wooden ties, every 

 spike being bedded in a cushion of compressed wood fibers, and each tie 

 being an elastic bed-plate. 



TRANSVERSE STRENGTH 



of wooden sleepers is an important consideration, for the bearing is fre- 

 quently more substantial in the center than at the ends of the timber, 

 and often oak ties are broken from this cause. It is probably true 

 that knotty, cross-grained and brash timbers are the ones which thus 

 give way. In making comparative tests, with white oak as a standard, 

 it should be remembered that the best grade of oak has not been used for ties 

 for many years ; it would be much too costly for this purpose. A sleeper 

 containing 45 feet b. m. would at $60 per 1,000 feet, its value for furniture 

 manufacture, cost $2.70, or five times the average price of ties on our American 

 tracks. 



It is not fair, therefore, to test catalpa, or other woods which may be 

 grown specially for use as sleepers, with white oak of a much higher grade 

 than is used in the track for sleepers. 



Cross ties are never suspended at the two ends, having to support the 

 weight of a train in their center, and it is not proper to demand of any 

 timber a far greater strain than could ever be required of it. Enough is 

 sufficient. 



COST OF PRODUCTION. 



Perhaps the average price of standard railway sleepers in the United 

 States maj' be sixty cents each, although the range is from thirty cents for 

 inferior to seventy-five cents, depending upon the competition among pur- 

 chasing lines and distance of haul. 



In considering timber culture for the production of ties, early maturity 

 of trees is an important factor, the cost of production being largely governed 

 by the time required to grow the wood, during which period interest, taxes 

 and expense of maintenance are accumulating. 



In portions of Europe, Asia and Africa, where wood is scarce, many 

 sleepers are imported from America, the expense of transportation by sea, 

 transfer at two docks, and freightage to points where required, is very large, 

 so that metal sleepers are in close competition with wood. If to this expense 

 for wooden ties there is added the cost of chemical impregnation, the cost 

 may even exceed, in some localities, that of metal sleepers. 



