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The period of service is diminished by heavy traffic because of in- 

 creased wear, and some species, hke soft maple and ehn, show less rel- 

 ative resistance to heavy than to light traffic when compared with ash, 

 hickory, and red oak. To meet this condition in lines where the traffic 

 exceeds ten million tons annually, tie plates are used which distribute 

 the load and prevent the cutting of the tie by the rail. 



The preservation of wood has been standardized by experience until 

 practically all commercial plants use either creosote or zinc chloride or 

 a combination of the two. The wood is impregnated with these materials 

 in closed cylinders under air pressure. The use of creosote is more 

 expensive, and gives greater length of service. The choice of the method 

 is determined by the effort to secure the lowest annual charge for re- 

 placements, which is derived from first cost of the treated tie and years 

 of service secured. As ties increase in price the tendency will be to sub- 

 stitute creosote for the cheaper processes. 



The following table, prepared for the use of one of the larger east- 

 ern roads, shows both the effect of preservation upon the period of serv- 

 ice and the shortening of this period resulting from excessive traffic. In 

 final analysis, it is the total work which the tie is called on to perform, 

 in terms of tons of traffic, which will limit the service which can be ex- 

 pected of cross-ties, no matter of what species. or how well preserved 

 and protected. Demand for tie timber will therefore increase in the 

 same proportion as the increase in tonnage, and regardless of efforts to 

 conserve the supply by preservative treatment. 



The extent to which this economic revolution in the practices of 

 railroads with respect to the utilization of cross-ties has progressed, is 

 shown by statistics of wood preservation for 1921. In that year, 

 55,383,515 cross-ties were treated in the United States, of which 

 54,327,471 were for use on steam railroads and 1,156,044 on electric 

 lines. As the annual consumption of ties is approximately 100,000,000 

 over one half of all ties are now treated. This includes practically all 

 the woods classed as "T", or needing the treatment. 



Within another decade, practically all ties except a certain per cent 

 of the more durable "U" ties and ties used by small roads, will receive 

 preservative treatment. The larger roads which have not already adopted 

 the practice in loto, are rapidly enlarging their percentage of treated to 

 untreated ties. Partial figures indicate that the roads with trackage in 

 Illinois used, during 1921, 41 per cent of treated ties, and several of 

 the larger systems increased this per cent substantially in 1922. 



