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be especially careful to avoid stringing lines too tight in warm weather. The increased sag necessary for aluminum makes the liability to crosses unduly high. Joints between copper and aluminum wire give a great deal of trouble, due to electrolytic action.
Preservation of Poles.— The great waste occasioned by the rapid decay of woods when in contact with the soil is very apparent in the case of poles. For a number of years past experiments have been carried on by private parties and by the United States Forest Service with a view to finding and perfecting methods of preventing such decay, and it may be stated that it is possible, through the proper application of certain preservatives, to increase the life of a pole from 50 to 100 per cent. The practice has proven a success economically. Not only does it lengthen the life of the pole, but it makes possible the utilization of many cheap local woods which, without preservative treatment, would be valueless for the purpose, thus reducing the cost of poles and transportation charges. In the principal European countries the practice of pole preservation is much more common than in this country, nearly every pole receiving a penetrating treatment with some preservative before being set. The economy of the process has been so well established that as it becomes generally understood the percentage of treated poles reported in the United States will no doubt rapidly increase and the methods used become more effective each year. The preservatives most commonly used are creosote oil, a solution of zinc chloride, and various proprietary preparations, usually antiseptic oils of low volatility.
The increase in the practice of really effective pole preservation in the United States has been retarded by the lack of pole-treating apparatus applicable to the needs of the small consumer. As a result, poles have been treated mainly by methods which do not require the use of a special treating plant and which add but few years to their service. The usual method is that of painting the lower end of the pole with the preservative.
A somewhat more effective method is that of dipping the pole in an open tank containing the preservative. By this operation all seasoning checks are thoroughly penetrated. A variation of this method is to stand the poles upright in a bath of the preservative, making the wood of the butt end of the pole decay proof by the absorption of large quantities of the oil or solution, through the action of a partial vacuum in the wood cells created by the alternate raising and lowering of the temperature of the bath. Satisfactory plants have been devised for this purpose which are economical for firms using considerable numbers of poles annually. A plant of this type and of large capacity was built during the year in California for the treatment of western yellow pine, western red cedar, and other local woods.
In parts of the South, conditions are so favor-. able to decay that it is desirable to treat the entire pole, and both commercial and private plants have been established for this purpose. The poles are placed in a closed cylinder and absorption of the preservative is secured by the use of pressure. Large numbers of pine poles have been treated by this method, which is found to be the most effective now in use.
Utility of Concrete Poles. -Reinforced concrete telegraph poles are being used by the Postal Telegraph Department of New Zealand on the line between Auckland and Hamilton. Over 1,200 of the poles have been set up. They measure 26 feet high and taper from 6 by 8 inches at the base to 6 by 6 inches at the top. The poles are claimed to be only slightly heavier than the wooden poles they have replaced. In making the concrete poles in large quantities, sectional wooden or metal molds are employed in connection with a portable concrete mixing plant and the endeavor is to produce them as near the point where they are to be used as possible to minimize danger of breaking in transportation. Obviously, the poles are reinforced with regular steel or iron reinforcing rods and are exceptionally strong and practically weather-proof, inasmuch as they are not affected by rotting at the ground line as are even the treated wooden posts. In molding
the concrete posts, wooden core pieces may be inserted in the mixture at various points where bolts for crossarms and braces are to be placed, and in this manner considerable drilling is obviated, because the wooden pieces may be easily removed when the concrete becomes hard. It is also considered good practice to place the crossarm bolts in position while the mixture is soft and after it sets they are retained firmly in place in the post. The molds may be made with holes suitably spaced to regulate the placing of bolts or other hardware, and thus insure that all poles of the same size will be duplicates of each other. Wherever wood is scarce, concrete construction offers advantages of moment and, of course, is more permanent in nature than any organic material that is subject to deterioration from oxidation would be. Materials for making concrete can be easily obtained in most all localities and as the art of mixing and pouring this material is generally understood by practically all laborers, concrete or artificial stone posts may be built cheaply enough, when their superior endurance is considered, to be used in all permanent installations in place of wood poles. .
Utility of Concrete in Saving Decayed Posts. -Electric light, power and telephone companies, in fact all electrical companies having occasion to use poles for overhead wires are, continually confronted with the problem of fighting decay of the poles at the ground line. As the price
Fig. 978.-Saving Decayed Posts with Concrete. of lumber is steadily increasing, a means of increasing the life of the poles in service is highly desirable.
A method of doing this has been developed in the shape of the National Pole Socket, outlined at Fig. 97g. This is a seamless steel tube about a quarter of an inch thick and of a total length of about seven feet. It is made in various diameters to fit different sizes of poles. Before shipment a heavy coating of asphaltum is applied, to protect the steel tube.