. American telephone practice . tion of a method, infrequently UNDERGROUND CABLE CONSTRUCTION. 837 practiced, of laying the cable directly in the ground without anyconduit whatever. The cheapest and simplest form of conduit which permits thedrawing in or withdrawal of the cables is that composed of creo-soted wood tubes, or pump logs, as they are commonly andappropriately termed. These are usually made in eight-foot lengths,having a square external section 4^x4^ inches, with a 3-inch tenon joint one and one-half inches long is used for securingproper alignment of the joint. Several view
. American telephone practice . tion of a method, infrequently UNDERGROUND CABLE CONSTRUCTION. 837 practiced, of laying the cable directly in the ground without anyconduit whatever. The cheapest and simplest form of conduit which permits thedrawing in or withdrawal of the cables is that composed of creo-soted wood tubes, or pump logs, as they are commonly andappropriately termed. These are usually made in eight-foot lengths,having a square external section 4^x4^ inches, with a 3-inch tenon joint one and one-half inches long is used for securingproper alignment of the joint. Several views of this tube are shownin Fig. 614. The wood is usually treated with creosote or dead oil of coaltar in the following manner: The lumber is laid on cars and runinto a large steel cylinder six feet in diameter, which is closed by aheavy iron door. It is first subjected to live steam at a temperatureof 2500 F. until the timber is heated through and through, the pur-pose of this being to coagulate the albumen in the sap. A vacuum. FIG. LOG CONDUIT. pump is next applied to the tank, exhausting all air and steam, thepump maintaining a vacuum of about twenty-six inches. Thisevaporates practically all of the sap and water from the wood, thusseasoning the timber. The next step in the process is to pump creo-sote oil previously heated to a temperature of ioo° to 1250 F. intothe tank until it is full. This is then placed under a pressure ofabout eighty pounds per square inch and the amount of creosotewhich is forced in after the filling of the tank is carefully measured,this being the amount that is taken up by the pores of the for the treatment require that from eight to twentypounds of the oil shall be absorbed by each cubic foot of or fifteen pounds is the average amount required for elec-trical purposes. As has been stated before, much trouble has ex-isted owing to the liberation of acetic acid from conduit treated withcreosote. It is cla
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