How Decay of Wood Is Prevented

If it is desired to save the expense of having two tanks—one for the hot and the other for the cold preservative—substantially the same results can be obtained more slowly by withdrawing the heat and allowing the hot tank to get cold.

A simple open-tank device successfully used by the Forest Service in treating fence posts is described as follows: The apparatus consists of a rectangular galvanizediron tank 5 feet 4 inches long, 2 feet 3 inches wide, and 3 feet 6 inches high. This tank is set snugly into a wooden box built of 1-inch planks and open at the top. The object of this box is to keep the tank from bulging when filled with creosote, to protect the tank from injury, and to keep the creosote from cooling too rapidly. When the posts are treated in winter or in cold regions, it is best to build an additional casing around the inner box, leaving a space of about 4 inches between them, and firmly packing this space with sawdust. The creosote will then seldom solidify over night, and may be more quickly heated.

The creosote is heated by fitting a series of seven 1-inch steam pipes in the bottom of the tank, coupled to the boiler of an engine. The amount of steam passing through the pipes is controlled by two valves—one placed between the tank and the boiler, to regulate the amount of steam entering the coils; and the other at the outlet of the coils, to control the pressure. By raising or lowering the pressure of steam in the coils, the creosote can be heated to any temperature desired. An apparatus of this kind makes it possible to keep the temperature of the creosote fairly constant, and gives very satisfactory results. It can of course be used only when some kind of steam boiler is available. It costs about $30.

Tanks built along the lines indicated give best results; but if means are not available for their construction, an old iron boiler or like vessel may be used. The essential requirements are that the creosote shall be heated in the vessel to about 215° F., and that the butts of the posts shall be submerged up to about 6 inches above their ground line. In special cases, where a thorough top treatment is necessary, the vessel should be of sufficient size to allow the whole post to be submerged.

The principal advantages of the open-tank method are that it is simple, comparatively cheap, especially adapted to the treating of small-sized material such as fence-posts, crossties, and mine timbers, and that with it practically any timber which has a fair amount of sapwood can be successfully treated.

The cost of an open-tank equipment for the treatment of posts, ties, and small timbers may range anywhere from $50 to $500, depending upon its completeness.

Bluing of Timber The sapwood of timber or lumber cut in warm, damp weather is very likely to "blue" or stain while air-drying. This discoloration does not lessen the strength of the wood; but it does damage the appearance, and affects the market value for many purposes. Sap stain is supposed to be caused by fungi of a different kind from those which produce decay, and is preventable by comparatively simple means. If the freshly cut lumber is dipped in a 6 to 12 per cent solution of bicarbonate of soda, and then piled in open fashion so that air circulates freely among the boards, there will be practically no bluing. There are few bad effects from the soda treatment, and it is not expensive; so it has been adopted by many lumber manufacturers—especially in the South, where staining is most likely to occur. A simple device carries the lumber on an endless chain through a tank of soda solution at the tail of the sawmill.

Protection from Marine Borers On the seacoast, piling and dock timbers are often destroyed by marine borers (usually teredo or shipworms), even more quickly than timber on land is destroyed by decay. The annual loss from this source is very great. In fact, in many places it is almost impossible to use wooden piles unless they are protected from borers. The best method of giving such protection is to apply a creosote treatment, since creosote is as distasteful to marine borers as it is to decay producing fungi. Well-creosoted yellow pine piles have been known to give 30 years or more of service in situations where, if unprotected, they would have been destroyed in a single year. The fierceness of the attack of these borers is indicated by the examples shown in the illustration (Plate 24).