BRUSH AND TANK POLE TREATMENTS.

INTRODUCTION.

The preservative treatment of railroad ties and piling has been practiced commercially for a number of years. About fifty treating plants are now being operated in this country, and the number increases each year. The treatment of telephone and telegraph poles has made no such progress, yet there is a strong desire on the part of progressive users to find a satisfactory method for prolonging the life of poles. From time to time experiments have been conducted by various telephone, telegraph, and railroad companies, but either the treatment was faulty or insufficient records of the treated poles were kept, and, as a result, neither reliable data nor satisfactory conclusions have been obtained.

In some cases the whole length of the pole has been treated in closed cylinders, but this expensive treatment is used only on poles to be set where the top as well as the part in the ground is subject to rapid decay. Often preservatives have been applied to the butt of poles with a brush, and when the poles were seasoned doubtless much good was accomplished. But when the oil had been applied to the outside of green, freshly cut poles they were found to decay practically as soon as untreated poles. Thereupon the preservative was declared valueless, and the experiment considered as proof that poles could not be satisfactorily treated by that method.

Consumers of poles are generally of the opinion that present conditions do not warrant a very large outlay for treatment; nevertheless, because of the diminishing supply, they demand that the length of service be increased. That seasoned wood is more durable than green in contact with the ground is generally admitted, but how much more is not known. Many also hold that wood which has been soaked in water is more durable than that which has not been soaked, but here again definite proof is lacking. For these reasons the Forest Service has undertaken to determine what treatments are most effective and what expense for treatment is justified by the resulting increased

service.

Circular 103 presented the results of experiments to determine the rate of seasoning of telephone poles. Mention was there made of a

[Cir. 104]

series of experiments to determine the effect of various preservative treatments in delaying their decay. The present circular describes the experimental treatments of these seasoned poles by the brush and by the open-tank methods. The latter is a new method developed by the Forest Service and promises excellent results in treating poles cheaply and effectively.

PLAN OF THE EXPERIMENTS.

The experiments were planned not only to afford data on the relative increase of life of treated over untreated timber, and on the value of different preservatives, but also to determine the effect upon the durability of poles of air seasoning, and of soaking in water with subsequent air seasoning.

The large question to be answered is, What is the best method of increasing the length of service of poles? This question, however, is very complicated and its answer can only be arrived at by answering a number of other more simple questions upon which it depends. The questions which these experiments are designed to answer are as follows:

1. What advantages have seasoned over unseasoned poles in taking treatment?

2. What is the increase in length of service of seasoned over green poles, both when untreated and treated?

3. Does submersion in water, with subsequent air seasoning, render poles more durable or easier of treatment than simple air seasoning? 4. Does the season of cutting affect treatment?

5. What preservatives are easiest of application and most effective? 6. What method of application is best?

Of these questions, 2, 3, 5, and 6 can be answered, in whole or in part, only after the lasting qualities of the poles have been tested in actual use. This test has already been begun by setting the poles in an experimental line; but some years must elapse before results will be obtainable. The present circular presents the information gathered in the course of administering the treatment, and throws light on the capacity of poles-green, seasoned, and soaked-to absorb preservatives, the degree of penetration secured with different preservatives, and the comparative cost of treatment by the brush and the open-tank methods.

To show what has been done to arrive at final conclusions as to the comparative effects upon durability of the different preservatives and different methods of handling and treating, there is appended a description of the experimental lines in which the poles have been set.

Seven preservatives were used in the experiments. All of these are regularly sold on the market for preserving wood and most of them

are protected by patent or trade-mark. All the preservatives are more or less modified distillates of coal tar or pine tar. Except for the preservative designated (D), which is common creosote or dead oil of coal tar, the names of the different preservatives are not given, but their composition is given in Appendix I. With one or two exceptions, the unnamed preservatives were given by the manufacturers for use in these experiments.

METHODS OF TREATMENT.

Two methods were employed in applying the preservative to the poles. On the larger number of poles the preservative was applied to the outside with a brush, allowing it to soak into the wood through its own power of penetration. All the different preservatives were tested by this method. The second method was to soak the butts of the poles in hot preservative in an open tank. In this method only one preservative, the dead oil of coal tar (D), was used.

It is generally conceded that the portion of a pole most subject to decay is that between 2 and 8 feet from the butt-about 20 square feet. This part fails when the remainder is still in a good state of preservation. It was therefore selected for treatment. When the pole is set the treated portion extends 2 feet above and 4 feet below the surface of the ground. From one to three coats were applied, according to directions received from the manufacturer. Most of the preservatives were heated to a temperature of from 150° to 175° F. Particular attention was paid to filling all checks and knot holes and to working the preservative into the wood, thus protecting against decay those parts most subject to attack. Careful notes were made of the condition of the poles as regards checks, knot holes, etc. The amount of preservative absorbed by each pole was accurately determined by recording the weight of the preservative before and after each treatment. The temperature of the preservative both before and after the treatment was also noted and recorded. In addition holes were bored into different parts of the treated portions of the poles, and the depth to which the preservative penetrated was closely observed.

OPEN-TANK TREATMENT.

The device for the open-tank process consisted of a steel tank resting on stone or brick walls in such a manner that a fire could be placed beneath it. The top of the tank was rectangular in shape, about 11 feet long and 6 feet wide. Its depth was about 4 feet at one end, tapering gradually to zero at the other. A vertical cross

PLATE 9' WIDE

were placed in the tank so that they lay at an angle of about hypotenuse of the triangle (fig. 1). The butt ends of four poles

FIG. 1.-Working drawing of open tank. (Lower diagram shows strengthening tees on bottom of tank.)

about 4 by 11 by 12 feet, the bottom of the tank forming the section of the length of the tank presented a right-angled triangle

20°, the tops of the poles resting on props. Creosote was poured into the tank until the poles were covered for a distance of about 8 feet from the butt, and was then heated to a temperature above the boiling point of water. This temperature was maintained until the air in the wood had been expanded and the water in the outer layers vaporized, and both, so far as possible, driven out. The theory of this process is more fully discussed in Circular 101, Forest Service. The preservative was then allowed to cool, thus producing a partial vacuum by the contraction of the air and the condensation of the steam remaining in the wood. The poles remained in the cooling liquid while the preservative, under atmospheric pressure, was forced into the wood. The entire time consumed by each treatment was about twenty-four hours, during which the temperature of the preservative was above the boiling point of water for eight or nine hours. Open-tank treatment was given to 160 seasoned and 24 green chestnut poles at Dover, N. J., and Thorndale, Pa. Each pole was weighed before being put into the tank and again immediately upon being taken out. In this manner the amount of preservative absorbed was determined. No account could be taken of the amount of moisture driven out of the wood during the time the preservative was heated above the boiling point of water, and therefore the amount actually absorbed may be slightly greater than appeared from the weights. However, since the seasoned poles were practically air dry the determinations are probably very nearly correct. In the case of the green poles, on the other hand, it is probable that the actual absorption was considerably greater than that shown.

CALCULATING THE COST OF TREATMENT.

During the treatments an effort was made to determine the itemized cost of treating the average pole, but many factors which would not be present in treatments on a commercial scale entered into the experiment and vitiated the results. In order, therefore, that the cost of the several treatments might be readily compared a constant labor charge and miscellaneous cost have been used.

For brush treatments it has been assumed that 6 men in two days can treat 100 poles with two coats of preservative at a cost of $22. The items making this cost are: Four men, at $1.75 per day for two days, $14; 2 men, at $1.50 per day for two days, $6; and miscellaneous expenses, including fuel and wear and tear of apparatus, $2. To the above cost of 22 cents per pole must be added the cost of the preservative absorbed by the average pole. This amount varies with the preservative and the locality.

For tank treatments it has been assumed that 6 men and 1 team of two horses can handle and treat 50 poles per day at a cost of $22.50.

489-No. 104-07 M-2