WOODS THAT ARE TO RECEIVE TREATMENT Some woods last naturally without treatment longer than other woods will last after they have been treated.
It is often well to consider the economy of treating non-durable woods that are tough and strong and that respond to treatment. For example, beech is desirable structurally save for the fact that it rots quickly in exposed places; yet it receives antiseptic solu tions better than white oak receives them and, after being suit ably processed, will last for a long time.
The results obtained with beech by the French are often quoted. Beech ties are seasoned for at least six months and are then kiln-dried for from sixty to eighty hours to expel the remaining moisture and to warm the pieces so that they will not chill the creosote. Each tie then receives an average of sixty pounds of creosote. Experience has led to the belief that such ties will last in the track for at least thirty years, and that they will finally fail by wear rather than by rot.' The ability of wood to receive preservative treatment is influ enced by the character and arrangement of its cell-elements. The presence of tyloses in the large vessels or pores of such woods as white oak and black locust interferes correspondingly with the treatment of these woods. As a rule, sapwood is more open to the passage of preservatives than is heartwood. Large quantities of yellow pine are now treated with preservative, while von Schrenk suggests, beech, maple, birch, red and swamp oaks, gum, hemlock, and even cottonwood as American species that should receive consideration in this Individual pieces, as well as species, vary from one another in receptivity. For this reason, as far as possible, charges should be made up of pieces that are nearly similar to one another. Re fractory pieces should receive such special attention as is neces sary to overcome extra resistance.
The tendency of preservatives to lodge near the surface of pieces should be recognized, and, whenever possible, timber should be cut, shaped, or fitted before it is treated.
1. Cheap woods, or those used in inexpensive or unimportant constructions, are seldom treated with preservatives at the present time in the United States. Woods are now treated only when they become costly, or when they are to be used in works that do not permit renewals or repairs at reasonable prices.
2. Zinc chloride and creosote are used more than all other wood preservatives.
3. Zinc chloride is soluble in water, and therefore cannot be used with woods that are to be exposed in marine positions. Neither is it known that it protects woods against marine and terrestrial woodborers. The principal field of zinc chloride as a wood preservative is with railway ties that cannot be economically treated with the more expensive creosote.
4. Experience has shown that wood can be protected against rot, and against marine and terrestrial woodborers, by the intel ligent use of sufficient quantities of good creosote.
5. Creosote is complex and variable. It should therefore be purchased from reputable dealers, and its properties should be controlled by specifications.
6. The details of wood-preserving processes call for knowledge, skill, and integrity on the part of the operator. A poor method well detailed may afford better results than a better method poorly detailed.