TREES AND FORESTRY 47 



extremely slow in growth. For piling, long-leaf, .short-leaf and loblolly 

 pine, white and red oak are used on the Atlantic Coast and the Gulf of 

 Mexico, while Douglas fir supplies the demand in the Pacific region. 



Under the waning supply of durable woods, experiments have been in 

 progress which prove that the power of posts, ties, poles, mine and wharf 

 timbers to resist decay in moist situations may be greatly enhanced by 

 treatment in a preservative fluid. So successful has been the work that it is 

 likely to revolutionize the market as regards these products. By treatment, 

 not onlv do the durable woods gain a lengthened period of service but also 

 less durable woods may be made to take the place of durable woods. The 

 United States Forest Service states the following concerning fence posts: 

 " Resistance of all treated posts to decay is alike, regardless of kind of wood 

 used; posts with much sapwood take a deeper impregnation of the pre- 

 servative." This means that the cheapest, least durable woods, like 

 poplars, will come into service for posts, leaving the durable woods for use 

 in interior finish and cabinetwork. According to the open-tank method of 

 t eatment (Fig. 38), formerly given the highest recommendation by the 

 United States Forest Service, the wood is kept immersed in coal-tar 

 creosote for a number of hours, depending on the kind of wood, and is 

 then plunged into cold creosote, or is left in the cooling preservative 

 over night. The wood should have been previously seasoned (Fig. 39) and 

 its sapwood should be saturated with the oil. Brush treatment, by which 

 the wood is painted with hot creosote, is less expensive, but also less effective 

 because of the slight penetration by the oil (Fig. 40). Treatment in closed 

 cylinders under pressure, is considered the best method as far as results are 

 concerned, but it is five times as expensive as the tank method. 



The effectiveness of the tank treatment lies in two facts, namely, (1) creo- 

 sote oil protects the wood from the entrance of water and (2) creosote — 

 being antiseptic — protects the wood from the attacks of bacteria and various 

 fungi which grow rapidly in damp situations and whose growth means decay 

 of the wood. The theory that insures the impregnation of the wood by 

 tank process is as follows: heating in the creosote expands the air contained 

 in the wood until much of it is driven out; plunging the wood into cold preser- 

 vative causes the air left to contract leaving a partial vacuum which is filled 

 at once by the cold oil forced in by atmospheric pressure (also by capillarity). 1 



Treatment of wharf timbers with creosote protects absolutely from 

 marine borers (Fig. 41). Zinc chloride is used to some extent in treatment 

 of woods but the resulting protection is not permanent because the preserva- 

 tive is soluble in water. 



i The importation of 25,000.000 gallons of creosote into New York City in 1908 was an 

 increase of 21,500,000 gallons over that of 1904. This indicates great development of wood 

 preservation. 



