632 



AIVIERICAN FORESTRY 



the large list of preservatives wliicli 

 have been tried, long experience has re- 

 duced the number which are of accepted 

 value to two ; namely, coal tar creosote 

 and zinc chloride. In 1910 the con- 

 sumption of creosote in the United 

 States totalled 63,266,000 gallons, of 

 which 38,640,000 gallons, or 69 per cent, 

 were imported ; wdiile zinc chloride was 

 used to the extent of 16,802,500 pounds. 

 The latter, which is a soluble mineral 

 salt, leaches out of the wood in wet 

 climates, and is of greatest value in 

 arid regions. Creosote is the preserva- 

 tive most generally used, present de- 

 velopments indicating the decreasing 

 use of zinc chloride alone ; although in 

 mixture with creosote, or with some 

 heavy oil as a seal, it promises excellent 

 results. 



The methods or processes by which 

 preservatives are introduced into wood 

 involve many technical details which 

 are not of general interest. Preserva- 

 tives are applied by pressure, open tank, 

 and brush application. Of these the 

 first is of greatest value and most wide- 

 ly used, open tank and brush treatments 

 being superficial and of value mainly 



where low cost is essential and facilities 

 for thorough treatment are not avail- 

 able. 



The usual type of wood-preserving 

 plant is equipped with from one to five 

 heavy boiler plate cylinders, from six 

 to seven feet in diameter and about 

 130 feet long. The additional equip- 

 ment necessary to operate the plant in- 

 cludes steam boilers, pressure and 

 vacuum pumj^s, air compressor, storage 

 tanks, etc. The cylinder has a heavy 

 door which can be tightly closed by 

 heavy pivoted bolts, tight-fitting gaskets 

 preventing the escape of the preserva- 

 tive under pressure. The ties or timber 

 for treatment are loaded on narrow- 

 gauge steel cylinder cars, and a whole 

 train — usually fifteen cars — is run bod- 

 ilv into the cylinder ; tracks being pro- 

 vided inside the cylinder and the cars 

 designed so that they just fit the avail- 

 able space. The heavy door is then 

 closed and the hot creosote introduced 

 from overhead tanks. Pressure is then 

 applied and increased up to 160 to 200 

 pounds per square inch, or until the 

 desired amount of absor])tion is ob- 

 tained. The oil is then dropped into 



cross sections of beech tie treated by the reuping process at stendal, 



<".i:rmanv. 



