sections of the poles that are to be treated are immersed in creosote. 

 The creosote is then heated by steam coils in the bottom of the tank, and 

 a temperature -of from 220 to 240 deg. F. is usually maintained for 10 to 

 12 hours. The heat causes the portion of the poles immersed in the creo- 

 sote to dry out and the air contained in the wood cells to expand so that 

 a certain portion of the air escapes. The circulation of steam through the 

 coils is then discontinued, allowing the creosote to cool. This causes the 

 air in the wood cells to contract, forming a low vacuum within the wood, 



Sketch 



influence of penetration on treatment of 

 Western Hel Odar Poles. 



which has a tendency to draw the creosote into the wood. After standing 

 in the cooling or cold creosote for 12 hours, the poles are removed from the 

 tank and are then ready for use. 



While in the main the results thus secured are excellent, the simple 

 open tank process is defective in many respects. The greatest penetration 

 (see second pole in illustration) is secured from the end of the pole, where 

 the injection of a preservative is unnecessary. Moreover, the penetration 

 of the creosote in the sapwood is very uneven and erratic. Some poles in 

 one batch may receive a very heavy treatment resulting in the use of an 



