The Durability and Preservation of Woods 253 



are secured if an even temperature can be maintained. 

 This is better accomplished by steam, which, however, is 

 not always to be had. The less surface the liquid has, the 

 less oil will be lost by volatilization; hence the tank 

 should not be of too large diameter. 



The Forest Service recommends surrounding the metal 

 tank with a plank framework inclosing a space 4 inches 

 wide between the tank and the boards. This space should 

 be packed with sawdust. This packing is especially 

 beneficial in cold climates. It prevents the too rapid 

 solidifying of the creosote. The erection of such a plant 

 will cost from $30 to $45. 



For this treatment the seasoned peeled posts are placed 

 in the tank of creosote, either wholly submerged or only 

 the butts under as is desired, and kept there from \ to 6 

 hours. The temperature of the creosote should be kept 

 as nearly as possible between 200° and 210°. The expan- 

 sion caused by the heat forces out much of the water and 

 air from the wood cells. 



The fires are then drawn and the posts left in the cool- 

 ing solution for J-14 hours. The cooling causes a 

 vacuum in the cells from which the water and air were 

 driven by the heat, and the creosote is forced into these 

 vacuums by the pressure of the atmosphere. Mr. Weiss of 

 the Forest Service thinks that a short hot bath and a long 

 cool bath probably will give the most economical results. 



If there are a large number of posts to be treated and it 

 is desirable to hurry the work, two tanks may be used, one 

 for the hot bath and the other for the cool. The posts 

 may then be transferred directly from one tank to the 

 other and the hot tank immediately refilled. This is an 



