THE PRESERVATIVE TREATMENT 



complishes the same result as the cool bath, but since the 

 hot oil cools slowly a longer time is required. When this 

 method is used the wood is frequently allowed to remain 

 in the oil over night. 



It is desirable in the open tank treatment to have the 

 sapwood entirely penetrated with the oil. This is some- 

 times difficult to accomplish and a shallower penetration 

 must then be accepted. A penetration of one-half to three- 

 fourths of an inch will give very good results, and even 

 lighter penetrations, while they are not as desirable, will 

 give sufficient protection to more than pay for the cost of 

 treating. With fence posts the treatment should extend up 

 far enough so that at least 6 inches of treated wood will be 

 above the ground line when the post is set. 



The length of time the wood is held in the hot and cool 

 bath should be determined by the penetration obtained and 

 the amount of oil absorbed. The penetration may be de*- 

 termined by boring a small hole, this hole to be plugged 

 with a creosoted plug before the post is set, or the timber 

 used. If the penetration is not sufficient the hot bath should 

 be lengthened. If the penetration is satisfactory, but too 

 much oil is absorbed, the cold or cooling bath should be 

 shortened. Some woods treat more readily than others, so 

 a general rule can not be given. 



The sapwood of most species treats more readily than 

 the heartwood, so sap lumber is preferable and round posts 

 are more suitable for treatment than split posts in which 

 heartwood is exposed. 



The amount of oil absorbed by fence posts will vary 

 with different kinds of wood and the size of the posts. In 

 general, it will be between four-tenths and six-tenths of a 

 gallon. In estimating the amount of oil necessary to treat 

 a given number of posts, enough oil to fill the treating tanks 

 to a height of about two feet should be added to the amount 

 to be absorbed by the posts. This amount of oil will, of 

 course, be left after the posts are treated. 



The Apparatus for the Open Tank Treatment consists 

 of one or two tanks (depending on whether the hot and 

 cold or hot and cooling method is used), thermometer, and 

 some means of heating the oil. The chief requirements of 

 the tanks are that they (i) shall be strong enough to hold 

 the weight of oil and timbers, (2) shall not leak, (3) shall 

 be deep enough so that the top of the oil will be a foot or 



Ten 



