49 



Sedlion 3. Prevention of Decay 



183. Decay can be prevented by excluding one of the 

 conditions necessary for the life of the fungi. If they can 

 be kept from entering, or if the air or water can be excluded, 

 or if the tissues can be poisoned, the timber can be rnade to 

 last indefinitely. Most of the preservatives act in more than 

 one way. Paints, for instance, coat the surface of the wood, 

 and exclude the spores, air, and water, and they also con- 

 tain poisonous substances. One of the best and cheapest 

 preservatives is creosote. This, like paint, excludes the 

 spores, air, and water; and the carbolic acid which it con- 

 tains poisons the tissues of the wood. 



184. Creosote is applied in different ways. One way is 

 to heat it and apply with a brush, like paint. This is a 

 cheap way; but it is not so effective as some of the others; 

 because the creosote does not go deeply into the wood. But 

 for shingles it is the most practicable; for if they are treated 

 in some other way before they are laid, they are apt to stick 

 together and become hard to handle and the creosote is hard 

 on the hands of the workmen. So it is best to lay the shin- 

 gles and then to apply the creosote with a brush, letting it flow 

 freely so that it will get into the cracks. 



185. Another method used mostly for treating posts, is 

 known as the open-tank method. The posts are placed in a 

 tank of hot creosote; and after 2 hours the hot liquid is 

 drawn off and cold creosote is run in. The posts are left in 

 the cold liquid for 2 hours and then removed. The heating 

 expands the air in the posts and drives it out. When the 

 cold liquid is turned on the pressure of the air on the outside 

 drives the creosote into the vacua that have been created. 

 The objection to this method is that the outfit costs about 



