NOTES ON CREOSOTING. 1 73 



moisture from rain and dew. As the seasoning process goes 

 on, however, the timber loses more and more its power of 

 taking up atmospheric moisture. This illustrates the process 

 of natural seasoning, which reduces the moisture content of 

 the log by 15 to 1 8 per cent. 



Daring the drying process certain obvious changes occur in 

 the logs, notably a process of splitting in the more exposed ends. 

 Cracks or shakes appear in all directions, either following the 

 course of the medullary rays or of the annual rings. As the 

 drying process continues, however, these disappear, and the 

 wood closes up again. The reason is obvious. The drying 

 process takes place through the surface, which dries first. As 

 this surface shrinks in drying, it can no longer cover the undried 

 central regions. With a continuation of the drying process, 

 however, the central region also loses moisture, and a re- 

 adjustment takes place, resulting in the closing up of the 

 fissures. 



Something must now be said in regard to the composition of 

 wood, in order to appreciate fully the meaning of the process of 

 creosoting. In the very young plant the component cells are 

 enveloped in cellulose, a substance similar in composition to 

 starch. As the cells grow older this cellulose is converted into 

 lignin, and the form of the wood cells is modified. Further, the 

 timber of comparatively old trees of most species is divided 

 into heartwood and sapwood. The former is the more durable 

 part of the wood, and in the case of some classes of timbers is 

 long-lived even if no preservative be applied. 



The sapwood contains much moisture, and it requires most 

 drying. When this moisture has been driven off in the process 

 of drying, it must be replaced by creosote oil, in order to render 

 the timber durable. 



Something may now be said as to the causes of decay. The 

 organic causes of decay include the action of bacteria and of 

 fungi. In a general way it may be said that these dissolve the 

 woody portions of the cells, reducing them to a condition in 

 which they can form food for the decay-producing organisms. 

 Such organisms usually begin their action from the outside, 

 and require moisture and warmth for their development. These 

 conditions are best fulfilled immediately below the surface of the 

 ground, or to give the technical expression used in regard to 

 fencing-posts — "between wind and water." These facts make 



