154 THE BOOK OF FORESTRY 



any place where the impregnation has been slight may 

 be attacked later with agencies of decay. 



The toredo, a boring mollusk found in tropical waters, 

 has been found to attack creosoted piles only where 

 blows of a sledge had dented the wood and diminished 

 the thickness of the treated layer. 



If care is used in controlling the temperature and 

 strength of the solution used, treated timbers will be 

 fully as strong as they were previously. Under new 

 methods, especially those in which creosote is used, 

 there is no chemical reaction between the wood fibers 

 and the preservative; the creosote simply forms a film 

 around the fiber. The amount of heat used in this 

 process can be carefully regulated but the amount of 

 moisture contained in the treated timber is of much 

 more importance. Creosote retards both the evaporation 

 and the taking up of water and therefore, if thoroughly 

 seasoned wood is treated, it will be practically im- 

 possible to take up any water afterward. But if the 

 wood is not thoroughly seasoned before treatment rapid 

 disintegration may take place. This is quite similar 

 to the dry rot that is found shortly after partially sea- 

 soned or green wood has been painted. 



Treatment with zinc chloride may produce unsatis- 

 factory results, especially if the timbers are not 

 thoroughly dried before being used. However, there 

 seems to be a chemical reaction in this case, for if too 

 strong a solution is used, the wood fibers are corroded 

 and a noticeable loss of strength occurs. 



The chemical treatment of wood to prevent decay 

 is long past the experimental stage in this country and 

 it is a practice certain to increase. In view of the 

 fact that decay alone is responsible for seventy per cent 

 of all the destruction of timber, economy demands that 



