48 PRACTICAL ARBORICULTURE 



WOOD PRESERVATION. 



From the earliest antiquity there have been methods of chemically treat- 

 ing wood, cloth, and even flesh, to preserve their substances from decay. The 

 Egyptians were better acquainted with this subject than is the world to-day. 

 Their mummies of sacred animals, as well as human beings, are in perfect 

 preservation after three thousand years have passed. The cloths, linen wrap- 

 pings of the dead, and wooden cases enclosing the mummies are all preserved. 



The Natron Lakes supplied the antiseptic materials, asphaltum and bitu- 

 men ; salt and precious spices were also used for this purpose. How well they 

 succeeded is seen by the objects now found in every museum. 



Other nations among the ancients practiced this art, and were familiar 

 with the properties of many antiseptics. 



In modern times various methods have been practiced for the economical 

 treatment of wood, for ocean piling where the teredo is destructive, and for 

 cross-ties, bridge timbers and other purposes. 



In Europe the base of these preservatives is creosote a product of wood 

 distillation. Owing to the greater cost and value of wood there than in Amer- 

 ica, this expensive process is considered economical. 



In America cheaper materials are sought for, and coal tar products take 

 the place of creosote, but are used under the name of creosoting. They are 

 not so enduring as the real wood creosote, yet are suited for the more expen- 

 sive works of bridges and piles. 



Railway ties are not as ye.t of such cost as to justify either of the above 

 methods, and resort is had to'the chloride of zinc solution. 



The wood to be treated is placed in air tight chambers into which live 

 steam is forced heating and separating the fermenting sap from the wood. 

 Afterward a vacuum is formed and this sap and moisture are drawn out of 

 the cells. The hot solution of zinc chloride is next forced into the vessel and 

 enters the pores of the wood. Glue and other substances are used to fix these 

 antiseptic materials in the wood. 



Artificial treatment of wood, however, is not to be compared with natural 

 preservatives. Substances in solution with water after being dried, may again 

 be dissolved and in time lose their antiseptic power, after which the wood is 

 subject to fungus attack. 



The catalpa gathers antiseptic substances from every soil in which it 

 grows, builds it into the fiber of the wood and these can only be dissolved 



