such as coal-tar creosote and other creosotes, mixtures of coal tar creosote 

 with coal tar, petroleum, or other oils, solutions of toxic chemicals such 

 as pentachlorophenol or copper naphthenate in selected petroleum oils or 

 other solvents, and various mixtures of these solutions with the byproduct 

 oils and mixtures. The waterborne preservatives include solutions of single 

 chemicals such as chromated zinc chloride (CZC) or chromated copper arsenate 

 (CCA), which are not resistant to leaching, and various formulations of two 

 or more chemicals that react after impregnation and drying to form compounds 

 with limited solubility and sometimes with high resistance to leaching. 



Preservatives vary greatly in effectiveness and in suitability for 

 different purposes and use conditions. The effectiveness of any preserva- 

 tive depends not only on the materials of which it is composed, but also 

 on the quantity injected into the wood, the depth of penetration, and the 

 conditions to which the treated material is exposed in service. 



(1) Coal-Tar Creosote . Coal-tar creosote is defined by the American 

 Wood Preservers Association as a preservative oil obtained by the distilla- 

 tion "of coal tar produced by high-temperature carbonization of bituminous 

 coal; it consists principally of liquid and solid aromatic hydrocarbons and 

 contains appreciable quantities of tar acids and tar bases; it is heavier 

 than water; and it has a continuous boiling range of at least 125° Celsius, 

 beginning at about 200 Celsius." Coal-tar creosote is highly effective and 

 is the most important and most extensively used wood preservative for 

 general purposes. Coal-tar creosote solutions vary and usually contain from 

 30 to 70 percent of coal tar by volume; the most prevalent mix contains 50 

 percent coal tar. 



(2) Chemicals Dissolved In Solvents Other Than Water . Preservatives 

 composed of toxic chemicals carried in nonaqueous solvents, such as petroleum- 

 oil distillates, are now being used to an increasing extent. These were 

 originally devised for the purpose of providing a clean treatment without 

 causing swelling of the wood and were originally applied by nonpressure 

 methods . 



A shortage of cresote that developed during World War II created an 

 active interest in the use of these preservatives as a possible substitute 

 for creosote, especially in the pressure treatment of poles. Particular 

 attention was directed to the chlorinated phenols, which are known to have 

 a high degree of toxicity. Pentachlorophenol is the best known and most 

 widely used in this group. Other preservatives of this type, which in the 

 past have been largely limited to use in surface treatments, are the metallic 

 naphthenates, such as copper naphthenate. The latter has also been used to 

 a limited extent for pressure-treated poles. 



Although some of these toxic chemicals, particularly pentachlorophenol, 

 have given excellent results over a considerable period of time, service 

 records are still inadequate to evaluate them completely in comparison with 

 coal-tar creosotes. 



(3) Waterborne Preservatives . A variety of chemicals in water 

 solution are used as wood preservatives. These include zinc chloride, 

 sodium fluoride, arsenic in various forms, copper sulfate, and similar toxic 

 chemicals. Most of these salts are used in combination with one or more 



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