576 



AMERICAN FORESTRY 



use, easily handled and applied, and not poisonous to 

 man or animal. Many things have been tried as wood 

 preservatives, the list ranging from common salt to 

 skimmed milk, and it is certain that experiments have 

 included several hundred materials. Of these, however, 

 probably not over twenty-five have in laboratory tests 

 been found to be really effective in checking or destroy- 

 ing the growth of fungi, and of this number only three 



BRUSH TREATMENT PROCESS 



.Applying refined creosote to telegraph poles and the samv 

 method may be used for all farm lumber. 



or four are of recognized value for general commercial 

 use. 



The best general preservative developed is coal tar 

 creosote, since it combines in greatest degree the essen- 

 tials called for. It is a by-product of coal tar, from 

 which so many materials, including dyes, drugs, per- 

 fumes, flavoring extracts, etc., are obtained. Creosote is, 

 in fact, a by-product of a by-product, since coal tar itself 

 is a by-product of coke ovens or illuminating gas plants. 

 It is a heavy dark brown liquid which in turn is com- 

 posed of many chemicals, including napthalene, which is 

 the common constituent of moth balls, and anthracene, 

 which is of high toxic value. Commercial creosote is of 

 various grades, ranging from that which is left over 

 from the distillation of coal tar to that which has been 

 refined by removing some of the lighter boiling fractions. 

 This means that the oils or products which would evap- 

 orate most quickly have been removed, leaving a material 

 which in viscosity and permanence is especially suited 

 for brush or open tank treatment oi wood. Another creo- 

 sote product is derived from so-called water-gas tar, this 

 being in part a petroleum product usually obtained from 

 illuminating gas plants. Other materials with a creosote 

 base or to which other products have been added are sold 

 under various trade names. A few of these have a high 

 preservative value and may be used to advantage. 



Another form of creosote is derived from wood tar 

 which is obtained in the destructive distillation of hard 

 woods. This is of materially different chemical com- 

 position, and while it has some preservative value, it has 

 not been generally adopted or used for wood preservation. 



An entirely separate and distinct group of wood pre 

 servatives is made up of various mineral salts, these in- 

 cluding sodium fluoride, chlorides, creosole, calcium, cop- 

 per sulphate and zinc chloride. The last is extensively 

 used in regions of low rainfall, or where the timber is 

 not in direct contact with moisture, and both alone and in 

 combination with creosote has been extensively applied 

 Tor the preservative treatment of railroad cross-ties in 

 the Middle West. Zinc chloride comes in the form of a 

 crystallized .salt, which is dissolved in water and injected 

 into the wood in about a three to five per cent solution. 



Of the various preservatives available the best for the 

 home builder, who must treat his wood with a brush or 

 by hot or cold baths in open tanks, is creosote, and of the 

 several grades and kinds the highest boiling oils, by which 



BASE OF PILLAR ROTTING 



The use of a wood preservative will prevent such decay as 

 is frequently seen in cases such as this one. 



is meant those which will show the least lost in evapora- 

 tion, are best. 



The best method of applying preservatives to timber 

 is by the pressure process which is used by practically 

 all large commercial companies. By this means the oil 

 or mineral salt is forced deeply into the tissues of the 

 wood, thus giving a thoroughness and permanence not 

 otherwise attainable. There are various processes, but 

 all use large and expensive apparatus by which vacuums 

 and heavy pressure may be applied in large treating cylin- 

 ders, which are usually six feet or more in diameter and 

 a hundred feet or more in length. Many of the large 

 railroad companies have their own pressure treating 

 plants, while commercial plants of the same character 

 are located in various parts of the country; especially at 

 or near seaports, which are the most advantageous points 

 for receiving and distributing both creosote oil and 

 lumber. 



The small consumer is likely to find difficulty in ob- 

 taining pressure treated timber for his needs, with the 



