ARTIFICIAL PRESERVATION OF TIMBER. 



351 



Occasionally a few of the processes are still advocated, but the general 

 belief now is that they do more harm than good. 



When the system of impregnation is employed, pressure is used to 

 drive the solutions into the wood. The solutions are usually heated, so 

 as to increase the amount pressed in, as hot solutions penetrate porous 

 matter more readily than cold. There are a number of materials in use 

 for impregnating wood, the most important of which are: 



Am . 



. •» \\ kit- ! r< 



W4m S m 



SECTION OF PILE TREATED WITH 

 DEAD OIL OF COAL TAR. 



SECTION OF PILE UNTREATED. 



THESE PILES WERE DRIVEN AT THE SAME TIME AND TAKEN UP TOGETHER. THEY ARE BOTH VIRGINIA YELLOW PINE. 

 THE CREOSOTED PILE WAS TREATED WITH 14 LI'S. OF OIL. THE TREATED ONES ARE GOOD FOR AN INDEFINITE 

 PERIOD, HAVING BEEN IN USE (c. R. R. OF N. J.) OVER 14 YEARS. 



Copper sulphate (CuSOj, 

 Zinc sulphate (ZnS0 4 ), 

 Zinc chloride (ZnCl 2 ), 

 Mercuric chloride (HgCl 2 ), 

 Aluminum sulphate [Al, (S0 4 ) 3 ], 



The products of coal-tar distillation, including, chiefly, creosote, or dead 

 oil of coal-tar. 



The theory upon which the injection of salts into wood is based is 

 that the salts act as poisons, killing the fungi or bacteria which grow 

 in wood and destroy it. The secret of success is in pressing in sufficient 

 of the salt so that it ma}' not be leached out for a long time — as these 

 salts are all soluble in water. 



