FOREST UTILIZATION 117 



XLIV. IMPREGNATION OF WOOD. 



Impregnation tends to increase the durability of wood by injecting an 

 antiseptic liquid and may mean a desirable or undesirable change of color, 

 and in some cases fireproofing. Little is known about the latter. 



Four principles may be applied : 



A. Immersion : 



I. The oldest method used was immersion in a strong solu- 

 tion of salt. European railroads place ties for eight days 

 in large tanks filled with a light solution of corrosive 

 sublimate. Nto other work required. The method is 

 called "Kyanizing." Drawbacks are that the liquid is 

 washed out on wet ground; that spikes do not hold well 

 . in the timber. Expense per cubic foot, 6 l /2C. 

 II. "Metalized" wood is obtained as follows: 



Immerse the wood in a solution of sulphate of iron ; then 

 smear the wood with chloride of calcium. In the outer 

 layers of the wood gypsum (sulphate of lime) is formed 

 together with chloride of iron. Such wood is impermea- 

 ble to water and has a metallic shine. 



B. Boiling: 



I. Boiling in salt water or in a solution of borax seems to be 

 a method rarely practiced. Boiling, however, with ex- 

 haust steam, when a black juice is forced out of the log, 

 is frequently seen abroad. 



In the latter case the log is practically steam dried. 

 II. "Franks" mixture consists of 95 % liquid manure and 5 % 

 of lime. It is pumped into large vats, within which the 

 wood is boiled for 3 to 8 days. The liquid enters to a 

 depth of about 3 inches and darkens the wood to a ma- 

 hogany tint. 



III. A method called "siderizing" injects by a .boiling process 

 a solution of copperas. The wood is then dried, and 

 liquid glass (a hot solution of silicate of aluminum) 

 smeared on the surface. By a chemical reaction silicates 

 of iron are formed in the outer layers, which are insolu- 

 ble in water and resist decomposition. The wood at the 

 same time obtains a beautiful gloss. 



C. Use of hydrostatic pressure : 



A solution of sulphate of copper (blue vitriol) is used after 

 Bouchefie. It is kept in a tank 30 ft. to 40 ft. above ground. 

 The timber must be fresh cut with the bark on and is spread 

 on a rough log-deck. At the big end of each stick a ring made 

 of rope is held in place by a board or heading nailed to the log. 

 A hose connected with the tank injects the liquid into the small 

 cleft formed between log and heading. After a few hours, drops 

 of vitriol appear at the small end, showing that the process is 

 complete. The pressure being slight, only the outer sappy layers 

 are impregnated. This method is largely used abroad, often in 



