IMPREGNATION OF WOOD. 181 



turned on for one to three hours, with a pressure of about twen- 

 ty-five pounds. This treatment softens the wood and dissolves 

 the sap. The air is then pumped out of the tank, which removes 

 the sap from the ties and leave-s a vacuum. When this has been 

 completed and the vacuum made, the impregnating material is 

 added under a pressure of about 120 pounds. This forces the 

 impregnating material into the cells of the wood. The preserva- 

 tive material used is made up one-third of a three per cent solu- 

 tion of chloride of zinc and two-thirds of dead oil (creosote oil). 

 Chloride of zinc was formerly used alone, but it was found that 

 it washed out after a few years, where the wood was laid in con- 

 tact with the ground, and thus the wood was liable to decay; 

 but by the addition of dead oil, which is itself a good antiseptic, 

 the cells of the wood were effectually sealed over and water pre- 

 vented from entering, and thus the chloride of zinc was pro- 

 tected and the process made more permanent, 'ihe cost of thi. 

 treatment in Hessen, Germany, is estimated at about twenty-two 

 cents per tie. 



Among the other processes for the preservation of wood are 

 the following: 



Kyanising Process. In this the ties are steeped in a solu- 

 tion of bichloride of mercury (corrosive sublimate), in the pro- 

 portion of about one part bichloride to one hundred parts, "by 

 weight, of water. The time required for this process is 'about 

 one whole day for each inch in thickness. This material is an 

 active poison, and must be handled carefully. It has given excel- 

 lent satisfaction in the preservation of timber which comes in 

 contact with the soil, but soon corrodes metal in contact with it. 



Boucherie Process. In this process the timber is impreg- 

 nated with a one per cent solution of sulphate of copper, either 

 by pressure in a closed vessel, or by applying it to the end of the 

 tie or log and forcing it through. This is an excellent antisep- 

 tic, and is said to have doubled the life of the Pine ties in Europe. 



Creosoting. This process is very extensively used, and has 

 given excellent satisfaction. The material is what is known as 

 dead oil, of coal tar, and is obtained by distilling coal. Naph- 

 thaline is its principal preservative. A similar oil, known as 

 wood creosote oil, is obtained by the distillation of Pine wood, 

 but is said to be much more soluble than the dead oil. and on 



