METHODS OF IXJECTIOX, 



669 



Fig. 29 



concluded, the air is sucked out of the wood by means of the air- 

 pump B and the injecting liquid (30 — 50 fold diluted chloride 

 of zinc, the latter containing 25% of zinc) is admitted through 

 the pipe h h into the cylinders, the air-pump still working for 

 some time. When the cylinder is full, the forcing-pump D 

 presses the liquid into the wood. In order to eftect this a 

 pressure of about 6 atmospheres is applied for | — 1| hours. 

 The injecting liquid is then drawn back into the reservoir, and 

 the truck removed with its 

 contents. The two cylinders 

 are used alternately. 



Quite recently it has become 

 the practice to omit the steam- 

 ing entirely and to dry the 

 wood, especially in creosoting 

 with tar-oil, &c. It is, how- 

 ever, desirable, in order to 

 render wood durable, that all 

 the nutritive material in the 

 sap should be withdrawn, which 

 is not the case when the wood 

 is dried. The drying is 

 effected in a drying-chamber, 

 heated to 175°— 250° F. The 

 wood is then placed in the 

 injecting cylinders, out of 

 which the air is drawn, and the 



tar-oil admitted at a temperature of 113°— 140° F. (45°— 60^ 

 C), and pressed into the wood in the same way as when chloride 

 of zinc is used. 



[Boulton* says that the presence of water in timber at the time of 

 creosoting is most prejudicial to successful injection, and that railway- 

 sleepers and other timber should be stacked and dried for several 

 months before injection. This precaution can easily be secured in 

 the case of railway-sleepers or telegraph-poles, but when timber is 

 sawn from logs kept in timber-ponds in the docks, it is difficult to 

 afford a proper time for stacking and drying it before creosoting. 



* S. B. Boulton, " An improvement in the process of Creosoting Timber." 



1"^-,^. 



u4 



Front of an injecting cylinder with 

 a truck laden with wood. 



