WOOD PRESERVATION IN FOREST CONSERVATION 633 



PINE TIES TAKEN FROM TRACKS OF PRUSSIAN 

 STATE RAILWAY AFTER TWENTY-THREE YEARS' 

 SERVICE. TREATED WITH ZINC CHLORIDE AND 

 CREOSOTE. 



an underground receiving tank, or 

 forced back by compressed air, and the 

 charge withdrawn. This covers the 

 essential steps of the so-called full cell 

 or Bethell process. Various modifica- 

 tions are made for special purposes, 

 such as preliminary steaming, followed 

 by a vacuum, to remove the saps ; initial 

 vacuum, before introducing the oil ; and 

 a final vacuum to recover surplus oil. 

 An economical process, known as the 

 Reuping, requires an initial air pres- 

 sure, followed by the introduction of 

 the oil without relieving the pressure. 

 At the end the compressed air in the 



wood forces out 40 to (><> per cent of 

 the oil originally injected, leaving only 

 the cell walls impregnated; hence the 

 name "emtpy cell" process. Another 

 process designed for a reduction in 

 initial cost is a mixture of creosote 

 and zinc chloride in sohiiioii. the two 

 liquids being agitated and kept in emul- 

 sion by a rotary pump, through which 

 tlu- entire mixture, in the cylinder. 

 passes every seven to ten minutes, even 

 while under pressure-. 



The tendency in this country, where 

 timber is still comparatively cheap, is 

 to economize in the treatment by using 



