Ii8 FOREST UTILIZATION 



the woods themselves, for telegraph poles of pine, spruce, fir etc. 

 " Expense per cubic foot, 4c. 



D. Use of steam pressure: 



The wood is dried thoroughly, then placed on small steel cars run- 

 ning into long cylinders or boilers, closed by a strong head. A 

 vacuum pump removes the sap water and causes a vacuum to 

 form in the wood itself. Then an antiseptic liquid is pressed'into 

 the boilers; temperature of liquid is 150 to 200. 



The liquids used are : 



(a) Chloride of zinc. 



(b) Creosote or rather cheap coal tar oils. 



(c) Gases of tar oils (so called thermo-carbolization). 



The creosoting method is used for ties and paving blocks. Creo- 

 soted timber holds nails well ; creosote is not washed out by 

 rain ; on the other hand, the darkened color of the wood is 

 sometimes objectionable. It is claimed that creosoting in the 

 United States has failed, probably because an extravagant amount 

 of the liquid has been pressed into the timber. In Germany the 

 expense per tie is only 63C as against $1.25 in the United States. 



E. Results : 



Heart wood is not as permeable and hence not as impregnable as sap 

 wood. Maple, birch, beech, spruce, sappy pine etc. are more 

 benefited by impregnation than white oak, longleaf pine etc. 

 Generally the duration of life of impregnated ties is increased 

 at the following ratio : Beech, 400% ; yellow pine and oak, 

 200% ; spruce, 50%. 



Obviously, every additional pound of preservative pressed into the 

 fibre has a lesser effect on the lastingness of the wood than the 

 preceding pound. For every woody species the limit must be 

 found at which additional impregnation proves unremunerative. 



