ARTIFICIAL PRESERVATION OF TIMBER. 357 



condensing point, and yet not too high. This is one of the points upon 

 which practical experience is necessary, and theorizing of little account. 



After this the oil is admitted into the cylinders while they are under 

 vacuum : and when all air has been withdrawn they are subjected to pressure 

 until the requisite amount (determined by gauges) has been forced into 

 the timber, which, if the timber has been properly prepared, is only a 

 small part of the process. If all the sap, moisture and vapor have been 

 extracted from the wood, the oil will enter the pores readily; but if these 

 have not been thoroughly withdrawn, no amount of pressure will be able 

 to force in the oil, since the two substances cannot occupy the same place 

 at the same time. It may be said that the whole secret of successful creo- 

 soting lies in getting the timber properly prepared for receiving the oil, 

 and for this the first and most important condition is that all fluids shall 

 be driven out. Where creosoting has failed to prevent rot or the attacks 

 of insects it has almost invariably been because the timber was not properly 

 prepared before impregnation; but when properly prepared and treated 

 with a sufficient quantity of oil, the wood is practically immune to rot, 

 impervious to marine and land wood-borers, and indestructible. 



There will be no decay in any part of the timber that has been per- 

 meated with the oil, but to have all parts saturated is expensive and unnec- 

 essary, for, after the timber has been thoroughly treated by the heat and 

 vacuum process (the finest form of artificial seasoning) it will last a long 

 time without any oil, and if the crevices and pores are sealed up with the 

 oil to a sufficient depth, the timber is as good as if the whole part had 

 been permeated with the oil. The quantity of oil to be injected depends 

 upon the use and the locality where the timber is to be placed. The attacks 

 of the land and water insects are worse in the South than at the North, 

 while wood used in underground work, such as electrical conduits, sewers 

 tunnels, etc., and in other locations subject to great dampness, is more 

 liable to succumb to wet-rot than is that employed above ground and in 

 dry atmospheres. In general, for marine purposes, not less than twelve 

 pounds per cubic foot is advised for the vicinity of New York, and from 

 fourteen to twenty-two pounds where the worm is bad. Twenty-four 

 pounds of oil is about the limit that is ever used. 



