SELLINGLUMBER 223 



briefly consists in placing the lumber to be treated in a suitable 

 tank or vat, the size depending upon the quantity to be treated. 

 The preservative should then be run into the tank or vat until the 

 lumber is entirely covered. Heat is then applied either by means 

 of steam coils or by a fire built under the tank. The preservative 

 is heated for anywhere from two to five hours, or longer if the 

 timber is very green, and the heat is then withdrawn. The lumber 

 is left in the cooling solution for from two to ten hours, depending 

 upon the size of the lumber treated and its condition prior to 

 treatment. The heating operation produces a vacuum within the 

 wood, and as the preservative cools, it is forced into the wood ment of 

 by atmospheric pressure. This process is admirably adapted to the Lumber 

 treatments of fence posts and bunches of shingles, and short 

 lengths of any kind of lumber. It is, however, possible to use 

 tanks long enough to take any length of structural timbers or 

 boards, and as the apparatus requires a comparatively small initial 

 investment, it will be practical for any retailer or any consumer 

 to build one of these plants himself and operate it with every 

 guarantee of success. Complete descriptions of the various types 

 of tanks can be obtained from the United States Forest Service 

 and government state institutions and universities. 



Most of the timber and lumber preserved is treated by one of 

 the so-called pressure processes. For these processes large cylin- 

 drical retorts are used, about six to seven feet in diameter and 

 100 to 160 feet in length, supplied with the necessary pipe lines, The Pressure- 

 pressure and vacuum pumps, storage tanks for the preservative, M^jJoITof 

 etc. The lumber or paving blocks are piled on small cars which Treating 

 are run into these retorts, and after varying applications of steam, um e 

 air pressure, vacuum, etc., the preservative is forced into the lum- 

 ber at pressure approximating 175 pounds. Careful records are 

 kept of the amounts of the various chemicals injected, because upon 

 this the final cost usually depends. 



The pressure processes may roughly be classed into the so- 

 called full-cell treatment, in which large amounts of preservative 

 are injected, and the so-called empty-cell treatments, in which E xperts 

 large amounts are initially injected and then withdrawn with the Should 

 exception of a small amount, the idea being to obtain the requisite Treatment 

 penetration and still leave only a small amount of preservative 

 in the timber, thereby reducing the cost. It should be remem- 

 bered that all preservative processes require considerable technical 

 chemical and physical knowledge, and in all cases careful super- 



