74 OP WOOD IS GENERAL 



septic solution is then forced in by pumps, preferably with steam 

 or heat, the whole process occupying less than an hour. About 



75 lbs. of creosote, however, are required for the impregnation of 

 an ordinary railway sleeper, and various attempts to reduce this 

 quantity by the use of some Hquid solvent have failed. Though it 

 is very difficult either to secure the penetration of the creosote or 

 to determine the amount absorbed, it is usually specified that from 

 8 to 13 lbs. of creosote shall be injected per cubic foot. Herr E. 

 Seidenschnur proposes that the timber be first steamed under 

 pressure, the air then exhausted by reduced pressure, and then 

 an emulsion of 15 per cent, of creosote, in a resin soap to which 

 water is added, forced in under a pressure of seven atmospheres. The 

 latest process of this class, known as the JSTodon-Bretonneau method, 

 is electrical. The timber is placed on a lead plate, connected with 

 the positive pole of a dynamo, in a tank filled with a solution, a 

 second lead plate, connected with the negative pole, being on top. 

 The circuit is completed through the wood ; and, within from 5 

 to 8 hours, the sap rises to the surface of the bath, the aseptic 

 solution replacing it in the pores of the wood. Artificial drying, or 

 a fortnight's natural seasoning in summer weather, will then com- 

 plete the process. Solutions of magnesium or zinc sulphate or of 

 borax are employed. 



Some recent trials undertaken by the United States Govern- 

 ment show that aU injection under pressure tends to lessen the 

 cohesive strength of the wood. 



Powellizing consists in boihng the wood in a saccharine solution 

 without pressure, so as to expel air and moisture and coagulate the 

 albumen, and then drying it at a high temperature. Green wood, 

 and some species, such as Spruce, which cannot readily be creosoted, 

 can be treated by this process ; and the wood is not only seasoned 

 within a few days of being felled, but small cracks are closed up, 

 the porosity of the wood is much diminished — a very important 

 point in connection with wood-paving — and its strength, tough- 

 ness, resiliency, and durability are enhanced. The process need not 

 discolour the wood, but may be made to bring out figure, and thus, 

 in more ways than one, render it possible to substitute a lower grade 

 timber for the more expensive grades now in use. The processed 

 wood will take paint or varnish, and is completely immune to the 

 attacks of dry rot. Having no unpleasant odour, poweUized wood 

 is adapted for furniture as well as for paving or railway sleepers ; 

 whilst a slight modification of the treatment protects it from the 

 attacks of termites. 



Such impregnation methods double or treble the Hfe of railway 

 sleepers. On the other hand, it should be remembered that paint 



