52 TECHNICAL PROPERTIES OF WOOD. 



more rapidly. Rainwater Las not much in fl nonce on wood which 

 has been thoroughly dried. 



Several systems of drying-chambers are in vogue, and hardly 

 any large industrial wood-establishments dispense with them, thus 

 effecting their purpose in a few weeks' time. As a rule, they 

 are built of masonry, and heated by steam-pipes to temperatures 

 between 50^ and 80^0. (112^ to 170^ Fahr.), whilst powerful 

 exhausters pump-out the air which has been rendered moist by 

 the timber and pump- in heated dry air. Large logs on trucks 

 are passed into such chambers on rails, and the hot-water pipes 

 run between the rails, whilst there are cold-water pipes in the 

 ■walls to cause a rapid circulation of the air. 



In England the principle of drying wood by currents of air 

 only slightly heated, but driven rapidly by revolving fans, is often 

 followed. 



The finer woods may be dried by packing in common salt, 

 which is highly hygroscopic, in air-tight chambers. Rene, a 

 pianoforte manufacturer at Stettin, in order to season his wood, 

 thoroughly exposed it in an air-tight chamber to ozonized 

 oxj^gen. This apparently oxidizes the contents of the sap, and 

 in 12 to 24 hours renders the wood as thoroughly seasoned as if 

 it had stood for years in the air. 



2. Absorption of Water hy Wood. 



A wood which dries quickly and thoroughly also absorbs 

 water again in the same degree, so that the more porous and 

 less resinous a wood is, the greater its exposed surface 

 and the damper the medium into which it is brought, the 

 more readily does it absorb water. Decaying wood absorbs 

 water readily, air-dried wood absorbs water much more slowly, 

 and wood which has been steamed is far less absorptive of water 

 than unsteamed wood. For an account of the absorption of 

 preservative substances by injection, the reader is referred to 

 the third part of this book. 



Whilst in most of the industrial uses of wood, rapid with- 

 drawal of water is required, there are some in which wood 

 should be as watertight as possible. This is especially the case 

 with staves for casks, which should part with as little of their 



