yi ON PREVEKTJJTS THE DUT-ROT IN "WO OB. 



of wood v/etted by rain in the open air. The water soon 

 Jzj waip.icot. evaporates, and little decay proceeds in the wood. So in the 

 wainscot, the surface next the room, though unprotected by 

 paint, will perhaps be long in rottinc^, because the room ad- 

 mits of currents of air, more especially when doors and 

 windows are frequently opened, so as to evaporate the super- 

 iicial moisture, though less quickly and effectually than in 

 the open air. But what is the case with the surface of tTie 

 pannel next the wall? The air, loaded with moisture, pene- 

 trates into that interstitial space, and deposits it by condensa- 

 tion on that surface. But there is afterward no current of 

 air to evaporate the water so deposited, which then slowly 

 decomposes and destroys that surface of the patinel. Such 

 is precisely the process .of the dry rot, which always begins 

 next the wall, and gradually proceeds to the painted or 

 outer surface of the wood. It resembles in its chief circum- 

 stances the decay of paper in a damp room ; and it precisely 

 resembles that of p;iper projecting from the wall on canvas, 

 vhich will still often happen, if the wall be subject to acquire 

 a. very considerable degree of coldness, though much more 

 $lowly than in the former case. 

 Other cases si' The same process obtains in all other cases. Whenever 

 '*'•*''• the wood is cooler than the air which it touches, the vapour 



is condensed upon it; and being exposed to no new heat or 

 current of air sufficient again to evaporate it, remains till 

 another fit of condensation affords a new supply. 



Thuo the process of corrosion and decomposition is con- 

 tinually supported, till the wood moulders away. 

 Dry-rot an iir.^ '^^^ ^^>""^' dry-rot is, therefore, so far from being expressive 

 proper term, of the real fact, tlrat decay proceeds under these circum- 

 stances more quickly than in the open air, precisely because 

 the wood is mwe constantly and uniformly wet; just as the 

 lower parts of poytb and rails, and any cavities in timber 

 exposed to the weather, rot sooner than those parts which 

 readily and speedily dry. 

 Cflusftof the The smell which \vg perceive on going into vaults or eel? 

 lars, where this process is going on, aristrs partly. from the 

 extrication of certain gases, mingled perhaps with some vo- 

 latile oily and partly from the effluvia of those vegetable sub- 

 stances; which have ak^dy been said to grow on it; and 



which. 



jme.. 



