I'd like to pass on some information I obtained from an enthusiast's European website on whisky. I have lost track now of the URL but will try to locate it again. The writer states clearly that in the 1800's, many continuous stills were made of wood and stones. That is, they would have looked like a wooden derrick with shelving containing a layers of stones. The steam, as in the metal continuous systems that replaced the wood affairs, would be introduced from the bottom and vaporise the alcohol from the falling wash. The author quotes the famous English whisky writer of the 19th century, Alfred Barnard, as stating that copper continuous systems were replacing the wood and stone constructions by the end of the 19th century. This is the first time I have read that continuous stills were made from something other than all-metal. The web site writer speculates that the wood and stone must have had a flavour impact on the whisky, and I agree. Also, he states this type of construction likely would have made the still less efficient than an all-metal still, and again this would seem likely. I must check Byrn (1875) again but do not recall him mentioning this kind of construction. It seems odd that a system which was an improvement of the older pot still distillation method would use materials that were less sophisticated, if that is the right word, than even the most basic pot stills then in use. (Think of the replica just used to make a Washington style rye whisky at Mount Vernon. It looks like a small dinosaur but is all metal). Because, simple as a pot still is in theory, one can't make them of wood, not at any rate if the combustion applied is direct flame or even I would think steam coil heating. Whereas one can see that shooting live steam through a porous wood and stone tower should not of itself lead to any danger of the wood burning. Those interested in recreating historic whiskeys might be minded to construct their own wooden continuous stills. Make sure you get the right permits first, though.