Abottt Chemistry of Paling Rails. 477 



that when coal-tar is used, it is partly this process, and partly that 

 of an ordinary drying paint, where an outer coating protects the 

 ligneous tissues from atmospheric oxygen. Coal-tar has a certain 

 drying power, paraffine oil or petroleum has not ; but, on the other 

 hand, these oils contain solids which infiltrate into the vegetable cells, 

 preventing chemical reaction. A recipe given in a recent number 

 looks more an exemplification of the principle that there can't be too 

 much of a good thing than a scientific method. 



The objections of M. Boucherie to the gallo-tannate of iron process 

 have a scientific foundation. No one doubts the preservative power 

 of gallic and tannic acids. It were to forget all the oak stumps from 

 innumerable peat bogs, black as ebony, but perfect as the day on which 

 they were immersed. Those old trees have not been exposed to the 

 immediate action of the atmosphere. But the posts used either for 

 telegraphic purposes or the harbour works, seasoned by Boucherie's 

 pyro-lignite of iron process, show very diiferent results. M. Kuhlman 

 has proved long ago that whenever iron in the state of union with 

 oxygen known as the protoxide enters wood a curious chemical re- 

 action ensues. The protoxide becomes the peroxide by taking more 

 oxygen from the atmosphere. But the iron is immediately robbed of 

 the oxygen it has newly acquired, by the compounds of the wood. 

 They do not long retain the stranger oxygen atoms they have cap- 

 tured, for water and carbonic acid are both formed, and so the wood 

 decays. IVtoreover so long as the iron remains in the wood these 

 processes are perpetual. Presh oxygen is seized from the air so soon 

 as that first captured disappears, and consequently the decay of the 

 wood continues. But though pyroligneous acid by itself is an excel- 

 lent preservative, it has been found when associated with its bad 

 neighbour iron protoxide to have a prejudicial effect ; so, too, of all 

 similar iron compounds. 



After all, a partial burning of the wood prevents the access of 

 oxygen into the interior. M. de Lapparent has introduced this 

 method into France. He has invented a lamp fed by tar and petro- 

 leum, which effects this semi-incineration very cheaply and expedi- 

 tiously. There seems no reason why our British lamp-makers should 

 not supply such a lamp specially adapted for railings and paling 

 stobs. French experience shows this method of wood preserving to be 

 admirable. Inventors should easily see how this can be conveniently 

 applied. Paraffine heavy oil, at present very much a waste product, 

 could be used, and a jet of steam directing the flame into the cylinder 

 containing the wood is all that is necessary for a quick and efficient 

 flame. 



VOL. I. 2 L 



