The Preservation of Timber. 287 



proposes to taa the timber by substituting for the sulphate of copper and 

 creosote a compound of tannic acid and iron. The object of injecting 

 various substances into wood is to poison them, so that germs and micro- 

 scopic growths may no longer live and propagate either on the surface or in 

 the interior, Now tannin is one of the most active and certain destroyers 

 of germs both vegetable and animal, which fact accounts for its preser- 

 vative agency. Besides, it is to tannin that is due the almost indefinite 

 preservation of leather. One peculiarity to be noticed in this process is, 

 that timber treated with this compound of tannin and iron, that is to say 

 a composition similar to ordinary writing ink, is turned black. 



The process of injecting timber with tannate of protoxide of iron is due to 

 M. Hatzfeld ; the Eastern Railway Company of France has experimented 

 with it on some sleepers, and the Telegraphic Department on some posts. 



M. Boucherie has denied in a note to the " Academic " the efficacy of 

 this process, contending that the attempts already made' to preserve 

 timber from dry-rot by injecting it with iron salts have yielded only 

 partially successful results, while sleepers treated with sulphate of copper 

 have lasted twenty-five years and more. Reply is made to these objections 

 by quoting — not the experiments of the laboratory or the workshop, but 

 those made by time itself It is not a rare circumstance to encounter in 

 earth of a ferruginous nature the trunks of very old oaks, blackened and 

 very perfectly preserved ; at Eouen, in 1830, some old oak paling was dis- 

 covered as black as ebony, and dating back to the Middle Ages. Not very 

 long ago, too, Norman vessels built of oak were discovered in an almost 

 perfect state of preservation in the neighbourhood of an iron mine in 

 Norway. It is more than probable that the preservation of the oak under 

 these circumstances is due to the tannin contained in the wood ; it follows, 

 therefore, that by introducing a substance rich in tannin into timber that 

 does not naturally possess it, its resistance to decay is increased. — Journal 

 of the Society of Arts. 



