PRESERVATION OF TIMBER. 105 



propagated with frightful rapidity, and disorganizes deeply and to a 

 great distance around the texture uf the wood where it once appears 

 These fungi are generally found on hoard ship, between the planking 

 and the ribs, in damp situations, and where the air is scarcely, if 

 ever, changed.* 



The temperature most favorable to the development of dry-rot has 

 been found to lie between 7" and 32" cent, or 45" and 90" F. These 

 are the extreme limits : below the minimum vegetation languishes ; 

 above the maximum, the fungi droop. With tliis piece of informa- 

 tion it was hoped that vessels might be freed from dry-rot by raising 

 the temperature sufficiently. The trials were made in winter in the 

 "Queen Charlotte," the air in the lower part of the ship being raised 

 as high as 55" cent, or 130" F. But the general result did not an- 

 swer expectations ; for although the fungi were destroyed in the low- 

 er part of the vessel, it was found that their growth was rather fa- 

 vored in places at a certain elevation above the kelson. The warm 

 air, in fact, as it rose through the timbers became robbed in its course, 

 and deposited the greater portion of the moisture wliich it had taken 

 up at a lower level. Above the orlop deck, consequently, there was 

 just about the temperature and the quantity of moisture most favora- 

 ble to the development of the fungi. The evil was therefore ohly 

 transplanted, not destroyed. It was now proposed to heat the 

 "'tween decks" at the same time as the hold, making use of due 

 ventilation ; but this method of p^-oceeding has not been put into prac- 

 tice. 



The extreme slowness of the growth of trees stands in strong con- 

 trast with the rapidity of their decay when they are reduced to the 

 shape of timber and employed in constructions of almost every kind. 

 In countries well advanced in civilization, every description of in- 

 dustry tends to consume timber, at the same time that an increas- 

 ing population is every day contracting the extent of forest land, 

 and diminishing the number of trees grown. In some countries, in- 

 deed, it is certain that the production of wood for all purposes, firing, 

 &c., &c., is no longer in relation with its consumption. Tlie price 

 of the article, necessarily high, is therefore tending continually to 

 rise ; and it is not surprising that various measures have been sug- 

 gested and essayed of giving this perishable material greater dura- 

 bility. 



The well-known great durability of certain trees, the teak, ebony, 

 lignum-vitae, &c , naturally led to the conclusion that the fatty or 

 resinous matters which they contain have the property of preserving 

 the W'Ood against the greater number of the ordinary causes of de- 

 cay ; and unctuous and resinous matters appear in fact to have been 

 the means most anciently employed to preserve wood from the air, 

 from moisture, and from \he attacks of insects. But it is scarcely 

 necessary, at the present time, to say that these varnishes only ac- 

 complish the object proposed in their application in a very imperfect 

 vi'ay ; paint and varnishes crack, rub, or scale off with the slightest 



• Dupin, Ann. de Chimie et de Physique, t. xvii. p. 291, 'ie s^rie. 



