18 



Preservation of Timber. 



Vol. Xll. 



timber has been known from the most re' 

 mote antiquity; he believes that he can even 

 recognise dry-rot in the sore called house- 

 leprosy, mentioned in the 14th chapter of 

 Leviticus, A ship attacked by dry-rot, be- 

 comes in a very short space of time unfit for 

 sea. The Foudroyant, of 80 guns, is often 

 quoted as an instance of its destructive pow- 

 ers : launched in 1798, she had to be taken 

 into dock and almost rebuilt so soon as 1802. 



The fungi which induce dry-rot have been 

 studied by Sowerby. Mr. Knowles signal- 

 izes two species in particular; one of which 

 he describes under the name of Xyloslroma 

 giganleum, the other under that of Boletus 

 lacrymans. The Xylostroma does not ex- 

 tend beyond the part where it is developed ; 

 but the Boletus, on the contrary, is propa- 

 gated with frightful rapidity, and disorgan- 

 izes deeply and to a great distance around 

 the texture of the wood where it once ap- 

 pears. These fungi are generally found on 

 board ship, between the planking and the 

 ribs, in damp situations, and where the air 

 is scarcely, if ever, changed. 



The temperature most favourable 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 this piece 

 of information 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 answer expecta- 

 tions; for although the fungi were destroyed 

 in the lower part of the vessel, it was found 

 that their growth was rather favoured in 

 places at a certain elevation above the kel 

 Bon, The warm air, in fact, as it rose 

 through the timbers became robbed in its 

 course, and deposited the greater portion of 

 the moisture which it had taken up at a 

 lower level. Above the orlop deck, conse- 

 quently, there was just about the tempera- 

 ture and the quantity of moisture most fa- 

 vourable to the development of the fungi 

 The evil was therefore only 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 proceeding has not been put into 

 practice. 



The extreme slowness of the growth of 

 trees, stands in strong contrast with the ra- 

 pidity of their decay when they are reduced 

 to the shape of timber and employed in con 

 Btructions of almost every kind. In coun 

 tries well advanced in civilization, every 



description of industry tends to consume 

 timber, at the same time that an increasing 

 population is every day contracting the ex- 

 tent of forest land, and diminishing the num- 

 ber of trees grown. In some countries, in- 

 deed, it is certain that the production of 

 wood for all purposes, firing, «Slc., &c., is no 

 onger in relation with its consumption. The 

 price of the article, necessarily high, is there- 

 fore tending continually to rise; and it is not 

 surprising that various measures have been 

 suggested and essayed of giving this perish- 

 able material greater durability. 



The well-known great durability of cer- 

 tain trees, the teak, ebony, lignum-vitag, &c., 

 naturally led to the conclusion that the fatty 

 or resinous matters which they contain have 

 the property of preserving the wood against 

 the greater number of the ordinary causes 

 of decay; and unctuous and resinous mat- 

 ters appear in fact to have been the means 

 most anciently employed to preserve wood 

 from the air, from moisture, and from the 

 attacks of insects. But it is scarcely neces- 

 sary, at the present time, to say that these 

 varnishes only accomplish the object pro- 

 posed in their application in a very imper- 

 fect way; paint and varnishes crack, rub, or 

 scale off with the slightest friction ; nor do 

 they always remove the causes of internal ' 

 decay; on the contrary, by preventing more 

 complete dryness, they sometimes even pro- 

 voke or favour them, when applied to tender, 

 that is, imperfectly seasoned wood. Merely 

 laid on the surface, indeed, it has always 

 been seen that varnishes of any kind were 

 but indifferent protectors; that a really good 

 preserver ought to penetrate the substance 

 of the wood, and unite with the tissue itself. 

 But herein lay the whole difliculty; how was 

 the needful penetration to be effected? for 

 the number of chemical substances, from 

 which good effects might reasonably be an- 

 ticipated, is pretty considerable, — unless, in- 

 deed, we find ourselves prevented from using 

 them by the consideration of the price; for 

 it is imperative that any preservative pro- 

 posed be extremely cheap. 



For a long time the only process for ef- 

 fecting the penetration of timber by sub- 

 stances proposed for its preservation was to 

 macerate them for a longer or shorter time 

 in a solution of the substance. But this 

 means was found as tardy of accomplishment 

 as it was ordinarily imperfectly effected ; to 

 have got to the heart of logs of large scant- 

 ling, years would have been required. Any 

 delay, however, in such circumstances, is of 

 itself a cause of enhanced price of the arti- 

 cle. By and by a variety of processes, the 

 element in one being pressure, in another 

 exhaustion, were put in practice, and very 



