No. I. 



Preservation of Timber. 



17 



Preservation of Timber. 



Timber is sometimes seasoined by previous 

 total immersion in water. It has been held 

 that this process favoured the thorough dry- 

 ing, by dissolving out certain deliquescent 

 salts which are found in the sap, and pre- 

 vented after-shrinking. However this may 

 be, it is quite certain that in warm countries 

 especially, it is advantageous to sink fresh- 

 cut timber in water, with a view to prevent 

 it from splitting, apparently in consequence 

 of drying too quickly. The old Venetian 

 sank for a season in the sea, the oak timber 

 which was destined for the construction of 

 their galleys. Elm and beech, in particular, 

 are said to improve greatly by the process 

 of submersion in salt water, and to dry after 

 wards perfectly by simple exposure to the 

 air. 



Duhamel advises strongly, that in ship- 

 building all timber from trees already on the 

 decline should be rigorously rejected; and 

 this the rather, that the most careful exami- 

 nation often fails at first to perceive any a 

 teration in the heart-wood of such trees, 

 although it never fails to show itself by and 

 by at a sufficient interval after the felling. 

 This is undoubtedly a precept which it would 

 be well to bear constantly in mind; but tim- 

 ber does not always carry within itself the 

 germs of its speedy decay; and that which 

 has been seasoned with the most scrupulous 

 care, and was originally of the best quality, 

 does not escape the rot when it is placed un 

 der unfavourable circumstances, any more 

 than that which was of inferior worth and 

 less carefully treated. 



Wood appears fo perish or decay through 

 three principal and appreciable causes, which 

 all require similar conditions to come into 

 play, viz., stagnant air, sufficient warmth, 

 and moisture. Like the generality of or- 

 ganic substances, wood, when moistened in 

 contact with the oxygen of the air, and un- 

 der the influence of a sufficiently high tem- 

 perature, undergoes decomposition of a kind 

 which has been compared to a slow combus- 

 tion, upon which we shall find occasion to 

 say more by and by. It is with a view to 

 escape this kind of decay as much as possi- 

 ble that timber is never, or ought never, to 

 be employed in the construction of ships and 

 buildings until it has been thoroughly sea- 

 soned. 



Besides this first cause of decay, vi'hich 

 may be prevented in a great measure by 

 using certain precautions, wood has still two 

 redoubtable enemies, insects and certain 

 plants of the family of the cryptogamia?. In 

 one case, the wood perisiies because it is fed 

 upon by certain animals which live and grow 



at its expense ; in the other it decays be- 

 cause it serves as the soil to one crop of 

 fungus after another which luxuriate on its 

 surface, while their roots penetrate deeply 

 into its interior. There is nothing in either 

 accident which excites astonishment, now 

 that we know the intimate constitution of 

 wood. We know, in fact, that among the 

 number of soluble principles which impreg- 

 nate the woody tissue, there is an azotized 

 matter analogous in its composition to those 

 that exist so abundantly in all the ordinary 

 esculent vegetables. There is, therefore, in 

 wood ample nourishment for the insects 

 which we find living on it; and if I state 

 now — reserving to myself the opportunity 

 of demonstrating the fact — that all organic 

 azotized matter becomes an active manure 

 by decaying, we shall understand how it 

 happens that plants, which have the power 

 of living in dark, warm, and damp places, 

 wax and multiply in the joistings of houses, 

 and in the ribs and planks of ships, causing 

 a dry rot, which separates the integral layers 

 of the wood, and reduces the strongest beams 

 to dust. 



The rapidity with which wood is, in some 

 circumstances, devoured by insects, is almost 

 incredible. Some years ago the thermites, or 

 white ants, spread in such strength through 

 the docks and arsenals of Rochelle and Ro- 

 chefort, that in a very short space of time 

 serious damage was done. A learned ento- 

 mologist, M. Audouin, commissioned by the 

 ministry to take information on the subject, 

 reported that the ravages committed by these 

 insects had been very considerable. But it 

 is principally in warmer climates, where the 

 temperature is steady throughout the year, 

 and where there is no winter, that the ther- 

 mites occasion the most alarming injury. 

 At Popayan, for example, it is difficult to 

 meet in a building, even of recent construc- 

 tion, with a piece of wood which is not 

 gnawed and ant-eaten. The hardest and 

 most compact woods do not always resist the 

 attacks of these insects, which, further, do 

 not spare every kind of odorous wood, cedar 

 for instance. In such countries it is altoge- 

 ther impossible to preserve books and papers. 

 I remember, in connection with this matter, 

 that having received instructions to examine 

 the archives of Anserma, one of the oldest 

 towns in Popayan, in 1830, I found nothing 

 but books illegible and in pieces; neverthe- 

 less, the date of the documents, which it 

 was my business to consult, could not have 

 been older than the year 1600. 



The dry rot, which results from the de- 

 velopment and growth of cryptogamic plants 

 upon wood, is the curse of navies. Mr. 

 Knowles is of opinion that this disease of 



