WOOD. 



is become rotten by age, when tlie pith, with numerous 

 adjoining layers of wood, have long fince been oblite- 

 rated. 



A tranfverfe feftion of the wood of a tree difplays 

 various veflels, and other parts, which microfcopic authors 

 take delight in exhibiting ; but, without a fcientific ex- 

 planation, little is to be learned from their plates, how- 

 ever beautiful to the eye. Siliceous petrifadlions, of oak- 

 wood efpecially, fine fpecimens of which are brought 

 from Hungary, (hew its vafcular ftrufture in the greatell 

 perfeftion. In the feftions to which we have juft al- 

 luded, the pith, with its highly cellular texture, makes a 

 confpicuous appearance in the centre. In the body of 

 the wood, the fap-veffels are generally the largeft and 

 mod numerous. Thefe, when young and tender, eafdy 

 difplay their fpiral coats, if pulled afunder longitudinally; 

 but are not found at all in the bark. Among them, in 

 the refinous trees like the fir, or any that abound with 

 fecreted fluids, as the fig. much larger vefTels are inter- 

 fpcrfed through the wood and bark, in which the pecu- 

 liar fecretions are lodged. But befides the determinate 

 and continued concentric layers of wood above-defcribed, 

 numerous thin plates are interfperfed, known to workmen, 

 efpecially in oak-wood, by the name of the Silver Grain. 

 (See that article.) Mr. Knight, who is there quoted, 

 further remarks, that if a board of Englifh oak be cut for 

 a floor, in fuch a direftion, that the lamina of the filver 

 grain lie parallel with the furface of the board, it is rarely 

 or never feen, when properly laid, to deviate from its true 

 horizontal pofition. But a board fawed, on the contrary, 

 acrofs the filver grain, " will, during many years, be inca- 

 pable of bearing changes of temperature, and of moillure, 

 without being warped ; nor will the itrength of numerous 

 nails be fufficient entirely to prevent the inconvenience 

 thence arlfing. That furface of a board of this kind which 

 grew neareft the centre of the tree, will always fhew a ten- 

 dency to become convex, and the oppofite one concave, if 

 placed in a fituation wherj both fides are equally expofed to 

 heat and moiilure." Knight, Phil. Tranf. for 1801, 34J. 

 This writer adds, that the fmall clefts in the furface of an 

 oak-tree, ft;ripped of its bark, and expofed to the fun and 

 air, are caufed by the plates of the filver grain having 

 parted from each other. They will long continue to open 

 and clofe again with the changes of the weather. In the 

 middle of a dry day they are open, but much lefs fo during 

 the night. After long expofure to the air and light, wood 

 lofes this property. Knight as above. 



A different degree of hardnefs, and in fome trees a re- 

 markable difference of colour, exills between a number of 

 the external concentric layers of the wood, and about as 

 many or more of thofe next the centre. Thefe latter are 

 called the heart of the timber ; the former the fap or 

 alburnum ; but thefe are vulgar appellations, and the latter 

 efpecially are improper. The trae aliurnum is the layer of new 

 unhardened wood of the prefent year, which alfo workmen 

 often term the fap. The Sap, properly fo called, is the 

 fluid from which all their fecretions, and even the wood 

 itfelf, are formed. (See that article.) Thofe who ufe 

 wood for mechanical purpofes are well aware of the above 

 difference between its different parts, however incorreft the 

 names by which they are diftinguillied. The fofter ex- 

 ternal layers have liale durability in coraparifin with the 

 heart. They retain more of the vital principle, and more 

 of the peculiar juices of the plant in a fluclaatmg condition, 

 liable to be afted upon by external or internal caufes, and 

 not yet united, in a fixed ftate, to the folid body of the old 



wood. This change, however, is not limited in any particu- 

 lar kind of tree to a determinate period in the age of each 

 layer of its wood, nor even to any determinate feries of the 

 concentric circles of any individual tree. It often extends 

 to a greater number of rings on one fide than on another. 

 The more vigour there is in a tree, or in any fide or portion 

 of its trunk, the fooner is the alburnum, to ufe its popular 

 denomination, made perfeft wood, or heart. 



The term wood, philofophically fpeaking, is not confined 

 to the fubflance of a tree. The central part of a root, dif- 

 tinguifhed from its bark, is the wood, and in many perennial 

 roots confifts, as we have already mentioned, of feveral dif- 

 tinft layers. In a carrot, the yellow part is the wood, en- 

 compafted by a thick reddifh bark. In a turnip, the woody 

 part is of ample dimenfions, while the bark is thin. 



A moft remarkable diflerence exifts between the folidity 

 of the viood in fome trees and in others. Some wood is fo 

 heavy as to fink in water ; fome is as light as cork, or even 

 lighter. In general, wood of different trees, of the fame 

 natural order, poffeffes fimilar properties and the fame de- 

 gree of value. But there is often, in the fame genus, a moft 

 remarkable difference between the fitnefs of the wood of 

 different fpecies, for particular purpofes. The oaks (fee 

 QuERCUs) abundantly exemplify this faft. The very hard 

 and ponderous timber of Q. Ilex, the live oak, however 

 lafl;ing in a dry fituation, is fo prone to deftruftion when 

 expofed to wet, as to be among the moft worthlefs in the 

 world ; its hardinefs and heavinefs only rendering it the lefs 

 fit for ufe, where it would be likely to endure. On the 

 other hand, many of this genus afford timber more or lefs 

 ufcfnl in every circumftance and fituation, among which our 

 Englifh Q. Robur Hands pre-eminent. See Timber. 



All kinds of wood are to be preferved from the worm, 

 and from many other occafions of decay, by oily fubftances, 

 particularly the effential oils of vegetables. Oil of fpike is 

 excellent, and oil of juniper, turpentine, or any other of 

 this kind, will ferve the purpofe ; thefe will preferve tables, 

 inftruments, &c. from being eaten to pieces by thefe ver- 

 min, and linfeed-oil will ferve in many cafes to the fame pur- 

 pofe ; probably nut-oil will do alfo, and this is a fweeter 

 oil, and a better varnifh for wood. 



The ingenious Dr. Hales, whofe attention was uniformly 

 direfted to fchemes of domeftic or national benefit, was in- 

 duced by the great damage done to fhipping by worms to 

 propofe various methods for preventing it. Oily, unftuous 

 materials, he apprehends, are not likely to penetrate deep 

 into oak, which has a watery fap ; but oil is known to pe- 

 netrate far into fir, ^nd to give it a very confiderable degree 

 of toughnefs. He therefore propofes to mix with oil ap- 

 plied to the fir-boards with which fhips are fheathcd fome 

 ingredient that is difagreeable to the worms ; and he appre- 

 hends that a fmall proportion of verdigrife ufed in the 

 operation of paying would be of great fervice : or if copper- 

 filings were. mixed with the paying, fea-water would turn 

 them into verdigrife. It might be ufeful to foak planks in 

 water ftrongly impregnated with verdigrife. 



Mr. Reid recommends the trial of the acid juice of tar, 

 prepared either vrith copperas or ochre, for preferving fhips 

 either from rotting or worms. 



In the Eaft Indies, it is faid, they have an effeftual way of 

 preventing worms from deftroying their fhips, by paying 

 them firft with a mixture of muftard, oil, and lime of fhells, 

 and hog's blood : they then fheath the fhip, and renew it 

 after fome years. 



The following receipt has been recommended by a perfon 

 who never knew it fail of fuccefs. Take loolbs. of the 



£iieil 



