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extra&, eflential oil, fugar, &c. all of whichmay be obtained from one or other kind ofwood, by applying thofe menftrua which dif-folve thefe fubftances in their natural ftate.But after the action of thefe menftrua has beenexhaufted, after wood has been long boiled inwater, alcohol, and weak acids, a fubftanceremains, which is not in any degree a£ted onby thefe, which burns in the open air withoutmelting, but with much flame and a pene-trating acid vapour, and leaves at laft only afmalhquantity of white earthy afh, from whicha fmall portion of alkali may be extracted.This fubftance is confidered as the pure woodyfibre, and has fome title to be confidered as adiftinft vegetable principle, as it has lome pro-perties peculiar to itfelf. The earth and alkali(or neutral falts, which, by ccmbuftion, furnifhthe alkali) muft however be.reckoned as foreignto the pure ligneous fibre, though they cannotbe extracted without entire diforganization ofthe wood.

It is not eafy to extract all the foluble partsof frefh wood, fuch as the refin and colouringmatter, without firft reducing it to very finedull, for M. Sennebier 1 found that even thethinneft {having of entire wood long refilledthe aflion of common menftrua. But afterbruifed wood has been long boiled alternatelyin water and alcohol, and again thoroughlydried, it then lofes fo much of its cohefionthat it may be reduced to very fine powder,from which a fubfequent application of thefame liquors wilj compleat the extradlion ofevery thing foluble.

The refidue, which is as pure woody fibre ascan be obtained, when heated ftrongly in aretort, without addition, yields a confiderablequantity of a red pungent acid liquor, whichhas long been confidered as a peculiar acid, andhas been called the pyroligneous , but later expe-riments render it probable that it is little elfethan the acetous holding fome empyreumatic oilin folution. Its general properties are defcribedunder the article Acetous Acid (Empyreumatic).But it is to be obferved that it is commonlyprocured by the Ample diftillation of wood un-prepared by any previous procefs, and of courfemay be mixed with a portion of all the otheringredients of wood which are volatile by fireand again condenfible in a liquid form •, nor dowe know of any experiments made in a fuffi-ciently large way, on the acid yielded by von which the action of water and alcoholprevioufly been exhaufted.

a Journ. Phj’f. Tom. xxzviu.

52 )

The pure ligneous fibre is. decompofed bybeing heated with ftrong nitric acid, and yieldsa very confiderable quantity of oxalic and malicacid. The caiiftic alkalies alfo foften, andfinally difiolve it.

The furface of wood is readily ftained by avariety of fubftances, and if thefe are allowedto remain in contaft with it they fink into thefubftance of the wood which often produces avery agreeable effetl in cabinet work, and fome-times gives to ordinary wood a very good re-fembiance of the more expenlive colouredwoods of foreign countries.

The following experiments to this purpofehave been made by Beckman. b Some maple woodwas firft fawed into thin flips about of an inchin thicknefs. One of thefe was immerfed in a fo-lution of dragon’s blood in oil of turpentine.After a confiderable time the wood had abforbedfo much of the refin as to fink in the liquor, andit was then of a fine mahogany colour, {hewingthe veins of the wood by a lighter {hade of red.Another flip of wood was dyed in the famemanner in a folution of gamboge in oil of tur-pentine, which gave a fine yellow, and by amixture of gamboge and dragon’s blood in dif-ferent proportions, a number of beautiful tintsmay be produced. Beech-wood was found totake the colour fooner, but it was lefs brilliant.A folution of thele refins in alcohol alfo an-fwered very well. With thefe kinusof fubftances,however, it is necefiary in order to produce agood colour, either to boil the wood in the li-quor, or at leaft to continue the digeftion fora confiderable time, fo that they can only beemployed to great advantage with fmall. pieces,fuch as are ufed for the finer kinds of inlayingor veneering, Hut many faline and metallicfolutions produce a more fpeedy effect inchanging the colour of wood, which may beapplied to a furface of any extent.

All the white woods are rendered muchwhiter by being foaked in a folution of alum.This is probably owing to a decompofition ofthe fait, and a depofition of its -earth within thepores of the wood in very fine divifion.

A deep black is given to wood in variousways. Oak and other woods that abound ingallic acid receive a black from the folutionsof iron, but thefe woods are comparativelyrare.

If concentrated fulphuric acid is fmearedover the furface of wood it blackens it veryfpeedily, and this colour fpreads deep within thewood in a few hours, its furface being at thek Nov, Com, Soc, Getting. Tqra. vii.