WOOD. 



fineft pitch ; melt it over a flow fire of coal, and add to it, 

 when melted, 30 lbs. of rolled brimftone grofsly bruifed, and 

 boil the whole till 30 lbs. are \vafted. The matter thus 

 prepared mud be kept in caflis in a cry place ; and when it 

 is to be ufed, melt icolbs. of it, and add gradually 35 lbs. 

 of brick-duft or marble-duft, fifted and well heated. The 

 compofition, when ufed, muft be very hot, and the boards 

 dry. 



An ingenious fliip-builder obferv;?, that turpentine and 

 brimftone form the beft compofition he has mot with, and 

 comes home from a voyage with leaft damage. 



Eaft India {hips are firft flieathed, and that fheathing is 

 filled with fmall broad-headed nails, which is a fafe and 

 effeflual defence from the worms, and foon becomes a con- 

 tinued cake of ruft, and not liable to be damaged by cables, 

 or common accidents. See Pay and Ships. 



The following, fays Dr. Hales, is an approved method 

 of preferving the boards and timber of out-door work : 

 viz. melt 6 lbs. of pitch, and add, by fifting, i lb. of dried 

 brown Spanifh, or whiting, and a quart of linfeed oil. 

 Hales's Ventilators, part i. p. 164. partii. p. 2S9, &c. 



Dr. Lewis obferves, that though tar has been ufed for 

 preferving wood, and alfo for coating common tile?, in imi- 

 tation of the black glazed tiles, which are fold at a much 

 higher price, both tar and pitch are of themfelves too foft 

 for thcfe intentions, being liable to be melted off by the 

 fummer heat : and, tlierefore, different powdery fubftances, 

 as afties, ochres, and other mineral pigments, have been 

 mixed with them. 



In the Swedifh Tranfaftions for 1740 and 1742, two 

 compofitions are recommended, which are faid to be firm, 

 durable, and glofly. One is prepared by melting the tar 

 over a gentle fire, fo as to make it fluid, but not to boil, 

 and ftirring in as much coal-duft or powdered charcoal as 

 will render it thick : the other is prepared by mixing the 

 melted tar with a fufBcient quantity of lamp-black. Coat- 

 ings formed of thefe mixtures are, however, liable to be 

 confiderably foftened by the heat of the fun. The mixture 

 of powdered pit-coal and melted tar, made of fuch a con- 

 fidence as to be freely fpread while warm with a brulh, is 

 lefs liable to foften than either of the other two. The tar 

 obtained from coal, in the method lately difcovered by the 

 earl of Dundonald, appears from various teftimonies of thofe 

 who have tried it to be much better calculated to preferve 

 .wood and iron, as well on land as in water, than vegetable 

 tar. It has alfo this peculiar advantage, that it will not ad- 

 mit or harbour thofe worms that are fo injurious to the bot- 

 toms of (hips at fea. See an Account of the Quahties and 

 Ufes of Coal and Coal-varnifli, &c. by the Earl of Dun- 

 donald, 8vo. 1785. 



Mr. Parkes recommends, for the prefervation of wood, 

 the tar which is obtained from the pyroligneous acid. See 

 Tar. 



Dr. Lewis obferves, that the coating or painting of wood 

 does not in all cafes contribute to its prefervation : unlefs 

 the wood be very thoroughly dry, efpecially thofe kinds of 

 wood whofe juices are not oily or refinous, the painting, by 

 confining the watery fap, haftens the corruption. Com. 

 Phil. Techn. p. 363, &c. On this fubjeift, fee Timber. 



Some of the Weft India trees afford a fort of timber 

 which, if it would anfwer in point of fize, would have 

 great advantages over any of the European wood, in Ihip- 

 building for the merchant-fervice, no worm ever touching 

 this timber. The acajou, or tree which produces the cafhew- 

 nut, is of this kind ; and there is a tree of Jamaica, known 

 by the name of the •white-iuood, which has exaftly the fame 



property, and fo have many other of their trees. Phil. 

 Tranf. N° 36. 



To feafon wood expediUoufly for fea-fervice, it has been 

 ufual to bake it in ovens. 



The art of moulding wood is mentioned by Mr. Boyle as 

 a defideratum in the art of carving. He fays he had been 

 credibly informed of its having been praftifed at the 

 Hague ; and fufpeds that it might have been performed by 

 fome menftruum that foftens the wood, and afterwards 

 allows it to harden again, in the manner that tortoift-ftiellis 

 moulded. Or, perhaps, by reducing the wood into a pow- 

 der, and then uniting it into a mafs with ftrong but thin 

 glue. And he adds, that having mixed faw-dull with a 

 fine glue made of ifinglafs, flightly ftraining out what was 

 faperfluous through a piece of linen, the remainder, formed 

 into a ball and dried, became fo hard as to rebound when 

 thrown againft the floor. Works abr. vol. i. p. 130. See 

 Glue. 



The people who work much in wood, and that about 

 fmall works, find a very furprifing difference in it, accord- 

 ing to the different feafons at which the tree was cut down, 

 and that not regularly the fame in regard to all fpecies, but 

 diff^erent in regard to each. The button-mould makers find 

 that the wood of the pear-tree, cut in fummer, works 

 tougheft ; holly, on the contrary, works tougheft when cut 

 in winter ; box is mcllowelt when it has been cut in fummer, 

 but hardell when cut about Eafter ; hawthorn works mel- 

 low when cut about Oftober, and the fervice is always 

 tough if cut in fummer. Merret's Notes on Neri, p. 263. 



It is a very well-known quahty of metals to be longer 

 and larger when hot, and fhorter and fmaller when cold ; a 

 thoufand experiments prove this, and the books of experi- 

 mental philofopliy have fufficiently expatiated upon it ; on 

 the contrary, it is found to be the property of wood, that 

 it is longeft in cold weather and (horteft in hot ; this change 

 is owing to the remains of the fap yet in the wood, which 

 being condenfed by cold, is enlarged in its furface, as all 

 liquors are, when frozen into ice ; and (brinks into a lefs 

 fpace or bulk again, when liquated by heat. 



It follows from this that all wood mult change its 

 furface more or lefs, according as it contains more or lefs 

 fap, and this may be made a teft of great ufe for the determin- 

 ing what kinds of wood have moft, and what leaft fap. 

 This would be a very valuable piece of knowledge, fince 

 there are many ufes for which that fort of wood mull always 

 ferve beft, which has the fmalleft quantity of fap remaining 

 in it. See Hygroscope. 



Thus, in the great article of preferving flour, no barrels 

 are at prefent ufed but thofe of feafoned dry oak ; the 

 whole advantage of this wood is, that it contains lefs fap 

 than others ; for the fap in the wood makes the flour damp, 

 and it then becomes rancid, and breeds worms. ( See Meal. ) 

 So that if any other wood can by this means be found out 

 to contain lefs fap, when dried in the common way, than 

 oak does, it will be fo much the better for this purpoie ; or, 

 if a cheaper wood (hould be found only to contam as little 

 fap as the oak, it would do as well, and the price of oak 

 would be faved in thefe veffels. 



A proper way of trying when the fap was fufficiently ex- 

 haled out of trees, might alfo be found by this experiment, 

 and much benefit would accrue from it ; for our (hips, when 

 made of timber not fufficiently dried, prove injurious to the 

 health of people on board ; and it has been remarked, both 

 by the French and ourfelves, that many more men in general 

 die in the firft voyage of a new (hip than in the fame tim« in 

 an old one ; and indeed the firft fix months are ufually ob- 

 4 F 3 fcrved 



