W O A

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ral, or grouped in bundles: tlieir furface isgenerally rough. The longitudinal fra£ture ofWitherite is between radiated and lamellar, andhas - a fliining lultre 5 the crofs fradlure is fine-grained uneven, and glimmering with a greafyluftre. Its fragments are wedge-fhaped. Themalfive variety often prelents fcapiform andwcdge-fliaped diftindt concretions. It is tranf-lucent, palling to femi-tranfparent. Its hard-nefs is about, equal to that of fiuor : it is brittleand eafily frangible. Sp. gr. 4.3.

Before the blow-pipe on charcoal it firftcrackles a little, and then melts into a whitilhenamel. Strong nitric acid has little or noeffedt upon it, but when very diluted, this men-ftruum diiTolves it readily with a copious efter-vefcence.

When pure it confifts of 78 Barytes

22 Carbonic acid

too

A fpeeimen from Anglezark afforded Klap-roth 98.246 Carbonated barytes• 1.703 Carbonated ftrontian0.043 Alumine with a little iron0.008 Carbonated copper

100.

Witherite is an a drive poifon to animals.

It was firft difcovered by Dr. Withering atAnglezark, in the north of Lancafhire: it hasfince been found in the Schlangenberg in Si-beria , and alfo near Neuberg in Upper Stiria.

It occurs at Anglezark in veins in flate,accompanied by heavy fpar, galena, blende, andcalamine.

WO AD. This valuable dyeing drug (theufe of which however has been a good dealfuperfeded by indigo) gives a full bodied andvery faft blue to wool, but not very bright,fo that it is always mixed with indigo at pre-fent. The mode of preparing the woad-vats ismentioned under the article Dyeing, p. 373.

The mode of cultivating and preparing thewoad in Thuringia is thus given by Wedelius.*Woad requires a very rich deep foil well ma-nured and tilled. The feed is put in the groundin February. In June the le'ves turn yellow-ilh, and the plant begins to flower, which isthe time for gathering the firft crop, which isdbne by mowing down the whole plant clofe tothe ground. It is then rinced in water andfpread out in the fun, and when dry enough it

1 Ephem, Nat. Cur.

is ground in mills to a fine pafle, which is fur-ther dried by ventilation. This pafte is thenmade up into cakes, which are heaped uponeach other in a covered room, whereby theyloon ferment, heat, and exhale a moft penetratingnaufeous ammoniacal odour which ipreads to agreat diftance : this fermentation is kept up fora fuflicient time, oecafionally watering thecakes when the heat is too great, till the wholefalls into a coarfe powder, in which fiate thewoad is again made up into balls, and is readyfor ufe.

The root of the plant throws out a freflt cropof young fhoots which are fit to cut in aboutfix weeks after the firft harveft, and aremanaged in the fame way, and fometimes, ifthe feafon continues dry and warm, a third, cropmay be got in the fame year, hut this is muchinferior to the two firft.

The fermentation of the woad plant is pecu-liarly violent, and attended with an uncom-monly naufeous fmell, and the produdrion of alarge quantity of ammonia. Much practicalfkill is required in the management of it, forif fuffered to heat too much the whole isconverted to a black effete mafs, and the bluecolour, for which the plant is cultivated, istotally deftvoyed. The fermentation is bothmoderated and prolonged by the great hardnefsof the cakes, which cannot eafily be broken uptill they crumble to pieces of themfelves by theirfpontaneous adrion.

When woad is diftilled per fe, it gives out aconfiderable quantity of ammonia along withthe other principles common to vegetable mat-ter. Nitric acid has but little adrion on it, inwhich it differs remarkably from indigo. Thecolour however is totally deftroyed. Accordingto the imperfedt experiments of Dijonval 1 ’, ful-phuric acid adts on woad with great vehemence,caufing much tumefadrion and difengagementof gas, and a folution is at laft effedted, which,diluted with water, is a faint undefiuable green,without any thing of the fine blue which dif-tinguiihes the fulphat of indigo. When woadis diffufed in water and kept for a time it fpee-dily putrefies, and gives a more penetrating andfetid fmell than moft vegetable or even animalmatter under fimilar circumftances.WOLFRAM. See Tungsten .

WOOD. Bois, F. Holz, G.

The wood of vegetables confifts obvioufly ofa denfe congeries of fibres abundantly impreg-nated with a variety of the natural juices ofthe plant, fuch as mucilage, refin, colouringfc Journ. Phyf. Tom. xi.

3 Q-.3