Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/966

 LAB

LAC-

the body of the furnace with its middle grate is fet upon the foot, it anfwers all the purpofes of a fhop-furnaee ufed by the apothecaries for decoction, infpiffation, ex- traction, and the like purpofes, where a naked fire only is required, and certain diililUtions and fublimations may alfo be performed conveniently by it.

It may in this ftate alio be conveniently made to ferve the purpofes of a balneum maria, an afli heat, a fand heat, or a Hill ftronrjer one for digeftion and fublimation, by only letting on it in tins ftate a vcflel of water, or one filled with aihes, land, or iron filings ; and thus feveral operations requiring the fame kind of 'heat may be carried on at the fame time. If inftead of a common pan or veffel to hold water, fand, &c. the ring or third part of the furnace, be fet on fur- ' niflied with its fet of pots, the whole is then a furnace fitted for that fort of diilillation called diilillation in capella vacua, where the retorts are contained in the cavity of the pots, and locked down therein without any vifible medium between. By this means many operations may be perform- ed in the diilillation and ieparation of bodies, that could not be worked upon to fo much advantage by any other method. Particularly the rectification of the ftrongeft acid fpirits, is very eafily and conveniently performed this way at very little expence.

If an iron pan be placed in the room of the ring juft men- tioned, the inftrument is then a calcining furnace, where ores of metals may be roaftcd, and lead, antimony, and the like bodies may be conveniently reduced to afhes. If the loweft grate be ufed inftead of the middle one, then ci- thera cold frill, or, as it is generally called, a hot one may be put into the body, and worked in the common manner with its head and refrigeratory. T'hus all the cordial waters may be made fpirits, may be rectified, and the effential oils diftilled by the fame means, as well as by the common fixed frills. The laft part or cover of the furnace, may fometimes be applied to the ring, fometimes only to the body of the fur- nace without the ring. The inftrument in this cafe be- comes a proper reverberatory furnace, and is ufeful for ce- mentation, cupellation, and the cflaying of ores ; and for di- 11 illing with a fire of fuppreffion, that is, where the fire is placed above as well as below the fubject, and the veffel that contains it.

A furnace of this nature has numerous advantages, not only ■over all the chemical furnaces in common ufe, but even over thofe of the mod celebrated ftructure and contrivance, de- fcribed by authors on particular occafions, not excepting thofe of Glauber and Vigani. Thofe nicely contrived furnaces are generally adapted to fome few particular purpofes, and yet this eafy kind anfwers in experiment thofe very purpofes better ; and at the fame time is of general ufe on all the other oc- cafions of chemifhy. Experience has fhewn, that it is better for the various ufes of Glauber's philofophical furnaces, than thofe very furnaces themfelves, though made for thefe very purpofes ; and for the higher operations as they are called of metallurgical chemiftry. For example, to ob- tain a pure fpirit of fait in plenty, Glauber orders the fait to be thrown upon the fire, and has contrivances to catch the rifing vapour ; but this is a tedious way, and turns to very little account in practice, nor is the matter much improved by quenching the coals in a brine of fea fait, and afterwards burning them for their fume ; but all that can be expected from thefe aukward contrivances, may be had commodioufly from the furnace here defcribed, where the fire being ani- mated by bellows, caufes the fire to burn more free, and the fuel to yield the fpirit it was impregnated with much more quickly and eafily, than in the furnace con- trived by that author for the purpofe, while the fuel is fup- plied by the door without any diiturbance to the operation. Sbaiv's Eff. on a Portable Laboratory.

There are many other curious philofophical experiments, which can be no way fo well done as with this kind of fur- nace, and many fcarcc at all without it. It is excellently fitted alfo for enamelling, making of partes, flaining of glafs, and making the artificial gems. And befide thefe and a number of other curious ufes ; it is extremely well fitted for all the common purpofes of fires. Any arttzan who requires fire in whatever manner in his bufinefs, may contrive to apply it in this manner as he will ; the offices of a common ftone in a kitchen, may alfo be very well fupplied by it, and the warming a room or vault, is as well done by it as by any of the common contrivances of froves, ovens, and other things, made purpofely for that ufe. The outer cafe of the furnace is to be made of good plate iron of a confiderable thicknefs, formed in feparate pieces of the figures expreffed in the plate, and its fize may be fuch as the operator chufes ; obferving only a due proportion in its feveral parts. The inner fides of all the parts muft be lined at lead an inch thick with a proper luting, which muft be carefully laid on and gently dried, the cracks which happen in the drying, being filled up with more of the fame luting. Windfor loam alone may be ufed to this purpofe, but the author himfelf recommends the following mixture. Take a buihel of Windfor loam, four quarts of brickduft, two quarts of powdered green glafs, two quarts of iron

filings, four handfuls of cow-hair, and eight handfuls of horfe-dung, thefe are all to be beat together, and a fuffict- ent quantity of bullocks blood added, to make the whole into a fiifF and uniform pafte, which is to be carefully fpread over every part of the furnace that the fire can touch.

LABOUR, in the fea language, is ufed when a fhip rolls and toffes much.

LABRAX, in zoology, a name given by fome to the lupus or fea wolf, called in Englifh the Baffe. WiUughbfs Hill. Pif. p. 272. See the article Basse.

LABRUS, in ichthyology, the name of a genus of fillies, the characters of which are thefe. They are of the acan- thopterygious tribe. The branchioftege membrane on each fide contains fix flender and flat bones, when trie fifh is full grown ; but in the young ones, five only can be count- ed. The teeth are large, and are placed in the jaws, and on three bones in the fauces, the upper ones hard and two in number, the lower one fingle, the palate and tongue are fmooth. There are thick and flefhy lips covering the teeth. The membrane of the back fin, contains in its fore part double rays anting from each bafe of thefe two, the one is prickly, the other foft and inoffenfive. The colour is generally beautiful and in moft of the fpecies elegantly variegated. The tail is generally undivided ; the fcales are large, foft and fmooth j and there are no appendices to the pylorus, j^r/erf/ Gen. Pifc. 27. The fpecies of this genus enumerated by Artedi are thefe. 1. The labrus with the fnout turning upwards, and with the tail circular at the end. This is the tardus vulgaris, and tinea marina, or fea tench of authors, and is called by our people in Cornwall, the wrafTe or old wife fiih. 2. The green labrus with a blue line on each fide. 3. The black labrus called by authors the tnerula. 4. The elegantly va- riegated labrus with the pectoral fins rounded at the ends. This is the pavo of Salvian. 5. The oblong green labrus with gold coloured irifes. 6. The blue and yellow labrus with very large fore teeth. 7. The four toothed green la- brus with a forked tail. 8. The fmall variegated labrus with two large teeth in the upper jaw. 9. The labrus with the lower jaw longeft with a forked tail, and variegated with tranfverfe black lines. 10. The labrus variegated with pur- ple, blue, yellow, green, and black. This is called by fome authors the fear us nanus.

The word labrus is truly Roman, and is ufed in the fame fenfe by Ovid and others, being probably derived from the word labra, lips ; this fifh having remarkable thick and pro- minent lips.

LABRUSCA, in botany, a name ufed by the old authors for black bryony. Ger. Emac. Ind. 2.

LABUYO, in natural hiftory, a name given by the inhabi- tants of the Philippine iflands, to a bird very common amono- them, and called by us the Urogallus. See Urogallus.

LABYRINTH (Cycl.) — Labyrinth, in gardening, isapartof the ground fo planted and difpofed, as to render it difficult when any one is in it to find the way out, and in the attempting to get out, there are to be as many ffops and difappointments laid in the way as poflible ; the center alfo is to be made difficult to be found. There arc two general ways of making them ; the firfl is with fingle hedges, and this is what has been molt practifed in England ; and this may be befl where there is, but a fmall fpot of ground allowed for the making them, but where there is room enough, the double hedges are greatly the moft eligible, and thefe are beft of all when there is a wood-work between them. The walks in laby- rinths fhould be gravelled, and fhould by no means be made too narrow. Thefe are to be fet with iron beams, and the pahfadoes ought to be twelve or fifteen feet high. Laby- rinths are only proper for large gardens, and the finell in the world is faid to be that of Verfailles. Miller's Gard. Diet,

LAC, mli. See Milk.

Lac Lun<z {Cycl.) — Dr. Plot gives this fofnl as a mark of good lime ftone ; but it has been obferved, that two quarries in Ireland where lac lunte was found, were of building ftone, but would not burn into lime. Phil. Tranf. 1^477. Sect. 9, See Agaric, Cycl. and Suppl.

LACCA, Gum Lace. The method of obtaining the fine red laque ufed by painters from this fubftance, is by the follow- ing fimple procefs. Boil the flick lace in water, filtre the de- coction, and evaporate the clear liquor to a drynefs over a gentle fire. The occafion of this eafy feparation is, that the beautiful red colour here feparated, adheres only nightly to the outfides of the flicks, broke off of the trees along with thegumlacc, and readily communicates itfelf to boiling water. Some of this flicking matter alfo adhering to the gum itfelf, it is proper to boil the whole together, for the gum does not at all prejudice the colour, nor dilTolve in boiling water. So that after this operation, the gum is as fit for making feal- ing wax as before ; and for all otherufes which do not require its colour. Shawls Lect. p. 178.

A tincture of gum lace may be thus prepared. Take two ounces qf gum lace, reduce it to a fine powder ; and make it into a fliff pafte with oil of tartar per deliquium j fet this in an open glafs to dry by a gentle heat, then re- move it to the open air, that it may relent and grow foft, then dry it again, and repeat this two or three times, at the 2 end