FUR

FUR

( 526 )

22 inches high, 20 in its largeft diameter, and15 in the fhorteft, lined with five bricks forabout three fourths of its height from the top,which forms the body of the furnace, and thefirft elbow of the chimney, whilft the lowerpart, which isnot lined, forms a very fpacious afh-pit. Being very heavy it is put upon caftors, bywhich, with the afliftance of the ring handles onthe fide, it may be moved along a floor withoutdifficulty, a, a, is the body of the furnace,which is cylindrical, but a little oblique, thatthe flame of the fluel may heat the fand-bathfomewhat more equally than if it were a flraightcylinder. The breadth of this cylinder is 8^inches, and its height 15; the grate c, liesacrofs the bottom. This fire place has the fol-lowing fix openings above the grate. Thehigheii is the large opening at the top, which,when a fand-heat is employed, receives thefand-bath i, and Fig. 82, and when this is notwanted, is covered by a thick iron plate linedwith clay, Fig. 80, in the center of which is afmall hole fitted -with a Hopper, Fig. 81, throughwhich the Hate of the fire may be feen withoutfcorching the face. The next opening is theelbow of the chimney, f, which widens as' foonas it takes a perpendicular direct ion, and for•the firft few inches forms a part of the ironcafe of the whole furnace, and is lined withclay, after which it is elongated by a conicaliron chimney, Fig. 79. Even this fmall lengthof flue is fufficient to keep up a very confiderableheat when the fire is well fupplied with fuel,but to raife it to the intenfity requifite formelting call iron, it is neceflary to add feveralfeet of iron pipe of the fame diameter as the topof Fig. 79. if it is let under an open brick chim-ney, or elfe (which is often more convenient)to clofe the throat of the brick chimney with aniron plate, leaving only a round hole in themiddle, into which the upper part of the pipe,Fig. 79. clofely fits. In this cafe no furtherlength of iron flue is required to give a veryftrong draught through the furnace, capable ofraifing heat enough for almoft any purpofe ofthe chemift. Oppofite the chimney hole in thebody of the furnace, and a little below it, is theopening e, e, which ferves to introduce fuelwhen the upper opening is engaged by the fand-bath, and the heat of the latter may alfo beleffened at pleafure by leaving this hole open,which caufes a draught of cold air to rulh indireftly round the bottom of the fand-bath.The next openings are two fmall round holes,g> placed direftly oppofite each other at rightangles with the perpendicular of the chimney,

and ferving to introduce an earthen or iron tube,the ufe of which will be explained under thearticle Hydrogen (Apparatus for). Below tliefeis the fixth opening, d, d, cut of the properfhape to receive a muffle for which it is in-tended. The openings e , d, and g, are properlyfitted with very thick ftoppers, which are fur-ther covered with pieces of iron plate clofelyHiding in grooves, in the way reprefented inFig. 77. The alh-pit is merely the lower partof the iron cafe that inclofes the whole furnace,and is furnilhed with two doors, b, b, by whichthe draught of air may be regulated. Therings h,h (of which there are two correfpondingones on the other fide) are intended to fupportupright pieces of thick iron wire, which, with acrafs wire over the top of the furnace, will ferveto fufpend any veffel or other body over or inthe furnace, as may be required.

A great variety of operations, and on a tole-rably large fcale, may be performed in this ufe-ful furnace, which is very durable, and beingheavy and fubftantial, it is not liable to be da-maged by accidental blows, or eafily difplaced ;and it is befides extremely fafe in a room, pro-vided the chimney is clean. The iron cafefhould be now and then rubbed with black leadto prevent its rufting. This arrangement ofthe chimney allows very free accefs to the bodyof the furnace, and the thicknefs of the wallsprevents the operator from being at all moleftedby tlie intenfenefs of the heat. It is the leaftconvenient for naked diftillation from an earthenor iron retort, for though fuch a veffel mightbe fet on a retort ftand with its beak projectingthrough the opening d , neither the fize norfhape of this opening are well adapted for thispurpofe, and to give a ftrong heat, a ftopper ofloft brick with a deep flanting groove mult firftbe fitted in.

Fig. 83 and 84, of PI. VIII. are a view andfeel ion of a Muffle Furnace,for very intenfe heat ,employed by Pott, and afterwards by Darcet,in experiments on the habitudes of earths andftones in long continued and violent heat. Theconftrufflion of this furnace is Ample and obvi-ous ; a, a, is the body of the furnace, in formof an oblong coffer, bulging out in the middle.c is the grate Handing over the afh-hole f ; e isthe hole for the muffle; b, b , is the dome or up-per piece of the furnace, with a very large doord, through which the fuel is introduced. Thedraught is raifed by a long perpendicular chim-ney, Fig. 85.

PI. II. Fig. 41. is the lower part of a fmallPortable Chamber Furnace , often ufed in the