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tuel infhinieil to a great degree ; at the same time that the heal,being rellected trom every part of' the fimuue excepting that nar-row passage where the smoke goes up, becomes very intense. Alargo-quantity of fuel may be put in at once, which will consumeslowly, afml thus require but little attention in comparison withthose furnaces w here no such precaution i- used. The sliding-platemay be made of cast iron in those furnaces where no great heat isexcited ; but in others tire-clay would In- more convenient. Thecontrivance, however, isscaicc applicable to those furnaces w heregreat quantities of metal are to be melted ; and accordingly thewaste of fuel there is immen-e. It is computed, that the ironworks of Catron in Stirlingshire consume annually as manv coals■as would be sufficient for a city containing 700,opt) inhabitants.The fourth intention, viz. that of regulating the heat, is accom-plished by allowing only a certain quantity of air to pass throughthe fuel. For this purpose, says Dr. Iliads, it is necessary to havethe command of the furnace below ; the pat ts above being frequentlytilled with small quantities of soot. The best method of managingthis is to shut up the door of the ash-hole perfectly dose, and tohave a Sft of round holes hearing a certain proportion to oneanother; and their areas being as 1, 2, i, S, Id, See. Seven oreight of these ought to be made in the door of the ash-pit, whic.liwill give a sufficient command over the tire. W hen the lire is tobe increased to the utmost, all the passages both above and below.ire to he thrown open, and the height of the vent augmented ,which, by increasing tbe height of the column of rnrelied air, in-creases also the motion of that through the fuel, and of consequencealso the heat of the furnace. Macquer recommends another tubeapplied to the a-h-pit, widest at the end farthest from the furnace,and tapering gradually towards it. The intention of this is toaugment the current and velocity of the air, bv it- being made to})a-s from a w ider into a narrower vent; but though this is no doubttrue, the air will not ultimately move with greater velocity thruif the tube w ere not there. It can only he useful therefore incases where the furnace is placed in a small room, and the tubeit-elf has a communication with the external air.

Furnace, Cupelling, or Furnace, Essaying, described inCramer’s Art of Essaying. See Hale EXXVII. tig. 1. Make withiron plates a hollow quadrangular prism, 11 inches broad and nineinches high, aa bb, ending at top in a hollow quadrangular pyra-mid, bb cc, seven inches high, terminating in an aperture at topseven inches square. This prism must be closed at bottom withanother iron plate, which serves as a basis or bottom to it, tut. 2.Near the bottotn make a door, c, three inches high, and liveinches broad, that leads to the ash-hole. 3. Above this door, andat the height of six inches from the basis, make another door,./', ofthe figure of a segment of a circle, four inches broad at its basis, and3£ inches high in the middle. 4. Then fasten three iron plateson'the fore-part of this furnace. Let the first of them, gg, 11inches long, and half an inch high, he fastened, so that its loweredge shall rest against the bottom of the furnace, with three erfour rivets: and in such a manner, that there may be between tin-upper edge of the said plate and the side of the furnace a grooveSo wide, as that the sliders of the lower door, kk, may be pul intoit, and freely move backwards and forwards therein ; these mustbe made of a thicker iron plate. The second iron plate, lih, 11incites long, three inches high, and perfectly parallel to the fore-going plate, must be fastened in tbe space between the two doors,in such maimer, that both the upper and the lower edges of it mayform a hollow groove with the side of the furnace. One of thesegrooves, which is turned downwards, serves to receive tln-'ipperedge of the sliders that shut the low er door, No. 2. The other,that turns upwards, is to receive the inferior edges of the sliders ofthe small door above, No. 3. The third plate, ii, w hich is liketiie first, inu-t he riveted close above the upper door, in suchmanner that it may form a groove turning downwards, ami con-tiguous to the upper edge ol the upper door, No. 3. 5. To shut

both doors, No. 2 and 3, adapt to each of them two sliders marieof iron plates, that they may move within the above-mentionedgrooves, kk, ii. licit the two sliders belonging to the upper door,No. 3, must have each a hole near the top; that is, one a smallhole one-fifth part of an inch broad, and one inch and a half long,;,i ; and the otlier a semicircular aperture, one inch high and twoinches broad, n. I ct, besides, each slider have a handle, that theys.tay be laid hold of when they are to be removed, 6. Moreover,

let live round hole.--, one inch broad, lie bored in the furnace ; twoof which must be made in the fore-part of the furnace, no, twoothers in the hack part; all at the height ol live inches from thebottom, but 3£ inches distant from each side of the furnace; and,finally, a filth hole, p, at the height of one inch above the upperedge of the upper door, 1 7. lit short, let the inside of the iur-

nace be armed with iron hook-, jutting out half an inch, and aboutthree incite:, distant from each other, to Ittslen the lute with whichthe furnace is to be covered over witliin. 8. Let then an iron,moveable, hollow, quadrangular py ramid, q, three inches high, beadapted to the upper aperture, tl, of the turn.we, at the basis seveninches broad, ending upwards in a hollow tube, r, three inches indiameter, two inches high, almost cylindrical, though somewhatconvergent at top. This prominent tube serves to support a fun-nel or line, which is almost cylindrical, hollow, made oi iron plates,ami two feet high ; and which, when a very strong tire is required,is put perpendicularly upon the shorter tube, in such a manner,that it enters close into it, one ami a half or two inches deep, andmay again he taken off at pleasure, when there is no need of sostrung a lire. This p\ ramidal cover, q, must have two handles,ss, adapted to it, that it may he laid hold of, and thus be taken offor put on again: and that this, being put on the aperture, d, of thefurnace, may not be easily thrown down, let an iron plate In;riveted to the right and left upper edge of the furnace, cc, andhe turned tlown towards the inside, so as to make a furrow open bo-,lore and behind, into which the lateral edges of the cover maventer and be fastened, and at pleasure be moved backwards antiforwards, whenever it must be put on or moved. !>. Let a squareledge, made of a thick iron plate, be fastened at the top of theupper edge of the lower door, c, to support the grate and the lute ;but it must be math-of tw o pieces, that it may In- easily introducedinto the cavity of the furnace. This assav-oveit must afterwardsl he covered over on the inside with lute, as follows.:—That thelire may he better confined, and that the iron may not he destroyedby growing red hot, the whole inside of the furnace must' hecovered over with lute, one linger or one linger and a half thick.The lute lit for this is described under Chemistry, lint beforeusing this lute, first put within the furnace small iron bars, equalin length to the diameter of the oven, quadrangular, prismutical,half an inch thick, having their extremities supported by a squareiron ledge, and three-fourths of an inch di-tanl from each other;and fasten them so, that their fiat sides may be oblique with regardto the; transverse section of the furnace, anti that llte two oppositeangles may look one upwards and the other downwards: the liarsmust not belaid ilat, but edgewise; by which situation the ashes ofthe fuel are prevented from being detained too long between theinterstices of the iron liars, and from making an obstruction thatwould oppose the free draught of the air. The furnace being thencovered over with lute, anil dried up by a gentle heat, is at last titfor docimastical operations, and especially for such as must he per-formed in the assay-oven. When an operation is to lie made inthis furnace, let through the Cornflower holes above described, no,before and behind, and directly opposite to each other, two ironbars one inch thick, and long enough that their extremities onevery side may jut a little out of the holes. These serve to sup-port'the mullle and its bottom. Tlu-n introduce the inutile throughthe upper aperture of the furnace, </, ami place it upon the abovedescribed iron bars, in such a manner that the open fore-side of itmav he contiguous to the inward border of the upper door, f.The fuel is introduced through the top of the furnace, d; thecover of which, q, on this account, must lie moveable, and notvery heavy. The best fuel is charcoal made of the hardest wood,especially ol beech, broken into small pieces of the bigness of aninch, wherewith the mullle must he covered over some incheshigh. Large pieces would not answer, because they could not fallthrough the narrow interstices, between the sides of the inutile andthose of the furnace, and of course could not sufficiently surroundthe circumlercnce ol tin* mufilc; so that there would he on everyside places void of fuel, and the lire would he either not strongenough or unequal, lint it, on the contrary, coals loo small wereUsed, then a great pari would fall immediately through the inter-stices of tiie grate into the ash-hole; the smallest parts of themwould turn loo soon intoashes, and by increasing tin- heap of ashes,obstruct the free draught of the air, which is here very requisite.A perfect management of the tire is necessary in performing ope-rations