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rations in this turn act*; therefore the chemical reader must giveattention to what follows. If the door of the ash-hole, c, i- cjuitoopen; uud the sliders of the upper door, J, drawn toward-, eachother, so as to touch one another in tin: middle of the door; and it,besides, the enter, </, and the funnel adapted to its tube, r, areupon the top, fl, of the furnace; the lire will he then ill the highestdegree possible ; though, in the mean time, it is hardly ever neces-sary to pot the funnel on, except in a very eold season: but if,alter having disposed the furnace in the manner just described, redburning coals arc put into the open tipper door,y| of it, the lireis still more increased thereby: however, this is very seldom ornever necessary. When the upper door is shut with oulv thatslider that has a narrow oblong hole in it, in. then the heat be-comes a little less; hut it diminishes still more when shut with theother slider, that lias it in a semiciicular hole, », which is largerthan that of the first slider: nav, the heat again is less when thetunnel put at the top of the cover is taken away, f inally, the doorot the ash-hole being either in part or totally shut, the heat is stilldiminished ; because the draught of air so necessary to excite thefire is thereby hindered: but if, besides all these, the upper doorbe opened w ide, then the cold air rushing into the niulilc, coolsthe bodies put under it, that are to be changed, to a degree incom-patible with any operation, as it will entirely hinder the boiling ofthe lead. If, during the operation, the lire begins to decay, or togrow unequal, it is a sign that there are places void of coals betweentlie sides of the furnace and those of the inutile; therefore, in thisease, the coals must lie stirred on every side with an iron rod, in-troduced through tiie upper hole, /i, ol the furnace, tliatthcv ninetall together, and thus act equally and in a proper maimer. 1 low-ever, the effect does not. always uniformly answer, even when theapparatus has been made with all the exactness nirntionud. Thecause of this difference lias most commonly its origin in the variousdi spositions of the air: lor as every lire is more excited, in propor-tion as tin* air, more condensed, and more quickly agitated, strikesthe fuel more violently (which the effect of the bellows plainlyshews;) it theme appears, that in warm and wet weather, whenthe atmosphere is light, the lire must he less efficacious in furnaces,that likewise, when several furnaces, situated near each other, areburning at the same time, the lire is in part suffocated, becausetlie circum-anibient air is thereby rendered more rare and lighter.The same effeet is produced by the sun, especially in summer,"hen it shines upon the place where the furnace is situated. Theatmosphere, on the contrary, being heavier in cold dry weather,excites a very great tire, l'he heat of the fire acts the strongerupon the bodies to be changed, as the mutllc put in the furnace is'ess; as it has more and larger segments cut out of it; as its sidesai 'e thinner ; in short, as there are more vessels placed in the hinderPart of it; or the contrary. In this rase, when many of the con-ditions requisite lor the exciting of tire are wanting, the artificer,"dth all his skill, will hardly be able to excite the fire to a sulii-t'ient degree, to perforin operations well,'in common assay-ovens,e ven though he uses bellows, and puts coals into the upper door ofihe furnace. For this reason, the grate ought to he put almostthree indies below the muffle, lest the air, riishingthrough the ash-mile, should cool the bottom of the nmttle, which happens in coni-"'on assav-ovens; and again, that the smaller coals, almostalreadyconsumed, and the ashes, may more easily tall through the inter-stices of the grate, and the larger coals still lit to keep up the lireretained. Lastly, the above-mentioned funnel is added, thatthe blowing of the tire being, by means ot it, increased as much asPossible, this may at last hi: carried to tlie requisite degree ; forthe lire may always be diminished at pleasure, but cannot alwayshe increased, without the assistance of a proper apparatus.
Furnace, Mr. Wai't’s Steam-engine. ’llie steam-enginetbrnace is described in the specification of the patent obtained forthe invention by Mr. Watt of Birmingham . llis “ improvedjnethods of constructing furnaces, or lire-places, consist in causingt'*e smoke or llame of the fresh luel, in its way to the lines or chim-lu ‘y, to pass, together with a current ot tresh air, through, oyer, oramong, fuel which has already ceased to smoke, or which is con-yerted into coaks, charcoal, or cinders, and w hicli E intensely hot;
y which means tlie smoke and grosser parts ot the (lame, byconi'iHq. int 0 c ] osc contact with, or by being brought iie.u unto, thea, d intensely* hot fuel, and being mixed yvith the current of tresh° r bnburnt air, are consumed, or converted into heat, or mlo pure•tame free from smoke.” This is done, “ limb by stopping up
every avenue or passage to the chimney or Hues, except such asare kit in the interdict s of the fuel, by placing the tresh fuel above,or nearer to the external air, than that which is already convertedinto coaks or charcoal; and by constructing the tire-places in’sucha manner that the llame, and t|ie air which animates the tire, mustpass downwards, or laterally, or horizontally, through tin* burningluel, and pass from the lower part, or internal end or side, ot thetire-place, to the tines or chiimicv. I n some eases, alter the (lamehas passed through the burning fuel, it is made to pass through avery hot funnel, line, or oven, before it comes to the bottom otthe boiler, or to the part of the furnace where it is proposed tomelt metals or perforin other offices, by which means the smoke isstill more effectually consumed. In other eases, the llame is car-ried immediately from the fire-place into the space under a boiler,or into the bed of a melting or other furnace. Fig. 2, I’late1.X.XYLI. shews a section of a tire-engine boiler, and its furnace,which has been chosen for an example of the application of thisnew method to the heating and evaporating of water. A A is theboiler, which may lie made of any form suitable to its use. BB isa line, surrounding the boiler as usual. C is the uptake, or pas-sage from the space under the boiler to the (lues. I) D is a funnelor flue for the llame to come from the (ire-place to the boiler. E Eis a place to contain theadies; and F isa door to take them out at,which must he kept continually shut during the time of working.(1 it is the tire-place: the fresh fuel is put in at G, and graduallycomes down as the fuel below eomsumes. The. part at 11 is veryhot, being tilled w ith the coaks or coals which have ceased tosmoke. I is an opening or openings, to admit fresh air, and regu-late the tire. K is a door into the space under the boiler; andwhich being opened, admits air, and stops the draught of the chim-ney when the operation is wanted to cease. Fig . .3 is a section ofthe same tire-place in the other direction ; in which M M is thehack of the tire-place; E the brick arch on which the fuel lies;anil E the ash-hole. Fig. 4 is ail outside view of the sune fire-place, shewing the air-holes I 1, and the ash-hole door E; and lig.■>, is a plan of the same, yvith part of the boiler seated ; taken in tlmline Z of tig. The dotted lines represent the tines, and thedarts point out the direction of the llame. The lire is lirst kindledupon the brick arch E, fig. 2; and when well-lighted, more fuelis gradually added until it is filled up to G. Care is taken to leaveproper interstices for the air to pass, either among the fuel, or be-tween the luel and the front-wall X ; and as much air is admittedat 1 1, as can be done without causing the smoke to ascend per-pendicularly, which it will always do it too much air is admitted at1 I. The dimensions of this tire-place are shewn by the scale, andare properly adjured for burning about 841b. of coals in an hour;where greater or less quantities are required to be burnt, tlie fur-nace must be enlarged or diminished; or, if much greater, morefurnaces than one must be employed. Fig . ti. represents this newlire-place as applied to a furnace for melting iron and other metals,and constructed without the funnel, or perpendicular tine 1) intig. 2. ’Hie same letters refer to the same parts in all these figures.Mr Watt also constructs these new fire-places so that the. part G 11lies sloping, or horizontal, and otherwise varies the figure or form,and proportions; but in all eases the principle is the same; thefresh or raw fuel being placed next the external air, and so that thesmoke or llame passes over or through the eoaked or.charred partof the fuel. He also occasionally covers the opening G, andcauses the air to enter only, or principally, at I I. In partici:' weases, he places the fresh luel on a grate as usual, as at A tig. /,and beyond that grate, or near at tlu: place where the llamepasses into the Hues or chimneys, lie places another smaller grateB, on which lie maintains a tire of charcoal, coaks, or coals, whichhave been previously burnt until they have ceased to smoke ; which,by giving intense beat and admitting some tresh air, consumes thesmoke ot the lirst lire. Lastly, he states his new invention to con-sist only in the method of consuming the smoke, and increasingthe heat, by causing the smoke and dame of the fresh fuel to passthrough very hot funnels or pipes, or among, through or near, fuel,which is intensely hot, and which lias ceased to smoke; and bymixing it yyith fresh air when in these circumstances; and inthe form and nature of the fire-places above mentioned : the boilersand oilier parts of the furnaces being such as are in common use.These new invented tire-places are also applicable to furnaces foralmost every other purpose.
Furnace, Mr. W. Thompson's Steam-Engine . In vol, iv. of
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