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lecture room, and fitted for a great variety ofpurpofes. The upper part (which is not heregiven) is a rounded dome terminated by a per-pendicular iron flue.

It is introduced here merely to (hew the ex-periment of procuring hydrogen, by paffing fleamthrough a heated iron tube, as will be furtherdeferibed.

The furnace itfelf is a neat iron cafe linedwith fire-brick, and furnifhed with openings fora variety of purpofes.

PI. it. Figs. 86, 87, 88, and 89, reprefent aview and lection of a Portable Blafl Furnace,of fimple confirmation and little expence, whichwas fuggefted to the writer of this article fromone of Dr. Lewis’s, and deferibed at large inthe Philofophical Magazine, vol. xvii. a and bFig. 86 and 87. are portions of two commonblack lead pots of the fame diameter, theloweft of which is inverted, and (lands upon afmooth ftone, i, which is fupported by an irontrivet about a foot from the ground. The pot,a, receives the blafl of the double bellows ashere reprefented, through the hole h. The upperpart of this pot (or what would be the bottomwhen ufed as a crucible) being confiderablythick, will allow of a final! hollow to be fcoopedout of its fubftance, through which a wide holemuft be drilled to the cavity below.* By thismeans the blafl riles in a perpendicular directionand equally into the pot b , inftead of fpendingitfelf chiefly on the fide oppofite to the bellows,which would Be the cafe if the lower pot wasnot inverted, b is the pot which contains thefuel and the crucible or other matter to beheated. It is prepared in the following manner :drill a hole through the bottom with a gimlet asexadtly in the center as poffible, and enlarge itto about the fize of a (hilling. This hole is notfor the paflage of air, but to receive a crucibleHand, c, and Fig. 89 in the form of a Hopper,which keeps it Heady. Then Hrike a circle withcompaffes on the fmoothed bottom of the pot b,round the center hole, and bore through it uponthe circle at equal difiances, four or fix large gim-let holes, in a flanting diredtion, fo that if length-ened they would all meet nearly in the middleof the pot. No extreme nicety however is ne-ceffary in the precife direction of thefe holes,but the general intention of the oblique directiongiven them is to concentrate the force of thefire upon the center where the crucible d isplaced. Thefe two pots are all that is effentialto the furnace, and when lighted charcoal orcinders are put in and the bellows worked, the

* This fcooped cavity is however by mi hake reprefented 1

blafl rifing from the lower pot divides itfelfequally through the four or fix blaft-hoies in thebottom of the upper pot, and very fpeedily raifesa very intenfe heat. No luting whatever is re-quired here, the pots are fimpiy ground fmoothwith water on any flat ftone, and when ufed aremerely placed in the manner here given. Asthey are only the lower parts of .he large cru-cibles, the chemift may often find what willanfwer his purpole from the crucibles that areflawed or otherwife damaged. ihe Hoppersare made very ealily out of the loft Windforbrick. The bellov.s are fixed to a heavy ftool,and their handle is lengthened to work eafier,but of courfe any other form of double-blaftbellows will anfwer as well. To protect the-eyes from the dazzling heat which is producedin the pot b, it is often advifeable to cover itwith the pot e, Fig. 88, which has a woodenhandle g, fixed into it, and an opening for theflame and fmoke j\ which may be turned awayfrom the operator.

The black-lead pots are the eafieft cut by anold thin tabie kniie deeply hacked or jagged.

PI. IX Fig. 90 and 91, is a plate and fedtionof the Reverberatory Furnace, ufed for roaftingand fmelting ores both in the large way, and,on a fmaller fcale, for experimental purpofes.In this furnace the fubftance to be heated is notin adtual contadt with the fuel, but is Hrewedon a feparate floor or hearth, placed betweenthe fuel and the chimney, and is heated bythe flame in its paflage through. The flooron which the ore is fpread is called the labora-tory, d, and is fometimes horizontal, but gene-rally on an inclined plane, Hoped from the fire-place to allow the metal when reduced andliquefied to colledt and fettle at the lower end.The floor of the laboratory is formed with fandmixed with a little clay, and well beaten intoa fmooth compadt lurfate, and this is fome-times further coated with a mixture of charcoalpowder and clay. The roof is vaulted, andlow, fo as to allow but a narrow fpace for thepaflage of the flame, but the precife curve to begiven it is of little confequence, provided it isas flat as is confiftent with due ftrength, inorder to contradt the fpace between it and thefloor. The loweft part of the floor of the labo-ratory e, is called the crucible, and is generallyleft uncovered when the furnace is charged, asit is intended to receive the melted metal, which,when a fulficient quantity is colledted, is drawnoff from time to time through the channel^which is kept plugged up with clay till thejeh deeper than the real thicknefs of the pot w ould allow-