( 529 ) FUR
molt of the five perpendicular chimnies. Thisis the only chimney the draught of which isnever difturbed by the reception of any otherflue. At the lower part of the afli-pit of thisfurnace is feen a fquare hole in PI. X. whichopens from behind, and is the termination ofthe brick canal, a. PI. XI. which runs beneaththe floor of the laboratory, and communicateswith the outer air at b b. 'I'he ufe of this isto afford an ample fupply of air to the furnacefrom without (and confequently cooler) whichmuch increafes its force; and alfo, more parti-cularly, to allow the operator when Handingbefore the furnace, to put a board to interceptthe draught from the room to the. afli-pit,which in winter is very troublefome from thechill which the cold air gives to the legs inr-ulhing by. The grate of this, as of all theother furnaces, is riot fixed in the brick work,but is fupported merely by two iron bars a littlebelow the bottom of the body of the furnace,upon which it Aides in with eafe, and whenworn out or damaged, may be entirely drawnaway by the opening of the afli-pit, and anotherput in its place. This is particularly ufeful inthe melting furnace, as the intenfe heat is veryapt to damage and deftroy the bars of the grate.
I is a furnace for Naked Dijtillation. Onefide of it is cut down the middle to admit thebeak of an earthen retort, and pieces of thickbrick properly hollowed are introduced overand under the beak to fill up the cavity. Aperpendicular feftion of this furnace is given illPI. XII. Fig. which is introduced chieflyas giving the proportions between the body ofthe furnace, the alh-pit, and the flues, which,wiil anfwer for all.
K is a Digejihig Sand Bath, or fquare flat-bottomed iron pot, fet over a fmall furnace andfilled with fand. On it evaporating pans and'any other glafs veflel may be conveniently placed,to receive a fafe and gradual heat. The flame inthis inftance does not immediately proceed from .the fuel to the chimney, but is caufed to pafsagain round the iron pan, as in the outline planK. PI. XI. The pan is alfo fhewn in PI. XII.Ug- 93-
L is a common Sand Bath Furnace. Infteadof the fand bath a boiler may be fet over thefire when wanted.
M is a flat furface level with the top of allthe furnaces, on which any thing may be fetaway, or which will very conveniently fupporta portable furnace, and for this latter purpofea fide opening is made in the upright chimney,.to which it is contiguous, which opens into it,
VOL. II.
about the fame height as the flue D, on theoppofite fide.
Near the top of the room are two fquaredoors reprefented on each fide of O, PI. X.which communicate with ea,ch of the uprightchimnies next the centre one, and may be openedoccafionally to let out any noxious fumes, or toinfert the pipe of a portable furnace.
'1 be whole of this range of furnaces, as al-ready mentioned, is fronted with a folid fereen,or kind of awning of mafonry, which fpringsfrom the cieiing contiguous with the wall of theroom, and comes down in a Hoping directionfo far forwards as to projefit over the front ofthe furnaces, and as low down as will admit aperlon to Hand conveniently under the lowermargin. This fereen, NN, PI. X. is reprefentedas broken away both in front of the upper partof the flue D, and alfo of the upper part of theface of the five perpendicular chimnies, fo as tolhew the doors on each iide of O, .which other-wife would be hid. All fmoke and noxiousfumes therefore, which efcape from this part ofthe laboratory, are caught by the fereen, andrifing to the top may readily be carried off byopening one of thefe doors.
PI. XII. Fig. 92. veprefents the iron door ofthe ftill and fand-bath furnaces, which is double,the inner one being connected to the outer by ahinge, which caufes it to open and ihut at thefame time. The lower door alfo is lomewhatuncommon in conftrudtion, having a circularopening round which revolves an iron plate,partly perforated, fo as to a£t as a regifter.
Fig. 95, 96, 97, 98, are Fire Tongs of variousconftruttion.
GAS. [Apparatus for fat mating fluids with.)
It is often required in chemical ope-rations toimpregnate water or other liquids with one orother of the gaffes, and a great many- ingeniouscontrivances have been invented for the purpofe.To effect it compleatly, the liquid mult be fofituated as to have a quantity of the gas confinedwith it in a clofe veflel, or conftantly pallingthrough it, and the abforption is always muchaflifted by artificial preflure or agitation, or bothtogether.
Some gaffes, fuch as carbonic acid ga's orfulpliuretted hydrogen, are fo foluble in waterthat this fluid may be made to take up a con Ado-rable quantity fimply by being fhaken togetherin a clofe phial, and therefore for extempora-neous purpofes, where the walte of a little ofthe gas is not an object, nothing more is necef-fary than to fill a common phial quite full ofdiftilled water, to invert it in a fmall tea-cup
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