FURNACE, 
trivance, after any procefs i is finifhed, the fire would have to 
burn itfelf out, and it would be ok ae troubleiuime 
to clean the furnace when it is choaked 
“he height of the fire-place muft be rated to ‘the purpofe 
ra 
The chimney of an air-furnace fhould Le as wide as the fum 
of all the interitices through which the air enters the fire, al- 
lowing nothing for friétion ; but as this is very confiderable, 
at leaft that ought to be double, fo that the chimney fhould 
never be lefs than half that of the furnace. 
The height of the chimney isthe next confideration. 
the prefent ftate of our knowledge we have no exaét rule 
or the height = chimneys of furnaces. Indeed it will de- 
circumftances, that it would be difficult to 
In 
ul 
eloc 
It is equally certain that the ace wall foe much hipeoer ee 
if the chimney be rough in the infide, but more particu- 
larly when it is crooked, or when the air is interrupted by 
having to move in any other direCtion than that of a per- 
pendicular 
When ore, the chimney confifts of an upright prifm 
or eylinder, having its interior furface as fmooth as poflible, it 
muft act to the greateft eae e poffible. 
f the chimney be ma brick, thofe fides of the 
db 
ai 
pered fire clay, that the interior furface may be free from 
cavities and other inequalit 
If the chimney confilts oe iron lined with clay, it fhould 
confilt of lengths of about two feet each. After each of | 
pieces are lined and well dried, but not hard baked, the 
fide fhould be fcraped or rubbed, to give them gre = 
y this means the height of the chimney may 
be increafed to reac ae whee the ordinary height; fince 
the above pieces or lengths may be fitted together and fepa~ 
rated ieee the ee alg gsi vn maxi imum of height 
afily aicertaimed by nae 
oe very imp nt circ anes ought to be at- 
tended to inthe conttruction of ‘chimneys : ihe ir which 
is heated in pafling arte a fire ody etain its heat, if 
poffible, till it clears the t the ema Although this 
Sa be effeCtually accomplithed, it may be effected as far 
s the non-conducting power of the materials of the chimney 
will = te 
Common bricks are very bad conduétors, and confeqr ient- 
ly not olla iadeoied for chimneys. But fome fire-bricksof loofe 
a lad are itill better coup as to nein ig heat. 
‘rounded witha fecond chimney, leaving a cavity between the 
two about the breadth of a brick. This cavity fhould be 
coak, or, what is be etter, powdered 
eated air would retain its original tempera- 
that the height is very foon limited, ‘and beyond au peint 
becomesanevil. It has been recommende db lice to 
make the chimney of a doul tube, and hi} — ‘the cavie 
ty w with powdered ‘charcoal. his means, however, the 
internal tube would become fo hot as to be eafily acted upon 
b 
foon be deftroyed. the y ween th tubes 
were to be filled with a foft compcfition of $ 0 
ime, clay and, making the cavity between the tubes 
about half the width of the inner tube, a j tube 
furnace itfelf, being lined to a proportionate thicknefs with 
the above compofition, would make a portable air-furnace 
capable of producing the greateft degrecs of heat. 
In thofe air-furnaces, where the fire-place is required to 
be ea rom the chimney and open at the top, fuch as 
Plate ll. fig. 3, the iney . required to be connected 
with the Gree lee an h called a flue. This 
flue muit always Pa one as an iypediment to the 
it of a furnace, and ought never to be ufed but w ae 
the eae of as chi nes - om | the ele is sae 
ly ne nt will 
cept that air of a furnace thould afcend as een 
cularly as poflible ; hence a horizontal flue ought in all cafes 
to be avoided, and it will be equally evident that this evil 
will be ftill greater when the air has to defcend, as in the 
furnace Plate II. 
A fU1i) LUC 
aright one, as in Plate I. fig. 1. 
eon advanced relative rf ae width of the 
the eae degree letlen 
the draught of the furnace. Hence ae flue fhould be the 
width ae the chimney as near as poffible. 
Although in ftri€tnefs all furnaces are air-furnacss, yet, as, 
we have above faid, they are ufually diftinguifhed into thofe 
where the air is forced through the fire by bellows, and thefe 
where the air enters by what is called the ia of the 
chimney. 
d ted either fr ir conftruction, 
or he scene ufes to which they are ee as will be 
feen inthe courfe of this article. Generally Coun the fur- 
naces ufed in chemical operations, and for melting and refin- 
ing metals, are of the latter kind - air-furnace ; and we fhall 
now pr ees to hws the parts and particular ufes, 
ae calculated to produce great 
RNA 
degrees o of ie — acai) adapted for a melting furnace 
of the fixed kind, and pofleffing all the advantages” to be 
given to it, is ee in Plate I. fig. 13 a@ 1s the ath- 
pit of the fieaaces 4 the grate; ¢ the fire-place 5 d the cover, 
which confifts on an iron fame alled up with fire brick. 
The cover flides fideways to open the furnace; g¢ is in place 
of the flue of the commen pa aeeds aci but here is made a nl 
