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Thofe intermedim fubAances ia which they plunge

thEir velfe!s are called

~alhJ .

They are either fluid or

folid :_The fluid baths are water, or its vapours. When

tbe diAilling ¡'elfe! is fet in water, the bath is called

D./"tnm

mar;«,

or the water·b"h; and the greatetl ue ·

gree of heat of which it is fufceptible is that of boiling wa–

ter. When the velfd is expofed ooly to the vapours which

exhale from water, this forms the vapour-bath: the

heat of which is

ne'~r1y

the fame with that of the

ha/tU-

11m mar;.r_

Thefe baths are ufefu l for di(lilling

~lfential

oils, ardent fpirits, fweel.fcenled waters; in a word, all

{ueh fub(laoces as cannOt bear a gremr hm without

prejudice either 10 their odour, or 10 fome of their 0-

Iher qualiues.

Baths may alfo be made of any other Buids, fueh as

oils, mercury,

&c.

wbich are capable of receiving and

eommunicating much more hM; but they are very fel–

dom ufed. When a more

eonfider~ble

decree.of

heat is

required, a bath is prtpared of any folid matter reduced

10 afine powder, [ueh as fand, afhes, filings of iron,

&c.

Tbe heat of thefe b,ltl!s may be pufhed fa far as to make

the bottom of the velfd become famtly red . By piun–

ging a thermommr ioto the bath, by the fide of the vef–

{el,

it is eafy to obferve the precife degree of heat ap–

plicd to the fubAloee on which you are working.

necelfary

th~t

the thermommrs employed on this ocea–

lion be conflruéted on good prinCipies, and fo eontrived

as tO be eafily campared lVith thofe of the

mo(l

ee!ebrmd

Dltural pbilofophers. Thofe of the illuArious Reaumur

are moll ured and be(l koolVn, ro that it 1V0uld not be

amirs to give them the preference. Wheo a greater heat

is required than any of thofe baths ean give, the veflels

mu(l be fet immediately on live·coals, or in a flaming

~re:

tbis is called working with a naked fire; and in

Ihis care it is much mnre difficult tban in the other tO

determine the degrm of heat.

There are reveral WJys of applying a naked fi,e. When

the heal or Bame is refleéted upoo the upper par! of the

velfel which is expored to the fire, this is calJed a rever–

berated heat.

melting heat is that which is (Irong e–

DQugh to fure

mo(l

bodies. A forging heat is Ihat of

fi,e IVhich is forcibly excited by the coollant bla(l of a

pair of bellows, or more. .

There is alfo another ron of fire which rems very

cammodioufiy for many oper,tions, becaufe it does nor

require to be fed or frequently mended : T his is , fford–

by aIamp with one or morewicks, and may be called

.Iamp.heat.

is rcarce em employed

bU[

tO heat

baths, in operations

~hich

require a gentle and long

COll–

ti.ued warmth: if it hathany fauh, it is that of growing

gradually honer.

AII there different ways of applying fi,e require fur–

nam or different cODllruélions: We fhall therefore de–

fcribe fucb as are of principal and moA necelfary ure.

Furnaces mu(l be divided into differeot pans or lIories,

each of whieh has its panicular ure and Dame.

The lower part of the furnace defigned for recciving

the afhes, and giving palfage to the air, is called the afh

hole

Thr.

,fh·hole is terminated aboye by a grm, the

afe of wlllch is

ruppon the coals and wood. which are

be burat chereon;

This

part is caUed the 6r.e-place.

.The

~re.place

is in like manDer lennioated above by fe–

vera l tron bm, which lie quite a-crofs it from right te>

left, in lines parallel to each other: The ure of thefe

bars is 10 fuflai n the velfels in which the operations are

to be performcd. The fpace above there

bar,

to the top

of the furnace is the upper

(Iory,

~nd

may be called the

hbomory of the furnace. Lafily, rome furnam are

quite comed above, by meanj of a kind of vaulted roof

called the dome.

. Furnaces have moreover feveral aperrures : one of

thef~

.s at the afh-hole, which gives pafi'age to the air, and

through whicb the afhes that fati Ihrough the grale are

raked out; this apenllre is ealled IheaOl-hole door: aa.

olher is at th« fire-place, through which the fire is fup–

plied with fuel, as occafion requires

Ihis is called the

moulh or door of the fire.place, or the 1I0ke-bole: there

is a Ihird in the upper

(Iory,

through which the neck of

Ihe vcfi'cl palfes; and a founh in the dome, for cmying

off Ihe fuliginofilies or combuUible mattm, which

calJ.

ed the cbimney.

To conelude, there are reveral other openings

ín

tfie

feveral pans of the furnace. the ufe whereof is 10 admil

Ihe air ioto tbofe places, and alfo, as they can be eafily

fhut, to incite or Oacken the aétivityof the fire, and ro tB

regulate it; which has procured Ihem the title of

re–

g jltrJ.

AII the other openings of the furnace fhould be

made t1 lbut very clofe, the better to allirl in governing

the fir(; by whieh meaos tbey likelVife

che o/lice of

regi(lers.

In arder 10 our forming a ju(l and generar idea of

lhe

con(lruétion of rurnaces, and or the dirpofition of the fe–

veral apenures in them, with a .iew 10 increafe or dillli.

oifh the aélivity of the fire, il will be proper to lay dowo.

as OIIr ground-work, cerraio principIes of natural philo–

fophy, lhe truth of

which.is

demoD(lcated byexperi,nce.

And fi rA, e.ery body knows that combullible maners

will not burn or conrume unlers they have a free commu–

nieatian wilh the air; iofomuch that if they be deprived

thereof, even when burning

moll

rapidly, they wih be

extinguifhed at once: that confequentlyeombunion is

grmly promOled by the frequent aceellion of frefh air

and that a llream of air, dir.eéted fo as to pars with im–

petuolity tbrough burning fuel, excues Ibe fire to tbe

greate(\- pofi'tble aélivity.

Secondly,

is cemio that Ihe air which touches or

comes nm ignited bodies- is heated, ratefied; and reo–

dered lighler Ihan the air about it

that is, further

di.

llant from the

centre.of

heal : and conrcquently that thi.

air fo heated and become lighter is necelfarily determined

thereby to arcend aod mount aloft, in order to make

room fOI tl13l which is lefs heated and not fo light,

which by il! weight and eia(licil)' tends tO oeoupy the

place quimd by the "ther. Another confequence hereor

is,. that if fire be kindled in

place inclorcd every where

but aboye and below,

curren! of air will be formed in

tha! place,

running.in

adlroélion from the bonom to the

10p ; ro that if any ligbt bodies be applied tO Ihe open–

ing below, they will be carried"p tOIVards the rire; but,

on the contrary, if they be held

the opening above,

Ihey will be impelled by a force whichwill drive them up

acd carry tbem awal from.lbe 6re.

'nirdly,