1000000030

lhe

ernri~fc;

Cet

il io , owltiog

C\l1'o~ce;

plll ,:0111 all

r\\',oo it, ami kt IItC", kiodlc r,r.ldllally. l(.,il""

11t~

fire

(" as 10 m,lke thc crucible ver)'

r~o

hoto Wheo yOIl ob–

fe,,", that the flaltlc halh acqUlred a purplc or hlt,<ilh–

glwl colollr, lIocover lhe (r\ll.lole, antl "ip iolO it ao

iron \ltre,

1\1

exa01l0e whelhrr or 00 Ihe CC1pper be in

fllfinn ,,.,d·:r Ihe charcII"1dua.

you lind it is, mu–

,Ierale Ihe force

lhe fire a lillle, and lel y01l1' crllcible

r"II.lill io Ihe fllrnace for a fcIV mioutes. Then take it

..111

aod lel it cool: yOIl will find yUllr copper of a gold

" ,Iollr, incrcafcd in weight a fOllnh, or pcrhaps a thinl

pal t, anJ yct very malleable.

The

IJtÍ! c.I"1IIi",,,.i,

is not lhe only Cub(lance with

wl,ich copper mal' be cOOl'erted ineo brafs, all other

OI CS containing zinc, lhe furnaee-c.l.lIl1ine· that fllblimcs

where fuch ores are \Volked, lutty, zinc io

fllb(l'l\e~,

01.1)'

be fllbaituted fur it, aod, likc il, will make "ely

nne br.lrs; but, in order lO [uc.:ceo, [undr)' l'recautions

are neeenary.

This procefs is a

Cort

of eemenlaliJn; for the calamine

doth not mele; onl)' Ihe zinc is convcrceJ inta npours,

and Ihen combines with the

corr.er

. On Ihis the [ucceCs

Ihe operation partl)' Jepends, as it is the means of the

copper's I'refen'ing its purit)' and maliedbility; becauCe

the otl'er metallic fubn anees that Ola)' be IInited with the

Oíe of zinc, or with tbe zinc ilCelf, not haviog the fame

vJlatility, eaonot be redueed tOvapours. lf you are ap–

prifcd that the calamine, or other ore of zinc ufed on

this oceafion, is contaminated \Vith a mixture of any o–

Iher metallic maner, you mun mingle luting eanh \Vilh

the eharcoal-duU and the malter containiog the zinc;

make il i"1O a niff pane \Vith water; of Ihis make a bed

at the botlom of your erllcible, and cam it hard down ;

lay the copper-plates thereon, cover lhem with eharcoal–

du!!, and then proeeed as before. By this meanI, \Vhen

the copper melts, it canOOl fall tO the bOltom of theccu–

eible, oor mix with the ore; but is borneup by the mix–

ture, and cannot combine wilh any thing but the zinc,

that rifes in vapours, and, paOing througb the lute, fixes

io the eopper.

LatÍ! Calaminarif,

or other ore of zinc, may be alfo

purified before it be ufed for making brafs; eCpeeially if

adulterated wil h lead ore, which is often Ihe cafe. For

this purpofe Ihe ore mlln be roaUed in a fire nrong e–

nough tO give a fmall degree of fufioo to the leaden mat–

ter; whieh

\ViII

thereby be reduced into larger, heavier,

and tougher malfes. The mon fubtile particles are dif–

fipaled io the torrefaaion, togelher wilh fome of the ca·

lamine. The calamine, on the contrary, is by roaniog

maoe more tender, liglmr, and much more friable. When

it is in this coooition, pllt it inlO a IVaflling tlay o\' fall

dip the tray in a velfel full of waler, and bruife Ihe mat–

ter il contaios. The \Vater will cmy oIT the lighte!!

powder, which is the calamine, and leave nothiog at the

boltom of lhe tray bU! the heavicfl fubn"ncc

that is,

lhe leaden mallCr, IVhich is to be rejcl'led as ufclef's.

The pówder of the calamine IVill fcttle at lhe bonomof

lhe veITd, where, afler pouring off the \Vater, it OIay be

fOllnd, and wCcu as above direélc.!.

In this optration the charcoal·uun {erves to prel'ent

bOlh the eopper and the zioc frolll beins nlcined: and

fol' tltis reafon, wheo you \Vork on a grea! quantity of

nt.\lel ials "t

onc~,

it is not neclnary to ufe fo much

ch,rcoal dnll, in proportion, as \Vhen you IVork bllt on

a fio:dl quantit:!; becaufe, the grealer the mafs of metal,

the Icfs calily \\'111 it calcine.

Tltollgh the CIIpper melts in this opecation, yet it is

fae fruOl "tiog oecelfary lo apply fueh a nrong fire as

copper

ulil~lIy

rClluires

mclt it, for the acceOion of the

zinc, on this occafion, communicates lOit a greal de–

gree of fufibility. The increafe of its weiílht is al[o

oIVing

the .quantity of zinc combined with it. Cop–

per ¡cqulres Iltll another advantage by its alfociation IVilh

this [emi-metal; for it remaios longer in tite fire without

"Icining.

Br.li

well prepareo ought

be malleable when colJ.

Hut in whate"er manocr

be oude, and \Vhatever pro–

ponion of zinc there be in it, it is cooUaotly fouod quile

unm.lleable

~'hen

red·hot.

Brafs mdted in a crucible, IVith

fieree heat, lakes

fire almon like zinc, and from its furface many while

Rowers aCcend, dancing aboul io Rakes Itke the

Rowers

of zinc. They are indeed the Rowers 01' zinc, and the

Rame of braCs urged by a flrong fire is no other than the

Rame of the zinc that is united \Vith the copper, aod then

burns. If brafs be thus kept long io fufion, it will lofe

almon all the zinc it contains.

will alfo lofe much

of its weight, aod il3 colour will be oear/y that of cop–

per,

is lherefore neeelfary, towards performing thi.

operation aright, tO feize the momen! when the copper

is fuffi eiendy impregnated witb zinc, wlten it hath ac–

quired the mon weight and lhe finen colour, with rhe

Ica(l detriment to its Jm'lility, Ihat is poOible, and thal

innant ro put out the fire ; becaufc, if lhe copper be ler!

longer in fufion, it will only lofe the zinc already united

wirh il. Skill acqllired by much praaice, and an ac–

qllaineance \Vith tite particular calamine employed, are

neeelfary to guide Ihe artin furely through thisoperation

for thúe ate very eonfiderable dilferences between the

[undry ores of zinc. Some of themeontain lead, and in

otlters lhere is iron. When the[e heterogeneous metals

come tO be mixed \Vith tite copper,- tbey do iodeed aug–

ment its weighl, but they render it at the fame time pale,

and make it very harfll. Some calamines require to be

roaneel before they can be ufed for lhis purpofe, and in

the lorrefaaion emit vapours of a volatire alkali, fuc–

ec~ded

by vapours of a fulphureous fpiril: others ex–

hale no vapours while roaning, aod may be employed

\Vithout any antecedent preparation. T hefe differeot

qllalitics mul! evidently produce grea! differenees in tbe

operatiun.

Brafs mal' alfo be made, as prince's metal ¡nel other

irnilations of gold are aanally made, by ufiog zioe in

fllbllance, innead of the ores thal contain it. But the[e

cOlllpolitioos have not, \Vhen cold, the duaility of bra[s

prfpareclwilh

lapiJ cala/NinariJ,

becauf" zinc is feldom

pllre, or free from a mixture of

I~ad.

Perhaps alfo the

ddfcrent m:Ulner in which the zinc unires with the eopper

mal' cootribute

Ihis variation.

To o!>viare litis incnnvcoienee, the zincmun be refineo

from'all alloy 01' Icad. The pr0l'eny of beiog inJilfo–

lublc by [ulphllr, which this

f~mi-mctal

polfeflcs, poinls

out