BRA 



are ffently mclmed before the metal is run into tlicm. 'n»e;c 

 pbtfs are afterwards laminated and mauutadurcd lU a thou- 



land different ways. _ r, r ,^.^ ...itl, 



The moll impouant properties of brafs, compared with 

 Conner, are the ioHowing : its colour is much bnghtcr, and 

 more approachipg lo gold; it is more ful.We than copper, 

 ZLkX from the ci?eumllance, that lefs than a copper- 

 re in. heat is fufficieht for tlie malang of bra s ; U ,skfs 

 TmM t.. rnrt, and to be aded on by the vail variety or 

 ! ane swhi h corrode copper ; and laftly, .t -s equally 

 ™ IkXle when cold, and more eKteniible than uther copper 

 rl ;t and hence is p.cuharlv titted to be niade mto wire. 

 Brafs, however, is only malleable when cold, by ham- 

 „ no-, brafs is found to become magnetic, perl-PS " • Y 

 "om tte particles of the iron hamn,er which may have b en 

 b^en ntoitsfurface; but this makes it neceffary to ulc 

 ■urhamm red brafs about compais.«eedks, and lim.lar m.ig- 

 r tic aUarafus. Tlic expantion of brafs has been vuy ae- 

 cirate? determined, as tl-is metal is mod commonly ufed 

 for mathematical and allronomical -'t"-- ;' ^'^t 

 utmoll prccilion is required. Mr. Smeaton found that 12 

 ndie iu kn..a. of call braft at 3^^ <:^p^nc,d by ibo 

 of ha (or at the boiling point ot water,) 225 ten 

 thoutdth parts of an inch : brafs wire in the fame circum- 

 £1"; expanded 232 parts; brafs 16 parts, with one of 

 uancL-a J, ,.,^^,.., The expanlion of hammered cop- 



pe"; ifo^W 04 p^rtrb^t that of ^.nc ,s 353 ^ f" ^hat brafs 

 Tolds a middle^'^^ace in this refpeft between its two compo- 



•" Tl^^ zmcisreadilv (eparated from braf. by fire. When bi;afs 

 is heated Irondv in open veffels to at kaft a copper-melting 

 La th z nc of- the b-afs takes^fire, and llowly burns away. 

 I thi i crtinned long enough, little f^^^^^^^"\^"^^ 

 thou At ftiU retaining a fmall portion o zmc, vvhich no fui- 



lrbrm:^:^ri^r:-^^^^ 



doubt el alf-. in manufacture,) by mixmg theoxyds of coj^- 

 cer and zmc, and reducing them together. This plan is 

 fneeniot: and the intimate°m,xture ot the two metals, the 

 Irfat obieft ,n brafs-making, is probably more rccuratdy 

 Sn dm this w-ay than ev^n by the common prucefs ot 

 obtamea in j f„ii„w,na experiment on this plan is 



"r "sage: Mix t'gethe'r 50'parts of oxyd of copper, 

 °I,LiL after the diitillation of verdigris (wh.ch is a very 

 remaining alter lie Q j , calaminaris, 400 parts 



n'^Kl^c'^ ilL a dTo^p r s of cLrcoal powder ; melt to- 



^bkA-e t 'fihfnctafe of v^eigh't g-f ^y t e 



eopp" is t e proportion which conllitutes the fineft bra s, 

 -li^'^hVt wluc^ ^pper wdl^-P -^s V ^S, ^"^ 

 S'^'tr tn£m: kc^^" When th^copper retains 

 .fifth of zmc the colour is not fo fine; and any quantity 

 ^ov ' :Vixr;ill be expel^d by the ^-^ even when e 



£r^'^:e;^te^:.r^K::i^^«;^^smthis 



er;iment the proof, that the copper now retains no more 

 than a fixth of zinc, and is tme brats. 



BRA 



Tlie analvils of brafs is a point of fon« conftqutnce, snd 



feveral modes have been propolcd, fome good, otheis detec 



"Ivafs may, in fome degree, be analykd by firongly l'"t- 

 ine in an open veflel, as above m.nlioncd. 1 lie zmc ll.eu 

 bifrns off, alid when no more l\:.me is g.ven out, the copper 

 is fuppokd to he pure. 15ut Dizc has found that this mode 

 is vcrv uncertain ; fo that no two allays of the lame lampk 

 conefpord, for it is not eafy to tell when all the zmc .. 

 burnt off that can thus be volatdi/.ed ; and the incrtale of 

 weight, caukd by the oxidation of part of the copp.r, 

 throws a further uncertainty on this mahod. 



Neither will a l-n,pk f Intion of brafs ni the fulphur.c, or 

 any other acid, and crvllall./.ation, anfwer the purpo.e ; for, 

 though mncl. of the crytlalli/.ed fnphat of copper n,ay ua- 

 dilybe picked out from the fulphat of zmc, the pc.kc 

 feparatioii of the two kinds of cryllals is impraa,caMe and 

 at laft one fpccies becomes mixed with a portion of the 

 other, even in the refpeaive cr) Hals. 



M. Dize propofcs the following methods : 

 1 Diffolve the brafs in nitric acid, which takes up the 

 copper and zinc, and kavcs any tin with which it is otteu 

 alloyed. Decompok the clear nitrated folut!on by pot-all., 

 rediffolve the precipitate in Uilphunc ac.d, and «.dd a pu:cc 

 of clean bright iron to the folntion, prevtoudy dilnt d w h 

 fix parts of water. The copper is thus precipitated .n the 

 metallic Rate, and the fulution now holds fulphat of iron, 

 and fulphat of zinc. Th.k M. Dize propoks to feparatc 

 bv -allic acid, which (lowly precipitates the iron, and leases 

 tlie "/.nc. Laltly, the fulphat of zinc may be decompokd 

 bv a carbonated alkali, and the quantity of zmc in the 

 carbonat may be eftimated according to proportions, which 

 will be prefentlv mentioned. . r ,, • „ 



This'^metl.od is ukful, but the kpaiation of the iron 

 fiom the zinc by tlie gallic acid, is exceffively ua.ou. bul- 

 phuretted hydrogen gas would be umch (liorter, and to be 



^'t Molve br.fs in nitric acid, dilute with fix parts of 

 Dure water, and immerk in the folut.on a cyhnder or bright 

 c an lead The copper fpeedily kparates m the meta he 

 ft te round the lead, winch kft takes its place^m the lolu- 

 tion. As this advances, the hquor loks its blue coK u 

 a^^d when all the copper is kparated, it becomes ilightly 

 ■Sow. To determine, however, whether al *'- -pper u 

 kparated, add a frelh clean piece of kad, av'd bod the folu- 

 tion for fome time. This now contains mtrat of kad, and 

 nk a of zinc. Sulphuric acid will precipitate thence the 

 1 d n he form of L infoluhk fulphat, and the mtrated 

 zTnc may then be decompokd by a carbonated alkah. Oa 

 tWs prel-ipitation, however, there are fome obkrvations to 

 be made. 'copper, when d.ffolvmg '"."'tnc -.d bfo bs 



he made. V-opper, wucn un.u. ■'■■£, — -- - , 



neary Vol itswaight of oxygen; but kad, under tlie 

 fame^mlunlnces, abloibs only J,%. Hence (as Vau- 

 q^inr^^wkson ^his fnbjea "^ ^he analy is of bra s xoo 

 mrts of copper diffolved in mttic acid would requne, tor 

 ^e dffox genation, (which takes P^-^ -'--.;- "^X 



aliic oxyd in folution is precipitated in a "^-^^^""^ f^'"^. .^Y 

 a other metal immerkd in it,) full 250 parts of kad, which 

 M is of courk oxK'ated in proportion as the copper preci- 

 pitates in the metallic form. But this large quantity of 

 ^xyd o lead cannot be held in folution by t!,e nitnc ac.d 



ex ept this is largely m excefs ; and this explains why, as 



M I)iz6 has obferved, a portion of oxyd of kad is apt to 

 orm at the latter end of the procefs, and to mix w.tl Ic 



cooper, fo as to require a fubkqnent operation to get c 

 "P , r,.p^ f,om It Nor will an excefs of ac.d er.inre the 



3yoSe5:^ci;hatedcopper;forM.Vauquehnni.dsthat 



^ ' Gg a 



