BRA

BRA

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metal Is not pure, but largely alloyed with themetal added as a precipitant. Therefore theloofe flocculent metal which forms around thepiece of lead is not pure copper, though it hasa perfect cupreous appearance, but is copperlargely alloyed with lead. Vauquelin foundthat if 50 grains of pure copper are diflolved inan excels of nitric acid, and then entirely pre-cipitated by metallic lead, of which about 220grains are required, the cupreous precipitatenow weighs 138 grains inltead of the original50, and therefore is not pure copper but analloy of 50 parts of copper with 88 parts oflead. This method therefore of analyfmg brafscannot be depended on, unlefs the cupreousprecipitate be afterwards feparately treated tofeparate the lead, which would render the ana-lyfis very complicated.

The following methods are given by Vau-quelin.

3. Diflolve a known weight of brafs in nitricacid ; put it into a well clofed bottle and addcauftic potafh to excefs, fo that there (hall be avery fenfible alkaline tafte in the liquor, fhakethe mixture well, and keep it fome time indigeftion. By this procefs the oxyds of copperand zinc are firft both precipitated by the alkali,and afterwards the zinc alone rediffolved in theexcefs of potafh, fo that the clear folution isoxyd of zinc in potafh, and the fediment leftundiflolved is the oxyd of copper. This oxydis brown and nearly of the colour of metalliccopper, but when thoroughly waflied and gentlydried, it only contains 65 per cent, of the pretal.If a previous allay has ihewn that the fpecimenof brafs contained only copper and zinc, whenthe weight of the former is known, that of theother may readily be inferred ; or elfe, the alka-line folution of zinc may be fuperfaturated withfulphuric acid, fo as firft to precipitate andafterwards to rediffolve the metal, when thefulphuric folution may be decompofed by acarbonated alkali. A very trifling quantity ofcopper paffes into the alkaline folution of zinc,occafioned by the action of a fmall quantity ofammonia, generated by the nitrated metals whencauftic alkali is added to them. If neceffarythis might be again feparated by a heat cau-tioufly kept below boiling, which would expelthe ammonia, the caufe of this error, but ifbrought fully to boil fome of the zinc wouldfeparate from the alkali and caufe a much greatererror than before.

4. Diflolve brafs in fulphuric acid, dilute withtwenty times as much water, and immerfe aflick of zinc exactly weighed. The copper

foon compleatly precipitates in the metallic:form, and requires only to be well walhed andweighed. The folution now contains only thezinc of the brafs, together with the zinc loftfrom the piece immerfed to precipitate the cop-per. By weighing the remainder of the ftickof zinc, and precipitating the whole by car-bonated potafli or foda, an eafy calculation willdetermine how much of the oxyd of zinc isderived from the zinc contained at firft in thebrafs. Or, more fimply, this may be inferredfrom the copper obtained, and the quantity ofbrafs originally employed.

It remains on the fubjeCt of analyfis to givethe conftituent parts of carbonat of zinc. M.Dize diflolved 100 parts of zinc in nitric acid,precipitated it by carbonated foda, and this pro-duct well wafhed and dried now weighed 180parts. Hence 100 parts of carbonat of zincthus prepared would indicate 55.5 of metalliczinc.

On the other hand Vauquelin found thatcarbonat of zinc obtained from the fulphat bycarbonated potafh, well walhed, and calcinedin a crucible to expel all the carbonic acid, con-tained 69 per cent, of metallic zinc. Hence,the carbonat obtained by Dize muft have beendried at a low temperature, probably that ofboiling water, and from either of the abovedata the proportion of zinc may be eftimated •,or elfe the carbonated oxyd may be mixed withabout a fourth of charcoal and ftrongly heatedin an earthen retort with the beak dipping inwater, by which the zinc will be reduced andwill rife into the neck of the retort, or partlyfall into the water beyond.

Analyfis fhews a vaft variety in the propor-tions of the different fpecies of brafs ufed incommerce. In general the extremes of thehigheft and loweft proportions of zinc are from12 to 2£ per cent, of the brafs. Even with fomuch as 25 per cent, of zinc, brafs, if well ma-nufactured, is perfectly malleable, though zincitfelf fcarcely yields to the hammer. M. Dizeanalized a fpecimen of remarkably fine brafsmade at Geneva, for the purpofe of efcapementwheels and the nicer parts of watch-making,the perfeCt bars of which bear a very high price.This metal unites great beauty of colour to avery fuperior degree of duCtility. It was foundto confift of 75 of copper with 25 of zinc, andprobably too the copper was Swedifh or femeof the finer forts. The comon brafs of Paris feems to contain about 13 per cent of 3 inc, theEnglifh probably more.

The ufes of brafs are too numerous to bex 3