BRA

BRA

( 170 )

alone, obtainable-front its oxyd in the fame waybut without the calamine. This brafs has avery fine colour like gold.

On this experiment M. Sage obferves thatthere appears to be a point of mutual faturationbetween the two metals, which is when thecopper retains one-fixth of zinc, and this por-tion it will retain however long it is heated,provided the iurface of' the melted metal becovered to protect the zinc from the action ofthe air; but if the brafs contains a greater pro-portion of zinc, precifely this excefs will efcape,even in covered veflels, and will burn when itcomes out to the air. The fame chemift alfoobferves that the colour is the fined at theabove proportion. Tliefe experiments feem torequire further confirmation, but at prefent wemay reckon that to be the moil perfedf bralswhich is compofed of about 14.28 per cent, ofzinc and 85.72 of copper, and which is notliable to any alteration in its conftituent partsby fucceflive or long continued fufions, providedthe accefs of air be prevented.

The analyfis of brafs has been attempted invarious ways, and feveral proceffes have beengiven of different merit.

Brafs may be to a certain degree analyfed byAmply being kept in fufion at a high heat withfree accefs of air. The zinc readily burns, andby far the greater part of it efcapes, and whenthe blue flame of the metal ceafes the analyfisis fuppofed to be compleat, the lofs of weighton the remaining metal indicating the quantityof zinc. But this is inaccurate from two caufes ;firlt, that a portion of zinc always remains inthe copper however long the heat be continued,and fecondly that part of the copper oxidates inthe procefs, and thereby gains an increafe ofweight. Both thefe circumftances thereforecontribute .to indicate a fmaller proportion ofzinc than is really the cafe.

A Ample folution of brafs in the fulphuricacid and fubfequent cryftallization has alfo beenrecommended, on the idea that the cryitals offulphat of zinc could readily be obtained feparatefrom thofe of the fulphat of copper. But thoughthis feparation takes place to a confiderable.degree it is not compleat, for at the laft thecryitals of each fait are fomewhat alloyed withthe other, and the trouble of picking out thecryitals when very fmall is extreme.

M. Dize E propofes the following methods.1. Diffolye the brafs in nitric acid, which takes.up the copper and zinc and leaves any tin with■which it is often alloyed. Decompofe the clear

t Jour, de Phyf. tom. 48.

nitrated folution by potalh, rediflblve the pre-cipitate in fulphuric acid, and add a piece ofclean bright iron to the folution, previouflydiluted with fix times as much water. Thecopper is by this means precipitated in a metallicHate, and the folution now holds fulphat of ironand fulphat of zinc. Add gallic acid, whichwill flowly feparate the iron and leave the zinc.Laltly, decompofe the fulphat of zinc by a car-bonated alkali, and eftimate the quantity of zinccontained in the carbonated oxyd of zinc thusobtained, by proportions which will be prefentlymentioned. The above method is ufeful, butthe feparation of the iron by the acid of galls isexceffively tedious.

2. Diffolve the brafs in nitric acid. Dilutewith fix parts of water, and immerfe in thefolution a cylinder of bright clean lead. Thecopper fpeedily feparates in the metallic formround the lead, which laft takes its place in thefolution. As this procefs advances the liquorlofes its blue colour, and when all the copperis feparated it is flightly yellow. To be certainthat no copper remains in the folution, add afrefh clean piece of lead and boil for fome time.The liquor now contains nitrat of lead andnitrat of zinc. Sulphuric acid will now pre-cipitate the lead in the form of an infolublefulphat, and the nitrated zinc may then bedecompofed by a carbonated alkali.

On this precipitation however there are feveralthings to be obferved. Copper, as Vauquelinremarks, h when diffolving in nitric acid abforbsnearly T W of its weight of oxygen, but leadunder the fame cireumftance abforbs only T ‘~.Hence 100 parts of copper diflolved in nitricacid would require for their difoxygenation (aprocefs which takes place whenever a metallicoxyd in folution is precipitated by the immerfionof another metal in its metallic ftate) full 250parts of lead, which laft is of courfe oxydatedin proportion as the copper is precipitated in themetallic form. But this large quantity of oxydof lead cannot be held in folution by the nitricacid, except this is largely in excels, and thisexplains the reafon of the appearance of aportion of oxyd of lead (as M. Dize has ob-ferved) which forms at the latter end of theprocefs and mix«s with the newly precipitatedmetallic copper, fo as to require a fubfequentoperation to feparate them. Nor will an excefsof nitric acid enfure the purity of the precipi-tated copper, for it happens here, as is nowfound to take place in very many of the regulinemetallic precipitates, that the newly-feparated*‘An. Chim. tom. s8.

1