ZIN

Z IN

I

( 4 99 )

Blende occurs in tranfition, primitive, andftratified mountains, but principally in the for-mer : it is found in veins almoft always accom-panied by galena, calcareous fpar and quartz,alfo by iron pyrites, fahlerz, native filver, greyantimony, fpathofe iron, copper pyrites, heavyfpar, &c. The Hungarian and Tranfilvanianblendes are often auriferous.

Blende abounds in Britain , and in mod ofthe other mining diftrifts of Europe .

§•2. AJfay and Analyfis.

Common Calamine , befides carbonat of zincand water, may alfo contain the carbonats ofiron, lead and lime. Its analyfis may be thusconducted, (a) Diffolve the pulverized ore indilute nitric acid and eftimate the carbonic acidfrom the lofs of weight during the folution.Then carefully neutralize the folution by alittle cauftic foda and evaporate it gently, addingfrom time to time a few drops of fulphat offoda as long as any precipitation takes place.

(b ) Having thus cautioufly brought it nearly todrynefs, digeft it in highly rectified alcohol,and afterwards in a little cold water whichwill take up every thing but the fulphats oflead and lime. ( c ) Thefe may then be fepa-rated by digeftion in very dilute fulphuricacid, which will take up the fulphat of lime,leaving the fulphat of Lead pure, (d) Neu-tralize the muriatic folution by foda, andevaporate nearly to drynefs; then add to therefidue alcohol, which will throw down thefulphat of Lime with a little fulphat of foda,this latter may then be wafhed away by a littlecold water. (r) The alcoholic folution b afterevaporation to drynefs may be digefted in caufticammonia, which will take up the oxyd of zincand leave behind the oxyd of Iron , (f) The al-kaline folution after being flightly fuperfaturatedwith muriatic acid, is to be decompofed by aperfeftly carbonated alkali, by which the zinc isprocured in the ftate of carbonat, and this, afteredulcoration, being diffolved by fulphuric acidand the folution ignited in a platina crucibleaffords dry fulphat of Zinc , containing 50 percent, of oxyd of zinc, (g) Thus all the com-ponent parts are afcertained except the water ;to determine the proportion of this take a frelhparcel of the ore, weigh it, and then ignite itfor half an hour, note the lofs of weight, andtransfer the. refidue into muriatic acid; if whileit diflolves in this fluid it gives out any gas letthe lofs of weight be noted ; then add togetherthe Ioffes by ignition and folution, dedutd fromthe fum the known weight of the carbonic acidand the refidue is water.

To analyfe the eleSric calamine diffolve thepulverized ore in dilute nitric acid, evaporatethe folution very (lowly, -4!molt to drynefs, thendigeft it in a large quantity of water and thefilex will remain undiffolved. If the filexretains the lead ochery tinge digeft it in dilutemuriatic acid, by which the adhering oxyd ofiron will be taken up. Then decompofe themuriatic folution by a carbonated alkali, andtransfer the oxyd thus obtained to the nitricfolution from which the filex has been fepa-rated. The reft of the analyfis is the fame asalready mentioned for common calamine.

The analyfis of Blende is confiderably morecomplicated. The fubftances that have beenobtained from it by decompofition are zinc, iron,lead, copper, arfenic, fulphur, filex, alumine andwater; nor is it by any means improbable thatthe whole of them fhould coexift in the famefpecimen, we lhall therefore proceed to mentionwhat appears to us as the belt method of fepa-rating thefe fubftances from each other.

a For the Watery let 200 grs. duly pulve-rized be put into a fmall coated glafs retort andgently ignited for a quarter of an hour; thefluid in the receiver will be water with fcarcelyany perceptible admixture of fulphurous acid.

b Now take another portion of the ore anddigeft it in repeated portions of dilute nitricaod till every thing foluble, is taken up ; waflithe refidue, weigh it and ignite it; the Sulphurwill bum off, and its amount may be eftimatedby the lofs of weight.

c The refidue, after the ignition of the ful-phur, is to be digefted in a little nitro-munaticacid till the infoluble portion becomes quitewhite, and is then pure Silex.

d To the nitric folution [b) add a few dropsof fulphated foda and evaporate it gently, con-tinuing to drop in from time to time a littlefulphated foda as long as any precipitationtakes place; when the whole is brought nearlyto drynefs digeft it in very dilute muriatic acid,which will take up every thing but the fulphatof Lead.

e Add together the nitro-muriatic folutions,(c, d) and decompofe the whole by carbonat offoda, then digeft the precipitate thus obtained incauftic ammonia, by which the zinc and copperwill be taken up.

f Saturate the preceding ammoniacal folutionwith muriatic acid, and then boil it, addingcauftic foda as long as any precipitate fallsdown; this precipitate is brown oxyd of Copper .

g The foda folution, now containing onlyoxyd of zinc, is to be faturated with muriatic3 R 2