C(>LI-i:( TIONS IN ECONOMIC GKOI.OGY AND .MLTALLlKCiY. 17!) 



(■;) (iiiliMia. lii'.uls, liiht Kiev*', si-ioinl ji;;; Holtl. (.MilHli. ) 



{[)) Hlfiiilo, clu'it, ln'juls, Hi'ttiiid and fliinl sii-ves, hccoihI jifj; sold. (.WlSl.) 



(10) liltMidf and cluTt, heads, foiirili sievo, second jig; recnishod. (r»(iH'^.) 



(11) Chert and Idendo, tiiiN, seeond jip. (r>61H;{.; 



(I'J) Cinshed tuo, yroatcr thiin l!i and IcHf* than 'ii uiilliinetrus, fed on first Hiove, 

 third Jig. {r.t;i.S4.) 



(i:?l Illi-nile iiud <herl. heads, Heoond nievi-, third jig; sold. (rj(3lwr>.) 



(11) lUende'anil ehert, heads, fonrth sieve, third .jig; recrnshed. C56186.) 



(l.'O Chert and lilende, tails, third jig. (.'itUd?.) 



(1(5) Crn.shed ore less than "J^ njillimeties, fed on lirstHiovc, fonrth jig. (.')G189.) 



(17) lUonde, heads, second sieve, fonrth Jig. (.')Gllll.) 



(Id) Blende and ehert, hutchwork, second sieve, fourth jig. (.%1'j;}. ) 



(ID) Ulende, heads, third sieve, fonrth jig. (5G11I2.) 



(20) Chert and hlende. tails, fonrth jig. (56190.) 



(•21) Galena, heads, lirst sieve, fifth jig. (SGldf^.) 



(22) Blende, heads, second sieve, lifthjig. (r)Gl'J4.) 



('i:$) Blende and ciiert. iiends, fonrth sieve, lifth jig. (56196.) 



(24) Ore, separattd from mine slimes hy screening. (5(1200.) 



(25) Blonile and eln it, Iniddle-heads, lirst treatment. (56197.) 

 (2li) Coarse sand, Imddle, lirst treatuient. (56201.) 



(27) Blende, biuldle-heads, second treatment; sold. (.56198.) 



(28) Tails, bnddle. (56199.) 



(29) Ore samiile, all sizes. (56U»5.) 



The Extraction of Zinc 



There is btit one universal method for extracting; zinc, and that is to 

 mix the oxidi/.i'd ores, or the roasted siilpltide ores, with carbon, and 

 lieat the mixture in a retort. When the i)roper temperature is reached, 

 the carbon will withdraw the oxygen from the /inc and leave it in the 

 metallic .state; but the temperature at which this reaction takes place 

 is such that the metallic; zinc is volatile, and is reduced in the form of 

 a vapor, and, tlierefore, after it has been reduced, it must be condensed 

 or cooled to the liiiuid state. Ziuc melts at W2o C, boils at 1200° C, 

 and is reduced l)y carbon at 1301P C 



The retorts in which the reduction takes place may be either oval or 

 round; they are set in brick-work furnaces, in rows, with their front 

 ends lower than the ba(;k and opening into the air. After the charge 

 is introduced, a suitable condenser, made of clay, is placed in the open 

 eiul of the retort and luted in. During the smelting the zinc condenses 

 and (.'ollects in these condensers, and is withdrawn from time to time. 

 The lower rows of ret(»i ts in thi* furnaces frt'<|uently get very h(»t, and 

 it is necessary to u.se an extra sheet-iron condenser, called a ''prolong.'' 

 It i.s \ery ditlicult to condense all the ziiu", and, with the utnu)st «'are, a 

 portion of it will oxidize, and a i)rodiHt known as "blue powder," con- 

 sisting of a mixture of oxide and nu'tallitt /inc, will be formed. In 

 careless working this may cau.se very serious losses. Coal is generally 

 used direct to heat the retorts, and the fuina<'e is called a ■* lielgiiin 

 furnace," but, in .several t'uses, gas made 1»\ the SuMuens jn'ocess has 

 l)een used viii-ri.<v;tnll\ . 



