ZINC. 



oftaliedrons ; fometimes truncated on the fummits. The 

 cryftaU are fmall, and either folitary, or radiating in groups, 

 like zeolite. The luftre is fliining, gliftening, and vitreous : 

 the ftruifture is imperfeAly lamelhr, or divergingly fibrous. 

 It is fometimes opaque, and fometiities tranflucent or tranf- 

 parent : it yields to the knife, but is much harder than 

 common calamine." The fpeciHc gravity is 3.4. When gently 

 heited it is ttiongly eletlric ; it i, infufible, and lofes about 

 1 2 per Cent, by ignition. It is foluble in muriatic acid with 

 efFervefcence ; the folution gelatinizes on cooling. Accord- 

 ing to Klaproth, its conftituent parts are, 



Oxyd of zinc - - - 66 

 Silex .... 33 



According to Smithfon, 

 Oxyd of zinc 

 Silex - 

 Water - 



99 



68.3 

 25. 



4-4 



97-7 



Calamine fometimes occurs in what are called fuppofiti- 

 tious cryftals, as if it had been moulded over cryftals of other 

 minerals, and the internal cryftal had difappeared. In Der- 

 byfhire, the working miners are of opinion, that the calamine 

 deftroys the lead-ores when they occur together ; or, as they 

 exprefs it, the calamine eats up the lead. That fome procefs 

 of decompofition or change takes place where thefe ores are 

 afTociated there can be no doubt ; but by what means this is 

 effefted we are at prefent ignorant. See Veins, Metallic. 



Calamine, commonly called lapis calaminaris, when cleaned 

 and roafted, is ufed for the fabrication of brafs, forming a 

 compound with copper. (See Brass.) Its ufes in the 

 making of brafs is of very high antiquity, being mentioned 

 by Ariftotle. 



Calamine is alfo the moft valuable ore from which metallic 

 y.inc is extrafted. 



The ufes of calamine were not known in England before 

 the reign of queen Elizabeth, and even fo late as the year 

 1700 it was commonly carried out of the kingdom as bal- 

 lad by the (hips which traded to Holland. The calamine 

 raifed in Derbyfhire about the year 1780 amounted to 1500 

 tons. Sixty years before that time the quantity got did not 

 exceed 40 tons, the greater part being thrown away through 

 ignorance of its nature and value. 



The drefling of calamine confifts principally in picking 

 out all the pieces of lead-ore, lime-ftone, iron-ftone, 

 heavy fpar, and other minerals mixed with it in the mine. 

 The picked calamine is then calcined in proper furnaces, and 

 lofes by calcination between a third and fourth part of its 

 weight, which is the carbonic acid. In great works, where 

 calamine is prepared for the brafs-makers, after its calcina- 

 tion, it is carefully picked again, the accidental ingredients 

 being rendered more difcernible by the action of fire. It is 

 afterwards ground to a fine powder, and wafhed in a gentle 

 rill of water, to free it from earthy particles with which it may 

 be intermixed ; for thefe being lighter are carried off by the 

 water : it is then made up for fa'e. 



A ton of the crude Derbyfhire calamine, as dug from the 

 mine, is reduced, by the various procefles it undergoes be- 

 fore it becomes fit forufe, to about twelve hundred weight. 

 Part of the zinc is loll in calcination, particularly if too 

 ilrong a fire be made : this is evident by the flame vifible 

 over the furnace. It would be prafticable to ufe calamine 

 without calcining it, for the carbonic acid would be expelled 



by the heat applied in making brafs ; but then there would 

 be feven or eight hundred weight put into the brafs pots 

 which would be of no ufe in the operation : it is therefore 

 better to get rid of fo large a quantity of unferviceable 

 matter, and thereby avoid alfo an increafed expence of car- 

 riage from the calamine-furnace to the places where the brafs 

 is made. Watfon's Chemical Effays, vol. iv. 



Blende comprifes various fulphurets of zinc, differing in 

 the proportion of their conftituent parts, and the admixture 

 of other mineral fubftances. 



Telle-M Blende, or Phofphorefcent Blende : Zinc Sulphurs 

 Jaune, Brongrniart — The prevailing colours of this ore are 

 yellow, pafHng into green, and fometimes hyacinth-red, 

 aurora-red, or brownifh-red. It occurs malTive, diffeminatcd, 

 and cryflaUized. The cryftals are generally fmall, middle- 

 fized, and fo clofely aggregated, that it is difficult to determine 

 the precife figure, which appears either the rhomboidal, the 

 dodecahedron, the oftahedron, or the tetrahedron. Yellow 

 blende is tranflucent, paffing into tranfparent, and has a fplen- 

 dent adamantine luftre. It yields to the knife, and affords 

 a yellowifh-grey or yellowifh-white ftreak : it is brittle. 

 The fpecific gravity rather exceeds 4 : according to Karf- 

 ton, it is 4.1. 



It decrepitates before the blow-pipe, and becomes grey ; 

 but is infufible either alone or with borax. By friftion it be- 

 comes phofphorefcent, and, according to Bergman, afts a< 

 powerful in this refpeft in water as in air. 



Foliated Brown Blende: Zinc Sulphure Brun, Brongniart. 

 — It is of a reddifh or yellowifh-brown, paffing into blackilh. 

 brown and dark red. It occurs maffive, diffeminated, and 

 cryftallized. The form of the cryftals is a rhomboidal do- 

 decahedron, either perfeft or truncated on the alternate 

 lateral angles and edges, or an oftahedron, either perfeA or 

 truncated. It occurs alfo in tetrahedrons, perfeft or trua. 

 cated, and in reftangular four-fided prifms, fix-fidedprifms, 

 and acicular cryftals. Sometimes the cryftals are joined, 

 forming a twin cryftal. The luftre is fhining or fplendent,and 

 either refinous, adamantine, or femi-metallic ; it has a ftraight 

 lamellar ftrufture, with a cleavage in fix direftions. It is 

 more or lefs tranflucent ; it yields to the knife, and affords 

 a yellowifh-grey or yellowifh-brown ftreak ; it is brittle, and 

 eafily frangible. The fpecific gravity of this ore varies from 

 3.7 to 4. It is infufible, and yields an hepatic odour when 

 digefted in fulphuric acids. The conftituent parts of blende 

 are given as under ; but fome varieties of foreign blende con. 

 tain filex, arfenic, and manganefe, which may be regarded 

 as accidental. 



Blende from Satilberg, according to Bergman : 



Zinc 

 Iron 



Sulphur - 

 Silex 

 Alumine 

 Water - 



44 



5 



17 



24 



5 

 S 



From Allonhead, in Northumberland, according to Dr. 



Thomfon ; 



Zinc - 

 Iron 

 Sulphur 

 Silex - 



58.8 



8.4 



23-5 



7- 



97-7 



Fibrous 



