1188 ZINC 



In almost every part of England where metalliferous limestone appears, there are 

 explorations for lead and zinc ores. The neighbourhood of Alston-moor, in Cum- 

 berland, of Gastleton and Matlock, in Derbyshire, and the small metalliferous belt 

 of Flintshire, are peculiarly marked for their mineral riches. On the north side 

 of the last county, calamine is worked in a rich mine of galena at Holywell, where it 

 presents the singular appearance of occurring only in the ramifications that the lead- 

 vein makes from east to west, and never in those from north to south ; while the 

 blende, abundantly present in this mine, is found indifferently in all directions. 



The second locality of calamine is in the magnesian limestone formation. The 

 calamine is disseminated through it in small contemporaneous veins, which, running 

 in all directions, form the appearance of a network. These veins have commonly a 

 thickness of only a few inches ; but in certain cases they extend to 4 feet, in conse- 

 quence of the union of several small ones into a single mass. There were formerly 

 explorations for calamine in the magnesian limestone, situated chiefly on the flanks of 

 the Mendip Hills, a chain which extends in the north-west and south-east direction, 

 from the Canal of Bristol to Frome. Calamine was chiefly worked in the parishes of 

 Phipham and Koborough, as also near Kickford and Broadfield-Doron, by means of a 

 great number of small shafts. The miners paid for the privilege of working a tax of 

 11. sterling per annum, to the Lords of the Treasury ; and they sold the ores, mixed 

 with a considerable quantity of carbonate of lime, at Phipham, after washing it 

 slightly in a sieve. Very little is at present worked in this district. Calamine is 

 now largely imported into this country from "Spain and the United States of America. 



METAIXTJRGY OF ZINC. 



Roasting of Ores. Blende, or sulphide of zinc is, previous to its treatment for 

 metal, carefully roasted in a reverberatory furnace, over the bottom of which it is 

 spread in a layer of about 4 inches in thickness. A strong heat is necessary for this 

 purpose, and during the operation the charge is frequently stirred with a strong iron 

 rake, with a view of exposing fresh surfaces to the gases of the furnace. The appa- 

 ratus most commonly employed in this country for roasting sulphide of zinc consists 

 of a reverberatory furnace about 36 feet in length and 9 feet in width, provided with 

 a fireplace of the usual construction. The sole or hearth of this apparatus is divided 

 into three distinct beds, of which that nearest the fire-bridge is 4 inches lower than 

 that which is next it, which is again 4 inches lower than that nearest the chimney. 

 In addition to the heat derived from the fireplace, the gases escaping from the re- 

 ducing furnaces are usually introduced immediately before the bridge, and a consider- 

 able economy of fuel is thereby effected. 



When the furnace has been sufficiently heated, a charge of 12 cwts. of raw blende 

 is introduced into the division nearest the chimney, and equally spread over the 

 bottom, care being taken to stir it from time to time by means of an iron rake, as 

 before described. After the expiration of about eight hours this charge is worked on 

 to the floor of the compartment forming the middle of the furnace, and a new 

 charge is introduced into the division next the chimney. About eight hours after 

 this charging the ore on the middle bed is worked on to the first, whilst that on the 

 hearth next the chimney is equally spread on the middle one and a new charge intro- 

 duced into the division next the stack. After the expiration of another period of 

 eight hours the charge on the first hearth is drawn, the ore on the middle and third 

 hearths moved forward, and a fourth charge introduced as before. In this way the 

 operation is continuous, and each furnace will effect the calcination of about 36 cwts. 

 of ordinary blende in the course of 24 hours. 



Calamine is usually prepared for smelting by calcination in a furnace resembling 

 an ordinary lime-kiln, the heat being often supplied by means of four fireplaces 

 arranged externally, and so placed that the heated gases may be drawn into it, and 

 regularly distributed through the interstices existing between the masses of ore. Calu- 

 mine subjected to this treatment commonly loses about one-third of its weight, and is 

 at the same time rendered so friable as easily to admit of being reduced to fine powder 

 by an ordinary edge-mill. 



Belgian Process. When this method of treating zinc ore is employed, the furnace 

 represented in Jiff. 2151 is commonly used. 



Pig. 2151 represents, on the left hand, a front elevation of the furnace, and on 

 the right a sectional elevation through the ash-pit and fireplace. F is the fireplace, 

 whilst A is the cavity into which are introduced the retorts destined for the distillation 

 of the metal. The products of combustion escape by the openings o into a flue, by 

 which they are conducted into the calciner for the purpose of economising the waste 

 heat These furnaces are either arranged in couples, back to back, or in groups of 

 four, for the purpose of rendering the structure more solid, and economising heat. 



