150 



METALLURGY 



MKTALS 



piece* roughly 1J inch in diameter, is raised to the 

 floor or pint form, 6, b, and by means of an openiu- 

 at r passed down to the crushing-rollers, r, r. These 

 are u-u:illy from 10 to 30 inches in diameter and at 

 le.i-t In indies long, made of dulled cast iron or 

 tee), and with a lever at d to keep them in POM 

 lion. Itelow the rollers a shoot conveys thecrushcd 

 ore to a series of sieves increasing in fineness from 

 the ton to tin- bottom, and what is separated liy 

 each sieve falls into a separate pit. Such pieces 

 of ore-stuff as are too large to go through the top 

 sieve or riddle fall into the raff- wheel or bucket - 

 wheel, and are by it raised again to the floor to he 

 recrushed. In Cornwall a sieve or riddle cylin- 

 drical in shape is used, and it slopes so that >i nil' 

 too large to go through its meshes is raised hy the 

 raff-wheel to get a second crushing. Only aliout 

 13 per cent of the ore-stuff crushed in the Cornish 

 mill exceeds 7J millimetres in size. 



For pulverising some ores tinstone and aurifer- 

 ous quartz, for example a stamping -mill is used. 

 It consist* of a series of upright shafts with a 

 weighty piece of iron at the bottom of each. They 

 are raised by means of an axle with projecting 

 cams, and then falling liy their own weight act like 

 hammers. Kxcept in chlorination and amalgama- 

 tion works (see (mi.D), the wet process of stamping 

 i> generally adopted that is, the cast-iron or steel 

 shoes of the stamps work upon cast iron or quart/. 

 bottoms placed in stamp troughs filled with water. 



Si/ing apparatus or sorting machines are cm- 

 ployed for dividing the crushed ore-stuff into grains 

 of several sizes. A common hand-riddle is the 

 simplest form of sizing implement. One kind of 

 apparatus in use consists of a series of flat-liottomed 

 > with graduated meshes placed on different 

 levels and mechanically agitated so as to pass the 

 stuff across the peifoiated liottoms. The tirst sieve 

 separates the largest grains, the second the next in 

 size, and so on. A rotating drum sieve or trommel 

 is, however, more frequently employed. It is placed 

 liori/ontaUy. and is to some extent conical in shape. 

 Sometimes it U one long continuous trommel in 

 sections, in which cose the finest st nil' passes through 

 the tirst section, the next larger through the second. 

 and soon through, snv, live or six divisions to the 

 largest grains. In oilier cases a system of separate 

 eonical trommels, in which the si/.ing takes place 

 from large to small grains, is employed. With the 

 trommel water is used, and, although its axis may 

 lie quite level, the falling angle of its shell together 

 with its motion ini|icls the ore stuff from the smaller 

 to the larger end. Trommels are used for clearing 

 off earthy matter and for draining off water from 

 ore as well as for si/.ing. 



After the ore Mull' lias Iwen sorted according to 

 the si/e of the grains, the next step is io sepaiate 

 l.y -|>eeilic gnnily the pure ore from the gangiie or 

 non metallic minerals associated with it. If the 

 reduced pailielei ! those of vein stuff containing 

 moie than one kind of me. these are also separated 

 liy gravity. If equal si/ed giains of galena, blende, 

 and quart/, whose respective densitic- ,-ue 7 ."', I. and 

 'J 7, are allowed to fall freely in some depth of water. 

 the three sill-stance* will separate into layers at the 

 Uittom, iii which case the lead ore (galena) will 

 form the lowest, the zinc, ore (blende) the middle, 

 and tin- quart/ the top layer. lint in hydraulic 

 jigger* (some are pneumatic) the column of water, 

 at nn*t under .'{ inches, is t., shallow to ad- 

 mit of separation by simply dropping the grains. 

 Consequently thcw are placed in a sieve im 

 MMd ill water, and subjected to a rcpcat-d up- 

 and down motion, in which theascciit of the jigging 

 Muff taken place by jerks, but in the de-cent it falls 

 freely. In thin way the lime ore. or at least the 

 beat ore, accumulates at tne liottom, and is usually 

 sufficiently rich for smelling. The gnngiie on the 



surface is skimmed oil" or otherwise removed. In 

 hand jigging the sieve is vigorously jerked in a tub 

 of water ; in the brake jigger the jerking motion is 

 produced by a hand lever and connecting rod ; and 

 in continuous jiggers mechanical contrivances are 

 used to carry into ditl'erent receptacles the mineral 

 giains separated UIHIII the sieve ill layers without 

 interrupting the jigging process. 



The dressing of line sandy, mealy, or slimy ore- 

 stuff, which is not suitable for jigging, is effected 

 on buddies or sloping tables. Huddles are inclined 

 planes, often circular, or rather conical in shape, 

 over which the line stuff suspended in water de- 

 scends. In doing so the heavier metallic particles 

 fall at the top of the table or cone while the lighter 

 waste is carried down to the foot. 



Fordetailed descriptions and illuatrationsof ore-dressing 

 machines, see Hunt's Britith Minimi ( 1 SN4 ) ; an exhaus- 

 tive report by E. F. Althnus in the Rtportt of Oic fhiln- 

 i/i I iA i-i Kjeh iiiHiim. 1STG ; and works on Metallurgy by 

 Roberta-Aunt (1891) and A. J. Hiorns (IS'.Hi). 



Metal Mountains. See ERZGEBIRGE. 



Metals. Although each metal is considered in 

 a separate article, there are various points regard- 

 ing the general physical and chemical characters 

 of these Indies, and the method of classifying 

 them, which require notice. A metal, from the 

 chemical point of view, is an element which can 

 replace hydrogen in an acid and thus form a salt. 

 Hydrogen itself is, chemically, considered to lie 

 a metal. Those elements which are mm metallic 

 in this sense are called metalloids. 



Amongst the chief rlt<-iiiirnl properties of metals 

 we notice their strong affinities to certain of the 

 non-metallic elements. All the metals, without ex- 

 ception, combine with oxygen, sulphur, and chlorine, 

 and often in several proportions, forming oxides, 

 sulphides (formerly termed sulplmrets), and chlor- 

 ides. Many of them combine with bromine, iodine, 

 and fluorine. The other compounds of this nature, 

 excepting carbide (formerly carburet) of iron, or 

 steel, and the hydrides of arsenic and antimony 

 (commonly known as arseniurcttcd and antinioniu- 

 retted hydrogen), which are of importance in toxi- 

 cologv, may be passed over without notice. The 

 metallic oxides are. without exception, solid bodies, 

 white or coloured, and usually present an earthy 

 appearance. Hence the old name of inrtnllir mix 

 applied to these oxides. Those oxides which are 

 termed basic possess the property of directly 

 uniting with the so-called oxv acids (such la 

 sulphuric, nitric, carliomc, and silicic- acid), and of 

 forming new chemical compounds of the second 

 order, termed Salts (q. v. ). The compounds of 

 the metals \\ith chlorine, iodine, bromine, and 

 fluorine- such, for instance, as chloride of sodium, 



or co ion salt, CINa are termed haloid salts. 



The same metal may often combine both with 

 chlorine and with oxygen in more than one pro- 

 (ortioti. For example, we have snltchloride of 

 mercury, Hg,rlj ; sulioxidc of mercury, HgjO ; 

 chloride of mercury, IlgCl. : ; oxide of mercury, 

 HgO. l-'or I he coni|Miuiids of the metals with 



Slllplmr. see Sf l.l'llfl!. 



The following are the most important of the 

 ji/iuxirtil iiroperties of the metals: (I) All metals, 

 unless when they are in a finely-pulverised form, 

 exhibit more or less of the characteristic lustre 

 termed metallic. Two of the non metallic ele- 

 ments, iodine and carlmn, in some forms also pre- 

 sent a metallic lustre. (2) All metals are good 

 conductors of heat and electricity, although in 

 very unequal degrees. (3) \Vjth tlie exception of 

 meicury, all the metals are solid at ordinary 

 tenijicraturcs. With the exception of gold, copper, 

 calcium, and strontium, the metals are, when light 

 is only once reflected from them, more or less white. 



