MINIM;. 



MINING. 



null wooden pipe* mad* tolerably air-tight are fixed in the pit from 

 new the bottom to MX or wren feet above the top, terminating in a 

 funnel-shaped wooden box, which it moved round to as always to (ace 

 the wind. The air ruahing in pssses down the pipe* to the bottom of 

 the abaft, in which a constant current is thus kept up (see Pig. 6). 

 When levels hare to be carried to any great distance without any com- 

 munication with the atmosphere, they are sometimes divided by a 

 " collar," or wooden platform placed a foot or two above the bottom, 

 and in this manner a sufficient current of air is obtained to enable the 

 miners to proceed. In the north of England a contrivance called the 

 " water blast " is often used in driving long level* into rising ground ; 

 it consists in putting down either a bore-hole or small shaft near the 

 end of the level, and turning a email stream of water into it, which 

 talk into a cistern placed at the bottom, and is found to carry with it 

 a sufficient current of air to ventilate the works. In coal-mines the 

 ventilation is much more difficult, and, from the rapid generation of 

 explosive gases, more important ahm. It is generally effected by two 

 shafta, one of which is called the "downcast" and the other the 

 " upcast " shaft, the latter of which occupies the highest situation 

 with reference to the dip of the coal, and has a large furnace con- 

 tinually burning near the bottom of it The air being considerably 

 rarefied at this point, an ascending current is formed, which pannes 

 upward* to the surface through the upcast shaft with considerable 

 velocity, causing a descending current to pass through the downcast 

 shaft to supply its place, and by a very ingenious arrangement of the 

 workings this current of pure atmospheric air is made to traverse 

 every part of the mine in succession aa it passes from one shaft to the 

 other. 



f-i traction. The extraction of the materials from mines will require 

 but little notice here, since it may be stated in general terms merely to 

 require the adaptation of an efficient prime mover to any convenient 

 form of winding apparatus : a purpose for which the steam-engine is 

 very usually employed, although where water-power can be obtained it 

 is equally effective. The horse-whim, or gin, as already noticed, is very 

 useful in small mines or isolated workings, and before the introduction 

 of more powerful machinery was very extensively employed for raising 

 ore and stuff from our mines. In shallow preliminary excavations the 

 common windlass is often employed, and in underground work is much 

 used for various purposes, especially in sinking winzes, and raising the 

 stuff from workings where no regular communications have been 

 opened. The extraction of an extensive mine is enormous : indeed the 

 quantity of ore raised is seldom more than one-third or one-fourth, 

 sometimes indeed a fifth, or less, of the mass of stuff which is brought 

 to the surface. At the Consolidated Mines in Cornwall, the daily 

 extraction is about 200 tons, a large proportion of which is raised from a 

 depth of from 200 to nearly 300 fathoms. In the coal-mines in the north 

 of England the extraction is still greater ; but here nearly the whole of 

 the mass raised is more or less valuable, coal-mines being much leas 

 incumbered with dead or unproductive works than those of the 

 metals. The South Helton Colliery, in Durham, sends about 600 tons 

 of coal " to bank " daily, and is capable of affording a much larger 

 extraction. 



Mttkaniml J'rrjxtrativn of Oret, or Drating. Having now traced 

 the nature and progress of those subterranean works by which access 

 is obtained to mineral and metalliferous deposits, and their produce 

 extracted, we may briefly glance at the mechanical processes of sepa- 

 ration, technically termed "dreeing," which fall within the province 

 of the miner, and to the carrying on of which a huge portion of the 

 surface-work* of every mine i* devoted. The object of dressing is to 

 separate as far as possible the earthy matter accompanying, and, as 

 before noticed, often mixed up with the ores, from the metallic portion, 

 which is alone valuable ; and the great principle upon which all the 

 varied apparatus and processes which are used in different mines, and 

 in different countries, to effect this purpose, entirely depend, is the 

 difference in specific gravity between earthy and metallic matter, the 

 one being generally double that of the other. 



The dressing-floors of ' mine are always arranged as near the mouths 

 of the principal shafts and levels as possible, the ore being conveyed to 

 them by a small railway; and they are always provided with an ade- 

 quate supply of water by an artificial channel or " leat." The floor 

 itself U paved, and there are on one or two sides ranges' of sheds for the 

 persons employed to work in, and buildings containing the apparatus 

 used in the operation, which commences by picking the ore, which in 

 brought from the mine in Urge irregular lumps, as blasted or broken 

 from the vein. These lumps, of which more than half U often merely 

 spar and veinstone, are broken into smaller pieces with hammers, an 

 operation commonly performed by boys and young women, when a 

 good deal of the sparry matter i* picked out by hand and at once 

 rejected : the residue is moderate-sized pieces of ore, more or less 

 mixed with veinstone, and often nearly free from it From rich veins 

 a large proportion of the ore i* obtained in a very pure state, and in 

 this cam it in only necessary to break down the Urge irregular masses 

 into small fragment* of a pretty equal sice, in order to render it 

 marketable and fit for the furnace, there being no earthy or sparry 

 matter to eparate from it This rich ore U immediately therefore 

 arranged in circular heaps upon the draung floor*, containing a certain 

 number of tons web, commonly fifteen or twenty, and in this state it 

 ha* much the appearance of fin* metallic gravel The poorer claw of 



ores, after being broken by hammers, and partially separated from the 

 matrix by picking, have still a great variety of manipulations to 

 undergo, which depend on the nature of the metal and the quality of 

 the ore itself. Of these process as it will be sufficient hure to notice 

 three, " crushing " or " grinding," " jigging," and " stamping," each of 

 which U performed by an appropriate machine. The crushing-mill, or 

 grinder, consists of one or more pairs of iron rollers, placed within a 

 very abort distance apart, an 1 kept in motion either by the direct 

 f a water-wheel or by cog-wheels attached to it. Immediately 

 above the rollers is a hopper, into which the lumps of poorer ore are 

 thrown, when, falling through between the rollers, they are completely 

 crushed into small fragments. In some crushing-mills there are two 

 or three pain of rollers, those below being placed very near together, 

 so M to reduce the stuff falling from above still finer, and by an inge- 

 nious application of sieves, kept in motion by the machine, the stuff 

 can be sorted into two or three different sizes. Although by passing 

 through the crushing-mill the ore, with its accompanying veinstone, 

 has been reduced to very small fragments, the two substances a; 

 as completely intermixed aa ever; but in the next process, by the 

 jigging-machine, or " brake-sieve," they are, to a considerable extent, 

 separated. ' This machine consists of a wooden frame, open at the top, 

 and provided with a strong screen, or iron grating, at the bottom : it 

 hangs over a cistern of water, being suspended to a long lever, the 

 motion of which alternately plunges it into the water and raises it out, 

 with a peculiar jerk each time. The ores being placed in the sieve, 

 and subjected for a short time to this operation, tin- licivy metallic 

 pieces settle at the bottom, while the lighter fragments of spar and 

 veinstone are thrown to the top, and every now and then very dexter- 

 ously skimmed off with a piece of board by a man who stands by. In 

 the operation of jigging, a very important separation i thus effected, 

 as three products are obtained by it the small rich particles of ore, 

 which pass through the sieve into the cistern below, and are removed 

 occasionally, as may be necessary; the larger rich fragments, which 

 occupy the bottom of the cistern ; and the poor earthy matter, which 

 forms a layer at the top. This last product, although poor, still con- 

 tains too much metal to be lost : it consists of small fragments of rock 

 or veinstone, many of which have small particles of ore either attached 

 to them or intermixed with them, and, to any eye but that of the 

 miner's, would appear quite worthless, no less from the small quantity 

 of the ore than the manifest difficulty nf separating it from such a mass 

 of stony matter. To extract the ore from this refuse matter, several 

 processes are used, which ore chiefly grinding between rollers placed 

 very close to each other, stamping to a fine powder by the stamping- 

 mill, and finally, washing upon an inclined plane. In this operation 

 the fine metallic mud or " ."lime." being carefully spread over the 

 inclined plane at the upper end, a gentle stream of water is allowed to 

 flow over it, which washes the light earthy particles towards the bottom, 

 leaving the heavier metallic ones in a very pure state towards the top. 

 As in this process, and indeed all other operations of dressing in which 

 a stream of water is employed, many of the smallest and most minute 

 particles of the ore are carried away by it, the waste of which, in an 

 extensive mine, would be considerable, it is arranged that all such 

 water shall pass into successive reservoirs, termed "slime-pit*," in 

 which the metallic particles fall to the bottom, and are from time to 

 time collected and subjected to tmch treatment as to obtain them in a 

 tolerably pure state, aa a good deal of earthy slime is always deposited 

 with them. 



It will be seen from the preceding notice that by repeated pulverisa- 

 tion, washing, and agitation, the metallic ores may be obtained at 

 length in a very pure state, the earthy matter with which they were 

 originally intermixed being by these processes almost entirely separated 

 from them. When subsequently placed in the furnace, this residual 

 earthy matter becomes fused together with limestone, used as a flux, 

 and Wins the vitrified matter termed " slag ; " while by continued 

 heat, the sulphur, oxygen, and other mineralising substances, which 

 are in a state of chemical combination with the metal, are entirely 

 driven off, and the hitter obtained in a pure state. These operations 

 constitute the process of metallurgy. 



Variation* of the Procett. Any further detail on the subject of 

 dressing would here be out of place ; yet it is necessary to observe. 

 that different ores require different processes, and that the general 

 outline indicated above is thus subject to considerable modification. 

 In the case of tin ore, which is very intimately disseminated in the 

 rock or veinstone, a very minute pulverisation is required : hence 

 stamping is most extensively practised in our tin-mines ; and as the 

 ores of this metal may be dressed so as to give a produce of CO or 60 

 per cent, very great attention is paid to this point, and the various 

 manipulations are carried on with a greater degree of attention than in 

 the case of Other metals. In the case of copper ores stamping is less 

 used, but jigging forms a very important process, and has consequently 

 undergone great improve .to years, having given rise to a very 



ingenious and uwtnl ii died the "patent separator," hi 



which the sieve is stationary, but the water kept in motion. This con- 

 trivance was invented by Mr. Thomas Petherick, manager of tin 

 Consols Mines in Cornwall, where it was successfully brought into 

 operation. The ores of the precious metals require also a peculiar 

 treatment, being generally in a state of minute subdivision, and 

 mixed up with a vast mass of earthy matter. Gold ores are usually 



