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 forms 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 latter obtained in a pure state. These operations constitute the process of metallurgy.
Variations of the Process.—Any further detail on tho subject of dressing would here be out of place; yet it is necessary to observe that different ores require different processes, and that tho 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 50 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 ether metals. In tho case of copper ores stamping is less used, but jigging forms a very important process, and has consequently undergone great improvements of late years, having given rise to a very ingenious and useful invention, called the " patent separator," in which the sieve is stationary, but the water kept in motion. This con trivance was invented by Mr. Thomas Petheriek, manager of the Fowcy Console Dlines 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. Oold ores are usually stamped, and silver ores ground to an exceedingly fine powder ; but from the great value of the metals, the process of washing-is carried on differently from that of others, and, in some cases, is dispensed with altogether.
Management and Internal Economy of Mines.—Having now taken a general view of mining operations, and the ancillary processes which they require, there is still an important branch of the subject which requires some notice, the management and internal economy of mines. As it is on the due regulation of this point that the success of mines in a very great degree depends, it has, both in this and other countries, received great attention, and been reduced to a system as perfect as possible. In England, more especially, all the practical improvements suggested by experience as essential to the profitable and well-regulated existence of large mining establishments have been freely adopted, as we are here unfettered by those formalities and restraints which influence the continental systems, individual interest being allowed unlimited scope. The nature and importance of the subject now under consideration cannot be better expressed than in the words of a gentleman of the highest eminence as a mining-engineer, Mr. John Taylor, who has thus treated it, in connection with late mechanical improvements in the art of mining :— "Important as the improvements are which we have contemplated in the instruments which the progress of physical science has placed in our hands, those which relate to the government of large bodies of workmen, to the inducement to active enterprise on the part of the Labouring miners, to the removal of difficulties in their way, or of placing them in circumstances most favourable to effective exertion, are even more important, and to this may be added the judicious application of those very inventions which have been noticed. It must
be recollected that, after all, the great expenditure in mining is for manual Labour, and that we have no means as yet devised for pene trating the rocks which contain mineral treasures but those afforded by the patient and unremitting labour of a great number of men. The regulation therefore of this force, and its due application, is, after all, more important to the success of mines than even the most ingenious mechanical expedients. As an army would undoubtedly fail, however well provided with the most perfect artillery and all the best constructed implements of war, unless the men of which it might be composed were well directed, their efforts well combined, and their courage well assured by reasonable prospects of success, so in mining we may collect and apply the most complete mechanical arrangements ; but if the greater power of manual labour be not wisely directed, no beneficial results can be expected." System of Tutwork and Tribute.—Such being the leading features of mining economy, we may proceed briefly to consider the manner in which they are practically carried into effect, more especially in the deep and extensive mines of Cornwall, where, both from the amount of capital and the number of men employed) every exertion has been made to perfect the mining system, the results of which have since been extended from thence to other parts of England. All the under ground work of mines in Cornwall, and indeed of most other districts, is of two distinct kinds : dead work, or that carried on in the rock or metalliferous deposit, for the purpose of trial and discovery ; and productive labour, which is employed in the actual breaking down and extraction of the ore. Now it is in the performance of the immense amount of manual Labour requisite in these operations, and in the subsequent process of dressing the ores, that the great expenditure of mining consists ; and the great merit of the Cornish plan lies in performing the whole by a system of contracts, which effectually unite for a time the interests of the miner and his employer, while, being renewed at moderate intervals, it continually allows of that re-adjust ment which the fluctuating circumstances of the mine may require. The dead work is denominated " tutwork," and the raising of ores " tribute; " these two species of emproyment being, by an excellent division of labour common in all mines, kept entirely separate and performed by different individuals, who thus acquire great skill and judgment in their peculiar occupations. The mode of payment adopted in tutwork and tribute is entirely different : in the former case, where the miner is employed in sinking shafts, driving levels, &e., the object being to extract as much useful labour as possible from him for a given sum, he is paid at so much per fathom, according to the work done ; in the latter case, where the quality of the ore raised is a consideration equally important with its quantity, the miner redeives a certain percentage on the actual value, being paid at the rate of so many shillings in the pound upon that value. The excellence of the above principle will readily be seen ; and its advantages are still further increased by the open and public manner in which the con tracts are made between the men and their employers, thus allowing of free competition as regards the former, and proving an equally effectivo check against oppression from the latter.