Chapter II: Application of Light-Gas (28)

Whenever the workings of the cuts _c_ in the first story are finished, those of the second, _a´ a´_, may be begun in the second; and thus by mounting from story to story, the whole deposit of ore may be taken out and replaced with rubbish. One great advantage of this method is, that nothing is lost; but it is not the only one. The facilities offered by the system of _cross workings_ for disposing of the rubbish, most frequently a nuisance to the miner, and expensive to get rid of, the solidity which it procures by the banking up, the consequent economy of timbering, and saving of expense in the excavation of the rock, reckoning from the second story, are so many important circumstances which recommend this mode of mining. Sometimes, indeed, rubbish may be wanted to fill up, but this may always be procured by a few accessory perforations; it being easy to establish in the vicinity of the workings a vast excavation in the form of a vault, or kind of subterraneous quarry, which may be allowed to fall in with proper precautions, and where rubbish will thus accumulate in a short time, at little cost.

_Fig._ 731. represents a section of the celebrated lead mines of Bleyberg in Carinthia, not far from Villach.

_b_, _c_, is the ridge of the mountains of compact limestone, in whose bosom the workings are carried on.

_e_, is the metalliferous valley, running from east to west, between the two parallel valleys of the Gail and the Drave, but at a level considerably above the waters of these rivers.

_f g_, is the direction of a great many vertical beds of metalliferous limestone.

On considering the direction and dip of the marly schist, and metalliferous limestone, in the space _w_, _w_, to the west of the line 1, _s_, it would appear that a great portion of this system of mountains has suffered a slip between 1, _s_, and a parallel one towards the east; whereby, probably, that vertical position of the strata has been produced, which exists through a considerable extent. The metalliferous limestone is covered to a certain thickness with a marly schist, and other more recent rocks. It is in this schist that the fine marble known under the name of the _lumachella of Bleyberg_ is quarried.

The galena occurs in the bosom of this rock in flattened masses, or blocks of a considerable volume, which are not separated from the rest of the calcareous beds by any seam. It is accompanied by zinc ore (_calamine_), especially in the upper parts of the mountain.

Several of the workable masses are indicated by _r_, _r_³; each presents itself as a solid analogous to a very elongated ellipse, whose axis dips, not according to the inclination of the surrounding rock, but to an oblique or intermediate line between this inclination, and the direction of the beds of limestone; as shown by _r w_, _r´ u_. Every thing indicates the contemporaneous formation of the limestone, and the lying beds of the lead ore.

The accidents or faults called _kluft_ (_rent_) at Bleyberg are visible on the surface of the ground. Experienced miners have remarked that the rich masses occur more frequently in the direction of these accidents than elsewhere.

It is in general by galleries cut horizontally in the body of the mountain, and at different levels, _s_, _g_, _s f_, that the miner advances towards the masses of ore _r_, _r_³. Many of these galleries are 500 fathoms long before they reach a workable mass. The several galleries are placed in communication by a few shafts, such as _t_; but few of these are sunk deeper than the level of the valley _e_.

The total length of the mines of Bleyberg is about 10,000 yards, parallel to the valley _e_; in which space there are 500 concessions granted by the government to various individuals or joint stock societies, either by themselves or associated with the government.

The metalliferous valley contains 5000 inhabitants, all deriving subsistence from the mines; 300 of whom are occupied in the government works.

Each concession has a number and a name; as Antoni, Christoph, Matthæus, Oswaldi, 2, 8, 36, &c.

_Fig._ 732 is a section in the quicksilver mine of Idria. 1. is the gray-limestone; 2. is a blackish slate; 5. is a grayish slate. Immediately above these transition rocks lies the bed containing the ores called _corallenerz_, which consist of an intimate mixture of sulphuret of mercury and argillaceous limestone; in which four men can cut out, in a month, 2-1/2 toises cube of rock.

_Fig._ 733. represents a section of part of the copper mine of Mansfeldt; containing the cellular limestone, called _rauchwacke_, always with the compact marl-limestone called zechstein; the cupreous schist, or _kupferschiefer_; the wall of grayish-white sandstone, called the _weisse liegende_; and the wall of red sandstone, or the _rothe liegende_. The thin dotted stratum at top is vegetable mould; the large dotted portion to the right of the figure is oolite; the vein at its side is sand; next is _rauchwacke_; and lastly, the main body of fetid limestone, or _stinkstein_.

_Fig._ 734. represents one of the Mansfeldt copper schist mines in the district called Burgoerner, or Preusshoheit.

1. Vegetable mould, with siliceous gravel.

2. Ferruginous clay or loam.

3. Sand, with fragments of quartz.

4. Red clay, a bed of variable thickness as well as the lower strata, according as the cupreous schist is nearer or farther from the surface.

5. Oolite (_roogenstein_).

6. Newer variegated sandstone, (_bunter sandstein_).

7. Newer gypsum; below which, there is

8. A bluish marly clay.

9. Stinkstone, or lucullite.

10. Friable grayish marl.

11. Older gypsum, a rock totally wanting in the other districts of the mines of Rothenberg; but abounding in Saxon Mansfeldt, where it includes vast caverns known among the miners by the name of _schlotten_, as indicated in the figure.

12. The calcareous rock called _zechstein_. The lower part of this stratum shows symptoms of the cupriferous schist that lies underneath. It presents three thin bands, differently modified, which the miner distinguishes as he descends by the names of the sterile or rotten (_faüle_) rock; the roof (_dachklotz_); and the main rock (_oberberg_.)

13. Is a bed of cupriferous schist (_kupferschiefer_), also called the _bitumino-marly_ schist, in which may be noted, in going down, but not marked in the figure:--

_a_, the _lochberg_, a seam 4 inches thick.
_b_, the _kammschale_, 1/4 of an inch thick.
_c_, the _kopfschale_, one inch thick.

These seams are not worth smelting; the following, however, are:--

_d_, the _schiefer kopf_, the main copper-schist, 2 inches thick.
_e_, a layer called _lochen_, one inch thick.

14. The wall of sandstone, resting upon a porphyry.

_Fig._ 735. is a section of the mines of Kiegelsdorf in Hessia, presenting--

1. Vegetable mould.

2. Limestone distinctly stratified, frequently of a yellowish colour, called _lagerhafter kalkstein_.

3. Clay, sometimes red, sometimes blue, sometimes a mixture of red, blue, and yellow.

4. The cellular limestone (_rauhkalk_). This rock differs both in nature and position from the rock of the same name at Mansfeldt.

5. Clay, usually red, containing veins of white gypsum, and fine crystals of selenite.

6. Massive gypsum of recent formation.

7. Fetid limestone, compact and blackish gray, or cellular and yellowish gray.

8. Pulverulent limestone, with solid fragments interspersed.

9. Compact marl-limestone, or _zechstein_, which changes from a brownish colour above to a blackish schist below, as it comes nearer the cupreous schist, which seems to form a part of it.

10. Cupreous schist (_kuperschiefer_), of which the bottom portion, from 4 to 6 inches thick, is that selected for metallurgic operations. Beneath it, is found the usual wall or bed of sandstone. A vein of cobalt ore _a_, which is rich only in the grayish-white sandstone (_weisse liegende_), traverses and deranges all the beds wherever it comes.

_Of working mines by fire._--The celebrated mine worked since the tenth century in the mountain called _Rammelsberg_, in the Hartz, to the south of Goslar, presents a stratified mass of ores, among the beds of the rock which constitute that mountain. The mineral deposit is situated in the earth, like an enormous inverted wedge, so that its thickness (power), inconsiderable near the surface of the ground, increases as it descends. At about 100 yards from its outcrop, reckoning in the direction of the slope of the deposit, it is divided into two portions or branches, which are separated from each other, throughout the whole known depth, by a mass of very hard clay slate, which passes into flinty slate. The substances composing the workable mass are copper and iron pyrites with sulphuret of lead (galena), accompanied by quartz, carbonate of lime, compact sulphate of baryta, and sometimes gray copper ore, sulphuret of zinc, and arsenical pyrites. The ores of lead and copper contain silver and gold, but in small proportion, particularly as to the last.

A mine so ancient as that of Rammelsberg, and which was formerly divided among several adventurous companies, cannot fail to present a great many shafts and excavations; but out of the 15 pits, only two are employed for the present workings; namely, those marked A B and E F, in _fig._ 736., by which the whole extraction and drainage are executed.--The general system of exploitation by fire, as practised in this mine, consists of the following operations:--

1. An advance is made towards the deposits of ore, successively at different levels, by transverse galleries which proceed from the shaft of extraction, and terminate at the wall of the stratiform mass.

2. There is formed in the level to be worked, large vaults in the heart of the ore, by means of fire, as we shall presently describe.

3. The floor of these vaults is raised up by means of terraces formed from the rubbish, in proportion as the roof is scooped out.

4. The ores detached by the fire from their bed, are picked and gathered; sometimes the larger blocks are blasted with gunpowder.

5. Lastly, the ores thus obtained are wheeled towards the shaft of extraction, and turned out to the day.

Let us now see how the excavation by fire is practised; and in that view, let us consider the state of the workings in the mines of Rammelsberg in 1809. We may remark in _fig._ 736. the regularity of the vaults previously scooped out above the level B C, and the other vaults which are in full activity of operation. It is, therefore, towards the lower levels that the new workings must be directed. For this purpose, the transverse gallery being already completed, there is prepared on the first of these floors a vault of exploitation at _b_, which eventually is to become similar to those of the superior levels. At the same time, there is commenced at the starting point below it, reached by a small well dug in the line of the mineral deposit, a transverse gallery in the rock, by means of blasting with gunpowder. The rock is also attacked at the starting-point by a similar _cut_, which advances to meet the first perforation. In this way, whenever the vaults of the level C are exhausted of ore and terraced up with rubbish, those of the level beneath it will be in full activity.

Others will then be prepared at a lower level; and the exploitation may afterwards be driven below this level by pursuing the same plan, by which the actual depth of excavation has been gained.

In workings by fire we must distinguish, 1. The case where it is necessary to open a vault immediately from the floor; 2. The case where the vault having already a certain elevation, it is necessary to heighten its roof. In the former case, the wall or floor of the mineral deposit is first penetrated by blasting with gunpowder. As soon as this penetration is effected over a certain length, parallel to the direction of the future vault, as happens at _b_, there is arranged on the bottom a horizontal layer of billets of firwood, over which other billets are piled in nearly a vertical position, which rest upon the ore, so that the flame in its expansion comes to play against the mineral mass to be detached. When after some similar operations, the flame of the pile can no longer reach the ore of the roof on account of its height, a small terrace of rubbish must be raised on the floor of the deposit; and over this terrace, a new pile of faggots is to be heaped up as above described. The ancient miners committed the fault of constantly placing such terraces close to the roof, and consequently arranging the faggots against this portion of the ore, so that the flame circulated from the roof down to the floor. The result of such procedure was the weakening of the roof, and the loss of much of the ore which could not be extracted from so unstable a fabric; and besides, much more wood was burned than at the present day, because the action of the flame was dissipated in part against the whole mass of the roof, instead of being concentred on the portion of the ore which it was desired to dislodge. Now, the flame is usually made to circulate from the floor to the roof, in commencing a new vault.

When the vault has already a certain height, care is always taken that between the roof of the vault and the rubbish on which the pile is arranged, no more than two yards of space should intervene, in order that the flame may embrace equally the whole concavity of the vault, and produce an uniform effect on all its parts. Here, the pile is formed of horizontal beds, disposed crosswise above one another, and presents four free vertical faces, whence it has been called a _chest_ by the miners.

It is usually on Saturday that the fire is applied to all the piles of faggots distributed through the course of the week. Those in the upper floors of exploitation are first burned, in order that the inferior piles may not obstruct by their vitiated air, the combustion of the former. Thus, at 4 o’clock in the morning, the fires are kindled in the upper ranges; from pile to pile, the fireman and his assistant descend towards the lower floors, which occupies them till 3 o’clock in the afternoon. Vainly should we endeavour to describe the majestic and terrific spectacle which the fire presents, as it unfolds its wings under its metallic vaults, soon filled with vast volumes of smoke and flame. Let us mark the useful effect which it produces.

When the flame has beat for a few instants on the beds of ore, a strong odour of sulphur, and sometimes of arsenic is perceived; and soon thereafter loud detonations are heard in the vaults. Suddenly the flame is seen to assume a blue colour, or even a white; and at this period, after a slight explosion, flakes of the ore, of greater or less magnitude, usually fall down on the fire, but the chief portion of the heated mineral still remains fixed to the vault. The ores pass now into a shattered and divided condition, which allows them afterwards to be detached by long forks of iron. In this manner the fire, volatilizing entirely some principles, such as sulphur, zinc, arsenic, and water, changing the aggregation of the constituent parts of the ore, and causing fissures by their unequal expansibilities, facilitates the excavation of such materials as resist by their tenacity the action of gunpowder.

The combustion goes on without any person entering the mine from Saturday evening till Monday morning, on which day, the fireman and his assistants proceed to extinguish the remains of the bonfires. On Monday also some piles are constructed in the parts where the effect of the former ones has been incomplete; and they are kindled after the workmen have quitted the mine. On Tuesday all hands are employed in detaching the ores, in sorting them, taking them out, and preparing new piles against the next Saturday.

The labour of a week consists for every man of five posts during the day, each of 8 hours, and of one post of four hours for Saturday. Moreover, an extra allowance is made to such workmen as employ themselves some posts during the night.

The labour of one compartment or _atelier_ of the mine consists therefore in arranging the faggots, in detaching the ore which has already experienced the action of the fire, in breaking the blocks obtained, in separating the ore from the _débris_ of the pile, and whenever it may be practicable or useful, in boring holes for blasting with gunpowder. The heat is so great in this kind of mine, that the men are obliged to work in it without clothing.

We have already remarked, that besides the working by fire, which is chiefly used here, recourse is sometimes had to blasting by gunpowder. This is done in order either to recover the bottom part or ground of the vaults on which the fire can act but imperfectly, to clear away some projections which would interfere with the effect of the pile, or lastly to strip the surrounding rock from the mass of the ore, and thence to obtain schist proper for the construction of the rubbish-terraces.

The blasting process is employed when the foremen of the workshop or mine-chamber judge that a hole well placed may separate enough of ore to pay the time, the repair of tools, and the gunpowder expended. But this indemnification is rarely obtained. The following statement will give an idea of the tenacity which the mineral deposit often presents.

In 1808, in a portion of the Rammelsberg mine, the ore, consisting of extremely compact iron and copper pyrites, was attacked by a single man, who bored a mining hole. After 11 posts of obstinate labour, occupying altogether 88 hours, the workman, being vigilantly superintended, had been able to advance the hole to a depth of no more than 4 inches; in doing which he had rendered entirely unserviceable 126 punches or borers, besides 26 others which had been re-tipped with steel, and 201 which had been sharpened; 6-1/4 pounds of oil had been consumed in giving him light; and half a pound of gunpowder was required for blasting the bore. It was found from a calculation made upon these facts by the administration of mines, that every inch deep of this hole cost, at their low price of labour, nearly a florin, value two shillings and sixpence.

It is therefore evident that though the timber, of which the consumption is prodigiously great, were much less abundant and dearer than it still is at Rammelsberg, mining by fire would be preferable to every other mode of exploitation. It is even certain, that on any supposition, the employment of gunpowder would not be practicable for every part of the mine; and if fuel came to fail, it would be requisite to renounce the workings at Rammelsberg, although this mountain still contains a large quantity of metals.

If in all mines the free circulation of air be an object of the highest importance, we must perceive how indispensable it must be in every part of a mine where the mode of exploitation maintains the temperature of the air at 112° Fahr., when the workmen return into it after the combustion of the piles, and in which besides it is necessary that this combustion be effected with activity in their absence. But in consequence of the extent and mutual ramifications of the workings, the number of the shafts, galleries, and their differences of level, the ventilation of the mine is in a manner spontaneously maintained. The high temperature is peculiarly favourable to it. The aid of art consists merely in placing some doors judiciously, which may be opened or shut at pleasure, to carry on the circulation of the air.

In considering the Rammelsberg from its summit, which rises about 400 yards above the town of Goslar, we observe, first, beds of slaty sandstone, which become the more horizontal the nearer they approach to the surface. At about 160 yards below the top level there occurs, in the bosom of the slaty graywacke, a powerful stratum of shells impasted in a ferruginous sandstone. See D, _fig._ 730. In descending towards the face of the ore, the parallel stratification of the clay-slate which forms its walls and roof grows more and more manifest. Here the slate is black, compact, and thinly foliated. The inclination of the different beds of rock is indicated at B. The substance of the workable mass is copper and iron pyrites, along with sulphuret of lead, accompanied by quartz, carbonate of lime, compact sulphate of baryta, and occasionally gray copper (_fahlerz_), sulphuret of zinc, and arsenical pyrites.

The ores are argentiferous and auriferous, but very slightly so, especially as to the gold. It is the ores of lead and copper which contain the silver, and in the latter the gold is found, but without its being well ascertained in what mineral it is deposited. Sometimes the copper occurs in the native state, or as copper of cementation. Beautiful crystals of sulphate of lime are found in the old workings.

In _figs._ 736. 737., A B is the shaft of extraction, called the _Kahnenkuhler_; N is the ventilation shaft, called _Breitlingerwetterschacht_; P is the extraction shaft, called _Innier-schacht_.

E F, is a new extraction-shaft, called _Neuer treibschacht_, by which also the water is pumped up; by A B, and E F, the whole extraction and draining are carried on. The ores are raised in these shafts to the level of the waggon-gallery (_galerie de roulage_) _i_, by the whims _l_, _q_, provided with ropes and buckets. 1, 2, 3, 4, _fig._ 736., represent the positions of four water-wheels for working the whims; the first two being employed in extracting the ores, the last two in draining. The driving stream is led to the wheel 1, along the drift _l_; whence it falls in succession upon the wheels 2, 3, 4. The general system of working consists of the following operation;--

1. The bed of ore is got at by the transverse galleries, _m_, _n_, _o_, _q_, _r_, _s_, which branch off from the extraction shaft, and terminate at the wall of the main bed;

2. Great vaults are scooped out at the level of the workings, by means of fire;

3. The roofs of these vaults are progressively propped with mounds of rubbish;

4. The ores thus detached, or by blasting with gunpowder, are then collected;

5. Lastly, they are wheeled out to the day; and washed near Z.

COMPARATIVE TABLE of celebrated MINES in EUROPE and AMERICA. By F. Burr, Esq. (_Quarterly Mining Review for July_, 1835, p. 60.)

+--------+--------------+--------------+--------------+--------------+
| |CONSOLIDATED |VETA GRANDE |MINE OF |MINE OF |
| |AND UNITED |MINES. |VALENCIANA. |HIMMELSFÜRST. |
| |MINES. | | | |
| +--------------+--------------+--------------+--------------+
| |(At present |(At present |(Richest of |(Richest of |
| |the richest |the richest |the Mexican |the Saxon |
| |mines in Corn-|mines in |mines at the |mines at the |
| |wall.) |Mexico.) |beginning of |beginning of |
| | | |the present |the present |
| | | |century.) |century.) |
| | | | | |
|Situa- |Two miles east|Four miles |One mile north|Two miles |
|tion |of Redruth. |north of |of Guanaxuato.|south-east of |
| | |Zacatecas. | |Freyberg. |
| | | | | |
|Eleva- |Elevation of |Elevation of |Elevation of |Elevation of |
|tion |the surface a-|the surface a-|the surface a-|the surface a-|
| |bove the level|bove the level|bove the level|bove the level|
| |of the sea, |of the sea, |of the sea, |of the sea, |
| |from 200 to |supposed to be|7,617 feet. |1,346 feet. |
| |300 ft.; depth|about 6000 |Elevation of |Elevation of |
| |of the bottom |feet. Eleva- |the bottom of |the bottom of |
| |of the mine |tion of the |the mine above|the mine above|
| |below the |bottom of the |the level of |the level of |
| |level of the |mine above the|the sea, 5,730|the sea, 263 |
| |sea, about |level of the |feet. |feet. |
| |1,370 feet. |sea, probably | | |
| | |near 5,000 | | |
| | |feet. | | |
| | | | | |
|Nature |The _Veta_ |The rock pre- |Primary clay |Transition |
|of the |_Madre_ of |vailing in the|slate resting |clay slate, |
|rock |Guanaxuato, |neighbourhood |immediately on|alternating |
| |upon which |of Freyberg, |granite, a |with dolomite,|
| |this mine is |in which this |short distance|and occasion- |
| |worked, tra- |and most of |westward of |ally with |
| |verses both |the other |the mines. The|greywacke. |
| |clay slate and|mines are |clay slate is |This clay |
| |porphyry, but |situate, is a |intersected by|slate is some-|
| |it is most |formation of |numerous chan-|times decom- |
| |productive in |primary |nels of por- |posed; it |
| |the former |gneiss. |phyry, which |rests on sye- |
| |rock. The clay| |have nearly |nitic rocks, |
| |slate is con- | |the same di- |and is in some|
| |sidered by | |rection as the|places covered|
| |Humboldt to | |mineral veins,|with porphyry.|
| |belong to the | |and are often | |
| |transition | |of consider- | |
| |class, but | |able width. | |
| |situate near | |The porphyry | |
| |the limits of | |sometimes | |
| |primary forma-| |appears also | |
| |tions. This | |to form large | |
| |rock in depth,| |irregular mas-| |
| |passes into | |ses in the | |
| |chlorite | |clay slate. | |
| |slate, and | |Both rocks are| |
| |talc slate. It| |traversed by | |
| |contains sub- | |veins of | |
| |ordinate beds | |quartz and | |
| |of syenite, | |clay inter- | |
| |hornblende | |secting the | |
| |slate, and | |metalliferous | |
| |serpentine. | |veins. | |
| |The porphyry | | | |
| |rests upon the| | | |
| |clay slate, | | | |
| |and is con- | | | |
| |formable to | | | |
| |it, both in | | | |
| |direction and | | | |
| |stratifica- | | | |
| |tion. | | | |
| | | | | |
|Nature |In the con- |One principal |One Veta (the |There are five|
|of the |solidated |vein (the |_Veta Madre_) |veins worked |
|metalli-|mines, the |_Veta Grande_)|which is often|in this mine. |
|ferous |eight follow- |which is gen- |separated into|The principal |
|deposits|ing lodes are |erally sepa- |three |vein (_Teich- |
| |extensively |rated into |branches, ex- |flache_) is |
| |worked:--Wheal|three |tending from |from one foot |
| |Fortune lode, |branches, and |130 to 160 |six inches, to|
| |Cusvea lode, |sometimes into|feet in width.|three feet in |
| |Deeble’s lode,|four. When |When not rami-|width, the |
| |Old lode, |ramified, the |fied, its |others are |
| |Taylor’s lode,|width extends |width varies |from six to 12|
| |Tregonning’s |to 60 or 70 |from 20 or 30 |inches wide. |
| |lode, Martin’s|feet; when |to 60 or 70 |The direction |
| |lode, and |united, it |feet, but is |of this vein, |
| |Glover’s lode.|varies from 8 |more commonly |is nearly |
| |In the united |or 10 to 20 or|from 40 to 50 |north and |
| |mines, the |30 feet. The |feet. The di- |south, its un-|
| |principal |branches are |rection of the|derlie is |
| |workings are |generally a- |vein, is |west, and a- |
| |upon the Old |bout 10 or 12 |north-west and|bout three |
| |lode, and a- |feet wide, and|south-east; |feet per fath-|
| |bout five or |the upper one |its underlie |om. Some of |
| |six others are|is most pro- |is south, and |the other |
| |more or less |ductive. |about five or |veins inter- |
| |productive. |The direction |six feet per |sect it. |
| |Numerous smal-|of the Veta |fathom. | |
| |ler lodes or |Grande, is | | |
| |“branches” oc-|from 30 to 40 | | |
| |cur also in |degrees south | | |
| |both mines. |of east, and | | |
| |The principal |north of west,| | |
| |lodes are from|and its under-| | |
| |2 or 3, to 7 |lie, from two | | |
| |or 8 feet |to three feet | | |
| |wide; the |per fathom | | |
| |“branches” are|south. Other | | |
| |generally 12 |veins of less | | |
| |or 18 inches |size, occur in| | |
| |wide. The di- |the neighbour-| | |
| |rection of the|hood of the | | |
| |lodes varies |Veta Grande, | | |
| |from nearly |which cross it| | |
| |east and west |at an acute | | |
| |to about 20 |angle. One of | | |
| |degrees north |these appears | | |
| |of east and |to heave the | | |
| |south of west.|vein for about| | |
| |The underlie |700 feet, be- | | |
| |of the princi-|ing the most | | |
| |pal lodes, is |remarkable de-| | |
| |from 2 to 3 |rangement of | | |
| |feet per fath-|the kind on | | |
| |om north, that|record. | | |
| |of the smaller| | | |
| |ones about the| | | |
| |same south. | | | |
| | | | | |
|Ores |Chiefly copper|Chiefly red |Sulphuret of |Argentiferous |
| |ore, occasion-||silver, na- |silver, native|sulphuret of |
| |ally native |tive silver, |silver, pris- |lead, native |
| |copper, blue |sulphuret of |matic black |silver, sul- |
| |and green car-|silver, and |silver, red |phuret of |
| |bonate of |argentiferous |silver, native|silver, red |
| |copper. Tin, |pyrites. |gold, argen- |silver. |
| |or oxide of | |tiferous | |
| |tin, also oc- | |galena. | |
| |curs, but not | | | |
| |in very great | | | |
| |abundance. | | | |
| | | | | |
|Produce |9-1/4 per |3-1/2 oz. per |Four ounces of|Six to seven |
|of the |cent. of fine |quintal. |silver per |ounces of sil-|
|ores |copper; aver- | |quintal of 100|ver per quin- |
| |age produce in| |lbs., equiva- |tal of 100 |
| |100 parts of | |lent to 2-1/2 |lbs. Equiva- |
| |ore. | |parts of metal|lent to from |
| | | |in 1,000 of |3-3/4 to 4-1/2|
| | | |ore, or 1/4 |parts of metal|
| | | |per cent. |in 1,000 of |
| | | | |ore, or from |
| | | | |3-8ths to |
| | | | |nearly 1/2 per|
| | | | |cent. |
| | | | | |
|Vein- |Chiefly |Chiefly |Quartz, ame- |Quartz, pearl-|
|stone |quartz, of |quartz, occa- |thyst, carbon-|spar, and cal-|
| |which many |sionally ame- |ate of lime, |careous spar. |
| |varieties oc- |thyst, carbon-|pearlspar, and| |
| |cur. |ate of lime, |hornstone. | |
| | |and sulphate | | |
| | |of barytes. | | |
| | | | | |
|Mineral |The ores are |The ores are |The ores are |The ores are |
|sub- |generally |generally |accompanied by|accompanied by|
|stances |accompanied by|accompanied by|blende, |blende, |
| |“gossan”[34] |blende, sul- |spathose iron,|spathose iron,|
| |in the backs |phuret of |copper and |and a little |
| |of the lodes, |antimony, and |iron pyrites. |iron and ar- |
| |by blende, and|iron pyrites. | |senical py- |
| |by iron, and | | |rites. |
| |arsenical | | | |
| |pyrites in | | | |
| |depth. | | | |
| | | | | |
|Depth of|_Woolf’s en-_ |_Tiro Gener-_ |_Tiro Gener- |_Franken- |
|the |_gine-shaft_, |_al_, 182 |al_, 310 fath-|schacht_, 180 |
|princi- |248 fathoms; |fathoms; |oms. |fathoms. |
|pal |Pearce’s _en-_|_Gallega_ | | |
|shafts |_gine-shaft_, |shaft, 138 | | |
| |275 fathoms. |fathoms. | | |
| |Some of the | | | |
| |other engine | | | |
| |shafts are | | | |
| |scarcely in- | | | |
| |ferior in | | | |
| |depth. | | | |
| | | | | |
|Depth of|At Woolf’s |There is no |There is no |The adit at |
|adit at |engine-shaft, |adit to this |adit to this |the shaft |
|the |13 fathoms. |mine. |mine. |called Fran- |
|princi- |The average | | |kenschacht is |
|pal |depth of the | | |47 fathoms in |
|shafts |adit at the | | |depth. |
| |other engine- | | | |
| |shafts is a- | | | |
| |bout 30 or 40 | | | |
| |fathoms. | | | |
| | | | | |
|Quantity|Varies from |About 80 gal- |The Valenciana|50 gallons per|
|of water|2,000 to 3,000|lons per min- |was a dry mine|minute. |
| |gallons per |ute. |from its com- | |
| |minute. | |mencement in | |
| | | |1760 to 1780, | |
| | | |when it first | |
| | | |became | |
| | | |troubled with | |
| | | |water, in con-| |
| | | |sequence of | |
| | | |some of the | |
| | | |workings being| |
| | | |inadvertently | |
| | | |communicated | |
| | | |with the ad- | |
| | | |joining mine | |
| | | |of Tepeyac; | |
| | | |which, al- | |
| | | |though upon | |
| | | |the same vein,| |
| | | |was extremely | |
| | | |wet. The quan-| |
| | | |tity of water | |
| | | |raised during | |
| | | |the late work-| |
| | | |ing appears to| |
| | | |have been a- | |
| | | |bout 110 gal- | |
| | | |lons per min- | |
| | | |ute, but the | |
| | | |regular influx| |
| | | |was much less.| |
| | | | | |
|Height |About 230 |On an average |310 fathoms. |133 fathoms. |
|to which|fathoms at the|about 150 | | |
|the |consolidated |fathoms. | | |
|water is|mines, at the | | | |
|raised |united mines, | | | |
| |about 110 | | | |
| |fathoms. | | | |
| | | | | |
|Power |9 steam-en- |Usually 10 |A steam-engine|Two water- |
|employed|gines; 3 of |malacates.[b] |of 30-inch |wheels, each |
|in |90-inch cylin-| |cylinder, and |42 feet in |
|drainage|der, 3 of 85, | |7 malacates. |diameter. |
| |1 of 80, and 2| | | |
| |of 65. A water| | | |
| |wheel, 48 feet| | | |
| |in diameter. | | | |
| | | | | |
|Probable|1,500 con- |32 horses con-|65 horses con-|16 horses con-|
|equiva- |stantly at |stantly work- |stantly at |stantly at |
|lent in |work, or a |ing, or a |work, or a |work or a |
|actual |total number |total number |total number |total number |
|horse- |of above |of about 100 |of about 200. |of about 50. |
|power |4,500. |horses.[c] | |[d] |
| | | | | |
|Average |12,700_l._ |20,000_l._ per|About |Cannot be as- |
|annual |taking the |annum.[c] |40,000_l._, |certained, but|
|expense |average of the| |per annum.[d] |evidently very|
|in |last ten | | |small.[d] |
|drainage|years.[a] | | | |
| | | | | |
|Quantity|16,400 tons of|21,380 tons of|32,500 tons of|630 tons of |
|of ore |copper ore, a |silver ore.[c]|silver ore.[d]|silver ore.[d]|
|annually|few tons of | | | |
|produced|tin ore.[a] | | | |
| | | | | |
|Produce |1,517 tons of |153,000 lbs. |221,900 lbs. |6,160 lbs. |
|in metal|fine copper, a|troy of sil- |troy silver. |troy of sil- |
| |little tin.[a]|ver.[c] |[d] |ver.[d] |
| | | | | |
|Total |119,800_l._[a]|423,400_l._ |About |About |
|returns,| |per annum.[c] |600,000_l._[d]|18,000_l._[d] |
|or value| | | | |
|of the | | | | |
|above | | | | |
| | | | | |
|Total |93,500_l._ ex-|252,170_l._ |197,900_l._ |9,500_l._ per |
|costs of|clusive of |per annum.[c] |per annum.[d] |annum.[d] |
|the mine|lord’s dues; | | | |
| |98,600_l._ in-| | | |
| |cluding lord’s| | | |
| |dues.[a] | | | |
| | | | | |
|Clear |21,000_l._ per|171,240_l._ |118,750_l._ |3,560_l._ per |
|profit |annum.[a] |per annum.[c] |per annum.[d] |annum.[d] |
|to the | | | | |
|proprie-| | | | |
|tors | | | | |
| | | | | |
|Amount |75,000_l._[a] |130,000_l._[c]|Cannot be as- |Cannot be as- |
|of | | |certained, but|certained, but|
|capital | | |known to have |probably very |
|invested| | |been very |small.[d] |
| | | |small.[d] | |
| | | | | |
|Interest|280 per cent. |Nearly 700 per|Not known, but|Not known, but|
|on |after paying |cent. after |certainly many|probably very |
|capital |back the orig-|paying back |hundred per |high.[d] |
|invested|inal capital. |the original |cent.[d] | |
| |[a] |capital.[c] | | |
| | | | | |
|Propor- |Costs exclu- |About 59-1/2 |Costs 60 per |Costs 73 per |
|tion of |sive of lord’s|per cent. |cent. In the |cent.[d] |
|costs to|dues, 78 per | |nine years | |
|returns |cent.[a] | |following, the| |
| | | |proportion was| |
| | | |80 per cent., | |
| | | |at the end of | |
| | | |that time the | |
| | | |working of the| |
| | | |mine was | |
| | | |stopped by the| |
| | | |revolution, in| |
| | | |the year 1809.| |
| | | |[d] | |
| | | | | |
|Number |About 2,500 |About 900, of |3,100 Indians |700 miners of |
|of men |persons, of |whom nearly |and Mestizoes,|whom 550 are |
|employed|whom about |600 are em- |of whom 1,800 |employed under|
| |1,450 are em- |ployed under |are employed |ground. |
| |ployed under |ground. |under ground. | |
| |ground. | | | |
| | | | | |
|Wages of|Probably about|About 8 or 9 |From 4 to 5 |About 1_s._ |
|the |3 shillings on|shillings per |shillings. |6_d._ per day.|
|mines |an average. |day. | | |
|per day | | | | |
| | | | | |
|Quantity| | |1,420 cwt.; |240 cwt.; |
|and ex- | | |value |value |
|pense of| | |15,830_l._ |1,070_l._ |
|powder | | | | |
| | | | | |
|Manner |Sold to the |Chiefly re- |Sold to the |Delivered to |
|in which|smelting com- |duced by the |Rescatadores, |the government|
|the ores|panies, and |company at the|and reduced by|reduction |
|are dis-|smelted by |hacienda of |smelting and |works in the |
|posed of|them at Swan- |Sanceda, by |amalgamation |neighbourhood |
| |sea, in South |smelting and |at haciendas, |of Freyberg, |
| |Wales. |amalgamation. |in the neigh- |where they are|
| | | |bourhood of |partly |
| | | |Guanaxuato. |smelted, and |
| | | | |partly amal- |
| | | | |gamated. |
+--------+--------------+--------------+--------------+--------------+

[a] Average of the last Ten Years.
[b] Malacate; a horse whim.
[c] Average of the last Six Years.
[d] Average year at the end of the Eighteenth Century.

[34] Gossan, or Gozzan; oxide of iron and quartz.

VENTILATION OF MINES.

When men penetrate by narrow passages into the interior of the earth, their respiration, joined to the combustion of candle and gunpowder, are not long of vitiating the air. The decomposition of wood contributes to the same effect, as also the mineral bed itself, especially in coal mines, by the carburetted hydrogen and carbonic acid evolved, and from the absorption of oxygen by pyrites. In many cases, arsenical and mercurial vapours are disengaged. Hence the necessity of maintaining in subterranean cavities a continual circulation of air, which may renew the atmosphere round the miners. The whole of the means employed to produce this effect, constitutes what is called the _ventilation of mines_.

These means are divided into _natural_ and _artificial_. The _natural means_ are the currents produced by the difference of density between the air of mines and the external air; the _artificial_ are air-exhausters or condensers, fires, &c.

The temperature of the air of the subterranean workings surpasses the mean temperature of the place in which the mine is opened. Hence it is lighter in winter, but in summer often heavier than the air of the atmosphere. For this reason, when the mine presents two openings at different levels, the air naturally flows out by the most elevated in winter, and by the lowest in summer. We may take advantage of this circumstance, to lead the air into the bottom of even a very long gallery, opening into the side of the mountain, by piercing a shaft into its roof at some distance from the entrance, and dividing the gallery by a horizontal floor into two parts, which have no mutual communication, except at the furthest extremity--the upper part communicating with the shaft, and the under with the mouth of the gallery. If the two compartments have different dimensions, the air in the smaller sooner comes into an equilibrium of temperature with the rock; and the difference of temperature of the two compartments is sufficient to produce a current. If a streamlet of water flows through this gallery, it facilitates the flow of the air along the lower compartment. If a mine has several openings situated on the same level, it rarely happens but some peculiar circumstance destroys, during the colds of winter and the heats of summer, the equilibrium of the air. But in spring and autumn, when the external air is nearly of the same temperature with that of the mines, the above-named causes are almost always too feeble to excite an issuing current. This effect is, however, frequently obtained by raising over one of the shafts a chimney 20 or 30 yards high, which alone produces the effect of an opening at a different level. It has been remarked that stormy weather usually deranges every system of ventilation. See PITCOAL and VENTILATION.

MINIUM. (Eng. and Fr., _Red lead_; _Mennige_, Germ.) This pigment is a peculiar oxide of lead, consisting of two atoms of the protoxide and one of the peroxide; but, as found in commerce, it always contains a little extra protoxide, or yellow massicot. It is prepared by calcining lead upon a reverberatory hearth with a slow fire, and frequent renewal of the surface with a rake, till it becomes an oxide, taking care not to fuse it. The calcined mass is triturated into a fine powder in a paint mill, where it is elutriated with a stream of water, to carry off the finely levigated particles, and to deposit them afterwards in tanks. The powder thus obtained being dried, is called massicot. It is converted into minium, by being put in quantities of about 50 pounds into iron trays, 1 foot square, and 4 or 5 inches deep. These are piled up upon the reverberatory hearth, and exposed during the night, for economy of fuel, to the residuary heat of the furnace, whereby the massicot absorbs more oxygen, and becomes partially red lead. This, after being stirred about, and subjected to a similar low calcining heat once and again, will be found to form a marketable red lead.

The best minium, however, called _orange mine_, is made by the slow calcination of good white lead (carbonate) in iron trays. If the lead contains either iron or copper, it affords a minium which cannot be employed with advantage in the manufacture of flint-glass, for pottery glazes, or for house-painting.

Dumas found several samples of red lead which he examined to consist of the chemical sesquioxide and the protoxide, in proportions varying from 50 of the former and 50 of the latter, to 95·3 of the former and 4·7 of the latter. The more oxygen gas it gives out when heated, the better it is, generally speaking. See NAPLES YELLOW.

MINT. (_Monnaie_, Fr.; _Münze_, Germ.) The chief use of gold and silver is to serve for the medium of exchange in the sale and purchase of commodities, a function for which they are pre-eminently fitted by their scarcity, by being unalterable by common agents, and condensing a great value in a small volume. It would be very inconvenient in general to barter objects of consumption against each other, because their carriage would be expensive, and their qualities, in many cases, easily injured by external agents, &c. Gold is exempt from spontaneous change, and little costly in conveyance. Mankind at a very early period recognised how much easier it was to exchange a certain weight of gold or silver for objects of commerce, than to barter these objects themselves; and thenceforth all agreed to pay for their purchases in bars or ingots of these precious metals. But as their intrinsic value depends upon their purity, it became necessary to stamp on these bars their standard quality and their weight.

The inconvenience of using ingots in general trade, on account of the difficulty of defining fractional values, has determined governments to coin pieces of money, that is, quantities of metal whose weight and standard were made known and guaranteed by the effigies of the prince. It is true, indeed, that kings have become frequently coiners of base money, by altering the weight and purity of the pieces apparently guaranteed by their impress. By such reductions modern coins represent less of the precious metal than they did long ago. The _ordonnance_ of 755, for the coining of _sous_ in France, proves that there was then as much fine silver in a single _sous_, as there is now in a piece of 5 francs. During the last two centuries, indeed, silver coins have been diminished two thirds in weight.

But since knowledge has become more generally diffused, it has been shown that these frauds are equally injurious to the prince and to public faith. A sovereign may, it is true, declare by a decree that a shilling-piece is to be held worth five; but let us consider the consequences of this decree. All the individuals who have rents or capital sums to receive, will be ruined, by getting in metallic value only one-fifth of what is due to them; for although the _nominal_ value should be the same as what they are entitled to, the intrinsic value would be but a fifth of the former; so that when they go to purchase the necessaries or comforts of life, the dealer who sells them will at once raise their price five-fold. Each article of merchandise would thus acquire a nominal price 5 times greater; and he who had received payment of a debt in that money, could not with it procure more than one-fifth of the goods he could have previously commanded. That fraudulent law would, therefore, favour the debtors at the expense of the creditors; and as the state is commonly a great debtor, especially when it has recourse to the depreciation of the currency, it is obvious, that however illicit the gain which it makes, it still does gain; and this is the reason why princes have so often tampered with the mint. But let us examine the other consequences of this decree.

If the sovereign is a debtor, he is also a creditor and consumer, and even the most considerable of any. The taxes which he imposes are paid him in this deteriorated money, returned to him at its nominal value; and the purveyors of his armies, his buildings, and his household, sell him their commodities only at the actual market price. We may infer from this simple development that the coin with which he pays for any object has the same intrinsic value as the object; and that the name given to the coin is of no consequence. The prince may call it a crown, a ducat, or a rix-dollar at his pleasure; and he may assign any value to it that his caprice may suggest, yet this will not affect its value; for this is fixed beyond his control by the general nature of things. The prince may, indeed, at the outset, have profited by defrauding his creditors, and by authorizing each debtor to imitate him, but he will soon lose whatever he may have gained; and he will thus learn to his cost that it was bad policy to sacrifice his character by giving an example of a fraud so truly unprofitable in the issue. Moreover, he will lose still as much in the following years, because his treasury will receive only one-fifth part of the taxes, unless he has quintupled the imposts. It may be said, indeed, that he might do the one thing along with the other. But every one knows that this power is neither generally permitted to princes, nor if it were, could it be safely exercised. Serious political crises would combine to endanger the stability of the government; which besides, as the main consumer in the nation, must lose always as much as it seems to gain.

It is therefore manifest that the alteration of the standard and weight of the coinage is at once a crime and a ruinous action for the sovereign power to commit; and hence such disastrous measures have been long abandoned in all well-regulated states. A gold sovereign is intrinsically worth 20 shillings minus the cost of coinage; for were it worth more, all our sovereign pieces would be exported or melted down, to obtain the difference of value, however trifling it might be; and were it worth less, it would be the source of loss similar to what the state occasions when it depreciates the coin.

To comprehend the true value of a coin, we must regard this piece as an article of merchandise, whose value depends, as that of every thing else, on its usefulness, the esteem in which it is held, and the demand for it in the market. Grain increases in value when there are few sellers and many buyers; gold and silver are in the same predicament. The value of these metals is much augmented, indeed, by the universal currency they obtain when struck into money; a value additional to what they possess as objects of the arts. This value of the precious metals changes with time and place, like that of every merchandise; their abundance, since the discovery of America, has greatly lowered their value; that is, with the same weight of metal, we cannot at the present day purchase the same quantity of corn, land, wool, &c. as formerly. In the countries where silver abounds, this metal has less value, or, in other terms, commodities are dearer. Hence the metal tends to resume its equilibrium in flowing into those places where it is rarer; which means, that the consumer prefers purchasing his commodities there rather than in another place, if he can easily transport them to where they are dearer.

It was formerly believed that a country is rich when it has a great deal of gold and silver; but this popular illusion has passed away. Spain has never been poorer than since the discovery of America, because its national industry has been ruined, and the capitals merely passed through its hands to spread over the rest of Europe, from which it was obliged to import every thing that its want of home manufactures made it necessary to procure from abroad. We may add to these, the prodigalities of the court, which, supposing its wealth inexhaustible, tried to corrupt all the ministers of the other powers, in furtherance of the chimera of universal dominion. The richest state is that in which there is most industry, whereby the inhabitants may procure every thing indispensable to the conveniences and comforts of life. Gold as a useful metal, and a medium of exchange, is undoubtedly very precious, and an adequate quantity for these exchanges must be had; but as it is good for very little besides, nay, as an excess is even hurtful, it soon begins to fly of itself towards the places where it is more needed or less common.

With regard to the relative value of gold and silver, several details have already been given in our view of the mineral wealth of the globe. Three centuries ago, an ounce of gold was worth at London or Paris 10 ounces of silver; now it may be exchanged for 15 ounces and a half.