Scenes and Adventures in the Semi-Alpine Region of the Ozark Mountains of Missouri and Arkansas Part 13

At Mine a Burton, there is found adhering to the sides of the log-hearth furnace, a grayish-white sublimated matter, of great weight, which I take to be a sublimate of lead. It is considered as chiefly sulphur or a.r.s.enic by the lead-smelters, and is thrown by as useless. It is found at every furnace, and a very large quant.i.ty could be annually collected.

This induced me to undertake some experiments on the subject. I was convinced, on reflection, that there could be no sulphur, at least no considerable quant.i.ty of sulphur, in it, from the fact that all sulphur, or other inflammable matter, expelled from the ore in the furnace, would undergo immediate combustion. This is also observable in the color of the flame while the ore is torrified. Indeed, every person conversant with the nature of this substance must know that it cannot be otherwise.

The furnace is entirely open, and does not rise over seven or eight feet in height; consequently, there is no opportunity for it to condense.

That the sulphuric acid is driven off, is undoubted; for, whenever sulphur is burned, this acid is set at liberty; but it has no opportunity for entering into a new combination within the body of a log furnace.

The idea of a.r.s.enic in the substance alluded to, is perfectly erroneous, and has originated in an ignorance of the nature of the ores of these mines. It is the _sulphuret of lead_, and not the _a.r.s.eniate_. That there is a small portion of silver and antimony in combination with the ore, is probable; but they too are mineralized by sulphur. Reflecting on this, I became convinced of the popular error, and, to ascertain the point, made the following experiments:

A. I took a lump of the sublimated matter, freed from adhering impurities, and reduced it to the state of a fine powder by pulverizing in an agate mortar, and trituration. Of this I mixed six parts with four of pulverized borax, and a little charcoal, and submitted it to the intense heat of a small chemical furnace. On removing the crucible, I found a b.u.t.ton of metallic lead in the bottom, weighing nearly four.

B. Dissolved a quant.i.ty of the powdered sublimate in nitric acid; it effected a ready solution, with violent effervescence. Poured on liquid carbonate of potash until no more precipitate fell. I then collected the precipitate, and washed away the superfluous alkali by clear water, and dried it in the shade. The result was a very fine, and a very white powder, of considerable weight. This was a carbonate of lead (white lead). With a quant.i.ty of the white lead thus made, I mixed linseed oil, and painted a board. The color was of the most delicate white, and it gave a good body. On inspecting this board several months afterwards, I found the color inclining a little to yellowish. But perhaps it stands as well as any white lead would, prepared from litharge, by solution in nitric or acetic acids, and precipitation by carbonated alkali.

C. Mixed eight parts of sublimate with twelve of muriate of soda, and fused in a crucible, with a tight cover, in a high heat. Result, a yellow, hard, heavy, vitrified ma.s.s, resembling muriate of soda and lead.

M'Kain's Mine is situated on a small stream called Dry creek, running into Big river not far from its junction with the Maramec. The mine is worthy of remark only on account of a body of steel-grained lead-ore found there. This ore is found to yield less lead in smelting than the common broad-grained ore, and, as may be inferred from its texture, contains silver.

So little has been done, of late years, in mining in the rock, that the character of the veins must be judged of from limited facts. But there can be no question, from what is known, that the true scene of mining operations is the rock.

Along the west banks of the Mississippi, and also in some of the interior valleys, we observe that the metal-bearing limestone rests on crystalline sandstone. Both preserve a horizontal position, and both are deposited, at the distance of about seventy miles south of Potosi, upon pre-existing formations of sienitic granite, embracing hornblende rock; some of the latter of which is porphyritic.

These primitive formations mark the geography of the country at the sources of the St. Francis. They form alpine peaks, through which the river forces its way. Mine a La Motte is within two miles east of this tract. These peaks have been raised to their present position without disturbing the horizontality of the limestones and sandstones. Hence the conclusion of their prior elevation.

At a still further southern point, and before reaching the banks of the St. Francis at Bettis's ferry, the horizontal rocks again appear. But, in this instance, sienitic and granitic boulders are scattered over the southern series of the calcareous strata, showing, with equal clearness, that the geological era of the boulder stratum was posterior to the deposition of the horizontal strata, and that the force which scattered the boulder stratum was from the north.

SECTION IV.

METHOD OF WORKING THE MINES.

The method of raising the ores, and the processes pursued in separating the metal, are, upon the whole, extremely simple. A pick-axe and shovel are the only tools in use for removing the earth; and the drill, rammer, and priming-rod, are added when it is necessary to blast. Having determined on the spot for digging, the process commences by measuring off a square of about eight feet, and throwing out the earth, spar, and gravel, until the miner sinks beneath the depth he can throw the earth.

An expert hand will pitch his earth clear out of the pit from a depth of ten, twelve, and even fifteen feet. At this depth a common windla.s.s and bucket are placed over the centre of the pit, and the digging continued by drawing up the earth, spar, and ores, if any are found, in the manner pursued in sinking a well. During his progress, the miner is notified of his approach to a body of ore, by small detached lumps occasionally found imbedded in the soil, within a few feet of the surface. Sometimes lumps on the top of the ground determine on the place for digging. The spar is also a sign by which he judges, as there is seldom a body of spar found without lead-ore. There are also other signs by which an experienced digger is advertised of his prospects, and encouraged to proceed with cheerfulness in his work. These are, peculiar appearances in the texture of the spar, and sometimes minute specks of ore scattered through it, the changes in the color, and other qualities of the earth, gravel, &c. If these appearances are promising, and bits of ore are occasionally met with, he is encouraged to sink down a great depth; but if they should fail, he is generally induced to abandon the pit, and commence at another place.

In searching for ore, the soil, the slope of the hills, spar, blossom, trees, &c., are taken as guides, and some are obstinately attached to these signs. Others, who have been fortunate in finding ore where these appearances were least promising, wholly disregard them, and pay no attention to rules. In general, there is a greater disposition to trust to luck and chance, and stumble upon ore, than by attending to mineral character, to be sure of success. As those who search by rules are generally incapable of those minute remarks on the distinguis.h.i.+ng character and geological situation of minerals, which are necessary in order to ensure success, it frequently happens that they meet with disappointments. An incident of this kind is enough to perplex a man who has not habituated himself to reasoning on the subject, and to weaken his belief in the affinity of ores and stones. Such a man will not stop to compare and reconcile facts, which are seemingly opposite, or to investigate the nature of general principles.

Hence miners exclaim on the uncertainty of finding ores by rules drawn from the observations of science; that the strata of the earth are irregular, and not to be depended upon like the rock formations in Europe; and that, in fine, we have no guides by which its mineral treasures are to be sought, and that, in so confused a soil, chance is the best guide. Such a man is more ready to follow the mysterious guidance of the divining-rod than the light of reason, and would be easily persuaded that fortune is more surely the result of blind chance, than of feasible schemes, well planned and well executed.

There would be, nevertheless, some truth in the uncertainties and the confusion complained of, were those circ.u.mstances among the observations of scientific men. But it will be hazarding little to say, that when such observations are made, there will be found as much regularity, harmony, and order, in the superposition of the strata, as generally exist. The few facts I have noticed, lead to this conclusion.

Having raised a sufficient quant.i.ty of ore for smelting, the next process consists in separating the spar, and cleaning the ore from all extraneous matter. This is done by small picks, tapered down to such a point that a careful hand may detach the smallest particle of adhering spar. It is necessary that the ore should be well cleaned, as it would otherwise prove refractory in smelting. If there be any lumps of uncommon size, they are beaten smaller. The object is to bring the lumps as near as may be to an uniform size, so that the heat may operate equally in desulphurating the ore. It is desirable that the lumps should be about the size of a man's two fists, or perhaps fifteen pounds'

weight; if too small, a difficulty and a waste is experienced in smelting. In this state, the ore is conveyed to the primary furnace, (see Plate I.) and piled on the logs prepared for its reception. When the charge is put in, which may in a common way be about five thousand pounds, it is surrounded by logs of wood, and covered over at the top, the fire being lit up at the mouth below. A gentle warmth is created at first, which is raised very gradually, and kept at this point for about twelve hours, to allow the sulphur to dissipate; the heat is then increased for the purpose of smelting the ore, and, in twelve hours more, the operation is completed, and the lead obtained. Wood is occasionally added as the process goes on, and there is a practical nicety required in keeping the furnace in proper order, regulating the draught of air, &c., so that some smelters are much more expert, and thereby extract a greater quant.i.ty of lead from a like body of ore, than others. This furnace is called the log furnace, and, so far as I know, is peculiar to this country. It is of a very simple construction, consisting of an inclined hearth, surrounded by walls on three sides, open at top, and with an arch for the admission of air below. Upon the whole, it appears well adapted to the present situation and circ.u.mstances of the people. It is cheap, simple, may be built at almost any place, and answers the purpose very well. A good furnace of this kind may be built at a cost of from fifty to sixty dollars, every expense considered; and one of the most considerable items in the sum total is the bill of the mason, who cannot be hired, in this region, to work for less than two dollars per day.

Plate I., Figure 1. _A Perspective View of the Log Furnace._

a, the front wall, 8 feet long, 7 feet in height, and 2 feet in thickness.

b b, the side walls, 8 feet long, and 2 feet thick.

c, the hearth, 2 feet wide, and 8 feet in length.

d d, the ledges on each side of the hearth, 10 inches in height, and 1 foot wide. These serve to elevate the logs above the hearth, at the same time creating a draught for the air, and pa.s.sage for the lead.

e, the eye of the furnace, or arch, 2 feet across at bottom, with an arch thrown in a half circle, or a flat stone laid across at the height of the ledges.

f, the iron ladle for dipping out the melted lead.

g, the iron mould. Every bar of lead cast in this, is called a _pig_.

h, the hole in the ground, for the reception of the lead as it runs from the furnace.

Figure 2, is a perspective view of the furnace from the back or open part. The same letters used in Figure 1 apply to the same parts of the furnace in this figure.

Figure 3. _Ground Plan._

_a_, the eye or arch in front.

_b b_, the side walls.

_c_, the hearth.

_d d_, the ledges.

[Ill.u.s.tration: _Log Hearth Furnace_ No. 1.

_For Smelting Lead Ore_]

The process of charging the furnace may be mentioned. Three large oak logs, rolled in from the back side, and resting at each end on these ledges, fill up the width of the furnace; small split logs are then set up all around on the two sides and front; the ore is then piled on until the furnace is full, and logs are then piled over it, beginning at the back, and continuing over to the front, so that the ore is completely surrounded by wood. This furnace is always built on the slope of a hill, as represented in Plate I., Fig. 1; and the hearth is laid on an angle of 45, so that it falls four feet in a distance of eight. Two furnaces of the size here described are generally built together, by which there is a saving of the expense of one wall, and the work is rendered stronger, one serving as a support to the other. Not only so, but the same number of hands will keep a double-eyed furnace in blast, which are required at a single one. It takes three hands, one to cart wood during the day-time, and the other two to relieve each other alternately, every twelve hours, at the furnace. When a charge is melted off, the furnace is cooled, new logs and upright pieces put in, and the whole operation begun anew. Twenty-four hours is the time generally allotted for each smelting, but it often takes thirty-six; and when there is bad wood and want of attention, it requires still longer, and indeed the result is never so good.

The ore is estimated to yield, in the large way, fifty per cent. the first smelting. A considerable portion of what is put in, however, does not become completely desulphurated, and is found in the bottom of the furnace after cooling. This is chiefly the smallest lumps, which have fallen through the apertures that burn between the logs, before they were thoroughly roasted, and thus, getting out of the way of the heat, lie entangled with the ashes. Some lumps, which are too large, also escape complete desulphuration, and either remain unmelted, or else, when the fire is raised, melt altogether into a kind of slag, and produce little or no metallic lead. This const.i.tutes what are called the lead-ashes. The larger pieces, consisting of ore but partially desulphurated, are carefully picked out from among the ashes, and added at the next smelting in the log furnace; while the remainder is thrown by in heaps for further examination.

The lead-ashes are still rich in lead, and, when a sufficient quant.i.ty has acc.u.mulated from repeated smeltings, it is taken off to a proper place contrived for the purpose, and separated from the cinders, wood-ashes, and other adhering impurities. This is done by was.h.i.+ng the whole in _buddles_, one set below another, in the manner of the potter, when it is necessary to _search_ his clays. The ashes, which consist of clotted lumps of a moderate hardness, are first pounded to a gross powder, and then introduced into the water through a sieve. The wood-ashes and other impurities, being lighter, swim on the top, and, by letting off the water, are thus carried away. Fresh water is added, the ashes briskly stirred with a hoe, and the water again let off, carrying a further portion of impurity with it. By repeating this operation several times, the lead-ashes are brought to the required degree of purity. Thus washed, they are carried to a furnace of a different construction, called the ash furnace (see Plate II.), and undergo a second smelting.

Plate II., Figure 1. _A Perspective View of the Ash Furnace._

_a_, the ash-pit, 2 feet wide, 6 feet long, and 20 inches in height.

_b_, the mouth of the fire-arch, a foot square.

_c_, the mouth of the flue, where the charge is put in.

_d_, the iron pot for the lead to flow in, when the furnace is tapped.

Figure 2, is a longitudinal section through the furnace, at right angles with the front, showing the curve of the arch, flue, &c.

_a_, the ash-pit.

_b_, the grates, 10 inches square, and 3 feet long; these are pieces of hewn stone.

_c_, the mouth of the fire-arch.

_d_, the _santee_, consisting of two stones, 3 feet long, and 3 feet 6 inches wide, with a thickness of 6 or 7 inches. They reach from the bottom of the ash-pit to a foot above the basin-stone, the interstice between them being rammed full of clay, and the whole measuring 18 inches across. (This keeps the lead, slag, &c., from running into the fire-arch, and is an important part of the furnace, requiring considerable skill and accuracy in the construction.)

_e_, the basin-stone, 4 feet square, and 1 foot thick.