Scenes and Adventures in the Semi-Alpine Region of the Ozark Mountains of Missouri and Arkansas Part 14

_f_, the flue, or throat, 10 feet long, 22 inches wide, and 11 inches in height. This must be continued a foot and a half over the mouth of the flue, or ap.r.o.n, making the whole length eleven and a half feet; some prefer the flue twelve and a half feet.

_g_, the mouth of the flue or ap.r.o.n, where the furnace is charged; this flares from 22 inches to 3 feet, in a distance of 3 feet, (as shown in Fig. 3.)

_h_, the fire-arch, 3 feet high in the centre, 18 inches high where the arch begins to spring, and the same over the centre of the basin-stone.

Figure 3. _Ground Plan._

From _a_ to _b_, 8 feet; from _b_ to _c_, 8 feet 6 inches; from _a_ to _d_, 8 feet 6 inches; from _e_ to _f_, 6 feet; from _e_ to _g_, 13 feet.

_h_, the basin, 4 feet long, and 22 inches wide, except in the centre, where it is 24 inches wide.

_i_, the flue.

_k_, the mouth of the flue, or ap.r.o.n, 3 feet at the front, and 22 inches in the rear.

_l_, the santee.

_m_, the fire-arch, with grates at bottom. (This is 22 inches wide at each end, 24 inches in the centre, and 5 feet long from the inside of its mouth to the santee.)

_n_, the mouth of the fire-arch.

_o_, the iron pot for the lead to flow into, set in the curve made in the wall for convenience of tapping.

_p_, the curve in the wall for drawing off the slag.

Figure 4, is a perspective view of the mouth of the flue where the furnace is charged.

From _a_ to _b_, 6 feet; from _a_ to _c_, 5 feet; from _a_ to _d_, 1 foot.

_c_, the mouth of the flue, 22 inches wide, and 11 high. (This flares out to 3 feet in the distance of 3 feet, the flue covering half of it, so that the heat may be thrown down on the ashes.)

[Ill.u.s.tration: _Ash Furnace_ No. 2 _For Smelting Lead Ashes. Missouri._ Fig. I. Fig. II. Fig. III. Fig. IV.]

One of the princ.i.p.al points to be attended to in building an ash-furnace is the elevation of the flue. It should rise 5 feet in 10; some prefer 5 in 11. If the ascent be too steep, the ore will run down into the basin before it gets hot, which is detrimental. If the ascent be too low, the bottom of the flue next to the basin will soon be eaten away by the heat, and thus in a short time undermine and destroy the furnace.

The flux employed is also a matter of moment. Sand, and pulverized flinty gravel, are mixed with the lead-ashes before smelting. The object of this is to promote the vitrification of the slag, which would otherwise remain stiff; the particles of revived lead would not sink through to the bottom, but remain entangled with it, and thus be lost.

Lime is also sometimes employed for the same purpose; and indeed any earth would operate as a flux to the scoriaceous part of the lead-ashes, if added in a due proportion, particularly the alkaline earths. Lime and barytes, both of which are afforded in plenty at the mines, might therefore be advantageously employed, when no sand or easy-melting silicious gravel could be obtained. Good fusible sands are readily attacked and liquefied by submitting to heat with oxides of lead, alkaline salts, or any other alkaline or metallic flux; hence their extreme utility in gla.s.s, enamels, and all other vitrescent mixtures.

When, therefore, silicious sand can be obtained, it will be found a more powerful flux to lead-ashes than either gravel, lime, spars, or any other substance, if we except the fluor spar. This is probably better adapted as a flux than even silicious sands; but it has not yet been brought to light at the lead-mines. Perhaps the lower strata of the earth may afford it. It is found at a lead-mine near Cave-in-Rock, on the right bank of the Ohio river, in the State of Illinois, and, with the exception of a little found at Northampton, Ma.s.sachusetts, is the only place where this rare, useful, and beautiful mineral, occurs in the United States.[17]

The situation for an ash-furnace is always chosen on the declivity of a hill, as represented in the plate. The inside work, or lining, consists of slabs of hewn limestone, laid in clay-mortar, and backed by solid masonry. Although a stone less adapted for furnaces could hardly be found, yet it is made here to answer the purpose, and is an evidence of the ingenuity of men in making a bad material answer when a good one cannot be found. No sandstone or freestone, of that refractory kind used in gla.s.s and iron furnaces, is afforded in this vicinity; and the smelters seem to prefer rebuilding their furnaces often, to incurring the expense of transporting good infusible sandstones from a distance.

It is not perhaps duly considered, that a furnace built of refractory materials, although expensive in the erection, would be sufficiently durable to warrant that expense, and outlast several built of limestone, which burn out every blast, and have to be rebuilt from the foundation.

Limestone is a combination of the pure earth _lime_ with _carbonic acid_ and _water_; it is a carbonate of lime. When subjected to a red heat, it parts with its carbonic acid and water, and, if the operation be continued long enough, is converted into quicklime. This effect, therefore, takes place as well in the lead-furnace as in the limekiln, and with this difference only--that in the former it is laid in a wall, protected in some degree from the heat, and will not part with its carbonic acid readily; while in the latter it is broken into comparatively small lumps, exposed to the heat on all sides, and is easily and readily converted into quicklime.

Nevertheless, although this calcination is constantly progressing, an ash-furnace will last from fifteen to twenty days, according to the skill which has been displayed in its construction, and the particular quality of the stone employed. When the stone partakes of clay (alumina), it runs into a variety of argillaceous limestone, and is manifestly better adapted to resist the effects of fire. Whenever the furnace is cooled, so that the stone can attract moisture from the atmosphere, it falls into quicklime. This change does not, however, take place rapidly; for the burning has seldom been uniform, and the stones have either been over-burned, or not burned enough; so that it requires several days, and even weeks, to a.s.sume the powdery state.

An ash-furnace, built of limestone, is estimated to cost a hundred dollars. This includes every expense, and such a furnace lasts during one blast, say fifteen or twenty days; perhaps, with great care, it will run a month. During this time, from sixty to ninety thousand pounds of lead ought to be made.

When a furnace is completed, it requires several days to dry it, and bring it to the proper state for smelting. About ten days are usually spent in this. The fire is begun very moderately at first, being only the warmth of a hot smoke, and is kept so for the first five days, by which means the moisture of the mortar and stone is gradually expelled, and without any danger of cracking the stone, or otherwise injuring the furnace. It is then raised a little every day until the furnace is brought up to a full red heat, when it is ready for the first charge of ashes.

The operation begins by shovelling a layer of ashes on the mouth of the flue, then adding a thin layer of sand or flinty gravel as a flux, and then more ashes; and so adding gravel and ashes alternately, until the required quant.i.ty is shovelled up. This is suffered to lie here and grow thoroughly hot before it is shoved down the flue into the basin; for, if introduced cold, it would check the heat too suddenly, and prove injurious in the result. When hot, the charge is shoved down the flue with a long-handled iron hoe, and another portion of ashes and gravel immediately shovelled on the mouth, suffered to heat, and then pushed down as before. This operation of heating and charging is continued until the furnace has a full charge, which may require about six hours, and in two hours more the furnace is ready for tapping. The slag, which is in a very fluid state on the top of the lead, is first drawn off, and the aperture closed up with stone and mortar. The smelter then goes to the opposite side of the furnace, and prepares for drawing off the lead by driving a stout sharp pointed iron bar through the side of the furnace, at a particular place contrived for this purpose. On removing the bar, the metallic lead flows out into a large iron pot set in the ground, and accompanied by a considerable quant.i.ty of a semi-metallic substance, called _zane_. This is lead not perfectly revived, being combined with some earthy particles, and oxide of lead. The zane occupies the top of the pot, and is first ladled out into hemispherical holes dug in the clay near by. This substance is of the consistence of the prepared sand used by bra.s.s-founders when hot, but acquires considerable solidity when cold. The metallic lead is then ladled into iron moulds of about eighteen inches in length, and yielding a pig of lead of about fifty pounds each. The quant.i.ty of zane made at each tapping is about equal to that of metallic lead. This is afterwards taken to the log furnace, and readily converted into lead. The lead made at the ash-furnace is not thought to be of so pure a quality as that of the first smelting made at the log furnace. It undoubtedly contains any other metals that may be combined with the ore, and is therefore more refractory. Such lead is thought to be a little harder, and some pretend to discover a lighter color.

The lead-ashes are reckoned to yield fifteen per cent. of lead (zane and all), which, added to the first smelting, makes an average product of sixty-five per cent. This estimate will hold good uniformly, when the ores have been properly dressed, and the smelting well performed. Any spar adhering to the ore, renders it refractory; blende and pyrites have the same effect. The latter is particularly injurious, as it consists chiefly of sulphur; a substance known to render all ores refractory.

The slag created by the ash-furnace is a heavy, black, gla.s.sy substance, well melted, and still containing a portion of lead. Some attempts have been made to obtain a further portion of lead from it, by smelting with charcoal in a blast-furnace; but the undertaking has not been attended with complete success, and is not generally thought to warrant the expense. The per centage of lead recovered from the slag is not estimated at over ten, and, with the utmost success, cannot be reckoned to exceed twelve.

Some practical and miscellaneous observations may here be added.

Metallic lead in the pig is now (Feb. 1819) worth $4 per cwt. at the mines. It sells for $4 50 on the banks of the Mississippi, at St.

Genevieve and Herculaneum; for $5 50 in New Orleans; and is quoted at $6 in Philadelphia. This is lower than has ever been known before, (except at one period,) and a consequent depression in the mining business is felt. There is a governmental duty of one cent per pound on all bar and pig lead imported into the United States; but it does not amount to a prohibition of foreign lead from our markets. Perhaps such a prohibition might be deemed expedient. It is what the lead-smelters here call for; and certainly the resources of this country are very ample, not only for supplying the domestic consumption, but for exportation.

Those who dig the ore do not always smelt it. The merchants are generally the smelters, and either employ their own slaves in raising the ore, or pay a stipulated price per cwt. to those who choose to dig.

For every hundred pounds of ore, properly cleaned, the digger receives two dollars. He works on his own account, and runs the risk of finding ore. It is estimated that an ordinary hand will raise a hundredweight per day, on an average of a year together. This, however, depends much upon luck; sometimes a vast body is fallen upon, with a few hours'

labor; at others, many weeks are spent without finding any. He who perseveres will, however, generally succeed; and the labor bestowed upon the most unpromising mine, is never wholly lost. The above average has been made by those long conversant with the business, and upon a full consideration of all risks.

Custom has established a number of laws among the miners, with regard to digging, which have a tendency to prevent disputes. Whenever a discovery is made, the person making it is ent.i.tled to claim the ground for twenty-five feet in every direction from his pit, giving him fifty feet square. Other diggers are each ent.i.tled to twelve feet square, which is just enough to sink a pit, and afford room for throwing out the earth.

Each one measures and stakes off his ground, and, though he should not begin to work for several days afterwards, no person will intrude upon it. On this spot he digs down, but is not allowed to run drifts horizontally, so as to break into or undermine the pits of others. If appearances are unpromising, or he strikes the rock, and chooses to abandon his pit, he can go on any unoccupied ground, and, observing the same precautions, begin anew. In such a case, the abandoned pit may be occupied by any other person; and sometimes large bodies of ore are found by the second occupant, by a little work, which would have richly rewarded the labors of the first, had he persevered.

In digging down from fifteen to twenty feet, the rock is generally struck; and as the signs of ore frequently give out on coming to the rock, many of the pits are carried no further. This rock is invariably limestone, though there are many varieties of it, the texture varying from very hard and compact, to soft and friable. The former is considered by the diggers as a flinty stone; the latter is called rotten limestone; and, from its crumbling between the fingers, and falling into grains, there is a variety of it called sandstone. It is all, however, a calcareous carbonate, will burn into quicklime, and, as I find on experiment, is completely soluble in nitric acid. As no remains or impressions of sh.e.l.ls, animalculae, or other traces of animal life, are to be found in it, I conclude it to be what geologists term metalliferous limestone; a conclusion which is strengthened by its semi-crystalline fracture. It exhibits regular stratification, being always found in horizontal ma.s.ses. How far this formation extends, it would be difficult to determine; but, so far as my observation goes, it is invariably the basis on which the mineral soil at Mine a Burton, and the numerous mines in its vicinity, reposes. It is overlaid by secondary limestone in various places on the banks of the Mississippi, between Cape Girardeau and St. Louis. It is also seen pa.s.sing into a variety of secondary marble, in several localities. I have seen no specimens of this mineral, however, which can be considered as a valuable material in sculpture.

I have already mentioned the per centage of lead obtained by smelting in the large way. I shall here add the result of an a.s.say made on the ore.

One hundred parts of ore yielded as follows:

Metallic lead 82 Sulphur driven off by torrefaction 11 Earthy matter, and further portion of sulphur, either combined with the scoria, or driven off by heat 7 by estimation.

--- 100

The ore experimented upon was the common ore of Mine a Burton, (galena.) I took a lump of the purest ore, completely freed from all sparry and other extraneous matter, beat it into a very gross powder, and roasted for an hour and a half in a moderate heat, with frequent stirring. On weighing the ma.s.s, it had lost 11 of sulphur. I now beat this to a very fine powder, and treated it with a strong flux of nitre and dry carbonate of soda, adding some iron filings to absorb the last portions of sulphur. The whole was enclosed in a good Hessian crucible, previously smeared with charcoal, with a luted cover, and exposed for twenty minutes to the high heat of a small chemical blast-furnace.

The richest species of galena, of which we have any account, is that of Durham, England. An a.n.a.lysis of a specimen of this ore by Dr. Thompson, gave the following result:

Lead 85 13 Sulphur 13 02 Oxide of iron 0 5 ----- 98 65

Many of the English, and nearly all the German ores, are, however, much poorer. Of five several experiments made by Vauquelin on ores from different mines in Germany, sixty-five per cent. of lead was the richest, and all were united with uncommon portions of carbonated lime and silex.

The b.u.t.ton of metallic lead found at the bottom of the crucible in chemical a.s.says, contains also the silver, and other metals, if any should be present in the ore. So also, in smelting in the large way, the metallic lead is always united with the other metals. When ores of lead contain any considerable portion of silver, they a.s.sume a fine steel grain; and the crystals, which are smaller than in common galena, oftener affect the octahedral, than the cubical figure. They are also harder to melt; and the lead obtained is not of so soft and malleable a nature as that procured from the broad-grained, easy-melting ore.

The proportion of silver in lead varies greatly. It is sometimes found to yield as high as twelve per cent., and is then called argentiferous lead-glance; but, in the poorest ores, it does not yield more than one ounce out of three hundred. To separate the silver from the lead, a process is pursued called the refining of lead, or cupellation. This is effected by exposing the lead to a moderate heat in a cupel, and removing the oxide as soon as it forms on the surface, until the whole is calcined, leaving the silver in the bottom of the cupel. The lead in this process is converted into litharge, the well-known substance of commerce; and the silver is afterwards refined by a second process, in which the last portions of lead are entirely got rid of. This process is known at the German refineries under the name of _silber brennen_, burning silver.

The rationale of cupellation is simply this. Lead on exposure to heat, with access of air, is covered by a thin pellicle or sc.u.m, called an oxide; and by removing this, another is formed; and so, by continuing to take off the oxide, the whole quant.i.ty of lead is converted into an oxide. It is called an oxide, because it is a combination of lead with oxygen (one of the principles of air and of water.) By this combination, an increase of weight takes place, so that a hundred pounds of bar-lead, converted into the state of an oxide, will weigh as much over a hundred, as the weight of the oxygen which it has attracted from the atmosphere.

Silver, however, on being exposed to heat in the same situation, cannot be converted into an oxide; it has no attractive power for oxygen.

Hence, when this metal is contained in a bar of lead, the lead only is oxygenated on exposure in a cupel; whilst the silver remains unaltered, but constantly concentrating and sinking, till the lead is all calcined.

This is known, to a practised eye, by the increased splendor a.s.sumed by the metal.

I do not think the ore of Mine a Burton contains a sufficient quant.i.ty of silver to render the separation an object. This is to be inferred from its mineralogical character, from the mathematical figure and size of the crystal, its color, splendor, &c. The territory is not, however, it is believed, deficient in ores which are valuable for the silver they contain. The head of White river, the Arkansas, the Maramec, and Strawberry rivers, all afford ores of lead, the appearance of which leads us to conclude they may yield silver in considerable quant.i.ty.

SECTION V.

ANNUAL PRODUCT, AND NUMBER OF HANDS EMPLOYED.