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bars, half-flats, and rods for wire; while the slabes are passed, when of a welding heat, through the grooved rollers. In this way of proceeding it matters not whether the iron is prepared from cold or red-short metal, nor is there any occasion for the use of finery, charcoal, coke, chafery, or hollow fire, or any blast by bellows, or otherwise; or the use of fluxes in any part of the process.

In one bar frequently two or more different kinds of iron may be observed, which run along its whole length; and scarcely a bar is ever found of entirely pure and homogeneous iron. This difference probably proceeds from the practice we have mentioned of mixing different kinds of ores together in the smelting; and also from the practice of mixing two or more pigs of cast-iron of different qualities in the finery of these, by which means the red-short and coldshort qualities of the different kinds are not, as we have already remarked, mutually counteracted or destroyed by each other, but each of these qualities is diminished in the mixed mass of iron, as much as this mass is larger than the part of the mass originally possessed of that quality; that is, if equal parts of red-short and of coldshort iron be mixed together, the mixed mass will be only half as red-short as the former part, and half as cold-short as the latter. For these different kinds of iron seem as if they were only capable of being interwoven and diffused through each other, but not of being intimately united or combined.

The quality of forged iron may be known by the texture which appears on breaking a bar. The best and toughest iron is that which has the most fibrous texture, and is of a clear grayish color. This fibrous appearance is given by the resistance which the particles of the iron make to their rupture. The next best iron is that whose texture consists of clear, whitish, small grains, intermixed with fibres. These two kinds are malleable both when hot and when cold, and have great tenacity. Cold-short iron is known by a texture consisting of large, shining plates, without fibres; and red-short iron is distinguished by its dark dull color, and by the transverse cracks and fissures on the surface and edges of the bars. The quality of iron may be much improved by violent compression, as by forging and rolling; especially when it is not long exposed to too violent heat, which is known to injure, and at length to destroy, its metallic properties.

A foundry of iron is, when calculated to do business on a large scale, situated near and connected with the ore and the blast furnaces, as here it is that the ore-smelting is done; and, where that is performed, castings can be executed better, and much cheaper, than when it is done at separate establishments; it is also better done, because, as more metal is heated at a time at such furnaces, there is a better chance of getting the castings perfect. It is cheaper from this very obvious circumstance, that, as the new metal is smelted, it is at once cast into the work required, instead of being run into pigs, as they are termed, to be re-heated in another furnace, and then to be founded. This additional heating,

with the cost of removal and labor, is saved by founding it into what is required at its first being smelted.

Im

Dr. Clarke's account of the iron mines he visited at Persberg, of which we furnish a graphic illustration, plate MINES, will be read with interest by the English metallurgist. The author's visit to these mines was made after he had personally inspected many of the principal works of the same nature in other countries, and especially in his own. For the last ten years of his life he had been much in the habit of seeing similar works: it is not therefore owing to any surprise at the novelty of the scene before him, that he has now to mention the astonishment he felt when he arrived at the mouth of one of the great Persberg mines; but he is fully prepared to say of it, and with truth, there is nothing like it in all that he has beheld elsewhere. 'For grandeur of effect, filling the mind of the spectator with a degree of wonder which amounts to awe, there is no place where human labor is exhibited under circumstances more tremendously striking. As we drew near to the wide and open abyss, a vast and sudden prospect of yawning caverns and of prodigious machinery prepared us for the descent. We approached the edge of the dreadful gulph whence the ore is raised, and ventured to look down; standing upon the verge of a sort of platform, constructed over it in such a manner as to command a view into the great opening, as far as the eye could penetrate amidst its gloomy depths: for, to the sight, it is bottomless. mense buckets suspended by rattling chains were passing, and we could perceive ladders scaling all the inward precipices. upon which the workpeople, reduced by their distance to pigmies in size, were ascending and descending. Far below the utmost of these figures, a deep and gaping gulf, the mouth of the lowermost pits, was, by its darkness, rendered impervious to the view. From the spot where we stood down to the place where the buckets are filled the distance might be about seventy-five fathoms; and as soon as any of these buckets emerged from the gloomy cavity we have mentioned, or until they entered into it in their descent, they were visible; but below this point they were hid in darkness.. The clanking of the chains, the groaning of the pumps, the hallooing of the miners, the creaking of the blocks and wheels, the trampling of horses, the beating of the hammers, and the loud and frequent subterraneous thunder from the blasting of the rocks by gunpowder, in the midst of all this scene of excavation and uproar, produced an effect which no stranger can behold unmoved. We descended with two of the miners and our interpreter into this abyss. The ladders, instead of being placed like those in our Cornish mines, upon a series of platforms as so many landingplaces, are lashed together in one unbroken line, extending many fathoms; and, being warped to suit the inclination or curvature of the sides of the precipices, they are not always perpendicular, but hang over in such a manner that even if a person held fast by his hands, and if his feet should happen to slip, they would fly off from the rock, and leave him suspended over the gulf. Yet such ladders are the only means of access

to the works below; and, as the laborers are not accustomed to receive strangers, they neither use the precautions, nor offer the assistance, usually afforded in more frequented mines. In the principal tin-mines of Cornwall the staves of the. ladders are alternate bars of wood and iron; here they were of wood only, and in some parts rotten and broken, making us often wish, during our descent, that we had never undertaken an exploit so hazardous. In addition to the danger to be apprehended from the damaged state of the ladders, the staves were covered with ice or mud, and thus rendered so cold and slippery that we could have no dependence upon our benumbed fingers, if our feet failed us. Then to complete our apprehensions, as we mentioned this to the miners, they said, Have a care! It was just so, talking about the staves, that one of our women fell, about four years ago as she was descending to her work.'' Fell,' said our Swedish interpreter, rather simply. and pray what became of her? Became of her,' continued the foremost of our guides, disengaging one of his hands from the ladder, and slapping it forcibly against his thigh, as if to illustrate the manner of the catastrophe, ⚫ she became (pankaka) a pancake.'

'As we descended farther from the surface, large masses of ice appeared, covering the sides of the precipices. Ice is raised in the buckets with the ore and rubble of the mine: it has also accumulated in such quantity in some of the lower chambers, that there are places where it is fifteen fathoms thick, and no change of temperature above prevents its increase. This seems to militate against a notion, now becoming prevalent, that the temperature of the air in mines increases directly as the depth from the surface, owing to the increasing temperature of the earth under the same circumstances; and in the same ratio; but it is explained by the width of this aperture at the mouth of the mine, which admits a free passage of atmospheric air. In our Cornish mines ice would not be preserved in a solid state at any considerable depth from the surface.

'After much fatigue, and no small share of apprehension, we at length reached the bottom of the mine. Here we had no sooner arrived, than our conductors, taking each of us by an arm, hurried us along through regions of thick-ribbed ice and darkness, into a vaulted level, through which we were to pass into the principal chamber of the mine. The noise of countless hammers, all in vehement action, increased as we kept along this level; until at length subduing every other sound we could no longer hear each other speak, notwithstanding our utmost efforts. At this moment we were ushered into a prodigious cavern, whence the sounds proceeded; and here, amidst falling waters, tumbling rocks, steam, ice, and gunpowder, about fifty miners were in the very height of their employment. The magnitude of the cavern, over all parts of which their labors were going on, was alone sufficient to prove that the iron ore is not deposited in veins, but beds. Above, below, on every side, and in every nook of this fearful dungeon, glimmering tapers disclosed the grim and anxious countenances of the miners. They were now driving bolts of iron into the rocks, to bore cavities for the gunpowder for

blasting. Scarcely had we recovered from the stupefaction occasioned by our first introduction into this Pandemonium, when we beheld, close to us, hags more horrible than perhaps it is possible for any other female figures to exhibit, holding their dim quivering tapers to our faces, and bellowing in our ears. One of the same sisterhood, snatching a lighted splinter of deal, darted to the spot where we stood, with eyes inflamed and distilling rheum, her hair clotted with mud, dugs naked and pendulous; and such a face, and such hideous yells, as it is impossible to describe :

Black it stood, as Night-fierce as ten Furies-
Terrible as hell.

If we could have heard what she said, we
should not have comprehended a syllable; but
as several other Parcæ, equally Gorgonian in
their aspect, passed swiftly by us, hastening tu-
multuously towards the entrance, we began to
perceive, that, if we remained longer in our pre-
sent situation, Atropos might indeed cut short
the threads of our existence; for the noise of the
hammers had now ceased, and a tremendous
blast was near the point of its explosion.
had scarcely retraced with all speed our steps
along the level, and were beginning to ascend the
ladders, when the full volume of the thunder
reached us, as if roaring with greater vehemence
because pent among the crashing rocks, whence,
being reverberated over all the mine, it seemed
to shake the earth itself with its terrible vibra-
tions.'

We

The following is an improved process for hardening steel. Articles manufactured of steel for the purpose of cutting are, almost without an exception, hardened from the anvil; in other words, they are taken from the forger to the hardener without undergoing any intermediate process; and such is the accustomed routine, that the mischief arising has escaped observation. The act of forging produces a strong scale or coating, which is spread over the whole of the blade; and, to make the evil still more formidable, this scale or coating is unequal in substance varying in proportion to the degree of heat communicated to the steel in forging; it is, partially, almost impenetrable to the action of water when immersed for the purpose of hardening. Hence it is that different degrees of hardness prevail in nearly every razor manufactured: this is evidently a positive defect; and, so long as it continues to exist, great difference of temperature must exist likewise. Razor-blades not unfrequently exhibit the fact here stated in a very striking manner: what are termed clouds, or parts of unequal polish, derive their origin from this cause, and clearly and distinctly, or rather distinctly though not clearly, show how far this partial coating has extended, and where the action of the water has been yielded to, and where resisted. It certainly cannot be matter of astonishment, that so few improvements have been made in the hardening of steel, when the evil here complained of so universally obtains as almost to warrant the supposition that no attempt has ever been made to remove it. The remedy, however, is easy and simple in the ex

treme, and so evidently efficient in its application, that it cannot but excite surprise, that, in the present highly improved state of our manufactures, such a communication should be made as a discovery entirely new.

Instead, therefore, of the customary mode of hardening the blade from the anvil, let it be passed immediately from the hands of the forger to the grinders; a slight application of the stone will remove the whole of the scale or coating, and the razor will then be properly prepared to undergo the operation of hardening with advantage. It will be easily ascertained, that steel in this state heats in the fire with greater regularity, and that when immersed, the obstacles being removed to the immediate action of the water on the body of the steel, the latter becomes equally hard from one extremity to the other. To this may be added that, as the lowest possible heat at which steel becomes hard is indubitably the best, the mode here recommended will be found the only one by which the process of hardening can be effected with a less portion of fire than is, or can be, required in any other way.

We will now direct our reader's attention to a very important, though simple process connected with the hardening and preservation of steel, for which the scientific world is mainly indebted to Mr. Pepys of the Poultry. In his manufactory the tempering, or reduction of the hardening, is not governed by the color only, but by a more accurate method; the exact variations of temperature are given in a fluid, into which a Fahrenheit's thermometer graduated to the boiling point of mercury is immersed, and the delieacy of this operation may be sufficiently understood from the various colors produced on the steel at the various temperatures shown by the thermometer. The change or scale takes place at 430°, and finishes at nearly 600°. Nine changes of colors are observable at about 20° distance of

each other.

[blocks in formation]

600 Blackish blue inclined to scale or oxyd. From 430 to 470 is chiefly employed for razors and some of the finer edged surgical instruments, 470 and 490 for penknives, and some pointed instruments. From 510 to 550 includes pocketknives, table-knives, carvers, scissors, &c., &c.

The experience of the workman is much required, and also a knowledge for what purpose the edge is to be employed, during these three ranges of temperature.

by a perusal of those parts that have been since translated by Mr. Raspe, which now makes the whole process both plain and intelligible. Amalgamation is the solution of metals in quicksilver. It depends on their elective affinities. Its object and use is either the purification of gold, silver, and other metals, or other mechanical purposes, of which there is no occasion to speak in this place.

The affinity of quicksilver with gold and silver was well known in the remotest antiquity. Vitruvius tells us how gold may be recovered by it from embroidery and old clothes. On this affinity also depends the gilding of metals and brass, which Pliny mentions. All our gold and silver smiths, and many other trades, are acquainted with it. From time immemorial quicksilver has been used in the streaming for gold, in order to purify, and collect into one body the gold dust, which is dispersed in the sands. To obtain these ends, the auriferous sand, brought into a smaller compass by washing, is mixed and triturated with quicksilver; and the amalgam, or solution of the gold, is pressed through a piece of leather, which separates the abundant quicksilver. The Gipsies on the banks of the Aranyos in Transylvania, the Russians on the banks of the Okka, the Americans in their stream works in Chili, and the Germans on the banks of the Rhine, use it in the same manner. The miner applied it for the same purposes, fetching auriferous stones from under ground, and pounding them to sand, which he afterwards triturated with quicksilver in particular mills. Of these quick mills, Agricola has left us an accurate account. Metallurgy being much improved in Germany since the days of Agricola, it was found that only part of the gold was extracted in these mills; that, to obtain the whole, the leavings must go to the fire; and that the gold taken up by the quicksilver must be parted from the silver. All this took away much of the credit of these quick mills; they began soon to be looked upon as superfluous. The gold was separated by washing, only from the first and richer stuff of the stamps; the poorer sorts went to the fire, and the gold was parted from silver by quartation. However, in some mines in the Zillerthal in Tirol, at Gasteris in Salzburgh, in some gold works in Savoy and Chili, which produce native gold, these quick mills are still in use for the purposes of dry or wet amalgamation. By Schlutter's account, the native silver of Kongsberg in Norway was also extracted in quick mills, till they fell into disrepute on account of the large quantities of silver they left in the residuum.

Burning and calcination of the ores promote amalgamation, in so far as it promotes their pulverisation, and assists the quicksilver, chiefly in Of amalgamation. The process of amalga- the treatment of gray silver and copper ores. The mation in procuring the precious metals, to which best symptom of sufficient calcination is their we have already briefly adverted, is but little change of color and loss of brightness. All practised in this country, and yet its value has bright ores must be calcined, but with great care been generally admitted by the leading chemists that no vitriol may be disengaged, for that both in South America and Europe. The prevents the amalgamation, or, by the subsequent treatise on this subject published by Baron saline additions, produces a salt, which dissolves Born in Germany is very rare, and but little the metals, and makes them unfit to unite with known in this country, and we have been favored the quicksilver. These and other circumstances

make fusion and treatment in furnaces frequently preferable to amalgamation, chiefly where there is plenty of wood and firing. Circumstances must determine whether it be better to grind and pulverise them before or after calcination. Their value and contents are better found by the calcination of the pulverised stuff. During the calcining fire it must be constantly stirred and turned about. From time to time some powder is taken from the furnace, and tried with quicksilver and salt, which presently shows the nature of the ore. The inspissation of the quicksilver, or the grain of the stuff, informs the artist whether or what addition it may require, and whether the calcination is perfected or not. The calcination of ores in lumps does not act equally upon all their parts; nor can the fire penetrate them every where. But it is attended with a smaller loss of dust, and saves much trouble and expense in the stamps and mills.

The irony ores, which resist the fire longer, are calcined with an addition of sulphur, or of sulphureous and antimonial stuff, proportioned to the iron they contain. Sulphureous and antimonial ores require calcination with iron scoria. The arsenical ores, or those which are mixed with orpiment and sandarac, are calcined with lead glance; and those which are infected with light or black bitumen must be exposed to the calcining fire with iron scoria or pounded lime

stone.

To determine the impurities of ores, and their proper additions, pound them coarsely, and throw them upon a heated iron plate. If the smoke be white or black, it is a symptom of white or black bitumen; if yellow, it argues orpiment; if red, sandarac; if yellow and greenish, it implies sulphur. The ores or halvan stuff must never be calcined with salt, for it would calcine the silver. The duration of the calcining fire cannot be determined but by the apparent loss of brightness and change of colors which the ores undergo, and by the test of quicksilver; if, when triturated with some of the calcined stuff, it remains white and pure, and takes a silver color, the calcination is completed. Besides this general rule, there are some other symptoms. If antimonial and sulphureous ores do no longer send forth a suffocating or disaagreeable smoke, if the thick black smoke of bituminous ores turns white, and if the silver in the stuff appears in white glittering sparks, in all these cases the calcination is perfected. Able masters will obtain the same and even in the calcination of paco's, negrillo's, and other vitriolic ores, though they require a longer calcining heat and various additions of alum and salt; but then they require no further addition in the subsequent operations, and the quicksilver will take up all their silver in the course of four days. Also less quicksilver will be lost; for, as there is no occasion for the frequent turning and working of the heap, it cannot be worked into impalpable and irrecoverable dust.

One circumstance cannot be too strongly recommended; it is, that vitriolic ores must always be lixiviated before they go to the calcining fire. If the calcined stuff be suspected of being vitriolic, it must be tried by quicksilver; if it takes

a lead color, the stuff must be washed till iron put into it does no longer take a copper color. The lixivium of the vitriolic stuff, or ore, is preserved as a useful addition to some ores.

Before the master dresses his heap, he mixes the fine and sifted powder, and takes a sample of three or four pounds for the assay by fire. According to the produce he calculates the contents of the whole for his government. Moreover, he tries the same with quicksilver, to come at the method how the whole is to be treated, and to learn what additions will be required. First he lixiviates the stuff, to extract the sulphate of copper. Then he takes one pound of the lixiviated stuff and tries it by trituration with salt and quicksilver, carefully observing its color and change. If the quicksilver takes the color and form of silver filings, and these quicksilver flakes turn thinner and thinner, it is proof that the amalgamation goes on successfully, and that there is no occasion for any addition. The whole is stirred from time to time, till the quicksilver seems to diminish, and to recover its natural globular form without dividing into small globules. Then the stuff is washed, all the silver being then completely taken up. Formerly the complete extraction of silver by amalgamation, without other additions, was looked upon as impossible; but the ores of Verenguela de Pacagés are actually treated only with quicksilver and salt, and yet they yield their full produce. If the quicksilver takes a lead color, which the Spanish miners call plomo, then the heap requires additions of iron, lead, tin, quicklime, and ashes; for, with them, any silver or ore may be amalgamated. If it turns black, iron is added; if a light lead color tin,; if a dark lead color, lead; if it takes a yellowish or gold color, which implies copper, it requires an addition of lime.

It often divides into small white powdery globules, in consequence of the gravity or hardness of the mineral. This chiefly happens in the amalgamation of lead glance, marcasite, and other bright minerals, or in that of uncalcined hard matrices or loadstones. It likewise arises from too much stirring; and may be obviated by previous calcination of the stuff, or by less stirring. Yet this quicksilver dust is hardly to be avoided in great operations. It serves the workmen for a measure of their progress, nay even for a direction how to operate. This dust is called by different names. The whitish dust, which arises simply from too great division, is called quicksilver dust. What arises from the amalgama of lead and tin is called dust of addition; and what comes from the silver amalgama, silver dust. They are easily distinguished. Quicksilver dust is white, without any quickness, hardly moving when the stuff is stirred with water; it rather sticks to the bottom, and on rubbing it between the fingers it clots into globules. The silver dust sinks towards the coarser stuff on the bottom, and floats about in larger or smaller flakes; rubbed and pressed between the fingers it turns into an amalgama. The dust of addition is, as it were, intermediate between the two. Pressed between the fingers, or rubbed, it unites with the quicksilver, which

had begun to combine with silver. These different powders are produced during the amalgamation and washing, by too frequent stirring and turning, chiefly when lead, marcasite, and irony ores are in the mixture; also by sulphate of copper, which in particular brings on this too minute division of the quicksilver; and likewise by too abundant addition of salt, which inspissates the water, and prevents the quicksilver particles from falling to the bottom. They are commonly of the color of quicksilver, and of a white, black, and lead color; like the color of the quicksilver they indicate the various imperfections of the heap in hand, and their respective remedies.

When the master is fully informed, by smaller assays, of the quality and produce of his stuff, of the additions it requires, and of the circumstances which may attend his operations, he accordingly regulates his heap and his proceedings. The heap is wetted with water and mixed with the proper quantity of salt. In the beginning, but one-third of the quicksilver and one-half of the tin and lead are added. During the first two days, it is but once turned over every day, because the quicksilver then uncombined with silver would be apt to fly into very minute globules, and consequently bring on great loss of quicksilver dust. Moreover, too much quicksilver chills the heap, and its amalgamation should rather be assisted by heat. For these reasons it is but gradually added; and though, for want of quicksilver, the work should but slowly proceed in the beginning, yet this may easily be remedied afterwards.

The additions of tin and lead are always thrown into the heap together with the quicksilver. Too much of either hurts the process, for they deaden the quicksilver, and make it unfit for taking up the silver.

Both quicksilver and other additions must be proportioned according to circumstances; observing that the quantities added at a time must be less and less, the more the amalgamation approaches perfection: otherwise the whole would be overloaded with, and swim in quicksilver, whereas it should be kept rather dry, and two parts of amalgama to be in the heap to one of quicksilver. Some masters are of opinion, that abundance and superfluity of quicksilver cannot be hurtful, provided there be a sufficient quantity or proportion of additional ingredients. But this very abundance is exceedingly hurtful, by the great quantity of quicksilver dust which must arise from the turning of the stuff; moreover, if by some accident the additional ingredients should be wasted or destroyed, the dust of addition will change into quicksilver dust, which, having hardly any weight, will not fall to the bottom, but swim on the surface, and run off with the water. If the addition is lime, the whole must be added at once, and the heap be turned over for two or three days, till the quicksilver is added. Too much prevents the combination of the two metals, and any inconveniency may be remedied but this.

The heaps are frequently turned and worked over, that the quicksilver may be thoroughly mixed with the stuff, and take up the silver con

VOL. XIV.

tained in it. The turning heats the quicksilver and so far assists its attraction. The frequent rubbing purifies the silver. From the difference of their constituent parts, the heaps and the difference of ores are subject to different accidents. The respective progress and obstacles of the amalgamation best appear by fine pulverisation of the stuff; and the quicksilver is the mirror in which all that appears clearly.

The quicksilver deadened by too abundant addition of lead, tin, iron, and lime, loses its oval and affects a vermicular form. Shaken in a glass or other vessel by itself, without any water, it adheres to the sides as it were in strings like thread. Thus circumstanced it is unfit for taking up silver. Its best remedy is sulphate of copper, or the lixivium of vitriolic ores, which was spoken of before. The other base metals, which by their cold nature had deadened the quicksilver, are changed by this sulphate of copper into copper, and the quicksilver is thereby warmed and restored to life and activity. For the same purpose copper powder is thrown into the heap, and vitriol is the chief ingredient of all the additions which are intended to warm the quicksilver. Thus copper ore is calcined, and when ground fine two parts of it are mixed with one part of salt. Then it is calcined once more, adding half a pound of brass filings to 1 cwt.; or equal parts of fine and coarse stuff and salt are calcined together; or equal parts of copper ore, coarse stuff, and salt; or equal parts of copper ore, coarse stuff, iron scoria, and of the fine silver stuff. They are formed into a paste and cakes which are calcined. These solvents must be thrown into the heap very, cautiously, and in consequence and by the direction of smaller assays, which determine what quantity of vitriol will do it good, or disagree with it. The heaps which have too much vitriol, and no additional remedies, give a lead color to the quicksilver. Its quickness is not affected, any more than that its smaller particles appear not in a convex but spherical form.

To obviate this evil, and to protect the quicksilver against the corrosion and action of the vitriol, iron is added, as having a particular power to recal it to life, and to bring it again into one body. But, as there is no certain rule for its proportion, small samples of the heap should be submitted to experiment, nor the heap be turned over till that proportion be fully determined. Sometimes, on examining the heap whilst it is turning, the quicksilver appears in small globules connected as a bunch of grapes. This implies salt, which covers the quicksilver and prevents its combination. It is remedied by the addition of some coarse stuff, which, on being turned with the heap, cleanses the quicksilver. Some add ashes; but the best and most natural remedy is alum, which abounds at Potosi, and whitens the silver. If the heap be not turned equally, and the quicksilver be not added at the proper time, or the silver does not unite with it, dry silver will arise, and lie on the coarser stuff like cobweb, which, if not skimmed off in time, is carried off by the washing water. To collect this dry silver, and the finest quicksilver dust, some silver amalgama is pressed upon

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