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all of which was a higher production, and less loss of metal in slags and by volatilization. This has been reached by a complete alteration of the shape of the furnaces, by increase of size, and the introduction of proportionately more compressed air through a larger number of tuyores. În regard to their shape, and the results obtained, two furnaces have come into especially prominent notice. These two are :
1. The Raschette furnace. It has an oblong rectangular cross-section and the form of an inverted truncated pyramid. Numerous tuyeres, cooled by running water, are placed in the long sides, in such a manner that the opposite
currents of air pass each other. 2. The Piltz furnace. It has a hexagonal, octagonal, or circular crosssection, and the shape of an inverted truncated pyramid or cone. Many tuyeres are placed radially around the furnace-center, the breast alone being withont them.
Both of these furnaces are furnaces with open breast, and both have the two most important principles in common, the application of more compressed air in a comparatively smaller space than in old-style furnaces, and a widening of the shaft toward the top. The first secures a more perfect and rapid combustion, and hence a more rapid fusion; the second causes the smelting zone to commence lower down in the furnace than formerly; the charges, lying firmly upon the slanting sides, force the gases and heat to pass through the whole column above, while the wider section above decreases the velocity of the upward current, and volatilization is to a great extent prevented.
But quite recently experience has taught in this country that a combi. nation of the form of the Raschette and Piltz, so to speak, produces still better results, the capacity of the furnace being thus increased, while the management is less difficult. Last spring two new furnaces were built at the works of the Eureka Consolidated Company, in Nevada. In order to test the comparative merits of a combination furnace avd the Piltz, Mr. Albert Arents, the metallurgist of the works, concluded to construct one furnace with elongated hearth, 3 feet wide by. 41 feet in depth, and 64 feet diameter at the top. The furnace was provided with ten water-tuyeres, four in each side and two in the back wall. The other furnace was a Piltz, of 4 feet diameter in the hearth, 6:1 feet at the top, and provided with twelve tnyeres placed radially around the center. Both furnaces were 10 feet high above the tuyeres, and worked admirably, but the combination furnace was found to smelt from onefifth to one-fourth more ore than the Piltz under the same circumstances. The same experience has been arrived at in the Hartz districts in Germany, where the best results are obtained with a circular furnace of 5 feet diameter at the top, having a bearth 20 inches wide and 31 feet deep, and seven tuyeres. In this furnace the loss of lead in the slag (althongh the same charge is used as in the other furnaces) disappears almost entirely, being only 1 per cent., while in the other furnaces it is from 2 to 4 per cent.
The best proportion of the hearth-area to the throat-area may be accepted as 1:24 for a height of from 10 to 12 feet. It is rarely necessary in the western districts to give a greater height to the furnaces. I am at present only aware of the existence of one which exceeds this height. This is situated in Bingham Cañon, Utah, and has to smelt very quartzose ores.
Before proceeding further, I shall give a general statement of the ele. mentary principles of metallurgical operations. It is true that the cur. rent text-books on metallurgy cover a good deal of this ground; but I deem it important to introduce this plain and practical résumé for the
benefit of those who cannot easily consult the best large works upon the subject. Many of these are in foreign languages, others are both dear and scarce, and all, it may be presumed, are more or less difficult of access in our remoter mining regions.
Minerals containing the useful metals in such quantities and in such a chemical combination as to make their extraction profitable, we term "ores," while their earthy portions we designate as their "matrix" or
gangue. In regard to subsequent metallurgical treatment, we can make the following practical classification :
1. Smelting ores, viz, ores containing base metals in notable quantities.
2. Dry ores, viz, ores containing noble metals and no base ones, or only in limited quantities.
It is my intention to speak here particularly of those pertaining to class 1.
Ores and gangue are always more or less intimately mixed. For the utilization of the metals it is, therefore, necessary to separate them from their gangue by artificial means, which are either of a mechanical or chemical nature. A mechanical separation alone is not sufficient to produce a merchantable product; it can only serve as preparatory to the chemical processes, among which that of smelting will be here specially considered. Smelting is a conversion of solid mineral or mineral and metallic masses into the fluid state by means of heat and chemicals, and the subsequent separation of the metallic from the earthy ingredients by means of their specific gravity. Although there are a great many methods in vogue for utilizing lead-ores by smelting, there are only two which have found application and justly claim attention in the mining regions of the Great Basin : (A) the English process of smelting in reverberatory furnaces, and (B) the blast-furnace process.
The former has some marked advantages over the latter: the possi. bility of using raw fuel; its exemption from the necessity of using blow. ing-engines, and the consequent saving of power; an easier control of manipulations, and the production of a lead of better quality in which the precious metals are concentrated. Its general application, however, greatly impaired by the fact that only comparatively pure ores can be treated successfully. Thus, ores containing a considerable percentage of other metals besides lead, as, for instance, zinc, copper, antimony, &c., or more than 4 per cent. of silica, are unfit for the reverberatory process, silicate of lead, which impedes the process of the operation and gives rise to the formation of rich residues, being formed in the latter case. In the former there is, besides loss in rich residues, also a large one by volatilization. In England the lead-ores subjected to this process contain about 80 per cent. of lead, the gangue generally being carbonate of lime. The English process in its unaltered form can, therefore, only be recommended for pure galenas with calcareous gangue, an ore not often obtained in the western mining districts. To my knowledge there is only one establishment in operation where ores are treated by this process, that of Messrs. Pascoe & Jennings, near Salt Lake City. Another one of this kind, that of Messrs. Robbins, is idle for want of the proper ores. I feel, therefore, justified in omitting to enter upon a more minute description of this process.
Compelled by the high prices of labor, transportation of materials and products, lack of cheap mineral coal, &c., the lead-smelters of the Great Basin have almost unanimously adopted the blast-furnace process of smelting. By its means they are enabled to obtain a salable product in
the shortest possible time, and with the least expense, the residues being so poor that they can be thrown away.
To insure success in smelting lead-ores, as all other ores, it is necessary to know their mineralogical character, as well as the chemical properties of the gangue in which they occur. A perfect separation of the ore from its matrix by hand being impossible, and a concentration by water being, in most cases, in the West impossible, on account of the insufficient supply of this liquid, the gangue accompanying the ore must be converted into a fusible compound, termed slag. Quartz, we know, is infusible by itself; so is lime; but if we mix both in the proper proportions, and expose them to the necessary heat, the result will be a fusi. ble compound. It has been found by actual experience that not the single compounds of silica and lime, or alumina, magnesia, &c., but double compounds of, say, silicate of lime and silicate of alumina, are the most fusible ones. Replacing one of these bases by alkalies, or the protoxides of the heavy metals, as, for instance, iron and manganese, we increase the fusibility of a slag within certain limits. The fusibility of a slag depends principally upon the proportion of silica to the bases contained in it. Mineral substances which serve to liquefy others not fusible by themselves we call fluxes. Under favorable circumstances an ore may contain all the slag-forming ingredients in the proper ratio, but only in a very few instances has nature graciously permitted such a coincidence, as, for example, in Eureka district, Nevada.
According to the ratio between silica and the bases, we discriminate four classes of fusible slags :
1. Tri-silicates, in which the silica contains three times the amount of oxygen present in the bases. As there is over 50 per cent. of silica in such slags, they require too high a temperature for their formation to be thought of in lead-smelting.
2. Bi-silicates, containing 50 per cent. of silicic acid and 50 per cent. bases, in which the amount of oxygen in the silica is twice as large as in the bases.
3. Singulo-silicates, with 30 per cent. silicic acid and 70 per cent. bases, the silica containing as much oxygen as the bases.
4. Sub-silicates, with 20 per cent. silicic acid and 80 per cent. bases, the amount of oxygen in the silica being less than that in the bases.
In the latter two the bases are predominant over the silicic acid, therefore they are termed “basic slags," while the first two are termed "acid slags." Chemists have taken the trouble to establish complicated formulas derived from accurate analyses of various slags; but, as they are rarely constant compounds, these formulas have hardly any practi. cal value for the metallurgist; he is content to know the percentage of silica and the quantity of the useful metal which he is endeavoring to obtain. An experienced smelter must be able to draw his conclusions from the appearance of his slag in both the fused and solid states.
The most desirable slag for lead-smelting is the singulo-silicate, or a mixture of bi-silicate with the former, with protoxide of iron prevailing. The singulo-silicates run with a bright-red color, and solidify very quickly with turgescence. The bubbles, after bursting, frequently discharge blue gaseous flames.
These slags have a vitreous, metallic luster, and a higher specific gravity than the bi-silicates, and are, therefore, more liable to entangle metallic particles. If lime and alumina are the prevalent bases, the heat required for their formation is much higher than in the case mentioned before. Such slags are generally pasty, run short, and form incoherent lumps. After solidification they have a honey-combed, stony,
or pumice-stone-like appearance, grayish-green color, and radiated, or lamellar-crystalline texture. An earthy singulo-silicate is really almost the least desirable slag for a lead-smelter.
Bi-silicates require a higber temperature, and consequently involve a larger consumption of fuel for their formation than singulo-silicates. They flow slowly like sirup, solidify very gradually, without cracking or bursting, and are not liable to form accretions in the furnace, like basic slags. They appear vitreous after chilling, have a conchoidal fracture, and generally a black color. Being saturated with silicic acid they corrode the furnace-lining much less than basic slags. Their specific gravity is lower and admits of a clean separation of metallic particles; but on the other band they are apt to take up a large percentage of oxide of lead, and so cause a loss of metal. Furthermore, for their formation it is necessary to have the ore reduced to at least pea-size, which condition is not fulfilled in western smelting-works, where crushers are generally used for breaking up coarse pieces of rock.
Sub-silicates are entirely out of the question, as they are only detrimental. If protoxide of iron is their principal base, they run in a thin stream, like fluid litharge, congeal very quickly, and easily form accre. tions in the furnace-bottom. Having a high specific gravity, they do not allow a clean separation from the metal. By their corrosive action on the lining, and their tendency to form accretions in the furnace, they shorten a campaign or run to a few days; hence, their production must be avoided.
As fluxes the following substances are used :
1. Acid slags, for their capability to take up bases, and as solvent agents.
2. Basic slags, for their capability of saturating themselves with silicic acid, and as diluting agents.
3. Iron-stone is a very efficient agent to slag silicic acid, i. e., quartz, being reduced in the furnace to protoxide of iron, which has a strong affinity for silicic acid, and forms an easily fusible slag. Its price varies in the western districts, according to local circumstances, from $5 to $25 per ton. The best quality for our purposes is hematite or magnetite. Hydrated iron-ores are too easily reduced to metallic iron, and ought to be burned before use. If free from quartz and slag they may be thrown into the furnace in pieces of fist size. Iron-ores are also used as desul. phurizing agents.
4. Soda is even better than the above as a solving agent for quartz, but it can only be had in a few localities at reasonable rates, the general price being from $60 to $80 per ton.
5. Lime, as a partial substitute for iron-stone in solving quartz. It is best used in pieces of pigeon-egg size. From the theoretical standpoiut burnt lime would be the best form, but as this is generally in a very fine state, it will partially be blown out at the top of the furnace or roll through the interstices of coal and ore, and thus be prevented from uniting with the silica in the desired proportion. Lime cannot be used by itself as a slagging agent for quartz. Lime-slag is smeary, not very liquid, and deranges the furnace very easily by clogging. The metal separates only imperfectly from it, which is the reason that so much metallic lead is wasted by being thrown away with the slag in some of the limestone districts.
6. Clay is only used on a very small scale as a partial substitute for quartz. It must be applied very cautiously, as it often arrives raw at the bottom of the furnace in the shape of dry, incandescent lumps, which stick to the walls and hearth.
7. Salt is used by some smelters of Utah who have a very indistinct comprehension of fluxes. Although they allege that it renders the slag liquid, this is an illusion. Any assayer knows that the salt does not enter into a chemical combination with gangues, but forins a slag by itself, which, on account of its lesser specific gravity, floats on the top of the other slag. I noticed slag of this kind at Mr. Easton's furnace, Salt Lake City. Besides its inefficiency upon earthy matters, salt acts injuriously upon the metal by forming volatile chlorides of lead and silver.
8. Iron pyrites has been ignorantly used as a miraculous sort of flux. To the skilled metallurgist the effects are obvious, viz, the production of a brittle, sulphureted metal, or of matte, no action upon gangues, and a clogging up of the furnace.
9. Quartz, in the form of coarse sand. It is used to furnish the acid for the slag in cases where the gangue of the ores is basic.
In addition to the fluxes enumerated above, I must mention some me. tallic products occasionally used for various purposes :
1. Iron, in the shape of tin scraps, pieces of wrought iron, cast iron, &c., is used to decompose galena, thereby forming sulphuret of iron, (iron-matte) and metallic lead. Owing to the high price of iron in Utah and Nevada, it is either replaced by the less efficient iron-stone, or rendered unnecessary by a previous roasting of the ores.
2. Litharge was intended to be added to poor lead-ores at Ogden, Dunne & Co.'s works at Eureka, Nevada, in order to prevent the precious metals from being carried into the iron-matte. Owing to the heavy expense of cupelling, and a change of the ore for the better, this purpose was abandoned.
3. Cinders, semi-fused matter from previous smeltings to extract the metals.
Fuel.—The only fuel used at present by the lead-smelters of the Great Basin is charcoal, the price of which ranges from 15 to 34 cents per bushel of 1.59 cubic feet, according to locality. The lowest rates are paid at the American Fork and Tintic districts, Utah, where timber is abundant; the highest at Little Cottonwood, Utah, which gets its coal from Truckee, California, by rail, and at Eureka, Nevada. In the latter place the enormous demand has materially influenced the price. The tive furnaces of the Eureka Consolidated Company, for instance, consume alone 4,600 bushels daily. The charcoal is chiefly burned from cedar, quaking aspen, mountain mahogany, and nut-pine wood. Nytpine coal is considered the best, and generally contracted for. The coalburners make their pits of various sizes, according to circumstances. A pit of 100 cords of green wood burns out in about fifteen or twenty days, and yields from 2,500 to 3,500 bushels of charcoal. The best coal is made about Eureka, Nevada, by experienced Italian coal-burners, the poorest in some places in Utah. The latter is generally made of small timber, and is full of brands and dross. The waste often reaches 15 per cent. As one ton of good, hard coke approximately produces the same effect as-200 bushels of charcoal, it would be a great benefit for the western smelters to use it. But the blast-engines used do not yield a sufficient pressure for a perfect combustion of coke, as experiments at the Eureka Consolidated have shown. The price of charcoal being steadily ou the increase, there will be a time when smelters will have to replace the former by coke. It may be reasonably expected that after the Utah Southern Railroad is finished, the development of those fiue beds of mineral coal in the southern part of that Territory will tend to the springing up of coke-industry, and so give a new impetus to smelting. Blast-engines.—The only blast-engines in use in Nevada and Utah are
H. Ex. 211-25