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tical treatment with the chemical analysis, needing every attention, care, and closely observed practice. Why, sir, your Journal has teemed with remarks on the treatment of gold quartz, while the subject of silver ore treatment is far more worthy the attention of the scientific man, as involving close research. Gold results in mechanical treatment, silver into that of chemical manipulation, and in its combinations with nearly all the common metals and minerals, in a variety of forms and states of mineralization.
The silver ore imported into this country is large in amount of tonnage at present, and is on the increase, yielding in some cases not more than 30 ozs. per ton, and running up from that ley to several thousands of ounces per ton. These ores may be said to be competed for by two or three houses only; there are a nuinber of bidders, but their offers are so short of the real value, that they excite a smile from the more knowing ones, who generally purchase to advantage. I have known the offers to vary as much as 95 per
cent. per ton of ore, and they excuse thernselves in making these offers on • the ground as shown in Prof. Plattner's experiments-viz., loss in treatment;
that they are never able to obtain any approach to the assay product in treating the bulk, and that they offer accordingly to keep themselves safe, or, in other words, to perpetuate their own ignorance.
The silver ores imported are treated by amalgamation, or by smelting. Their amalgamation is conducted after the usual process, by mixing cominon salt in quantities (generally having a reference to the percentage of silver contained in the ores); a mixture is thereby etfected which, on being roasted, the silver in the ores undergoes a chemical change, which converts it into chloride of silver from its previous state of mineralization. It is then requisite, either in barrels, or by other means, to bring it into intimate contact with mercury. The quantity necessary of quicksilver also depends on the percentage of richness for silver, which is taken up by chemical affinity in the form of amalgam, aided by using scraps of iron, and, in some cases, a little lime. Now, in this process, roasting the ore is the great hinge on which the success of the treatinent depends; hence the importance of Prof. Plattner's experiments. The other process is that of smelting, but the silver ores are generally roasted per se, and afterwards mixed in varied proportions with ordinary lead ores, which both act as a flux and take up the silver, which is subsequently obtained by desilverizing the lead in the ordinary way, the roasting loss occurring as a matter of course, alluded to by Prof. Plattner.
Now, sir, in iny practice in amalgamation of silver ores, I obtained the best results from using 12 per cent. of salt for ores containing 100 ozs. of silver per ton, increasing or diminishing that quantity as the richness or otherwise of the ore for silver warranted, using about 650 lbs. of mercury per ton of ore, as I always found an excess of these menstrums to be attended with benefits in practice over and beyond the chemical formulary of theory, adding some scrap iron and a little lime for some classes of ore.
In the roasting of silver ores for sinelting I always used a little salt, the quantity entirely depending on the character and extent of the mineralization. Now in theory, the salt would be found to form a chloride of silver; in practice it does no such thing—that is, if you do not exceed a certain limit, which is to be ascertained by an analysis of the ore treated as to the quantity of sulphur, arsenic, or other matter it contains; and by the use of salt in roasting I found a very manifest benefit of results.
I fear that I havo trespassed too much on your valuable space with my crude remarks, but must hope some others more competent will give us their views on a subject of great interest to the trade of this country. My bodily indisposition prevents me from giving all the details I could wish in this communication, but I would like to see our School of Miners imitating Prof. Plattner.- London Jour.
WILLIAM J. TENNEY.
CONTENTS OF N(). III., VOL. VII. .
LY AND PRACTICALLY CONSIDERED.-By Wx. TRURAN, C. E. 123
IV. DIRECTIONS FOR COLLECTING, PRESERVING AND TRANSPORT-
-By Prof. J. HENRY
V. RIDGWAY FARM AND LAND COMPANY'S PROPERTY.-GEOLOG
ICAL REPORT.-By Dr. CHARLES T. JACKSON .
JOURNAL OF VINING LAWS AND REGULATIONS.
Decision of the Supreme Court of the United States, in the Suit between the Min
nesota and National Mining Companies
TCOALS AND COLLIERIES.
A Visit to the Lackawanna Coal-Fields
Mines, Mining Operations, Metallnrgy, fc., de.
VOL. VII.—SEPTEMBER, 1856.—No. III.
ART. I. - THE IRON MANUFACTURE OF GREAT BRITAIN-.
THEORETICALLY AND PRACTICALLY CONSIDERED, BY WM. Truran, C. E. No. 8.
(Continued from page 58, vol. 7.)
SECTION VII.-THE BLAST, OR COMPRESSED) ATMOSPHERIC AIR
EMPLOYED IN SMELTING.
DENSITY OF THE BLAST. The pressure or density of the blast is a matter of considerable importance in smelting. It is regulated by the height of the fur. nace; size of the hearth; and qualities of the fuel. In the infancy of the manufacture, owing to the low state of mechanical science, the blowing machines employed were very deficient in the power necessary for compressing the air. The blast obtained was inferior in quantity and of a low pressure; but the furnaces were of small capacity, and the produce of iron was on the same limited scale. With the improvements in the manufacture of machinery, attention was directed to the blowing machinery of iron works; greater volumes of blast, compressed to a higher density, were obtained ; and with additional blowing power, the capacity and height of the furnace was increased, and the produce of metal augmented in a similar ratio.
The density of the blast is dependent on the height of the fur. nace, inasmuch that the greater or lesser weight of the column of solid materials affects the density of the stratum of fuel under combustion. But the blast furnaces of the present day are built nearly of one uniform height;-a deviation of more than 5 feet from the average height is rare. The variation, then, in the pressure exerted by the superincumbent materials on the fuel, from the greater or lesser height of the column in different furnaces, is not great, and may safely be omitted. Therefore, in proportioning the density and volume of the blast, we must consider the internal dimensions of the furnace, and the qualities of the fuel, as the governing agents.
In the present state of the manufacture, 2 lbs. to the square VOL. VII.-8
inch is a minimum degree of compression. A few years since, the experiment of a lower blast was tried at the Wingerworth furnaces, but after great expense and waste of material, it was finally abandoned, and a blast of 27 to 2 lbs. to the square inch substituted. And more recently we have witnessed numerous instances of the injurious effects produced by a weak scattered blast on the make and quality of the crude iron.
The maximum density of blast is dependent, to a certain extent, on the fuel. If the coal is of a hard compact structure, containing a large percentage of carbon, a pressure of 4 to 5 lbs. to the inch may advantageously be adopted. With a weak, friable coal, containing a low percentage of carbon, 2 to 24 lbs. is very commonly used. The dense cokes of a highly bituminous coal support a blast of 21 to 34 lbs.
As a general rule, from which we have scen no exceptions, the density of blast applicable to any given coal-the other conditions being equal—is proportionable to the density of the coke produced from such coal. IIence, the hardest and heaviest coke will carry the strongest blast, and vice versa.
Generally speaking, the increase in the density of the blast bas not kept pace with the enlargements of the blast furnace, and yet they are directly dependent on each other. The density must be such, that the requisite quantity of atmospheric air penetrates to the opposite side of the hearth, in order to maintain active combustion in the fuel descending farthest from the tuyere. The wider the hearth the more numerous will be the obstructions to its passage across. Any increase, then, in the width of the hearth should be met by a corresponding increase in the density of the blast. The degree of compression is undoubtedly carried farther now than formerly, but it is not sufficient for the large hearths constructed.
In the old blast furnaces the width of the hearth seldom exceeded 3 feet; through a mass of materials of this thickness only had the blast to penetrate. For this purpose the density usually was 1} to 2 lbs. If the obstruction offered by the thickness of material required a blast of this density for the perfect combustion of the fuel, it is very evident that with a wider hearth a proportionately higher density is required. If to penetrate 3 feet required a mean pressure of 14 lbs. to penetrate twice the distance requires twice the pressure, or 34 lbs. to the square inch. Considering the pressure of 18 lbs. as suitable for the 3 feet hearth, an approximation may be made to the pressure required for any other width. The 14 lbs. to 3 feet, is equal to six tenths of a pound nearly for each foot. Hearths are now constructed up to 8 feet in breadth: for such, the pressure of blast should, by this rule, be 44 lbs. to the inch. For the more common breadth of 6 feet the pressure will be 34 lbs ; but in practice a lower density is used.' Partly from not justly considering the relation