1st. Let us take the case of a charcoal furnace working with cold-blast at a pressure of 1 lbs. per square inch and burning one ton of carbon at the tuyeres per ton of pig iron produced. In this case 1 × 4.33 = 5.77 tons of blast per ton of pig iron. T1. = 0.0278. 5.77 tons x 0.238 x 280.3° × 0.0278 577 tons X 0.238 x 7.8° = 10.7 ton-Centigrade heat units per ton of pig iron. 2d. In the example (A), given by Mr. Bell in his work on the Chemical Phenomena of Iron Smelting (Section XXVIII), of a furnace having a capacity of 11,500 cubic feet, and smelting Cleveland ironstone, The pressure of the blast is not stated, but is assumed to be four This is equivalent to 1260 cwt.-Centigrade heat units, which are the units Mr. Bell employs in his calculations. 3d. In the Cedar Point furnace, working with anthracite and with blast heated in Whitwell stoves, the calculation of the heat requirements of which is given by Mr. Witherbee in the Transactions of this Institute (vol. v, p. 618), Q5.481 tons of blast per ton of pig iron. The pressure of the blast is not stated but is assumed to be about 7 lbs. per square inch. In this last case the amount of heat absorbed in heating the blast to its original temperature is seen to be considerable, owing to the fact that both the temperature and the pressure of the blast are high. Those who are not familiar with heat calculations may obtain a more definite idea of the extent of this loss of heat by observing the loss in temperature which the blast suffers during its expansion, (T, — T2). This amounts to 108° C. (194° F.) in the case in question, so that, while the temperature of the blast as recorded after leaving the hot-blast oven is 704° C., its temperature after its expansion is less than 600° C. It must be remembered, that these results are exact only upon the assumptions which we have made, viz.: 1st. That the back pressure in the furnace is equal to that of the external atmosphere. 2d. That the blast is first cooled to the full extent by its expansion, before its temperature is again raised by the heat in the furnace. 3d. That the pressure at the tuyeres is equal to that in the receiver. Since there is always an excess of pressure above that of the atmosphere in the hearth of a furnace while it is in blast, the amount. of heat actually abstracted from the hearth to restore to the blast its original temperature will be less than the amount which would be obtained by calculation from the formula given above. The gases produced in the hearth, however, as they rise through the furnace are subjected to a constantly diminishing pressure which finally, at the throat, differs very slightly from that of the external atmosphere. In consequence of this diminution of pressure the gases expand, and in so doing absorb a certain quantity of heat. This loss of pressure from the hearth to the throat is, however, small, so that, although the nature of the gas and the law of expansion are different from those to which our formula applies, still we would not commit an error of importance if we assumed that the amount of heat required to restore that lost in the expansion of the gases in the furnace is equal to the difference between the result obtained by our formula and the amount of heat actually abstracted from the hearth. The total heat requirement of the furnace due to the expansion both of the blast and of the gases would thus be nearly equal to that obtained by our formula, but it must be remembered that of this total heat requirement a portion only, although much the larger portion, that namely, due to the expansion of the blast, is abstracted directly from the hearth, the remainder, or that due to the expansion of the gases, being absorbed throughout the whole of the furnace above the hearth. With regard to the second assumption, if the blast be not cooled to the full extent at first, but receive heat from the furnace with sufficient rapidity to prevent the full diminution of its temperature which would otherwise result from its expansion, the amount of heat absorbed by it, to restore or maintain its original temperature, would be greater than that obtained by our formula, since the amount of heat converted into work would be greater. If this assumption is not correct, however, I think it likely to be so nearly accurate that the error involved in its adoption must be slight. The error introduced by the third assumption may readily be avoided by giving to p' in the formula the value of the pressure at the tuyeres, which may be obtained directly by experiment, or by deducting from the pressure, recorded at the receiver, the mean loss of pressure from receiver to tuyeres, which has been determined by previous experiments. In this way the small loss of heat, due to the expansion of the blast from its pressure at the point where its temperature is observed to that at the tuyeres, will be neglected, but as the difference of pressure is very slight, the loss thus neglected will be inconsiderable. It appears from the above, that the results obtained by the formula which we have deduced, while they cannot claim absolute accuracy, are sufficiently close approximations for ordinary purposes, and the errors in them are probably quite within the limits of error admissible in such calculations as that of the heat requirements of a blast furnace. THE EUREKA LODE, OF EUREKA, EASTERN NEVADA. BY W. S. KEYES, SAN FRANCISCO, CALIFORNIA. EASTERN NEVADA. THE State of Nevada, known par excellence as "the Silver State," occupies the major portion of the wide plateau, or so-called Great Basin, lying between the Sierra Nevada range on the west and the Wahsatch range of the Rocky Mountains on the east. It extends from the 114th degree to the 120th degree of longitude, west of Greenwich. It is limited, on the north, by the 42d degree of latitude, and on the extreme south by the 35th degree of latitude. Its general shape is that of an irregular parallelogram, from which the lower or southwestern portion has been cut off by a diagonal southeasterly line; the missing portion forms a part of the State of California on the west. The Great Basin is made up of a succession of low hills, or minor mountain ranges, running very nearly north and south, with long valleys between them. All of these mountains are more or less metalliferous. On the western rim, marking the eastern flank or foothills of the Sierra, we find granites, porphyries, and propylites. Here we note the great Comstock lode, with its free-milling gold and silver ores, and still further south the once prominent and the now reviving gold and silver-bearing districts of Esmeralda County, Nevada, and of Morro County, California. Next, at some distance to the east, we find the mining districts at and near Unionville, in Humboldt County. Still further to the east we find the Battle Mountain copper-silver district, north from the railroad, and southerly therefrom the Austin or Reese River, Belmont, and other districts. Still further east and north of the railroad, we find the Tuscarora, a new district of very great promise, and the Cornucopia district; and south of these the Cortez, Eureka, Morey, and Danville districts. Eastward again lie the Cherry Creek, White Pine, Sacramento, Patterson, Bristol, and Pioche districts, and, most easterly of all, the Deep Creek and other purely lead-bearing districts, which assimilate most nearly to the smelting-ore mines of the Territory of Utah. Very nearly in the middle of Eastern Nevada, we find a belt of carboniferous strata, commencing in the vicinity of the town of Carlin, on the line of the Central Pacific Railroad, passing southwardly about 25 miles east of the town of Eureka, and reappearing a little west of south at a point from 100 to 150 miles east of the town of Darwin, in the State of California. The coal seams of this belt are, in its northern part, thin, and rendered very impure by a large proportion of intercalated black bituminous shales, so that, up to the present time, they have proved of slight commercial importance. Those farther south, on the other hand, are reported to be large, and may, possibly, in the future, become available for the use of railroads and smelting works. The western portion of the State carries, predominantly, "freemilling" ores, or such as readily yield the precious metals by simple amalgamation. The eastern portion, however, with the exception of the Tuscarora, Cornucopia, Cherry Creek, Pioche, and some minor districts, carries in the main, the lead or smelting ores. Eastern Nevada is made up almost entirely of a succession of irregularly connected low mountain ranges, running northerly and southerly, which are due to the elevation of the beds of dolomitic or mountain limestone, with intercalated strata of sandstones, quartzites, and calcareous and argillaceous shales. The valleys between the ranges are filled mainly with the products of erosion, and have an average altitude of between 4000 and 6000 feet above the sea-level. The primal granites are visible at a few places, as, for example, in Steptoe Valley, where they show gold quartz veins, and, father south, on or near the same parallel, while the intrusive rocks, porphyries, and lavas, with the accompanying trachytic tufas, are found almost invariably in the vicinity of the metal-bearing districts. The limestones have been determined as belonging to the paleozoic series of rocks of the Cambrian, Silurian, and Devonian eras, and the explorations on the fortieth parallel, under the direction of Mr. Clarence King, have shown their maximum thickness to exceed 30,000 feet. The uplifting of these strata has given rise to the north and south mountain ranges, and hence we observe the anticlinal folds, dipping, |
