12 feet between pan-room floor and tail-race. - 44 feet, total fall. == The wing is subdivided as follows: 42 by 16 feet, engine-room; 42 by 22 feet, boiler-room; and is built so as to bring the crank-shaft of the engine level with the cam-shaft. The ore-house has a capacity of 350 tons when filled to the level of the dump-boards. There is a niche 8 by 10 feet in the center of its lower side for a Varney and Rix rock-breaker, the mouth of which is level with the ore-house floor. The drier, 52 by 10 feet, is divided into two equal portions, having each its own fire-place (6 by 2 feet in the clear) and chimney. Each has four flues, built of common brick, which are covered over with cast-iron plates, 36 by 30 by inches, joined at their ends by countersunk bolts and flanges. The straight dry-crushing battery of thirty stamps is divided into six batteries, each pair having one cam-shaft in common. The battery is a knee one, and has nothing peculiar in its construction. The stems are of 3-inch turned iron, placed 10 inches from centers, and weigh 750 pounds mounted, viz: The batteries make 98 drops of 8 inches per minute, and discharge on both sides, the stamps rising in the order 1, 4, 2, 5, 3. The screens have an inclination of 13 degrees from the perpendicular, No. 40 (1,600 meshes to the square inch) being used on the front and No. 30 wire screen on the back side. The batteries are fed by C. P. Stanford's selffeeder, which does its work satisfactorily. Double-armed cams are in use, constructed after an evolute of a circle, the distance between centers of cam-shaft and stem being 43 inches. When a stamp drops 98 times per minute, the time during which one rises, drops, and is at rest, is The time (t) of rising, by construction is t1=0.263 second. The time (2) required in falling 8 inches is t3 = t − (t1 + t2) = 0.612 (0.263 +0.204) = 0.145 second. - Rittinger, in his Aufbereitungskunde, gives as an empirical rule that the stamp requires 0.2 second rest. But the friction in a California battery is less than in a German one. In addition, we find, by construction, that at the instant the stamp touches the mortar, the highest point of the ascending cam is 32 inches below the tappet, allowing a sufficient modulus of safety. The theoretical horse-power required by the battery, when making 98 drops of 8 inches per minute is, calling n = 98 = number of drops per minute, h = = drop in feet, Fifty-five tons of ore per day for thirty-one successive days is the best record of the battlry; and forty-six tons of ore per day for fifty-four successive days is the worst record. (The stems had been worn so as to prevent the proper fitting of the guides.) In the first case we find that one horse-power per twenty-four hours crushes A set of shoes and dies lasts about five months, and a set of cams about fifteen months. The pans are placed at right angles to the battery, in two rows of eight each, 15 inches below the level of the pan-room floor. They are the common flat-bottom pans, with steam-chamber, built by II. J. Booth & Co., 4 feet in diameter, 32 inches deep, making 57 revolutions per minute, and holding 25 cwt. of dry pulp. Five feet lower, to each two pans, is placed one Belden settler, with wooden shoes, 74 feet in diameter, 23 feet deep, making 11 revolutions per minute, and discharging the amalgam through a siphon. The settlers have each four plugs placed respectively 6, 12, 17, and 22 inches from the top. The lowest plug is only removed during the clean-up. Five and a half feet lower are the agitators, one to each two settlers, 63 feet in diameter, 2 feet deep, making 17 revolutions per minute. They dis charge into the tail-race, and can be run down by means of plugs. Two Knox pans, 4 feet in diameter, are used to clean the amalgam. There are four retorts, 14 inches in diameter and 6 feet long, each set in a furnace separate and independent from all the rest. Each of the two melting-furnaces is capable of holding a No. 50 graphite crucible. A set of pan-shoes and dies lasts about four months. The machinery is driven by a 140 nominal horse-power horizontal engine furnished with Scott & Eckart's governor and cut-off, built by H. J. Booth & Co., San Francisco, who also constructed all of the other ma chinery of the mill. Steam is furnished by three tubular boilers, 52 inches in diameter, 16 feet long, and each containing 51 3-inch tubes. The boilers are in one bank, with no dividing walls. The ore is principally chloride of silver in silicified limestone. An analysis of an average of South Aurora pulp, worked during six months, gives the following composition: The ore is hauled to the mill by teams and unloaded on the dumpingfloor, where it drops 8 feet into the ore-house. Thence it passes through the breaker, where it is reduced to egg-size, caught in an apron, and then distributed over the drier by means of wheelbarrows. Here it is turned until it is dry, then shoveled into wheelbarrows, and emptied into the hoppers of the self-feeders. The ore leaves the battery as very fine pulp, a mechanical analysis giving: As the pulp is discharged from the battery it is caught in cars, which, when full, are run out, weighed, and charged into the pans in quantities of 20 to 25 cwt., according to the rapidity with which the battery furnishes it. Method employed in working the ore. The pans to be charged are filled partly with water; the pulp, 20 pounds of salt, and 4 pound of commercial cyanide of potassium, (containing 55 per cent. K Cy, c. p.,) to each part, are added; the whole is thinned down to the necessary consistency with water. (When the shoes and dies are new, about 200 pounds of amalgam and quicksilver remain undischarged in the pan.) The muller is then let down and left to grind for four and a half hours, then 250 pounds of quicksilver are added, and the grinding is continued for one hour. The muller is then raised so as to give the amalgam a chance to collect. Seven and a half hours after charging, sixty pounds of quicksilver are added, and the mass is thinned down with water. Eight hours after charging, the contents are run off into the settler, and the pan is ready for a new charge. Should, at any time during the charge, the quicksilver appear in bad condition, it is remedied by adding a small piece of cyanide of potassium. The settler receives the contents of two pans, and all the additional water it will hold. The arms are kept revolving, the amalgam sinks to the bottom, collects at the siphon, and escapes through it into a tub. Six hours afterward the first plug is drawn, and a stream of water turned into the settler, the surplus, with the suspended sands, escaping into the agitator. Seven to seven and a half hours after the settler receives the charge, the second and third plugs, respectively, are drawn. The settlers are cleansed of the deposited sands every forty-eight hours. They are recharged in the pans with the pulp. The agitators receive the tailings from the settlers. They pass merely through these, so that the suspended sands and amalgam may have an opportunity to settle. A small stream of water runs continually into the agitator. The remainder run through the tail-race to the tailings-pile, where they are settled. The agitators are, once in twenty-four hours, relieved of the deposited sands which are recharged into the pans. These sands usually assay 50 per cent. of the ore-value. The amalgam which passes through the siphons of the settlers is strained through No. 5 canvas strainers, and then carried to the cleaning-pans. There it is diluted with quicksilver and water, and a small piece of cyanide of potassium is added, stream is turned on, and the muller H. Ex. 211-13 is allowed to revolve for a few hours. If any iron shows itself, it is removed with a magnet, and then the amalgam is strained as dry as possible. When 1,000 to 1,200 pounds of amalgam have accumulated, it is retorted and melted in the usual manner. Sampling.-Every half hour the sampler goes around the battery, catching some of the pulp as it falls into the cars. This is placed in a box, the contents of which are thoroughly mixed every twelve hours. From this an average sample is taken, which is assayed. The tailingssample is taken from the agitator half an hour after the second plug is drawn from the settler, dried, and assayed, and if it shows over 20 per cent. of the pulp-assay, the ore is not amalgamating well, which must be remedied. The work of the mill during the past year can be seen from the following table: County assessor's returns of ore worked in White Pine district for the quarter ending March 31, 1870. |