The battery-room, with ore-bin, etc., is situated on the west side of the mill, and is 100 feet in length by 58 feet in width. Immediately adjoining this, on the east, on a terrace a few feet lower, is the amalgamating-room, containing the pans, settlers, and other amalgamating apparatus. This room is 120 feet in length by 92 feet in depth. East of this, and a few feet lower down, is the room containing the agitators and other apparatus connected therewith. This room is 92 feet in length by 20 feet in width. North of the amalgamating-room is the engine-room, containing the engine and boilers. This room is 92 feet long by 58 feet in width. Near the mill stands a handsome office, 20×30 feet in size; and to the eastward, and distant from the mill some 30 feet, is the retort-house, built of brick, and 20×60 feet in size.
To drive the whole of the machinery of the works there is a compound condensing-engine of 600-horse power. This engine has two cylinders, the first 24×48 inches, and the second 48×48 inches in size. The steam is admitted to the first or “initial cylinder,” where it is cut off at half stroke. It then passes into the second or “expansion cylinder,” which, being twice the size of the first and having four times its capacity in cubical contents, gives an expansion of eight bulks—twice in the first cylinder, and four times in the second. After the steam has left the expansion cylinder, instead of exhausting in the open air it exhausts into a condenser, where it gains an additional power equal to the atmospheric pressure at the altitude of Virginia. The main shaft from this engine is 14 inches in diameter, and weighs 15,000 pounds. On this shaft is a fly-wheel (which is also a band-wheel and carries the large belt by which the batteries are driven) 18 feet in diameter and weighing 16½ tons. On the extreme end of the main driving shaft is coupled a shaft 11 inches in diameter, which extends into the amalgamating-room and drives the pans and settlers—indeed, all the machinery except that connected with the batteries. The whole weight of the engine is about 50 tons, and it stands on a foundation of 450 cubic yards of masonry, laid in cement, the weight of which is over 600 tons. There are in this room four pair of boilers, eight in all, each of which is 54 inches in diameter, and 16 feet in length. All of these boilers can be used simultaneously, or each pair can be run separately—just as may be required. From the floor of the engine-room to the ridge of the roof the distance is 50 feet. The west side of this, and of some of the adjoining rooms, is formed by a stone wall 22 feet in height. In these walls there are in all, 4,000 perches of mason-work—all trachyte rock. The smoke-stacks of the boilers are four in number, and each is 42 inches in diameter and 90 feet in height. In this room are two large steam-pumps for use in feeding the boilers, or to be used for fighting fire, if need be; each being supplied with hose of sufficient length to reach to any part of the building.
About 28 cords of wood are used per day—10,080 per annum. This wood is brought to the mill from a side-track of the Virginia and Truckee Railroad, on a truck which holds exactly one cord. Thus is the wood measured as it is delivered. The truck dumps the wood into a chute, which carries it down into the boiler-room, and it is landed just in front of the furnaces, where it is wanted.
We will now return to the west side of the mill and ascend to its extreme top, even above the roof. Here, above the roof, comes in a large car-track, leading directly from the main shaft of the hoisting-works at the mine. This track is 278 feet in length, and is housed in for its entire length. It is handsomely finished off, contains windows its whole length, is painted a light brown color, and strikingly resembles a rope-walk.
When the cages bring to the top of the shaft the cars loaded with ore, a carman is standing ready, who takes the car from the cage and pushes it before him over an iron track to the chutes which lead down through the roof of the mill into the huge ore-bin below. This car-track, and the long building covering it, are supported upon a strong trestle-work constructed of large square timbers, and rising forty-four feet above the surface of the ground in the highest part. To keep the stamps supplied with ore requires one car-load to be sent out from the shaft every five minutes during the day and night. Although the cars were at first pushed out over the track by hand, they are now made up into trains of ten, and are hauled by a mule from the hoisting-works to the mill.
The ore, on being dumped into the chutes at the top of the mill, descends to the centre, from each side. The chutes have in their bottoms what are called “grizzlies”—iron bars placed three inches apart so as to form a screen—through which the fine ore drops into the bin below, while the coarse rock rolls on down and is dumped on a floor above the ore-bin, and about its centre, where stands the rock-breaker.
The rock-breaker is a heavy piece of machinery, which in appearance, and the principle upon which it works, not a little resembles a huge nut-cracker or lemon-squeezer. It is the same kind of machine that is used in some cities for chewing up rock for macadamizing streets, and which is known as a “masticator.”
The coarse rock being crushed in the rock-breaker is carried into the ore-bin by a chute. In the main chutes above are what are called distributing chutes, which are chutes that carry the descending ore far away from the centre of the bin. But for this arrangement, all of the ore would fall in the middle of the bin, which is 110 feet in length.
In the battery-room are ranged in a row, north and south through the building, six batteries of ten stamps each, or sixty stamps in all. Each stamp weighs 800 pounds. Each set of ten stamps works independently of each other set, and can be stopped and started at will by simply moving a sort of brake or clutch. The whole of the stamps and the apparatus connected therewith, are driven by a belt from the main fly and band-wheel (mentioned above), which belt is 24 inches in width and 160 feet in length. This runs the counter-shaft in front of the batteries, and from the pullies on this counter-shaft there are belts 14 inches in width and 60 feet in length, which run each battery of ten stamps. The main belt, which drives the whole of this machinery, runs at the rate of 3,600 feet per minute.
From the ore-bin the ore descends into the Tulloch self-feeders, one of which machines is required for every five stamps, or twelve in all. These do the whole work of feeding. The ore is not touched by anyone after it falls into the bin. Two men are able to keep watch over all the feeders supplying ore to the whole sixty stamps. The feeder is the invention of James Tulloch, of California, and is a very valuable labor-saving apparatus. The feeders are self-regulating, the motion of the stamps in dropping, operating them. When there is too much ore in the battery, the tappet of the stamp does not fall sufficiently low to strike the end of the rod attached to the feed-table, and no more rock enters the battery for a time; but as the rock is worked out, the feeder again begins to operate. In most of the mills the ore is still fed into the batteries, with shovels, by men known as “feeders.” When the feeding is done by hand, the amount of ore reduced in a given time, depends much on the men who do the work. They must put under the stamps all the ore they can crush, and no more. This must be done constantly throughout the twenty-hours for weeks and months.