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number and length of strokes, feeding (by regulator f,) discharge, (by regulators, g'g',) outlet of water, products and refuse, (by holes, m' m" m",) the receptacle C' will receive the heaviest ore, receptacle C" an intermediate class of ore, box D gangue, or rock fit for the stamp-mill. The products of the jigging process, and the further operations they have to pass through, vary in accordance with the mineralogical character and the size of the treated material.

m

D

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SECTION of ca

Fine Dolores ore will give galena and lead carbonate in receptacle C', blende in receptacle C", and calcspar in box D; coarse Dolores ore, galena and carbonate in C', blende, mixed with galena, carbonate and spar in C", spar, with little blende, and traces of leadore in D. In this case it is necessary to submit the crushed products from C" and D to further dressing operations.

The power necessary to drive this jigger depends upon the area of pistons, and upon the number and length of piston-strokes. Half a horse-power is in all cases sufficient to work a jigger of 18 by 18 inches piston area. The quantity of material worked in a certain time is greatest if the stuff is rich and of middle size. Of poor copper-ore, 6 to 7 cubic feet are worked in an hour. Some details of construction. Most of the constructive details of a jigger built of wood can be seen from the cut, without further explanation. If acid water is to be used for the jigging operation, wood is the best material; and, besides, it is the cheapest. Leaks in a well-constructed wooden jigger-box are usually calked by dirt after the jigger has been used for some time, and, besides, it is of no practical account if a few drops of water leak from a vessel through which to 1 cubic foot is run per second. The outside walls of the jigger-box should be at least 3 inches thick, the interior partition-walls 2 to 23 inches. The planks forming these walls should be united by hard-wood wedges filling grooves. It must be remembered that soft and dry wood expands transversely about inch per foot by soaking. A wooden box constructed in accordance with the cut remains not only tight enough, but it can also be easily taken apart, and put together. Grooves in the side walls hold the bottom, which is stiffened by transverse rails; the end walls are fastened in the bottom and side walls, the long partition in the bottom and the end walls, the short partitions in the bottom, long partition, and front walls. Bottom rails and posts form a frame around the box, and by pieces between the rear wall and long partitionwall the whole construction is secured. The discharge-holes m' m'' m''' should not be closed otherwise than by wooden plugs or exterior trapdoors, which by weights working on knee levers are pressed against nozzles. Close above the bottom are gates i for cleaning the chambers A B' B" D'when they become obstructed by dirt.

The pistons do not slide directly on the walls of partitions B' and B",

but on hard-wood linings, which can be replaced, piece by piece, if necessary. The main valves and c", of rubber, are stiffened by thin sheet-covers; their wooden valve-seats are kept in place by buttons. Each piston is covered by four light rubber valves.

The meshes in sieve-beds FF" and in screens must be fine enough to prevent the ore from passing through. But it is not necessary to use as many different sets of sieve-beds and filtrating screens as there are sizes of ore. Two sets answer all practical wants. Wire gauze, with very fine meshes, which has to be used if the finest stuff is worked, should always be protected against too speedy abrasion by wrappers of coarser gauze. The frames covered with wire cloth (F' F",

rest loosely upon and behind wooden strips, and are kept in position by the large frame H, which is common for all compartments in the front part of the jigger. This frame contains the ridges c' and c", and the gates f, h', h', which move in grooves; f is kept in position by friction only, h' and h" by wing-screws besides.

Behind frame H and sieve-beds F' and F" move the piston-rods in spacious grooves. The lever-heads receiving the motion from cams L must be covered with steel; the counter-weights Q are made of disks of metal, kept in place by eye-bolts. By replacing one or more of those metal disks by wooden disks, and by moving them nearer to or farther from the fulcrum o, it is easy to change the velocity of the rising pistons at pleasure.

H. Ex. 211-32

CHAPTER XXII.

WIRE-ROPE TRANSPORTATION.

In my report, rendered 1870, for the year 1869, will be found (pages 579 to 581) some remarks on wire ropes, to which I take pleasure in adding the following notes upon steel cables, kindly furnished me by Mr. A. S. Hallidie, of San Francisco.

Steel-wire flat ropes are in general use throughout California and Nevada, more particularly at Gold Hill and Virginia City. The durability of steel rope, as compared to iron ropes, is as 6 to 5. The weight (for equal strength) of steel rope, as compared with iron rope, is as 6 to 10. The life of a steel rope working in the Virginia City mines, hoisting at the rate of 1,000 feet per minute, 6 to 8 hoists per hour, for a vertical height of 1,000 feet, is, on the average, about two years. The steel wire of which the rope is composed is especially manufactured for this purpose, ordinary steel wire being unsuitable. The best wire does not become brittle after two years' wear, but possesses still the admirable quality of being tough as lead and hard as steel.

The great tensile strength of steel wire recommends it strongly for the purpose of hoisting from great depths. A 13-gauge steel wire sustains a breaking-strain of 1,400 pounds; whereas the same size best charcoal bright wire sustains a breaking-strain of but 770 pounds; and the steel wire will bear, without breaking, two turns over its own part.

The importance of using ropes of high tensile strength, such as steel alone affords, may be illustrated by the case of a rope manufactured by Mr. Hallidie about the first of January. This rope was 2,000 feet long, 5 inches wide, inch thick, 9,360 pounds in weight, and made of iron wire. The breaking-strain of this rope was estimated at 72,000 pounds, and the working load should be one-sixth of this, or 12,000 pounds. Subtracting from the latter amount the weight of the rope itself, we have 2,840 pounds as the weight of cage and ore that could be safely hoisted; that is, 22 per cent. of working load.

Now, a steel rope of the same capacity would weigh only 4,800 pounds, and the weight of cage and ore that could be safely hoisted would be 7,200 pounds, or 60 per cent. of the working load; and there would be a saving in dead work equal to the difference in weight of the ropes, or 4,560,000 foot-pounds at each hoist. For rough work, moreover, the steel rope has an advantage, inasmuch as it stands abrasion much better than iron.

In round wire ropes steel again shows its superiority over iron, both in its life and useful effects. The life of a round steel wire rope varies according to the character of the hoisting-machinery. In many cases such ropes have lasted three and four years. As a rule, the drum and pulleys should be 100 times the size of the rope.

Endless wire-rope tramways.-The use of endless wire ropes for aboveground transportation, which was alluded to in my report of 1870, (page 568,) has been perfected on a somewhat different principle, already mentioned in Chapter I of this report, and now to be more fully described and illustrated.

In the rough mountainous portions of the gold and silver mining regions of the Pacific coast, there is an immense amount of ore which

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