feed-slit, r, and the discharge, s. The bolts, m, hold the housings firmly to the posts, and wedges driven between them and the guides press them closely to the sills below.

Each battery contains usually four or five, now and then three, seldom six stamps.

The iron stamp consists of four parts: the head, the stem, the collar, and the shoe. These are all cylindrical in form.

The cast-iron head, A, has the same diameter as the shoe, and is 18 to 20 inches long. Its lower surface is provided with a conical recess 6 to 7 inches deep, to receive the shank of the shoe, and a similar recess is bored in its upper surface for the lower extremity of the stem. The interior end of each of these recesses is intersected by a mortise passing through the stamp-head, so that by driving a wedge through this opening the shoe or stem may be loosened and forced out when necessary. In some cases the lower end of the head is turned down in the lathe to receive a wrought-iron ring, & to 1 inch thick and 1 to 2 inches high.

The wrought-iron stem, B, has a length of 9 to 11 feet, and varies in thickness, according to the weight of the stamp, from 2 to 3 inches. The lower end is turned to a somewhat conical form to fit the recess in the top of the head. The upper end is also turned down a little for some distance to permit the collar or tappet to be slid over the stem to its place. In some cases the stem has a screw-thread in the neighborhood of the collar, and the latter has a place for a key, by means of which the collar can be screwed up or down on the stem, and then keyed fast in the desired position.

The collar, C, consists of a hollow cast-iron cylinder, 5 to 8 inches in height, 2 to 3 inches thick below, and somewhat conical above. The interior is turned to fit the stem, or with a screw-thread. The lower working surface is sometimes protected with a steel ring; but ordinarily the lower, cylindrical part of the collar, about 2 inches high, is merely made of chilled iron.

The shoe, D, is always of cast iron, the butt, up to within 3 of an inch of the shank, being chilled and the rest cast in sand. The shank is 4 to 6 inches long, having below half the diameter of the butt, and contracting conically upwards, as shown in the engraving. The diameter of the shoe varies between 63 and 10 inches, the ordinary limits being 7 and 9 inches.

In setting up the stamp, the stem is driven into the head, the collar either simply slipped over and driven down or screwed on, and then keyed fast. The shoe is set in the mortar under the stamp, the shank is surrounded with thin wooden wedges, pointed upwards and kept in place with a string. Then the stamp is allowed to fall, and the shank wedges itself into the head with sufficient firmness to remain fixed. With every subsequent fall of the whole stamp the several parts tend to wedge more tightly into one another. The only exception is the collar, in case it is screwed on.

*

The weight of the stamp varies between 300 and 750 pounds.* Most

According to Mr. Hague, the Colorado stamps, as a general rule, are heavier, run more slowly, and with greater fall than is usual in the mills of California and Nevada. Some of them weigh 900 pounds each; and although the mills of most recent construction have generally adopted a 500-pound or 600-pound stamp, the average is probably somewhat higher than that at present. Personally, I incline to the opinion that 600 pounds will be found a practically convenient weight, permitting on one hand a high rate of speed, and securing a sufficiently powerful blow with a moderate fall. As regards speed of running, see remarks in my last report, and a chapter in the present volume, further on.-R. W. R.

frequently it is between 400 and 600 pounds, and so divided that the weights of head, stem, collar, and shoe, have about the proportion of 5:3: 1: 2. All the stamps of a battery have the same weight. About 9 pounds is the weight per square inch of crushing surface.

The sum of the working surfaces of the shoes is to the mortar-bed about as 1:24. The interval between the shoes and between those at each end and the end of the mortar is 2 to 14 inches.

The cam-shaft (Fig. 1, n) is generally of wrought iron, and has half the diameter of the shoes. It is always rigged (in Colorado) with double cams. It rests on journals attached to the battery-posts, generally on the side of the discharge. Its center is 7 to 9 inches from that of the stamp-stem. It is generally placed about half way between the upper and lower guides, though there are departures from this practice. În large mills there is a cam-shaft for every, say, twenty stamps.

The cams (Fig. 1, o) are of cast iron, have a T-section, and are curved to the involute of a circle. The two cams of each pair are cast together on a ring 5 to 6 inches long, and 13 to 2 inches thick, which is slipped over the cam-shaft and keyed fast. The working face of the cams, 2 to 3 inches wide and 1 to 2 inches deep, is chilled. In some cases the two cams are screwed instead of cast to the ring, or each cam is cast with half a ring, and the two halves are screwed together. In this way the replacement of a broken or worn-out one is greatly facilitated.‡

The lift varies between 10 and 18 inches. It is usually 11 to 14 inches, representing a length of cam-curve of 18 to 21 inches. The difference between the theoretical maximum lift of the cams and the fall of the stamp is quite considerable, amounting with new shoes and dies to 8 to 10 inches. The lift is not changed by raising the collar as the shoes and dies wear away, since this, in most cases, in consequence of the manner in which the latter is fixed on the stem, would be a work of difficulty.

Power is obtained sometimes from overshot water-wheels, (more seldom, turbines;) and in lack of the necessary water, from steam-engines of every kind. The steam pressure averages three to four atmospheres, and is produced in flue-boilers and tubular-boilers, the universal fuel being wood. The power is generally transmitted (from a steam-engine directly, from a water-wheel through spur-wheel gearing) by means of a belt and pulleys (Fig. 1, ul) to a shaft u, and from this through two spur-wheels vv to the cam-shaft.

Auxiliary arrangements.-To facilitate operations around the upper part of the battery frame, a shelf or scaffolding is laid on one or both sides, usually a little above the lower guides, (Fig. 1, p.)

As a special aid in "catching up" the stamps, a wrought-iron lever is sometimes employed, (Fig. 2,) having a hooked support with an eye at the upper extremity. This eye slips over a bolt-head in the upper guidetimber, and the fulcrum-bar or support then hangs vertical. At the highest point of the stroke the toe of the lever is inserted under the collar, and the latter is lifted just out of reach of the cam-a position in which it is kept as long as desired (for repairs or other purposes) by means of a prop from the lower guide-beam. When the lever is not

*It is now common in good mills to gear each battery of five stamps with separate cam-shafts, pulleys, &c., so that the stoppage of one battery would not hinder the rest. In this way, different batteries may be run at different speeds-an important matter when the material to be crushed varies in character.-R. W. R.

+ Slightly modified at the end.-R. W. R.

Some good millmen prefer single cams, and a higher rate of revolution for the shaft. I do not remember seeing such in Colorado.-R. W. R.

used, it is necessary in order to hang up a single stamp to stop the whole battery, remove the housing on the feed side, and pry up the stamp to the desired point, where it is held, as before, by a prop.

The battery-water is supplied to the mortar through a wooden trough (Fig. 1, q) attached to the frame above the lower guides, and provided, opposite each stamp, with a pipe which terminates over the guidethimble, g2, so that the escaping water first cools this cast-iron thimble, and then, running down the stamp, enters the mortar. But rarely is the supply of water so arranged as to be separately regulated for each battery. In winter the battery-water is warmed by allowing the exhaust steam of the engine to pass through the trough or box conducting it, or an iron pipe is used instead and passed through a furnace.

The rock is charged through the housing, by means of a slit (Fig. 1, r) extending the whole length of the battery, about 4 inches wide, and vertical above, but inclined below at an angle of 48° to the mortar, so that the rock rolls in against the upper half of the stamp-head, when the latter is at its lowest. The interval between the side of the mortar and the stamp is here 3 to 4 inches. The sides of the charging-slit, r, are lined with strong sheet-iron.

The larger fragments of rock are frequently spalled by machinery. For this purpose crushers or stone-breakers are almost universally employed, when any machine is used, having upright jaws, one of which is moved by means of a fly-wheel and eccentric.*

The discharge takes place only on the long side of the battery (generally on one side only) and in most cases through the screen. These are of sheet steel or Russia iron, about 0.4 millimeters thick, and punched with holes 8 millimeters long and about 3 millimeters wide, of which there are about 7 to the square inch. The screens are so set as to bring on the inside the rim of the holes, turned up in punching. They are set in openings cut in the housing, and made fast by means of closefitting panes of iron or wood, and wedges. The height of the dischargelevel above the die varies between 10 and 15 inches, and is ordinarily 11 to 12 inches.

For the purpose of amalgamating in the battery the free gold contained in the rock, amalgamated copper-plates (Fig. 1, t) are set under the charging and discharging openings, that is, immediately over the lower, iron part, of the battery-box, along its entire length. They are 8 inches and 4 inches wide (together, one foot) and incline about 450 to the horizon. Occasionally these copper plates are also introduced at the ends of the mortar. They either rest on the cast-iron mortar below, or (usually) upon iron pegs, fixed in the housings, and they are held at their ends in grooves. The plate of the rear wall is set in a wooden frame, and can be by means of a handle removed or introduced at will. The plates in front and at the sides, which are screwed fast, are only accessible after removal of the screen or the rear housings.

Immediately below the discharge-screen a wooden apron or table, (Fig. 1, t',) covered with copper, 10 to 12 feet long, and 5 or 6 inches wider than the distance between the battery-posts, is attached to the housings.

Mr. Reichenecker's description of the stone-breaker is omitted, the machine being thoroughly explained in my last report, page 648. Mr. R. says one thing, namely, that the jaws are lined with corrugated plates of steel, which I think must be a mistake. The use of chilled cast-iron for this purpose is almost universal; and where it is departed from (as in Dodge's crusher) soft wrought iron, without corrugation, is substi-tuted.-R. W. R.

These screens differ from those of other localities, which are punched with circular holes and named after the sizes of needles.-R. W. R.