crushing is an iron box or trough, 4 or 5 feet in length and depth, and 12 inches in inside width, cast solid. The feed-slit is 3 or 4 inches wide, and the discharge-opening is 12 to 18 inches high, the lower edge being 2 or 3 inches above the top of the die. The single discharge is generally used. The screens are of brass wire-cloth, 40 to 60 meshes to the inch, or (as is preferred for wet-crushing) of Russia sheet iron, perforated with holes to inch in diameter. The dies are cylindrical, 4 to 6 inches high, and usually cast on a square flat base, with truncated corners, so as to fill the bottom of the mortar, and yet be easily removed when necessary.

The stamp-stems are usually of turned wrought iron, about 3 inches in diameter, 10 to 12 feet long, and slightly tapered below to fit the sockets in the heads. The latter are cylinders of tough cast iron, about 8 inches in diameter and 15 inches high. The socket for the stem is about 7 inches deep. A similar, but larger, socket in the lower end of the head receives the shank of the shoe. Each end of the stamphead is encircled with a stout wrought-iron hoop, shrunk upon it like a tire.

The shoes are usually about 8 inches in diameter and 6 inches high, with a tapering shank about 5 inches high and 4 to 5 inches thick where it joins the shoe proper. They are made of the hardest white iron, and are replaced when worn down to about one inch in height.

The collar or tappet, preferred in California and Nevada, is Wheeler's gib-tappet, which is cylindrical in form, (effecting the revolution of the stem during the lift,) and differs from others of that pattern in the manner of its attachment to the stem. This is effected, not by tapering the stem or cutting the screw-thread or key-seat upon it, but by means of a gib and two keys, which clamp the collar to the stem at any desired point.

The rotary motion of the stamp, imparted by the friction of the cam against the tappet, is in very general use in Nevada. This is one of the advantages offered by the use of round shoes, stems, and tappets. The revolving cam, meeting the tappet and raising the stamp, causes it, while being lifted, to make a partial revolution about its vertical axis, which rotary motion being continued during the free fall of the stamp, produces a grinding effect between the shoe and die upon the substance to be crushed. Not only is the effective duty of the stamp at each blow increased in this way, but the shoe wears down much more evenly than when it falls without such rotary motion.†

The guides, which are of wood, and supported by the cross-timbers of the battery-frame, are placed, one set below the tappet, about a foot above the top of the mortar, and the other set near the top of the stem, so that six inches or a foot of the latter may project above.

*The manner in which shoes, heads, and stems are attached together in practice is described in the chapter on the Colorado process in this report.-R. W. R.

I have copied this paragraph verbatim from Professor Hague's chapter; but I must take leave to doubt the existence of an effective grinding action, such as he describes, at least from stamps run at ordinary speed, say 30 to 70 drops per minute. The circular revolving stamps have their advantages, no doubt; the chief ones being convenience and regularity of wear. But their dynamic advantage, if it exists at all, is much overrated, as the statistics of the best square stamps will show. If I remember correctly, some comparative tests, made under the superintendence of Mr. S. S. Robinson, in one of the largest stamp-mills of the Lake Superior copper region, did not indicate a greater crushing capacity for the revolving stamps. And it may well be questioned whether the most recent German batteries (which still retain the square stamp) are not as effective as our own. -R. W. R.

The cams are of tough cast iron, and usually double-armed. The proper curve of the face is the involute of a circle, the radius of which is equal to the distance between the center of the cam-shaft and the center of the stamp-stem. This form keeps the bottom of the tappet constantly perpendicular to the radius of the cam-curve, and thus lifts the stamp vertically and uniformly. The involute is described in prac tice by cutting from a thin board a circular piece, the radius of which is equal to the horizontal distance between the centers of shaft and stem, as above. At a given point on the periphery is fixed one end of a thread, having the length of the greatest desired lift of the stamp, and to the other end of the thread is attached a pencil-point. The circular piece, with the attached thread wound on its periphery, is laid on a smooth board, on which the involute is to be traced, and the thread, being constantly stretched "taut," is unwound until it forms a tangent to the circle at the point where the other end is attached. The line described by the pencil-point is the desired curve. This is frequently modified somewhat, receiving a greater curvature at each end, to diminish the shock of catching the stamp and the wear upon the tip of the cam in letting it fall again.

The face of the cam is 2 to 24 inches wide. It is placed as near the stamp-stem as is possible without contact. The cams are keyed or wedged to the iron cam-shaft, which varies in diameter from 4 to 6 or 7 inches, according to its work. In some mills a single cam-shaft drives all the batteries; but short shafts, one for each battery or pair of batteries, are preferred, as permitting stoppage of part of the mill without interfering with the rest.t

A common order of fall in the usual five-stamp battery is 3, 5, 2, 4, 1‡ The weight of stamps in most general use is between 600 and 700 pounds. They are usually run at about 70 or 80, sometimes 90 or even 100, blows per minute. They drop from 7 to 10 inches, according to their speed, the greater number of blows per minute requiring shorter lift. In wetcrushing on Comstock quartz, and discharging through No. 5 or No. 6 screen, the average duty is about two tons in twenty-four hours.§ In some mills it is said to reach three tons.

Feeding is usually performed by hand, but in some mills automatic feeders are employed, which give satisfaction. The arrangement com prises a hopper filled with ore,|| and a chute, leading to the feed-slit of the battery, so inclined that when agitated it will cause the ore to slide down. The chute is hung on a pivot, and a rod is attached in such a manner that the tappet will strike upon it when the stamp falls so far as to require a fresh supply of rock. The shock agitates the chute and causes the ore to move down and fall into the battery.

The consumption of water is usually between 250 and 300 cubic feet per ton of rock treated, or from one-third to one-half of a cubic foot per stamp per minute. This, includes, however, the water used in the pans, which does not pass through the batteries, and which amounts, perhaps, to one-twelfth or one eighth of a cubic foot per stamp per minute, leav

*See remarks on this subject at page 734 of my last report.-R. W. R. This arrangement also permits the regulation of speed for each battery, according to the nature of ore crushed, etc. In a mill so arranged, experiments to determine the best rate of speed could be easily instituted.-R. W. R.

See my last report, page 736.-R. W. R.

Two tons daily for a 650-pound stamp, falling 8 inches and giving 75 blows per minute, represent 1.91 tons per horse-power developed at the stamp, a high efficiency, due to speed and the use of Blake's crusher.-R. W. R.

See pages 663, 664, 736 of my last report.-R. W. R.

ing one-fourth of a cubic foot and upward of battery-water per stamp per minute.*

The mills of Virginia City and Gold Hill, that have no springs or other sources of water of their own, are supplied by the Virginia and Gold Hill Water Company. This company obtains water by means of tunnels driven into the hill-side for the purpose, and by purchase from mining companies of their underground waters. Under ordinary cir cumstances the supply from sources above Virginia City is sufficient for that place, to say nothing of the sources in mines and tunnels lower down. In seasons of drought some inconvenience is experienced.

Water is measured by the miners' inch-the quantity that will pass through an orifice one inch square in the side of the measuring-box, under a head, usually of six inches. In California the aperture is usu ally made two inches high, and as long as need be to furnish the desired number of inches, and the water in the measuring-box at one side of the supply flume is allowed to stand about six inches above the middle line of the orifice. But this practice is not uniform, and hence the miners' inch has not an invariable value.

The quantity of water that will pass through an orifice one inch square under a head of six inches, determined by multiplying the area of the orifice by the theoretical orifice √2gh, and taking two-thirds of the product as effective discharge, is 0.02633 cubic feet per second, 1.578 cubie feet per minute, or 94.68 cubic feet per hour.t

Grinding and amalgamating.—This is performed in pans of various kinds. The objects sought in the different forms of pans are: The most effective form of grinding surface, combining uniform wear with economy of power; free circulation of the pulp; uniform and thorough distribution of the mercury, and the proper degree of heat, insuring favorable conditions for amalgamation; simplicity and cheapness; ease of management and repair; large capacity and economy of time, labor, and material. Probably the highest degree of excellence in all these particulars is not found in any one pan.‡

The most noticeable difference in pans is. that of the bottom and grinding surfaces, some being flat, and others conical or curved. Opinions differ as to this feature, but the prevailing opinion seems to favor the flat bottom, though other forms of grinding surface have theoretical advantages, and some pans embodying them, such as Wheeler & Randall's conoidal, and Hepburn & Peterson's conical, are held in high esteem.§ The flat-bottomed pan usually gives more uniform wear, and the various parts of the flat muller are simpler and more easily handled and replaced. The flat muller, carrying its load of thick pulp, requires more power, but, it is claimed, distributes the quicksilver more thoroughly, and thus assists amalgamation.

*The average in Colorado is 28 cubic feet of water per cubic foot (125 pounds) of rich ore, or 33 per foot (108 pounds) of poor ore. Per stamp per minute the average is about one-fourth of a cubic foot.-R. W. R.

This is considerably less than the popular estimate of the (not miners') inch, which is 4,032 cubic inches, or 145.86 pounds of water per minute. (See Mr. J. Ross Browne's second report on Mineral Resources, etc., page 184.) Mr. J. Arthur Phillips (Mining and Metallurgy of Gold and Silver, p. 152) agrees exactly with Professor Hague making 60 cubic feet per second equal to 2,280 miners' inches. (See also, for instances of different measurement, my last report, page 477.)—R. W. R.

I omit much on Professor Hague's remarks on pans, since the subject was treated at some length in my last report. His general opinions are, however, fairly given in abridged form.-R. W. R.

Where the pan is used more for amalgamation than grinding, as in the case of roasted ores, the flat bottom is certainly preferable.-R. W. R.

Wheeler's ordinary flat-bottomed amalgamator treats a charge of 800 to 1,000 pounds in about four hours; Varney's, about the same; Hepburn & Peterson's, 1,500 pounds, four hours. Wheeler & Randall's takes 3,000 pounds.

McCone's, Horn's, and Fountain's pans have much larger dimensions. They are all flat-bottomed, and are particularly well adapted to the treatment of tailings and low-grade ores. It is claimed in their favor that they treat a charge of ore three or four times as large as that of the ordinary pans in the same or but little longer time, thus economiz ing labor and power. One large pan requires much less machinery and fewer auxiliary parts than three or four smaller ones of equal aggre gate capacity. The attention of the workman is more concentrated, and there is a much smaller loss, proportionately, by wastage of ore, quicksilver, and other materials. While the time allowed for amalga mation is much less in the larger charge than in the smaller one, in proportion to the quantity of ore treated, the results so far seem to be nearly or equally as good. These considerations are of special importance in the working of low-grade ores, which can only be done profitably on a large scale and at small expense per ton, and in which the loss of a small percentage of the value is comparatively trifling in amount. The McCoue pan takes 4,500 pounds of pulp, and sometimes more, at a single charge. The Fountain pan works 3,000 to 4,000 pounds of sand at a charge, or about ten tons of tailings daily.

The pans are generally of cast iron, but some varieties have wooden or sheet-iron sides.*

In charging, the mullert is raised a little so as to revolve freely, water, is admitted through hose, and the sand is shoveled in. Steam is introduced either into a steam-chamber in the bottom, or directly into the pulp, the latter method giving higher temperature, but, unless care is taken, too much diluting the pulp, which should be liquid enough for free circulation and thick enough to maintain suspension and equal dis tribution of the quicksilver. Sometimes both methods are employed, steam being admitted first into the pulp, and afterward into the chamber. Frequently wooden covers to the pans assist in retaining the heat, which, under proper management, may be kept at or near 200° Fahrenheit. When in the use of live steam the pulp becomes too thin, the sup ply of steam is cut off, the covers removed, and the pulp allowed to thicken by the evaporation of the water, while the temperature is maintained by means of the steam-chamber. Another advantage of the steam-chamber is that the exhaust steam from the engine may be used in it, while for use in the pulp steam is taken directly from the boilers, because the exhaust steam is charged with oil from the cylinder, which injures the amalgamation.

After the commencement of grinding, the muller is gradually lowered and allowed to make about 60 or 70 revolutions a minute. In an hour or two the sand should be reduced to fine pulp. When this has been accomplished, and by some millmen at an earlier stage, even at the beginning, quicksilver is supplied by pressing it through canvas, so as to scatter it upon the pulp in a finely divided condition; the muller is

*And some have wooden sides and stone bottoms. Each form has its advocatesR.W.R.

The details of arrangement of mullers, driers, shoes, and dies, are omitted in this abstract. For the general arrangement of the mill see my last report, plate opposite page 114. The mill there given is for dry-crushing. For wet-crushing the drying Hoor e would be omitted, and tanks introduced to catch the pulp between the battery and the pans. Otherwise the arrangements of the two classes have a general similarity.-R. W. R.

slightly raised from the bottom to avoid too great friction, which would flour the mercury, and the action is continued for two hours longer. The quantity of quicksilver varies in different mills, the ordinary supply being about 60 or 70 pounds to a charge of 1,200 or 1,500 pounds. In some mills a quantity, varying from 75 to 200, or even 300 pounds, is put into a pan when starting after a clean-up, and subsequently a regular addition of 50 or 60 pounds is made with each charge.

The "chemicals" employed to assist amalgamation now consist chiefly of sulphate of copper and salt. The long list of materials, including tobacco-juice and sage-tea, which have been at various times recommended, has been reduced to these two. The quantity used varies from a quarter or half pound to three or four pounds to each charge of ore; the two substances being employed in different proportions at different mills. It is doubtful whether their use effects any beneficial result, at least in the manner and proportions in which they are at present employed.t Different mills illustrate the use of both reagents, of either separately, and of neither, upon apparently similar ores, and with apparently equal

success.

After about two hours of grinding, and two or three of amalgamation, the pulp is diluted and discharged into a settler. This is usually a large wooden or iron tub, containing a revolving stirrer, which makes about 15 revolutions per minute, and gently agitates the pulp, to facilitate the settling of the amalgam and quicksilver. In some mills two pans are discharged simultaneously into one settler, and the operation of settling occupies the four hours required to grind and amalgamate another charge. In others, only two hours are allowed for settling, and the two pans connected with each settler are discharged alternately. The amount of water used in diluting the pulp during discharge, or afterward, added in the settler, and the speed of the stirrer, are important conditions of the separation. If the pulp is too thick, the metal remains suspended; if too thin, the sand settles with the metal. Too violent a motion has also the former effect, and too slow a motion the latter. The lighter portion of the pulp is drawn off through holes in the side of the settler, opened at successive intervals by withdrawing plugs at successively lower levels. The quicksilver and amalgam are finally discharged at the bottom.§ In some mills a second settler, called an agitator, receives the stream of pulp from the first, and saves its heaviest portions.

In the arrangement of the mill, the stamp-batteries are placed in one line, with the spalling and charging floor behind them, where the ore is broken and fed to the mortars. The batteries discharge the ore by means of aprons or launders into the settling tanks. From these it is removed with shovels, and either thrown directly or carried in a car to the pans, which are ranged, when practicable, in a line parallel with the batteries and below them. The settlers again stand in front of the pans in a line, and on a sufficiently lower level to permit the discharge of the pans into them. Below the separators are the agitators or other contrivances, to prevent the escape of quicksilver and amalgam.

Power is usually communicated by gearing or belting from a lineshaft in front of the batteries. Belt-pulleys on this shaft transmit power

And sulphuric acid.-R. W. R.

Janin successfully used bluestone and salt on refractory slimes, but in proportions ten or twelve times as great as these.-R. W. R.

An old large pan may sometimes be employed; but all, except the largest pans, are too small.-R. W. R.

See drawings and description of a similar apparatus, the "dolly-tub," in the chapter on the Colorado processes, in this volume.-R. W. R.