than the regular involute, at each end of the cam. This is done so as to ease the contact, by allowing the cam to commence to act upon the tappet at the least practicable distance from the axis of the cam-shaft, where the concussion is least, and to prevent the outer end from scraping or tearing along the face of the tappet. This end is also cut out on one or both sides so as to prevent the corner from cutting the circular edge of the tappet. The face of the tappet should always be at right angles with the radius of the curvature of the cam at every part of its course. In practice it is usual to construct the cam-curve by means of a string and pencil. This string must be as long as the required lift or rise of the stamp, added to the distance between the axis of the cam-shaft and the axis of the stem. A circular disk of wood, with a radius equal to the last-mentioned distance, is provided, and, the string being fastened at the edge, is wound upon its periphery. It is placed upon a flat surface or sheet of paper; a pencil is fastened at the free end of the string, and the latter is unwound, being kept taut, while the point of the pencil traces a line upon the paper until the string becomes tangent to the circle at the point of attachment. This gives the involute with sufficient accuracy, and it is modified in practice as already mentioned. The cam-shaft is made of round iron, usually 4 inches in diameter, turned and finished off, and having one and sometimes two key-seats cut in it longitudinally between the bearings for the purpose of fastening the cams in their places. One shaft is sometimes made to run fifteen or more stamps; but an independent cam-shaft for each 5-stamp battery is preferable. If there is a line of several batteries a counter-shaft is used. The stamps are held and guided in position in the mortar by guides above and below the tappet. These guides are, by preference, made of hard wood rather than metal. They are made in halves so that by dressing off the two opposing edges they may be readily refitted to the stem when they are too much worn away. Oak is preferred; but in its absence pine is substituted. The friction of metal guides is injurious to the stems. The guides for a battery of iron stemstamps made in France in 1867, by Messrs. Huet & Geyler for the mines of Serena, Spain, were made of brass, like ordinary journal boxes, and the cams worked through a slot in the centre of the stem

THE STAMP BATTERIES OF CALIFORNIA.

Having now described the various parts of a battery in some detail, it may be well to direct attention to their combination so as to form a complete stamp-battery such as is now in use in the best mills upon the Pacific slope. The annexed figure will serve to indicate the general appearance and arrangement of one of these batteries and the frame for its support. This is a sectional elevation of a self-feeding stamp battery, as constructed for working gold quartz. The frame is of pine timber securely braced and held by tie-rods. One end of the iron mortar is supposed to be removed so as to show the interior. The hopper-shaped box, C, is the self-feeding arrangement. It is shaken at each blow of the stamp by means of an upper tappet which strikes upon one arm of a lever, by which motion is communicated to the forward end of the feed-box, C. It will be observed that the cam-shaft is driven by a belt running from a counter pulley below. The double cam is shown, and the movable arm or bar used to hold or "hang up" the stamp when the battery is not in action. The scale of this drawing is about one-quarter of an inch to one foot.

F

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Battery for working gold quartz.

The next figure shows the construction of a battery and its frame for a wet-crushing silver mill. The ore, after passing through a Blake's rock-breaker, is received in the feeding box mounted upon rollers. From this it drops into the mortar. This mortar is made with grates upon each side. The stamped ore, after settling in vats, is worked by charges in pans. The framework of this battery is different from the preceding, but the arrangements for feeding, hanging up stamps, &c., are similar.

This is a compact and portable form of battery, designed and patented by W. H. Howland. It was introduced to the notice of the mill-men of California and Nevada several years ago, and was at first used to a considerable extent, but was gradually replaced in nearly all the mills by the ordinary straight battery. These batteries were early adopted by Mr. A. B. Paul, in the mills erected by him below Gold Hill, and he has recently given his opinion of their merits as follows: "No act of mine. in mining has been more criticised than the adopting of these batteries in my Washoe operations. Their adoption was no blind work, as I had used them for three successive years previous, and in no test with other mills was I beat in returns. I had then, and have now, great faith in

their principle. It certainly is in the right direction. They will, in time, I am confident, become popular, especially when introduced with the later improvements, on account of their simplicity, efficient working, and cheapness."

It is claimed by the inventor that very great improvements in the construction have recently been made, based upon the experience of seven years of constant working of the old style of the rotary iron battery. It is now offered by the Miners' Foundry to miners as a "new and highly improved rotary quartz mill," of less cost than the straight batteries, and requiring less power.

The construction is shown by the figure, page 666. The whole battery is of iron; the stamps are set in a circle around a central vertical shaft carrying the cams. Motion is imparted to this shaft by means of bevel-gearing. The cams are thus carried round horizontally, and lift each stamp in succession. These rotary batteries are cast in three sections. The first section has the mortar or base, screen frames and feed openings in one piece; the second section contains the lower guide boxes, (which are of wood,) driving gears, and cam-wheel; the upper section contains the upper guide-boxes. These three sections are bolted together, with thin pieces of wood-packing between each. The stems, tappets, stamps, shoes, and dies are the same as in the ordinary cast straight batteries.

The openings for delivery through screens of the ordinary construction are seen at the base. The stamped stuff collects in the annular trough, cast in one piece with the mortar, so that there is no leakage, and is discharged by a chute at one side. It is claimed as one of the advantages of this improved form that there is more metal in the mortar or base than in the old form of rotary battery, and that the leakage at the base of the column, the jar and loosening of bolts, and the wear of guide-boxes, formerly complained of, are now entirely obviated.

Its compactness and lightness as compared with the ordinary straight battery, and its being complete in itself, not requiring timber framing and supports, commend it specially to those who wish to work their ores in districts remote from supplies of timber. Mr. W. D. Gray, the superintendent of the mill of the Imperial Company, at Gold Hill, Nevada, writes to Mr. Howland, February, 1869, as follows respecting the rotary battery:

Yours of 10th instant is at hand, in which you speak of having just finished and shipped for White Pine an 8-stamp rotary battery, made from a new and improved set of patterns. For a new country, where lumber is scarce and labor necessarily high, there is no battery now in use that will equal yours. The little time required to set it up ready to run is an important consideration. The greatest objection urged against the rotary battery has been the cost of keeping them in repair, compared with the straight battery. But my experience for the last eight years proves this a mistake. The annual report of the Imperial Silver Mining Company shows quite a percentage in favor of the Gold Hill mill (five 8-stamp rotary batteries) over the Rock Point mill, both in cost of repairs, expense of running, and yield per ton of ore worked-the first of which I have had charge of for the last five years. The Rock Point mill, run by water, has straight batteries. I think this comparison can be fully substantiated, as far as expense of repairs is concerned; also as compared with any other mill run in Storey County for the last five years.

The mill above referred to was designed for the Grant District, and weighed, when complete, less than six tons. The stamps weighed 600 pounds each, and were designed to make 100 drops per minute. When working up to its full capacity it will crush from twelve to sixteen tons, dry, in twenty-four hours. The total height of the machine is about eight feet, and the weight of the mortar is 3,000 pounds.

WILSON'S STEAM STAMPS.

One of the most successful of the attempts to apply steam direct to the stems of stamps has been made by Mr. T. R. Wilson, of Philadel