to state here. Theory and practice seem to concur in this matter, at least, and I can only hope that the promise of this really original invention will be realized in large work.

FARRAND'S AMALGAMATOR AND SEPARATOR.

This is a machine which attracted some attention in 1864, but was never extensively used. The motion is not rotary, but reciprocating. The machine consists of a semi-cylindrical, trough-shaped vessel, the interior of which is furnished with movable concave dies, to be replaced when worn out, as in ordinary pans. The mullers are convex, and attached to a substantial shaft, by which they are moved back and forward by crank or eccentric motion. The mullers are held to their places by springs of moderate strength, the pressure of which may be easily regulated. The oscillating motion of the mullers serves to keep the pulp in a constant state of agitation, thoroughly mixing it, and passing it under the mullers without resort to any of the various expedients employed in pans where a circular motion is maintained. In working this amalgamator no quicksilver is placed in the pulp until the trituration is completed. That done, the mullers are raised, so as to completely break contact with the dies, the quicksilver sprinkled into the mass, and the machine set in motion again, the mullers simply acting as stirrers.

PANS NOW MOST IN USE.

The experience with the great variety of pans that have been made has led at last to the adoption of the more simple forms, in which the grinding is effected beween horizontal flat surfaces instead of the curved and conical bottoms. In the pans now most in use, these flat grinding surfaces form an annular floor around the central cone, through which the vertical shaft passes. This central cone is no longer used for grinding, and is made much smaller than formerly. Wood is now also substituted for the sides of the pan, as will be seen by the inspection of the annexed figure of Patton's pan.

PATTON'S PAN.

It will be noted that the wooden sides are vertical and that the staves are held by a strong iron hoop upon an iron flange or shoulder of the bedplate, which rises in the inside of the pan as high as the top of the muller, this being as high as there is much friction or exposure to the leakage of quicksilver. The bottom is cast in one piece and has a chamber below it for the admission of steam to

heat the pulp and

H. Ex. Doc. 207-44

Patton's Pan.

promote amalgamation. The pan or tub is five feet in diameter and two feet deep. The motion of the muller is given by bevel-gearing below. The distance between the grinding surfaces is controlled by raising or lowering the muller by means of a screw working in the top of the vertical shaft.

Wheeler's pan, as now made with vertical wood sides, is shown by the next figure.

WHEELER'S PAN.

It is five feet in diameter, but not

Wheeler's Pan.

quite so deep as Patton's, and the attachment of the

staves to the bot tom plate is differ ent. There is also a wider annular space between the dies and muller and the sides. The distance be tween the muller and the dies is reg ulated by a screw with a hand-wheel upon the outside of the pan, which. by means of a bent lever at the bottom, raises the vertical shaft and so lifts the muller.

This arrangement is the same as used in the older forms of Wheeler's apparatus.

Messrs. Booth & Co. make a similar pan with sheet-iron sides. The annular space between the dies and the sides is not so great, but the cast bottom plate rises higher, and is thus more secure against Teak age. The sheet-iron rim or side is not only light, but it has this ad vantage, that when left dry for a time it will not shrink and crack as the wooden tubs must inevitably do.

COX'S PAN.

This is a large, heavy pan, in which the hard gravel cement of the deep placers is broken by revolving arms. Since the pebbles and boulders of this material are usually barren, while the cement between them carries the gold, it is desirable to relieve the stamp-mills from the necessity of crushing the former. The pan is provided with a grating below, through which the finer and auriferous material falls when freed from the boulders, and can be conveyed to the mill, while the boulders remain in the pan, and are removed as they accumulate, and thrown away. It is claimed that this device effects a great saving in the cost of cement-crushing. It was introducd in 1868, I believe, and I have no reports of actual results, though several machines are said to be in use in Nevada County, California, and elsewhere. It resembles the grinding and amalgamating pans only in name and external form.

Horn's pan, as shown by the last figure of this series, is cast in one piece and is slightly flaring. A depressed annular space three inches wide is left around the dies and is traversed, as the muller rotates, by an arm, which extend to the bottom. The muller is raised by a screw at the top similar to that used for Patton's pan.

This pan, like all the others here figured, is made with a double bottom,

SECTION V.-SEPARATION AND CONCENTRATION.

CHAPTER LXXXI.

THE CONCENTRATION OF AURIFEROUS ALLUVIUM.

As generally used in mining "concentration" refers to the enrichment by mechanical means of the ores that have been raised from veins. So restricted, it may be said that in the mining regions of the west it is confined chiefly to the separation of gold and sulphurets from quartz. But the grand washing operations of the placer gold miner are properly classed with those of concentration. With the aid of water he sweeps away the earth and gravel, and collects the grains of gold, which, by reason of their greater weight, remain behind.

The simplest and most common implements used for concentration are the miner's pan and the horn-spoon. The pan, so much used in California, not only for prospecting but in cleaning up sluices and mills, is at pres ent stamped out of one piece of the best quality of Russia iron, and is a far better article than was formerly in use. It resembles an ordinary tin milk-pan in form, but its sides are more sloping and it is strengthened by a stout wire in the rim. In the gold region of the Carolinas and Georgia, the pan formerly employed was either the ordinary iron frying pan or a light steel pan, a little deeper, and elliptical in form.

The horn-spoon is a very convenient instrument for washing out samples of crushed vein stuff, or any soft material supposed to contain gold. It has one great advantage over a metallic surface, that it does not become enfilmed with air or grease, so as to prevent the perfect contact of the water on its surface. It is made from the large end of the horn of an ox, cut obliquely, and then scraped down to a suitable thickness. A horn that is black at one end makes the best spoon. Its lightness and durability, as well as many other good qualities, make it a favorite implement with gold prospectors.

The batea is another form of washing implement for prospecting and testing. It is a shallow circular plate, made from a single piece of wood, usually by turning in a lathe, and is about twenty inches in diameter and two and a half inches deep at the centre, from which the slope is regular and unbroken to the outer edge. It is much used at the gold mines and washings in Brazil; but in California it is not much known, its use being confined, I believe, to one or two experts who have attained the peculiar skilled manipulation it requires.

The cradle, the tom, and various rockers, are forms of concentrating apparatus familiar to most miners, which need not be here described.

SLUICING.

Sluicing is the simplest form of concentration upon a large scale. It is simply the employment of a current of water upon an inclined plane, which sweeps onward the finer and lighter substances more rapidly than the heavier, and thus effects a separation.

The ordinary board sluice is made of rough pine boards, in sections twelve feet in length, so that they can be fitted one into the other and