GOLD. —Amalgamation.
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means a considerable quantity of metal is removed,and thus prevented from passing down the sluiceswhich immediately succeed this apron. To everymill of four or five stamps there are three sets, eachconsisting of two sluices, together about 16 feet long,and having an incline of about 1 in 16. They arecovered with blankets, two sets being used at a time,while the third is employed when the blankets ofeither of the others are being washed; the washingsfrom them are introduced into an amalgamator whichmay vary in construction; that usually employed isknown as Atwood’s amalgamation, and is representedin elevation in Fig. 19. It consists of two hollowcylindrical troughs, t, t, about 18 inches long, of woodor iron, filled with mercury. The washings areswept from a box at the head of the apparatus overthese troughs by a current of water heated to about120° Fahr., where they are agitated by woodencylinders provided with arms of such a length as justto touch the mercury, and rotating in a directionopposed to the current. By a system of levers, shownabove atm, the pipe, p, which supplieswater is caused to rotate in such amanner as to secure a regular supplyof washings to the troughs, on leavingwhich the stream passes over a seriesof riffles filled with mercury. Theskimmings removed from time to timefrom the various parts of this appara-tus are ground and amalgamated inpans which vary much in their detailsof construction. The forms mostemployed at the present day are thosedesigned by Patton, Wheeler, Cox,
Horn, and Booth & Co., and the ar-rangement of a Wheeler pan is shownin Fig. 1, Plate I. It consists of ashallow cylindrical basin of wood oriron, about 4 feet in diameter, and18 inches deep, provided with a flatiron bottom, to which dies are attached, and beneathwhich is a steam - chest, in order to be ableto heat the contents when necessary. From thecentre rises a conical tube in which a vertical shaft,carrying a “ muller-plate,” rotates, receiving itsmotion from bevel gearing below. To the muller-plate are fixed shoes at intervals, and the distancebetween these and the dies can be adjusted by ahand-wheel at the side of the pan, which, through alever, raises or lowers the steel block in which theextremity of the shaft rotates. The removal of themuller from the pan for the purpose of cleaning isaccomplished by running it up a screw on the shaft.When the Knox pan is used 100 lbs. of skimmings areintroduced, and water added until the pulp just ad-heres to a stick. After about three hours’ grinding thetemperature is raised by heating the steam chest, anda cupful of equal parts of saltpetre and sal ammoniacis added, together with about 5 lbs. of mercury. Afterthree hours further working water is added and afew handfuls of caustic lime, when the diluted pulp,now nearly filling the pan, is stirred for abouttwenty minutes and discharged, without stopping
the motion of the muller, first from an upper, andsubsequently from a lower plug-hole. This pulp,which frequently contains as much as 100 dols.of gold per ton, passes into an appliance verysimilar to a pan, called a settler, and shown insection in Fig. 2, Plate I. This is a circular box, inwhich revolves a central axis carrying arms, and tothese iron shoes are attached. The shoes do notcome in contact with the bottom, but are faced withwooden rubbers, in order to keep the heavier partsof the pulp thoroughly stirred. Water is introducedduring the operation, and the thinned pulp can bodrawn off at plugged holes from time to time. Aniron bowl to contain mercury is attached, com-municating with a radial gutter cast in the ironbottom of the settler. The sulphurets, &c., re-covered by this process, are treated by the chlorina-tion process presently to be described.
The sands, after passing the blankets, and alsothose from the amalgamators, discharge into theEureka rubbers, shown in plan and part section in
Figs. 20, 21, in which the particles of gold are cleanedand brightened by rubbing, and are to some extentcollected by means of amalgamated copper plates.The apparatus consists of a rectangular cast-ironbox, a A, 7 inches deep and 4 feet 8 inches square,provided with a false bottom of cast-iron dies orplates, b, b, b, alternating with strips of soft wood,c, c, c, on which cast-iron shoes, d, d, d, fastened toa wooden frame, B, receive a rectilinear motion byrods connected with an eccentric. Beneath theseshoes are fixed wooden boards carrying amalga-mated copper plates. The eccentric makes aboutfifty-five revolutions per minute, and one rubber issufficient to treat the sands from four or five stamps.On leaving the rubbers the sands pass over amalga-mated copper plates from 20 to 30 feet in length,and having a gradient of 1 in 24.
The amalgam obtained is purified by being rubbedin iron mortars with the addition of mercury, a cur-rent of water being at the same time caused to passover it, and everything so removed is returned tothe pan. The resulting amalgam is then squeezedthrough canvas bags, and the mass left transferred