100

GOLD. —Coining.

duced on an iron carriage into a furnace, where theywere left for about twenty minutes. On being with-drawn, they were dipped into cold water. Silverfillets were also annealed, but resting on iron plates,the copper of the outer surface being thus oxidized.This oxide was subsequently removed by introduc-ing the metal into hot sulphuric acid, as will presentlybe described. Bars only half or three-eighths of aninch in thickness are being gradually introduced forall denominations of coin; and it is found possible,when these are employed, to bring the fillets tothe requisite thickness without annealing.

The last mill through which the metal is caused topass is capable of more accurate adjustment thanthose employed for the preliminary rolling, and byits means th e fillets are brought as nearly as possibleto the required thickness of the coin.

When a fillet has passed through this gauging mill,the operator, in order to ascertain whether the dis-tance between the rollers is correctly adjusted, cutsout a blank by means of a small hand screw press,provided with a ring-cutter and die suitable to theparticular size of coin to be ultimately produced.This blank he weighs, and if its weight be withinthe working remedy the rollers are known to be therequired distance apart. It is found, however,impossible in practice to roll a fillet uniform inthickness in its whole width ; in consequence of therollers yielding, the centre is perceptibly thickerthan the edges, a fault which, if not corrected, wouldlargely increase the amount of coin rejected onaccount of its being out of remedy as to weight.The apparatus employed in order to secure thisuniformity is the draw-bench ; and although severalattempts have been made to complete the adjustmentby means of rolling mills, no machine has given suchgood results. Before being operated upon by thisinstrument, one end of each of the fillets is intro-duced into a flatting mill, the object of which is todiminish its thickness to such an extent that it maybe easily introduced between the two fixed edges ofthe draw-bench.

Adjusting Fillets .—There are in the Mint twobenches, each capable of drawing two fillets at once,and being about II feet long by 2J feet broad. Twoendless chains pass along the whole length, and aresupported on a drum at one end, while they arecaused to travel along the bench by means of gear-ing driven by the steam engine, and situated at theopposite end, the loose half of each chain returningunderneath the bench. Each link of the chains isprovided with a short transverse bar, by means ofwhich motion is given to the small carriage or“ dog” after it has gripped the thin end of the fillet.The principal part of this apparatus by which thethickness is adjusted remains to be described. Itconsists of a strong rectangular frame of cast iron,having a vertical height of 20 inches and a width of13 inches. In it are placed two solid blocks of metal,the lower of which is rigidly fixed by means ofscrews, and the upper is capable of a slight motionin a vertical plane by means of a very accuratelycut screw, provided with a micrometer adjustment,

while the distance between the two blocks can beadjusted by means of two screws with capstan heads,placed between them. There is a clear interval oflj inch between these blocks, while to the top ofthe lower and the base of the upper block smallaccurately-turned polished cylinders of fine steel, 3inches long and three quarters of an inch in diameter,are rigidly fixed, touching the blocks along their wholelength. These cylinders do not rotate, but formedges, between which the fillets are drawn by meansof the dog; and this is so constructed that immedi-ately on gripping the end of a fillet it is drawntowards the opposite end of the bench, at which thedriving gear is situated. It will thus be seen that suchan arrangement for diminishing the thickness differsessentially from the rolling mill, (1) in the fact thatthe faces between which the metal passes are fixed;and (2) the thickness of the blocks being very greatin proportion to the width of the faces, the possi-bility of their bending is considerably diminished.The thickness of the fillets is tested in the samemanner as it was on passing the gauging mill—bycutting out a blank of the size of the coin to be pro-duced. Whereas, however, in the former case theworking remedy was 05 grain for sovereign fillets,in the latter it is 02 grain.

The heat produced by the friction between thesteel faces and fillet is very great, and an abundantsupply of oil must be kept up in order to diminishthis as much as possible. All those fillets which arefound to be of the correct thickness are cleaned, cutinto lengths of about 15 inches, and passed into anadjoining room, where the next operation of cuttingout blanks is conducted.

Cutting out Blanks .—The apparatus employed forthis purpose in the British Mint is of ancient con-struction, and quite unfitted for the requirements ofthe present day; were it not that the Mint will, in allprobability, shortly be removed from its present siteand completely rearranged, the cutting out presswould long ago have been replaced by machineryof a more convenient and less noisy description.The blanks are cut out by means of punches, the die,which is made of a size corresponding to that of thecoins required, exactly fitting into a ring-cutter fixedbelow. There are twelve screw-presses arranged ina circle, and all driven by one large driving wheelsituated overhead, and rotating in a horizontal plane,each press being separately assisted in its downwardmotion by a vacuum cylinder and piston situatedbeyond the walls of the press-room; this piston israised during the ascent of the cutter, a motion whichis brought about by the large driving wheel. Theposition of the fillet under the die is adjusted entirelyby the eye, the object of course being to cut theblanks as close as possible, in order to diminish theamount of loss which must ensue on remelting theremainder of the fillet from which the discs have beenremoved, called scissel. In only one continentalmint, that at Copenhagen , is machinery similar tothat in our Mint employed; in all others the screwpress has been replaced by the crank or eccentricpress. It is generally driven by a strap to a pulley on