GOLD. —Coining.

99

uniform length- of about 24 inches, and the breadthand thickness vary with the different denominationsof coins.

After being marked with letters indicating theday on which they were melted, and numbers toshow the pot on that particular day, two bars aretaken from each pot, and from the top of one (theextreme end having been previously removed bymeans of a cutting machine) and the bottom of theother, samples are removed for assay. The “ legalremedy ” or amount of variation permitted in fine-ness from the actual prescribed composition (916'GGin the case of gold, and 925-0 in that of silver) is forthe former 2 parts in 1000, above or below, and forthe latter 4 parts. Those employed in practice,however, are considerably less than above stated, inorder both to insure against the possibility of anycoins being issued “ out of remedy,” and to allowfor those slight variations in composition whichalways take place during the subsequent operationsof coining. When the bars cast from a pot are foundto differ in composition from the required standardby more than this workingremedy they are “ stopped,”and melted with such anamount of fine metal or copperas may be found by calcula-tion to be necessary to con-vert them to the requiredstandard.

In consequence of the con-traction which the bars under-go on cooling the upper endsare hollow, and must bo re-moved from all those whichare ascertained to be of the requisite composition.This is done by means of an ordinary cutting machinein the melting-house, where they are also nowtrimmed and cleaned by means of a rotating cylin-drical file, driven by steam power.

It may be well to explain that the above accountdescribes the method actually practised in the Eng-lish Mint, where modifications are from time to timeintroduced; moreover, in no continental mint areoperations conducted in a precisely similar manner.Thus, it is frequently the practice to transfer themelted alloy from the crucibles to the moulds bymeans of iron ladles lined with clay. So general isthis practice, that in the case of silver, in only onemint, that of Madrid , is the pot removed from thefurnace as in England. Advantages are claimed forboth systems, and Mr. Napier, reporting on theEuropean mints, points out the following:—“Thecrucible loft in the furnace will last two or threetimes longer; the metal is kept hot to the end; riskof accident from the breaking of the crucible isavoided, as well as the trouble of raking out the fireto remove the crucible, and the frequent resetting ofit; a larger quantity can be melted at once, and themeans employed for pouring are simpler. On theother side it may be urged, that direct pouring isquicker, and requires less labour, exposes the menless to the heat of the furnace, and empties the

crucible entirely.” In the British Mint the mouldsare formed of a series of cast - iron bars having a Tsection; the alternate ones being reversed form aseries of spaces thus—TJ_T_LTJLT_L—of a size de-pendent on the width of flange. On the Continent,however, almost without exception, the moulds arerecessed only on one portion, the covering portionbeing plain, a form which can be manufactured atless expense.

Rolling .—The bars having been thus prepared, areremoved to the rolling room, where they are reducedin thickness to as nearly as possible that of the par-ticular coin for which they have boon prepared. Inorder to effect this it is necessary that they be passedthrough a series of rolling mills, in which thedistances between the rolls gradually decrease fromsomewhat less than the primary thickness of the barto that of the coin to be produced. The rollers

Fig. 28.

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through which the metal is first passed are of heavyconstruction, as represented in the engraving, andneed not be specially described, further than to statethat the distance between the rollers, which areabout 10 inches in diameter, is adjusted by meansof two similar and carefully cut screws, the ends ofwhich abut on the brasses of the upper rollers ;motion is given to both simultaneously by worm-wheels fixed at their upper ends, these being causedto rotate equally by two similar worms fixed on oneand the same axis. In these “ breaking down ”mills both rolls are driven by toothed gearing, asystem, however, which gives rise to irregularities inthe thickness of the “ fillets,” as the bars are calledafter being reduced to the required thickness. Insome continental mints, in consequence, the upperroller is left free to be turned by the friction of thepassing fillet, the power being communicated to thelower roll only.

Formerly when thick bars were employed (that is,1 inch in thickness), the constant pressure causedthe metal to become extremely hard, a circumstancewhich materially interfered with the final adjustmentof the thickness, and had to be counteracted byannealing the fillets from time to time. This con-sisted in inclosing them (in the case of gold) incopper tubes made without solder, and which could,after the lids had been carefully luted on, be intro-