Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/512

Rh 490 improve the appearance of the finished coin by removing all traces of impurity from the surface of the blank. It has, however, been abandoned in the British mint except in the case of some of the smaller silver coins, mainly because the soft superficial layer of metal wears away with undue rapidity. Certain precautions suggested in 1869 by Mr Hill, the superintendent of the operative department, for avoiding oxidation or tarnishing of the metal during coinage rendered the abolition of the process possible. Coining The blanks receive the impression which constitutes them coins press. from engraved dies. Each is placed in the lower of two dies, and the upper die is brought forcibly down upon it. The lateral escape of the metal is prevented by a collar which surrounds the blank while it is being struck. This collar may be either plain or engraved, and if the latter is the case any device or ornament it may bear will be imparted to the edge of the blank. The coining presses used in various mints may be divided into three types : (1) the screw press worked by atmospheric pressure, (2) the excentric press, and (3) the lever press. The first of these (see Ency. Brit., 8th ed., vol. vii. p. 92) has now been abandoned. In the excentric press the power is applied to a shaft bearing an excentric which acts by means of a connecting rod upon a verti cal slide holding the die which is brought down on the blank. This form of press is used in the mint at Constantinople, where the atmo spheric screw press is also still retained. Of the third type, the lever press, there are two modifications, devised respectively by Thonnelier and by Uhlhorn. The details of the Uhlhorn press have been improved by Messrs R. Heaton & Sons of Birmingham ; and, their superiority to the old vacuum screw press having been demon strated by careful experiments, they have been finally adopted in the newly arranged mint, which contains fourteen of them. This press is shown in figs. 10 and 11. It is driven from below the floor of the press-room by bands which pass over fast and loose pulleys on the same shaft that bears the fly-wheel. The loose pulley, however, is only used when it is necessary to stop the machine entirely, as the fly-wheel is permitted to revolve without imparting motion to the shaft so long as a lever M, worked from the front of the machine, does not cause the fly-wheel to be con nected with the driving wheel by means of two pins. The dies are placed in the front part of the machine (fig. 10). The lower one is firmly fixed to the bed, while the upper is held at A by the upper of two jaws F and A, or levers, the fulcra of which are so close together as almost to coincide, the lower jaw A bearing the collar which encircles the blank while it is being converted into a coin ; the upper jaw F, A, governed by the weighted lever H shown below the bed of the machine, has a tendency to rise a sufficient distance to admit the blank between the upper and lower die. A crank B on the shaft bearing the fly-wheel is connected by a rod C with the bent lever D, and this bent lever, acting through the toggle joint and a piece of metal E connected with the jaw that bears the Fig. 12. upper die, forces it down, and thus squeezes the blank between the upper and lower dies. A cam on the crank shaft acting on the lower of the two levers G shown below the bed of the machine causes the lower jaw A bearing the collar which surrounded the blank to be depressed sufficiently to leave the finished coin freely resting on the lower die, from whence it is driven down the shoot N by the next blank in succession. Coins are produced at rates varying from 60 to 120 a minute, 90 a minute giving the best results. The blanks to be converted into coins are placed on the slide J, and the advance of each blank in succession is regulated by the rod called the &quot; layer on &quot; K, the backward and forward movement of which is also regulated by an excentric on the crank shaft. The details of this part of the machine are shown in plan, fig. 12. Auto- The last operation before the finished coin is returned to the mint matic office for issue to the public is the weighing each gold or silver piece balance, separately. This is effected in the American and in most Continental mints by hand, but in England automatic balances of beautiful construction are employed. They were originally devised for separating worn pieces from those of current weight, but they are now employed to distinguish between &quot;light,&quot; &quot;heavy, &quot;and &quot;good&quot; pieces, the latter alone being permitted to pass into circulation. In the newly arranged department thirty such machines are provided. Each is driven from overhead shafting by means of gut lines* The driving pulleys derive their motion from a small atmospheric engine, which is found to give more satisfactory results than would be the case if the steam-engine were employed directly. Each balance is worked by a cone pulley A (fig. 13) by a gut line passing round it from the loose pulleys B, the necessary ten sion being imparted to the line by means of a spring C. The tension of the line is, however, but slight, for if the action of the balance is arrested by accident the cord slides over the cone pulley A without turning it. It will be obvious that the use of the cone pulley enables the machine to be driven with varying degrees of speed. The toothed wheel D is mounted on the spindle which bears the driving pulley A, but it acts only through the intervention of a friction cheek, which is so lightly screwed against the driving wheel that it would cease to act if the machine should be accidentally deranged. The wheel D sets in motion the wheels E, E, E&quot;. The cam F, acting on the curved extremity of the rocking frame G, causes the slide H to bring forward one of a series of coins (arranged in the hopper I) until it rests on the plate J of the balance beam, of which beam a portion is shown in an enlarged drawing above the balance, while the plate that receives the coin is also shown in a separate drawing to the left of the machine. Another cam K then comes into play, and enables the forceps, shown at L, to release the rod M to which the balance plate J is attached. The forceps L serves to keep the rod steady while the coin is being placed on the plate J. A rod shown at N is then raised by the cam 0, the lower extremity of the rod being kept steady by a pin sliding in a hole in the bottom plate of the balance, and its upper end by a pin which works into the central support of the balance beam. At the base of this rod N, and at right angles to it, there is a metallic bar QQ, the ends of which pass through stirrups in the pendants M and P from the opposite ends of the beam. The elevation of this horizon tal rod by the cam simultaneously releases both ends of the beam, and the coin placed on the beam plate has then, for the first time, a direct influence on the beam. If the coin is &quot;too light&quot; the counterpoise R in the cage at the end of the rod P will raise the coin, and the revolution of the machine then causes part of the cam K to permit a spring to close the forceps L and to hold the pendant M firm. An indicating finger T then falls, and by means of a horizontal lever UU, which fits into one of three inverted steps on the bottom of the shoot V, determines over which of three orifices W, W,W&quot; in the bottom plate of the balance this shoot shall stand. In the meantime the advance of the slide H brings the next piece forward, and displaces the coin which has hitherto occupied the beam plate J, forcing the coin down the shoot V, and thence through the orifice &quot;W into a receptacle, external to the balance, destined for the reception of &quot;light coin.&quot; If this next piece should be &quot;too heavy &quot; it will not only raise the counterpoise Rbut will also elevate a little wire S, which would otherwise remain indisturbed on a support. This little wire represents the &quot;working remedy&quot; for the particular denomination of coin in question, which, for safety, is less by rl^th of a grain than the remedy permitted by law. The undue weight of the &quot;heavy coin &quot; will depress the right end of the balance beam and its pendant M to the lowest possible point, and the indicating finger T will, in this case, determine that the rod UU shall occupy the lowest step of the shoot V, which will conse quently stand over the orifice W&quot; in the bottom plate of the balance which communicates with the receptacle for the &quot;heavy&quot; coins, and the heavy coin on the beam plate will be driven down the shoot by the next coin in succession. If the coin which is next brought forward by the slide H should be a &quot;good&quot; one, that is, if it is within the working &quot;remedy,&quot; its action will be as follows. It may be slightly heavier than the counterpoise, but not sufficiently heavy to lift both the counterpoise and the remedy wire. The balance beam consequently remains approximately horizontal, and the indicating finger T will cause the rod UU to strike the centre step of the shoot V, which will then stand over the central orifice W in the bed plate which communicates with a receptacle for &quot;good&quot; coins, into which the coin will find its way, as soon as it is driven from the beam plate by the next coin of the series. It will be evident that this excellent appliance both weighs and classifies the coins. About twenty-three coins are passed through it in a minute. In order to show the importance of extreme accuracy in weighing, it may be pointed out that, although by the Coinage Act of 1870 the &quot;remedy &quot; or allowed variation above or below the standard weight of a sovereign is only -J-th of a grain, yet in a million sterling of sovereigns the difference between the least and the greatest weight the law allows would be no less than 3244. The manufacture of coin is not the only work which is performed in the Royal Mint. All medals issued to the