Bible Encyclopedias
Mint

History of Minting

The earliest metallic money did not consist of coins, but of unminted metal in the form of rings and other ornaments or of weapons, which were used for thousands of years by the Egyptian, Chaldean and Assyrian Empires (see NuMIS Matics). According to Herodotus, the first mint was probably that established by Gyges in Lydia towards the end of the 8th century B.C. for the coining of gold, silver and electrum, an 1 Lenormant, La Monnaie dans l'antiquite', i. 82.

alloy of gold and silver found in a natural state.' Silver was coined in the island of Aegina soon afterwards. The art of coining was introduced by the Greeks into Italy and other countries bordering on the Mediterranean and into Persia and India. Subsequently the Romans laid the foundations of modern minting. Coining originated independently in China at a later date than in the western world, and spread from China to Japan and Korea. Coins may be made by casting in moulds or by striking between engraved dies. The Romans cast their larger copper coins, in clay moulds carrying distinctive markings, not because they knew nothing of striking, but because it was not suitable for such large masses of metal. Casting is now used only by counterfeiters. The most ancient coins were cast in bulletshaped or conical moulds and marked on one side by means of a die which was struck with a hammer. The " blank " or unmarked piece of metal was placed on a small anvil (ambos), and the die was held in position with tongs. The reverse or lower side of the coin received a rectangular mark made by the sharp edges of the little anvil. Subsequently the;: anvil was marked in various ways, and decorated with letters and figures of beasts, and later still the ambos was replaced by a reverse die. The spherical blanks soon gave place to lenticular-shaped ones. The blank was made red-hot and struck between cold dies. One blow was usually insufficient, and the method was similar to that still used in striking medals in high relief, except that the blank is now allowed to cool before being struck. With the substitution of iron for bronze as the material for dies, about A.D. 300, the practice of striking the blanks while they were hot was gradually discarded. 2 In the middle ages bars of metal were cast and hammered out on an anvil. Portions of the flattened sheets were then cut out with shears, struck between dies and again trimmed with shears. A similar method had been used in Egypt under the Ptolemies (c. 300 B.C.) but had been forgotten. Square pieces of metal were also cut from cast bars, converted into round disks by hammering and then struck between dies. In striking, the lower die was fixed into a block of wood, and the blank piece of metal laid upon it by hand. The upper die was then placed on the blank, and kept in position by means of a holder round which was placed a roll of lead to protect the hand of the operator while heavy blows were struck with a hammer. An early improvement was the introduction of a tool resembling a pair of tongs, the two dies being placed one at the extremity of each leg. This avoided the necessity of readjusting the dies between blows, and ensured greater accuracy in the impression. Minting by means of a falling weight (monkey press) intervened between the hand hammers and the screw press in many places. In Birmingham in particular this system became highly developed and was long in use. A. Olivier introduced screw presses for striking coins, together with rolls for reducing the cast bars and machines for punching-out round disks from flattened sheets of metal, in Paris in 1553. After being discarded in 1585, except for making medals, they were reintroduced by J. Varin in 1640 and the practice of hammering was forbidden in 1645.3 In England the new machinery was tried in London in 1561, but abandoned soon afterwards; it was finally adopted in 1662, although the old pieces continued in circulation until 1696. At first the rolls were driven by workmen by means of cranks, but later they were worked by horses, mules or water-power. Steam-power was applied to them by Matthew Boulton and Watt in Birmingham in 1788, and was adopted by the Royal Mint, London, in 1810. Recently the practice of driving rolls by electricity has been growing, the advantage being that each pair of rolls can be driven independently without the intervention of cumbrous shafting. Boulton and Watt's screw press, invented in 1788 and used at the Royal Mint until 1881, was worked by atmospheric pressure applied to a piston. The piston was in communication with a vacuum vessel from which the air had been pumped by steam power.

History of British Mints. Britain there are evidences of 1 Op. cit. i. 136. , Herodotus i. 94.

E. Dumas, L'Emission des monnaies decimales de bronze, p. 14.

3 Ibid. p. 19.

the existence of mints before the arrival of the Romans. The Romans at first imported their coins, and no Roman mints were established until about the end of the 3rd century, when coins were being struck at London and Colchester. 4 In Anglo-Saxon times Athelstan appears to have been the first monarch who enacted regulations for the mints.' He promulgated laws about the year 928, appointing a large number of " moneyers " or " mynteres," London being assigned eight, Canterbury seven, other important towns various numbers and all smaller boroughs one moneyer each. The necessity for so many mints lay in the imperfect means of communication. At an early period, probably about A.D. 1 000, the dies were made in London and issued to the other mints. The moneyers, who were elected by the burgesses, were responsible for the manufacture of the coin, and according to Madox were liable at the time of Henry II. to be summoned to Westminster to take part in the trials of the pyx. 6 If there was any deficiency in the weight of the fineness of the coin the moneyers were punished as traitors. These moneyers appear to have been abolished about 1180, 7 when officers were appointed to supervise the coinage on behalf of the king, and the name "moneyer " was applied to contractors who manufactured the coin under superintendence and were not responsible to the king for its weight and fineness. The moneyers continued to manufacture the coin of the realm until the year 1850, when the work was entrusted to civil servants. In the reign of Henry III. the principal officers of the Mint were the master, who manufactured the coin under a contract, the warden or paymaster who acted on behalf of the Crown, the assay master (also a king's officer) who was responsible for the fineness of the coin, the cuneator or superintendent of the engravers of the dies, and the moneyer. One of the most important duties of the warden was the collection from the contractor of the seigniorage which was claimed by the sovereign by virtue of his prerogative as a source of revenue to the Crown. In 1718 Sir Isaac Newton was made master of the Mint, and in that capacity as contractor for the coinage he amassed a considerable fortune. 8 As the work of the Mint became more extensive and more complicated other officers were added and their duties were varied from time to time. The present administration of the English Mint is based on arrangements made in 1870, when the establishment was reorganized. The office of master of the Mint is held by the chancellor of the exchequer for the time being, without salary, but the actual administrative work of the department is entrusted to the deputy master and comptroller. The receipt of bullion and the delivery of coin from the Mint is under the charge of the chief clerk, the manufacture of coin is in the hands of the superintendent of the operative department, and the valuation of the bullion by assay, and matters relating to the fineness of the coin are entrusted to the chemist and assayer. The date of the establishment of the Mint in the Tower of London is unknown. There is a reference to it dated 1229 and a clear reference dated 1329.9 According to Ruding, there were over fifty mints in the reign of Edward the Confessor. After the Norman Conquest the mints increased to about seventy, a greater number than now exists in the world, but they were gradually reduced and in the reign of Edward I. there were only twelve. Ruding enumerates 128 mints operated at various times in the United Kingdom, including some established by usurpation, as in the reign of Stephen by certain barons, and also mints established by grants to ecclesiastics to be worked for their own profit. The provincial mints were all closed just before the reign of Mary, who coined in London only. Charles I. set up small mints in various towns, and for the great re-coinage in the reign of William III. mints were established at York, Chester, Exeter, Bristol and Norwich, but were soon abandoned. Wood's copper money for Ireland and America was coined at Wolverhampton (1700-1722), and the tradesmen's tokens were struck at various towns. Copper coins were struck by Boulton at Soho, Birmingham, 4 H. A. Grueber, Coins of Great Britain and Ireland, p. viii.

5 Rogers Ruding, Annals of the Coinage, 3rd ed. ii. 235.

s Grueber, op. cit. p. xxv. 8 Ruding, op. cit. i. 35.

7 Ibid. p. xxvi. 9 Ibid. ii. 292, 294.

in 1788, and a colonial bronze coinage was executed at this establishment as recently as the year 1875. There is another mint in Birmingham worked by a private company (" The Mint, Birmingham, Limited "), where coinages for foreign governments are executed and in addition silver and bronze colonial coins are occasionally manufactured under the supervision of the London Mint. The existing London Mint was erected on Tower Hill in 1810. Minting in Scotland began in the reign of David I. (1124-1153) and ceased in 1709, two years after the Act of Union, in which it had been expressly stipulated that a mint should be continued in Scotland. 1 Coinage in Dublin began in AngloSaxon times and came to an end in the reign of William III.2 The other Irish mints were of little importance.

British Dominions

Turning to mints in British Dominions beyond the Seas, Ruding enumerates twenty-six mints in France and Flanders used by British monarchs between 1186 and 1513, and Anglo-Hanoverian coins were struck at Clausthal, Zellerfeld and Hanover in the period 1714-1837. In India 3 the earliest English mint was that at Madras which was bought by the East India Company in 1620, reorganized more than once and finally closed in 1869. The Calcutta mint was established by the East India Company in 1757, but other mints in Bengal continued to be used till about 1835, when the Calcutta mint was rebuilt. The Bombay mint was set up about the year 1671, but the coins were made by hammer and anvil until 1800. The Calcutta and Bombay mints are still in operation. A mint was opened in Hong-Kong in 1866 but was closed in 1868 and the machinery sold to Japan. In Australia there are three mints, Sydney, opened in 1855, Melbourne, opened in 1872, and Perth, opened in 1899. Up to 1909 only sovereigns and half-sovereigns were struck at these establishments, but in Iwo arrangements were made for a Commonwealth silver coinage. A mint at Ottawa was opened in 1908 for the manufacture of all Canadian coins as well as English sovereigns.

Other Countries

In the United States the Philadelphia mint was opened in 1792, but only manual or horse power was used until 1836, when steam was introduced. Other mints are now in operation at New Orleans, San Francisco and Denver. In most European countries a single mint situated at the capital is found to be sufficient, but there are six mints in the German Empire and two in Austria-Hungary. In China 26 mints were at work in 1906. There are also mints at Osaka, Bangkok and Teheran, and the Seoul mint was at work in 1904. In Mexico 11 mints formerly existed, but one only, in the city of Mexico, remained open in 1907. In South America there are mints at Lima, Santiago, Buenos Ayres and Tegucigalpa. No mints are in operation in Africa. In all there are nearly 70 mints in the world.

The Supply of Bullion to Mints

In England, in the middle ages, the king was accustomed to send in to the mint the produce of his own silver mines, and claimed the exclusive privilege of purchasing the precious metals. The right of levying seigniorage, however, was sometimes waived by the king to encourage his subjects to bring gold and silver to the mint, and several instances are recorded in which the aid of alchemists was called in to effect the transmutation of baser metals into gold. Seigniorage was abolished for both gold and silver in 1666, when it was provided that no charge should be made at the Mint for coining and assaying. Finally in 1816 the free coinage of silver was brought to an end. At present all gold bullion brought to the Mint is weighed and portions are cut off for assay. The amount of gold in standard ounces (916.6 fine) corresponding to the " imported " bullion is thus ascertained, and on the application of the importer the gold is coined and delivered to him in the form of sovereigns and half-sovereigns at the rate of £3, 17s. 102d. per standard ounce troy, no deduction being made for wastage, seigniorage, the purchase of alloy metal, or the expense of manufacture. As a considerable time elapses between the receipt of bullion by the Mint and the delivery of the coin, it is generally 1 Grueber, op. cit. p. liv. 2 Ruding, op. cit. ii. 245.

3 W. J. Hocking, Catalogue of Coins in the Royal Mint, i. 272, 275 and 279.

more profitable for the holder of gold bullion to sell it to the Bank of England or dispose of it in some other way. The result is that the gold presented for coinage is almost always sent from the Bank of England, which suffers no loss of interest during the coinage of the bullion, because bank-notes have already been issued against it. Silver bullion, and the copper, tin and zinc required to make up bronze, are bought by the Mint and manufactured into coin, which is kept in stock and issued as it may be required. One ounce of standard silver, which contains 925 parts of silver and 75 of copper per 1000, is converted into 5s. 6d. in silver coin, whatever may be the market price of silver bullion. This seldom exceeded Sod. per ounce in the years 1893-1907. Coinage bronze consists of copper 95 parts, tin 4 parts and zinc I part, and a ton yields X44 8 in pence or £ 373, 6s. 8d. in halfpence or farthings. The difference between the nominal value of silver and bronze coin and its intrinsic value is retained by the state to cover the expenses of manufacture and as a source of profit. It corresponds to the seigniorage levied by the king on all coinages down to the reign of Charles II. In return, the Mint receives at its nominal value for recoinage the worn gold and silver coin which is withdrawn from circulation by the Bank of England and some other banks. In spite of the cost of this recoinage, however, the profit on the issue of new silver and bronze usually exceeds in each year the total expenditure of the Mint. Gold and silver are delivered in a refined state suitable for immediate conversion into coin. In general, only old coin, ingots resulting from the melting of coin, and " fine " ingots are received. Fine gold ingots (the " bar gold " of commerce) are usually about 400 oz. troy in weight, and contain from 990 to 999.5 p a rts of gold per 1000, the remainder being chiefly silver. Fine silver ingots usually weigh from l000 to 1200 oz. troy and contain from 995 to 999 parts of silver per 1000. The ingots are valued by weighing and assaying, and a calculation is made as to the amount of copper required for melting with them to produce the standard alloy. The two standard alloys consist respectively of gold 916.6, copper 83.3 and of silver 925, copper 75. All gold coins received at the Bank are weighed on automatic balances (see below) and those below the lowest legal current weight are separated. The lowest current weight is 1 22.5 grains for sovereigns and 61.125 grains for half-sovereigns corresponding to losses by wear of about o. 6% and o.8% respectively. The average age on withdrawal is about 24 years for sovereigns and 15 years for half-sovereigns. Silver coins are not weighed but are selected for withdrawal when they present a worn appearance. The average deficiency in weight of worn silver coin received at the Mint is from 8 to 10%, and the mean age somewhat less than 50 years. In European mints generally little difficulty is experienced in procuring refined gold and silver for coinage. In Australia, the United States, Japan and some other countries, the Mints receive unrefined gold from the mines and refine it before it is coined. A charge for refining is made in all cases. A refinery was attached to the London Mint from 1816 to 1851, but was then let on lease and left to private enterprise. The operations employed in the manufacture of gold and silver coin are as follow: (1) Melting the metal and casting it into bars. (2) Rolling the bars into strips or " fillets." (3) Cutting out disks or blanks from the fillets. (4) Adjusting the weight of the blanks (this is omitted in some mints). (5) " Marking " or edge-rolling the blanks to produce a raised rim or to impress a design on the edge. (6) Annealing the blanks and (in some mints) cleaning them in acid.

(7) Striking the blanks between dies surrounded by a collar.

(8) Weighing each coin. Among the incidental operations are (a) the valuation of the bullion by weighing and assaying it; (b) " rating" the bullion, or calculating the amount of copper to be added to make up the standard alloy; (c) recovering the values from ground-up crucibles, ashes and floor sweepings (the Mint " sweep "); (d) assaying the melted bars; (e) " pyxing " the finished coin or selecting specimens to be weighed and assayed; (f) " telling " or counting the coin.

Melting

Formerly bullion was melted in crucibles made of refractory clay, but they are liable to crack and require careful handling These were succeeded by iron crucibles, especially for melting silver, and these have now been generally replaced by graphite (plumbago) crucibles made of a mixture of clay and graphite. Good graphite crucibles can be used many times in succession if they are heated gradually each time, but they are usually discarded after about fifteen or twenty meltings. At the Royal Mint gold is melted in crucibles about 10 in. in height and 82 in. in diameter at the widest part. The charge is from 1200 to 1300 oz. (37.3 to 40'5 kilograms) of metal. The furnace is 12 in. square and 2 ft. deep from the fire-bars to the cover. An old crucible is cut off about 2 in. from the bottom and the bottom piece is inverted and placed on the fire-bars as a support for the crucible. The " muffle," a graphite cylinder 6 in. in height, is placed on the crucible to allow room for long bars to be melted in the crucible and to prevent the surrounding and C is the flue, common to two furnaces and leading to the stack. The handle D, acting through the gear wheels E, F, G and H, turns the cogwheel K, which moves the curved rack of the cradle and tips the crucible M. The molten metal is poured into the moulds N, which are carried on wheels running on rails Q. The parts of the range of moulds are brought tightly together and held in position by the bars 0 and the screw P, and when one mould is filled the carrier is moved forward on its rails by wheels worked by a handle also shown in the figure. In some other mints still larger crucibles are used, containing various amounts up to about moo kilograms or over 30,000 oz. In foreign mints the molten metal is generally transferred from the crucible to the moulds by dipping crucibles or iron ladles covered with clay. Gas is used as fuel for the melting furnaces at Philadelphia. It is cleaner than coke and is said to FIG. I. - Furnace Apparatus.

coke from falling into it. The flue, of about 5 in. square, communicates with a stack 60 ft. high. In many mints the flues pass into condensing chambers where volatilized gold and silver are recovered. The crucible is at a red heat when the gold is charged in, the copper being added last, and a graphite lid put on the crucible to check loss by volatilization. The charge is completely melted in about half an hour, and it is then thoroughly mixed by stirring with a graphite rod. The crucible is then lifted out by circular tongs suspended in such a way that two men can take part in the; operation. The contents are poured by hand into moulds which are contained side by side in an iron carriage running on wheels, fig. 1, OP. The molten gold, which is of a pale green colour, solidifies at once in the iron moulds, and the bars can be taken out immediately. Bars from which sovereigns are to be coined are 22 in. long, 18 in. wide and 2 in. thick, and about seven such bars are cast from one pot. The rough edges of the bars are removed by a circular revolving file, and the hollow ends are cut off. Pieces are cut out for assay, and the bars are then ready for rolling. The amount of gold melted in an ordinary day's work is two tons to two and a half tons, of the value of £250,000 to £300,000. For silver larger crucibles are used, containing/about 5000 oz. troy (155 kilograms). They are heated in circular furnaces 21 in. in diameter and lifted out with circular tongs suspended from a travelling crane which is worked by electricity. The crucible is placed in the pouring cradle, which has been in use since 1816, and is shown in fig. 1. Here A is the iron cover surrounding the furnaces, B is the revolving lid of a furnace, save time and to reduce the loss of the precious metals. At Denver and Ottawa the fuel used is " first distillate " oil, which is found to be cheaper than either naphtha or gas. The oil is pumped from buried tanks and warmed to about 90° F. before it reaches the burners at the furnaces. At the Denver mint the crucibles are used for from twelve to fifteen meltings with oil fuel, whereas they were soon destroyed when gas was employed. A charge of 6000 oz. of gold is melted in about an hour. The melting losses amount to about 0.2 per moo of gold and o6 per loon of silver in the Royal Mint. The losses are caused by volatilization, by the absorption of metal by the crucible, stirring rod, &c., and by occasional projection of particles from the pot into the furnace. The ash-pit is lined with iron plates to facilitate the recovery of metal accidentally spilt. All crucibles and other materials which might contain precious metal are ground up and washed in a pan, and the pannings together with a selection from the floor sweepings are remelted. The residues (the Mint " sweep ") are sold to refiners or ore-smelters.

Rolling

The cast bars are reduced to the thickness of the coin by repeated passages between rolls. These are cylinders of cast iron or steel from 6 in. to 15 in. in diameter set parallel to one another with a small interval between, and revolved by electric or steam power. They are divided into breaking-down and finishing rolls, the latter being of smaller diameter than the former. The power is usually transmitted through toothed wheels, each roll being driven independently in some cases, while sometimes power is applied to the lower roll only, the upper roll being coupled to it. The power required for breaking down mint bars amounts to from 25 to 35 h.p. The bars are fed to the rolls by hand. Heavy pinches are applied at first, the space between the rolls being diminished by a hand-screw of ter each passage of the bars through them. When the bars are nearly to gauge, light pinches are given, the power required by finishing rolls being about 5 h.p. only. The reduction in thickness of the bars is accompanied by a slight increase in their width and a very great increase in their length, so that it is generally necessary to cut partly rolled bars into two parts to keep them of convenient dimensions. By repeated passages through the rolls the bars are hardened, and to facilitate further reduction they are usually softened by annealing before being passed to the finishing rolls. In some mints the fillets are annealed frequently, the fillets for one-mark pieces at the Berlin mint, for example, being annealed four times in the course of rolling. In this case the bars are reduced from 52 mm. in thickness to 14 mm. by being passed thirteen times through the rolls. At the Vienna mint the practice has been to anneal silver bars after each passage through the rolls. On the other hand, in the United States mints, the use of very carefully refined metal has made it possible to discontinue the annealing of partly rolled bars. In the Royal Mint silver bars are annealed once during rolling by passing through a Bates & Peard gas furnace. The fillets are placed on an endless chain which moves slowly through the furnace, returning underneath. At each end of the furnace is a trough of water which covers the furnace mouth, so that air is prevented from entering the furnace. The chain dips below the water, then rises into the furnace and passes down into the other trough on its way out. The result is that so long as the fillets are hot they are kept from contact with the air and blackening of the metal is prevented. In some mints the drag-bench or draw-bench is used after the rolls to equalize the thickness of the fillets. The fillet is drawn between two little steel cylinders which do not revolve and are held rigidly in position. The principle resembles that used in wire drawing. It was introduced by Sir John Barton at the Royal Mint in 1816 and was abandoned there in 1905. The thickness of the FIG. 2. - Gauge Plate.

fillets is measured by the gauge-plate shown in fig. 2. When they have been reduced to the correct thickness they are examined by the " tryer," who cuts out one or two blanks from each fillet with a hand machine and weighs them on a delicate balance. If the weight of the blank is slightly below the standard weight, a somewhat larger cutter is used, so that the blanks may be of correct weight. If the blank is too heavy the fillet may of course be passed through the rolls again.

Remedy

The degree of accuracy required is indicated by the " remedy " allowance for weight, which is different for each coin, and is the maximum difference from the standard weight which is allowed by law. In the sovereign it is 0.2 grain or about 1.62 per moo. As the mean thickness of a sovereign is 0.0466 in., the remedy for weight corresponds to a difference of less than in. in the thickness of the fillet. The remedy for English silver coins varies from 2 grains or 4.58 per moo in the case of the crown, to 0.087 grain or 11.97 per moo in the case of the silver penny. The remedies for weight on foreign coins are in general greater than those allowed in the British Empire, averaging 2 per moo for gold coins. Reference may here be made to the similar working margin allowed in respect of the fineness of gold and silver. In England the remedy for fineness is 2 per moo on gold coins and 4 per moo on silver coins above and below the legal standard. Thus gold coins would be within the limits if they contained between 914.6 and 918.6 parts of gold per 1000. Remedies are intended to cover accidental variations from the exact standard and are now generally used only in this way. In former times, however, advantage was sometimes taken of the remedy as a means of profit. In the reign of Queen Elizabeth, the master of the Mint, finding the allowance under his contract to be insufficient, availed himself of the remedy on the silver coinage, which amounted to 6±d. on the pound troy, or about 8.7 per 1000.

Cutting Blanks

The cutting machine used in the Mint is shown in fig. 3. The revolution of an eccentric A causes two short steel cylinders or cutters mounted on a block of iron B, suitably guided, to enter two holes in a plate fixed to the bed of the machine. When the fillet FF is brought above the holes, the cutters descend and force disks of metal through the holes. After each descent of the cutters, the fillet is advanced by small gripping rolls C C' C" worked by a ratchet wheel E driven from the shaft which bears the eccentric A. The disks fall down the tube G to a receptacle on the floor. The cutters are so placed as to remove blanks in the manner shown in fig. 4, this arrangement leaving less " scissel " or residual metal than any other. In the case of very large silver coins only one blank is cut in the width of the fillet, but bronze fillets are made wider so that three penny blanks are cut out at each stroke of the machine. The cutting machines at the Mint work at 160 revolutions per minute, so that each of the eleven machines would be capable of cutting 19,200 blanks in an hour if it could be fed continuously. The scissel, which amounts to about 30% of the metal operated on, is returned in bundles to the melting house.

Marking

The blanks are then passed to an edge rolling machine, by which they are thickened at the edge so as to form a rim to protect the finished coin from wear. This operation is called marking, because originally the edges FIG. 4.

were not only thickened but were also marked with an inscription. This is still done in the case of many foreign coins. The letters are sometimes sunk and sometimes raised. Like the graining or " milling " on the edge of many coins, the inscriptions were intended to put a stop to the practice of clipping and filing coins, which was prevalent in the 16th and 17th centuries. They also render the manufacture of counterfeit FIG. 3. - Cutting Machine. coin more difficult. At the Royal Mint the blanks are passed between the parallel faces of a revolving steel plate and fixed block. The plate has a circular groove in its face and the block has a corresponding curved groove. The blank passes between these grooves. The distance between the block and the plate is adjusted so as to be slightly less than the diameter of the blank, and the result is that the edge of the blank is thickened and its diameter reduced before it escapes from the machine. About 720 blanks are passed through this machine per minute. In marking machines in some foreign mints the groove is in the periphery of the revolving wheel, and the grooved block is curved (fig. 5).

Annealing and Blanching the Blanks

The blanks are next softened by annealing, and are then thoroughly cleaned before being passed to the coining presses. In England gold and copper blanks are protected from oxidation, and after their passage through the furnace are merely washed in colanders with water and dried with sawdust in a rotating drum. Silver blanks, however, are passed through rotary gas furnaces in which no attempt is made to exclude the air. The blanks are charged into a hopper at one end of the furnace and conveyed towards the other end by a revolving Archimedean screw. The blanks fall through an aperture after having been heated for a few minutes. They are at a dull red heat and are allowed to cool gradually in the air and become blackened by the formation on the surface of a film of oxide of copper. This is removed by solution in hot dilute sulphuric acid and a layer of pure frosted silver is left on the surface, which appears dead white in colour, and has lost its metallic lustre. The operation is called " blanching." A similar method was formerly used for gold coins in England and is still employed in some mints. The removal of part of the copper from the blank raises the percentage of silver contained in them and this is allowed for by adding an equivalent amount of copper to the metal when it is melted. The amount of copper removed from silver blanks containing 900 to 925 parts of silver per moo is from o6 to Io per 1000. The process will probably be abandoned as soon as the tarnishing of the metal during rolling and annealing can be avoided.