concentration works of the Greeks, but we cannot be absolutely certain
at what period in the history of these mines crushing and concentration
were introduced. While the mines were worked with great activity prior
to 500 B.C. (see note 6, p. 27), it was quite feasible for the ancient
miner to have smelted these argentiferous lead ores direct. However, at
some period prior to the decadence of the mines in the 3rd Century B.C.,
there was in use an extensive system of milling and concentration. For
the following details we are indebted mostly to Edouard Ardaillon (_Les
Mines Du Laurion dans l'Antiquite_, Chap. IV.). The ore was first
hand-picked (in 1869 one portion of these rejects was estimated at
7,000,000 tons) and afterward it was apparently crushed in stone mortars
some 16 to 24 inches in diameter, and thence passed to the mills. These
mills, which crushed dry, were of the upper and lower millstone order,
like the old-fashioned flour mills, and were turned by hand. The stones
were capable of adjustment in such a way as to yield different sizes.
The sand was sifted and the oversize returned to the mills. From the
mills it was taken to washing plants, which consisted essentially of an
inclined area, below which a canal, sometimes with riffles, led through
a series of basins, ultimately returning the water again to near the
head of the area. These washing areas, constructed with great care, were
made of stone cemented over smoothly, and were so efficiently done as to
remain still intact. In washing, a workman brushed upward the pulp
placed on the inclined upper portion of the area, thus concentrating
there a considerable proportion of the galena; what escaped had an
opportunity to settle in the sequence of basins, somewhat on the order
of the buddle. A quotation by Strabo (III, 2, 10) from the lost work of
Polybius (200-125 B.C.) also indicates concentration of lead-silver ores
in Spain previous to the Christian era: "Polybius speaking of the silver
mines of New Carthage, tells us that they are extremely large, distant
from the city about 20 stadia, and occupy a circuit of 400 stadia, that
there are 40,000 men regularly engaged in them, and that they yield
daily to the Roman people (a revenue of) 25,000 drachmae. The rest of
the process I pass over, as it is too long, but as for the silver ore
collected, he tells us that it is broken up, and sifted through sieves
over water; that what remains is to be again broken, and the water
having been strained off, it is to be sifted and broken a third time.
The dregs which remain after the fifth time are to be melted, and the
lead being poured off, the silver is obtained pure. These silver mines
still exist; however, they are no longer the property of the state,
neither these nor those elsewhere, but are possessed by private
individuals. The gold mines, on the contrary, nearly all belong to the
state. Both at Castlon and other places there are singular lead mines
worked. They contain a small proportion of silver, but not sufficient to
pay for the expense of refining." (Hamilton's Translation, Vol. I., p.
222). While Pliny gives considerable information on vein mining and on
alluvial washing, the following obscure passage (XXXIII, 21) appears to
be the only reference to concentration of ores: "That which is dug out
is crushed, washed, roasted, and ground to powder. This powder is called
_apitascudes_, while the silver (lead?) which becomes disengaged in the
furnace is called _sudor_ (sweat). That which is ejected from the
chimney is called _scoria_ as with other metals. In the case of gold
this _scoria_ is crushed and melted again." It is evident enough from
these quotations that the Ancients by "washing" and "sifting," grasped
the practical effect of differences in specific gravity of the various
components of an ore. Such processes are barely mentioned by other
mediaeval authors, such as Theophilus, Biringuccio, etc., and thus the
account in this chapter is the first tangible technical description.
Lead mining has been in active progress in Derbyshire since the 13th
century, and concentration was done on an inclined board until the 16th
century, when William Humphrey (see below) introduced the jigging sieve.
Some further notes on this industry will be found in note 1, p. 77.
However, the buddle and strake which appear at that time, are but modest
improvements over the board described by Agatharchides in the quotation
above.
The ancient crushing appliances, as indicated by the ancient authors and
by the Greek and Roman remains scattered over Europe, were hand-mortars
and mill-stones of the same order as those with which they ground flour.
The stamp-mill, the next advance over grinding in mill-stones, seems to
have been invented some time late in the 15th or early in the 16th
centuries, but who invented it is unknown. Beckmann (Hist. of
Inventions, II, p. 335) says: "In the year 1519 the process of sifting
and wet-stamping was established at Joachimsthal by Paul Grommestetter,
a native of Schwarz, named on that account the Schwarzer, whom Melzer
praises as an ingenious and active washer; and we are told that he had
before introduced the same improvements at Schneeberg. Soon after, that
is in 1521, a large stamping-work was erected at Joachimsthal, and the
process of washing was begun. A considerable saving was thus made, as a
great many metallic particles were before left in the washed sand, which
was either thrown away or used as mortar for building. In the year 1525,
Hans Poertner employed at Schlackenwalde the wet method of stamping,
whereas before that period the ore there was ground. In the Harz this
invention was introduced at Wildenmann by Peter Philip, who was
assay-master there soon after the works at the Upper Harz were resumed
by Duke Henry the Younger, about the year 1524. This we learn from the
papers of Herdan Hacke or Haecke, who was preacher at Wildenmann in
1572."
In view of the great amount of direct and indirect reference to tin
mining in Cornwall, covering four centuries prior to Agricola, it would
be natural to expect some statement bearing upon the treatment of ore.
Curiously enough, while alluvial washing and smelting of the black-tin
are often referred to, there is nothing that we have been able to find,
prior to Richard Carew's "Survey of Cornwall" (London, 1602, p. 12)
which gives any tangible evidence on the technical phases of
ore-dressing. In any event, an inspection of charters, tax-rolls,
Stannary Court proceedings, etc., prior to that date gives the
impression that vein mining was a very minor portion of the source of
production. Although Carew's work dates 45 years after Agricola, his
description is of interest: "As much almost dooth it exceede credite,
that the Tynne, for and in so small quantitie digged up with so great
toyle, and passing afterwards thorow the managing of so many hands, ere
it comes to sale, should be any way able to acquite the cost: for being
once brought above ground in the stone, it is first broken in peeces
with hammers; and then carryed, either in waynes, or on horses' backs,
to a stamping mill, where three, and in some places sixe great logges of
timber, bounde at the ends with yron, and lifted up and downe by a
wheele, driven with the water, doe break it smaller. If the stones be
over-moyst, they are dried by the fire in an yron cradle or grate. From
the stamping mill, it passeth to the crazing mill, which betweene two
grinding stones, turned also with a water-wheel, bruseth the same to a
find sand; howbeit, of late times they mostly use wet stampers, and so
have no need of the crazing mills for their best stuffe, but only for
the crust of their tayles. The streame, after it hath forsaken the mill,
is made to fall by certayne degrees, one somewhat distant from another;
upon each of which, at every discent, lyeth a greene turfe, three or
foure foote square, and one foote thick. On this the Tinner layeth a
certayne portion of the sandie Tinne, and with his shovel softly tosseth
the same to and fro, that, through this stirring, the water which
runneth over it may wash away the light earth from the Tinne, which of a
heavier substance lyeth fast on the turfe. Having so clensed one
portion, he setteth the same aside, and beginneth with another, until
his labour take end with his taske. The best of those turfes (for all
sorts serve not) are fetched about two miles to the eastwards of S.
Michael's Mount, where at low water they cast aside the sand, and dig
them up; they are full of rootes of trees, and on some of them nuts have
been found, which confirmeth my former assertion of the sea's intrusion.
After it is thus washed, they put the remnant into a wooden dish, broad,
flat, and round, being about two foote over, and having two handles
fastened at the sides, by which they softly shogge the same to and fro
in the water betweene their legges, as they sit over it, untill
whatsoever of the earthie substance that was yet left be flitted away.
Some of later time, with a sleighter invention, and lighter labour, doe
cause certayne boyes to stir it up and down with their feete, which
worketh the same effect; the residue, after this often clensing, they
call Blacke Tynne."
It will be noticed that the "wet stampers" and the buddle--worked with
"boyes feete"--are "innovations of late times." And the interesting
question arises as to whether Cornwall did not derive the stamp-mill,
buddle, and strake, from the Germans. The first adequate detailed
description of Cornish appliances is that of Pryce (_Mineralogia
Cornubiensis_, London, 1778) where the apparatus is identical with that
described by Agricola 130 years before. The word "stamper" of Cornwall
is of German origin, from _stampfer_, or, as it is often written in old
German works, _stamper_. However, the pursuit of the subject through
etymology ends here, for no derivatives in German can be found for
buddle, tye, strake, or other collateral terms. The first tangible
evidence of German influence is to be found in Carew who, continuing
after the above quotation, states: "But sithence I gathered stickes to
the building of this poore nest, Sir Francis Godolphin (whose kind helpe
hath much advanced this my playing labour) entertained a Dutch Mynerall
man, and taking light from his experience, but building thereon farre
more profitable conclusions of his owne invention, hath practised a more
saving way in these matters, and besides, made Tynne with good profit of
that refuse which Tynners rejected as nothing worth." Beyond this
quotation we can find no direct evidence of the influence of "Dutch
Mynerall men" in Cornish tin mining at this time. There can be no doubt,
however, that in copper mining in Cornwall and elsewhere in England, the
"Dutch Mynerall men" did play a large part in the latter part of the
16th Century. Pettus (_Fodinae Regales_, London, 1670, p. 20) states that
"about the third year of Queen Elizabeth (1561) she by the advice of her
Council sent over for some Germans experienced in mines, and being
supplied, she, on the tenth of October, in the sixth of her reign,
granted the mines of eight counties ... to Houghsetter, a German whose
name and family still continue in Cardiganshire." Elizabeth granted
large mining rights to various Germans, and the opening paragraphs of
two out of several Charters may be quoted in point. This grant is dated
1565, and in part reads: "ELIZABETH, by the Grace of God, Queen of
England, France, and Ireland, Defender of the Faith, &c. To all Men to
whom these Letters Patents shall come, Greeting. Where heretofore we
have granted Privileges to Cornelius de Voz, for the Mining and Digging
in our Realm of England, for Allom and Copperas, and for divers Ewers of
Metals that were to be found in digging for the said Allom and Copperas,
incidently and consequently without fraud or guile, as by the same our
Privilege may appear. And where we also moved, by credible Report to us
made, of one Daniel Houghsetter, a German born, and of his Skill and
Knowledge of and in all manner of Mines, of Metals and Minerals, have
given and granted Privilege to Thomas Thurland, Clerk, one of our
Chaplains, and Master of the Hospital of Savoy, and to the same Daniel,
for digging and mining for all manner of Ewers of Gold, Silver, Copper,
and Quicksilver, within our Counties of York, Lancaster, Cumberland,
Westmorland, Cornwall, Devon, Gloucester, and Worcester, and within our
Principality of Wales; and with the same further to deal, as by our said
Privilege thereof granted and made to the said Thomas Thurland and
Daniel Houghsetter may appear. _And_ we now being minded that the said
Commodities, and all other Treasures of the Earth, in all other Places
of our Realm of England...." On the same date another grant reads:
"ELIZABETH, by the Grace of God, Queen of England, France, and Ireland,
Defender of the Faith, &c. To all Men to whom these our Letters Patents
shall come, Greeting. Where we have received credible Information that
our faithful and well-beloved Subject William Humfrey, Saymaster of our
Mint within our Tower of London, by his great Endeavour, Labour, and
Charge, hath brought into this our Realm of England one Christopher
Shutz, an Almain, born at _St. Annen Berg_, under the Obedience of the
Electer of Saxony; a Workman as it is reported, of great Cunning,
Knowledge, and Experience, as well in the finding of the Calamin Stone,
call'd in Latin, _lapis calaminaris_, and in the right and proper use
and commodity thereof, for the Composition of the mix'd Metal commonly
call'd _latten_, etc." Col. Grant-Francis, in his most valuable
collection (Smelting of Copper in the Swansea District, London, 1881)
has published a collection of correspondence relating to early mining
and smelting operations in Great Britain. And among them (p. 1., etc.)
are letters in the years 1583-6 from William Carnsewe and others to
Thomas Smyth, with regard to the first smelter erected at Neath, which
was based upon copper mines in Cornwall. He mentions "Mr. Weston's (a
partner) provydence in bringynge hys Dutch myners hether to aplye such
businys in this countrye ys more to be commendyd than his ignorance of
our countrymen's actyvytyes in suche matters." The principal "Dutche
Mineral Master" referred to was one Ulrick Frosse, who had charge of the
mine at Perin Sands in Cornwall, and subsequently of the smelter at
Neath. Further on is given (p. 25) a Report by Jochim Gaunse upon the
Smelting of copper ores at Keswick in Cumberland in 1581, referred to in
note 2, p. 267. The Daniel Hochstetter mentioned in the Charter above,
together with other German and English gentlemen, formed the "Company of
Mines Royal" and among the properties worked were those with which
Gaunse's report is concerned. There is in the Record Office, London
(Exchequer K.R. Com. Derby 611. Eliz.) the record of an interesting
inquisition into Derbyshire methods in which a then recent great
improvement was the jigging sieve, the introduction of which was due to
William Humphrey (mentioned above). It is possible that he learned of it
from the German with whom he was associated. Much more evidence of the
activity of the Germans in English mining at this period can be adduced.
On the other hand, Cornwall has laid claims to having taught the art of
tin mining and metallurgy to the Germans. Matthew Paris, a Benedictine
monk, by birth an Englishman, who died in 1259, relates (_Historia Major
Angliae_, London, 1571) that a Cornishman who fled to Germany on account
of a murder, first discovered tin there in 1241, and that in consequence
the price of tin fell greatly. This statement is recalled with great
persistence by many writers on Cornwall. (Camden, _Britannia_, London,
1586; Borlase, Natural History of Cornwall, Oxford, 1758; Pryce,
_Mineralogia Cornubiensis_, London, 1778, p. 70, and others).
[11] _Lapidibus liquescentibus_. (See note 15, p. 380).
[12] HISTORICAL NOTE ON AMALGAMATION. The recovery of gold by the use of
mercury possibly dates from Roman times, but the application of the
process to silver does not seem to go back prior to the 16th Century.
Quicksilver was well-known to the Greeks, and is described by
Theophrastus (105) and others (see note 58, p. 432, on quicksilver).
However, the Greeks made no mention of its use for amalgamation, and, in
fact, Dioscorides (V, 70) says "it is kept in vessels of glass, lead,
tin or silver; if kept in vessels of any other kind it consumes them and
flows away." It was used by them for medicinal purposes. The Romans
amalgamated gold with mercury, but whether they took advantage of the
principle to recover gold from ores we do not know. Vitruvius (VII, 8)
makes the following statement:--"If quicksilver be placed in a vessel
and a stone of a hundred pounds' weight be placed on it, it will swim at
the top, and will, notwithstanding its weight, be incapable of pressing
the liquid so as to break or separate it. If this be taken out, and only
a single scruple of gold be put in, that will not swim, but immediately
descend to the bottom. This is a proof that the gravity of a body does
not depend on its weight, but on its nature. Quicksilver is used for
many purposes; without it, neither silver nor brass can be properly
gilt. When gold is embroidered on a garment which is worn out and no
longer fit for use, the cloth is burnt over the fire in earthen pots;
the ashes are thrown into water and quicksilver added to them; this
collects all the particles of gold and unites with them. The water is
then poured off and the residuum placed in a cloth, which, when squeezed
with the hands, suffers the liquid quicksilver to pass through the pores
of the cloth, but retains the gold in a mass within it." (Gwilt's
Trans., p. 217). Pliny is rather more explicit (XXXIII, 32): "All floats
on it (quicksilver) except gold. This it draws into itself, and on that
account is the best means of purifying; for, on being repeatedly
agitated in earthen pots it casts out the other things and the
impurities. These things being rejected, in order that it may give up
the gold, it is squeezed in prepared skins, through which, exuding like
perspiration, it leaves the gold pure." It may be noted particularly
that both these authors state that gold is the only substance that does
not float, and, moreover, nowhere do we find any reference to silver
combining with mercury, although Beckmann (Hist. of Inventions, Vol. I,
p. 14) not only states that the above passage from Pliny refers to
silver, but in further error, attributes the origin of silver
amalgamation of ores to the Spaniards in the Indies.
The Alchemists of the Middle Ages were well aware that silver would
amalgamate with mercury. There is, however, difficulty in any conclusion
that it was applied by them to separating silver or gold from ore. The
involved gibberish in which most of their utterances was couched,
obscures most of their reactions in any event. The School of Geber
(Appendix B) held that all metals were a compound of "spiritual" mercury
and sulphur, and they clearly amalgamated silver with mercury, and
separated them by distillation. The _Probierbuechlein_ (1520?) describes
a method of recovering silver from the cement used in parting gold and
silver, by mixing the cement (silver chlorides) with quicksilver.
Agricola nowhere in this work mentions the treatment of silver ores by
amalgamation, although he was familiar with Biringuccio (_De La
Pirotechnia_), as he himself mentions in the Preface. This work,
published at least ten years before _De Re Metallica_, contains the
first comprehensive account of silver amalgamation. There is more than
usual interest in the description, because, not only did it precede _De
Re Metallica_, but it is also a specific explanation of the fundamental
essentials of the Patio Process long before the date when the Spaniards
could possibly have invented that process in Mexico. We quote Mr. A.
Dick's translation from Percy (Metallurgy of Silver and Gold, p. 560):
"He was certainly endowed with much useful and ingenious thought who
invented the short method of extracting metal from the sweepings
produced by those arts which have to do with gold and silver, every
substance left in the refuse by smelters, and also the substance from
certain ores themselves, without the labour of fusing, but by the sole
means and virtue of mercury. To effect this, a large basin is first
constructed of stone or timber and walled, into which is fitted a
millstone made to turn like that of a mill. Into the hollow of this
basin is placed matter containing gold (_della materia vra che tiene
oro_), well ground in a mortar and afterward washed and dried; and, with
the above-mentioned millstone, it is ground while being moistened with
vinegar, or water, in which has been dissolved corrosive sublimate
(_solimato_), verdigris (_verde rame_), and common salt. Over these
materials is then put as much mercury as will cover them; they are then
stirred for an hour or two, by turning the millstone, either by hand, or
horse-power, according to the plan adopted, bearing in mind that the
more the mercury and the materials are bruised together by the
millstone, the more the mercury may be trusted to have taken up the
substance which the materials contain. The mercury, in this condition,
can then be separated from the earthy matter by a sieve, or by washing,
and thus you will recover the auriferous mercury (_el vro mercurio_).
After this, by driving off the mercury by means of a flask (_i.e._, by
heating in a retort or an alembic), or by passing it through a bag,
there will remain, at the bottom, the gold, silver, or copper, or
whatever metal was placed in the basin under the millstone to be ground.
Having been desirous of knowing this secret, I gave to him who taught it
to me a ring with a diamond worth 25 ducats; he also required me to give
him the eighth part of any profit I might make by using it. This I
wished to tell you, not that you should return the ducats to me for
teaching you the secret, but in order that you should esteem it all the
more and hold it dear."
In another part of the treatise Biringuccio states that washed
(concentrated) ores may be ultimately reduced either by lead or mercury.
Concerning these silver concentrates he writes: "Afterward drenching
them with vinegar in which has been put green copper (_i.e._,
verdigris); or drenching them with water in which has been dissolved
vitriol and green copper...." He next describes how this material should
be ground with mercury. The question as to who was the inventor of
silver amalgamation will probably never be cleared up. According to
Ulloa (_Relacion Historica Del Viage a la America Meridional_, Madrid,
1748) Dom Pedro Fernandes De Velasco discovered the process in Mexico in
1566. The earliest technical account is that of Father Joseph De Acosta
(_Historia Natural y Moral de las Indias_, Seville, 1590, English trans.
Edward Grimston, London, 1604, re-published by the Hakluyt Society,
1880). Acosta was born in 1540, and spent the years 1570 to 1585 in
Peru, and 1586 in Mexico. It may be noted that Potosi was discovered in
1545. He states that refining silver with mercury was introduced at
Potosi by Pedro Fernandes de Velasco from Mexico in 1571, and states
(Grimston's Trans., Vol. I, p. 219): "... They put the powder of the
metall into the vessels upon furnaces, whereas they anoint it and
mortifie it with brine, putting to every fiftie quintalles of powder
five quintalles of salt. And this they do for that the salt separates
the earth and filth, to the end the quicksilver may the more easily draw
the silver unto it. After, they put quicksilver into a piece of holland
and presse it out upon the metall, which goes forth like a dewe, alwaies
turning and stirring the metall, to the end it may be well incorporate.
Before the invention of these furnaces of fire, they did often mingle
their metall with quicksilver in great troughes, letting it settle some
daies, and did then mix it and stirre it againe, until they thought all
the quicksilver were well incorporate with the silver, the which
continued twentie daies and more, and at least nine daies." Frequent
mention of the different methods of silver amalgamation is made by the
Spanish writers subsequent to this time, the best account being that of
Alonso Barba, a priest. Barba was a native of Lepe, in Andalusia, and
followed his calling at various places in Peru from about 1600 to about
1630, and at one time held the Curacy of St. Bernard at Potosi. In 1640
he published at Madrid his _Arte de los Metales_, etc., in five books.
The first two books of this work were translated into English by the
Earl of Sandwich, and published in London in 1674, under the title "The
First Book of the Art of Metals." This translation is equally wretched
with those in French and German, as might be expected from the
translators' total lack of technical understanding. Among the methods of
silver amalgamation described by Barba is one which, upon later
"discovery" at Virginia City, is now known as the "Washoe Process." None
of the Spanish writers, so far as we know, make reference to
Biringuccio's account, and the question arises whether the Patio Process
was an importation from Europe or whether it was re-invented in Mexico.
While there is no direct evidence on the point, the presumption is in
favour of the former.
The general introduction of the amalgamation of silver ores into Central
Europe seems to have been very slow, and over 200 years elapsed after
its adoption in Peru and Mexico before it received serious attention by
the German Metallurgists. Ignaz Elder v. Born was the first to establish
the process effectually in Europe, he having in 1784 erected a
"quick-mill" at Glasshutte, near Shemnitz. He published an elaborate
account of a process which he claimed as his own, under the title _Ueber
das Anquicken der Gold und Silberhaeltigen Erze_, Vienna, 1786. The only
thing new in his process seems to have been mechanical agitation.
According to Born, a Spaniard named Don Juan de Corduba, in the year
1588, applied to the Court at Vienna offering to extract silver from
ores with mercury. Various tests were carried out under the celebrated
Lazarus Erckern, and although it appears that some vitriol and salt were
used, the trials apparently failed, for Erckern concluded his report
with the advice: "That their Lordships should not suffer any more
expense to be thrown away upon this experiment." Born's work was
translated into English by R. E. Raspe, under the title--"Baron Inigo
Born's New Process of Amalgamation, etc.," London, 1791. Some interest
attaches to Raspe, in that he was not only the author of "Baron
Munchausen," but was also the villain in Scott's "Antiquary." Raspe was
a German Professor at Cassel, who fled to England to avoid arrest for
theft. He worked at various mines in Cornwall, and in 1791 involved Sir
John Sinclair in a fruitless mine, but disappeared before that was
known. The incident was finally used by Sir Walter Scott in this novel.
[13] _Aurum in ea remanet purum_. This same error of assuming squeezed
amalgam to be pure gold occurs in Pliny; see previous footnote.
[14] George, Duke of Saxony, surnamed "The Bearded," was born 1471, and
died 1539. He was chiefly known for his bitter opposition to the
Reformation.
[15] The Julian Alps are a section east of the Carnic Alps and lie north
of Trieste. The term Rhaetian Alps is applied to that section along the
Swiss Italian Boundary, about north of Lake Como.
[16] Ancient Lusitania comprised Portugal and some neighbouring portions
of Spain.
[17] Colchis, the traditional land of the Golden Fleece, lay between the
Caucasus on the north, Armenia on the south, and the Black Sea on the
west. If Agricola's account of the metallurgical purpose of the fleece
is correct, then Jason must have had real cause for complaint as to the
tangible results of his expedition. The fact that we hear nothing of the
fleece after the day it was taken from the dragon would thus support
Agricola's theory. Tons of ink have been expended during the past thirty
centuries in explanations of what the fleece really was. These
explanations range through the supernatural and metallurgical, but more
recent writers have endeavoured to construct the journey of the
Argonauts into an epic of the development of the Greek trade in gold
with the Euxine. We will not attempt to traverse them from a
metallurgical point of view further than to maintain that Agricola's
explanation is as probable and equally as ingenious as any other,
although Strabo (XI, 2, 19.) gives much the same view long before.
Alluvial mining--gold washing--being as old as the first glimmer of
civilization, it is referred to, directly or indirectly, by a great
majority of ancient writers, poets, historians, geographers, and
naturalists. Early Egyptian inscriptions often refer to this industry,
but from the point of view of technical methods the description by Pliny
is practically the only one of interest, and in Pliny's chapter on the
subject, alluvial is badly confused with vein mining. This passage
(XXXIII, 21) is as follows: "Gold is found in the world in three ways,
to say nothing of that found in India by the ants, and in Scythia by the
Griffins. The first is as gold dust found in streams, as, for instance,
in the Tagus in Spain, in the Padus in Italy, in the Hebrus in Thracia,
in the Pactolus in Asia, and in the Ganges in India; indeed, there is no
gold found more perfect than this, as the current polishes it thoroughly
by attrition.... Others by equal labour and greater expense bring rivers
from the mountain heights, often a hundred miles, for the purpose of
washing this debris. The ditches thus made are called _corrugi_, from
our word _corrivatio_, I suppose; and these entail a thousand fresh
labours. The fall must be steep, that the water may rush down from very
high places, rather than flow gently. The ditches across the valleys are
joined by aqueducts, and in other places, impassable rocks have to be
cut away and forced to make room for troughs of hollowed-out logs. Those
who cut the rocks are suspended by ropes, so that to those who watch
them from a distance, the workmen seem not so much beasts as birds.
Hanging thus, they take the levels and trace the lines which the ditch
is to take; and thus, where there is no place for man's footstep,
streams are dragged by men. The water is vitiated for washing if the
current of the stream carries mud with it. This kind of earth is called
_urium_, hence these ditches are laid out to carry the water over beds
of pebbles to avoid this _urium_. When they have reached the head of the
fall, at the top of the mountain, reservoirs are excavated a couple of
hundred feet long and wide, and about ten feet deep. In these reservoirs
there are generally five gates left, about three feet square, so that
when the reservoir is full, the gates are opened, and the torrent bursts
forth with such violence that the rocks are hurled along. When they have
reached the plain there is yet more labour. Trenches called _agogae_ are
dug for the flow of the water. The bottoms of these are spread at
regular intervals with _ulex_ to catch the gold. This _ulex_ is similar
to rosemary, rough and prickly. The sides, too, are closed in with
planks and are suspended when crossing precipitous spots. The earth is
carried to the sea and thus the shattered mountain is washed away and
scattered; and this deposition of the earth in the sea has extended the
shore of Spain.... The gold procured from _arrugiae_ does not require to
be melted, but is already pure gold. It is found in lumps, in shafts as
well, sometimes even exceeding ten _librae_ in weight. These lumps are
called _palagae_ and _palacurnae_, while the small grains are called
_baluce_. The Ulex is dried and burnt and the ashes are washed on a bed
of grassy turf in order that the gold may settle thereon."
[19] _Carbunculus Carchedonius_--Carthaginian carbuncle. The German is
given by Agricola in the _Interpretatio_ as _granat_, _i.e._, garnet.
[20] As the concentration of crushed tin ore has been exhaustively
treated of already, the descriptions from here on probably refer
entirely to alluvial tin.
[21] From a metallurgical point of view all of these operations are
roasting. Even to-day, however, the expression "burning" tin is in use
in some parts of Cornwall, and in former times it was general.
[22] There can be no doubt that these are mattes, as will develop in
Book IX. The German term in the Glossary for _panes ex pyrite_ is
_stein_, the same as the modern German for matte. Orpiment and realgar
are the yellow and red arsenical sulphides. The _cadmia_ was no doubt
the cobalt-arsenic minerals (see note on p. 112). The "solidified
juices" were generally anything that could be expelled short of
smelting, _i.e._, roasted off or leached out, as shown in note 4, p. 1;
they embrace the sulphates, salts, sulphur, bitumen, and arsenical
sulphides, etc. For further information on leaching out the sulphates,
alum, etc., see note 10, p. 564.
BOOK IX.[1]
Since I have written of the varied work of preparing the ores, I will
now write of the various methods of smelting them. Although those who
burn, roast and calcine[2] the ore, take from it something which is
mixed or combined with the metals; and those who crush it with stamps
take away much; and those who wash, screen and sort it, take away still
more; yet they cannot remove all which conceals the metal from the eye
and renders it crude and unformed. Wherefore smelting is necessary, for
by this means earths, solidified juices, and stones are separated from
the metals so that they obtain their proper colour and become pure, and
may be of great use to mankind in many ways. When the ore is smelted,
those things which were mixed with the metal before it was melted are
driven forth, because the metal is perfected by fire in this manner.
Since metalliferous ores differ greatly amongst themselves, first as to
the metals which they contain, then as to the quantity of the metal
which is in them, and then by the fact that some are rapidly melted by
fire and others slowly, there are, therefore, many methods of smelting.
Constant practice has taught the smelters by which of these methods
they can obtain the most metal from any one ore. Moreover, while
sometimes there are many methods of smelting the same ore, by which an
equal weight of metal is melted out, yet one is done at a greater cost
and labour than the others. Ore is either melted with a furnace or
without one; if smelted with a furnace the tap-hole is either
temporarily closed or always open, and if smelted without a furnace, it
is done either in pots or in trenches. But in order to make this matter
clearer, I will describe each in detail, beginning with the buildings
and the furnaces.
A wall which will be called the "second wall" is constructed of brick
or stone, two feet and as many palms thick, in order that it may be
strong enough to bear the weight. It is built fifteen feet high, and its
length depends on the number of furnaces which are put in the works;
there are usually six furnaces, rarely more, and often less. There are
three furnace walls, a back one which is against the "second" wall, and
two side ones, of which I will speak later. These should be made of
natural stone, as this is more serviceable than burnt bricks, because
bricks soon become defective and crumble away, when the smelter or his
deputy chips off the accretions which adhere to the walls when the ore
is smelted. Natural stone resists injury by the fire and lasts a long
time, especially that which is soft and devoid of cracks; but, on the
contrary, that which is hard and has many cracks is burst asunder by the
fire and destroyed. For this reason, furnaces which are made of the
latter are easily weakened by the fire, and when the accretions are
chipped off they crumble to pieces. The front furnace wall should be
made of brick, and there should be in the lower part a mouth three palms
wide and one and a half feet high, when the hearth is completed. A hole
slanting upward, three palms long, is made through the back furnace
wall, at the height of a cubit, before the hearth has been prepared;
through this hole and a hole one foot long in the "second" wall--as the
back of this wall has an arch--is inserted a pipe of iron or bronze, in
which are fixed the nozzles of the bellows. The whole of the front
furnace wall is not more than five feet high, so that the ore may be
conveniently put into the furnace, together with those things which the
master needs for his work of smelting. Both the side walls of the
furnace are six feet high, and the back one seven feet, and they are
three palms thick. The interior of the furnace is five palms wide, six
palms and a digit long, the width being measured by the space which lies
between the two side walls, and the length by the space between the
front and the back walls; however, the upper part of the furnace widens
out somewhat.
[Illustration 357 (Blast Furnaces): A--Furnaces. B--Forehearths.]
There are two doors in the second wall if there are six furnaces, one of
the doors being between the second and third furnaces and the other
between the fourth and fifth furnaces. They are a cubit wide and six
feet high, in order that the smelters may not have mishaps in coming and
going. It is necessary to have a door to the right of the first furnace,
and similarly one to the left of the last, whether the wall is longer or
not. The second wall is carried further when the rooms for the
cupellation furnaces, or any other building, adjoin the rooms for the
blast furnaces, these buildings being only divided by a partition. The
smelter, and the ones who attend to the first and the last furnaces, if
they wish to look at the bellows or to do anything else, go out through
the doors at the end of the wall, and the other people go through the
other doors, which are the common ones. The furnaces are placed at a
distance of six feet from one another, in order that the smelters and
their assistants may more easily sustain the fierceness of the heat.
Inasmuch as the interior of each furnace is five palms wide and each is
six feet distant from the other, and inasmuch as there is a space of
four feet three palms at the right side of the first furnace and as much
at the left side of the last furnace, and there are to be six furnaces
in one building, then it is necessary to make the second wall fifty-two
feet long; because the total of the widths of all of the furnaces is
seven and a half feet, the total of the spaces between the furnaces is
thirty feet, the space on the outer sides of the first and last furnaces
is nine feet and two palms, and the thickness of the two transverse
walls is five feet, which make a total measurement of fifty-two feet.[3]
Outside each furnace hearth there is a small pit full of powder which is
compressed by ramming, and in this manner is made the forehearth which
receives the metal flowing from the furnaces. Of this I will speak
later.
[Illustration 358 (Blast Furnaces): A--Furnaces. B--Forehearth. C--Door.
D--Water tank. E--Stone which covers it. F--Material of the vent walls.
G--Stone which covers it. H--Pipe exhaling the vapour.]
Buried about a cubit under the forehearth and the hearth of the furnace
is a transverse water-tank, three feet long, three palms wide and a
cubit deep. It is made of stone or brick, with a stone cover, for if it
were not covered, the heat would draw the moisture from below and the
vapour might be blown into the hearth of the furnace as well as into the
forehearth, and would dampen the blast. The moisture would vitiate the
blast, and part of the metal would be absorbed and part would be mixed
with the slags, and in this manner the melting would be greatly damaged.
From each water-tank is built a walled vent, to the same depth as the
tank, but six digits wide; this vent slopes upward, and sooner or
later penetrates through to the other side of the wall, against which
the furnace is built. At the end of this vent there is an opening where
the steam, into which the water has been converted, is exhausted through
a copper or iron tube or pipe. This method of making the tank and the
vent is much the best. Another kind has a similar vent but a different
tank, for it does not lie transversely under the forehearth, but
lengthwise; it is two feet and a palm long, and a foot and three palms
wide, and a foot and a palm deep. This method of making tanks is not
condemned by us, as is the construction of those tanks without a vent;
the latter, which have no opening into the air through which the vapour
may discharge freely, are indeed to be condemned.
[Illustration 359 (Bellows for blast furnaces)]
Fifteen feet behind the second wall is constructed the first wall,
thirteen feet high. In both of these are fixed roof beams[4], which are
a foot wide and thick, and nineteen feet and a palm long; these are
placed three feet distant from one another. As the second wall is two
feet higher than the first wall, recesses are cut in the back of it two
feet high, one foot wide, and a palm deep, and in these recesses, as it
were in mortises, are placed one end of each of the beams. Into these
ends are mortised the bottoms of just as many posts; these posts are
twenty-four feet high, three palms wide and thick, and from the tops of
the posts the same number of rafters stretch downward to the ends of the
beams superimposed on the first wall; the upper ends of the rafters are
mortised into the posts and the lower ends are mortised into the ends of
the beams laid on the first wall; the rafters support the roof, which
consists of burnt tiles. Each separate rafter is propped up by a
separate timber, which is a cross-beam, and is joined to its post.
Planks close together are affixed to the posts above the furnaces; these
planks are about two digits thick and a palm wide, and they, together
with the wicker work interposed between the timbers, are covered with
lute so that there may be no risk of fire to the timbers and
wicker-work. In this practical manner is constructed the back part of
the works, which contains the bellows, their frames, the mechanism for
compressing the bellows, and the instrument for distending them, of all
of which I will speak hereafter.
[Illustration 361 (Plan of Smelter Building): The four long walls:
A--First. B--Second. C--Third. D--Fourth. The seven transverse walls:
E--First. F--Second. G--Third. H--Fourth. I--Fifth. K--Sixth.
L--Seventh, or middle.]
In front of the furnaces is constructed the third long wall and likewise
the fourth. Both are nine feet high, but of the same length and
thickness as the other two, the fourth being nine feet distant from the
third; the third is twenty-one and a half feet from the second. At a
distance of twelve feet from the second wall, four posts seven and a
half feet high, a cubit wide and thick, are set upon rock laid
underneath. Into the tops of the posts the roof beam is mortised; this
roof beam is two feet and as many palms longer than the distance between
the second and the fifth transverse walls, in order that its ends may
rest on the transverse walls. If there should not be so long a beam at
hand, two are substituted for it. As the length of the long beam is as
above, and as the posts are equidistant, it is necessary that the posts
should be a distance of nine feet, one palm, two and two-fifths digits
from each other, and the end ones this distance from the transverse
walls. On this longitudinal beam and to the third and fourth walls are
fixed twelve secondary beams twenty-four feet long, one foot wide, three
palms thick, and distant from each other three feet, one palm, and two
digits. In these secondary beams, where they rest on the longitudinal
beams, are mortised the ends of the same number of rafters as there are
posts which stand on the second wall. The ends of the rafters do not
reach to the tops of the posts, but are two feet away from them, that
through this opening, which is like the open part of a forge, the
furnaces can emit their fumes. In order that the rafters should not fall
down, they are supported partly by iron rods, which extend from each
rafter to the opposite post, and partly supported by a few tie-beams,
which in the same manner extend from some rafters to the posts opposite,
and give them stability. To these tie-beams, as well as to the rafters
which face the posts, a number of boards, about two digits thick and a
palm wide, are fixed at a distance of a palm from each other, and are
covered with lute so that they do not catch fire. In the secondary
beams, where they are laid on the fourth wall, are mortised the lower
ends of the same number of rafters as those in a set of rafters[5]
opposite them. From the third long wall these rafters are joined and
tied to the ends of the opposite rafters, so that they may not slip, and
besides they are strengthened with substructures which are made of cross
and oblique timbers. The rafters support the roof.
In this manner the front part of the building is made, and is divided
into three parts; the first part is twelve feet wide and is under the
hood, which consists of two walls, one vertical and one inclined. The
second part is the same number of feet wide and is for the reception of
the ore to be smelted, the fluxes, the charcoal, and other things which
are needed by the smelter. The third part is nine feet wide and contains
two separate rooms of equal size, in one of which is the assay furnace,
while the other contains the metal to be melted in the cupellation
furnaces. It is thus necessary that in the building there should be,
besides the four long walls, seven transverse walls, of which the first
is constructed from the upper end of the first long wall to the upper
end of the second long wall; the second proceeds from the end of this to
the end of the third long wall; the third likewise from this end of the
last extends to the end of the fourth long wall; the fourth leads from
the lower end of the first long wall to the lower end of the second long
wall; the fifth extends from the end of this to the end of the third
long wall; the sixth extends from this last end to the end of the fourth
long wall; the seventh divides into two parts the space between the
third and fourth long walls.
To return to the back part of the building, in which, as I said, are the
bellows[6], their frames, the machinery for compressing them, and the
instrument for distending them. Each bellows consists of a body and a
head. The body is composed of two "boards," two bows, and two hides. The
upper board is a palm thick, five feet and three palms long, and two and
a half feet wide at the back part, where each of the sides is a little
curved, and it is a cubit wide at the front part near the head. The
whole of the body of the bellows tapers toward the head. That which we
now call the "board" consists of two pieces of pine, joined and glued
together, and of two strips of linden wood which bind the edges of the
board, these being seven digits wide at the back, and in front near the
head of the bellows one and a half digits wide. These strips are glued
to the boards, so that there shall be less damage from the iron nails
driven through the hide. There are some people who do not surround the
boards with strips, but use boards only, which are very thick. The upper
board has an aperture and a handle; the aperture is in the middle of the
board and is one foot three palms distant from where the board joins the
head of the bellows, and is six digits long and four wide. The lid for
this aperture is two palms and a digit long and wide, and three digits
thick; toward the back of the lid is a little notch cut into the surface
so that it may be caught by the hand; a groove is cut out of the top of
the front and sides, so that it may engage in mouldings a palm wide and
three digits thick, which are also cut out in a similar manner under the
edges. Now, when the lid is drawn forward the hole is closed, and when
drawn back it is opened; the smelter opens the aperture a little so that
the air may escape from the bellows through it, if he fears the hides
might be burst when the bellows are too vigorously and quickly inflated;
he, however, closes the aperture if the hides are ruptured and the air
escapes. Others perforate the upper board with two or three round holes
in the same place as the rectangular one, and they insert plugs in them
which they draw out when it is necessary. The wooden handle is seven
palms long, or even longer, in order that it may extend outside;
one-half of this handle, two palms wide and one thick, is glued to the
end of the board and fastened with pegs covered with glue; the other
half projects beyond the board, and is rounded and seven digits thick.
Besides this, to the handle and to the board is fixed a cleat two feet
long, as many palms wide and one palm thick, and to the under side of
the same board, at a distance of three palms from the end, is fixed
another cleat two feet long, in order that the board may sustain the
force of distension and compression; these two cleats are glued to the
board, and are fastened to it with pegs covered with glue.
The lower bellows-board, like the upper, is made of two pieces of pine
and of two strips of linden wood, all glued together; it is of the same
width and thickness as the upper board, but is a cubit longer, this
extension being part of the head of which I have more to say a little
later. This lower bellows-board has an air-hole and an iron ring. The
air-hole is about a cubit distant from the posterior end, and it is
midway between the sides of the bellows-board, and is a foot long and
three palms wide; it is divided into equal parts by a small rib which
forms part of the board, and is not cut from it; this rib is a palm long
and one-third of a digit wide. The flap of the air-hole is a foot and
three digits long, three palms and as many digits wide; it is a thin
board covered with goat skin, the hairy part of which is turned toward
the ground. There is fixed to one end of the flap, with small iron
nails, one-half of a doubled piece of leather a palm wide and as long as
the flap is wide; the other half of the leather, which is behind the
flap, is twice perforated, as is also the bellows-board, and these
perforations are seven digits apart. Passing through these a string is
tied on the under side of the board; and thus the flap when tied to the
board does not fall away. In this manner are made the flap and the
air-hole, so when the bellows are distended the flap opens, when
compressed it closes. At a distance of about a foot beyond the air-hole
a slightly elliptical iron ring, two palms long and one wide, is
fastened by means of an iron staple to the under part of the
bellows-board; it is at a distance of three palms from the back of the
bellows. In order that the lower bellows-board may remain stationary, a
wooden bolt is driven into the ring, after it penetrates through the
hole in the transverse supporting plank which forms part of the frame
for the bellows. There are some who dispense with the ring and fasten
the bellows-board to the frame with two iron screws something like
nails.
The bows are placed between the two boards and are of the same length as
the upper board. They are both made of four pieces of linden wood three
digits thick, of which the two long ones are seven digits wide at the
back and two and a half at the front; the third piece, which is at the
back, is two palms wide. The ends of the bows are a little more than a
digit thick, and are mortised to the long pieces, and both having been
bored through, wooden pegs covered with glue are fixed in the holes;
they are thus joined and glued to the long pieces. Each of the ends is
bowed (_arcuatur_) to meet the end of the long part of the bow, whence
its name "bow" originated. The fourth piece keeps the ends of the bow
distended, and is placed a cubit distant from the head of the bellows;
the ends of this piece are mortised into the ends of the bow and are
joined and glued to them; its length without the tenons is a foot, and
its width a palm and two digits. There are, besides, two other very
small pieces glued to the head of the bellows and to the lower board,
and fastened to them by wooden pegs covered with glue, and they are
three palms and two digits long, one palm high, and a digit thick, one
half being slightly cut away. These pieces keep the ends of the bow away
from the hole in the bellows-head, for if they were not there, the ends,
forced inward by the great and frequent movement, would be broken.
The leather is of ox-hide or horse-hide, but that of the ox is far
preferable to that of the horse. Each of these hides, for there are two,
is three and a half feet wide where they are joined at the back part of
the bellows. A long leathern thong is laid along each of the
bellows-boards and each of the bows, and fastened by T-shaped iron nails
five digits long; each of the horns of the nails is two and a half
digits long and half a digit wide. The hide is attached to the
bellows-boards by means of these nails, so that a horn of one nail
almost touches the horn of the next; but it is different with the bows,
for the hide is fastened to the back piece of the bow by only two nails,
and to the two long pieces by four nails. In this practical manner they
put ten nails in one bow and the same number in the other. Sometimes
when the smelter is afraid that the vigorous motion of the bellows may
pull or tear the hide from the bows, he also fastens it with little
strips of pine by means of another kind of nail, but these strips cannot
be fastened to the back pieces of the bow, because these are somewhat
bent. Some people do not fix the hide to the bellows-boards and bows by
iron nails, but by iron screws, screwed at the same time through strips
laid over the hide. This method of fastening the hide is less used than
the other, although there is no doubt that it surpasses it in
excellence.
Lastly, the head of the bellows, like the rest of the body, consists of
two boards, and of a nozzle besides. The upper board is one cubit long,
one and a half palms thick. The lower board is part of the whole of the
lower bellows-board; it is of the same length as the upper piece, but a
palm and a digit thick. From these two glued together is made the head,
into which, when it has been perforated, the nozzle is fixed. The back
part of the head, where it is attached to the rest of the bellows-body,
is a cubit wide, but three palms forward it becomes two digits narrower.
Afterward it is somewhat cut away so that the front end may be rounded,
until it is two palms and as many digits in diameter, at which point it
is bound with an iron ring three digits wide.
The nozzle is a pipe made of a thin plate of iron; the diameter in front
is three digits, while at the back, where it is encased in the head of
the bellows, it is a palm high and two palms wide. It thus gradually
widens out, especially at the back, in order that a copious wind can
penetrate into it; the whole nozzle is three feet long.
[Illustration 365 (Bellows for blast furnaces): A--Upper bellows-board.
B--Lower bellows-board. C--The two pieces of wood of which each
consists. D--Posterior arched part of each. E--Tapered front part of
each. F--Pieces of linden wood. G--Aperture in the upper board. H--Lid.
I--Little mouldings of wood. K--Handle. L--Cleat on the outside. The
cleat inside I am not able to depict. M--Interior of the lower
bellows-board. N--Part of the head. O--Air-hole. P--Supporting bar.
Q--Flap. R--Hide. S--Thong. T--Exterior of the lower board. V--Staple.
X--Ring. Y--Bow. Z--Its long pieces. AA--Back piece of the bow. BB--The
bowed ends. CC--Crossbar distending the bow. DD--The two little pieces.
EE--Hide. FF--Nail. GG--Horn of the nail. HH--A screw. II--Long thong.
KK--Head. LL--Its lower board. MM--Its upper board. NN--Nozzle. OO--The
whole of the lower bellows-board. PP--The two exterior plates of the
head hinges. QQ--Their curved piece. RR--Middle plate of the head.
SS--The two outer plates of the upper bellows-board. TT--Its middle
plate. VV--Little axle. XX--Whole bellows.]
The upper bellows-board is joined to the head of the bellows in the
following way. An iron plate[7], a palm wide and one and a half palms
long, is first fastened to the head at a distance of three digits from
the end; from this plate there projects a piece three digits long and
two wide, curved in a small circle. The other side has a similar plate.
Then in the same part of the upper board are fixed two other iron
plates, distant two digits from the edge, each of which are six digits
wide and seven long; in each of these plates the middle part is cut away
for a little more than three digits in length and for two in depth, so
that the curved part of the plates on the head corresponding to them may
fit into this cut out part. From both sides of each plate there project
pieces, three digits long and two digits wide, similarly curved into
small circles. A little iron pin is passed through these curved pieces
of the plates, like a little axle, so that the upper board of the
bellows may turn upon it. The little axle is six digits long and a
little more than a digit thick, and a small groove is cut out of the
upper board, where the plates are fastened to it, in such a manner that
the little axle when fixed to the plates may not fall out. Both plates
fastened to the bellows-board are affixed by four iron nails, of which
the heads are on the inner part of the board, whereas the points,
clinched at the top, are transformed into heads, so to speak. Each of
the other plates is fastened to the head of the bellows by means of a
nail with a wide head, and by two other nails of which the heads are on
the edge of the bellows-head. Midway between the two plates on the
bellows-board there remains a space two palms wide, which is covered by
an iron plate fastened to the board by little nails; and another plate
corresponding to this is fastened to the head between the other two
plates; they are two palms and the same number of digits wide.
The hide is common to the head as to all the other parts of the body;
the plates are covered with it, as well as the front part of the upper
bellows-board, and both the bows and the back of the head of the
bellows, so that the wind may not escape from that part of the bellows.
It is three palms and as many digits wide, and long enough to extend
from one of the sides of the lower board over the back of the upper; it
is fastened by many T-headed nails on one side to the upper board, and
on the other side to the head of the bellows, and both ends are fastened
to the lower bellows-board.
In the above manner the bellows is made. As two are required for each
furnace, it is necessary to have twelve bellows, if there are to be six
furnaces in one works.
[Illustration 368 (Bellows for blast furnaces): A--Front sill. B--Back
sill. C--Front posts. D--Their slots. E--Beam imposed upon them.
F--Higher posts. G--Their slots. H--Beam imposed upon them. I--Timber
joined in the mortises of the posts. K--Planks. L--Transverse supporting
planks. M--The holes in them. N--Pipe. O--Its front end. P--Its rear
end.]
Now it is time to describe their framework. First, two sills a little
shorter than the furnace wall are placed on the ground. The front one of
these is three palms wide and thick, and the back one three palms and
two digits. The front one is two feet distant from the back wall of the
furnace, and the back one is six feet three palms distant from the front
one. They are set into the earth, that they may remain firm; there are
some who accomplish this by means of pegs which, through several holes,
penetrate deeply into the ground.
Then twelve short posts are erected, whose lower ends are mortised into
the sill that is near the back of the furnace wall; these posts are two
feet high, exclusive of the tenons, and are three palms and the same
number of digits wide, and two palms thick. A slot one and a half palms
wide is cut through them, beginning two palms from the bottom and
extending for a height of three palms. All the posts are not placed at
the same intervals, the first being at a distance of three feet five
digits from the second, and likewise the third from the fourth, but the
second is two feet one palm and three digits from the third; the
intervals between the other posts are arranged in the same manner, equal
and unequal, of which each four pertain to two furnaces. The upper ends
of these posts are mortised into a transverse beam which is twelve feet,
two palms, and three digits long, and projects five digits beyond the
first post and to the same distance beyond the fourth; it is two palms
and the same number of digits wide, and two palms thick. Since each
separate transverse beam supports four bellows, it is necessary to have
three of them.
Behind the twelve short posts the same number of higher posts are
erected, of which each has the middle part of the lower end cut out, so
that its two resulting lower ends are mortised into the back sill; these
posts, exclusive of the tenons, are twelve feet and two palms high, and
are five palms wide and two palms thick. They are cut out from the
bottom upward, the slot being four feet and five digits high and six
digits wide. The upper ends of these posts are mortised into a long beam
imposed upon them; this long beam is placed close under the timbers
which extend from the wall at the back of the furnace to the first long
wall; the beam is three palms wide and two palms thick, and forty-three
feet long. If such a long one is not at hand, two or three may be
substituted for it, which when joined together make up that length.
These higher posts are not placed at equal distances, but the first is
at a distance of two feet three palms one digit from the second, and the
third is at the same distance from the fourth; while the second is at a
distance of one foot three palms and the same number of digits from the
third, and in the same manner the rest of the posts are arranged at
equal and unequal intervals. Moreover, there is in every post, where it
faces the shorter post, a mortise at a foot and a digit above the slot;
in these mortises of the four posts is tenoned a timber which itself has
four mortises. Tenons are enclosed in mortises in order that they may be
better joined, and they are transfixed with wooden pins. This timber is
thirteen feet three palms one digit long, and it projects beyond the
first post a distance of two palms and two digits, and to the same
number of palms and digits beyond the fourth post. It is two palms and
as many digits wide, and also two palms thick. As there are twelve posts
it is necessary to have three timbers of this kind.
On each of these timbers, and on each of the cross-beams which are laid
upon the shorter posts, are placed four planks, each nine feet long, two
palms three digits wide, and two palms one digit thick. The first plank
is five feet one palm one digit distant from the second, at the front as
well as at the back, for each separate plank is placed outside of the
posts. The third is at the same distance from the fourth, but the second
is one foot and three digits distant from the third. In the same manner
the rest of the eight planks are arranged at intervals, the fifth from
the sixth and the seventh from the eighth are at the same distances as
the first from the second and the third from the fourth; the sixth is at
the same distance from the seventh as the second from the third.
Two planks support one transverse plank six feet long, one foot wide,
one palm thick, placed at a distance of three feet and two palms from
the back posts. When there are six of these supporting planks, on each
separate one are placed two bellows; the lower bellows-boards project a
palm beyond them. From each of the bellows-boards an iron ring descends
through a hole in its supporting plank, and a wooden peg is driven into
the ring, so that the bellows-board may remain stationary, as I stated
above.
The two bellows communicate, each by its own plank, to the back of a
copper pipe in which are set both of the nozzles, and their ends are
tightly fastened in it. The pipe is made of a rolled copper or iron
plate, a foot and two palms and the same number of digits long; the
plate is half a digit thick, but a digit thick at the back. The interior
of the pipe is three digits wide, and two and a half digits high in the
front, for it is not absolutely round; and at the back it is a foot and
two palms and three digits in diameter. The plate from which the pipe is
made is not entirely joined up, but at the front there is left a crack
half a digit wide, increasing at the back to three digits. This pipe is
placed in the hole in the furnace, which, as I said, was in the middle
of the wall and the arch. The nozzles of the bellows, placed in this
pipe, are a distance of five digits from its front end.
[Illustration 370 (Bellows for blast furnaces): A--Lever which when
depressed by means of a cam compresses the bellows. B--Slots through the
posts. C--Bar. D--Iron implement with a rectangular link. E--Iron
instrument with round ring. F--Handle of bellows. G--Upper post.
H--Upper lever. I--Box with equal sides. K--Box narrow at the bottom.
L--Pegs driven into the upper lever.]
The levers are of the same number as the bellows, and when depressed by
the cams of the long axle they compress the bellows. These levers are
eight feet three palms long, one palm wide and thick, and the ends are
inserted in the slots of the posts; they project beyond the front posts
to a distance of two palms, and the same distance beyond the back posts
in order that each may have its end depressed by its two cams on the
axle. The cams not only penetrate into the slots of the back posts, but
project three digits beyond them. An iron pin is set in round holes made
through both sides of the slot of each front post, at three palms and as
many digits from the bottom; the pin penetrates the lever, which turns
about it when depressed or raised. The back of the lever for the length
of a cubit is a palm and a digit wider than the rest, and is perforated;
in this hole is engaged a bar six feet and two palms long, three digits
wide, and about one and one-half digits thick; it is somewhat hooked at
the upper end, and approaches the handle of the bellows. Under the lever
there is a nail, which penetrates through a hole in the bar, so that the
lever and bar may move together. The bar is perforated in the upper end
at a distance of six digits from the top; this hole is two palms long
and a digit wide, and in it is engaged the hook of an iron implement
which is a digit thick. At the upper part this implement has either a
round or square opening, like a link, and at the lower end is hooked;
the link is two digits high and wide and the hook is three digits long;
the middle part between the link and the hook is three palms and two
digits long. The link of this implement engages either the handle of the
bellows, or else a large ring which does engage it. This iron ring is a
digit thick, two palms wide on the inside of the upper part, and two
digits in the lower part, and this iron ring, not unlike the first one,
engages the handle of the bellows. The iron ring either has its narrower
part turned upward, and in it is engaged the ring of another iron
implement, similar to the first, whose hook, extending upward, grips the
rope fastened to the iron ring holding the end of the second lever, of
which I will speak presently; or else the iron ring grips this lever,
and then in its hook is engaged the ring of the other implement whose
ring engages the handle of the bellows, and in this case the rope is
dispensed with.
Resting on beams fixed in the two walls is a longitudinal beam, at a
distance of four and a half feet from the back posts; it is two palms
wide, one and a half palms thick. There are mortised into this
longitudinal beam the lower ends of upper posts three palms wide and two
thick, which are six feet two palms high, exclusive of their tenons. The
upper ends of these posts are mortised into an upper longitudinal beam,
which lies close under the rafters of the building; this upper
longitudinal beam is two palms wide and one thick. The upper posts have
a slot cut out upward from a point two feet from the bottom, and the
slot is two feet high and six digits wide. Through these upper posts a
round hole is bored from one side to the other at a point three feet one
palm from the bottom, and a small iron axle penetrates through the hole
and is fastened there. Around this small iron axle turns the second
lever when it is depressed and raised. This lever is eight feet long,
and its other end is three digits wider than the rest of the lever; at
this widest point is a hole two digits wide and three high, in which is
fixed an iron ring, to which is tied the rope I have mentioned; it is
five palms long, its upper loop is two palms and as many digits wide,
and the lower one is one palm one digit wide. This half of the second
lever, the end of which I have just mentioned, is three palms high and
one wide; it projects three feet beyond the slot of the post on which it
turns; the other end, which faces the back wall of the furnaces, is one
foot and a palm high and a foot wide.
On this part of the lever stands and is fixed a box three and a half
feet long, one foot and one palm wide, and half a foot deep; but these
measurements vary; sometimes the bottom of this box is narrower,
sometimes equal in width to the top. In either case, it is filled with
stones and earth to make it heavy, but the smelters have to be on their
guard and make provision against the stones falling out, owing to the
constant motion; this is prevented by means of an iron band which is
placed over the top, both ends being wedge-shaped and driven into the
lever so that the stones can be held in. Some people, in place of the
box, drive four or more pegs into the lever and put mud between them,
the required amount being added to the weight or taken away from it.
There remains to be considered the method of using this machine. The
lower lever, being depressed by the cams, compresses the bellows, and
the compression drives the air through the nozzle. Then the weight of
the box on the other end of the upper lever raises the upper
bellows-board, and the air is drawn in, entering through the air-hole.
[Illustration 372 (Bellows for blast furnaces): A--Axle. B--Water-wheel.
C--Drum composed of rundles. D--Other axle. E--Toothed wheel. F--Its
spokes. G--Its segments. H--Its teeth. I--Cams of the axle.]
The machine whose cams depress the lower lever is made as follows. First
there is an axle, on whose end outside the building is a water-wheel; at
the other end, which is inside the building, is a drum made of rundles.
This drum is composed of two double hubs, a foot apart, which are five
digits thick, the radius all round being a foot and two digits; but they
are double, because each hub is composed of two discs, equally thick,
fastened together with wooden pegs glued in. These hubs are sometimes
covered above and around by iron plates. The rundles are thirty in
number, a foot and two palms and the same number of digits long, with
each end fastened into a hub; they are rounded, three digits in
diameter, and the same number of digits apart. In this practical manner
is made the drum composed of rundles.
There is a toothed wheel, two palms and a digit thick, on the end of
another axle; this wheel is composed of a double disc[8]. The inner disc
is composed of four segments a palm thick, everywhere two palms and a
digit wide. The outer disc, like the inner, is made of four segments,
and is a palm and a digit thick; it is not equally wide, but where the
head of the spokes are inserted it is a foot and a palm and digit wide,
while on each side of the spokes it becomes a little narrower, until the
narrowest part is only two palms and the same number of digits wide. The
outer segments are joined to the inner ones in such a manner that, on
the one hand, an outer segment ends in the middle of an inner one, and,
on the other hand, the ends of the inner segments are joined in the
middle of the outer ones; there is no doubt that by this kind of joining
the wheel is made stronger. The outer segments are fastened to the inner
by means of a large number of wooden pegs. Each segment, measured over
its round back, is four feet and three palms long. There are four
spokes, each two palms wide and a palm and a digit thick; their length,
excluding the tenons, being two feet and three digits. One end of the
spoke is mortised into the axle, where it is firmly fastened with pegs;
the wide part of the other end, in the shape of a triangle, is mortised
into the outer segment opposite it, keeping the shape of the same as far
as the segment ascends. They also are joined together with wooden pegs
glued in, and these pegs are driven into the spokes under the inner
disc. The parts of the spokes in the shape of the triangle are on the
inside; the outer part is simple. This triangle has two sides equal, the
erect ones as is evident, which are a palm long; the lower side is not
of the same length, but is five digits long, and a mortise of the same
shape is cut out of the segments. The wheel has sixty teeth, since it is
necessary that the rundle drum should revolve twice while the toothed
wheel revolves once. The teeth are a foot long, and project one palm
from the inner disc of the wheel, and three digits from the outer disc;
they are a palm wide and two and a half digits thick, and it is
necessary that they should be three digits apart, as were the rundles.
The axle should have a thickness in proportion to the spokes and the
segments. As it has two cams to depress each of the levers, it is
necessary that it should have twenty-four cams, which project beyond it
a foot and a palm and a digit. The cams are of almost semicircular
shape, of which the widest part is three palms and a digit wide, and
they are a palm thick; they are distributed according to the four sides
of the axle, on the upper, the lower and the two lateral sides. The axle
has twelve holes, of which the first penetrates through from the upper
side to the lower, the second from one lateral side to the other; the
first hole is four feet two palms distant from the second; each
alternate one of these holes is made in the same direction, and they are
arranged at equal intervals. Each single cam must be opposite another;
the first is inserted into the upper part of the first hole, the second
into the lower part of the same hole, and so fixed by pegs that they do
not fall out; the third cam is inserted into that part of the second
hole which is on the right side, and the fourth into that part on the
left. In like manner all the cams are inserted into the consecutive
holes, for which reason it happens that the cams depress the levers of
the bellows in rotation. Finally we must not omit to state that this is
only one of many such axles having cams and a water-wheel.
I have arrived thus far with many words, and yet it is not unreasonable
that I have in this place pursued the subject minutely, since the
smelting of all the metals, to which I am about to proceed, could not be
undertaken without it.
The ores of gold, silver, copper, and lead, are smelted in a furnace by
four different methods. The first method is for the rich ores of gold or
silver, the second for the mediocre ores, the third for the poor ores,
and the fourth method is for those ores which contain copper or lead,
whether they contain precious metals or are wanting in them. The
smelting of the first ores is performed in the furnace of which the
tap-hole is intermittently closed; the other three ores are melted in
furnaces of which the tap-holes are always open.
[Illustration 373 (Stamp-mill): A--Charcoal. B--Mortar-box. C--Stamps.]
First, I will speak of the manner in which the furnaces are prepared for
the smelting of the ores, and of the first method of smelting. The
powder from which the hearth and forehearth should be made is composed
of charcoal and earth (clay?). The charcoal is crushed by the stamps in
a mortar-box, the front of which is closed by a board at the top, while
the charcoal, crushed to powder, is removed through the open part
below; the stamps are not shod with iron, but are made entirely of wood,
although at the lower part they are bound round at the wide part by an
iron band.
[Illustration 374 (Clay Washing): A--Tub. B--Sieve. C--Rods.
D--Bench-frame.]
The powder into which the charcoal is crushed is thrown on to a sieve
whose bottom consists of interwoven withes of wood. The sieve is drawn
backward and forward over two wooden or iron rods placed in a triangular
position on a tub, or over a bench-frame set on the floor of the
building; the powder which falls into the tub or on to the floor is of
suitable size, but the pieces of small charcoal which remain in the
sieve are emptied out and thrown back under the stamps.
[Illustration 375 (Clay Washing): A--Screen. B--Poles. C--Shovel.
D--Two-wheeled cart. E--Hand-sieve. F--Narrow boards. G--Box. H--Covered
pit.]
When the earth is dug up it is first exposed to the sun that it may dry.
Later on it is thrown with a shovel on to a screen--set up obliquely and
supported by poles,--made of thick, loosely woven hazel withes, and in
this way the fine earth and its small lumps pass through the holes of
the screen, but the clods and stones do not pass through, but run down
to the ground. The earth which passes through the screen is conveyed in
a two-wheeled cart to the works and there sifted. This sieve, which is
not dissimilar to the one described above, is drawn backward and
forward upon narrow boards of equal length placed over a long box; the
powder which falls through the sieve into the box is suitable for the
mixture; the lumps that remain in the sieve are thrown away by some
people, but by others they are placed under the stamps. This powdered
earth is mixed with powdered charcoal, moistened, and thrown into a pit,
and in order that it may remain good for a long time, the pit is covered
up with boards so that the mixture may not become contaminated.
[Illustration 377 (Implements for Furnace Work): A--Furnace. B--Ladder.
C--Board fixed to it. D--Hoe. E--Five-toothed rake. F--Wooden spatula.
G--Broom. H--Rammer. I--Rammer, same diameter. K--Two wooden spatulas.
L--Curved blade. M--Bronze rammer. N--Another bronze rammer. O--Wide
spatula. P--Rod. Q--Wicker basket. R--Two buckets of leather in which
water is carried for putting out a conflagration, should the _officina_
catch fire. S--Brass pump with which the water is squirted out. T--Two
hooks. V--Rake. X--Workman beating the clay with an iron implement.]
They take two parts of pulverised charcoal and one part of powdered
earth, and mix them well together with a rake; the mixture is moistened
by pouring water over it so that it may easily be made into shapes
resembling snowballs; if the powder be light it is moistened with more
water, if heavy with less. The interior of the new furnace is lined with
lute, so that the cracks in the walls, if there are any, may be filled
up, but especially in order to preserve the rock from injury by fire. In
old furnaces in which ore has been melted, as soon as the rocks have
cooled the assistant chips away, with a spatula, the accretions which
adhere to the walls, and then breaks them up with an iron hoe or a rake
with five teeth. The cracks of the furnace are first filled in with
fragments of rock or brick, which he does by passing his hand into the
furnace through its mouth, or else, having placed a ladder against it,
he mounts by the rungs to the upper open part of the furnace. To the
upper part of the ladder a board is fastened that he may lean and
recline against it. Then standing on the same ladder, with a wooden
spatula, he smears the furnace walls over with lute; this spatula is
four feet long, a digit thick, and for a foot upward from the bottom it
is a palm wide, or even wider, generally two and a half digits. He
spreads the lute equally over the inner walls of the furnace. The mouth
of the copper pipe[9] should not protrude from the lute, lest sows[10]
form round about it and thus impede the melting, for the furnace bellows
could not force a blast through them. Then the same assistant throws a
little powdered charcoal into the pit of the forehearth and sprinkles it
with pulverised earth. Afterward, with a bucket he pours water into it
and sweeps this all over the forehearth pit, and with the broom drives
the turbid water into the furnace hearth and likewise sweeps it out.
Next he throws the mixed and moistened powder into the furnace, and then
a second time mounting the steps of the ladder, he introduces the rammer
into the furnace and pounds the powder so that the hearth is made solid.
The rammer is rounded and three palms long; at the bottom it is five
digits in diameter, at the top three and a half, therefore it is made in
the form of a truncated cone; the handle of the rammer is round and five
feet long and two and a half digits thick; the upper part of the
rammer, where the handle is inserted, is bound with an iron band two
digits wide. There are some who, instead, use two rounded rammers three
and a half digits in diameter, the same at the bottom as at the top.
Some people prefer two wooden spatulas, or a rammer spatula.
In a similar manner, mixed and moistened powder is thrown and pounded
with a rammer in the forehearth pit, which is outside the furnace. When
this is nearly completed, powder is again put in, and pushed with the
rammer up toward the protruding copper pipe, so that from a point a
digit under the mouth of the copper pipe the hearth slopes down into the
crucible of the forehearth,[11] and the metal can run down. The same is
repeated until the forehearth pit is full, then afterward this is
hollowed out with a curved blade; this blade is of iron, two palms and
as many digits long, three digits wide, blunt at the top and sharp at
the bottom. The crucible of the forehearth must be round, a foot in
diameter and two palms deep if it has to contain a _centumpondium_ of
lead, or if only seventy _librae_, then three palms in diameter and two
palms deep like the other. When the forehearth has been hollowed out it
is pounded with a round bronze rammer. This is five digits high and the
same in diameter, having a curved round handle one and a half digits
thick; or else another bronze rammer is used, which is fashioned in the
shape of a cone, truncated at the top, on which is imposed another cut
away at the bottom, so that the middle part of the rammer may be grasped
by the hand; this is six digits high, and five digits in diameter at the
lower end and four at the top. Some use in its place a wooden spatula
two and a half palms wide at the lower end and one palm thick.
The assistant, having prepared the forehearth, returns to the furnace
and besmears both sides as well as the top of the mouth with simple
lute. In the lower part of the mouth he places lute that has been dipped
in charcoal dust, to guard against the risk of the lute attracting to
itself the powder of the hearth and vitiating it. Next he lays in the
mouth of the furnace a straight round rod three quarters of a foot long
and three digits in diameter. Afterward he places a piece of charcoal on
the lute, of the same length and width as the mouth, so that it is
entirely closed up; if there be not at hand one piece of charcoal so
large, he takes two instead. When the mouth is thus closed up, he throws
into the furnace a wicker basket full of charcoal, and in order that the
piece of charcoal with which the mouth of the furnace is closed should
not then fall out, the master holds it in with his hand. The pieces of
charcoal which are thrown into the furnace should be of medium size, for
if they are large they impede the blast of the bellows and prevent it
from blowing through the tap-hole of the furnace into the forehearth to
heat it. Then the master covers over the charcoal, placed at the mouth
of the furnace, with lute and extracts the wooden rod, and thus the
furnace is prepared. Afterward the assistant throws four or five larger
baskets full of charcoal into the furnace, filling it right up; he also
throws a little charcoal into the forehearth, and places glowing coals
upon it in order that it may be kindled, but in order that the flames of
this fire should not enter through the tap-hole of the furnace and fire
the charcoal inside, he covers the tap-hole with lute or closes it with
fragments of pottery. Some do not warm the forehearth the same evening,
but place large charcoals round the edge of it, one leaning on the
other; those who follow the first method sweep out the forehearth in the
morning, and clean out the little pieces of charcoal and cinders, while
those who follow the latter method take, early in the morning, burning
firebrands, which have been prepared by the watchman of the works, and
place them on the charcoal.
At the fourth hour the master begins his work. He first inserts a small
piece of glowing coal into the furnace, through the bronze nozzle-pipe
of the bellows, and blows up the fire with the bellows; thus within the
space of half an hour the forehearth, as well as the hearth, becomes
warmed, and of course more quickly if on the preceding day ores have
been smelted in the same furnace, but if not then it warms more slowly.
If the hearth and forehearth are not warmed before the ore to be smelted
is thrown in, the furnace is injured and the metals lost; or if the
powder from which both are made is damp in summer or frozen in winter,
they will be cracked, and, giving out a sound like thunder, they will
blow out the metals and other substances with great peril to the
workmen. After the furnace has been warmed, the master throws in slags,
and these, when melted, flow out through the tap-hole into the
forehearth. Then he closes up the tap-hole at once with mixed lute and
charcoal dust; this plug he fastens with his hand to a round wooden
rammer that is five digits thick, two palms high, with a handle three
feet long. The smelter extracts the slags from the forehearth with a
hooked bar; if the ore to be smelted is rich in gold or silver he puts
into the forehearth a _centumpondium_ of lead, or half as much if the
ore is poor, because the former requires much lead, the latter little;
he immediately throws burning firebrands on to the lead so that it
melts. Afterward he performs everything according to the usual manner
and order, whereby he first throws into the furnace as many cakes melted
from pyrites[12], as he requires to smelt the ore; then he puts in two
wicker baskets full of ore with litharge and hearth-lead[13], and stones
which fuse easily by fire of the second order, all mixed together; then
one wicker basket full of charcoal, and lastly the slags. The furnace
now being filled with all the things I have mentioned, the ore is slowly
smelted; he does not put too much of it against the back wall of the
furnace, lest sows should form around the nozzles of the bellows and the
blast be impeded and the fire burn less fiercely.
This, indeed, is the custom of many most excellent smelters, who know
how to govern the four elements[14]. They combine in right proportion
the ores, which are part earth, placing no more than is suitable in the
furnaces; they pour in the needful quantity of water; they moderate with
skill the air from the bellows; they throw the ore into that part of the
fire which burns fiercely. The master sprinkles water into each part of
the furnace to dampen the charcoal slightly, so that the minute parts of
ore may adhere to it, which otherwise the blast of the bellows and the
force of the fire would agitate and blow away with the fumes. But as the
nature of the ores to be smelted varies, the smelters have to arrange
the hearth now high, now low, and to place the pipe in which the nozzles
of the bellows are inserted sometimes on a great and sometimes at a
slight angle, so that the blast of the bellows may blow into the
furnace in either a mild or a vigorous manner. For those ores which heat
and fuse easily, a low hearth is necessary for the work of the smelters,
and the pipe must be placed at a gentle angle to produce a mild blast
from the bellows. On the contrary, those ores that heat and fuse slowly
must have a high hearth, and the pipe must be placed at a steep incline
in order to blow a strong blast of the bellows, and it is necessary, for
this kind of ore, to have a very hot furnace in which slags, or cakes
melted from pyrites, or stones which melt easily in the fire[15], are
first melted, so that the ore should not settle in the hearth of the
furnace and obstruct and choke up the tap-hole, as the minute metallic
particles that have been washed from the ores are wont to do. Large
bellows have wide nozzles, for if they were narrow the copious and
strong blast would be too much compressed and too acutely blown into the
furnace, and then the melted material would be chilled, and would form
sows around the nozzle, and thus obstruct the opening into the furnace,
which would cause great damage to the proprietors' property. If the ores
agglomerate and do not fuse, the smelter, mounting on the ladder placed
against the side of the furnace, divides the charge with a pointed or
hooked bar, which he also pushes down into the pipe in which the nozzle
of the bellows is placed, and by a downward movement dislodges the ore
and the sows from around it.
After a quarter of an hour, when the lead which the assistant has placed
in the forehearth is melted, the master opens the tap-hole of the
furnace with a tapping-bar. This bar is made of iron, is three and a
half feet long, the forward end pointed and a little curved, and the
back end hollow so that into it may be inserted a wooden handle, which
is three feet long and thick enough to be well grasped by the hand. The
slag first flows from the furnace into the forehearth, and in it are
stones mixed with metal or with the metal adhering to them partly
altered, the slag also containing earth and solidified juices. After
this the material from the melted pyrites flows out, and then the molten
lead contained in the forehearth absorbs the gold and silver. When that
which has run out has stood for some time in the forehearth, in order to
be able to separate one from the other, the master first either skims
off the slags with the hooked bar or else lifts them off with an iron
fork; the slags, as they are very light, float on the top. He next draws
off the cakes of melted pyrites, which as they are of medium weight hold
the middle place; he leaves in the forehearth the alloy of gold or
silver with the lead, for these being the heaviest, sink to the bottom.
As, however, there is a difference in slags, the uppermost containing
little metal, the middle more, and the lowest much, he puts these away
separately, each in its own place, in order that to each heap, when it
is re-smelted, he may add the proper fluxes, and can put in as much lead
as is demanded for the metal in the slag; when the slag is re-melted, if
it emits much odour, there is some metal in it; if it emits no odour,
then it contains none. He puts the cakes of melted pyrites away
separately, as they were nearest in the forehearth to the metal, and
contain a little more of it than the slags; from all these cakes a
conical mound is built up, by always placing the widest of them at the
bottom. The hooked bar has a hook on the end, hence its name; otherwise
it is similar to other bars.
[Illustration 383 (Blast Furnaces): A, B, C--Three furnaces. At the
first stands the smelter, who with a ladle pours the alloy out of the
forehearth into the moulds. D--Forehearth. E--Ladle. F--Moulds. G--Round
wooden rammer. H--Tapping-bar. At the second furnace stands the smelter,
who opens the tap-hole with his tapping-bar. The assistant, standing on
steps placed against the third furnace which has been broken open, chips
off the accretions. I--Steps. K--Spatula. L--The other hooked bar.
M--Mine captain carrying a cake, in which he has stuck the pick, to the
scales to be weighed. N--Another mine captain opens a chest in which his
things are kept.]
Afterward the master closes up the tap-hole and fills the furnace with
the same materials I described above, and again, the ores having been
melted, he opens the tap-hole, and with a hooked bar extracts the slags
and the cakes melted from pyrites, which have run down into the
forehearth. He repeats the same operation until a certain and definite
part of the ore has been smelted, and the day's work is at an end; if
the ore was rich the work is finished in eight hours; if poor, it takes
a longer time. But if the ore was so rich as to be smelted in less than
eight hours, another operation is in the meanwhile combined with the
first, and both are performed in the space of ten hours. When all the
ore has been smelted, he throws into the furnace a basket full of
litharge or hearth-lead, so that the metal which has remained in the
accretions may run out with these when melted. When he has finally drawn
out of the forehearth the slags and the cakes melted from pyrites, he
takes out, with a ladle, the lead alloyed with gold or silver and pours
it into little iron or copper pans, three palms wide and as many digits
deep, but first lined on the inside with lute and dried by warming, lest
the glowing molten substances should break through. The iron ladle is
two palms wide, and in other respects it is similar to the others, all
of which have a sufficiently long iron shaft, so that the fire should
not burn the wooden part of the handle. When the alloy has been poured
out of the forehearth, the smelter foreman and the mine captain weigh
the cakes.
Then the master breaks out the whole of the mouth of the furnace with a
crowbar, and with that other hooked bar, the rabble and the five-toothed
rake, he extracts the accretions and the charcoal. This crowbar is not
unlike the other hooked one, but larger and wider; the handle of the
rabble is six feet long and is half of iron and half of wood. The
furnace having cooled, the master chips off the accretions clinging to
the walls with a rectangular spatula six digits long, a palm broad, and
sharp on the front edge; it has a round handle four feet long, half of
it being of iron and half of wood. This is the first method of smelting
ores.
Because they generally consist of unequal constituents, some of which
melt rapidly and others slowly, the ores rich in gold and silver cannot
be smelted as rapidly or as easily by the other methods as they can by
the first method, for three important reasons. The first reason is that,
as often as the closed tap-hole of the furnace is opened with a
tapping-bar, so often can the smelter observe whether the ore is
melting too quickly or too slowly, or whether it is flaming in scattered
bits, and not uniting in one mass; in the first case the ore is smelting
too slowly and not without great expense; in the second case the metal
mixes with the slag which flows out of the furnace into the forehearth,
wherefore there is the expense of melting it again; in the third case,
the metal is consumed by the violence of the fire. Each of these evils
has its remedy; if the ore melts slowly or does not come together, it is
necessary to add some amount of fluxes which melt the ore; or if they
melt too readily, to decrease the amount.
The second reason is that each time that the furnace is opened with a
tapping-bar, it flows out into the forehearth, and the smelter is able
to test the alloy of gold and lead or of silver with lead, which is
called _stannum_.[16] When the tap-hole is opened the second or third
time, this test shows us whether the alloy of gold or silver has become
richer, or whether the lead is too debilitated and wanting in strength
to absorb any more gold or silver. If it has become richer, some portion
of lead added to it should renew its strength; if it has not become
richer, it is poured out of the forehearth that it may be replaced with
fresh lead.
The third reason is that if the tap-hole of the furnace is always open
when the ore and other things are being smelted, the fluxes, which are
easily melted, run out of the furnace before the rich gold and silver
ores, for these are sometimes of a kind that oppose and resist melting
by the fire for a longer period. It follows in this case, that some part
of the ore is either consumed or is mixed with the accretions, and as a
result little lumps of ore not yet melted are now and then found in the
accretions. Therefore when these ores are being smelted, the tap-hole of
the furnace should be closed for a time, as it is necessary to heat and
mix the ore and the fluxes at the same time; since the fluxes fuse more
rapidly than the ore, when the molten fluxes are held in the furnace,
they thus melt the ore which does not readily fuse or mix with the lead.
The lead absorbs the gold or silver, just as tin or lead when melted in
the forehearth absorbs the other unmelted metal which has been thrown
into it. But if the molten matter is poured upon that which is not
molten, it runs off on all sides and consequently does not melt it. It
follows from all this that ores rich in gold or silver, when put into a
furnace with its tap-hole always open, cannot for that reason be smelted
so successfully as in one where the tap-hole is closed for a time, so
that during this time the ore may be melted by the molten fluxes.
Afterward, when the tap-hole has been opened, they flow into the
forehearth and mix there with the molten lead. This method of smelting
the ores is used by us and by the Bohemians.
[Illustration 385 (Blast Furnaces): A, B--Two furnaces. C--Forehearths.
D--Dipping-pot. The smelter standing by the first furnace draws off the
slags with a hooked bar. E--Hooked bar. F--Slags. G--The assistant
drawing a bucket of water which he pours over the glowing slags to
quench them. H--Basket made of twigs of wood intertwined. I--Rabble.
K--Ore to be smelted. L--The master stands at the other furnace and
prepares the forehearth by ramming it with two rammers. M--Crowbar.]
The three remaining methods of smelting ores are similar to each other
in that the tap-holes of the furnaces always remain open, so that the
molten metals may continually run out. They differ greatly from each
other, however, for the tap-hole of the first of this kind is deeper
in the furnace and narrower than that of the third, and besides it is
invisible and concealed. It easily discharges into the forehearth, which
is one and a half feet higher than the floor of the building, in order
that below it to the left a dipping-pot can be made. When the forehearth
is nearly full of the slags, which well up from the invisible tap-hole
of the furnace, they are skimmed off from the top with a hooked bar;
then the alloy of gold or silver with lead and the melted pyrites, being
uncovered, flow into the dipping-pot, and the latter are made into
cakes; these cakes are broken and thrown back into the furnace so that
all their metal may be smelted out. The alloy is poured into little iron
moulds.
The smelter, besides lead and cognate things, uses fluxes which combine
with the ore, of which I gave a sufficient account in Book VII. The
metals which are melted from ores that fuse readily in the fire, are
profitable because they are smelted in a short time, while those which
are difficult to fuse are not as profitable, because they take a long
time. When fluxes remain in the furnace and do not melt, they are not
suitable; for this reason, accretions and slags are the most convenient
for smelting, because they melt quickly. It is necessary to have an
industrious and experienced smelter, who in the first place takes care
not to put into the furnace more ores mixed with fluxes than it can
accommodate.
The powder out of which this furnace hearth and the adjoining forehearth
and the dipping-pot are usually made, consists mostly of equal
proportions of charcoal dust and of earth, or of equal parts of the same
and of ashes. When the hearth of the furnace is prepared, a rod that
will reach to the forehearth is put into it, higher up if the ore to be
smelted readily fuses, and lower down if it fuses with difficulty. When
the dipping-pot and forehearth are finished, the rod is drawn out of the
furnace so that the tap-hole is open, and through it the molten material
flows continuously into the forehearth, which should be very near the
furnace in order that it may keep very hot and the alloy thus be made
purer. If the ore to be smelted does not melt easily, the hearth of the
furnace must not be made too sloping, lest the molten fluxes should run
down into the forehearth before the ore is smelted, and the metal thus
remain in the accretions on the sides of the furnace. The smelter must
not ram the hearth so much that it becomes too hard, nor make the
mistake of ramming the lower part of the mouth to make it hard, for it
could not breathe[17], nor could the molten matter flow freely out of
the furnace. The ore which does not readily melt is thrown as much as
possible to the back of the furnace, and toward that part where the fire
burns very fiercely, so that it may be smelted longer. In this way the
smelter may direct it whither he wills. Only when it glows at the part
near the bellows' nozzle does it signify that all the ore is smelted
which has been thrown to the side of the furnace in which the nozzles
are placed. If the ore is easily melted, one or two wicker baskets full
are thrown into the front part of the furnace so that the fire, being
driven back by it, may also smelt the ore and the sows that form round
about the nozzles of the bellows. This process of smelting is very
ancient among the Tyrolese[18], but not so old among the Bohemians.
[Illustration 387 (Blast Furnaces): A, B--Two furnaces. C--Forehearth.
D--Dipping-pots. The master stands at the one furnace and draws away the
slags with an iron fork. E--Iron fork. F--Wooden hoe with which the
cakes of melted pyrites are drawn out. G--The forehearth crucible:
one-half inside is to be seen open in the other furnace. H--The half
outside the furnace. I--The assistant prepares the forehearth, which is
separated from the furnace that it may be seen. K--Bar. L--Wooden
rammer. M--Ladder. N--Ladle.]
The second method of smelting ores stands in a measure midway between
that one performed in a furnace of which the tap-hole is closed
intermittently, and the first of the methods performed in a furnace
where the tap-hole is always open. In this manner are smelted the ores
of gold and silver that are neither very rich nor very poor, but
mediocre, which fuse easily and are readily absorbed by the lead. It was
found that in this way a large quantity of ore could be smelted at one
operation without much labour or great expense, and could thus be
alloyed with lead. This furnace has two crucibles, one of which is half
inside the furnace and half outside, so that the lead being put into
this crucible, the part of the lead which is in the furnace absorbs the
metals of the ores which easily fuse; the other crucible is lower, and
the alloy and the molten pyrites run into it. Those who make use of this
method of smelting, tap the alloy of gold or silver with lead from the
upper crucible once or twice if need be, and throw in other lead or
litharge, and each absorbs that flux which is nearest. This method of
smelting is in use in Styria[19].
[Illustration 389 (Furnaces): A, B--Two furnaces. C--Tap-holes of
furnaces. D--Forehearths. E--Their tap-holes. F--Dipping-pots. G--At the
one furnace stands the smelter carrying a wicker basket full of
charcoal. At the other furnace stands a smelter who with the third
hooked bar breaks away the material which has frozen the tap-hole of the
furnace. H--Hooked bar. I--Heap of charcoal. K--Barrow on which is a box
made of wicker work in which the coals are measured. L--Iron spade.]
The furnace in the third method of smelting ores has the tap-hole
likewise open, but the furnace is higher and wider than the others, and
its bellows are larger; for these reasons a larger charge of the ore can
be thrown into it. When the mines yield a great abundance of ore for the
smelter, they smelt in the same furnace continuously for three days and
three nights, providing there be no defect either in the hearth or in
the forehearth. In this kind of a furnace almost every kind of accretion
will be found. The forehearth of the furnace is not unlike the
forehearth of the first furnace of all, except that it has a tap-hole.
However, because large charges of ore are smelted uninterruptedly, and
the melted material runs out and the slags are skimmed off, there is
need for a second forehearth crucible, into which the molten material
runs through an opened tap-hole when the first is full. When a smelter
has spent twelve hours' labour on this work, another always takes his
place. The ores of copper and lead and the poorest ores of gold and
silver are smelted by this method, because they cannot be smelted by the
other three methods on account of the greater expense occasioned. Yet by
this method a _centumpondium_ of ore containing only one or two
_drachmae_ of gold, or only a half to one _uncia_, of silver,[20] can be
smelted; because there is a large amount of ore in each charge, smelting
is continuous, and without expensive fluxes such as lead, litharge, and
hearth-lead. In this method of smelting we must use only cupriferous
pyrites which easily melt in the fire, in truth the cakes melted out
from this, if they no longer absorb much gold or silver, are
replenished again from crude pyrites alone. If from this poor ore, with
melted pyrites alone, material for cakes cannot be made, there are added
other fluxes which have not previously been melted. These fluxes are,
namely, lead ore, stones easily fused by fire of the second order and
sand made from them, limestone, _tophus_, white schist, and iron
stone[21].
Although this method of smelting ores is rough and might not seem to be
of great use, yet it is clever and useful; for a great weight of ores,
in which the gold, silver, or copper are in small quantities, may be
reduced into a few cakes containing all the metal. If on being first
melted they are too crude to be suitable for the second melting, in
which the lead absorbs the precious metals that are in the cakes, or in
which the copper is melted out of them, yet they can be made suitable if
they are repeatedly roasted, sometimes as often as seven or eight times,
as I have explained in the last book. Smelters of this kind are so
clever and expert, that in smelting they take out all the gold and
silver which the assayer in assaying the ores has stated to be contained
in them, because if during the first operation, when he makes the cakes,
there is a _drachma_ of gold or half an _uncia_ of silver lost from the
ores, the smelter obtains it from the slags by the second smelting. This
method of smelting ores is old and very common to most of those who use
other methods.
[Illustration 393 (Lead smelting Furnaces): A--Furnace of the Carni.
B--Low wall. C--Wood. D--Ore dripping lead. E--Large crucible.
F--Moulds. G--Ladle. H--Slabs of lead. I--Rectangular hole at the back
of the furnace. K--Saxon furnace. L--Opening in the back of the furnace.
M--Wood. N--Upper crucible. O--Dipping-pot. P--Westphalian method of
melting. Q--Heaps of charcoal. R--Straw. S--Wide slabs. T--Crucibles.
V--Polish hearth.]
Although lead ores are usually smelted in the third furnace--whose
tap-hole is always open,--yet not a few people melt them in special
furnaces by a method which I will briefly explain. The _Carni_[22] first
burn such lead ores, and afterward break and crush them with large round
mallets. Between the two low walls of a hearth, which is inside a
furnace made of and vaulted with a rock that resists injury by the fire
and does not burn into chalk, they place green wood with a layer of dry
wood on the top of it; then they throw the ore on to this, and when the
wood is kindled the lead drips down and runs on to the underlying
sloping hearth[23]. This hearth is made of pulverised charcoal and
earth, as is also a large crucible, one-half of which lies under the
furnace and the other half outside it, into which runs the lead. The
smelter, having first skimmed off the slags and other things with a hoe,
pours the lead with a ladle into moulds, taking out the cakes after they
have cooled. At the back of the furnace is a rectangular hole, so that
the fire may be allowed more draught, and so that the smelter can crawl
through it into the furnace if necessity demands.
The Saxons who inhabit Gittelde, when smelting lead ore in a furnace not
unlike a baking oven, put the wood in through a hole at the back of the
furnace, and when it begins to burn vigorously the lead trickles out of
the ore into a forehearth. When this is full, the smelting being
accomplished, the tap-hole is opened with a bar, and in this way the
lead, together with the slags, runs into the dipping-pots below.
Afterward the cakes of lead, when they are cold, are taken from the
moulds.
In Westphalia they heap up ten wagon-loads of charcoal on some hillside
which adjoins a level place, and the top of the heap being made flat,
straw is thrown upon it to the thickness of three or four digits. On the
top of this is laid as much pure lead ore as the heap can bear; then
the charcoal is kindled, and when the wind blows, it fans the fire so
that the ore is smelted. In this wise the lead, trickling down from the
heap, flows on to the level and forms broad thin slabs. A few hundred
pounds of lead ore are kept at hand, which, if things go well, are
scattered over the heap. These broad slabs are impure and are laid upon
dry wood which in turn is placed on green wood laid over a large
crucible, and the former having been kindled, the lead is re-melted.
The Poles use a hearth of bricks four feet high, sloping on both sides
and plastered with lute. On the upper level part of the hearth large
pieces of wood are piled, and on these is placed small wood with lute
put in between; over the top are laid wood shavings, and upon these
again pure lead ore covered with large pieces of wood. When these are
kindled, the ore melts and runs down on to the lower layer of wood;
and when this is consumed by the fire, the metal is collected. If
necessity demand, it is melted over and over again in the same manner,
but it is finally melted by means of wood laid over the large crucible,
the slabs of lead being placed upon it.
The concentrates from washing are smelted together with slags (fluxes?)
in a third furnace, of which the tap-hole is always open.
[Illustration 395 (Blast Furnaces): A--Furnaces. B--Vaulted roof.
C--Columns. D--Dust-chamber. E--Opening. F--Chimney. G--Window. H--Door.
I--Chute.]
It is worth while to build vaulted dust-chambers over the furnaces,
especially over those in which the precious ores are to be smelted, in
order that the thicker part of the fumes, in which metals are not
wanting, may be caught and saved. In this way two or more furnaces are
combined under the same vaulted ceiling, which is supported by the wall,
against which the furnaces are built, and by four columns. Under this
the smelters of the ore perform their work. There are two openings
through which the fumes rise from the furnaces into the wide vaulted
chamber, and the wider this is the more fumes it collects; in the middle
of this chamber over the arch is an opening three palms high and two
wide. This catches the fumes of both furnaces, which have risen up from
both sides of the vaulted chamber to its arch, and have fallen again
because they could not force their way out; and they thus pass out
through the opening mentioned, into the chimney which the Greeks call
[Greek: kapnodoche], the name being taken from the object. The chimney
has thin iron plates fastened into the walls, to which the thinner
metallic substances adhere when ascending with the fumes. The thicker
metallic substances, or _cadmia_,[25] adhere to the vaulted chamber, and
often harden into stalactites. On one side of the chamber is a window in
which are set panes of glass, so that the light may be transmitted, but
the fumes kept in; on the other side is a door, which is kept entirely
closed while the ores are being smelted in the furnaces, so that none of
the fumes may escape. It is opened in order that the workman, passing
through it, may be enabled to enter the chamber and remove the soot and
_pompholyx_[26] and chip off the _cadmia_; this sweeping is done twice
a year. The soot mixed with _pompholyx_ and the _cadmia_, being chipped
off, is thrown down through a long chute made of four boards joined in
the shape of a rectangle, that they should not fly away. They fall on to
the floor, and are sprinkled with salt water, and are again smelted with
ore and litharge, and become an emolument to the proprietors. Such
chambers, which catch the metallic substances that rise with the fumes,
are profitable for all metalliferous ores; but especially for the minute
metallic particles collected by washing crushed ores and rock, because
these usually fly out with the fire of the furnaces.
I have explained the four general methods of smelting ores; now I will
state how the ores of each metal are smelted, or how the metal is
obtained from the ore. I will begin with gold. Its sand, the
concentrates from washing, or the gold dust collected in any other
manner, should very often not be smelted, but should be mixed with
quicksilver and washed with tepid water, so that all the impurities may
be eliminated. This method I explained in Book VII. Or they are placed
in the _aqua_ which separates gold from silver, for this also separates
its impurities. In this method we see the gold sink in the glass
ampulla, and after all the _aqua_ has been drained from the particles,
it frequently remains as a gold-coloured residue at the bottom; this
powder, when it has been moistened with oil made from argol[27], is then
dried and placed in a crucible, where it is melted with borax or with
saltpetre and salt; or the same very fine dust is thrown into molten
silver, which absorbs it, and from this it is again parted by _aqua
valens_[28].
It is necessary to smelt gold ore either outside the blast furnace in a
crucible, or inside the blast furnace; in the former case a small charge
of ore is used, in the latter a large charge of it. _Rudis_ gold, of
whatever colour it is, is crushed with a _libra_ each of sulphur and
salt, a third of a _libra_ of copper, and a quarter of a _libra_ of
argol; they should be melted in a crucible on a slow fire for three
hours, then the alloy is put into molten silver that it may melt more
rapidly. Or a _libra_ of the same crude gold, crushed up, is mixed
together with half a _libra_ of _stibium_ likewise crushed, and put into
a crucible with half an _uncia_ of copper filings, and heated until they
melt, then a sixth part of granulated lead is thrown into the same
crucible. As soon as the mixture emits an odour, iron-filings are added
to it, or if these are not at hand, iron hammer-scales, for both of
these break the strength of the _stibium_. When the fire consumes it,
not alone with it is some strength of the _stibium_ consumed, but some
particles of gold and also of silver, if it be mixed with the gold[29].
When the button has been taken out of the crucible and cooled, it is
melted in a cupel, first until the antimony is exhaled, and thereafter
until the lead is separated from it.
Crushed pyrites which contains gold is smelted in the same way; it and
the _stibium_ should be of equal weight and in truth the gold may be
made from them in a number of different ways[30]. One part of crushed
material is mixed with six parts of copper, one part of sulphur, half a
part of salt, and they are all placed in a pot and over them is poured
wine distilled by heating liquid argol in an ampulla. The pot is covered
and smeared over with lute and is put in a hot place, so that the
mixture moistened with wine may dry for the space of six days, then it
is heated for three hours over a gentle fire that it may combine more
rapidly with the lead. Finally it is put into a cupel and the gold is
separated from the lead[31].
Or else one _libra_ of the concentrates from washing pyrites, or other
stones to which gold adheres, is mixed with half a _libra_ of salt, half
a _libra_ of argol, a third of a _libra_ of glass-galls, a sixth of a
_libra_ of gold or silver slags, and a _sicilicus_ of copper. The
crucible into which these are put, after it has been covered with a lid,
is sealed with lute and placed in a small furnace that is provided with
small holes through which the air is drawn in, and then it is heated
until it turns red and the substances put in have alloyed; this should
take place within four or five hours. The alloy having cooled, it is
again crushed to powder and a pound of litharge is added to it; then it
is heated again in another crucible until it melts. The button is taken
out, purged of slag, and placed in a cupel, where the gold is separated
from the lead.
Or to a _libra_ of the powder prepared from such metalliferous
concentrates, is added a _libra_ each of salt, of saltpetre, of argol,
and of glass-galls, and it is heated until it melts. When cooled and
crushed, it is washed, then to it is added a _libra_ of silver, a third
of copper filings, a sixth of litharge, and it is likewise heated again
until it melts. After the button has been purged of slag, it is put into
the cupel, and the gold and silver are separated from the lead; the gold
is parted from the silver with _aqua valens_. Or else a _libra_ of the
powder prepared from such metalliferous concentrates, a quarter of a
_libra_ of copper filings, and two _librae_ of that second powder[32]
which fuses ores, are heated until they melt. The mixture when cooled is
again reduced to powder, roasted and washed, and in this manner a blue
powder is obtained. Of this, and silver, and that second powder which
fuses ores, a _libra_ each are taken, together with three _librae_ of
lead, and a quarter of a _libra_ of copper, and they are heated together
until they melt; then the button is treated as before. Or else a _libra_
of the powder prepared from such metalliferous concentrates, half a
_libra_ of saltpetre, and a quarter of a _libra_ of salt are heated
until they melt. The alloy when cooled is again crushed to powder, one
_libra_ of which is absorbed by four pounds of molten silver. Or else a
_libra_ of the powder made from that kind of concentrates, together with
a _libra_ of sulphur, a _libra_ and a half of salt, a third of a _libra_
of salt made from argol, and a third of a _libra_ of copper resolved
into powder with sulphur, are heated until they melt. Afterward the lead
is re-melted, and the gold is separated from the other metals. Or else a
_libra_ of the powder of this kind of concentrates, together with two
_librae_ of salt, half a _libra_ of sulphur, and one _libra_ of
litharge, are heated, and from these the gold is melted out. By these
and similar methods concentrates containing gold, if there be a small
quantity of them or if they are very rich, can be smelted outside the
blast furnace.
If there be much of them and they are poor, then they are smelted in the
blast furnace, especially the ore which is not crushed to powder, and
particularly when the gold mines yield an abundance of it[33]. The gold
concentrates mixed with litharge and hearth-lead, to which are added
iron-scales, are smelted in the blast furnace whose tap-hole is
intermittently closed, or else in the first or the second furnaces in
which the tap-hole is always open. In this manner an alloy of gold and
lead is obtained which is put into the cupellation furnace. Two parts of
roasted pyrites or _cadmia_ which contain gold, are put with one part of
unroasted, and are smelted together in the third furnace whose tap-hole
is always open, and are made into cakes. When these cakes have been
repeatedly roasted, they are re-smelted in the furnace whose tap-hole is
temporarily closed, or in one of the two others whose tap-holes are
always open. In this manner the lead absorbs the gold, whether pure or
argentiferous or cupriferous, and the alloy is taken to the cupellation
furnace. Pyrites, or other gold ore which is mixed with much material
that is consumed by fire and flies out of the furnace, is melted with
stone from which iron is melted, if this is at hand. Six parts of such
pyrites, or of gold ore reduced to powder and sifted, four of stone from
which iron is made, likewise crushed, and three of slaked lime, are
mixed together and moistened with water; to these are added two and a
half parts of the cakes which contain some copper, together with one and
a half parts of slag. A basketful of fragments of the cakes is thrown
into the furnace, then the mixture of other things, and then the slag.
Now when the middle part of the forehearth is filled with the molten
material which runs down from the furnace, the slags are first skimmed
off, and then the cakes made of pyrites; afterward the alloy of copper,
gold and silver, which settles at the bottom, is taken out. The cakes
are gently roasted and re-smelted with lead, and made into cakes, which
are carried to other works. The alloy of copper, gold, and silver is not
roasted, but is re-melted again in a crucible with an equal portion of
lead. Cakes are also made much richer in copper and gold than those I
spoke of. In order that the alloy of gold and silver may be made
richer, to eighteen _librae_ of it are added forty-eight _librae_ of
crude ore, three _librae_ of the stone from which iron is made, and
three-quarters of a _libra_ of the cakes made from pyrites, and mixed
with lead, all are heated together in the crucible until they melt. When
the slag and the cakes melted from pyrites have been skimmed off, the
alloy is carried to other furnaces.
There now follows silver, of which the native silver or the lumps of
_rudis_ silver[34] obtained from the mines are not smelted in the blast
furnaces, but in small iron pans, of which I will speak at the proper
place; these lumps are heated and thrown into molten silver-lead alloy
in the cupellation furnace when the silver is being separated from the
lead, and refined. The tiny flakes or tiny lumps of silver adhering to
stones or marble or rocks, or again the same little lumps mixed with
earth, or silver not pure enough, should be smelted in the furnace of
which the tap-hole is only closed for a short time, together with cakes
melted from pyrites, with silver slags, and with stones which easily
fuse in fire of the second order.
In order that particles of silver should not fly away[35] from the lumps
of ore consisting of minute threads of pure silver and twigs of native
silver, they are enclosed in a pot, and are placed in the same furnace
where the rest of the silver ores are being smelted. Some people smelt
lumps of native silver not sufficiently pure, in pots or triangular
crucibles, whose lids are sealed with lute. They do not place these pots
in the blast furnace, but arrange them in the assay furnace into which
the draught of the air blows through small holes. To one part of the
native silver they add three parts of powdered litharge, as many parts
of hearth-lead, half a part of galena[36], and a small quantity of salt
and iron-scales. The alloy which settles at the bottom of the other
substances in the pot is carried to the cupellation furnace, and the
slags are re-melted with the other silver slags. They crush under the
stamps and wash the pots or crucibles to which silver-lead alloy or
slags adhere, and having collected the concentrates they smelt them
together with the slags. This method of smelting _rudis_ silver, if
there is a small quantity of it, is the best, because the smallest
portion of silver does not fly out of the pot or the crucible, and get
lost.
If bismuth ore or antimony ore or lead ore[37] contains silver, it is
smelted with the other ores of silver; likewise galena or pyrites, if
there is a small amount of it. If there be much galena, whether it
contain a large or a small amount of silver, it is smelted separately
from the others; which process I will explain a little further on.
Because lead and copper ores and their metals have much in common with
silver ores, it is fitting that I should say a great deal concerning
them, both now and later on. Also in the same manner, pyrites are
smelted separately if there be much of them. To three parts of roasted
lead or copper ore and one part of crude ore, are added concentrates if
they were made by washing the same ore, together with slags, and all are
put in the third furnace whose tap-hole is always open. Cakes are made
from this charge, which, when they have been quenched with water, are
roasted. Of these roasted cakes generally four parts are again mixed
with one part of crude pyrites and re-melted in the same furnace. Cakes
are again made from this charge, and if there is a large amount of
copper in these cakes, copper is made immediately after they have been
roasted and re-melted; if there is little copper in the cakes they are
also roasted, but they are re-smelted with a little soft slag. In this
method the molten lead in the forehearth absorbs the silver. From the
pyritic material which floats on the top of the forehearth are made
cakes for the third time, and from them when they have been roasted and
re-smelted is made copper. Similarly, three parts of roasted
_cadmia_[38] in which there is silver, are mixed with one part of crude
pyrites, together with slag, and this charge is smelted and cakes are
made from it; these cakes having been roasted are re-smelted in the same
furnace. By this method the lead contained in the forehearth absorbs the
silver, and the silver-lead is taken to the cupellation furnace. Crude
quartz and stones which easily fuse in fire of the third order, together
with other ores in which there is a small amount of silver, ought to be
mixed with crude roasted pyrites or _cadmia_, because the roasted cakes
of pyrites or _cadmia_ cannot be profitably smelted separately. In a
similar manner earths which contain little silver are mixed with the
same; but if pyrites and _cadmia_ are not available to the smelter, he
smelts such silver ores and earths with litharge, hearth-lead, slags,
and stones which easily melt in the fire. The concentrates[39]
originating from the washing of _rudis_ silver, after first being
roasted[40] until they melt, are smelted with mixed litharge and
hearth-lead, or else, after being moistened with water, they are smelted
with cakes made from pyrites and _cadmia_. By neither of these methods
do (the concentrates) fall back in the furnace, or fly out of it, driven
by the blast of the bellows and the agitation of the fire. If the
concentrates originated from galena they are smelted with it after
having been roasted; and if from pyrites, then with pyrites.
Pure copper ore, whether it is its own colour or is tinged with
chrysocolla or azure, and copper glance, or grey or black _rudis_
copper, is smelted in a furnace of which the tap-hole is closed for a
very short time, or else is always open[41]. If there is a large amount
of silver in the ore it is run into the forehearth, and the greater part
of the silver is absorbed by the molten lead, and the remainder is sold
with the copper to the proprietor of the works in which silver is parted
from copper[42]. If there is a small amount of silver in the ore, no
lead is put into the forehearth to absorb the silver, and the
above-mentioned proprietors buy it in with the copper; if there be no
silver, copper is made direct. If such copper ore contains some minerals
which do not easily melt, as pyrites or _cadmia metallica fossilis_[43],
or stone from which iron is melted, then crude pyrites which easily fuse
are added to it, together with slag. From this charge, when smelted,
they make cakes; and from these, when they have been roasted as much as
is necessary and re-smelted, the copper is made. But if there be some
silver in the cakes, for which an outlay of lead has to be made, then it
is first run into the forehearth, and the molten lead absorbs the
silver.
Indeed, _rudis_ copper ore of inferior quality, whether ash-coloured or
purple, blackish and occasionally in parts blue, is smelted in the first
furnace whose tap-hole is always open. This is the method of the
Tyrolese. To as much _rudis_ copper ore as will fill eighteen vessels,
each of which holds almost as much as seven Roman _moduli_[44], the
first smelter--for there are three--adds three cartloads of lead slags,
one cartload of schist, one fifth of a _centumpondium_ of stones which
easily fuse in the fire, besides a small quantity of concentrates
collected from copper slag and accretions, all of which he smelts for
the space of twelve hours, and from which he makes six _centumpondia_ of
primary cakes and one-half of a _centumpondium_ of alloy. One half of
the latter consists of copper and silver, and it settles to the bottom
of the forehearth. In every _centumpondium_ of the cakes there is half a
_libra_ of silver and sometimes half an _uncia_ besides; in the half of
a _centumpondium_ of the alloy there is a _bes_ or three-quarters of
silver. In this way every week, if the work is for six days, thirty-six
_centumpondia_ of cakes are made and three _centumpondia_ of alloy, in
all of which there is often almost twenty-four _librae_ of silver. The
second smelter separates from the primary cakes the greater part of the
silver by absorbing it in lead. To eighteen _centumpondia_ of cakes made
from crude copper ore, he adds twelve _centumpondia_ of hearth-lead and
litharge, three _centumpondia_ of stones from which lead is smelted,
five _centumpondia_ of hard cakes rich in silver, and two _centumpondia_
of exhausted liquation cakes[45]; he adds besides, some of the slags
resulting from smelting crude copper, together with a small quantity of
concentrates made from accretions, all of which he melts for the space
of twelve hours, and makes eighteen _centumpondia_ of secondary cakes,
and twelve _centumpondia_ of copper-lead-silver alloy; in each
_centumpondium_ of the latter there is half a _libra_ of silver. After
he has taken off the cakes with a hooked bar, he pours the alloy out
into copper or iron moulds; by this method they make four cakes of
alloy, which are carried to the works in which silver is parted from
copper. On the following day, the same smelter, taking eighteen
_centumpondia_ of the secondary cakes, again adds twelve _centumpondia_
of hearth-lead and litharge, three _centumpondia_ of stones from which
lead is smelted, five _centumpondia_ of hard cakes rich in silver,
together with slags from the smelting of the primary cakes, and with
concentrates washed from the accretions which are usually made at that
time. This charge is likewise smelted for the space of twelve hours, and
he makes as many as thirteen _centumpondia_ of tertiary cakes and eleven
_centumpondia_ of copper-lead-silver alloy, each _centumpondium_ of
which contains one-third of a _libra_ and half an _uncia_ of silver.
When he has skimmed off the tertiary cakes with a hooked bar, the alloy
is poured into copper moulds, and by this method four cakes of alloy are
made, which, like the preceding four cakes of alloy, are carried to the
works in which silver is parted from copper. By this method the second
smelter makes primary cakes on alternate days and secondary cakes on the
intermediate days. The third smelter takes eleven cartloads of the
tertiary cakes and adds to them three cartloads of hard cakes poor in
silver, together with the slag from smelting the secondary cakes, and
the concentrates from the accretions which are usually made at that
time. From this charge when smelted, he makes twenty _centumpondia_ of
quaternary cakes, which are called "hard cakes," and also fifteen
_centumpondia_ of those "hard cakes rich in silver," each
_centumpondium_ of which contains a third of a _libra_ of silver. These
latter cakes the second smelter, as I said before, adds to the primary
and secondary cakes when he re-melts them. In the same way, from eleven
cartloads of quaternary cakes thrice roasted, he makes the "final"
cakes, of which one _centumpondium_ contains only half an _uncia_ of
silver. In this operation he also makes fifteen _centumpondia_ of "hard
cakes poor in silver," in each _centumpondium_ of which is a sixth of a
_libra_ of silver. These hard cakes the third smelter, as I have said,
adds to the tertiary cakes when he re-smelts them, while from the
"final" cakes, thrice roasted and re-smelted, is made black copper[46].
The _rudis_ copper from which pure copper is made, if it contains little
silver or if it does not easily melt, is first smelted in the third
furnace of which the tap-hole is always open; and from this are made
cakes, which after being seven times roasted are re-smelted, and from
these copper is melted out; the cakes of copper are carried to a furnace
of another kind, in which they are melted for the third time, in order
that in the copper "bottoms" there may be more silver, while in the
"tops" there may be less, which process is explained in Book XI.
Pyrites, when they contain not only copper, but also silver, are
smelted in the manner I described when I treated of ores of silver. But
if they are poor in silver, and if the copper which is melted out of
them cannot easily be treated, they are smelted according to the method
which I last explained.
Finally, the copper schists containing bitumen or sulphur are roasted,
and then smelted with stones which easily fuse in a fire of the second
order, and are made into cakes, on the top of which the slags float.
From these cakes, usually roasted seven times and re-melted, are melted
out slags and two kinds of cakes; one kind is of copper and occupies the
bottom of the crucible, and these are sold to the proprietors of the
works in which silver is parted from copper; the other kind of cakes are
usually re-melted with primary cakes. If the schist contains but a small
amount of copper, it is burned, crushed under the stamps, washed and
sieved, and the concentrates obtained from it are melted down; from this
are made cakes from which, when roasted, copper is made. If either
chrysocolla or azure, or yellow or black earth containing copper and
silver, adheres to the schist, it is not washed, but is crushed and
smelted with stones which easily fuse in fire of the second order.
Lead ore, whether it be _molybdaena_[47], pyrites, (galena?) or stone
from which it is melted, is often smelted in a special furnace, of which
I have spoken above, but no less often in the third furnace of which the
tap-hole is always open. The hearth and forehearth are made from powder
containing a small portion of iron hammer-scales; iron slag forms the
principal flux for such ores; both of these the expert smelters consider
useful and to the owner's advantage, because it is the nature of iron to
attract lead. If it is _molybdaena_ or the stone from which lead is
smelted, then the lead runs down from the furnace into the forehearth,
and when the slags have been skimmed off, the lead is poured out with a
ladle. If pyrites are smelted, the first to flow from the furnace into
the forehearth, as may be seen at Goslar, is a white molten substance,
injurious and noxious to silver, for it consumes it. For this reason the
slags which float on the top having been skimmed off, this substance is
poured out; or if it hardens, then it is taken out with a hooked bar;
and the walls of the furnace exude the same substance[48]. Then the
_stannum_ runs out of the furnace into the forehearth; this is an alloy
of lead and silver. From the silver-lead alloy they first skim off the
slags, not rarely white, as some pyrites[49] are, and afterward they
skim off the cakes of pyrites, if there are any. In these cakes there is
usually some copper; but since there is usually but a very small
quantity, and as the forest charcoal is not abundant, no copper is made
from them. From the silver-lead poured into iron moulds they likewise
make cakes; when these cakes have been melted in the cupellation
furnace, the silver is parted from the lead, because part of the lead is
transformed into litharge and part into hearth-lead, from which in the
blast furnace on re-melting they make de-silverized lead, for in this
lead each _centumpondium_ contains only a _drachma_ of silver, when
before the silver was parted from it each _centumpondium_ contained more
or less than three _unciae_ of silver[50].
The little black stones[51] and others from which tin is made, are
smelted in their own kind of furnace, which should be narrower than the
other furnaces, that there may be only the small fire which is necessary
for this ore. These furnaces are higher, that the height may compensate
for the narrowness and make them of almost the same capacity as the
other furnaces. At the top, in front, they are closed and on the other
side they are open, where there are steps, because they cannot have the
steps in front on account of the forehearth; the smelters ascend by
these steps to put the tin-stone into the furnace. The hearth of the
furnace is not made of powdered earth and charcoal, but on the floor of
the works are placed sandstones which are not too hard; these are set on
a slight slope, and are two and three-quarters feet long, the same
number of feet wide, and two feet thick, for the thicker they are the
longer they last in the fire. Around them is constructed a rectangular
furnace eight or nine feet high, of broad sandstones, or of those common
substances which by nature are composed of diverse materials[52]. On the
inside the furnace is everywhere evenly covered with lute. The upper
part of the interior is two feet long and one foot wide, but below it is
not so long and wide. Above it are two hood-walls, between which the
fumes ascend from the furnace into the dust chamber, and through this
they escape by a narrow opening in the roof. The sandstones are sloped
at the bed of the furnace, so that the tin melted from the tin-stone may
flow through the tap-hole of the furnace into the forehearth.[53]
As there is no need for the smelters to have a fierce fire, it is not
necessary to place the nozzles of the bellows in bronze or iron pipes,
but only through a hole in the furnace wall. They place the bellows
higher at the back so that the blast from the nozzles may blow straight
toward the tap-hole of the furnace. That it may not be too fierce, the
nozzles are wide, for if the fire were fiercer, tin could not be melted
out from the tin-stone, as it would be consumed and turned into ashes.
Near the steps is a hollowed stone, in which is placed the tin-stone to
be smelted; as often as the smelter throws into the furnace an iron
shovel-ful of this tin-stone, he puts on charcoal that was first put
into a vat and washed with water to be cleansed from the grit and small
stones which adhere to it, lest they melt at the same time as the
tin-stone and obstruct the tap-hole and impede the flow of tin from the
furnace. The tap-hole of the furnace is always open; in front of it is a
forehearth a little more than half a foot deep, three-quarters of two
feet long and one foot wide; this is lined with lute, and the tin from
the tap-hole flows into it. On one side of the forehearth is a low wall,
three-quarters of a foot wider and one foot longer than the forehearth,
on which lies charcoal powder. On the other side the floor of the
building slopes, so that the slags may conveniently run down and be
carried away. As soon as the tin begins to run from the tap-hole of the
furnace into the forehearth, the smelter scrapes down some of the
powdered charcoal into it from the wall, so that the slags may be
separated from the hot metal, and so that it may be covered, lest any
part of it, being very hot, should fly away with the fumes. If after the
slag has been skimmed off, the powder does not cover up the whole of the
tin, the smelter draws a little more charcoal off the wall with a
scraper. After he has opened the tap-hole of the forehearth with a
tapping-bar, in order that the tin can flow into the tapping-pot,
likewise smeared with lute, he again closes the tap-hole with pure lute
or lute mixed with powdered charcoal. The smelter, if he be diligent and
experienced, has brooms at hand with which he sweeps down the walls
above the furnace; to these walls and to the dust chamber minute
tin-stones sometimes adhere with part of the fumes. If he be not
sufficiently experienced in these matters and has melted at the same
time all of the tin-stone,--which is commonly of three sizes, large,
medium, and very small,--not a little waste of the proprietor's tin
results; because, before the large or the medium sizes have melted, the
small have either been burnt up in the furnace, or else, flying up from
it, they not only adhere to the walls but also fall in the dust chamber.
The owner of the works has the sweepings by right from the owner of the
ore. For the above reasons the most experienced smelter melts them down
separately; indeed, he melts the very small size in a wider furnace, the
medium in a medium-sized furnace, and the largest size in the narrowest
furnace. When he melts down the small size he uses a gentle blast from
the bellows, with the medium-sized a moderate one, with the large size a
violent blast; and when he smelts the first size he needs a slow fire,
for the second a medium one, and for the third a fierce one; yet he uses
a much less fierce fire than when he smelts the ores of gold, silver, or
copper. When the workmen have spent three consecutive days and nights in
this work, as is usual, they have finished their labours; in this time
they are able to melt out a large weight of small sized tin-stone which
melts quickly, but less of the large ones which melt slowly, and a
moderate quantity of the medium-sized which holds the middle course.
Those who do not smelt the tin-stone in furnaces made sometimes wide,
sometimes medium, or sometimes narrow, in order that great loss should
not be occasioned, throw in first the smallest size, then the medium,
then the large size, and finally those which are not quite pure; and the
blast of the bellows is altered as required. In order that the tin-stone
thrown into the furnace should not roll off from the large charcoal into
the forehearth before the tin is melted out of it, the smelter uses
small charcoal; first some of this moistened with water is placed in the
furnace, and then he frequently repeats this succession of charcoal and
tin-stone.
The tin-stone, collected from material which during the summer was
washed in a ditch through which a stream was diverted, and during the
winter was screened on a perforated iron plate, is smelted in a furnace
a palm wider than that in which the fine tin-stone dug out of the earth
is smelted. For the smelting of these, a more vigorous blast of the
bellows and a fiercer fire is needed than for the smelting of the large
tin-stone. Whichever kind of tin-stone is being smelted, if the tin
first flows from the furnace, much of it is made, and if slags first
flow from the furnace, then only a little. It happens that the tin-stone
is mixed with the slags when it is either less pure or ferruginous--that
is, not enough roasted--and is imperfect when put into the furnace, or
when it has been put in in a larger quantity than was necessary; then,
although it may be pure and melt easily, the ore either runs out of the
furnace at the same time, mixed with the slags, or else it settles so
firmly at the bottom of the furnace that the operation of smelting being
necessarily interrupted, the furnace freezes up.
[Illustration 415 (Tin smelting Furnaces): A--Furnace. B--Its tap-hole.
C--Forehearth. D--Its tap-hole. E--Slags. F--Scraper. G--Dipping-pot.
H--Walls of the chimney. I--Broom. K--Copper plate. L--Latticework bars.
M--Iron seal or die. N--Hammer.]
The tap-hole of the forehearth is opened and the tin is diverted into
the dipping-pot, and as often as the slags flow down the sloping floor
of the building they are skimmed off with a rabble; as soon as the tin
has run out of the forehearth, the tap-hole is again closed up with lute
mixed with powdered charcoal. Glowing coals are put in the dipping-pot
so that the tin, after it has run out, should not get chilled. If the
metal is so impure that nothing can be made from it, the material which
has run out is made into cakes to be re-smelted in the hearth, of which
I shall have something to say later; if the metal is pure, it is poured
immediately upon thick copper plates, at first in straight lines and
then transversely over these to make a lattice. Each of these lattice
bars is impressed with an iron die; if the tin was melted out of ore
excavated from mines, then one stamp only, namely, that of the
Magistrate, is usually imprinted, but if it is made from tin-stone
collected on the ground after washing, then it is impressed with two
seals, one the Magistrate's and the other a fork which the washers use.
Generally, three of this kind of lattice bars are beaten and amalgamated
into one mass with a wooden mallet.
The slags that are skimmed off are afterward thrown with an iron shovel
into a small trough hollowed from a tree, and are cleansed from
charcoal by agitation; when taken out they are broken up with a square
iron mallet, and then they are re-melted with the fine tin-stone next
smelted. There are some who crush the slags three times under wet stamps
and re-melt them three times; if a large quantity of this be smelted
while still wet, little tin is melted from it, because the slag, soon
melted again, flows from the furnace into the forehearth. Under the wet
stamps are also crushed the lute and broken rock with which such
furnaces are lined, and also the accretions, which often contain fine
tin-stone, either not melted or half-melted, and also prills of tin. The
tin-stone not yet melted runs out through the screen into a trough, and
is washed in the same way as tin-stone, while the partly melted and the
prills of tin are taken from the mortar-box and washed in the sieve on
which not very minute particles remain, and thence to the canvas strake.
The soot which adheres to that part of the chimney which emits the
smoke, also often contains very fine tin-stone which flies from the
furnace with the fumes, and this is washed in the strake which I have
just mentioned, and in other sluices. The prills of tin and the partly
melted tin-stone that are contained in the lute and broken rock with
which the furnace is lined, and in the remnants of the tin from the
forehearth and the dipping-pot, are smelted together with the tin-stone.
When tin-stone has been smelted for three days and as many nights in a
furnace prepared as I have said above, some little particles of the rock
from which the furnace is constructed become loosened by the fire and
fall down; and then the bellows being taken away, the furnace is broken
through at the back, and the accretions are first chipped off with
hammers, and afterward the whole of the interior of the furnace is
re-fitted with the prepared sandstone, and again evenly lined with lute.
The sandstone placed on the bed of the furnace, if it has become faulty,
is taken out, and another is laid down in its place; those rocks which
are too large the smelter chips off and fits with a sharp pick.
[Illustration 417 (Tin smelting Furnaces): A--Furnaces. B--Forehearths.
C--Their tap-holes. D--Dipping-pots. E--Pillars. F--Dust-chamber.
G--Window. H--Chimneys. I--Tub in which the coals are washed.]
Some build two furnaces against the wall just like those I have
described, and above them build a vaulted ceiling supported by the wall
and by four pillars. Through holes in the vaulted ceiling the fumes from
the furnaces ascend into a dust chamber, similar to the one described
before, except that there is a window on each side and there is no door.
The smelters, when they have to clear away the flue-dust, mount by the
steps at the side of the furnaces, and climb by ladders into the dust
chamber through the apertures in the vaulted ceilings over the furnaces.
They then remove the flue-dust from everywhere and collect it in
baskets, which are passed from one to the other and emptied. This dust
chamber differs from the other described, in the fact that the chimneys,
of which it has two, are not dissimilar to those of a house; they
receive the fumes which, being unable to escape through the upper part
of the chamber, are turned back and re-ascend and release the tin; thus
the tin set free by the fire and turned to ash, and the little
tin-stones which fly up with the fumes, remain in the dust chamber or
else adhere to copper plates in the chimney.
[Illustration 418 (Refining Tin): A--Hearths. B--Dipping-pots. C--Wood.
D--Cakes. E--Ladle. F--Copper plate. G--Lattice-shaped bars. H--Iron
dies. I--Wooden mallet. K--Mass of tin bars. L--Shovel.]
If the tin is so impure that it cracks when struck with the hammer, it
is not immediately made into lattice-like bars, but into the cakes which
I have spoken of before, and these are refined by melting again on a
hearth. This hearth consists of sandstones, which slope toward the
centre and a little toward a dipping-pot; at their joints they are
covered with lute. Dry logs are arranged on each side, alternately
upright and lengthwise, and more closely in the middle; on this wood are
placed five or six cakes of tin which all together weigh about six
_centumpondia_; the wood having been kindled, the tin drips down and
flows continuously into the dipping-pot which is on the floor. The
impure tin sinks to the bottom of this dipping-pot and the pure tin
floats on the top; then both are ladled out by the master, who first
takes out the pure tin, and by pouring it over thick plates of copper
makes lattice-like bars. Afterward he takes out the impure tin from
which he makes cakes; he discriminates between them, when he ladles and
pours, by the ease or difficulty of the flow. One _centumpondium_ of the
lattice-like bars sells for more than a _centumpondium_ of cakes, for
the price of the former exceeds the price of the latter by a gold
coin[54]. These lattice-like bars are lighter than the others, and when
five of them are pounded and amalgamated with a wooden mallet, a mass is
made which is stamped with an iron die. There are some who do not make a
dipping-pot on the floor for the tin to run into, but in the hearth
itself; out of this the master, having removed the charcoal, ladles the
tin and pours it over the copper-plate. The dross which adheres to the
wood and the charcoal, having been collected, is re-smelted in the
furnace.
[Illustration 419 (Blast Furnaces): A--Furnace. B--Bellows. C--Iron
Disc. D--Nozzle. E--Wooden Disc. F--Blow-hole. G--Handle. H--Haft.
I--Hoops. K--Masses of tin.]