FOOTNOTES:
[Pg 491][1] The whole of this Book is devoted to the subject of the separation of silver from copper by liquation, except pages [530]-[9] on copper refining, and page [544] on the separation of silver from iron. We believe a brief outline of the liquation process here will refresh the mind of the reader, and enable him to peruse the Book with more satisfaction. The fundamental principle of the process is that if a copper-lead alloy, containing a large excess of lead, be heated in a reducing atmosphere, above the melting point of lead but below that of copper, the lead will liquate out and carry with it a large proportion of the silver. As the results are imperfect, the process cannot be carried through in one operation, and a large amount of bye-products is created which must be worked up subsequently. The process, as here described, falls into six stages. 1st, Melting the copper and lead in a blast furnace to form "liquation cakes"—that is, the "leading." If the copper contain too little silver to warrant liquation directly, then the copper is previously enriched by melting and drawing off from a settling pot the less argentiferous "tops" from the metal, liquation cakes being made from the enriched "bottoms." 2nd, Liquation of the argentiferous lead from the copper. This work was carried out in a special furnace, to which the admission of air was prevented as much as possible in order to prevent oxidation. 3rd, "Drying" the residual copper, which retained some lead, in a furnace with a free admission of air. The temperature was raised to a higher degree than in the liquation furnace, and the expelled lead was oxidized. 4th, Cupellation of the argentiferous lead. 5th, Refining of the residual copper from the "drying" furnace by oxidation of impurities and poling in a "refining furnace." 6th, Re-alloy and re-liquation of the bye-products. These consist of: a, "slags" from "leading"; b, "slags" from "drying"; c, "slags" from refining of the copper. All of these "slags" were mainly lead oxides, containing some cuprous oxides and silica from the furnace linings; d, "thorns" from liquation; e, "thorns" from "drying"; f, "thorns" from skimmings during cupellation; these were again largely lead oxides, but contained rather more copper and less silica than the "slags"; g, "ash-coloured copper," being scales from the "dried" copper, were cuprous oxides, containing considerable lead oxides; h, concentrates from furnace accretions, crushed bricks, &c.
The discussion of detailed features of the process has been reserved to notes attached to the actual text, to which the reader is referred. As to the general result of liquation, Karsten (see [below]) estimates the losses in the liquation of the equivalent of 100 lbs. of argentiferous copper to amount to 32-35 lbs. of lead and 5 to 6 lbs. of copper. Percy (see [below]) quotes results at Lautenthal in the Upper Harz for the years 1857-60, showing losses of 25% of the silver, 9.1% of the copper, and 36.37 lbs. of lead to the 100 lbs. of copper, or say, 16% of the lead; and a cost of £8 6s. per ton of copper. The theoretical considerations involved in liquation have not been satisfactorily determined. Those who may wish to pursue the subject will find repeated descriptions and much discussion in the following works, which have been freely consulted in the notes which follow upon particular features of the process. It may be mentioned that Agricola's treatment of the subject is more able than any down to the 18th century. Ercker (Beschreibung Allerfürnemsten Mineralischen, etc., Prague, 1574). Lohneys (Bericht vom Bergwercken, etc., Zellerfeldt, 1617). Schlüter (Gründlicher Unterricht [Pg 492]von Hütte-Werken, Braunschweig, 1738). Karsten (System der Metallurgie V. and Archiv für Bergbau und Hüttenwesen, 1st series, 1825). Berthier (Annales des Mines, 1825, II.). Percy (Metallurgy of Silver and Gold, London, 1880).
Nomenclature.—This process held a very prominent position in German metallurgy for over four centuries, and came to have a well-defined nomenclature of its own, which has never found complete equivalents in English, our metallurgical writers to the present day adopting more or less of the German terms. Agricola apparently found no little difficulty in adapting Latin words to his purpose, but stubbornly adhered to his practice of using no German at the expense of long explanatory clauses. The following table, prepared for convenience in translation, is reproduced. The German terms are spelled after the manner used in most English metallurgies, some of them appear in Agricola's Glossary to De Re Metallica.
| English. | Latin. | German. |
| Blast furnace | Prima fornax | Schmeltzofen |
| Liquation furnace | Fornax in qua argentum et plumbum ab aere secernuntur | Saigernofen |
| Drying furnace | Fornax in qua aerei panes fathiscentes torrentur | Darrofen |
| Refining hearth | Fornax in qua panes aerei torrefacti coquuntur | Gaarherd |
| Cupellation furnace | Secunda fornax, or fornax in qua plumbum ab argento separatur | Treibherd |
| Leading | Mistura | Frischen |
| Liquating | Stillare, or distillare | Saigern |
| "Drying" | Torrere | Darren |
| Refining | Aes ex panibus torrefactis conficere | Gaarmachen |
| Liquation cakes | Panes ex aere ac plumbo misti | Saigerstock |
| Exhausted liquation cakes | Panes fathiscentes | Kiehnstock, or Kinstocke |
| "Dried" cakes | Panes torrefacti | Darrlinge |
| Slags: | ||
| from leading | Recrementa (with explanatory phrases) | Frischschlacke |
| " drying | " " " | Darrost |
| " refining | " " " | Gaarschlacke |
| Liquation thorns | Spinae (with explanatory phrases) | Saigerdörner, or Röstdörner |
| Thorns from "drying" | " " " | Darrsöhle |
| " " cupellation | " " " | Abstrich |
| Silver-lead or liquated silver-lead | Stannum | Saigerwerk or saigerblei |
| Ash-coloured copper | Aes cinereum | Pickschiefer or schifer |
| Furnace accretions or "accretions" | Cadmiae | Offenbrüche |
[Pg 494] Historical Note.—So far as we are aware, this is the first complete discussion of this process, although it is briefly mentioned by one writer before Agricola—that is, by Biringuccio (III, 5, 8), who wrote ten years before this work was sent to the printer. His account is very incomplete, for he describes only the bare liquation, and states that the copper is re-melted with lead and re-liquated until the silver is sufficiently abstracted. He neither mentions "drying" nor any of the bye-products. In his directions the silver-lead alloy was cupelled and the copper ultimately refined, obviously by oxidation and poling, although he omits the pole. In A.D. 1150 Theophilus (p. 305, Hendrie's Trans.) describes melting lead out of copper ore, which would be a form of liquation so far as separation of these two metals is concerned, but obviously not a process for separating silver from copper. This passage is quoted in the note on copper smelting (Note on p. [405]). A process of such well-developed and complicated a character must have come from a period long before Agricola; but further than such a surmise, there appears little to be recorded. Liquation has been during the last fifty years displaced by other methods, because it was not only tedious and expensive, but the losses of metal were considerable.
[2] Paries,—"Partition" or "wall." The author uses this term throughout in distinction to murus, usually applying the latter to the walls of the building and the former to furnace walls, chimney walls, etc. In order to gain clarity, we have introduced the term "hood" in distinction to "chimney," and so far as possible refer to the paries of these constructions and furnaces as "side of the furnace," "side of the hood," etc.
[Pg 495][4] From this point on, the construction of the roofs, in the absence of illustration, is hopeless of intelligent translation. The constant repetition of "tignum," "tigillum," "trabs," for at least fifteen different construction members becomes most hopelessly involved, especially as the author attempts to distinguish between them in a sort of "House-that-Jack-built" arrangement of explanatory clauses.
[Pg 496][5] In the original text this is given as the "fifth," a manifest impossibility.
[7] If Roman weights, this would be 5.6 short tons, and 7.5 tons if German centner is meant.
[Pg 501][8] This is, no doubt, a reference to Pliny's statement (XXXIII, 35) regarding litharge at Puteoli. This passage from Pliny is given in the footnote on p. [466]. Puteoli was situated on the Bay of Naples.
[Pg 503][9] By this expression is apparently meant the "bottoms" produced in enriching copper, as described on p. [510].
[Pg 504][10] The details of the preparation of liquation cakes—"leading"—were matters of great concern to the old metallurgists. The size of the cakes, the proportion of silver in the original copper and in the liquated lead, the proportion of lead and silver left in the residual cakes, all had to be reached by a series of compromises among militant forces. The cakes were generally two and one-half to three and one-half inches thick and about two feet in diameter, and [Pg 505]weighed 225 to 375 lbs. This size was wonderfully persistent from Agricola down to modern times; and was, no doubt, based on sound experience. If the cakes were too small, they required proportionately more fuel and labour; whilst if too large, the copper began to melt before the maximum lead was liquated. The ratio of the copper and lead was regulated by the necessity of enough copper to leave a substantial sponge mass the shape of the original cake, and not so large a proportion as to imprison the lead. That is, if the copper be in too small proportion the cakes break down; and if in too large, then insufficient lead liquates out, and the extraction of silver decreases. Ercker (p. 106-9) insists on the equivalent of about 3 copper to 9.5 lead; Lohneys (p. 99), 3 copper to 9 or 10 lead. Schlüter (p. 479, etc.) insists on a ration of 3 copper to about 11 lead. Kerl (Handbuch Der Metallurgischen Hüttenkunde, 1855; Vol. III., p. 116) gives 3 copper to 6 to 7 parts lead. Agricola gives variable amounts of 3 parts copper to from 8 to 12 parts lead. As to the ratio of silver in the copper, or to the cakes, there does not, except the limit of payability, seem to have been any difficulty on the minimum side. On the other hand, Ercker, Lohneys, Schlüter, and Karsten all contend that if the silver ran above a certain proportion, the copper would retain considerable silver. These authors give the outside ratio of silver permissible for good results in one liquation at what would be equivalent to 45 to 65 ozs. per ton of cakes, or about 190 to 250 ozs. per ton on the original copper. It will be seen, however, that Agricola's cakes greatly exceed these values. A difficulty did arise when the copper ran low in silver, in that the liquated lead was too poor to cupel, and in such case the lead was used over again, until it became rich enough for this purpose. According to Karsten, copper containing less than an equivalent of 80 to 90 ozs. per ton could not be liquated profitably, although the Upper Harz copper, according to Kerl, containing the equivalent of about 50 ozs. per ton, was liquated at a profit. In such a case the cakes would run only 12 to 14 ozs. per ton. It will be noticed that in the eight cases given by Agricola the copper ran from 97 to over 580 ozs. per ton, and in the description of enrichment of copper "bottoms" the original copper runs 85 ozs., and "it cannot be separated easily"; as a result, it is raised to 110 ozs. per ton before treatment. In addition to the following tabulation of the proportions here given by Agricola, the reader should refer to footnotes [15] and [17], where four more combinations are tabulated. It will be observed from [Pg 506]this table that with the increasing richness of copper an increased proportion of lead was added, so that the products were of similar value. It has been assumed (see [footnote 13 p. 509]), that Roman weights are intended. It is not to be expected that metallurgical results of this period will "tie up" with the exactness of the modern operator's, and it has not been considered necessary to calculate beyond the nearest pennyweight. Where two or more values are given by the author the average has been taken.
| 1st Charge. | 2nd Charge. | 3rd Charge. | 4th Charge. | |
| Amount of argentiferous copper | 211.8 lbs. | 211.8 lbs. | 211.8 lbs. | 211.8 lbs. |
| Amount of lead | 564.8 " | 635.4 " | 776.6 " | 847.2 " |
| Weight of each cake | 193.5 " | 211.5 " | 247.1 " | 264.75 " |
| Average value of charge | 56 ozs. 3 dwts. | 62 ozs. 4 dwts. | 64 ozs. 4 dwts. | 66 ozs. 7 dwts. |
| Per cent. of copper | 27.2% | 25% | 21.4% | 20% |
| Average value of original copper per ton | 207 ozs. 4 dwts. | 251 ozs. 3 dwts. | 299 ozs. 15 dwts. | 332 ozs. 3 dwts. |
| Weight of argentiferous lead liquated out | 423.6 lbs. | 494.2 lbs. | 635.4 lbs. | 706 lbs. |
| Average value of liquated lead per ton | 79 ozs. | 79 ozs. | 79 ozs. | 85 ozs. |
| Weight of residues (residual copper and thorns) | 353 lbs. | 353 lbs. | 353 lbs. | 353 lbs. |
| Average value of residues per ton | 34 ozs. | 34 ozs. | 34 ozs. | 34 ozs. to 38 ozs. |
| Extraction of silver into the argentiferous lead | 76.5% | 73.4% | 79% | 85.3% |
[Pg 509][12] An analysis of this "slag" by Karsten (Archiv. 1st Series IX, p. 24) showed 63.2% lead oxide, 5.1% cuprous oxide, 20.1% silica (from the fuel and furnace linings), together with some iron alumina, etc. The pompholyx and spodos were largely zinc oxide (see note, p. [394]).
[13] This description of a centumpondium which weighed either 1331/3 librae, or 1463/4 librae, adds confusion to an already much mixed subject (see [Appendix C].). Assuming the German pfundt to weigh 7,219 troy grains, and the Roman libra 4,946 grains, then a centner would weigh 145.95 librae, which checks up fairly well with the second case; but under what circumstances a centner can weigh 1331/3 librae we are unable to record. At first sight it might appear from this statement that where Agricola uses the word centumpondium he means the German centner. On the other hand, in the previous five or six pages the expressions one-third, five-sixths, ten-twelfths of a libra are used, which are even divisions of the Roman 12 unciae to one libra, and are used where they manifestly mean divisions of 12 units. If Agricola had in mind the German scale, and were using the libra for a pfundt of 16 untzen, these divisions would amount to fractions, and would not total the sicilicus and drachma quantities given, nor would they total any of the possibly synonymous divisions of the German untzen (see also page [254]).
[14] If we assume Roman weights, the charge in the first case can be tabulated as follows, and for convenience will be called the fifth charge:—
| 5th Charge (3 cakes). | |
| Amount of copper | 211.8 lbs. |
| Amount of lead | 635.4 lbs. |
| Weight of each cake | 282.4 lbs. |
| Average value of charge | 218 ozs. 18 dwts. |
| Per cent. of copper | 25% |
| Average value of original copper per ton | 583 ozs. 6 dwts. 16 grs. |
| Weight of argentiferous lead liquated out | 494.2 lbs. |
| Average value of liquated lead per ton | 352 ozs. 8 dwts. |
| Weight of residues | 353 lbs. |
| Average value of residues per ton | 20 ozs. (about). |
| Extraction of silver into the argentiferous lead | 94% |
The results given in the second case where the copper contains 2 librae and a bes per centumpondium do not tie together at all, for each liquation cake should contain 3 librae 91/2 unciae, instead of 11/2 librae and 1/2 uncia of silver.
[Pg 510][15] In this enrichment of copper by the "settling" of the silver in the molten mass the original copper ran, in the two cases given, 60 ozs. 15 dwts. and 85 ozs. 1 dwt. per ton. The whole charge weighed 2,685 lbs., and contained in the second case 114 ozs. Troy, omitting fractions. On melting, 1,060 lbs. were drawn off as "tops," containing 24 ozs. of silver, or running 45 ozs. per ton, and there remained 1,625 lbs. of "bottoms," containing 90 ozs. of silver, or averaging 110 ozs. per ton. It will be noticed later on in the description of making liquation cakes from these copper bottoms, that the author alters the value from one-third librae, a semi-uncia and a drachma per centumpondium to one-third of a libra, i.e., from 110 ozs. to 97 ozs. 4 dwts. per ton. In the Glossary this furnace is described as a spleisofen, i.e., a refining hearth.
[Pg 511][16] The latter part of this paragraph presents great difficulties. The term "refining furnace" is given in the Latin as the "second furnace," an expression usually applied to the cupellation furnace. The whole question of refining is exhaustively discussed on pages [530] to [539]. Exactly what material is meant by the term red (rubrum), yellow (fulvum) and caldarium copper is somewhat uncertain. They are given in the German text simply as rot, geel, and lebeter kupfer, and apparently all were "coarse" copper of different characters destined for the refinery. The author states in De Natura Fossilium (p. 334): "Copper has a red colour peculiar to itself; this colour in smelted copper is considered the most excellent. It, however, varies. In some it is red, as in the copper smelted at Neusohl.... Other copper is prepared in the smelters where silver is separated from copper, which is called yellow copper (luteum), and is regulare. In the same place a dark yellow copper is made which is called caldarium, taking its name among the Germans from a caldron.... Regulare differs from caldarium in that the former is not only fusible, but also malleable; while the latter is, indeed, fusible, but is not ductile, for it breaks when struck with the hammer." Later on in De Re Metallica (p. [542]) he describes yellow copper as made from "baser" liquation thorns and from exhausted liquation cakes made from thorns. These products were necessarily impure, as they contained, among other things, the concentrates from furnace accretions. Therefore, there was ample source for zinc, arsenic or other metallics which would lighten the colour. Caldarium copper is described by Pliny (see note, p. [404]), and was, no doubt, "coarse" copper, and apparently Agricola adopted this term from that source, as we have found it used nowhere else. On page [542] the author describes making caldarium copper from a mixture of yellow copper and a peculiar cadmia, which he describes as the "slags" from refining copper. These "slags," which are the result of oxidation and poling, would contain almost any of the metallic impurities of the original ore, antimony, lead, arsenic, zinc, cobalt, etc. Coming from these two sources the caldarium must have been, indeed, impure.
[Pg 512][17] The liquation of these low-grade copper "bottoms" required that the liquated lead should be re-used again to make up fresh liquation cakes, in order that it might eventually become rich enough to warrant cupellation. In the following table the "poor" silver-lead is designated (A) the "medium" (B) and the "rich" (C). The three charges here given are designated sixth, seventh, and eighth for purposes of reference. It will be seen that the data is insufficient to complete the ninth and tenth. Moreover, while the author gives directions for making four cakes, he says the charge consists of five, and it has, therefore, been necessary to reduce the volume of products given to this basis.
| 6th Charge. | 7th Charge. | 8th Charge. | |
| Amount of copper bottoms | 176.5 lbs. | 176.5 lbs. | 176.5 lbs. |
| Amount of lead | 282.4 lbs. (slags) | 564.8 lbs. of (A) | 635.4 lbs. of (B) |
| Amount of de-silverized lead | 494.2 lbs. | 211.8 lbs. | 141.2 lbs. (A) |
| Weight of each cake | 238.3 lbs. | 238.3 lbs. | 238.3 lbs. |
| Average value of charge per ton | 22 ozs. 5 dwts. | 35 ozs. 15 dwts. | 50 ozs. 5 dwts. |
| Per cent. of copper | 18.5% | 18.5% | 18.5% |
| Average value per ton original copper | 97 ozs. 4 dwts. | 97 ozs. 4 dwts. | 97 ozs. 4 dwts. |
| Average value per ton of | 90 ozs. 2 dwts. (slags) | 28 ozs. 5 dwts. (A) | 28 ozs. 5 dwts. (A) |
| Average value per ton of | 3 ozs. 1 dwt. (lead) | 3 ozs. 1 dwt. (lead) | 42 ozs. 10 dwts. (B) |
| Weight of liquated lead | 550.6 lbs. | ||
| Average value of the liquated lead per ton | 28 ozs. 5 dwts. (A) | 42 ozs. 10 dwts. (B) | 63 ozs. 16 dwts. (C) |
| Weight of exhausted liquation cakes | 225.9 lbs. | ||
| Average value of the exhausted liquation cakes per ton | 12 ozs. 3 dwts. | ||
| Weight of liquation thorns | 169.4 lbs. | ||
| Average value of the liquation thorns per ton | 18 ozs. 4 dwts. | ||
| Extraction of silver into the liquated lead | 71% |
[Pg 520][18] For the liquation it was necessary to maintain a reducing atmosphere, otherwise the lead would oxidize; this was secured by keeping the cakes well covered with charcoal and by preventing the entrance of air as much as possible. Moreover, it was necessary to preserve a fairly even temperature. The proportions of copper and lead in the three liquation products vary considerably, depending upon the method of conducting the process and the original proportions. From the authors consulted (see note p. [492]) an average would be about as follows:—The residual copper—exhausted liquation cakes—ran from 25 to 33% lead; the liquated lead from 2 to 3% copper; and the liquation thorns, which were largely oxidized, contained about 15% copper oxides, 80% lead oxides, together with impurities, such as antimony, arsenic, etc. The proportions of the various products would obviously depend upon the care in conducting the operation; too high temperature and the admission of air would increase the copper melted and oxidize more lead, and thus increase the liquation thorns. There are insufficient data in Agricola to adduce conclusions as to the actual ratios produced. The results given for the 6th charge ([note 17, p. 512]) would indicate about 30% lead in the residual copper, and would indicate that the original charge was divided into about 24% of residual copper, 18% of liquation thorns, and 57% of liquated lead. This, however, was an unusually large proportion of liquation thorns, some of the authors giving instances of as low as 5%.
[Pg 522][19] The first instance given, of 44 centumpondia (3,109 lbs.) lead and one centumpondium (70.6 lbs.) copper, would indicate that the liquated lead contained 2.2% copper. The second, of 46 centumpondia (3,250 lbs.) lead and 11/2 centumpondia copper (106 lbs.), would indicate 3% copper; and in the third, 120 centumpondia (8,478 lbs.) lead and six copper (424 lbs.) would show 4.76% copper. This charge of 120 centumpondia in the cupellation furnace would normally make more than 110 centumpondia of litharge and 30 of hearth-lead, i.e., saturated furnace bottoms. The copper would be largely found in the silver-lead "which does not melt," at the margin of the crucible. These skimmings are afterward referred to as "thorns." It is difficult to understand what is meant by the expression that the silver which is in the copper is mixed with the remaining (reliquo) silver. The coppery skimmings from the cupellation furnace are referred to again in [Note 28, p. 539].
[Pg 523][20] A further amount of lead could be obtained in the first liquation, but a higher temperature is necessary, which was more economical to secure in the "drying" furnace. Therefore, the "drying" was really an extension of liquation; but as air was admitted the lead and copper melted out were oxidized. The products were the final residual copper, called by Agricola the "dried" copper, together with lead and copper oxides, called by him the "slags," and the scale of copper and lead oxides termed by him the "ash-coloured copper." The German metallurgists distinguished two kinds of slag: the first and principal one, the darrost, and the second the darrsöhle, this latter differing only in that it contained more impurities from the floor of the furnace, and remained behind until the furnace cooled. Agricola possibly refers to these as "more liquation thorns," because in describing the treatment of the bye-products he refers to thorns from the process, whereas in the description of "drying" he usually refers to "slags." A number of analyses of these products, given by Karsten, show the "dried" copper to contain from 82.7 to 90.6% copper, and from 9.4 to 17.3% lead; the "slag" to contain 76.5 to 85.1% lead oxide, and from 4.1 to 7.8% cuprous oxide, with 9 to 13% silica from the furnace bottoms, together with some other [Pg 524]impurities; the "ash-coloured copper" to contain about 60% cuprous oxide and 30% lead oxide, with some metallic copper and minor impurities. An average of proportions given by various authors shows, roughly, that out of 100 centners of "exhausted" liquation cakes, containing about 70% copper and 30% lead, there were about 63 centners of "dried" copper, 38 centners of "slag," and 61/2 centners of "ash-coloured copper." According to Karsten, the process fell into stages; first, at low temperature some metallic lead appeared; second, during an increasing temperature for over 14 to 15 hours the slags ran out; third, there was a period of four hours of lower temperature to allow time for the lead to diffuse from the interior of the cakes; and fourth, during a period of eight hours the temperature was again increased. In fact, the latter portion of the process ended with the economic limit between leaving some lead in the copper and driving too much copper into the "slags." Agricola gives the silver contents of the "dried" copper as 3 drachmae to 1 centumpondium, or equal to about 9 ozs. per ton; and assuming that the copper finally recovered from the bye-products ran no higher, then the first four charges (see note on p. [506]) would show a reduction in the silver values of from 95 to 97%; the 7th and 8th charges (note on p. [512]) of about 90%.
[21] If Roman weights, this would equal from 6,360 lbs. to 7,066 lbs.
[Pg 529][22] One half uncia, or three drachmae of silver would equal either 12 ozs. or 9 ozs. per ton. If we assume the values given for residual copper in the first four charges (note p. [506]) of 34 ozs., this would mean an extraction of, roughly, 65% of the silver from the exhausted liquation cakes.
[Pg 530][23] See [note 29, p. 540].
[Pg 533][24] Assuming Roman weights:
| 2 | centumpondia | = | 141.3 | lbs. |
| 21/2 | " | = | 176.6 | " |
| 3 | " | = | 211.9 | " |
| 31/2 | " | = | 248.2 | " |
| 6 | " | = | 423.9 | " |
[Pg 535][25] This description of refining copper in an open hearth by oxidation with a blast and "poling"—the gaarmachen of the Germans—is so accurate, and the process is so little changed in some parts of Saxony, that it might have been written in the 20th century instead of the 16th. The best account of the old practice in Saxony after Agricola is to be found in Schlüter's Hütte Werken (Braunschweig, 1738, Chap. CXVIII.). The process has largely been displaced by electrolytic methods, but is still in use in most refineries as a step in electrolytic work. It may be unnecessary to repeat that the process is one of subjecting the molten mass of impure metal to a strong and continuous blast, and as a result, not only are the impurities to a considerable extent directly oxidized and taken off as a slag, but also a considerable amount of copper is turned into cuprous oxide. This cuprous oxide mostly melts and diffuses through the metallic copper, and readily parting with its oxygen to the impurities further facilitates their complete oxidation. The blast is continued until the impurities are practically eliminated, and at this stage the molten metal contains a great deal of dissolved cuprous oxide, which must be reduced. This is done by introducing a billet of green wood ("poling"), the dry distillation of which generates large quantities of gases, which reduce the oxide. The state of the metal is even to-day in some localities tested by dipping into it the point of an iron rod; if it be at the proper state the adhering copper has a net-like appearance, should be easily loosened from the rod by dipping in water, is of a reddish-copper colour and should be quite pliable; if the metal is not yet refined, the sample is thick, smooth, and detachable with difficulty; if over-refined, it is thick and brittle. By allowing water to run on to the surface of the molten metal, thin cakes are successively formed and taken off. These cakes were the article known to commerce over several centuries as "rosetta copper." The first few cakes are discarded as containing impurities or slag, and if the metal be of good quality the cakes are thin and of a red colour. Their colour and thinness, therefore, become a criterion of purity. The cover of charcoal or charcoal dust maintained upon the surface of the metal tended to retard oxidation, but prevented volatilization and helped to secure the impurities as a slag instead. Karsten (Archiv., 1st series, p. 46) gives several analyses of the [Pg 536]slag from refining "dried" copper, showing it to contain from 51.7 to 67.4% lead oxide, 6.2 to 19.2% cuprous oxide, and 21.4 to 23.9 silica (from the furnace bottoms), with minor quantities of iron, antimony, etc. The "bubbles" referred to by Agricola were apparently the shower of copper globules which takes place upon the evolution of sulphur dioxide, due to the reaction of the cuprous oxide upon any remaining sulphide of copper when the mass begins to cool.
Historical Note.—It is impossible to say how the Ancients refined copper, beyond the fact that they often re-smelted it. Such notes as we can find are set out in the note on copper smelting ([note 42, p. 402]). The first authentic reference to poling is in Theophilus (1150 to 1200 A.D., Hendrie's translation, p. 313), which shows a very good understanding of this method of refining copper:—"Of the Purification of Copper. Take an iron dish of the size you wish, and line it inside and out with clay strongly beaten and mixed, and it is carefully dried. Then place it before a forge upon the coals, so that when the bellows act upon it the wind may issue partly within and partly above it, and not below it. And very small coals being placed round it, place the copper in it equally, and add over it a heap of coals. When by blowing a long time this has become melted, uncover it and cast immediately fine ashes of coals over it, and stir it with a thin and dry piece of wood as if mixing it, and you will directly see the burnt lead adhere to these ashes like a glue, which being cast out again superpose coals, and blowing for a long time, as at first, again uncover it, and then do as you did before. You do this until at length by cooking it you can withdraw the lead entirely. Then pour it over the mould which you have prepared for this, and you will thus prove if it be pure. Hold it with the pincers, glowing as it is, before it has become cold, and strike it with a large hammer strongly over the anvil, and if it be broken or split you must liquefy it anew as before. If, however, it should remain sound, you will cool it in water, and you cook other (copper) in the same manner." Biringuccio (III, 8) in 1540 describes the process briefly, but omits the poling, an essential in the production of malleable copper.
[Pg 538][26] Pompholyx and spodos were impure zinc oxides (see [note 26, p. 394]).
The copper flowers were no doubt cupric oxide. They were used by the Ancients for medicinal purposes. Dioscorides (V, 48) says: "Of flowers of copper, which some call the scrapings of old nails, the best is friable; it is gold-coloured when rubbed, is like millet in shape and size, is moderately bright, and somewhat astringent. It should not be mixed with copper filings, with which it is often adulterated. But this deception is easily detected, for when bitten in the teeth the filings are malleable. It (the flowers) is made when the copper fused in a furnace has run into the receptacle through the spout pertaining to it, for then the workmen engaged in this trade cleanse it from dirt and pour clear water over it in order to cool it; from this sudden condensation the copper spits and throws out the aforesaid flowers." Pliny (XXXIV, 24) says: "The flower, too, of copper (æris flos) is used in medicine. This is made by fusing copper, and then removing it to another furnace, where the repeated blast makes the metal separate into small scales like millet, known as flowers. These scales also fall off when the cakes of metal are cooled in water; they become red, too, like the scales of copper known as 'lepis,' by use of which the flowers of copper are adulterated, it being also sold for it. These are made when hammering the nails that are [Pg 539]made from the cakes of copper. All these methods are carried on in the works of Cyprus; the difference between these substances is that the squamae (copper scales) are detached from hammering the cakes, while the flower falls off spontaneously." Agricola (De Nat. Fos., p. 352) notes that "flowers of copper (flos æris) have the same properties as 'roasted copper.'"
[27] It seems scarcely necessary to discuss in detail the complicated "flow scheme" of the various minor bye-products. They are all re-introduced into the liquation circuit, and thereby are created other bye-products of the same kind ad infinitum. Further notes are given on:—
| Liquation thorns | Note | [28]. |
| Slags | " | [30]. |
| Ash-coloured copper | " | [29]. |
| Concentrates | " | [33]. |
| Cadmia | " | [32]. |
There are no data given, either by Agricola or the later authors, which allow satisfactory calculation of the relative quantities of these products. A rough estimate from the data given in previous notes would indicate that in one liquation only about 70% of the original copper came out as refined copper, and that about 70% of the original lead would go to the cupellation furnace, i.e., about 30% of the original metal sent to the blast furnace would go into the "thorns," "slags," and "ash-coloured copper." The ultimate losses were very great, as given before (p. [491]), they probably amounted to 25% of the silver, 9% copper, and 16% of the lead.
[28] There were the following classes of thorns:—
| 1st. | From liquation. |
| 2nd. | From drying. |
| 3rd. | From cupellation. |
In a general way, according to the later authors, they were largely lead oxide, and contained from 5% to 20% cuprous oxide. If a calculation be made backward from the products given as the result of the charge described, it would appear that in this case they must have contained at least one-fifth copper. The silver in these liquation cakes would run about 24 ozs. per ton, in the liquated lead about 36 ozs. per ton, and in the liquation thorns 24 ozs. per ton. The extraction into the liquated lead would be about 80% of the silver.
[Pg 540][29] The "ash-coloured copper" is a cuprous oxide, containing some 3% lead oxide; and if Agricola means they contained two unciae of silver to the centumpondium, then they ran about 48 ozs. per ton, and would contain much more silver than the mass.
[Pg 541][30] There are three principal "slags" mentioned—
| 1st. | Slag from "leading." |
| 2nd. | Slag from "drying." |
| 3rd. | Slag from refining the copper. |
From the analyses quoted by various authors these ran from 52% to 85% lead oxide, 5% to 30% cuprous oxide, and considerable silica from the furnace bottoms. They were reduced in the main into liquation cakes, although Agricola mentions instances of the metal reduced from "slags" being taken directly to the "drying" furnace. Such liquation cakes would run very low in silver, and at the values given only averaged 12 ozs. per ton; therefore the liquated lead running the same value as the cakes, or less than half that of the "poor" lead mentioned in [Note 17, p. 512], could not have been cupelled directly.
[Pg 542][31] See [Note 16, p. 511], for discussion of yellow and caldarium copper.
[32] This cadmia is given in the Glossary and the German translation as kobelt. A discussion of this substance is given in the note on p. [112]; and it is sufficient to state here that in Agricola's time the metal cobalt was unknown, and the substances designated cadmia and cobaltum were arsenical-cobalt-zinc minerals. A metal made from "slag" from refining, together with "base" thorns, would be very impure; for the latter, according to the paragraph on concentrates a little later on, would contain the furnace accretions, and would thus be undoubtedly zincky. It is just possible that the term kobelt was used by the German smelters at this time in the sense of an epithet—"black devil" (see [Note 21, p. 214]).
[33] It is somewhat difficult to see exactly the meaning of base (vile) and precious (preciosum) in this connection. While "base" could mean impure, "precious" could hardly mean pure, and while "precious" could mean high value in silver, the reverse does not seem entirely apropos. It is possible that "bad" and "good" would be more appropriate terms.
[Pg 543][34] The skimmings from the molten lead in the early stages of cupellation have been discussed in [Note 28, p. 539]. They are probably called thorns here because of the large amount of copper in them. The lead from liquation would contain 2% to 3% of copper, and this would be largely recovered in these skimmings, although there would be some copper in the furnace bottoms—hearth-lead—and the litharge. These "thorns" are apparently fairly rich, four unciae to the centumpondium being equivalent to about 97 ozs. per ton, and they are only added to low-grade liquation material.
[Pg 544][35] Particulis aeris tusi. Unless this be the fine concentrates from crushing the material mentioned, we are unable to explain the expression.
[36] This operation would bring down a button of antimony under an iron matte, by de-sulphurizing the antimony. It would seem scarcely necessary to add lead before cupellation. This process is given in an assay method, in the Probierbüchlein (folio 31) 50 years before De Re Metallica: "How to separate silver from iron: Take that silver which is in iron plechen (plachmal), pulverize it finely, take the same iron or plec one part, spiesglasz (antimony sulphide) one part, leave them to melt in a crucible placed in a closed windtofen. When it is melted, let it cool, break the crucible, chip off the button that is in the bottom, and melt it in a crucible with as much lead. Then break the crucible, and seek from the button in the cupel, and you will find what silver it contains."
BOOK XII.
reviously I have dealt with the methods of separating silver from copper. There now remains the portion which treats of solidified juices; and whereas they might be considered as alien to things metallic, nevertheless, the reasons why they should not be separated from it I have explained in the [second book].
Solidified juices are either prepared from waters in which nature or art has infused them, or they are produced from the liquid juices themselves, or from stony minerals. Sagacious people, at first observing the waters of some lakes to be naturally full of juices which thickened on being dried up by the heat of the sun and thus became solidified juices, drew such waters into other places, or diverted them into low-lying places adjoining hills, so that the heat of the sun should likewise cause them to condense. Subsequently, because they observed that in this wise the solidified juices could be made only in summer, and then not in all countries, but only in hot and temperate regions in which it seldom rains in summer, they boiled them in vessels over a fire until they began to thicken. In this manner, at all times of the year, in all regions, even the coldest, solidified juices could be obtained from solutions of such juices, whether made by nature or by art. Afterward, when they saw juices drip from some roasted stones, they cooked these in pots in order to obtain solidified juices in this wise also. It is worth the trouble to learn the proportions and the methods by which these are made.
I will therefore begin with salt, which is made from water either salty by nature, or by the labour of man, or else from a solution of salt, or from lye, likewise salty. Water which is salty by nature, is condensed and converted into salt in salt-pits by the heat of the sun, or else by the heat of a fire in pans or pots or trenches. That which is made salty by art, is also condensed by fire and changed into salt. There should be as many salt-pits dug as the circumstance of the place permits, but there should not be more made than can be used, although we ought to make as much salt as we can sell. The depth of salt-pits should be moderate, and the bottom should be level, so that all the water is evaporated from the salt by the heat of the sun. The salt-pits should first be encrusted with salt, so that they may not suck up the water. The method of pouring or leading sea-water into salt-pits is very old, and is still in use in many places. The method is not less old, but less common, to pour well-water into salt-pits, as was done in Babylon, for which Pliny is the authority, and in Cappadocia, where they used not only well-water, but also spring-water. In all hot countries salt-water and lake-water are conducted, poured or carried into salt-pits, and, being dried by the heat of the sun, are converted into salt.[1] While the salt-water contained in the salt-pits is being heated by the sun, if they be flooded with great and frequent showers of rain the evaporation is hindered. If this happens rarely, the salt acquires a disagreeable[2] flavour, and in this case the salt-pits have to be filled with other sweet water.
They construct the greater part of the fireplace of rock-salt and of clay mixed with salt and moistened with brine, for such walls are greatly hardened by the fire. These fireplaces are made eight and a half feet long, seven and three quarters feet wide, and, if wood is burned in them, nearly four feet high; but if straw is burned in them, they are six feet high. An iron rod, about four feet long, is engaged in a hole in an iron foot, which stands on the base of the middle of the furnace mouth. This mouth is three feet in width, and has a door which opens inward; through it they throw in the straw.
The wooden dipper holds ten Roman sextarii, and the cask holds eight dippers full[3]. The brine drawn up from the well is poured into such casks and carried by porters, as I have said before, into the shed and poured into a tub, and in those places where the brine is very strong it is at once transferred with the dippers into the caldron. That brine which is less strong is thrown into a small tub with a deep ladle, the spoon and handle of which are hewn out of one piece of wood. In this tub rock-salt is placed in order that the water should be made more salty, and it is then run off through a launder which leads into the caldron. From thirty-seven dippersful of brine the master or his deputy, at Halle in Saxony,[4] makes two cone-shaped pieces of salt. Each master has a helper, or in the place of a helper his wife assists him in his work, and, in addition, a youth who throws wood or straw under the caldron. He, on account of the great heat of the workshop, wears a straw cap on his head and a breech cloth, being otherwise quite naked. As soon as the master has poured the first dipperful of brine into the caldron the youth sets fire to the wood and straw laid under it. If the firewood is bundles of faggots or brushwood, the salt will be white, but if straw is burned, then it is not infrequently blackish, for the sparks, which are drawn up with the smoke into the hood, fall down again into the water and colour it black.
In different localities the salt is moulded into different shapes. In the baskets the salt assumes the form of a cone; it is not moulded in baskets alone, but also in moulds into which they throw the salt, which are made in the likeness of many objects, as for instance tablets. These tablets and cones are kept in the higher part of the third room of the house, or else on the flat bench of the same height, in order that they may dry better in the warm air. In the manner I have described, a master and his helper continue one after the other, alternately boiling the brine and moulding the salt, day and night, with the exception only of the annual feast days. No caldron is able to stand the fire for more than half a year. The master pours in water and washes it out every week; when it is washed out he puts straw under it and pounds it; new caldrons he washes three times in the first two weeks, and afterward twice. In this manner the incrustations fall from the bottom; if they are not cleared off, the salt would have to be made more slowly over a fiercer fire, which requires more brine and burns the plates of the caldron. If any cracks make their appearance in the caldron they are filled up with cement. The salt made during the first two weeks is not so good, being usually stained by the rust at the bottom where incrustations have not yet adhered.
Although salt made in this manner is prepared only from the brine of springs and wells, yet it is also possible to use this method in the case of river-, lake-, and sea-water, and also of those waters which are artificially salted. For in places where rock-salt is dug, the impure and the broken pieces are thrown into fresh water, which, when boiled, condenses into salt. Some, indeed, boil sea-salt in fresh water again, and mould the salt into the little cones and other shapes.
The purest and most transparent, because free from salt, is made if it is drawn off at the thickening stage, according to the following method. There are poured into the caldron the same number of amphorae of the solution as of congii of the lye of which I have already spoken, and into the same caldron is thrown as much of the already made saltpetre as the solution and lye will dissolve. As soon as the mixture effervesces and forms scum, it is transferred to a vat, into which on a cloth has been thrown washed sand obtained from a river. Soon afterward the plug is drawn out of the hole at the bottom, and the mixture, having percolated through the sand, escapes into a tub. It is then reduced by boiling in one or another of the caldrons, until the greater part of the solution has evaporated; but as soon as it is well boiled and forms scum, a little lye is poured into it. Then it is transferred to another vat in which there are small rods, to which it adheres and congeals in two days if there is but little of it, or if there is much in three days, or at the most in four days; if it does not condense, it is poured back into the caldron and re-boiled down to half; then it is transferred to the vat to cool. The process must be repeated as often as is necessary.
Others refine saltpetre by another method, for with it they fill a pot made of copper, and, covering it with a copper lid, set it over live coals, where it is heated until it melts. They do not cement down the lid, but it has a handle, and can be lifted for them to see whether or not the melting has taken place. When it has melted, powdered sulphur is sprinkled in, and if the pot set on the fire does not light it, the sulphur kindles, whereby the thick, greasy matter floating on the saltpetre burns up, and when it is consumed the saltpetre is pure. Soon afterward the pot is removed from the fire, and later, when cold, the purest saltpetre is taken out, which has the appearance of white marble, the earthy residue then remains at the bottom. The earths from which the solution was made, together with branches of oak or similar trees, are exposed under the open sky and sprinkled with water containing saltpetre. After remaining thus for five or six years, they are again ready to be made into a solution.
Pure saltpetre which has rested many years in the earth, and that which exudes from the stone walls of wine cellars and dark places, is mixed with the first solution and evaporated by boiling.
Thus far I have described the methods of making nitrum, which are not less varied or multifarious than those for making salt. Now I propose to describe the methods of making alum,[10] which are likewise neither all alike, nor simple, because it is made from boiling aluminous water until it condenses to alum, or else from boiling a solution of alum which is obtained from a kind of earth, or from rocks, or from pyrites, or other minerals.
If vitriol forms part of the aluminous ore, the material is dissolved in water without being mixed with urine, but it is necessary to pour that into the clear and pure solution when it is to be re-boiled. This separates the vitriol from the alum, for by this method the latter sinks to the bottom of the caldron, while the former floats on the top; both must be poured separately into smaller vessels, and from these into vats to condense. If, however, when the solution was re-boiled they did not separate, then they must be poured from the smaller vessels into larger vessels and covered over; then the vitriol separating from the alum, it condenses. Both are cut out and put to dry in the hot room, and are ready to be sold; the solution which did not congeal in the vessels and vats is again poured back into the caldron to be re-boiled. The earth which settled at the bottom of the caldron is carried back to the tanks, and, together with the ore, is again dissolved with water and urine. The earth which remains in the tanks after the solution has been drawn off is emptied in a heap, and daily becomes more and more aluminous in the same way as the earth from which saltpetre was made, but fuller of its juices, wherefore it is again thrown into the tanks and percolated by water.
Alum is also made from crude pyrites and other aluminous mixtures. It is first roasted in an enclosed area; then, after being exposed for some months to the air in order to soften it, it is thrown into vats and dissolved. After this the solution is poured into the leaden rectangular pans and boiled until it condenses into alum. The pyrites and other stones which are not mixed with alum alone, but which also contain vitriol, as is most usually the case, are both treated in the manner which I have already described. Finally, if metal is contained in the pyrites and other rock, this material must be dried, and from it either gold, silver, or copper is made in a furnace.
Vitriol[11] can be made by four different methods; by two of these methods from water containing vitriol; by one method from a solution of melanteria, sory and chalcitis; and by another method from earth or stones mixed with vitriol.
By the third method vitriol is made out of melanteria and sory. If the mines give an abundant supply of melanteria and sory, it is better to reject the chalcitis, and especially the misy, for from these the vitriol is impure, particularly from the misy. These materials having been dug and thrown into the tanks, they are first dissolved with water; then, in order to recover the pyrites from which copper is not rarely smelted and which forms a sediment at the bottom of the tanks, the solution is transferred to other vats, which are nine feet wide and three feet deep. Twigs and wood which float on the surface are lifted out with a broom made of twigs, and afterward all the sediment settles at the bottom of this vat. The solution is poured into a rectangular leaden caldron eight feet long, three feet wide, and the same in depth. In this caldron it is boiled until it becomes thick and viscous, when it is poured into a launder, through which it runs into another leaden caldron of the same size as the one described before.
The vitriolous pyrites, which are to be numbered among the mixtures (mistura), are roasted as in the case of alum, and dissolved with water, and the solution is boiled in leaden caldrons until it condenses into vitriol. Both alum and vitriol are often made out of these, and it is no wonder, for these juices are cognate, and only differ in the one point,—that the former is less, the latter more, earthy. That pyrites which contains metal must be smelted in the furnace. In the same manner, from other mixtures of vitriolic and metalliferous material are made vitriol and metal. Indeed, if ores of vitriolous pyrites abound, the miners split small logs down the centre and cut them off in lengths as long as the drifts and tunnels are wide, in which they lay them down transversely; but, that they may be stable, they are laid on the ground with the wide side down and the round side up, and they touch each other at the bottom, but not at the top. The intermediate space is filled with pyrites, and the same crushed are scattered over the wood, so that, coming in or going out, the road is flat and even. Since the drifts or tunnels drip with water, these pyrites are soaked, and from them are freed the vitriol and cognate things. If the water ceases to drip, these dry and harden, and then they are raised from the shafts, together with the pyrites not yet dissolved in the water, or they are carried out from the tunnels; then they are thrown into vats or tanks, and boiling water having been poured over them, the vitriol is freed and the pyrites are dissolved. This green solution is transferred to other vats or tanks, that it may be made clear and pure; it is then boiled in the lead caldrons until it thickens; afterward it is poured into wooden tubs, where it condenses on rods, or reeds, or twigs, into green vitriol.
Sulphur is made from sulphurous waters, from sulphurous ores, and from sulphurous mixtures. These waters are poured into the leaden caldrons and boiled until they condense into sulphur. From this latter, heated together with iron-scales, and transferred into pots, which are afterward covered with lute and refined sulphur, another sulphur is made, which we call caballinum.[12]
There remains glass, the preparation of which belongs here, for the reason that it is obtained by the power of fire and subtle art from certain solidified juices and from coarse or fine sand. It is transparent, as are certain solidified juices, gems, and stones; and can be melted like fusible stones and metals. First I must speak of the materials from which glass is made; then of the furnaces in which it is melted; then of the methods by which it is produced.
It is made from fusible stones and from solidified juices, or from other juicy substances which are connected by a natural relationship. Stones which are fusible, if they are white and translucent, are more excellent than the others, for which reason crystals take the first place. From these, when pounded, the most excellent transparent glass was made in India, with which no other could be compared, as Pliny relates. The second place is accorded to stones which, although not so hard as crystal, are yet just as white and transparent. The third is given to white stones, which are not transparent. It is necessary, however, first of all to heat all these, and afterward they are subjected to the pestle in order to break and crush them into coarse sand, and then they are passed through a sieve. If this kind of coarse or fine sand is found by the glass-makers near the mouth of a river, it saves them much labour in burning and crushing. As regards the solidified juices, the first place is given to soda; the second to white and translucent rock-salt; the third to salts which are made from lye, from the ashes of the musk ivy, or from other salty herbs. Yet there are some who give to this latter, and not to the former, the second place. One part of coarse or fine sand made from fusible stones should be mixed with two parts of soda or of rock-salt or of herb salts, to which are added minute particles of magnes.[16] It is true that in our day, as much as in ancient times, there exists the belief in the singular power of the latter to attract to itself the vitreous liquid just as it does iron, and by attracting it to purify and transform green or yellow into white; and afterward fire consumes the magnes. When the said juices are not to be had, two parts of the ashes of oak or holmoak, or of hard oak or Turkey oak, or if these be not available, of beech or pine, are mixed with one part of coarse or fine sand, and a small quantity of salt is added, made from salt water or sea-water, and a small particle of magnes; but these make a less white and translucent glass. The ashes should be made from old trees, of which the trunk at a height of six feet is hollowed out and fire is put in, and thus the whole tree is consumed and converted into ashes. This is done in winter when the snow lies long, or in summer when it does not rain, for the showers at other times of the year, by mixing the ashes with earth, render them impure; for this reason, at such times, these same trees are cut up into many pieces and burned under cover, and are thus converted into ashes.
This third furnace is rectangular, eight feet long and six feet wide; it also consists of two chambers, of which the lower has a mouth in front, so that firewood may be placed on the hearth which is on the ground. On each side of this opening in the wall of the lower chamber is a recess for oblong earthenware receptacles, which are about four feet long, two feet high, and one and a half feet wide. The upper chamber has two holes, one on the right side, the other on the left, of such height and width that earthenware receptacles may be conveniently placed in them. These latter receptacles are three feet long, one and a half feet high, the lower part one foot wide, and the upper part rounded. In these receptacles the glass articles, which have been blown, are placed so that they may cool in a milder temperature; if they were not cooled slowly they would burst asunder. When the vessels are taken from the upper chamber, they are immediately placed in the receptacles to cool.
Those who lack the first furnace in the evening, when they have accomplished their day's work, place the material in the pots, so that the heat during the night may melt it and turn it into glass. Two boys alternately, during night and day, keep up the fire by throwing dry wood on to the hearth. Those who have but one furnace use the second sort, made with three chambers. Then in the evening they pour the material into the pots, and in the morning, having extracted the fused material, they make the glass objects, which they place in the upper chamber, as do the others.
The second furnace consists either of two or three chambers, the first of which is made of unburnt bricks dried in the sun. These bricks are made of a kind of clay that cannot be easily melted by fire nor resolved into powder; this clay is cleaned of small stones and beaten with rods. The bricks are laid with the same kind of clay instead of lime. From the same clay the potters also make their vessels and pots, which they dry in the shade. These two parts having been completed, there remains the third.
The glass-makers make divers things, such as goblets, cups, ewers, flasks, dishes, plates, panes of glass, animals, trees, and ships, all of which excellent and wonderful works I have seen when I spent two whole years in Venice some time ago. Especially at the time of the Feast of the Ascension they were on sale at Morano, where are located the most celebrated glass-works. These I saw on other occasions, and when, for a certain reason, I visited Andrea Naugerio in his house which he had there, and conversed with him and Francisco Asulano.
END OF BOOK XII.