De Re Metallica
Georg Agricola
 The book consists of a preface and twelve chapters, labelled books I to XII, without titles. It also has numerous woodcuts that provide annotated diagrams illustrating equipment and processes described in the text. Agricola addresses the book to prominent German aristocrats, the most important of whom were Maurice, Elector of Saxony and his brother Augustus, who were his main patrons. He then describes the works of ancient and contemporary writers on mining and metallurgy, the chief ancient source being Pliny the Elder. Agricola describes several books contemporary to him, the chief being a booklet by Calbus of Freiberg in German. The works of alchemists are then described. Agricola does not reject the idea of alchemy, but notes that alchemical writings are obscure and that we do not read of any of the masters who became rich. He then describes fraudulent alchemists, who deserve the death penalty. Agricola completes his introduction by explaining that, since no other author has described the art of metals completely, he has written this work, setting forth his scheme for twelve books. Finally, he again directly addresses his audience of German princes, explaining the wealth that can be gained from this art. This book consists of the arguments used against the art and Agricola's counter arguments. He explains that mining and prospecting are not just a matter of luck and hard work; there is specialized knowledge that must be learned. A miner should have knowledge of philosophy, medicine, astronomy, surveying, arithmetic, architecture, drawing and law, though few are masters of the whole craft and most are specialists. This section is full of classical references and shows Agricola's classical education to its fullest. The arguments range from philosophical objections to gold and silver as being intrinsically worthless, to the danger of mining to its workers and its destruction of the areas in which it is carried out. He argues that without metals, no other activity such as architecture or agriculture are possible. The dangers to miners are dismissed; most deaths and injuries are caused by carelessness and other occupations are hazardous too. Clearing woods for fuel is advantageous as the land can be farmed. Mines tend to be in mountains and gloomy valleys with little economic value. The loss of food from the forests destroyed can be replaced by purchase from profits, and metals have been placed underground by God and man is right to extract and use them. Finally, Agricola argues that mining is an honorable and profitable occupation. This book describes the miner and the finding of veins. Agricola assumes that his audience is the mine owner, or an investor in mines. He advises owners to live at the mine and to appoint good deputies. It is recommended to buy shares in mines that have not started to produce as well as existing mines to balance the risks. The next section of this book recommends areas where miners should search. These are generally mountains with wood available for fuel and a good supply of water. A navigable river can be used to bring fuel, but only gold or gemstones can be mined if no fuel is available. The roads must be good and the area healthy. Agricola describes searching streams for metals and gems that have been washed from the veins. He also suggests looking for exposed veins and also describes the effects of metals on the overlying vegetation. He recommends trenching to investigate veins beneath the surface. He then describes dowsing with a forked twig although he rejects the method himself. Finally he comments on the practice of naming veins or shafts. This book is a description of the various types of veins that can be found. There are 30 illustrations of different forms of these veins, forming the majority of Book III. Agricola also describes a compass to determine the direction of veins and mentions that some writers claim that veins lying in certain directions are richer, although he provides counter-examples. He also mentions the theory that the sun draws the metals in veins to the surface, although he himself doubts this. Finally he explains that gold is not generated in the beds of streams and rivers and east-west streams are not more productive than others inherently. Gold occurs in streams because it is torn from veins by the water. This book describes how an official, the Bergmeister, is in charge of mining. He marks out the land into areas called meers when a vein is discovered. The rest of the book covers the laws of mining. There is a section on how the mine can be divided into shares. The roles of various other officials in regulating mines and taxing the production are stated. The shifts of the miners are fixed. The chief trades in the mine are listed and are regulated by both the Bergmeister and their foremen. This book covers underground mining and surveying. When a vein below ground is to be exploited a shaft is begun and a wooden shed with a windlass is placed above it. The tunnel dug at the bottom follows the vein and is just big enough for a man. The entire vein should be removed. Sometimes the tunnel eventually connects with a tunnel mouth in a hill side. Stringers and cross veins should be explored with cross tunnels or shafts when they occur. Agricola next describes that gold, silver, copper and mercury can be found as native metals, the others very rarely. Gold and silver ores are described in detail. Agricola then states that it is rarely worthwhile digging for other metals unless the ores are rich. Gems are found in some mines, but rarely have their own veins, lodestone is found in iron mines and emery in silver mines. Various minerals and colours of earths can be used to give indications of the presence of metal ores. The actual mineworking varies with the hardness of the rock, the softest is worked with a pick and requires shoring with wood, the hardest is usually broken with fire. Iron wedges, hammers and crowbars are used to break other rocks. Noxious gases and the ingress of water are described. Methods for lining tunnels and shafts with timber are described. The book concludes with a long treatise on surveying, showing the instruments required and techniques for determining the course of veins and tunnels. Surveyors allow veins to be followed, but also prevent mines removing ore from other claims and stop mine workings from breaking into other workings. This book is extensively illustrated and describes the tools and machinery associated with mining. Handtools and different sorts of buckets, wheelbarrows and trucks on wooded plankways are described. Packs for horses and sledges are used to carry loads above ground. Agricola then provides details of various kinds of machines for lifting weights. Some of these are man-powered and some powered by up to four horses or by waterwheels. Horizontal drive shafts along tunnels allow lifting in shafts not directly connected to the surface. If this is not possible treadmills will be installed underground. Instead of lifting weights similar machines use chains of buckets to lift water. Agricola also describes several designs of piston force pumps which are either man or animal powered or powered by waterwheels. Because these pumps can only lift water about 24 feet batteries of pumps are required for the deepest mines. Water pipe designs are also covered in this section. Designs of wind scoop for ventilating shafts or forced air using fans or bellows are also described. Finally ladders and lifts using wicker cages are used to get miners up and down shafts. This book deals with assaying techniques. Various designs of furnaces are detailed. Then cupellation, crucibles, scorifiers and muffles are described. The correct method of preparation of the cupels is covered in detail with beech ashes being preferred. Various other additives and formulae are described, but Agricola does not judge between them. Triangular crucibles and scorifiers are made of fatty clay with a temper of ground up crucibles or bricks. Agricola then describes in detail which substances should be added as fluxes as well as lead for smelting or assaying. The choice is made by which colour the ore burns out which gives an indication of the metals present. The lead should be silver-free or be assayed separately. The prepared ore is wrapped in paper, placed on a scorifier and then placed under a muffle covered in burning charcoal in the furnace. The cupel should be heated at the same time. The scorifier is removed and the metal transferred to the cupel. Alteratively the ore can be smelted in a triangular crucible, and then have lead mixed with it when it is added to the cupel. The cupel is placed in the furnace and copper is separated into the lead which forms lithage in the cupel leaving the noble metal. Gold and silver are parted using an aqua which is probably nitric acid. Agricola describes precautions for ensuring the amount of lead is correct and also describes the amalgamation of gold with mercury. Assay techniques for base metals such as tin are described as well as techniques for alloys such as silver tin. The use of a touchstone to assay gold and silver is discussed. Finally detailed arithmetical examples show the calculations needed to give the yield from the assay. In this book Agricola provides a detailed account of beneficiation of different ores. He describes the processes involved in ore sorting, roasting and crushing. The use of water for washing ores is discussed in great detail, e.g. the use of launders and washing tables. Several different types of machinery for crushing ore and washing it are illustrated and different techniques for different metals and different regions are described. This book describes smelting, which Agricola describes as perfecting the metal by fire. The design of furnaces is first explained. These are very similar for smelting different metals, constructed of brick or soft stone with a brick front and mechanically driven bellows at the rear. At the front is a pit called the fore-hearth to receive the metal. The furnace is charged with beneficiated ore and crushed charcoal and lit. In some gold and silver smelting a lot of slag is produced because of the relative poverty of the ore and the tap hole has to be opened at various times to remove different slag materials. When the furnace is ready, the forehearth is filled with molten lead into which the furnace is tapped. In other furnaces the smelting can be continuous, and lead is placed into the furnace if there is none in the ore. The slag is skimmed off the top of the metal as it is tapped. The lead containing the gold is separated by cupellation, the metal rich slags are re-smelted. Other smelting processes are similar, but lead is not added. Agricola also describes making crucible steel and distilling mercury and bismuth in this book. Agricola describes parting silver from gold in this book by using acids. He also describes heating with antimony sulphide (stibium), which would give silver sulphide and a mixture of gold and antimony. The gold and silver can then be recovered with cupellation. Gold can also be parted using salts or using mercury. Large scale cupellation using a cupellation hearth is also covered in this book This book describes separating silver from copper or iron. This is achieved by adding large amounts of lead at a temperature just above the melting point of lead. The lead will liquate out with the silver. This process will need to be repeated several times. The lead and silver can be separated by cupellation. This describes the preparation of what Agricola calls "juices": salt, soda, nitre, alum, vitriol, saltpetre, sulphur and bitumen. Finally glass making is covered. Agricola seems less secure about this process. He is not clear about making glass from the raw ingredients but clearer about remelting glass to make objects.