Tin

Tin is a metal full of history


Contents

  1. Introduction
  2. Some Metallurgical History
  3. Properties of Tin
  4. Chemistry of Tin
  5. Mineralogy and Production of Tin
  6. Uses of Tin
  7. References

Introduction

The symbol in the title is the alchemical symbol for tin, the sign of Jupiter.

The word "tin" is cognate with the German "Zinn," describing a soft, white metal with a low melting point. Its two main uses, both past and present, have been the coating of other metals, and in alloys. The alloy with copper, bronze, is of outstanding significance. In Latin, copper or any of its alloys were called aes. In Greek, the equivalent word was calkos. The essential thing was the ruddy color, different from that of gold or the white metals. Tin itself was kassiteros in Greek, but in Latin it was plumbum candidum, "white lead." Plumbum was the generic name for soft white metals with low melting points. Lead proper was plumbum nigrum, "black lead," because of the dark streak it gave when rubbed on something. The term stannum was mostly used for an alloy of lead and silver obtained in the winning of silver. Not until the 6th century was it applied to tin, but thereafter was commonly used in this sense.

The prettiest word for tin is the Spanish estaño. It evolved from stannum by first becoming stanno (the m never was strongly pronounced in Latin, and mostly nasalized the u). Then the Goths had problems with "st" so it became estanno. Finally, the double n merged into ñ when the spelling was regularized, and we have the final form. Italian stagno suffered a similar transformation (gn = ñ). The French étain is closer to the English (and Dutch) tin. Indeed, the second syllable would be prounounced just as "tin" would be. In Russian, tin is ólovo, while in Welsh it is alcam, truly different sounds.

The chemical ideas of the time considered lead, tin and anything like them as flavors of one basic substance. All you had to do was add the right spices to turn them into one another. The ores were earth, and lacked fire to make them shiny. Ores absorbed the fire and became metals. This kind of chemistry was worthless for metallurgy, but must be kept in mind when considering history. It was not to change until around 1800, and even then the fundamental reasons (electrical forces) were not known for another century. Our very useful knowledge of chemistry is a very recent development.

This article discusses the properties of tin, its uses in industry, and all the curious tin lore that could be found.

Some Metallurgical History

Metals are important enough in the human story to be used to characterize eras of development: Copper Age, Bronze Age, Iron Age. Nevertheless, relics are few, and our knowledge of the early exploitation of metals is almost nonexistent. In such an exigency, Science fabricates stories that seem plausible to plug the gap, and these are copied from author to author until they become a solid part of the edifice of knowledge.

Some metals can be picked up off the ground in metallic form, and hammered into attractive ornaments. Such native metals are gold (Au), silver (Ag), copper (Cu), platinum (Pt) and iron (Fe). These occurrences are very rare, but once they are found, the area is combed over diligently for more. How many nuggets have you discovered in your walks? None of these native metals are good for much more than trinkets. Native iron, which occurs (very rarely) in the earth as well as in meteorites, is very hard to work and would have to be admired as crusty lumps. In the New World, there was no metallurgy; the gold found by Cortez and Pizarro had to be laboriously collected, the copper ornaments were not coveted by the invaders, and everyone was unaware of the enormous wealth in silver that lay concealed in the black sulphate.

In the Old World, all the early civilizations--in China, India, Mesopotamia and Egypt--arose without metal, as Neolithic communities that settled, herded, farmed and built in mud brick. Copper, bronze and iron then appeared in succession, each granting significant advantages in tools and weapons. None of the appearances were random, and the techniques spread by diffusion, suggesting that the developments were the product of ingenuity, not chance, and very hard-won.

The story is that some gormless hunters built a campfire on copper ore, and, lo, copper ran forth. "By Orm, that's copper!" one exclaimed. Another hammered at it, enthusing "We've got copper, copper galore!" Now, the usual campfire is not hot enough to melt copper, and building the fire on the ore would not do much good, and besides copper ore does not present itself in large areas good for campfire hearths. If it were produced, it would look like the rest of the black clinker in the ashes. It is more likely (but we do not know) that the ore was thrown onto the fire because someone wanted to see what would happen. You do not see many campers throwing stones or earth (lumps of ore would be useless) on a fire, or combing through the ashes for valuable things.

Once you do start throwing crushed rocks on fires, there are many possibilities. Most of them do not produce metals. The rocks have to be very carefully selected. However, if you are in the middle of a mineralized area such as western Cornwall, many curious rocks are available, a good number of which will give you metal. Many ores (an ore is a mineral from which a metal can be profitably extracted) are sulphides, such as Cu2S, chalcocite. When you heat such a sulphide in air, the reaction 3Cu2S + 2O2 → 2Cu2O + 2SO2 takes place, creating cuprous oxide instead of cuprous sulphide. It is best not to stand downwind. This is the process of roasting an ore to drive off the sulphur.

If we did this on a goodly fire, the heat would have driven the volatiles out of the fuel (wood), leaving carbon, and then the air would have formed carbon monoxide: 2C + O2 → 2CO. Of course, in the usual fire this monoxide would burn to carbon dioxide, but here it can react with the cuprous oxide: Cu2O + CO → Cu2 + CO2. It is said to reduce the copper to the metallic state, which is done by adding electrons to it. This cannot happen unless the ore is finely enough divided for the monoxide to get to it. This process is called smelting. If the fire is hot enough (1083°C) the copper will melt and run out. The early metallurgist, however, normally got his copper as a clinkery mass that had to be hammered, annealed and rehammered before it looked like anything. This is said to have happened in Mesopotamia and Cyprus (in the West) around 3500 BC, but the date cannot be trusted. How can you date something when you really don't know what it was?

Although this looks easy, and we can understand it with our current knowledge of chemistry, in practice it was not a simple operation and required experience and technique: it was, indeed, an art. It is interesting that religion did not seem to play a very great role in creating metallurgy; only afterwards did priests see an opportunity to profit from superstitious awe. Bloody sacrifices were encouraged to prevent failures, and, of course, donations to priests would not be refused. The uselessness of religion in metallurgy seems to have been realized at an early date, and in classical times it played little role, in spite of the superstitious tendencies of the general population. In medieval times, malicious spirits were blamed for making ores barren, and for ruining the product, when the real problem was a useless theory of chemistry.

The campfire theory extends to the production of bronze. Now our worthy hunters build their fire on a mixed copper and tin ore, and out pours bronze. "By Orm, look at this stuff! It's hard and would take a good edge! We rule!" This is even less likely than the accidental discovery of copper, as was pointed out by the Hoovers. Copper and tin ores do not usually occur in the same places (they do in Cornwall, but bronze did not come from there). However, once you start throwing curious crushed rocks on fires to see what happens, you are likely to see other metals, of which lead, tin and iron are the most probable. Lead and tin will run out of any serious fire as liquids, surely making an early metallurgist's day. Iron will remain as a black, spongy clinker, since the melting point of iron is 1535°C, well above the capacities of any simple fire. In fact, when fires are blown by bellows (an early invention) too vigorous blowing would melt the iron, and it would absorb impurities like carbon, and so would be ruined. Iron is a special case, and its technique is complex.

Bronze weapons are said to have been found in Britain and dated from 1800 BC. This seems roughly correct, but I would like to know what the "bronze" is, and how the date was determined. Impure copper does not count as "bronze" in this respect. Bronze has to be made by design.

If you do this with mercury or zinc ores, the metal vaporizes instead, and you do not get any nice, bright liquid metal. These metals were discovered a bit later, in classical times, when someone examined the flues of furnaces that had been fed a suitable diet, and then the corresponding ores were identified. In early times it is possible that copper, tin and lead were all known. Bronze was probably always made deliberately by the addition of tin to molten copper. This required a bellows-blown furnace that would reach white heat. The properties of bronze depend very sensitively on the amount of added tin, so "accidental" alloys would not be very useful or promising.

From the beginnings of the use of metals from ores, then, the roasting and smelting processes have been used, with carbon as the reducing agent. At first, the carbon was from the charcoal created in the fire, but later it was always a purer product made by charcoal-burning. Metallurgy took place in the woods and the hills, its secrets carefully guarded to preserve monopoly, just as in the present day. Today, all the rich ores that taught mankind metallurgy are exhausted. If we had to start over again, it could not be done, at least for several million years, to allow weathering to work its wonders, or for new fluids to deposit primary ores.

Properties of Tin

Tin (Sn), atomic number 50, atomic weight 118.70, is a member of column IVA of the periodic table, five elements whose outer electron configuration is s2p2. Its mates are carbon (C), silicon (Si), germanium (Ge) and lead (Pb). These elements are remarkable in that they are commonly used in the pure form. Carbon is found as graphite, charcoal and coal; silicon and germanium are semiconductors, tin is found in tinplate, and lead as pipes and sheathing of electrical cables. Carbon is extraordiarily important as the basis of organic compounds, since it can form long covalently-bonded chains and rings. Carbon is nonmetallic, silicon and germanium intermediate, tin and lead metallic. It is useful to compare tin with the other elements in its column.

Tin has the unusually low melting point of 231.85°C, and the unusually high boiling point of 2260, 2270 or 2687°C, according to different authorities. This great range makes it easy to form alloys without loss in vaporization. Its latent heat of melting is 14.32 cal/g, its specific heat 0.055 cal/g-K, and its thermal conductivity is 0.1528 cal/cm-s-K. The electrical resistivity of tin is 11.5 μΩ-cm. The coefficient of linear thermal expansion is 16 x 10 per °C. Its tensile strength is low, about 2000 psi, and its Young's modulus is 5.9-7.8 x 106 psi. It is quite soft, Mohs 1.8 or Brinell 5.0 (1000 kg, 10 mm).

Tin exists in three allotropic forms. Below 18°C, the stable form is α-tin, or grey tin, with a diamond structure (like carbon, silicon and germanium) and a density of 5.765 g/cc. The lattice constant a = 0.6942 nm, and the melting point is 230°C. It is a semiconductor with a band gap of 0.08V. It is a crumbly gray nonmetal. From 18°C to 161°C, the stable form is β-tin, or white tin, a metal of tetragonal crystal structure and a density of 7.2984. This is the normal appearance of tin. The recrystallization to α-tin is very slow unless the temperature is lowered to -40°C or so, and then may take place in days. When this destroyed Russian organ pipes, it was thought to be the work of the "tin pest." Finally, from 161°C to the melting point, γ-tin has about the same density, but rhombic crystal form. Besides tin, only carbon (graphite and diamond), oxygen (oxygen and ozone) and phosphorus (red and white) exist in allotropic forms.

When β-tin is bent, it emits a sound called "tin cry" from the shearing movement between the crystal grains. This can more often be sensed by touch as a kind of grating rather than as an actual sound. Tin is remarkably lighter than the lead it resembles, which can be surprising when it is hefted.

Chemistry of Tin

Tin exhibits the oxidation states +2 and +4, like lead. In the +2 state, it is basic and behaves like a metal. In the +4 state, it is amphoteric and can behave in an acidic manner in alkaline solution. The oxidation state +2 is called stannous, and the +4 state is called stannic. Tin is soluble in dilute mineral acids, and in hot potassium hydroxide, but is not attacked by food acids and alkalies. An acid solution tends to preserve the stannous state, in which tin is a powerful reducing agent, happily furnishing two electrons to anything that wants them. An alkaline solution generally results in hydrolysis, and the formation of gelatinous hydrated oxides, such as Sn(OH)4, which can serve as a mordant, like the aluminium hydroxides.

The chlorides are important compounds. Stannous chloride, SnCl2, is a reducing agent. Its hydrate, SnCl2·H2O, called "tin salt," forms Sn(OH)Cl on hydrolysis. Anhydrous stannic chloride, SnCl4 is a liquid that boils at 114.1°C, recalling carbon tetrachloride, but reacting quite differently because of the amphoteric nature of tin. In water, the reaction is SnCl4 + 4H2O → 4HCl + Sn(OH)4. Stannic chloride can be made by treating tin cans with chlorine gas in the absolute absence of water. The chlorine does not attack the iron. SnCl4·5H2O is called "butter of tin," but should not be spread on your toast. Hydrochloric acid reacts with SnCl4 to form chlorostannic acid: 2HCl + SnCl4 → H2SnCl6. This weak acid can form salts, such as (NH4)2SnCl6, called "pink salt" although it is colorless.

Tin forms SnH4, stannane, after the example of methane. I can find no properties of this gas, only mention of its mere existence, but it must be curious. As an acidic element, tin forms H2SnO3, metastannic acid, and H2SnS3, thiostannic acid. A salt of thiostannic acid is important in qualitative analysis, where the reaction SnS2 + Na2S → Na2SnS3 is used to dissolve the sulphide so that tin can be separated from the other cations in its group. Tin forms unstable nitrates, Sn(NO3)2·20H2O, with an extraordinary amount of water of crystallization, Sn(NO3)4, that decomposes at 50°C, and SnO·Sn(NO3)2, which has the temerity to explode when heated.

Metallic tin can be regarded as safe, and presents no hazard of poisoning even when in contact with food. There is no vapor to worry about. Soluble tin compounds are, like all soluble compounds of heavy metals, not good snacks. Give warm soapy water or other emetic, and seek medical help. Emetics are no longer as heartily advised as before, since some poisons can cause damage going either way. This is not the case with most heavy metal poisons, however, which do not damage tissue on contact. Epsom salts will do no good, since stannous sulphate is soluble.

Mineralogy and Production of Tin

The primary (that is, originally deposited) tin ore is probably stannite, a mixed sulphide, Cu2FeSnS4, "tin pyrites," which is altered by supergene enrichment to cassiterite, SnO2, the heavy, dark "tinstone" that is found in river gravels as well as in veins. Cornwall was a notable and historic source of cassiterite, but the last mine has now closed in this small but interesting mining district. Much larger amounts were found in the gravels of Malaysia, Indonesia and Thailand, which supply "stream tin" or "Straits tin" from placer deposits. Until 1946, the Straits Settlements was the name of the area that is now Malaysia, and long the chief source of tin. Bolivia and China also contain economic deposits of vein ore, and Brazil and Russia have now become major producers as the traditional sources become depleted. Southeast Asia now produces about 35%, South America 30%, China and Russia 21% of the world's tin. Tin is rare, and will be long gone by the end of the century. The United States has little tin ore of any kind, only traces, and now imports over 85% of its needs. This figure would seem to be closer to 100%, but what is included is not specified in the statistics. In 1988, the U.S. smelted 1467 metric tons of tin from imported ores, recovered 15,249 tons as secondary tin (from tin cans), and imported 43,493 tons of metal. The average price was $4.41 per pound. The world production is about 200,000 tons annually, and an approximately equal amount is held in the U.S. strategic reserves.

The main suppliers of tin to the ancient world were the Phoenicians, who carried on a trade based on their mines and smelters in the Iberian peninsula, and (traditionally) on trade with Cornwall. Greek literature mentions the Cassiterides, the "tin islands," but just what these were is not clear. Cornwall is not an island. The nearby Scilly Isles are isles, but have no tin. It was probably just a mythological source for the tin brought by the Phoenicians. The Phoenician trade began before 1500 BC. It was probably the Phoenicians who spread tin, and with it bronze, around the Mediterranean.

The lean ores currently available must be treated to remove as much of the sulphides of lead, bismuth, antimony, zinc, silver, copper and iron as possible. These sulphides cannot be eliminated easily by gravity separation in water, since they are heavy like cassiterite. There has been some success with differential flotation, however. The ore is roasted to eliminate sulphides, and leached with hydrochloric acid to dissolve the iron, copper, bismuth and zinc impurities. Then it is treated with chlorine to form chlorides of lead, bismuth, antimony and silver, which are leached out with dilute acids.

The concentrated ore is then smelted in a blast furnace or a reverberatory furnace with coke or anthracite screenings to produce liquid tin. The slags generally contain a goodly amount of tin, and tin is lost in flue gases. The reverberatory furnace gives better recovery. The slag must be re-treated to recover the 10% to 25% of tin that it contains. The tin is refined pyrolytically or electrolytically. The electrolytic process was developed by Asarco after World War I, and resembles the refining of copper.

The interruption of tin supplies early in World War II led to panicked construction of a tin smelter at Texas City, Texas, the Longhorn Smelter, to use low-grade ore from Bolivia that was less subject to interception. Construction began in October 1941, and the first ingots were poured in April, 1942. The Texas site also had ample hydrochloric acid, a by-product of neighboring industries, and natural gas for fuel. I do not know the current status of this smelter, but it would have been very difficult to operate it economically after the war in the face of international competition. Bolivia has been able to rely on cocaine in the absence of ore sales, so the U.S. supports it as a Good Neighbor either way.

Uses of Tin

The chief use of tin, by tonnage, was for years the manufacture of tin plate. This is thin sheet steel with a coating of tin only about 2.3 μm thick. The tin adheres strongly and uniformly to the steel, protecting it from attack. A typical tin plate alloy is 88 Sn, 7.5 Pb, 4 Cu, 0.5 Sb. Cans made of tinplate are used for food products, since the tin was not attacked by most foods in the absence of air (if it were, glass jars or lacquer would have to be used). On examining modern cans, I find that other coatings are now used in many cases, though tin is still found. If it is really tinplate, the individual crystals can be seen in the coating, and the coating is white and attractive. I found that pineapple comes in real tin cans. The tin used in tinplate is not lost, since it can be reclaimed using chlorine. However, only a part of all cans can be recycled in this way, since the collection procedures in small towns and the country are unsuitable. Tin plate is used in many ways, such as roofing and as the "tin" or telltale in a squash court.

Tin plate was originally made by the "hot dip" process in which clean iron strip is passed through molten tin. Practically all tin plate is now made electrolytically, since the thickness can be better controlled. Tin is electrolytically plated from an acid solution of SnSO4, or from an alkaline solution of a stannate. Tin does not give cathodic protection to steel, as zinc does, so it is very important that the tin coating be continuous. Any pinholes will corrode easily. Fortunately, tin gives a very complete cover. Although food acids will not attack tin in the absence of air, the presence of air may lead to attack. This can often be seen if food is left in an open can for a while.

The thickness of tin plating is specified commercially by the weight of tin used per base box. A base box consists of 112 sheets, 14" x 20", or 62,720 sq. in., counting both sides. One pound of tin per base box corresponds to a thickness 0f 59 μin. The usual tin plate is 1.0-2.5 lb. tin per base box.

Iron cannot be coated with lead by hot-dipping, since lead does not wet iron. A good coating does result, however, if some metal is added that wets both iron and lead, such as tin, or if the steel is given a thin coat of copper. This is also the reason why solder must contain tin, in addition to its lowering of the melting point. Terne plate is a covering of tin and lead alloy, 75 Pb and 25 Sn a typical composition. The metal covered is usually heavy-gauge steel, not the thin strip used for tinplate. Lead gives good resistance against sulphuric acid. Tin plate can easily be given a coating of lead by hot dipping.

A tinsmith is a worker in tinplate, who cuts, embosses and forms the metal, and solders seams in it. He may also repair leaks in tinplate items by soldering, or by applying a patch with solder. Excellent such work was done in colonial Mexico, together with silver work. We also have the tinker, which may be related, but the Oxford Concise says etym. dub., unfortunately. A tinker makes small repairs, which may include patching and soldering, which is called tinkering. The name has become attached to the Irish travellers, of whom many are itinerant tinkers. The word is recorded from the 13th century (early for English), and has no cognate in Dutch or German.

The Romans often dipped copper dishes into molten tin to give a better taste to the drinks taken with the tinned items. Anyone who has drunk a Moscow Mule, vodka and ginger beer, in a copper mug, will see the point. The metallic taste of copper is not always desired. Copper also reacts with the fillings in your teeth, which are higher on the electrochemical scale.

Molten tin has been used to cast window glass, in the Pilkington float glass process. The glass is poured out on the hot tin, which gives it a smooth surface. Tin is heavier than glass, has a high boiling point, low vapor pressure, and does not react with the constituents of glass.

At the beginning of World War II, tin was not only widely used in tinplate, but as tinfoil and tin collapsible tubes as well. The metal in this latter use could be an alloy, but it would be mainly tin. A common tinfoil alloy was 92 Sn, 8 Zn. Cigarettes, sweets and chewing gum came wrapped in tinfoil, while toothpaste was supplied in tin tubes. These were actually very good and attractive containers. When the tin supply was threatened, these uses appeared nonessential, and a search was mounted for substitutes. I cannot find the composition of the substitute alloy used for toothpaste tubes, but it could well be a lead alloy, since the toothpaste would keep the lead in an insoluble form. Aluminum foil has replaced tinfoil generally. It was almost as satisfactory, although not as pleasantly soft as tinfoil, but could be rolled out as thinly. Metal toothpaste tubes were replaced by plastic (probably in a lead scare), and they really do not do as well, refusing to stay compressed. The old metal tubes rolled up nicely.

One encyclopedia says that tin is used in toothpaste. Probably the same way glass is used in jam.

The use of tin that was essential to the war effort was its use in alloys. It is in this use that there are few alternatives to tin. A large amount of tin is used in solders, of which it is the principal ingredient, typically 60 Sn 40 Pb. The phrase "to tin a soldering iron" means to flux it, apply solder, and wipe until it is evenly coated. For more information on solders, see Lead. Pewter is an alloy ranging from pure tin to 74 Sn, 20 Pb, 3 Cu, 3 Sb. Two popular alloys have 6 Sb, 2 Cu and 4 Sb, 2 Cu, with the rest tin, or tin and lead. Pure tin is rather too soft, and the alloy hardens it a little. It is an easily workable metal for pots, platters and plates, an inexpensive substitute for silver. At today's prices for tin, it is not much less expensive than silver, however. Another important use is in bearing metals, for which the same article should be consulted. However, the principal alloy of tin is its alloy with copper, bronze. This was one of the first alloys used by man, and the first to be made on purpose to critical specifications. We have already mentioned that it is very unlikely that bronze was discovered by accident.

The strength of a bronze increases with the tin content, while its toughness and malleability decrease. The strength is a maximum at about 30%, and rapidly decreases for more tin, but at this point the bronze is hard and brittle. There is an intermetallic compound Cu3Sn that has something to do with this. For coinage, 95 Cu, 5 Sn is a good alloy, still looking like copper, but with added strength and hardness that allow it to stand up in circulation. The alloy 95 Cu, 4 Sn, 1 Zn is also used. The U.S. large cents that were struck in 1808-1814 used a purer copper than those before and after, and they wore noticeably badly. 90 Cu, 10 Sn makes a strong, tough alloy called "gun metal" from an obvious application. With more tin than 85 Cu, 15 Sn, the bronze is called "bell metal" because its hardness makes a live, resonant bell. The Liberty Bell, cast in London, cracked when rung in Philadelphia, showing the drawbacks of high-tin bronze. My great-grandfather leaped over the barrier and rang it again at the Centennial Exhibition in 1876, futher damaging it. 67 Cu and 33 Sn give "speculum metal," a very hard white alloy (mainly Cu3Sn) that makes an excellent mirror when polished. This is the range of useful bronze alloys, and shows the general trend of their properties. The exact proportions of Cu and Sn in any particular alloy may vary from the numbers quoted, of course. Bronze is significantly improved by small additions of phosphorus, which de-oxygenates the alloy and cleans up the grain boundaries. This is the main effect of the addition, not any addition of phosphorus to the alloy, which is deleterious. Phosphor bronze is an excellent bronze, often used for springs. The very hard intermetallic compound Cu3P is formed with higher phosphorus content, and makes a brittle bronze with only special uses. The term "bronze" is used for some alloys that contain no, or very little, tin, to show that they have superior qualities. Aluminium bronze, 90 Cu, 10 Al is an example (and a very good alloy, besides).

A typical bronze for English "copper" coins was 97 Cu, 2.5 Zn, 0.5 Sn. U.S. coins contained no tin, unless the alloy for the early half-cents and cents, imported from England, contained a little tin. English copper coins were traditionally the halfpenny and the farthing (1/4 penny). From 1684 to 1692 halfpennies and farthings were issued in tin, with the date and the legend "nummorum famulus" ("servant of the coinage") on the rim. Some had a copper plug in the middle, to retain the link with copper. This was the only use I can find of tin in coinage, since tin would not not be hard enough for circulation, and it was also costly. Not even the Straits Settlements or Malaya has issued tin coins. Incidentally, the penny was a silver coin down to 1797, when it became the familiar large copper coin, last issued in 1967. The phrase "bright as a penny" referred to the small, shiny silver penny, now only found in Maundy Money. It certainly does not refer to a copper penny or cent, and especially not to the dingy zinc cents of today's U. S. money.

Tin is also preferred for organ pipes. It is said to give a better sound than aluminium or zinc. Cymbals are made from a high-tin bronze, 80-85 Cu, 15-20 Sn, which is a bell metal and gives a bright sound.

Ancient Egypt was very poor in metals, which had to be imported or scratched from a few mines in the Sinai. Copper weapons, hardened only by the impurities that happened to be in the metal, were no match for the bronze weapons coming from Mesopotamia. The Second Intermediate Period, 1759-1539 BC, may have been a time of weakness in the face of the bronze of the Hyksos, who established their capital in Avaris. Ahmose, King of Thebes and founder of the 17th dynasty finally overcame Avaris in 1530 BC, perhaps with the new bronze weapons glittering in his army. The Egyptian histories that I have say nothing about copper or brass, in spite of its undoubted importance, though ceremonial weapons of gold and copper are pictured. These times are called "Middle Bronze Age," though what this means in terms of Egypt is not clear. Archaeologists are not very careful about their chemistry or metallurgy. It does seem to be the time that the Phoenician trade in tin rose from obscurity. Tin was the secret weapon of the time, which could make hard, sharp weapons. Homer's Trojan War was fought with bronze weapons and armor.

Bronze itself finally fell before the warlike iron of the Hittites and the Celts. Iron could be hardened after the weapon was formed, and could make a weapon with a hard edge and a tough core, which would shatter a bronze sword. The Dorian Greeks were armed with steel, which overcame the bronze-wielding Mycenaeans. The properties of bronze were determined mainly by the alloy, and a hard alloy like weapons bronze could not be work-hardened by hammering, as iron could. Copper had been hardened in this way, but even so was no match for bronze or iron. Now bronze was mainly used for statuary of high quality.

References

Properties of tin and its compounds are found passim in handbooks such as the Handbook of Chemistry and Physics, Lange's Handbook of Chemistry, and Kent's Mechanical Engineer's Handbook.

G. Agricola, De Re Metallica (1556). H. C. Hoover and L. H. Hoover, transl. (New York: Dover, 1950).

W. N. Jones, Inorganic Chemistry (Philadelphia: Blakiston, 1949), Chapter 31.

J. L. Bray, Non-Ferrous Production Metallurgy (New York: John Wiley & Sons, 1947), Chapter 23.

R. A. Higgins, Engineering Metallurgy, 3rd ed. (London: The English Universities Press, 1971).


Return to Physics Index

Composed by J. B. Calvert
Created 12 November 2002
Last revised 4 December 2002