The story of copper

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Foreword

Telling the story of a metal so old and yet so modern in its applications has been a fascinating task. My hope is that the printed page will carry over to the reader some of the enduring romance of copper and that every copper-containing object that comes within his view will have a new background.

Necessarily there is little in the following pages that is not more fully told in some frankly technical book. The bulk of the material presented is, like the processes and uses that are described, the common heritage of mankind. As Herbert Hoover says in an introduction to one of his books: ‘‘If any may think that there is insufficient reference to previous writers let him endeavor to find to whom the origin of our methods should be credited.’’ I have, however, attempted to include in the reading references the principal sources of more detailed and technical information on copper.

In gathering the material for this book I have had the aid and encouragement of so many people that it would be difficult to thank them all. I am especially erateful to Dr. Edwin E. Slosson, director of Science Service, for his constant advice and criticism and the models of popular science writing that are furnished in his books. I want to acknowledge the cooperation that I have received from Mrs. Davis in the writing vii

Vill FOREWORD of this book. Without her encouragement, without her collaboration on the portions of the volume that treat of chemistry and art, without her constant aid in checking the information and typing the manuscript, the completion of this book would have been impossible. Among those to whom I am especially erateful for advice, information, and criticism are: Dr. Walter Hough of the Smithsonian Institution, Dr. T. T. Read of the United States Bureau of Mines, Dr. W. F. Meggers, Dr. G. K. Burgess and Dr. H. 8. Rawdon of the United States Bureau of Standards, and Captain H. A. C. Jenison of the United States Geological Survey.

Watson Davis.

Introduction

One who is writing the history of copper does not have to arouse an interest in the subject. He has only to maintain and extend it.

For every one knows copper, however little he may know about it. The first object to attract the infant eye was very likely the brass knob of a bed or door. He early learned the monetary value of the metal by finding that it was legal tender for saccharine delights at the candy-shop or slot-machine.

So also in the childhood of the race was copper the first known of the useful metals. Some savage scientist, unknown to fame, picked up a piece of jagged red rock that seemed more serviceable as a knife than the familiar flake of flint. But when he tried to sharpen the edge with a stone hammer he found that instead of _ chipping off in little shell-shaped scales, the strange material gave way beneath the hammer-blows without breaking and so could be beaten into any desired form.

We may imagine the pride with which the prehistoric inventor exhibited his new-fangled knife or spear-head to his tribesmen, but we may also surmise that they laughed at him for carrying around such a queer contraption, and that when he demonstrated its superiority over flint he was robbed of his invention by some less original but stronger warrior. For we cannot suppose that troglodyte society was so superior to ix a INTRODUCTION ours that an inventor would then meet any better fate than he does nowadays.

Comparatively few people know how beautiful copper is because comparatively few people have ever really seen it. What most have seen is but the painted face of copper, the mask it puts on when exposed to the world. To see the metal as it really is one must strip it of its concealing coat by heating it to redness in a glass tube through which hot hydrogen gas is streaming. Then the copper is revealed as a shining silvery metal, delicately tinted with pink, like the inner petals of a rose, less gaudy than gold, less steely than platinum.

But draw the copper from the closed tube and let a breath of air strike it and instantly a red blush spreads over its face, deepening to a red flush as a baby’s skin burns in a seaside sun. This soon darkens to a dull bronze, and further action of the air and moisture gives it a greenish or bluish tint. This fine patina is highly esteemed by artists and antiquarians on roofs and statues, but our municipal authorities call it ‘‘verdigris’’ and scratch it off occasionally with a sand-blast. They had better leave it on for both esthetic and economic reasons, for the bare metal cannot stand exposure, and no paint is more protective than this that is made by the atmospheric agencies against which protection is sought. Coins and castings, coated with the patina, are preserved intact for thousands of years though buried in the damp soil where iron implements would soon vanish in a heap of rust. :

The readiness with which copper forms affinities with various elements gave it the name of ‘‘the mere-

INTRODUCTION x1 tricious metal,’’ as the alchemists called it. But this very versatility has its value for human needs, since copper in combination assumes many beautiful and useful forms. The greens and blues of malachite and azurite are gorgeous as any gems, yet they may be had in masses large enough to make table-tops and mantelpieces. Glass and pottery get various hues from traces of copper, and ‘‘blue vitriol’’ is equally familiar to the electrician and to the horticulturist.

Copper is a good mixer. It enlarges its field of usefulness by alliances with other metals. Tin gives it the hardness of bronze. Zine gives it the golden glitter of brass. With nickel and zinc it makes a passable silver. With aluminum, which man has lately learned to extract from common clay, it forms new and useful alloys. The noble metals, gold and silver, in their proudest capacity as coins and jewelry gain strength by combination with the more plebeian copper.

Copper got its fame from the fairest of the goddesses, who chose it as the metal for her mirror. This was, it must be confessed, ‘‘Hobson’s choice,’’ for Venus is older than she looks, and when she rose from the sea, somewhere off the island of Cyprus, her first request was for a looking-glass that she might see for herself the reason for the admiration she perceived in all men’s eyes. She was not content like Narcissus with the pallid reflection of a pool, which besides could not be carried around with her, and so she sought for a suitable metal. There were only two known at the time, gold and copper. Gold she rejected; not, we must assume, on the ground of expense, for Venus has never lacked admirers eager to xi INTRODUCTION pay for her luxuries, but probably because gold cast a sallow tinge on her countenance, while copper brightened the tint of her auburn locks and endowed her cheeks with a blush like that of modest maidens.

Anyhow the looking-glass of the Cyprian Aphrodite became the symbol of her sex and is still to be found as such ? in our modern manuals of botany and zoology.

The cyprium from the Cyprian isle became the cuprum of the Romans and the copper of the English, and the metal from which was fashioned the jewelry of goddesses and queens was made into pots and pans and cheapest of coins. A copper button that was proudly worn by a Pharaoh of 4400 3.c, has been found in an Egyptian tomb, but it is not nearly so elegant as the buttons that the elevator-boy laa displays on his uniform.

‘“Not worth a copper,’’ is the nadir of value, yet copper is worth much to the world and never more than now in this Age of Electricity. Light and power are conveyed to our cities and homes by conduits of metallic wires through which flow streams of minute electrons as water flows through pipes. But it makes a great difference in the freedom of the flow what metal is used for the wire. Here copper comes into play, for its conductivity is almost as good as that of silver and much better than iron. A pure copper wire will convey five and three quarters times as much current as an iron wire of the same diameter.

But the copper must be pure. Even the minutest admixture of some other element will impede the electrical current just as a little dirt in a water-pipe

INTRODUCTION X1il will keep us standing in the cold waiting for the bathtub to fill up. Copper is almost human in its sensitiveness to poisons, Arsenic to the amount of 0.0013 per cent will lower the electrical conductivity of a copper wire by 1 per cent. This infinitesimal amount of arsenic, little more than one part in a hundred thousand, would therefore reduce the range of the telephone wire from a hundred miles to ninety-nine and add correspondingly to the cost of service. So the electricians have demanded of the refiners delivery in thousand-ton lots of copper more free from foreign elements than that which used to pass in the laboratory as ‘‘chemically pure.’’

If the cloud of smoke is to be lifted from our cities, if our factories are to be made clean and our homes convenient, by the substitution of electric power for coal burning, it will be by aid of this humble element. Copper is not so conspicuous as steel yet it is almost as indispensable to the maintenance of modern civilization. Itis to increase the popular appreciation of the importance of copper that this book has been written. Here my colleague in Science Service, Mr. Watson Davis, has told ‘‘The Story of Copper’’ in a way to interest those who have no special knowledge of chemistry or concern with metallurgy. Yet I think even those who consider themselves well informed on the subject will find some things new to them as they turn over the pages.

Epwin EK. Stosson Director of Science Service, Washington.

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CHAPTER

Contents

Man’s Bronze Key to CIvmnizaATION . THE GENESIS OF COPPER

THe EartH’s HERITAGE OF COPPER WINNING METAL FROM THE HartTH From Eartu to Inegors

CopPER’sS INSIDE STORY .

Chapter II The Genesis Of Copper

In the beginning, perhaps, all matter was the same. There was no copper. Clouds of stuff, many, many times less dense than our earthly clouds of to-day, floated aimless through universal space, which was and still is cold, lifeless, and void. By processes that our astronomers are only now beginning to understand, nebule were converted into giant stars, like Betelgeuze, deep red, larger than our whole solar system but still much less dense than our star, the sun; then after countless eons these became whiter stars, and later they cooled to red again. In some rare cases at some auspicious time a few of these stars unburdened themselves of part of their substance and formed a circling, dependent company of planets. One of these —and, in fact, the only one that we are sure does exist—is the solar system of which our earth is one of the members.

What is copper metal now may have been something else in the beginning. Why we think this was so is another story, which will be told later. After more countless eons one of these revolving planets, our earth, arrived at the point in earthly evolution when some of the elements that had been formed during the ages of stellar evolution were ready to separate 32

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CHALCOPYRITE ORE

The rock is a piece of chalcopyrite ore, and the blocks show the quantities of copper, iron, and sulphur contained in it. Chalcopyrite is the color of gold. This mineral is a double sulphide of copper and iron, and contains 34.6 per cent copper, 30.5 per cent iron, and 34.9 per cent sulphur. The chunk of ore in the picture weighs 12 Ibs. 10 oz. The block of iron at the top weighs 3 lbs. 15 oz., the block of copper in the middle weighs 4 lbs. 4 oz., and the block of sulphur at the bottom weighs 4 lbs. 7 oz.

out from the common mass of matter and isolate themselves. This time came when the earth cooled down. The surface began to look somewhat as it does now in places, and there began the series of events resulting in the segregation of copper and other minerals, seemingly for man’s particular benefit. By personal inspection, man knows only an infinitesimal part of the universe. He is beginning to be acquainted with the surface of the land fairly well, although there are still vast areas that he has only scratched. The great expanse of the ocean floor is a wild land for future explorers. In only a few places has man drilled into the interior of the earth, and below a mile and - a half downward the inside of the eight-thousand-mile ball on which we live is entirely unknown. The greatest upward height reached by him is a bare five miles, and beyond twenty miles even the thinnest trace of earthly atmosphere begins to disappear. Despite its apparent minuteness, the surface of our earth is all that we have to live on, and most of us consider it quite enough. All the copper we can hope to have and use exists on it or within a mile of it, and we must make the best of it. In the center of the earth there may be many cubic miles of copper, but why should we even think about it just now? It is true that this earth of ours receives an importation now and then in the form of meteorites, but these are not frequent enough to keep our museums well supplied, and careful chemical analysis shows that they contain only about one hundredth of 1 per cent. of copper. If we look at a table showing the average composition of the rocks of the earth’s crust as determined by many chemical analyses of rocks, we see copper in a decidedly subordinate place. It ranks twenty-fourth, sandwiched between lithium and cerium. Above it, and more abundant, we see aluminum, iron, magnesium, chromium, nickel, and other metallic elements. The crust of the earth has larger amounts of all these elements than copper; only two thousandths of 1 per cent. of the crust is copper, or, saying it differently, there would be only one ton of copper in fifty thousand tons of earth’s crust if we could assume that all copper were evenly distributed. Yet because nature has placed the total amount of copper in relatively easy form for man’s exploitation, there are to-day relatively large amounts of copper available for use.

Now that we know how much copper there is, it is appropriate that we be formally introduced to the copper mineral family, which is responsible for the copper of the world. Some of them we have already met informally in the first chapter, and we shall become intimately acquainted with all of them as our story goes on. |

First comes the bachelor of the copper family: native or free copper. It is quite the purest and most solitary member; it is the metal itself. In size, native copper occurs from small grains to great masses several hundred tons in weight, and it may also be found in threads and wires and in distorted crystals and twisted groups. It is not a very hard substance, but the finger nail is too soft to scratch native copper. Native copper is found in twenty-seven States of the Union; in the upper part of copper deposits at the

Coro Coro Mines in Bolivia; the Faroe Islands; Atacama, Chile; and Wallaroo, South Australia; with other deposits elsewhere. But it occurs native in quantity principally in the Lake Superior district, where the Indians worked it long before the white man arrived.

The greatest and most important offshoot of the copper family came about through the intermarriage of sulphur and copper. The sulphur family is rather a troublesome group, and when man divorces these two elements so that he may utilize the copper alone he has more difficulty in performing the separation than he does when copper is married to some milder element such as oxygen. Sulphur, though, does its share in the work of the world, as after the divorce it is often put into service for the manufacture of sulphuric acid.

Next let us become acquainted with covellite, otherwise known as indigo copper. According to its ancestry it is about two thirds copper and one third sulphur. In complexion it is a very dark indigo-blue, and it is considered by many to be the most beautiful of all the copper mineral family. As an ore, however, it is rare, although it is produced in large quantities from one mine at Butte, Montana. In the chemical world covellite is known as cupric sulphide, and the name is written CuS in the abbreviated language of chemists.

The other member of the copper sulphide family is the most important copper ore in America. Its name is chalcocite,—otherwise copper glance and vitreous copper,—and its lineage shows 79.8 per cent. of copper and 20.2 per cent. of sulphur. Its abbreviated name is Cu,S8. Chalcocite is lead-gray and often has a coat of blue or green tarnish. Often large masses of it have been found, and in the Butte Mine in Montana and the Bonanza Mine, Copper River, Alaska, veins occur whose measurement is more than twenty feet across.

A member of the family that often lives closely associated with chaleocite is bornite. An additional element has contributed to the make-up of bornite, and if we look into its ancestry we find 11.2 per cent. of iron, in addition to 63.8 per cent. of copper and 25.5 per cent. of sulphur, or more simply expressed Cu;FeS, This mineral is also known by several other names: erubescite, purple copper, variegated copper, peacock copper, and horse-flesh copper. It gets these varied names because when first broken open it is of a peculiar red-brown color, which tarnishes to deep blue and purple tints, often variegated. Bornite is an important ore in many mines, notably in some of those at Butte, Montana, in Chile, in South Africa, in Tasmania, and in a few Australian mines. |

Another of the family is chalcopyrite, which, judged by its appearance, might be Cresus himself. It has a true gold color, if you do not happen to see its frequent iridescent tarnish, and it looks genuine enough to fulfil your expectations and yield much gold. But it resembles its cousin, pyrite, or iron sulphide, which has earned the name of ‘‘fool’s gold,’’ and its color is better called brassy than gold. Instead of gold, chalcopyrite is made up of nearly equal amounts of copper, a baser metal, iron, and sulphur; to be exact, the division is 34.5 per cent. copper, 30.5 per cent. iron, 35.0 per cent. sulphur. It is also known as copper pyrite and yellow copper ore. This mineral, whose code name is CuleSs, is often regarded as the mineral from which many other copper minerals are descended; and, in addition to its primary nature, it is geographically the most common copper mineral of the ore deposits of the world, though not the prevailing mineral in the greatest producing mines in this country. .

The sulphide branch of the copper family has intermarried with still other elements on the metallic side. When this occurred with arsenic, enargite resulted; and when antimony was the addition, the new mineral was tetrahedrite. i

Until a few years ago enargite, known in chemical circles as sulpharsenide of copper, or Cu,AsS,, was not considered of great commercial importance, but it has since been found that it is one of the great ores of the world, yielding probably 3 per cent. of the copper. One third of the ore at Butte, Montana, is enargite. This mineral is grayish-black and brittle, and the fact that it contains 19.1 per cent. arsenic caused some persons to scorn it before electrolytic refining provided a method of purifying it. Sometimes, in some kinds of enargite, zinc or iron will be found replacing part of the copper, and the arsenic may have antimony substituted for it in part.

When antimony, sulphur, and copper combine, tetrahedrite, otherwise gray copper ore, is formed. Itis a variable mineral, and sometimes we find that the copper is partly replaced by iron, zinc, lead, mercury, or silver, while arsenic substitutes for antimony. As its nickname implies, it is a light steel-gray to iron-black mineral; and though it is one of the most frequent minerals in copper deposits it is not an important ore, as it seldom occurs in large quantities. Wherever it occurs it usually carries valuable silver along with it.

Next comes the airy branch of the family, formed of a combination of oxygen and copper. The evolution of this branch is usually through a divorce of sulphur from copper with a subsequent marriage of copper to oxygen. Cuprite, Cu,O, also known by the names of red oxide of copper and ruby copper ore, is usually some shade of red or brown, and it virtually always occurs with the carbonates, malachite and azurite, to whom we shall be introduced shortly. In the early development of copper deposits cuprite was an important mineral because it was at the top of the deposits, but now it has had to relinquish the most important place in production to the sulphide members of the copper family.

The carbonate family, closely related to the oxide branch, is a flashy group, which does a large amount of painting. Most important is malachite, whose color is green; but, occurring close to malachite, the blue mineral azurite will often be found. Malachite, which has the long code of Cu,(OH).CO; is the most important oxidized ore of copper, and it is not only useful but ornamental. In the Russian mines of the Ural district are obtained large and solid masses from which vases and other works of art are eut. You can buy copper ore in a jewelry store in your city, if you know what to ask for or can pick it out from the array of semi-precious stones. Many of the brooches and dinner rings containing green stones, often banded with concentric rings, are set with nothing more than the copper ore, malachite. This ore is a little less than two thirds copper, but it often dissipates its strength and color so much that many of the wide-spread deposits cannot be mined on a paying basis. It covers much ground, and a little of it will stain a very large amount of rock. Worst of all, it is deceitful, as it colors thin and worthless incrustations or nodules of worthless material and disguises them as valuable ore. Azurite is malachite’s companion, and, like it, is a carbonate, descended, through the union of water, from _ decomposing members of the sulphide family coming into contact with limestone. Chemically it is known as Cu;(OH).(CO;),.. The light azure too deep rich blue of azurite contrasts well with malachite’s green, and in some localities such as Morenci, Arizona, and Laurium, Greece, nature has been thoughtful enough to form them into concentric bands so that we may easily admire the beautiful comparison. Often it shows off its beauty in splendid crystals, and it is better known for its beauty than for its producing value as an ore.

Chrysocolla is another highly colored ore of copper, and it is the single important representative of the copper silicate family. If we investigate its composition we find 45.2 parts of copper oxide, 34.3 parts of silica, and 20.5 parts of water. Its peculiarity is that it never occurs in crystals, and you may mistake its impure earthy blue and green for a piece of kaolin colored by copper. Often it will be seen with an opal-like

40 THE STORY OF COPPHR or enamel-like structure. Its most important occurrence is in Arizona, where large areas are underlaid by it, and it is also found in Chile and Belgian Congo.

I shall list the other but minor members of the copper mineral family, mentioning their closest relatives among the important copper minerals. Famatinite is closely related to enargite, the only difference being that famatinite has antimony as a constituent, while enargite has arsenic. Tenorite, better known as melaconite or black oxide of copper, is a member of the oxide family similarly to euprite, but its code name is CuO, and it is black. It is not very important, although it has the distinction of being formed at the present time by the vapors from the voleano Vesuvius. When blue vitriol or copper sulphate occurs as a mineral it is known as chaleanthite. Like the artificial product it is blue and glassy, and if you tasted it you would find it disagreeably metallic. This is an ore that mine water sometimes leaches out and saves man the trouble of both the mining and the preliminary treatment. Brochantite is another sulphate mineral. Chlorine’s intermixture with the copper family has resulted in a basic chloride called atacamite, and in Chile and South Australia, this is an ore of some importance.

It has been estimated that chalcocite and chalcopyrite are together responsible for about three quarters of the world’s production; chalcocite probably produces half of the world’s copper alone. Native copper, chiefly from the Michigan region, is responsible for about 6 per cent. of the world total and, because of the large masses at Butte, enargite contributes about

3 percent. The rest of the production comes largely from oxide ores, with the other minerals doing their small bit.

Man is interested in the elements with which copper has intermarried, not only because through science and experience he has discovered that certain ores are > usually found under certain conditions, but also because he has to divorce copper from the combining elements before he can use this metal. For the second reason, also, he is interested in the gangue that copper minerals associate themselves with. By the term ‘‘rangue’’ the geologist indicates the rocks and minerals that surround copper ore. These rocks and minerals may be very interesting and, in their proper place, useful, but when they prevent a great density of copper population they are gangue and nothing more. Some kinds of gangues are less troublesome than others, and if they are present in the proper proportion with the proper members of the copper mineral family they may even aid in the process of getting rid of themselves. Quartz, the common mineral, is the commonest gangue of copper ores. Calcite, the carbonate of lime, and siderite, the carbonate of iron, are also common in some deposits but are plentiful in only a few of the greatest mines of the world. Very often the gangue is not composed of these relatively pure minerals but is earthy and a highly altered country rock. Barite, rhodochrosite, and fluorite are other troublesome neighbors of copper ore that man must remove before copper can be obtained.

Pyrite, or iron sulphide, is also a common companion of copper minerals, particularly the sulphides, but, as we shall see later, it often provides fuel that results in the divorce of copper and sulphur. Iron oxide, or hematite, and other metallic oxides also often form the gangue of copper minerals. |

There are some metallic minerals that are deleterious in copper ores, although if they were alone they would be prized as a source of other metals. Zine and copper do not get along very well in mineral form, although after they achieve the metallic state they often form a successful partnership under the name of brass. Sphalerite, zinc sulphide, is considered the most obnoxious of such harmful minerals, and to discourage it ‘ smelters have established a ‘‘zine penalty’’ which takes the form of a fine if the sphalerite in copper ore is over 10 per cent. Bismuth, arsenic, antimony, tellurium, and selenium minerals are very objectionable associates of copper ores, but electrolytic refining of copper eliminates them and the trouble they cause.

The past history of the copper ores is nearly as mixed and difficult to untangle as human genealogies. So many things have happened in the geologic ages of the earth to complicate the lineage of even one particular spot rich in copper that it often takes years for geologists to find to their satisfaction the probable descent. Each kind of copper deposit has characteristics all its own, and though the types of copper deposits have not been separated very distinctly, their genesis is probably better known than that of the different races of the human kind. Complicated and uncertain as the past of copper may be, it is useful to make an attempt at unraveling it, because through knowing its past, man can better determine the present location of copper.

Gaze at the ocean, visit a voleano, or admire a hot spring. If you do, it is likely that you are unknowingly witnessing the most recent creation of copper deposits. Sad to say, these new communities of cop per deposits, while ‘‘nouveau,’’ are not ‘‘riche,’’ and no great exploitable deposits are being formed in this way. Copper salts and copper oxide are deposited by voleaniec vapors and: gases in the rifts about active voleanoes. Several vein-forming hot springs are known, and one in which copper minerals are being deposited is at Boulder Hot Springs, Montana. Sometimes cold copper-bearing waters are found, but these can usually be traced to oxidizing ore deposits. Copper minerals deposited in the organic muds of sea lagoons, while well-known, are a scientific curiosity rather than examples of how the workable ores used to-day were laid down. Nature at work to-day concentrating copper gives us a chance to see a small part of the geological drama that resulted in the ore deposits that man now works.