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diff --git a/24762-8.txt b/24762-8.txt new file mode 100644 index 0000000..d98d9de --- /dev/null +++ b/24762-8.txt @@ -0,0 +1,3022 @@ +The Project Gutenberg EBook of Diggers in the Earth, by Eva March Tappan + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Diggers in the Earth + +Author: Eva March Tappan + +Release Date: March 6, 2008 [EBook #24762] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK DIGGERS IN THE EARTH *** + + + + +Produced by Diane Monico and The Online Distributed +Proofreading Team at https://www.pgdp.net (This file was +produced from images generously made available by The +Internet Archive/American Libraries.) + + + + + + + + + +THE INDUSTRIAL READERS + +_Book II_ + +DIGGERS IN THE +EARTH + +BY + +EVA MARCH TAPPAN, Ph.D. + +_Author of "England's Story," "American Hero Stories," +"Old World Hero Stories," "Story of the Greek People," +"Story of the Roman People," etc. Editor of +"The Children's Hour."_ + +[Illustration] + +HOUGHTON MIFFLIN COMPANY + +BOSTON NEW YORK CHICAGO + + + + +THE INDUSTRIAL READERS + +By Eva March Tappan + + I. THE FARMER AND HIS FRIENDS. 50 cents. + + II. DIGGERS IN THE EARTH. 50 cents. + +III. MAKERS OF MANY THINGS. 50 cents. + + IV. TRAVELERS AND TRAVELING. 50 cents. + +The foregoing are list prices, postpaid + + +COPYRIGHT, 1916, BY EVA MARCH TAPPAN +ALL RIGHTS RESERVED + +_First printing April 1916;_ +_Reprinted December 1916_ + + +The Riverside Press +CAMBRIDGE, MASSACHUSETTS +U. S. A. + + + + +PREFACE + + +The four books of this series have been written not merely to provide +agreeable reading matter for children, but to give them information. +When a child can look at a steel pen not simply as an article +furnished by the city for his use, but rather as the result of many +interesting processes, he has made a distinct growth in intelligence. +When he has begun to apprehend the fruitfulness of the earth, both +above ground and below, and the best way in which its products may be +utilized and carried to the places where they are needed, he has not +only acquired a knowledge of many kinds of industrial life which may +help him to choose his life-work wisely from among them; but he has +learned the dependence of one person upon other persons, of one part +of the world upon other parts, and the necessity of peaceful +intercourse. Best of all, he has learned to see. Wordsworth's familiar +lines say of a man whose eyes had not been opened,-- + + "A primrose by a river's brim + A yellow primrose was to him, + And it was nothing more." + +These books are planned to show the children that there is "something +more"; to broaden their horizon; to reveal to them what invention has +accomplished and what wide room for invention still remains; to teach +them that reward comes to the man who improves his output beyond the +task of the moment; and that success is waiting not for him who works +because he must, but him who works because he may. + +Acknowledgment is due to the Lehigh Valley Railroad, Jones Brothers +Company, Alpha Portland Cement Company, Dwight W. Woodbridge, the Utah +Copper Company, the Aluminum Company of America, the Diamond Crystal +Salt Company, T. W. Rickard, and others, whose advice and criticism +have been of most valuable aid in the preparation of this volume. + + EVA MARCH TAPPAN. + + + + +CONTENTS + + I. IN A COAL MINE 1 + + II. DOWN IN THE QUARRIES 11 + + III. HOUSES OF SAND 21 + + IV. BRICKS, THEIR FAULTS AND THEIR VIRTUES 31 + + V. AT THE GOLD DIGGINGS 39 + + VI. THE STORY OF A SILVER MINE 48 + + VII. IRON, THE EVERYDAY METAL 57 + +VIII. OUR GOOD FRIEND COPPER 65 + + IX. THE NEW METAL, ALUMINUM 76 + + X. THE OIL IN OUR LAMPS 84 + + XI. LITTLE GRAINS OF SALT 95 + + + + +LIST OF ILLUSTRATIONS + + +A STRUCTURAL STEEL APARTMENT BUILDING vi + +HOW A COAL MINE LOOKS ABOVEGROUND 5 + +MINERS AND THEIR MINE 10 + +OPENING A GRANITE QUARRY 13 + +BUILDING A CONCRETE ROAD 27 + +IN A NEW JERSEY BRICK MILL 33 + +HYDRAULIC GOLD MINING 41 + +THE STORY OF A SPOON 51 + +IN THE STEEL FOUNDRY 61 + +IN A COPPER SMELTER 67 + +A "MOVIE" OF AN ALUMINUM FUNNEL 79 + +A CALIFORNIA OIL FIELD 87 + + + + +[Illustration: A STRUCTURAL STEEL APARTMENT BUILDING + +_Courtesy American Bridge Co._ + +First the steel frame, then the floors, then the stone or brick shell, +then the interior finishing--this is how the building is made.] + + + + +THE INDUSTRIAL READERS + +BOOK II + +DIGGERS IN THE EARTH + + + + +I + +IN A COAL MINE + + +Did you ever wonder how beds of coal happened to be in the earth? This +is their story. + +Centuries ago, so many thousand centuries that even the most learned +men can only guess at their number, strange things were coming to +pass. The air was so moist and cloudy that the sun's rays had hard +work to get through. It was warm, nevertheless, for the crust of the +earth was not nearly so thick as it is now, and much heat came from +the earth itself. Many plants and trees grow best in warm, moist air; +and such plants flourished in those days. Some of their descendants +are living now, but they are dwarfs, while their ancestors were +giants. There is a little "horse-tail" growing in our meadows, and +there are ferns and club mosses almost everywhere. These are some of +the descendants; but many of their ancestors were forty or fifty feet +high. They grew very fast, especially in swamps; and when they died, +there was no lack of others to take their places. Dead leaves fell and +heaped up around them. Stumps stood and decayed, just as they do in +our forests to-day. Every year the soft, black, decaying mass grew +deeper. As the crust of the earth was so thin, it bent and wrinkled +easily. It often sank in one place and rose in another. When these +low, swampy places sank, water rushed over them, pressing down upon +them with a great weight and sweeping in sand and clay. Now, if you +burn a heap of wood in the open air, the carbon in the wood burns and +only a pile of ashes remains. "Burning" means that the carbon in the +wood unites with the oxygen gas in the air. If you cover the wood +before you light it, so that only a little oxygen reaches it, much of +the carbon is left, in the form of charcoal. + +When wood decays, its carbon unites with the oxygen of the air; and so +decay is really a sort of burning. In the forests of to-day the +leaves, and at length the trees themselves, fall and decay in the open +air; but at the time when our coal was forming, the water kept the air +away, and much carbon was left. This is the way coal was made. Some of +the layers, or strata, are fifty or sixty feet thick, and some are +hardly thicker than paper. On top of each one is a stratum of +sandstone or dark-gray shale. This was made by the sand and mud which +were brought in by the water. These shaly rocks split easily into +sheets and show beautiful fossil impressions of ferns. There are also +impressions of the bark and fruit of trees, together with shells, +crinoids, corals, remains of fishes and flying lizards, and some few +trilobites,--crablike animals with a shell somewhat like the back of +a lobster, but marked into three divisions or lobes, from which its +name comes. + +Since the crust of the earth was so thin and yielding, it wrinkled up +as the earth cooled, much as the skin of an apple wrinkles when the +apple dries. This brought some of the strata of coal to the surface, +and after a while people discovered that it would burn. If a vein of +coal cropped out on a man's farm, he broke some of it up with his +pickaxe, shoveled it into his wheelbarrow, and wheeled it home. After +a while hundreds of thousands of people wanted coal; and now it had to +be mined. In some places the coal stratum was horizontal and cropped +out on the side of a hill, so that a level road could be dug straight +into it. In other places the coal was so near the surface that it +could be quarried under the open sky, just as granite is quarried. +Generally, however, if you wish to visit a coal mine, you go to a +shaft, a square, black well sometimes deeper than the height of three +or four ordinary church steeples. You get into the "cage," a great +steel box, and are lowered down, down, down. At last the cage stops +and you are at the bottom of the mine. The miners' faces, hands, +overalls, are all black with coal dust. They wear tiny lamps on their +caps, and as they come near the walls of coal, it sparkles as it +catches the light. Here and there hangs an electric lamp. It is doing +its best to give out light, but its glass is thick with coal dust. The +low roof is held up by stout wooden timbers and pillars of coal. A +long passageway stretches off into a blacker darkness than you ever +dreamed of. Suddenly there is a blaze of red light far down the +passage, a roar, a medley of all sorts of noises,--the rattling of +chains, the clattering of couplings, the shouts of men, the crash of +coal falling into the bins. It is a locomotive dragging its line of +cars loaded with coal. In a few minutes it rushes back with empty cars +to have them refilled. + +All along this passageway are "rooms," that is, chambers which have +been made by digging out the coal. Above them is a vast amount of +earth and rock, sometimes hundreds of feet in thickness. There is +always danger that the roof will cave in, and so the rooms are not +made large, and great pillars of coal are left to hold up the roof. + +Not many years ago the miner used to do all the work with his muscles; +now machines do most of it. The miner then had to lie down on his side +near the wall of coal in his "room" and cut into it, close to the +floor, as far as his pickaxe would reach. Then he bored a hole into +the top of the coal, pushed in a cartridge, thrust in a slender squib, +lighted it, and ran for his life. The cartridge exploded, and perhaps +a ton or two of coal fell. The miner's helper shoveled this into a car +and pushed it out of the room to join the long string of cars. + +[Illustration: HOW A COAL MINE LOOKS ABOVEGROUND + +All that shows on the surface is the machinery shed where the various +engines work to keep the air fresh, and bring up the miners and the +coal.] + +That is the way mining used to be done. In these days a man with a +small machine for cutting coal comes first. He puts his cutter on the +floor against the wall of coal and turns on the electricity. _Chip, +chip_, grinds the machine, eating its way swiftly into the coal, and +soon there is a deep cut all along the side of the room. The man and +his machine go elsewhere, and the first room is left for its next +visitors. They come in the evening and bore holes for the blasting. +Once these holes were bored by hand, but now they are made with +powerful drills that work by compressed air. A little later other men +come and set off cartridges. In the morning when the dust has settled +and the smoke has blown away, the loaders appear with their shovels +and load the coal into the cars. Then it is raised to the surface and +made ready for market. + +Did you ever notice that some pieces of coal are dull and smutty, +while others are hard and bright? The dull coal is called bituminous, +because it contains more bitumen or mineral pitch. This is often sold +as "run-of-mine" coal,--that is, just as it comes from the mine, +whether in big pieces or in little ones; but sometimes it is passed +over screens, and in this process the dust and smaller bits drop out. + +The second kind of coal, the sort that is hard and bright, is +anthracite. Its name is connected with a Greek word meaning ruby. It +burns with a glow, but does not blaze. Most of the anthracite coal is +used in houses, and householders will not buy it unless the pieces are +of nearly the same size and free from dirt, coal dust, and slate. The +work of preparation is done in odd-shaped buildings called "breakers." +One part of a breaker is often a hundred or a hundred and fifty feet +in height. The coal is carried to the top of the breaker. From there +it makes a journey to the ground, but something happens to it every +little way. It goes between rollers, which crush it; then over +screens, through which the smaller pieces fall. Sometimes the screens +are so made that the coal will pass over them, while the thin, flat +pieces of slate will fall through. In spite of all this, bits of coal +mixed with slate sometimes slide down with the coal, and these are +picked out by boys. A better way of getting rid of them is now coming +into use. This is to put the coal and slate into moving water. The +slate is heavier than the coal, and sinks; and so the coal can easily +be separated from it. Dealers have names for the various sizes of +coal. "Egg" must be between two and two and five eighths inches in +diameter; "nut" between three fourths and one and one eighth inches; +"pea" between one half and three fourths of an inch. + +Mining coal is dangerous work. Any blow of the pickaxe may break into +a vein of water which will burst out and flood the mine. The wooden +props which support the roof may break, or the pillars of coal may not +be large enough; and the roof may fall in and crush the workers. There +are always poisonous gases. The coal, as has been said before, was +made under water, and therefore the gas which was formed in the +decaying leaves and wood could not escape. It is always bubbling out +from the coal, and at any moment a pickaxe may break into a hole that +is full of it. One kind of gas is called "choke-damp," because it +chokes or suffocates any one who breathes it. There is also +"white-damp," the gas which you see burning with a pretty blue flame +over a hot coal fire. Worst of all is the "fire-damp." If you stir up +the water in a marsh, you will see bubbles of it rise to the surface. +It is harmless in a marsh, but quite the opposite in a mine. When it +unites with a certain amount of air, it becomes explosive, and the +least bit of flame will cause a terrible explosion. Even coal dust may +explode if the air is full of it, and it is suddenly set in motion by +too heavy a blast of powder. + +Miners used to work by candlelight. Every one knew how dangerous this +was; but no one found any better way until, about a hundred years ago, +Sir Humphry Davy noticed something which other people had not +observed. He discovered that flame would not pass through fine wire +gauze, and he made a safety lamp in which a little oil lamp was placed +in a round funnel of wire gauze. The light, but not the flame, would +pass through it; and all safety lamps that burn oil have been made on +this principle. The electric lamp, however, is now in general use. The +miner wears it on his cap, and between his shoulders he carries a +small, light storage battery. Even with safety lamps, however, there +are sometimes explosions. The only way to make a mine at all safe from +dangerous gases is to keep it full of fresh, pure air. There is no +wind to blow through the chambers and passages, and therefore air has +to be forced in. One way is to keep a large fire at the bottom of the +air shaft. If you stand on a stepladder, you will feel that the top of +the room is much warmer than the floor. This is because hot air +rises; and in a mine, the hot air over the fire rises and sucks the +foul air and gas out of the mine, and fresh air rushes in to take its +place. Another way is by a "fan," a machine that forces fresh air into +the mine. + +[Illustration: MINERS AND THEIR MINE + +Notice the safety lamps in the men's caps, and the little railroad on +which the cars of coal and ore travel, hauled by the useful mule.] + +So it is that by hard work and much danger we get coal for burning. +Now, coal is dirty and heavy. A coal fire is hard to kindle and hard +to put out, and the ashes are decidedly disagreeable to handle. And +after all, we do not really burn the coal itself, but only the gas +from it which results from the union of carbon and oxygen. In some +places natural gas, as it is called, which comes directly from some +storehouse in the ground, is used in stoves and furnaces and +fireplaces for both heating and cooking; and perhaps before long gas +will be manufactured so cheaply and can be used so safely and +comfortably that we shall not have to burn coal at all, but can use +gas for all purposes--unless electricity should take its place. + + + + +II + +DOWN IN THE QUARRIES + + +When walking in the country one day I came to a beautiful pond by the +side of the road. The water was almost as clear as air, and as I +looked down into it, I could see that the bottom was made of granite. +The farther shores were cliffs of clean granite thirty or forty feet +high and coming down to the water's edge. The marks of tools could be +seen on them, showing where blocks of stone had evidently been split +off. I picked up a piece of the rock and examined it closely. It +proved to be made up of three kinds of material. First, there were +tiny sparkling bits of mica. In some places there are mica mines +yielding big sheets of this curious mineral which is used in the doors +of stoves and the little windows of automobile curtains. With the +point of a knife the bits in my piece of granite could be split into +tiny sheets as thin as paper. The second material was quartz. This was +grayish-white and looked somewhat like glass. The third material was +feldspar. This, too, was whitish, but one or two sides of each bit +were flat, as if they had not been broken, but split. This is the most +common kind of granite. There are many varieties. Some of them are +almost white, some dark gray, others pale pink, and yet others deep +red. It is found in more than half the States of the Union. + +This quarry had been given up and allowed to fill with water; but it +was a granite country, and farther down the road there was another, +where scores of men were hard at work. This second quarry was part-way +up a hill; or rather, it was a hill of granite which men were digging +out and carrying away. When they began to open the quarry, much of the +rock was covered with dirt and loose stones, and even the granite that +showed aboveground was worn and broken and stained. This is called +"trap rock." The easiest way to get rid of it is to blast with +dynamite and then carry away the dirt and fragments. Next comes the +getting out of great masses of rock to use, some of them perhaps long +enough to make the pillars of a large building. + +[Illustration: OPENING A GRANITE QUARRY + +_Courtesy Jones Brothers Company._ + +The first thing to do is to strip off the soil from the stone. Then, +as the blocks are cut out, the big derrick lifts and loads them on +waiting cars.] + +Now, granite is a hard stone, but there is no special difficulty in +cutting it if you know how. In the old days, when people wished to +split a big boulder, they sometimes built a fire beside it, and when +it was well heated, they dropped a heavy iron ball upon it. King's +Chapel in Boston was built of stone broken in this way. To break from +a cliff, however, a block of granite big enough to make a long pillar +is a different matter, and this is what the men were doing. First of +all, the foreman had examined the quarry till he had found a stratum +of the right thickness. He had marked where the ends were to come, and +the men had drilled holes down to the bottom of the stratum. Then he +had drawn a line at the back along where he wished the split to be, +and the men had drilled on this line also a row of holes. Next came +the blasting. If one very heavy charge had been exploded, it would +probably have shattered the whole mass, or at any rate have injured it +badly. Instead of this, they put into each hole a light charge of +coarse powder and covered it with sand. These were all fired at the +same instant, and thus the great block was loosened from the wall. +Sometimes there seems to be no sign of strata, and then a line of +horizontal holes must be drilled where the bottom of the block is to +be. After this comes what is called the "plug-and-feather" process. +Into each hole are placed two pieces of iron, shaped like a pencil +split down the middle. These are the "feathers." The "plug" is a small +steel wedge that is put between the iron pieces. Then two men with +hammers go down the line and strike each wedge almost as gently as if +it was a nut whose kernel they were afraid of crushing. They go down +the line again, striking as softly as before. Then, if you look +closely, you can see a tiny crack between the holes. There is more +hammering, the crack stretches farther, a few of the wedges are driven +deeper and the others drop out. The block splits off. A mighty chain +is then wound about it, the steam derrick lifts it, lays it gently +upon a car, and it is carried to the shed to be cut into shape, +smoothed, and perhaps polished. + +In almost every kind of work new methods are invented after a while. +In quarrying, however, the same old methods are in use. The only +difference is that, instead of the work being done by muscle, it is +done by compressed air or steam or electricity. Compressed air or +steam works the drill and the sledgehammer. The drill is held by an +arm, but the arm is a long steel rod which is only guided by the +workman. Not the horse-sweep of old times, but the steam derrick and +the electric hoist lift the heavy blocks from the quarry. Polishing +used to be a very slow, expensive operation, because it was all done +by the strength of some one's right arm, but now, although it takes as +much work as ever, this work is done by machinery. To "point" a piece +of stone, or give it a somewhat smooth surface, is done now with tools +worked by compressed air. After this, the stone is rubbed--by +machinery, of course--with water and emery, then by wet felt covered +with pumice or polishing putty. A few years ago two young Vermonters +invented a machine that would saw granite. This saw has no teeth, but +only blades of iron. Between these blades and the piece of granite, +however, shot of chilled steel are poured; and they do the real +cutting. + +Granite has long been used in building wherever a strong, solid +material was needed; but until the sand blast was tried, people +thought it impossible to do fine work in this stone. There was a firm +in Vermont, however, who believed in the sand blast. They had a +contract with the Government to furnish several thousand headstones +for national cemeteries. Cutting the names would be slow and costly; +so they made letters and figures of iron, stuck them to the stones, +and turned on the blast. If a sand blast is only fast enough, it will +cut stone harder than itself. The blast was turned upon a stone for +five minutes. Then the iron letters were removed. There stood in +raised letters the name, company, regiment, and rank of the soldier, +while a quarter of an inch of the rest of the stone, which the iron +letters had not protected, had been cut away. By means of the sand +blast it has become possible to do beautiful carving even in material +as hard as granite. + +Granite looks so solid that people used to think it was fireproof; but +it is really poor material in a great fire. Most substances expand +when they are heated; but the three substances of which granite is +made do not expand alike, and so they tend to break apart and the +granite crumbles. + +A marble quarry is even more interesting than a granite quarry. If you +stand on a hill in a part of the country where marble is worked, you +will see white ledges cropping out here and there. The little villages +are white because many of the houses are built of marble. Then, too, +there are great marble quarries flashing in the sunshine. Sometimes a +marble quarry is chiefly on the surface. Sometimes the marble +stretches into the earth, and the cutting follows it until a great +cavern is made, perhaps two or three hundred feet deep. A roof is +often built to keep out the rain and snow. It keeps out the light, +too, and on rainy days the roof, together with the smoke and steam of +the engines, makes the bottom of the quarry a gloomy place. Everywhere +there are slender ladders with men running up and down them. There +are shouts of the men, clanking of chains, and puffing of locomotives. + +Marble is cut out in somewhat the same way as granite, but a valuable +machine called a "channeler" is much used. This machine runs back and +forth, cutting a channel two inches wide along the ends and back and +sometimes the bottom of the block to be taken out. + +Marble is so much softer than granite that it is far more easy to +work. Cutting it is a simple matter. The saw, which is a smooth flat +blade of iron, swings back and forth, while between it and the marble +sand and water are fed. It does not exactly _cut_, but rubs, its way +through. The round holes in the tops of washstands are cut by saws +like this, only bent in the form of a cylinder and turned round and +round, going in a little deeper at each revolution. A queer sort of +saw is coming into use. It is a cord made of three steel wires twisted +loosely together. This cord is stretched tightly over pulleys and +moves very rapidly. Every little ridge of the cord strikes the stone +and cuts a little of it away. + +There are varieties of marble without end. The purest and daintiest is +the white of which statues are carved; but there are black, red, +yellow, gray, blue, green, pink, and orange in all shades. Many are +beautifully marked. The inner walls of buildings are sometimes covered +with thin slabs of marble. These are often carefully split, and the +two pieces put up side by side, so that the pattern on one is reversed +on the other. Certain kinds of marble contain fossils or remains of +coral and other animals that lived hundreds of thousands of years ago. +In some marbles there are so many that the stone seems to be almost +made of them. When a slab is cut and polished, the fossils are of +course cut into; but even then we can sometimes see their shape. One +of the most common is the crinoid. This was really an animal, but it +looked somewhat like a closed pond lily with a long stem, and people +used to call it the stone lily. This stem is made up of little flat +rings looking like bits of a pipestem. The stems are often broken up +and these bits are scattered through the marble. The animals whose +shells help to make marble lived in the ocean, and when they died sank +to the bottom. Many of the shells were broken by the beating of the +waves, but both broken shells and whole ones became united and +hardened into limestone, one kind of which we call marble. Common +chalk is another kind. Blackboard crayons are made of this: so are +whitewash and whiting for cleaning silver and making putty. + +Another stone that builders would be sorry to do without is slate. +This, too, was formed at the bottom of the sea. Rivers brought down +fine particles of clay, which settled, were covered by other matter, +and finally became stone. It was formed in layers, of course, but, +queerly enough, it splits at right angles to its bottom line. Just why +it does this is not quite certain, but the action is thought to be due +to heat and long, slow pressure, which will do wonderful things, as in +the case of coal. This splitting is a great convenience for the +people who want to use it for roofing and for blackboards. Blocks of +slate are loosened by blasting, and are taken to the splitting-shed. + +Splitting slate needs care, and a man who is not careful should never +try to work in a slate quarry. The splitting begins by one man's +dividing the block into pieces about two inches thick and somewhat +larger than the slates are to be when finished. The way he does this +is to cut a little notch in one end of the block with his "sculpin +chisel" and make a groove from this across the block. He must then set +his chisel into the groove, strike it with a mallet, and split the +slate to the bottom. This sounds easy, but it needs skill. Slate has +sometimes its own notions of behavior, and it does not always care to +split in a straight line exactly perpendicular to the bottom of the +stratum. The man keeps it wet so that he can see the crack more +plainly, and if that crack turns back a little to the right, he must +turn it to the left by striking the sculpin toward the left, or +perhaps by striking a rather heavy blow on the left of the stone +itself. Now the chief splitter takes it, and with a broad thin chisel +he splits it into plates becoming thinner at each split. The second +assistant trims these into the proper shape and size with either a +heavy knife or a machine. Slate can be sawed and planed; but whatever +is done to it should be done when it first comes from the quarry, for +then it is not so likely to break. It would be very much cheaper if so +much was not broken and wasted at the quarries and in the splitting. +It is said that in Wales sometimes one hundred tons of stone are +broken up to get between three and four tons of good slate. Within the +last few years the quarrymen have been using channeling machines and +getting out the slate in great masses instead of small blocks. This is +not so wasteful by any means; but even now there is room for new and +helpful inventions. + + + + +III + +HOUSES OF SAND + + +If you wanted to build a house, of what should you build it? In a new +country, people generally use wood; but after a time wood grows +expensive. Moreover, wood catches fire easily; therefore, as a country +becomes more thickly settled and people live close together in cities, +stone and brick are used. Large cities do not allow the building of +wooden houses within a certain distance from the center, and sometimes +even the use of wooden shingles is forbidden. Of late years large +numbers of "concrete" or "cement" houses have been built. Our +grandfathers would have opened their eyes wide at the suggestion of a +house built of sand, and would have felt anxious at every rainfall +lest their homes should suddenly melt away. Even after thousands of +concrete buildings were in use, many people still feared that they +would not stand the cold winters and hot summers of the United States; +but it has been proved that concrete is a success provided it is +properly made. + +No one can succeed in any work unless he understands how it should be +done. Concrete is made of Portland cement, mixed with sand and water +and either broken stone, gravel, cinders, or slag; but if any one +thinks that he can mix these together without knowing how and produce +good concrete, he will make a bad mistake rather than a good building +material. + +First, he must buy Portland cement of the best quality. This cement is +made of limestone and clay, or marl, chalk, and slag. These are +crushed and ground and put into a kiln which is heated up to 2500° or +3000°F.; that is, from twelve to fourteen times as hot as boiling +water. The stone fuses sufficiently to form a sort of clinker. After +this has cooled, it is ground so fine that the greater part of it will +pass through a sieve having 40,000 meshes to the square inch. To every +hundred pounds of this powder, about three pounds of gypsum is added. +The mixture is then put into the bags in which we see it for sale in +the stores. This powder is so greedy for water that it will absorb the +moisture from the air around it. Even in the bags, it begins to harden +as soon as it gets some moisture; and as soon as it hardens, it is of +no use. The moral of that is to keep your cement in a dry place. + +The second substance needed in concrete is broken stone or gravel. Of +course a hard rock must be selected, such as granite or trap rock. +Limestone calcines in a heat exceeding 1000° F., and therefore it +cannot be used in fireproof construction. Soft rock, like slate or +shale or soft sandstone, will not answer because it is not strong +enough. Gravel is always hard. If you look at a cut in a gravel bank, +you will usually see strata of sand and then strata of rounded pebbles +of different sizes. The sand was once an ancient sea beach; the +pebbles were dashed up on it by waves or storms or some change of +currents. They were at first only broken bits of rock, but after being +rolled about for a few thousand years in the ocean and on the shore, +the corners were all rounded. Soft rock would have been ground to +powder by such treatment. Sometimes, if there is to be no great strain +on the concrete, cinders or pieces of brick may be used instead of +stone; and for some purposes they answer very well. + +The third substance used in concrete is sand; but it must be the right +kind of sand, having both fine and coarse grains. These grains need to +be sharp, or the cement will not stick to them well. They must also be +clean, that is, free from dirt. If you rub sand between your hands, +and it soils them, then there is clay or loam with it, and it must not +be used in making concrete unless it is thoroughly washed. Another way +of testing it is to put it into a glass jar partly full of water and +shake it. Then let it settle. If there is soil in the sand, it will +appear as a stratum of mud on top of the sand. + +The water with which these three substances are to be mixed must be +clean and must contain no acid and no strong alkali. As a general +rule, there must be twice as much broken stone as sand. When people +first make concrete, they often expect too much of their materials. A +good rule for the strongest sort of cement, strong enough for floors +on which heavy machines are to stand, is one fourth of a barrel of +cement, half a barrel of sand, and one barrel of gravel or broken +stone. Apparently this would make one and three fourths barrels; but +in reality it makes only about one barrel, because the sand fills in +the spaces between the gravel, and the cement fills in the spaces +between the grains of sand. + +There are many sorts of machines on the market for mixing the +materials; but small quantities can just as well be mixed by hand. The +"mixing-bowl" is a platform, and on this the sand is laid. Then comes +the cement; and these two must be shoveled together several times. +While this is being done, the broken stone or gravel must be wet, and +now it is put on top of the sand and cement and well shoveled +together, with just enough water added so that the mass will almost +bear the weight of a man. + +Concrete is impatient to be hardening, and if it is not put into the +right place, it will begin promptly to harden in the wrong place, and +nothing can be done with it afterwards. If it is to be made in blocks, +the moulds must be ready and the concrete put into them at once and +well tamped down. For such uses as beams and the sides of tanks where +great strength is needed, the cement is often "reinforced," that is, +rods of iron or steel are embedded in it. For floors, a sheet of woven +wire is often stretched out and embedded. At first only solid blocks, +made to imitate rough stone, were used for houses, but the hollow +block soon took their place. This is cheaper; houses built this way +are warmer in winter and cooler in summer; and it prevents moisture +from working through the walls. Many cities have regulations about the +use of hollow blocks, all the more strict because concrete is +comparatively new as a building material. In Philadelphia the blocks +must be composed of at least one barrel of Portland cement to five +barrels of crushed rock or gravel. They must be three weeks old or +more before being used; the lintels and sills of the doors must be +reinforced; and every block must be marked, so that if the building +should not prove to be of proper strength, the maker may be known. +There would seem, however, to be little question of the quality of the +blocks, for samples must pass the tests of the Bureau of Building +Inspection. + +Even better than the hollow block is the method of making the four +walls of a house at once by building double walls of boards and +pouring in the concrete. When this has hardened, the boards are +removed, and whatever sort of finish the owner prefers is given to the +walls. They can be treated by spatter-work, pebble dash, or in other +ways before the cement is fully set, or by bush hammering and tool +work after the cement has hardened. Coloring matter can be mixed with +the cement in the first place; and if the owner decides to change the +color after the house is completed, he can paint it with a thin cement +of coloring matter mixed with plaster of Paris. + +A concrete house has several advantages. In the first place, it will +not burn. Neither will granite, but granite will fall to pieces in a +hot fire. Granite is made of quartz, mica, and feldspar, as has been +said before. These three do not expand alike in heat; and therefore +great flakes of the stone split off, so that it really seems to melt +away. A well-made concrete is not affected by fire. It will not burn, +and it will not carry heat to make other things burn. For a concrete +house no paint is needed and less fuel will be required to keep it +warm. If the floors are made with even a very little slant, +"house-cleaning" consists of removing the furniture and turning on the +hose. Water-tank, sink, washtubs, and bathtubs can be cast in concrete +and given a smooth finish. Wooden floors can be laid over the +concrete, or a border of wood can be put around each room for tacking +down carpets or rugs. A concrete house may be as ornamental as the +owner chooses, for columns and cornices and mouldings can easily be +made of concrete; and if they are cast in sand, as iron is, they will +have a finish like sandstone. + +It is somewhat troublesome to lay concrete in very cold weather, +because of the danger of freezing and cracking. Sometimes the +materials are heated, and after the concrete is in place, straw or +sand or sawdust is spread over it. These will keep it warm for several +hours, and so give the concrete a chance to "set." Sometimes a canvas +house is built over the work. When a concrete dam was to be built in +the Province of Quebec and the mercury was 20° below zero, the +contractors built a canvas house over one portion of the dam and set +up iron stoves in it. When this part was completed, they took down the +house and built it up again over another portion of the dam. +Sometimes salt is used. Salt water is heavier than fresh water and +will not freeze so easily. Therefore salt put into the water used in +making the concrete will enable it to endure more cold without +freezing; but not more than one pound of salt to twelve gallons of +water should be used. + +[Illustration: BUILDING A CONCRETE ROAD + +_Courtesy Alpha Portland Cement Co._ + +The concrete mixer travels along the prepared roadbed, and after it +follow the workmen with levelers and stamps.] + +Concrete objects to being frozen before it is "set," but it is +exceedingly accommodating about working under water. It must, of +course, be carried in some way through the water to its proper place +without being washed away, but this is easily done. Sometimes it is +let down in great buckets closed at the top, but with a hinged bottom +that will open when the bucket strikes the rock or soil where the +material is to be left. Sometimes it is poured down through a tube. +Sometimes it is dropped in sacks made of cloth. This cloth must be +coarse, so that enough of the concrete will ooze through it to unite +the bag and its contents with what is below it and make a solid mass. +Sometimes even paper bags have been successfully used. The concrete, +made rather dry, is poured into the bags and they are slid down a +chute. The paper soon becomes soft and breaks, and lets the concrete +out. Sometimes concrete blocks are moulded on land and lowered by a +derrick, while a diver stands ready to see that they go into their +proper places. + +Concrete is used for houses, churches, factories, walls, sidewalks, +steps, foundations, sewers, chimneys, piers, cellar bottoms, cisterns, +tunnels, and even bridges. In the country, it is used for silos, barn +floors, ice houses, bins for vegetables, box stalls for horses, +doghouses, henhouses, fence posts, and drinking-troughs. It is of very +great value in filling cavities in decaying trees. All the decayed +wood must be cut out, and some long nails driven from within the +cavity part-way toward the outside, so as to help hold the concrete. +Then it is poured in and allowed to harden. If the cavity is so large +that there is danger of the trunk's breaking, an iron pipe may be set +in to strengthen it. If this is encased in concrete, it will not rust. +A horizontal limb with a large cavity may be strengthened by bending a +piece of piping and running one part of it into the limb and the other +into the trunk, then filling the whole cavity with concrete. If the +bark is trimmed in such a way as to slant in toward the cavity, it +will sometimes grow entirely over it. + +Concrete is also used for stucco work, that is, for plastering the +outside of buildings. If the building to be stuccoed is of brick or +stone, the only preparation needed is to clean it and wet it; then put +on the plaster between one and two inches thick. A wooden house must +first be covered with two thicknesses of roofing-paper, then by wire +lathing. The concrete will squeeze through the lathing and set. Stucco +work is nothing new, and if it is well done, it is lasting. + +Concrete has been used for many purposes besides building, and the +number of purposes increases rapidly. For blackboards, refrigerator +linings, and railroad ties it has been found available, and for poles +or posts of all sizes it has already proved itself a success. It has +even been suggested as an excellent material for boats, if reinforced; +and minute directions are given by one writer for making a concrete +rowboat. To do this, the wooden boat to be copied is hung up just +above the ground, and clay built around it, leaving a space between +boat and clay as thick as the concrete boat is to be. The wooden boat +is covered with paper and greased, then the concrete is poured into +the space between the boat and the clay mould; and when it hardens and +the wooden boat is removed, there is a boat of stone--or so the +directions declare; but I think most people would prefer one of wood. +However it may be with rowboats, concrete is taking an important place +in the construction of battleships, a backing for armor being made of +it instead of teakwood. The Arizona is built in this way. + +Concrete that is carelessly made is very poor stuff, and dangerous to +use, for it is not at all reliable and may give out at any time; but +concrete that is made of the best materials and properly put together +is an exceedingly valuable article. + + + + +IV + +BRICKS, THEIR FAULTS AND THEIR VIRTUES + + +The simplest way to make a brick is to fill a mould with soft clay, +then take it out and let it stiffen, and then put it in the sun to +dry. This is the way in which the "adobe" bricks of Central America +are made. They answer very well in countries where there is little +rain; but one or two heavy downpours would be likely to melt a house +built of such material. + +Clay is a kind of earth containing mostly alumina and silica or sand, +that can be mixed with water, moulded into any shape, retain that +shape after it is dry, and become hard by being burned. If you want to +make a china cup, you must have a fine sort of clay called "kaolin," +which is pure white when it is fired and is not very common; but if +you want to make bricks, it will not be at all difficult to find a +suitable clay bank. And yet the clay, even for bricks, must be of the +right kind. If it contains too much silica (sand), the brick will not +mould well; if too much alumina it will be weak; if too much iron, it +will lose its shape in burning; if too much lime, it will be +flesh-colored when it is burned. + +If you want to find out whether a building-brick is of good quality, +there are some tests that a boy or girl can apply as well as any one. +First, look the brick over and note whether it is straight and true, +and whether the edges and corners are sharp. Strike it, and see +whether it gives a clear, ringing sound. Then weigh it and soak it in +water for twenty-four hours. Weigh it again, and if it is more than +one fifth heavier than it was before soaking, it is not of the first +quality. + +After the clay has been dug, it must be "tempered," that is, mixed +with water and about one third or one fourth as much sand as clay, and +left overnight in a "soak pit," a square pit about five feet deep. In +the morning the workmen shovel the mass over and feed it into the +machines for forming the bricks. The mixing is better done, however, +in a "ring pit." This is a circular pit twenty-five or thirty feet in +diameter, three feet deep, and lined with boards or brick. A big iron +wheel works from the center to the edge and back again for several +hours, through and through the clay. A method even better than this is +to put the clay and sand and water into a great trough, in which there +is a long shaft bristling with knives. The shaft revolves, mixes the +clay, and pushes it along to the end of the trough. This is called +"pugging," and the whole thing--trough, shaft, and knives--is a "pug +mill." + +In the old days bricks were always made by hand. The moulder stood in +front of a wet table whereon lay a heap of soft clay. He either wet or +sanded his mould to keep it from sticking. Meanwhile, his assistant +had cut a piece of clay and rolled it and patted it into the shape of +the mould. In making bricks, there can be no patching; the mould +must be filled at one stroke, or else there will be folds in the +brick. To make a good brick, the moulder lifts the clay up above his +head and throws it into the mould with all his force. Then he presses +it into the corners with his thumbs, scrapes off with a strip of wood +any extra clay, or cuts it off with a wire, smooths the surface of the +brick, puts mould and brick upon a board, jerks the mould up and +proceeds to make another brick. + +[Illustration: IN A NEW JERSEY BRICK MILL + +_Copyright by Underwood and Underwood._ + +This man is moulding a fire-brick to its final shape.] + +No matter how expert a moulder may be, brick-making by hand is slow +work, and in most places machines are used. In what is called the +"soft-mud" process, the clay is pushed on by the pug mill to the end +of the trough. There stands a mould for six bricks. A plunger forces +the clay into it, the mould is emptied, and in a single hour five +thousand bricks can be made. By what is called the "stiff-mud" +process, the stiff clay is put into a machine with an opening the size +of the end or side of a brick. The machine forces the clay through +this opening, cuts it off at the proper moment; and so makes bricks by +the thousand without either mould or moulder. A third way of making +brick is by what is called the "dry process." The clay is pulverized +and filled into moulds the length and breadth of a brick, but much +deeper, and with neither top nor bottom. One plunger from above and +another from below strike the clay in the mould with much force, and +make the fine, smooth brick known as "pressed brick." All this is done +by machinery, and some machines make six bricks at a time. These +"dry" bricks are fragile before they are burned, and must be handled +with great care. + +Bricks cannot be put into the kiln while they are still wet, for when +a brick is drying, it is a delicate article. It objects to being too +hot or too cold, and it will not stand showers or drafts. In some way +about a pound of water must be dried out of each brick; but if you try +to hurry the drying, the brick turns sulky, refuses to have anything +more to do with you, and proceeds to crack. To dry, bricks are +sometimes spread on floors; or piled up in racks on short pieces of +board called "pallets"; and sometimes they are put upon little cars +and run slowly through heated tunnels. The last is the best way for +people who are in a hurry, for it takes only from twenty-four to +thirty-six hours to make the bricks ready to go to the kiln to be +burned. + +In one sort of kiln, the bricks themselves make the kiln. They are +piled up in arches, but left a little way apart so the hot air can +move freely among them. The sides of the structure are covered with +burnt brick and mud, but the top is left open to allow the steam from +the hot bricks to escape. The fires are in flues that are left at the +bottom. They must burn slowly at first, but after a while, some forty +to sixty hours, the heat becomes intense. Thus far the bricks have +been grayish or cream-colored, but now, if there is iron in them, they +turn red; if there is lime, they turn yellow; if a large amount of +lime, they become flesh-colored. Besides this sort of kiln, which is +torn down when the bricks are sufficiently burned, there is also the +permanent kiln, which has fixed side walls and either an open or +closed top. Then, too, there is a "continuous" kiln. This has a number +of chambers, and the heat from each one passes into the next; so that +bricks in one chamber may be just warming up while in another they are +ready to be taken out. + +When the bricks come out of the kiln, some of them are good and some +are not. Those that were on the outside are not burned enough; those +next it are not well baked, but can be used for the middle of thick +walls. The next ones are of good quality; but those directly over the +fires are so hard and brittle that they are of little use except for +pavements. + +Paving-bricks, however, are not to be despised. They are not as smooth +and well finished as pressed brick, but they are exceedingly useful. +They need as much care in making as any others, and they must be +burned in a much hotter fire to make them dense and hard. The tests +for paving-bricks are quite different from those for ordinary +building-brick. If first-class paving-bricks weighing fifty pounds are +soaked in water for twenty hours, they take up so little water that +they will not weigh more than fifty-one or fifty-one and a half pounds +when taken out. To find out how hard they are, the bricks are weighed +and shaken about with foundry shot for a number of hours. Then they +are weighed again to see how much of their material has been rubbed +off. A third test is to put one brick on edge into a crushing machine +to see how much pressure it will stand. Paving-brick is cheaper than +granite blocks, and if it has a good foundation of concrete covered +with sand, it will last about three fourths as long. Brick is less +noisy than stone and is easier to clean. + +Not so very long ago, when particularly handsome bricks were needed +for the outside of walls and other places where they would be +conspicuous, they were "re-pressed"; that is, they were made by hand +or in a "soft-mud" machine, and then, after drying for a while, were +put into a re-pressing machine to give them a smooth finish. These +machines are still used, but they are hardly necessary, for the +"dry-clay" brick machine will turn out a smooth brick in one +operation. + +Another substance which is made of almost the same materials as brick +is terra cotta. To make this, fire brick, bits of pottery, partly +burned clay, and fine white sand are ground to a powder and mixed very +thoroughly. This mixture is moulded, dried, and burned. Until +recently, all terra cotta was of the color that is called by that +name, but now it is made in gray, white, and bronze as well. + +Bricks are laid in mortar, and this makes a wall one solid mass and +stronger than it could be without any cement. But mortar does more +than this. It is more elastic than brick, and therefore, when a wall +settles, the mortar yields a little, and this often prevents the +bricks from cracking. Bricks are always thirsty, and if one is laid in +mortar, it will suck the moisture out of it almost as a sponge will +suck up water. The mortar thus has no chance to set, and so is not +strong as it should be. That is why the bricklayer wets his bricks, +especially in summer, before he puts them in place. Lime or cement +mortar will not set in freezing weather, and a brick building put up +in the winter is in danger of tumbling down when the warm days of +spring arrive. + +This thirstiness of bricks is their greatest fault. Three or four days +of driving rain will sometimes wet through a brick wall two feet +thick, crumbling the plaster and spoiling the wallpaper. That is why +it is a poor plan to plaster directly on the brick wall of a house. +"Furring" strips, as they are called, or narrow strips of wood, should +be fastened on first and the laths nailed to these, or the wall can be +painted or oiled on the outside. The best way, however, though more +expensive, is to build the wall double. Then there is air between the +two thicknesses of brick. Air is a poor conductor of heat; so in +summer it keeps the heat out, and in winter it keeps it in. + +But brick will suck up water from the ground as well as from a storm; +and therefore, when a brick house is to be built in a wet place, there +ought to be a three-eighths-inch layer of something waterproof, like +asphalt and coal tar, put on top of one of the layers of brickwork to +prevent the moisture from creeping up. + +Bricks have their faults, but they will not burn, and when properly +used, they make a most comfortable and enduring house. + + + + +V + +AT THE GOLD DIGGINGS + + +When gold was first discovered in California, in 1848, people from all +over the world made a frantic rush to get there, every one of them +hoping that he would be lucky enough to make his fortune, and fearing +lest the precious metal should be gone before he could even begin to +dig. The gold that these men gathered came from what were called +"placers"; that is, masses of gravel and sand along the beds of +mountain streams. Each miner had a pan of tin or iron, which he filled +half-full of the gravel, or "pay dirt," as the miners called it. Then, +holding it under water, he shook off the stones and mud over the side +of the pan, leaving grains of gold mixed with black sand at the +bottom. This black sand was iron, and after a while the miners removed +it with a magnet, dried what remained, and blew away the dust, leaving +only the grains of gold. + +Another contrivance which soon came into use was the "cradle." This +was a long box, sometimes only a hollowed-out log. At the top was a +sieve which sifted out the stones. Nailed to the bottom of the cradle +were small cleats of wood, or "riffles," which kept the water from +running so fast as to sweep the gold out of the cradle with it. The +cradle was placed on rockers and was also tilted slightly. The miner +shoveled the gravel into the top of the cradle and his partner rocked +it. The sieve kept back the stones, the water broke up the lumps of +earth and gravel and washed them down the cradle, and the grains of +gold were stopped by the riffles, and sank to the bottom. Sometimes +the "pay dirt" continued under a stream. To get at it, the miners +often built a little canal and turned the water into a new channel; +then they could work on the former bed of the river. + +Before many years had passed, the gold that was near the surface had +been gathered. The miners then followed the streams up into the +mountains, and found that much of the gold had come from beds where in +ancient times rivers had flowed. There was gold still remaining in +these beds, but it was poorly distributed, the miners thought. +Sometimes there would be quite an amount in one place, and then the +miner would dig for days without finding any more. Even worse than +this was the fact that these gravel beds were not on the top of the +ground, but were covered up with soil and trees. Evidently the slow +work with pans and cradles would not pay here; but it occurred to some +one that if a powerful stream of water could be directed against the +great banks of earth, as water is directed against a burning building, +they would crumble, the dirt could be washed down sluices, and the +gold be saved. This was done. Great reservoirs were built high up in +the mountains, and water was brought by means of ditches or pipes to a +convenient place. Then it was allowed to rush furiously through a +hose and nozzle, and the great stream coming with tremendous force was +played upon the banks of gravel. The banks crumbled, the gravel was +washed into a string of sluices, or long boxes with riffles to catch +the gold. Soon the miners found that if quicksilver was put into these +sluices, it would unite with the gold and make a sort of paste called +"amalgam." Then if this amalgam was heated, the quicksilver would be +driven off in the form of gas, and the gold would remain in a +beautiful yellow mass. + +[Illustration: HYDRAULIC GOLD MINING + +A placer mine at Gold Point, California, where tremendous streams of +water under high pressure are busy washing away the side of a +gold-bearing hill.] + +The ancient rivers had also carried gold to the valleys, and to +collect this a dredge, which the miners called a "gold ship," came +into use. The "ship" part of this machine is an immense flat scow. +Stretching out from one end is something which looks like a moving +ladder. This is the support of an endless chain of buckets, each of +which can bite into the gravel and take a mouthful of five or six +hundred pounds. They drop this gravel into a big drum which is +continually revolving. Water flows through the drum, and washes out +the sand and bits of gold over large tables, where by means of riffles +and quicksilver the gold is captured. This scow was usually on dry +land at first; but its digging soon made a lake, and then it floated. +It must be more fascinating to hold a pan in your own hands and pick +out little grains of gold or perhaps even a big piece of it with your +own fingers, but if the gravel is good the dredge makes more money. + +In Alaska the great difficulty in mining is that, except at the +surface, the ground is frozen all the year round. At first, the miners +used to thaw the place where they wished to dig by building wood +fires; but this was a slow method, and now the thawing is done by +steam. They carry the steam in a pipe to the place where the digging +is to be done, and send it through a hose. At the end of the hose is a +pointed steel tube. They hammer this tube into the ground and let some +steam pass through the nozzle. This softens the ground so that picks +and shovels may be used. There is generally cold enough in Alaska, but +once at least the miners had to manufacture it. The gold-bearing +gravel was deep, the ground was flat, and it was often overflowed. +They set up a freezing plant, and shut in their land with a bulkhead +of ice several feet thick. Then they pumped out what water was already +in and did their work with no more trouble. + +When gold began to grow less in the California gravel, the miners +looked for it in the rocks on the mountain-side. The placer miners +laughed at them and called their shafts "coyote holes"; but in time +the placers failed, while nearly all of our gold to-day comes from +veins of white quartz in the rocks. A vein of gold is the most +capricious thing in the world. It may be so tiny that it can hardly be +seen, then widen and grow rich in gold, then suddenly come to an end. +This is why a new mine is so uncertain an enterprise. The gold may +hold out and bring fortunes to the investors, or it may fail, and then +all they will have to show for their money is the memory that they +put it into a hole in the ground. The managers of a few of the +well-established mines, however, have explored so far as to make sure +that there is gold enough for many years of digging. + +The mining engineer must be a very wide-awake man. It is not enough +for him simply to remember what was taught him in the schools of +mining; he must be bright enough to invent new ways of meeting +difficulties. No two mines are alike, and he must be ready for all +sorts of emergencies. A gold mine now consists of a shaft or pit dug +several hundred feet down into the rock, with levels or galleries +running off from it and with big openings like rooms made where the +rock was dug out. The roofs of the rooms are supported by great +timbers. To break away the rock, the miner makes a hole with a rock +drill worked by electricity or compressed air, puts powder or dynamite +into the hole and explodes it. The broken rock is then raised to the +surface and crushed in a "stamping mill." Here the ore is fed into a +great steel box called a "mortar." Five immense hammers, often +weighing a thousand pounds apiece, drop down upon the ore, one after +another, until it is fine enough to go through a wire screen in the +front of the box. When two hundred or more of these hammers are +pounding away with all their might, a stamping mill is a pretty noisy +place. The ore, crushed to a fine mud, now runs over sloping tables +covered with copper. Sticking to the top of the copper is a film of +quicksilver. This holds fast whatever gold there may be and makes an +amalgam, which is scraped off from time to time, and the quicksilver +is driven from the gold by heat. + +Gold that is not united with other metals is called "free milling +gold." Much of it, however, is found in combination with one metal or +another, and is known as "rebellious" or "refractory" gold. Such gold +may sometimes be set free by heat, and sometimes by chemicals. One way +is by the use of chlorine gas, and the story of it sounds almost like +"The house that Jack built." It might run somewhat like this: This is +the salt that furnishes the chlorine. This is the chlorine gas that +unites with the gold. This is the chloride that is formed when the +chlorine gas unites with the gold. This is the water that washes from +the tank the chloride that is formed when the chlorine gas unites with +the gold. This is the sulphate of iron that unites with the chlorine +gas of the chloride that the water washes from the tank that is formed +when the chlorine gas unites with the gold--and leaves the gold free. + +Another method is by the use of cyanide. More than a century ago a +chemist discovered that if gold was put into water containing a little +cyanide, the gold would dissolve, while quartz and any metals that +might be united with the gold would settle in the tank. The water in +which the gold is dissolved is now run into boxes full of shavings of +zinc and is "precipitated" upon them; that is, the tiny particles of +gold in the water fall upon the zinc and cling to it. Zinc melts more +easily than gold, so if this gilded zinc is put into a furnace, the +zinc melts and the gold is set free. + +Very often gold is found combined with lead or copper. It must then be +melted or smelted in great furnaces. The metal is heavier than the +rock and settles to the bottom of the furnace. It is then drawn off +and the gold is separated from the other metals, usually by +electricity. + +Sometimes large pieces of gold called "nuggets" are found by miners. +The largest one known was found in Australia. It weighed 190 pounds +and was worth $42,000. Sometimes spongy lumps of gold are found; but +as a general thing gold comes from the little specks scattered through +veins in rock, and much work has to be done before it can be made into +coins or jewelry. It is too soft for such uses unless some alloy, +usually copper or silver, is mixed with it to make it harder. +Sometimes it is desirable to know how much alloy has been added. The +jeweler then makes a line with the article on a peculiar kind of black +stone called a "touchstone," and by the color of the golden mark he +can tell fairly well how nearly pure the article is. To be more +accurate, he pours nitric acid upon the mark. This eats away the alloy +and leaves only the gold. + +Gold is a wonderful metal. It is of beautiful color; it can be +hammered so thin that the light will shine through it; few acids +affect it, and the oxygen which eats away iron does not harm it. Pure +gold is spoken of as being "twenty-four carats fine," from _carat_, an +old weight equal to one twenty-fourth of an ounce troy. Watchcases +are from eight to eighteen carats fine; chains are seldom more than +fourteen; and the gold coins of the United States are about eleven +parts of gold and one of copper. Coins wear in passing from one person +to another, and that is why the edges are milled, so that it may be +more easily seen when they have become too light to be used as coins. +When such pieces come into the hands of the Government, they must be +recoined. + + + + +VI + +THE STORY OF A SILVER MINE + + +A man who goes out in search of a mine is called a "prospector." The +best prospector is a man who has learned to keep his eyes open and to +recognize the signs of gold and silver and other metals. A faithful +friend goes with him, a donkey or mule which carries his bacon and +beans, blankets, saucepan, and a few tools, such as a pan, pick, +shovel, hammer, and axe. Sometimes the prospector also takes with him +a magnifying glass and a little acid to test specimens, but usually he +trusts to his eyes alone. + +When these few things have been brought together, the prospector and +the donkey set out. They wander over the hills and down into the +canyons. If a rock is stained red, the prospector examines it to see +whether it contains iron; if it is green, he looks for copper. In the +canyons and along the creeks he often tests the gravel for traces of +some valuable metal. If he finds any of these traces along the stream, +he follows them on the bank until they stop; then he carefully +examines the bank of the stream or the nearest hillside. If he +continues to find bits of metal, they will lead him to a vein of ore, +from which they have been broken by the wind, rain, and frost. + +Generally a prospector is looking for some one special metal, and in +his search he often overlooks some other metal; for instance, +thousands of the gold-seekers who rushed to California in 1849 hurried +through Nevada on their way. If they had only known what was under +their feet, they would have taken their picks and shovels and begun to +dig, instead of trying to get out of the region as soon as might be. +Ten years later, the California placers were becoming exhausted, and +miners began to go elsewhere in their search for gold. + +Among those who were working in what is now the State of Nevada were +two Irishmen who had been unlucky in California and had fared no +better in Nevada. They wanted to go somewhere else, but they had not +money enough for the journey; so they kept on with their work at the +foot of Mount Davidson, washing the gravel and saving the little gold +that they found. They were annoyed by some heavy black stuff that +united with the quicksilver in their cradles, interfered with the +saving of the gold, and put them in a very bad temper. At length a man +named Henry Comstock came along, who told them that this black stuff +was silver ore. They examined the mountain-side, and discovered the +outcrop or edge of a great vein containing gold and also silver. It is +no wonder that people rushed from the east and west to the wonderful +new mines, for it was plain that these new "diggings" were not mere +placers, but rich veins that many years of working might not exhaust. +Every newcomer hoped to discover a vein; and within a year or two the +district around the Comstock lode was full of deep shafts, many of +them abandoned and half-hidden by low brush, but some of them yielding +quantities of gold and silver. Before this, there had been only about +a thousand people in what is now Nevada, but in two years after the +discovery of silver, there were 16,000, and a new Territory was +formed. + +The miners knew how to get gold out of ore, but silver was another +matter, and some of it was difficult to extract. They had so much +trouble that they were ready to believe in any treatment of the ore, +no matter how absurd, that promised to help them out of their +difficulties. Some of them were actually persuaded that the juice of +the wild sagebrush would bring the silver out. It is no wonder that +they were troubled, for in the Comstock lode were not only gold and +silver, but ten or twelve other metals or combinations of silver with +something else. At length processes were invented for treating the +different kinds of ore. Some kinds were crushed in a stamping mill, +then ground to a powder and mixed with quicksilver or mercury. This +mercury united with both the gold and the silver, making an amalgam. +The amalgam, together with the finely ground ore, was put into a +"settler," and here the heavy amalgam sank to the bottom and was then +strained. The extra mercury was collected, and the amalgam was put +into a retort or kettle and heated. The mercury became a gas and was +driven off from the gold and silver, then caught in a vessel cool +enough to condense it, just as a cold plate held in steam will +collect drops of water. Sometimes the ore was mixed with copper and +lead. In that case common salt and copper sulphate were used. Some ore +had to be roasted in a furnace in order to drive off the sulphur. + +[Illustration: THE STORY OF A SPOON + +_Courtesy The Gorham Co._ + +(1) Silver strip blanked. (2) Pinched. (3) Graded. (4) Outlining of +Handle. (5) Stamped Handle. (6) Spoon completely trimmed. (7, 8) +Finished spoons.] + +There were great and unusual dangers to be met in getting the ore. The +vein of quartz which bore it was fifty or sixty feet wide. Some was +hard, and some so soft and crumbling that pillars would not hold up +the roof. The passageways were then lined with heavy logs standing on +either side, other logs laid across their tops, and all bolted firmly +together. Nevertheless, they twisted and fell, and slowly but +certainly the whole mass of earth and rock, two hundred or more feet +in thickness, was coming down upon the heads of the miners. The work +on the Comstock mines had come to an end unless a man could be found +able to invent some system of support not laid down in the books. The +man was found. He took short, square timbers five or six feet long, +put them together as if they were the sides and ends of square boxes, +and piled them one above another, making hollow pillars. He fastened +these firmly together and filled the space inside with waste rock, +thus making strong, solid pillars that would support almost any weight +that could be put upon them. + +There were two other dangers, water and heat. The vein was porous and +water was constantly trickling out of it. Then, too, there were "water +pockets," or natural reservoirs in the rock, and any moment the +stroke of a pick might let out a torrent and force the miners to run +for their lives. Sometimes minerals were dissolved in this water, and +the men with closed eyes and swollen faces had to be hurried to the +surface for treatment. Powerful pumps had to be used and the water +sent away through long lines of pipes. This water was warm, and in +very deep workings in the Comstock vein it was boiling hot. Even with +quantities of ice sent down to cool them, the men could work in some +places only a short time. + +In San Francisco there was a mining engineer named Adolph Sutro who +planned to remedy these troubles by driving a big four-mile tunnel +through the heart of the mountain, letting out the hot water and the +foul air. The owners of some of the mines joined him in raising the +money, and the tunnel was dug. Through this the water ran out. The +mines were freed of foul air and fresh air was driven in. + +The Comstock lode has given up an amazing amount of precious metal. +Between 1860 and 1890 it produced $340,000,000. After 1890, however, +its product grew less. The vein was not so rich, the price of silver +fell, while the cost of mining it at great depths increased. Not +nearly so much was mined, and at length water rose in the mines up to +the level of the Sutro Tunnel. In 1900 new machinery was put in and +new methods were adopted, such as treating the tailings with cyanide +and so saving much of the precious metal from them. From the beginning +the Comstock mines have been so ready to follow improved methods that +they have been called the mining school of the world. + +Great quantities of silver are used for making jewelry and for +tableware. The one objection to its use is that silver likes to unite +with sulphur, and thus the silver easily becomes black. There is +sulphur in the yolk of an egg and that is why the spoon with which it +has been eaten turns black. Even if silverware is not used, it +tarnishes, especially in towns, because there is so much sulphureted +hydrogen in the air. In perfectly pure air, it would not tarnish. +Silver is harder than gold, but not hard enough to be used without +some alloy, usually copper. Tableware is "solid" even if it contains +alloy enough to stiffen it. It is "plated" if it is made of some +cheaper metal and covered with silver. The old way of doing this was +to fasten with bits of solder a thin sheet of silver to the cup or +vase or whatever was in hand and heat it. This did fairly well for +large, smooth articles; but it was almost impossible to finish the +edges of spoons so as not to show the two metals. If you look at a +plated spoon to-day, however, you will find that there is no break at +the edge, and so far as you can tell by the eye, it is solid silver. +If you look on the back of the spoon, you will perhaps see "Rogers +Bros. 1846." These men were the first silvermakers in this country to +plate tableware by electricity. To make a spoon, they formed one out +of iron or copper and made sure that it was perfectly clean. Then +across a bath of silver cyanide, potassium cyanide, and water they +laid two metal rods, and from these they hung a spoon at one end and a +plate of silver at the other. These rods were connected with the two +poles of a battery. The electrical current passed through them, +released the silver from the silver cyanide, and this was deposited +upon the spoon. The cyanide that had lost its silver took enough more +from the silver plate to make up. The amount of silver on the spoon +depends upon the length of time it remains in the bath. It is weighed +before plating and again afterwards, to make sure that the proper +amount of silver has been deposited upon it. On the back of many +plated articles you will see the words "Triple plate" or "Quadruple +plate." If the article has been made by a reliable firm, this means +that the triple plate it manufactures contains three times as much +silver as "single plate," and that quadruple plate contains four times +as much. A piece of silver looks just as well if it has stayed in the +bath only a few minutes, but of course it has taken on so little +silver that this will soon wear off and show the cheaper metal. + +A large amount of silver is used for coins. When the United States +needs dollars, half-dollars, quarters, and dimes, notice is given and +offers are called for, stating the quantity for sale and its price. +When it is delivered, it is first of all "assayed"; that is, tested to +find out how nearly pure it is and how much it is worth. Next it is +refined, or purified from other metals, mixed with a little copper to +harden it, then melted again and poured into moulds to make bars. If +dollars are to be made, the bar is made thinner by passing it between +heavy rollers, and blanks for dollars are cut out with a die. These +blanks are weighed and every one that is too heavy or too light is put +back to be melted over again. Thus far these dollars are only round, +smooth pieces of metal. They must be milled to give them a rough edge, +and they must be stamped. For stamping, the piece of metal is placed +between two dies, one above and one below, and these close upon it +with a force of one hundred and fifty tons. Every part of the process +of manufacturing money is carried on with the utmost care. The places +where coins are made are called "mints." The United States has four; +the oldest is in Philadelphia, and there are branch mints in San +Francisco, New Orleans, and Denver. Coins minted in Philadelphia have +no distinguishing mark; but coins minted in San Francisco are marked +with a tiny "S"; if minted in New Orleans, with an "O"; and if in +Denver, with a "D." + + + + +VII + +IRON, THE EVERYDAY METAL + + +Did you ever realize that your food and clothes, your books, and the +house in which you live all depend upon iron? Vegetables, grains, and +fruits are cultivated with iron tools; fish are caught with iron +hooks, and many iron articles are used in the care and sale of meat. +Clothes are woven on iron looms, sewed with iron needles, and fastened +together with buttons containing iron. Books are printed and bound by +iron machines, and sometimes written with iron pens or on iron +typewriters. Houses are put together with nails; and indeed, there is +hardly an article in use that could be made as well or as easily if +iron was not plenty. If you were making a world and wanted to give the +people the most useful metal possible, the gift would have to be iron; +and the wisest thing you could do would be to put it everywhere, but +in such forms that the people would have to use their brains to make +it of service. + +This is just the way with the iron in our world. Wherever you see a +bank of red sand or red clay or a little brook which leaves a red mark +on the ground as it flows, there is iron. Iron is in most soils, in +red bricks, in garnets, in ripening apples, and even in your own +blood. It forms one twentieth part of the crust of the earth. Iron +dissolves in water if you give it time enough. If you leave a steel +tool out of doors on a wet night, it will rust; that is, some of the +iron will unite with the oxygen of the water. This is rather +inconvenient, and yet in another way this dissolving is a great +benefit. Through the millions of years that are past, the oxygen of +the rain has dissolved the iron in the hills and has worked it down, +so that now it is in great beds of ore or in rich "pockets" that are +often of generous size. One of them, which is now being mined in +Minnesota, is more than two miles long, half a mile wide, and of great +thickness. The rains are still at work washing down iron from the +hills. They carry the tiny particles along as easily as possible until +they come upon limestone. Then, almost as if it was frightened, the +brook drops its iron and runs away as fast as it can. Sometimes it +flows into a pond or bog in which are certain minute plants or animals +that act as limestone does, and the particles of iron fall to the +bottom of the pond. In colonial days much of the iron worked in +America was taken from these deposits. One kind of iron is of special +interest because it comes directly from the sky, and falls in the +shape of stones called "meteorites," some of which weigh many tons. In +some of the old fables about wonderful heroes, the stories sometimes +declare that the swords with which they accomplished their deeds of +prowess fell straight from the heavens, which probably means that they +were made of meteoric iron. Fortunately for the people and their +homes, meteorites are not common, but every large museum has +specimens of them. + +It is not especially difficult to make iron if you have the ore, a +charcoal fire in a little oven of stones, and a pair of bellows. Put +on layers of charcoal alternating with layers of ore, blow the +bellows, and by and by you will have a lump of iron. It is not really +melted, but it can be pounded and worked. This is called the "Catalan +method," because the people of Catalonia in Spain made iron in this +way. It is still used by the natives of the interior of Africa. But if +all the iron was made by this method, it would be far more costly than +gold. The man who makes iron in these days must have an immense "blast +furnace," perhaps one hundred feet high, a real "pillar of fire." Into +this furnace are dropped masses of ore, and with it coke to make it +hotter and limestone to carry off the silica slag, or worthless part. +To increase the heat, blasts of hot air are blown into the bottom of +the furnace. This air is heated by passing it through great steel +cylinders as high as the furnace. The fuel used is nothing more than +the gases which come out at the top of the furnace. + +The slag is so much lighter than iron that when the ore is melted the +slag floats on top just as oil floats on water, and can be drained out +of the furnace through a higher opening than that through which the +iron flows. The slag tap is open most of the time, but the iron tap is +opened only once in about six hours. It is a magnificent sight when a +furnace is "tapped" and the stream of iron drawn off. Imagine a great +shed, dark and gloomy, with many workmen hurrying about to make ready +for what is to come. The floor is of sand and slopes down from the +furnace. Through the center of this floor runs a long ditch straight +from the furnace to the end of the shed. Opening from it on both sides +are many smaller ditches; and connecting with these are little +gravelike depressions two or three feet long and as close together as +can be. These are called "pigs." When the time has come, the workmen +gather about the furnace, and with a long bar they drill into the +hard-baked clay of the tapping hole. Suddenly it breaks, and with a +rush and a roar the crimson flood of molten iron gushes out. It flows +down the trench into the ditches, then into the pigs, till their whole +pattern is marked out in glowing iron. Now the blast begins to drive +great beautiful sparks through the tapping hole. This means that the +molten iron is exhausted. The blast is turned off, and the "mud-gun" +is brought into position and shoots balls of clay into the tapping +hole to close it for another melting, or "drive." The crimson pigs +become rose-red, darken, and turn gray. The men play streams of water +over them and the building is filled with vapor. As soon as the pigs +are cool enough, they are carted away and piled up outside the +building. + +In some iron works moulds of pressed steel carried on an endless chain +are used instead of sand floors. The chain carries them past the mouth +of a trough full of melted iron. They are filled, borne under water +to be cooled, and then dropped upon cars. A first-class machine can +make twenty pigs a minute. + +[Illustration: IN THE STEEL FOUNDRY + +It is a dangerous business to visit a steel mill. Tremendous kettles +travel overhead on huge cranes, hot metal flows from unexpected +places, and there is a constant glow and steam and roar everywhere to +confuse the unwary.] + +Most of the iron made in blast furnaces is turned into steel. Steel +has been made for centuries, but until a few years ago the process was +slow and costly. A workman's steel tools were treasures, and a good +jackknife was a valuable article. Railroads were using iron rails. +They soon wore out, but at the suggestion to use steel, the presidents +of the roads would have exclaimed, "Steel, indeed! We might as well +use silver!" Trains needed to be longer and heavier, but iron rails +and bridges could not stand the strain. Land in cities was becoming +more valuable; higher buildings were needed, but stone was too +expensive. Everywhere there was a call for a metal that should be +strong and cheap. Iron was plentiful, but steel was dear. A cheaper +method of making iron into steel was needed; and whenever there is +pressing need of an invention, it is almost sure to come. Before long, +what is known as the "Bessemer process" was invented. One great +difficulty in the manufacture of steel was to leave just the right +amount of carbon in the iron. Bessemer simply took it all out, and +then put back exactly what was needed. Molten iron, tons and tons of +it, is run into an immense pear-shaped vessel called a "converter." +Fierce blasts of air are forced in from below. These unite with the +carbon and destroy it. There is a roar, a clatter, and a clang. +Terrible flames of glowing red shoot up. Suddenly they change from red +to yellow, then to white; and this is the signal that the carbon has +been burned out. The enormously heavy converter is so perfectly poised +that a child can move it. The workmen now tilt it and drop in whatever +carbon is needed. The molten steel is poured into square moulds, +forming masses called "blooms," and is carried away. More iron is put +into the converter, and the work begins again. + +The Bessemer process makes enormous masses of steel and makes it very +cheaply; but it has one fault--it is too quick. The converter roars +away for a few minutes, till the carbon and other impurities are +burned out; and the men have no control over the operation. In what is +called the "open-hearth" process, pig iron, scrap iron, and ore are +melted together with whatever other substances may be needed to make +the particular kind of steel desired. This process takes much longer +than the Bessemer, but it can be controlled. Open-hearth steel is more +homogeneous,--that is, more nearly alike all the way through,--and is +better for some purposes, while for others the Bessemer is preferred. + +Steel is hard and strong, but it has two faults. A steel bar will +stand a very heavy blow and not break, but if it is struck gently many +thousand times, it sometimes crystallizes and may snap. A steel rail +may carry a train for years and then may crystallize and break and +cause a wreck. Inventors are at work discovering alloys to prevent +this crystallization. The second fault of steel is that it rusts and +loses its strength. That is why an iron bridge or fence must be kept +painted to protect it from the moisture in the air. + +If all the iron that is in use should suddenly disappear, did you ever +think what would happen? Houses, churches, skyscrapers, and bridges +would fall to the ground. Railroad trains, automobiles, and carriages +would become heaps of rubbish. Ships would fall apart and become only +scattered planks floating on the surface of the water. Clocks and +watches would become empty cases. There would be no machines for +manufacturing or for agriculture, not even a spade to dig a garden. +Everybody would be out of work. If you wish to see how it would seem, +try for an hour to use nothing that is of iron or has been made by +using iron. + + + + +VIII + +OUR GOOD FRIEND COPPER + + +Where did rocks come from? + +Some were deposited in water, like limestone and like the shale and +sandstone that lie over the strata of coal. Others were made by fire, +and were thrown up in a melted state from the interior of the earth. +Such rocks are the Giant's Causeway in Ireland and the Palisades of +the Hudson River. They are called "igneous" rocks, from the Latin word +_ignis_ meaning "fire." + +When the igneous rocks were thrown up to the surface of the earth, +they brought various metals with them. How the metals happened to be +there ready to be brought up, no one knows. Some people think they +were dissolved in water and then deposited; others think that +electricity had something to do with their formation. However that may +be, metals were brought up with the igneous rocks, and one of these +metals is copper. + +Now, to one who did not know how to work iron, copper was indeed a +wonderful treasure, for it made very good knives and spoons. The +people who lived in this country long before the Indians came +understood how to use it, and after a while the Indians themselves +found out its value. They did not trouble themselves to dig for it; +they simply picked it up from the ground, good pure metal in lumps; +and with stones for hammers they beat it into knives. + +There was only one place in what is now the United States where they +could do this, and that was in northern Michigan. A long point of land +stretches out into Lake Superior as if it was trying to see what could +be found there. Just beyond its reach is Isle Royal; and in these two +places there was plenty of copper, enough for the Indians, enough for +the people who have come after them, and enough for a great many more. +One piece of copper which the Indians did not pick up, and the United +States Government did, is the famous Ontonagon Boulder, so called +because it was found near the Ontonagon River. It weighs more than +three tons. The Indians would have been glad to make use of it, but it +was too hard for their tools, and so they are said to have worshiped +it as a god. It is now in the National Museum in Washington. + +The lumps of copper, such as those which delighted the hearts of the +Indians, are known to-day as "barrel" copper, because they are of a +good size to be dropped into barrels and carried away for smelting. +The great boulders which the Indians could not use are called "mass" +copper. Sometimes they weigh as much as five hundred tons. The copper +in them is almost pure, and a big boulder is worth perhaps $200,000. +Nevertheless, the mine-owners do not rejoice when they come upon such +a mass in their digging, for it cannot be either dug or blasted, and +has to be cut away with chisels of chilled steel. Now, a mine may be +wonderfully rich in metal, but if working it costs too much, then +another mine with less metal but more easily worked will pay better. +So it is with these great masses of copper. They are interesting to +study and they look well in museums, but they do not pay so well as +the "stamp" copper which is found in humble little bits in the gangue, +or the rock of the vein, and has to be pounded in a stamp mill. This +gangue is dug out and broken up as in mines of other metals. The +copper is much heavier than the rock, so it is easy to get rid of the +worthless gangue by means of a flow of water. The gangue of the +Michigan mines is exceedingly hard, but the stamps are so powerful +that one can crush five hundred tons in less than twenty-four hours. +Some copper can be taken out of the mortars at once, but the rest of +the broken gangue is fed to jigs, or screens, which are kept under +jets of water. The water is thrown up from below and the lighter rock +is tossed away, while the heavier copper falls through the tiny holes +in the screens. + +[Illustration: IN A COPPER SMELTER + +The men are pouring hot copper into moulds for castings.] + +After the ore has been through all these experiences, it comes out +looking like dark-colored sand or coarse brown sugar. It is not +interesting, and no one who saw it for the first time would ever fancy +that it was going to turn into something beautiful. It is dumped into +freight cars and trundled off to the smelting furnaces. But however +uninteresting it looks, it is well worth while to follow these cars to +see what happens to it at the smelters. First of all, even before it +goes into the smelting furnace, it must be roasted. There is usually +sulphur combined with the copper, and roasting will get rid of much of +it. In some places this is done by building up a great heap of ore +with a little wood. The wood is kindled, and by the time it has burned +out, the sulphur in the ore has begun to burn, and in a good-sized +heap it will continue to burn for perhaps two months. + +Such a heap is a good thing to keep away from, for the fumes of +sulphur are very disagreeable. Indeed, they will kill trees and other +growing things wherever the wind may carry them, even several miles +away. The managers of mines of copper as well as of gold and silver +have learned to economize; and it has been found that instead of +letting these fumes go into the air, they may be made to pass through +acid chambers lined with zinc and full of water. The water holds the +fumes, and can be used in making sulphuric acid. + +After the ore has been roasted, it is put into the furnace for +smelting. If you should make an oven and put into it a mixture of wood +and roasted copper, that would be a smelting furnace. Set the wood on +fire, pump in air to make the flame hot, and if your furnace could be +made hot enough,--that is, 2300° F., or about eleven times as hot as +boiling water,--you could smelt copper. Of course the furnace of a +real smelting factory will hold tons and tons of copper ore and has +all sorts of improvements, but after all it is in principle only an +oven with wood and ore and draft. Another sort of furnace, which is +better for some kinds of ore, has a grate for the fire and a bed above +it for the copper. + +Imagine an enormous furnace holding between two and three hundred tons +of metal and burning with such a terrific heat that by contrast +boiling water would seem cool and comfortable. Suddenly, while you +stand looking at it, but a long way off, a door flies open and the +most beautiful cascade--only it is not a waterfall, but a _copper_ +fall--pours out. It looks like red, red gold, rich and wonderful, with +little flames of red and blue dancing over it. It might almost be one +of the fire-breathing dragons of the old story-books; and if it should +get loose, it would devour whomever it touched far quicker than any +dragon. It hardly seems as if any one could manage such a monster; but +it looks easy, after you have seen it done. An enormous horizontal +wheel revolves slowly. On its edge are moulds shaped like bricks, but +much larger. On the hub of the wheel a workman sits to direct the +filling of these. A set of them is filled, and moves on, and others +take their place. When they are partly cooled, another workman, at the +farther side of the wheel, pries them out of the mould and drops them +into water. Then by the aid of the fingers of a machine and those of +men, they are loaded upon cars. + +In copper there is often some gold and silver. The precious metals do +not make the copper any better, and if they can be separated from it, +they are well worth the trouble. This is done by electricity. It is so +successful that the metallurgists are hoping soon to take a long step +ahead and by means of electricity to produce refined copper directly +from the ore. Indeed, this has been done already in the laboratories, +but before the managers of mines can employ the method, a way of +making it less expensive must be discovered. + +No mine that wastes anything is as well managed as it might be; and +superintendents are constantly on the watch for cheaper methods and +for ways to make the refuse matter of use. Even the scoria, or slag +from the furnaces, has been found to be good for something, and now it +is made into a coarse sort of brick that for certain rough uses is of +value. By the way, the shaft of a copper mine, the Red Jacket, has +shown itself of use in a manner that no one expected, namely, it helps +to prove that the earth turns around. This shaft is the deepest mining +shaft in the world, and when you get into the cage, you go down a full +mile toward the center of the earth. If you drop any article into the +shaft, it always strikes the east side before reaching the bottom. The +only way to explain this is that the earth turns toward the east. + +Copper mixed with zinc forms brass, which is harder than copper alone. +It tarnishes, though not so easily as copper; but a coat of varnish +will protect it till the varnish wears off. A good way to find out the +many uses of brass and to see how valuable they are is to go along the +street and through a house and make a list. On the street you will see +signs, harness buckles, and buttons, everywhere. Look on the +automobiles and fire engines for a fine display of brass, polished and +shining. In the house you will find brass bedsteads, curtain rods, +faucets, pipes, drawerpulls, candlesticks, gas and electric fixtures, +lamps, the works of clocks and watches, and scores of other things. +You will not have any idea how many they are till you begin to count. + +Copper mixed with tin forms bronze. Go into a hardware store and look +at the samples of bronze outside of each drawer, and you will be +surprised that there are so many. Bronze does not change even when in +the open air for ages. That is one reason why it has always been so +much used for statues. There are two strange facts about this mixture. +One is that bronze is harder than either copper or tin. The other is +that if you mix one pint of melted copper with one pint of tin, the +mixture will be less than a quart. Just why these things are so, no +one is quite certain. Mathematics declares that the whole is equal to +the sum of its parts; but in this one case the whole seems to be less +than the sum of its parts. + +Another reason why bronze is so much used for statues is that the +castings are smooth. I once went to a foundry to have a brass ornament +shaped somewhat like a cone made for a clock. The foundryman formed a +mould in clay and poured the melted brass into it. When it had cooled, +the mould was broken off and the ornament taken out; but it was of no +use because it was so full of little hollows that it could not be made +smooth without cutting away a great deal of it. The man had to try +three times before he succeeded in making one that could be polished. +If it had been made of bronze, there would have been no trouble, +because bronze, hard as it is after it cools, flows when it is melted +almost as easily as molasses and fills every little nook and corner of +the mould. + +A famous Latin poet named Horace, who lived two thousand years ago, +wrote of his poems, "I have reared a monument more lasting than +bronze"; and he was right, for few statues have endured from his day +to ours, but his poems are still read and admired. + +Bells are made of bronze, about three quarters copper and one quarter +tin. It is thought that much copper gives a deep, full tone, and that +much tin with, sometimes, zinc makes the tone sharp. The age of a bell +has something to do with its sound being rich and mellow; but the +bellmaker has even more, for he must understand not only how to cast +it, but also how to tune it. If you tap a large bell, it will, if +properly tuned, sound a clear note. Tap it just on the curve of the +top, and it will give a note exactly one octave above the first. If +the note of the bell is too low, it can be made higher by cutting away +a little from the inner rim. If it is too high, it can be made lower +by filing on the inside a little above the rim. Many of the old bells +contain the gifts of silver and gold which were thrown in by people +who watched their founding. The most famous bell in the United States +is the "Liberty Bell" of Independence Hall, in Philadelphia, which +rang when Independence was adopted by Congress. This was founded in +England long before the Revolution and later was melted and founded +again in the United States. + +It would not be easy to get on without brass and bronze; but even +these alloys are not so necessary as copper by itself. It is so strong +that it is used in boiler tubes of locomotives, as roofing for +buildings and railroad coaches, in the great pans and vats of the +sugar factories and refineries. A copper ore called "malachite," which +shows many shades of green, beautifully blended and mingled, is used +for the tops of tables. Wooden ships are often "copper-bottomed"; that +is, sheets of copper are nailed to that part of the hull which is +under water in order to prevent barnacles from making their homes on +it, and so lessening the speed of the vessel. + +People often say that the latter half of the nineteenth century was +the Age of Steel, because so many new uses for steel were found at +that time. The twentieth century promises to be the Age of +Electricity, and electricity must have copper. Formerly iron was used +for telegraph wires; but it needs much more electricity to carry power +or light or heat or a telegraphic message over an iron wire than one +of copper. Moreover, iron will rust and will not stretch in storms +like copper, and so needs renewing much oftener. Electric lighting and +the telephone are everywhere, even on the summits of mountains and in +mines a mile below the earth's surface. Electric power, if a +waterfall furnishes the electricity, is the cheapest power known. The +common blue vitriol is one form of copper, and to this we owe many of +our electric conveniences. It is used in all wet batteries, and so it +rings our doorbells for us. It also sprays our apple and peach trees, +and is a very valuable article. Indeed, copper in all its forms, pure +and alloyed, is one of our best and most helpful friends. + + + + +IX + +THE NEW METAL, ALUMINUM + + +Not many years ago a college boy read about an interesting metal +called "aluminum." It was as strong as iron, but weighed only one +third as much, and moisture would not make it rust. It was made of a +substance called "alumina," and a French chemist had declared that the +clay banks were full of it; and yet it cost as much as silver. It had +been used in France for jewelry and knicknacks, and a rattle of it had +been presented to the baby son of the Emperor of France as a great +rarity. + +The college boy thought by day and dreamed by night of the metal that +was everywhere, but that might as well be nowhere, so far as getting +at it was concerned. At the age of twenty-one, the young man +graduated, but even his new diploma could not keep his mind away from +aluminum. He borrowed the college laboratory and set to work. For +seven or eight months he tried mixing the metal with various +substances to see if it would not dissolve. At length he tried a stone +from Greenland called "cryolite," which had already been used for +making a kind of porcelain. The name of this stone comes from two +Greek words meaning "ice stone," and it is so called because it melts +so easily. The young student melted it and found that it would +dissolve alumina. Then he ran an electric current through the melted +mass, and there was a deposit of aluminum. This young man, just out of +college, had discovered a process that resulted in reducing the cost +of aluminum from twelve dollars a pound to eighteen cents. Meanwhile a +Frenchman of the same age had been working away by himself, and made +the same discovery only two months later. + +Aluminum is now made from a mineral called "bauxite," found chiefly in +Georgia, Alabama, and Arkansas. Mining it is much more agreeable than +coal mining, for the work is done aboveground. The bauxite is in beds +or strata which often cover the hills like a blanket. First of all, +the mine is "stripped,"--that is, the soil which covers the ore is +removed,--and then the mining is done in great steps eight or ten feet +high, if a hill is to be worked. There is some variety in mining +bauxite, for it occurs in three forms. First, it may be a rock, which +has to be blasted in order to loosen it. Second, it may be in the form +of gray or red clay. Third, it occurs in round masses, sometimes no +larger than peas, and sometimes an inch in diameter. In this form it +can easily be loosened with a pickaxe, and shoveled into cars to be +carried to the mill. Bauxite is a rather mischievous mineral and +sometimes acts as if it delighted in playing tricks upon managers of +mines. The ore may not change in the least in its appearance, and yet +it may suddenly have become much richer or much poorer. Therefore the +superintendent has to give his ore a chemical test every little while +to make sure that all things are going on well. + +This bauxite is purified, and the result is a fine white powder, which +is pure alumina, and consists of the metal aluminum and the gas +oxygen. Cryolite is now melted by electricity. The white powder is put +into it, and dissolves just as sugar dissolves in water. The +electricity keeps on working, and now it separates the alumina into +its two parts. The aluminum is a little heavier than the melted +cryolite, and therefore it settles and may be drawn off at the bottom +of the melting-pot. + +There are a good many reasons why aluminum is useful. As has been said +it is strong and light and does not rust in moisture. You can beat it +into sheets as thin as gold leaf, and you can draw it into the finest +wire. It is softer than silver, and it can be punched into almost any +form. It is the most accommodating of metals. You can hammer it in the +cold until it becomes as hard as soft iron. Then, if you need to have +it soft again, it will become so by melting. It takes a fine polish +and is not affected, as silver is, by the fumes which are thrown off +by burning coal; and so keeps its color when silver would turn black. +Salt water does not hurt it in the least, and few of the acids affect +it. Another good quality is that it conducts electricity excellently. +It is true that copper will do the same work with a smaller wire; but +the aluminum is much lighter and so cheap that the larger wire of +aluminum costs less than the smaller one of copper, and its use for +this purpose is on the increase. It conducts heat as well as silver. +If you put one spoon of aluminum, one of silver, and one that is +"plated" into a cup of hot water, the handles of the first two will +almost burn your fingers before the third is at all uncomfortable to +touch. + +[Illustration: A "MOVIE" OF AN ALUMINUM FUNNEL + +_Courtesy The Aluminum Cooking Utensil Company._ + +Seventeen other operations are necessary after the thirteenth stamping +operation before the funnel is ready to be sold. And after all this +work, we can buy it for 35 cents at any hardware store.] + +Aluminum is found not only in clay and indeed in most rocks except +sandstone and limestone, but also in several of the precious stones, +in the yellow topaz, the blue sapphire and lapis-lazuli, and the red +garnet and ruby. It might look down upon some of its metallic +relatives, but it is friendly with them all, and perfectly willing to +form alloys with most of them. A single ounce of it put into a ton of +steel as the latter is being poured out will drive away the gases +which often make little holes in castings. Mixed with copper it makes +a beautiful bronze which has the yellow gleam of gold, but is hard to +work. When a piece of jewelry looks like gold, but is sold at too low +a price to be "real," it may be aluminum bronze, very pretty at first, +but before long its luster will vanish. Aluminum bronze is not good +for jewelry, but it is good for many uses, especially for bearings in +machinery. Aluminum mixed with even a very little silver has the color +and brightness of silver. The most common alloys with aluminum are +zinc, copper, and manganese, but in such small quantities that they do +not change its appearance. + +With so many good qualities and so few bad ones, it is small wonder +that aluminum is employed for more purposes than can be counted. A +very few years ago it was only an interesting curiosity, but now it is +one of the hardest-worked metals. Automobiles in particular owe a +great deal to its help. When they first began to be common, in +1904-05, the engines were less powerful than they are now made, and +aluminum was largely employed in order to lessen the weight. Before +long it was in use for carburetors, bodies, gear-boxes, fenders, +hoods, and many other parts of the machine. Makers of electric +apparatus use aluminum instead of brass. The frames of opera glasses +and of cameras are made of it. Travelers and soldiers and campers, +people to whom every extra ounce of weight counts, are glad enough to +have dishes of aluminum. The accommodating metal is even used for +"wallpaper," and threads of it are combined with silk to give a +specially brilliant effect on the stage. It can be made into a paint +which will protect iron from rust; and will make woodwork partially +fireproof. + +Aluminum has been gladly employed by the manufacturers of all sorts of +articles, but nowhere has its welcome been more cordial than in the +kitchen. Any one who has ever lifted the heavy iron kettles which were +in use not so very many years ago will realize what an improvement it +is to have kettles made of aluminum. But aluminum has other advantages +besides its lightness. If any food containing a weak acid, like +vinegar and water, is put into a copper kettle, some of the copper +dissolves and goes into the food; acid does not affect aluminum except +to brighten it if it has been discolored by an alkali like soda. "Tin" +dishes, so called, are only iron with a coating of tin. The tin soon +wears off, and the iron rusts; aluminum does not rust in moisture. A +strong alkali will destroy it, but no alkali in common use in the +kitchen is strong enough to do more harm than to change the color, and +a weak acid will restore that. Enameled ware, especially if it is +white, looks dainty and attractive; but the enamel is likely to chip +off, and, too, if the dish "boils dry," the food in it and the dish +itself are spoiled. Aluminum never chips, and it holds the heat in +such a manner as to make all parts of the dish equally hot. Food, +then, is not so likely to "burn down," but if it does, only the part +that sticks will taste scorched; and no matter how many times a dish +"boils dry," it will never break. If you make a dent in it, you can +easily pound it back into shape again. It is said that an aluminum +teakettle one sixteenth of an inch in diameter can be bent almost +double before it will break. + +Aluminum dishes are made in two ways. Sometimes they are cast, and +sometimes they are drawn on a machine. If one is to be smaller at the +top, as in the case of a coffeepot, it is drawn out into a cylinder, +then put on a revolving spindle. As it whirls around, a tool is held +against it wherever it is to be made smaller, and very soon the +coffeepot is in shape. The spout is soldered on, but even the solder +is made chiefly of aluminum. + +Aluminum dishes may become battered and bruised, but they need never +be thrown away. There is an old story of some enchanted slippers which +brought misfortune to whoever owned them. The man who possessed them +tried his best to get rid of the troublesome articles, but they always +returned. So it is with an aluminum dish. Bend it, burn it, put acid +into it, do what you will to get rid of it, but like the slippers it +remains with you. Unlike them, however, it brings good fortune, +because it saves time and trouble and patience and money. + +A few years ago the motive power for most manufactures was steam. +Electricity is rapidly taking its place; and if aluminum was good for +nothing else save to act as a conductor of electricity in its various +applications, there would even then be a great future before it. + + + + +X + +THE OIL IN OUR LAMPS + + +Probably the first man who went to a spring for a drink and found oil +floating on the water was decidedly annoyed. He did not care in the +least where the oil came from or what it was good for; he was thirsty, +and it had spoiled his drink, and that was enough for him. We know now +that oil comes chiefly from strata of coarse sandstone, but we are not +quite sure how it happened to be there. The sand which formed these +strata was deposited by water ages and ages ago--we are certain of +that. Another thing that we are certain of is that where the strata +lie flat, there is no oil. Hot substances become smaller as they cool; +and as the earth grew cooler, it became smaller. The crust of the +earth wrinkled as the skin of an apple does when it dries. In the tops +of these great sandstone wrinkles there is often gas; and below the +gas is the place where oil is found. There is no use in looking for +petroleum where the folds of the strata are very sharp, because in +that case the strata crack and let the oil flow away. It is not in +pools, but the porous stone holds it just as a sponge holds water. If +you drop a little oil upon a stone even much less porous than +sandstone, it will not be easy to wipe it off, because some of it will +have sunk into the stone. + +In many places the gas forces its way out, and is piped to carry to +houses for light and heat. Not far above Niagara Falls there was a +spring of gas which flowed for years. An iron pipe was put down, and +when the gas was lighted, the flame shot up three or four feet. The +gas came with such force that a handkerchief put over the end of the +pipe would not burn, though the flame would blaze away above it. In +the country of the fire worshipers, on the shores of the Caspian Sea, +fires of natural gas have been burning for ages, kindled, perhaps, by +lightning centuries ago. There is a vast supply of oil in this place; +and indeed there is hardly a country that has not more or less of it. + +In the United States the colonists soon learned that there was +petroleum in what is now the State of New York; but New York was a +long way from the Atlantic seaboard in those days, and they went on +contentedly burning candles or sperm whale oil, or, a little later, a +rather dangerous liquid which was known as "fluid." The Indians +believed that the oil which appeared in the springs was a good +medicine. They threw their blankets upon the water, and when these had +become saturated with the oil, they wrung them out and sold the oil. +Those were the times when if a medicine only tasted and smelled bad +enough, people never doubted that it would cure all their diseases, +and they gladly bought the oil of the Indians. + +When at last it became clear to the members of an enterprising company +that oil for use in lamps could be made from petroleum, they secured +some land in Pennsylvania that seemed promising and set to work to +dig a well. But the more they dug, the more the loose dirt fell in +upon them. Fortunately for the company, the superintendent had brains, +and he thought out a way to get the better of the crumbling soil. He +simply drove down an iron pipe to the sandstone which contained the +oil, and set his borer at work within the pipe. One morning he found +that the oil had gushed in nearly to the top of the well. He had +"struck oil." + +This was about ten years after the rush to California for gold, and +now that this cheaper and quicker method of making a well had been +invented, there was almost as much of a rush to Pennsylvania for oil. +With every penny that they could beg or borrow, people from the East +hurried to the westward to buy or lease a piece of land in the hope of +making their fortunes. A song of the day had for its refrain,-- + + "Stocks par, stocks up, + Then on the wane; + Everybody's troubled with + Oil on the brain." + +In the course of a year or two, the first "gusher" was discovered. The +workmen had drilled down some four or five hundred feet and were +working away peacefully, when a furious stream of oil burst forth +which hurled the tools high up into the air. Hundreds of barrels +gushed out every day, and soon other gushers were discovered. The most +famous one in the world is at Lakeview, California. For months it +produced fifty thousand barrels of oil a day, and threw it up three +hundred and fifty feet into the air in a black column, spraying the +country with oil for a mile around. The oil flowed away in a river, +and for a time no one could plan any way to stop it or store it. At +last, however, a mammoth tank was built around the well and made firm +with stones and bags of earth. This was soon full of oil; and with all +this vast weight of oil pressing down upon it, the stream could not +rise more than a few feet above the surface. Just why oil should come +out with such force, the geologists are not quite certain; but it is +thought to result from a pressure of gas upon the sandstone containing +it. The flow almost always becomes less and less, and after a time the +most generous well has to be pumped. + +[Illustration: A CALIFORNIA OIL FIELD + +For scenery, one should not go to an oil field. Looks, smell, and oil +alike are unpleasant, but every oil derrick covers a fortune and helps +to make our machinery run smoothly.] + +An "oil field" may extend over thousands of square miles; but within +this field there are always "pools"; that is, certain smaller fields, +where oil is found. When a man thinks there is oil in a certain spot, +sometimes he buys the land if he is able; but oftener he gets +permission of the owner to bore a well, agreeing to pay him a royalty; +that is, a certain percentage of all the oil that is produced. When +this has been arranged, he builds his derrick. This consists of four +strong upright beams firmly held together by crossbeams. It stands +directly over the place where the well is to be dug. It is from thirty +to eighty feet in height, according to the depth at which it is hoped +to find oil. There must also be an engine house to provide the power +for drilling. An iron pipe eight or ten inches in diameter is driven +down through the soil until it comes to rock. Now the regular drilling +begins. At the top of the derrick is a pulley. Over the pulley passes +a stout rope to which the heavy drilling tools--the "string of tools," +as they are called--are fastened. The drilling goes on day and night. +The drill makes the hole, and the sand pump sucks out the water and +loose bits of stone. When the drill has gone to the bottom of the +strata which carry water, the sides of the bore are cased to keep the +water out; then the drilling continues, but now the drill makes its +way into the oil-bearing sandstone. + +There is nothing certain about the search for oil. In some places it +is near the surface, in others it is perhaps three or four thousand +feet down. The well may prove to be a gusher and pour out hundreds of +thousands of gallons a day; or the oil may refuse to rise to the +surface and have to be pumped out even at the first. Naturally, no one +is prepared for a gusher, and millions of gallons have often flowed +away before any arrangements could be made for storing the oil. +Sometimes a well that gives only a moderate flow can be made to yield +generously by exploding a heavy charge of dynamite at the bottom, to +break up the rock and, it is always hoped, to open some new +oil-holding crevice that the drill has not reached. + +Crude petroleum is a dark, disagreeable, bad-smelling liquid; and +before it can be of much use, it must be refined. For several years it +was carried in barrels from the oil fields to Pittsburgh by wagon and +boat, a slow, expensive process, and generally unsatisfactory to all +but the teamsters. Then came the railroads. They provided iron tanks +in the shape of a cylinder fastened to freight cars, much like those +employed to-day. There was only one difficulty about sending oil by +rail, and that was that it still had to be hauled by team to the +railroad, sometimes a number of miles. At length, some one said to +himself, "Why cannot we simply run a pipe directly from the well to +the railroad?" This was done. Pumping engines were put in a few miles +apart, and the invention was a success in the eyes of all but the +teamsters. In spite of their opposition, however, pipe-lines +increased. + +Before this it had been necessary to build the refineries as near the +oil regions as possible in order to save the expense of carrying the +oil; but now they could be built wherever it was most convenient. +To-day oil can be brought at a small expense from west of the +Mississippi River to the Atlantic seaboard, refined, and distributed +throughout that part of the country, or loaded into "tankers,"--that +is, steamships containing strong tanks of steel,--and so taken across +the ocean. The pipes are made of iron and are six or eight inches or +more in diameter. In using them one difficulty was found which has +been overcome in an ingenious fashion. Sometimes they become choked by +the impurities of the oil and the flow is lessened. Then a "go-devil" +is put into them. This is shaped like a cartridge, is about three +feet in length, composed of springs and plates of iron and so flexible +that it can turn around a corner. It is so made that as it slips down +the current of oil, it whirls around and in so doing its nose of sharp +blades scrapes the pipes clean. + +The pipes go over hills and through swamps. They cross rivers +sometimes by means of bridges, and sometimes they are anchored to the +bed of the stream. If they have to go through a salt marsh, they are +laid in concrete to preserve the iron. If these lines were suddenly +destroyed and oil had to be carried in the old way, kerosene would +become an expensive luxury. + +Getting the oil out of the ground and carried to the refineries is not +all of the business by any means. The early oils crusted on the lamp +wicks, their smell was unendurable, and they were given to exploding. +Evidently, if oil was to be used for lighting, it must be improved, +and the first step was to distil it. To distil anything means to boil +it and collect the vapor. If you hold a piece of cold earthenware in +the steam of a teakettle, water will collect on it. This is distilled +water, and is purer than that in the kettle. Petroleum was at first +distilled in a rough way; but now it is done with the utmost care and +exactness. The crude oil is pumped into boilers holding six hundred +barrels or more. The fires are started, and the oil soon begins to +turn into vapor. This vapor passes through coils of pipe or long, +straight, parallel pipes. Cold water is pumped over these pipes, the +vapor turns into a liquid again, and we have kerosene oil. + +This is the outline of the process, but it is a small part of the +actual work in all its details. Kerosene oil is only one of the many +substances found in petroleum. Fortunately, some of these substances +are light, like gasoline and benzine; some, like kerosene, are +heavier; and paraffin and tar are heaviest of all. There are also +gases, which pass off first and are saved to help keep the furnace +going. Then come the others, one by one, according to their weight. +The stillman keeps close watch, and when the color and appearance of +the distillate changes, he turns it off into another tank. This +process is called "fractional distillation," and the various products +are called "fractions." No two kinds of petroleum and no two oil wells +are just alike, and it needs a skillful man to manage either. + +Even after all this distillation, the kerosene still chars the wick +somewhat--which prevents the wick from drawing up the oil +properly--and it still has a disagreeable smell. To fit it for burning +in lamps, it must be treated with sulphuric acid, which carries away +some of the impurities, and then with caustic soda, which carries away +others. Before it can be put on the market, it is examined to see +whether it is of the proper color. Then come three important tests. +The first is to see that it is of the proper weight. If it is too +heavy, it will not burn freely enough; if it is too light, then there +is too much of the lighter oils in it for safety. The second test is +the "flash test." The object of this is to see how hot the oil must be +before it gives off a vapor which will burn. The third, the "burning +test," is to discover how hot the oil must be before it will take fire +and burn on the surface. Most civilized countries make definite laws +forbidding the sale of kerosene oil that is not up to a standard of +safety. Oil for use in lamps should have an open flash test of at +least 100° F. and a burning point of not less than 125° F. + +We say that we burn oil in our lamps, but what we really do is to heat +the oil until it gives off gas, and then we burn the gas. To keep the +flame regular and help on the burning, we use a chimney on the lamp. +The hot air rises in the chimney and the cold air underneath rushes in +to take its place and brings oxygen to the flame. In a close, stuffy +room no lamp will give a good clear light, because there is not oxygen +enough for its flame. Let in fresh air, and the light will be +brighter. If you hold a cold plate in the flame before the chimney is +put on, soot or carbon will be deposited. A lamp gives light because +these particles of carbon become so hot that they glow. In lamps using +a "mantle," there is the glow not only of these particles, but also of +the mantle. In a wax candle, we light the wick, its heat melts the wax +and carries it to the flame. When the wax is made hot enough, it +becomes gas, and we burn the gas, not the wax. Wax alone will melt, +but not take fire even if a burning match is held to it. The reason is +that the match does not give heat enough to turn the wax into gas. But +put a bit of wax upon a bed of burning coals, where there is a good +supply of heat, and it will turn into gas and burn. + +The products made from petroleum are as different in their character +and uses as paraffin and naphtha. Some of them are used for oiling +machinery; tar is used for dyes; naphtha dissolves resin to use in +varnish; benzine is the great cleanser of clothes, printers' types, +and almost everything else; gasoline runs automobiles, motors, and +many sorts of engines; paraffin makes candles, seals jelly glasses, +covers the heads of matches so that they are no longer spoiled by +being wet, and makes the ever-useful "waxed paper"; printers' ink and +waterproof roofing-paper both owe a debt to petroleum. Even in +medicine, though a little petroleum is no longer looked upon as a +cure-all, vaseline, one of its products, is of great value. It can be +mixed with drugs without changing their character, and it does not +become rancid. For these reasons, salves and other ointments can be +mixed with it and preserved for years. + + + + +XI + +LITTLE GRAINS OF SALT + + +The most interesting mine in the world is that of Wieliczka in Poland. +In it there are some thirty miles of streets and alleys; there are +churches with pillars, shrines, and statues; there are stairs, +monuments, and restaurants; there is a ballroom three hundred feet +long and one hundred and ninety feet high, with beautiful chandeliers, +and in it is a carven throne whereon the Emperor Franz Joseph sat when +he visited the mine. There are lakes crossed by ferryboats. There is a +railroad station for the mule trains which bear the precious mineral +salt, for this is a salt mine, and shrines, statues, churches, +chandeliers--everything--are all cut out of salt. + +This mine has been worked for at least eight hundred years and still +has salt enough to supply all Europe for ages. The mass of salt is +believed to be five hundred miles long, fifty miles wide, and nearly a +quarter of a mile thick. It is so pure that it is sold just as it +comes from the mine, either in blocks or finely ground. This mine is a +wonderful place to visit, almost like an enchanted palace, for as the +torchlight strikes the crystals of salt, they flash and sparkle as if +the wall was covered with rubies and diamonds. + +There is nothing like an enchanted palace in any salt mine of the +United States, no statues or chapels or chandeliers. There is only a +hole in the ground, where mining is carried on in much the same manner +as in other kinds of mines. The shaft is sunk and lined with timbers +to keep the dirt from falling in, just as in other mines. In working +salt mines, however, water is almost as bad as earth, and therefore a +layer of clay is put between the timbers and the earth. There are the +usual galleries and pillars, with roof and floor of salt. The workmen +try to get the salt out in lumps or blocks as far as possible, and so +they bore in drill holes and then blast with dynamite or powder. The +salt is loaded upon little cars, running on tracks, and is carried up +the shaft and to the top of a breaker, usually more than one hundred +feet above the surface of the ground. There it is dumped upon a screen +of iron bars, which lets the fine salt fall through. The large lumps +are sold without crushing or sifting, and are used for cattle and +sheep. + +One of the great deposits of salt is in southeastern California. It is +thought that the Gulf of California used to run much farther north +than it now does, and that the earth rose, shutting away part of it +from the ocean. This imprisoned water was full of salt. In time it +dried, and the sand blew over it till it was far underground. A better +way than digging was found to work it, as will be seen later; but +while digging was going on, the workmen built a cottage of blocks of +salt, clear and glassy. The little rain that falls there melted the +blocks only enough to unite them firmly together; and there the house +has stood for many years. + +Countries that have no deposits of rock salt can easily get plenty of +salt from the water of the ocean if they only have a seacoast. About +one thirtieth of the ocean water is salt, and if the water is +evaporated, the salt can be collected without difficulty. France makes +a great deal of salt in this way. When a man goes into the +manufacture, or rather, the collecting of salt, he first of all buys +or rents a piece of land,--perhaps several acres of it,--that lies +just above high water, and makes it as level as possible. Unless it is +very firm land, he covers it with clay, so that the water will not +soak through it. Then he divides it into large square basins, making +each a little lower than the one before it. Close beside the highest +basin he makes a reservoir which at high tide receives water from the +ocean. This flows slowly from the reservoir through one basin after +another, becoming more and more salt as the water evaporates. At +length the water is gone, and the salt remains. The workmen take +wooden scrapers and push the salt toward the walls of the basins and +then shovel it up on the dikes and heap it into creamy cones that +sparkle in the sunshine. The dikes are narrow, raised pathways beside +the basins and between them. As you walk along on top of them, you can +smell a faint violet perfume from the salt. Thatch is put over the +cones to protect them from the rain, and there they stand till some of +the impurities drain away. This salt is not perfectly white, because +the workmen cannot help scraping up a little of the gray or reddish +clay with it. Most of it is sold as it is, nevertheless, for many +people have an absurd notion that the darker it is the purer it is. +For those who wish to buy white salt it is sent to a refinery to be +washed with pure water, then boiled down and dried. + +So it is that the sun helps to manufacture salt. In some of the colder +countries, frost does the same work, but in a very different manner. +When salt water freezes, the _water_ freezes, but the salt does not, +and a piece of salt water ice is almost as pure as that made of fresh +water. Of course, after part of the water in a basin of salt water has +been frozen out, what is left is more salt than it was at first, and +after the freezing has been repeated several times, only a little +water remains, and evaporation will soon carry this away, leaving only +salt in the basin, waiting to be purified. + +Not very many years ago one of the encyclopędias remarked that "the +deposits of salt in the United States are unimportant." This was true +as far as the working of them was concerned, but in 1913 the United +States produced more than 34,000,000 barrels. Part of this was made by +evaporation of the waters of salt springs, and a small share from +Great Salt Lake in Utah. The early settlers in Utah used to gather +salt from the shallow bays or lagoons where the water evaporated +during the summer; but now dams of earth hold back the water in a +reservoir. In the spring the pumps are put to work and the reservoir +is soon filled with water. This is left to stand and give the +impurities a chance to settle to the bottom. Then it is allowed to +flow into smaller basins, while more water is pumped into the +reservoir. When autumn comes, the crop of salt is ready to be +harvested. It is in the form of a crust three to six inches thick, +some of it in large crystals, and some fine-grained. This crust is +broken by ploughs, and the salt is heaped up into great cones and left +for the rain to wash clean. Then it goes to the mill for purifying. +The water of Great Salt Lake is much more salty than that of the +ocean. It preserves timber remarkably well, and often salt from the +lake is put around telephone poles, seventy-five pounds being dropped +into the hole for each one. It has been suggested to soak timber in +the Lake, and then paint it with creosote to keep the wet out and the +salt in. + +Salt is also made from the waters of salt springs, which the Indians +thought were the homes of evil spirits. At Salton, in California, an +area of more than one thousand acres, which lies two hundred and +sixty-four feet below sea level, is flooded with water from salt +springs. When this water has evaporated, all these acres are covered +with salt ten to twenty inches thick, and as dazzlingly white as if it +was snow. This great field is ploughed up with a massive four-wheeled +implement called a "salt-plough." It is run by steam and needs two men +to manage it. The heavy steel ploughshare breaks up the salt crust, +making broad, shallow furrows and throwing the salt in ridges on both +sides. The plough has hardly moved on before the crust begins to form +again. This broken crust is worked in water by men with hoes in order +to remove the bits of earth that stick to it, then piled up into cones +to drain, loaded upon flat trucks, and carried to the breaker. The +salt fields are wonderfully beautiful in the moonlight, but not very +agreeable to work in, for the mercury often reaches 140° F., and the +air is so full of particles of salt that the workers feel an intense +thirst, which the warm, brackish water does not satisfy. The work is +done by Indians and Japanese, for white people cannot endure the heat. + +A large portion of the salt used in the United States comes directly +from rock salt strata, hundreds of feet below the surface of the +ground. These were perhaps the bed of the ocean ages and ages ago. +There is a great extent of the beds in New York, Michigan, Ohio, +Kansas, and other States. In Michigan there is a stratum of rock salt +thirty to two hundred and fifty feet thick and some fifteen hundred to +two thousand feet below the surface. To mine this would be a difficult +and expensive undertaking, and a far better way has been discovered. +First, a pipe is forced down through the surface dirt, the limestone, +and the shale to the salt stratum. The drill works inside this pipe +and bores a hole for a six-inch pipe directly into the salt. A +three-inch pipe is let down inside of the six-inch pipe, and water is +forced down through the smaller pipe. It dissolves the salt, becomes +brine, and rises through the space between the two pipes. It is +carried through troughs to some great tanks, and from these it flows +into "grain-settlers," then into the "grainers" proper, where the +grains of salt settle. At the bottom of the grainers are steam pipes, +and these make the brine so hot that before long little crystals of +salt are seen floating on the surface of the water. Crystals form much +better if the water is perfectly smooth, and to bring this about a +very little oil is poured into the grainer. It spreads over the +surface in the thinnest film that can be imagined. The water +evaporates, and the tiny crystals grow, one joining to another as they +do in rock candy. When they become larger, they drop to the bottom of +the grainer. They are now swept along in a trough to a "pocket," +carried up by an endless chain of buckets, and then wheeled away to +the packinghouse. + +The finest salt is made by using vacuum pans. These are great cans out +of which the air is pumped, and into which the brine flows. This +brine, heated by steam pipes, begins to boil, and as the steam from it +rises, it has to pass through a pipe at the top and is thus carried +into a small tank into which cold water is flowing. The cold makes the +steam condense into water, which runs off. The condensed water +occupies less space than the steam and so maintains the vacuum in the +pan. For a perfect vacuum the brine is boiled at less than 100° F., +while in an open pan or grainer it requires 226° to boil brine. The +brine is soon so rich in salt that tiny crystals begin to form. These +are taken out and dried. If you look at some grains of table salt +through a magnifying glass, you can see that each grain is a tiny +cubical crystal. Sometimes two or three are united, and often the +corners are rounded off and worn, but they show plainly that they are +little cubes. + +Most of the salt used on our tables is made by the vacuum process or +by an improved method which produces tiny flakes of salt similar to +snowflakes. The salt brine is heated to a high temperature and +filtered. In the filters the impurities are taken out, and this +process gives us very pure salt. The tiny flakes dissolve more easily +than the cubes of salt, and thus flavor food more readily. + +With a few savage tribes salt is regarded as a great luxury, but with +most peoples it is looked upon as a necessity. Some of the early races +thought a salt spring was a special gift of the gods, and in their +sacrifices they always used salt. In later times to sit "above the +salt," between the great ornamental salt cellar and the master of the +house, was a mark of honor. Less distinguished guests were seated +"below the salt." To "eat a man's salt" and then be unfaithful to him +has always been looked upon as a shameful act; and with some of the +savages, so long as a stranger "ate his salt,"--that is, was a guest +in the house of any one of them,--he was safe. To "eat salt together" +is an expression of friendliness. Cakes of salt have been used as +money in various parts of Africa and Asia. "Attic salt" means wit, +because the Athenians, who lived in Attica, were famous for their +keen, delicate wit. To take a story or a statement "with a grain of +salt" means not to accept it entirely, but only to believe it +partially. When Christ told his disciples that they were "the salt of +the earth," he meant that their lives and teaching would influence +others just as salt affects every article of food and changes its +flavor. Our word "salary" comes from the Latin word _sal_, meaning +salt; and _salarium_, or "salt-money," was money given for paying +one's expenses on a journey. Living without salt would be a difficult +matter. Cattle that have been shut away from it for a while are almost +wild to get it. Farmers living among the mountains sometimes drive +their cattle to a mountain pasture to remain there through the summer, +and every little while they go up to salt the animals. The cattle know +the call and know that it means salt; and I have seen them come +rushing down the mountain-side and through the woods, over fallen +trees, through briers, and down slippery rocks, bellowing as they +came, and plunging head first in a wild frenzy to get to the pieces of +rock salt that were waiting for them. + + * * * * * + + + + +FIRST YEAR IN NUMBER + +35 cents net. Postpaid + +An Introductory Book to Precede any Series of Arithmetics + +BY + +FRANKLIN S. HOYT + +_Formerly Assistant Superintendent of Schools, Indianapolis_ + +AND + +HARRIET E. PEET + +_Instructor in Methods of Teaching Arithmetic, State Normal School, +Salem, Massachusetts_ + +The work is based upon the familiar experiences and activities of +children, and follows as closely as possible the child's own method of +acquiring new knowledge and skill. + +Thus we have lessons based on playing store, making tickets, mailing +letters, fishing, etc. Every step is made interesting, but no time is +wasted in mere entertainment. + + * * * * * + +_By the same authors_ + +THE EVERYDAY ARITHMETICS + +THREE-BOOK COURSE + +Book One, grades II-IV $.40 +Book Two, grades V-VI .40 +Book Three, grades VII-VIII .45 + +TWO-BOOK COURSE + +Book One, grades II-IV. $.40 +Book Two, grades V-VIII. .72 + +Course of Study (with answers) $.25 + +_Distinctive Features_ + +1. Their socialized point of view--all problems and topics taken from +the everyday life of children, home interests, community interests, +common business and industries. 2. 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