Читать книгу Stories of Useful Inventions - Forman Samuel Eagle - Страница 6

After men had learned how to use fire for cooking and heating and lighting they slowly learned how to use it when working with metals. In the earliest times metals were not used. For long ages stone was the only material that man could fashion and shape to his use. During this period, sometimes called the "stone age," weapons were made of stone; dishes and cooking utensils were made of stone; and even the poor, rude tools of the age were made of stone (Fig. 1).

FIG. 1. – IMPLEMENTS OF THE STONE AGE.

FIG. 2. – IMPLEMENTS OF THE BRONZE AGE.

In the course of time man learned how to make his implements and weapons of metals as well as of stone. It is generally thought that bronze was the first metal to be used and that the "stone age" was followed directly by the "bronze age," a period when all utensils, weapons, and tools were made of bronze (Fig. 2). It is easy to believe that bronze was used before iron, for bronze is made of a mixture of tin and copper and these two metals are often found in their pure or natural state. Whenever primitive man, therefore, found pieces of pure copper and tin, he could take the two metals and by melting them could easily mix them and make bronze of them. This bronze he could fashion to his use. There is no doubt that he did this at a very early age. In nearly all parts of the world there are proofs that in primitive times, many articles were made of bronze.

If primitive man were slow to learn the use of iron it was not because this metal was scarce, for iron is everywhere. "Wherever, as we go up and down, we see a red-colored surface, or a reddish tint upon the solid substances of the earth, we see iron – the bank of red clay, the red brick, the red paint upon the house wall, the complexion of rosy youth, or my lady's ribbon. Even the rosy apple derives its tint from iron which it contains."8 But although iron is so abundant it is seldom found in its pure or natural state. It is nearly always mixed with other substances, the mixture being known as iron ore. Primitive man could find copper and tin in their pure state but the only pure iron he could find was the little which fell from heaven in the form of meteors, and even this was not perfectly pure for meteoric iron is also mixed slightly with other metals.

The iron which lay about primitive man in such abundance was buried and locked tightly in an ore. To separate the iron from the other substances of the ore was by no means an easy thing to do. Iron can best be extracted from the ore by putting the ore in a fire and melting out the iron. Place some iron ore in a fire and if the fire is hot enough – and it must be very hot indeed – the iron will leave the ore and will gather into a lump at the bottom of the fire. To separate the iron from its ore in this way is to make iron. When and where man first learned the secret of making iron is of course unknown. A camp-fire in some part of the world may have shown to man the first lump of iron, or a forest fire sweeping along and melting ores in its path may have given the first hint for the manufacture of iron.

Iron making at first doubtless consisted in simply melting the ore in an open heap of burning wood or charcoal, for charcoal is an excellent fuel for smelting (melting) ores. But this open-fire method was wasteful and tedious and at a very early date the smelting of the ore was done in a rude sort of a furnace. A hole ten or twelve feet deep was dug in the side of a hill. In the hole were placed charcoal and iron ore, first a layer of charcoal, then a layer of the ore. At the top of the mass there was an opening and at the bottom there were several openings. When the mass was set on fire the openings produced a good strong draft, the charcoal was consumed, and the ore was smelted. The product was a lump of wrought iron, known as the bloom.

FIG. 3. – THE PRIMITIVE FORGE.

FIG. 4. – BELLOWS WORKED BY THE FEET.

FIG. 5. – THE WOODEN BELLOWS.

The hillside furnace worked well enough when the wind was favorable, but when the wind was unfavorable there was no draft and no iron could be made. So ironmakers found a way by which the air could be driven into the furnace by artificial means. They invented the bellows, a blowing apparatus (Fig. 3) which was usually made of goat skins sewed together and which was operated either by the hands or by the feet (Fig. 4). Sometimes the bellows consisted of a hollow log in which a piston was worked up and down (Fig. 5). After the invention of the bellows, ironmakers could make their iron whenever and wherever they pleased, for they could force air into their furnaces at any time and at any place. This rude bellows forcing a draft of air into a half-closed furnace filled with a burning mass of charcoal and iron ore was the first form of the forge, one of the greatest of all inventions.

With the invention of the forge the stone age gradually passed away and the iron age was ushered in. Tools and weapons could now be made of iron. And great was the difference between iron tools and stone tools. To cut down a tree with a flint hatchet required the labor of a man for a month, while to clear a forest with such an implement was an impossible task. But the forge gave to man iron for the sharp cutting tools, for the ax and knife and chisel and saw. With these he became the master of wood and he could now easily cut down trees and build houses and make furniture and wagons and boats.

As time went on and man advanced in civilization, iron was found to be the most useful of metals. Iron can be shaped into many forms. It can be drawn into wire of any desired length or fineness, it may be bent in any direction, it may be sharpened, or hardened, or softened, at pleasure. "Iron accommodates itself to all our wants and desires and even to our caprices. It is equally serviceable to the arts, the sciences, to agriculture and war; the same ore furnishes the sword, the plowshare, the scythe, the pruning-hook, the needle, the spring of a watch or of a carriage, the chisel, the chain, the anchor, the compass and the bomb. It is a medicine of much virtue and the only metal friendly to the human frame."9

A metal that was so useful was needed in large quantities, yet the primitive forge could turn out only small quantities of iron. A day's labor at the bellows would produce a lump weighing only fifteen or twenty pounds. As a result of this slowness in manufacture there was always in primitive and ancient times a scarcity of iron. Indeed in some countries iron was a precious metal, almost as precious as silver or gold. In many countries, it is true, there were thousands of forges at work, but in no country was the supply of iron equal to the demand. The old forge could not supply the demand, yet centuries passed before any great improvement was made in the progress of iron making.

FIG. 6. – A BLAST FURNACE OF THE MIDDLE AGES.

Near the close of the Middle Ages improvements upon the primitive forge began to be made. In the sixteenth century ironmakers in Germany began to smelt ore in closed furnaces and to build their furnaces higher and to make them larger (Fig. 6). Sometimes they built their furnaces to a height of twenty or thirty feet. About this time also a better and a stronger blast was invented. Water-power instead of hand-power began to be used for operating the bellows. In some cases wooden bellows – great wooden pistons working in tubs – were substituted for the old bellows of leather. By the end of the sixteenth century so many improvements had been made upon the primitive forge that it no longer resembled the forge of ancient times. So the new forge received a new name and was called a blast furnace.10 You should observe, however, that the blast furnace was simply the old forge built with a large closed furnace and provided with a more powerful blast.

The invention of the blast furnace marked the beginning of a new era in the history of iron making. In the first place there was produced in the blast furnace a kind of iron that was entirely different from that which was produced in the primitive forge. In the primitive forge there was made a lump of practically pure unmelted iron, known as wrought iron. In the blast furnace there was produced a somewhat impure grade of melted iron, known as cast iron, or pig11 iron. In the second place, the blast furnace produced iron in quantities vastly greater than it was ever produced by the old forge. In the blast furnace more iron could be made in a day than could be made by the forge in a month. In some of the early blast furnaces a thousand pounds of iron could be made at one melting and we read of one early furnace that produced 150 tons of iron in a year.

FIG. 7. – MAKING CHARCOAL.

But even with the blast furnace it was still difficult to make enough iron to supply the ever-increasing demands of the industrial world. In the sixteenth and seventeenth centuries machinery was brought into use more than ever before and of course more iron was needed for the construction of the machines. There was ore enough for all the iron that was needed but it was difficult to get fuel enough to smelt the ore. Charcoal was still used as the fuel for smelting (Fig. 7), and in order to get wood for the charcoal great inroads were made upon the forests. In England in the early part of the eighteenth century Parliament had to put a check upon the manufacture of iron in certain counties in order to save the forests of those counties from utter destruction. It then became plain that if iron making were to be continued on a large scale a new kind of fuel would have to be used in the furnaces. So men set their wits to work to find a new kind of fuel. As far back as 1619 Dud Dudley in the county of Warwick, England, undertook to use ordinary soft coal in his furnaces but his experiment was not very successful or very profitable. More than a century after this an English ironmaker named Abraham Darby began (in 1735) to use charred coal in his blast furnaces, and his experiments were successful. Here was the new fuel which was so badly needed. Charred coal is simply coke and coke could be had in abundance. So the new fuel was soon used in all parts of England and by the end of the eighteenth century coke was driving charcoal out of blast furnaces (Fig. 8).

FIG. 8. – A PITTSBURGH COKE OVEN.

FIG. 9. – A MODERN BLAST FURNACE.

About the time the use of coke for smelting became general, an Englishman named Neilson brought about another great change in the process of iron making. Before Neilson's time the blast driven into the furnace had always been one of cold air. Neilson learned that if the air before entering the furnace were heated to a temperature of 600 degrees it would melt twice the amount of ore and thus produce twice the amount of iron without any increase in the amount of fuel. So he invented (in 1828) a hot blast for the blast furnace (Fig. 9). With the use of coke and with the hot blast the production of iron increased enormously. But there was need for all the iron that could be made. Indeed it seems that the world can never get too much iron. About the time the hot blast was invented iron chains instead of ropes began to be used for holding anchors, iron plows began to be made in great numbers (p. 83), iron pipes instead of hollow wooden logs began to be used as water-mains in cities, and iron rails began to be used on railroads. To supply iron for all these purposes kept ironmakers busy enough, even though they burned coke in their furnaces and made use of the hot air blast.

But ironmakers were soon to become busier than ever before. About the middle of the nineteenth century Sir Henry Bessemer invented a new process of making steel. Steel is only iron mixed with a small amount of carbon. Ironmakers have known how to make steel – and good steel, too – for thousands of years, but before the days of Bessemer the process had always been slow and tedious, and the cost of steel had always been very great. Bessemer undertook to make steel in large quantities and at low prices. In his experiments amid showers of molten metal he often risked his life, but his perseverance and courage were rewarded. By 1858 he had invented a process by which tons of molten iron could be run into a furnace and in a few minutes be converted into a fine quality of steel. This invention of Bessemer was the last great step in the history of the forge.

From copyright stereograph by Underwood & Underwood, N. Y.

FIG. 10. – GREAT STEEL RAIL PASSING THROUGH ROLLER STEEL MILL.

Now that steel could be made in great quantities and at a low cost it was put to uses never dreamed of in former times. Soon the railroad rail was made of steel (Fig. 10), bridges were made of steel, ships of war were plated with steel. Then ocean grayhounds and battleships were made of steel, still later steel freight cars and steel passenger coaches were introduced, while in our own time we see vast quantities of steel used in the building of houses. So while the invention of Bessemer marked the last step in the history of the forge it also marked the ending of the Age of Iron and the beginning of the wonderful age in which we live – the Age of Steel.