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 _pig_[11] iron. In the second place, the blast furnace produced iron in quant.i.ties 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.

[Ill.u.s.tration: 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 _c.o.ke_ and c.o.ke 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 c.o.ke was driving charcoal out of blast furnaces (Fig. 8).

About the time the use of c.o.ke 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 c.o.ke 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 c.o.ke in their furnaces and made use of the hot air blast.

[Ill.u.s.tration: FIG. 8.--A PITTSBURGH c.o.kE OVEN.]

[Ill.u.s.tration: FIG. 9.--A MODERN BLAST FURNACE.]

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 quant.i.ties 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.

[Ill.u.s.tration:

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

FIG. 10.--GREAT STEEL RAIL Pa.s.sING THROUGH ROLLER STEEL MILL.]

Now that steel could be made in great quant.i.ties 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 pa.s.senger coaches were introduced, while in our own time we see vast quant.i.ties 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.

FOOTNOTES:

[8] J. R. Smith, "The Story of Iron and Steel," p. 3.

[9] From "Five Black Arts," p. 311.

[10] The old forge continued to be used by the side of the blast furnace for centuries, and of course where it was used it was still called a forge. Thus we are told that in Maryland in 1761, there were eight furnaces and ten forges. It is said that as late as twenty-five years ago in certain parts of the Appalachian regions the American mountaineer still worked the little primitive forge to make his iron.

[11] It was given the name of _pig_ iron because when the molten metal ran into the impressions made for it upon the sanded floor and cooled, it a.s.sumed a shape resembling a family of little pigs.

THE STEAM-ENGINE

We have now traced the steps by which man mastered the art of kindling a fire quickly and easily and have followed the progress that has been made in the most common uses of fire. But the story of a most important use of fire remains to be told, the story of its use in doing man's _work_. How important this use is, how much of the world's work is done through the agency of fire, a little reflection will make plain. Fire makes steam and what does steam do? Its services are so many you could hardly name all of them. The great and many services of steam are made possible by the fire-engine, or _steam-engine_, and the story of this wonderful invention will now be told.

That steam has the power to move things must have been learned almost as soon as fire was used to boil water. Heat water until it boils and the steam that is formed is bound to move something unless it is allowed to escape freely. It will burst the vessel if an outlet is not provided.

That is why a spout has been placed on the tea-kettle. Where there is cooking, steam is abundant and the first experiments in steam were doubtless made in the kitchen (Fig. 1). It has been said that the idea of the steam-engine first occurred to Adam as he watched his wife's kettle boil.

[Ill.u.s.tration: FIG. 1.--FIRST EXPERIMENTS WITH STEAM.]

Whatever may have happened in ancient kitchens, we are certain that there were no steam-engines until many centuries after Adam. The beginnings of this invention are not shrouded in so much mystery as are those of the match and the lamp and the forge. In giving an account of the steam-engine we can mention names and give dates from the very beginning of the story. We know what the first steam-engine was like and we know who made it and when and where it was made. It was made 120 B. C. by Hero, a philosopher of Alexandria in Egypt. It was like the one shown in Figure 2. The boy applies the fire to the steam-tight vessel _p_ and when steam is formed it pa.s.ses up through the tube _o_ and enters the globe which turns easily on the pivots. The steam, when it has filled the globe, rushes out of the short tubes _w_ and _z_ projecting from opposite sides of the globe and bent at the end in opposite directions. As it rushes out of the tubes the steam strikes against the air and the reaction causes the globe to revolve, just as in yards we sometimes see jets of water causing bent tubes to revolve. This was Hero's engine, the first steam-engine ever made.

[Ill.u.s.tration: FIG. 2.--HERO'S ENGINE, 120 B. C.]

Hero's engine was used only as a toy and it seems to represent all the ancients knew about the power of steam and all they did with it. It is not strange that they did not know more for there is no general rule by which discoveries are made. Sometimes even enlightened peoples have for centuries remained blind to the simplest principles of nature. The Greeks and Romans with all their culture and wisdom were ignorant of some of the plainest facts of science. It is a little strange, however, that after Hero's discovery was made known, men did not profit by it. It would seem that eager and persistent attempts would have been made at once to have steam do useful work, as well as furnish amus.e.m.e.nt. But such was not the case. Hero's countrymen paid but little attention to his invention and the steam-engine pa.s.sed almost completely out of men's minds and did not again attract attention for nearly seventeen hundred years.

About the end of the fifteenth century Europe began to awaken from a long slumber and by the end of the sixteenth century its eyes were wide open. Everywhere men were now trying to learn all they could. The study of steam was taken up in earnest about the middle of the sixteenth century and by the middle of the next century quite a little had been learned of its nature and power. In 1629 an Italian, Branca by name, described in a book a steam-engine which would furnish power for pounding drugs in a mortar. There was no more need for such a machine then than there is now and of course the inventor aroused no interest in his engine. You can easily understand how Branca's engine (Fig. 3) works. The steam causes the wheels and the cylinder to revolve. As the cylinder revolves, a cleat on it catches a cleat on the pestle and lifts the pestle a short distance and then lets it fall. Here the pestle instead of being raised by a human hand is raised by the force of steam.

This engine would be more interesting if an engine had actually been made, but there is no reason to believe that Branca ever made the engine he described. We owe much to him, nevertheless, for suggesting how steam might be put to doing useful work.

[Ill.u.s.tration: FIG. 3.--BRANCA'S ENGINE, 1629.]

It was not very long before an Englishman put into practice what the Italian had only suggested. Edward Somerset, the Second Marquis of Worcester, in 1663 built a steam-engine that raised to the height of forty feet four large buckets of water in four minutes of time. This was the first useful work ever done by steam. Figure 4 shows the construction of Worcester's engine.

[Ill.u.s.tration: FIG. 4.--WORCESTER'S ENGINE, 1663.]

In this engine there was one improvement over former engines which was of the greatest importance: there was one vessel in which the steam was generated and another in which the steam did its work. The steam-engine now consisted of two great divisions, the boiler and the engine proper.

Worcester spent a large part of his fortune in trying to improve the steam-engine, yet he received neither profit nor honor as a reward. He died poor and his name was soon forgotten. His service to the world was nevertheless very great. In his time the mines of England had been sunk very deep into the earth; and the deeper they were sunk the greater was the difficulty of lifting the water out of them and keeping them dry.

The water was lifted up from the mines by means of buckets drawn by horses or oxen (Fig. 5). Sometimes it took several hundred horses to keep the water out of a single mine. It was Worcester's object to construct an engine that would do the work of the horses. The engine he built could not do this, yet it furnished the idea--and the idea is often the most important thing. It was not long before engines built upon Worcester's plan were doing useful work at the mines. At the opening of the eighteenth century the steam-engine had been put to work and was serving man in England and throughout the continent of Europe.

[Ill.u.s.tration: FIG. 5.--AN ANCIENT METHOD OF DRAWING WATER.]

[Ill.u.s.tration: FIG. 6.--PAPIN'S ENGINE, 1690.]

The first engines were not safe. Often the steam pressed too heavily upon the sides of the vessel in which it was compressed and there were explosions. About 1680 Denis Papin, a Frenchman, invented the _safety valve_, that is a valve that opens of its own accord and lets out steam when there is more in the vessel than ought to be there. About ten years later Papin gave the world another most valuable idea. In Worcester's engine the steam in the steam chest pressed directly on the water that was to be forced up. Papin showed a better way. He invented the engine shown in Figure 6. In this engine a small quant.i.ty of water was placed in the bottom of the cylinder _A_. Fitting closely in the cylinder was a _piston_ _B_ such as Papin had seen used in ordinary pumps. We will suppose that the piston is near the bottom of the cylinder and that a fire is built underneath. The bottom being made of very thin metal the water is rapidly converted into steam and thus drives the piston up to the top as shown in the figure. Here a latch _E_ catches the piston-rod _H_ and holds the piston up until it is time for it to descend. Now the fire is removed and the steam, becoming cold, is condensed and a vacuum is formed below the piston. The latch _E_ now releases the rod _H_ and the piston is driven down by the air above it, pulling with it the rope _L_ which pa.s.ses over the pulleys _TT_. As the rope descends it lifts a weight _W_ or does other useful work. As the inventor of the piston Papin ranks among the greatest of those whose names are connected with the development of the steam-engine.

Our story has now brought us to the early part of the eighteenth century. Everywhere men were now trying to make the most of the ideas of Worcester and Papin. The mines were growing very deep. As the water in them was getting beyond control something extraordinary had to be done.

Now it seems that whenever the world is in need of an extraordinary service someone is found to render that service. The man who built the engine that was needed was a humble blacksmith of Dartmouth, England, Thomas Newcomen. This master mechanic in 1705 constructed the best steam-engine the world had yet seen. We must study Newcomen's engine (Fig. 7) very carefully. The large beam _ii_ moved freely up and down on the pivot _v_. One end of the beam was connected with the heavy pump-rod _k_ by means of a rope or chain working in a groove and the other end was connected with the rod _r_ in the same way. When steam from the boiler _b_ pa.s.sed through the valve _d_ into the cylinder (steam-chest) _a_ it raised the piston _s_ and with it the piston-rod _r_ thus slackening the rope and allowing the opposite end of the beam to be pulled down by the weight of the pump-rod _k_. As soon as the piston _s_ reached the top of the cylinder the steam was shut off by means of the valve _d_ and the valve _f_ was turned and a jet of cold water from the tank _g_ was injected into the cylinder _a_ with the steam. The jet of cold water condensed the steam rapidly--steam is always condensed rapidly when anything cold comes in contact with it--and the water formed by the condensation escaped through the pipe _p_ into the tank _o_. As soon as the steam in _a_ is condensed, a vacuum was formed in the cylinder and the atmosphere above forced the piston down and at the same time pulled the pump-rod _k_ up and lifted water from the well or mine. When the piston reached the bottom of the cylinder the valve _d_ was opened and the piston again ascended. Thus the beam is made to go up and down and the pumping goes on. Notice that steam pushes the piston one way and the atmosphere pushes it back.

[Ill.u.s.tration: FIG. 7.--NEWCOMEN'S ENGINE, 1705.]

In Newcomen's engine the valves (_f_ and _d_) at first were opened and shut (at each stroke of the piston) by an attendant, usually a boy. In 1713 a boy named Humphrey Potter, in order to get some time for play, by means of strings and latches, caused the beam in its motion to open and shut the valves without human aid. We must not despise Humphrey because his purpose was to gain time for play. The purpose of almost all inventions is to save human labor so that men may have more time for amus.e.m.e.nt and rest. Humphrey Potter ought to be remembered not as a lazy boy but as a great inventor. His strings and latches improved the engine wonderfully (Fig. 8). Before his invention the piston made only six or eight strokes a minute; after the valves were made to open and shut by the motion of the beam, it made fifteen or sixteen strokes a minute and the engine did more than twice as much work.

[Ill.u.s.tration: FIG. 8.--HUMPHREY POTTER'S LATCHES AND STRINGS.]

Newcomen's engine as improved by Potter and others grew rapidly into favor. It was used most commonly to pump water out of the mines but it was put to other uses. In and about London it was used to supply water to large houses and in 1752 a flour mill near Bristol was driven by a steam-engine. In Holland Newcomen's engines were used to a.s.sist the wind-mills in draining lakes.

[Ill.u.s.tration: FIG. 9.--JAMES WATT STRIVING TO IMPROVE NEWCOMEN'S ENGINE.]

For nearly seventy-five years engines were everywhere built after the Newcomen pattern. Improvements in a small way were added now and then but no very important change was made until the latter part of the eighteenth century, when the steam-engine was made by James Watt practically what it is to-day. This great inventor spent years in making improvements upon Newcomen's engine (Fig. 9) and when his labors were finished he had done more for the steam-engine than any man who ever lived. We must try to learn _what_ he did. We can learn what Watt did by studying Figure 10. Here P is a piston working in a cylinder A _closed at both ends_. By the side of the cylinder is a _valve-chest_ C into which steam pa.s.ses from the pipe T. Connecting C with the cylinder there are _two_ openings, one at the top of the cylinder and the other at the bottom. The valve-chest is provided with valves which are worked by means of the rod F, which moves up and down with the beam B, thanks to Humphrey Potter for the hint. The valves are so arranged that when steam enters the opening at the top of the cylinder it is shut off from the opening at the bottom, and when it enters the opening at the bottom it is shut off from the opening at the top. When the opening at the bottom is closed the steam will rush in at the upper opening and push the piston downward; when the piston has nearly reached the bottom of the cylinder the upper opening will be closed and steam will rush in at the bottom of the steam chest and push the piston upwards. Here was _one_ of the things done by Watt for the engine: he contrived to make the steam push the piston down as well as up. You have observed that in Newcomen's engine steam was used only to push the piston _up_, the atmosphere being relied upon to push it down. Thus we may say that Watt's engine was the first _real steam-engine_, for it was the first that was worked entirely by steam. All engines before it had been worked partly by steam and partly by air.

[Ill.u.s.tration: FIG. 10.--WATT'S ENGINE.]

Watt's greatest improvement upon the steam-engine is yet to be mentioned. In Newcomen's engine when the cold water was injected into the cylinder it cooled the piston and when steam was let into the cylinder again a part of it, striking the cold piston, was condensed before it had time to do any work and the power of this part of the steam was lost. Watt did not allow the piston to get cold, for he did not inject any cold water into the cylinder. In his engine as soon as the steam did its work it was carried off through the pipe _M_ to the vessel _N_ and there condensed by means of a jet of water which was injected into _N_ (called the _condenser_) by means of a pump _E_ worked by the motion of the beam, thanks again to Humphrey Potter for the idea.

This condensation of the steam outside of the cylinder and at a distance from it prevented the piston (and cylinder) from getting cold. In other words, in the Watt engine when steam entered the cylinder it went straight to work pushing the piston. No steam was lost and no power was lost and the cost of running the engine was greatly reduced.

It cannot be said that Watt invented the steam-engine--no one can claim that honor--yet he did so much to make it better that he well deserves the epitaph which is inscribed on his monument in Westminster Abbey.

This inscription is as follows:

NOT TO PERPETUATE A NAME WHICH MUST ENDURE WHILE THE PEACEFUL ARTS FLOURISH BUT TO SHEW THAT MANKIND HAVE LEARNT TO HONOR THOSE WHO BEST DESERVE THEIR GRAt.i.tUDE THE KING HIS MINISTERS AND MANY OF THE n.o.bLES AND COMMONERS OF THE REALM RAISED THIS MONUMENT TO JAMES WATT WHO DIRECTING THE FORCE OF AN ORIGINAL GENIUS EARLY EXERCISED IN PHILOSOPHIC RESEARCH TO THE IMPROVEMENT OF THE STEAM ENGINE ENLARGED THE RESOURCES OF HIS COUNTRY INCREASED THE POWER OF MAN AND ROSE TO AN EMINENT PLACE AMONG THE MOST ILl.u.s.tRIOUS FOLLOWERS OF SCIENCE AND THE REAL BENEFACTORS OF THE WORLD BORN AT GREENOCH MDCCx.x.xVI DIED AT HEATHFIELD IN STAFFORDSHIRE MDCCCXIX