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with the danger of falling walls added, a more dreadful catastrophe can hardly be imagined.

With the usual form of boiler construction this is almost unavoidable. The crownsheet is usually supported from the roof of the boiler by a large number of iron rods called "stay bolts," riveted on the inside of the firebox where their heads are constantly subjected to the most intense heat. When red heat is attained in the crownsheet through lack of water, the heads of the stay bolts are the first parts to be affected, and under pressure from within, pull through and leave the sheets unsupported and at the mercy of the terrific stored energy.

As far as the external appearance is concerned the Jacobs-Shupert firebox does not differ greatly from others, the unique features being within the boiler itself. One need only to glance at the photographs of the partly constructed firebox to realize the immensely superior strength it possesses over the old type. The top and sides instead of being made of single sheets as in the old design are constructed in U shaped sections a few inches in width, formed to the arch of the box, riveted together and reinforced

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The Firebox Of An Ordinary Boiler After Explosion From Lack Of Water.

The crownshtM't h;is boon torn away, leaving the stay bolts.

by vertical plates running in retreat from the fire. The plates are perforated with large holes to permit the free circulation of water and steam.

It is hardly necessary to state that this construction will withstand much more overheating than the common type of boiler.

What we are all most interested to know is whether our lives will be safer on a train behind an engine equipped with such a boiler, and so a brief description of the test to which it was recently subjected may be of interest.

On September 26th last, in the presence of many engineers from various cities and two representatives of the Interstate Commerce Commission, the above mentioned railway officials subjected a boiler equipped with a firebox of this design to a low-water test. This boiler was taken from one of the company's highest grade locomotives and set up in a large vacant tract of land in the neighborhood of their shops. The firebox was equipped to burn oil. The boiler was fitted with two steam gauges, one to verify the other, and two water glasses, one to show the height of the water above the crownsheet, the other, the distance it might fall below during the test. A pump was also set up at a distance to supply water during the experiment.

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fallen about five inches below the crownsheet and a temperature of 1,125 degrees in the firebox was recorded by a pyrometer. In other words, the crownsheet had attained a good working heat. At this point the fire was shut off and cold water turned in the boiler until the steam pressure was somewhat reduced. In spite of this terrific treatment, and the fact that at the time the crownsheet was red hot, the boiler withheld a pressure of 230 pounds to the square inch, and showed no Mil effects further than a few trifling leaks due to expansion of the plates

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under the intense heat applied during the test.

The pressure gauges, height of water, and records of temperature were observed by an engineer in a steel firebox chained to a flat car a short distance from the boiler. The remainder of the audience witnessed the proceedings through a telescope from a safe distance.

Statistics of the test are of little interest, but the trial is the most severe that has ever been given any boiler and one which the common type could not have withstood. It further demonstrates that a boiler so equipped could not, under the common conditions which cause explosions, create a disaster such as we so often read of in the daily papers. Because of the reinforcement of the firebox, little or no damage could result even if a blowout should take place in one of the sections, as it would be so small as to amount practically to the opening of a valve for the relief of the unusual pressure.

It is greatly to be hoped, if this form of boiler construction solves the explosion problem, that it may be adopted throughout the world, wherever boilers arc in use.

DAMMING THE MISSISSIPPI

By

F. G. MOORHEAD

NOT far from the spot where Jim Bludsoe ran the Prairie Belle aground and "held her nozzle agin the bank till the last galoot was ashore,'' a mile-wide dam is being built which will completely change the contour and topography of the Mississippi River and the historic land thereabouts. Incidentally a steamboat canal, nine miles long, built forty years ago at a cost of $8,000,000, is to be completely drowned out, with not a stick or a stone left to show where it once made possible the passage of the treacherous Des Moines rapids.

The sons of the men who damned the Mississippi a generation ago are now busily engaged in damming it. The work will occupy two years more, but already

a thousand men are working, beaver like, 'to throw across the mighty river a structure of cement and stone which shall hold the rushing waters in check and subserviently render up to its master 250,000 horse-power with which to run the factories, mills, and workshops of the very heart of the grain belt. Already, on both sides of the Mississippi, the dam has begun to assume shape. Two gangs of men are throwing out abutments and creeping toward each other across a watery path. Twenty million dollars will be spent before the two gangs meet, but the investment is considered a good one by some of the shrewdest financiers of the country.

For over sixty years Keokuk has dreamed of harnessing the turbulent waters of the Mississippi and making the Des Moines rapids do the work of man. As long ago as 1848 the Mississippi River Improvement Association was formed, with a capital of $1,000,000, its objects being to improve navigation and harness the water power that might be developed in the process. The Civil War passed and still the project remained a dream. The United States government went a long ways toward shattering the dream for all time by building a ninemile canal alongside of the perilous rapids where many a steamboat and many a raft had met demolition, establishing three locks for the purpose of raising and lowering craft from one level to another. Flowing through the high, limestone gorges on either side, step by step the solid lime rock of the river's

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xjttom drops twenty-four feet to the navigable depths of the open river below Keokuk. At an annual cost of $50,000 the government has maintained this canal for forty years. Within the next two years it will have disappeared under twenty feet of water, part of the bed of a new inland lake forty miles long and from one to five miles wide. For the dream of two-thirds of a century is being realized at last. Five years ago, after numberless disheartening failures, a bill was passed through Congress granting a franchise and the first glimmerings of a realized dream began to appear.

It was no small task to get both houses of Congress to agree on a franchise which establishes the precedent of building a dam entirely across the country's largest river. Hut the Keokuk boosters were shrewd. They introduced old river pilots and captains before the committees to testify that the dam would improve navigation rather than hinder it; they

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enlisted the co-operation of the army engineers and voluntarily agreed to replace the canal and its three locks with a single lock, which would answer every purpose, and the twenty-year old dry dock with a new one, and from now to the end of time to supply the power to operate the new lock and the new dry dock, absolutely free of charge. On January 27, 1905, the lower house passed the bill granting the desired franchise. On February 2, it passed the Senate and on February 9, 1905, President Roosevelt signed the bill.

Immediately there began the hunt for capital. The bill required that the work begin within five years and be completed within ten. It was not until a month or two before the five-year limit had expired that work actually began. Even then the doubters remained, crying that the limestone cliffs were being uncovered simply to keep the franchise and that the dam would never be built. But as the weeks passed and the gangs of workmen grew, from a few score to several hundred, and the approaches to the dam on the Illinois shore gradually began to show, the scoffers fled and all Keokuk joined in such a jubilation as the old Mississippi Valley has not known since the palmy days of steamboat racing. On January 8, 1910, definite announcement was made that the dam would be built. By the first of February several score of men were at work. The construction was continued uninterrupted from that time, and early in December, 1910. five hundred men started to work on the Iowa shore.

Mr. Hugh L. Cooper, the engineer in charge, has given Keokuk assurances that the work can be completed in thirty months. The first year has been one of preparation mainly, but the end of 1911 will find the dam well under way, extending out from both the Iowa and the Illinois shores, and the power house practically completed.

The project gives to the Mississippi Valley the largest water-power development in the entire country, with the single exception of the combined plants at Niagara Falls, and the largest dam in the world, with the single exception of the Assouan dam across the Nile in Egypt. There will be required in the construction 500,000 cubic yards of masonry, 500,000 barrels of cement, and 7,000 tons of steel.

The dam, including abutments, will be 4,700 feet long. It will extend from a point a little north of the center of the town of Hamilton, Illinois, due westward across the river to a point near the Iowa shore, under the bluffs at Keokuk, where the power house, 1.400 feet long, will link shore with shore. The mammoth dam will be of solid concrete, thirty-five feet wide on the bottom and about thirty feet high. The upper stream face will be vertical with a rounded top eight feet wide, the lower side ending in a curve connecting with the bottom, so that the water coming over will not fall, but slide down the face and be given a horizontal direction at the bottom of the river. The whole height is thirty-seven feet, the dam being locked into the rock bottom seven feet deep, to prevent any

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