BOILER EXPLOSIONS AND THEIR CAUSES.

The subject of boiler explosions has been discussed at great length during the past year in English scientific periodicals. In the London Engineer and London Mechanics' Magazine, editorial articles and contributions from correspondents have appeared weekly, in which various theories have been advanced, attacked, and defended; and the conflict still goes on. The discussion has excited our attention not only on account of its nature, but also because of the persons who have taken part in it, such as C. Wye Williams, the author of a valuable work on combustion; D. K. Clark, author of the incomparable work on locomotive engineering, and Zerah Colburn (now in London), an able American writer on railway engineering topics. Quite a number of others, whose names we omit, have also taken part in the discussion. There is still some apparent mystery connected with the phenomena of boiler explosions, or we would not have so many notions and theories floating about respecting their causes. The most common theory of boiler explosions is that of accumulated over-pressure of steam generated by the heat in the furnace. This theory embraces defects in the boiler, also the absence of a sufficient quantity of water, whereby the metal is permitted to become red hot and weak, and is capable of explaining most of the explosions which have occurred.

The theory of C. W. Williams is to the effect that steam is concentrated in the water under pressure in a steam boiler, like carbonic acid gas in soda water, and when it is relieved of pressure it suddenly assumes a violent expansive action.

The theory of D. K. Clark consists in considering the water in the boiler necessary to produce an explosion, by acting like a projectile with a bounding force against the metal.

Mr. Zerah Colburn's hypothesis consists in assuming that when water, heated with steam above atmospheric pressure, is suddenly relieved of pressure by a large rupture, a considerable amount of the water is instantly flashed, gunpowder-like, into steam. —Scientific

American.

NOVEL ARRANGEMENT OF STEAM BOILERS.

At the meeting of the Society of Civil Engineers of Vienna, Austria, M. Strecker communicated a very ingenious and simple mode of preventing the burning of steam boilers. This apparatus, invented by M. J. Haswell, director of the Vienna Locomotive Factory, consists in introducing into the interior of the boiler a small turbine, which continually drives the water from the bottom towards the front of the boiler; thus on the one hand cooling the walls which are most liable to overheat, and on the other facilitating the formation of steam.

WORKING STEAM EXPANSIVELY.

During the winter of 1860-61, experiments were made, under order of the Secretary of the Navy, by a Board of Chief Engineers

of the Naval Engineer Corps, to determine certain questions in reference to the economy of steam expansion. Previous experiments made by the chief officer of the Board had induced him to assert the fallacy of the commonly received doctrine of economy in expansion, and these observations were undertaken to pursue the investigation on a more perfect engine, and with greater care. A report of the results has been published by the Navy Department, from which the following facts are derived:

The vessel selected to test the relative merits of expansive and non-expansive steam in cylinders was the Michigan, a government paddle-wheel steamer lying at Erie, Pa. The larboard engine only was used, and it was employed in exerting its power to paddle the water aft while secured at the dock. Each experiment lasted seventytwo consecutive hours, during which the engine was neither stopped nor slowed down, nor in any way changed in condition. It was always operated several hours, so as to get the steam to the same pressure, the fires in proper order, and all things adjusted correctly, before each experiment was actually commenced. The water in the boiler was gauged, and the quantity fed in was accurately measured. Every pound of coal fed into the furnaces was carefully weighed; indicator cards were taken, and everything arranged to insure accuracy. The results of seven experiments, cutting off at 11, 10, 1, 0, 1, 1, 4ths of the stroke, are given in a tabulated form. Five of these were performed with Ormsby bituminous coal, and the other two with anthracite and Brookfield coal. The pressure in the boilers above the atmosphere was 195 lbs. the lowest, 22 lbs. the highest. The quantities of water consumed were 39.942 lbs. per total horse power, cutting off at 11 stroke; 30.881, at 7; 29.416, at 4; 30.592, at; 29.841, at 1; 30.715, at 1; 32.044, at These are important items, demanding careful scrutiny.

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The water fed into the boiler was carefully measured in a tank, and it was found that just in proportion as expansion was extended, there was a proportionally greater loss of steam in the cylinder by condensation a great deal more steam flowed into the cylinder than was accounted for by the indicator. Thus, cutting off at 11 of the stroke, the loss was 2.91; at 7, 6.60; at 4, 18.14; at, 33.07; at 1, 30.84; at 1, 33.66, and at, not less than 37.16 per cent. not accounted for. In short, the conclusions from these experiments are, that so much condensation takes place in the cylinder by the cooling action of expansion, that no economy results from using highly expanded steam. It is true that somewhat more power is developed in the same cylinder by expansion, but by using smaller cylinders, proportioned to the power required without expansion, the economy is on the side of non-expansion, both with respect to fuel and the cost of machinery. These conclusions, it must be evident, are of a very radical and revolutionary character, inasmuch as they affect principles which have been accepted in practice from a very early period in the history of the steam engine applied to actual work. They differ from the whole tenor of experimental observations and theoretical deductions, and, if accepted by the profession, would modify at once our proportions of working parts, and our applications of power. But it should be also stated, that these conclusions are not universally ac

cepted, and, indeed, are considered by some high authorities as based on faulty and incorrect experimentation.

SUPERHEATED STEAM.

Much has been written within the last few years relative to the above topic, and there can be no doubt that, if superheated steam is properly used, a saving of fuel may be effected. Many of the statements published, however, have made the success too great. Some time since the English Pacific mail steamers had their engines arranged to use highly superheated steam (450 to 500 degrees), and for a while the change was regarded as beneficial. It is now, however, found that this high heat is very destructive to the engines, injuring the cylinders, pistons, valve faces, and valves; and so great has the injury been, that they have commenced to take out and much reduce the number of superheating tubes.

COAL AND WOOD-BURNING LOCOMOTIVES.

By a late report of John O. Sterns, Esq., superintendent of the New Jersey Central Railroad, we learn that very fair tests have been made with wood and coal-burning engines on that road, all of which have terminated favorably for coal, as it regards economy. There are thirty-eight locomotives, six of which have been altered from wood to bituminous coal-burners; twenty-four burn wood, and eight anthracite coal.

During the last two years and nine months, the wood-burning engines have run 1,353,909 miles, the anthracite coal engines 165,585, and the bituminous engines 112,757 miles. Regarding the performance of these three classes of engines, Mr. Sterns says: "The three comparatively perfect anthracite engines make a saving in fuel of seven cents per mile over three equally good wood engines, and the difference in cost for repairs cannot exceed three cents per mile, leaving a net saving of four cents per mile run by substituting anthracite coal for wood. . . From our past experience, I am satisfied there is a saving by using bituminous coal instead of wood, of about three cents per mile, and that it is expedient to alter several of our wood-burning freight engines to burn bituminous coal, especially as the change is easily and cheaply made."

The wood used by this company is oak, rated at five dollars per cord; the bituminous coal is the same cost per ton, while the anthracite is set down at three dollars per ton. The wood-burning engines run at the rate of 28.3 miles per cord; three good anthracite coal engines average 31 miles to a ton of coal. Mr. Sterns states that if all the freight trains on the New Jersey Central Railroad had been drawn by good anthracite coal engines, twenty thousand dollars would have been saved to the company last year alone. Where wood is very cheap, as in Canada and on some of the Southern railroads, of course it is preferable to use it; but wherever it can be shown that coal is cheaper than wood on any railroad, those who have the management of affairs are culpable if they run wood-burning engines. Scientific American.

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NEW MODE OF WARMING RAILROAD CARS.

Experiments with a new system of heating railroad cars have been instituted by M. Delcambre, in various parts of France, and have been recently repeated on the Paris and Montargis section of the Lyons line. By this plan, the steam which escapes from the locomotive is carried by a caoutchouc pipe to the first carriage, and there made to pass through conduits of copper, placed in the roof and the floor, to the end of the vehicle, where it is received into another flexible pipe, and carried on to the next carriage, and so on from one vehicle to another to the end of the train, where it escapes. The fixing and removing of the caoutchouc pipes is accomplished with the greatest facility, and the passage of the steam through the conduits presents no inconvenience to the passengers. By means of the new plan a temperature of 59° Fahrenheit was obtained on an excessively cold day, and at a merely nominal expense.

LOCOMOTIVES ON COMMON ROADS.

In anticipation of the adoption and use of locomotives on common roads, to the perfection of which considerable attention has been of late paid in England, a bill has been introduced into Parliament for their regulation. It exacts that the weight on each pair of wheels is not to exceed one ton and a half. The use of locomotives destructive to highways or dangerous to the public is to be prohibited by the Secretary of State, so as to prevent the excessive wear and tear. The weight of locomotives over county, parish, or suspension bridges is not to exceed fifteen tons, and any damage is to be made good. The locomotives are to consume their own smoke. Two persons are to drive and conduct every locomotive, and red lights are to be fixed conspicuously in front of locomotives and wagons one hour after sunset till one hour before sunrise. The speed of locomotives on highways is not to exceed ten miles an hour, and through towns, cities, or villages, five. No locomotive is to be used within the city of London more than seven feet in width and with wheels six inches wide.

MILITARY ARCHITECTURE OF THE MIDDLE AGES.

The above is the title of a work recently published in France, by M. Viollet-le-Duc, and translated into English by Mr. MacDermott. We derive from its pages the following items of information.

There are two great eras in military architecture: the first being the result of the Crusades, when the passive system of defence was superseded by an activity equal to that required for an attack; and the second being that marked by the introduction of gunpowder. The commencement of the latter era was the starting-point from which the subject has gradually been divested of everything like picturesque effect, till it has resolved itself, in the aspect of its fabrics, into the terrible uniformity and ugliness recognized by the term barrack style. In so far as a revival of pictorial results might be beneficial, the essay, with its telling illustrations, may be of service;

but, au reste, the days of castle-building are departed. Castles were essentially a feature of feudalism, and it would be meaningless to revive them. Nevertheless, it is interesting to trace in the compass of a few pages the successive steps made by generations of men, through centuries of time, towards the protection of their possessions or the acquisition of new territory. Until the middle of the fourteenth century, the defence was stronger than the attack, the balance of power, in the absence of gunpowder, being in favor of the massiveness of the architecture. Thus, in Norman times, the defence relied mainly upon its passive force, the height of the walls defying all attempts at escalade, the strength of the gates resisting all efforts at forcing them. But towards the end of the fourteenth century, the attack became superior to the defence, and so it has remained, the converging fire of besiegers having advantage over the diverging fire of the besieged. Not only this, but the whole scheme of warfare has been altered by the application of modern appliances. In old times, the attack and defence were subdivided into parts, and thence into parts again; each tower of a castle being a separate fort, and again each story of that tower capable of separate and strong defence; so that the action took place on sites crowded with infinity of unexpected contrivances, and depended in great measure upon individual prowess. The use of gunpowder demanded a wider range, an enlarged field of operations, and united action. The futility of the axiom that whatever defends should be defended, was perceived by Machiavelli, who laid down as a primary rule the inadvisability of any complexity of the kind in the construction of fortresses.

M. Viollet-le-Duc has chosen for especial illustration the Chateau Gaillard, the fortress built by Richard Cœur de Lion on the Seine for the protection of the capital of his Norman territory,- - Rouen. With all due deference to the French architect and antiquary, this must be considered as essentially an English castle as that of Newcastle-upon-Tyne. The details, which are amply illustrated, prove that the lion-hearted monarch was a most skilful architect, engineer, and master of defence. This is one of the new lights by which to read history, for which we should express ourselves indebted to M. Viollet-le-Duc. The castle was built under the immediate superintendence of Richard, and, with all its subtle contrivances and defences, was completed in a twelvemonth; when he is said thus to have apostrophized it:— "Qu'elle est belle, ma fille d'un an!" The outworks were so extensive that a town, known as Petit Andeley, arose within their enclosure. The enceinte of the principal portion of the castle presents a variety to the usual mode of building prevalent, which must be ascribed to the genius of Richard. It consisted of massive masonry arranged in a succession of segments of a circle, connected by a series of short curtains of an even length. keep also differed from the common type. It was a mighty tower, strengthened by a girth of reversed pyramids, through the broad bases of which, on a level with the summit of the tower, were machicolations for close defence; and these were surmounted with a crenellated parapet, which was pierced with loop-holes. Notwithstanding the immense strength of this fortress, it fell before the skill of the

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