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SCIENTIFIC AMERICAN SUPPLEMENT NO. 561
NEW YORK, OCTOBER 2, 1886
Scientific American Supplement. Vol. XXII., No. 561.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
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TABLE OF CONTENTS.
I. BOTANY.—A Century Plant in Bloom.—Interesting account of the recent blossoming of an Agave Americana at Auburn, N.Y. 8965
Alpine Flowers in the Pyrenees.—1 illustration. 8965
II. CHEMISTRY.—Probable Isolation of Fluorine.—Decomposition of hydrofluoric acid by an electric current.—By M.H. MOISSAN.—Production of a new body, possibly fluorine, or perfluoride of hydrogen. 8963
The Determination of Nitric Acid by the Absorption of Nitric Oxide in a Standard Solution of Permanganate of Potash.— By H.N. MORSE and A.F. LINN. Full description of a new and important volumetric determination.—1 illustration. 8964
Water of Crystallization.—By W.W.J. NICOL, M.A., D.Sc.— Discussion of the state of water of crystallization in a salt in solution. 8964
III. ENGINEERING.—Combustion, Fire Boxes, and Steam Boilers—By JOHN A. COLEMAN.—Address before the June Convention of the Master Mechanics' Association. 8953
Compound Hydraulic Presses.—Different forms of presses designed for pressing bales for shipment.—Very fully illustrated by 8 figures. 8951
Examination Papers in General Construction.—Eighty-six questions in engineering propounded by the civil service examiners of New York city. 8956
IV. MEDICINE AND PHYSIOLOGY.—A New Apparatus for the Study of Cardiac Drugs.—By WILLIAM GILMAN THOMPSON, M.D.—Ingenious application of instantaneous photography to the study of heart movements.—Apparatus and views produced.—3 illustrations. 8966
Creosote a Specific for Erysipelas,—A new cure for this complaint. 8966
V. METALLURGY.—Primitive Iron Manufacture.—Iron furnace and blowing apparatus in use in Bengal.—2 illustrations. 8962
VI. MINING ENGINEERING.—The Catastrophe at Chancelade.— Application of photography to investigating mine disasters. —4 illustrations. 8962
VII. MISCELLANEOUS.—Celebration of the 500th Anniversary of the University of Heidelberg. August, 1886. 8957
Useful Bags and How to Make Them.—Interesting paper on the trunk makers' art.—4 illustrations. 8960
VIII. NAVAL ENGINEERING.—Atlantic Steamers.—By W. JOHN.— Exhaustive comparison of representative Atlantic liners and war ships.—3 illustrations. 8954
Jet Propellers.—Hydraulic propulsion of vessels.— Mathematical examination of this subject. 8951
IX. ORDNANCE.—The New Army Gun.—Description of the 8-inch steel gun as manufactured at the West Point, N.Y., Foundry.—1 illustration. 8952
X. PHYSICS.—A New Thermo Regulator.—1 illustration. 8959
Cohesion and Cohesion Figures.—By WILLIAM ACKROYD, F.I.C.—Laws of vortex rings examined, and relation of solubility to cohesion. 8963
Pipette for taking the Density of Liquids.—Apparatus and calculations for use.—1 illustration. 8959
XI. TECHNOLOGY.—Impurities in Photographic Chemicals, and Tests for Same.—Table referred to in a paper read before the Birmingham Photographic Society by G.M. Jones, M.P.S. 8957
Molasses, how made.—Work on Plantations Graphically Described.* 8961
Optical errors and human mistakes.—By ERNST GUNDLACH.—On the examination of optical glasses.—A paper read before the Buffalo meeting of the A.A.A.S. 8963
Soap.—By HENRY LEFFMANN, Ph.D. 8962
Somzee's New Gas Burners.—Interesting description of regenerative burners.—9 figures. 8958
The Clamond Gas Burner.—Of value as a supplement to the above named article, describing an incandescent burner. —1 illustration. 8959
Wood Oil.—A new industry worked on the large scale in Sweden. 8962
* Transcriber's Note: "Work on Plantations..." was originally part of TOC entry "Optical Errors..."
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COMPOUND HYDRAULIC PRESSES.
In a hydraulic packing press, the work done by the ram during one stroke may be roughly divided into two periods, in the first of which the resistance, although gradually increasing, may be called light, while in the second the resistance is heavy. The former of these two periods embraces the greater part of the stroke, and it is only a small proportion at the end which requires the exercise of the full power of the press to bring the material to the determined degree of consolidation. Consequently, if a hydraulic press is to be worked so as to waste no time, it requires to be provided with means by which its table may be made to rise rapidly during the portion of the stroke when the resistance is small, and afterward more slowly when the entire power of the pumps is being expended upon the final squeeze. Many methods of obtaining this end have been devised, and are in common use both here and abroad. It is, however, more particularly in the packing of raw material that such appliances are useful, since the goods pressed into bales in this country are not usually of a very yielding nature, and consequently do not require a long stroke to bring them to a high state of compression. In India and Egypt, from whence cotton is sent in bales, presses must have a long stroke; and unless they can be worked rapidly, a very considerable amount of plant is required to get through a moderate quantity of work. To meet the necessities of these countries, Mr. Watson has devised several forms of press in which not only is the table made to rise rapidly through the greater part of its stroke, but the rams are kept almost constantly in motion, so that the time occupied in filling the box with raw cotton and in placing the ties round the bales is not lost.
We illustrate four forms of Mr. Watson's presses, Fig. 1 being an earlier construction, which, although very rapid at the date at which it was brought out, has been far surpassed in celerity by the arrangements shown in Figs. 3 to 8. It was introduced in 1873, and forty-three presses according to this design were sent to India by the makers, Messrs. Fawcett, Preston & Co., of Phoenix Foundry, Liverpool, between that year and 1880. Four presses of this kind are worked by one engine, having a cylinder 20 in. by 3 ft. stroke, and driving eighteen to twenty pumps of varying diameter and short stroke. The press has two long-stroke rams, LL, of small diameter, to compress the loose material, and two short-stroke rams, FF, of large diameter, to give the final squeeze. These two pairs of rams act alternately, the one pair being idle while the other is in operation. The lashing of the bale takes place while the larger rams are in action, the bale being supported on the grid, B, which is pushed under it through grooves formed in the press-head, S (Fig. 1). When the grid is in place the press-head can be lowered, and the box be filled, while the bale is receiving its final squeeze from the inverted rams above.
In Figs. 1 and 2 the press is shown in the position it would occupy if the bale, M, were just completed and ready to be pushed out, and the box, N, were full of material. The filling doors, CC, are shown turned back level with the floor, the main doors, AA, are open, as are also the end doors, KK, to admit the men to fasten up the bale. If water be admitted to the subsidiary cylinder, H, the head, G, and two rams, FF, will be raised, and then the bale, M, can be thrown out finished. All the doors are now closed and water admitted to the rams, LL. These immediately rise, pushing the contents of the box, N, before them, and compressing them until the table, S, reaches the level of the grid, B. At this moment the tappet rod, D, shuts off the water, and withdraws the bolt of the doors, AA, which fly open. The grid, B (Fig. 2), is then run through the grooves in the press-head, S, and the rams, LL, are allowed to descend ready for a baling cloth to be inserted through the doors, EE, and for the box, N, to be refilled. At the same time the head, G, comes down on to the bale and compresses it still further, while the men are at work lashing it. When the material is in hanks, like jute, the rams, LL, are lowered slowly, while a man standing inside the box, at about the level of the floor, packs the material neatly on the table.
These presses can be worked with great rapidity, the average output during a day varying from 21 to 28 bales an hour. The consumption of coal per bale is 9 lb. of Bengal coal, in value about 3/4d. The density of the cotton bales produced is about 45 lb. per cubic foot, 400 lb. measuring a little under 9 cubic feet for shipment. In the case of jute or jute roots, the same weight occupies 10 cubic feet on an average. But rapid as this press is in action, the necessities of recent business in India have called for still more expeditious working, and to meet this demand Mr. Watson produced his compound press, in which the economy of time is carried to its utmost development. By the addition of a second pair of long-stroke rams the output of the press has been trebled, being raised to 80 bales per hour. To effect this, there is one pair of powerful rams, as in the press just described, but two pairs of the long-stroke rams. Further, each pair of the small-diameter rams is fitted with two boxes, one of which is always being filled while the other is being pressed. The rams in rising compress the material into a small cell or box, situated above the box in which raw cotton is thrown. On the top of the ram head there is a loose lashing plate, which, at the finish of the action of the rams, is locked in the cell by bolts actuated by a suitable locking gear. While in this cell the bale has the lashing ropes put round it, and then it is placed under the large rams for the final squeeze, during which the ties or ropes are permanently secured. Thus neither of the small presses has even to wait while its box is being filled, or while the previously pressed bale is being lashed. Even in the large press, when the ties are finally fastened, the time occupied does not exceed three-quarters of a minute, and is often much less.
This press is shown in Figs. 3 and 4. The small rams are arranged at either side of the large ones, which, in this case, are not inverted. To each of the smaller presses there is a pair of boxes mounted on a vertical column, around which they can revolve to bring either box over the rain head. When the left hand rams rise, the material is delivered into the cell, D, which previously has had its doors (Fig. 4) closed. To permit of the cell, D, being moved out of the way, it is mounted so that it can revolve on one of the columns of the main press, first into the position shown at B (Fig. 4), and afterward to C (Fig. 3). While at D, the bale in the cell (called from its construction a revolver) is partly lashed, the ties or ropes being put into position. It is then rotated until it comes over the large rams, where the bale is still more compressed and secured.
It must be admitted that this press provides for the greatest possible economy of time, and for the largest output, for the capital employed, which can be attained. The rams and the men are constantly in action, and not a single moment is lost. For filling each box 78 seconds are allowed, and there is ample time for the preliminary lashing.
Figs. 5 and 6 show a modification of this press, designed to turn out sixty bales per hour. It has only one set of long-stroke rams, with three revolvers. The bale receives its preliminary lashing while in the position, B (Fig. 6). Fifty-three seconds are available for filling the box, and the same time for the preliminary lashing. It is found, however, that three-quarters of a minute is sufficient for the complete hooping of a bale.
Figs. 7 and 8 show a similar press intended for jute pressing. This has only one box, which is fixed, as the material has to be packed in an orderly manner. Its speed is sixty bales an hour.—Engineering.
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JET PROPELLERS.—HYDRAULIC PROPULSION OF VESSELS.
Certain mechanical devices appear to exercise a remarkable influence on some minds, and engineers are blamed for not adopting them, in no very measured terms in some cases. It is not in any way necessary that these devices should have been invented by the men who advocate their adoption, in order to secure that advocacy. The intrinsic attractions of the scheme suffice to evoke eulogy; and engineers sometimes find it very difficult to make those who believe in such devices understand that there are valid reasons standing in the way of their adoption. One such device is hydraulic propulsion. A correspondent in a recent impression suggested its immediate and extended use in yachts at all events, and we willingly published his letter, because the system does no doubt lend itself very freely to adoption for a particular class of yachts, namely, those provided with auxiliary power only. But because this is the case it must not be assumed that the jet propeller is better than screw or paddle-wheel propulsion; and it is just as well, before, correspondence extends further, that we should explain why and in what way it is not satisfactory. The arguments to be urged in favor of hydraulic propulsion are many and cogent; but it will not fail to strike our readers, we think, that all these arguments refer, not to the efficiency of the system, but to its convenience. A ship with a hydraulic propeller can sail without let or hindrance; a powerful pump is provided, which will deal with an enormous leak, and so on. If all the good things which hydraulic propulsion promises could be had combined with a fair efficiency, then the days of the screw propeller and the paddle wheel would be numbered; but the efficiency of the hydraulic propeller is very low, and we hope to make the reason why it is low intelligible to readers who are ignorant of mathematics. Those who are not ignorant of them will find no difficulty in applying them to what we have to say, and arriving at similar conclusions in a different way.
Professor Greenhill has advanced in our pages a new theory of the screw propeller. As the series of papers in which he puts forward his theory is not complete, we shall not in any way criticise it; but we must point out that the view he takes is not that taken by other writers and reasoners on the subject, and in any case it will not apply to hydraulic propulsion. For these reasons we shall adhere in what we are about to advance to the propositions laid down by Professor Rankine, as the exponent of the hitherto received theory of the whole subject. When a screw or paddle wheel is put in motion, a body of water is driven astern and the ship is driven ahead. Water, from its excessive mobility, is incapable of giving any resistance to the screw or paddle save that due to its inertia. If, for example, we conceive of the existence of a sea without any inertia, then we can readily understand that the water composing such a sea would offer no resistance to being pushed astern by paddle or screw. When a gun is fired, the weapon moves in one direction—this is called its recoil—while the shot moves in another direction. The same principal—pace Professor Greenhill—operates to cause the movement of a ship. The water is driven in one direction, the ship in another. Now, Professor Rankine has laid down the proposition that, other things being equal, that propeller must be most efficient which sends the largest quantity of water astern at the slowest speed. This is a very important proposition, and it should be fully grasped and understood in all its bearings. The reason why of it is very simple. Returning for a moment to our gun, we see that a certain amount of work is done on it in causing it to recoil; but the whole of the work done by the powder is, other things being equal, a constant quantity. The sum of the work done on the shot and on the gun in causing their motions is equal to the energy expended by the powder, consequently the more work we do on the gun, the less is available for the shot. It can be shown that, if the gun weighed no more than the shot, when the charge was ignited the gun and the shot would proceed in opposite directions at similar velocities—very much less than that which the shot would have had had the gun been held fast, and very much greater than the gun would have had if its weight were, as is usually the case, much in excess of that of the shot. In like manner, part of the work of a steam engine is done in driving the ship ahead, and part in pushing the water astern. An increase in the weight of water is equivalent to an augmentation in the weight of our gun and its carriage—of all that, in short, takes part in the recoil.
But, it will be urged, it is just the same thing to drive a large body of water astern at a slow speed as a small body at a high speed. This is the favorite fallacy of the advocates of hydraulic propulsion. The turbine or centrifugal pump put into the ship drives astern through the nozzles at each side a comparatively small body of water at a very high velocity. In some early experiments we believe that a velocity of 88 ft. per second, or 60 miles an hour, was maintained. A screw propeller operating with an enormously larger blade area than any pump can have, drives astern at very slow speed a vast weight of water at every revolution; therefore, unless it can be shown that the result is the same whether we use high speed and small quantities or low speed and large quantities, the case of the hydraulic propeller is hopeless. But this cannot be done. It is a fact, on the contrary, that the work wasted on the water increases in a very rapid ratio with its speed. The work stored up in the moving water is expressed in foot pounds by the formula
W v squared / 2g
where W stands for the weight of the water, and v for its velocity. But the work stored in the water must have been derived from the engine; consequently the waste of engine power augments, not in the ratio of the speed of the water, but in the ratio of the square of its speed. Thus if a screw sends 100 tons of water astern at a speed of 10 ft. per second per second, the work wasted will be 156 foot tons per second in round numbers. If a hydraulic propeller sent 10 tons astern at 100 ft. per second per second, the work done on it would be 1,562 foot tons per second, or ten times as much. But the reaction effort, or thrust on the ship, would be the same in both cases. The waste of energy would, under such circumstances, be ten times as great with the hydraulic propeller as with the screw. In other words, the slip would be magnified in that proportion. Of course, it will be understood that we are not taking into account resistances, and defects proper to the screw, from which hydraulic propulsion is free, nor are we considering certain drawbacks to the efficiency of the hydraulic propeller, from which the screw is exempt; all that we are dealing with is the waste of power in the shape of work done in moving water astern which we do not want to move, but cannot help moving. If our readers have followed us so far, they will now understand the bearing of Rankine's proposition, that that propeller is best which moves the greatest quantity of water astern at the slowest speed. The weight of water moved is one factor of the thrust, and consequently the greater that weight, other things being equal, the greater the propelling force brought to bear on the ship.
It may be urged, and with propriety, that the results obtained in practice with the jet propeller are more favorable than our reasoning would indicate as possible; but it will be seen that we have taken no notice of conditions which seriously affect the performance of a screw. There is no doubt that it puts water in motion not astern. It twists it up in a rope, so to speak. Its skin frictional resistance is very great. In a word, in comparing the hydraulic system with the normal system, we are comparing two very imperfect things together; but the fact remains, and applies up to a certain point, that the hydraulic propeller must be very inefficient, because it, of all propellers, drives the smallest quantity of water astern at the highest velocity.
There is, moreover, another and a very serious defect in the hydraulic propeller as usually made, which is that every ton of water passed through it has the velocity of the ship herself suddenly imparted to it. That is to say, the ship has to drag water with her. To illustrate our meaning, let us suppose that a canal boat passes below a stage or platform a mile long, on which are arranged a series of sacks of corn. Let it further be supposed that as the canal boat passes along the platform, at a speed of say five miles an hour, one sack shall be dropped into the boat and another dropped overboard continuously. It is evident that each sack, while it remains in the boat, will have a speed the same as that of the boat, though it had none before. Work consequently is done on each sack, in overcoming its inertia by imparting a velocity of five miles an hour to it, and all this work must be done by the horse towing on the bank. In like manner the hydraulic propeller boat is continually taking in tons of water, imparting her own velocity to them, and then throwing them overboard. The loss of efficiency from this source may become enormous. So great, indeed, is the resistance due to this cause that it precludes the notion of anything like high speeds being attained. We do not mean to assert that a moderate degree of efficiency may not be got from hydraulic propulsion, but it can only be had by making the quantity of water sent astern as great as possible and its velocity as small as possible. That is to say, very large nozzles must be employed. Again, provision will have to be made for sending the water through the propeller in such a way that it shall have as little as possible of the motion of the ship imparted to it. But as soon as we begin to reduce these principles to practice, it will be seen that we get something very like a paddle wheel hung in the middle of the boat and working through an aperture in her hull, or else a screw propeller put into a tube traversing her from stem to stern.
We may sum up by saying that the hydraulic propeller is less efficient than the screw, because it does more work on the water and less on the boat; and that the boat in turn does more work on the water than does one propelled by a screw, because she has to take in thousands of tons per hour and impart to them a velocity equal to her own. Part of this work is got back again in a way sufficiently obvious, but not all. If it were all wasted, the efficiency of the hydraulic propeller would be so low that nothing would be heard about it, and we certainly should not have written this article.—The Engineer.
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THE NEW ARMY GUN.
The cut we give is from a photograph taken shortly after the recent firings. The carriage upon which it is mounted is the one designed by the Department and manufactured by the West Point Foundry, about six months since. It was designed as a proof carriage for this gun and also for the 10 inch steel gun in course of construction. It is adapted to the larger gun by introducing two steel bushing rings fitted into the cheeks of carriage to secure the trunnion of the gun.
The gun represented is an 8 inch, all steel, breech-loading rifle, manufactured by the West Point Foundry, upon designs from the Army Ordnance Bureau. The tube and jacket were obtained from Whitworth, and the hoops and the breech mechanism forgings from the Midvale Steel Company. The total weight of the gun is 13 tons; total length, including breech mechanism, 271 inches; length of bore in front of gas check, 30 calibers; powder space in chamber, 3,109 cubic inches; charge, 100 pounds. The tube extends back to breech recess from muzzle, in one solid piece. The breech block is carried in the jacket, the thread cut in the rear portion of the jacket. The jacket extends forward and is shrunk over the tube about 871/2 inches. The re-enforce is strengthened by two rows of steel hoops; the trunnion hoops form one of the outer layers. In front of the jacket a single row of hoops is shrunk on the tube and extends toward the muzzle, leaving 91 inches of the muzzle end of the tube unhooped. The second row of hoops is shrunk on forward of the trunnion hoops for a length of 38 inches to strengthen the gun, and the hoop portion forms three conical frustums. The elastic resistance of the gun to tangential rupture over the powder chamber is computed by Claverino and kindred formulas to be 54,000 lb. per square inch.
The breech mechanism is modeled after the De Bange system. The block has three smooth and three threaded sectors, and is locked in place by one-sixth of a turn of a block, and secured by the eccentric end of a heavy lever, which revolves into a cut made in the rear breech of the gun. The gas check consists of a pad made of two steel plates or cups, between which is a pad of asbestos and mutton suet formed under heavy pressure. The rifling consists of narrow grooves and bands, 45 of each. The depth of the groove is six one-hundredths of an inch.
Although the gun is designed for a charge of 100 pounds, it is believed that it can be increased to 105 pounds without giving dangerous pressure, and the intention is to increase the charge to that amount when the new powder is received from Du Pont.
The following is a very full synopsis of the official report of the preliminary firings—13 rounds—with this gun:
The first seven rounds were fired with German cocoa powder, which was received from Watervliet Arsenal. There were two kinds of cartridges, one kind weighing 85 pounds, and having 30 grains in each layer, the other weighing 100 lb., and having 27 grains in each layer. In two of the first seven rounds the weight of the charge was 65 pounds, the projectiles weighing 182 and 286 pounds; in the next two rounds charges of 85 pounds were fired, the projectiles, as before, weighing 182 and 286 pounds, while in the last three of the rounds fired with cocoa powder the charge was 100 lb., while the weight of the projectile was 182, 235, and 286 pounds. At the seventh round was fired the normal charge, 100 lb. of powder and a projectile weighing 286 pounds, for which the gun was designed. The mean pressure for this round, determined by two crusher gauges, was 32,800 pounds, and the velocity at 150 feet was 1,787 feet.
Two kinds of Du Pont's brown prismatic powder, marked P.A. and P.I., were then fired. With the normal charge of P.A. powder (round 12 of the record), the mean pressure was 35,450 pounds, the velocity at 150 feet was 1,812 feet. For P.I. powder (round 13 of the record), the pressure was 26,925 pounds, the velocity was 1,702 feet, and a considerable amount of unconsumed powder was ejected, showing that the P.I. powder is not a suitable one for this piece. The highest pressure indicated with the normal charge of P.A. powder was 36,200 pounds, exceeding by 1,200 pounds the provisional limit of pressure.
At the fifth round the breech block opened with some difficulty, and an examination showed that the resistance resulted from the diametral enlargement of the rear plate. Directions have been given to correct this defect. The star gauge records show that no material change took place in the diameter of the chamber or the bore. From 30 inches to 54 inches (measured from base of the breech), there was a diminution in diameter of from 0.001 in. to 0.002 in.; in rear of 30 inches there was no change. No enlargement in the shot chamber exceeded 0.001 in. From the bottom of the bore (the beginning of the rifling) to the muzzle the average enlargements were as follows: in. to 6 in., 0.005 in.; 7 in. to 14 in., 0.003 in.; 15 in. to 29 in., 0.002 in.; 30 in. to muzzle, 0.002 to 0.001 in.
After the third round the joint between the D. and D. rings opened slightly on the top, and measured after the 13th round showed that the opening was about 0.004 in. wide. It cannot at present be stated whether or not this opening increased during firing, but the defect has been noted and will be carefully observed. Enough cocoa powder remains to allow a comparison to be made with such brown prismatic powder as may be adopted finally. No firing has been done as yet to test the best position for the bands, but it will take place as soon as enough of some standard powder is obtained to fire ten consecutive rounds.—Army and Navy Journal.
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COMBUSTION, FIRE-BOXES, AND STEAM BOILERS.[1]
[Footnote 1: Address before the June Convention of the Master Mechanics' Association.]
By JOHN A. COLEMAN.
Mr. Chairman and gentlemen: I was rash enough some time ago to promise to prepare a paper for this occasion, the fulfillment of which prior engagements have absolutely prevented.
I would greatly prefer to be let off altogether, but I do not like to break down when expected to do anything; and if you have the patience to listen for a few minutes to the reflections of an "outsider," I will endeavor to put what I have to say in as concise form as I can, in such manner as will do no harm, even if it does no good.
For many years I was connected with steam engineering. I was once with the Corliss Steam Engine Company, and afterward was the agent of Mr. Joseph Harrison, of Russian fame, for the introduction of his safety boilers.
That brought me into contact with the heavy manufacturers throughout the Eastern States, and during that long experience I was particularly impressed with a peculiarity common to the mill owners, which, I believe it may be said with truth, is equally common to those interested in locomotive engineering, namely, how much we overlook common, every-day facts. For instance, we burn coal; that is, we think we do, and boilers are put into mills and upon railroads, and we suppose we are burning coal under them, when in reality we are only partially doing so. We think that because coal is consumed it necessarily is burned, but such is frequently very far from the fact.
I wish upon the present occasion to make merely a sort of general statement of what I conceive to be combustion, and what I conceive to be a boiler, and then to try to make a useful application of these ideas to the locomotive.
Treating first the subject of combustion, let us take the top of the grate-bars as our starting point. When we shovel coal upon the grate bars and ignite it, what happens first? We separate the two constituents of coal, the carbon from the hydrogen. We make a gas works. Carbon by itself will burn no more than a stone; neither will hydrogen. It requires a given number of equivalents of oxygen to mix with so many equivalents of carbon, and a given number of equivalents of oxygen to mix with so many of hydrogen to form that union which is necessary to produce heat. This requires time, space, and air, and one thing more, viz., heat.
I presume that most of you have read Charles Williams' treatise upon "Combustion," which was published many years ago, and which until recently was often quoted as an absolute authority upon the art of burning fuel under boilers. Mr. Williams in his treatise accurately describes the chemistry of combustion, but he has misled the world for fifty years by an error in reasoning and the failure to discuss a certain mechanical fact connected with the combination of gases in the process of combustion. He said: "What is the use of heating the air put into a furnace? If you take a cubic foot of air, it contains just so many atoms of oxygen, neither more nor less. If the air be heated, you cause it to assume double its volume, but you have not added a single atom of oxygen, and you will require twice the space for its passage between the grate bars, and twice the space in the furnace, which is a nuisance; but if the air could be frozen, it would be condensed, and more atoms of oxygen could be crowded into the cubic foot, and the fire would receive a corresponding advantage." Mr. Williams proceeded upon this theory, and died without solving the perplexing mystery of as frequent failure as success which attended his experiments with steamship boilers. The only successes which he obtained were misleading, because they were made with boilers so badly proportioned for their work that almost any change would produce benefit.
Successful combustion requires something more than the necessary chemical elements of carbon, hydrogen, and oxygen, for it requires something to cook the elements, so to speak, and that is heat, and for this reason: When the coal is volatilized in the furnace, what would be a cubic foot of gas, if cold, is itself heated and its volume increased to double its normal proportion. It is thin and attenuated. The cold air which is introduced to the furnace is denser than the gas. With dampers wide open in the chimney, and the gases and air passing into the flues with a velocity of 40 feet per second, they strike the colder surface of the tubes, and are cooled below the point of combustion before they have had time to become assimilated; and although an opponent in a debate upon steam boiler tests once stated that his thermometer in the chimney showed only 250 degrees, and indicated that all the value that was practical had been obtained from the coal, I took the liberty to maintain that a chemist might have analyzed the gases and shown there were dollars in them; and that if the thermometer had been removed from the chimney and placed in the pile of coal outside the boiler, it would have gone still lower; but it would not have proved the value to have been extracted from the coal, for it was not the complete test to apply.
The condition of things in the furnace may be illustrated thus: If we should mingle a quart of molasses and a gallon of water, it would require considerable manipulation and some time to cause them to unite. Why? Because one element is so much denser than the other; but if we should mix a quart of the gallon of water with the quart of molasses, and render their densities somewhere near the density of the remaining water, and then pour the masses together, there would be a more speedy commingling of the two. And so with the furnace. I have always maintained that every furnace should be lined with fire-brick, in order that it shall be so intensely hot when the air enters that the air shall instantly be heated to the same degree of tenuity as the hot gases themselves, and the two will then unite like a flash—and that is heat. And here is the solution of the Wye Williams mystery of failure when cold air was introduced upon the top of a fire to aid combustion. The proof of the necessity for heat to aid the chemical assimilation of the volatilized coal elements is seen in starting a fire in a common stove. At first there is only a blue flame, in which the hand may be held; but wait until the lining becomes white hot, and then throw on a little coal, and you will find a totally different result. It is also seen in the Siemens gas furnace, with which you are doubtless familiar. There is the introduction of gas with its necessary complement of air. Until the furnace and retorts become heated, the air and gas flutter through only partially united, and do little good; but as soon as the retorts and furnace become thoroughly hot, the same gas and air will melt a fire-brick.
These are common phenomena, which are familiar, but apt to be unnoticed; but they logically point to the truth that no furnaces should present a cooling medium in contact with fuel which is undergoing this process of digestion, so to speak. It will be very evident, I think, from these facts that water-legs in direct contact with a fire are a mistake. They tend to check a fire as far as their influence extends, as a thin sheet of ice upon the stomach after dinner would check digestion, and for the same reason, namely, the abstraction of heat from a chemical process. If fire-brick could be laid around a locomotive furnace, and the grate, of course, kept of the same area as before, it is my belief that a very important advantage would be at once apparent. An old-fashioned cast iron heater always produced a treacherous fire. It would grow dead around the outside next to the cold iron; but put a fire-clay lining into it, and it was as good as any other stove.
If I have now made clear what I mean by making heat, we will next consider the steam boiler. What is a steam boiler? It is a thing to absorb heat. The bottom line of this science is the bottom of a pot over a fire, which is the best boiler surface in the world; there is water upon one side of a piece of iron and heat against the other. One square foot of the iron will transmit through it a given number of units of heat into the water at a given temperature in a given time; two square feet twice as many, and three, three times as many, and so on. Put a cover upon the pot, and seal it tight, leave an orifice for the steam, and that is a steam boiler with all its mysteries.
The old-fashioned, plain cylinder boiler is a plain cylindrical pot over the fire. If enough plain cylinder boilers presenting the requisite number of square feet of absorbing surface are put into a cotton mill, experience has shown that they will make a yard of cotton cloth about as cheaply as tubular boilers. If this is so, why do not all put them in? Because it is the crudest and most expensive form of boiler when its enormous area of ground, brickwork, and its fittings are considered. Not all have the money or the room for them. To produce space, the area is drawn in sidewise and lengthwise, but we must have the necessary amount of square feet of absorbing surface, consequently the boiler is doubled up, so to speak, and we have a "flue boiler." We draw in sidewise and lengthwise once more and double up the surface again, and that is a "tubular boiler." That includes all the "mystery" on that subject.
Now, we find among the mills, just as I imagine we should upon the railroads, that the almost universal tendency is to put in too small boilers and furnaces. To skimp at boilers is to spend at the coal yard. Small boilers mean heavy and over-deep fires, and rapid destruction of apparatus. In sugar houses you will see this frequently illustrated, and will find 16 inch fires upon their grates.
We have found that, as we could persuade mill owners to put in more boilers and extend their furnaces, so that coal could be burned moderately and time for combustion afforded, we often saved as high as 1,000 tons in a yearly consumption of 4,000.
Now, when the ordinary locomotive sends particles of coal into the cars in which I am riding, I do not think it would be unfair criticism to say that the process of combustion was not properly carried out. When we see dense volumes of gas emitted from the stack, it is evident that a portion of the hard dollars which were paid for the coal are being uselessly thrown into the air; and it will be well to remember that only a little of the unburnt gas is visible to the eye.
One point I wish to make is this: We find, as I have said, that as we spread out with boilers and furnaces in the mills, so that we can take matters deliberately, we save money.
Now, coming again to locomotives. I think, if we examine the subject carefully, the fact will strike us a little curiously. The first locomotive built in Philadelphia weighed about 14 tons. Judging from the cut I have seen, I should think her furnace might have been 30 inches square. We have gone from that little 14 ton engine to machines of 50 and 60 tons—perhaps more. The engines have been increased over four times, but I will ask you if the furnace areas have been increased (applause) in proportion? Some of the furnaces of the engines are six feet by three, but that is an increase of less than 3 to 1 of furnace, as against 4 to 1 of weight of engine.
When my attention was first called to this matter, I had supposed, as most people do who are outside of the railway profession, that there was something subtile and mysterious about railway engineering that none but those brought up to the business could understand. Possibly it is so, and I am merely making suggestions for what they are worth, but I think the position I have taken in this matter was established by some experiments of three weeks' duration, which I conducted between Milan and Como, in Italy, for the Italian government, in pulling freight trains up grades of 100 feet to the mile. The experiments were made with an engine built by the Reading Railroad.
We competed with English, French, Belgian, and Austrian engines. These machines required the best of fuel to perform the mountain service, and could use coal dust only when it was pressed into brick. We used in the Reading Railroad machine different fuels upon different days, making the road trip of 120 miles each day with one kind of fuel. We used coal dust scraped up in the yards, also the best Cardiff coal, anthracite, and five kinds of Italian lignite, the best of which possesses about half the combustible value of coal.
The results in drawing heavy freight trains were equally good with each fuel, the engine having at all times an abundance of steam on heavy grades, no smoke nor cinders, and no collection of cinders in the forward part of the engine.
The fireman arranged his fires at a station, and did little or nothing except to smoke his pipe and enjoy the scenery until he reached the next station. An incident occurred to prove that we were not playing with the machine. They told me one morning that we should be given a load of 25 per cent less than the maximum load of an engine of her class (30 tons). We started up the 100 foot grade, and found we could barely crawl, and our engineer got furious over it. He thought they were repeating a trick already attempted by screwing down a brake in ascending a grade. We detected it, however, and found a pair of wheels nearly red hot. Upon this occasion we found nothing amiss, except full cars where they had reported only a light load. We pulled to the top of the hill, the steam blowing off furiously all the time.
This was a new experience to the Italians, and might surprise some Americans. When we arrived at the station, the inspector-general and his corps of engineers were evidently amazed, and it was evident we had captured them. He said to me, "I can congratulate you, signor, on possession of a superb machine."
Afterward one of the engineers said to me: "Do not let it be known that I told you what you have hauled or I shall lose my place, but you have drawn 50 per cent more than the maximum load of one of our 40 ton engines." I said: "You attempted to 'stall' us, and when you try it again, be fair enough to give me a flat of pig iron, and as you pack cars on one end I will pack pig iron upon the engine until she will stick to the track, but rest assured that you will not be able to get that steam down." The experience with that engine proves conclusively to my mind that the general principles of steam making are the same for both stationary and locomotive practice. The grand secret of the success of that Wootten engine was the enormous area of the grate surface, being, if I remember correctly, 7 by 9 feet, permitting thin fires to be carried and complete combustion to be obtained before the gases reached the boiler tubes. An enormous crown sheet was presented, and that is where the bulk of the work of any boiler is done.
Thin fires accomplish this. As already stated, a given amount of coal generates a given amount of gas, and this gas requires a given amount of air or oxygen. This air must be supplied through the grate bars and then pass through the interstices of the mass of heated coal. It requires about 10 cubic feet of air to consume one cubic foot of gas. In stationary boilers we find that if we use "pea" and "dust" coal, an extremely thin layer must be used, or the 10 feet of air per foot of gas cannot pass through it; if "chestnut" coal be used, the thickness may be increased somewhat; "stove size" allows a thickness of six inches, and "lump" much thicker, if any wise man could be found who would use that coarse, uneconomical size. Of course, I am speaking of anthracite coal. Opinions differ about "soft coal," but the same general principle applies as regards an unobstructed passage of air through the hot bed of coal.
Now, it will be agreed that the locomotive of the future must be improved to keep up with the times. Fierce competition requires increased efficiency and reduced expenses. I am told by you railroad gentlemen that the freight business of the country doubles every ten years. Trains follow close upon each other. What are you going to do? Are you to double, treble, or quadruple your tracks?
It seems to me much remains yet to be done with the locomotive. We must burn a great deal less coal for the steam we make, and after we have made steam we must use that steam up more thoroughly. In the short cylinder required by locomotive service, the steam, entering at the initial pressure pushes the piston to the opposite end, and it then rushes out of the exhaust strong enough to drive another piston. Of every four dollars' worth of coal consumed, at least two dollars worth is absolutely thrown away. Or, of every ten thousand dollars spent for fuel, five thousand dollars are absolutely wasted. How can we save this? It would seem obvious that if steam rushes from the exhaust of an engine strong enough to drive another engine, the common sense of the thing would be to put another engine alongside and let the steam drive it, and we should get just so much more out of our four dollars' worth of coal. It seems evident that we must follow the lead of the steamship men, and compound the locomotive engine, as they have done with the marine engine.
Next we must attack the extravagant furnace, and increase its area and reduce the depth of the bed of coal. The difficulty of making this change seemed to me to be removed, on examining an engine on the Providence & Bristol Railroad, the other day. The machine was made at the Mason Works, of Taunton. It was an engine and tender combined, the truck being at the rear end of the tender, and the driver placed well in advance of the fire-box, so that the maximum weight of both engine and tender rested upon the drivers. In thus removing the drivers from the proximity of the fire-box, abundant facility is afforded for widening the fire-box, so as to obtain a grate area as large as that of the Wootten engine or of a stationary boiler. It seems to me the increase of grate area can be obtained only by widening; for a length of more than six or seven feet is very hard upon the fireman. You certainly cannot get more power by deepening present fire-boxes, except by an enormously increased waste of fuel, which all will concede is already sufficiently extravagant.
In arriving at the conclusion of these hasty and I fear somewhat incoherent remarks, I would say that the object aimed at for the improvement of the locomotive would be reached, first, by making steam economically, by employing such increased grate area as will permit running thin fires and moderate or comparatively slow draught; and, secondly, in economically using the steam which has been economically made by compounding the engine.
I have given you merely the views of an "outsider," who has had a somewhat extensive experience in stationary engineering, and who has observed locomotive practice in many parts of the world. These views are offered for what they are worth, as suggestions for future thought in designing engines, and as a sort of refresher upon rudimentary points which long familiarity with every-day phenomena causes us at times to overlook. I trust that your deliberations may aid in the speedy reduction of the expenses of transporting freight and passengers, for the benefit of the railroad companies and, in their turn, the advantage of the people at large.
* * * * *
ATLANTIC STEAMERS.[1]
[Footnote 1: A paper recently read before the Institution of Naval Architects.]
By W. JOHN.
The author said that he hoped to bring before the meeting impartially certain facts which might be of interest, and which, when recorded in the pages of the "Transactions," might be found of some use as data for future reference. In dealing with passenger steamers, he would do so principally from a shipbuilder's point of view; but the moment he commenced to think over Atlantic passenger ships as a shipbuilder, he was met by the question whether the present tendency toward divorcing the passenger and cargo trade from each other is likely to continue or not. If the answer is yes, then it seems to become an important question, for the present at least, how to build, on moderately small dimensions, the fastest, safest, and most economical passenger steamer, using all the most modern improvements to make her commodious and luxurious, and an easy sea boat into the bargain. If cargo is still to be carried in the passenger ships of the future, a moderate speed only will be aimed at in the immediate future, and every effort will be devoted to economy of fuel, comfort, and safety, with a fair carrying capacity. This latter policy is one which may possibly prevail at least for a time, as it has powerful supporters in Liverpool; but he could not help thinking that very high speeds—higher than we have yet attained—must eventually gain the day. He also thought that they were on the eve of important movements, which will indicate what the next step in the passenger trade is to be; for it must be remembered, among other things, that none of our present English transatlantic liners, even the latest, have yet been fitted with the latest modern improvements for economy of fuel or quick combustion, such as triple expansion engines or forced draught. They must, therefore, be at some disadvantage, other things being equal, compared with the ships of the future possessing them. The Great Eastern steaming up Milford Haven about twenty-five years ago between two lines of the channel fleet of old—two and three decked wooden line-of-battle ships—the whole fleet saluting with yards manned, was a sight to be remembered. More than this, that ship, with all her mournful career, has been a useful lesson and a useful warning to all naval architects who seriously study their profession—a lesson of what can be done in the safe construction of huge floating structures, and a warning that the highest flights of constructive genius may prove abortive if not strictly subordinated to the practical conditions and commercial requirements of the times. The Sirius and Great Western crossed the Atlantic in 1838, and in 1840 the first ship of the since celebrated Cunard Company made her first voyage. This was the Britannia, which, with her sister ships, the Arcadia, Caledonia, and Columbia, kept up the mail service regularly at a speed of about 81/2 knots an hour. The Britannia was 207 ft. in length between perpendiculars, and 34 ft. 4 in. extreme breadth, 22 ft. 6 in. depth of hold, 423 horse power—nominal—and 1,153 tons burden, built of wood, and propelled by paddles. In 1860 the Collins Line started in opposition to the Cunard, and, after a series of disasters, collapsed in 1858. This was three years after the Persia, the first Cunarder built of iron, had been completed. In 1850, also, the Inman Line was started with the City of Glasgow, of 1,600 tons builders' measurement, and 350 horse power. She was built of iron, and was the first screw steamer sent across the Atlantic from Liverpool with passengers, and was the pioneer of the great emigrant trade which Mr. Inman, above all others, did so much to develop and make cheap and comfortable for the emigrants themselves, as well as profitable to his company. That the builders of the celebrated old Great Britain, in 1843, and Mr. Inman, in 1850, should have pronounced so decisively in favor of the screw propeller in preference to the paddle for ocean steaming is a proof of their true practical judgment, which time and practical experience have made abundantly clear. While the Cunard Company went on developing its fleet from the early wood paddle steamer Britannia of 1,130 tons in 1840 to the iron paddle steamers Persia, etc., in 1858, the iron screw steamer China of 1862, to the still more important screw steamers Bothnia and Scythia, vessels of 4,335 tons, in 1874, the Inman and other lines were as rapidly developing in speed and size, if not in numbers. The year 1874 is memorable, for it saw the White Star steamers Britannic and Germanic put into the water, as well as the Inman steamer City of Berlin and the two before mentioned Cunard steamers, Bothnia and Scythia. By the addition of these two ships to their fleet the White Star Line, although started only in 1870, reached a front rank position in the New York passenger trade. The author gave in separate tables the logs of several of these ships, some from published documents and some kindly furnished by the owners. The Great Western had crossed the Atlantic from Bristol to New York in 15 days as early as 1838. The first Cunard steamer, the Britannic, was about the same speed, from 81/4 to 81/2 knots an hour. The average duration of the Cunard voyages in the year 1856 was 12.67 days from Liverpool to New York, and 11.03 days from New York to Liverpool. The Bothnia, in 1874, reduced the passage to about nine days. The White Star Britannic, in 1876, averaged 7 days 18 hours 26 minutes outward from Queenstown to New York, and 9 days 6 hours 44 minutes homeward, and has averaged for the last ten years 8 days 9 hours 36 minutes outward, and 8 days 1 hour 48 minutes homeward. The City of Berlin, of the Inman Line, also built in 1874, 8 days 10 hours 56 minutes, and homeward 8 days 2 hours 37 minutes; and for the nine years from 1875 to 1883 inclusive, averaged outward 8 days 19 hours 56 seconds, and inward 8 days 8 hours 34 seconds; or, putting it into rounder figures, the Britannic had reduced the average passage between the two points to 81/4 days, and the City of Berlin to 81/2 days. From the year 1874 on to 1879 no further advance was made in Atlantic steaming, but in that year the Arizona was added to the Guion Line, and it soon became evident that another important stride had been made in the Atlantic passenger trade, which would lead to most important results. The results, as we all know, have been sufficiently startling. The Guion Line, which had started in 1866 with the Manhattan, had now the fastest passenger ship on the Atlantic. In spite of burning some fifty per cent. more coal than the Britannic, the ship was an obvious commercial success. The spirited policy which brought her into existence was appreciated by the public, and the other lines had to move forward. Then followed a period of rivalry, the Cunard Company building the Gallia and Servia, the Inman Company the City of Rome, and the Guion Line the Alaska, all of which were completed in 1881, and afterward the Oregon for the Guion Line—1883—the Aurania the same year for the Cunard Company, and, later still, the America for the National Line, and the Umbria and Etruria for the Cunard Company in 1885.
Since the completion of the Etruria, for various reasons there has been a pause in the tremendous strides made since 1879, and we may briefly review the results. Taking the Britannic as a standard with her ten years' average of 81/4 days across, and her quickest passage of 7 days 10 hours 53 seconds, we have now the following steamers of higher speeds. Taking them in the order of their absolutely fastest passage out or home, they stand thus:
TABLE I.
-+ -+ + -+ Days. Hours. Mins. + + -+ 1 Etruria. 6 5 31 2 Umbria (sister ship). slightly longer. 3 Oregon. 6 10 35 4 America. 6 13 44 5 City of Rome. 6 18 0 6 Alaska. 6 18 37 7 Servia. 6 23 55 8 Aurania. 7 1 1 -+ -+ + -+
It will thus be seen that from the 15 days' passage or thereabout, of the earliest Atlantic steamers, we had got down in the days of the Scotia to about 9 days; in the Britannic to 81/4 days, and, at the present time, we have got to 61/4 days, with seven ships afloat that have done the passage under seven days, and capable of making their average passages range between 61/2 and 71/4 days.
Ranged in order of gross tonnage, these eight vessels stand as follows:
TABLE II.
1. City of Rome. 8,144 2. Oregon. 7,375 3. Aurania. 7,269 4. Servia. 7,212 5. Umbria. 7,129 6. Etruria. 7,100 7. Alaska. 6,586 8. America. 5,528
Here the America shows to advantage, for while being eighth in size she is fourth in point of speed, and from what the author can learn, although he had no authenticated details on the subject, he believed she is economical in coal consumption. He might perhaps be permitted to say that one of the most difficult subjects in connection with the propulsion of ships on which to get absolutely accurate data is that of coal consumption. The records of six to eight hours' trials for the purpose of ascertaining the coal consumption are absolutely worthless, as all shipbuilders and engineers know, and so far as English ships are concerned they are never attempted. Foreign owners frequently stipulate for such trials in their contracts with English shipbuilders, and get wonderfully economical results on paper, but the fact that the trials only extend over a few hours renders them valueless, however carefully the coal may be weighed during that period. An authentic record of the absolute quantity of coal consumed, say by each of the eight fastest Atlantic liners, together with their average indicated horse power on the voyage, for a series of voyages, would be extremely valuable.
He gave, in Table III., the consumption per indicated horse power per hour for a number of ships. This table affords valuable data, for it gives, in addition to the dimensions, the moulded draught of water, the midship area, the displacement, the indicated horse power, the speed on trial, the coefficients for the lines both from the block or parallelopipedon, and also from the midship section prism, together with the length and angle of entrance obtained by Kirk's rule, the Admiralty displacement coefficient, together with the coal consumption per day and per indicated horse power per hour.
This table, as will be seen, contains some of the most important of the Atlantic liners, and also a number of other typical ships, which will add a variety to its interest and a value to it. The coefficient, which is contained in the thirteenth column of the table, viz.:
Dis 2/3 x speed cubed ————————————- I.H.P. x sqrt(entrance.) ———————- 10
generally comes out for ships of similar type more nearly a constant in the true sense of the word than the corresponding Admiralty constant. As an example, we have the curves of resistance and horse power for the City of Rome and the Normandie, a large vessel of 6,000 tons, which the Barrow Company built for the Compagnie Generale Transatlantique, in which the coefficient of fineness and the form of the lines pretty closely resemble each other below water; and if we take from the curves the corresponding speeds and horse powers, and work out the constants by the two systems, we have at 14 knots the Admiralty constant for the City of Rome 322.2, and for the Normandie 304.8; and taking for a modified form of constant, the City of Rome gives 253.7 and the Normandie 251.9, which, as will be seen, are much closer together. Similarly, at 15 knots the Admiralty constant for the City of Rome is 310, and for the Normandie 295.2, while a modified constant comes out for the former at 245, and for the latter 244, again agreeing almost identically. The same at 16 knots, for the City of Rome the Admiralty constant comes out 297.6, and for the Normandie 282.8, while a modified constant comes out for the two ships 234.4 and 233.7 respectively, again showing marked agreement. It may be mentioned that in these two ships the engines are of a similar type, being three-crank tandem engines, and the propellers have in both pitch and surface practically the same proportions to the power and speed. The value of these modified constants will probably be found to increase as the speeds increase up to the limit and beyond that point at which wave resistance becomes an important factor.
TABLE III
- - - - Name. Length. Breadth. Moulded Midship Displacement. draught. area. - - - - ft. in. ft. in. ft. in. City of Rome 542 6 52 0 21 51/2 1031 11,230 Normandie 459 4 49 11 19 93/4 892 7,975 Furnessia 445 0 44 6 22 21/2 893 8,578 Arizona 450 0 45 11/2 18 9 758 6,415 Orient 445 0 46 0 21 41/2 904 7,770 Stirling Castle 420 0 50 0 22 3 990 7,600 Elbe 420 0 44 9 20 0 807 6,350 Pembroke Castle 400 0 42 0 17 0 648 5,130 Umbria and Etruria 500 0 57 0 22 6 1090 9,860 Aurania 470 0 57 0 20 0 1020 8,800 America 441 8 51 3 - - 6,500 Oregon 501 0 54 2 23 8 1150 11,000 Servia 515 0 52 0 23 31/2 1046 10,960 Scotia, P.S. 369 0 47 6 19 9 867 6,000 Alaska 500 0 50 0 21 0 949 9,210 Aller 438 0 48 0 21 0 907 7,447 Ems 430 0 46 10 20 71/2 877 7,030 - - - -
- - - - Name Indicated Speed. Block Midship Prismatic H.P. coefficient section midship coefficient section coefficient - - - - City of Rome 11,890 18.235 .649 .925 .702 Normandie 6,959 16.66 .614 .901 .681 Furnessia 4,045 14 .682 .903 .755 Arizona 6,300 17 .589 .895 .658 Orient 5,433 15.538 .621 .919 .676 Stirling Castle 8,396 18.4 .569 .889 .639 Elbe 5,665 16.571 .591 .901 .655 Pembroke Castle 2,435.8 13.25 .623 .623 .692 Umbria and Etruria 14,321 20.18 .538 .896 .637 Aurania 8,500 17.5 .575 .942 .632 America - 17.8 Oregon 13,300 18.3 .599 .849 .67 Servia 10,300 16.9 .610 .862 .71 Scotia, P.S. 4,632 14.31 .605 .92 .65 Alaska - .614 .904 .679 Aller 7,974 17.9 .590 .899 .656 Ems 7,251 17.55 .593 .907 .652 - - - -
+ + -+ -+ Name. D 2/3 x S cubed D 2/3 x S cubed Kirk's system. - I.H.P. + -+ -+ I.H.P. x /ent. Length of Angle. - entrance. 10 + + -+ -+ -+ City of Rome 255 201.3 161.27 8 deg. 29' Normandie 265 219.5 146.41 8 deg. 44' Furnessia 284 273 108.7 10 deg. 28' Arizona 269.2 217 153.79 7 deg. 30' Orient 270.8 225 144.17 8 deg. 21' Stirling Castle 286.8 233.7 151.3 8 deg. 22' Elbe 275.5 229 144.6 7 deg. 56' Pembroke Castle 284 258 122.9 8 deg. 49' Umbria and Etruria 260 191.8 184 6 deg. 52' Aurania 266 204.6 170 8 deg. 38' America - - - - Oregon 227.9 190 164.3 9 deg. 39' Servia 231 192 145.3 10 deg. 42' Scotia, P.S. 208.9 186 126.8 13 deg. 21' Alaska - - 160.23 8 deg. 2' Aller 277 225 150.6 8 deg. 10' Ems 273 223 149.4 8 deg. 40' + + -+ -+ -+
+ + + + + Name. Coal Cylinders Boilers Working consumption Pressure -+ + -+ + + -+ Per Per Diameter Stroke Heating Bar day I.H.P. surface surface + -+ + -+ + + -+ + Ins. Ins. lbs. /3 @ 46 City of Rome 185 2.2 3 @ 86 / 72 29,286 1398 90 /3 @ 35-7/16 Normandie 148 2 3 @ 74-7/8 / 67 21,404 756 85.2 Furnessia 97 2.2 49-100 66 10,396 440 90 /1 @ 62 Arizona - - 2 @ 90 / 66 90 /1 @ 60 Orient - - 2 @ 85 / 60 75 /1 @ 62 Stirling Castle - - 2 @ 90 / 66 21,161 787 100 /1 @ 60 Elbe - - 2 @ 85 / 60 - Pembroke Castle 44 1.7 43 and 86 57 7,896 288 99 Umbria and /1 @ 71 Etruria 315 2.1 2 @ 105 / 72 38,817 1606 110 /1 @ 68 Aurania 215 2.2 2 @ 91 / 72 23,284 1001 - /1 @ 63 America 185 - 2 @ 91 / 66 882 - /1 @ 70 Oregon 310 2.2 2 @ 104 / 72 38,047 1428 110 /1 @ 72 Servia 205 2 2 @ 100 / 78 27,483 1014 - Scotia, P.S. 168 3.4 - /1 @ 68 Alaska - - 2 @ 100 / 72 100 /1 @ 44 Aller - - 1 @ 70 72 22,630 799 150 1 @ 100 / /1 @ 62 Ems - - 2 @ 86 / 60 19,700 780 100 + -+ + -+ + + -+ +
Mean speed of a voyage across the Atlantic Ocean.
The author next considered the strains to which a ship is exposed, and stated that he had before him the calculations for three of the largest vessels, two of them of iron and the other of steel; and he found, in the case of the iron, the maximum tension on the gunwale during the greatest hogging strains likely to be endured at sea would not exceed about six tons per square inch, while in the case of the steel ship it is only about 61/2 tons. These strains are well within the limits of safety, and a comparison of the scantlings of these with the others justifies the assertion as to their general safety from a structural point of view. The sections of these three ships are shown in Figs. 1, 2, and 3, with their principal scantlings. It will be seen from these sections that the three ships differ materially in their mode of construction. In the case of Fig. 1, which represents the City of Rome, the largest of the three, it will be seen that the main framing of the vessel is entirely transverse, with very heavy keelsons in the bottom, and large partial bulkheads or web frames, and the outside plating arranged on what is termed the edge to edge principle, with a great portion of it double. In the next section, Fig. 2, the Servia, which is built of steel, on the other hand, the bottom is built on the longitudinal cellular system, the first application, he believed, of this system to an Atlantic liner. The plating of the Servia is of the usual alternate outer and inner strake system, partly double; while the third section, the Oregon, approaches more nearly to the ordinary system of framing and plating usually adopted, but it will be seen that she was well tied in the bottom by very heavy intercostal and plate keelsons, as well as in the top by heavy stringers and sheer strakes, with much of her plating doubled, and heavy web frames inside. The author next considered the question of stability, and went on to deal with the subject of twin screws, and stated that the Barrow Shipbuilding Company has done more in the way of planning and designing for the adoption of twin screws lately than for any other mode of propulsion, and this chiefly for passenger steamers. He did not attach much importance to the particular form of the blade either in single or twin screws, as he believed so long as the disk area, the surface, and pitch were properly adjusted to the speed of the vessel, and to enable the engines to use, at the maximum speed, just the full quantity of steam that the boilers can make, we have got pretty nearly as far as we can get. To fix these dimensions of the propeller accurately at the present time, and without further knowledge of the action of the screw on the water, was, he thought, impossible. All the rules and formulae are empirical. The best one he knew is given in Table IV., due to Mr. Thom, the head of the Barrow Company's engineering drawing office, and at present acting manager, who has used it for some years in practice. These formulae are based upon the assumption that the area of propeller disk should be proportional to the indicated horse power, divided by the cube of the speed, and the same with the projected area of the propeller and also the surface.
TABLE IV.
Particulars of Propellers and Constants.
- - Length Proj. Feet per Ship. of Disk surf. minute. ship. constant. constant. Speed of tips. - - City of Rome. 542 220 69 4,715 Normandie 459 250 66 4,099 Furnessia 445 223 69 3,654 Eden 300 211 64 3,080 Yorouba 270 213 63 3,202 Taygete 260 238 56 3,166 Kow-shing 250 171 69 3,369 S.Y. Monarch 152 221 65 4,040 S.Y. Aries 138 179 56 2,986 Twin screw Fenella 200 244 64 2,890 Twin screw H.M.S. Fearless[2] 220 277 67 5,022 Twin screw H.M.S. Iris - 454[6] 135[6] - Twin screw H.M.S. Iris [3] 300 412 221 - Twin screw H.M.S. Iris [4] 300 346 99 4,961 Twin screw H.M.S. Iris [5] 300 439 82 5,309 - - -
[Footnote 2: Estimated with a speed of 17.5 knots and 3,370 I.H.P.]
[Footnote 3: With the first propeller at the estimated speed of 17.5 knots and 7,000 I.H.P.]
[Footnote 4: With four bladed modified Griffith's on actual trial.]
[Footnote 5: With two bladed modified Griffith's on actual trial.]
[Footnote 6: Constants obtained from first propeller calculated from a speed of 18.5 knots and 7,500 I.H.P.
Area of propeller disk x speed of ship in knots. cubed Disk constant = ————————————————————————— I.H.P.
Projected Projected area of propeller x speed of ships in knots. cubed area = ——————————————————————————— of constants I.H.P.
Expanded area constants may be obtained and used in the same way.]
The discussion which followed was opened by Mr. Holt. He said that if they were to have greater speed on the Atlantic, there was one point which was not alluded to in the paper, and that was the total abolition of cargo on board the great passenger steamers. If vessels were built solely for passenger traffic, they would be able to insure greater speed by reason of the greater slightness in build and the additional space at the command of the designer. The existing Atlantic express steamer was far too heavy, and might, if cargo was dispensed with, be made with finer lines and more yacht-like. He looked on the proposition to fit such vessels with longitudinal bulkheads with great fear. If a collision took place—such, for example, as that which sunk the Oregon—water would get access to one side only of the ship, and it was not at all improbable that if a sea was on, she would turn right over. At all events, very serious risk would be involved.
Mr. W.H. White, Chief Constructor to the Admiralty, said the question of twin screw propulsion was one of special interest to himself, and had been so for many years. In 1878 he dealt with it as fully as he then could on the basis of the Admiralty data, and he then ventured to say everything in favor of twin screws that Mr. John had said in his paper. If greater power than that now used in such a ship as the Etruria, for example, were demanded, two screws must be used. Good as are the results obtained with the Etruria, it was by no means certain that still better might not be had. If she had been fitted with two screws instead of one, very great advantage would be gained by the greater submergence of the twin screws, as thus racing would be almost wholly prevented.
Mr. Calvert urged that more attention should be devoted to studying the relative values of different portions of the propeller.
The sitting was then suspended. In the afternoon, as we have already stated, the members visited the steamship Germanic on the invitation of Messrs. Ismay, Imrie & Co., subsequently proceeding to Messrs. Cope Brothers' tobacco works, and thence to the exhibition, where the dinner of the Institution took place in the evening.
On Friday morning no paper was read; some official business was transacted, and this being done, the discussion on Mr. John's paper was resumed.
Mr. Biles remarked that there were many advantages in the use of twin screws which had not been sufficiently taken into account. When a ship with twin screws was being handled in dock there was greater maneuvering power, and therefore less liability for the ship to come in contact with the walls, although, if she did so, there would be greater probability of damage to the propellers. He thought means could be easily devised of protecting the screws when the ship was in dock. Another of the incidental advantages connected with twin screws was that smaller engines and smaller propellers were required, and therefore they might run them at a higher speed. They would also get lighter machinery with twin screws, and there would be less liability to have bad castings and forgings in the smaller engines, and of course the cost would be less.
With respect to the question of the middle line bulkheads, he could not quite agree with Mr. John as to the great advantages of them in a big passenger steamer. He thought there would be greater difficulty in managing a ship so built if she was in danger of sinking. Increased subdivision in a longitudinal direction was a very desirable thing, and almost necessary for a condition of immunity from sinking. In future Atlantic steamers longitudinal bulkheads should be placed not in the middle line, but nearer the sides of the ships, and they should recognize the fact that they had engines and boilers in different compartments, and make arrangements whereby the ship would still float, although the doors in these compartments were kept open. The proper way to arrive at that was to have a ship with great beam, and to have two longitudinal bulkheads at considerable distances from the sides of the ship, subdivided as completely as possible, both under and above water, so that, even supposing they got water into the space between one bulkhead and the side of the ship, they would have sufficient buoyancy in the other parts of the ship to keep her afloat. Broad ships must necessarily mean deep ships, in order to have comfort at sea. They were limited in length, and first came the question how many passengers they wanted to carry. The experience of a ship like the America—which was only 400 ft. in length—showed it was not necessary to go to great length to have great speed. A ship of 400 ft. to 430 ft. in length, 65 ft. of beam, and with a depth of 45 ft., would be a ship of proper dimensions for the Atlantic trade, and he believed it quite possible to build a vessel of special construction of about 7,000 tons gross register which should steam with less consumption of coal than the Umbria and Etruria at a rate of 22 knots, crossing the Atlantic from Liverpool to New York in six days. He thought that was likely to be the vessel of the future, and that it would be quite as commercially successful as the Umbria or Etruria.
Mr. J. Campbell remarked that at present the great American liners had only the ordinary compound engines, and he thought that, instead of converting them to triple expansion, they should take a step further at once, and adopt quadruple expansion engines. This class of engines was being very successfully built in various parts of the country. He should recommend the adoption of a three-crank six-cylinder engine.
Mr. Hamilton did not think it had been demonstrated that greater efficiency had been got out of twin screws than out of single screws; but there was no doubt they would tend to additional safety.
Mr. Martell said that when they had got satisfactory data, twin screws would be adopted for ships requiring great speed; but they had not got that data at present.
Admiral Sir John Hay, referring to twin screws as applying to sea-going steamers which might be employed for imperial defense, said it was quite certain that the defense of their extended commerce would always require to be assisted by ships such as the Oregon and other magnificent vessels which had been used for that purpose on a recent occasion. He believed that for war purposes the twin screw was recognized by all naval men as having very many advantages. If that were so, it was quite evident that it would be a great advantage, under such conditions as occurred at the loss of the Oregon, if the compartments could be made completely water-tight; and the twin screw, with the separation of the ship longitudinally, gave them the very greatest possible protection. They could not trust to bulkheads that were only closed occasionally by doors. What was required for war purposes was the entire and complete isolation of different parts of the ship, having always practically closed communications between them.
Mr. John then replied on the general discussion. He was pleased to find that they had faith in the future of the twin screw and of subdivision. The public had a right to demand greater safety than they at present had on the Atlantic, or could have with a single screw.
* * * * *
EXAMINATION QUESTIONS IN GENERAL CONSTRUCTION.
The following is a copy of the last examination paper given to candidates who are desirous of employment in the constructive departments of the municipality of New York:
N.B.—In case candidate does not remember formula or method of solving any problem submitted to him, let him name any work upon the subject where such formula or method may be found.
1. What is civil engineering?
2. Have you ever pursued a course of study in any educational institution, or with any civil engineer, which would fit you for the position of assistant engineer? If so, state when and with whom; state also, in detail, what experience you have had.
3. Have you ever had responsible charge of any public work? If so, state particulars.
4. Solve the following according to the algebraic signs:
——————————————————— / (6-2/7 - 4-3/9) x 8-7/16 / ———————————— x 67873.367, and show your work. / 4-4/12
5. The population of a certain town in 1880 was 7,095; it having increased 25 per cent. in ten years, what was it in 1870? Show your work.
6. How many feet, board measure, in the flooring of a room 20 feet by 30 feet and 21/2 inches thick?
7. Find value of x and y in the following equations:
2 x + 3 y = 33 4 x - y = 17.
8. Find value of x in equation x squared - x - 40 = 170.
9. Find value of x in equation
———— a / a squared - x squared x - + / ———- = - b / x squared b
10. Explain the meaning of the expression a1/2 x b3/4.
11. What is a logarithm?
12. What is the base of the common system?
13. In making what calculations are logarithms useful?
14. How do you find the logarithm of a number in a table of logarithms?
15. What are similar triangles?
16. How are similar triangles proportioned to each other?
17. The sides of a polygon being prolonged, what is the sum of all the exterior angles equal to?
18. How do you pass the circumference of a circle through three given points not in the same straight line?
19. How do you describe a square in a circle?
20. In the triangle, b being a right angle, what proportion does d b bear to a d and d c?
21. How do you inscribe a regular hexagon in a circle?
22. What proportion do circumference and areas of circles bear to their radii?
23. How do you find the area of a regular polygon?
24. Of an irregular polygon?
25. Of a circle?
26. How do you find the solid contents of a cylinder?
27. Of a wedge?
28. Of a pyramid?
29. Find the contents of the wedge, base 20 feet by 30 feet, height 10 feet, edge 15 feet.
30. State the prismoidal formula; would you use it in calculating earthwork?
31. Is a simple question in calculating areas.—Ed. Eng. News.
32. How many and what parts of a plane triangle must be given to find the rest?
33. Define the terms sine, co-sine, tangent, and co-tangent.
34. What are natural sines, co-sines, etc.?
35. What is a table of logarithmic sines, co-sines, etc.?
30. Two sides and two angles of a plane triangle being given, how do you find the other parts?
37. When two sides of a plane triangle and their included angles are given, how do you find the other parts?
38. In the right-angled triangle, A B H express algebraically the value of the sine, co-sine, tangent, and co-tangent of angle A in terms of a, b, and h, they being the altitude, base, and hypothenuse of the triangle.
39. What is the law of gravitation?
40. Do you understand that there is any difference in the meaning of the terms gravitation and gravity?
41. What is the law of falling bodies?
42. Express algebraically this law, taking v = velocity of falling body; g = acceleration of gravity; and h = height.
43. What is the center of gravity of a body?
44. How is it found?
45. Where is the center of gravity of a homogeneous body whose sides are all rectangles?
46. What is the specific gravity of a body?
47. What is the standard for solids and liquids?
48. What for gases?
49. What laws govern the pressure of liquids at rest?
50. How do you find the number of gallons of water to the cubic foot?
51. What is the weight of a gallon of water?
52. What is the pressure per square inch on the side of a vessel at the depth of 10 feet below the surface of the water?
53. What will be the theoretical volume of discharge per second from a reservoir through a pipe 1 foot in diameter, discharging at a depth of 100 feet below the surface of the water?
54. How many gallons of water will be discharged through a pipe 1 foot in diameter, 328 feet long, head 131/2 feet, coefficient of flow = 0.007?
55. State how many men are needed to make up a full party for a survey of a preliminary line or location of a public work, such as a railroad or aqueduct.
56. State also their several duties.
57. For what purpose is the magnetic needle used in surveying land?
58. What is a traverse table and for what used?
59. How do you set out a circular curved line upon the ground?
60. If an obstacle occurs to alignment, state how you would overcome it upon straight lines, also upon curves.
61. The radius of a curve being given, and angle of intersection of the two tangents, how do you find the length of the tangent from their intersection to the beginning of the curve?
62. Describe an engineer's transit, and name its adjustments.
63. Describe a Y level, and name its adjustments.
64. How many kinds of leveling rods do you know of?
65. State how they are graduated, and how they can be read to the 1/1000 of a foot.
66. Show a form of field-book for transit notes used when "running" curves, and place thereon notes of a 5 deg. curve for 1,000, with two intermediate "set-ups."
67. Show a form of level-book, and place therein sufficient figures to show your method.
68. What are cross-sections?
69. How do you set slope stakes for excavation and embankment?
70. What is a grade line?
71. What proportion of the breaking weight of a beam would you consider a safe load?
72. With the load uniformly distributed, what fractional part of the whole weight may be considered, in all calculations, as being carried at the center?
73. Suppose a beam supported at both ends, and take w = weight, l = length of beam, b = breadth, d = depth, s = breaking weight. Express algebraically the value of s in terms of the other quantities.
74. Sectional area being 36 square inches, which would be the stronger section, 6 by 6 or 4 by 9?
75. Make a design for a pair of rafters, connected by a tie-beam, for a roof 30 feet span, showing the dimensions of the several parts and the manner of connecting them. State in detail your method of obtaining the several dimensions.
76. How do you apply the principle of the parallelogram of forces in determining the strain on the various members of a structure? Illustrate graphically.
77. What should be the thickness at the top and base of a retaining wall 15 feet high, built to retain ordinary earth? Show your method of obtaining the required dimensions, also a sketch of the wall, showing how it should be founded.
78. A reservoir is to be built, depth of water 10 feet. If the walls are built of masonry, find the thickness of the same, and state how they should be built. Show your work. |
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