SCIENTIFIC AMERICAN SUPPLEMENT NO. 794
NEW YORK, March 21, 1891
Scientific American Supplement. Vol. XXXI., No. 794.
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.—New Race of Dwarf Dahlias.—A new and valuable flowering plant, with portrait of the introducer.—1 illustration.
II. CHEMISTRY.—Carbon in Organic Substances.—By J. MESSINGER.— An improved method of determining carbon by inorganic combustions.—1 illustration.
III. CIVIL ENGINEERING.—A New Integrator.—By Prof. KARL PEARSON. M.A.—An apparatus for use for the engineer in working up areas, indicator diagrams, etc.—4 illustrations.
Best Diameter of Car Wheels.—The size of car wheels from the standpoint of American engineering.—A plea for a moderate sized wheel.
Improved Overhead Steam Traveling Crane.—A crane constructed for use in steel works.—Great power and range.—3 illustrations.
Some Hints on Spiking Track.—A most practical article for telling exactly how to conduct the operation on the ground.—1 illustration.
IV. ELECTRICITY.—Electrical Laboratory for Amateurs.—By GEO. M. HOPKINS.—A simple collection of apparatus for conducting a complete series of electrical experiments.—17 illustrations.
The Action of the Silent Discharge on Chlorine.—How an electric discharge affects chlorine gas.—An important negative result.
V. ETHNOLOGY.—Some Winnebago Arts.—An interesting article upon the arts of the Winnebago Indians.—A recent paper before the New York Academy of Sciences.
VI. MEDICINE AND HYGIENE.—The Philosophy of Consumption. —By Dr. J.S. CHRISTISON.—A review of the present theories of consumption, and the role played in it by its bacillus.
VII. MUSIC.—Spacing the Frets on a Banjo Neck.—By Prof. C.W. MACCORD.—A most practical treatment of this subject, with full explanations.—1 illustration.
VIII. ORDNANCE.—High Explosives in Warfare.—By Commander F.M. BARBER, U.S.N.—An elaborate review of modern explosives in their applicability to ordnance, etc.
The Experiments at the Annapolis Proving Grounds.—The recent tests at Annapolis described and illustrated.—Views of the projectiles, plates, etc.—3 illustrations.
IX. PHYSICS.—Araeo-Picnometer.—An entirely novel form of hydrometer, of very extended use and application.—1 illustration.
X. TECHNOLOGY.—Fabric for Upholstery Purposes.—Full technical description of the method of producing a new and characteristic fabric.—1 illustration.
Gaseous Illuminants.—By Prof. VIVIAN B. LEWES.—Continuation of this important article, treating of the water gas and special processes, with analyses.
Glove Making.—Early history of glove making in America.—Its present aspects and processes.
Reversible Ingrain or Pro-Brussels Carpet.—An imitation of Brussels carpet on the Ingrain principle.—Full description of the process of making.—3 illustrations.
The Manufacture and Use of Plaster of Paris.—An excellent treatment of a subject hitherto little written about.—Full particulars of the manufacturing process.
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IMPROVED OVERHEAD STEAM TRAVELING CRANE.
We show in Fig. 1 a general view, and in Figs. 2 and 3 a side elevation and plan of an overhead steam traveling crane, which has been constructed by Mr. Thomas Smith, of Rodley, near Leeds, for use in a steel works, to lift, lower, and travel with loads up to 15 tons. For our engravings and description we are indebted to Industries. The crane is designed for hoisting and lowering while traveling transversely or longitudinally, and all the movements are readily controlled from the cage, which is placed at one end of and underneath the transverse beams, and from which the load can be readily seen. All the gear wheels are of steel and have double helical teeth; the shafts are also of steel, and the principal bearings are adjustable and bushed with hard gun metal. This crane has a separate pair of engines for each motion, which are supplied with steam by the multitubular boiler placed in the cage as shown. The hoisting motions consist of double purchase gearing, with grooved drum, treble best iron chain with block and hook, driven by one pair of 8 in. by 12 in. engines. The transverse traveling motion consists of gearing, chain, and carriage on four tram wheels, with grooved chain pulleys, driven by the second pair of 6 in. by 10 in. engines, and the longitudinal traveling motion driven by the other pair of 8 in. by 12 in. engines. The transverse beams are wrought iron riveted box girders, firmly secured to the end carriages, which are mounted on four double flanged steel-tired wheels, set to suit a 38 foot span.
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BEST DIAMETER CAR WHEELS.
[Footnote 1: By Samuel Porcher, assistant engineer motive power department, Pennsylvania Railroad. Read at a regular meeting of the New York Railroad Club, Feb. 19, 1891.]
It goes almost without saying that for any given service we want the best car wheel, and in general it is evident that this is the one best adapted to the efficient, safe and prompt movement of trains, to the necessary limitations improved by details of construction, and also the one most economical in maintenance and manufacture.
It is our aim this afternoon to look into this question in so far as the diameter of the wheel affects it, and in doing it we must consider what liability there is to breakage or derangement of the parts of the wheel, hot journals, bent axles, the effect of the weight of the wheel itself, and the effect upon the track and riding of the car, handling at wrecks and in the shop, the first cost of repairs, the mileage, methods of manufacture, the service for which the wheel is intended and the material of which it is made.
Confining ourselves to freight and passenger service, and to cast iron and steel wheels in the general acceptation of the term as being the most interesting, we know that cast iron is not as strong as wrought iron or steel, that the tendency of a rotating wheel to burst is directly proportional to its diameter, and that the difficulty of making a suitable and perfect casting increases with the diameter. Cast iron, therefore, would receive no attention if it were not for its far greater cheapness as compared to wrought iron or steel. This fact makes its use either wholly or in part very desirable for freight service, and even causes some roads in this country, notably the one with which I am connected, to find it profitable to develop and perfect the cast iron wheel for use in all but special cases.
Steel, on the other hand, notwithstanding its great cost, is coming more and more into favor, and has the great recommendations of strength and safety. It is also of such a nature that wheels tired with it run much further before being unfit for further service than those made of cast iron, and consequently renewals are less frequent. The inference would seem to be that a combination of steel and cast iron would effect the desirable safeness with the greatest cheapness; but up to the present this state of affairs has not yet been realized to the proper extent, because of the labor and cost necessary to accomplish this combination and the weakness involved in the manner of joining the two kinds of material together.
Taking up the consideration of the diameter of the wheel now, and allowing that on the score of economy cast iron must be used for wheels in freight service, we are led to reflect that here heavy loads are carried, and there is a growing tendency to increase them by letting the floor of the car down to a level with the draft timbers. All this makes it desirable to have the wheels strong and small to avoid bent axles and broken flanges, to enable us to build a strong truck, to reduce the dead weight of cars to a minimum, and have wrecks quickly cleared away. The time has not yet come when we have to consider seriously hot journals arising from high speed on freight trains, and a reasonable degree only of easy riding is required. The effect on the track is, however, a matter of moment. Judging from the above, I should say that no wheel larger than one 33 in. in diameter should be used under freight cars. Since experience in passenger service shows that larger cast iron wheels do not make greater mileage and cost more per 1,000 miles run, and that cast iron wheels smaller than 33 in., while sometimes costing less per 1,000 miles run, are more troublesome in the end, it is apparent that 33 in. is the best diameter for the wheels we have to use in freight service.
When we take up passenger service we come to a much more difficult and interesting part of the subject, for here we must consider it in all its bearings, and meet the complications that varying conditions of place and service impose. In consequence, I do not believe we can recommend one diameter for all passenger car wheels although such a state of simplicity would be most desirable. For instance, in a sandy country where competition is active, and consequently speed is high and maintained for a length of time without interruption, I would scarcely hesitate to recommend the use of cast iron for car wheels, because steel will wear out so rapidly in such a place that its use will be unsatisfactory. If then cast iron is used, we will find that we cannot make with it as large a wheel as we may determine is desirable when steel is used. And just to follow this line out to its close I will state here that we find that 36 in. seems to be the maximum satisfactory diameter for cast iron wheels, because this size does not give greater mileage than 33 in., costs more per 1,000 miles run, and seems to be nearer the limit for good foundry results. On the other hand, a 36 in. wheel rides well and gives immunity from hot boxes—a most fruitful source of annoyance in sandy districts. It is also easily applicable where all modern appliances under the car are found, including good brake rigging. In all passenger service, then, I would recommend 36 in. as the best diameter for cast iron wheels.
Next taking up steel wheels, a great deal might be said about the different makes and patterns, but as the diameter of wheels of this kind is not limited practically to any extent by the methods of manufacture, except as to the fastening of the wheel and tire together, we will note this point only. Tires might be so deeply cut into for the introduction of a retaining ring that a small wheel would be unduly weakened after a few turnings.
On the other hand, when centers and tires are held together by springing the former into the latter under pressure, it is possible that a tire of larger diameter might be overstrained. But allowing that the method of manufacture does not limit the diameter of a steel wheel as it does a cast iron one, the claim that the larger diameter is the best is open to debate at least, and, I believe, is proved to the contrary on several accounts. It is argued that increasing the diameter of a wheel increases its total mileage in proportion, or even more. Whether this be so or not, there are two other very objectionable features that come with an increase in diameter—the wheel becomes more costly and weighs more, without giving in all cases a proportionate return. We have to do more work in starting and stopping, and in lifting the large wheel over the hills, and when the diameter exceeds a certain figure we have to pay more per 1,000 miles run. I am very firmly convinced that the matter of dead weight should receive more attention than it does, with a view to reducing it. The weight of six pairs of 42 in. wheels and axles alone is 15,000 to 16,000 lb.
The matter of brakes is coming up for more attention in these days of high speed, heavy cars and crowded roads, and the total available braking power, which has hitherto been but partially taken advantage of, must be fully utilized. I refer to the fact that many of our wheels in six-wheel trucks have gone unbraked where they should not. As the height of cars and length of trucks cannot well be increased for obvious reasons, it is necessary to keep the size of the wheels within the limits that will enable us to get efficient brakes on all of them that carry any weight. This is not easy with a 42 in. wheel in a six-wheel truck, which is usually the kind that requires most adjustment and repairs after long runs. The Pullman Co. has recognized this fact, and is now replacing its 42 in. wheel with one 38 in. in diameter.
A 42 in. wheel with 4 in. journal has a greater leverage wherewith to overcome the resistance of journal friction than the 38 in. wheel with the same journal, and even more than the 36 in. and 33 in. wheels with 33/4 in. and 31/2 in. journals respectively, but the fact remains that the same amount of work has to be done in overcoming the friction in each case, and what may be gained in ease of starting with the large wheel is lost in time necessary to do it, and in the extra weight put into motion.
A large wheel increases the liability to bent axles in curving on account of greater leverage unless the size and weight of the axle are increased to correspond, and the wheel itself must be made stronger. A four or six wheel truck will not retain its squareness and dependent good riding qualities so well with 42 in. wheels as with 33 in. ones. Besides the brakes, the pipes for air and steam under the cars interfere with large wheels, and as a consequence of all this 42 in. wheels have been replaced by 36 in. ones to some extent in some places with satisfactory results. On one road in particular so strong is the inclination away from large wheels that 30 in. is advocated as the proper size for passenger cars.
On the other hand, there is no doubt a car wheel may be too small, for the tires of small wheels probably do not get as much working up under the rolls, and therefore are not as tough or homogeneous. Small wheels are more destructive to frogs and rail joints. They revolve faster at a given speed, and when below a certain size increase the liability to hot journals if carrying the weight they can bear without detriment to the rest of the wheel. Speed alone I am not willing to admit is the most prolific source of hot boxes. The weight per square inch upon the bearing is a very important factor. I have found by careful examination of a great many cars that the number of hot boxes bears a close relation to the weight per square inch on the journal and the character of lubrication, and is not so much affected by the size of wheel or speed. These observations were made upon 42 in., 36 in. and 33 in. wheels in the same trains. We find, furthermore, that while a 3-3/8 in. journal on a 33 in. wheel is apt to heat under our passenger coaches, a 33/4 in., even when worn 3-5/8 in., journal on a 36 in. wheel runs uniformly cool. In 1890 on one division there were about 180 hot boxes with the small wheel, against 29 with the larger one, with a preponderance of the latter size in service and cars of the same weight over them.
I do not know that there is any more tendency for a large wheel to slide than a small one under the action of the brakes, but large wheels wear out more brake shoes than small ones, if there is any difference in this particular.
My conclusions are that 42 in. is too large a diameter for steel wheels in ordinary passenger service, and that 36 in. is right. But as steel-tired wheels usually become 3 in. smaller in diameter before wearing out, the wheel should be about 38 in. in diameter when new. Such a wheel can be easily put under all passenger cars and will not have become too small when worn out. A great many roads are using 36 in. wheels, but when their tires have lost 3 in. diameter they have become 33 in. wheels, which I think too small.
There are many things I have left unsaid, and I am aware that some of the members of the club have had most satisfactory service with 42 in. wheels so far as exemption from all trouble is concerned, and others have never seen any reason for departing from the most used size of 33 in.
One more word about lightness. A wrought iron or cast steel center, 8 or 9 light spokes on a light rim inside a steel tire, makes the lightest wheel, and one that ought to be in this country, as it is elsewhere, the cheapest not made of cast iron.
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A NEW INTEGRATOR.
[Footnote 1: A paper read before the University College Engineering Society on January 22.—Engineering.]
BY PROFESSOR KARL PEARSON, M.A.
As I fear the title of my paper to our Society to-night contains two misstatements of fact in its three words, I must commence by correcting it. In the first place, the instrument to which I propose to draw your attention to-night is, in the narrow sense of the words, neither an integrator nor new. The name "integrator" has been especially applied to a class of instruments which measure off on a scale attached to them the magnitude of an area, arc, or other quantity. Such instruments do not, as a rule, represent their results graphically, and we may take, as characteristic examples of them, Amsler's planimeter and some of the sphere integrating machines.
An integrator which draws an absolute picture of the sum or integral is better termed an "integraph." The distinction is an important and valuable one, for while the integraph theoretically can do all the work of the integrator, the latter gives us in niggardly fashion one narrow answer, et praeterea nil. The superiority of the integraph over the integrator cannot be better pointed out than by a concrete example. The integrator could determine by one process, the bending moment, from the shear curve, at any one chosen point of a beam; the integraph would, by an equally simple single process, gives us the bending moment at all points of the beam.
In the language of the mathematician, the integrator gives only that miserly result, a definite integral, but the integraph yields an indefinite integral, a picture of the result at all times or all points—a much greater boon in most mechanical and physical investigations. Members of our Society as students of University College have probably become acquainted with a process termed "drawing the sum curve from the primitive curve." Many have probably found this process somewhat wearisome; but this is not an unmixed evil, as the irksomeness of any manual process has more than once led to the invention of a valuable machine by the would-be idler. Thus our innate desire to take things easy is a real incentive to progress. It was some such desire as this on my part which led me, three years ago, to inquire whether a practical instrument had not been, or could not be, constructed to draw sum curves. Such an instrument is an integraph, and the one I have to describe to you to-night is the outcome of that inquiry. It is something better than my title, for it is an integraph, and not an integrator.
Before I turn to its claims to be considered new, I must first remind you of the importance of an instrument of this kind to the draughtsman. I put aside its purely mechanical applications, where it has been, or can be, attached to the indicators of steam engines, to dynamometers, dynamos, and a variety of other instruments where mechanical integration is of value. These lie entirely outside my field, and I propose only to refer to a few of the possible services of the integrator when used by hand, and not attached to a machine.
The simple finding of areas we may omit, as the planimeter will do that equally well. But of purely graphical processes which the integraph will undertake for us, I may mention the discovery of centroids, of moments of inertia (or second moments), of a scale of logarithms, of the real roots of cubic equations, and of equations of higher order (with, however, increasing labor). Further, the calculation of the cost of cutting and embanking for railways by the method of Bruckner & Culmann, the solution of a very considerable number of rather complex differential equations, various problems in the storage of water, and a great variety of statistical questions may all be completely dealt with, or very much simplified by aid of the integraph.
In graphical statics proper the integraph draws successively the curves of shear, bending moment slope, and deflection for simple beams; it does the like service for continuous beams, after certain analytical or graphical calculations have first been made; it can further lighten greatly the graphical work in the treatment of masonry arches and of metal ribs. In graphical hydrostatics it finds centers of pressure and gives a complete solution for the shear and bending moment, curves in ships, besides curves for their stability. In graphical dynamics the applications of the integraph seem still more numerous. It enables us to pass from curves of acceleration to curves of speed, and from curves of speed to curves of position. Applied to the curve of energy of either a particle or the index point of a rigid body, it enables us by the aid of easy auxiliary processes to ascertain speeds and curves of action. In a slightly altered form, that of "inverse summation," we can pass from curves of action to curves of position, and deal with a great range of resisted motions, the analysis of which still puzzles the pure mathematician; the variations of motion in flywheels, connecting rods, and innumerable other parts of mechanism, may all be calculated with much greater ease by the aid of an integraph. Shortly, it is the fundamental instrument of graphic dynamics.
It would be needless to further multiply the instances of its application; the questions we have rather to ask are: Can a practical instrument be made which will serve all these purposes? Has such an instrument been already put upon the market? If I have to answer these questions in the negative, it is rather a doubtful negative, for the instrument I have to show you to-night goes so far, and suggests so many modifications and possibilities, which would take it so much further, that it is very close to bringing the practical solution to the problem.
Let me here lay down the conditions which seem essential to a practical integraph. These are, I think, the following:
1. The price must be such that it is within the reach of the ordinary draughtsman's pocket. The Amsler's planimeter at L2 10s. or L3 may be said to satisfy this first condition. The price for the first complex integraph designed by Coradi was L24 to L30. The modified form in which I show it to-night is estimated to cost retail L14. Till an equally efficient instrument can be produced for L5 I shall not consider the price practical. If the error of its reading be not sensibly greater than that of a planimeter, it is certainly worth double the money.
2. The instrument must not be liable to get out of order by fair handling and a reasonable amount of wear and tear. I cannot speak at present with certainty as to how far our integraph satisfies this condition; it is rather too complex to quite win my confidence in this respect.
3. It must be capable of being used on the ordinary drawing board, and of having a fairly wide range on it, i.e., it must not be limited to working where the primitive is at one part only of the board.
This condition takes out of every day practical drawing use the integraph invented by Professors James and Sir William Thomson, in which the sum curve is drawn on a revolving cylinder. It is essential that the sum curve should be drawn on the board not far from the primitive, and that this sum curve can be summed once or twice again without difficulty. The time involved in drawing the four sum curves, for example, required in passing from the load curve to the deflection curve of a simple beam, if these curves were drawn on different pieces of paper and had to be shifted on and off cylinders, would probably be as long as the ordinary graphical processes. Coradi's integraph works on an ordinary drawing board, but since there are nearly 10 inches between the guide point and tracer, the sum curve is thrown 10 inches behind the primitive in each integration. Thus a double summation requires say 26 inches of board, and it is impossible to integrate thrice without reproducing the primitive. The fact that the primitive and sum curve are not plotted off on the same base is also troublesome for comparison, and involves scaling of a new base for each summation. I have endeavored to obviate this by always drawing the second sum curve on a thin piece of paper pinned to the board, which can then be moved back to the position of the first primitive. But this shifting, of course, involves additional labor, and is also a source of error.
I should like to see the trace and guide chariots on the same line of rails, one below the other, were this possible without producing the bad effect of a skew, pull or push.
4. The practical integraph must not have a greater maximum error than 2 per cent. The mathematical calculations, which are correct to five or six places of decimals, are only a source of danger to the practical calculator of stresses and strains. They tend to disguise the important fact that he cannot possibly know the properties of the material within 2 per cent. error, and therefore there is not only a waste of time, but a false feeling of accuracy engendered by human and mechanical calculation which is over-refined for technical purposes.
For comparative purposes I have measured the areas of circles of 1 inch, 2 inches, and 3 inches radius, the guide being taken round the circumference by means of a "control lineal," first with an ordinary Amsler's planimeter and then with the integraph. I have obtained the following results:
- - - By integraph. Radius By of Calculated Planimeter. Upper Upper circle. areas. Middle. end. Middle. end. p=2 in. p=2 in. p=4 in. p=4 in. - - in. 1 3.14159 3.140 3.140 3.138 3.120 3.120 2 12.56636 12.55 12.36* 12.546 12.568 12.552 3 28.27431 28.24 ...... ...... 28.280 28.288 - -
* Cross bar had to be moved during tracing.
From this it follows that the error of the planimeter is less than 0.1 per cent. and that of the integraph about 0.5 per cent. Obviously we could make this error much less if we excluded small areas measured with large polar distances, or such polar distances that the cross bar must be shifted. Excluding such cases, we see that the accuracy of the integraph scarcely falls behind that of the planimeter and is quite efficient for practical purposes. It must be borne in mind that the above measurements were made with the "control lineal," an arrangement which carries the guide round a circle of the exact test area. In most cases the curve has to be followed by hand, and the error will be greater—greater probably for the integraph than for the planimeter, as the former is distinctly hard to guide well.
I think, then, we should be safe in saying that the error of the integraph is not likely to be greater and is probably less than 2 per cent., so that in this respect the instrument may be considered a practical one.
5. A further condition for a good integraph is that it should have a wide range of polar distances, and that it should be easily set at those distances.
One of the conditions I gave to the maker of the instrument was that it should be able to take all polar distances from one to ten half-inches. This condition he can scarcely be said to have fulfilled. With polar distances of 1/2 inch and 1 inch, the machine works unsatisfactorily, which indeed might have been foreseen from the construction of its sliding bars. It works best from 2.5 inches to 5 inches, and this is the range to which I think we ought to confine the present type of instrument. As the last conditions I may note that:
6. A practical integraph ought to be easy to read.
7. Draw a good clear curve.
The scale on the present instrument is very inconvenient, as it is often almost out of sight; the curve it draws, on the other hand, I consider very satisfactory, when the pencil is loaded, say, with a planimeter weight. On the whole, I think you will agree with me that this integraph goes a good way, if not the whole way, toward fulfilling the conditions of a practical instrument.
I next turn to its construction and the claim it has to be considered in any way new. Let me briefly remind our members of the process by which an element Q R of the sum curve (Fig. 1) corresponding to the point P on the primitive is drawn; P M being the mid-ordinate of L N, a horizontal element, P B is drawn perpendicular to any vertical line A B; and O A being a constant distance termed the base or "polar distance," Q R is drawn between the ordinates of L and W, parallel to O B. If P' be the point where P M meets Q R, we note the following relationship of P' to P.
1. If P moves along a horizontal line, O B remains unchanged, and, therefore, Q R or P' must move in the straight line Q R parallel to O B.
2. If P moves along a vertical line, P' does not change, but Q R turns round it, remaining parallel to O B.
Without taking the trouble, as I ought to have done, to inquire what previous investigations had achieved in this matter, I thought, three years ago, I could get an apparatus to save me the trouble of drawing sum curves, made somewhat after the following fashion.
P (Fig. 2) is the guide or point to be taken round the primitive. It is attached to a block, D, which works along the bar, B C, which in its turn moves on the four wheels, e e f f, upon the frame R S U T fixed upon the drawing board. O A is fixed perpendicular to R U, and is such that O may be fixed at various points to determine the polar distance. O B D is a light bar passing freely through B and forming one side of a parallel ruler of two or more points, g g, h h, i i. Along i i is a slot and in this works a loaded block containing a wheel P', whose plane is always parallel to i i. This block also passes through a slot in D E, an arm at right angles to B C. A little consideration will show that P', if worked at all, would trace out the sum curve of P.
It was only when I showed the rough idea of this to Professor Kennedy, with the view of ascertaining what would be the amount of back-lash and friction, that I learned that Mr. Boys had already invented a very similar integrator. In his model the double parallel ruler is replaced by two endless strings and pulleys, and the bar, B C, by a T square.
Although this integrator was afterward made in a less crude form, I do not think it has ever been a practical instrument for the draughtsman. Shortly afterward I came across a work by Abdank-Abakanowicz, entitled "Les Integraphes," being a study of a "new kind of mechanical integrator."
The new kind of integrator was really only an independent version of Boys' instrument, but in many respects a great improvement. The real merit will ultimately belong to the scientific instrument maker who constructs an instrument reasonably cheap and capable of efficient practical service. Abdank-Abakanowicz's integrator however certainly went further in the practical direction than any previously constructed. The drawing board machines, it is true, of rather a complex nature, were actually exhibited to the Paris Academy, but no more have been made. The instrument before me was made by Coradi, of Zurich, on conditions laid down by me, namely, that the cost should not exceed L14, and that polar distances should range between one and ten half-inches. The first machine made by Coradi on these lines was, by a misunderstanding, sold in Germany, but the one I exhibit is the first, I believe, that has reached England, and to this extent I may, perhaps, be permitted to call it new. I look upon it rather as a suggestion upon which a still more practical instrument can be made in this country than as a perfect model. I believe there would be a wide sale for such an instrument were it once generally known to exist, and, what is more to work efficiently. It remains for me to point out in what the Abdank-Abakanowicz, or, rather, Coradi, integraph differs from Boys' instrument.
Two points deserve special attention. In the first place, the fixed frame is abolished, and the horizontal motion of P (Fig. 3), the guide point, is produced by putting the whole frame on friction rollers; in the second place, as a necessary result of the first change, the guide point carries about with it its own polar system, which renders the changes in length of "rays" much more manageable. f f, f' f' is a frame moving on four roughed wheels, e e e e, so that it can only move in the direction, f', which we may term horizontal. f f and f' f' are rails guiding the chariots, A and B, from f to f and from f' to f'. Of these chariots, A contains the guide point, P, to trace out the primitive with, and B the pencil, P', to draw the sum curve, i.e., the tracer. The chariot, B, like Boys' tracer, is heavily loaded. g g is a horizontal bar rigidly attached to the crossbars, q q and q' q', of the frame. On g g is a movable pivot, to which h, which determines the pole, k0 h being the polar distance. k0 is the position of a second point, k, on the chariot, A, when the guide point, P, is on the initial line, g g. l l is a bar with a long slot in it, in which work the pivots, h and k; this bar represents the "ray." A projecting arm k k' has been introduced to enable me to shorten the polar distance down to 2 in. and under by removing the pivot, k to k'. m m is a bar attached to the block, n, which runs on l l, so that m m is always perpendicular to l l. On the chariot, B, is another bar, m' m', capable of turning round the pivot, d, and always maintained parallel to m m by the rods, m m', m m'. Attached to m' m' is a wheel, w, whose axis is parallel to m' m'. This wheel, therefore, always moves perpendicular to m' m', and therefore to m m; hence it moves parallel to the ray, h k. A pencil, P', attached traces out the sum curve. If we wish to use the machine as an integrator, we have merely to measure the vertical distance traversed by P', or the distance B has run along f' f'. This is done by means of a scale on f f'. If k be brought down to k0, w runs parallel to g g, or P' traces out a horizontal straight line, which is thus the base line. If k be fixed as near as possible to k0, which is done by means of a screw in f f at k0, the chariot, B, can be run down f' f' as nearly opposite to k0 as can be guessed at; a horizontal line may then be drawn as base line, and the guide point, P, brought into this line by a clamping screw with which it is provided. The instrument is then ready for action. There is a brake on one of the roughed wheels to check or stop the motion of the integraph when required.
The instrument works best when the chariots, A and B, are about opposite to each other; when they are at opposite extremities of f f and f' f' respectively, the pull at P tends to produce a skewing couple. If the chariot, B, could be put upon f f and work, if needful, by a double parallelogram from m m, we should have, excepting the skew pull, some great practical advantages. We might throw the whole of the weight of the machine on the one pair of friction wheels, and replace the other pair by a single wheel, the portion q' f' f' q' of the machine virtually disappearing. Three wheels, of course, would be a real improvement. Further, we should have the sum curve and primitive drawn to the same base line, and the simplification in the number of parts ought largely to reduce the cost of the instrument.
To be able to perform "inverse summation" (which in the language of differential calculus is to find y as a function of x, when we are given y=f(dy/dx), and not dy/dx=f(x) as usual), we only want a means of making the plane of the wheel, w, parallel instead of perpendicular to m' m', and it is easy to design a modification in the construction which will allow of this change.
I hope the above description of the integraph may have made its construction and method of working sufficiently clear. Those of you who have a taste for mechanical work, and the necessary tools, might, I think, with some patience, construct a workable integraph. I expect the pivots would be the hardest part of the work. I hope, some day, myself to have another instrument made with a more readily changeable polar distance, with trace and guide points working in the same vertical, and a wheel permitting of inverse summation. If this project is ever carried out, I hope I may be permitted to communicate further particulars to our society.
* * * * *
After some forty years of immersion in the waters of the pool of Echoschacht, not far from Hermannstadt, several human bodies have been brought to the surface in a state of perfect preservation.
* * * * *
SOME HINTS ON SPIKING TRACK.
The usual dimensions of track spikes are 51/2 X 9.16 inches square, their weight about half a pound each. Their common defects are brittleness and imperfect points. In spiking track, the most important points to be attended to are the proper spacing of the ties and driving the spikes in such a manner that the ties shall be held in place at right angles to the track and the rails in true gauge; to insure the latter, the track gauge should always be used when spiking the gauge side, the rail being held to proper position by a lining bar. The gauge should be kept about 6 or 8 in. ahead of the tie being spiked and should not be lifted until the spikes are driven home; gauges should be tested regularly and every morning when they are to be used all day, so as to insure a true gauge all the time. The two inner spikes should be set on one side of the tie and the two outer spikes on the other, as indicated in the accompanying sketch. This prevents the tie from slewing around, and thus deranging the gauge of the track, as well as interfering with the proper spacing of the ties. The joints and centers should be spiked first, which will bring the rails to their proper position on the ties, which in turn will assist intermediate spiking. Each tie should be carefully gauged as spiked and, as before indicated, the ties with the broadest faces being selected for the joints.
In gauging ties it is very convenient to have measured off on the handles of the mauls in the hands of the forward spikers the distance from the outside of the rail to the end of the tie. This distance will then be gauged on the tie, when it will be lifted to the rail and securely spiked; the gauge is then used, and the loose rail held in place with the lining bar as previously indicated, loose gauge being given on curves, in accordance with directions of the engineer, the allowance for which is about 1/8 in. on a 2 deg. curve, up to about 3/4 in. on a 12 deg. curve.
This widening of the gauge should begin on the tangent, back of the P.C., the full amount of excess over true gauge being reached by the time the P.C. is reached and continue all the way around the curve, running from the P.T. in the same manner as back of the P.C.
The spikes should always be driven home straight and at right angles with the face of the ties. When the foreman in charge of the track-laying work sees a spiker, when the spike is nearly home, strike the spike head laterally, which is done to make it lie snugly to the rail, he should at once check such imperfect work and put the man who does it at other work. The foreman in charge of gang of spikers should be experienced in this branch of the work, and by weeding out imperfect workers, can soon get together a first-rate gang of spikers. But no trouble will be experienced from carelessly driven spikes, if the tie has the spike holes bored into it, before laying. This is considered good practice, but rather expensive.
For boring the holes quickly and accurately, a proper template should be made, by which the ties are marked for the borers, who should be provided with boring machines, by the use of which a hole, square with the face of the tie is bored. The boring machines should be so arranged as not to cut the hole beyond the required depth, which should be slightly less than the length of the spike. The diameter of the holes should be about 1-16 of an inch less than the thickness of the spike. This not only does away with the spike tearing its way through the timber and thus injuring its fiber to a great extent and causing it to be much more susceptible to rot, but it is said to increase the adhesion of the spike in hard wood ties at least 50 per cent. But in order that the best results may be obtained, the spike should be flattened on either side of the sloping point, which will generally prevent it leaving the hole.
The spikers should carefully avoid striking the rail with their mauls, as such carelessness often produces fracture, which sometimes causes the rail to break in two at such points, which is liable to produce derailment and serious accident. Spike mauls should weigh not less than nine nor more than ten pounds, and should be on straight handles, not less than 3 ft. long. After considerable use, the face of the maul will become somewhat rounded, and when this takes place it should be sent to the shop to be redressed. The last blow on the spike should be only sufficiently hard to cause its throat to fit snugly on the rail; a harder blow will often fracture the spike in such a manner as to cause the head in a short time to break off and leave the rail unsupported at that point. Foremen should not allow a spike to be pulled, especially in frosty weather, until it has been first struck a light blow to break the rust and loosen its hold in the wood. The filling of old spike holes with wooden plugs is bad practice, for the reason that they will cause the spike in a short time to slip from its place; to fill the holes with sand is much better, and spikes driven in holes so filled will hold much more firmly. The best form of spike I have seen is the curved safety railroad spike; this spike takes in the tie a position which enables it to resist the thrust of the rail against it much more effectually than the ordinary spike can possibly do. I have seen in good condition, one of these curved spikes which was said to have been driven eight times. The cost of the curved safety spike is more than that of the ordinary spike, but it is better made, holds the track better, and, I believe, is worth more than the difference asked for it.—J.A. Hall, on Construction and Maintenance of Track, before American Society of Civil Engineers.
* * * * *
THE EXPERIMENTS AT THE ANNAPOLIS PROVING GROUNDS.
The desperate war that has been waging between the gun and armor plate, ever since the period when protective plates were first applied to naval constructions, is familiar to all. In this conflict the advantage seems to lean toward the side of the gun, the power of penetration of which can be increased to almost indefinite limits, at least theoretically, while we quickly reach the extreme thicknesses of metal that can be practically employed for the protection of ships.
So, in recent times, researches have been making upon the efficacy of armor plating, no longer in its exaggeration of thickness, but in the intrinsic quality of the metal of which it is composed. Metallurgists have applied themselves to the work and have thus brought out various products, among which the plates called "compound," of Messrs. Cammell & Co., have obtained a great notoriety. These plates, formed of a true plating of steel upon a bed of soft iron, have been much in vogue in the English navy, and seemed as if they were to be adopted about everywhere.
The Creusot works alone, of all competitors, were able to fight against the general infatuation. Many comparative experiments had already demonstrated the superiority of the Creusot "all steel" plates over the Cammell plates, but Messrs. Schneider & Go. were not willing to stop here, and finally produced the new nickel steel plate, which is by far superior to their steel plates.
Some comparative trials of these various armor plates have recently been made by a military commission of the United States at the Annapolis proving grounds. Three plates, one a Cammell, the second a steel, and the third a nickel steel (the two last from Creusot), were here submitted to firing, under absolutely identical conditions.
Our engravings show the proving grounds and the details of the arrangements adopted for backing the plates.
Of the three plates, the Cammell was the thickest (11 in.) The steel one was 103/4 in. in thickness, and the nickel steel 101/2 in. The last, therefore, was at a disadvantage with respect to the two others.
The plates were arranged tangentially to an arc of a circle whose center was occupied by the pivot of the gun, and consequently at right angles with the latter. The piece employed was a 6 in. gun, 35 calibers in length. The distance of its muzzle from the plates attacked was 28 ft.
The charge was 44 lb. of brown prismatic powder. The projectile was a 100 lb. Holtzer shell. Under these circumstances, the initial velocity was 2,074 ft. and the energy at the impact was 9,970,396 ft. lb.
A beginning was made by firing four shots at each plate in the bisectrix of the corners. Then the 6 in. gun was replaced by an 8 in. one, throwing a 209 lb. Firth projectile, with an energy at the impact of 20,795,000 ft. lb.
Each of the plates then received in its center a final blow from this projectile.
Our engraving represents the state of the plates after this last shot.
There is no need of being a great expert in questions of artillery to discover on what side the superiority is found, and to see that the Cammell plate, almost entirely in fragments, is absolutely incapable of protection, while its two competitors are still in a state to resist.
In one of our engravings may be seen, too, the state of the shells after each of the three shots.
The commission immediately and unanimously classified the three plates in the following order of superiority: (1) Nickel steel; (2) all steel; (3) compound.
This triumph of French industry merits mention so much the more in that it was obtained in a series of experiments made in a foreign country—that is to say, under indisputable conditions of impartiality.-L'Illustration.
* * * * *
HIGH EXPLOSIVES IN WARFARE.
[Footnote 1: A lecture delivered before the Franklin Institute, Philadelphia, November 28, 1890. From the Journal of the Institute.]
BY COMMANDER F.M. BARBER, U.S.N.
In commencing my paper this evening I desire to call your attention to the fact that I am dealing with a subject which, though not theoretical, is still hardly practical, for as a matter of fact high explosives cannot be said to have yet been regularly used in warfare, and I hope you will pardon me if in consequence my statements appear in some respects unsatisfactory and my theories unsound. My subject, however, is no more obscure than future naval warfare generally. All civilized nations are spending millions of money for fighting purposes directly in opposition to the higher feelings of the better class of their inhabitants. The political atmosphere of Europe is the cause of this, but its consequence is the development of theoretical plans of ships which are no sooner commenced than the rapid march of mechanical, chemical, and electrical science shows them to be faulty in some particular feature, and others are laid down only to be superseded in their turn.
None of these crafts are obsolete (to use the popular expression of the day). All are theoretically better than any which have stood the test of battle; but each excels its predecessor in some particular feature. The use of high explosives is the direct cause of the very latest transformations in marine architecture, and is destined to work still greater changes; but it will require a war between the most civilized nations of the world, and a long war, to either confirm or condemn the many theoretical machines and methods of destruction that modern science has produced. I say a war between the most civilized nations, since it is only they that can supply the educated intellect that is necessary to both attack and defense. Under other circumstances false conclusions as to weapons and results are certain to be drawn.
At the bombardment of Alexandria, the English armorclads, with their rifled guns, were not nearly as efficient against the feeble chalk fortifications as our wooden ships would have been with smooth bore guns. On the other hand I saw on shore after the bombardment hundreds of torpedoes and miles of cable that the Egyptians did not understand how to use. The French war with China was equally unsatisfactory from a military point of view. The Chinese at Foochow were annihilated because the French opened fire first, and the only shell that penetrated a French ironclad was filled with lamp black instead of powder. The national riots that we are accustomed to hear of in South America are likewise of little instructive value; they buy their weapons of more civilized people, but there is always something fatally defective about the tactics pursued in using them. It may be said in general terms that in these days of extreme power in fighting machines, the greater the efficiency the less the simplicity and the more knowledge required in the care of the weapons. When powder was merely powder the advice of the old adage to "trust in God and keep your powder dry" was ample to maintain the efficiency of the powder for all purposes; but nowadays if you keep your powder dry you will burst your gun, and if you keep your gun-cotton dry you are liable to blow up your ship.
It is rather difficult to-day to define what high explosives are, in contradistinction to gunpowder. Thirty years ago we could say that powder was a mechanical mixture and the others were chemical compounds; but of late years this difference has disappeared.
The dynamical difference, however, still remains. Gunpowder in its most efficient form is a slow-burning composition, which exerts a relatively low pressure and continues it for a long time and to a great distance. High explosives, on the contrary, in their most efficient form, are extremely quick-burning substances, which exert an enormous pressure within a limited radius. Ordinary black gunpowder consists of a mechanical mixture of seventy-five per cent. of saltpeter, fifteen per cent of charcoal, and ten per cent. of sulphur. The most important of the high explosives are formed by the action of nitric acid upon organic substances or other hydrocarbons, the compound radical NO2 being substituted for a portion of the hydrogen in the substance. The bodies thus formed are in a condition of unstable equilibrium; but if well made from good material, they become stable in their instability, very much like Prince Rupert's drops, those little glass pellets which endure almost any amount of rough usage; but once cracked, fly into infinitesimal fragments.
The power exerted by these nitro-substitution products is due to the fact that they detonate, i.e., they are instantaneously converted into colorless gas at a very high temperature, and in addition they have almost no solid residue. Nitro-glycerine actually leaves none at all, while gunpowder leaves sixty-eight per cent. The first departure in gunpowder from the old-time constituents of black powder just mentioned was for the purpose of obtaining less pressure and slower combustion than could be produced by mere granulating or caking. This was accomplished by using underburned charcoal, together with sugar and about one and one-half per cent. of water. This is the brown powder most generally used at present and with satisfactory results; but the abstraction of its moisture increases its rapidity of combustion to a dangerous degree, besides which the underburned charcoal is itself unstable.
The next change demanded is smokelessness, and to accomplish it recourse is had to the high explosive field, mechanically mixing various substances with them to reduce and regulate their rapidity of action. Just now some form of gun-cotton is most in use mixed with nitrate of ammonia, camphor and other articles. The tendency of these mixtures is to absorb moisture, and the gun-cotton in them to decompose, and there is no smokeless powder which can to-day be considered successful. Such a powder, however, will undoubtedly be an accomplished fact in the near future. Military men seem to be a great deal at variance as to its value in the field, but there can be no doubt of its value for naval purposes; it is a necessity forced upon us by the development of torpedo warfare.
First came the simple torpedo, at the end of an ordinary boat's spar. Then came the special torpedo boat with its great speed, then the revolving cannon and rapid-fire gun to meet the torpedo boat. At present the possible rapidity of fire is much greater than can be utilized, on account of the smoke; hence the necessity of smokeless powder. Smokelessness is, however, principally a martial demand that has been made upon the science of explosives and has attracted public attention on that account. The commercial demands for various other properties have been much greater than the military, and between gunpowder near one end of the line in point of power and nitro-glycerine near the other, there are now over 350 different explosives manufactured, and most of these have been invented within the last twenty years.
The simplest application of high explosives in warfare is in connection with torpedoes, since within the same bulk a much more efficient substance can be obtained than gunpowder, and with reasonable care there is very little danger of premature explosions by reason of accidental shocks.
Torpedoes were made by the Chinese many years ago, they were tried in our war of independence, and also by the Russians during the Crimean war; but the first practical and successful use of them as a recognized weapon was during our war of secession, when thirty-seven vessels were either sunk or seriously injured by them. Gunpowder was used in these torpedoes, though it is stated that attempts were made to use other substances without success. Since that time all maritime nations have made a close study of the subject and have adopted various high explosives, according to the results of their experiments. In general terms it may be stated that explosive chemical compounds have been found more suitable than explosive mixtures, because of the uniformity of direction in which they exert their pressure, and from the fact that water does not injure them. Mixtures may be very powerful, but they are erratic and require tight cases. In the United States we use dynamite for harbor mines. It is composed of seventy-five per cent. nitro-glycerine and twenty-five per cent. silica; but blasting gelatine and forcite gelatine will probably be adopted, when they can be satisfactorily manufactured here, as they are more powerful. The former is composed of ninety-two per cent. of nitro-glycerine and eight per cent. of gun-cotton, and the latter of ninety-five per cent. of nitro-gelatine and five per cent. unnitrated cellulose.
For naval use we have adopted gun-cotton as being the most convenient. In Europe gun-cotton is generally used for both fixed mines and movable torpedoes; Russia, Austria, and Italy use blasting gelatine also.
In actual warfare but little experience has been had. Two Peruvian vessels were sunk by dynamite in the Chili-Peruvian war, one Turk by means of gun-cotton during the Turco-Russian war of 1877, and two Chinese by gun-cotton in the Franco-Chinese war of 1884.
In making experiments to determine the relative strength of the different explosives under water, very curious and puzzling results have been obtained. Nitro-glycerine being the simplest and most complete in its chemical decomposition, and apparently the most powerful in air, it was natural to suppose that it would be the same in submarine work, but it was found by Gen. Abbot, at Willets Point, after repeated experiments, as shown in his report of 1881, that it was not so powerful in its effect by twenty per cent. as dynamite No. 1, although the dynamite contained twenty-five per cent. of an absolutely inert substance. His idea was that it was too quick in its action, and, since water is slightly compressible, a minute fraction of time is required in the development of the full force of the explosive. Gen. Abbot's results for intensity of action per unit of weight of the most important substances is as follows:
Blasting gelatine........................... 142 Forcite " ........................... 133 Dynamite No. 1.............................. 100 Gun-cotton, wet............................. 87 Nitro-glycerine............................. 81 Gunpowder.............................. 20 to 50
Col. Bucknill, of the Royal Engineers, in his publication of 1888, gives the following:
Blasting gelatine........................... 142 Forcite " ........................... 133 Dynamite No. 1.............................. 100 Gun-cotton, dry............................. 100 " " ............................. 80 Gunpowder................................... 25
In both tables dynamite No. 1 is assumed as the standard of comparison. Col. Bucknill states that his gun-cotton results differ from Gen. Abbot's, because he experimented with much larger quantities, viz., 500-pound charges. Gen. Abbot's experiments led him to believe that an instantaneous mean pressure of 6,500 pounds per square inch would give a fatal blow to the double bottom of a modern armorclad, and he developed a formula which gives this blow with blasting gelatine at the following distances under water, viz.:
Pounds. At 5 feet.................................. 4 " 10 " .................................. 17 " 20 " .................................. 67 " 30 " .................................. 160 " 40 " .................................. 311
Col. Bucknill's experiments caused him to believe that a pressure of 12,000 pounds per square inch is required, and his formula, which is somewhat different from Abbot's, gives widely different results at close quarters, but they approach each other as the distance increases.
His results are as follows: Pounds. At 5 feet................................ 231/2 " 10 " ................................ 75 " 20 " ................................ 177 " 30 " ................................ 274 " 40 " ................................ 369
Regarding the comparative effects of gunpowder and the high explosives, I think Gen. Abbot's estimate of a varying value for powder is more admissible than the fixed value assigned by Col. Bucknill. Gunpowder gives a push and detonating compounds a shock; as the quantities increase, the push reaches farther than the shock. According to Gen. Abbot, 100 pounds of dynamite No. 1 will have a destructive horizontal range of 16.3 feet, while the same amount of gunpowder will only have a range of 3.3 feet. Five hundred pounds of dynamite, however, will have a horizontal range of 35 feet, and 500 pounds of gunpowder will have 19.5 feet; the ratio has diminished from five to two. Whether 6,500 pounds or 12,000 pounds per square inch is necessary to crush the bottom of an armorclad will depend largely upon how far apart the frames of the ship are spaced and what other bracing is supplied, as well as many local circumstances. It is difficult to judge exactly of these matters. Some four years ago the Italian government adopted treble bottoms for their heaviest ships as a result of experiments with seventy-five pounds of gun-cotton (the charge of an ordinary Whitehead locomotive torpedo) against a caisson which was a fac-simile of a portion of the proposed ships. Only two of the bottoms were broken through, and when the space between the two inner bottoms was filled with coal, only the outer bottom was broken. According to the formulae of either Abbot or Bucknill, there should have been a local pressure of at least 300,000 pounds per square inch on the outer skin, and yet judicious interior arrangements rendered it harmless to the target. It would not, however, be safe to conclude that the torpedo was thus vanquished; the immediate result was simply to create a demand for larger locomotive torpedoes for local application, and but little light was thrown upon the results which might be anticipated from a large mine at a greater distance, whose radius of explosive effect would embrace a larger portion of the ship, and especially if the ship were nearly over the torpedo. The local effect of a detonation is different from the transmitted shock. Experiments in England have shown that 500 pounds of gun-cotton at forty feet below any ship will sink her, and at a horizontal distance of 100 feet, damage to the interior pipes and machinery is to be expected.
The fact that the high explosives are so much heavier than gunpowder has an important bearing on the size of the containing case. Their sp. gr. is as follows:
Nitro-glycerine............................ 1.6 Blasting gelatine.......................... 1.45 Forcite " .......................... 1.51 Dynamite No. 1............................. 1.6 Wet gun-cotton............................. 1.32 Dry " ............................. 1.06 Gunpowder.................................. 0.9
Their relative efficiency under water per cubic foot, according to Bucknill, is as follows:
Blasting gelatine.......................... 1.38 Forcite " .......................... 1.27 Dynamite No. 1............................. 1.00 Dry gun-cotton............................. 0.66 Wet " ............................. 0.66 Gunpowder.................................. 0.14
The wet gun-cotton has twenty-five per cent. of added water.
Mines for harbor defense are of two kinds—buoyant and ground. The buoyant are usually spherical, and contain from 400 to 500 pounds of explosive. They bring the charge near to the ship's bottom, but are difficult to manage in a tideway, and can be easily found by dragging. The ground mines can be made of any size and are not easily found by dragging, but are of little value in very deep water. They are either cylindrical or hemispherical in shape, and contain from 500 to 1,500 pounds of explosive in from thirty to eighty feet of water. Mines of any kind are exceedingly difficult to render efficient when the water is over 100 feet deep. On account of the tendency of all high explosives to detonate by influence or sympathy, and the liability of the cases to collapse by great exterior pressure, harbor mines are separated a certain distance, according as they are buoyant or ground, and according to the nature of the explosive.
Five hundred pounds buoyant gun-cotton mines require 320 feet spacing.
Five hundred pounds buoyant blasting gelatine mines require 450 feet spacing.
Six hundred pounds ground gun-cotton mines require 180 feet spacing.
Six hundred pounds ground blasting gelatine mines require 230 feet spacing.
Of torpedoes, other than those described, we have several modern varieties; submarine projectiles, submarine rockets, automobile and controllable locomotive torpedoes. The first two varieties, though feasible, are not developed and have not yet advanced beyond the experimental stage. Of the automobile, we have the Whitehead, Swartzkopf and Howell. The first two are propelled by means of compressed air and an engine; the last by the stored-up energy of a heavy fly-wheel. Generally speaking, they are cigar-shaped crafts, from 10 to 18 feet long and 15 to 17 inches in diameter, capable of carrying from 75 to 250 pounds of explosive at a rate of 25 to 30 knots for 400 yards, at any depth at which they may be set. Of the controllable locomotive torpedoes, the three representative types are the Patrick, Sims and Brennan. They are in general terms cigar boats, about 40 feet long and 2 feet in diameter, carrying charges of 400 pounds of explosive. The Patrick and Sims are maintained at a constant depth under water by means of a float. The Brennan has diving rudders like a Whitehead or a Howell. The Patrick is driven by means of carbonic acid gas through an engine, and is controlled by an electric wire from shore. The Sims is driven by electricity from a dynamo on shore through a cable to an electric engine in the torpedo. The Brennan is driven and controlled by means of two fine steel wires wound on reels in the torpedo, the reels being geared to the propeller shafts. The wires are led to corresponding reels on shore, and these are rapidly revolved by means of an engine. A brake on each shore reel controls the torpedo. The speed of all these torpedoes is about 19 knots, and their effective range one mile.
A Whitehead was successfully used in the Turco-Russian war of 1877. The Turkish vessel previously mentioned was sunk by one.
Blasting gelatine, dynamite and gun-cotton are capable of many applications to engineering purposes on shore in time of war, and in most cases they are better than powder. They received the serious attention of French engineers during the siege of Paris, and were employed in the various sorties which were made from the city, in throwing down walls, bursting guns, etc. An explosive for such purposes, and indeed for most military uses, should satisfy the following conditions:
(1) Very shattering in its effects.
(2) Insensible to shocks of projectiles.
(4) Easy and safe to manipulate.
(5) Easy to insert a fuse.
(6) Great stability at all natural temperatures and when used in wet localities.
Neither blasting gelatine, dynamite nor gun-cotton fulfills all these conditions; but they satisfy many of them and are more powerful than other substances. For the destruction of walls, trees, rails, bridges, etc., it is simply necessary to attach to them small bags of explosive, which are ignited by means of blasters' fuse and a cap of fulminate of mercury, or by an electric fuse.
We now come to the application of high explosives to warfare in the shape of bursting charges for shells. This is the latest phase of the problem, and it is undoubtedly fraught with the most important consequences to both attack and defense. Difficult as it has been to obtain an exact estimate of the force of different explosives under water, the problem is far greater out of the water and under the ordinary conditions of shell fire; the principal obstacle being in the fact that it is physically impossible to control the force of large quantities in order to measure it, and small quantities give irregular results. Theoretically, the matter has been accomplished by Berthelot, the head of the French government "Commission of Explosives," by calculating the volume of gas produced, heat developed, etc.; and this method is excellent for obtaining a fair idea of the specific pressure of any new explosive that may be brought forward, and determining whether it is worth while to investigate it further; but the explosives differ so much from each other in point of sensitiveness, weight, physical condition, velocity of explosive wave, influence of temperature and humidity, that we cannot determine from mere theoretical considerations all that we would like to know. Various methods of arriving at comparative values have been tried, but the figures are very variable, as will be seen by the following tables. Berthelot's commission, some ten years ago, exploded ten to thirty grammes of each in 300 pound blocks of lead and measured the increased size of the hole thus made. The relative result was:
No. 1 dynamite 1.0 Dry gun-cotton 1.17 Nitro-glycerine 1.20
Powder blew out and could not be measured.
Mr. R.C. Williams, at the Boston Institute of Technology, in the winter of 1888 and 1889, tried the same method, but used six grammes in forty-five pound blocks of lead. He obtained a relative result of—
No. 1 dynamite 1.0 Dry gun-cotton 1.37 Nitro-glycerine 2.51 Explosive gelatine 2.57 Forcite gelatine 2.7 Warm nitro-glycerine 2.7 Gunpowder 0.1
The powder gave great trouble in this case, also, by blowing out.
M. Chalon, a French engineer, obtained some years ago, with a small mortar, firing a projectile of thirty kilos and using a charge of ten grammes of each explosives, the following ranges:
Meters. Blasting powder 2.6 No. 1 dynamite 31.4 Forcite of 75 per cent. N.G. 43.6 Blasting gelatine 45.0
Roux and Sarran obtained by experiments in bursting small bomb shells the following comparative strengths of ranges:
Powder 1.0 Gun-cotton 6.5 Nitro-glycerine 10.0
In actual blasting work the results vary altogether with the nature of the material encountered, and with the result that is desired to be accomplished, viz., throwing out, shattering, or mere displacement.
Chalon gives for quarrying:
Powder 1 Dynamite No. 2, containing 50 per cent. nitro-glycerine 3
For open blasting:
Dynamite No. 3, containing 30 per cent. N.G. 1.0 Dynamite No. 1, containing 75 per cent. N.G. 2.5 Blasting gelatine 3.5
Dynamite No. 3, containing 30 per cent. N.G. 1 Dynamite No. 1, containing 75 per cent. N.G. 3 Explosive gelatine 19
Finally Berthelot's theoretical calculations give a specific pressure of—
Powder 1 Dynamite 13 Gun-cotton 14 Nitro-glycerine 16 Blasting gelatine 17
It will be observed that the practical results vary largely from the theoretical values, but they seem to indicate that gun-cotton and No. 1 dynamite are very nearly equal to each other, and that in the nitro-glycerine compounds, except where gun-cotton is added, the force appears to be nearly in proportion to the nitro-glycerine contained. From the foregoing it seems fair to estimate roughly the values of bursting charges of shells as follows:
Powder 1 Gun-cotton and dynamite 6 to 10 Nitro-glycerine 13 to 15 Blasting gelatine 15 to 17
Attention has been turned in Europe for more than thirty years toward firing high explosives in shells; but it is only within very late years that results have been reached which are claimed as satisfactory, and it is exceedingly difficult to obtain reliable accounts even of these. Dynamite was fired in Sweden in 1867 in small quantities, and a few years later it was fired in France. But two difficulties soon presented themselves. If the quantity of nitro-glycerine in dynamite was small, it could be fired in ordinary shells, but the effect was no better than with gunpowder. If the dynamite was stronger in nitro-glycerine, it took but a small quantity to burst the gun.
As early as 1864, dry gun-cotton was safely fired in shells in small quantities, but when a sufficient quantity to fill the shell cavity was used, the gun burst. Some few years ago it was found that if the gun-cotton was either wet or soaked in paraffin, it could be fired with safety from powder guns in ordinary shells, provided the quantity was small in proportion to the total weight of the shell—say five or six per cent. But a new difficulty arises from the fact that it breaks the shell up into very small pieces, and it is an unsettled question among artillerists whether more damage is done to an enemy by breaking a shell into comparatively large pieces and dispersing them a long distance with a bursting charge of powder, which has a propulsive force, or by breaking it with a detonating compound into fine pieces, which are not driven nearly so far. When used against troops there is also the objection to the high explosive shell that it makes scarcely any smoke in bursting, and smoke at this point is useful to the artillerist in rectifying his aim.
In the matter of shells for piercing armor, however, there are no two opinions regarding the nature of the bursting charge. To pierce modern armor at all a shell must be made of forged steel, so thick that the capacity of the cavity for the bursting charge is reduced to one-fourth or one-fifth of what it is in the common shell; the result is that a charge of powder is frequently not powerful enough to burst the shell at all; it simply blows the plug out of the filling hole in the rear. In addition it is found that in passing through armor, the heat generated is so great that the powder is prematurely ignited.
If then we can fill the small cavity in the shell with an explosive which will not ignite prematurely, and yet will burst the shell properly after it has passed through the armor, the problem will be solved. Wet or paraffined gun-cotton can be made sluggish enough to satisfy the first condition; but at present the difficulty is to make it explode at all. The more sluggish the gun-cotton, the more powerful must be the fuse exploders to detonate it, and such exploders are themselves liable to premature ignition in passing through the armor.
The Italians and Germans claim to have accomplished the desired result up to a thickness of five inches of armor; gun-cotton and fuse both working well. But the English authorities say that no one has yet accomplished it. The Austrians claim to have succeeded in this direction within the last year with a new explosive called ecrastite (supposed to be blasting gelatine combined with sulphate or hydrochlorate of ammonia, and claimed to be one and one-half times as powerful as dynamite).
With a gun of 8.24 inches caliber and an armor-piercing shell weighing 206.6 pounds, containing a bursting charge of 15.88 pounds of ecrastite, they are said to have perforated two plates four inches thick, and entered a third four-inch plate where the shell exploded. There is a weak point in this account in the fact that the powder capacity of the shell is said to be 4.4 pounds.
This amount is approximately correct, judging from our own eight-inch armor-piercing shell, but if this is true, there could not have been more than nine pounds of ecrastite in the shell instead of sixteen, or else there is an exceedingly small proportion of blasting gelatine in ecrastite, and if that is the case it is not one and one-half times as powerful as dynamite. If it is weak stuff, it is probably insensitive, and even if it were strong, one swallow does not make a summer. The English fired quantities of blasting gelatine from a two-inch Nordenfeldt gun in 1884, but when they tried it in a seven-inch gun, in 1885, they burst the gun at once.
I have only analyzed this Austrian case, because the statement is taken from this year's annual report of the Office of Naval Intelligence, which is an excellent authority, and to illustrate the fact that of the thousands of accounts, which we see in foreign and domestic newspapers, concerning the successful use of high explosives in shells, fully ninety per cent. are totally unreliable. In many cases they are in the nature of a prospectus from the inventors of explosives or methods of firing, who are aware of the fact that it is almost impossible to dispute any statements that they may choose to make regarding the power of their new compounds, and thinking, as most of them do, that power alone is required.
Referring to the qualities that I have previously cited as being required in a high explosive for military purposes, it is sooner or later found that nearly all the novelties proposed lack some of the essentials and soon disappear from the advertising world only to be succeeded by others. The most common defect is lack of keeping qualities. They will either absorb moisture or will evaporate; or further chemical action will go on among the constituents, making them dangerously sensitive or completely inert, or they will separate mechanically according to their specific gravities.
For further clearness on the subject of the shell charges which have so far been discussed, the following table is added of weight and sizes of shells for United States naval guns, with their bursting charges of powder:
6-inch com. cast steel shell 31/2 to 4 cal. long, wt. 100 lb., charge 6 lb. 8 " " " " " 250 " 141/2 lb. 10 " " " " " 500 " 27 " 12 " " " " " 850 " 45 "
ARMOR-PIERCING FORGED STEEL SHELL.
6-inch, 3 calibers long, weight 100 lb, charge 11/2 lb. 8 " " " 250 " 3 " 10 " " " 500 " 51/2 " 12 " " " 850 " 11 "
The chief efficiency of small quantities of high explosives having reduced itself to the case of armor-piercing projectiles, it next became evident that there was an entirely new field for high explosives into which powder had entered but little, and this was the introduction of huge torpedo shells, which did nor rely for their efficiency upon the dispersion of the pieces of the shell, but upon the devastating force of the bursting charge itself upon everything within the radius of its explosive effect. It is in this field that we may look for the most remarkable results, and it is here that the absolute power of the explosive thrown is of the utmost importance, provided that it can be safely used. Attention was at once turned in Europe to the manufacture of large projectiles with great capacity for bursting charges, and it has resulted in the production of a class of shells 41/2 to 6 calibers long, with walls only 0.4 of an inch thick. (If they are made thinner, they will swell and jam in the gun when fired.)
These shells are used in long guns up to 6 and 81/2 inches caliber, and in mortars up to 11.2 inches. They are made from disks of steel, 3 to 4 feet in diameter and 1 inch thick, and are forced into shape by hydraulic presses. The base is usually screwed in, but some of the German shell are made in two halves which screw together. The Italians were the first in this new field of investigation, but the Germans soon followed, and after trying various materials were at length reasonably successful with gun-cotton soaked in paraffin. Their 8.4 inch mortar shells of 5 calibers contain 42 pounds; those of 6 calibers contain 57 pounds; and the 11.2 inch mortar shells of 5 calibers contain 110 pounds.
The projectile velocity used with the mortars is about 800 f.s. The effect of these shells against ordinary masonry and earth fortifications is very great. The charge of forty-two pounds has broken through a masonry vault of three feet four inches thick, covered with two feet eight inches of cement and with three to five feet of earth over all. The shell containing fifty-seven pounds, at a range of two and one-half miles, broke through a similar vault covered with ten feet of earth; but with seventeen feet of earth the vault resisted. In 1883, experiments at Kummersdorf showed that a shell containing the fifty-seven pound charge would excavate in sand a crater sixteen feet in diameter and eight feet deep, with a capacity of twenty-two cubic yards. The Italians have had similar experiences; but it is notable that in both Germany and Italy several guns and mortars have burst. The velocity in the guns is not believed to exceed 1,200 to 1,300 f.s., and it is not thought that the quantity of gun-cotton is as great in the gun shells as in the mortars. I have lately been informed on good authority that the use of gun-cotton shells has been abandoned in the German navy as too dangerous.
The French, in their investigations in this field, found gun-cotton too inconvenient, and decided upon melenite. This substance has probably attracted more attention in the military world than all others combined, on account of the fabulous qualities that have been ascribed to it. Its composition was for a long time entirely a secret; but it is now thought to consist principally of picric acid, which is formed by the action of nitric acid upon phenol or phenyillic alcohol, a constituent of coal tar. The actual nature of melenite is not positively known, as the French government, after buying it from the inventor, Turpin, are said to have added other articles and improved it. This is probable, since French experiments in firing against a partially armored vessel, the Bellequense, developed an enormous destructive effect, while the English, who afterward bought it, conducted similar experiments against the Resistance, and obtained no better results than with powder. The proof that the Bellequense experiments were deemed of great value by the French lies in the fact that they immediately laid down a frigate—Dupuy de Lome—in which four-inch armor is used, not only on the side, but about the gun stations, to protect the men; this thickness having been found sufficient to keep out melenite shell. In most armorclads, the armor is very heavy about the vitals, but the guns are frequently much exposed.
The best authenticated composition for melenite consists of picric acid, gun cotton and gum arabic, and lately it is stated that the French have added cresilite to it. Cresilite is another product of coal tar. Melenite is normally only three times as strong as gunpowder; but it is said to owe its destructive qualities in shells to the powerful character of the exploder which ignites it. It has been known for some years that all explosives (including gunpowder) are capable of two orders of explosion according as they are merely ignited or excited by a weak fuse or as they are powerfully shocked by a more vigorous excitant. Fulminate of mercury has been found most serviceable for the latter purpose. With melenite the French have reproduced all the results that the Germans have effected with gun-cotton and have found that a shell containing 119 pounds of it will penetrate nearly ten feet of solid cement, but will not penetrate armored turrets six to eight inches thick. The French claim that melenite has an advantage over gun-cotton in not being so dangerous to handle and being insensible to shock or friction, and they have obtained a velocity of 1,300 f.s. with the 88 inch mortar and claim to have obtained 2,000 f.s. in long guns up to 62 inch caliber. However this may be, they are known to have had severe accidents at the manufactory at Belfort and at least one 56 inch gun was burst at the Bellequense experiments in firing a sixty-six pound shell containing twenty-eight pounds of melenite. The French are said to have large quantities of melenite shells in store, but they are not issued to service.
Probably one reason why we have so many conflicting yet positive accounts of great successes in Europe with torpedo shells is because each nation wishes its neighbors to think that it is prepared for all eventualities, and they are obliged to keep on hand large quantities of some explosive, whether they have confidence in it or not. Fortunately we are not so situated, but singularly enough what we have done in the field of high explosive projection has been accomplished by private enterprise, and we have attacked the problem at exactly the opposite point from which European nations have undertaken it. While they have assumed that the powder gun with its powerful and relatively irregular pressures was a necessity and have endeavored to modify the explosive to suit it, we have taken the explosive as we have found it, and have adapted the gun to the explosive. At present the prominent weapon in this new field is the pneumatic gun, but it is obvious that steam, carbonic acid gas, ammonia or any other moderate and regulatable pressure can be used as well as compressed air; it is merely a question of mechanical convenience.