Chapter 4

The former motion increases in rapidity, while the latter decreases; therefore at some point they will become equal in velocity, and the openings of the two ports will be the same; and the question is, Will this maximum effective port area give a sufficient supply of steam?

This diagram is the same as the one actually used in the engine under consideration, in which it was required to follow a minimum distance of 5 inches in the stroke of 22. Under these conditions it is found that the actual port opening for that point of cutting off is three-fifths of that allowed when following full stroke, whereas the speed of the piston at the time when this maximum opening occurs is less than half its greatest speed.

This, it would seem, is ample; but we now find the eccentric, K, no longer in the right position for backing; when the engine is reversed it ought to be at, P, the angle, POL, being equal to the angle, KOL. By leaving it free, therefore, to move upon the shaft, by the means above described, through the angle, KOP, the desired object is accomplished. The real eccentricity is now reduced in the proportion of OK to OH, while the lengths of the cut-off valves, and what is equally important, their travel over the back of the main valve, are reduced in the proportion of CK to CH, in this instance nearly one-half; a gain quite sufficient to warrant the adoption of the expedient.

The third, and perhaps the most notable, peculiarity is the manner of suspending and operating the main link. As before stated, this link is used only for reversing, and is therefore always in "full gear" in one direction or the other; and the striking feature of the arrangement here used is that, whether going ahead or backing, there is _no slipping of the link upon the link block_.

The link itself is of the simplest form, being merely a curved flat bar, L, in which are two holes, A and B (Fig. 7), by which the link is hung upon the pins, which project from the sides of the eccentric rods at their upper ends.

This is most clearly shown in Fig. 8, which is a top view of the reversing gear. The link block is a socket, open on the side next to the eccentric rods, but closed on the side opposite, from which projects the journal, J, as shown in Fig. 9, which is a vertical section by the plane, XY. This journal turns freely in the outer end of a lever, M, which transmits the reciprocating motion to the valve, through the rock-shaft, O, and another lever, N. Connected with the lever, M, by the bridge-piece, K, and facing it, is a slotted arm, G, as shown in the end view, Fig. 10. The center line of this slot lies in the plane which contains the axes of the journal, J, and of the shaft, O.

A block, E, is fitted to slide in the slotted arm, G; and in this block is fixed a pin, P. A bridle-rod, R, connects P with the pin, A, of one of the eccentric-rods, prolonged for that purpose as shown in Fig. 8; and a suspension-rod, S, connects the same pin, P, with the upper end of the reversing lever, T, which is operated by the worm and sector. The distance, JO, in Fig. 10, or in other words the length of the lever, M, is precisely equal to the distance, AB, in Fig. 7, measured in a right line; and the rods, R and S, from center to center of the eyes, are also each of precisely this same length. Further, the axis about which the reversing lever, T, vibrates is so situated that when that lever, as in Fig 11, is thrown full to the left, the pin in its upper end is exactly in line with the rock-shaft, O.

When the parts are in this position, the suspension-rod, S, the arm, G, and the lever, M, will be as one piece, and their motions will be identical, consisting simply of vibration about the axis of the rock-shaft, O. The motion of the lever, M, is then due solely to the pin, B, which is in this case exactly in line with the journal, J, so that the result is the same as though this eccentric rod were connected directly to the lever; and the pin, P, being also in line with B and J, and kept so by the suspension-rod, S, it will be seen that the bridle-rod, R, will move with the link, L, as though the two were rigidly fastened together.

When the reversing lever, T, is thrown full to the right, as in Fig. 12, the pin, P, is drawn to the inner end of the slot in the arm, G, and is thus exactly in line with the rock-shaft, O. The suspension-rod, S, will, therefore, be at rest; but the pin, A, will have been drawn, by the bridle-rod, R, into line with the journal, J, and the bridle-rod itself will now vibrate with the lever, M, whose sole motion will be derived from the pin, A.

There is, then, no block slip whatever when the link thus suspended and operated is run in "full gear," either forward or backward.

If this arrangement be used in cases where the link is used as an expansion device, there will be, of course, some block slip while running in the intermediate gears. But even then, it is to be observed that the motion of the pin, A, relatively to the rocker arm is one of vibration about the moving center, J; and its motion relatively to the sliding block, E, is one of vibration about the center, P, whose motion relatively to E is a small amount of sliding in the direction of the slot, due to the fact that the rocker arm itself, which virtually carries the block, E, vibrates about O, while the suspension-rod, S, vibrates about another fixed center. It will thus be seen that, finally, the block slip will be determined by the difference in curvature of arcs _which curve in the same direction_, whether the engine be running forward or backward; whereas in the common modes of suspension the block slip in one direction is substantially the half sum of the curvatures of two arcs curving in opposite directions.

Consequently it would appear that the average action of the new arrangement would be at least equal to that of the old in respect to reducing the block slip when running in the intermediate gears, while in the full gears it entirely obviates that objectionable feature.

* * * * *

THE NEW RUSSIAN TORPEDO BOAT, THE POTI.

The Russian government has just had built at the shipyards of Mr. Normand, the celebrated Havre engineer, a torpedo boat called the Poti, which we herewith illustrate. This vessel perceptibly differs from all others of her class, at least as regards her model. Her extremities, which are strongly depressed in the upperworks, and the excessive inclination of her sides, give the boat as a whole a certain resemblance to the rams of our navy, such as the Taureau and Tigre.

A transverse section of the Poti approaches an ellipse in shape. Her water lines are exceedingly fine, and, in point of elegance, in no wise cede to those of the most renowned yachts. The vessel is entirely of steel, and her dimensions are as follows: Length, 28 meters; extreme breadth, 3.6 meters; depth, 2.5 meters; draught, 1.9 meters; displacement, 66 tons. The engine, which is a compound one, is of 600 H.P. The minimum speed required is 18 knots, or 33-34 meters, per hour, and it will probably reach 40 kilometers.

The vessel will be armed with 4 Whitehead torpedoes of 5.8 m., and 2 Hotchkiss guns of 40 cm. Her supply of coal will be sufficient for a voyage of 1000 nautical miles at a speed of 11 knots.--_L'Illustration_.

* * * * *

A NEW STEAMER PROPELLED BY HYDRAULIC REACTION.

The oar, the helix, and the paddle-wheel constitute at present the means of propulsion that are exclusively employed when one has recourse to a motive power for effecting the propulsion of a boat. The sail constitutes an entirely different mode, and should not figure in our enumeration, considering the essentially variable character of the force utilized.

In all these propellers, we have only an imitation, very often a rude one, of the processes which nature puts in play in fishes and mollusks, and the mode that we now wish to make known is without contradiction that which imitates these the best.

Hydraulic propulsion by reaction consists, in principle, in effecting a movement of boats, by sucking in water at the bow and forcing it out at the stern. This is a very old idea. Naturalists cite whole families of mollusks that move about in this way with great rapidity. It is probable that such was the origin of the first idea of this mode of operating. However this may be, as long ago as 1661 a patent was taken out in England, on this principle, by Toogood & Hayes. After this we find the patents of Allen (1729) and Rumsay (1788). In France, Daniel Bernouilli presented to the Académic des Sciences a similar project during the last century.

Mr. Seydell was the first to build a vessel on this principle. This ship, which was called the Enterprise, was of 100 tons burden, and was constructed at Edinburgh for marine fishery. The success of this was incomplete, but it was sufficient to show all the advantage that could be got from the idea. Another boat, the Albert, was built at Stettin, after the same type and at about the same epoch; and the question was considered of placing a reaction propeller upon the Great Eastern.

About 1860 the question was taken up again by the house of Cokerill de Seraing, which built the Seraing No. 2, that did service as an excursion boat between Liége and Seraing. The propeller of this consisted of a strong centrifugal pump, with vertical axis, actuated by a low pressure engine. This pump sucked water into a perforated channel at the bottom of the boat, and forced it through a spiral pipe to the propelling tubes. These latter consisted of two elbowed pipes issuing from the sides of the vessel and capable of pivoting in the exhaust ports in such a way as to each turn its mouth downward at will, backward or forward. The water expelled by the elbowed pipes reacted through pressure, as in the hydraulic tourniquet of cabinets of physics, and effected the propulsion of the vessel. Upon turning the two mouths of the propelling tubes backward, the boat was thrust forward, and, when they were turned toward the front, she was thrust backward. When one was turned toward the front and the other toward the stern, the boat swung around. Finally, when the two mouths were placed vertically the boat remained immovable. All the evolutions were easy, even without the help of the rudder, and the ways in which the propelling tubes could be placed were capable of being varied _ad infinitum_ by a system of levers.

The Seraing No. 2 had an engine of a nominal power of 40 horses, and took on an average 30 minutes to make the trip, backward and forward, of 85 kilometers, with four stoppages.

The success obtained was perfect, and the running was most satisfactory. It was remarked, only, that from the standpoint of effective duty it would have been desirable to reduce the velocity of the water at its exit from the propellers.

Mr. Poillon attributes the small effective performance to the system employed for putting the water in motion. At time of Mr. Seraing's experiments, only centrifugal force pumps were known, and the theoretic effective duty of these, whatever be the peculiar system of construction, cannot exceed 66 per cent., and, in practice, falls to 40 or 50 per cent. in the majority of cases.

It is probable, then, that in making use of those new rotary pumps where effective duty reaches and often exceeds 80 per cent., we might obtain much better results, and it is this that justifies the new researches that have been undertaken by Messrs. Maginot & Pinette, whose first experiments we are about to make known.

In order to have it understood what interest attaches to these researches, let us state the principal advantages that this mode of propulsion will have over the helix and paddle wheel: The width of side-wheel boats will be reduced by from 20 to 30 per cent., and the draught of water will be diminished in screw steamers to that of the hull itself; the maneuver in which the power of the engine might be directly employed will be simplified; a machine will be had of a sensibly constant speed, and without change in its running; the production of waves capable of injuring the banks of canals will be avoided; the propeller will be capable of being utilized as a bilge pump; all vibration will be suppressed; the boat will be able to run at any speed under good conditions, while the helix works well only when the speed of the vessel corresponds to its pitch; it will be possible to put the propelling apparatus under water; and, finally, it will be possible to run the pump directly by the shaft of the high speed engine, without intermediate gearing, which is something that would prove a very great advantage in the case of electric pleasure boats actuated by piles and accumulators and dynamo-electric machines.

We now arrive at Messrs. Maginot & Pinette's system, the description of which will be greatly facilitated by the diagram that accompanies this article. The inventors have employed a boat 14 meters in length by 1.8 m. in width, and 65 centimeters draught behind and 32 in front. The section of the midship beam is 70 square decimeters, and that of the exhaust port is 4. At a speed of 2.2 meters per second the tractive stress, K, is from 10 to 11 kilogrammes. At a speed of 13.5 kilometers per hour, or 3.75 meters per second, the engine develops a power of 12 horses. The piston is 19 centimeters in diameter, and has a stroke of 15 centimeters. The shaft, in common, of the pump and engine makes 410 revolutions per minute. It will be seen from the figure that suction occurs at the lower part of the hull, at A, and that the water is forced out at B, to impel the vessel forward. C and C' are the tubes for putting the vessel about, and DD' the tubes for causing her to run backward. Owing to the tubes, C, C', the rudder has but small dimensions and is only used for _directing_ the boat. The vessel may be turned about _in situ_ by opening one of the receiving tubes, according to the side toward which it is desired to turn.

This boat is as yet only in an experimental state, and the first trials of her that have recently been made upon the Saône have shown the necessity of certain modifications that the inventors are now at work upon.--_La Nature_.

* * * * *

A NEW FORM OF FLEXIBLE BAND DYNAMOMETER.

[Footnote: Read before Section G of British Association.]

By Professor W.C. UNWIN.

In the ordinary strap dynamometer a flexible band, sometimes carrying segments of wood blocks, is hung over a pulley rotated by the motor, the power of which is to be measured. If the pulley turns with left-handed rotation, the friction would carry the strap toward the left, unless the weight, Q, were greater than P. If the belt does not slip in either direction when the pulley rotates under it, then Q-P exactly measures the friction on the surface of the pulley; and V being the surface velocity of the pulley (Q-P)V, is exactly the work consumed by the dynamometer. But the work consumed in friction can be expressed in another way. Putting [theta] for the arc embraced by the belt, and [mu] for the coefficient of friction,

Q/P = [epsilon]^{[mu]^{[theta]}},

or for a given arc of contact Q = [kappa]P, where [kappa] depends only on the coefficient of friction, increasing as [mu] increases, and _vice versa_. Hence, for the belt to remain at rest with two fixed weights, Q and P, it is necessary that the coefficient of friction should be exactly constant. But this constancy cannot be obtained. The coefficient of friction varies with the condition of lubrication of the surface of the pulley, which alters during the running and with every change in the velocity and temperature of the rubbing surfaces. Consequently, in a dynamometer in this simple form more or less violent oscillations of the weights are set up, which cannot be directly controlled without impairing the accuracy of the dynamometer. Professors Ayrton and Perry have recently used a modification of this dynamometer, in which the part of the cord nearest to P is larger and rougher than the part nearest to Q. The effect of this is that when the coefficients of friction increase, Q rises a little, and diminishes the amount of the rougher cord in contact, and _vice versa_. Thus reducing the friction, notwithstanding the increase of the coefficient. This is very ingenious, and the only objection to it, if it is an objection, is that only a purely empirical adjustment of the friction can be obtained, and that the range of the adjustment cannot be very great. If in place of one of the weights we use a spring balance, as in Figs. 2 and 3, we get a dynamometer which automatically adjusts itself to changes in the coefficient of friction.

For any increase in the coefficient, the spring in Fig. 2 lengthens, Q increases, and the frictional resistance on the surface of the pulley increases, both in consequence of the increase of Q, which increases the pressure on the pulley, and of the increase of the coefficient of friction. Similarly for any increase of the coefficient of friction, the spring in Fig. 3 shortens, P diminishes, and the friction on the surface of the pulley diminishes so far as the diminution of P diminishes the normal pressure, but on the whole increases in consequence of the increase of the coefficient of friction. The value of the friction on the surface of the pulley, however, is more constant for a given variation of the frictional coefficient in Fig. 3 than in Fig. 2, and the variation of the difference of tensions to be measured is less. Fig. 3, therefore, is the better form.

A numerical calculation here may be useful. Supposing the break set to a given difference of tension, Q-P, and that in consequence of any cause the coefficient of friction increases 20 per cent., the difference of tensions for an ordinary value of the coefficient of friction would increase from 1.5 P to 2 P in Fig. 2, and from 1.5 P to 1.67 P in Fig. 3. That is, the vibration of the spring, and the possible error of measurement of the difference of tension would be much greater in Fig. 2 than in Fig. 3. It has recently occurred to the author that a further change in the dynamometer would make the friction on the pulley still more independent of changes in the coefficient of friction, and consequently the measurement of the work absorbed still more accurate. Suppose the cord taken twice over a pulley fixed on the shaft driven by the motor and round a fixed pulley, C.

For clearness, the pulleys, A B, are shown of different sizes, but they are more conveniently of the same size. Further, let the spring balance be at the free end of the cord toward which the pulley runs. Then it will be found that a variation of 20 per cent. in the friction produces a somewhat greater variation of P than in Fig. 3. But P is now so much smaller than before that Q-P is much less affected by any error in the estimate of P. An alteration of 20 per cent. in the friction will only alter the quantity Q-P from 5.25 P to 5.55 P, or an alteration of less than 6 per cent.

To put it in another way, the errors in the use of dynamometer are due to the vibration of the spring which measures P, and are caused by variations of the coefficient of friction of the dynamometer. By making P very much smaller than in the usual form of the dynamometer, any errors in determining it have much less influence on the measurement of the work absorbed. We may go further. The cord may be taken over four pulleys; in that case a variation of 20 per cent. in the frictional coefficient only alters the total friction on the pulleys 1¼ percent. P is now so insignificant compared with Q that an error in determining it is of comparatively little consequence.

The dynamometer is now more powerful in absorbing work than in the form Fig. 3. As to the practical construction of the brake, the author thinks that simple wires for the flexible bands, lying in V grooves in the pulleys, of no great acuteness, would give the greatest resistance with the least variation of the coefficient of friction; the heat developed being in that case neutralized by a jet of water on the pulley. It would be quite possible with a pulley of say 3 feet diameter, and running at 50 feet of surface velocity per second, to have a sufficiently flexible wire, capable of carrying 100 lb. as the greater load, Q. Now with these proportions a brake of the form in Fig. 3 would, with a probable value of the coefficient of friction, absorb 6 horse power. With a brake in the form Fig. 4, 8.2 horse power would be absorbed; and with a brake in the form Fig. 5, 8.8 horse power would be absorbed. But since it would be easy to have two, three, or more wires side by side, each carrying its load of 100 lb., large amounts of horsepower could be conveniently absorbed and measured.

* * * * *

SEE'S GAS STOVE.

This stove consists of two or more superposed pipes provided with radiators. A gas burner is placed at the entrance of either the upper or lower pipe, according to circumstances. The products of combustion are discharged through a pipe of small diameter, which may be readily inserted into an already existing chimney or be hidden behind the wainscoting. The heat furnished by the gas flame is so well absorbed by radiation from the radiator rings that the gases, on making their exit, have no longer a temperature of more than from 35 to 40 degrees.

The apparatus, which is simple, compact, and cheap, is surrounded on all sides with an ornamented sheet iron casing. Being entirely of cast iron, it will last for a long time. The joints, being of asbestos, are absolutely tight, so as to prevent the escape of bad odors. The water due to the condensation of the gases is led through a small pipe out of doors or into a vessel from whence it may evaporate anew, so as not to change the hygrometric state of the air. The consumption of gas is very small, it taking but 250 liters per hour to heat a room of 80 cubic meters to a temperature of 18° C.--_Revue Industrielle_.

* * * * *

The number of persons killed by wild animals and snakes in India last year was 22,125, against 21,427 in the previous year, and of cattle, 46,707, against 44,669. Of the human beings destroyed, 2,606 were killed by wild animals, and 19,519 by snakes. Of the deaths occasioned by the attacks of wild animals, 895 were caused by tigers, 278 by wolves, 207 by leopards, 356 by jackals, and 202 by alligators; 18,591 wild animals and 322,421 snakes were destroyed, for which the Government paid rewards amounting to 141,653 rupees.

* * * * *

RECTIFICATION OF ALCOHOL BY ELECTRICITY.

Some time ago, Mr. Laurent Naudin, it will be remembered,[1] devised a method of converting the aldehydes that give a bad taste and odor to impure spirits, into alcohol, through electrolytic hydrogen, the apparatus first employed being a zinc-copper couple, and afterward electrolyzers with platinum plates.

[Footnote 1: See SCIENTIFIC AMERICAN SUPPLEMENT of July 29, 1882, p. 5472.]