Source: Results of Experiments made with the Fumific Impeller tending to supersede the Steam Engine for Navigation
Author: Alexander Gordon, Member of the Institution of Civil Engineers
Date: Feb. 10th, 1847, London, Effingham Wilson, Royal Exchange
There are two methods of moving bodies by inanimate power contained in those bodies. One is by combination of combustibles and a supporter of combustion in furnaces of boilers, for the generation of steam. The other is also by the combination of combustibles and a supporter of combustion; but it is in a rocket-case, for the generation of very elastic aeriform matter.
The first is the method known to us in locomotion, whether by water or by railway. The second method has not yet been employed as a means of intercommunication. The intimate combination of the combustibles and the supporter of combustion in a rocket-case, has been admirably adapted for the projection of signals and of missiles of war, but is not yet adapted to the necessities of the carrying trade, where much safer mechanical and chemical actions are required.
The locomotive powers, both of the steam-engine and of the rocket, is derived solely from the action or agency of heat, and I request especial attention to the two methods by which the same power of heat has been used. That of steam is the result of a transmission of part of the heat from the fire to the water, and thence through the elegant apparatus which has dignified the names of Watt and of Trevethic.
The locomotive power of the rocket is had by the direct application of the hot products of combustion themselves, for impelling these bodies in air or in water, without the intervention of machinery; and, let it be observed, that it is by making use of all the heat generated and all the heated bodies put into motion. It is impossible to deny that heat is the source of power in the instances referred to.
The steam-engine owes its general adoption to the beauty of its mechanical adaptations to the necessities of tender and easily condensed steam, which mechanical adaptations are of no use when permanently elastic, heat-carrying bodies are to be employed instead of steam.
From time to time, the law of the specific heats of water and of air, which is so decidedly in favour of the latter (see Appendix A), has led men of high mechanical attainments to venture from what may be called the steam-channel, and to attempt the formation of a prime mover, by bringing the improvements of the steam-engine to subserve the application of air heated by transmission, or the application of the products immediately obtained from combustion, and thus to actuate some modification or imitation of the steam engine.
They took the steam-engine as their prototype; I take the rocket as mine. They differed from their pattern by changing the elastic medium only; I differ from my pattern by changing the supply of the support for combustion and of the application of the power when generated. The particulars are described in the specification of my patent, of date 3rd March, 1845; also in the “Mechanics' Magazine,” October 1845, and in “A Description of the Fumific Impeller,” which was published by Dalton.
It is only necessary to say here, that machinery, whatever may be its beauty, cannot add to the power of heat as the prime mover. On the contrary, it always wastes part of the power by non-appropriation, friction, radiation, and leakage.
The power of a steam-engine is obviously more in the steam pipe which conveys the steam from the boiler to the engine, than in the engine, and it is more in the furnace than any where else. It is really in the chemical action of combustion in the furnace, but we find the only available part of it in the steam-pipe; the engine, machinery, and paddles of a steam-vessel being nothing more than the arrangement necessary in applying steam to operate indirectly upon the water, and thus to impel the ship in her desired course. In using steam, we must operate indirectly upon the water, because all attempts made for applying the rush of steam along the steam-pipe under and directly upon water in the manner of a rocket, have failed, by reason of the condensation of that steam whenever it comes into contact with the water upon which its power was wished to act.
It is of the utmost importance to the right understanding of this paper, that these facts be kept in mind.
In a steam-ship making a passage across the North Atlantic Ocean, the power of heat used for impelling her, are the currents of steam of a certain pressure rushing along the two main steam pipes from the boilers, which, multiplied into the sum of the areas of these pipes and by the pressure (adding the value of the vacuum), constitute and express the power of heat which impels her. These currents of power are in constant flow, and correspond in their velocity to the ship's rate of going.
We have just seen that these streams of steam-power are not disposable for use by directing them at once against the sea. We shall now observe that, what cannot be done by steam, can be done by hot air, or by the hot products of combustion; currents of which may be discharged at once under water backward to impel the vessel forward, or forward when the vessel is to be impelled backward. These currents being permanently elastic, do not collapse as steam does; and, being tenacious of their heat, the necessary impact can be had to move the ship in her required course.
The Congreve rocket is impelled without any machinery and without steam. The impelling composition consisting of combustibles and a supporter of combustion, selected, proportioned, and intimately mixed for augmenting volume by a fresh arrangement of particles, and for producing the aeriform fluid at a high temperature. There is a mass of this intimate mixture within the case, which, independent of any oxygen from the atmosphere, forms, in a few seconds, a fumific impulse, which discharges itself through the “throat” of the rocket.
The composition produces 500 times its bulk of gas at the mean temperature of the air, whilst its elastic force is increased by the heat to not less than 2000. One of the largest rockets now used in the English service, for either bombardment or field-work, is called a 32-pounder Congreve rocket. The entire weight, with composition, clay, iron, stick, and the gunpowder for bursting the cast-iron head at the end of the range, is 33 lbs. The length of the head and case is 2 feet, the external diameter 3 7/10 inches. The rocket-composition occupies an interior cylindrical space of 3.5 inches diameter, x 21 inches long; and this composition weighs 10 lbs.
The combustion of this 10 lbs. of composition, and its rush a tergo, projects the rocket over a base line of 3450 yards (or only 70 yards short of two miles) in seven seconds. Here, then, is an instance of much higher velocity than that of any machinery or implement, not even excepting a cannon-ball.
We need not discuss here the rocket's flight (see Appendix B). The fact of its flight in the air, and of its passage through water and even through loose sand, is enough for my purpose of shewing the direct action or reaction of the hot products of combustion for navigation.
Having constructed a small model-boat with a brass rocket case in the keel, I made a course of rocket experiments with different compositions. The result of several experiments may be stated as follows: the model-boat displaced 15 lbs. weight of water, and a common 1 ounce rocket, inflamed under water, impelled this boat 30 feet in 4 seconds, or at a rate rather over 5 miles per hour.
In all of these small experiments a perfect impact was obtained on the instant of inflammation, and so great was this, which may be called the initial velocity, that the small vessel skimmed the surface with less draft of water than she had when at rest.
Being thus satisfied that, if I could economically apply a continuous stream or streams of hot products of combustion of requisite pressure, and at a velocity little above the speed required of the ship, I should probably supersede the steam-engine for purposes of navigation, I proceeded with the following experiment.
The approval of some friends, and also of some who to me were strangers, was encouraging. These were gentlemen of high chemical and philosophical attainments. Among the latter was Captain Sir Thomas Hastings, R.N., whose extensive and intimate knowledge of what is now done and may be done in gunnery and rocket practice particularly fitted him to express an opinion upon the proposition; and I must not omit the name of Professor Baden Powell, of Oxford.
To these two gentlemen in particular I am much indebted for the unasked and unexpected encouragement they have given me in a matter where engineers have been unconcerned, or unable to appreciate the invention, or unwilling to be troubled in the matter.
The difficulty I have had in convincing any steam-engine men has been very great. They bring everything to that machine as the standard of excellence, and seem (with very few exceptions) to disbelieve, practically, that heat is the source of power in the machine which they idolise, and that the same heat is available, independent of water, steam, and the numerous elegant contrivances and appliances which are rendered necessary for using the tender and easily condensed stream.
Those engineers and steam-boat parties who could believe in the possibility of obtaining power by the hot products of combustion, directly applied as I propose, could not see how a sufficient impact could be obtained to impel the boat in her course with sufficient economy. Therefore, I determined to demonstrate the fact at once by an experiment on a sufficiently large scale.
The experiments of Mr. Ericcson, of Mr. Robert Stein, of Mr. Sterling, and of Sir George Cayley, shewed how the continuous production or presentation of hot air could be relied upon.
The proposers of hot-air engines have taken the steam-engine, subsequent to the discoveries of Newcomen, as their model, whilst they should have reverted at once to the engines of Savery and of Papin. They should be referred to the Marquis of Worcester's scantlings, and even to the smokejack of Hieronymus Cardan.
The Marquis of Worcester employed the pressure of steam to act at once and directly upon the water which he desired to put into motion. Savery, also, used steam in direct connexion with the water. Dennis Papin improved on these by interposing a loose floating piston between the steam and the water to be moved.
Now, had any one of these latter used, instead of steam, the hot products of combustion from a close furnace, the steam-engine would not now be the only available inanimate artificial power in use for such purposes as raising water, and for navigation.
The streams of hot products of combustion from Sir George Cayley's close furnaces to his engine cylinders were as regular and as powerful as the stream of steam along any main steam-pipe.
All previous attempts to make hot-air engines have been by following the form of the steam-engine. I attempted to make close furnaces imitate a rocket, and the following will shew with what Success :
Into a boat 26 feet long and 4.5 broad, I fitted a close furnace, or retort, and a common small forge bellows. The accompanying drawing exhibits the whole arrangement. The close furnace being opened at top and at bottom, an intense fire was got up; the bonnets at top and at bottom were then luted and fitted tight.
The upper or reservoir portion of the bellows was not used. Each stroke of the lower portion of the bellows passed air through the close fire for the hot products of combustion to rush out against the water, as shewn at C. The boat, when tried with this apparatus, weighed in all 4375 lbs., in other words, that weight of water was displaced by her flotation when the discharge-pipe C was immersed 12 inches.
Each stroke of the portable forge-bellows sent cold air into the close furnace. The appropriation of oxygen to support combustion was instantaneous; and the heating of all the aeriform body which passed off by C was also instantaneous. The products of combustion, almost altogether aeriform, but also occasionally mixed with smoke, dust, and ashes, rushed out (at a temperature of 800° or 900°) by the pipe C, which was three inches in diameter.
Not to be tedious; A narration of mistakes and disappointments may be avoided, and the action or reaction of the arrangement shewn on the drawing, explained. A valve being, of course, in the cold-air pipe, between the bellows and the furnace (and, as has been said, the upper chamber of the bellows inoperative), I sent a succession of blasts into the bottom of the furnace, and, consequently, up through the intense fire, to find its way out under water by the pipe C.
The first blast, by one man, always started the boat (weighing nearly 2 tons) from a state of rest 3 feet in 2 seconds; and I believe that no two men, with oars or sculls, with all the advantage of their flexor and extensor muscles, could do more. And neither paddle-wheels nor the Archimedian screw can start the same weight into such motion in the same time.
I several times repeated these experiments upon what may be called the initial velocity had by the first blast, or jet, or shot. The leaky and sinking condition of the old boat, broken and out of shape by liftings by a crane, prevented my continuing the course of experiments so far as to be able to take her rate, consumption of fuel, and the line-haulage power necessary for the same rate. These latter points will be more fully illustrated when I shall have fitted a larger vessel with several close furnaces, and with blowers either actuated by a steam-engine, or kept in motion by part of the power of the vessel's own velocity through the water.
Enough has, however, been done to shew the value of the discharge proposed. There are several chemical means for increasing the power and rapidity of the currents, for starting suddenly, or for increasing the ship's rate in cases of emergency. A succession of such discharges will give the required accellerated velocity, and the shipwright can arrange to have them in the bilges, after-body, or other parts of a ship, so that one or more discharge-pipes may deliver their power backward to send the ship a-head; or forward to send her astern; or backward on one side, and forward on the other side; to bring the ship about, or direct her head to any given point.
The fire, and one man blowing air, has, we have seen above, done the work of two men. From which it follows, that suitable close furnaces, blown by a 50-horse-power steam-engine, will do the work of 100 horses in impelling the vessel; and so on in proportion.
Even let a sceptical reader doubt my accuracy as to the one man's power being, with the fire, equal to two men's power in rowing, let him even insist that one man with oars could do as much as this man did with the products of combustion, such a reader cannot reasonably deny that shipshape vessels can be impelled, without smoke, chimnies, paddles, or screws, by the mere discharge of the hot products of combustion, whilst the blowing is effected by a steam-engine, which may be worked from a boiler or boilers, which may be made to surround and embrace the close furnaces.
I may now anticipate the possibility of expression of any doubt upon the economy and safety of impelling vessels by the direct application of the hot products of combustion.
The economy will be greater than in the steam-engine for several reasons:
Because the expansion of a gaseous body by heat is greater than that of steam: Because 1 lb. of fuel will raise 7 8/10 lbs. of water 1212°, or 19 lbs. of water 480°; and 1 lb. of the same fuel raises 29 lb. of air 1212°, or 74 lbs. of air 480° (see Appendix C):
Because the steam-engine does not and cannot use all the heat generated in the furnaces; 500° pass off at the top of the steam boat chimney, and what heat the engine can use has to overcome the friction, the drag of the air-pump, the feeds, waste water, &c.; whilst by using the hot products of combustion, as shown in this paper, all the heat of the furnaces is applied; there is little friction but that of the air-pumps or blowers, and only half the power obtained in the furnace is required to work the blowers.
Another feature in the proposed mode of impulsion is that, whilst the working economy of a steam-engine depends upon slow combustion in the furnaces, and a uniform and limited speed of the machinery, the working economy of the proposed system is rather promoted by rapidity of combustion, and is capable of being worked slowly by gentle currents, or jets, or puffs; or fast by roaring blasts, there being no machinery which can be injured.
The safety of the proposed impulse is not affected by a store of power in many tons of boiling water ready to burst into steam ; it may be assured by their being no store of power whatever.
Perhaps this mode of impelling bodies is the nearest approach to the variable intensities of animal power, where the combinations of oxygen and carbon are more slow or more rapid as the same size of lungs may require it to be for slow motion or for the fleetest course of the animal.