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SCIENTIFIC AMERICAN SUPPLEMENT NO. 441
NEW YORK, JUNE 14, 1884
Scientific American Supplement. Vol. XVII., No. 441.
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. CHEMISTRY AND METALLURGY.—On Electrolysis.—Precipitation of lead, thallium, silver, bismuth, manganese, etc.—By H. SCHUCHT
The Electro-Chemical Equivalent of Silver
Zircon.—How it can be rendered soluble.—By F. STOLBA
A New Process for Making Wrought Iron Directly from the Ore. —Comparison with other processes.—With descriptions and engravings of the apparatus used
Some Remarks on the Determination of Hardness in Water
On the changes which Take Place in the Conversion of Hay into Ensilage.—By F.J. Lloyd
II. ENGINEERING AND MECHANICS.—Faure's Machine for Decorticating Sugar Cane.—With full description and 13 figures
The Generation of Steam and the Thermodynamic Problems Involved.—By WM. ANDERSON.—Apparatus used in the experimental determination of the heat of combustion and the laws which govern its development.—Ingredients of fuel.—Potential energy of fuel.—With 7 figures and several tables
Planetary Wheel Trains.—Rotations of the wheels relatively to the train arm.—By Prof. C.W. MACCORD
The Pantanemone.—A New Windwheel.—1 engraving
Relvas's New Life Boat.—With engraving
Experiments with Double Barreled Guns and Rifles. —Cause of the divergence of the charge.—4 figures
Improved Ball Turning Machine.—1 figure
Cooling Apparatus for Injection Water.—With engraving
Corrugated Disk Pulleys.—1 engraving
III. TECHNOLOGY.—A New Standard Light
Dr. Feussner's New Polarizing Prism.—Points of difference between the old and new prisms.—By P.R. SLEEMAN
Density and Pressure of Detonating Gas
IV. ELECTRICITY, LIGHT, ETC.—Early History of the Telegraph. —Pyrsia, or the system of telegraphy among the Greeks. —Communication by means of characters and the telescope. —Introduction of the magnetic telegraph between Baltimore and Washington
The Kravogl Electro Motor and its Conversion Into a Dynamo Electric Machine.—5 figures
Bornhardt's Electric Machine for Blasting in Mines. —15 figures
Pritchett's Electric Fire Alarm.—1 figure
A Standard Thermopile
Telephonic Transmission without Receivers.—Some of the apparatus exhibited at the annual meeting of the French Society of Physics.—Telephonic transmission through a chain of persons
Diffraction Phenomena during Total Solar Eclipses.—By G.D. Hiscox
V. BOTANY AND HORTICULTURE.—Gum Diseases in Trees.— Cause and contagion of the same
Drinkstone Park.—Trees and plants cultivated therein.— With 2 engravings
VI. MEDICINE AND HYGIENE.—Miryachit.—A newly-discovered disease of the nervous system, and its analogues.—By WM. A. HAMMOND
VII. MISCELLANEOUS.—Turkish Baths for Horses.—With diagram.
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FAURE'S MACHINE FOR DECORTICATING SUGAR-CANE.
The object of the apparatus shown in the accompanying engraving is to effect a separation of the tough epidermis of the sugar-cane from the internal spongy pith which is to be pressed. Its function consists in isolating and separating the cells from their cortex, and in putting them in direct contact with the rollers or cylinders of the mill. After their passage into the apparatus, which is naturally placed in a line with the endless chain that carries them to the mill, the canes arrive in less compact layers, pass through much narrower spaces, and finally undergo a more efficient pressure, which is shown by an abundant flow of juice. The first trials of the machine were made in 1879 at the Pointe Simon Works, at Martinique, with the small type that was shown at the Paris Exhibition of 1878. These experiments, which were applied to a work of 3,000 kilos of cane per hour, gave entire satisfaction, and decided the owners of three of the colonial works (Pointe Simon, Larcinty, and Marin) to adopt it for the season of 1880.
The apparatus is shown in longitudinal section in Fig. 1, and in plan in Fig. 2.
Fig. 3 gives a transverse section passing through the line 3-4, and Fig. 4 an external view on the side whence the decorticated canes make their exit from the apparatus.
The other figures relate to details that will be referred to further along.
The Decorticating Cylinder.—The principal part of the apparatus is a hollow drum, A, of cast iron, 430 mm. in internal diameter by 1.41 m. in length, which is keyed at its two extremities to the shaft, a. Externally, this drum (which is represented apart in transverse section in Fig. 5) has the form of an octagonal prism with well dressed projections between which are fixed the eight plates, C, that constitute the decorticating cylinder. These plates, which are of tempered cast iron, and one of which is shown in transverse section in Fig. 7, when once in place form a cylindrical surface provided with 48 helicoidal, dentate channels. The length of these plates is 470 mm. There are three of them in the direction of the generatrices of the cylinder, and this makes a total of 24. All are strengthened by ribs (as shown in Fig. 8), and each is fixed by 4 bolts, c, 20mm. in diameter. The pitch of the helices of each tooth is very elongated, and reaches about 7.52 m. The depth of the toothing is 18 mm.
Frame and Endless Chain.—The cylinder thus constructed rotates with a velocity of 50 revolutions per minute over a cylindrical vessel, B', cast in a piece with the frame, B. This vessel is lined with two series of tempered cast iron plates, D and D', called exit and entrance plates, which rest thereon, through the intermedium of well dressed pedicels, and which are held in place by six 20-millimeter bolts. Their length is 708 mm. The entrance plates, D, are provided with 6 spiral channels, whose pitch is equal to that of the channels of the decorticating cylinder, C, and in the same direction. The depth of the toothing is 10 mm.
The exit plates, D', are provided with 7 spiral channels of the same pitch and direction as those of the preceding, but the depth of which increases from 2 to 10 mm. The axis of the decorticating cylinder does not coincide with that of the vessel, B', so that the free interval for the passage of the cane continues to diminish from the entrance to the exit.
The passage of the cane to the decorticator gives rise to a small quantity of juice, which flows through two orifices, b', into a sort of cast iron trough, G, suspended beneath the vessel. The cane, which is brought to the apparatus by an endless belt, empties in a conduit formed of an inclined bottom, E, of plate iron, and two cast iron sides provided with ribs. These sides rest upon the two ends of the vessel, B', and are cross-braced by two flat bars, e, to which is bolted the bottom, E. This conduit is prolonged beyond the decorticating cylinder by an inclined chute, F, the bottom of which is made of plate iron 7 mm. thick and the sides of the same material 9 mm. thick. The hollow frame, B, whose general form is like that of a saddle, carries the bearings, b, in which revolves the shaft, a. One of these bearings is represented in detail in Figs. 9 and 10. It will be seen that the cap is held by bolts with sunken heads, and that the bearing on the bushes is through horizontal surfaces only. In a piece with this frame are cast two similar brackets, B squared, which support the axle, h, of the endless chain. To this axle, whose diameter is 100 mm., are keyed, toward the extremities, the pinions, H, to which correspond the endless pitch chains, i. These latter are formed, as may be seen in Figs. 11 and 12, of two series of links. The shorter of these latter are only 100 mm. in length, while the longer are 210 mm., and are hollowed out so as to receive the butts of the boards, I. The chain thus formed passes over two pitch pinions, J, like the pinions, H, that are mounted at the extremities of an axle, j, that revolves in bearings, I', whose position with regard to the apparatus is capable of being varied so as to slacken or tauten the chain, I. This arrangement is shown in elevation in Fig. 13.
Transmission.—The driving shaft, k, revolves in a pillow block, K, cast in a piece with the frame, B. It is usually actuated by a special motor, and carries a fly-wheel (not shown in the figure for want of space). It receives in addition a cog-wheel, L, which transmits its motion to the decorticating cylinder through, the intermedium of a large wooden-toothed gear wheel, L'. The shaft, a, whose diameter is 228 mm., actuates in its turn, through the pinions, M' and M, the pitch pinion, N, upon whose prolonged hub is keyed the pinion, M. This latter is mounted loosely upon the intermediate axle, m. Motion is transmitted to the driving shaft, h, of the endless chain, I, by an ordinary pitch chain, through a gearing which is shown in Fig. 12. The pitch pinion, N', is cast in a piece with a hollow friction cone, N squared, which is mounted loosely upon the shaft, h, and to which corresponds a second friction cone, O. This latter is connected by a key to a socket, o, upon which it slides, and which is itself keyed to the shaft, h. The hub of the cone, O, is connected by a ring with a bronze nut, p, mounted at the threaded end of the shaft, h, and carrying a hand-wheel, P. It is only necessary to turn this latter in one direction or the other in order to throw the two cones into or out of gear.
If we allow that the motor has a velocity of 70 revolutions per minute, the decorticating cylinder will run at the rate of 50, and the sugar-cane will move forward at the rate of 12 meters per minute.
This new machine is a very simple and powerful one. The decortication is effected with wonderful rapidity, and the canes, opened throughout their entire length and at all points of their circumference, leave the apparatus in a state that allows of no doubt as to what the result of the pressure will be that they have to undergo. There is no tearing, no trituration, no loss of juice, but merely a simple preparation for a rational pressure effected under most favorable conditions.
The apparatus, which is made in several sizes, has already received numerous applications in Martinique, Trinidad, Cuba, Antigua, St. Domingo, Peru, Australia, the Mauritius Islands, and Brazil.—Publication Industrielle.
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MOVING A BRIDGE.
An interesting piece of engineering work has recently been accomplished at Bristol, England, which consisted in the moving of a foot-bridge 134 feet in length, bodily, down the river a considerable distance. The pontoons by means of which the bridge was floated to its new position consisted of four 80-ton barges, braced together so as to form one solid structure 64 feet in width, and were placed in position soon after the tide commenced to rise. At six o'clock A.M. the top of the stages, which was 24 feet above the water, touched the under part of the bridge, and in a quarter of an hour later both ends rose from their foundations. When the tide had risen 4 ft. the stage and bridge were floated to the new position, when at 8.30 the girders dropped on to their beds.
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THE GENERATION OF STEAM, AND THE THERMODYNAMIC PROBLEMS INVOLVED.[1]
[Footnote 1: Lecture delivered at the Institution of Civil Engineers, session 1883-84. For the illustrations we are indebted to the courtesy of Mr. J. Forrest, the secretary.]
By Mr. WILLIAM ANDERSON, M.I.C.E.
It will not be necessary to commence this lecture by explaining the origin of fuel; it will be sufficient if I remind you that it is to the action of the complex rays of the sun upon the foliage of plants that we mainly owe our supply of combustibles. The tree trunks and branches of our forests, as well as the subterranean deposits of coal and naphtha, at one time formed portions of the atmosphere in the form of carbonic acid gas; that gas was decomposed by the energy of the solar rays, the carbon and the oxygen were placed in positions of advantage with respect to each other—endowed with potential energy; and it is my duty this evening to show how we can best make use of these relations, and by once more combining the constituents of fuel with the oxygen of the air, reverse the action which caused the growth of the plants, that is to say, by destroying the plant reproduce the heat and light which fostered it. The energy which can be set free by this process cannot be greater than that derived originally from the sun, and which, acting through the frail mechanism of green leaves, tore asunder the strong bonds of chemical affinity wherein the carbon and oxygen were hound, converting the former into the ligneous portions of the plants and setting the latter free for other uses. The power thus silently exerted is enormous; for every ton of carbon separated in twelve hours necessitates an expenditure of energy represented by at least 1,058 horse power, but the action is spread over an enormous area of leaf surface, rendered necessary by the small proportion of carbonic acid contained in the air, by measure only 1/2000 part, and hence the action is silent and imperceptible. It is now conceded on all hands that what is termed heat is the energy of molecular motion, and that this motion is convertible into various kinds and obeys the general laws relating to motion. Two substances brought within the range of chemical affinity unite with more or less violence; the motion of transition of the particles is transformed, wholly or in part, into a vibratory or rotary motion, either of the particles themselves or the interatomic ether; and according to the quality of the motions we are as a rule, besides other effects, made conscious of heat or light, or of both. When these emanations come to be examined they are found to be complex in the extreme, intimately bound up together, and yet capable of being separated and analyzed.
As soon as the law of definite chemical combination was firmly established, the circumstance that changes of temperature accompanied most chemical combinations was noticed, and chemists were not long in suspecting that the amount of heat developed or absorbed by chemical reaction should be as much a property of the substances entering into combination as their atomic weights. Solid ground for this expectation lies in the dynamic theory of heat. A body of water at a given height is competent by its fall to produce a definite and invariable quantity of heat or work, and in the same way two substances falling together in chemical union acquire a definite amount of kinetic energy, which, if not expended in the work of molecular changes, may also by suitable arrangements be made to manifest a definite and invariable quantity of heat.
At the end of last century Lavoisier and Laplace, and after them, down to our own time, Dulong, Desprez, Favre and Silbermann, Andrews, Berthelot, Thomson, and others, devoted much time and labor to the experimental determination of the heat of combustion and the laws which governed its development. Messrs. Favre and Silbermann, in particular, between the years 1845 and 1852, carried out a splendid series of experiments by means of the apparatus partly represented in Fig. 1 (opposite), which is a drawing one-third the natural size of the calorimeter employed. It consisted essentially of a combustion chamber formed of thin copper, gilt internally. The upper part of the chamber was fitted with a cover through which the combustible could be introduced, with a pipe for a gas jet, with a peep hole closed by adiathermanous but transparent substances, alum and glass, and with a branch leading to a thin copper coil surrounding the lower part of the chamber and descending below it. The whole of this portion of the apparatus was plunged into a thin copper vessel, silvered internally and filled with water, which was kept thoroughly mixed by means of agitators. This second vessel stood inside a third one, the sides and bottom of which were covered with the skins of swans with the down on, and the whole was immersed in a fourth vessel tilled with water, kept at the average temperature of the laboratory. Suitable thermometers of great delicacy were provided, and all manner of precautions were taken to prevent loss of heat.
It is impossible not to admire the ingenuity and skill exhibited in the details of the apparatus, in the various accessories for generating and storing the gases used, and for absorbing and weighing the products of combustion; but it is a matter of regret that the experiments should have been carried out on so small a scale. For example, the little cage which held the solid fuel tested was only 5/8 inch diameter by barely 2 inches high, and held only 38 grains of charcoal, the combustion occupying about sixteen minutes. Favre and Silbermann adopted the plan of ascertaining the weight of the substances consumed by calculation from the weight of the products of combustion. Carbonic acid was absorbed by caustic potash, as also was carbonic oxide, after having been oxidized to carbonic acid by heated oxide of copper, and the vapor of water was absorbed by concentrated sulphuric acid. The adoption of this system showed that it was in any case necessary to analyze the products of combustion in order to detect imperfect action. Thus, in the case of substances containing carbon, carbonic oxide was always present to a variable extent with the carbonic acid, and corrections were necessary in order to determine the total heat due to the complete combination of the substance with oxygen. Another advantage gained was that the absorption of the products of combustion prevents any sensible alteration in the volumes during the process, so that corrections for the heat absorbed in the work of displacing the atmosphere were not required. The experiments on various substances were repeated many times. The mean results for those in which we are immediately interested are given in Table I., next column.
Comparison with later determinations have established their substantial accuracy. The general conclusion arrived at is thus stated:
"As a rule there is an equality between the heat disengaged or absorbed in the acts, respectively, of chemical combination or decomposition of the same elements, so that the heat evolved during the combination of two simple or com-pound substances is equal to the heat absorbed at the time of their chemical segregation."
TABLE I.—SUBSTANCES ENTERING INTO THE COMPOSITION OF FUEL.
- - - - Heat evolved in Symbol and Atomic the Combustion of Weight. 1 lb. of Fuel. + In Pounds In of Water British Evaporated Before After Thermal from and Combustion Combustion Units. at 212 deg.. + Hydrogen burned H 1 H2O 18 62,032 64.21 in oxygen. - + Carbon burned to C 12 CO 28 4,451 4.61 carbonic oxide. -+ Carbon burned to C 12 CO2 44 14,544 15.06 carbonic acid. - + Carbonic oxide burned CO 28 CO2 44 4,326 4.48 to carbonic acid. -+ Olefiant gas (ethylene) C2H4 28 2CO2 124 21,343 22.09 burnt in oxygen. 2H2O - + Marsh gas (methane) CH4 16 2CO2 80 23,513 24.34 burnt in oxygen. 2H2O -+
Composition of air—
by volume 0.788 N + 0.197 O + 0.001 CO2 + 0.014 H2O —————————————————————————— by weight 0.771 N + 0.218 O + 0.009 CO2 + 0.017 H2O
This law is, however, subject to some apparent exceptions. Carbon burned in protoxide of nitrogen, or laughing gas, N{2}O, produces about 38 per cent. more heat than the same substance burned in pure oxygen, notwithstanding that the work of decomposing the protoxide of nitrogen has to be performed. In marsh gas, or methane, CH{4}, again, the energy of combustion is considerably less than that due to the burning of its carbon and hydrogen separately. These exceptions probably arise from the circumstance that the energy of chemical action is absorbed to a greater or less degree in effecting molecular changes, as, for example, the combustion of 1 pound of nitrogen to form protoxide of nitrogen results in the absorption of 1,157 units of heat. Berthelot states, as one of the fundamental principles of thermochemistry, "that the quantity of heat evolved is the measure of the sum of the chemical and physical work accomplished in the reaction"; and such a law will no doubt account for the phenomena above noted. The equivalent heat of combustion of the compounds we have practically to deal with has been experimentally determined, and therefore constitutes a secure basis on which to establish calculations of the caloric value of fuel; and in doing so, with respect to substances composed of carbon, hydrogen, and oxygen, it is convenient to reduce the hydrogen to its heat-producing equivalent of carbon. The heat of combustion of hydrogen being 62,032 units, that of carbon 14,544 units, it follows that 4.265 times the weight of hydrogen will represent an equivalent amount of carbon. With respect to the oxygen, it is found that it exists in combination with the hydrogen in the form of water, and, being combined already, abstracts its combining equivalent of hydrogen from the efficient ingredients of the fuel; and hence hydrogen, to the extent of 1/8 of the weight of the oxygen, must be deducted. The general formula then becomes:
Heat of combustion = 14,544 {C + 4.265 (H-(O/8))},
and water evaporated from and at 212 deg., taking 966 units as the heat necessary to evaporate 1 pound of water,
lb. evaporated = 15.06 {C + 4.265 (H-(O/8))},
carbon, hydrogen, and oxygen being taken at their weight per cent. in the fuel. Strictly speaking, marsh gas should be separately determined. It often happens that available energy is not in a form in which it can be applied directly to our needs. The water flowing down from the mountains in the neighborhood of the Alpine tunnels was competent to provide the power necessary for boring through them, but it was not in a form in which it could be directly applied. The kinetic energy of the water had first to be changed into the potential energy of air under pressure, then, in that form, by suitable mechanism, it was used with signal success to disintegrate and excavate the hard rock of the tunnels. The energy resulting from combustion is also incapable of being directly transformed into useful motive power; it must first be converted into potential force of steam or air at high temperature and pressure, and then applied by means of suitable heat engines to produce the motions we require. It is probably to this circumstance that we must attribute the slowness of the human race to take advantage of the energy of combustion. The history of the steam engine hardly dates back 200 years, a very small fraction of the centuries during which man has existed, even since historic times.
The apparatus by means of which the potential energy of fuel with respect to oxygen is converted into the potential energy of steam, we call a steam boiler; and although it has neither cylinder nor piston, crank nor fly wheel, I claim for it that it is a veritable heat engine, because it transmits the undulations and vibrations caused by the energy of chemical combination in the fuel to the water in the boiler; these motions expend themselves in overcoming the liquid cohesion of the water and imparting to its molecules that vigor of motion which converts them into the molecules of a gas which, impinging on the surfaces which confine it and form the steam space, declare their presence and energy in the shape of pressure and temperature. A steam pumping engine, which furnishes water under high pressure to raise loads by means of hydraulic cranes, is not more truly a heat engine than a simple boiler, for the latter converts the latent energy of fuel into the latent energy of steam, just as the pumping engine converts the latent energy of steam into the latent energy of the pumped-up accumulator or the hoisted weight.
If I am justified in taking this view, then I am justified in applying to my heat engine the general principles laid down in 1824 by Sadi Carnot, namely, that the proportion of work which can be obtained out of any substance working between two temperatures depends entirely and solely upon the difference between the temperatures at the beginning and end of the operation; that is to say, if T be the higher temperature at the beginning, and t the lower temperature at the end of the action, then the maximum possible work to be got out of the substance will be a function of (T-t). The greatest range of temperature possible or conceivable is from the absolute temperature of the substance at the commencement of the operation down to absolute zero of temperature, and the fraction of this which can be utilized is the ratio which the range of temperature through which the substance is working bears to the absolute temperature at the commencement of the action. If W = the greatest amount of effect to be expected, T and t the absolute temperatures, and H the total quantity of heat (expressed in foot pounds or in water evaporated, as the case may be) potential in the substance at the higher temperature, T, at the beginning of the operation, then Carnot's law is expressed by the equation:
/ T - t W = H( ———- ) T /
I will illustrate this important doctrine in the manner which Carnot himself suggested.
Fig. 2 represents a hillside rising from the sea. Some distance up there is a lake, L, fed by streams coming down from a still higher level. Lower down on the slope is a millpond, P, the tail race from which falls into the sea. At the millpond is established a factory, the turbine driving which is supplied with water by a pipe descending from the lake, L. Datum is the mean sea level; the level of the lake is T, and of the millpond t. Q is the weight of water falling through the turbine per minute. The mean sea level is the lowest level to which the water can possibly fall; hence its greatest potential energy, that of its position in the lake, = QT = H. The water is working between the absolute levels, T and t; hence, according to Carnot, the maximum effect, W, to be expected is—
/ T - t W = H( ———- ) T / / T - t but H = QT [therefore] W = Q T( ———- ) T /
W = Q (T - t),
that is to say, the greatest amount of work which can be expected is found by multiplying the weight of water into the clear fall, which is, of course, self-evident.
Now, how can the quantity of work to be got out of a given weight of water be increased without in any way improving the efficiency of the turbine? In two ways:
1. By collecting the water higher up the mountain, and by that means increasing T.
2. By placing the turbine lower down, nearer the sea, and by that means reducing t.
Now, the sea level corresponds to the absolute zero of temperature, and the heights T and t to the maximum and minimum temperatures between which the substance is working; therefore similarly, the way to increase the efficiency of a heat engine, such as a boiler, is to raise the temperature of the furnace to the utmost, and reduce the heat of the smoke to the lowest possible point. It should be noted, in addition, that it is immaterial what liquid there may be in the lake; whether water, oil, mercury, or what not, the law will equally apply, and so in a heat engine, the nature of the working substance, provided that it does not change its physical state during a cycle, does not affect the question of efficiency with which the heat being expended is so utilized. To make this matter clearer, and give it a practical bearing, I will give the symbols a numerical value, and for this purpose I will, for the sake of simplicity, suppose that the fuel used is pure carbon, such as coke or charcoal, the heat of combustion of which is 14,544 units, that the specific heat of air, and of the products of combustion at constant pressure, is 0.238, that only sufficient air is passed through the fire to supply the quantity of oxygen theoretically required for the combustion of the carbon, and that the temperature of the air is at 60 deg. Fahrenheit = 520 deg. absolute. The symbol T represents the absolute temperature of the furnace, a value which is easily calculated in the following manner: 1 lb. of carbon requires 2-2/3 lb. of oxygen to convert it into carbonic acid, and this quantity is furnished by 12.2 lb. of air, the result being 13.2 lb. of gases, heated by 14,544 units of heat due to the energy of combustion; therefore:
14,544 units T = 520 deg. + ————————— = 5,150 deg. absolute. 13.2 lb. X 0.238
The lower temperature, t, we may take as that of the feed water, say at 100 deg. or 560 deg. absolute, for by means of artificial draught and sufficiently extending the heating surface, the temperature of the smoke may be reduced to very nearly that of the feed water. Under such circumstances the proportion of heat which can be realized is
5,150 deg. - 560 deg. = ———————- = 0.891; 5,150 deg.
that is to say, under the extremely favorable if not impracticable conditions assumed, there must be a loss of 11 per cent. Next, to give a numerical value to the potential energy, H, to be derived from a pound of carbon, calculating from absolute zero, the specific heat of carbon being 0.25, and absolute temperature of air 520 deg.:
Units. 1 lb. of carbon X 0.25 X 520 = 130 12.2 of air X 0.238 X 520 = 1,485 Heat of combustion = 14,544 ——— 16,159 Deduct heat equivalent to work of displacing atmosphere by products of } combustion raised from 60 deg. to 100 deg., } 32 or from 149.8 cubic feet to 161.3 } cubic feet, / ——— Total units of heat available 16,127
Equal to 16.69 lb. of water evaporated from and at 212 deg.. Hence the greatest possible evaporation from and at 212 deg. from a lb. of carbon—
16,159 u. X 0.891 - 32 u. W = —————————————- = 14.87 lb. 966 u.
I will now take a definite case, and compare the potential energy of a certain kind of fuel with the results actually obtained. For this purpose the boiler of the eight-horse portable engine, which gained the first prize at the Cardiff show of the Royal Agricultural Society in 1872, will serve very well, because the trials, all the details of which are set forth very fully in vol. ix. of the Journal of the Society, were carried out with great care and skill by Sir Frederick Bramwell and the late Mr. Menelaus; indeed, the only fact left undetermined was the temperature of the furnace, an omission due to the want of a trustworthy pyrometer, a want which has not been satisfied to this day.[2]
[Footnote 2: In the fifty-second volume of the Proceedings (1887-78), page 154, will be found a remarkable experiment on the evaporative power of a vertical boiler with internal circulating pipes. The experiment was conducted by Sir Frederick Bramwell and Dr. Russell, and is remarkable in this respect, that the quantity of air admitted to the fuel, the loss by convection and radiation, and the composition of the smoke were determined. The facts observed were as follows:
Steam pressure 53 lb................................... = 300.6 deg. F. lb. Fuel—Water in coke and wood........................... 26.08 Ash.............................................. 10.53 Hydrogen, oxygen, nitrogen, and sulphur.......... 7.18 ——— Total non-combustible..................... 43.79 Carbon, being useful combustible................. 194.46 ——— Total fuel................................ 238.25
Air per pound of carbon................................ 17-1/8 lb. Time of experiment..................................... 4 h. 12 min. Water evaporated from 60 deg. into steam at 53 lb. pressure 1,620 lb. Heat lost by radiation and convection.................. 70,430 units. Mean temperature of chimney............................ 700 deg. F. " " " air................................ 70 deg. F.
No combustible gas was found in the chimney.
I will apply Carnot's doctrine to this case.
Potential energy of the fuel with respect to absolute zero: Units. 239.25 lb. x 530 deg. abs. x 0.238 ...................... = 30,053 194.46 lb. x 17-1/8 x 530 deg. x 0.238, the weight and heat of air....................... 420,660 194.46 x 14,544 units heat of combustion of carbon... 2,828,200 ————- Total energy 3,278,813 Heat absorbed in evaporating 26.08 lb. of water in fuel............................................ -29,888 ————- Available energy.......................... 3,248,425
Temperature of furnace—
The whole of the fuel was heated up, but the heat absorbed in the evaporation of the water lowered the temperature of the furnace, and must be deducted from the heat of combustion.
Units. Heat of combustion................................... 2,828,200 " " evaporation of 26.08 lb. water............... -29,888 ————- Available heat of combustion.............. 2,798,312
Dividing by 238.25 lb. gives the heat per 1 lb. of fuel used................................... = 11,745 units. And temperature of furnace: 11,745 units/(18.125 lb. x 0.238) + 530 deg.......... = 3,253 deg. Temperature of chimney 700 deg. + 460 deg................ = 1,160 deg. Maximum duty (3,253 deg. - 1,160 deg.)/3,253 deg............. = 0.643 deg.
Work of displacing atmosphere by smoke at 700 deg.: Cubic feet. Volumes of gases at 70 deg......................... = 228.3 " " " " 700 deg......................... = 499.8 ——- Increase of volume.................... 271.5
Units. Work done= (194.46 lb. x 271.5 cub. ft. x 144 sq. in. x 15 lb.) /722 units ..................................... = 147,720 Maximum amount of work to be expected = 3,248,425 x 0.643.............................. = 2,101,700 Deduct work of displacing atmosphere............. = 147,720 ————- Available work........................ 1,953,980
Actual work done: Units. 1,620 lb. of water raised from 60 deg. and turned into steam at 53 lb..... ...................... = 1,855,900 Loss by radiation and convection................. 70,430 10-1/2 lb. ashes left, say at 500 deg................ 1,129 ————- Total work actually done.............. 1,927,459 Unaccounted for.................................. 26,521 ————- Calculated available work........................ 1,953,980
The unaccounted-for work, therefore, amounts to only 11/2 per cent. of the calculated available work.
Sir Frederick Bramwell ingeniously arranged his data in the form of a balance sheet, and showed 253,979 units unaccounted for; but if from this we deduct the work lost in displacing the air, the unaccounted-for heat falls to less than 4 per cent. of the total heat of combustion. These results show how extremely accurate the observations must have been, and that the loss mainly arises from convection and radiation from the boiler.]
The data necessary for our purpose are:
Steam pressure 80 lb. temperature 324 deg. = 784 deg. absolute. Mean temperature of smoke 389 deg. = 849 deg. " Water evaporated per 1 lb of coal, from and at 212 deg. 11.83 lb. Temperature of the air 60 deg. = 520 deg. absolute. " of feed water 209 deg. = 669 deg. " Heating surface 220 square feet. Grate surface 3.29 feet. Coal burnt per hour 41 lb.
The fuel used was a smokeless Welsh coal, from the Llangennech colleries. It was analyzed by Mr. Snelus, of the Dowlais Ironworks, and in Table II. are exhibited the details of its composition, and the weight and volume of air required for its combustion. The total heat of combustion in 1 lb of water evaporated:
= 15.06 x (0.8497 + 4.265 x (0.426 - 0.035/8)) = 15.24 lb. of water from and at 212 deg. = 14,727 units of heat.
TABLE II.—PROPERTIES OF LLANGENNECH COAL.
-+ + + -+ Products of Oxygen Combustion at 32 deg. F. Analyses required + + + of 1 lb. for of Coal. Combustion. Cubic Volume Pounds. feet. per cent. -+ + + + + Carbon........... 0.8497 2.266 25.3 11.1 Hydrogen......... 0.0426 0.309 7.6 3.4 Oxygen........... 0.0350 - - - Sulphur.......... 0.0042 - - - Nitrogen......... 0.1045 - 0.18 Ash.............. 0.0540 - - + + + 85.5 Total........... 1.0000 2.572 - 9-1/3.lb nitrogen - - 118.9 6 lb. excess of air. - - 71.4 + + + + + Total cubic feet of products per 1 lb. of coal........... 226.4 100.0 -+ + + + +
The temperature of the furnace not having been determined, we must calculate it on the supposition, which will be justified later on, that 50 per cent more air was admitted than was theoretically necessary to supply the oxygen required for perfect combustion. This would make 18 lb. of air per 1 lb. of coal; consequently 19 lb. of gases would be heated by 14,727 units of heat. Hence:
14,727 u. T = ———————— = 3,257 deg. 19 lb. x 0.238
above the temperatures of the air, or 3,777 deg. absolute. The temperature of the smoke, t, was 849 deg. absolute; hence the maximum duty would be
3,777 deg. - 849 deg. ———————- = 0.7752. 3,777 deg.
The specific heat of coal is very nearly that of gases at constant pressure, and may, without sensible error, be taken as such. The potential energy of 1 lb. of coal, therefore, with reference to the oxygen with which it will combine, and calculated from absolute zero, is:
Units. 19 lb. of coal and air at the temperature of the air contained 19 lb. x 520 deg. x 0.238 2,350 Heat of combustion 14,727 ———- 17,078 Deduct heat expended in displacing atmosphere 151 cubic feet - 422 ——— Total potential energy 16,656
Hence work to be expected from the boiler:
/ 3,777 deg. - 849 deg. = 17,078 units X ( ———————- ) - 422 units 3,777 deg. / ——————————————————————— = 13.27 lb. 966 units
of water evaporated from and at 212 deg., corresponding to 12,819 units. The actual result obtained was 11.83 lb.; hence the efficiency of this boiler was
11.83 ———- = 0.892. 13.27
I have already claimed for a boiler that it is a veritable heat engine, and I have ventured to construct an indicator diagram to illustrate its working. The rate of transfer of heat from the furnace to the water in the boiler, at any given point, is some way proportional to the difference of temperature, and the quantity of heat in the gases is proportional to their temperatures. Draw a base line representing -460 deg. Fahr., the absolute zero of temperature. At one end erect an ordinate, upon which set off T = 3,777 deg., the temperature of the furnace. At 849 deg. = t, on the scale of temperature, draw a line parallel to the base, and mark on it a length proportional to the heating surface of the boiler; join T by a diagonal with the extremity of this line, and drop a perpendicular on to the zero line. The temperature of the water in the boiler being uniform, the ordinates bounded by the sloping line, and by the line, t, will at any point be approximately proportional to the rate of transmission of heat, and the shaded area above t will be proportional to the quantity of heat imparted to the water. Join T by another diagonal with extremity of the heating surface on the zero line, then the larger triangle, standing on the zero line, will represent the whole of the heat of combustion, and the ratio of the two triangles will be as the lengths of their respective bases, that is, as (T - t) / T, which is the expression we have already used. The heating surface was 220 square feet, and it was competent to transmit the energy developed by 41 lb. of coal consumed per hour = 12,819 u. x 41 u. = 525,572 units, equal to an average of 2,389 units per square foot per hour; this value will correspond to the mean pressure in an ordinary diagram, for it is a measure of the energy with which molecular motion is transferred from the heated gases to the boiler-plate, and so to the water. The mean rate of transmission, multiplied by the area of heating surface, gives the area of the shaded portion of the figure, which is the total work which should have been done, that is to say, the work of evaporating 544 lb. of water per hour. The actual work done, however, was only 485 lb. To give the speculations we have indulged in a practical turn, it will be necessary to examine in detail the terms of Carnot's formula. Carnot labored under great disadvantages. He adhered to the emission theory of heat; he was unacquainted with its dynamic equivalent; he did not know the reason of the difference between the specific heat of air at constant pressure and at constant volume, the idea of an absolute zero of temperature had not been broached; but the genius of the man, while it made him lament the want of knowledge which he felt must be attainable, also enabled him to penetrate the gloom by which he was surrounded, and enunciate propositions respecting the theory of heat engines, which the knowledge we now possess enables us to admit as true. His propositions are:
1. The motive power of heat is independent of the agents employed to develop it, and its quantity is determined solely by the temperature of the bodies between which the final transfer of caloric takes place.
2. The temperature of the agent must in the first instance be raised to the highest degree possible in order to obtain a great fall of caloric, and as a consequence a large production of motive power.
3. For the same reason the cooling of the agent must be carried to as low a degree as possible.
4. Matters must be so arranged that the passage of the elastic agent from the higher to the lower temperature must be due to an increase of volume, that is to say, the cooling of the agent must be caused by its rarefaction.
This last proposition indicates the defective information which Carnot possessed. He knew that expansion of the elastic agent was accompanied by a fall of temperature, but he did not know that that fall was due to the conversion of heat into work. We should state this clause more correctly by saying that "the cooling of the agent must be caused by the external work it performs." In accordance with these propositions, it is immaterial what the heated gases or vapors in the furnace of a boiler may be, provided that they cool by doing external work and, in passing over the boiler surfaces, impart their heat energy to the water. The temperature of the furnace, it follows, must be kept as high as possible. The process of combustion is usually complex. First, in the case of coal, close to the fire-bars complete combustion of the red hot carbon takes place, and the heat so developed distills the volatile hydrocarbons and moisture in the upper layers of the fuel. The inflammable gases ignite on or near the surface of the fuel, if there be a sufficient supply of air, and burn with a bright flame for a considerable distance around the boiler. If the layer of fuel be thin, the carbonic acid formed in the first instance passes through the fuel and mixes with the other gases. If, however, the layer of fuel be thick, and the supply of air through the bars insufficient, the carbonic acid is decomposed by the red hot coke, and twice the volume of carbonic oxide is produced, and this, making its way through the fuel, burns with a pale blue flame on the surface, the result, as far as evolution of heat is concerned, being the same as if the intermediate decomposition of carbonic acid had not taken place. This property of coal has been taken advantage of by the late Sir W. Siemens in his gas producer, where the supply of air is purposely limited, in order that neither the hydrocarbons separated by distillation, nor the carbonic oxide formed in the thick layer of fuel, may be consumed in the producer, but remain in the form of crude gas, to be utilized in his regenerative furnaces.
(To be continued.)
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[Continued from SUPPLEMENT No. 437, page 6970.]
PLANETARY WHEEL-TRAINS.
By Prof. C.W. MACCORD, Sc.D.
II.
It has already been shown that the rotations of all the wheels of a planetary train, relatively to the train-arm, are the same when the arm is in motion as they would be if it were fixed. Now, in Fig. 14, let A be the first and F the last wheel of an incomplete train, that is, one having but one sun-wheel. As before, let these be so connected by intermediate gearing that, when T is stationary, a rotation of A through m degrees shall drive F through n degrees: and also as before, let T in the same time move through a degrees. Then, if m' represent the total motion of A, we have again,
m' = m + a, or m = m' - a.
This is, clearly, the motion of A relatively to the fixed frame of the machine; and is measured from a fixed vertical line through the center of A. Now, if we wish to express the total motion of F relatively to the same fixed frame, we must measure it from a vertical line through the center of F, wherever that maybe; which gives in this case:
n' = n + a, or n = n' - a.
but with respect to the train-arm when at rest, we have:
ang. vel. A n —————— = —-, whence again ang. vel. F m
n' - a n ——— = —- . m' - a m
This is the manner in which the equation is deduced by Prof. Willis, who expressly states that it applies whether the last wheel F is or is not concentric with the first wheel A, and also that the train may be composed of any combinations which transmit rotation with both a constant velocity ratio and a constant directional relation. He designates the quantities m', n', absolute revolutions, as distinguished from the relative revolutions (that is, revolutions relatively to the train-arm), indicated by the quantities m, n: adding, "Hence it appears that the absolute revolutions of the wheels of epicyclic trains are equal to the sum of their relative revolutions to the arm, and of the arm itself, when they take place in the same direction, and equal to the difference of these revolutions when in the opposite direction."
In this deduction of the formula, as in that of Prof. Rankine, all the motions are supposed to have the same direction, corresponding to that of the hands of the clock; and in its application to any given train, the signs of the terms must be changed in case of any contrary motion, as explained in the preceding article.
And both the deduction and the application, in reference to these incomplete trains in which the last wheel is carried by the train-arm, clearly involve and depend upon the resolving of a motion of revolution into the components of a circular translation and a rotation, in the manner previously discussed.
To illustrate: Take the simple case of two equal wheels, Fig. 15, of which the central one A is fixed. Supposing first A for the moment released and the arm to be fixed, we see that the two wheels will turn in opposite directions with equal velocities, which gives n/m = -1; but when A is fixed and T revolves, we have m' = 0, whence in the general formula
n' - a ——— = -1, or n' = 2 a; -a
which means, being interpreted, that F makes two rotations about its axis during one revolution of T, and in the same direction. Again, let A and F be equal in the 3-wheel train, Fig. 16, the former being fixed as before. In this case we have:
n —- = 1, m' = 0, which gives m
n' - a ———- = 1, [therefore] n' = 0; -a
that is to say, the wheel F, which now evidently has a motion of circular translation, does not rotate at all about its axis during the revolution of the train-arm.
All this is perfectly consistent, clearly, with the hypothesis that the motion of circular translation is a simple one, and the motion of revolution about a fixed axis is a compound one.
Whether the hypothesis was made to substantiate the formula, or the formula constructed to suit the hypothesis, is not a matter of consequence. In either case, no difficulty will arise so long as the equation is applied only to cases in which, as in those here mentioned, that motion of revolution can be resolved into those components.
When the definition of an epicyclic train is restricted as it is by Prof. Rankine, the consideration of the hypothesis in question is entirely eliminated, and whether it be accepted or rejected, the whole matter is reduced to merely adding the motion of the train-arm to the rotation of each sun-wheel.
But in attempting to apply this formula in analyzing the action of an incomplete train, we are required to add this motion of the train-arm, not only to that of a sun-wheel, but to that of a planet-wheel. This is evidently possible in the examples shown in Figs. 15 and 16, because the motions to be added are in all respects similar: the trains are composed of spur-wheels, and the motions, whether of revolution, translation, or rotation, take place in parallel planes perpendicular to parallel axes. This condition, which we have emphasized, be it observed, must hold true with regard to the motions of the first and last wheels and the train-arm, in order to make this addition possible. It is not essential that spur-wheels should be used exclusively or even at all; for instance, in Fig. 16, A and F may be made bevel or screw-wheels, without affecting the action or the analysis; but the train-arm in all cases revolves around the central axis of the system, that is, about the axis of A, and to this the axis of F must be parallel, in order to render the deduction of the formula, as made by Prof. Willis, and also by Prof. Goodeve, correct, or even possible.
This will be seen by an examination of Fig. 17; in which A and B are two equal spur-wheels, E and F two equal bevel wheels, B and E being secured to the same shaft, and A being fixed to the frame H. As the arm T goes round, B will also turn in its bearings in the same direction: let this direction be that of the clock, when the apparatus is viewed from above, then the motion of F will also have the same direction, when viewed from the central vertical axis, as shown at F': and let these directions be considered as positive. It is perfectly clear that F will turn in its bearings, in the direction indicated, at a rate precisely equal to that of the train-arm. Let P be a pointer carried by F, and R a dial fixed to T; and let the pointer be vertical when OO is the plane containing the axes of A, B, and E. Then, when F has gone through any angle a measured from OO, the pointer will have turned from its original vertical position through an equal angle, as shown also at F'.
Now, there is no conceivable sense in which the motion of T can be said to be added to the rotation of F about its axis, and the expression "absolute revolution," as applied to the motion of the last wheel in this train, is absolutely meaningless.
Nevertheless, Prof. Goodeve states (Elements of Mechanism, p. 165) that "We may of course apply the general formula in the case of bevel wheels just as in that of spur wheels." Let us try the experiment; when the train-arm is stationary, and A released and turned to the right, F turns to the left at the same rate, whence:
n —- = -1; also m' = 0 when A is fixed, m
and the equation becomes
n' - a ——— = -1, [therefore] n' = 2a: - a
or in other words F turns twice on its axis during one revolution of T: a result too palpably absurd to require any comment. We have seen that this identical result was obtained in the case of Fig. 15, and it would, of course, be the same were the formula applied to Figs. 5 and 6; whereas it has never, so far as we are aware, been pretended that a miter or a bevel wheel will make more than one rotation about its axis in rolling once around an equal fixed one.
Again, if the formula be general, it should apply equally well to a train of screw wheels: let us take, for example, the single pair shown in Fig. 8, of which, when T is fixed, the velocity ratio is unity. The directional relation, however, depends upon the direction in which the wheels are twisted: so that in applying the formula, we shall have n/m = +1, if the helices of both wheels are right handed, and n/m = -1, if they are both left handed. Thus the formula leads to the surprising conclusion, that when A is fixed and T revolves, the planet-wheel B will revolve about its axis twice as fast as T moves, in one case, while in the other it will not revolve at all.
A favorite illustration of the peculiarities of epicyclic mechanism, introduced both by Prof. Willis and Prof. Goodeve, is found in the contrivance known as Ferguson's Mechanical Paradox, shown in Fig. 18. This consists of a fixed sun-wheel A, engaging with a planet-wheel B of the same diameter. Upon the shaft of B are secured the three thin wheels E, G, I, each having 20 teeth, and in gear with the three others F, H, K, which turn freely upon a stud fixed in the train-arm, and have respectively 19, 20, and 21 teeth. In applying the general formula, we have the following results:
n 20 n' - a 1 For the wheel F, —- = —— = ————-, [therefore] n' = - —— a. m 19 -a 19
n n' - a " " " H, —- = 1 = ————, [therefore] n' = 0. m -a
n 20 n' - a 1 " " " K, —- = —— = ————-, [therefore] n' = + —— a. m 21 -a 21
The paradoxical appearance, then, consists in this, that although the drivers of the three last wheels each have the same number of teeth, yet the central one, H, having a motion of circular translation, remains always parallel to itself, and relatively to it the upper one seems to turn in the same direction as the train-arm, and the lower in the contrary direction. And the appearance is accepted, too, as a reality; being explained, agreeably to the analysis just given, by saying that H has no absolute rotation about its axis, while the other wheels have; that of F being positive and that of K negative.
The Mechanical Paradox, it is clear, may be regarded as composed of three separate trains, each of which is precisely like that of Fig. 16: and that, again, differs from the one of Fig. 15 only in the addition of a third wheel. Now, we submit that the train shown in Fig. 17 is mechanically equivalent to that of Fig. 15; the velocity ratio and the directional relation being the same in both. And if in Fig. 17 we remove the index P, and fix upon its shaft three wheels like E, G, and I of Fig. 18, we shall have a combination mechanically equivalent to Ferguson's Paradox, the three last wheels rotating in vertical planes about horizontal axes. The relative motions of those three wheels will be the same, obviously, as in Fig. 18; and according to the formula their absolute motions are the same, and we are invited to perceive that the central one does not rotate at all about its axis.
But it does rotate, nevertheless; and this unquestioned fact is of itself enough to show that there is something wrong with the formula as applied to trains like those in question. What that something is, we think, has been made clear by what precedes; since it is impossible in any sense to add together motions which are unlike, it will be seen that in order to obtain an intelligible result in cases like these, the equation must be of the form n'/(m' - a) = n/m. We shall then have:
n 20 n' 20 For the wheel F, —- = —— = ——, [therefore] n' = - —— a; m 19 -a 19
n n' For the wheel H, —- = 1 = ——, [therefore] n' = -a; m -a
n 20 n' 20 For the wheel K, —- = —— = ——, [therefore] n' = - —— a, m 21 -a 21
which corresponds with the actual state of things; all three wheels rotate in the same direction, the central one at the same rate as the train arm, one a little more rapidly and the third a little more slowly.
It is, then, absolutely necessary to make this modification in the general formula, in order to apply it in determining the rotations of any wheel of an epicyclic train whose axis is not parallel to that of the sun-wheels. And in this modified form it applies equally well to the original arrangement of Ferguson's paradox, if we abandon the artificial distinction between "absolute" and "relative" rotations of the planet-wheels, and regard a spur-wheel, like any other, as rotating on its axis when it turns in its bearings; the action of the device shown in Fig. 18 being thus explained by saying that the wheel H turns once backward during each forward revolution of the train-arm, while F turns a little more and K a little less than once, in the same direction. In this way the classification and analysis of these combinations are made more simple and consistent, and the incongruities above pointed out are avoided; since, without regard to the kind of gearing employed or the relative positions of the axes, we have the two equations:
n' - a n I. ———— = —-, for all complete trains; m' - a m
n' n II. ———— = —-, for all incomplete trains. m' - a m
As another example of the difference in the application of these formulae, let us take Watt's sun and planet wheels, Fig. 19. This device, as is well known, was employed by the illustrious inventor as a substitute for the crank, which some one had succeeded in patenting. It consists merely of two wheels A and F connected by the link T; A being keyed on the shaft of the engine and F being rigidly secured to the connecting-rod. Suppose the rod to be of infinite length, so as to remain always parallel to itself, and the two wheels to be of equal size.
Then, according to Prof. Willis' analysis, we shall have—
n' - a n -s ———— = —- = -1, n' = 0, [therefore] ———— = -1, whence m' - a m m' - a
-a = a - m', or m = 2a.
The other view of the question is, that F turns once backward in its bearings during each forward revolution of T; whence in Eq. 2 we have—
n' n ———— = —- = -1, n' = -a, m' - a m
-a [therefore] ———— -1, which gives -a = a - m', or m' = 2a, m' - a
as before.
It is next to be remarked, that the errors which arise from applying Eq. I. to incomplete trains may in some cases counterbalance and neutralize each other, so that the final result is correct.
For example, take the combination shown in Fig. 20. This consists of a train-arm T revolving about the vertical axis OO of the fixed wheel A, which is equal in diameter to F, which receives its motion by the intervention of one idle wheel carried by a stud S fixed in the arm. The second train-arm T' is fixed to the shaft of F and turns with it; A' is secured to the arm T, and F' is actuated by A' also through a single idler carried by T'.
We have here a compound train, consisting of two simple planetary trains, A—F and A'—F'; and its action is to be determined by considering them separately. First suppose T' to be removed and find the motion of F; next suppose F to be removed and T fixed, and find the rotation of F'; and finally combine these results, noting that the motion of T' is the same as that of F, and the motion of A' the same as that of T.
Then, according to the analysis of Prof. Willis, we shall have (substituting the symbol t for a in the equation of the second train, in order to avoid confusion):
n n' - a 1. Train A—F. —- = 1 = ————; m' = 0, m m' - a
n' - a whence ———— = 1, n' = 0, = rot. of F. a
n n' - t 2. Train A'—F'. —- = 1 = ————; m' = 0, m m' - t
n' - t whence again ———— = 1, t = 0, = rot. of F'. -t
Of these results, the first is explicable as being the absolute rotation of F, but the second is not; and it will be readily seen that the former would have been equally absurd, had the axis LL been inclined instead of vertical. But in either case we should find the errors neutralized upon combining the two, for according to the theory now under consideration, the wheel A', being fixed to T, turns once upon its axis each time that train arm revolves, and in the same direction; and the revolutions of T' equal the rotations of F, whence finally in train A'—F' we have:
n n' - t 3. —- = 1 = ————; in which t = 0, m' = a, m m' - t
n' - 0 which gives ————- = 1, or n' = a. a - 0
This is, unquestionably, correct; and indeed it is quite obvious that the effect upon F' is the same, whether we say that during a revolution of T the wheel A' turns once forward and T' not at all, or adopt the other view and assert that T' turns once backward and A' not at all. But the latter view has the advantage of giving concordant results when the trains are considered separately, and that without regard to the relative positions of the axes or the kind of gearing employed. Analyzing the action upon this hypothesis, we have:
In train A—F:
n n' n' —- = 1 = ————; m' = 0, [therefore] —— = 1, or n' = -a; m m' - a -a
In train A'—F':
n' n' n' —- = 1 = ————; m' = 0, [therefore] —— = 1, or n' = -t; m m' - t -t
In combining, we have in the latter train m' = 0, t = -a, whence
n n' n' —- = 1 = ———— gives —— = 1, or n' = a, as before. m m' - t +a
Now it happens that the only examples given by Prof. Willis of incomplete trains in which the axis of a planet-wheel whose motion is to be determined is not parallel to the central axis of the system, are similar to the one just discussed; the wheel in question being carried by a secondary train-arm which derives its motion from a wheel of the primary train.
The application of his general equation in these cases gives results which agree with observed facts; and it would seem that this circumstance, in connection doubtless with the complexity of these compound trains, led him to the too hasty conclusion that the formula would hold true in all cases; although we are still left to wonder at his overlooking the fact that in these very cases the "absolute" and the "relative" rotations of the last wheel are identical.
In Fig. 21 is shown a combination consisting also of two distinct trains, in which, however, there is but one train-arm T turning freely upon the horizontal shaft OO, to which shaft the wheels A', F, are secured; the train-arm has two studs, upon which turn the idlers B B', and also carries the bearings of the last wheel F'; the first wheel A is annular, and fixed to the frame of the machine. Let it be required to determine the results of one revolution of the crank H, the numbers of teeth being assigned as follows:
A = 60, F = 30, A' = 60, F' = 10.
We shall then have, for the train ABF (Eq. I.),
n 60 n' - a —- = - —— = -2 = ————, in which n' = 1, m' = 0, m 30 m' - a'
1 - a 1 whence -2 = ———-, 2a = 1 - a, 3a = 1, a = —-. -a 3
And for the train A'B'F' (Eq. II.),
n 60 n' 1 —- = —— = 6 = ————, in which a = —-, m' = 1, m 10 m' - a' 3
n' whence 6 = —————-, or n' = 4. 1 - (1/3)
That is, the last wheel F' turns four times about the axis LL during one revolution of the crank H. But according to Profs. Willis and Goodeve, we should have for the second train:
n 60 n' - a 1 —- = —— = 6 = ————, in which a = —-, m' = 1, m 10 m' - a' 3
n' - (1/3) which gives 6 = —————-, n' - (1/3) = 4, n' = 4-1/3, 1 - (1/3)
or four and one-third revolutions of F' for one of H.
This result, no doubt, might be near enough to the truth to serve all practical purposes in the application of this mechanism to its original object, which was that of paring apples, impaled upon the fork K; but it can hardly be regarded as entirely satisfactory in a general way; nor can the analysis which renders such a result possible.
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THE PANTANEMONE.
The need of irrigating prairies, inundating vines, drying marshes, and accumulating electricity cheaply has, for some time past, led to a search for some means of utilizing the forces of nature better than has ever hitherto been done. Wind, which figures in the first rank as a force, has thus far, with all the mills known to us, rendered services that are much inferior to those that we have a right to expect from it with improved apparatus; for the work produced, whatever the velocity of the wind, has never been greater than that that could be effected by wind of seven meters per second. But, thanks to the experiments of recent years, we are now obtaining an effective performance double that which we did with apparatus on the old system.
Desirous of making known the efforts that have been made in this direction, we lately described Mr. Dumont's atmospheric turbine. In speaking of this apparatus we stated that aerial motors generally stop or are destroyed in high winds. Recently, Mr. Sanderson has communicated to us the result of some experiments that he has been making for years back by means of an apparatus which he styles a pantanemone.
The engraving that we give of this machine shows merely a cabinet model of it; and it goes without saying that it is simply designed to exhibit the principle upon which its construction is based.
Two plane surfaces in the form of semicircles are mounted at right angles to each other upon a horizontal shaft, and at an angle of 45 deg. with respect to the latter. It results from this that the apparatus will operate (even without being set) whatever be the direction of the wind, except when it blows perpendicularly upon the axle, thus permitting (owing to the impossibility of reducing the surfaces) of three-score days more work per year being obtained than can be with other mills. Three distinct apparatus have been successively constructed. The first of these has been running for nine years in the vicinity of Poissy, where it lifts about 40,000 liters of water to a height of 20 meters every 24 hours, in a wind of a velocity of from 7 to 8 meters per second. The second raises about 150,000 liters of water to the Villejuif reservoir, at a height of 10 meters, every 24 hours, in a wind of from 5 to 6 meters. The third supplies the laboratory of the Montsouris observatory.
The first is not directible, the second may be directed by hand, and the third is directed automatically. These three machines defied the hurricane of the 26th of last January.—La Nature.
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RELVAS'S NEW LIFE-BOAT.
The Spanish and Portuguese papers have recently made known some interesting experiments that have been made by Mr. Carlos Relvas with a new life-boat which parts the waves with great facility and exhibits remarkable stability. This boat, which is shown in front view in one of the corners of our engraving, is T-shaped, and consists of a very thin keel connected with the side-timbers by iron rods. Cushions of cork and canvas are adapted to the upper part, and, when the boat is on the sea, it has the appearance of an ordinary canoe, although, as may be seen, it differs essentially therefrom in the submerged part. When the sea is heavy, says Mr. Relvas, and the high waves are tumbling over each other, they pass over my boat, and are powerless to capsize it. My boat clears waves that others are obliged to recoil before. It has the advantage of being able to move forward, whatever be the fury of the sea, and is capable, besides, of approaching rocks without any danger of its being broken.
A committee was appointed by the Portuguese government to examine this new life-boat, and comparative experiments were made with it and an ordinary life-boat at Porto on a very rough sea. Mr. Relvas's boat was manned by eight rowers all provided with cork girdles, while the government life-boat was manned by twelve rowers and a pilot, all likewise wearing cork girdles. The chief of the maritime department, an engineer of the Portuguese navy and a Portuguese deputy were present at the trial in a pilot boat. The three boats proceeded to the entrance of the bar, where the sea was roughest, and numerous spectators collected upon the shore and wharfs followed their evolutions from afar.
The experiments began at half past three o'clock in the afternoon. The two life-boats shot forward to seek the most furious waves, and were seen from afar to surmount the billows and then suddenly disappear. It was a spectacle as moving as it was curious. It was observed that Mr. Relvas's boat cleft the waves, while the other floated upon their surface like a nut-shell. After an hour's navigation the two boats returned to their starting point.
The official committee that presided over these experiments has again found in this new boat decided advantages, and has pointed out to its inventor a few slight modifications that will render it still more efficient.—La Nature.
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EXPERIMENTS WITH DOUBLE-BARRELED GUNS AND RIFLES.
The series of experiments we are about to describe has recently been made by Mr. Horatio Phillips, a practical gun maker of London. The results will no doubt prove of interest to those concerned in the use or manufacture of firearms.
The reason that the two barrels of a shot gun or rifle will, if put together parallel, throw their charges in diverging lines has never yet been satisfactorily accounted for, although many plausible and ingenious theories have been advanced for the purpose. The natural supposition would be that this divergence resulted from the axes of the barrels not being in the same vertical plane as the center line of the stock. That this is not the true explanation of the fact, the following experiment would tend to prove.
Fig. 1 represents a single barrel fitted with sights and firmly attached to a heavy block of beech. This was placed on an ordinary rifle rest, being fastened thereto by a pin at the corner, A, the block and barrel being free to revolve upon the pin as a center. Several shots were fired both with the pin in position and with it removed, the barrel being carefully pointed at the target each time. No practical difference in the accuracy of fire was discernible under either condition. When the pin was holding the corner of the block, the recoil caused the barrel to move from right to left in a circular path; but when the pin was removed, so that the block was not attached to the rest in any way, the recoil took place in a line with the axis of the bore. It will be observed that the conditions which are present when a double barreled gun is fired in the ordinary way from the shoulder were in some respects much exaggerated in the apparatus, for the pin was a distance of 3 in. laterally from the axis of the barrel, whereas the center of resistance of the stock of a gun against the shoulder would ordinarily be about one-sixth of this distance from the axis of the barrel. This experiment would apparently tend to prove that the recoil does not appreciably affect the path of the projectile, as it would seem that the latter must clear the muzzle before any considerable movement of the barrel takes place.
With a view to obtain a further confirmation of the result of this experiment, it was repeated in a different form by a number of shots being fired from a "cross-eyed" rifle,[1] in which the sights were fixed in the center of the rib. Very accurate shooting was obtained with this arm.
[Footnote 1: A cross-eyed rifle is one made with a crooked stock for the purpose of shooting from the right shoulder, aim being taken with the left eye.]
A second theory, often broached, in order to account for the divergence of the charge, is that the barrel which is not being fired, by its vis inertia in some way causes the shot to diverge. In order to test this, Mr. Phillips took a single rifle and secured it near the muzzle to a heavy block of metal, when the accuracy of the shooting was in no way impaired.
So far the experiments were of a negative character, and the next step was made with a view to discover the actual cause of the divergence referred to. A single barrel was now taken, to which a template was fitted, in order to record its exact length. The barrel was then subjected to a heavy internal hydrostatic pressure. Under this treatment it expanded circumferentially and at the same time was reduced in length. This, it was considered, gave a clew to the solution of the problem. A pair of barrels was now taken and a template fitted accurately to the side of the right-hand one. As the template fitted the barrel when the latter was not subject to internal pressure, upon such pressure being applied any alterations that might ensue in the length or contour of the barrel could be duly noted. The right-hand barrel was then subjected to internal hydrostatic pressure. The result is shown in an exaggerated form in Fig. 2. It will be seen that both barrels are bent into an arched form. This would be caused by the barrel under pressure becoming extended circumferentially, and thereby reduced in length, because the metal that is required to supply the increased circumference is taken to some extent from the length, although the substance of metal in the walls of the barrel by its expansion contributes also to the increased diameter. A simple illustration of this effect is supplied by subjecting an India-rubber tube to internal pressure. Supposing the material to be sufficiently elastic and the pressure strong enough, the tube would ultimately assume a spherical form. It is a well known fact that heavy barrels with light charges give less divergence than light barrels with heavy charges.
After the above experiments it was hoped that, if a pair of barrels were put together parallel and soldered only for a space of 3 in. at the breech end, and were then coupled by two encircling rings joined together as in Fig. 4, the left-hand ring only being soldered to the barrel, very accurate shooting would be obtained. For, it was argued, that by these means the barrel under fire would be able to contract without affecting or being affected by the other barrel; that on the right-hand, it will be seen by the illustration, was the one to slide in its ring.
A pair of able 0.500 bore express rifle barrels were accordingly fitted in this way. Fig. 3 shows the arrangement with the rings in position. Upon firing these barrels with ordinary express charges it was found that the lines of fire from each barrel respectively crossed each other, the bullet from the right-hand barrel striking the target 10 in. to the left of the bull's eye, while the left barrel placed its projectile a similar distance in the opposite direction; or, as would be technically said, the barrels crossed 20 in. at 100 yards, the latter distance being the range at which the experiment was made. These last results have been accounted for in the following manner: The two barrels were rigidly joined for a space of 3 in., and for that distance they would behave in a manner similar to that illustrated in Fig. 2, and were they not coupled at the muzzles by the connecting rings they would shoot very wide, the charges taking diverging courses. When the connecting rings are fitted on, the barrel not being fired will remain practically straight, and, as it is coupled to the barrel being fired by the rings, the muzzle of the latter will be restrained from pointing outward.
The result will be as shown in an exaggerated manner by the dotted lines on the right barrel in Fig. 3.
It would appear from these experiments that when very accurate shooting is required at long ranges with double-barreled rifles, they should be mounted in a manner similar to that adopted in the manufacture of the Nordenfelt machine gun, in which weapon the barrels are fitted into a plate at the extreme breech end, the muzzles projecting through holes bored to receive them in a metal plate. No unequal expansion would then take place, and the barrels would be free to become shorter independently of each other. We give the above experiments on the authority of their author, who, we believe, has taken great pains to render them as exhaustive as possible, so far as they go.—Engineering.
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BALL TURNING MACHINE.
The distinguishing feature in the ball turning machine shown opposite is that the tool is stationary, while the work revolves in two directions simultaneously. In the case of an ordinary spherical object, such as brass clack ball, the casting is made from a perfect pattern having two small caps or shanks, in which the centers are also marked to avoid centering by hand. It is fixed in the machine between two centers carried on a face plate or chuck, with which they revolve. One of these centers, when the machine is in motion, receives a continuous rotary motion about its axis from a wormwheel, D. This is driven by a worm, C, carried on a shaft at the back of the chuck, and driven itself by a wormwheel, B, which gears with a screw which rides loosely upon the mandrel, and is kept from rotating by a finger on the headstock. This center, in its rotation, carries with it the ball, which is thus slowly moved round an axis parallel to the face plate, at the same time that it revolves about the axis of the mandrel, the result being that the tool cuts upon the ball a scroll, of which each convolution is approximately a circle, and lies in a plane parallel to the line of centers.
When the chuck is set for one size of ball, which may be done in a few minutes, any quantity of that diameter may be turned without further adjustment. A roughing cut for a 2 in. ball may be done in one minute, and a finishing cut leaving the ball quite bright in the same time. The two paps are cut off within one-sixteenth of an inch and then broken off, and the ball finished in the usual way. On account of the work being geometrically true, the finishing by the ferrule tool is done in one quarter of the time usually required.
The chuck may be applied to an ordinary lathe or may be combined with a special machine tool, as show in our illustration. In the latter case everything is arranged in the most handy way for rapid working, and six brass balls of 2 in. in diameter can be turned and finished in an hour. The machine is specially adapted for turning ball valves for pumps, pulsometers, and the like, and in the larger sizes for turning governor balls and spherical nuts for armor plates, and is manufactured by Messrs. Wilkinson and Lister, of Bradford Road Iron Works, Keighley.—Engineering.
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COOLING APPARATUS FOR INJECTION WATER.
It often happens in towns and where manufactories are crowded together, that the supply of water for condensing purposes is very small, and consequently that it attains an inconveniently high temperature under unfavorable conditions of weather, resulting in the deterioration of the vacuum and a consequent increase in the consumption of fuel. To remedy or to diminish this difficulty, Messrs. Boase and Miller, of London, have brought out the water cooler illustrated above. This consists, says Engineering, of a revolving basket of wire gauze surrounding an inner stationary vessel pierced with numerous small holes, through which the heated water discharged by the air pump finds its way into the basket, to be thrown out in the form of fine spray to a distance of 20 ft. at each side. The drops are received in the tank or pond, and in their rapid passage through the air are sufficiently cooled to be again injected into the condenser.
The illustration shows a cooler having a basket three feet in diameter, revolving at 300 revolutions per minute, and discharging into a tank 40 ft. square. It requires 3 to 4 indicated horse-power to drive it, and will cool 300 gallons per minute. The following decrease of temperature has been observed in actual practice: Water entering at 95 deg. fell 20 deg. in temperature; water entering at 100 deg. to 110 deg. fell 25 deg.; and water entering at 110 deg. to 120 deg. fell 30 deg. The machine with which these trials were made was so placed that the top of the basket was four ft. from the surface of the water in the pond. With a greater elevation, as shown in the engraving, better results can be obtained.
The advantages claimed for the cooler are that by its means the temperature of the injection water can be reduced, the cost and size of cooling ponds can be diminished, and condensing engines can be employed where hitherto they have not been possible. The apparatus has been for two years in operation at several large factories, and there is every reason to believe that its use will extend, as it supplies a real want in a very simple and ingenious manner. Messrs. Duncan Brothers, of Dundee and 32 Queen Victoria Street, E.C., are the manufacturers.
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CORRUGATED DISK PULLEYS.
This is a pulley recently introduced by Messrs. J. and E. Hall, of Dartford Eng. With the exception of the boss, which is cast, it is composed entirely of steel or sheet iron. In place of the usual arms a continuous web of corrugated sheet metal connects the boss to the rim; this web is attached to the boss by means of Spence's metal. Inside the rim, which is flanged inward, a double hoop iron ring is fixed for strengthening purposes. The advantageous disposition of metal obtained by means of the corrugated web enables the pulley to be made of a given strength with less weight of material, and from this cause and also on account of being accurately balanced these pulleys are well adapted for high speeds.
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[KANSAS CITY REVIEW.]
EARLY HISTORY OF THE TELEGRAPH.
Although the electric telegraph is, comparatively speaking, a recent invention, yet methods of communication at a distance, by means of signals, have probably existed in all ages and in all nations. There is reason to believe that among the Greeks a system of telegraphy was in use, as the burning of Troy was certainly known in Greece very soon after it happened, and before any person had returned from Troy. Polybius names the different instruments used by the ancients for communicating information—"pyrsia," because the signals were always made by means of fire lights. At first they communicated information of events in an imperfect manner, but a new method was invented by Cleoxenus, which was much improved by Polybius, as he himself informs us, and which may be described as follows:
Take the letters of the alphabet and arrange them on a board in five columns, each column containing five letters; then the man who signals would hold up with his left hand a number of torches which would represent the number of the column from which the letter is to be taken, and with his right hand a number of torches that will represent the particular letter in that column that is to be taken. It is thus easy to understand how the letters of a short sentence are communicated from station to station as far as required. This is the pyrsia or telegraph of Polybius.
It seems that the Romans had a method of telegraphing in their walled cities, either by a hollow formed in the masonry, or by a tube fixed thereto so as to confine the sound, in order to convey information to any part they liked. This method of communicating is in the present age frequently employed in the well known speaking tubes. It does not appear that the moderns had thought of such a thing as a telegraph until 1661, when the Marquis of Worcester, in his "Century of Inventions," affirmed that he had discovered a method by which a man could hold discourse with his correspondent as far as they could reach, by night as well as by day; he did not, however, describe this invention.
Dr. Hooke delivered a discourse before the Royal Society in 1684, showing how to communicate at great distances. In this discourse he asserts the possibility of conveying intelligence from one place to another at a distance of 120 miles as rapidly as a man can write what he would have sent. He takes to his aid the then recent invention of the telescope, and explains how characters exposed at one station on the top of one hill may be made visible to the next station on the top of the next hill. He invented twenty-four simple characters, each formed of a combination of three deal boards, each character representing a letter by the use of cords; these characters were pushed from behind a screen and exposed, and then withdrawn behind the screen again. It was not, however, until the French revolution that the telegraph was applied to practical purposes; but about the end of 1703 telegraphic communication was established between Paris and the frontiers, and shortly afterward telegraphs were introduced into England.
The history of the invention and introduction of the electric telegraph by Prof. Morse is one of inexhaustible interest, and every incident relating to it is worthy of preservation. The incidents described below will be found of special interest. The article is from the pen of the late Judge Neilson Poe, and was the last paper written by him. He prepared it during his recent illness, the letter embodied in it from Mr. Latrobe being of course obtained at the time of its date. It is as follows:
On the 5th of April, 1843, when the monthly meeting of the directors of the Baltimore & Ohio Railroad Company was about to adjourn, the President, the Hon. Louis McLane, rose with a paper in his hand which he said he had almost overlooked, and which the Secretary would read. It proved to be an application from Prof. Morse for the privilege of laying the wires of his electric telegraph along the line of the railroad between Baltimore and Washington, and was accompanied by a communication from B.H. Latrobe, Esq., Chief Engineer, recommending the project as worthy of encouragement.
On motion of John Spear Nicholas, seconded by the Hon. John P. Kennedy, the following resolution was then considered:
Resolved, "That the President be authorized to afford Mr. Morse such facilities as may be requisite to give his invention a proper trial upon the Washington road, provided in his opinion and in that of the engineer it can be done without injury to the road and without embarrassment to the operations of the company, and provided Mr. Morse will concede to the company the use of the telegraph upon the road without expense, and reserving to the company the right of discontinuing the use if, upon experiment, it should prove in any manner injurious."
"Whatever," said Mr. McLane, "may be our individual opinions as to the feasibility of Mr. Morse's invention, it seems to me that it is our duty to concede to him the privilege he asks, and to lend him all the aid in our power, especially as the resolution carefully protects the company against all present or future injury to its works, and secures us the right of requiring its removal at any time."
[In view of the fact that no railroad can now be run safely without the aid of the telegraph, the cautious care with which the right to remove it if it should become a nuisance was reserved, strikes one at this day as nearly ludicrous.]
A short pause ensued, and the assent of the company was about to be assumed, when one of the older directors, famed for the vigilance with which he watched even the most trivial measure, begged to be heard.
He admitted that the rights and interests of the work were all carefully guarded by the terms of the resolution, and that the company was not called upon to lay out any of its means for the promotion of the scheme. But notwithstanding all this, he did not feel, as a conscientious man, that he could, without further examination, give his vote for the resolution. He knew that this idea of Mr. Morse, however plausible it might appear to theorists and dreamers, and so-called men of science, was regarded by all practical people as destined, like many other similar projects, to certain failure, and must consequently result in loss and possibly ruin to Mr. Morse. For one, he felt conscientiously scrupulous in giving a vote which would aid or tempt a visionary enthusiast to ruin himself.
Fortunately, the views of this cautious, practical man did not prevail. A few words from the mover of the resolution, Mr. Nicholas, who still lives to behold the wonders he helped to create, and from Mr. Kennedy, without whose aid the appropriation would not have passed the House of Representatives, relieved the other directors from all fear of contributing to Mr. Morse's ruin, and the resolution was adopted. Of the President and thirty directors who took part in this transaction, only three, Samuel W. Smith, John Spear Nicholas, and the writer, survive. Under it Morse at once entered upon that test of his invention whose fruits are now enjoyed by the people of all the continents.
It was not, however, until the spring of 1844 that he had his line and its appointments in such a condition as to allow the transmission of messages between the two cities, and it was in May of that year that the incident occurred which has chiefly led to the writing of this paper.
MR. LATROBE'S RECOLLECTIONS.
MY DEAR MR. POE: Agreeably to my promise, this morning I put on paper my recollection of the introduction of the magnetic telegraph between Baltimore and Washington. I was counsel of the Baltimore & Ohio Railroad Co. at the time, and calling on Mr. Louis McLane, the President, on some professional matter, was asked in the course of conversation whether I knew anything about an electric telegraph which the inventor, who had obtained an appropriation from Congress, wanted to lay down on the Washington branch of the road. He said he expected Mr. Morse, the inventor, to call on him, when he would introduce me to him, and would be glad if I took an opportunity to go over the subject with him and afterward let him, Mr. McLane, know what I thought about it. While we were yet speaking, Mr. Morse made his appearance, and when Mr. McLane introduced me he referred to the fact that, as I had been educated at West Point, I might the more readily understand the scientific bearings of Mr. Morse's invention. The President's office being no place for prolonged conversation, it was agreed that Mr. Morse should take tea at my dwelling, when we would go over the whole subject. We met accordingly, and it was late in the night before we parted. Mr. Morse went over the history of his invention from the beginning with an interest and enthusiasm that had survived the wearying toil of an application to Congress, and with the aid of diagrams drawn on the instant made me master of the matter, and wrote for me the telegraphic alphabet which is still in use over the world. Not a small part of what Mr. Morse said on this occasion had reference to the future of his invention, its influence upon communities and individuals, and I remember regarding as the wild speculations of an active imagination what he prophesied in this connection, and which I have lived to see even more than realized. Nor was his conversation confined to his invention. A distinguished artist, an educated gentleman, an observant traveler, it was delightful to hear him talk, and at this late day I recall few more pleasant evenings than the only one I passed in his company. |
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