plungers, C and D, work air-tight for a pumping operations, for which they are portion of their length, driving cranks usually applied, the water pumped can set at 95° on the shaft above. The be made to circulate in the casing, and method of packing is most ingenious, so act as a cooler; but, in common with consisting of two reversed leather col- nearly all hot air engines, they are heavy lars, which seem to wear satisfactorily, in proportion to their power. Hot-air although in direct communication with engines, then, have decided advantages, the heating chamber. A is the cooling and in the country their employment or compression cylinder, in which, by the might, and probably will be, profitably device of an annulus of air between the extended. plunger and casing E, round which water Compressed air has been applied to circulates, a rapid cooling can be transmit power for a variety of objects; effected; and in the same way an annu- but the purpose for which, on a small lus of air in the other, or working cylin- scale, it seems specially adapted, is to suder B, enables a rapid transfer of heat persede manual and animal labor in rock to take place when this is necessary. boring and mining operations. For mine The action is as follows: When the air in and tunnels there are many advantages C is compressed by hand at starting to attending its use; for not only is the air about its original volume, the rising of which is compressed by external machinthe piston B, which is of equal area, ena- ery of great importance for ventilation, bles it to be transferred without change of but the fall in temperature by expansion, volume to that cylinder with which there which accompanies the necessary loss of is a communication. Here the heating, heat occasioned by its use, is valuable, which is facilitated by the shape of the as tending to reduce the temperature in bottom of the plunger, takes place, and close and heated workings. The princithe consequent expansion causes the pal objects to which it is put are for uncontinuance of the upstroke of D. Upon derground haulage, pumping, and rock the return stroke of D, the air is trans- boring or coal-cutting operations. The ferred to the compression cylinder, but first of these has been considered by is made on the way to give up heat to Mr. W. Daniel, in a paper before the Inthe thin plates in the regenerator H, of stitution of Mechanical Engineers,* and which a partial view is shown, and this is rather applied to motors of a size not heat is restored when the repetition of here dealt with; the second may use the first operation takes place; the rest any of the ordinary steam pumps; but of the heat which must be abstracted is it is the last which is particularly an extaken away by the water in the casing, ample of the successful application of and the engine now continues to work, machinery to replace individual physical the difference between the positive work effort. A vast amount of attention and in the working cylinder, and the nega- ingenuity have been bestowed upon rocktive work in the compression cylinder boring and coal-cutting apparatus, of being the effective work. The HP. which drilling shot holes in the former engine has been found to consume 4 is the most important and toilsome part pounds of coke per hour; the 1-HP. a of the labor required, and one to which little more than twice that amount. One was tested at the Royal Agricultural Show at Birmingham, and the work done by pumping showed a consumption of 13 pounds of coal per hour per HP., or a little more than that used by the pulsometer pump, or of that in the Tangye pump, in the experiments already referred to. The cost of coal for a week's work of six days, working ten hours a day, is advertised not to exceed 28. 6d. for a HP. engine. These engines are thus economical; they are reliable and simple in action, and require no skilled attendant; they are safe, and, in the application of motive power has been most beneficial. Only one form of rock borer will be described, but one which, at the Bristol docks, has proved efficient and durable. Figs. 12 and 13 are two views of the drill of R. Schram; the action simply imitates that of hand boring, viz., a succession of blows, accompanied by a turning motion. The machine consists of a strong cylinder supported by three legs, in which works a solid piston rod, driven by a double piston, the end of the rod carrying the * Vide Institution of Mechanical Engineers. ceedings, 1874, p. 204. Pro drill. The blows are given as rapidly as but when the drill and piston rod make 400 or 500 per minute, by means of the the in-stroke, the spiral rod running into valve ff, which acts in a somewhat simi- the former, and being itself held firmly, lar way to that of the special pump; turns it through the necessary angle; in when the opening o, shown by dotted the out-stroke no turning takes place. lines, in the cylinder is open to the press- The feeding is effected by the handure of the air, the opposite end of the screw T. valve will be also under pressure, and will remain in one position; but directly it is opened to the exhaust, by the edge of the piston passing it, the end of the valve will also be opened to the exhaust, the pressure removed, and the valve thrown over, and the action on the piston reversed. Fig. 13. Similarly for the opening o', communicating with the other end of the valve. The second action, or turning, is effected by means of a small piston p, shown in section, Fig. 13, which acts at right angles to the stroke of the drill, but is not quite in the same center line, and therefore every stroke it takes will turn the ratchet wheel w, which is in that line, and, consequently, the position of a spiral rod s fitting into the end of the piston rod. This happens when the drill is down, and the spiral rod free from it; It is well known that compressed air necessarily involves considerable loss, from the fact that most of the heat developed by compression cannot at present be retained, so as to act when the converse expansion takes place in the motor. This subject has been fully treated, both theoretically and experimentally, by many engineers, especially in France. From Mr. Robinson's paper,* already referred to, the total loss appears to be never in practice less than 50 per cent. of the energy used in compression, and sometimes as much as 75 per cent. Again, the result of some experiments by Mr. W. Daniel shows a loss† from 54.2 per cent., with 19 pounds per square inch air pressure, to 74.2 with 40 pounds air pressure. But the work lost is more than compensated for by the attendant advantages, and where, as in the Mont Cenis tunnel, a natural head of water can be employed, it must be superior to all other agents; though for purposes above ground, notwithstanding several attempts to introduce it, and except in the . Westinghouse brake, the loss with compressed air is sufficient to prevent its general adoption, and even rock-boring drills are then worked by steam. WATER. A natural head of water was, perhaps, the first power applied to take the place of manual labor, and though used all over the world on a large scale, and in Switzerland and some other countries for small powers-where mountain streams are employed even for such domestic purposes as churning and rocking cradles-yet in this country the extension of small water motors has been confined almost entirely to towns having artificial sources of supply. Nevertheless, as has been forcibly brought forward on several occasions of late, the natural power at * Vide Minutes of Proceedings Inst. C. E., vol. xlix., p. 17 et seq. ceedings, 1874, p. 210. + Vide Institution of Mechanical Engineers. Pro The two sources of water power in a town are: (1) The reservoirs for supplying water for domestic purposes. (2) The accumulators specially erected for obtaining a head of water. azine," and referred to by him in a paper before the Institution,† that "the water already supplied to towns for domestic purposes could in many cases be advantageously employed for working cranes, printing presses, and in short, all kinds of machines where manual labor was usually employed." This is an artificial source, since steam engines are generally present running to waste might, by sources will in towns, no doubt, continue means of more efficient transmitting to be principally used. Still in the country agencies, be taken advantage of. There small water wheels, or turbines, are often are several instances in which this is be- conveniently applied, and many of the ing done, as at Tortona, in Italy, where, former have been erected by Mr. W. since 1876, the force of the torrent Anderson, M. Inst. C. E. (of the firm of Scrivia has been made to supersede Messrs. Easton and Anderson), of 0.018, steam by applying telodynamic transmis- 0.04, 0.26, &c., HP., chiefly for pumping sion, and a daily saving of 60 per cent. purposes. * in cost thereby effected.* Again, on the estates of M. Menier, the power derived from the river Marne is used, by means of electric transmission, for ploughing and other agricultural purposes, and it is proposed to extend it to a distance of 3 miles from the source. Also, in Ameri- Up to the year 1849 the supply in ca the use of the almost boundless sup- towns was drawn from reservoirs, and it ply of natural head of water is being was one of the original ideas, set forth rapidly extended for similar labor-saving in a letter by Sir W. Armstrong, F.R.S., objects; but it is a significant fact with V.-P. Inst. C.E., to the Mechanics' Magregard to this country, that although Sir W. Armstrong, who, if not the first, has certainly been the chief, engineer in introducing the present hydraulic system, was led to the subject by noticing the waste above referred to. His first idea, like that of many others, was to prevent that waste, and he has established a magnificent system, not, however, based upon the use of the natural employed to raise the water into the ressource of power, but upon a source ervoirs. The expense, however, is a seriwhose essential principle is the produc- ous consideration, for it must be rememtion of an artificial head of water-in bered that the water is supplied for a most cases by the use of steam. The different purpose, and the head is only fact is, that the supply of power refer- made sufficiently great to distribute the red to must be turned into work at its water to the summit of the various source, or stored up under a, so to speak, buildings, and in London, for instance, higher pressure; since, when it is the it is not even so great as that. Besides power of the water, and not the water being small, the pressure is found to itself that is required, the proportional vary considerably, and not only by diurloss by transmission would otherwise nal changes, due to reasonable causesrender its use impracticable. Now the it being, for example, 45 pounds per obvious advantages to small industries square inch at Westminster in the mornfrom localization seems to account for ing, and rising to somewhat over 60 the undoubted tendency in this country pounds in the afternoon, and in Bristol to cary on small manufactories in towns, from 40 pounds to 70 pounds-but also to which the power must be conveyed: to sudden and erratic changes, most trytherefore, their connection with the nat- ing to the water motor employed. The ural source is an important problem, the consumer is, nevertheless, charged for solution of which necessitates (1) an the quantity used, independently of the abundant supply, and (2) an efficient pressure; and as inquiry seems to indimeans of transmission. England cannot cate that this is often highest in the be said to be rich in the former, and the latter is far from being in a satisfactory or settled state; so that, until the want of fuel is more keenly felt, artificial towns where the average pressure is lowest, the system must be far from satisfactory. These causes no doubt led to * Vide Transactions Inst. C. E. of Ireland, vol. ix., p. + Vide Minutes of Proceedings Inst. C.E., vol. 1., p. 66. 78. the second method, viz., the use of the olutions per minute. The inward-flow accumulator for supplying water under turbine of Professor James Thomson is considerable pressure, which brought made to very small sizes; but in a letter out the advantages of water as an agent, to the author the inventor says: "I do and showed its superiority under great not recommend any kind of turbines for pressures, from its incompressible na- ordinary use with very small water supture, which both renders it capable of plies and high-water pressures." The transmitting great power and at the reaction wheel can be made to work same time obviates all danger from ex- economically up to moderately high plosion; and the size of the motor can pressures, because the radius of its disbe so reduced as to render the amount charge orifices can be increased, and so of water used but trifling. The press- the law connecting the head with the ure under which the water is used has linear velocity of the jet (which is veeverything to do with the kind of motor locity=8/h) can be nearly satisfied. In employed; and before comparing the a paper read by Mr. W. C. Kernot, M. cost of the two foregoing modes of supply, the types of apparatus must be discussed. No doubt the motors giving the highest efficiency, under proper conditions, are turbines and reaction wheels, but these conditions are such as to exclude them for water under much pressure, and even with water from the mains the use of the former is practically out of the question, for the linear velocity of the rim of the wheel should bear some ratio to the velocity due to that pressure, and as the size of the wheel diminishes, its number of revolutions must, for a constant head of water, increase; so that to obtain any reasonable efficiency, the velocity for a very small wheel would have to be as much as 4,000 or 5,000 rev i A., C. E.,* at Melbourne, a small motor of this kind, shown in Fig. 14, is advocated, in which, by means of a counterweight a, one arm is dispensed with, and the hydraulic radius doubled, all sharp bends are avoided, and, as a result of experiment, with a consumption of 2.8 gallons of water per minute (at 1s. per 1,000 gallons), pressure by gauge 75 pounds per square inch, speed of 1,300 revolutions per minute; 0.055 HP. were obtained to drive a small lathe, the efficiency being 40 per cent. An ingenious form of governor was used, in which the increased speed by the centrifugal force of a weight, closed the orifice of escape and acted most effectually to check the *Notes on Small Motors. Royal Society of Vic toria, Oct. 9, 1879. racing and variation in speed, reducing the length. One side conveys the water unwater used from 2.8 gallons per minute der pressure to the cylinders by ports, in full work, to 0.75 gallon when all the which, when the cylinders are in an inmachinery was disconnected. There are clined position, communicate with cornumberless cases in which such a motor responding ports in their. basis; in a as the foregoing might be advantageously employed in towns, and where its use would compare favorably in efficiency with some of the engines at present chiefly employed and known as "waterpressure engines." The form of water-pressure engine which is almost universally adopted for obtaining rotary motion is the oscillating type. A sectional view is shown in Fig. 15 of Haags' engine, which is ex Fig. 15. Fig. 16. similar manner the other side conveys away the water when the cylinder is inclined in the opposite direction. Experiments were made with a dynamometer upon two of these, through the kindness of Mr. Camp, of Bristol, the inventor of hair brushing machinery, and which was used for that purpose, the other being erected at The Institution of Civil Engineers, Great George Street, for driving tensively used on the continent, and is largely supplied by Schmid, of Zurich, where small water motors are used to the number of one hundred and thirteen, as alluded to by Mr. E. Matheson, M. Inst. C. E.* The action of the engine is extremely simple. The oscillation of the cylinder about its center alternately opens the opposite ends of the cylinder to the supply and exhaust of water. There seems to be a large amount of clearance by the long ports which would entail waste, but otherwise the engine is cheap and efficient. It is being introduced into this country by Messrs. Bailey and Co., of Manchester. Another form is Rambottom's patent, of which a general view is shown in Fig. 16. This, from its small first cost and simplicity of action, is at present the most extensively used in this country. Three cylinders oscillate about their lower extremities, and work upon a hollow cast-iron pipe, which is divided into two parts by a vertical diametral partition running its whole *Vide Minutes of Proceedings Inst. C. E., vol. xlix. p. 35. |