« AnteriorContinuar »
London and North-Western and the Midland Railways. steam, and thus heats the metal and prevents undue conThe Birmingham and Warwick Canal forms one boundary densation of the working steam, while it is comparatively of this plot. The fuel to be used under the boilers is gas inactive in heating the back-pressure steam. In criticism obtained from Wilson's eight-hundredweight producers. of this argument, it may be remarked that towards the end Eighteen of Lane's water-tube boilers will supply six of the stroke (during the last quarter of the stroke) this engines to produce the 6000 horse-power aimed at at first piston-jacket surface giving heat to the exhaust-steam is Air is admitted to the furnaces through gridiron sliding greater than a side-jacket would offer. For three-quarters shutters, by nieans of which the supply is hand-regulated. of the stroke, however, it is less. It mixes with the gas in a mixing-chamber immediately Each cylinder is connected with the fly-wheel shaft by below the front end of the furnace. The roof of this a cross-beam. Over each end of each bean stands a mixing-chamber is an arch of perforated bricks, and these single-acting, air-compressing cylinder of 26 inches diabricks becoming highly heated the mixed air and gas is meter and 48-inch stroke. Each engine thus drives six raised to a high temperature before being ignited. No of these air-pumps ; and, since the speed is ninety double special means have so far been considered necessary to strokes per minute, the volumetric capacity of the com. prevent risk of lighting back into the mixing-chamber. pressors of each engine is close on 8000 cubic feet per The production of gas in the producers is controlled by minute. the steam jet blown in at the foot of each. The steam for The pressure in the mains is to be 45 pounds per square these jets is supplied from a special donkey boiler. The inch above the atmosphere, and the delivery-valves are exwhole of the steam jets are throttled down by the action pected to lift a little before three-quarters of the compressor of a governor that runs, so to speak, in equilibrium with piston-stroke is finished. Thus the volume of ait com. the air-pressure in the mains. The engine drives a small pressed to the above pressure delivered per minute air-pump, which forces air into one end of a small cylinder, by each engine is taken as about 2000 cubic feel. to the other end of which the air from the mains is ad
The ratio of pressures is 597 = 4:06. Thus, if the committed. If the pressure rises in the mains above standard,
147 the piston of this cylinder is moved, and this movement is pression curve were isothermal, the valves would lift, as communicated by suitable gearing to the throttle-valve above assumed, at 75 of the stroke. If it were adiabatic
, regulating the steam jet to the producers. The production this pressure ratio would correspond to a ratio of final to of gas, and therefore the production of heat by its com- initial volume of 367, and the valves would lift at 63 of bustion under the boilers, are thus automatically regulated the stroke. If the curve lay exactly mid-way between in accordance with the requirements, so that the air- these iwo, or were according to the law poc v-*, the pressure in the mains is prevented from varying outside ratio of final to initial volume would be '31, and the valves certain narrow limits. In connection with this part of the would lift at '69 of the stroke. In the latter case the scheme we may point out that it seems to be a mistake volume delivered would be 31 x 8000 = 2480 cubic feet not to throttle the entrance-areas for the air to the fur- per minute. Calculating simply from the product of this naces automatically and simultaneously with the regulation
volume by 45 pounds per square inch pressure (i.e. from of the gas supply. The chief advantage in using gas the work the air could do in an air-engine without clear. instead of solid fuel lies certainly in the power of obtaining ance, without expansion, and without more than atmoperfect combustion by thorough admixture and careful spheric back pressure), this would give about 487 horseproportioning of air to fuel. This advantage is sacrificed power delivered in the consumer's engines for each engine if the air supply is not diminished and increased simul- developing 1000 horse power at the central station. Two taneously with, and in the same proportion as, that of gas. indicator-cards taken from two air-compressing cylinders We suspect also that it will be found desirable not to rely at Frood Colliery, near Wrexham, give very difiereat solely on the throttling of the steam blast as at present results, possibly because one compressor was near the intended ; the more direct and rapid action of a throttle steam-engine cylinder, and was heated by it, while the valve between the producer and the boiler-furnace will be other was not. The compression-curve from the one highly advantageous, if not necessary. By means of cylinder corresponds with the relation por 2-425, while simple mechanical relays, actuated either by the steam or that from the other corresponds to p« 1-106. The latter by the compressed air, there can be no difficulty in con. curve is thus much steeper even than the adiabatic, and trolling these three sets of throttle-valves by the action of would indicate that the air was actually heated by conduca single governor.
tion or radiation during its compression. Such healing The steam-pressure is to be 160 pounds per square could hardly have taken place to such an extent as to inch. Each set of three boilers supplies an engine of account for the above very high index, and the more pro1000 horse-power. The engine is of the triple-expansion bable explanation is that ihe air was steam-laden as it was type ; the high-, intermediate-, and low-pressure cylinders taken in, and that the extra rise of pressure is really due having the diameters 20, 30, and 49 inches, and a common to that of the steam in the mixture consequent on the rise stroke of 48 inches. The areas of the three pistons are of the temperature. thus in the ratios 1, 21, and 6. The cranks are at 120° to It is desirable to keep down the compression.curve as each other. The high-pressure and intermediate cylinders nearly as possible to the isothermal line, because by doing are steam-jacketed at the sides. The low-pressure cylinder so the area of the compressor indicator-card, and there is not jacketed, but a novel arrangement of steam-jacket- fore the work to be done by the engines, is kept down to ing its piston is adopted. The piston is hollow, and its minimum ; whereas no advantage can be derived from steam is led into its interior by a tube which is parallel to the increase of temperature obtained by adiabatic com. the piston-rod, and moves to and fro through a stuffing pression, because this is rapidly lost by cooling in the gland in the cylinder cover, projecting into a larger tube pipes long before the air is utilised in the air-engine it screwed on the gland and supplied with steam direct from drives. It is worth noticing that, because of the air being the boiler. The argument in favour of this arrangement discharged from the compressors through valves which is that side-jacketing of the low-pressure cylinder involves automatically lift when a certain designed pressure is a large absolute waste of heat that goes towards heating reached, this loss of power due to cooling in the pipes is the exhaust-steam as it leaves the cylinder on its way to effected rather by a contraction of volume than by a the condenser ; this loss of heat by the jacket steam being diminution of pressure. The decreasing-pressure gradient noxious, not only because it is pure wasie, but also because along the pipes is very small, and is due solely to fricit raises the back pressure against the piston. The fresh tional and viscous resistance to the flow, and to variation steam in the hollow piston sweeps over the inside surface of velocity consequent on variation of section. of the cylinder just in front of the incoming working In order to approximate to isothermal compression,
Mr. Sturgeon has adopted very special cooling arrange that the steam is supplied to the piston-jacket of the lowments for his compressors. Firstly, the air used is all pressure engine cylinder ; but this refinement has not taken through the roof of the engine-house, and thus been deemed necessary in the design as at present heating by contact with the boilers and engines below is adopted. avoided. It is filtered of deleterious dirt in entering The compressor piston-face travels a little beyond the through the roof. Secondly, the compressor cylinders are position assumed by the flat face of this delivery-valve surrounded by ample water jackets, through which a con- when the latter is closed. During the momentary pause tinual fresh-water circulation is kept up: Thirdly, the at the end of the stroke, the valve therefore falls into delivery-valve—it is a single large disk of slightly greater actual contact with the piston-face, and the two descend diameter than the cylinder—is made hollow, and through together until the valve is landed on its seat. Thus the it a cold-water circulation is kept up, the water being clearance space is reduced absolutely to zero. spread out in a thin radial stream across the valve face The suction-valves are somewhat similarly arranged so over which the air flows as it leaves the cylinder. This as to reduce the clearance at the other end of the stroke cooling-water is supplied to the hollow valve through a to a very small amount. The cooling-water is circulated tube sliding in a stuffing-box in the cylinder cover. A by gravity from a tank giving a head of 20 feet. The further development of this system would be a supply of water is pumped into this tank from the canal, and the cooling water to the face of the piston after the manner power spent in pumping this water is a partial set-off
against the economy resulting from the approximation to projecting rings, and between these is poured, in the isothermal compression ; but the power thus gained molten state, through a hole in the socket-coupling, a soft greatly outweighs the work spent in this pumping. metal that expands during solidification. We rather doubt
As at present designed, the air-pipes are of wrought- whether this last design will give sufficient tensive strength iron plate, riveted, but a new design for plate-steel tubes to the joint. Tensive strength is required simply is being considered. The pipes are to be laid in concrete because there are necessarily bends in the pipe here and tunnels, which free them from all pressure of superincum- there. bent soil or paving, and will always be very accessible for The air is supplied to the consumer through a registerexamination and repair. They are of 24 inches diameter near ing meter. This meter is similar in construction to the central station, and diminish to 7 inches in the smallest Beale's gas exhauster. It consists of two cylinders, one branches. The joints are given a small degree of flexi- inside the other. Both are 4 inches long; the outer one bility. In one design they are formed by two angle- has a diameter of 14 and the inner a diameter of 93 irons riveted to the outside ends of the two pipes, a hard inches. The outer one is fixed, and is furnished with an rubber ring of circular section being placed between the inlet and an outlet opening. The inner cylinder revolves flanges thus formed, and the flanges being drawn together freely on a fixed axis, distant }(14-93) = 21 inches away by bolts. In another design a sort of double-socket from the centre of the outer case, so that the two cylinders coupling-piece covers the ends of both pipes for a few always touch along a fixed line. Two sliding shutters inches; the end of each pipe has formed on it two slightly project from a slot through the centre of the revolving 278
cylinder. By means of a pin and a pair of sliding blocks pure rolling action at one or other side of its tread. The running in circular grooves cut on the inner surface of, wearing might not be of much consequence in itself, ex and concentric with, the fixed cylinder, these shutters are
cept that it gradually vitiates the accuracy of the indica. drawn out and in from the revolving cylinder so as always tion; and besides, the velocity ratio is uncertain because of to keep in contact with the fixed one. During one revolu
the contact taking place over a perceptible range of radius. tion these shutters sweep through the meter a volume of There ought to be an idle roller between the disks opposite air about '17 cubic feet.
the driving roller, and both disks ought to be pressed in. This rotation is reduced three times by worm-gearing wards by springs, instead of one only. But the chief in being transmitted to the counter-box, so that a single defect is in the principle of the construction, which does dial with two concentric circular scales, which are read
not make the dial-indication proportional to PV as it by two fingers like the hour- and minute-hands of a common ought to do. If R, be the disk radius at which the roller clock, is sufficient to register up to a million cubic would stand when zero pressure existed in the Bourdon feet. Fig. I shows this meter. It is driven by a small tube, and if ( be the inward movement per pound per difference of air-pressure between the inlet and outlet.
square inch rise of pressure, and if r be the radius of the The Company intend to charge at the rate of 5d. per roller, then at pressure P the contact radius on the disk 1000 cubic feet at standard pressure of 45 pounds per
will be R. - CP, and the fractional revolution of the disk square inch. If the air were used in an engine without per revolution of the roller is
This is not proexpansion, without clearance space, and without back pressure above the atmosphere, this would correspond to portional to P as it ought to be. Its differential coa cost per hour per indicated horse-power of
efficient with respect to P should be constant, whereas it
(r 60 X 33000 X 5
The converse gearing ought to 1:53 pence.
(R.- CP) 144 X 45 X 1000 Under the conditions of actual practice the writer calcu- geared positively with the disk, and the disk should drive
be substituted ; that is, the volume-meter should be lates that at the above rate of 51. per 1000 cibic feet, assuming intelligent and economical management, each
R, - CP
indicated horse-power will cost per hour from 2d. down to as low as 1}l., excluding cost of engine attendance and depreciation, and interest on first cost of engine. The standard pressure at which the air is sold at the with the centre of the disk. It also seems a pity, when
the roller, the point of contact for zero pressure coinciding above price being 45 pounds per square inch, a reduction a Bourdon tube that measures the pressure exists in any of price per cubic foot has to be made if the pressure of the supply be less than this pressure. This is effected by should not be made visible by the simple addition of a
case in the meter, that its measurement of the pressure introducing a variable velocity-gear between the volume-pointer and graduated dial. meter and the dial-counter. This arrangement is shown The registrations of all the meters in the whole district in Fig. 2. The rotation is transmitted to a small roller on a spindle one large central counter, so that the engineers in charge
are telegraphed to the central station and added up on capable of sliding in its bearings parallelly to its own axis. It drives å disk on the counter-arbour by rolling consumption with the duty of the engines, known from
may have means of continually comparing the actual contact
. The end of the roller-spindle is linked to the ordinary engine continuous counters, and of detecting and end of the tube of a Bourdon pressure-gauge. As the serious Yeakage that might occur in consequence of breads pressure rises, the
roller is thus pushed nearer the centre age of a main or branch pipe. The telegraphing apparten of the disk, and gives this disk, therefore, an increasing is shown in Fig. 3. The counting disk is divided into ton fraction of a revolution per revolution of the roller. The equal “divisions, each roller really lies between two disks, but the one is “idle” small metal projections. and serves simply to support the roller in pressing against underneath a contact-maker, they allow the passage of a
As these come successively the driven disk.
current, which moves the finger of the ceotral counter badly designed in detail
. The roller has a rubber tyre branches to the separate meters, is sufficient for the whole This integrator is wholly wrong in principle, and it is round it, and therefore touches the disk at different radii, district, the earth return being used. As the counter-disk and thus must rapidly wear away, owing to the want of moves slowly, special means must be taken to break the
contact instantaneously after it is made ; otherwise all but taken i atmosphere below atmospheric pressure. The one of the indications of several meters, whose times of point F is taken on the same isothermal as C ; thus D F is contact with the tooth on the disk overlapped, would fail the loss of volume consequent on the air cooling in the to be registered at the central station, and should the pipes down to atmospheric temperature. The diastoppage of any one engine in the district happen to gram E F G H is the indicator-diagram for an engine driven occur while this tooth of its meter was in contact the by the air without loss of initial pressure below the comwhole registering apparatus would cease to act for an pressor pressure, without clearance, without expansion, indefinite time.
and with a back pressure i atmosphere above atmoThe contact-breaker is shown in Fig. 3, at the left-hand spheric pressure. The same back pressure is used for all side. The momentary current caused on making contact the other engine diagrams. The diagrams E FIK H, magnetiscs an electro-magnet, which, by attracting its | E F LMH, and EFNH are diagrams for engines with armature, draws the contact-maker (which is mounted on similar conditions, and with ratios of expansion 1}, 2, and a piece of watch-spring) past the tooth into such a position 25; that is, with cuts off , }, and ?, the last being that that it catches belind a small plate of insulating material that brings the final pressure down to no atmosphere. at the back of the tooth, which prevents it springing again The expansion-curve FIL N is taken as adiabatic.
If into contact with the latter when the armature of the } atmosphere be lost in frictional and viscous resistance magnet is released.
to flow through the pipes, by obstructions at bends, passage Fig. 4 explains the calculation of the thermodynamic through meter, &c., or by sudden change of section of efficiency of this mode of transmission of power. It is pipe, then the admission line is lowered to P Q. The drawn for unit volume of atmospheric air drawn into the effect of clearance is to cut off a part of the diagram by a air-pumps. The pressures are reckoned in atmospheres. vertical line at the left-hand end.' This vertical line is not A B C D E is the indicator-diagram showing the work done drawn in the diagram, because its position varies with the by the compressor-pump. The compression-curve CD is grade of expansion employed in calculating the following taken according to the law po v-1.2 because it seems pro- results the clearance has in each case been taken as in the bable that this index may be reached with the efficient volume of the cylinder. The area of the compressorwater-cooling system adopted. The suction-line AB is diagram is 16, and the efficiency is in each case obtained
by dividing the engine-diagram area by 16, and multi- engine. This can hardly be accomplished even if the engine plying this quotient by y's. This l is the ratio between be situated close to the central works. It need hardly be the compressor-diagram and that of the central station pointed out that the expansion will not usually be carried engine which drives it, the mechanical inefficiency of this so far as to bring the working pressure to near equality central plant being taken as tu. The results are most with the back pressure ; in fact, to do so is decidedly very clearly shown in tabular form.
bad practice, and does not lead to economy in the brakeTable of Efficiencies of Transmission of Power by Air power, especially when depreciation and interest on first compressed to 45 pounds per square inch
cost of the engine is taken into account.
With good Efficiency
management, from 30 to 50 per cent. efficiency may be Ratio of expansion
expected. No loss of initial pressure
In a paper read by Mr. Sturgeon before the British No clearance
'72 | Association last summer, he gives a table of calculated Back pressure l'i atmos.
efficiencies ranging from 32 to 84. These calculations Initial pressure 38 atmos.
| include allowances of 2 per cent. for valve-resistance and No clearance
64 ... '69 leakage past compressor-piston ; 13 per cent. for leakage, Back pressure l'1 atmos.
friction, and wire-drawing in the pipes; and 8 per cent. No loss of initial pressure
for clearance and back pressure in the consumer's engine. Clearance t'a vol. of cyl. *39 *50 57
Except the last, these allowances are much more liberal Back pressure I'I aimos.
than those that have been made in calculating the above Initial pressure 3.8 atmos
table. On the same basis as ours have been made, Mr. Clearance ou vol. of cyl. *36 47 54 57 Sturgeon's calculations would have given considerably Back pressure l'i armos.
higher figures than the above '32 to 84. But the higher The last two sections of this table comprise the limits figures in Mr. Sturgeon's table are obtained by supposing of practicable results. The highest efficiency shown is 60 that the consumer heats the air by a gas-stove, before per cent This could only be obtained by avoiding abso- passing it into his engine, up to temperatures from 212° F. lutely all loss of pressure between compressors and air- to 320°F. How the resulting figures can be in any sense
called efficiencies” it is difficult to understand. The generally displayed in selecting worthy local objects, such as consumer is supposed to supply a large extra amount of museums, improved science schools, and the like. All this of power at his own cost by burning gas to heat the air, course is admirable and entirely to be applauded, but believing as and it seems an extremely evident misuse of the word “ efficiency” to apply it to the ratio of the diagram so got properly conducted, doing more good for the future development
we do that there is a possibility of the Imperial Institute, il to the diagram of the central station engine. By a little more liberal burning of gas, the efficiency obtained by
of science and commerce in Greater Britain than any other single this method could quite easily be made higher than unity organisation can possibly effect, we hope that it will not be On the same principle we might calculate the efficiency starved in favour of merely local objects. We hear that the women of a steam-engine by taking the ratio of the indicator- of England have already subscribed a noble sum. This no doubt card from the steam cylinder to that taken from the feed- | Her Majesty will hand over to the Institute, if it is organised 50 pump that supplies water to the boiler, and thus obtain an as to command the confidence and respect of the various leaders efficiency of, let us say, 50,000 per cent. This is a reductio of opinion in this country and in the colonies. ad absurdum of the method of calculation which is perfectly legitimate and logical.
R. H. S. MANY of our readers will attach much importance to Colonel
Donnelly's letter, which appears in another column. A large
increase in the number of students anxious to enter the Normal THE CLASSIFICATION OF THE CÆCILIANS School of Science and Royal School of Mines was of course 10 IN a paper on the structure and affinities of the be expected, and we are glad that this influx has induced:he de
Amphiumidæ, published in the newly-issued part of partment to take steps to increase the accommodation, and at the the Proceedings of the American Philosophical Society same time to insist upon one of the best possible forms of (vol. xxiii. No. 123), Prof. Cope has put forward some entrance examination; a strict inquiry, namely, into the educational views as to the position of the Cæcilians or Apodous history of each candidate for admission. Batrachians in the Systema Naturæ, which are worthy of careful consideration. The Cæcilians, Prof. Cope observes, The Norwegian Government has presented a Bill to the are generally regarded as representing a distinct order of Storthing for fixing a standard time for the whole of Norway, the Batrachian class, which bears the name “ Apoda," or The standard time proposed is Greenwich time plus one hour.
Gymnophiona.” The definition of this order given by Mr. Boulenger in his recently published Catalogue of the
MR. W. BILDWIN SPENCER, Fellow of Lincoln College, specimens of these animals in the British Museum is : Oxford, has been appointed to the Chair of Biology in the
No limbs ; tail rudimentary ; males with an intro- University of Melbourne, and will leave England in about three mittent copulatory organ; adapted for burrowing.”. Of weeks. Mr. Spencer distinguished himself lately by his these definitions Prof. Cope maintains that not one is of important memoir on the pineal eye in lizards. ordinal value. “The tail in some Cæcilians is distinct. The intromittent copulatory organ in such species as
A NUMBER of eminent men of science have addressed a Dermophis mexicanus, Gymnophis proximus, and Herpete memorial to the President, Vice-Presidents, and Council of the ochrocephala is not a special organ, but merely the everted Royal College of Surgeons of England, suggesting that the cloaca. The hard papillæ observed by Gunther in legacy bequeathed to the College by the late Sir Erasmus Ichthyophis glutinosus are wanting in the above-men- Wilson might with advantage be devoted to the establishment tioned species, and the protrusion of the cloaca is per- of an institution having for its object " physiological and pathoformed by two special muscles.”. As regards the absence of limbs in the Cæcilians, Prof. institution in England has long been fell, and more especially or
logical research." It is pointed out that the want of such an Cope points out that the extremely rudimentary character of these organs in Amphiuma is well known, and that late, when we have had to look to Berlin for infrination respect their non-existence has no greater claim to be considered ing tubercle, and to Paris for experiments on the prevention of as of ordinal value in the Batrachians than in the adjoin. hydrophobia. That the Government will do anything in the ing class of Reptiles, where it is in some cases not even a matter no one is so sanguine as to believe ; and it is hardly " family” character. Looking to these facts, Prof. Cope more probable that the want will ever be supplied by public proposes to unite the Cæcilians with the Urodele subscription. There is, therefore, much to be said for the preBatrachians, and to class them only as a family, sent proposal, and the authorities of the College of Surgeons "Cæciliidæ," connected with the more typical forms of will, no doubt, give it due attention. It seems strange that in the group through the Amphiumidæ.
London there should be nothing like the splendid laboratories Messrs. Sarasin, who have recently published a most interesting account of their observations on the develop which exist not only in the capital cities of Europe, but in comment of a species of Cæcilian in Ceylon,' seem to have paratively small German towns, such as Bonn, Strasburg, and come to nearly the same conclusions as to the correct Leipzig. systematic position of this group of Batrachians.
UNIVERSITY COLLEGE, Liverpool, has reason to congratulate itself on having some remarkably generous and enlightened
friends. On Tuesday last it was announced at a meeting of the NOTES
College Council that Mr. Thomas Harrison, shipowner, or The Prince of Wales has requested the President of the Royal | Liverpool, bad endowed the Chair of Engineering with 10,000/ Society to join the Committee appointed to advise on the organisa. Only a few weeks ago Sir Andrew Walker, also a citizen tion of the proposed Imperial Institute.
of Liverpool, gave 15,00ɔl. to build Engineering Laboratories. We have referred elsewhere to some of the possible results of On Thursday last the honorary freedom of the City of London the meetings held last week in favour of the Imperial Institute. was conferred upon Mr. H. M. Stanley, in recognition of his Some very striking features which have been developed in con services as a traveller and explorer in Africa. The presentation nection with this movement during the last week are, first of all, was made at a special meeting of the Court of Common Council the considerable desire which has been evinced, to enrich various in the new council chamber at the Guildhall. The City Chamlocalities with some Jubilee memorial, and, again, the wisdom berlain, in making the presentation, referred to "the remark "Ueber die Entwicklungsgeschichte von Epicrium glutinosum,” Arb.
able development of journalistic enterprise during the Victoria Lool. Inst. Würzburg, vii. p. 292 (1885)
era," observing that Ms. Stanley was the first member of "the