Lapas attēli
PDF
ePub

steam.

cannot generate a sufficient quantity of on the sides of the vessel a pressure, which to be continually jerking, and consequently

But when a speed of eight miles is the result of its elastic sorce, and which opening and shutting continually the valve, per hour only is required, and for an aver gives the exact measure of that force. If, the weight was replaced by a spring, and age train of twenty-four wagons, which, in the vessel being already filled with steam, that is the manner in which the valves are going up the line empty, are equal to a la fresh quantity is continually added, the at present constructed. load of about sixty tons on a level ground, elastic force of the steam will augment the most convenient boilers have been more and more, and consequently also the $ 2. Of the Levers and Spring-Balance. found to be those with one returning tube. pressure it produces on every square inch

It will easily be conceived that no exact They generate a sufficient quantity of of the surface of the vessel. Now, if at

calculation can be established of the power of steam for the work required of them, and one point of the vessel there be an aper

locomotive engines, without knowing exact. have the advantage of being cheap in re-ture, closed with a moveable piece supgard to prime cost and repairs, as their form|porting a certain weight, it is clear that, Illy the pressure of steam in the boiler, which

is the intenseness of the propelling force of is simple, and they are entirety made of as soon as the steam contained in the vesiron, whilst the tube boilers require the use | sel produces upon the moveable plate a the motion. If we were to depend on the of copper.

pressure equal to that of the weight which nominal pressure of the engine, that is to Besides the difference in the form of the holds it down in the opposite direction, the say, the pressure declared by the constructboilers, the other parts of the engine differ plate will begin to be lifted up; the passage or, great mistakes might be incurred : for

it sometimes happens that, with a view to also. The cylinders are placed on the will then be opened, and the steam escapoutside, and in a vertical position. The ing through the aperture, will show that give to a locomotive engine the appearance motion is not communicated from the pisits pressure was equal to the weight that of executing more than others, though at

the same pressure, its pressure is declared ton to the engine by a crank in the axle, loaded the plate or valve.

to be 50 lbs. per square inch, whilst it but by a rod on the outside of the wheel, It must, however, be observed, that the really is 60 or 70 lbs. Moreover, the calresting upon a pin fixed in one of the resistance which opposes the egress of the culation of the pressure is generally so inspokes

. Those engines have in general || steam does not consist only in the weight correctly made, that scarcely any dependsix equal wheels, of four feet diameter that has been placed on the valve. Besides ance can be placed upon it. each. Two of the wheels are worked by that weight, the atmosphere produces also We have therefore been obliged to make the cylinders, as has been just explained ; on the valve a certain pressure, as well as a particular study of that part of our suband the four others are attached to the first upon every other body with which it comes ject. by connecting rods, that cause them to act in contact. That pressure is known to be

We shall first give the manner of ascerall together.

equal to 14.7 lbs. per square inch. It is taining the pressure by weighing and measThe weight of these engines varies. therefore the weight, added to the pressure uring the different parts of the valve appaSetting aside the three which we have of the atmosphere, that gives the real meas-ratus, in case one should have no mercurial mentioned as being on the model of the ure of the elastic force of the steam; while

gauge. We shall afterwards show the Liverpool ones, and which weigh only the weight alone represents only the sur-|| cause of some mistakes which may be inabout five tons and a half, the average plus of the pressure over the atmospheric curred by that mode of calculation, and weight of the others is from ten to twelve pressure, or what is called the effective which are avoided by using the mercurial

pressure of the steam.

Consequently, steam-gauge. Lastly, we shall point out All those engines are supported on when a valve has a surface of five square the uncertainty to which also that instrusprings. In some of the older ones, the inches, and supports a weight of 250 lbs., ment is liable, and we shall water of the boiler, pressing upon small which, divided between the five square to be used instead of it.

propose another moveable pistons, and pressed itself by the inches, gives a resistance of 50 lbs. per We have said, that, to produce on the steam contained in the boiler

, was intended inch, that amount of 50 lbs. expresses the valve a great pressure without being ento supersede the springs; but though that effective pressure of the steam, a valuation cumbered with a considerable weight, a system displayed a great deal of ingenuity, frequently made use of on account of its lever is employed. M (fig. 16) being the the spring it formed was found in practice convenience for calculation, whereas, 64.7 boiler, and $ the valve, C is a fixed point to be too variable, and the system was lbs. is the real resistance opposed, and to which is fastened one of the ends of the given up.

therefore the real pressure of the steam. lever BC. The lever presses at the point The usual proportions adopted for the

This is the principle on which are es-|| A on the valve by means of a pin, and at engines on that railway are the following : tablished the means of judging the amount the point B it supports a weight, or to Cylinder

144 inches.

of pressure in locomotive engines. How-speak more accurately, it is drawn by a Siroke

16

ever, as those engines are required to work spring equal to a given weight. Wheels

4 feet.

with at least 50 lbs. effective pressure per The diameter of the valve, the propor

square inch, and as, in order to give passage, |tions of the lever, and the weight suspendEffective pressure

48 lbs. per sq. in. if necessary, to all the steam generated in||ed at the point B, or at least the weight reThe pressure, however, varies according the boiler, a valve must not have less than presented by the tension of the spring being to the ascertained solidity of the boiler

. 24 inches diameter, or 5 square inches sur-given, it will be easy to deduce from them When the sheets of which'it is formed be: face , it follows of course that if a weight is the pressure resulting on each square

inch gin to grow very thin, the pressure is to be applied directly upon the valve, it of the surface of the valve. And, vice versa, sometimes reduced to 36 lbs. only per must be equal to 250 lbs. Such a weighil it will also be easy to know what weight square inch; in other circumstances, it is, would afterwards render it very difficult to ought to be applied to the point B, in order on the contrary, increased to 60 lbs.

lift up the valve with the hand, which fre

| to produce at A a given pressure. For, if quently becomes necessary in the working P represent the weight suspended at B, that

of the engine, and particularly to ascertain weight will produce on A a pressure CHAPTER II. whether the valve may not have contracted

BC OF THE PRESSURE IN STEAM-ENGINES. an adhesion to its seat which would make | px

AC

which will consequently be the it useless. ARTICLE I.

It was therefore necessary to produce whole pressure produced on the valve ; and the pressure by means of a lever; for, if if S represent the surface of the valve in we suppose the lever divided in the pro

BC DING TO THE LEVERS AND THE SPRING- portion of 5 to 1, a weight of 50 lbs. sus

Px inches

AC will be the pressure propended at the end will be sufficient to produce the required pressure without the dis

S § 1. Of the principle on which that calcu- advantage of having a considerable weight duced on each square inch of the surface of lation is founded,

to move. But, on the other hand, as, in the valve. When an elastic fluid is confined in a the rapid motion of the engines, a weight The levers and valves used by the dif, olased vessel, it produces in every direction euspended at the end of a lover was foundl|ferent constructors of ongines vary con

tons.

Weight

11 tons.

OF THE

PRESSURE

CALCULATED

ACCOR

BALANCE

1

Pex

siderably in their proportions. But, among to it, the divisions may easily be verified,||aperture of the lever at that place, and those proportions there is one, first used by after the balance is graduated.

then, with another spring-balance, the Mr. Edward Bury, of Liverpool, which pos When on the engine, the foot P of the lever must be weighed by means of the sesses an uncontested advantage over all balance, where the object to be weighed string. It is clear that the weight marked other combinations of that sort. It consists would be suspended, is fixed in a solid by the second balance will be the pressure in taking for the proportions between the manner to the boiler; and the rod T, which produced by the lever at the place of the two branches of the lever the ratio of the would be held in the hand in common valve; to that must be added the weight area of the valve to the unit of surface. | weighing, is fastened to the end of the lever. of the disk of the valve, which must By that means the weight P suspended at This rod passes through an aperture cu also be weighed separately, by putting B gives immediately the pressure produced through the end of the lever, and is fixed it into the basin of a common pair of on the valve per unit of surface. Suppos- || above it by a screw which rests upon the scales. When the levers have a total ing it should be required to establish a valve lever. When it is required that this balance length of 3 feet with the usual thickness, of 24 inches diameter, which make very shall produce a pressure of 10 lbs., nothing they commonly weigh 27 lbs, or 28 lbs, at nearly 5 squre inches surface, and that. in more is necessary than to lower the screw the place of the valve. The disk of a valve consequence, the ratio between the two until the spring rises to the point marking of 24 inches diameter, and half an inch branches of the lever has been taken as 5 10 lbs., and the same for any other weight. || thick, weighs in general about 10 ounces.

BC to 1, that is to say,

Vice versa, the steam being in the boiler There is therefore a weight of 28} lbs. that AC at an unknown degree of pressure, if we

to be divided on the whole surface of the pressing the weight suspended at B, it is loosen gradually the screw until the steam valve; so that if that surface is equal to clear that the pressure produced at A will begins to raise the valve, that is to say, inch. When the levers are only 15 inches

5 square inches, it makes 54 lbs. per square BC be P * AT=5P. This will, therefore, the pressure of the spring, the pressure of long, they generally weigh 71 lbs. at the be the total weight on the valve, and the the steam will be known, for the degree with the disk, 8 lbs. 8 oz., and divided besurface of the valve being 5 square

inches,

then marked by the index will show the the weight or pressure per inch will be

tween the 5 square inches, a little more weight which is equal to it.

than 11 lbs. per inch. 5P

2. To know the weight of the part of 5 =P. The same would take place if, || 9 3. Of the corrections to be made to the

Weight marked by the Spring-balance. the balance supported by the lever, the having a valve 3 inches in diameter, which

balance ought to be taken to pieces, and gives 7 square inches for the surface, the The mode we have just explained is the the spring with its rod weighed separately, ratio between the branches of lever were to one commonly used to calculate the pres. However, this operation may be avoided be taken as 7 to 1.

sure on the valve.

However, it will easily by taking the balance in one's hand, and We have said that, to the weight which | be conceived, by the manner in which the suspending it in the contrary direction in ought to be snspended at the end of the spring-balance acts upon the valve, that, which it is placed in the common act of lever at B, is substituted the equivalent to know the pressure which really opposes weighing, that is to to say, with the foot pressure of a spring. This spring is a spiral, the egress of the steam, it is not sufficient above and the rod below; the weight which by being more or less compressed, to read the degree where the index stops, marked by the index will then be equal to is able to support in equilibrium, and and to calculate the effect produced at the the difference between the weight of the consequently to represent larger or smaller end of the lever, as we have done above. rod and spring, and the weight of the weights. In other words, it is a spring bal. In fact, first, besides the weight represent-foot. If, therefore, the total weight of the ance, such as is used for weighing in daily

ed by the spring, and which would be sus- balance be known, which is easy, by

pended at the end of the lever, it is clear placing it in the basin of a common pair This balance consists of a rod T (fig. 16) certain degree of pressure ; for before the may easily be calculated, and consequent

that the weight of the lever itself causes a of scales, the weight of each of its parts which is held in the hand, and to which is steam is able to raise an ounce of the ly also the weight of the rod and spring: fastened a plate with a narrow oblong aper- Ispring, it must raise the whole weight of ture in it. Behind this plate, and in all the lever.

In fact, the degrees having been marked

The same takes place in re-l on the balance when in its usual situation, cylindrical tube, is a spring, the foot of gard to the disk of the valve, which must zero was inscribed at the point where the which rests on the basis L, which is fixedbe raised before the steam can have any index stood when the spring bore no weight to the plate. At its other end, this same action on the balance. 2. When any ob- at all, or more exactly when it only bore spring is pressed by a moveable transverse ject is weighed with the hand, that object the weight of the foot. Afterwards fresh bar mn. At the bottom of the aparatus is is suspended at the bottom of the balance, weights were successively added, and for a rod P, to which are fastened the objects but then the hand supports the upper part, each of them the corresponding number that are to be weighed. The prolongation that is to say, the rod, with the spring to was inscribed on the plate, always omitof the bar mn projects throngh the aperture which it is fastened ; and that effort is not ting the weight of the foot, which in fact of the plate, and is terminated by an index taken into account, because it does not make ought not to be reckoned. The numbers which appears on the outside, and which a part of the weight. Here, on the con inscribed on the plate represent, conseslides up and down the aperture, in propor-trary, the rod, the screw, and the spring;quently, the real tension of the spring;

les3 tion as the spring is more or less com- are an additional weight' really suspended the weight of the foot of the balance. pressed. Divisions are engraved along that at the end of the lever, over and above the Now, by turning the balance upside down, same aperture. In order to mark them, pressure marked by the spring; they must the spring is drawn by the weight of the known weights of 1 lb., 2 lbs. &c., are suc- all be raised before the spring can be pres.rod and spring which it then bears. If it cessively suspended at P, and according sed upon in any way, and can register any had borne a weight equal to that of the as those weights, by pressing on the spring, effort; they must therefore be taken into foot, it would have marked zero; if

, the ecause the index to rise, the corresponding account

. The true pressure which takes fore, it marks 2 lbs. or 3 lbs., the rod and divisions are marked. The consequence of place on the valve will consequently not spring weigh 2 lbs. or 3 lbs. more than the this is, that when an object of unknown be known, until are added to the weightfoot. weight is suspended at P, and makes the marked in the balance: 1. The pressure

Supposing thus: B to be the total index rise to the point marked 10, that is to produced by the weight of the lever at the weight of the balance, T the weight of the say, to the same point to which a known place of the valve: 2. The pressure pro-|| rod and spring, and Þ' the weight of the weight of 10 lbs. made it rise, we concludeduced at the end of the lever by the weight foot; if the balance turned upside down that that object also weighs 10 lbs. This of the rod and spring of the balance.

shows m weight, we shall have is the sort of balance which is used for 1. To know the effect of the lever on the

:T-P; measuring the pressure in locomotive en-valve, the lever must be unfastoned from but, on the other hand, the weight of the ginos, Wo see that, by taking it off from the balance; a string must be wound balance is equal to the weght of its two the engine, and suspending known weightaround the pin A, or passed through the parts, or

occurrences.

;

2

4+1.5

2

2

even

B=P' +T:

which they completely fill, it is very clear||inferior diameter, an error will thus be come adding therefore together these two equa-| that the steam can only act upon their in- mitted of 5 lbs pressure per inch, which tions, we find

ferior surface; consequently, the area we error might be still greater if the raising of B+m

have here above expressed by S, must be the valve should happen to be more considB+m=2 T, or T

taken after the inferior diameter of the erable. Moreover, as there is no practical

valve. By calculating in that manner, the means by which to learn by how much the When the valves have a lever of 15 inch-exact pressure will indeed be found for diameter of the valve is augmented by the es only, the balance used weighs general-levery case in which the valve still touched |raising, the consequence will be that the ly 4 lbs., and when turned upside down, the seat, or, if raised at all, was only so for mode of calculation explained here above, it marks 14 lb.; so in that case the weight, an instant, or in a very small degree; but even with the corrections we have made, of the rod and spring is

whenever the steam, being generated in will apply exactly only to those cases

greater quantity than it is expended by where the valve just begins to be raised, T= 2.75 lbs.,

the cylinders, escapes with force through or lets scarcely any steam escape ; but the

the valve, it raises considerably the disk of greater the raising the more iné calculawhich is the weight to be added at the the valve; the consequence then is, that, ied amount will surpass the real pressure. end of the lever ; that is to say, to the instead of acting on the inferior surface of We shall see hereafter examples of this. weight already marked by the balance.

the valve, it evidently acts on a greater But still this is not all. If the pressure When the valve has a lever of 3 feet, surface, and which is the greater the more of the steam in the boiler must be deduced the balance requires smaller divisions. It the valve is raised. For instance, in fig. from maasurements taken on the engine, it usually weighs only 2 lbs., and turned up. 20 it acts on the surface cd instead of act. must also be observed that it frequently side down, mark3 14 lbs., which gives in ing on ab. In that case the area $ ought happens, in order to make the construction that case for the weight of the rod and to be calculated on cd, and not on ab. But more easy, that the miter of the valve is spring

how are we to know cd, unless we calcu- made to join the sides of its seat only with2+1.5

late it by the rising of the valve, which is in a certain breadth, as may be seen in fig. T=

1.75 lbs.:

a very difficult, if not an impossible, opera- 21. The consequence is, that the surface adding therefore those weights to those tion? Moreover, the difficulty is complica: |ab, or the inferior part of the valve, which marked by the index of the balance, and ted by the circumstance that, from a tob has been measured, is not the surface upon taking besides into the account the weight the pressure of the steam acts directly to which the pressure is divided. The real of the lever

, as mentioned above, we shall raise the valve ; but from c to a and from diameter in this case is cd, if therefore then have the real pressure produced by 6 to d the action of the steam takes place there be between ab and cd a difference, the whole apparatus on the valve. Di.only in a lateral direction, and according to for instance, of one-eighth of an inch, this viding it by the area of the valve, the re an angle, which varies in proportion as the

difference

may produce, as well as in the sult will be the pressure effected upon each valve is more or less raised. unit of surface.

The effect of this alteration in the diam. case of the raising of the valve, a differ

ence of 4 to 5 lbs. in the pressure. MisFrom this we see that, with a long lever,|| eter of the valve, which at first sight ap

takes is in

may

be avoided in that respect, by the error of pressure per square inch may|pears to be of very small consequence,

measuring not only the inferior diameter of amount to 7 lbs. or 8 lbs., and that,

fact very considerable. Let us suppose, with a short lever, it may be 3 lbs. or 4 lbs., for instance, that we have a valve of 2.50 the valve, but also the diameter of its seat.

There still, however, remains the blowing which is still considerable.

inches diameter at the bottom, and 3 Keeping the preceding notation, that is inches at the top, of which we shall find of the valve, the exact appreciation of which to say, P being the weight shown by the several examples hereafter. Let us further escapes all manner of calculation.

The mercurial gauge, which we are going index, T the weight of the rod and spring, suppose that, by the effect of the blowing L the weight of the lever, weighed as of the steam, the valve has been raised so to describe, is the means of avoiding both mentioned above, and D the weight of the as to have increased its real diameter causes of error; but that instrument is exdisk, lastly BC and AC being the arms of only by one-eighth of an inch; that is to pensive, and as yet so scarce, that in all the the lever, and S the surface of the valve insay, that it is become 24 inches instead of factories and on all the railways, except square inches

, the pressure produced per 24 inches, or 2.625 inches, instead of 2.50 the Liverpool one, there is at present no unit of surface will be

inches. The surface of the circle being ex- other mode of ascertaining the pressure BC

pressed by * . d?, where d stands for the than those explained above.
(P + T) +L+D diameter and a = 3.1416, the proportion
AC

of the circumference to the diameter, the
surface of the valve, which was at first

ARTICLE I I.
It is for not having taken these consid-
erations into account that we find so often x 3.1416 x 2.5 = 4.91 sq. inches,
locoinotive engines spring-balances,|| has become

§ 1. Construction and use of the Mercuwhich are supposed to be fixed at 50 lbs.

rial Steam-gauge. pressure per inch, but which are really fix: | * * 3.1416 * 2.625= 5.41 square inches. ed at 55 lbs. or '60 lbs. We shall soon Consequently, if we suppose the total

The calculations we have made may be have frequent occasion to apply and verify weight supported by the valve, including sufficiently exact for a great number of these principles, which by that means will the levers, rod, disk, &c., to be 245 lbs., cases,

Still they present some degree of be rendered perfectly clear.

that weight, when the valve is shut, will complication that makes them inconvenient; represent a pressure per square inch of

besides, they cannot be made without meas$ 4. Of the Miter of the Valves.

245

uring and weighing different parts of the These are not the only causes from

-= 50 lbs.; engine, which operations require time and

4.91 which errors may result. There are two

care, and can only take place when the enothers which are frequently met with in and when the valve is raised, that same gine is at rest. We may therefore easily the valuation of the pressure of locomotive weight will only represent a pressure of

conceive the great utility of an instrument engines, and which are not so easy to cor

which at first sight, and by its bare inspec

= 45.27 lbs.; rect as those we have just mentioned.

5.41

tion, will give the oxact measure of the In order that the valves may exactly by which we see that the same weight pressure of the steam. By means of such close the opening to which they are ap- marked by the balance corresponds to very an instrument, all cases, even those of the plied, without being subject to contract an different pressures of steam, when the valve raised valve, present no longer any diffiadhesion with the seat that supports them,l. is shut or when it is raised.

culty, and the necessity of calculation itit is necessary to make them slightly con Continuing, in the case of a blowing self may be dispensed with. The only ical, or at last with a slanting border. valve, to calculate upon what is called the thing required is, the possibility of submitWhen these valves rest upon their seat,|| diameter of the valve, that is to say, on itsting the engine to the proof.

S

or THE MERCURIAL STEAM-GAUGE.

on

245

1

or

=

P' =

sure.

The instrument used with that view is,||immediately rise in it to a considerable and all high-pressure steam engines it is the mercurial steam-gauge, constructed on height, and cause by that means a surplus this which is to be considered. The colthe same principle as the common barom- of pressure which would make the resultumn of mercury, the weight of which we eter. Mbm (fig. 18) is a tube containing || false. But by means of the reservoir FG, have expressed by P, having for its basis mercury, which ought not to rise above the the condensation-water, in proportion as it the basis of the tube which we shall express two points M and m. FG is the water re- is formed, is divided over a surface of 7 | by b, and for its height the height 2x, its servoir. It must not contain water above square inches, on which, consequently, it volume will be 2bx ; representing the the cock E, the use of which is to get rid produces an imperceptible difference in density of the mercury, 28bx will be the of the surplus of water that may have been height. As it is known that the pressure mass of the whole column, and g expressproduced by condensation on some former | of the water on the unit of surface dependsing the accelerating force of gravitation, experiment. R is an opening closed by a solely on its height, the consequence of 2góbr will be weight; that is to say, that cock, and through which mercury or water this arrangement of the instrument is, that we shall have may, when wanted, be introduced into the in- | the surplus of pressure caused by the con

P=2g8b. strument. Lastly, C is an ajutage on which densed steam is so small, that it

may

be By the same reason being the density a tube is screwed, the other end of which || neglected without any inaccuracy. of the water, the weight P' of the column reaches the boiler of the engine. This tube To graduate the scale of the instrument, of water will be expressed by go'br, its bais flexible, and usually made of tin ; it forms we may begin by marking, first, the point sis being also b, and its height Mz' the communication of the mercurial gauge zero. For this, the mercury and the water But the density of the water being expressed with the engine. At the point where it being poured in, as said above, the two by 1, that of the mercury is expressed by reaches the engine, it is screwed on an aju-branches must be left to communicate 13.568; thus we have tage fixed to the boiler, and kept close by a freely with the atmosphere, and the point cock. where the index stops will be the point 8 13.568

13.568 To prepare the instrument for use, an ad-sought, for that is the position which the and consequently ditional quantity of mercury is poured into float naturally takes when the branch Mb

gobu it by the aperture R, in order to be surebears no more than the atmospheric pres

13.568 that the instrument contains mercury at If the two branches of the bent tube least to the height Mm. After this the were to contain nothing but mercury, it is

On the other side, the effective pressure screwbolt M is unscrewed, so that if there clear that the point corresponding to zero

(

ap), in whatever manner it be expressed, happen to be too much mercury it may run in the rising branch would be at m, as the may be replaced by the weight of a column off. When this is done the screwbolt is re-mercury would in that case stand on a level of mercury, that would produce the same placed, and an additional quantity of water in the two branches. Instead of that, the pressure on the basis b. If then h be is also poured through R into the reservoir | mercury in the branch M supports a certain the height of that column, which it is easy FG, and, should there be too much, it also weight of water, that is to say, the weight

to calculate, we shall have runs off through the cock E. Then the in- of the column EM; it will consequently and the equation of equilibrium will thus be

w-p=gobh; strument is put in communication with the tend to descend in that branch and to rise boiler. The steam, arriving through the tube in the other. However, if the float is made

gob.r

2gb : +gobh, C in the upper part of the reservoir FG, to weigh as much as the column of water,

13.568 presses on the water by virtue of its elastic the level will remain the same as if there or force ; it consequently presses the mercury were only mercury in both the branches. down in the branch mb which is open at the top,

(2–13 The other extreme point of the scale must

13.568 until the weight of the mercury, thus raised, | afterwards be marked. Let w be the pres- This equation gives is equal to the pressure of the steam issuing sure we want to equilibrate ; supposing the

13.568 x = hx

=h x 0.51913. from the boiler. A float borne on the sur-equlibrium established, let z be the height

26.136 face of the mercury, at the point m, rises in at which, by virtue of that same pressure

The height h of a column of mercury, proportion as that surface in the tube; and an w, the mercury will stand above its natural which may represent a given pressure, is index suspended to a thread which passes level in the branch m. The mercury hav- easily found ; for we know that a column over a communication-pulleyp, falls between ing risen in the branch m to the height x, of mercury, one inch high, presses on its the two tubes in proportion as the mercury it must have fallen by an equal quantity in basis at the rate of 0.4948 lb. per square rises in the branch bm, and shows upon the other branch; for the mercury added inch. The height of any other column graduated scale the variations that occur in on the one side can only proceed from may thus be proportionably calculated. If, the level of the mercury in the different what has been taken off on the other. The for instance, we wish it to represent a presexperiments. Supposing the length of the mercury in the branch M will therefore at sure of 70 lbs., its height will be found by instrument from M to 6 be 61 feet, or 78 the same time be at the point x', and the the following proportion : inches, the ascending column may, if neces- whole part of that branch from the point x'

70

0:4948:1::70: h = xl=141.47; sary, contain 156 inches of mercury; and to the point M will be filled by the water

0.4948 as a column of 156 inches of mercury from the reservoir. If through the point x' so, that by this value of h, x will be with a basis of 1 square inch weighs about we draw an horizontal plane, the mercury x = 141.47 in. X 0.51913= 6 ft. If in. ; 80 lbs., such a column may serve to meas- which is under that plane will equilibrate it- that is to say, that to correspond to an ef. ure an effective pressure amounting to 80|self in two branches; we have therefore fective pressure of 70 lbs., the height of lbs. per square inch.

nothing to do with it, and need only con- the mercury must be 6 feet 1} inches. The reservoir FG is a cylinder 3 inches sider the conditions of equilibrium for those The same calculation is applicable to in diameter and 6 inches high. The use parts which are above the plane in the two any intermediate point that may be sought, of the water it contains is to keep the branches. Now, we have on the one side but it would be unnecessary trouble ; for, branch Mb constantly full of water, in pro- the pressure more the weight of a col-knowing the point corresponding to zero, portion as the mercury descends in that sumn of wate rhigh M.x'=r; and on the other and that which corresponds to the maxibranch. This is the reason why that re-|| side, we have a column of mercury high mum pressure of the instrument, we have servoir is a great deal larger than the tube, 2x more the weight of the atmosphere. P only to divide the interval into equal parts, and its capacity is calculated so as to be being thew eight of the column of mercury, and the scale will be suitably graduated, able, in case of need, to fill the whole P' that of the column of water, and p that of having seen that the general value of x de. branch. If this precaution were to be the atınosphere, we shall have, there being pends solely on the corresponding value of omitted, the water formed by condensation an equilibrium,

h, and is proportional to it. in the instrument during the experiment P+ P= P' t os, or P= P' + (w — p). This mercurial gauge being once conwould fall in the tube, which being very Icop), which is the surplus of the real structed and graduated, whenever any narrow, having, for instance, no more than pressure of the steam over the atmospheric doubt may be entertained in regard to the one-half square inch area, the water would pressure, is called the effective pressure ; || pressure of an engine, nothing more is ne

1

= h.

lb.

in.

lbs.

in.

in.

not.

cessary than to bring it under the instru- is generated too much. The valve will same degrees through which it rose during ment, and by that means the pressure may therefore begin to emit an enormous quan- | the work, and by observing at the same be ascertained, in whatever state the valve tity of superfluous steam, which in order to time the mercurial gauge, we find for each may be at the time, whether blowing or escape will raise the valve ; but if we ob- of those degrees the corresponding pres

serve that the valve cannot rise without sure. That is the means we employed in ga. Of the pressure of the Steam in Lo- pressing on the spring, and consequently our experiments. comotive Engines while travelling.

without augmenting the tension of the We brought successively under the in

spring, we will find that the steam can only strument all the engines we had made use When we make use of the mercurial|escape by increasing its pressure ; and, in of, and for each of them, as they all differ gauge to discover the pressure during an fact, the pressure will immediately rise on sin some point from one another, we deterexperiment, attention must be given to a the balance several pounds per square inch, mined the corresponding degrees of the circumstance we are going to describe. If, in proportion to the violence of the fire and mercurial gauge with the divisions of the the valve once regulated, the engine were the construction of the engine. How great spring-balance. to keep an equal pressure of steam during then is the error committed by continuing its whole journey, nothing more would be to calculate the effective pressure at 50 RAILROAD TO CINCINNATI.—The followwanting than to try it once for all before lbs., because we suppose that the valveling from the Charleston Courier of Thursstarting. Having fixed the valve at the giving way at that point cannot suffer the day last, should incite our citizens to meet point at which we wish to work, the engine steam to rise above it.

and send delegates to the Knoxville Con.

vention. might be brought under the instrument ; When the steam, in escaping, raises the

The Charleston Courier - We are inand the pressure being determined that valve to a given height, the greater the bal- || formed that General Hayne, Chairman of corresponds to that point, provided no ance-lever is, the more the index will be the Commissioners eharged with the direcother alteration be made to the spring-bal- displaced on the scale, and consequently, tion of the survey of a route for the proance of the valve, the pressure of the en-the greater will be the increase of tension posed road, left the city yesterday morning gine for every instant of the journey would of the spring; thus, in engines with a long by the railroad, for the mountains, where be known.

lever, the augmentation of the pressure Captain Williams and his brigade of engiIt is thus that many persons calculate, will be, cæteris paribus, more considerable neers are now engaged in making the sur

veys. We also understand that Lieutenant whether or not use has been made of the || than in those where the lever is shorter.

We shall soon see that the Atlas engine, || turned from surveying the route of a rail

Colcock, late of the army, who has just re, mercurial gauge. When they have found that an engine lifts up its valve exactly at

which has a short lever, with a valve of 21 road from Branchville to Columbia, has 50 lbs. effective pressure per square inch,

inches diameter, is able, while overcoming been engaged by the Commissioners as an that very moment the valve is considered

difficult obstacles, to raise its pressure from Assistant Engineer, and will proceed imas giving a free egress to the steam, and it || 53 lbs. to 56 lbs. ; and that the Fury en-mediately to the mountains to join Captain is concluded thence that the steam will gine, which has a long lever, with a valve Williams. Colonel Brisbane, also, who re. never rise above 50 lbs., unless the valve of 3 inches in diameter, is able, in the turned from the Florida campaign the day undergoes an alteration.

before yesterday, will, we understand, ensame circumstances, to raise its pressure

Experience, however , proves that this reasoning is false. ||from 53 lbs. to 624 lbs. These variations gage in the work as soon as he can make

the necessary arrangements.

Of the serIf we observe a locomotive engine with

in the pressure depend, in each engine, invices of Col. Gadsden, the Commissioners some attention, we shall very soon see that the first place, on the augmentation of the have been deprived by his military engagenothing is more variable than the resistance created by the obstacle or the ments in Florida. It is still hoped, how

pressure of steam in its boiler, although the valve diminution of the speed; and, in the se- ever, that he may be able to join the Comhas undergone no alteration.

If the engine

cond place, on the dimensions of the valves,missioners in time to give them the benefit runs rapidly with a moderate train, and levers, and balances, and the evaporating of his judgment and experience at the meetcomes to a slight inclination of the road, power, that is to say, the quantity of steaming to be held at Flat Rock on the 20th June,

or, at all events, that he will be able to alhowever small that inclination may be, it generated by the engine.

tend the Knoxville Convention, on the 4th immediately produces a considerable in This increase of pressure in locomotive July, as one of the delegates from this city. crease of traction, because the gravity of engines, when they meet obstacles that In consequence of the information given by the whole mass on the inclined plane be-icompel them to diminish their velocity, gives Gen. Hayne to the meeting of citizens on comes an additional resistance for the en- | the engines with long valve-levers consid- Saturday last, of the astonishing perform- : gine ; and the effect of this increase oferable advantage over those with short ance of locomotive engines on the Baltitraction will be so much the more percept-| levers, whenever it is necessary to ascend stated in the public prints) acclivitiss of up

more and Ohio Railroad-overcoming (as ible on the engine, the less the resistance an inclined plane. This advantage, it is wards of 200 feet—it has been determined was which the train offered when on the true, is only gained by submitting the en to request some of our delegates to proceed level parts of the road. It is thus that a load gine to a higher pressure, and might also to Baltimore, to obtain the necessary infor. of one ton, which on a level road requires a be acquired with short lever engines by mation to be laid before the Convention at traction of 8 lbs. only, presents nearly four lowering the screw of the spring-balance, Knoxville, on the 4th July. We believe times much if it has to ascend an acliv- so as to increase the pressure in the boiler that one or two of the gentlemen composing ity of jóg, the gravity of one ton or 22.40|| in the same proportion ; but the fact it-II the delegation, have consented to perform lbs. on that inclination being 32,40 = 28.40|self would evidently seem the proof of a have no doubt that others will unite in it,

this important and interesting duty, and we lbs. The consequence of that sudden in- superior working, and would even be in- if it should be deemed necessary. crease of resistance is therefore that the explicable, were we to look

upon engine, as soon as it arrives at the foot of sure as never passing 50 lbs.

The following interesting article on iron the inclined plane, must diminish consider The variations in the pressure which we

railroads in France, is extracted from the ably its velocity. Supposing that in its have just mentioned, take place while the Journal de l Industriel et du Capitaliste : preceding course it spent 450 cylinders of engine is travelling, that is to say, while it occupy at this moment the attention of

“ 'Three grand undertakings especially steam per minute, and in consequence of is separated from the mercurial gauge. I speculators, namely, iron railroads from the accidental obstacle it must overcome,| Therefore, if an engine has been working Paris to Rouen and the sea, from Paris to, it is obliged to reduce its velocity to one-in a given circumstance, or with a known Orleahs, and from Paris to Lille. Several third of what it was before, it will evident- load, and that we want to ascertain at what lines have been proposed to join Paris to ly spend no more than 160 cylinders per pressure it was then working, we must Rouen and the sea. 'The line surveyed by minute ; nevertheless, the fire violently write down exactly, during the experiment, the administration passes by the side of excited by the preceding course will con- the degrees successively inscribed on the Pontoise, traverses Gisors, goes from thenee tinue to generate the same quantity. That balance ; then, when the engine has left off proceeds on the right by the valley of la

to the Bosc-le-Hard, and from that point steam, it is true, will be spent at a greater working, we bring it under the mercurial Saye to the Dieppe, and from the same pressure ; but experience shows that the gange, and by animating the fire sufficiently point on the left to Harre. A brench pass. surplus of prossure does not bulance whai to naka the bulanco ropass through all thelling hy; Blainville would rogoh Rouen 'near

as

the pres

« iepriekšējāTurpināt »