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steam-boat" New England" from a "pressure of steam, produced in the ordinary way, but accumulated to a degree of tension which the boilers were unable to sustain."*

4. If the apparatus devised for the lowpressure boiler has been rendered inoperative, the high-pressure boiler has had to contend with peculiar difficulties. No gauge applicable to it has yet been brought into use. The open gauge must be of undue height, or cumbrous in its serpentine form; and the closed gauge requires great nicety in construction, and a correction for the temperature of the air enclosed in it. A graduated safety valve would give the engineer desirable information, and has been to a certain extent used. The engineer of a locomotive-engine, where the spring weighing-machines are used with the safety-valves, has it in his power to ascertain, at any moment, the pressure within the boiler.

He has, it is true, besides, the power of keeping the valve down even when the pressure within may be unsafe, but then he and his assistants would probably be the only victims of its abuse.

5. The extraordinary and fatal increase of pressure which the Committee have above shown to be produced designedly at times, has at others been attributed to the adhesion of the safety-valve. A practical engineer, Mr. John B. Calhoun, has given a remarkable instance of this kind+ as occurring to a safety-valve on the boiler of the steam-boat "Legislator," then navigating the Hudson. The mercury-gauge indicating an undue pressure within the boiler without the raising of the valve, the engineer endeavoured first to raise it by a cord which passed into the fire-room: failing in this he went to the top of the boiler where the valve was, and moved the weight upon it towards the fulcrum, but without effect. He then applied his force at the end of the lever to raise it, when suddenly the valve opened with a loud report, and the flow of steam commencing, lasted some time before the elasticity had diminished to its usual degree.

6. In this case, there can be but little

The part marked with inverted commas is the conclusion drawn by an able Committee who investigated the cause of this expl sion. It is unpleasant to see in this case, how those concerned in the press of steam, were biassed in their views given to the Committee, and communicated, as the Cosaltee testify, as honest convictions, and without intention to deceive. The engine-men were not injured by the explosion. The form of these boilers was no doubt defective, and one part of them will be commented on hereafter. The two boilers exploded almost simultaneously.-Jour. Frank. Inst., vol. xiii. pp. 55 and 126.

+ Account of an extraordinary adhesion of the safety-valve of the boiler on board the steam-boat Legislator, on the Hudson. By the Engineer. Jour. Frank. Inst., vol. v. p. 355.

doubt that the valve had corroded upon its seat, or was fastened by the drying of oil, or other matter, to it. The carelessness of the fireman who had charge of the boiler, and whose duty it was probably to raise the valve from time to time, is fully proved by his allowing the steam to get so high, that the rod of the mercury-gauge was against the boiler-deck, without giving notice to the engineer. Had not the latter observed, from the rapid working of the engine, that the steam was high, and investigated the matter, the lives of many would, no doubt, have been sacrificed.

7. The experiments made by M. Clement Desormest on the tendency of disks, when placed in front of an aperture, through which air is forcibly issuing, to approach it, led him to condemn the safety-valve entirely, and especially the disk form. This sentence does not seem to the Committee to be just,§ since the tendency upward, under the most favourable circumstances to its action, is very limited in amount, and may easily be counteracted by a device, which will lessen the acting weight, when a safety-valve is raised. Besides, the proportion which the area of the disk bears to that of the aperture materially affects the amount of this tendency, and is, in practice, very much less than was used in the experiments of M. Clement. The ingenious experiments of M. Hachette and Messrs. Hopkins and Roberts, of Manchester, have shown the truth of these remarks.|| 1f,

Notice in Franklin Journal, vol. iv. p. 97. See also explanations of the phenomenon offered by Jacob Perkins, Esq. in the same volume, p. 252, and in London Jour. Arts, vol. xiii. p. 275. By Dr. Hare in Journ. Frank. Inst. vol. ii. p. 58. By James F. Espys, Esq. in the same vol. p. 59, and by Asa Spencer, Esq in the same vol. p. 61, also remarks on p. 203.

In this view the Commit'ee coincide entirely with M Arage. See Annuaire du Bureau des Long. 1830, p. 157, and Jour. Frank. Inst. vol. v. p. 408. In fact, the Committee named in the next note did not sustain the deduction, above referred to in the text, remarking, in very guarded terms, that the limits within which the phenomenon occurs were then not sufficiently known to decide upon the possibility of an accident from it.

and

M. Hachette, who investigated this subject, shows in a strong point of view the effect of the relative proportions of the disks. When one is not many times the other in size, it is impossible to satisfy the conditions of the problem. Annales de Chim. et de Phys. vol. xxxv. p. 44, &c. The Committee who examined this subject in its relation to the steam engine, consisting of MM. Biot, Poisson, avier, made an experiment in which with a disk, nearly six times the diameter of the opening, and a pressure of steam about 2*8 atmospheres, the tendency to adhesion when the disk was 01 of an inch from the opening, was but half a pound. Annales de Chim. et de Phys. vol. xxxvi. p. 70. In the experiments of Messrs. Hopkins and Roberts, with an excess of pressure in the effluent air of 05 of an atmosphere over atmospheric pressure; the total tendency to adhesion at its maximum, was but '005 of an atmosphere, with an opening of 2%

however, this action were allowed to have full effect, by dimensions in the valve expressly intended to produce it, an increased area of valve would entirely obviate the objection. Different effective means of lessening the acting weight, on the rise of a safety valve have been used or proposed, such as that employed by MM. Arago and Dulong* in their experiments, on the elastic force of steam at different temperatures, or the very similar one, described by Mr. L. Hebert in his interesting communication to this Committee. In them the weight rolls towards the fulcrum when the valve opens. The Committee apprehend that this form, although very effective while in order, would tend by disuse to lose its power of action. They would prefer, in practice, a construction similar to the second form proposed by Mr. Hebert in which the lever being curved effects the same object, while the weight is not required to be moveable. They intend to recommend a suitable form of lever of this kind.

The practice of passing the stem of a safety-valve through a stuffing-box, as it is calculated entirely to defeat the object of the valve, should never be allowed. In fact, the more open to inspection all the parts of the apparatus are the better. If it is necessary to carry off the steam from that which the engine-man has the control of, it can be accomplished without resort to packing.

9. There can be no doubt that the form of

the safety-valve materially influences the certainty of its action. Although the diskvalve was early recommended, the nicety of workmanship required to make it tight has limited its use, and perhaps the experiments of M Clement have produced a prejudice against it. The cone, which is in common use, may be more easily tightened when perfectly fitting the seat; but this very fact is an objection to it. No pressure can cause the disk valve to prevent the escape of steam, if the valve and seat be clean, unless they have been ground to fit. The Committee adopted this form of valve in their experiments, and in no instance was undue adhe

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a disk of eight inches in diameter, the total tendency was increased from 32 oz. avoirdupois, to 48 oz.; and with disks 44 inches diameter and under, no such tendency was manifested, the aperture of efflux remaining the same. Minchester Trans. vol. v. N. S. and Jour. Frank. Inst. vol. x. p. 188. * Annales de Chimie et de Phys, vol. xliii. + See Replies to Circular of Committee on Explosions, No. XI.

In that of MM. Arago and Dulong there was also an arm projecting on the opposite side of the fulcrum from that n which the weight keeping down the valve was placed; upon this a weight rolle from the tuleruin on opening the valve.'

Report of Committee on Explosions, Part I. pp. 71, &c. Jour. Frank, Inst. vol. xvii. p. 228.

sion observed. Throughout their experiments, the pressure of the steam corresponding to the opening of the valve with its different weights, was noted by the steam-gauge, or by the temperature of the water within the boiler. No means were used to keep the valve in other than what might be considered fair working order, but when, from the action of dirt, it had become leaky, the grinding upon the seat was very easily performed, and restored its efficiency. Two valves of the same form were used, and the comparison of the calculated pressures due to the weight upon the valve, with the observed pressures at which the valve rose entirely, or leaked so badly as to require additional weight, uniformly gave the former in excess. The average ratio in the experiments was 1 to 1035, the former number representing the observed, and the latter the calculated, pres

sure.

10. These conclusions are sustained, in a general way, by the success which has attended the recommendations of the Select Committee of the British House of Commons. The law, based upon their investigations, requires that there should be two safety valves upon every boiler, one of which is out of the control of the engineer,-and further provides a penalty for the overloading of either valve, by any person whatever.

In

11. In addition to two safety-valves, the regulations for the safety of the steam-engine in France, require two tusible plates or plugs, of suitable diameter. to be attached to every boiler. These plugs are intended to act by the heat of the enclosed steam, and to give way when it has reached a certain point the application of them which we are now considering, they are exposed to a pressure corresponding to the temperature, and in order to prevent them from giving way as they verge towards the fusing point, they are covered with wire, or with perforated disks or gratings of metal.

12. This mean of safety was made the subject of elaborate experiments by this Com

The regulations relating to the safety-valves of steam-boat boilers, are as follows:

That every such boiler shall be provided with two sufficient safety-valves, one of which should be inaccessible to the engine-man, and the other accessible to him and to the persons on board the packet.

That the inspector shall examine such safetyvalves, and shall certify what is the pressure at which such safety-valves shall open, which pressure shall not exceed one-third of that by which the boiler has been proved, nor one-sixth of that which by calculation it shall be reckoned to sustain.

That a penalty shall be inflicted on any person placing additional weight on either of the safelyvalves.

Of twenty three witnesses, practical engineers and others, examined by the Parliamentary Commi tee, seventeen recommended explicitly the ad'ditional safety-valve, out of the control of the engine-man.

mittee. The result was, that when alloys of tin, lead, and bismuth, such as are used for fusible plates, are exposed to heat and pressure, parts of them soften at temperatures below that at which the entire plate would become liquid. Being exposed to pressure, these fluid parts are forced out,† leaving a less fusible mass. In one case described by the Committee, this operation was carried so far before the plate gave way, that from a plate melting at 254° to 275° Fahr., was produced a mass fusible only at 312° to 345°. One part of the alloy which oozed out was found to melt at 223o and another at 233°. To this action a fusiole

* Report of the Committee on Explosions, of the Franklin Institute, Part I p. 23. "V. Inquiry in relation to plates of fusible alloys." Jour. Frank. Inst. vol. xvii. p. 74.

This fact, but to a limited extent, seems to have been noticed by M. Gualtier de Claubry, who did not, however, follow out the suggestion. Recueil Industriel, 1829.

The entire series of conclusions from these experiments, which formed one of the most interesting branches of the Committee's investigations, are as follows:

"The conclusions deduced from the foregoing experiments, on metallic alloys, may be thus stated.

1st. The impurities of common lead, tin, and bismuth, are usually not such as to affec materially the tusing points of their alloys.

2d. When mixed in equivalent proportions, tin and lead tormed alloys, not presenting the characters of distinct chemical compounds, in definite proportions The alloys between the range of one equivalent of tin to one of lead, and one equivalent of tin to six of lead, varied considerable in the interval between the temperature of commencing to lose fluidity, and that at which a thermometer, immersed in the solid.fying metal, became stationary. These different alloys produce nearly the same stationary temperature in a thermometer plunged into the solidifying metal.

"3d Fusible metal plates, covered by a perforated metallic disk, and placed upon a steamboiler, show signs of a fluidity at the disk, before the steam has a tained the temperature of fusion of the alloy of which the pla e is composed. This fluid metal oozes through the perforations in the disk, and the plate thus loves much of its ubstance before finally giving vent to the steam

"4th. The under parts of the plate are not kept from fusion by a protecting filin of oxide there -formed.

5th. The thickness of the plate is not important, provided only that it is sufficiently trong to resist the pressure of the steam at temperatures below its point of fusion.

"6th. The temperature at which the plates are cast, and the rate of cooling of the cast metal, do not affect the temperature at which the plates give vent to sieart.

"7th. The effect stated in conclusion third, is explained by the nature of the alloys used, which are formed of portions of different fluidities; the more fluid parts are forced out by the pressure of the steam, leaving the less fusible. These latter, in general, are bn st, not meited.

"8th. By pressure in a receptacle provided with small openings, this effect of separating the differently fluid portions of an alloy, may be imitated.

"9th Fusible alloys, used to indicate the temperature of any part of a steam-boner, -hould not be xposed to the pressure of the steam, at least not in such a way that the separation of the differ

plug would be also exposed, and the Committee are of opinion that no method of application in which the pressure acts upon these compounds can be efficient in practice.

In the experiments referred to, the plates being thin, were generally burst by pressure; not, however, acting precisely as thin plates of copper or iron would have done, but being partially softened by heat.

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13. While the Committee deem it very desirable that a convenient steam-gauge applicable to high-pressure boilers should be devised, they consider that until this is done, a substitute should be furnished in a graduated safety-valve, marked with numbers expressing directly in pounds to the square inch the bursting|| pressure of the steam, and within the control of the engine-man. This would act as a convenient, and, for practice, a sufficiently exact method of knowing what he ought always to be informed of, the bursting pressure in the ordinary working of the boiler. Besides this, however, there should be a lock-up valve, for the original weighting of which there should be a proper responsible agent, and which should be capable of being raised by the engineman, but not of being kept down. With a valve of this kind of sufficient dimensions, of proper form, and duly weighed, the Committee believe that danger from gradually increasing pressure might be entirely avoided.

A thermometer suitably graduated and passing into the steam or water of the boiler, would prove, under ordinary circumstances, a useful gauge, and may be conveniently applied as described in a subsequent part of this Report.

14. With a view to meet the dangers which have been discussed in this section, the Committee would make the following recommendations, the means of carrying out the principal of which, by law, will be found suggested at the close of the Report:

First. That every boiler be provided with two safety valves each of which shall be competent to discharge the steam, made in the ordinary working of the engine. The

ently fusible constituents of the alloys may be effected."-Report of Com, on Expl. Part I. p. 34, and Jour, of Frank. Inst. vol. xvii. p. 84.

The Committee regret that the hydrostatic safety-valve of Mr. Ewbank has not been brought into use. It would answer, by a slight modification, as a gauge, and no doubt can exist of its being applic ble to the stationary engine. The oscillation of the liquid may interfere with its operation on board of steam boats, but to what extent the Committee are not prepared to say. See description and figures, Jour. Frank. Inst. vol. ix. p. 64, and vol. x. p. 2.

This term is used to signify the excess of pressure of the steam within, over atmospheric pressure, in contradistinction to the working pressure, which is used to express the total elastic force of the

steam.

first of these valves should be graduated by the maker of the engine, and have stamped upon the lever by which it is weighed, the bursting pressure at which it will open, by calculation, when the moveable weight is placed at the several notches. The pressure corresponding to the last notch to be equal to the bursting pressure, under which the engine is to work. The second valve to have a weight fixed immoveably upon it, the pres sure of which upon the seat, together with that of the atmosphere upon the valve, is equal to the working pressure of the engine. This valve should be so arranged as to admit of raising, but not of placing additional weight upon it. To this end it should be enclosed. The rise allowed by the inclosure should rather exceed half the radius of the valve-seat.

Second. The Committee recommend to constructors the disk-valve. The diameter of the disk should not exceed once and a half that of the valve-seat, as a less ratio than this will leave sufficient margin, and any sensible tendency to close from the effect of the issuing current will certainly be avoided.

Third. That a cord be attached to the lock-up valve, by which it may be raised at the same time with the free valve. And that the working of each be ascertained at least every two hours.

Fourth. That an open mercury-gauge be provided for each boiler of every engine not carrying more than two atmospheres of working pressure. The height of the mercury to be indicated by a float which shall truly mark upon a graduated scale the bursting pressure in inches.

For high-pressure boilers they recommend the thermometer, graduated to show the pres. sures corresponding to the temperatures of saturated steam, as a convenient gauge.

Fifth. That the lever of the lock-up valve be bent upwards at the end, so that in rising it shall relieve the valve of part of the weight. A suitable proportion for such relief would be about one-tenth of the pressure derived from the weight, and the height of the bend above the lever should be regulated to meet this.

The lever would have a form similar to the annexed. The part a g, which is turned

a

up, may be straight or otherwise. The adjustment should be made so that de is nearly nine-tenths of ac. g being the centre of gravity of the ball, lever, &c. will lie a little out of the centre of the weight, towards the fulcrum.

Sixth. As there can be no doubt that the competition in regard to speed is, or has been, a strong temptation to an undue increase of pressure by engineers or firemen, it should be expressly prohibited by law.

(To be continued.)

APPLICA

ON A DEFINITE RIGHT LINE,
BLE TO PARTICULAR PURPOSES IN ALL
COUNTRIES.

Sir, In reading various literary publications, as they occasionally appear in different countries, much inconvenience does frequently arise from the want of a general scale of measure, which is equally intelligible to all civilised nations. Distances described in one language are difficult of comprehension in another, and are often ascertained with little accuracy by researches of considerable labour. Similar disadvantages, proceeding from the absence of some fixed standard, as a right line, obscure many interesting de tails of scientific volumes. The altitude of mountains, the breadth of rivers, the dimensions of ancient monuments or of modern edifices, are often imperfectly communicated to our ideas by the most intelligent travellers who write in a foreign language.

No interference with any national scale is proposed as an object of these suggestions; those will all of them remain undisturbed. The purpose now contemplated is the determination of a right line, having a positive longitudinal dimension; and which, as a common scale, may be used in scientific communications, either independently of, or as an explanatory appendage to, any national standard. It may be made to resemble one of two scales upon a map, or upon the first page of a book; and will have as definable a relation to the scales of all countries as to that of any one of them. At present there is no particular scale which is generally understood in different countries, and which can serve to make the standard measure of any one of them intelligible to all the others.

To become useful, the new scale must, in its most limited application, be Enropean; an honour to which it can only

become entitled by being the production of scientific men. The attainment of this object would be most effectively accomplished by the co-operation of a few leading Societies of different states, to whose judgment and accuracy general deference might be implicitly conceded. To those persons who possess a competent knowledge of the subject these ideas are submitted. The writer will not attempt to carry his inquiries to any result beyond the explanations of this paper.

When the sun enters into the vernal equinox, he may be supposed to pass, from the meridianal point, over an arc of a circle containing 45°. The conditions being precisely stated, and remaining perpetually unchanged, his passage over that space at the same annual epochi will be always the same, without any variaand if the circle he denoted, the chord of the same arc will be always the same without any variation. That right line may be called the solar scale; and it can be verified by a practical scientific experiment.

tion;

When the radius of a circle is known, the chord of a given are becomes known also. These may be determined optionally by scientific men, so that the scale shall have some moderate dimension which may be considered most useful in scientific communications generally. The operations to verify the scale will follow the construction of the instruments to be employed for that purpose. Let two

But

pendulums, alike in all circumstances, be constructed, each having precisely the length of the proposed radius. If these are simultaneously made to vibrate from a position perfectly horizontal, their viIrations will continue to be simultaneous, and will be alike in every respect. in the proposed experiment, they must be made to vibrate separately. When one pendulum has completed sixty vibrations, the other must be made to repeat and continue the movements with the greatest precision; and the two pendulums must be thus alternately made to pass through sixty similar vibrations each, so that the whole requisite number of vibrations can be summed up at the conclusion of the experiment, with the same exactness (or as nearly so as possible,) as if the movements had been performed by a single pendulum. The operation, which can be thus regulated

with two pendulums, can in any number of instances be made by two other pendulums which shall be in all respects the same as the former; and if the operation is conducted in the same point of latitude, the results in every instance ought to be the same without any variation. The duration of the first and of the sixtieth vibration may be alike or unlike, the circumstance will not affect the final result, because the mean duration of all the vibrations, collectively, will be the same in all experiments which are made with the same pendulums under conditions which are all of them precisely the same. The pendulums will move through a definite number of unequal arcs, while the sun moves over one definite arc.

At the fortieth degree of latitude let a small plane surface be prepared with a vertical rod in the centre; and from the middle of that rod as a centre, let there be described a circle, whose radius shall be the length of one of the prepared equal pendulums. Let the meridional point be marked in the circumference of the circle, and a second point be placed distantly from the first, so that it may truly denote an arc of forty-five degrees, As soon as the equinoxial sun enters the meridional point, let the pendulum vibrations commence, and be carefully continued by the two alternating instru ments till the sun enters into the point of forty-five degrees. The number of vibrations accomplished ought then to be most accurately recorded. This number of vibrations will denote the length of the pendulum, or the radius of the circle; and as the radius so found in the same place will be always the same, the chord of forty-five degrees, so found, will be the same also. In any subsequent experiments, however multiplied in the same latitude, if the pendulums are taken too long, the given number of vibrations will not be completed during the equinoxial sun's passage from one point to the other of the given arc; and if the pendulums are too short, the number of vibrations will be exceeded at the prescribed completion of the sun's passage. The real length of pendulum, or the real radius of the circle, and also the given chord, can always be truly ascertained by a professional gentleman of high scientific attainments; and no other person ought to attempt so delicate an operation.

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