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61. Different modes of remedying the evil under discussion, and to be applied to the boilers themselves have been suggested.

The first of these which came before the Committee, and which we believe has been applied in practice, was by Mr. James J. Rush. Doors are placed in the flues, at a point furthest from the fire-end, which, when opened, check the draught through the furnace and flues, and consequently prevent their becoming unduly heated. These are to be thrown open at each landing place. They do not, however, meet the case of accidental careening of the boat, unless made self-acting by expanding rods, as was proposed by Mr. Rush. They expose the flues to the action of air containing its full supply of oxygen, and must tend therefore to oxidize them more rapidly than in the ordinary wear of the engine.

62. The other devices before the Committee are those of Mr. C. Evans,* and of Mr. J. S. Williams. The first places the mouth of the feeding-pipe just below the proper level of the water in the boiler, so that it shall be laid bare by a change of level, and the water be prevented from escaping from the higher boilers. This would remedy the evil, except in cases where the careening was sufficiently long continued to exhaust the upper boilers of water by the ordinary working of the engine; those boilers of which the supply pipes are bare not being likely to receive any supply from the pump. Mr. Williams places the supply pipes below the boilers and feeds through valves opening upwards, which of course prevent any return of water. The valves in this machine and also those proposed by Mr. Evans, to prevent any escape of water from the higher boilers, would be objectionable. The method of cleansing the pipes proposed by Mr. Evans is very ingenious.

63. After a careful examination of these devices, the Committee are of opinion that they present but partial remedies for the evils which they are intended to meet, and they consider that nothing less than detaching these boilers from each other, and feeding them singly, or at most in pairs, will prove effectual. They would therefore, respectfully, but earnestly, urge this upon constructors and owners.

64. Fourth. Are there cases in which the metal of a boiler may become unduly heated when in contact with water?

After much reflection and examination the Committee are of opinion that such cases may occur. They believe that such have occurred, though not frequently, and that with the common thicknesses of iron and copper boilers, and modes of arranging the furnaces, there is very little liability of their occurrence. Still it is well to recognise that such may be the case, as it may prevent accident by watchfulness in the use of a new construction of boiler, or application of the fire.

65. Mr. F. Graff mentions specially an instance "in which the heads of the bolts burning off over the fire-place, and the joints parting;" "the boiling water passed into the ash pit." From his known carefulness, there is no reason to suspect that there was sediment in this boiler, which was one of the low pressure boilers used at the Philadelphia water-works.

66. Mr. Hebert§ gives two cases, in the first three different rents of an

V Replies to Circular, &c. No. XXII.

Jour. Frank. Inst. vol. viii. p. 289. The method adopted by Mr. W. C. Redfield, places the means of feeding separately, or in the connected way, within the control of the engineer. This was not presented to the Committee, but may be found alluded to in the Documents of the House of Representatives of the United States, 1832-3, No. 478, p. 17.

+ Letter to Councils. Replies to Circular, &c., 4th of No. I.

Replies, &c. No. XI.

iron boiler occurred at the same spot, at different times. Previous to the first "disruption, there was observed a bulging, or swelling out, of the metal, which gradually increased until it became nearly of a hemispherical figure, when it burst open and let the water out of the boiler into the fire. The boiler was repaired by putting a thick patch of malleable plate iron over the hole, when after about six weeks wear and exposure to the fire, this metal bulged out again, and burst asunder; a third patch was substituted, and in about a similar period of time was destroyed in like manner.” “The cause of these ruptures appeared upon investigation to be owing to a par tial and very intense heat impinging against that particular spot where they took place.' If to this detail had been added proofs that the first rupture was not caused by sediment, nor by a defect in the metal, the evidence would have been complete. It is not, however, probable, that either of these causes were actually operative, since the second and third plates are stated to have bulged out, in the manner of the first, and if sediment had collected at this spot, it could not thrice have escaped notice. The defect in malleable iron, to which the Committee alluded above, is the want of connection in parts of a plate, resulting from imperfect welding before rolling, and which sometimes separates the plates into distinct layers, for a considerable extent.

In the communication just referred to, Mr. Hebert further states, that the disruption of a boiler, occurring twice in the same place, was traced by Mr. John Martineau, a respectable engineer of London, to the imping. ing of a current of air upon this spot.

67. A case apparently of the kind now under discussion, but which was found subsequently, to be due to the imperfect union of the parts of a sheet of metal of the boiler is as follows: Part of a boiler belonging to Messrs. Merrick and Agnew, of this city, was observed to be protruded, in a similar way to that described by Mr. Hebert. Suspecting the presence of sediment, the boiler was examined and found to be clean. It was a cylindrical boiler, of wrought iron, the fire applied on the exterior and at one end, and without interior flues. The fuel was anthracite coal. The effect was next attributed to the intense local heat produced by this fuel, and the grate bars being lowered the swelling made no further progress. It has been since ascertained that there was a separation into laminæ of the iron, at this place, requiring the removal of part of the sheet.

68. While, then, the evidence in the cases preceding the last is certainly incomplete, the Committee conceive that they are leaning towards the side of safety by admitting the possibility of the occurrence of danger, to the engineer and fireman at least, from peculiarities in the arrangement of a boiler, or of the fire which heats it.

69. In these remarks it has been supposed that there is a considerable column of water over the metal; if that should not be the case it may well happen that the steam-bubbles will form so numerously on, or near, the iron as to allow it, while they rest there, to become heated above what it would be, if the water were in absolute contact with the metal. This will espe cially occur with a viscid fluid, such as salt water, or water with much sedi ment suspended.

70. The views suggested by the several sections of the preceding head are the following:

*Replies, &c., No. II. Communication of "an Engineer." Philos. Mag, vol, i, p、

1. The feeding of a steamboat boiler should not be done at intervals, but go on throughout the working of the engine.

When the engine is stopped, as at a landing, or to take up passengers, &c., the water should still be supplied by the engine itself, or by a subsidiary one, or by hand. In this case the free safety valve should be raised. The practice of wasting water by opening a valve, when the forcing-pump is not in action, is considered dangerous.

2. If the water should by any accident get down so as to expose a flue or flues, the fire should be in part extinguished, to cool the boiler before adding water. If the engine is at rest, in such a case, it should not be put in motion. If it is in motion it should be slackened, or stopped, the furnace doors opened, and the heat got down. Then water may be thrown in. The opening of a safety valve should in such a case be avoided. The engineer should remember that as life is at stake, he cannot be too prudent Such a condition of things, however, ought never to be allowed to occur, and the responsibility for the danger which results must rest upon the master, the engineer, and his assistants.

3. If a self-regulating apparatus for the supply of water is used it should be closely watched, and on no account be implicitly trusted to. It may be a convenience, but can, in no case, be a substitute for human care.

4. For ascertaining the level of the water within a boiler, the Committee recommend the glass tube water-gauge, a form of which is shown in the foregoing pages (p. 296).

5. The Committee recommend for every boiler a fusible metal apparatus, the metal of which shall be inclosed in a tube, so as not to expose it to pressure.

In boilers without flues it should be attached at the water-line; in those with flues, at the highest part of the flues; or if level, at the part likely to be most rapidly heated, as at the juncture of several flues into one, a sudden change of direction, or the place of most active combustion of the fire.

The form described in the report (pp. 297-298,) is convenient, and the lever should act upon a bell, and upon a small cock. The apparatus should be inclosed, the master of the steamboat having the key of the inclosure, which should further be so arranged as to protect the apparatus from the weather. The quantity of metal should be no greater than is required to keep the rod in its place. The metal should be regulated so as to melt at a temperature of fifteen degrees above that corresponding to the working pressure Tables for this purpose, will be found annexed.†

This difference of pressure corresponds at a pressure of two atmospheres, to half an atmosphere or one-half the bursting pressure, and at eleven atmospheres to rather more than two atmospheres, or one-fifth of the bursting pressure. The difference is not, however, too great at low pressures, because an excess of strength may rather be expected in the low pressure boilers as now made, and the alloys, containing bismuth, pass through the different states from solidity to liquidity, by slow degrees.

While correcting the proof sheets of this No. of the Journal, we notice in the LONDON MAGAZINE OF POPULAR SCIENCE, for last month, (September, 1836,) a paltry criticism of this proposition of the Committee-"to enclose the fusible metal in a case in which it shall not be exposed to the pressure of the steam, but only to its heating effect."-After quoting the sentence, the Magazine critic, triumphing in the fancied discovery of a good American bull, exclaims-"but cui bono?-for what purpose?the metal is in a case! not exposed to the pressure of the steam! How then is it to act efficaciously as a means of relief to a boiler dangerously increasing in temperature? How is it to act at all, though fluid as in a crucible?" The conclusion he then arrives

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If the metal is melted, the injection of water, or the opening of the furnace doors, will reduce the temperature of the heated parts; or lower the pressure of the steam if that should have been too high, and the safety valves be out of order.

By sounding with the rod, it will be ascertained when the metal is about to recongeal, as it becomes a soft solid into which the rod may be forced. If, accidentally, the metal congeals without taking in the rod, the end of the latter being heated, will melt the fusible alloy.

If the safety-valves do their duty, this metal will never be melted by increase of temperature, caused by an increase in the elastic force of the steam.

6. The true remedy for undue heating of boilers by deposites is fre quently cleansing them. When this is impracticable, blowing out should be cautiously resorted to, so as not to lay the flues bare of water. The danger from these deposites is especially great in salt water, and muddy water mixed with calcareous matters. It should be guarded against by ascertaining the time required for the water used, to make a sensible deposite. No general rule in regard to this can be given, since boilers in different places and even those fed by springs at short distances apart are liable to deposites in different times.

Negligence on this point will always produce the rapid destruction of a boiler, and may cause it to burst, or even to explode.

No substitute for the care just recommended, has yet been found. 7. The following table of fusible alloys applicable to boilers working at pressures from one to thirteen atmospheres, is deduced from the experi ments of the Committee.* The alloys are those determined approximately, which at temperatures severally 15° Fah. above the working temperatures will allow a metallic stem to be drawn out from the mass. The principles which guided the Committee in their experiments may be seen by referring to Part I. of their Report (p. 36, &c.) The proportions are given in parts by weight. Table of alloys for use in closed tubes, and with a metallic stem.

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at is, "There must be a district in Pennsylvania where the Shamrock is worn"! And he further thinks, that our sage Committee would be likely to propose, as the best means of preventing the loss of a key which would alone open a box, to shut it up the box! We recommend to this ingenious critic to read this part of the report of the Committee carefully over again, and try whether he can discover no good reason sug gested for enclosing the fusible alloy in a tube,—and no substantial answer to his cui bono?-If his own vision should fail him, perhaps he will do us the favour to borrow that of some intelligent friend. We are not aware that the "Shamrock" is at all indige. nous to this country, though we have thistles and thorns a plenty.

• Report of Com. on Expl. Part I. p. 36. Jour. Frank Inst. vol. xvii. p. 86.

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13.2

Lead.

Description of the new Coining Presses lately introduced into the U. S. Mint, Philadelphia. By FRANKLIN PEALE, Esq.

TO THE COMMITTEE ON PUBLICATIONS.

GENTLEMEN:-After seven months of experience, it will not be considered premature, to send for publication, a brief notice of the Coining Press, a model of which I had the pleasure to exhibit and describe, at one of the Conversation Meetings at the Institute last year.

This press has been in operation since the 23rd of March last, the period of the first coinage by steam in the Mint of the United States; and the results, which are more than satisfactory, have authorized us to proceed with the most perfect confidence in the formation of the presses for the Branch Mints at New Orleans, and at Charlotte and Dahlonega, in North Carolina and Georgia; also, with the manufacture of others for the use of this Mint, all of which, it is probable, will be completed at an early period in the coming year. Side view of the Press.

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The above design exhibits a side view of the medium size press, intended to strike eagles, quarter dollars, and cents. Three grades have been adopted, corresponding in linear proportions to the numbers 9, 7 and f suited to all the denominations of our coin respectively.

The design exhibits the general proportions and arrangement of part consisting of a shaft with a fast and loose pulley to receive motion by mean of a strap from the moving power, whether water, steam, horse, or hand:

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