second portion which oozed out from the first plate, fused at between 230° and 233°, Fah., and a portion of that from the second plate was fluid at about 2351° Fah. The parts which were left, of the first plate, were a soft solid, at 2991, fluid at one edge, at 312°, and entirely fluid at 345°. The portions left, of the second plate, lost their cohesion, and could be broken by pounding, into small particles or grains, at 300°; and the whole was fluid at 356° Fah. A comparison of these results appears in the annexed table. First ooze. Fluid. 223° First plate, To pursue this subject further, by the clue thus obtained, only freeing the different oozes from accidental admixture, a small iron cylinder was made, closed at one end, and perforated near the closed end with a number of minute holes, not larger than the stem of a common pin. Into the cylinder was fitted, nearly tight, an iron piston, with a rod, to apply pressure. An alloy having been made and introduced into the cylinder, the whole could be heated in an oil bath to any desired temperature; and pressure being applied to the piston, the liquid parts would ooze out, through the small apertures near the end of the tube. The first alloy experimented upon was the same in composition with that just referred to; being composed of eight of bismuth, eight of lead, and seven of tin, by weight. This alloy was fluid at 2544° Fah. At a temperature of 229°, some drops of fluid metal were forced out by pressure, and at about 2394 other portions were forced out. Both melted at 227° Fah. The portion left was a soft solid at 2763° Fah.; fluid at 29010 The alloy of one atom of lead, one of tin, and one of bismuth, is fluid at 2734° Fah., and that of one atom of lead, one of tin, and two of bismuth, at 219° Fah. These experiments, the committee deem conclusive in regard to the use of fusible plates in the ordinary way, and they conceive that substituting fusible plugs of greater thickness, say half an inch, as has been directed by a recent ordinance in France, would not serve as a remedy to the defect thus exposed. The true remedy is to be sought in inclosing 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: the more fluid parts of the metal will then not be exposed to be forced out of the mass; and the whole will become fluid as if exposed to heat in a crucible. With this view of the subject, trial was made of an apparatus described by Professor A. D. Bache, in the Journal of the Franklin Institute, for October, 1832, under the title of an "alarm to be applied to the interior flues of steam-boilers."* This apparatus is obviously as applicable to a common boiler as to one with interior flues; the following description of it is given in the journal. แ "A tube of iron, or copper," according to the material of the boiler, "closed at the lower end, passes through the top of the boiler, its closed end reaching "the flue to which it is attached." "This tube, it will be observed, affords a "ready access to the flue, to ascertain its temperature, without any restraint "from packing." "A mass of fusible metal placed at the bottom of the tube," "will become fluid very nearly as soon as the flue takes the temperature of "fusion of the alloy." "To show when the metal at the bottom of the tube "becomes fluid, a stem is attached with a cord and weight," "or with a lever "and weight." "The weight and longer arm of the lever, descending, may be This paper was published in 1832, and the experiments of the Committee were made in 1833-4. 66 ❝once. "made to ring a bell, or, by appropriate attachments, to turn a cock, permit. ting just enough steam to issue to give the alarm, and then to be closed at A projection on the lower end of the rod prevents it from being "drawn from the metal until this latter is fused, and by widening the lower part of the tube, making it slightly tapering, the metal is kept from being "drawn out by the rod." 66 P M K B In the annexed figure "AB is a sec. tion through the top of the boiler; CD, a corresponding section of its flue, EH represents a tube closed at the lower end, which is attached to the upper side of the flue. The mode of attachment by a projection on the tube and a ring screwed to the flue, is shown in the figure, as also the stuffing box, RS, through which the upper end of the tube passes. The lower part HI, of the tube, is made tapering, to retain the fusible metal. KL is the stem, the lower part being inclosed by the fusible metal, the upper part attached by a chain to a lever KP. The weight M, draws the rod KL upwards, and on the fusion the alloy HI, carries the lever below the bell N, which, being attached to a spring, rings an alarm." H D The form of this apparatus, which was subjected to trial by the committee, was essentially the same with that described. One of the tubes in which the thermometers were ordinarily placed, was used to contain the fusible metal, and as giving the more severe test, the short one entering only into the steam, was selected. For the convenience of removing the metal, it was placed in a metallic case, fitting loosely into the iron tube, and having a wire attached, by which it could be drawn out of the tube. This certainly diminished the sensibility of the apparatus, particularly, as the case was quite as thick as the inclosing tube, and as there was a small space between its convex surface and that of the tube; it was required, however, for the convenience of the experiments. The results of the several trials are contained in the following table. The temperature was registered by the adjoining thermometer dipping into the water of the boiler, and already often referred to; it was raised as rapidly as possible in all the experiments except the first. The first four trials were made on an occasion specially devoted to this purpose, the last two were made incidentally when upon another subject. Tempera Number of ture. Trial. REMARKS. Fab. Stem rises. No particular attention paid to raising the temperature rapidly. Stem rises. Steam raised rapidly. Metal drawn out and suffered to cool, re-deposited cold in tube. Stem rises. Metal drawn out and cooled. Steam at 250°, when metal was replaced. Steam raised to 274° in 3 minutes. 274 4 274 Stem rises. Stem rises. Metal remains a soft solid, so that the stem can be drawn out, until 2402. A fact noticed during the experiments on fusible alloys was again verified in these experiments; namely, that the mixtures of metals require a considerable time to change their state of solidity or of fluidity, so that in the former case they may be heated above the true temperature of fluidity, and in the latter case they may be cooled much below this temperature, without solidifying. The alloy used in these experiments, appears to have put the apparatus very fully upon its trial in this respect, and the experiments were performed so rapidly as to give a further severe test. On the occasion devoted to the trials when the steam was not urged up with its greatest rapidity, the stem was drawn out at 268°, when more rapidly at 270°, and with the fire at its maximum intensity, when the water was raised in temperature 24° in three minutes, the stem was drawn out at 274°. In other experiments it gave way at 256°. The range is 18° Fah., corresponding at ten atmospheres, to less than two atmospheres, under the test of very severe comparisons. There appears no reason to doubt, that when tested by no more rigid modes than practice would furnish, this apparatus would not only apply as an alarm to prevent undue heating of the parts of the boiler, but as a manageable, and useful check, in ordinary cases, upon the safety valve. Conclusions. 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 affect materially the fusing points of their alloys. 2d. When mixed in equivalent proportions, tin and lead formed 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 considerably in the interval between the temperature of commencing to lose fluidity, and that at which a thermometer, immersed in the solidifying metal, became stationary. These different alloys produced 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 steam-boiler, show signs of fluidity at the disk, before the steam has attained the temperature of fusion of the alloy of which the plate is composed. This fluid metal oozes through the perforations in the disk, and the plate thus loses much of its substance before finally giving vent to the steam. 4th. The under parts of the plate are not kept from fusion by a protecting film of oxide there formed. 5th. The thickness of the plate is not important, provided only that it is sufficiently strong 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 steam. 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 burst, not melted. Sth. 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 VOL. XVII.-No. 2.-FEBRUARY, 1836. 11 boiler, should not be exposed to the pressure of the steam; at least not in such a way that the separation of the differently fusible constituents of the alloys may be effected. Fusing Points of Alloys applicable to Steam Boilers. The committee next proceed to give the results of their trials to determine metallic alloys proper to be applied to steam-boilers. This problem admits, of course, of a great variety of solutions. The metals used were limited to tin, lead, and bismuth; but still different mixtures of these may be made which will give alloys of the same fusing point. The property which was most desirable in these alloys was a small range of temperature in changing from the liquid to the solid state. This property, it will be seen, is difficult to attain, and the less fusible alloys of the first table, as well as the more fusible ones of the third, do not possess it. For the higher temperatures, alloys of lead and tin are applicable, and the question is reduced to an examination of the fusing points of different mixtures. The greater proportions of lead might be inferred to give the higher fusing points, and the less proportions the lower ones. Beginning with the alloy of equal weights of tin and lead, the following table gives fusing points between 355° and 503° Fah. The stationary points were taken as already described; all the alloys in the table, except the first, were hard before the stationary point occurred, and therefore this point indicated, in these cases, some internal change in the solid, and did not correspond to the passage from the liquid to the solid state. This seems not to have occurred to Mr. Parke, who speaks of having taken this point as corresponding to that of congelation. It should be observed, however, that his table of alloys shows a variety in the fusing points, which is incompatible with the observations of the committee, supposing the stationary point to have been taken in each case as the fusing point. The alloys passing gradually from the fluid to the solid state, an attempt was made to seize the more remarkable points, as referred to in the table; but these can only be considered as approximately determined. Direct experiments were, in most cases, made upon the temperature at which the metal refused to allow a metallic stem to be withdrawn. This was the case when the metal, from the state of a soft solid, began to acquire hardness. The next object was to diminish the relative proportion of lead, so as to determine the most fusible alloy of the two metals. The results obtained will be seen in the following table. The lead was the same in each case; namely, eight parts by weight. REMARKS. 353 * 415, with tempe rature rising. 4269. Hard solid, at Hard at 437°. Eight parts of Liquid metal Stationary REMARKS. Parts. Fah. Fah. * Began above this point. In these three cases the alloy congeals in thin plates, at the surface, and is a sandy solid below, at the sides. A liquid, with solid portions, at stationary tempera ture. * Hardens in round masses, which, at the stationary point, are surrounded by a liquid. The table of alloys by Parke, before referred to, gives a considerable variation in the melting points of the alloys in the above table. He makes the stationary point of the alloy of eight to eight, 372° Fah.; that of eight lead and ten tin, 352°; that of eight lead to twelve tin, 336°; this latter being the most fusible of the alloys of lead and tin. That the alloy, in equal parts, has not a fusing point varying much from that just given, the committee were able to determine from various specimens of metal. With pure lead and grain tin, they found, for eight lead and nine tin, nearly the same as the foregoing, the stationary point to be, in different experiments, 355°, 356°, and 35510. With one specimen of common lead the stationary point of an alloy of equal parts of lead and tin was 356° Fah. This lead melted at 606°, and the tin at 442. The committee have no greater reason to suspect the accuracy of their other results. In all these cases the stationary point occurs when the metal begins to solidify. It appears, then, by the foregoing table, that very little change is effected in the fusing point of the alloy of equal parts of tin and lead, by increasing the quantity of the more fusible metal. A curious coincidence is shown between the stationary point of these alloys and of those in which the lead is increased. The two intervals, which are best determined in the table, between the temperature at which fluidity begins to be lost, and that at which the metal becomes solid, are seventeen and fourteen degrees. When the lead becomes considerable in quantity, the passage from the fluid to the solid state is by such minute mechanical changes, as to extend through a long series of temperatures. This is even more especially the case when bismuth also enters largely into the alloy; instructive examples of which occur in the following table. |