88 REPORT OF EXPERIMENTA ON THE EXPLOSIONS OF STEAM-BOILERS. first trials, was that described to the Committee by Mr. Hartshorne, of Cincinnati. This was a prismatic box of brass, of suitable dimensions; one face of which was supplied by a glass plate; this box, being put in communication with the boiler, by two pipes, one entering from the steam, the other from the water, the level of the water was seen through the glass plate. This apparatus was attached to the experimental boiler, and its indications compared with those of the gauge-cocks in the experiments already detailed. On relieving the water from pressure, the water within the gauge was agitated; during the further foaming its oscillations did not amount to half an inch, so that the hydrostatic level was truly shown by it; and further, on closing the openings, the fluid in the gauge became tranquil at the mean level of its oscillations, showing that it had fallen with the fall of the water within, caused by the escape of steam. An instructive experiment to the same purport was made on the occasion of a fracture in one of the glass windows, described as placed in the ends of the boiler. The account taken from the minutes of the day's experiments is as follows: The temperature being at 292° Fahr., and the pressure indicated by the gauge four atmospheres, the north window of the boiler, which had a flaw in it, cracked across the middle, and nearly horizontally; steam issued slowly through the crack; on looking into the boiler a foaming at the end where the steam was escaping was observed. The crack rapidly enlarging, the steam issued in quantities through it; the water was in general agitation throughout the boiler, running out at the crack, though its hydrostatic level was at the bottom of the window, about one inch and a quarter below the crack, and being distinctly seen at the opposite window, foaming near the top of the glass; the water-level gauge began to fall, oscillating not half an inch in its fall. The safety-valve was now opened by hand, so as to waste the water with great rapidity. The water still issued through the crack, the water-level gauge falling. On closing the valve the water settled down, becoming comparatively tranquil; the water-gauge remained at the same level: it had, therefore, indicated constantly the true level unaffected by the foaming, except in slight oscillations. In fact, this gauge shows truly the height of the water within the boiler, until the foam rises so high as to pour over through the upper connecting tube. The idea was suggested that by placing the gauge-cocks in a prism, connected above with the steam, and below with the water in the boiler, the true level of the water would be indicated, Such a cock was, therefore, applied to the box of the water-gauge; its opening produced a local feaming in the gauge, which brought water through the cock, although the true level was much below it. The area of this cock was nearly equal to the area of that which opened into the steam chamber of the boiler. In relation to the form of the water-gauge, as already described, it does not seem to offer as many advantages as the tube which has been adapted to the boilers of some of the English locomotive engines.* The glass plate requires the support of horizontal bars, which are objectionable, or it must be reduced so much in breadth that the level is obscurely seen through it; the strain upon the plate being unequal, it is very liable to fracture; such fractures repeatedly took place near the centre of the plates in the gauge used by the Committee. To the use of the glass gauge for the highpressure engine, an objection occurs, from the effect produced by high steam upon the glass, apparently by its action on the alkali; by which the transparency of the glass is gradually destroyed. A similar effect was recorded by Cagniard de Latour, in his experiments on liquids at high temperatures, confined in glass tubes.+ As far as the ex periments of the Committee have gone, they show that green glass is not so readily injured; and as it is easily procured in tubes, a further reason appears for preferring the tube in practice, to the plate. An attempt which was made to substitute windows of mica in the boiler for those of glass, bears upon the use of that mineral for the plate of the water-gauge; as does also another attempt which was made to protect the glass plates by a lamina of that mineral. The mica exfoliated under the action of the steam which insinuated itself between the laminæ through cracks which were invisible, if existing, before the experiment, or which may have been produced by the steam itself; the lamina were separated, and thus the steam quickly found a more or less direct passage through the plate. The tube-gauge which was substituted for the prism is shown in figs. 1 and 2. w x is the tube of green glass passing into the The application of such a gauge to a locomotive-engine can give but little idea of its use for & stationary engine. The jarring in the locomotive must constantly expose the gauge to fracture, and perhaps may prevent its use. The glass water-gauge has been adopted in at least one of the boats plying between New York and Amboy, New Jersey, be longing to Messrs. Stevens; and the Committee understands, are also in use upon their locomotiveengines. it See also recent experiments on the action, of water at high temperatures upon glass, by Professor Turner, of the University of London. Royal So. eiety's Trans. for 1834, stuffing-boxes, w'and x'; the stuffing enables an adjustment to be made for the unequal expansion of the glass and metal by heat, and prevents fracture on the subsequent cooling of the apparatus. y and z, fig. 1, are passages connecting the tube with the boiler; these have conical terminations, by which the pipe is readily attached to, and detached from, the tubes y and z, which are screwed into the boiler, and are provided with stopcocks: coupling screws might, in practice, be substituted for these conical terminations. To protect the tube, w x, from currents of bair, it was surrounded by a second tube, loosely applied. A scale was attached to wx, to indicate the level of the water within the boiler. The tube being transparent, shows the levels of the water more readily than it scand be seen in the prism before referred to, which was opaque on three of the vertical sides. 4 9 The gauge used was nine inches and threequarters in length. The upper part being so near the top of the boiler as only to be affected by the foaming, in extreme cases; the lower part so near to the bottom that the level of the water was indicated, unless when very low indeed, The position of the lower communication of the gauge with the boiler soon showed a defect, to which the instrument must be always more or less liable, namely, to the ob. struction of the lower passage by sediment. To remedy this, a stop-cock was attached to the lower part of the gauge, as at x', fig. 1, and through it, when open, water could be blown, by the pressure of the steam in the boiler, so as to remove any obstruction. This method is to be preferred to that of closing the upper communication with the boiler, while the lower one remains open; in which case the sediment is driven up into the glass tube, soiling it, accumulating there, and affording only a temporary remedy. When the obstruction in the pipe is not removed on opening the cock, a wire inserted will effectually clear the passage. tol In connexion with this subject, the Committee experimented upon the method proposed by Mr. Thomas Ewbank, of New York, for lessening or preventing the foaming here stated to occur. The remarks of Mr. Ewbank are to the following effect:"When steam is raised in a boiler, and the engine not working, the water within (if the flues are sufficiently covered) is probably on a level and nearly at rest; but as soon as the >steam is admitted into the cylinder, it causes an ebullition of the water, which rises towards the mouth of the steam-pipe, in consequence of the portion of the pressure upon it being suddenly removed at every stroke The inaccuracy of the common gaugecock as a means of detecting the true height of the water in a boiler, arises chiefly from two causes; firstly, from the agitation of the water while steam is being withdrawn from the boiler to supply the engine, or through the safety-valve; and, secondly, from the current or rush of steam produced towards the aperture of a gauge-cock when it is open; in consequence of which the water, though previously at rest, is agitated and carried out through it. "The last-mentioned defect may be lessened by a perforated tube (see the accompanying figures) attached to the end of the 90 REPORT OF EXPERIMENTS ON THE EXPLOSIONS OF STEAM-BOILERS. passes through the head of the boiler in the usual way, and is then united to a perpendicular pipe, open at both ends, and about two or three inches in diameter. The lower end of the pipe is four or five inches below the surface of the water, and its upper end is carried as far above the level as may be convenient."" When this cock is opened no current can be formed in the direction of its aperture, and the water in the tube P (which will, of course, be at the general level of the water in the boiler) will not be so subject to agitation."* To test the idea that the foam which issues through the gauge-cock is produced by a rush of steam towards the aperture, and the method proposed by Mr. Ewbank for lessening it, tin pipes, ten inches and three-eighths in length, and three-eighths of an inch in diameter, with seventy-nine perforations, each about two hundredths of an inch in diameter, were attached to the central and lowest gauge-cocks b and c, fig. 1. When the level of the water within was about five-eighths of an inch below the cock c, or nearly two inches and four-tenths below the cock b, on opening the lowest cock, the steam being at a pressure of two atmospheres and twotenths, a very little water mixed with the steam, passed through the opening of the cock; on opening the middle cock b, water and steam flowed through c; on closing this and opening the highest cock a, less water issued through c. When both a and b were opened, the water flowed copiously through c. At the close of this experiment, the glass water gauge showed that the level of the water within the boiler was one inch below the lowest cock. In another experiment the water being one inch and a half below the lowest cock; c being opened, no water issued; c and b being opened, a very little water issued through c; a, b, and c, being opened, a little water was mixed with the steam. The facts thus elicited are in accordance with the preceding observations of the Com Journal of the Franklin Institute, vol. x. pp. 80, 81; 1832. "Supplement to the communication of Thomas Ewbank, Esq. of New York, to the Committee on Explosions." mittee in relation to the 'general foaming which takes place when an aperture is made in any part of the boiler. The great respect which they entertain for the ingenious author of this device, on account of the valuable contributions which he has made to them, induced them to give this full trial of his suggestion. The third form of apparatus would out off the access of water from the general foaming, until it reached the level of the lowest apertures; but it would substitute a local foaming which would effectually, if not equally, prevent the true hydrostatic level from being indicated: in this respect it is nearly equiva lent to the gauge-cock, already described, as applied to the water-gauge. The various floats which have been applied to show the level of the water within a boiler are well known. They have never obtained favour in this country, and are con sidered particularly objectionable in their application to the high-pressure boiler,on account of the motion within. The stuffingbox, commonly used to pass the index-rod of the float through the top of the boiler, is objectionable, and different devices have been originated with a view to remedy this difficulty. That of Mr. Thomas Ewbank, of New York, described in volume xvi. of the Journal of the Franklin Institute, is highly ingenious, and is reported by him to have stood the test of experience in his small boiler, producing steam of rather less than five atmospheres. The apparatus of the Committee did not furnish facilities for a proper trial of this Abat; and, besides, such a trial would be inadequate to test its use in practice. A float serving to give an alarm by the issuing of steam, was made the subject of a few experiments, and answered well, as far as those trials went. Long use, however, could alone determine, perfectly, the peculiar liabilities to derangement in this apparatus. The float alluded to is shown on fig. 4 (p. 83). The requisite buoyancy is given to the metallic pyramid a, which is solid, by the weight, acting as a counterpoise over the fulcrum c. The whole apparatus is attached to the top of the boiler by the screwd, and the nute and the working parts are thus entirely within the boiler. When the water is at the proper level fg, the shoulders hand i are in the same horizontal line, and the disks kl, which are pressed against the shoulders by two springs shown in the figure, close the apertures km, and In, which, when open, permit steam to escape from the boiler. Should the water sink below its proper level, 'the equili brium of the pyramid a being destroyed, the shoulder i would press against the disk 4, remove it from the aperture, and permit steam to escape through In; should the water, on the contrary, rise above the proper level, steam would escape through km. The force of the springs which close these openings, should, of course, be duly proportioned, as they will determine the sensibility of the apparatus. The details of construction are clearly shown in the figure, which is drawn to a scale.* The quantity of steam which would escape by the small opening In, while it would serve as an alarm, would not materially diminish the supply of water within the boiler. The float used by the Committee was found to be sensible to less than three-tenths of an inch in the change of level; it could have been made more sensitive by increasing the breadth between the shoulders, so as to bring them in contact with the disks, as shown in the figure. Effect of Foaming on the Elasticity of the Steam within the Boiler. This point was the next proposed for examination. When an opening is made in a boiler, of which the sides are head, will the effect be to diminish the elasticity of the steam within, by permitting its escape, of will the water thrown upon the heated sides by the foaming which results, be converted so rapidly into steam as actually to increase the elasticity of the vapour within? It is obviously difficult to obtain an answer to a query involving so many conditions. It might be expected, however, that a small boiler would afford satisfactory means of making a fair trial of the question, since the size of the openings could be varied very easily, so as to make them comparatively small, or very great. The position of the boiler used by the Committee in its furnace was such, that the sides could be very readily heated; thus placing it in favourable circumstances to increase the elasticity of the steam by producing a foaming within. The apparatus was therefore adapted to make the desired trial. M. Arago, in his Essay on the Explosions of Steam-boilers, states, that MM. Tabareau and Rey, at Lyons, found on opening a large stop-cock, connected with a small highpressure boiler, that the safety-valve rose, showing an increase of pressure within. The boiler was placed naked upon a fire of char In the figure, the shoulders and i, do not rise high enough; they should overlap the disks more, that no depression or elevation of the water may earry them clear of the disks: coal, and the part not containing water was surrounded by flame. The experiments of MM. Arago and Dulong, at Paris, were at tended with a contrary result, the opening of a safety-valve being always accompanied by a diminution in the elasticity of the steam within. The circumstances, however, were not the same as those in the experiment of MM. Tabareau and Rey. To repeat this experiment, a hot fire was made beneath the boiler, and when the water had fallen to about three inches above the 'lowest line of the cylinder, the experiment was commenced, the pressure being about three atmospheres and a half. A stop-cock of 03 sq. inches in area, 70th part of the area of the water surface at the beginning of the experiment, delivering per second, at three and a half atmospheres, about four hundred and nine cubic inches of steam was first opened; next the safety-valve was raised, either in part or entirely, the area when entirely raised, being 208 sq. inches, or Tooths of the water surface, and capable of delivering, in one second, at three and a half atmospheres, a bulk of steam nearly nine times that of the steam chamber. The water level falling by the waste caused in the experiments, the steam soon became surcharged with heat, and the iron of the boiler, from near the water line to more than one-third of the distance from the lowest line to the middle of the convex surface, became, on each side of the water-line, heated until it attained redness, passing, of course, through the temperature of maximum vaporization of the water thrown by the foaming upon the iron. The experiments were made at intervals, until all the water was exhausted. Water was then injected in small quantities, and with the bottom of the boiler for the most part,red hot, the trials were repeated. It will be seen from the following table, that the result was uniformly a diminished elasticity of the steam within, as shown by the fall of the mercury in the steam-gauge. The pressures varied, in the former part of the experiments, from three and a half to eight atmospheres. The first column of the table contains remarks referring to the level of the water within the boiler. The second to the opening made. The third is the temperature indicated by the thermometer, M, fig. 1, before referred to, as passing nearly to the bottom of the boiler. The fourth, the height of the mercury-gauge, before making the opening. The fifth, the height immediately after making the opening, unless the contrary is stated in the sixth column, which contains remarks relating to the effect on the gauge. The seventh column contains general remarks. MACKINTOSH'S ELECTRICAL Sir, Whilst residing in Paris (from which capital I have lately arrived), my attention was directed by M. de la KMember of the French Institute, to a theory of the solar system which, if I am rightly informed, appeared originally in the pages of the Mechanics' Magazine, and upon which, with your permission, I would offer a few observations. In the first place, I would remark, that Mr. Mackintosh has, by referring all motion to the agency of electricity, attempted more than the present state of our knowledge, or the arguments which he has advanced in support of that proposition, will sustain. That electricity may be the primary cause of all motion, I will readily admit; but until the field of knowledge has been widened and extended by the researches of experimental philosophy, we bave no data whereby we can satis THEORY OF THE UNIVERSE. factorily determine this point. Before we attempt to build a system, we must lay a solid foundation of facts sufficient to support the superstructure; from a want of this necessary precaution, many a fine, system has tumbled to pieces. In the concluding part of this theory, I find the following rather formidable sentence:-"We presume that the geometrical demonstrations of the Newtonian philosophy will not be affected, whether we ascribe the effects to the agency of electricity, a power of whose existence we are assured by the evidence of the senses -or whether we refer them to gravitation, a conventional term, adopted for the purpose of explaining a certain effect resulting from no known cause." If hy this it is intended to substitute magnetic or electric attraction for that "certain effect which is generally understood |