OF THE FRANKLIN INSTITUTE Of the State of Pennsylvania, AND MECHANICS REGISTER; DEVOTED TO Mechanical & Physical Science, the Arts & Manufactures, AND THE RECORDING OF AMERICAN AND OTHER PATENTED INVENTIONS. JANUARY, 1836. Practical and Theoretical Mechanics. Report of Experiments made by the Committee of the Franklin Institute of Pennsylvania, on the Explosions of Steam-Boilers, at the request of the Treasury Department of the United States. THE Committee of the Franklin Institute on the Explosions of Steam-Boilers, respectfully present to the Secretary of the Treasury, their report of the experiments undertaken at the request of the department. The queries which were submitted by the committee, to the officer at whose request the experiments were instituted,* have formed the basis of the labours of the committee. They have, however, availed themselves of the privilege accorded, of trying such other experiments as might grow out of the investigation, or as they might deem of special interest. The object of the experiments was to test the truth or falsity of the various causes assigned for the explosions of steam-boilers, with a view to the remedies either proposed, or which may be consequent upon the result of the investigation. The causes being accurately known, the attention of ingenious men is led away from false suppositions, which can only waste their time and talent, if taken as the basis of their plans for safety; greater hope is afforded of an efficient remedy; applications of an indirect, or it may be of a positively injurious sort, are avoided; and if the causes be found to be such as for the present, to baffle ingenuity in their removal, the attention is directed more fixedly towards the means of protection against the effects of such accidents. The committee hope that the results of their inquiries will not be found with out fruit. It was the aim of the committee to provide for the experiments an apparatus of such dimensions as to furnish results applicable to practice, without being so great as to be managed with difficulty, or to increase, unnecessarily, the danger incident to parts of the investigation. To arrange the apparatus and complete the details, they secured the services of an able and experienced *The Hon. S. D. Ingham. late Secretary of the Treasury of the United States. mechanic, David H. Mason, by whom, or under whose direction, the nicer parts of the work were executed, and who assisted, also, in the experiments. The committee propose first to give a general description of the apparatus used, followed by details in the more complex parts; next to report the results of their examination upon each of the questions proposed for investigation. GENERAL DESCRIPTION OF THE APPARATUS. The boiler used by the committee, and represented in Plates 1, 2, and 3, was twelve inches in interior diameter, two feet ten and a quarter inches in length within, and one-fourth of an inch thick; of rolled iron, with the heads rivetted in the usual manner. Plate 1 is a side view, and 2 and 3 are end views of the boiler, and of the apparatus connected therewith. The boiler was placed horizontally in a furnace, the fire surface extending about half way round the cylinder. The furnace was arranged for a charcoal fire, the grate bars extending the whole length of the boiler, and the fire being applied through nearly the whole length. The draught entered by an opening, closed in the usual manner, and left the furnace through a flue placed at one end and side of the boiler. It will be convenient to use the terms fire end or front of the boiler, in reference to the proximity to the furnace door, and back end of the boiler. In Plate 2, A is the ash-pit door, B the furnace door, and in 1 and 3, C is the furnace chimney. In order to examine, readily, the interior of the boiler dufing the progress of the experiments, each head was provided with a glass window, (D, Plates 2 and 3.) The glass used was three-eighths of an inch thick. The openings in the ends, which were rectangular, were two and a half by one and threequarter inches wide. At first a glass plate, rather larger than the rectangle just mentioned, was applied to the opening, and kept in its place by four strips of brass secured to the heads, on which a rectangular frame, having the surface next to the glass accurately ground, was secured; the pressure of the steam keeping the glass against this frame, closed the boiler. Fractures occurring frequently from the rapidly varying, and often considerable, pressures within the boiler, and taking place by pressing the middle part outwards, as was proved by examining the fractures, frames with cross bars, see Plates 2 and 3, having the interior surface carefully ground, were used. The difficulty of properly adapting the surface of these frames to the glass having been removed, they were used in the later experiments, and were found to afford a sufficiently good view of the interior of the boiler, notwithstanding the obstruction by the cross bars. Three gauge cocks were placed in the front head of the boiler; their positions will be particularly stated hereafter; they are shown in Plates 1 and 2, at a, b, and c. To the same head and by the side of the gauge cocks, a glass water gauge (w, x, Plates 1 and 2) was attached, a particular description of which will be given in the detail of experiments made to compare its performance with that of the gauge cocks. To supply the boiler with water, a forcing pump E E F G, Plates 1 and 3, was placed near the back end. This pump was of the ordinary construction, with a solid plunger and conical valves; the diameter of the pump was one inch, and the play of the piston one inch and three-quarters. The diameter of the pipe, F G, by which the water was conveyed from the pump to the boiler, was three hundredths of an inch. By a coupling screw, this pipe could be connected with either of the stop cocks, d, e, Plate 3, in the back end of the boiler: the opening of these cocks was two hundredths of an inch in diame ter. To ascertain the elasticity of the steam within the boiler, a closed steam gauge (H, Plates 1 and 3) was used, a particular description of the construction, &c. of which will be given. This instrument was placed upon the same stand (I, Plates 1 and 3) which supported the pump, so that the same experimenter could observe its indications and attend to the working of the pump. The cistern of the gauge was connected by a flexible pipe, f, g, with the upper part of the boiler. The safety valve is shown on the top of the boiler, (K, Plate 1,) midway between the heads. The graduation of it required much pains, and will receive a separate discussion. Near the safety valve is represented at L, Plates 1 and 3, the fusible plate apparatus, consisting of a sliding plate of iron, moved by a lever. On the other side of the safety valve are the thermometers, M and N, Plate 1, plunged into iron tubes to give the temperature of the steam and water within the boiler. Above this appears the reservoir, O, containing the water intended to maintain the scales of the thermometers at a constant temperature. All these parts require a more detailed description. DETAILS OF THE APPARATUS. Of the Steam Gauge. The steam gauge consisted of a glass tube closed at the upper, and open at the lower end, which passed steam-tight into a reservoir for mercury: when this reservoir was connected wth the boiler the pressure of the steam raised the mercury into the gauge tube, compressing the air which the tube contained. The first mercurial gauge which was made was broken by a sudden access of surcharged steam, in the experiments upon that subject, and was replaced by a second one. The method of graduation, and in general the description of the second gauge, will serve also for the first; the details, only, varied slightly. The glass gauge tube was 26.43 inches in length. To the lower end was connected an iron ferule, terminated above by a projecting ring. This ring was pressed upon the upper end of the pipe, h, Plate 1, by a coupling screw, which served to form a tight juncture between the gauge and the cistern. The cistern i was a cylindrical vessel of cast iron, having the two projecting tubes h and k upon which screws were cut; the first of them has been alluded to as giving a passage to the glass tube of the gauge; the second was coupled by the pipe fg, Plates 1 and 3, to the boiler. The gauge tube was not of precisely equal diameter throughout, and it was judged more accurate to graduate small portions of it into equal volumes. This was done by introducing equal measures of air from the point of a sliding-rod gas measure (Hare's); this operation was performed repeatedly, and by multiple measures to verify the results, until the marks made for the equal volumes, on a paper scale attached to the tube, coincided, in the various trials. The lengths of the spaces occupied by the equal volumes were then carefully measured upon the brass scale to be used with the gauge. The slight differences between the lengths given by adjacent parts of the tube, showed that it might be considered as divided into so many small portions of uniform diameter. The mercury rising into the gauge tube from the cistern when pressure is applied, the level of the cistern is necessarily depressed; the amount of the correction for this depends upon the relation between the areas of the cistern and tube, supposed uniform. The areas of the cistern were found to be, within the limits of its use, sensibly the same; those of the tube might be so assumed for such a purpose: the ratio was therefore found by filling the gauge tube with mercury, and pouring this into the cistern, noting the rise produced; comparing this with the mean length of the tube, the ratio of depression in the gauge for elevation in the tube was found to be as .01 to 1. The air withi |