attached to it, but was found to be unable to pull it up the grade over which the car was propelled by magnetism six miles and hour. It required five men and this horse to get the car over this grade, and it was lighter by two tons than when driven by magnetic power, and moreover, when it ascended this grade at six miles an hour, the power of the battery was not fully ups and I have discovered a cause of great additional friction when the engine was in action, the remedy for which is obviousa In regard to the doctrine of Liebig, that the zinc cannot give out more power than the coal required to smelt it, it is unfortu: nate, and though entertaining the highest respect for his reputation and ability, I must pronounce vita a practical absurdity. It is reasonable to suppose that a given amount of zine combining with oxygen, would not eliminate more heat than would be required to overcome this affinity, but we have no proof of any such relation of electricity to heat as to make the mechanical power of the one the measure of the mechanical power of the other. Whatever may be the connection and analogy between heat and electricity, we must consider them as distinct forces in their mechanical relations. In the combustion of coal we develope heat as the motive force, and no electricity; in the oxidation of zinc in the battery, we develope both heat and electricity, the latter only being the motive force. The absolutism of forces regulating affinities may be interesting as a matter of speculation, but, as furnishing a practical estimate for the amount of mechanical or available power, it cannot stand, and necessarily involves the unwarrantable assumption that the whole power or inherent force may be eliminated and rendered available in each case. But Liebig goes still fur ther: he maintains that the heating power of the current is the equivalent of its mechanical power through electro-magnetism; or, in other words, that the heat developed by the passage of the current ought to raise steam enough to furnish a power equivalent to the electro-magnetic power of the same current, and from the fact that the mechani cal force derived from steam raised by the heating power of the current is so small compared with that obtained by the com bustion of coal, he arrives at the conclusion that electro-magnetic power" can never be used." The speculation is thus pursued up to a point where facts are brought in to its support, and fortunately where facts enough can be adduced to subvert the whole doc. trine. I will take but one, and one that can be easily admitted; or, rather, I will propound a question, "How many pairs of plates would be required to operate through their calorific or steam power the lever of the receiving magnet in Morse's Telegraph, say through a circuit of 80 miles? I saw an experiment some years ago at the Capitol, when gunpowder was fired through this length of circuit, the powder being at the Capitol and the battery at Baltimore. Fifty pairs of Grove's battery, such as they used for the telegraph, would not ignite a platico num wire one-thousandth of an inch in diameter. It finally required seventy-five pairs to fire the powder. Ten pairs of such plates will work the receiving magnet through this circuit vigorously. I leave it to mechanical minds here to form their own conclusions. The truth is, that the cost of electro-magnetic power, or any other power is circumstantial, and the attempt to predicate the whole economy of magnetic power upon the cost of coal and cost of zinc, and the fact that coal is found native and zinc not, is, in effect, to make Nature's laws and operations amenable to market prices and other contingencies. ON THE CONSTRUCTION OF STEAM BOILERS (Continued from vol. liv., p. 509.) L In the flat ends of cylindrical boilers, and those of the marine construction, the same rule applies as regards construction; and the due proportions of the parts, as in those of the locomotive boilers, must be closely adhered to. Every description of boiler used in manufactories, and also those on board of steamers, should in my opinion be constructed to a bursting pressure of 400 to 500 lbs. on the square inch, and locomotive 1 engine boilers, which are subjected to a much severer duty, to a bursting pressure of 600 to 700 lbs. It now only remains for me to state that internal flues, such as contain the furnace in 1 the interior of the boiler, should be kept as near as possible to the cylindrical form; and as wrought iron will yield to a force tending to crush it of about one-half of what would tear it asunder, the flue should in no case exceed one-half the diameter of the boiler, and with the same thickness of plates it may be considered equally safe to the other parts. In fact, the force of compression is so dif-h ferent to that of tention, that I should advise the diameter of the internal flues to be in the ratio of 1 to 2f instead of 1 to 2 of the diameter of the boiler. Various notions are entertained as to the causes of boiler explosions, and scientific men are not always agreed as to whether they arise from excessive pressure due to the accumulation of heat, or to some other cause, such as the explosion of hydrogen gas, generated by the decomposition of water suddenly thrown on heated plates, of which we have an exceedingly indefinite con ception. That of the decomposition of water is, I believe, a somewhat prevalent opinion, but I apprehend it cannot be the invariable cause, inasmuch as in that case: we must assume the boilers to be nearly empty of water, and the plates over the furnace red hotpor 2431 It is not unreasonable to suppose that a force of such sudden origin, and so immediate and destructive in its effects, should suggest the presence of an explosive mix. ture, but I think it will be difficult, if not impossible, to account for the accumulation of a sufficient quantity of hydrogen without the presence of oxygen and other gases, in their due proportions, to form an explosive: compound. Now, as these equivalents can not be generated all at once by the simple decomposition of water (admitting for the moment that the water is decomposed) we must look for some other cause for the fatal and destructive accidents which of late years have been so prevalent. In treating of this subject, I hope to show not only what are the probable causes of explosion, but what appears equally important, what are not the causes. So many theories (some of them exceedingly problematical) have been brought forward on the occasion of disastrous explosions, that it requires the utmost care and attention to circumstances before they are generally admitted. To acquire satisfactory evidence as to the precise condition of the boiler and furnaces before an explosion is next to impossible, as most frequently the parties in charge, and from whose mismanagement and neglect we may in many cases date the ori gin of the occurrence, are the first to become the victims of their own indiscretion, and we can only judge from the havoc and devastation that ensues as to the immediate cause of the event. a From this it follows that, in many of the explosions on record, few, if any of the real circumstances of the case are made known, and we are left to draw conclusions from the appearances of the ruptured parts, and the terrific consequences which too fre quently follow as a result. This want of evidence as to the precise condition of a boiler with all its valves and mountings, preceding an explosion, is, much, to be regretted, as it causes a degree of mystery to surround the whole transaction; and the vague and sometimes inaccurate testimony of witnesses, but too often baffles all attempts at research, and creates additional cause of alarm to all those exposed to the occurrence of similar dangers. 19 19qing 8.3 In the discussion of this subject I shall, however, endeavour to trace from a number: of examples in which I have been personally engaged, and from others which have comme to my knowledge the causes which have led to the disastrous effects... In my attempts to ascertain facts by as course of reasoning which I shall have to follow in this investigation, I could wish it. to be understood that it is not my intention to raise doubts and fears in the public mind, calculated to arrest the progress of commer cial enterprise, or to cripple the energies of mechanical skill. On the contrary, I am most anxious to promote the advancement. of the useful arts, to increase our confidence in the application of increased pressure, and to secure within moderate bounds the economical and useful employment of one of the most powerful agents ever known in the history of practical science. My object. in this inquiry will, therefore, be to enlarge our sphere of action by a more comprehensive knowledge of the subject on which it treats; to induce greater caution along with improved construction; and to insure confidence in all those requirements essential to the public security For the attainment of these objects it will be necessary to divide the subject into the following heads 1st. Boiler explosions arising from accumulated internal pressure 2nd. Explosions from deficiency of water. 3rd. Explosions produced from collapse. 4th. Explosions from defective construction.. יין 5th. Explosions arising from mismanagement or ignorance; and 6th. The remedies applicable for the prevention of these accidents. ett 1st. Boiler explosions arising from accumulated internal pressure. In nine cases out of ten a continuous increasing pressure of steam, without the means of escape is probably the immediate cause of explosion; in some instances it arises from deficiency of water, but accidents of this kind are comparatively few.in number, as we often find in tracing the causes that they have their origin in undue pressure, emanating from progressive accumulation of steam of great force and intensity. Let us take an example to some of which I am able to referand we shall find that a boiler under the influence of a furnace in active combustion (as the recipient of heat) will generate an immense quantity of steam, and unless this is carried off by the safety valve or the usual channels when generated, the greatest danger may be apprehended by the continuous increase of pressure that is taking place within the boiler. Suppose that from some cause the steam thus accumulated does not escape with the same rapidity with which it is generated, that the safety valves are either inadequate to the full discharge of the surplus steam, or that they are entirely inoperative, which is sometimes the case, and we have at once the clue to the injurious consequences which, as a matter of fact, are sure to follow. The event maybe procrastinated, and repeated trials of the antagonist forces from within and the resistance of the plates from without may occur without any apparent danger, but these experiments often repeated will at length injure the resisting powers of the material, and the ultimatum will be the arrival of the fatal moment when the balance of the two forces is destroyed and explosion ensues. How very often do we find this to be the true cause of accidents arising from extreme internal pressure, and how very easily these accidents might be avoided by the attachment of proper safety valves to allow the steam to escape and relieve the boiler of those severe trials which ultimately lead to destruction. If a boiler, whose generative power be equal to 100, be worked at a pressure of 10 lbs. on the square inch, the area of the safety valve should also be equal to 100, in order to prevent a continuous increase of pressure; or in case of the adhesion of any of the valves, it is desirable that their areas should, collectively, be equal to 100. If two or more valves are used, 100 or 120 would then be the measure of outlet. Under these precautions, and a boiler so constructed, the risk of accident is greatly diminished; and provided one of the valves is kept in working order, beyond the reach of interference by the engineer, or any other person, we may venture to assume that the means of escape are at hand, irrespective of the temporary stoppage of the usual channels for carrying off the steam. So many accidents have occurred from this cause-the defective state of the safety valves-that I must request attention whilst I enumerate a few of the most prominent cases that have come before me. In the year 1845 a tremendous explosion took place at a cotton mill in Bolton. The boilers, three in number, were situated under the mill, and from unequal capacity in the safety valves, and even those imperfect, as they were probably fast, a terrific explosion of the weakest boiler took place, which tore up the plates along the bottom, and the steam having no outlet at the top, not only burst out the end next the furnace, demolishing the building in that direction, but tearing up the top on the opposite side, the boiler was projected upwards in an oblique direction, carrying the floors, walls, and every other obstruction before it; ultimately it lodged itself across the railway at some distance from the building. Looking at the disastrous consequences of this accident, and the number of persons-from sixteen to eighteen-who lost their lives on the occasion, it became a subject of deep interest to the community that a close investigation should immediately be instituted, and a recommendation followed that every precaution should be used in the construction as well as the management of boilers. The next fatal occurrence on record in this district was a boiler at Ashton-underLyne, which exploded under similar circumstances, namely, from excessive interior pressure, when four or five lives were lostand again at Hyde, where a similar accident occurred from the same cause, which was afterwards traced to the insane act of the stoker or engineer, who prevented all means for the steam to escape by tying down the safety valve. There was a boiler exploded at Malaga, in Spain, some years since, and my reason for noticing it in this place is to show that explosions may be apprehended from other causes than those enumerated in the divisions of this inquiry, and that is incrustation. Dr. Ritterbandt says-in a paper read before the Institution of Civil Engineers, by an eminent chemist, Mr. West -"That a sudden evolution of steam under circumstances of incrustation is no uncommon occurrence." In several instances I have known this to be the case, particularly in marine boilers, where the incrustation from salt water becomes a serious grievance, either as regards the duration of the boiler, or the economy of fuel. If it were supposed, as Dr. Ritterbandt observes, that the boiler was incrusted to the extent of half an inch, it would at once be seen that nothing was more easy than to heat the boiler strongly, even to a red heat, without the immediate contact of water. Under these circumstances, the hardened deposits being firmly attached to the plates, and forming an imperfect conductor of heat, would greatly increase the temperature of the iron, and the great difference of temperature thus induced between the material-and the greater expansibility of the iron-would cause the incrustation to separate from the plates, and the water rushing in between them would generate a considerable charge of highly elastic steam, and thus endanger the security of the boiler. These phenomena were singularly exemplified in the Malaga explosion, which is thus described by Mr. Hick:-" I have ascertained that a very thick incrustation of salt was found on the lower part of the boiler, immediately over the fire, and so far as it extended, the plates appear to have been red hot, thereby much weakened, and hence the explosion. The ordinary working pressure of the boiler is 130 lbs. per square inch, and perhaps at the time of the explosion very much above that pressure, as there was only one small safety-valve of 2 ins. diameter. The boiler was only 2 feet 6 ins. diameter, and 20 feet long. Incrustation, exclusive of being dangerous, is attended with great expense and injury to the boiler by its removal. In the case of the transatlantic, oriental, or other long sea-going vessels-even after the use of brine-pumps, blowing out, &c. a very large amount of incrustation is formed, and considerable sums of money are expended each voyage to remove it. Other explosions of a more recent date are those which occurred at Bradford and Halifax. They are still fresh in the recollection of the public mind, and are so well known as not to require notice in this place. I cannot, however, leave this part of the subject without reverting to an accident which occurred on the Lancashire and Yorkshire Railway, which had its origin in the same cause- excessive internal pressure. This accident is the more peculiar as it led to a long mathematical disquisition as to the nature of the forces, which produced results at once curious and interesting. The conclusions which I arrived at, although practically right, were, however, considered by some mathematically wrong, as they were firmly combatted by several eminent mathematicians; and notwithstanding the number of algebraic formulas, and the learned discussions of my friends on that occasion, I have been unable to change the opinions I then formed to others more conclusive. The accident here alluded to, occurred to the Irk locomotive engine, which in February, 1845, blew up and killed the driver, stoker, and another person who was standing near the spot at the time. A great difference of opinion as to the cause of this accident was prevalent in the minds of those who witnessed the explosion, some attributing it to a crack in the copper fire-box, and others to the weakness of the stays over the top; neither of these opinions were, however, correct, as it was afterwards demonstrated that the material was not only entirely free from cracks and flaws, but the stays were proved sufficient to resist a pressure of 150 to 200 lbs. on the square inch. The true cause was afterwards ascertained to arise from the fastening down of the safety valve of the engine (an active fire being in opera tion under the boiler at the time), which was under the shed, with the steam up, ready to start with the early morning train. The effect of this was the forcing down of the top of the copper fire-box upon the blazing embers of the furnace, which, acting upon the principle of the rocket, elevated the boiler and engine of 20 tons weight to a height of 30 feet, which, in its ascent, made a summerset in the air, passed through the roof of the shed, and ultimately landed at a distance of 60 yards from its original position. The question which excited most interest, was the absolute force required to fracture the fire-box, its peculiar properties, when once liberated, and the elastic or continuous powers in operation, which forced the engine from its place to an elevation of 30 feet from the position on which it stood. An elaborate mathematical discussion ensued relative to the nature of these forces, which ended in the opinion that a pressure sufficient to rupture the fire-box was, by its continuous action, sufficient to elevate the boiler and produce the results which followed. Another reason was assignednamely, that an accumulated force of elastic vapour, at a high temperature, with no outlet through the valves, having suddenly burst upon the glowing embers of the furnace, would charge the products of combustion with their equivalents of oxygen, and hence explosion followed. Whether one or both of these two causes were in operation is probably difficult to determine; at all events, we have in many instances precisely the same results produced from similar causes, and unless greater precaution is used in the prevention of excessive pressure, we may naturally expect a repetition of the same fatal results. (To be continued.) SPECIFICATIONS OF ENGLISH PATENTS ENROLLED DURING THE WEEK ENDING JULY 3, 1851. WILLIAM HODGSON GRATRIX, of Salford, engineer. For certain improvements in the method of producing or manufactur ing velvets or other piled fabrics. Patent dated December 26, 1850. These improvements are applicable only to those descriptions of velvet and other piled fabrics in which the pile is produced by the weft thread, and the cut is consequently made in the direction of the warp. Claims.-1. A method of producing or manufacturing velvets or other piled fabrics by weaving the pile threads over a series of fine longitudinal knives with elongated points of wire-such knives being stationary, and having their cutting ends or extremities attached to a suitable holding frame (and being kept in a state of tension by weights attached to their points), so that simultaneously with the weaving, the portions of the weft intended to form the pile slides consecutively upon the points of the knives as the cloth is woven, until it arrives at the cutting portions of the knives, by which the weft thread is severed, the velvet or other fabric being then wound upon the cloth beam as usual. 2. A method of producing or manufacturing velvets and other piled fabrics, by weaving in the cloth, a series of fine wires, passing through the spaces between the pile threads and the cloth, which wires are subsequently separated or removed from the cloth by passing the fabric between two rollers or bowls (one composed of a yielding material, such as paper-the second of metal), acting by friction or pressure, so as to sever the pile threads, and leave the velvet or other fabric complete. GEORGE EDWARD DERING, of Lockleys, Herts, Esq. For improvements in the means of and apparatus for communicating intelligence by electricity. Patent dated December 27, 1850. The improvements claimed under this patent comprehend 1. The use of elastic supports in place of axes of suspension for telegraphic arrangements. [This system is particularly appli. cable to the indicators and other similar moveable parts, whether such moving parts are permanent magnets, or composed of metal rendered temporarily magnetic.] 2. A method or methods of applying the force of gravity to restore magnetic needles and other similar telegraphic arrangements to their position of rest, after having been set in motion, by the passage of currents through coils placed in juxtaposition with them. [In one arrangement for this purpose, the centre of gravity of the needle is placed immediately below the centre of motion, by attaching to the needle (which is itself equally balanced on either side of the centre of motion), a button of metal of sufficient weight to bring the needle quickly to rest-the principle here adopted being that of the quick beat of a short pendulum as compared with that of a long one. Another method of effecting the same object is, to suspend the needle from its upper end, which is provided with a triangular aperture, through which is passed a hook of circular wire, which forms the suspender. According to a third method, the needles are suspended by magnetic attraction.] 3. A method of applying electro-magnetic coils to produce motion for telegraphic purposes. [In this arrangement the needle is placed or suspended in a vertical position, and instead of being influenced by deflection, is caused to vibrate by the direct attractive and repulsive action of coils, which are so placed that their axes are parallel to or in the plane of vibration of the needle. The same method of producing motion is equally applicable to needles moving on a central pivot or suspended by their upper extremity.] 4. An arrangement for telegraphic alarums, by which, when included in the same circuit with the signalling apparatus, they are prevented sounding during the ordinary working of the instruments, though ready to be acted on at any moment when required. (This is effected in double needle telegraphs by reserving from use in sending messages, one particular signal or motion of one or both needles, and employing that motion only when it is desired to sound the alarum.) 5. A method of transmitting secret intelligence to any one or more stations on a line at choice without the use of an extra wire. [Each station is provided with a metallic disc, capable of revolving by a step-by-step motion worked at pleasure by a current in the ordinary manner, and having pieces of ivory or non-conducting material, let into the surface of its periphery which revolves in contact with a metallic spring.] The bearings of the disc and the spring are both in connection with the extremity of the coil which actuates the indicator motion, the coil being in the same circuit with the line wire. When the discs are caused to revolve, and the springs rest on the conducting sur. faces, a short circuit is established which permits the passage of the electricity from end to end of the line wires without affecting the indicating instruments; but when the springs rest on the non-conducting materials, then the short circuit will be broken, the indicator brought into the line wire circuit, and the messages delivered as in the ordinary working of the telegraph. In order to prevent the working of the discs under ordinary circumstances, it will be requisite to adopt some such as the following system: that is, to employ the reverse current to produce the step-by-step motion of the discs when a current in one direction only is used for the conveyance of messages, or to arrange the step-by-step motion so that it shall remain unaffected, except when increased battery power is applied. 6. A method of counteracting the effects of currents of atmospheric electricity by introducing into the circuit an opposing current of equal force [produced by a galvanic battery or other suitable means]. 7. The use of pairs of conducting surfaces, for the purpose of carrying off atmo |