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fact admits of a very easy explanation. On the exit of a portion of steam from the boiler, there is instantaneously generated a corresponding, or rather, there is reason to suppose, a greater quantity; for the undulatory motion given to the body of steam in the boiler, by opening the steam-cock, will, for an instant, withdraw a part of the pressure from the surface of the water, which will, so to speak, embrace the moment to send off an amount of steam corresponding to its temperature, and the amount of pressure removed. But the steam wave produced, in the first instance, in the direction of the steam pipe, being reflected back from the top of the boiler, must produce upon the bottom a greater pressure than before existed, when the whole contents were in a quiescent state. Add to this a quantity of steam, which we can easily suppose to be generated by waves of water laving high upon the heated sides of the boiler, consequent on the motion of the vessel; and there can be little difficulty in seeing why rupture may be produced under the circumstance of the engine starting, in a boiler already distended by steam, to the full strength of its vulnerable points. This explanation comprehends the celebrated case of the explosion of Messrs. Ferey's boiler, at Essonne, in France, which took place on opening the safety-valve, and likewise the explosion of two of Mr. Steele's three boilers at Lyons. In this case, these steamboat boilers were connected together, and the safety valve was fastened down to increase the pressure of steam. Shortly after one boiler exploded, and broke the connecting pipes. This, according to the received opinion—that by withdrawing a portion of steam, the pressure and danger are thereby instantly diminished-ought to have saved the other two boilers, by acting as safety-valves to them; they nevertheless exploded in succession.

With the facts before us of the retention of the steam, and the previously weak state of the crown plate-the only part of the boiler ruptured-there cannot exist much difficulty in comprehending the case before us, There is little necessity for supposing a deficiency of water in the boiler, and certainly none for supposing the crown to have been red hot at the time of rupture. It is true that the catastrophe may be explained on such a supposition-not by the decomposition of water, and the generation of hydrogen gas. We feel very confident that no case of explosion, under like circumstances, can be traced to such a cause. But, as already noticed, heated plates, by having a quantity of water laved upon them, readily give out their heat, and create an additional quantity of steam, and, in consequence, an additional aggregate pressure within the boiler. We are not, however, prepared to believe that the danger of over-heating boilers lies in the quantity of steam which is thereby produced on the admission of water;-the danger is to be apprehended from the suddenness with which it is produced. The heat even of red hot iron is small when viewed in connexion with the quantity of heat requisite to convert water into steam; but being a good conductor, it parts with its heat to the water with great facility, and under the conditions supposed, we can readily imagine that it will send off from its surface a volume of steam of great momentary elasticity. It is, moreover, to

be' remarked, that a sudden development of steam in a boiler will exert its force, in the first instance, against the bottom; and it is only when this has sustained the concentrated shock without injury, that the force is reverberated, and allowed to distribute itself over the whole interior. Many cases of explosion, where a portion of incrustation had become loosened, and allowed the water suddenly to come into contact with an over-heated plate, may be referred directly to the instantaneous expenditure of the force at that point; and even under ordinary circumstances, the bottom-upon which the steam forms— sustains a greater amount of pressure than any equal superior surface.

Viewing the circumstances, therefore, as we may, we are brought to the conclusions, that the steam force due to the elasticity is expended upon the parts-the bottom and sides, in the first instance,—of a boiler before it comes to act upon the safety-valve, and in all cases where this valve is loaded to such an extent as to retain the steam within, at an elasticity approaching the cohesive strength of the weakest part of the boiler, any undulatory motion communicated to the mass of steam, or any sudden evolution of steam, from whatever cause the one, or the other, may arise, must be attended with great danger of explosion. This danger is thought to be lessened by employing more than one safety-valve, and by enlarging the capacity where one is only used, and there cannot be a doubt but that this is to a certain extent correct; there must at least be sufficient egress provided for the superfluous steam generated; but the only real safety lies in loading the valve-supposing it to be of moderate size-at a minimum of the proved strength of the boiler. To this condition add the no less important one, that the engines and boiler are under the management of trained, intelligent, and properly behaved engineersmen who know something more about an engine than "to put on and off the steam"-and we feel very confident, that disasters, such as that which has engaged our attention, will, in future, be very rare. This is a subject, indeed, which has long since been ready for legislative interference. Parliament is at length beginning to bestir itself in behalf of railway travelers; but the lives of steamboat passengers are equally precious and surely if it be thought necessary that the engine-man, in the one case, should be able to satisfy a board of examiners, regarding his fitness for the duties incumbent upon him, we have an equal right to expect that those who may rather choose

"To steam it o'er the glassy wave,"

shall not be left to the care of men, whose fitness for their task is left to be judged of by persons, whose first consideration is the payment of the least possible amount of wages. Some have been calling out for the appointment of a government inspector at all our steamboat stations; we go a step further, and would place an accredited inspector in every vessel propelled by a steam engine. Glasgow Mech. & Eng. Mag.

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Description of an improved Tilting Apparatus for emptying Wagons at the termini of railways, shipping places, &c., as used at the Magheramorne Lime Works, Ireland. By JAMES THOMSON, Esq., F.R.S.E., M.R.I.A., F.R.S.S.A., Civ. Eng., Glasgow.*

The apparatus may be generally described as consisting of three parts, viz:

1st. The cast-iron brackets, or quadrants, for supporting the machine, a, a, a.

2d. The tilting-frame upon which the wagon is placed b, b; and 3d. The malleable iron-swings for suspending the frame to the brackets, c, c.

[graphic]

Face of Wharf

The supporting brackets, a, a, a, are bolted to the wooden frame, d, d, of a movable shipping platform, by means of which the apparatus is advanced at pleasure, and made to project beyond the wharf, so as to discharge the wagon immediately over the hold of the vessel. The tilting-frame is formed of two cast-iron cheeks, or sides, as shown in fig. 3, having in each two slots, or grooves, for attaching to the swings, and for adjustment of the apparatus. These sides of the frame are connected together by two flat malleable iron stays, e, e, as represented in fig. 2, with two bolts in each end, and a light iron stay, f, at the curved ends.

* Read before the Royal Scottish Society of Arts, and working model exhibited 10th of January, 1842, and the Society's Honorary Silver Medal awarded 14th November, 1842.

The swings are attached to the frame by means of snubs, g, g, which are bolted vertically to the lower ends of the swings, and horizontally to the sides of the frame, the bolts passing through the grooves, or slots, already mentioned, in which they are movablethe upper ends of the swings work upon malleable iron journals fastened in the top of the cast-iron brackets. When the apparatus is properly adjusted, which is done by moving the tilting-frame forward, or backward, upon the swings, by means of the adjusting slots, the wagon, on taking its position, should be so placed that its centre of gravity may be slightly in advance of the point of suspension.

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The rails to the tilting-frame are laid with a gentle declivity, so that the wagon may be brought upon it with a slight impetus just sufficient to set the frame in motion-the wagon will then immediately fall into a position ready to discharge, as shown in fig. 2, when, by a simple contrivance, which may be effected in various ways, the door of the wagon is opened from behind by a handle and connecting rod communicating with the door latch, and the load discharged.

While loaded, the position of the wagon will of itself remain the same, being in equilibrio; but immediately after it is discharged, and consequently the centre of gravity thrown behind the point of suspension, the tendency of the wagon is then to resume the horizontal position, which, however, it is prevented from doing by means of the spur, h, until completely emptied the spur is then disengaged, and the wagon resumes its level position ready to be removed.

The whole operation of discharging a wagon, of whatever weight, is effected with perfect safety and facility in a few seconds, and one very important desideratum is supplied by this apparatus, viz.,-the practicability of discharging wagons of different dimensions and different sized wheels upon the same tilting-frame.

The advantages of the apparatus have been fully tested at the Magheramorne Lime Works, in Ireland, where they were first applied, and have since been in constant operation for the last three years, discharging wagons of three tons with 24-inch wheels, and wagons of only 20 cwt. and 20-inch wheels, with perfect facility and expedition-the cost of each apparatus not exceeding from £10 to £11 complete.

Edin. New Philos. Journ.

Manufacture of Oil of Vitriol from Iron Pyrites.

The manufacture of sulphuric acid and soda is carried on conjointly, in a factory at Belgium, in the following manner:-The residua of the roasted pyrites are mixed with an excess of sea salt, having previously ascertained the contents of sulphate of iron contained therein. The mixture is then heated in an appropriate furnace, arranged so as to collect the muriatic acid. The sulphate of soda formed, is obtained by solution and crystalization; the peroxide of iron remaining is separated by elutriation into two parts; the most finely divided is dried and mixed with grease, or palm oil, serving as a lubricator for machinery, for which it is admirably adapted; whilst the coarser portions are made into balls, dried, and used as mineral iron for the puddling furnace. In factories where soda is not made concurrently with sulphuric acid, in place of procuring the sulphate of iron from the roasted pyrites, it will be more advantageous to distil these residua, the sulphate of iron being first dried, so as to obtain the fuming sulphuric acid of Nordhausen, as it is termed. It would be very easy to arrange the apparatus in such a manner that the sulphurous acid, arising from the decomposition of part of the sulphate of iron, should be conducted into leaden receivers, or chambers. By such an arrangement, nothing would be lost, since the colcothar, or peroxide of iron, remaining after the process has been completed, is always available.

Lond. Min. Journ.

An Enormous Steam Engine.

An enormous steam engine, by far the largest ever constructed, is now in process of manufacture at Harvey & Co's. foundry, Hayle; the piston-rod, which was forged last week, is 19 feet long, 13 inches diameter in the middle, and 16 inches in the core; and weighs 3 tons 16 cwt. It will work in an 80-inch cylinder, which will stand in the middle of another cylinder, of 144 inches diameter. Five other pistonrods will work between the inner and outer cylinders. We conclude, for this has not been explained to us, that the piston of the external giant cylinder will be perforated in the middle for the 80-inch cylinder to stand in it, and will work between the two. The 80-inch cylinder was cast last week, and the large one will be cast soon. The pumps are to be 64 inches in diameter; a measurement which may afford some idea of the size of the engine. It is intended for draining Hær

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