screwed down the steam-valve, closing every outlet, without ever thinking of the fire that was blazing under the boiler. Under such circumstances what could be expected but a 'blow up?' A madman rushing with a lighted match into a powder-magazine could not act with greater insanity. Such, however, has been the case, and this has resulted from want of thought, or, what is worse, from the total absence of that kind of knowledge which the employer as well as the workman should always

possess.

I have on former occasions stated that I am not an advocate for legislative interference either in the construction or management of boilers; but seeing the danger attending on the use of these vessels when placed under the control of ignorance and incapacity, I would forego many considerations in order to secure the services of a more judicious and intelligent class of men than has hitherto been employed in the care and management of steam and the steam-engine. The reforms necessary to be introduced may be made by the owners of steam-engines, steamboats, railways, and others engaged in the use and application of this important element. A desire to enforce more judicious and stringent regulations, to remunerate talent, and to employ only those whose good conduct and superior knowledge entitle them to confidence, is the only sure guarantee of public safety and the prosperity of the employer.

Lastly. The remedies applicable for the prevention of accidents arising from explosions.

Having noticed in the foregoing heads most of the causes tending to produce boiler explosions, it now only remains to draw such inferences as will enable us to point out the circumstances which it is desirable to cultivate and those which it is desirable to avoid. These circumstances I have endeavoured to class in such a way

as to bring the subject prominently forward, and to point out under each head, first, the causes which lead to accident; and, secondly, the means necessary to be observed in avoiding it. In a general summary it may not, however, be inexpedient briefly to recapitulate these statements, in order to impress more forcibly upon the mind of those concerned the necessity for care and consideration in the use of steam, one of the most powerful agents ever yet employed, or ever placed at the disposal of mankind.

In

One of the most scientific nations of Europe places the greatest confidence, as a means of safety, in the use of a fusible metal plate on the top of the boiler. These plates are alloys of tin and lead, with a small portion of bismuth, in such proportions as will ensure fusion at a temperature considerably below that of molten lead. In France the greatest importance is attached to these alloys, and in order to ensure certainty as to the definite proportions, the plates are prepared at the Royal, now the Imperial Mint, where they may be purchased duly prepared for use. this country these alloys are not generally in use; but in this respect I think we are wrong, as boiler explosions are not so frequent in France as in this country, and high-pressure steam, from its superior economy, is more extensively used in France than in England. In my own practice I invariably insert a fusion plate, or a lead rivet one inch in diameter, immediately over the fire-place, and I have found these metallic plugs a great security in the event of a scarcity of water in the boiler. I am persuaded many dangerous explosions may be avoided by the use of this simple and effective precaution; and as pure lead melts at 640°, we may infer from this circumstance that notice will be given and relief obtained before the internal pressure of the steam exceeds that of the resisting powers of the heated plates. As this simple precaution is so easily accomplished, I would advise

its general adoption. It can do no harm to the boiler, and may be the means of averting explosions and the destruction of many valuable lives.

The fusible metal plates, as used in France, are generally covered by a perforated metallic disc, which protects the alloy of which the plate is composed, and allows it to ooze through as soon as the steam has attained the temperature necessary to ensure the fusion of the plate. The nature of the alloy is, however, somewhat curious, as the different equivalents have different degrees of fluidity, and the portion which is the first to melt is found out by the pressure of the steam causing the adhesion of the less fusible parts, but in a most imperfect state, and incapable of resisting the internal force of the steam. The result of these compounds is, the fusion of one portion of the alloy and the fracture of the other, which is generally burst by pressure.

This latter description of fusible plate is different to the lead plug over the fire, which is fused at 640° by the heat of the furnace, and the other, by the temperature of the steam, when raised to the fusible point of the alloy, which varies from 280° to 350°.

Another method is the bursting plate, fixed in a frame and attached to some convenient part of the upper side of the boiler; this plate should be of such thickness and of such ductility as to cause rupture whenever the pressure greatly exceeds that of the weight on the safety-valve. There can be no doubt that such an apparatus, if made with a sufficiently large opening, would relieve the boiler; but the objections to this and several other devices are the frequent bursting of those plates, and the effect which every change of pressure has upon the material in reducing its powers of resistance, and thus increasing the uncertainty as to the amount of pressure in the boiler; besides, there is the expense and loss of time connected with the renewal of the plates.

It has already been noticed that one of the most important securities against explosions is a duly proportioned boiler, well constructed; and to this must be added ample means for the escape of the steam on every occasion when the usual channels have been suddenly stopped. The only legitimate outlets under these circumstances appear to me to be the safety-valves, which, connected with this inquiry, are indispensable to security. Every boiler should therefore have two safety-valves, either of them of sufficient capacity to carry off the quantity of steam generated by the boiler. One of these valves should be of the common construction, and the other beyond the reach of the engineer or any other person.

Fig. 7, is a sketch of the lock-up safety-valve as I have been accustomed to construct it. A is the valve. B is a shell

of thin brass, opening on a hinge and secured by a padlock; it is of such a diameter as to allow the waste steam to escape in the direction of the arrows. C is the weight, which may be fixed at any part of the lever, to give the desired amount of pressure, but which cannot be fixed or

altered unless the boiler is opened to allow a man to get inside. D is a handle, having a long slot, by which the valve may be relieved or tried at any time, to obviate the liability of its corroding or being jammed; the engineer cannot, however, put any additional weight upon the valve by this handle, and hence its security.

Whilst tracing the causes of explosions from a deficiency of water in the boiler, I have recommended as the usual precautions, good pumps, self-acting feeders, water-cocks, glass gauges, floats, alarms, and other indicators which mark the changes and variation in the height of the water. To these may be added the steam whistle, but, above all, the constant inspection of a careful, sober, and judicious engineer. Above all other means, however ingeniously devised, this is the most essential to security, for on that official depends, not only the security of the property under his charge, but also the interests of his family, and the lives of all those within the immediate influence of his operations. One of the most important considerations in this and every other department of management is cleanliness and the careful attention of a good engineer.

Explosions produced from collapse of the external shell on the condensation of the steam, have their origin in causes entirely different from those which arise from a deficiency of water, and the only remedy that can be applied is the vacuum valve and the cylindrical or spheroidal form of boiler.

Defective construction is unquestionably one of the greatest sources of the frightful accidents which we are so frequently called upon to witness. No man should be allowed unlimited exercise of judgment on a question of such vital importance as the construction of a boiler, unless he is duly qualified by matured experience in the theoretical and practical knowledge of form, strength of materials, and other requirements requisite to ensure the maximum of sound construction. It appears to me