ON THE CAUSES OF INJURY TO STEAM BOILERS.-BY C. W. WILLIAMS, ESQ.

Sir,-In my last paper on this subject, I explained some of the causes of those injuries to which steam-boilers are exposed, and dwelt on the circumstance, that the sediment assumes two distinct forms, namely, that of a solid crystallized incrustation, and of a loose mud-like body, held merely in suspension. I showed that the first could not be the cause of injury to the iron plates of boilers, inasmuch as it was itself a good conductor of heat; whereas the second the floating matter--would become a positive non-conductor, if allowed to subside, when the boiler had been at rest for some hours, and when it would assume the dry hard consistence of plaster of Paris.

I now propose to give further proofs of the conductibility of this solid crystallized incrustation, and draw some important inferences therefrom. I had two pins constructed, to act as conductors, each three inches long and three-quarters of an inch square, one made of iron, and the other cut from a large slab of incrustation taken from the interior of a marine boiler. These were inserted into separate vessels, containing water, the one end projecting half an inch into the water, through the side, and the remaining part projecting outwards, to receive the heat from a powerful gas-burner. These vessels were so protected, that no heat could reach them, except what passed longitudinally, and exclusively through the conductor pins; consequently, the water received no heat except what was conveyed, by conduction, through those pins.

By means of the iron conductor pin, the water was made to boil in 13 minutes, and by the incrustation conductor pin, in 17 minutes. That the pins themselves were not raised to any inconveniently high temperature was proved by the fact, that when suddenly removed from the flame, which was very intense, and while the water was fiercely boiling, the pins themselves were at a temperature so low as to allow the finger to be pressed against them without inconvenience; it certainly did not appear to be above 500 or 600 degrees a temperature far too low to produce any injurious effect on their structure. This experiment resembled the well known one of taking a kettle

containing boiling water from the fire, and placing it on the hand, for an instant, and without injury. I may here observe, that I was not able to discover any difference between the temperature of the two conductor pins.

Now, since no heat was received by the water, in either case, except what passed longitudinally through the conductor pins, it is manifest that the entire heat which raised the water to the boiling point, and maintained it in a state of active ebullition, must have passed through a vertical section of the side of the vessel, of but three-quarters of an inch square. This experiment therefore proved, first, that this three-quarter-inch surface of the boiler plate was sufficient for the transmission of a quantity of heat out of all proportion greater than could have been transmitted by such area under ordinary circumstances; second, that this incrustation, (which was crystallized sulphate of lime,) possessed an admirable conducting property; and, third, that no possible injury could be sustained by the conductor itself, so long as its temperature remained so low.

The first of these facts shows how erroneous have been our previous modes of estimating the evaporative power of any kind of boiler, or fuel, by calculations drawn from the mere areas of the exposed plates; while it proves that much may yet be done in this department of the boiler. The second shows that, in this crystallized state of the deposit, it cannot be the cause of injury to the plates, although the uncrystallized or loose matter, if allowed to settle and become hard, becomes a mischievous nonconductor, and the direct source of injury from overheating and bulging. The third proves, that if the recipient body to which the heat is conveyed be able to absorb the heat as fast as it is passed through the conducting body, no injury can be sustained by the latter, seeing that this solid mass of incrustation, (hitherto supposed to be a bad conductor,) itself remaining unaffected, was equal to the conveyance of a very powerful heat, through no less than three inches; while, in fact, it never reaches to above half an inch in thickness on those parts of boiler plates which are exposed to the greatest heat.

Now, to apply these facts, and the in

ON THE CAUSES OF INJURY TO STEAM BOILERS.

ferences to which they lead, to practice. We find that, so long as the water is maintained in contact with the plates through which heat is conveyed by conduction, no injury will be sustained. But the question arises-what is there to interrupt this contact, and what other recipients than water, are to be met with in boilers? In land engine boilers, no injury can arise to the plates from any circumstance connected with the furnace or fuel, beyond the ordinary wear and tear, (the sources of which will be hereafter examined,) if due attention be paid to cleanliness in the interior, and maintaining the water at its proper level. Marine boilers, however, from their peculiarity of construction, are subject to another source of injury, and which is too often destructive of the plates connected with their furnaces and the parts adjacent. This peculiarity consists of numerous vertical narrow passages. In these, the steam, as fast as it is generated, becomes, by reason of its ascending current, so mixed with the water, as seriously to obstruct the free and continued access of the latter to the plates. This also takes place to the greatest extent in those parts which are exposed to the highest temperature, since such ascending current of steam is necessarily the greatest where the heat is greatest, namely, in the side plates of the furnaces. The consequence is, that these side plates, through which the heat is conveyed to the interior of such narrow passages, are more frequently overheated and bulged than other parts, though exposed to even a still higher temperature from the direct action of the flame.

The heating of the side plates of the furnaces of marine boilers, may therefore be said to arise solely from the circumstance, that by reason of the conflicting currents of steam and water, in those narrow passages, or water-ways, the recipient, being then a mixture of water and steam, (too often of the latter alone,) the heat cannot be taken up as rapidly as the metal conveys it, and the usual consequences of over heating necessarily follow.

This interposition of steam, where water alone should be found, and its inevitably injurious consequences, were strikingly illustrated in the first boilers of the transatlantic steam ship, the Liverpool. In these boilers, the water spaces were

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above 5 feet perpendicular, and but 5 inches wide, thus leaving a space of but 24 inches for the water approaching the side plates of each of the furnaces, and the steam generated by the heat received through such plates. This steam was necessarily so great in quantity, as to prevent the access of the water, and in fact became itself the recipient of the heat from the furnaces; the consequence was, that the plates became overheated, bulged, and cracked, and extensive injury was sustained by them during every voyage. Not unfrequently they required to be wholly removed and replaced at a considerable expense before a new voyage could be commenced.

That steam, in fact, was the recipient of the heat in those narrow passages, where water should always predominate, was proved by a very simple and conclusive experiment of the engineer, during one of his voyages. He introduced a trial pipe in the space, (erroneously, in this instance, called the water-space,) between two of the furnaces, and on a level with the fuel-the inner end opening into such space, and the outer end projecting outside the boiler, and being furnished with a stop-cock. The result proved his anticipation; for on trying this pipe, when the furnace was active, he could never draw off any thing but steam. This circumstance was clusive, that although the water continued at its proper level in the boiler, yet, by reason of the confined nature of the passages, and the absence of a free circulation and access of the water, (at the very place, which of all others, required its continual presence,) the steam, a bad recipient, had usurped its place. This source of injury continuing, the furnace side plates, as constantly, were deranged, while the roofs and other parts remained sound to the last.

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From the instance here adduced, it does not follow that any given width of water-space is necessary, or that narrow spaces must always be injurious. I have frequently observed that spaces of but 3 inches wide between the furnaces have been unattended with injury to the plates. The cause of injury then, arising from the predominance of steam instead of water, is rather to be traced to other circumstances connected with the circuJation of the water in the boiler, and the aids or impediments it receives from the

SUGGESTIONS FOR THE IMPROVEMENT OF CANAL NAVIGATION.

tern into the garden, with which I took another course.

This syphon consists of a piece of halfinch drawn tin tubing, such as is used by gas fitters, 15 feet long and gths of an inch in diameter externally; the longer leg of the syphon is about 8 feet, the short leg about 4 feet in length: the former is led down a brick wall, to which it is lightly secured by wall-hooks; the latter dips into the cistern. At the latter end of October last, before the frost set in, having no further occasion for any water in my garden, I emptied the syphon, but afterwards shut the cockwhich terminates its lower leg. One day, last week, I attempted to refill the syphon by exhausting the air from its longer leg, but failing in this, I began to look for the cause, when, to my great surprise, I found the empty pipe had actually burst about 9 inches above the cock; not a mere slit, but a palpable enlargement of the pipe, and a rupture exactly as shown in the accompanying sketch. The only pressure that I can conceive to have been operating

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shorter leg, a pressure that would seem to be altogether inadequate to account for the effect produced.

We have frequently heard of the bursting of gas-pipes, an idea which I have always scouted, seeing that the pressure within them never exceeds that of an inch of water, and yet this fact has been most confidently asserted as the cause of several destructive fires. It happens unfortunately in these cases, that as soon as the gas becomes ignited at the aperture thus made, the metal is almost instantly melted, and prevents any observation being made. The positive bursting of such pipes, however, under slight pressure, or in consequence of some disintegrating property of the metal of which they are composed, seems to be demonstrated by the fact which I am now describing. The explanation of this phenomenon is of infinite importance to our domestic safety, as proving the liability to accident from this hitherto unperceived cause, and it also becomes desirable to know whether leaden pipes are subject to the same law.

The alternate expansion and partial contraction of leaden pipes, is well understood; how far tin may be subject to a like influence, and whether this will go any way towards explaining the phenomenon in question, I leave your better informed readers to explain. Any persons interested in this question are welcome to inspect the ruptured pipe, which shall remain untouched for a week or so. I remain, Sir,

Yours respectfully,
WM. BADDELEY.

29, Alfred-street, Islington, February 3, 1842.

SUGGESTIONS FOR THE IMPROVEMENT
OF CANAL NAVIGATION.

Sir,-During the rapid progress of railways our canals have been less thought of, but there is no doubt but the present mode of canal conveyance may be much improved. The principal object to be gained is a quicker transit of goods or passengers, which can only be effected by the boats passing along the canals at greater speed and by being less detain ed at the locks. It is admitted that a boat at a quick speed meets with less resistance than one at a slow speed. We have had reports of several trials of boats being