boiler, is liable to sudden and large fluctuations. These boilers are fired from each end, as in the cases of several of the boilers we have already described, and there are four boilers in all to supply the engines with steam. The cylinders are 62 inches in diameter, and the length of the stroke 5 feet 9 inches. The boilers are 10 feet long each, making the length 20 feet when placed back to back, or with a passage between the ends, and measuring over the furnacemouths about 23 feet, as in the case of the former boilers. The width across the boiler, at the widest part, is about 7 feet, and there is a passage between the boilers, making the total width of the boilers about 15 feet. The height is 9 feet, but the whole of the space above the top of the boiler is occupied with funnels, pipes, and steam chests, whereas in the former plan coal was carried above the boiler. The saving Fig. 100.

Fig. 101.

9. 6.

C

-7.9

-1 squ

stoys.

1 round

13 round

Scale three-eighths inch=1 foot.

BOILERS OF THE STEAMER MADRID, BY MESSRS. MILLER, RAVENHILL, AND CO.
Longitudinal Section.

Figs. 102 and 103 represent upon a larger scale a set of tubular boilers constructed by Messrs. Miller, Ravenhill, & Co., for the steamer Madrid. These drawings so completely illustrate themselves that they do not require any description.

Figs. 104 to 109 illustrate the causes of explosion of a tubular boiler in the steamer Cricket, a small vessel plying upon the Thames. The causes of this accident were ably investigated by Mr. Baker in a series of articles published in the Mining Journal, from which paper these cuts are taken. Mr. Baker very clearly shewed that the explosion had its origin in a gross malformation of the boiler, whereby its strength was impaired, while the safety valves were at the same time prevented from acting efficiently, so that no ordinary amount of careful management could have imparted safety to such a boiler.

Fig. 104 is a longitudinal section of the boiler of the Cricket in its original state. A, is the bottom of the funnel; B, the steam dome; C, the safety valve chest fitted with Salter's spring balance acting on the end of a lever; D, waste steam pipe; E, casing over steam dome; F, blast pipe; G, furnace; H, H, H, tubes; J, lower part of ash-pit, the plate of which, originally ths thick, was wasted by corrosion from leakage, &c., until it was only ths thick when the rupture

Scale one-eighth inch=1 foot.

BOILERS OF THE QUEEN STEAMER BY MESSRS. RENNIE. Longitudinal Section. Elevation.

If any considerable pressure of steam be employed in this boiler, it will be necessary to stay down the boiler top very firmly, both to the tops of the furnaces and the bottom of the boiler; for the force acting against the boiler top, and tending to raise it upwards, will be immense, if a high pressure be adopted. To stay the boiler top to the tops of the furnaces alone would not be sufficient, for the tops of the furnaces might alter their form, and the stays would then be of very little avail. The stays to the bottom of the boiler, however, if carried in the usual way, would have to be

Figs. 118, 119.

Ο

.2.0...

Figs. 110, 111, 112, and 113. represent a marine boiler with upright tubes, a kind of boiler to which we have already made several allusions, and which, we are persuaded, will before long come into extensive use. This boiler, it will be remarked, has the water outside of the tubes, and the upper portion of the tubes does not pass through the water, but only through the steam, by which the steam is thoroughly dried, and any inconvenience from priming counteracted. We have another specimen of this boiler to give, and shall reserve what we have to say about the plan until we come to it.

Figs. 114, 115, 116, 117, 118, and 119. represent the boilers of the Queen steamer, a river vessel, constructed by Messrs. Rennie, and well

cession of iron arches over the furnace tops, to keep them in shape after the fashion practised in Stephenson's locomotives, and to stay the boiler top to these.

Figs. 120, 121. represent another boiler with upright tubes (having the water outside of them), the design of Messrs. Rennie. This boiler is intended to supply steam to an engine on land, and its exterior is therefore composed of a cylinder of brick-work, between which and the boiler shell the smoke is made to circulate on its way to the chimney. This brick cylinder is surmounted by a cast-iron dome, the edge of which fits into a groove containing sand, and access can readily be had to the ends of the tubes by raising up this dome by the tackle applied to the eye fixed in its centre. This kind of boiler is identical in all its important features with that repre

fire-grate is 20-96, and the proportion of fire to heating surface is 1 to 20 nearly. One of these boilers supplies the engine of the vessel with steam, the cylinder of which is 26 inches in diameter, and the length of stroke 38 inches, the number of strokes per minute, 35 light, 26 to 30 when towing. The consumption of fuel is 10 cwt. of coal per four hours, including getting up steam. The tubes are of iron, and show no symptoms of injury from the application of heat above the water level. In some of the boilers constructed on this plan the lower tube plate has cracked between the tubes, and we think the breadth of an inch of iron between the tubes is insufficient in most cases. It would be an improvement, we think, to zigzag the tubes, which would leave more iron between the tubes, and, at the same time, would not prevent the introduction of an instrument to scrape them when necessary, at least diagonally. It would be very expedient, too, to defend the tube plate from the heat of the fire by a fire-brick dome perforated opposite to each tube. In that case, however, it would be necessary to give an additional tube surface, as more heat would then pass into the tubes than if such a dome were not employed. It is one drawback to the merits of this boiler, that it will be liable we fear to corrode internally more rapidly than common boilers. One of the most influential causes of internal corrosion appears to be the existence of surcharged steam within the boiler, and in this kind of boiler the steam is almost necessarily surcharged to some extent. The surcharging, however, will be less considerable if there be a large heating surface, which may easily be given. It will be necessary in applying boilers of this construction to steam vessels to adopt means of blowing out the supersalted water very effectually, else the scale may fall from the tubes upon the tube plate, and occasion injury.

One very obvious objection to this plan of boiler will present itself to our practical readers, which is, that a deposit either of silt or scale will be liable to take place on the top of the tube plate, which will, in consequence, very soon burn out. This evil is to a great extent met by our suggestion to interpose a fire-brick dome between the tube plate and the fire; but we have not been able to discover that any sensible inconvenience has arisen from such depositures in boilers of this construction, even without the expedient we have just described. The agitation of the water, caused by the ascent of the steam up through it, is a powerful antidote to any settlement where it is going on, and the particles of matter mingled with the water, and out of which scale is fabricated, find their way by degrees to the sides of the boiler, where the water is tranquil, and there they finally settle. It is expedient, however, in boilers of this kind, either to blow off very frequently, or to have brine pumps, which change the water in the boiler rather faster than usual. It would be a further improvement to place a collecting vessel within each boiler. Instruments of this kind have hitherto been very little used in steam vessels, but in land boilers they have long been employed with advantage, though in that case the advantage is of less account. We shall at a more advanced stage of our progress give some specimens of collecting vessels as applicable to marine boilers, but may here, for the sake of making our recommendation intelligible, explain the simplest form of collecting vessel as applied to waggon boilers.

Fig. 122.

LAND BOILER WITH UPRIGHT TUBES, BY MESSRS. RENNIE.
Transverse Section.

sented in figs. 110, 111, 112, and 113. That boiler, however, is intended for a steam vessel, and is, indeed, the boiler of one of the tug vessels working upon the Thames. As we happen to have a very high opinion of this variety of boiler, we must consider its merits in some detail, and therefore refer back our readers to figs. 110, 111, 112, and 113, as it is to that specimen our remarks chiefly apply.

The diameter of that boiler is 6 feet; height, 11 feet 6 inches; diameter of fire-box, 5 feet 2 inches; distance from top of bars to lower tube plate, 1 foot 6 inches; distance from top of bars to ashpit bottom, 1 foot 7 inches; length of tubes, 8 feet; diameter of tubes, 2 inches; distance from centre to centre of tubes, 3 inches; diameter of tube plate, 3 feet 10 inches. There is a clear space of 1 foot 2 inches all round, between the tubes and the boiler shell. The height to which the water rises along the tubes is 5 feet, leaving 3 feet of the tubes to traverse the steam space. There are 145 tubes in all, and, reckoning their effective length at 5 feet, the effective tube surface is 381.53 feet. The fire-box surface is 20.96 feet, making a total of 412-03 square feet of effective heating surface. The area of the

У

ISOMETRICAL VIEW OF WAGGON BOILER WITH SEDIMENT COLLECTOR, BY R. ARMSTRONG, MANCHESTER.

We must first, however, premise that the addition of particles of extraneous matter to boiling water facilitates the extrication of the steam, and, in many cases, lowers the temperature at which ebullition is carried on. The generation of steam is most active in those situations where those particles exist, so that, indeed, the steam appears as if it came out of them, and the particles are continually buoyed up by the steam in its ascent, and prevented from settling where the ebullition is active. If a vessel with a narrow mouth be immerged in a boiler under such circumstances as to preserve the water within it in a tranquil state, the vessel will speedily become filled with depositure resembling mortar, which, could it have settled, would have been indurated into scale. Of this cirN

70

cumstance advantage is taken in the construction of collecting vessels, for if the whole of the water in a boiler be in a state of ebullition except a portion contained in an internal vessel, into that vessel the depositure will find its way, and from thence it may be removed by blowing out. Fig. 122. represents a collecting vessel attached to a common waggon boiler which will illustrate the means of applying these principles in prac

Fig. 123.

CORNISH BOILER AT MR. THOMAS CUBITT'S FACTORY, BY MESSRS. RENNIE. Longitudinal Section.

Fig. 124.

with a crucial passage between them, and the athwartship passage need only be of a width sufficient to enable the attendants to light and clean the fires. We cannot here enter into the details of the application, but may remark that in those cases in which it may be inconvenient to drop the coal upon the fire through a slit from the top of the boiler, it will probably be found the best way to combine the boilers, so that one revolving grate will suffice for two sets of tubes, and the coals may then be introduced Fig. 126.

соо

CORNISH BOILER AT MR. THOMAS CUBITT'S FACTORY, BY MESSRS. RENNIE. Bird's Eye View.

tice. a a represents the boiler, which has been cut, and a part removed for the purpose of showing the interior. b is a box into which the depositure falls through the neck c, within which is another cylinder, or rather frustrum of a cone, which may be raised or lowered to suit the water level and other circumstances. These parts are all made of sheet iron. d is an agitator for stirring up the depositure within the box previously to blowing out, for which purpose a rod passes through a stuffing box on the boiler top furnished with a handle, which may be turned round. presents the pipe through which the depositure is discharged, f the blowoff cock, and g the bottom of the boiler. It would be easy in a boiler

e re

Fig. 127.

with upright tubes to convert one or more of the tubes into collecting mouths leading to a sediment vessel underneath.

The remarks which we have already made respecting this species of boiler are sufficient, we conceive, to show that the objections which might be brought against it are not of an insuperable character. Its recommendations, however, are not of a negative kind, and it possesses two of weight enough, we conceive, to entitle it to a preference over most kinds hitherto projected. The first is, that if the steam be taken off by a perforated pipe there will be but little priming; and the second, that the construction facilitates the introduction of the revolving grate described in page 53, and which, we anticipate will come into general use for steam vessels. There is nothing in the revolving grate too complicated for such an application, and it would be a matter of great importance to have the furnaces of steam

Scale two tenths inch-1 foot.

BOILER OF STEAMER ZEPHYR, BY MESSRS. HORTON AND SON, LIVERPOOL. Longitudinal Section.