can be varied from 10 to 500 lb. or more, almost instantly.

From the above figures it will be understood that there is a considerable saving of space and weight as compared with the ordinary type of boiler, and the absence of water gauge and other fittings makes the boiler attendant's work very light. The working of the boiler as regards the water supply is practically automatic, and with the addition of a thermostatic regulator controlled by the temperature of the steam, the fuel supply can also be made automatic. Thus it is not impossible to have a fair sized steam launch with all the machinery directly controlled from the bridge, and it would only be necessary to have one man in the engine room to look after the lubrication and such matters.

As to the form given to the coils, the diagram, Fig. 19, shows the usual method of bending

Fig. 19.-Flash Boiler. these. By reversing each alternate coil, the tubes of one come over the spaces in those adjacent to it, as shown by the dotted lines. The feed pump is continually at work, and any excess of water is bye-passed back to the water tank by the steam actuated relief valve, only as much water is fed to the boiler as is required for the work being done by the engine. This feed pump is usually driven by the main engines, but for large boilers there are advantages gained by employing a separate engine for the pump. Thus when first starting the boiler, the small engine is more easily turned round by hand

till sufficient water has been forced into the boiler to make steam enough to run the pump engine. Also the stopping of the main engines does not stop the feed pump, so that there is always plenty of steam available for re-starting the engines. The feed may be regulated by controlling the speed of the pump engine as well as with the relief valve.

A safety valve on the steam pipe is advisable for use in emergencies, as under certain circumstances the pressure will run up to a very high figure almost instantaneously, as for instance when the boiler is working at, or near, its maximum capacity and the engine is suddenly stopped. In this event the pressure will rise in a few seconds to an alarming extent provided the fire is good, and no relief valve is fitted. The writer has experimented with a steam car of his own design (flash boiler) having an ordinary screw down stop valve, hand operated, in lieu of a safety valve proper. This stop valve when opened allowed the water in the boiler coils to return to the feed tank, being connected to the feed pipe in between the check valve and the boiler coils. When the car was running the steam pressure normally stood at 400 lb. Immediately the throttle valve was closed the pressure gauge needle ran around the dial till it pressed hard against the stop pin at the zero end of the scale, and was bent. This gauge read to 800 lb. and there was the usual gap between the two extremities of the scale. Considering this gap, and the force required to bend the needle, the actual pressure could not have been far short of 2,000 lb. per sq. in., and this was reached in less than thirty seconds after closing the throttle valve. As a rule the hand relief valve was opened simultaneously with the closing of the throttle, so that the pressure seldom rose over 500 lb.

When working with such high temperatures as are usual with flash boilers many curious facts are observed. The temperature of the steam is in no way dependent upon the pressure as in ordinary practice. It is frequently the case that the temperature will be well over 1,000° Fahr. with only 5 lb. pressure, while at other times the pressure will be 800 lb. or more, with a temperature below 700° Fahr. It may seem to be a paradox, but in practice it requires less surface to condense highly super

heated steam than for saturated. The writer noticed that as long as the boiler of his car was delivering "red hot" steam, only water was discharged from the condenser outlet. When by reason of the fire being low, or the boiler being overloaded, saturated steam passed through the engine, the condenser discharged less water but showed steam. On the occasion of a test of a fairly large flash boiler in a room of less than 1,200 cub. ft. contents, there was no trace of moisture on the windows or walls, although the steam from over 180 gallons of water was exhausted from the engine directly into the atmosphere in the room. The external temperature was not much above freezing, yet the windows were hardly at all obscured. Those who were present at the test complained of pronounced drowsiness, and this, in conjunction with the absence of moisture of condensation, would appear to indicate that the water was disassociated into its constituent gases.

Engines intended for use with highly superheated steam should be designed on gas engine lines. Stuffing boxes, slide, and piston valves 'are all inadmissible. Trunk piston, and poppet valves work well if suitable lubricating oil is employed. The valves are operated by cams in the usual manner, but the cam shaft is adapted to be moved along to bring either of two sets of cams into operation, for forward and backward running, respectively. Alteration of cut off is easily effected by so forming the steam admission cams as to permit of the valves being held open for a longer or shorter period according to the position of the cams. with respect to the valve spindles. The cams are made to open the steam valves always at the same point of the piston stroke, while the "trailing" side of the cams is made spirally to alter the time the valve remains open. superheat of from 800° to 1,000° Fahr., the ports and passages for the steam may be about one half the area usually allowed for saturated steam, owing to the much higher speed with which superheated steam will pass through the ports. For the same reason all joints must be perfectly steamtight. A very small leak will reduce the pressure to a much greater extent than would be thought possible.

For a

At the present time there are no reliable

rules and formula for flash boiler design such as we have for ordinary boiler practice. Many experiments are necessary before a really satisfactory plant can be designed as things stand at present, but the flash boiler is just as capable of being reduced to a scientific basis as any other type of steam generator, instead of being a matter of trial and error as it is to-day.

Flash Point.-Denotes the temperature at which an oil or fat bursts into flame. See Oils, Tempering.

Flask. A Moulding Box.

Flat-Bit Tongs.-See Smiths' Tools. Flat Ends, or Flat Surfaces.-This has reference only to the strength of such surfaces when unstayed. When flat surfaces are stayed the strength due to staying has to be estimated. Flat unstayed surfaces are used commonly for the covers of steam domes, and the shell crowns and furnace crowns of vertical boilers and other vessels. The alternative is cambered ends, or Dished Ends, which are stronger. There are three conditions of pressure possible :—(1) That of a flat plate supported round its edges and uniformly loaded. (2) That in which it sustains a concentrated load about the centre, neither of which conditions hardly occur in practice. (3) That in which a plate uniformly loaded is fixed encastre round the edges. This is the only one applicable to boiler work, though not quite the same as union by a flanged joint. Unwin's formulæ are-

Where ƒ

r

2 2.2

t2 = 0000125 x P x 2

The above formulæ make the strength of plates vary directly as the square of the thickness, and inversely as the radius. Experiments by Mr R. Wilson and Mr Nichols did not justify these, and they gave a higher strength than the formulæ do.

These experiments were conducted on flat ends attached to a cylindrical shell 2 ft. 6 in. diameter. In one case a flanged end in. thick was tested to bursting. At 25 lb. there was a deflection of in.; at 50 lb., of in.; at 65 lb., of 3 in. Until 65 lb. there was no

permanent set on removal of the pressure, when it amounted to in. 3 At 300 lb. the plate burst, with a permanent set of 13 in.

32

The practical issue is that flat unstayed plates are not to be used for any but small areas, but if unstayed, dished or cambered ends must be adopted.

A flat plate is subject to incessant deflections under pressure and release therefrom, which result in grooving, even though the elastic limit is not passed. Hence the importance of stayed plates.

The problem of the strength and elasticity of

a flat end is affected by the method of its attachment. It is a question of avoiding the extremes of too great rigidity, and of too great elasticity. A rigid plate is not suitable for some situations in which other parts are attached to it that will be subject to variations in length due to changes in temperature; the end plates of Lancashire and Cornish boilers, for example, to which the furnace flues are attached; and the crown plates of vertical boilers, which must yield before the expansion of the uptake and fire-box. For these reasons a flanged attachment is better than an angle iron ring fastening. But to secure the fullest advantages of flanging, the flange must be turned with a large radius, say from 11⁄2 in. to 2 in., being equal to from three to four times the thickness of the plate. Then as the plate alternately bulges and flattens with alteration of temperature, there is no narrow annular area of metal subject to excessive local bending, as with an angle iron ring mode of attachment, but the bending stresses are distributed over the convexity of the flanging.

For this reason angle rings are never now used for the attachment of the crowns and shells in vertical boilers. And the practice of fastening the back end plates of Cornish and Lancashire boilers to their shells with angle rings is much less frequently adopted than formerly. Flat File.-See Files. Flat Gouge. See Gouge.

Flat Ramming.-Finishing the surface of a mould with a rammer having a flat face, following the detailed consolidation of the sand done with a pegging rammer.

Flat Rope.--See Wire Ropes. Flats, or Flat Bars.-Rolled bars of iron or steel of rectangular, but not square sections

Flattening Plates.- Plates have to be flattened by the plater and boiler-maker before they can be worked up into plane portions. They are treated either by hand or in the Flattening Rolls. The first is the older and less satisfactory method, though still of necessity largely adopted; the second is better in all respects.

When a plate becomes bent, that is because the concave side is shorter than the convex one. It is therefore useless to hammer the convex

side with the idea of bending it back. The other side must be struck in order to extend the metal, and force it to unbend of its own accord. So that flattening a plate is not primarily a bending operation, though bending is the result obtained.

Plates are seldom buckled or curved uniformly, but in places, and the parts adjacent enclose the buckle. The remedy then is not to hammer on the buckle, but on the adjacent parts, and so by extending these to leave the buckle freedom of movement.

As the amount of stretching is extremely minute, it is easy to see that by injudicious and excessive hammering the last state of a plate might become worse than the first. A disadvantage, too, is the possible injury to the plates set up by the hammer blows. This cannot be avoided by heating the plates, because they could not be straightened while hot. This is an argument for flattening in rolls. Here the action is similar to that of bending. The forces operate over a large area, and the metal is coerced without concussion, or local indentation of the metal.

A good deal can be done in the ordinary bending rolls in the partial straightening of plates. The worst of the kinks can be taken out thus, leaving less work for the hammer on the levelling block.

Flattening Rolls, or Mangle, or Plate Straightening Machine.-A machine used for straightening plates by passing them between a series of rolls, generally three below and four above. The top rolls are usually the adjustable ones, but sometimes the lower ones are. Three passes generally suffice to straighten a plate. The first two passes camber the plate, the first in one direction, the second in the other, the third straightens. Sometimes two passes, the second being the straightening, suffice. Many machines of this kind combine provision for bending as well as straightening, by making some of the rolls removable.

Fig. 20, Plate II., shows a plate-flattening machine by Francis Berry & Sons, having seven rollers, four of which are adjustable and can be raised or lowered together, or the two outer ones can be raised and lowered separately. The three driven rollers have pinions keyed on their

ends.

All the handles and levers are brought to one end, so that the workman has complete command without shifting his position.

Flatter. See Fullering, Smiths' Tools. Flat Turret Lathe.-A special type of lathe, in which instead of the ordinary turret with tools held in horizontal holes, and against vertical faces, a flat horizontal turn-table kind of support is employed, upon which the tool holders are clamped, a feature possessing certain advantages.

Figs. 21 and 22, Plate II., show the Hartness flat turret lathe, with the cross-sliding head, a new feature added to enable wide facing operations to be performed, by feeding the head across, while a tool held in the turret remains stationary. A single belt pulley drives the headstock spindle, through a set of changespeed gears, enabling a large range of speeds to be obtained. The turret is fed up either by hand, or power, stops being fitted to arrest the travel at predetermined points. The turning tools used are of the "box" form, with veeguides, and the screwing dies are of the opening type.

Fleming & Ferguson Boiler.-A watertube boiler designed specially for the merchant service. Its principal feature is that the steam drum is made sufficiently large, and the tubes short enough to permit of withdrawing and replacing the tubes within the diameter of the drum. The boiler belongs to the accelerated circulation type, most of which have a fundamental resemblance in the possession of two smaller water chambers connected with tubes straight or curved to the upper or steam drum. In the Fleming & Ferguson these tubes are curved outwardly on each side of the axis, joining the upper and lower drums. Both banks of tubes cross to some extent; an increased spacing at the upper ends provides for this overlap of tubes. Around this central design many modifications have been made. The number of bottom drums has been increased, boilers are single or double-ended, and grates run longitudinally or transversely.

tube expanding and beading, &c. The Stow shaft consists of a number of coiled wires one within another, running in a flexible outer covering, so that the whole may be bent without affecting the rotations. At one end the revolving centre is driven either by a ropepulley, or by electric motor, and is connected at the other to the drill or other tool being operated. A suspension frame holds the ropepulley end steady, by means of a counterweight. The flexible shaft is then moved about to any position within its range. The revolving section must be well greased with tallow or lard, or animal oil.

The Wicksteed shaft comprises a number of flexible or universal joints connecting short lengths of shaft, running within a flexible metallic cover, oil being contained within the latter.

Flexible Tubing. This is employed in cases where a non-rigid connection must be made between supplies of water, steam, gas, oil, air, &c. The hose is variously made of rubber, and rubber with compositions, leather, canvas, asbestos, and the flexible metallic (bronze or steel) tubes. Protection is afforded when

necessary,

as mentioned under Armoured Hose, except in the case of the metallic kind, which is self-protective. Pressures up to 350 lb. per square inch can be withstood.

Flitch Beam.-A beam, Fig. 23, consisting of a balk which has been sawn through the heart and bolted together again with the heart portion turned outwards, and a wrought-iron plate inserted between the halves. The turning of the heart portion of the wood outwards allows more thorough seasoning than is possible in a solid balk, and consequently the timber keeps sounder and more permanent in form; besides which there can be no unseen interior defects, such as heart shakes. Since the introduction of steel girders flitch beams are not often employed.

8:

Fig. 23. Flitch Beam.

Float Cut.-See Files.

Float Gauge.—An old form of low water

gauge employed in egg-ended and wagon boilers. Also used in tanks to indicate the height of the water. The chain to which the float-of wood -is attached is brought over a pulley, and a pointer at the other end moves on an index.

Floating Crane.-Floating cranes are constructed over a wide range of powers and types according to the special service required. The largest class is fitted on board a self-propelling vessel, and has hoisting, revolving, and derricking motions. Its lifting power sometimes attains 100 tons, and its dimensions are such that it may range alongside and plumb the centre of the largest steamships. The work of such a crane is to deposit boilers and machinery on vessels undergoing repair, or to place heavy cargo on board a vessel without the necessity of bringing her to a special wharf for that purpose; in this way a steamer may receive cargo whilst still under the coal tips. Such cranes are made with or without variable ballast, which may take the form of either rolling weights, or ballast tanks and suitable pumps.

A different class of floating crane, but still of considerable capacity, is used in harbour construction, and consists of a fixed jib at one end of a pontoon. There is no revolving or derricking motion, all movement required being obtained by manoeuvring the pontoon; hoisting gear is of course provided. The work of this type of crane consists chiefly in depositing the concrete blocks of a breakwater, and removing large boulders met with in dredging, &c.

A smaller class of floating crane is used for dredging rivers and channels, for coaling lighters, &c. It is usually an ordinary fixed steam crane on a rectangular pontoon, and fitted with hoisting, revolving, and derricking motions; if it is to be employed for dredging, a suitable grab or excavator is used according to the nature of the material to be handled.