shorter ones, hence in long fire-grates, the bars are cast in two or in three lengths, so that lengths of 2 ft. 6 in. or 3 ft. shall not be exceeded.

Bars elongate in time with heat, hence they must be slack-fitted when new. Often one end is tapered to rest on a tapered bearer, Fig. 6, c, so that the bar can slide thereon during expansion by heat.

Wrought-iron bars do not stand so well as cast, and they need only be used where there is some risk of fracture occurring. The quality of cast iron for bars should be hard, nearly white, which may be obtained by remelting inferior scrap. Grey iron burns away too quickly.

Fig. 7 shows a patent form of fire-bar by Messrs Whitehead Bros., the principal feature of which is the angular shape in place of the ordinary vertical. Some of these have been in use for five and a half years without showing sensible wear. The chief advantage gained is that the air (or steam) cannot impinge on the crown of the furnace, being deflected by the angle, so that the fuel is consumed in a very complete manner, with avoidance of smoke. The bars are strung together on rods. They will work in connection with mechanical stokers.

Fire-box.-Denotes specifically a furnace of rectangular or box shape

as used in the locomotive type of boiler; since a cylindrical furnace is not termed a fire-box, though its function is identical.

A locomotive fire-box is rectangular in plan, and nearly so in longitudinal and cross sections, but the sides are tapered upwards to allow of the free movement of the globules of steam. Such a design involves the free employment of stays, since the conditions of steam generation limit the thickness of furnace plates. The problem then becomes that of the transmission of the stresses to the stays, and leaving the areas unsupported by stays very small. The strength of each screwed stay is calculated to sustain the stress over the area immediately encircling it, and it is in tension. The girder stays, when such are used on the crown, are subject to bending action.

The next most striking feature of a fire-box is its large size, and its value as heating surface. In an average locomotive this is equal to about 1,500 square feet, or about 5 cubic feet per square foot of grate area. From one-third to over one-half the total heat produced by combustion is absorbed by the fire-box, notwithstanding that its heating surface is only about one-tenth or one-twelfth that of the tubes. Hence in endeavours to increase steaming capacity, attention is given to increasing the fire-box surface and efficiency rather than that of the tubes.

The fire-box is often termed the inner fire-box to distinguish it from the casing, or outer firebox. It comprises the tube plate, the back plate, which has the fire hole, and the wrapper or covering plate. These are united to the throat plate, to the back plate of the casing, and to the wrapper plate of the casing.

The means of union are the foundation ring below, the screwed stays, the girder or sling stays, when used, the fire-hole ring, and the expanded ends of the fire-tubes.

Angle irons, formerly used, have given place to flanging, and hand flanging to that of the hydraulic press. The flanges of the tube and fire-hole plates face each other, and the wrapper plate is riveted to them.

The fire-box casing and the fire-box are riveted up separately, then the first named is riveted

to the barrel, and afterwards the fire-box is inserted complete with its girder stays. The foundation and fire-hole rings are inserted at the same time, and held with bolts while the rivet holes are drilled, and all riveted up.

The material used in fire-boxes is generally copper in this country, and steel in the United States. Steel has the advantage of higher ductility and of greater hardness to withstand the cutting action of the draught and fuel. The great disadvantage is its liability to crack.

Copper is better able to resist the effect of extremes of temperature than steel, and it is always worth its cost as metal. It is better if not absolutely pure, a trace of arsenic imparting a hardness to its surface. It is specified generally to have a tensile strength of 14 tons per square inch, and an elongation of 40 to 45 per cent. in 4 inches. It is required to bend double cold without sign of fracture.

Copper is used for stays in almost all cases, being better able than iron or steel to withstand the bending strains due to expansion and contraction of the fire-boxes. The central portions are turned down to give greater elasticity, and to avoid keen angles.

Fire-Bricks.-Furnace bricks made from fire-clays of a highly refractory character. They are prepared like ordinary bricks, by moulding, followed by air drying, and by exposure to heat for several days in kilns, in which they are allowed to cool down after the withdrawal of the fires. They shrink considerably during drying, by as much as from in. to in. in length, the amount depending on the mixture of the clays. There is no fire-brick suitable for all classes of furnaces, but alkalies in any case must be low, as their presence increases fusibility. Silica bricks, though suitable for the roofs of reverberatory furnaces, would be useless for the bottom of a furnace, where they come into contact with metallic oxides. Also, though a fire-clay may be highly refractory, yet the wide and sudden variations in temperature present in furnaces would crack bricks made from that alone. To prevent this, the raw clay is first exposed to the action of the atmosphere, and then other substances are added as binding materials, such as burnt fire-clay, old bricks, powdered graphite, crushed coke, quartz, silicious

sand, &c. The bricks are moulded in shapes to suit the class of furnaces, or the position occupied in the furnaces.

Fire Bridge. The bridge at the back of the furnace tubes in Lancashire and Cornish boilers. Its function is partly to prevent the fuel from being pushed off the farther ends of the grate-bars, partly to promote the mixture of the hot gases and air by retarding their escape into the flues.

Curious results have happened in regard to the height of fire-bridges. A high bridge impedes draught, and causes risk of overheating the top of the flue immediately above. Tentative alterations of 2 in. or 3 in. in height have sometimes made great differences in the efficiency of combustion. General rules are: The air passage may be one-sixth the area of the fire-grate. Or, allow about 12 square inches of area above the bridge for each square foot of grate surface. In a 2 ft. 9 in. flue the top of the bridge is from 9 in. to 12 in. below the top of the flue. The length of one brick is the usual width of the bridge,—not more.

Fire-Clay. Fire-clays occur chiefly in the coal measures of the Carboniferous strata, but they include many different varieties differing in degree of fusibility, due chiefly to the variations in the proportions of free, and of combined silicon. They are essentially hydrated aluminous silicates, with lime and magnesia in the form of carbonates; iron pyrites, free silicon, potash, and soda, with water. A good fire-clay should be as free as possible from calcic carbonate, iron pyrites, and ferrous oxide; each of which at high temperatures will combine with the free silica of the clay. The presence of alkalies impairs the refractory character of the clay. Stourbridge clay contains the following :—Si, 63-30; Al, 23:30; Ca, 73; FeO, 1·80; Water, combined and hygroscopic, 10-30. South Wales clay contains Si, 67-12; Al, 21-18; Potash, 2·02; Lime, 32; Mg, 84; FeO3, 185; Water, combined and hygroscopic, 6-21, with a trace of organic matter.

Fire Engine. The modern fire engine is an excellent example of the multum in parvo principle. It would be difficult to name a machine which comprises so much highly efficient mechanism in so small a compass. Necessity has

been the mother of invention. Little by little successive improvements have been effected. The annals of the great fire engine building firms are reckoned by the dates of these improvements, which are interesting records of those practical advances the sum of which goes to the making of the modern fire engine.

The capacity of such an engine may be gathered from the fact that the largest standard size made by Shand, Mason, & Co. is capable of pumping 1,000 gallons a minute, sending a 2-in. diameter jet to a height of 205 ft. and is of 95 I.H.P. Yet this mechanism is got into an over-all space of 14 ft. 6 in. long, by 6 ft. 6 in. wide, by 8 ft. 6 in. high. Such a result is only possible by virtue of the high efficiency of the design, the economy of space, the reduction of weight in materials, without sacrifice of strength, and a thousand and one details the beauty of which only the engineer is able to appreciate to the full. The machine, like the locomotive, is absolutely the product of evolution.

Fire engines range from small hand appliances to motor engines of large pumping capacities. The horse-drawn steam pumping engine has held its position for many years, but is being pressed by the motor propelled engines, which travel much faster, but cost more for maintenance. The manual fire engine is suitable for localities where fires are rare, or for private use in buildings, or on estates. The pumps in this class of machine are usually worked by levers. Their capacity at best is much less than that of the average steam fire engine, but they can deal effectively with small fires. A chemical mixture instead of water is often pumped on fires that have not gained much headway, thus avoiding the damage that large quantities of water generally cause. Nozzles of different diameters are used at the end of the hose, according to the rate at which the water is being pumped, and the distance it has to be thrown. Attachments are also provided for throwing the water in a spray, covering a large area close at hand if desirable.

The manual fire engine of Messrs Merryweather & Sons, Ltd., dates from 1851, and successive improvements have been made by which these engines have been rendered more powerful without increase in weight. The

"Greenwich" type embodies the firm's best prac

tice in this and numerous other details. In the No. 3 size, being that most frequently used, twenty-two men can pump 136 gallons per minute, 120 ft. high, an excellent performance for a manual engine. In one of larger size, thirty men will pump 150 gallons per minute, 130 ft. high.

The construction of the Merryweather manual engine (Fig. 8, Plate I.) includes the following parts:-The cistern, of copper, mounted on wheels of wrought iron. Longitudinal pockets of teak and mahogany attached to the cistern carry the suction hoses, strainer, branch pipes, and wrenches. The cistern contains two pumps which are actuated by pumping levers, on the long handles of which, of steel tube, the men work. The pumps, plungers, valves and valve-box are of gun-metal, and are provided with an air vessel of copper, so making perfect provision against rust. The valves can be examined and re-ground on their seats. The pumps will draw water either from their own cistern or through a suction pipe. They will draw water 25 ft. vertically through a suction pipe, or they may be fed by buckets at the hinder end of the cistern. Two or more engines should be used when the water supply is situated at a long distance from the fire, one being located close to the water, pumping into the one at the fire. The force with which water is thrown is as efficient as the quantity in extinguishing a fire.

Merryweather engines for 46, 38, and 30 men will pump through 1,000 ft. of delivery hose, those for 26 and 22 men through 750 ft., while the smaller engines will pump through lengths varying from 300 ft. to 600 ft. But this assumes a moderate distance only from the water level to the place of discharge.

The latest Merryweather steam fire engine is the "Greenwich Gem." It embodies a number of excellent features. The vertical boiler has water tubes, both inclined, and curved for elasticity. The firm holds strongly to the practice of rear stoking, in preference to that at the side. The advantages are that the engine driver can light up and attend to the fire while en route, that he is not hampered at all by narrow streets, and that the condition of the fire can be seen continuously.

To avoid difficulty in making hose connections, these for suction and delivery are extended on each side of the extreme rear of the frames, where they are connected up out of the way of the engine driver.

The engines and pumps, situated at the front of the boiler, are a compact piece of work. They are of the vertical double-cylinder type, the cylinders being uppermost. These are of cast iron, and lagged, the slide-valves being situated in a central steam chest. The pumps are of gun-metal, cast with the crankshaft bearings, and connected to the cylinders with turned steel stays. They are double-acting, driven direct from the steam pistons, the rods having slotted crossheads to drive the crankshaft from which the slide-valves are worked. A point to note in the pumps is the accessibility of the valves, which are exposed on the removal of a Cover on the valve chest. The mere loosening of a nut removes a pair of valves, and a damaged valve can be replaced within from 3 to 4 minutes from the time of stopping to restarting the engines. The valves are of indiarubber, and the guards and gratings are secured with copper studs. A by-pass valve in the pump opens a communication, between the suction and delivery passages, so that the engine may start against a head of water in the hose.

Messrs Merryweather have an oil-fired engine, the motor "Fire King" supplied to the London County Council and others. It will travel at speeds of from 25 to 30 miles an hour, can ascend gradients of 1 in 6, and its capacity is 500 gallons a minute, throwing a 14-in. jet to a height of 160 ft. The boiler is petroleum fired. Complexity of parts has been avoided by making the same cylinders and pistons furnish both the pumping and the motive power. As both operations are never required simultaneously this is very easily done through a countershaft which can be thrown in or out of gear. Steam can be raised to working pressure in from 6 to 8 minutes, from cold water, or in 60 seconds if a low pressure is kept up continuously by a gas burner or oil heater while the engine is in the station. The engine carries water and fuel for several hours' working, which includes either travelling on the road, or pumping when it has

reached its destination. The wheels are fitted with solid rubber tyres and non-skid chains.

Fig. 9, Plate I., illustrates this type of engine, which is similar to those supplied to London. It has the addition of a chemical engine for first-aid, which is carried under the main box in front, and the reel for chemical hose is fitted above the box as illustrated.

The following very brief remarks have reference to the more salient points of the Shand, Mason fire engines:-Fig. 10, Plate I. As rapid steam raising is essential, the boiler claims first attention. This is a vertical type with inclined water-tubes, crossing the fire-box in each alternate row at right angles. The working pressure is 125 lb. to the square inch. The fire can be lighted and steam of 100 lb. pressure can be raised from cold water under ordinary circumstances in 8 to 10 minutes while travelling, without any stoking; but by the use of a new exhauster fan arrangement, the times mentioned are reduced to 5 and 6 minutes. Yorkshire iron is used in the boiler, with the longitudinal seams welded, and brass tubes.

The engines are of the double vertical type, adopted since 1889. They work directly on to double-acting vertical pumps, the two being rigidly connected. Two piston rods convey the movement of each piston to its pump rod. The crankshaft is driven by connecting rods of special type running from a joint in the head or cross piece of each pump rod. The eccentrics for working the slide-valves of the engines are situated at the ends of the crankshaft. The piston rods, and the rods for the slide-valves and pumps are of bronze, the pumps of gun-metal, and all surfaces with which the water comes in contact are of these alloys, or of copper, so that corrosion cannot occur when an engine has been idle for a considerable period. The moving parts are balanced to work steadily at high speeds..

By means of the oil-fuel apparatus, adopted since 1893, steam can be raised to 100 lb. in from 1 to 1 minute, when 20 or 30 lb. of steam is maintained, as in the London Fire Stations. One great advantage is that there are no sparks or flying cinders escaping from the chimney, another is that no preparation of the furnace is necessary when the engine re

turns to the station. Another improvement is the boiler heater a miniature crossss-tube boiler -by the use of which a low steam pressure may be automatically maintained while the engines are at the fire station. It may be regulated from boiling point merely, to 20 or 30 lb. pressure of steam. Variable steam expansion has been adopted since 1898, by varying the point of cut-off from three-fourths to one-half the stroke. The amount is read on an index plate at the back of the lever that operates the expansion gear. Besides the economy secured, fewer sparks escape from the chimney, due to the softness of the exhaust.

Side stoking is adopted in preference to stoking at the rear. The principal advantage claimed is that the engine driver and the firemen are not in one another's way at critical times when stoking, and the coupling up of hose has to be done with all speed. Another point in its favour is that the pumps can be arranged considerably lower, giving a decided advantage when pumping from a depth, the lowering of the centre of gravity also allowing the engine to travel better.

Fire engines may often be employed for other duties than extinguishing fires; as for transferring water from one site to another, or removing water from places where it is not wanted, for flushing sewers, and washing silt and mud from places where it has collected, for washing buildings, irrigating land, &c. Floating fire-pumps are also used on rivers for extinguishing fires.

Fire Flues.-Furnace Flues, as distinguished from smoke flues.

Fireproof Structures. An absolutely An absolutely fireproof structure may be regarded as impossible if material that would burn is stored within it, or inflammable buildings are close to it. No building can sustain without damage the application of intense heat unequally applied, and sudden cooling by cold water. Even without the latter the effect of expansion by heat is almost necessarily disastrous.

When iron began to take the place of wood for the framework of floors and roofs it was supposed that as the materials were not inflammable the buildings could not be injured by fire. But experience has shown that the expansion

and bending of wrought members in a fire is more dangerous to the walls of a building than if such members were of wood. Cast iron seldom gets hot enough to bend, but it often cracks under the application of cold water in a fire. Stone cracks also when subjected to great heat.

The best fire-resisting materials are brick-work, including fire-brick, terra-cotta, &c., and concrete, and plaster. These are the materials that are used in all fire-resisting structures, but iron and steel are generally employed also, protected by the other materials, provision being made where possible for the greater expansion of the metal. Brick-work alone is used largely, and brick arches are preferred to joists or girders over openings in walls.

To prevent fires in one room or floor spreading to others it is also necessary to have means of closing all doorways, stairways, and windows, so that they shall be as impassable barriers to the fire as the walls and floors themselves. building, therefore, with open stairways or lifts, wood doors, and no protection to windows is not fire-resisting.

A

Next to brick-work used alone, reinforced concrete is the best fire-resisting material for building. The metal embedded in the concrete is protected from the heat to a great extent, and the combination gives great strength with less bulk than would generally be required if brick-work alone was employed. In floors especially, brick arches would occupy too much depth. For exterior walls the appearance of concrete is not considered equal to bricks, nor is there quite so much advantage in employing it as in the case of floors. In floors, metal or wood joists are usually essential, and these can be more easily protected by concrete or plaster than by brick-work. There are innumerable methods of constructing such floors.

Special attention has naturally been paid to the construction of fireproof floors, because formerly when they were of wood they invariably became burnt out, while the brick walls remained standing, or suffered injury only through the breakdown of the floors. As brickwork for floors is generally impossible, a combination of metal and concrete is the alternative, and the methods of arranging this combination are numerous. Where girders