Cast into a circular shape with ribs on the circumference, connection to the resistance being made by three contact pins projecting through three holes in the shell.

CARBON USED AS RESISTANCE MATERIAL.

In many instances, carbon is used as the resistance material as in curling irons, in which a thin pencil of carbon consuming 25 watts, is placed in the circular tongue, which is usually made of aluminium. A pencil of carbon is also used in one of the latest types of radiators, which consist of lamps about 10 in. long and 2 in. in diameter. The contained carbon filament is about 1-16th in. in diameter, and about 13 in. long, being bent in the middle to form a single loop, each lamp consuming about 250 to 300 watts, with usually four lamps in each radiator.

One of the most useful sources of heat is the electric arc, which is used extensively in many metallurgical and chemical processes. It is also used in a few domestic and similar appliances. Professor Ougrimoff, of Moscow, has designed a water heater of 98 per cent. efficiency, in which he uses the electric arc to splendid advantage (fig. 1). This heater, which can be used for many chemical processes and distilleries, consists of a crucible of cast iron in the bottom of which is placed powdered graphite. Above this crucible and regulated by a wheel and worm-screw is a large carbon rod, which is connected to the positive pole, the crucible being connected to the negative pole, so that when the arc is set up, the greater heat will be produced in the

crucible. The heating chamber, chiefly consisting of the crucible, is, with the exception of the top, surrounded by the water to be heated, and when the arc is struck, the resistance of the graphite is sufficient to prevent short circuits. The arc is also used in soldering irons which are made under the Byng patents in this country. The arc is allowed to play between the carbon rod and copper bit, and heats up the latter to a temperature sufficient for use on large work, The enamel system of heating is certainly the most prominent.

Another type of electric heater which is well worth mentioning, and that is the electric welder (fig. 2). The heating effect being proportional to the square of the current, by transforming a high pressure current of small amperage down to one of low pressure and high amperage, it can be used to soften or melt any metal required. From 10,000 to 40,000 amperes per square inch are generally allowed for welding purposes. This welder is an automatic one for welding the links of chains. The chain is fed in at one side with open links and leaves, the other side with the ends of each link welded. Automatic welders are made by this firm for welding bars, rings, spokes to wheels, and orna mental work on to their frames.

A welding transformer weighing 1,000 lb. is used for softening Harveyised armour plates upon which some work is required to be performed after they have been hardened and placed in position. The current is gradually raised to about 10,000, and with a surface of

square inch, then gradually decreased so that the portion heated shall be soft when the current is entirely switched off.

A method used for raising bars of metal to a welding temperature is to dip them into a lead-lined tank containing an aqueous solution such as potassium carbonate or borax, and the heat caused by the high resistance

its support and proper

object of the whole work. As to the best size, the conditions are too complex to lay down any general rule, but where the conditions are very severe it is better to employ one of the bronze alloys rather than a copper wire of larger size. On the subject of position of the wire in relation to track, but assuming that centre wiring is adopted, span-wire construction will be the prevailing type. The flexibility of spanwire construction greatly reduces the blow upon the The soldered ear is the best form of attachment

ears.

The River Hooghly, which provides the navigable approach to Calcutta, the capital of India, is the most western outlet of the Ganges delta. It possesses the special interest of occupying an intermediate position between tideless and tidal rivers; for, whilst forming one of the many branches of the Ganges delta, like the branches of the tideless, deltaic Mississippi, Danube, and Nile, it flows through an expanding estuary into the sea, like the tidal Seine, Elbe, and Rhine.

On entering the estuary, there soon ceases to be any regularly defined navigable channel; and the course selected for the buoyed channel, through a series of long, deep, pools separated by wide shoals, or bars, over which the depth is under three fathoms at the lowest low water, is merely the line which best combines

the greatest available depth with stability and shelter. Various proposals have been made at different times for the improvement of the river, comprising practically all the various methods available for the purpose, namely, diversion of tributaries, diversion of the river across bends, regulation of the river by training works and training-walls, dredging, and dredging and regulation works; but hitherto, beyond a few experimental spurs constructed in the Moyapur reach about 1866, no improvement works have been carried out.

There do not appear to be any peculiar conditions in the case of the Hooghly rendering it incapable of improvement at the worst shoals above its estuary, as has been often asserted; and it is hoped that a careful study of the physical conditions of the river, rendered possible by the excellent charts published during the last twenty years, may lead to a satisfactory solution of the problem as to the best means of improving the river for navigation.

THE SMOKE PROBLEM.

was an

At the monthly meeting of the Institution of Engineers and Shipbuilders in Scotland, there interesting discussion on Mr. E. J. Rowan's recent paper on this subject.

Mr. Andrews pointed out that the various authorities quoted by Mr. Rowan in connection with the principles of combustion did not, he thought, agree very well, except on the point that there should be a good supply of air. He did not know if any of the authorities quoted were agreed as to where the air should be admitted, and that was the very point that they knew least about in the actual stoking of furnaces. The stoker had no means of knowing how much air was admitted or how it was admitted, and with a door in front of him he just pitched in coal as the fire required it. How could they expect to get much else but black smoke under such conditions. The stoker ought to be able to take an interest in what was happening during the process of combustion, and there should be some means to enable him to see what was going on.

Mr. Gillespie thought they should concern themselves less with the smoke problem and turn their attention more in the direction of the utilisation of smoke. Smoke, of course, was gas, and that gas had been used in connection with blast-furnaces, etc. He thought it would be quite possible and economical in the case of a work where there were five or six steam boilers to put down a plant for the recovery of the tar and ammonia. The full value of the coal might be got from the recovery obtained under such a system.

STIRLING WATER-TUBE BOILER.

At the meeting of the Staffordshire Iron and Steel Institute on the 21st inst., Mr. Cyril E. Tarbolton read a paper on "The Stirling Water-Tube Boiler," with notes on the purification of feed water by the thermal system. The following is an abstract of the paper.

The author pointed out that the chief points to be aimed at in the design of generating plant are economy of working, economy in maintenance, economy in first cost, and safety. In Mr. Bryan Dawkin's work "The Heat Efficiency of Steam Boilers," it appears that while 107 tests of Lancashire boilers give an average efficiency of 624 per cent., the Stirling boiler shows an efficiency of 766 per cent., and an average of the ten tests on Stirling boilers given in table on page 204 shows 75.8 per cent. efficiency. In this connection the extremely high efficiency of the boiler fixed at the Sheffield Corporation Lighting Station should be mentioned. Roughly speaking, it may be said that with a water tube boiler, the same efficiency will be obtained as with a Lancashire boiler and economiser, while much larger units can be employed, reducing the first cost very considerably. There is also a saving in floor space with the Stirling boiler.

An ingenious mechanism for cleaning water-tube boilers is described in detail by the author. It consists of a small turbine, the rotating parts of which carry arms and cutters. The whole turbine is dropped into the tube from the upper end, and is connected by 1 in. hose pipe with the feed pump or other water system at from 100 to 140 lb. pressure. The water having been turned on, the turbine is caused to rotate at a high rate of speed, and the tapping motion of the arms rapidly removes the scale from the tubes; while the exhaust water washes this down in advance into the lower drum.

The Stirling boiler, which is of the vertical tube type, consists essentially of three steam drums, and two mud drums, connected by four main banks or tubes. The tubes, 3 in. diameter, are of weldless steel, and are simply expanded into the drums. They are all bent to the same radius, being curved at each end so that they enter the drums radially.

The front and central steam drums are connected both above and below the water level, while the central and back steam drums are connected above the water level only. The two mud drums are connected together.

The three steam drums are carried by a steel framing and from them the water drums are suspended. These are kept quite clear of the side walls and foundations,

so that they are free to rise and fall with the expansion of the tubes. In practice these drums drop about in. from their position when cold. Another point to be observed is that owing to the spring in the curved tubes, any tendency there may be to unequal expansion in the same bank of tubes, does not lead to leaky joints.

DETAILS OF CONSTRUCTION.

The feed water enters the boiler at the back steam drum, at a part most remote from the fire, and since there is no under-water connection with the central steam drum, its passage must necessarily be down the last bank of tubes, where it is gradually heated up, causing most of the scale to be deposited, the sediment falling into the rear water drum, The water in the front section over the fierce heat of the fire is thus left clean, and the life of the tubes greatly prolonged thereby. This arrangement of the feed enables water to be used which, under ordinary circumstances, would be quite unsuitable for tubulous boilers.

Owing to this construction the circulation is practically perfect, as the tubes are nearly vertical and cach has a free outlet into the steam drums. In the horizontally inclined type of water-tube boiler, the tubes are certainly straight so far as cleaning is concerned, but considered from the point of view of circulation, the Stirling boiler has a distinct advantage, since there are no right-angle turns, due to headers, etc., that have to be negotiated.

The nearly vertical position of the tube gives an exceedingly large combustion chamber, and it may also be noted that the tubes are staggered to split up the hot gases, while all the surfaces subject to pressure are cylindrical.

The boiler is also remarkably free from any tendency to prime. A test was made by Professor Ewing on the Stirling boilers supplied to the Brompton and Kensington Electric Supply Company, in order to show the maximum evaporation that could be obtained with forced draught. This worked out at 7'4 lb. water per square foot of h.s. per hour, or nearly double the normal capacity, and the amount of moisture in the steam was only 063 per cent.

As an example of the ease with which tubes may be scaled by the turbine cleaner, the author was recently informed by the engineer of a large steel works in Sheffield that at the end of a six months' run, three men with a turbine are able to thoroughly clean a Stirling boiler of a size equal to two 30 by 8 Lancashire boilers in one day.

Stirling boilers are also made with three steam drums and one mud drum for marine work, and for use where space is restricted; and again with two steam drums

and

3. Cornish Stirling Stirling Stirling Boiler and Boiler Boiler Boiler Tubeand

4.

The writer would like to mention a mechanical device which he came across many years ago in Mexico,

and

Furnace. Furnace. Furnace. Furnace.

The accompanying diagram shows the arrangement of this device, and it will be seen that the bell-rope from the shaft, whether vertical or inclined, winds round a drum made of wood with the sides bolted on; galvanised iron wire rope, in. in diameter, is generally used. An L shaped lever is bolted to one side of the drum, to one end of which is attaehed a rope communicating with the engine-room.

A special feature of the apparatus is the counterweight, which consists of an iron cylinder (generally a small oil drum), which can be filled with scraps of iron, etc., so that it just counter-balances the weight of the bell-rope. This makes it possible to pull the bell-rope with but very slight exertion, so that if one is riding in a cage or bucket, at a medium speed, it is possible to give a signal to stop if necessary. The counter-weight rests on a bracket and usually a guard is placed around it so as to prevent the possibility of its tipping over.

With this device, moreover, a gong can be satisfactorily used, for overstraining is prevented by the lug A on the signal drum.

To Gong in Engine Room

STREET LIGHTING BY ELECTRICAL

ARC LAMPS.

At the meeting of the Glasgow Local Section of the Institution of Electrical Engineers, held at Glasgow on the 10th inst., Mr. H. B. Maxwell read a paper on this subject, of which the following is an abstract :

The chief reason that arc lighting has not been more extensively used for street lighting is that station engineers do not charge low enough rates to make it commercially practicable, probably because they do not realise that street lighting has a load factor of over 42 per cent.

If arc lighting is adopted the following points should be considered: size and type of lamp to be used; height of lamp from ground; distance between lamps; position of lamps; whether trimming shall be with lowering gear or ladders; whether circuits should be connected to distributors or not; switching gear, etc., in the poles, and charge to be made per lamp per

annum.

The first point to be considered is, whether open or enclosed arc should be used. The open type is much superior for street lighting, as it is much cheaper to maintain, and the colour of the light is very much better. Only five enclosed lamps can be run in series on 480 volts, as against ten open, if allowance is made for the resistance of cables, etc., and a 6-ampere enclosed lamp does not give as much light as a 10-ampere open. Enclosed lamps also do not run well in series. The author is of opinion that the 10-ampere open type arc lamp, pendant from a swan neck or bracket, in all streets will be found most satisfactory. Globes should undoubtedly be plain opalescent of such a density that the carbons are quite visible during the daytime.

The height of a 10-ampere arc from the ground level should be 20 ft., and, except in streets with very fast and heavy traffic the distance apart is not of such importance as that lamps should invariably be placed at street corners so as to get the maximum efficiency from the lamps. In main streets, where there are tramways, the lamps may be placed from 60 to 80 yards apart to suit the corners; in less frequented streets this may be increased to 90 yards; and in side streets to 100 yards, or even more in special cases.

The author is of opinion that it is most necessary to control the street arc circuits direct from the station

by separate feeders. It is essential to have in the base of every pole at least an isolating switch and a substitutional resistance.

The latter are very necessary,

as without them the circuits are liable to be seriously overrun in the event of lamps failing, owing to shortness

It may be noted that charges on capital and for current will form over 80 per cent, of the total cost of the lamp if Id. per unit is charged for current. It is therefore to these two items the author looks for any large reduction in price, although it is essential that the other items should be kept down if cheap arc lighting is required.

Seven per cent. should be allowed for interest, sinking fund, and depreciation.

The only items that should be included in the charge for current for street lighting are the works costs, exclusive of wages (which should not be increased at all by the addition of a street lighting load), and interest, sinking fund, and depreciation on the capital cost for boiler, generator, and condenser plant. The cost of all cables, feeders, and switchboards has already been debited against the capital cost of the street lighting, so that £40 per kilowatt demanded, even after providing for a small amount of spare plant, will be more than sufficient to cover the increased cost of station plant due to the street lighting. Eight per cent. interest, etc., on this sum will be a charge of £3 4s. per kilowatt per annum, which, at 3,500 units per kilowatt per annum, works out at o‘22d. per unit. Any other items, such as insurance or office costs that may be increased by the addition of street lighting, will be amply provided for by o'o3d., so that a station can supply for street lighting at the following rate: works costs-wages +0.25d.