“The cover this week shows the Birchenough Bridge and is reproduced from a photograph provided by Dorman Long and Company Ltd. The building of this magnificent structure, the thrid longest single-arch span in the world, is described fully in a chapter in this Part. The bridge has a total length of 1,240 feet and the great arch rises to a height of 280 feet above the River Sabi in Southern Rhodesia.”
THE steam boiler, in the same way as the engines it drives, has undergone many and great changes since the days of Newcomen. The different forms owe their origin to a variety of circumstances. The marine water tube boiler, for example, has to be as light as possible, economical in fuel, able to supply steam at a high rate and capable of withstanding high pressures.
One of the best known forms of water tube boiler is the Yarrow boiler, of which six examples are seen below in the maker’s works. These particular boilers were made for the Southern Railway Company's cross-Channel steamers. The two boilers at the left hand, which are only partly erected, show the principles of construction. Three steel drums are arranged at the corners of a triangle, the two bottom drums being connected to the top one by a number of straight tubes.
The tubes and drums comprise the water space, the working water level being about halfway up the top drum. The holes in the ends of the drums, closed by strong covers when the boilers are working, enable men to get inside the drums and clean the inner surface of the tubes without difficulty. The furnace occupies the tent-shaped space under the tubes, the grate extending between the lower drums but at a lower level.
The boilers are enclosed in steel casings lined firebrick. The casings are in place in the four boilers to
the right and are finished at the top with a rectangular opening which is connected by a trunk to the funnel. The hot gases from the blazing fuel pass outwards between and over the tubes and thus reach the upper part of the casing. The gases, however, do some more work before they leave the boiler.
The small drums carried on the water drums have a number of tubes extending from them into the stream of the hot gases. The steam from the upper part of the top drum passes into the small drums, through their tubes, and emerges at the other end of the drums to go to the turbines perfectly dry and hot. This part of the boiler is the superheater. Above the superheater is the air heater, another mass of tubes situated in the gas stream. The air supplied to the furnaces passes through these tubes and the gas flows outside them. The object of heating the air is to ensure better combustion in the furnace, and thus to secure greater economy.
The boilers are fired with coal, but not by hand in the old way. Instead, the furnaces are fitted with automatic mechanical stokers, a recent arrangement in a ship, and the stokeholds are “closed”, that is, air is supplied to them under pressure by means of fans. Each boiler is capable of providing 16,000 lb of steam an hour at a pressure of 250 lb. per sq. in. and a temperature, on leaving the superheater, of 500° Fahr. The air is heated to about 380° Fahr. by the time it reaches the furnaces. The fuel used is Kent coal, the collieries being close to Dover, from which the steamers - train ferries - start for Dunkirk, France. The Yarrow boiler is extensively used also on land.
An invaluable link in the communications of Southern Rhodesia is the Birchenough Bridge, across the River Sabi. This imposing steel structure in the heart of Africa is the third longest single-arch span in the world. The mighty bridges of the world are almost invariably situated near great commercial and industrial centres. New York and San Francisco, for instance, among the great cities of the world, are the sites of many of the world’s largest and most famous bridges. Imagine, therefore, the thrill and the sense of wonder that must come upon a traveller in the jungle of Southern Rhodesia when he sees a tremendous structure of steel towering above the trees. For over the Sabi River the road is carried by the Birchenough Bridge, the third longest single-arch bridge in the world. It was designed by Mr. Ralph Freeman, and built by Dorman Long and Co, Ltd, of Middlesbrough. The Birchenough Bridge, described in this chapter by F E Dean, is one of the most convincing examples of the way in which the engineer can bring the amenities of civilization into the interior of such a continent as Africa. The famous bridge across the Zambezi River near the Victoria Falls is another bridge situated away from a commercial or industrial centre. This, too, was designed by Mr. Ralph Freeman and built by Dorman Long and Co. With a total length of 1,240 feet, the great arch of steel rises to a height of 280 feet above the river. The bridge shortens by 150 miles the journey between Bulawayo, a commercial centre of Southern Rhodesia, and Chipingi and the Melsetter district along the border of Portuguese East Africa. The bridge has an interesting connexion with the largest single-arch bridge in the world, that which spans Sydney Harbour, New South Wales. Steel cables with a diameter of 2¾ in were used during the building of the great arch across Sydney Harbour, and these same cables are now suspended from the arch of the Birchenough Bridge to carry the main cross girders of the deck. This chapter is the ninth in the series on Linking the World’s Highways.
Repair Shops at Port Augusta
REPAIR SHOPS in connexion with the building of the Australian Transcontinental Railway were built at Port Augusta, at the head of Spencer Gulf. Work on the line to Kalgoorlie began from Port Augusta on September 14, 1912.
Electric Lighting Developments
Unremitting research has been responsible for striking improvements in the electric illumination of houses, streets, docks and airports. The tungsten filament lamp remains the standard for domestic lighting, but for other purposes great advances have been made with electric-discharge lamps of various types. The problems of adequate lighting for streets which carry a considerable amount of traffic at night is one that is continuously exercising the ingenuity of electrical engineers. In this chapter, L H Thomas deals with this and similar problems. He describes how these problems are being solved by research engineers. In their laboratories ther are many cleverly arranged instruments for testing electric lamps and for experimenting with new forms of illumination by electricity. Second only in importance to the problem of street lighting is that of the illumination of airports at night so that aircraft may identify them and land in safety. How this is done will also be described. The various types of gas-discharge lamps used for outdoor illumination will be detailed. This is the fifth article in the series on the Romance of Industry.
The Birchenough Bridge
Photogravure Supplement - 3
THE CABLEWAY ACROSS THE RIVER was suspended from two steel towers, 1,400 feet apart. The cableway was used to transport materials and plant across the River Sabi during the building of the Birchenough Bridge. Electric power for driving the cableway and cranes was obtained from two portable generating sets driven by high-speed diesel engines.
Modern Street Lighting
MODERN STREET LIGHTING, seen from the vehicle driver’s point of view. The most notable feature is the absence of pools of light and areas of darkness on the road surface. The lamps are mounted at such a height that they do not cause undue dazzle to the road user. Electric-discharge tubes are sued: mercury-vapour tubes giving a bluish-white illumination and sodium tubes giving a yellow colour.
The Birchenough Bridge
Photogravure Supplement - 2
THE ROADWAY along the deck of the Birchenough Bridge is 18 feet wide. On either side of this are the footways. The main cross girders of the deck can be seen projecting from the line of the roadway at intervals of 40 feet. The ends of these girders are suspended from the great arch by steel cables with a diameter of 2¾ in. These cables were used as anchorages suring the building of the arch. The same cables had been used in the building of the Sydney Harbour Bridge. Beneath the roadway and running the whole length of the deck is a huge horizontal truss, 48 feet wide, which keeps the suspended portion rigid against the pressure of the wind.
Power and the Plough
Agriculture, the world’s oldest and most important industry, has in comparatively recent years been revolutionized by the application of ingenious machinery to its many operations, which include ploughing, sowing, harvesting and threshing. One of the most important industries in the world is agriculture, and in this sphere the engineer has proved of the greatest assistance. So important is the engineer’s part in agriculture, that at Oxford University there is an Institute for Research in Agricultural Engineering. In the same way as motor cars are displacing the horse-drawn vehicles from the roads, so the horses that draw the plough are slowly giving way to petrol-driven or diesel-engined tractors on the larger farms. In this chapter are described the ingenious mechanical ploughs that are used in conjunction with agricultural tractors. Among these agricultural machines one of the most ingenious is the mechanical harvester. In the huge grain districts of Russia and America these harvesters pass into a vast field of standing wheat and leave behind them nothing but stubble and thousands of bushels of grain tied up in sacks.
(Pages 649- 655)
Airport Floodlighting Unit
AIRPORT FLOODLIGHTING UNIT in which tubular lamps with long filaments are mounted in front of specially designed parabolic mirrors. The unit may be rotated or its elevation may be changed by hand. A 9-kilowatts floodlight of this type gives a maximum candle-power along the beam of more than one and a half million, and will illuminated an area of about 7,700,000 square feet.
The Birchenough Bridge - 2
MASSICE CONCRETE SKEWBACK set in the solid rock. Four of these skewbacks carry the bearings for the steel pins on which the arch of the Birchenough Bridge is supported. The thrust of the arch amounts to 1,200 tons on each bearing, equivalent to a pressure of 25 tons per square foot on the concrete foundation.
The Birchenough Bridge
1,500 TONS OF STEEL were used for the arch span of the Birchenough Bridge. The same amount was used for the Victoria Falls Bridge, which has a span less than half the length. The total length of the Birchenough bridge is 1,240 feet, and the enormous arch rises 280 feet above the River Sabi.
Oil Refining in Iran(Part 1)
The cultivation of date palms was almost the only industry on the island of Abadan, in the Persian Gulf, at the beginning of the twentieth century. To-day the island has the largest and most modern oil refinery in the Eastern Hemisphere. This chapter by Howard Barry deals with the work of a modern oil refinery. The plant in question is situated at Abadan, at the head of the Persian Gulf. Oil is brought to the refinery by pipe line from oilfields more than 100 miles inland. Over 7,000,000 gallons of crude oil are delivered every day to be treated and refined in this huge modern plant, where nearly 11,000 men are employed. This article is concluded in part 23.
The Birchenough Bridge
A SPAN OF 1,080 FEET carries the road across the River Sabi, near the towns of Chipingi and Umtali, Southern Rhodesia. The Birchenough Bridge shortens the journey from Chipingi to Bulawayo by 150 miles, and has made it possible to travel by road from Capetown to the Congo in all seasons. Before the bridge was built a detour of 600 miles was necessary.
Combined Harvester and Thresher
COMBINED HARVESTER AND THRESHER at work on a farm at Elmscott, Suffolk. This machine cuts and threshes corn in one operation. With two men working the machine it will cut and thresh forty acres of corn in one day. Without the machine it would take fifteen men several days merely to cut and bundle the corn obtained from the same area.
A Threshing Machine
SECTIONAL VIEW OF A THRESHING MACHINE. Used generally in the farmyard, the thresher has its machinery contained in a rectangular box carried on four wheels for transport purposes. Driving power comes from an independent source. In this type of thresher corn is fed in a conveyer under cutting knives (left) and passes between a bladed drum and what is known as a concave. This is a curved grating of iron wire, through which the grain, with the chaff, falls on to an inclined reciprocating screen. The straw passed through a series of risers which toss it up and drop it on to a reciprocating floor. A rotary blower, seen between the wheels, creates the air blast which blows away the chaff.
The Oilfield at Masjid-i-Sulaiman
A VAST OILFIELD is situated at Masjid-i-Sulaiman, among the foothills of the Iranian plateau, about 130 miles inland from the Persian Gulf. An enormous pipe line links Majid-i-Sulaiman and another oilfield at Haft Kel with the great refinery at Abadan.