THE AMERICAN LOCOMOTIVE OF TO-DAY.

HE loading gauge of American railways permits

THE loading sou rolling stock of large size; the

extreme width is often more than 10 ft., and the extreme height of the chimneys of some engines is over 15 ft. The weight of rolling stock of this kind is naturally considerable.

Helped by the possession of a loading gauge of such dimensions, and being able to find work for a great many very big locomotives both in goods and passenger traffic, the American designers show in their work the most striking example of the modern tendency towards building engines of size and power as great as are compatible with the nature of the lines over which they are to run. Big modern engines with their tenders frequently weigh in working order as much as 150 tons; this weight, spread over a total wheel-base of about 60 ft. is by no means small, but when the weights put upon the driving and coupled wheels are considered, the figures are much more striking. Eight coupled goods engines have as much as 90 tons upon the coupled wheels, extending over a wheel base of no more that 17 ft., and some four-coupled express engines have 27 tons upon the driving wheels and 25 tons upon the coupled wheels. The power of the boiler is commensurate with the weight of the engine, the grate area being often more than 50 square feet, and the total heating surface between 3,000 and 4,000 square feet.

FIREBOX CONSTRUCTION.

In order to get so large a grate area it is necessary to make the firebox very wide; it is therefore spread out above the frames and wheels. With grates up to about 6 ft. wide there is still room to construct a cab of the ordinary pattern, from which the driver can get a sufficiently good view of the line in front of him. Sometimes grates much wider than this are used, and it is then necessary to put a cab for the driver on the barrel of the boiler, while the fireman occupies the usual position. This involves separating the men-a most undesirable arrangement-and this construction is therefore not much favoured. As the grate has to be above the trailing wheels the firebox must be made shallow, and there is often no room for a brick arch, or any arrangement of that nature. The back of the firebox often slants backwards from top to bottom, to enable the fireman to deal more easily with a long grate. Both firebox and firebox shell are usually

round topped; Belpaire fireboxes are largely used by the Pennsylvania Railway only. The round-topped arrangement facilitates the removal of scale and dirt when the boiler is washed out. Fireboxes are invariably made of steel; if the sheets are bent to a sufficiently large radius at the angles, they appear to give little trouble by cracking and will last two years in ordinary work before requiring heavy repairs. The stays are pitched at about 4 in. spaces.

BOILERS, ETC.

The centre line of the boiler is frequently as much as 9 ft. 6 in. above the rails. The barrel of the boiler is made of two, three, or four steel plates riveted one inside the other, the one nearer the smoke box inside, the one further away from it; one of the barrel plates is usually taper, and the firebox shell is usually taper also. The largest internal diameter of the boiler barrel is sometimes more than 7 ft. The tubes, also of steel, are, as a rule, 2 in. in diameter, except when they are very long-18 ft. to 20 ft.—when they are generally 2 in. in diameter. At the firebox end the tubes are fixed into the tubeplate by copper ferrules being interposed between tube and tubeplate, after which the tubes are expanded in the usual way. There is a dome a short distance in front of the firebox. The safety valves are usually placed above the firebox; they are generally set to blow off at about 200 lb. per square inch in simple engines, and sometimes at as much as 225 lb. in compound engines.

The frames are composed of a series of more or less parallel bars of rectangular section, arranged one above the other and joined together at intervals to secure sufficient stiffness. The cylinders are placed outside the frames (in some new compound engines there are inside cylinders as well. Their centre line is generally an inch or two above the centre of the driving wheels. The slide valves are usually of the balanced type, placed above the cylinders and worked through rocking levers from valve gear of the Stephenson pattern. Piston valves are also used to a certain extent, generally with interior admission; they seem to give satisfactory results without any special arrangements being made to allow of the release of water trapped in the cylinders. All the weight of the revolving parts and about twothirds of the weight of reciprocating parts is usually balanced by revolving weights in the driving and coupled wheels. Some designers calculate the proportion of the weight of the reciprocating parts to be

balanced by deducting a certain part of the total weight of the engine from the weight of these parts and then balancing the rest. A certain proportion of the balance weight is put in each of the driving and coupled wheels, but a greater proportion in the former than in the latter.

COMPOUNDING.

The great majority of engines are simple, but various types of both two and four-cylinder compound engines are in use. Two-cylinder compound engines are not much more complicated than simple engines; they are probably a little more expensive to build, and a little more troublesome to work, and superior economy in fuel is practically the only advantage aimed at in using them. Four-cylinder compound engines, however, are different, and, if the cylinders and motion are suitably arranged, they have, besides the advantages of economy the further advantage of imposing a much less severe strain on the road than two-cylinder engines with the same weight upon the driving wheels.

With the American four-cylinder designs, till quite recently, the two cylinders on either side were always placed one behind the other, or one below the other, and, in either case the high-pressure and low-pressure pistons on the same side of the engine moved in the same direction at the same time. If the high-pressure and low-pressure pistons on the same side move in the same direction at the same time, they do not balance each other, and, as with four cylinders, the weight of the reciprocating parts is greater than with the two-cylinders, the disturbing force due to the motion of these parts is, in comparison with a two-cylinder engine, increased instead of diminshed; the American designers, clinging to simplicity, did not for a long time try to secure what is probably the chief advantage of the four-cylinder system. Quite lately, however, fourcylinder compound engines have been introduced with one pair of outside and one pair of inside cylinders, the two sets of reciprocating parts on either side of the engine being made approximately to balance one another by the cranks being set at 180 deg. There are various designs of engine embodying this idea; one of them (built on the de Glehn system, and almost precisely like the latest engine on the Paris-Orleans line) has been imported from France. The indications are that these engines will prove successful. Equalising levers are employed generally in connection with the springs of all the wheels.

The smoke-box is cylindrical, and of considerable length. For the purpose of preventing the throwing

of sparks, there is in it a baffle-plate, fixed obliquely in front of the tubes, against which the sparks strike, and there is also a wire netting to fill up the space

between the baffle-plate and the front end of the smoke-box. The blast pipe is often double, the exhaust from each cylinder escaping by a separate nozzle, but lately the practice has come in of using the blastpipe, with a single nozzle, the advantage of which is that it can be set perfectly central to the chimney. The blast-pipe orifice is not variable. A single-nozzle blast-pipe for an express engine, with 21-in. cylinders and 50 square feet of grate, would, under ordinary circumstances, be given an orifice about 5 in. in diameter.

The cab is very big, but the fire-box often takes up so much space inside it that there is not a great deal of room left. The driver has a seat on the right-hand side; the handle of the pull-out regulator is within easy reach, and the reversing level is close by him, so he can remain seated the whole time.

RECENT IMPROVEMENTS.

Except shunting engines, practically all engines have either a leading bogie or a leading radial axle. The bogie is generally of the swing-link type, but lately some have been built with the side-play, controlled by means of springs, with which arrangement it is considered that the front end of the engine is less free to swing from side to side. The driving wheels of four-coupled express engines are generally between 6 ft. 6 in. and 7 ft. in diameter, of goods engines about 5 ft. The commonest type of passenger engine has a leading bogie and four wheels coupled behind, more than a quarter of the total number of engines in the country being of this design. Of late, in order to be able to get in a bigger grate, many four-coupled express engines have been built with ten wheels, a small pair of trailing wheels being added under the footplate; engines of this design are sometimes fitted with an arrangement for taking some of the weight off the uncoupled wheels, and throwing it on to the coupled wheels at starting. The commonest type of goods engine has ten wheels, eight coupled behind, with a small pair of leading wheels, but there are a great many eight-wheeled six-coupled goods engines. There are also a very large number of ten-wheel engines, with a leading bogie, and six wheels coupled behind, the diameter of the coupled wheels being anything up to 6 ft. 6 in. Lately some twelve-wheel engines have been built for express work, with a leading bogie, six-coupled wheels of large diameter, and a small pair of trailing wheels. Shunting engines have four or six wheels, all coupled. Tank engines are very few in number; it seems to be thought difficult to provide a tank large enough to enable the engines to remain at work a sufficiently long time without stopping to take water. Some

shunting engines are provided with tanks carrying 3,700 gallons of water. The tenders used with express engines, even when fitted with a water scoop, are built with a capacity of 5,000 gallons. As there is often room for ten tons of coal as well, the total weight of a loaded tender is frequently as much as sixty tons. The tenders almost always run on two four-wheel bogies; on those used with shunting engines, the tank slopes downwards towards the back end, so that the driver may get a better view when running tender first.

A fair price for a big eight-coupled goods engine with tender complete would be £3,700, and for a big ten-wheel four-coupled express engine a little less. In regions where oil is cheap a great many engines are run with oil fuel alone. The water before being supplied to the tenders is often chemically purified. From a report by the Hon. Robert Collier, Third Secretary in His Majesty's Embassy at Washington.

ELECTRIC TRACTION.

While electricity is almost exclusively used as the motive power of the extremely numerous tramways in every part of the country, on railways it is used to a very limited extent only; the overhead railways of New York and Chicago are the most conspicuous instances. For working trains through tunnels where the traffic is intense, and for suburban work in general. it is probable that electricity will be more and more used as the motive power, but the prospect of anything like a revolution in the direction of its being employed to work long distance railway traffic seems remote.

LOCOMOTIVE PERFORMANCES.

Two journeys were performed on the footplate for the purpose of making direct observations of the work of the biggest express engines: I, with a very fast train; 2, with a very heavy train.

(To be continued.)

Sir William Preece, K.C.B., chairman; Commander H. W. Richmond, R.N., Mr. C. H. Wordingham, and Mr. L. J. Steele, representing the Admiralty ; Colonel H. C. L. Holden, R.A., and Captain A. H. Dumaresq, R.E., representing the War Office; Mr. A. P. Trotter, representing the Board of Trade; Mr. J. Gavey, C.B., representing the Post Office; Dr. R. T. Glazebrook, representing the National Physical Laboratory; Colonel R. E. B. Crompton, C.B.; Major Philip Cardew, R.E. (ret.); and Messrs. W. A. Chamen, Philip Dawson, S. Z. de Ferranti, Robert Kaye Gray, Mark Robinson, R. Percy Sellon, Alexander Siemens, John F. C. Snell, Charles P. Sparks, and James Swinburne; Mr. Leslie S. Robertson, M. Inst.C.E., is of course, the secretary; the electrical assistant secretary being C. le Maistre, A.M. Inst. E.E

In the standardisation of electrical machinery, the permissible temperature rise is one of the most important points to be decided, and the Generator Sub-Committee (Colonel R. E. Crompton, C.B., chairman), who have this matter under consideration, felt that no recommendation upon this particular subject could be arrived at until reliable experimental data had been obtained. It was decided to request the National Physical Laboratory to undertake this investigation, and the Sub-Committee on Physical Standards was formed to assist and consult with Dr. Glazebrook. It is confidently hoped that the results of these experiments, which, through the courtesy of the manufacturers, the committee have been enabled to carry out, will prove of material assistance in bringing to a successful issue the committee's deliberations with regard to the temperature rise to be recommended in electrical machinery.

The Committee tender their thanks to the director of the National Physical Laboratory, to Mr. E. H. Rayner, who carried out the experimental work under Dr. Glazebrook's direction, and to the staffs of the various manufacturers for their practical assistance

during the actual running of the tests. Thanks are also tendered to the following manufacturers: Messrs. The British Electric Transformer Co., Ltd., the British Thomson-Houston Co., Ltd., the British Westinghouse Electric and Manufacturing Co., Ltd., Bruce, Peebles and Co., Ltd., Crompton and Co., Ltd., Dick, Kerr and Co., Ltd., Johnson and Phillips, Mather and Platt, Ltd., Siemens Bros. and Co., Ltd., and Willans and Robinson, Ltd., for their kind cooperation in building the test coils, and so furthering the work of the committee.

OBJECT OF THE EXPERIMENTS.

The main object of the experiments has been to determine generally the relation between the maximum temperature in the interior of any coil, taken by means of a thermo-junction, and the mean temperature of the same coil taken by rise in resistance. The determination of the mean temperature of any coil is a comparatively easy matter, it may be quite accurately obtained from the increase of resistance of the copper composing the winding. It is, of course, quite obvious that the outside of the winding must be at a lower and that part of the inside must be at a higher temperature than the mean.

The highest temperature and the corresponding mean temperature have been determined for the committee from experiments carried out on field coils of various sizes kindly made by different manufacturers, under actual running conditions, and also at the National Physical Laboratory. A paper entitled, The Rise of Temperature in the Field Coils of Dynamos," by E. Brown, M.Sc. (Proceedings of the Institution of Electrical Engineers, 1901, Part 152, Vol. XXX.), was consulted, and, although the field coils experimented upon were those of a small two-pole machine, the diagrams there given were of considerable assistance and served as a basis for determining the probable position at which the highest temperature might be expected to occur.

THERMO-JUNCTIONS.

A thermo-junction of iron-eureka was employed in measuring the temperature, as this combination has a high thermo-electric voltage which is very fairly linear over the range required. The thermo-junction