114 



NA TURE 



[November 25, 1909 



customers who give the order to the electrical engineer, it 

 seems likely that the single-phase system will be the one 

 more generally adopted ; and, indeed, a very respectable 

 beginning has within the last four years already been made 

 on the Continent, where single-phase vehicles aggregating 

 more than loo.ooo horse-power are at work or on order. 



In Italy considerable progress is also being made. The 

 Government has decided to electrify eleven sections on 

 the State Railways, aggregating 337 miles of track, but 

 on the three-phase system. Thus the battle of the phases 

 is still undecided. The decision of the Italian State Rail- 

 ways to use three-phases, whilst in Germany, Austria, 

 England, Sweden, and America the single-phase system is 

 preferred, is highly interesting. Mr. Verola, the chief 

 engineer of the electrical department of the Italian State 

 Railways, was good enough to explain the reason for this 

 choice. The following is an abstract of his letter : — 



'■ In the case of the three lines (Pontodecimo-Busalla, 

 Bardonecchia Modane, and Savona-Ceva) which are about 

 to be opened, the service is extremely heavy, trains of 

 400 tons and over having to be hauled up on long grades 

 of 25 to 35 per mil. at a speed of 45 km. per hour. 

 With the three-phase system it is possible to comply with 

 these conditions by using two locomotives. These weigh 

 each 60 tons, and develop each at the i-hour rating 

 2000 horse-power. With the single-phase system the 

 weight of the motors would be at least doubled, resuUing 

 in a greater expenditure of energy. The advantages of 

 wider speed adjustment in running and better efficiency in 

 starting are not of importance on these lines. It is prob- 

 able that also some future electrifications will be on the 

 three-phase system, notably that of the prolongation of the 

 Valtellin line to Milan, which will shortly be taken in 

 hand. It is, however, highly probable that some other 

 lines will be worked single-phase. One of these is the 

 hne Turin-Pinerolo-Torre-Pelice, where widely different 

 speeds are necessary, the maximum being So km. per hour 

 for loo-ton passenger trains." 



In Switzerland the Federal Government appointed some 

 years ago a committee of electrical and railway engineers 

 to report generally on the question of electrifying the Swiss 

 railways. The first report dealt with the amount of power 

 required, the second some standards connected with the 

 future electrical service, whilst a third report dealt with 

 the question of a standard frequency, but on the question 

 whether the single- or the three-phase system is to be 

 chosen the committee has not yet pronounced an opinion. 

 From private conversations I have had with Swiss railway 

 men, I incline to the belief that the decision will be in 

 favour of the single-phase system, especially since, bv the 

 use of the Deri type of motor, it has been found possible 

 greatly to simplify and also lighten the accessory equip- 

 ment. The first test of this motor for traction was made 

 on the three-phase Engelberg railway, one phase only being 

 used. No resistances, auto-transformer, contactors, regu"^ 

 lating switches, or controllers of the usual construction are 

 required. The starting and the regulation of the tractive 

 force and speed is effected simply by shifting the brushes. 

 Thus all the driver has to do is to attend to a hand-wheel, 

 the motion of which is transmitted to the brush rockers 

 by positive mechanical gearing. 



Winding Engines and Rolling Mills. 

 Dynamic storage in some such way as first applied by 

 Ilgner to winding engines, and voltage regulation on what 

 may broadly be called the Ward-Leonard system, have 

 made it possible to satisfy the very severe conditions' under 

 which winding engines and rolling mills have to work. 

 A good example of modern English practice in direct- 

 current rolling-mill electrification is the plant supplied by 

 the Electric Construction Company, Ltd., of Wolver- 

 hampton, to the steel works of Sir Alfred Hickman, Ltd., 

 of Bilston. The makers have given me the following par- 

 ticulars : — The flywheel set consists of a 2000-horse-power 

 direct-current motor, two 2S-ton flywheels and two 

 generators capable of giving any voltage between —1000 

 and + 1000 volts. The excitation of the motor is adjusted 

 automatically so as to produce a speed variation of the 

 flywheels between 290 and 350 revolutions per minute. The 

 energy given out when dropping from the higher to the 

 lower speed is 46,000 horse-power seconds. This set sup- 

 NO. 2091, VOL. 82] 



plies power to a cogging and a barring mill. The cogging- 

 mill motor works a 30-inch mill, and when cogging down 

 ingots of 3 tons weight has to develop 4800 horse-power, 

 and for two-second periods once an hour 9600 horse-power. 

 The barring-mill motor works a 24-inch mill, and has to 

 develop 6000 horse-power, and for two-second periods once 

 an hour 12,000 horse-power. The maximum speed is 120 

 revolutions per minute, and the time occupied in reversing 

 from maximum speed in one direction to that in the other 

 direction is six seconds. As an example of a reversible 

 mill driven by three-phase current I take that supplied by 

 the British Thomson-Houston Company, Ltd., to Messrs. 

 Dorman, Long and Co., Ltd. It is a cogging mill with 

 rolls 28-inch centres, and the normal speed is 70, the maxi- 

 mum speed 90, revolutions per minute. The flywheel set 

 consists of a three-phase 950-horse-power non-synchronous 

 motor, coupled to a looo-kw. 400-volt direct-current 

 generator and a 30-ton flywheel. The speed limits are 400 

 and 480 revolutions per minute, and the maximum peri- 

 pheral speed of the flywheel is 295 feet per second. The 

 mill motor is rated at 1200 horse-power, and has an over- 

 load capacity for short periods of 3600 horse-power. The 

 time required for reversing from full speed in one direc- 

 tion to full speed in the other direction is four seconds. 

 The mill deals with i8oo-lb. billets 12 inches square, re- 

 ducing them to 3-inch square bars in fourteen passes. The 

 output is 15 tons per hour. 



Electric Steel Furnaces. 



In the manufacture of steel from pig and the refining 

 of steel electrically the experimental stage has long been 

 passed, and the practical results obtained are eminently 

 satisfactory. Even where, owing to the price of power, the 

 electric process is no cheaper than the thermic process, 

 the former enables the steel refiner to achieve results with 

 certainty and regularity which under the old methods are 

 hardly attainable at all, or only, so to say, by good luck. 



In the furnace electricity is merely used to produce a 

 large amount of heat locally. All furnaces are worked 

 with alternating currents, the heat being produced either 

 in an arc or by the passage of the current through the 

 metal itself. In an arc furnace for a capacity of 2 to 3 

 tons the average energy required per ton of finished steel 

 is about 1000 kw. -hours when the charge is introduced 

 cold, and about 400 kw. -hours when it is introduced in a 

 molten state. 



A drawback inseparable from the employment of electric 

 arcs is the great fluctuation in the load, making it 

 impossible to work an arc furnace from a circuit which 

 supplies other consumers. This difficulty is overcome with 

 the so-called " induction furnace," where the heating is by 

 ohmic resistance. In the latest type of induction furnace 

 the energy required per ton of steel if the charge is intro- 

 duced in a molten state is 125 kw. -hours for rails and 

 250 kw. -hours for tool steel. 



The electric furnace for steel making and steel refining 

 is now an important accessory in steel works, and 

 thousands of tons of steel are produced annually, both in 

 furnaces of the arc and in those of the induction type. 



Fixation of Atmospheric Nitrogen. 



Of the many methods devised for fixing atmospheric 

 nitrogen with the object of producing a fertiliser to re- 

 place Chili saltpetre, I can only refer to three which have 

 attained considerable importance. 



The Birkeland-Eyde process is in use in the Notodden 

 factory. This is fitted with four 7000-kw. generators and 

 thirty-two furnaces, and has a yearly production of 20,000 

 tons of nitrate of lime, and a second factory on the 

 Rjukan Fall is in course of construction. 



The Frank-Caro process is not, strictly speaking, elec- 

 trical, yet it has only become commercially possible by the 

 aid of electricity. The raw materials for this process are 

 calcium carbide and nitrogen, the former being produced 

 by electricity in the well-known way, and the latter by 

 liquefying air in a Linde machine and subsequent frac- 

 tional distillation. The carbide is brought to glowing heat 

 in a closed, externally fired retort, and the nitrogen passed 

 through. The reaction is CaCj-(-N, = CaCN. + C. 



A new process for the production of nitrous compounds, 

 which is the invention of Messrs. Schoenherr and Hesz- 



