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 ACCUMULATORS — ACETYLENE 35 on tramcars. The cells add largely to the weight of the the hollow. For work like this, the cells ought to have a low lesistance and it is desirable that the shunt-wound dynamo shall Tramways. car; there is much expense in handling, owing have a falling characteristic. Compound-wound boosters are to the substitution of charged for discharged used to help the accumulators to share the load, cells every few hours; and there is a very rapid deteriora- sometimes fig. 34 is a diagram of the arrangement. The following data tion of the plates, consequent upon shaking and the heavy illustrate the way m which accumulators are employed in the starting currents. For these reasons the use of cells on station belonging to the Plymouth Corporation. Alternate current the cars has not generally been a commercial success, ^ used for lighting and continuous current for the tramway line. though at the present time a few lines are being run. Phere are two combined sets ; that is, engine, alternator, and tramway generator coupied on the same shaft. Other and lamer The following table gives some particulars of two systems alternators are in use during the “peak” of the load. In the worked by “ chloride ” cells :— combined sets the alternator and generator are each 100 kilowatt machines; the Beiliss engine is 150 b.h.p. The engine is Items. therefore only large enough to drive either of the machines at Birmingham. Paris. full load hut can run both at any combination of load not greater Weight of battery in pounds. 6048 6615 than 100 K.w. total. The generator gives 535 volts, and is Average discharge in amperes during run 50 35 in parallel with 260 cells of the Tudor type. The cars begin Maximum discharge during run 120-150 100-120 to run at 7.30 a.m. The cells and one generator are in parallel i.ength of run with one charge in miles. 45 37 sharing the tramway load through the day, with results verv Speed in miles 8 to 15 8 to 15 similar to those shown in Fig. 33. The alternator on the same jSio. of piassengers carried 50 50 shaft supplies the small day lighting load. When the evening load comes on, the direct current generators are uncoupled At Birmingham some cells have completed 20,000 car fighting the accumulators take the tramway work, and the total engine miles before renewal was necessary. Cost of renewal per power is available for running the fully-loaded alternators. This continues till the cars stop at 11 o’clock, by which time the car mile is approxi- lighting load has gone down again. The pressure of the cells has mately If penny. diminished from 520 to 475 volts. A generator is now coupled up But if the accumu- and charges the accumulators from 11 p.m. to 2.30 or therelators be used in the abouts ; a booster adding from 70 to 130 volts, as may be required central or a sub- .he booster motor takes from 15 to 20 amperes at 530 volts dependstation, there are ln ^i°j• 71® outpuload t from dynamo.conditions These arrangements well-distributed and its economical of working forgive sucha

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Fig. 33. many advantages. In a traction station, the load varies so rapidly that the plant is generally working at a low average load factor ; and the machinery must be capable of meeting the maximum demand, while the average load does not exceed one-half of the maximum. Now accumulators will take the peaks of the load, relieving the machinery from sudden jerks, and further allowing the running plant to be reduced to that which suffices for the average load. Some idea of the significance of this may be gained from Fig. 33. I he cells are in parallel with the generator. Eight cars were running. Ihe thick line A shows the dynamo current, varying 10m 115 to 150 amperes. The line current varies from 0 to 375 ampeies. It is evident that engine and generator are kept fully loaded, the cells supplying the peaks and taking a charge during

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O Fig 34. machinery as is at any time running, while the cells are a stand-by for exciting plant, &c. The following books and papers may be consulted in addition to those already cited :—• Plants. Recherches sur I'tilectricitt. Paris, 1879.—Gladstone and Tribe. Chemistry of Secondary Batteries. London, 1884. Reynier. L’Accumulateur Voltaique. Paris, 1888. Heim Die Akkumulatoren. Berlin, 1889.—Hoppe. Die Akkumulatorenfur Elektricitat. Berlin, 1892.—Schoop. HandbuchfurAkkumulatoren Stuttgart, 1898.—Frankland. “Chemistry of Storage Batteries ” Proc. Roy. Soc. 1883.—Reynier. “ Essai sur la Theorie Chimique des Accumulateurs,” Jour. Soc. Franc., d. Phys. 1884. Heim. “ U. d. Einfluss der Sauredichte auf die Kapazitiit der Akk. ” Elek. Zeits. 1889. Kohlrausch u. Heim. “ Ergebnisse von Yersuchen an Akk. fur Stationshetrieb,” Elek. Zeits. 1889. Harriotts. “La Theorie Chimique des Accumulateurs Plomb.,” Bull. Soc. Intern, des Electriciens, 1892.—E. J. Wade. Secondary Batteries. London, 1901. ^^

klumene or ethine, is one of the gaseous The molecule is represented by the formula C0H2. It is compounds of hydrogen and carbon, and on analysis is a clear, colourless gas, having a density of 0-92. When found to contain— prepared by the action of water upon calcium carbide, it has a very strong and penetrating Physical Carbon ...... 92-3 odour, but when it is thoroughly purified from ^ Hydrogen 7-7 sulphuretted and phosphuretted hydrogen, which are invariably present with it in minute traces, this extremely 100-0